mddp project – desalination in israel

Desalination: Group 2 Executive Summary

i

Author: KK, PS, SA & ED

2010

MDDP Project – Desalination in Israel

Group Members:

Salah Ali (SA)

Peter Brown (PB)

Elizabeth Drake (ED)

Norliza Jabar (NJ)

Kularajh Kandasamy (KK)

Prashanth Srinivasan (PS)

Supervisors:

Gerry Parke

Carl Sofield

Nigel Seaton

Desalination: Group 2 Executive Summary

ii

Author: KK, PS, SA & ED

Executive Summary

Over the years, Israel has supplied water to its population by extracting water from its natural

sources, such as the Sea of Galilee, mountain aquifers and coastal aquifers. Over reliance on these

sources has depleted them, to a point where the level is critically low.

Desalination has been successfully implemented in Israel, on a large scale, to bridge the gap

between water demand and supply. This project looks at the various aspects and challenges

associated with the design of another desalination plant in the region along the Mediterranean

coast.

This desalination plant is designed to produce 110 million m3 of water annually over the design

period of 20 years. The production capacity was determined by considering the future population

growth of Israel and an analysis of projected water demand and supply. This amount contributes

5% of Israel‟s total potable water demand.

The two desalination technologies explored were Multi Stage Flash Distillation (MSFD) and

Reverse Osmosis (RO); on critical examination, it was found that MSFD is inefficient compared

to RO. This is illustrated by the specific energy requirements, which for MSFD ranges from 49.66

kWh/m3 – 99.74 kWh/m

3. On the other hand, RO requires only 3.41 kWh/m

3, which is an order of

magnitude smaller than the MSFD requirement.

As part of the sustainable agenda, a green power source has been developed, that provides energy

to the desalination plant. Due to the abundant amount of sunlight available in Israel, especially in

Negev desert, a solar power plant was chosen. By utilizing state of the art technology,

concentrated solar power was implemented to convert thermal solar energy into electricity. This is

transported to the desalination plant through the national grid. Water is distributed to the

consumer sectors in the Southern regions of the country through the National Water Carrier

(NWC).

The price of water emanating from the scheme is estimated at £0.47/m3 of water produced. This

price could prove detrimental to the project, as there are cheaper water sources already available.

Desalination: Group 2 Table of contents

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Table of contents

Contents

Executive Summary ........................................................................................................................... i

Table of contents ............................................................................................................................. iii

Table of figures ............................................................................................................................... xii

Table of tables ................................................................................................................................xvi

1 Introduction .............................................................................................................................. 1

2 Problems ................................................................................................................................... 2

2.1 Water Supply and Demand ............................................................................................... 2

2.2 Geopolitical Issues ............................................................................................................ 3

2.3 Reliability of Design .......................................................................................................... 4

3 Scheme design .......................................................................................................................... 5

3.1 Design Principle ................................................................................................................ 5

3.2 Basic Schematic ................................................................................................................ 5

3.3 Plant Statistics ................................................................................................................. 6

4 Location .................................................................................................................................... 7

4.1 Introduction ...................................................................................................................... 7

4.2 Location of the Process Plant ........................................................................................... 8

4.3 Process Location ............................................................................................................. 10

5 Process .................................................................................................................................... 13

5.1 Pre-Treatment Process Description................................................................................ 13

5.1.1 Intake system .......................................................................................................... 13

5.1.2 Conventional and non-conventional pre-treatment .............................................. 17


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5.1.3 Filtration and backwash ......................................................................................... 21

5.1.4 Coagulant use ......................................................................................................... 23

5.2 Post treatment ............................................................................................................... 23

5.2.1 Blending with a treated saline water source .......................................................... 25

5.2.2 Selected post-treatment method ........................................................................... 26

5.3 Total operating cost and equipment cost for the pre and post treatment sections...... 30

5.3.1 Total operating Cost ............................................................................................... 30

5.3.2 Cost of resin replacement ...................................................................................... 30

5.3.3 Cost of UF membrane Replacement ...................................................................... 30

5.3.4 Total Equipment Cost ............................................................................................. 31

5.4 Multi Stage Flash Distillation (MSFD) ............................................................................. 32

5.4.1 Process description ................................................................................................. 32

5.4.2 Key variables affecting process operation .............................................................. 33

5.4.3 Calculation procedure ............................................................................................ 34

5.4.4 Varying MSFD energy requirements ...................................................................... 34

5.5 Reverse osmosis (RO) ..................................................................................................... 35

5.5.1 Process description ................................................................................................. 35

5.5.2 RO membranes ....................................................................................................... 36

5.5.3 Main process parameters ....................................................................................... 36

5.5.4 Energy recovery device ........................................................................................... 38

5.5.5 Boron treatment ..................................................................................................... 38

5.5.6 Calculations ............................................................................................................ 39

5.5.7 Cost of RO trains and pumps (excluding pre- and post-treatment) ....................... 52


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5.5.8 RO process schematic ............................................................................................. 52

6 Structure ................................................................................................................................. 53

6.1 Reverse Osmosis Process Plant ...................................................................................... 53

6.1.1 Introduction ............................................................................................................ 53

6.1.2 Floor Design and Layout ......................................................................................... 54

6.1.3 Quantification of actions, load combinations and general safety criteria ............. 57

6.1.4 Loads Summary ...................................................................................................... 59

6.1.5 Design of Members ................................................................................................ 59

6.1.6 Bracing and Gable post ........................................................................................... 60

6.1.7 Future Expansion .................................................................................................... 61

6.1.8 Cost summary ......................................................................................................... 61

6.2 Foundation design .......................................................................................................... 62

6.2.1 Choice of foundation: ............................................................................................. 62

6.2.2 Bear Capacity of the Soil: ........................................................................................ 62

6.2.3 Raft analysis ............................................................................................................ 65

6.3 Base plate design ............................................................................................................ 70

6.4 Monopole Design ........................................................................................................... 73

6.4.1 Introduction ............................................................................................................ 73

6.4.2 Tower Requirements .............................................................................................. 73

6.4.3 Choice of Structural Material & Design .................................................................. 73

6.4.4 Design Method ....................................................................................................... 74

6.4.5 Design Requirements ............................................................................................. 74

6.4.6 Quantification of Actions, Load Combinations and General Safety Criteria .......... 75


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6.4.7 Discussion on validity of design & other considerations ........................................ 82

6.4.8 Fatigue of Structure ................................................................................................ 84

7 Solar fields .............................................................................................................................. 85

7.1 Solar Field ....................................................................................................................... 85

7.1.1 Introduction ............................................................................................................ 85

7.1.2 System concept ...................................................................................................... 85

.................................................................................................................................................. 87

7.1.3 Geometrical Positioning ......................................................................................... 88

7.1.4 Heliostat System ..................................................................................................... 89

7.1.5 Receiver Design ...................................................................................................... 92

7.2 Energy generation calculation ........................................................................................ 94

7.3 Sizing of Solar Plant Process Equipments ....................................................................... 97

7.3.1 Turbine.................................................................................................................... 97

7.3.2 Condenser ............................................................................................................... 98

7.3.3 Solar plant Pump .................................................................................................... 98

7.3.4 Solar tower receiver ............................................................................................... 99

7.4 Cost of solar plant process equipment ........................................................................... 99

8 Electrical systems ................................................................................................................. 100

8.1 Introduction of Power Usages for Solar-RO Desalination Plant ................................... 100

8.2 Active, Reactive, and Apparent Power ......................................................................... 100

8.3 Transferring Power to National Grid Power Station .................................................... 100

8.4 Comparing HVDC versus HVAC Power Transmission ................................................... 101

8.5 The Electrical Distribution System ................................................................................ 103

8.6 System Description ....................................................................................................... 107


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8.6.1 Main Generator .................................................................................................... 107

8.6.2 Bus Duct ................................................................................................................ 107

8.6.3 Step-up Power Transformer ................................................................................. 108

8.6.4 Auxiliary Transformer ........................................................................................... 109

8.6.5 Start-up Transformer ............................................................................................ 109

8.6.6 Voltage Switchgear ............................................................................................... 109

8.6.7 Secondary Unit Substations .................................................................................. 109

8.7 Business in Selling the Excess Energy ........................................................................... 109

9 Infrastructure........................................................................................................................ 111

9.1 Introduction .................................................................................................................. 111

9.2 The Importance of Infrastructure on the Operational Success of a Plant.................... 111

9.3 Impact Infrastructure has on Location Choice ............................................................. 111

9.4 The Plant’s Requirements............................................................................................. 112

9.5 Integration Considerations ........................................................................................... 112

10 Integration ........................................................................................................................ 113

10.1 Introduction .................................................................................................................. 113

10.2 The national water carrier (NWC) ................................................................................ 113

10.3 Power ............................................................................................................................ 116

11 Finance ............................................................................................................................. 118

11.1 Introduction .................................................................................................................. 118

11.2 Price of Water ............................................................................................................... 118

11.3 Carbon Offset Arrangement ......................................................................................... 118

11.4 Project risk .................................................................................................................... 119

11.5 Financing Source ........................................................................................................... 119


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11.6 Project Main Cost ......................................................................................................... 120

11.6.1 Land and site development .................................................................................. 121

11.6.2 Civil works ............................................................................................................. 121

11.6.3 Plant & Machinery for RO unit ............................................................................. 121

11.6.4 Power Plant Cost .................................................................................................. 121

11.6.5 Solar System ......................................................................................................... 121

11.7 Soft cost ........................................................................................................................ 121

11.7.1 Miscellaneous Fixed Assets .................................................................................. 121

11.8 Appraisal Analysis ......................................................................................................... 122

11.9 Net present value (NPV) ............................................................................................... 124

12 Future demand ................................................................................................................. 126

12.1 Introduction .................................................................................................................. 126

12.2 Population Growth ....................................................................................................... 126

12.3 Standard of Living ......................................................................................................... 127

12.4 Total Demand Projections ............................................................................................ 128

12.4.1 Agricultural consumption forecast ....................................................................... 129

12.4.2 Industrial consumption forecast .......................................................................... 129

12.4.3 Domestic consumption forecast ........................................................................... 129

12.4.4 Aquifer rehabilitation and neighboring entities ................................................... 130

12.4.5 Total Supply Projections ....................................................................................... 130

13 Sustainability .................................................................................................................... 131

13.1 Introduction .................................................................................................................. 131

13.2 The Energy Intensiveness of Desalination and its Implications.................................... 131

13.3 Power Source, the Key to Sustainability ....................................................................... 132


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13.4 Desalination Across the Globe; are there any lessons to be learnt?............................ 134

13.5 Other Factors ................................................................................................................ 135

13.6 Sustainable Power in Israel; possibilities and current technologies ............................ 136

13.7 Sea Water; a limitless supply? ...................................................................................... 136

13.8 The Benefits of a Sustainable Solution ......................................................................... 137

13.9 The Schemes Sustainability Credential ......................................................................... 137

14 Environmental impact ...................................................................................................... 139

14.1 Intake ............................................................................................................................ 139

14.2 Pre-treatment ............................................................................................................... 139

14.3 Chemicals used in pre-treatment: Coagulant as FeCl3 and NaOCl ............................... 140

14.4 Post-treatment ............................................................................................................. 140

14.5 Brine Disposal ............................................................................................................... 140

15 Durability of design........................................................................................................... 142

15.1 Reliability of the system & technological advances: .................................................... 142

15.2 Structural Design .......................................................................................................... 143

16 Construction programme ................................................................................................. 145

17 Conclusion ........................................................................................................................ 148

18 Nomenclature ................................................................................................................... 150

19 Bibliography ...................................................................................................................... 153

20 Appendix A ....................................................................................................................... 164

20.1 Cost of pre and post treatment sections ...................................................................... 164

20.2 Israel reverse osmosis desalination plant .................................................................... 165

20.3 Solar plant simulation ................................................................................................... 166

20.4 ChemCad stream report ............................................................................................... 167


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20.5 Calcite bed pressure drop............................................................................................. 168

20.6 Resin bed pressure drop ............................................................................................... 168

20.7 MSFD detailed calculations .......................................................................................... 169

20.7.1 Boiling point elevation (BPE) ................................................................................ 169

20.7.2 Process parameters and energy consumption calculation .................................. 170

20.8 MSFD calculation summary .......................................................................................... 175

20.9 MSFD energy requirement ........................................................................................... 177

20.10 Reverse osmosis illustration ..................................................................................... 178

20.11 RO membrane........................................................................................................... 178

20.12 Pressure exchanger .................................................................................................. 178

20.13 SPSP .......................................................................................................................... 179

20.14 RO process schematic ............................................................................................... 180

20.15 Wind Actions ............................................................................................................ 181

20.15.1 Peak velocity pressure qp(z) .............................................................................. 181

20.15.2 External Pressure coefficients (cpe) ................................................................... 182

20.16 Rafter and Column Design ........................................................................................ 184

20.17 Bill of Quantities ....................................................................................................... 186

20.18 Foundation design .................................................................................................... 188

20.18.1 Ground Conditions: .......................................................................................... 188

20.18.2 Loads on the structure...................................................................................... 188

20.18.3 Bearing capacity ............................................................................................... 189

20.18.4 Safe Bearing Capacity ....................................................................................... 190

20.18.5 Load combination and arrangement ................................................................ 191


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20.18.6 Fire Resistance .................................................................................................. 192

20.18.7 Cover ................................................................................................................. 192

20.18.8 Raft Analysis ..................................................................................................... 193

20.18.9 Shear Reinforcement ........................................................................................ 196

20.19 Bar bending............................................................................................................... 198

20.20 Power system ........................................................................................................... 200

20.21 Power generation calculation ................................................................................... 201

20.22 Engineering sections costing .................................................................................... 202

20.23 Plant and machinery costs ........................................................................................ 203

20.24 Variable costs............................................................................................................ 206

20.25 Main crust of the project .......................................................................................... 206

20.26 CSP Plant annotation ................................................................................................ 207

20.27 Israel population growth .......................................................................................... 208

20.28 Water demand projections....................................................................................... 209

20.29 Annual population growth rate ................................................................................ 209

20.30 Agriculture treated water requirement ................................................................... 209

20.31 Total industrial water consumption projection ........................................................ 210

20.32 Treated water industrial consumption projection ................................................... 211

20.33 Aquifer rehabilitation and landscaping water demand ............................................ 211

Desalination: Group 2 Table of figures

xii

Table of figures

Figure 1 : RO and power plant scheme design ................................................................................. 5

Figure 2 : Solar plant location (Google Maps, 2010) ........................................................................ 9

Figure 3 : Process Location (Google Maps, 2010) .......................................................................... 10

Figure 4 : Location of NWC and local pumping stations (Merokot, 2010) .................................... 11

Figure 5 : Process Plants Location (Google Maps, 2010) ............................................................... 12

Figure 6: Block diagram of the pre-treatment section ................................................................... 13

Figure 7: Cross-section of seabed intake system based on filter bed (Peters,Thomas;

Pintó,Domènec, 2008) .................................................................................................................... 15

Figure 8: Diagram showing the intake pipes .................................................................................. 16

Figure 9: Post-treatment block diagram ........................................................................................ 24

Figure 10: Variation of energy requirement of an MSFD unit with number of stages at a TBT of

90°C ................................................................................................................................................ 35

Figure 11: Variation of energy requirement of a 40 stage MSFD unit with TBT ............................ 35

Figure 12: A simplified RO membrane (Source: Self) ..................................................................... 42

Figure 13: Typical single-bay portal frame (PRIMECON.CO.ZA, 2009) ........................................... 53

Figure 14: RO plant layout .............................................................................................................. 55

Figure 15: Structural diagram ......................................................................................................... 55

Figure 16: RO plant site layout ....................................................................................................... 56

Figure 17: Location of Desalination Plant ....................................................................................... 57

Figure 18: 3D Illustration of Desalination Plant ............................................................................. 57

Figure 19: Portal frame ................................................................................................................... 57

Figure 20: Transverse and longitudinal wind loads ........................................................................ 59


xiii

Figure 21: Worst Load case ............................................................................................................ 60

Figure 22: LUSAS BM Diagram ........................................................................................................ 60

Figure 23 : Transverse strip reinforcement .................................................................................... 69

Figure 24 : Longitudinal strip reinforcement .................................................................................. 69

Figure 25: Column dimensions and arrangement .......................................................................... 71

Figure 26: Figure showing the economical advantage steel towers have below 120m when

compared to concrete towers ........................................................................................................ 74

Figure 27: Cross section showing foundation connection and pipe detailing. .............................. 75

Figure 28: Cross section showing how local section split away for buckling analysis, also shows

vertical stiffener layout. ................................................................................................................. 81

Figure 29: Cross section showing stiffeners and flange connection detailing which will be present

at each of the 5 mid connections (note gap between flange plates is only present for clarity). ... 83

Figure 30: Figure showing detailing required around Man Access with additional stiffener

sections being indicated in red. ...................................................................................................... 84

Figure 31 : Single system consisting of one tower with a duel cavity receiver and two heliostat

fields (North and South). ................................................................................................................ 86

Figure 32: Example of heliostat field providing optimum energy output ...................................... 88

Figure 33: Rectangular heliostat field efficiency, red indicates most efficient location ................ 90

Figure 34: Schematic showing heliostat system ............................................................................. 90

Figure 35: Schematic showing heliostat system ............................................................................. 91

Figure 36: NASA Earth Observatory, 2009. Solar Towers near Seville, Spain, [photograph]

http://earthobservatory.nasa.gov/IOTD/view.php?id=40204 [accessed 20/12/10] ............... Error!

Bookmark not defined.

Figure 37: Photo showing complex arrangement of heliostat fields in arced configuration at PS10

and PS20 in Seville, Spain. .............................................................................................................. 93


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Figure 38: HVDC and HVAC Transmission system cost. Breakeven shows at 500km between HVAC

and HVDC ...................................................................................................................................... 103

Figure 39: Comparison of AC transmission line (purple line) over the ultra-Higher Voltage DC

(green line). The graph shows the cost approximation in million USD versus the percentage of

line losses. Picture on the right shows one line of 800kV DC and seven line of 500kV AC. Source:

Video of HVDC (ABB, 2004). ......................................................................................................... 103

Figure 40: Basic diagram for AC transmission line ....................................................................... 104

Figure 41: SLD for Solar Thermal power plant system. Solar Grid .......................................... 105

Figure 42: SLD of three stages of the system. GridRO .............................................................. 106

Figure 43: National water carrier (Mekorot, 2007) ...................................................................... 114

Figure 44: NWC - Longitudinal section ......................................................................................... 115

Figure 45: Integration to NWC ..................................................................................................... 116

Figure 46: Graph shows the different between Revenues – Operating cost with no green gadget

and Revenues –Operating Cost with green gadget ...................................................................... 122

Figure 47: The net cumulative cash flow for 20 years operation ................................................. 122

Figure 48: Shows the net and cumulative cash flow from starting year until 20 years later ....... 124

Figure 49: NPV for 8%, 12%, 15% and 17% of discount rate for 20 years .................................... 125

Figure 50: Total projected population of Israel ............................................................................ 127

Figure 51: Consumption per person per year .............................................................................. 128

Figure 52: Desalination breakdown, globally and in Israel (Lattemann and Höpner, 2008) ........ 134

Figure 53 : Installed desalting capacity by process and raw water quality (Zhou and Tol, 2004) 135

Figure 54: Israel Reverse Osmosis Desalination Block Diagram ................................................... 165

Figure 55: Solar plant Simulation ................................................................................................. 166

Figure 56: ChemCad stream report .............................................................................................. 167

Figure 57: Calcite bed pressure drop ........................................................................................... 168


xv

Figure 58: Resin bed pressure drop .............................................................................................. 168

Figure 59: Osmosis and reverse osmosis ((Smith and Shaw, N.D.), Pg.1) .................................... 178

Figure 60: A Spiral Wound Membrane element ((Fritzmann et al., 2007), Pg. 24) ...................... 178

Figure 61: Pressure Exchangers ((Fritzmann et al., 2007), Pg. 32) ............................................... 178

Figure 62: A typical SPSP set up (Source: (Rybar et al., 2010), Pg. 189) ...................................... 179

Figure 63 : RO process schematic ................................................................................................. 180

Figure 64: Pressure coefficients for transverse and longitudinal wind actions ........................... 183

Figure 65: Final external coefficients ........................................................................................... 184

Figure 66: Transverse and longitudinal wind actions on the structure ........................................ 184

Figure 67: Members ..................................................................................................................... 184

Figure 68: Wind load carried by the bracing ................................................................................ 185

Figure 69: Load carried by the gable post .................................................................................... 186

Figure 70 : Geological Data For Rishon Lezion- Process Plant Location (Geological survey of Israel,

2010) ............................................................................................................................................. 188

Figure 71 : Raft Foundation Layout for Process Plant including Column and Middle Strip Details

...................................................................................................................................................... 192

Figure 72 : Barbending schedule .................................................................................................. 198

Figure 73: CSP plant ...................................................................................................................... 207

Figure 74: Annual population growth rate of Israel (THE WORLD BANK, 2010) ......................... 209

Figure 75: Total treated water requirement – agriculture ........................................................... 210

Figure 76: Total annual industrial consumption projection ......................................................... 210

Figure 77: Total treated water consumption for industrial sector ............................................... 211

Figure 78: Aquifer rehabilitation and landscaping water demand .............................................. 211

Desalination: Group 2 Table of tables

xvi

Table of tables

Table 1: Cost of chemicals used in pre and post treatment sections............................................. 30

Table 2: UF Membrane Replacement Cost ..................................................................................... 30

Table 3: Total Capital Employed For Pre and Post Treatment section........................................... 31

Table 4: Summary of results of a 1st pass pressure vessel containing 6 membranes ................... 45

Table 5: Key parameters associated with 2nd pass membranes ................................................... 45

Table 6: Rear end permeate feed salinity and boron concentration from the 1st pass ................. 46

Table 7: Summary of results of a 2nd pass pressure vessel containing 6 membranes .................. 47

Table 8: Table to calculate blended permeate salinity .................................................................. 48

Table 9: Booster pump and 2nd stage pump power consumption ............................................... 51

Table 10: Cost of the RO trains and pumps .................................................................................... 52

Table 11: Summary of actions ........................................................................................................ 59

Table 12 : Calculated data .............................................................................................................. 79

Table 13: A comparison of different CSP systems .......................................................................... 87

Table 14: Solar plant parameters ................................................................................................... 96

Table 15: Range of voltage (AMOTT, Prof. Nick, 2010) ................................................................ 107

Table 16: Debt to equity ratio breaks up ...................................................................................... 119

Table 17: The project main crust .................................................................................................. 120

Table 18: Percentage is calculated from the original cost of land development, buildings,

installation of equipment, machinery and any other related to the project cost. Taken from PKF

Israel Tax Guide 2009 (PKF, 2009). ............................................................................................... 120

Table 19: Shows the base case scenario of the energy save percentage based on the application

of green gadget ............................................................................................................................ 123

Desalination: Group 2 Table of tables

xvii

Table 20: Water consumption per person ................................................................................... 128

Table 21: Projected total potable water demand ........................................................................ 130

Table 22: Projected total water supply ........................................................................................ 130

Table 23: Applicability of power source for sustainable desalination in Israel ............................ 133

Table 24 : List of abbreviations ..................................................................................................... 150

Table 25 : List of symbols ............................................................................................................. 151

Table 26 : Total cost of equipment in pre- and post-treatment sections .................................... 164

Table 27: Summary of an MSFD unit with 40 stages and a TBT of 110°C .................................... 175

Table 28: MSFD desalination energy requirement ...................................................................... 177

Table 29: External pressure coefficients (cpe) on the walls (Clause 7.2.2 (EN 1991-1-4)) ............ 182

Table 30: External pressure coefficients (cpe) on the roofs (Clause 7.2.5 (EN 1991-1-4)) ............ 183

Table 31: Portal frame cost summary .......................................................................................... 186

Table 32 : Power system calculation ............................................................................................ 200

Table 33 : Power generation calculation ...................................................................................... 201

Table 34 : Costing for RO plant and power plant ......................................................................... 202

Table 35 : Plant and machinery costs ........................................................................................... 203

Table 36 : Variable costs ............................................................................................................... 206

Table 37: Main crust of the project .............................................................................................. 206

Table 38: Population growth (actual and projected) of Israel (THE WORLD BANK, 2010) .......... 208

Table 39: Official water demand projections (DREIZIN, Y et al., 2008) ........................................ 209

Desalination: Group 2 Introduction

1

Section 1 Author: KK, ED & PS

1 Introduction

Water is an indispensable resource, required for the day-to-day activities of a population. Often,

the standard of living is dictated by the quality and quantity of potable water available. However,

globally, a very small percentage of the naturally occurring water, in the form of groundwater

aquifers, is available for consumption, with the remainder deemed unfit for human consumption,

either as a result of being too salty (seawater) or due to being locked up in ice caps and glaciers.

An ever-increasing population, coupled with changing environmental conditions, further

exacerbates the problem, resulting in water scarcity in most parts of the developing world.

One such country, which faces an acute problem of water scarcity, is Israel. The country faces an

uphill battle in meeting the water demand, created by an ever-increasing quality of life and a

rising population. This, coupled with dwindling supplies, created by over-pumping of natural

water resources, causes an unsustainable situation. Over reliance on these natural resources will

cause early depletion, resulting in Israel becoming extremely vulnerable. Lack of an alternate

method of providing the population with water will eventually force Israel to import water from

neighbouring countries. This is not ideal, as Israel lies in a politically volatile region, where the

relations between countries are strained.

Desalination provides a long-term solution to Israel‟s problem of water shortage. It is a process

that utilizes either distillation or membrane technology to produce potable water from seawater or

brackish water, whose main constituents are sodium and chloride ions. Due to the magnitude of

the problem described above, Israel has invested significantly in desalination technology. There

are currently 4 desalination plants in operation along the Mediterranean coast, one of which is the

world‟s largest seawater reverse osmosis desalination plant. A further 2 desalination plants are

scheduled to start operation by 2015.

To narrow the gap between supply and demand, an additional desalination plant must be

introduced. The scope of this project is to design a desalination plant that is both sustainable and

feasible. The issue of climate change, due to greenhouse gas (GHG) emissions has been extremely

well documented. Therefore, it is of unparalleled importance that the power to operate the

desalination plant is derived from a low greenhouse gas-emitting source. There are several

renewable alternatives available; this project will explore those alternatives.

Desalination: Group 2 Problems

2

Section 2 Author: ED

2 Problems

The water crisis in the Middle East is an ancient and regional problem. This section will detail

factors that make the problem of providing potable water via the means of desalination very

specific and individual to the region of Israel.

2.1 Water Supply and Demand

Due to Israel‟s population distribution and the climate variation between the North and the South

of the country, there is a gap between the water that the population requires and that what is

demanded. As mentioned, in order to bridge this gap the country has turned to desalination.

Currently, the situation is that the North and Coastal regions of the country have the largest

proportion of the population. These regions also have a wetter climate. However, the South with

its dry and arid climate also relies on the rainfall from the North for its water supply. The

Southern regions of the country has a smaller proportion of the population, but has shown signs

that it is these Southern regions, in specific the cities which are having the greatest increase in

population and proportion of agriculture (CENTRAL BUREAU OF STATISTICS, 2009). In

order to compensate for this, water is carried from the rainier Northern regions of the country and

the Sea of Galilee down to the South via the National Water Carrier (NWC), which was

constructed in the 1950s. However, even with such measures in place there is still a deficit of

water with too much reliance being placed on both the rainfall and the natural water sources. One

of the main problems with this approach is that the rainfall within the country is getting less

predictable and reliable due to changes caused by global climate change. This means that the

natural water resources are not getting fully replenished and therefore are at risk of being polluted

through salt-water intrusion (BEYTH, M., N.D.). Due to the way in which the National Water

Carrier distributes the source, the location of the desalination plant does not limit the area which it

will supply potable water. For example, whether it is in the Southern or Northern regions of the

country, so long as it is connected to the NWC, it will still aid in supplying the whole of the

country with an increase in water supply either directly or through replenishment of resources.

As mentioned, two of the major factors controlling the availability and replenishment of the water

resources in Israel are the annual rainfall and the physical geography. There are three natural

water resources in Israel, one surface water resource, the Lake of Galilee and two groundwater

ones, the Coastal Aquifer and the Mountain Aquifer. The majority of the natural groundwater

aquifers lie along the Coastal and Mountainous regions of the country, which only adds to the

lack of water resources in the South. Currently, natural resources provide 1470 million cubic

meters of potable water per year; this is around 60% of the total country‟s potable water supply

(DREIZIN, Y. ET AL., 2007). However, there is still potential to over pump the resources, as


3


Israel is not the only country to rely on the aquifers as a source of potable drinking water. They

therefore have a „red line‟ level, which details the point at which the resource is being over

pumped which can lead to potential water pollution and ecological problems. Unfortunately, due

to Israel‟s heavy reliance on the resource and recent low levels of rainfall, water levels have fallen

below this level. This shows the importance of supplementing these natural water resources in

order to prevent any irreversible damage.

In order to complete both a realistic and suitable design for the desalination plant, the capacity of

the plant will have to be carefully considered. This will ensure that it produces enough water, not

only for today but also for the whole design life of the plant. There are a number of factors that

will have to be considered here. Those, which are subject to change and uncertainty, include

changes in climate and population increase/decrease/distribution. Changes that may occur to the

country‟s climate are a very important consideration for the construction of a desalination plant in

Israel. Firstly, due to the fact that the region is already heavily reliant on rain water as a water

source and secondly due to the fact that this rain currently falls unevenly over the region.

2.2 Geopolitical Issues

Pressure has always been placed on Israel‟s water system due to increased levels of immigration

into the country. The situation has become further pressurised in recent years for a number of

reasons such as increasing population and a higher standard of living.

Traditionally, Israel has obtained all its water from fresh water supplies, which has included using

more than its fair share of the Jordan River. However in 1967, the „Six day war‟ broke out which

resulted in a number of changes relating to water management in the Middle East. The war caused

the water situation in the Middle East to be altered, with Israel showing how serious it was about

gaining control of the natural water resources. Firstly, two engineering projects were destroyed,

which upon completion would have limited the flow of water to the upper and lower Jordan River

and thus reducing the water available to Israel. Secondly, Israel‟s water supplies increased by

50% and it gained control of the headwaters of the Jordan River, the Mountain Aquifer and the

Banias River (SHERMAN, M., 1999).

The West Bank Mountain aquifer and the Sea of Galilee provide Israel with around 60% of its

fresh water (approximately 1 billion m3/year). Due to the central location of the aquifer, there

have been many debates over the use of the resource. Currently, Israel controls 80% of the

resource and leaving the Palestinians with the remaining 20% (JEWISH VIRTUAL LIBRARY,

2009). However, the Palestinians say that they are being prevented from using their own

proportion of this water resource by the Israeli military. This, in turn means that they have been

forced to purchase water from their occupiers at massively over inflated rates. In addition to this,


4


Palestinian publications state that Israel allocates up to five times more water to its own citizens

than Palestinians. However, in response to this, Israel states that in fact Palestine has fair access to

the water and that they simply mismanage the resources (BBC, 2002).

The Golan Heights is a mountainous region in Southwest Syria, with borders to the Jordan River,

Lake Tiberias and Hula Valley. It is a significant water resource in the region. Since the 1967 war,

two-thirds of the region is controlled by Israel. The area has been subject to many battles of

control, with Syria attempting and failing to regain control on many occasions. The heights are

not only advantageous because of their water producing properties, but they also give Israel a

vantage point to oversee Syria‟s movements as well as providing a natural buffer against any

military action from the country. The new Israeli government, elected in February 2009 states a

tougher line over the Golan, as Syria wishes to reinstate the pre-1967 borders, which would result

in Israel losing control of the Sea of Galilee. This ongoing dispute gives an indication of the

volatility of land ownership, boundaries and water within the region (BBC, 2010).

2.3 Reliability of Design

Due to the inherent importance of water and the fact that the plant will provide water for

domestic, industrial and agricultural uses shows the significance of having a reliably method of

water production. This will be especially important in the rural and remote areas, such as those in

Southern Israel where the water from the desalination plant may well be the only source of

potable water. The design of the plant should be as simple as possible and based on proven

technology. However, with this emphasis cannot be taken away from new and innovative systems,

which may enable financial and environmental advantages. Care should also be taken to ensure

that any redundancy of parts of the system should not mean a complete shut-down in operation of

the plant. Even when the plant is designed with a high level of reliability in mind, there is always

the chance that the unexpected could happen. Therefore, in order to overcome this, the

desalination plant‟s capacity should be increased as a means of supplying excess water to

compensate should there be a break down in the system. To further this, a good level of storage,

such as that which can be provided through the use of the National Water Carrier means that any

unreliability can be further accounted for.

Desalination: Group 2 Scheme design

5

Section 3 Author: PB

3 Scheme design

The section provides a very broad overview of the methodology of operation of the power source

and desalination system.

3.1 Design Principle

To take solar energy and convert it as efficiently as possible into a usable energy source for

desalination, which would provide Israel with a sustainable and environmentally friendly sources

of clean drinking water.

3.2 Basic Schematic

In South East Israel in the Negev Dessert, a concentrated solar power plant utilises the strong and

consistent solar radiation experienced here, using it to generate electricity. This process involves

thousands of heliostats (solar panels), which directs sunlight and reflects its intensity on to

receivers, to superheat water, thereby creating steam. The steam is used to drive turbines,

producing electricity. The water is in a closed loop and so is condensed and returned back to the

receivers making the system as efficient as possible. This electricity produced is sent to the grid

where closer to the coast it is used to power pumps and any auxiliary plant required for a reverse

osmosis (RO) treatment system. This system uses the principles of membrane osmosis, utilising

the effect pressure has to reverse the process allowing clean water to be separated from the saline

component of sea water creating potable drinking water.

Figure 1 : RO and power plant scheme design

Desalination: Group 2 Scheme design

6


This solution utilises the advantages of solar power in the Negev Desert with a sea water

desalination plant on the coast near to large population centres such as Tel Aviv that demand

potable water. Financial gain is also found by supplying Israel‟s grid with energy in the day and

then drawing some of this back in the night when electricity is less expensive. This also allows the

RO process to run at an optimised rate, 24 hours a day.

3.3 Plant Statistics

Water Quantity Required: 100 million m3/year

Total Plant Capacity: 110 million m3/year

Sea Water Intake Requirement: 200 million m3/year

Number of Heliostats: 512,000

Number of Towers: 32 (detailed calculation in Section 7)

Number of Receivers: 32

Steam Temperature: 440˚C (used in Section 7.3)

Steam Pressure: 60bar (used in Section 7.3)

Number of Steam Turbines: 2

Power Produced: 50MW

Power Supplied to the Grid: 50MW

Power Taken from the Grid: 50MW

Combined Area of Membranes: 100000m2

Total RO Plant Footprint: 1.6km2

Total CSP Plant Footprint: 1.6km2

Desalination: Group 2 Location

7


4 Location

4.1 Introduction Israel is located along the Eastern edge of the Mediterranean Sea with borders to Lebanon, Syria,

Jordan, The West Bank, Egypt and The Gaza Strip. Although a relatively small country with an

area of approximately 20,700 square kilometres (FEDERAL RESEARCH DIVISION, 2004),

Israel is geographically diverse with the Negev desert in the South and the Lebanon and Chouf

mountain ranges in the North. The South of the country is renowned for its dry and arid climate,

whilst the North of the country has a wetter and cooler Mediterranean climate. However, even

with the wetter climate in the North, there is a lack of replenishment of the natural water resources

in the country. As is the case with many Middle Eastern countries, this lack of clean drinking

water can lead to severe political tensions, both within and between countries, and Israel has been

no exception to this. With a population of around 7.5 million (CENTRAL BUREAU OF

STATISTICS, 2009) and the majority of the citizens being situated in the North and Coastal

regions of the country, there is a disjointed population distribution and water demand. This has

led to water disputes and water rationing being necessary in order to protect the exploitation of the

countries natural water resources. Specific information on the issues faced by constructing a

desalination plant in Israel can be found in the Section 2 of this report.

This section of the report will detail specifics on the location of both the process plant and the

solar power plant. Due to the fact that the power production and the Reverse Osmosis process

plant require very different qualities, a decision was made to separate the location of the

processes. For example, the solar power plant requires a very dry and hot climate, which tends to

be further inland, whereas the process plant has to be located close to the sea in order to prevent

excessive lengths of piping. The separation of the processes has been made possible by the fact

that Israel is well connected, both nationally and regionally, by its water supply system and

national grid. It is therefore possible to house the solar power plant in a different location to the

reverse osmosis plant and use the national grid as a means to transport the electricity produced to

the location where it will be utilised. The following details the advantages that can be gained

through the separation of the two different sites:

It allows the most to be made of Israel‟s natural resources, i.e. the desert‟s sunlight

for a power plant and the coast‟s proximity to the sea for the desalination plant.

It will help to reduce the costs of the project due to the fact that the solar power plant

can be located separately from the Coastal desalination plant where the land is more

expensive and less available.


8


It takes advantage of the large expanses of wasteland available in the Southern desert

region of the country.

It limits disruption, as fewer pipelines have to be constructed.

Using the National Grid as means of transporting energy provides electrical storage

and allows there to be a back-up power supply should there be a deficit of power

created by the solar power plant.

The National Water Carrier (NWC) can be used to transport water from the RO plant

further South; this helps integrate the system into Israel‟s current water resources and

provide water to the largest coastal populaces.

4.2 Location of the Process Plant One of the most important considerations for the location of the process site is the area‟s water

demand, which is linked to population centres. In order to fully consider the capability and future

capacity of the site, it is important that the projected demands of the country are considered. The

full extent of these future capacities can be calculated through both the design life of the plant

(approximately 20 years) and the predicted population increase. The aim is that through careful

planning and implementation there will be optimal geographic distribution of the total

desalination capacities at the end of the planning horizon.

Through evaluation of the current trends in population growth, it shows that it is the South of the

country, in particular within the cities, where the greatest growth of population will be seen (CBS,

2009). This can be seen as good justification for situating the plant in the South, as it is this steady

growth in demand, which is the driving force behind the country‟s developing water shortages. To

further this, the Mediterranean Coastal region is also attracting an increasing population, which is

an appropriate location for the development of a desalination plant due to its proximity to the

water source. It is important to bear in mind that unlike many other industries such as agriculture,

these increased demands will be for a good quality and reliable source of water, which can be

supplied through the desalination plant. It is at this point that the location and reliability of the

current, natural water sources should be scrutinised. Around 80% of the renewable water

resources (i.e. the Coastal and Mountain aquifer and the Sea of Galilee) are located in the North,

leaving the South with a disproportionately small amount of the water supplies. This is

exasperated by the South‟s lack of rainwater from its dry and arid climate. Through this, there is a

general indication that a South Coast desalination plant location is most appropriate.

The most apparent parameter required to optimise the production of energy through the solar

process is sunlight. The best climate for solar power production is inland in the Southern area of

the Negev Desert. The climate here is drier and sunnier than anywhere else in the country. More


9


specifically, the Negev Desert is a well-suited location for the power plant as the land is cheap

and readily available. This will help to reduce the costs of the project and allow a cheaper source

of potable water to be developed. The solar plant itself will require a reasonable amount of land,

this can be well accounted for in the desert due to the large expanse of cheap, undeveloped land

being available. This is also important to aid the potential to house future expansion as well as to

minimise the use of land, which may need special permission or have any historical preservations.

As mentioned, due to the national grid it is possible to locate the power plant in a relatively

undeveloped area as Israel is well connected by its national grid. Through consideration of the

main towns in the South of Israel, Beersheba is a very well suited location for the solar power

plant (see Figure 2). The town is the largest in the Negev desert and has sufficient infrastructure

in order to support the construction and operation of the solar power plant. This infrastructure

includes good connections to the national grid, good transportation links and other industries. By

situation the plant close to other infrastructures there are the added benefits of shared security,

roads and access, and the service facilities. To further this, Beersheba is the solar capital of Israel

with the vast majority of the solar industry being situated in the city. This gives the area the

advantage that there will be specialists in the areas (both as workers, labourers and professionals)

as well as giving evidence that this is the best area to sight such an industry.

Figure 2 : Solar plant location (Google Maps, 2010)


10


Figure 3 : Process Location (Google Maps, 2010)

4.3 Process Location

Through locating the process plant on the Coastal Region of Israel, South of Tel Aviv and close to

the town of Palmachim (see Figure 3), there are a number of advantages. Firstly, considering the

population growth issues, which were discussed earlier, Palmachim is far enough South to help

deliver good quality water to the areas of Ashdod and Ashkelon. In addition to this, being close to

the expanding capital of Tel Aviv means that there will always be a demand for water. However,

through Israel‟s integrated and interconnected national and regional water supply systems, local

needs can be supplied through these grids. The NWC can be used in order to adjust the flow of

water in order to meet the demand to the South of the desalination plant‟s site. Through this any

excess water produced can therefore be used further up the system or as a means of replenishment

for the Natural Water sources such as the Sea of Galilee, thus aiding in the prevention of over

pumping. Through the use of the National Water Carrier, only large blocs of water are relevant to

national planning, meaning that the vast majority of the country‟s water can be supplied through a

relatively small number of large capacity plants. One of the advantages of this approach is that it

takes advantage of the economies of scale and therefore causes a reduction in the price of water.


11


In addition to this, the proximity of the site to the Gaza Strip must be considered. The Gaza Strip

and Israel have a history of violence and if the plant is located close to the Israeli-Gaza border,

there is the potential that it may become a terrorism target. The importance to avoid this situation

is huge. By locating the plant near to Tel Aviv in a slightly more Northern position, it‟s proximity

to the Gaza strip is decreased thus reducing the likelihood that it will be a target for these attacks.

In order to fully utilise the NWC, the most favourable points for trying to integrate a large

production plant are close to an existing pumping station and operational reservoir. This was

therefore a key consideration in choosing Palmachim as a location for the new RO site. Figure 4

shows the site in relation to both the NWC and closest pumping station.

Figure 4 : Location of NWC and local pumping stations (Merokot, 2010)

More specifically, the plant will be located to the North of Palmachim and South of Tel Aviv in

an area where other industrial processes are located. The following image, Figure 5 details this

location. As can be seen, it is close to the inlet, close to infrastructure and a good road system and

yet, the location is well suited to house an industrial development as it is unlikely to cause a huge

amount of disruption.

Pumping

Station

NWC


12


Figure 5 : Process Plants Location (Google Maps, 2010)

The following gives a better insight into the quantitative data that backs up the reasoning behind

choosing Palmachim as the location for the process plant:

The sea water intake line will be approximately 2km

The product delivery line (i.e. distance to the NWC) is approximately 10km

There are low land costs, due to the „waste land‟ nature of the site of approximately 50

USD/sq.m

(DREIZIN, Y. ET AL, 2007) (GOOGLE MAPS, 2010)

Having relatively short water intake line as well as delivery line results in reduced costs for the

project both capitally and operationally. This also limits disruption to the local environment. Also,

the distance from existing sources of seawater contamination should also be considered along

with any potential sources of contamination e.g. oil spills.

Process location

Desalination: Group 2 Process

13

Section 5 Author: SA

5 Process

5.1 Pre-Treatment Process Description

Untreated seawater contains biological substances and solid particles that will cause membrane

fouling and deposit on process equipments. Therefore the intake and pre-treatment method employed

will determine significantly the amount of biological substances and solid concentrations in the

seawater feed to the RO membrane.

Figure 6: Block diagram of the pre-treatment section

The designed pre-treatment section of the desalination plant consists of (1) Intake system, (2) Intake

wells, (3) Intake pumps, (4) Coagulant storage and pump, (5) Ultrafiltration membranes, (6) Filtrate

tank, (7) Backwash pumps, (8) Sodium hypochlorite storage and pump. Each of the stages in the pre-

treatment section is described and sized in the following pages along with related information and

information related to other available processes. The process block diagram can be found in

Appendix A.

5.1.1 Intake system

Selecting the appropriate intake method is the first important decision to be made in any desalination

process. Intake point and intake system used doesn‟t only affect feed water quality but also affect

marine life and marine environment. Below are brief descriptions of the different types of intake

methods along with more detailed information about the selected intake system.

5.1.1.1 Conventional open seawater intake system

In a conventional open seawater intake system, seawater is taken directly by pipes, using active or

passive screens of different kind (PETERS, T. ET. AL., 2008); this can be either surface water intake

or deep water intake. Deep water intake is widely used because water quality is much better at low sea


14


levels. Open intake using active screens causes a problem to the process due to acceleration of

biological fouling risk in the system which has negative effects on operating costs and availability of

plant (PETERS, T. ET. AL., 2008) the strong water suction of open intake system poses a risk of

impingement and entrainment for marine life. Very small particles and organisms will easily pass

through the intake screens and into the plant and significantly deteriorate feed water quality.

5.1.1.2 Indirect seawater intake with Beach wells

Beach wells can be both vertical and radial bore holes constructed on the beach side (LENNTECH,

N.D.). They make use of the sandy soil as natural prefiltration and thus deliver a better feed water

quality. More importantly, the danger of impingement and entrainment is avoided. However, beach

wells depend on geological conditions and can only provide limited water volumes which are

generally not enough for large plants which makes them unsuitable for the purpose of this design.

5.1.1.3 Indirect seawater intake with HDD-based Neodren technology

This technology is based on horizontal drains, consisting of patented special porous filter pipes, that

are acting as wells (PETERS, T. ET. AL., 2008). Higher intake volumes can be delivered by

Horizontal Directional Drilling (HDD). This technique installs pipelines under the seabed. The water,

pre-filtered by the geological layers, can be collected in sufficient quantities, independent of waves,

currents and tides (PETERS,T. ET. AL., 2007). The advantages of this system is that it allows a

constant intake of seawater with no turbidity and the sand of the sea bed will act as a natural pre-filter

hence producing filtered seawater.

HDD is not suitable for all geologic conditions and is difficult to construct and to maintain (PETERS,

T. ET. AL., 2008) this system was initially considered as the intake method for the desalination plant.

The quoted maximum specific flow for each drain is 150 l/s/drain at this rate the required number of

drains will be around 60 drains at 600 metres long and 0.7 m in diameter. Too many unknowns

prevented the design and selection of this system.

5.1.1.4 Indirect seawater intake with seabed filtration based on buried pipes (Chosen

intake system)

The idea of this system is based on slow sand filtration. A filtration bed is constructed under the sea

floor using several layers like crushed stone, gravel, replaced sand and original sand as it can be seen

from Figure 7. The buried pipes under the constructed bed collect clear seawater, which permeates

the sand on the ocean floor, without installing structures which might affect the surrounding

environment (FUKUOKA DISTRICT WATERWORKS, N.D.). A natural, biological filtration

process reduces organic and suspended solids loading on the desalination plant. Therefore, additional

pre-treatment is not required (LONGBEACH WATER, N.D.)


15


Figure 7: Cross-section of seabed intake system based on filter bed (Peters,Thomas; Pintó,Domènec,

2008)

The designed sand filtration rate is at ~ 5.9 m3 per m

2 of sand bed, at this slow filtration rate, the

filtration bed is virtually maintenance free, requires no backwashing, cleaning, treatment, recharging,

and rehabilitation (LONGBEACH WATER, N.D.). The flow rate and operation of the system is

unaffected by wave action and tidal forces, in fact tidal forces improve operation as they act as a

natural cleaning agent for the beach sand (LONGBEACH WATER, N.D.).

5.1.1.5 Intake system used in Uminonakamichi Nata Sea Water Desalination plant

Fukuoka, Japan

Long Beach Water Department has constructed the under ocean intake system in Fukuoka

desalination plant which produces 13.2 MGD. The intake system was constructed in 2005 and is still

operational today. The reported average filtration rate is at 5.1 m3 per m

2 of sand bed and there is no

increase in head loss across the sand filters during the operational time indicating that there is no

waste/solids build up on the sand beds and hence no need for backwashing and maintenance also the

sand beds were not affected by a magnitude 6.6 earthquake on July 16, 2007. (LONGBEACH

WATER, N.D.). The report from the working desalination plant showed that sand filter effluent has a

Silt Density Index (SDI) of 2, this will greatly reduce workload of the ultra filtration membranes.

In summary, this system is tested and is operational. Filtration rate has the potential to be increased

which will result in smaller intake areas and hence lower capital cost. The system is environmentally

friendly while in operation, there are no structures above the seabed that could affect marine life and

marine environment.


16


5.1.1.6 Design of intake system

Figure 8: Diagram showing the intake pipes

The intake system will be made of sand beds consisting of engineered sand at a depth of 1.5 m,

grading crushed stones at a depth of 0.3 m and crush stones at a depth of 2.3 m. Each sand bed will

have a network of pipes underneath the seabed to transport the filtered water to the desalination plant.

Filtration rate = 0.1 gpm/ft2 = 5.9 m

3/m

2 this is the required filtration rate, however the average

filtration rate of a working plant is around 5.1 m3 per m

2 of sand bed

To achieve the required target of potable water, a total of 764277 m3/day of seawater is required,

therefore total sand bed area required will =

m2

There will be 4 identical sand bed areas each providing identical flows of seawater, therefore

Area of each sand bed

37453 m

2

Selecting a bed length at 350 metres the bed width will =

107 m

Bed dimensions: Bed length = 350 m, bed width = 107 m, bed area = 37450 m2

Volume of engineered sand in each bed = 1.5 × 37450 = 56175 m3

Volume of grading crushed stones in each bed = 0.3 × 37450 = 1124 m3

Volume of crush stones in each bed = 2.3 × 37450 = 86135 m3

Main water collecting pipe: Length of the water collecting main pipe = 350 m

Number of main water collecting pipes = 4, diameter of collecting pipe = 1.8 m

Length of collecting pipe = 350 m

Water collecting branch pipe: Length of collecting branch pipe = 48.2 m, Diameter of collecting

branch pipe = 0.6 m, Pitch = 5 m, Total number of branch pipes in each bed = 113


17


Total number of branch pipes in all beds = 450

Each bed will be connected to water well by a PVC pipe of diameter 1.7 m and a length of 640 m

offshore. The intake wells are designed to hold the incoming water for a maximum of 10 minutes.

5.1.1.7 Water intake wells

4 identical seawater intake wells placed below sea level, at a capacity of 1327 m3 each. At this

capacity, each intake well is capable of holding feed seawater for 10 minutes from each bed.

Total volume of water produced by each bed = Area of bed × flow per m2 of bed

= 37453 m2 × 5.1 m

3/m

2 = 191069 m

3/day

Total volume of water held for 10 minutes = (191069/1440) × 10 = 1327 m3

5.1.1.8 Water intake pumps

4 variable speed pumps, each connected, to one water well, will be used. The pumps are designed to

increase the feed water pressure to 3 bars and pump the seawater feed directly to the UF membrane.

Ph = q ρ g h / (3.6 106)

Ph = power (kW), q = flow capacity (m3/h), ρ = density of fluid (kg/m

3), g = gravity (9.81 m/s

2), h =

differential head (m)

Calculating power required for each pump:

Volumetric flow rate from each bed = 191069 m3/day, q =

= 7961 m

3/h

Average Seawater density ρ = 1022 kg/m3,

Differential head h = 30 m, g = 9.81 m/s

2

Pump power required =

= 665 kW

Ps = Ph / η η = 0.75

Where Ps = shaft power (kW), η = pump efficiency: Ps =

Total power required = 887 × 4 = 3.55 MW

Pump material of construction: Stainless steel

5.1.2 Conventional and non-conventional pre-treatment

Pre-treatment technology is divided into conventional pre-treatment and non-conventional pre-

treatment. Conventional pre-treatment includes disinfection, coagulation/flocculation and filtration

process (PRIHASTO, N. ET.AL, 2009). Conventional pre-treatment is a complex, chemical based

process that has been widely used as the method for pre-treatment for seawater and brackish water RO

plants. This way of pre-treating seawater is being replaced slowly by non-conventional pre-treatment

such as microfiltration, ultrafiltration and the beachwell system (PRIHASTO, N. ET.AL, 2009). Pre-

treating seawater plays a vital role both economically and environmentally. The economical


18


importance of pre-treating seawater is due to the fact that the method selected for pre-treatment will

determine RO feed quality and hence determine RO flux rate and RO membrane life time.

5.1.2.1 Conventional pre-treatment

A typical conventional pre-treatment process will heavily depend on many different chemicals and

processes to achieve the required RO feed quality. In a conventional pre-treatment a flocculent is first

added to the incoming seawater stream to effectively neutralise like charges and allow suspended

solids to group together in flocks (GREENLEE, LF. ET. AL, 2009) creating large size clusters out of

the dispersed particles.

Adding flocculent to the seawater is also a shared practice in the non-conventional membrane pre-

treatment but at considerably low dosages. Flocculants are typically small, positively charged

molecules; both inorganic and organic coagulants are used. Inorganic coagulants include iron or

aluminium salts such as ferric chloride or aluminium sulphate while organic coagulants are typically

cationic, polymers such as dimethyldiallylammonium chloride or polyamines (GREENLEE, LF. ET.

AL, 2009)

After flocculent dosage the seawater stream is passed through multimedia filtration units. More

flocculent is dosed to the stream leaving the multimedia filtration units, to create more large clusters

and these will be separated from the seawater stream using sand filters. Turbidity of media filtration

permeate is often around 0.1 NTU and SDI is commonly reduced by a factor of 2 (GREENLEE, LF.

ET. AL, 2009)

The seawater is further injected with acid as disinfection. Acid dosing is followed by dechlorination in

an attempt to remove chlorine by using chemicals such as sodium bisulfite or using granular-activated

carbon to prevent RO membrane damage (PRIHASTO, N. ET.AL, 2009).The dechlorinated seawater

goes through a final filtration step, through cartridge filters that act as a final polishing step to remove

larger particles that passed through media filtration.

Variations in feed water can cause variations in conventional pre-treatment effectiveness

(GREENLEE, LF. ET. AL, 2009) often, colloids and suspended particles pass through conventional

pre-treatment and contribute to difficult to remove RO membrane fouling (GREENLEE, LF. ET. AL,

2009). This problem in consistency and the fact that the conventional pre-treatment is a chemical

hungry process which could affect marine life, prevented the selection of this method as the pre-

treatment for this process.

5.1.2.2 Non-conventional pre-treatment

Non-conventional pre-treatment is a membrane based pre-treatment, it uses larger pore size membrane

compare to RO membrane such as microfiltration, ultrafiltration and nanofiltration membranes. MF


19


and UF membranes has gradually gained acceptance as the preferred pre-treatment to RO in recent

years. UF can remove all suspended particles and some of dissolved organic compounds, with the

removal rating dependent upon their molecular mass and on the molecular mass cut-off of the

membrane (PRIHASTO, N. ET.AL, 2009).

The membranes act as a defined barrier between the RO system and any suspended particles, they can

lower feed water SDI to less than 2 and turbidity to less than 0.05 NTU and hence produce the

required feed quality to the RO membrane (GREENLEE, LF. ET. AL, 2009)The real advantage of

using a membrane pre-treatment is the fact that it always provides a consistent feed quality compare

to conventional pre-treatment. Membrane pre-treatment reduces the general aging and destruction of

RO membranes by feed water components, RO membrane replacement decreases, as well as the

frequency of chemical cleaning (GREENLEE, LF. ET. AL, 2009)

Of the three different membranes, ultrafiltration membranes represent the best balance between

contaminant removals and permeate production. UF membranes have smaller pore sizes than MF

membranes and higher flux than NF membranes also UF membranes are cheaper than NF membranes.

(GREENLEE, LF. ET. AL, 2009). Cost wise, using UF membranes does not increase the cost

associated with the pre-treatment. The additional cost of having to replace the UF membranes at the

end of their useful life time is more than offset by the cost reduction in use of chemicals (mainly

coagulant) (KNOPS,F. ET. AL., 2007)

5.1.2.2.1 Ashdod, Mediterranean Sea Pilot Plant

The UF membrane was tested against a conventional pre-treatment process in Ashdod Israel; the

results show that ultrafiltration membranes produced consistent permeate quality compare to

conventional system.

The SDI15 was reduced to 2.6–3.8 for conventional system and 2.1–3.0 for the UF membrane system.

Nevertheless, during the storm periods when there was a high concentration of suspended solids in the

feed water the UF pre-treatment performed significantly better than the conventional system.

(PRIHASTO, N. ET.AL, 2009)

The UF membranes have been tested in many pilot plants and currently operational in many

desalination plants. The above findings encouraged the use of UF membrane as the pre-treatment

system for this process.

5.1.2.3 Ultrafiltration membrane

There are different types of UF membranes. The most expensive type is the tubular ceramic

membranes, due to their high resistant. This high price makes them uncompetitive for seawater pre-

treatment and limits their uses for special processes only (GILLE, D. ET. AL., 2005). On other scale,


20


the cheapest type of UF membranes are spiral-wound membranes, this type of UF membrane requires

spacers in the middle which affects backwash effectiveness and hence is not recommended for

seawater desalination (GILLE, D. ET. AL., 2005).

The hollow fibre membranes provide the better of the two mentioned types; they are reasonably

priced and can be used for seawater desalination. There are three different kinds of hollow fine fibre

ultrafiltration membranes available. The single hollow fine fibre, the submerged hollow fine fibre and

multi-bore membranes (GILLE, D. ET. AL., 2005).The multi bore membrane is the selected

ultrafiltration membrane used for this design.

5.1.2.3.1 Multibore membrane

The Multibore UF membranes specifically the dizzer® XL 0.9 MB 60 W made by Inge are hollow

fibre membranes with 7 capillaries integrated into a single fibre, they are made of modified

polyethersulfone (PESM). This UF membrane has a molecular weight cut-off of 100.000–150.000

Dalton (pore diameter 20 nm). Flow direction during filtration is from inside of the capillaries to

outside of the fibre. The foamy support structure surrounding the 7 integrated capillaries guarantees

extraordinary stability and full membrane integrity during operation and cleaning. Inner diameter of

the capillaries is 0.9 mm; outer diameter is 4.3 mm (BU-RASHID, K. ET. AL., 2007).

The dizzer® XL has 60 m² membrane surface area and has a flux rate during filtration that range

between 60-180 l/m2h.The transmembrane pressure during filtration range between 0.1-1.5 bar

(INGE, N.D.). The UF system was designed using Inge‟s T-Rack vario unit, specifically the TR-80-4-

V. This unit has 4 rows and supports 80 dizzer® XL 0.9 MB 60 W membranes which provides 4800

m2 of membrane surface area (INGE, N.D.). The T-Rack unit has a length of 7 m and width of 1.4 m

and will occupy a very small area. This type of membrane was reported to be operational for 8 years

with no breakage, also this membrane have boosted the water treatment capacity by 20% without any

increase in the module‟s size (inge).

The operating philosophy of the UF system is to keep the transmembrane pressure (TMP), the main

indicator of membrane fouling, at a continuously low level close to the initial 0.1 to 0.2 bar of a new

module (INGE, N. D. ). Therefore the selected transmembrane pressure for this design is at 0.2 bar.

The average reported permeability for this membrane at seawater operating condition is at 350

l/m2hbar (INGE, N. D. ).

5.1.2.4 Membrane Design Calculations

The T-Rack system contains the dizzer® XL 0.9 MB 60 W, a specifically designed ultrafiltration

membrane for seawater desalination as mentioned before. The area of each membrane = 60 m2, and

TR-80-4-V rack contains 80 membranes so total membrane area in each TR-80-4-V rack = 60 × 80 =

4800 m2. Average reported permeability at seawater desalination process = 350 l/m

2hbar.


21


The idea is to try and keep the transmembrane pressure as low as possible and average reported

transmembrane pressure for seawater desalination process is at 0.2 bar therefore flux rate can be

calculated Jw = Lw∆P. where Jw is the flux, Lw is the permeability and ∆P is the transmembrane

pressure, therefore. Jw = 350 × 0.2 = 70 l/m2h

During the filtration step all the feed is converted to permeate, therefore

Feed flow rate = permeate = 31844892 l/h

Total area of membrane required to treat this amount =

= 454927 m

2

Total number of TR-80-4-V rack =

= 95 racks

Cost of 1 T-Rack system delivered to Israel = 135,0001 Euro

Conversion rate on the day of calculation = 0.849647

Total cost of 1 T-Rack in £ = 135000 × 0.849647 = 114702

Total cost of all the required racks in £ = 114702 × 95 = 12794822

The installed cost £ = 20087871

5.1.3 Filtration and backwash

Backwashing the membrane is required to remove all particulates accumulated during the filtration

time it destroys the accumulated foulant layer which diminishes the active membrane surface. The

backwash frequency may vary from 20 min to every few hours depending on the system and the feed-

water quality (XU, J. ET. AL., 2007). The average reported filtration rate of this type of membrane at

operational around the Mediterranean Sea was found to be around 40-45 minutes (Inge, World Water

and Environmental Engineering). The selected filtration duration for this design is 40 minutes of

filtration, followed by membrane backwash. Efficiency of regular backwash depends on backwash

duration, filtration duration, and backwash flow rate (XU, J. ET. AL., 2007).

It can be observed that UF permeate flow decreases with filtration duration, which indicated that the

longer the filtration duration, the stronger the accumulated foulants. However, backwash water

volume decreases with filtration duration. Thus, the cost-oriented optimization of UF plant design

requires the selection of an appropriate values of backwash frequency and backwash duration (XU, J.

ET. AL., 2007)

1 (Doron Meyer)


22


Backwash rate is given by Inge for dizzer® XL 0.9 MB 60 W at 230 l/m

2h (INGE, N.D.) and the

backwash duration at 50 s. a chemically enhanced backwash is also performed for 10 s using 20 ppm

Sodium Hypochlorite (XU, J. ET. AL., 2008)

5.1.3.1.1 Backwash and backwash rate calculations

The backwash rate given by the manufacturer = 230 l/m2h

Backwash duration = 50 s

Total filtrate required for washing 1 m2 of membrane =

× 50 = 3.194 l/m

2 = 0.003194 m

3/m

2

Total filtrate required for washing all the membranes (1 backwash) = 0.003194 × 454927 = 1453 m3

As stated in the background information the average duration of filtration is 40 minutes and therefore

a backwash is required every 40 minutes, and assuming total operational hours per day = 24

Therefore number of backwashes required = (24×60)/40 = 36 washes

The total volume of filtrate required for backwashing every day = 1453 × 36 = 52317 m3/day

Total filtrate produced every day = 764277 m3/day

% of permeate used for backwashing =

× 100 = 7 %, therefore recovery of this UF system =

93%

5.1.3.1.2 Backwash pump power requirement

Total filtrate required for backwashing = 52317 m3/day = 2180 m

3/h

Density of seawater = 1022 kg/m3, Differential head= 15 m, Gravity = 9.81 m/s

2

Ph =

= 91 kW, η = 0.75

Ps =

= 121 kW

Number of backwash pumps required =3

Power rating of each pump =40.5 kW

5.1.3.1.3 Sodium Hypochlorite consumption, storage and pump

Sodium Hypochlorite will be used during backwash and it needs to be available and stored for 30

days. Amount of NaOCl required = 20 ppm and amount of filtrate used for backwash = 2180 m3/h

NaOCl will be used for 20% of the time, therefore amount of filtrate used with NaOCl = 2180 × 0.20

= 435 m3/h = 445563 kg/h

NaOCl required = 445563 × 20 = 8911262 mg/h = 8.91 kg/h

Therefore total amount of storage required for 30 days = (8.91 × 24) × 30 = 6416 kg

Density of NaOCl at storage conditions = 5583 kg/m3


23


Volume of NaOCl storage tank =

= 1.1 m

3

Price2 of NaOCl per ton = £ 139, Pump power requirement = 0.056 W

5.1.4 Coagulant use

Affect of adding coagulant before UF membrane has been investigated in many research, however the

affect of adding FeCl3 before the multibore membranes was performed at the IWW Rheinisch-

Westfalisches Institut fur Wasser, Mulheim, Germany. The tests showed that, the iron injected as

FeCl3 builds up on the membrane surface acting as a pre-filter to UF membrane. It protects the

membrane from irreversible fouling by dissolved organic compounds (DOC), because these

compounds get connected to the Fe-flocs and can be backwashed instead of blocking pores of the

membrane. (BU-RASHID, K. ET. AL., 2007). The dosage of coagulant is very important, high

dosage will result in sludge deposits build up in pipes and valves between the injection point and the

membrane. 0.3 ppm of FeCl3 was found to be sufficient at a pilot plant in Ashdod, Israel

(GLUECKSTERN, P. ET. AL., 2002)

5.1.4.1 Coagulant consumption, storage and Pump

Coagulant used: FeCl3, Amount of Coagulant required = 0.3 ppm. Mass flow rate of seawater =

32545479 kg/h. Flow of coagulant required = 0.3 × 32545479 = 9763643 mg/h = 9.8 kg/h

Density of FeCl3= 2895 kg/m3 therefore storage is required for 30 days therefore coagulant to be

stored = 9.8 × 24 × 30 = 7030 kg/month. Total volume = 7030/2895 = 2.43 m3

Price3 per Ton = £ 474, Storage tank material of construction: Titanium

Pump power requirement = 0.08 W

5.1.4.2 Filtrate storage Tank

Two filtrate storage tanks are designed to hold a maximum of 5 minutes of feed volume flow rate

each. Feed volumetric flow rate = 31845 m3/h, Volume of filtrate tank =

× 5 = 2654 m

3

Number of tanks = 2 and the volume of both tanks = 2 × 2654 = 5307 m3

5.2 Post treatment

The produced desalinated water should meet all the standards required, this includes meeting drinking

water standards and also water produced should be non-aggressive and non-corrosive. RO permeate

2 (allianceonline)

3 (Shijiazhuang Jinghua Magnesium Co.)


24


may be corrosive to water distribution systems, and mixing such water with other water sources in the

distribution system can result in corrosion of metallic constituents and in “red water” events

(BIRNHACK, L. ET. AL., 2008)

The red water is caused mostly by iron oxides detaching from the internal surface of metal pipes into

the water and arriving at the consumer‟s tap with a characteristic yellow-brown-red colour


Three parameters are considered to control the chemical stability of drinking water: The ability of the

water to withstand changes in pH when a strong base or a strong acid are added to it is considered the

first parameter, the tendency of the water to precipitate CaCO3, the concentration of soluble Ca2+

ions

in the water and the fourth relevant parameter, pH, is a dependant parameter that is determined by the

values of the previous three. (BIRNHACK, L. ET. AL., 2008).

Figure 9: Post-treatment block diagram

The designed post-treatment section of this desalination plant consists of the following (1) CO2

storage, (2) Sulphuric acid storage and pump, (3) Pump, (4) Calcite bed reactor, (5) Ion exchanger

columns, (6) Sodium hydroxide storage and pump, (7) Product water storage and pump. Further

information about each step will be discussed in more detail in the coming few pages

The Israeli Ministry of Health have accepted the proposed quality criteria set by the Committee for

the Update of Water Quality Standards appointed in 2005. They proposed that all desalinated water

produced in Israel should have the following quality; Alkalinity > 80, 80 < [Ca2+

] < 120, 3 < CCPP <

10 (all concentrations in mg/L asCaCO3), and pH < 8.5. (BIRNHACK, L. ET. AL., 2008). The

following paragraphs looks at the possible ways of treating desalinated water starting with blending

with a treated saline water source.


25


5.2.1 Blending with a treated saline water source

This method of treating desalinated water only achieves partial stabilisation by blending the

desalinated water with mineral rich waters such as brackish ground waters or seawater. This way of

treating desalinated water is generally undertaken only for distillates from thermal desalination

facilities because the TDS values obtained from SWRO plants are already high and blending is not

necessary. This way of post treatment does not achieve all the necessary required water quality

requirements and further CO2 and either lime or limestone treatment will still be required (WITHERS,

A., 2005)

5.2.1.1 Using chemicals to stabilise desalinated water

Re-carbonation and remineralisation using chemicals is the wide used method of post treatment. The

following is some of the combinations and chemicals used to achieve the water quality required.

5.2.1.1.1 Method 1: Using carbon dioxide and excess hydrated lime

2CO2 + Ca (OH) 2 Ca (HCO3)2, this method is commonly used to add alkalinity to water to make

it non-aggressive and non-corrosive. It is simple and widely used in the treatment of desalinated

water. The major complication with this process is associated with the lime systems (WITHERS, A.,

2005). The use of hydrated lime slurry will increase product water turbidity if hydrated lime below

96% Ca (OH) 2 is used without the use of saturators. This problem can be avoided by using hydrated

lime of 98% Ca (OH) 2 (WITHERS, A., 2005)

5.2.1.1.2 Method 2: Using carbon dioxide through a bed of limestone

CO2 + CaCO3 + H20 Ca (HCO3)2

This method theoretically requires half the amount of carbon dioxide compare to the first method.

However, in practice, the CO2 requirement of the limestone process compared to the lime process

could typically be 65-85% of the required CO2 quantity used within the lime process. This process is

more complex compare to the lime process and requires additional plant items (WITHERS, A., 2005)

5.2.1.1.3 Method 3: Using hydrated lime and sodium carbonate

Ca (OH) 2 + Na2CO3 CaCO3 + 2NaOH

This treatment is more appropriate to natural water containing some alkalinity and free CO2. Sodium

carbonate is expensive and due to high operating costs this method is not used in large desalination

plants (WITHERS, A., 2005)

Direct dosage of chemicals is usually expensive and when desalinated water is diluted with other

water sources further chemical dosage usually becomes unavoidable, if all criteria are to be met

Therefore, processes that are based on dissolving CaCO3 (typically calcite) for alkalinity and Ca2+


26


supply are most cost effective, particularly in places where CaCO3(s) is readily available (e.g. Israel).


5.2.2 Selected post-treatment method

The selected method of post treatment is based on the method developed by Liat Birnhack, Shaul

Oren, Orly Lehmann and Ori Lahav. They developed a way of providing treated water that meets the

Israeli water quality standards and at the same time provide water rich in Mg2+

ions. The reason

behind their interest in providing water rich in Mg2+

ions is based on the recent WHO publication

which stresses the role of Mg2+

in drinking water on the human body and the possible implications of

magnesium deficiency on the public health. WHO has recently recommended a minimum

concentration of 10 mgMg/l in all drinking waters (BIRNHACK, L. ET. AL., 2010). Low magnesium

status has been implicated in hypertension, coronary heart disease, type 2 diabetes mellitus and

metabolic syndrome. (COTRUVO, J. ET. AL., 2009)

The process is based on calcite dissolution using H2SO4 and CO2 for alkalinity and Ca2+

ions supply

and subsequently replacing part of Ca2+

ions with Mg2+

ions that originate from seawater. Separating

Mg2+

from seawater is carried out using a specific IX resin (BIRNHACK, L. ET. AL., 2010).

The post treatment process is divided into 4 steps, 1st step is the acidification step in which both

sulphuric acid and carbon dioxide are used to increase the acidity of the seawater. The 2nd

step is the

calcite dissolution step in which the acidic seawater reacts with the calcite and Ca2+

are produced, the

3rd

step is the ion exchange step in which Ca2+

rich seawater pass through a resin bed loaded with

Mg2+

ions. The final and 4th step is the addition of sodium hydroxide and storage.

5.2.2.1 Acidification Step

In order to enhance calcite dissolution kinetics, water pH must be reduced before it is introduced into

the calcite reactor. Typically H2SO4 and CO2 (g) are used to lower the pH of the seawater prior to

entering the calcite beds. The advantage of using a strong acid such as H2SO4 is that pH can be

lowered to any desired value, which results in rapid CaCO3 dissolution kinetics and hence relatively

small calcite packed bed reactors are required.

The major disadvantage of this process is the fact that it is bound to yield a ratio of approximately 2 to

1 between Ca2+

and alkalinity concentrations what this means is that the Ca2+

concentration will be

higher than the upper limit of 120 mg/L as CaCO3. Another disadvantage of this process is the release

of substantial amount of SO42-

to the water (BIRNHACK, L. ET. AL., 2008).

Using a combination of both acids results in an intermediate split flow and thus also in intermediate

reactor sizes. The required water standards will also be met by further dosing NaOH (BIRNHACK, L.

ET. AL., 2010).


27


5.2.2.2 Calculating total amount of sulphuric acid and carbon dioxide required:

50% of the treated seawater produced by the RO membrane will go through to the post treatment

section, while the rest 50% goes to storage.

5.2.2.3 Sulphuric acid consumption, storage and pump

Sulphuric acid required = 65 mg/l4 of product water. Volumetric flow rate of RO permeate =12557 m

3

Permeate to go through to the post treatment section = 12557 × 0.5 = 6278 m3/h = 6278538 l/h

Sulphuric acid required = 65 × 6278538 = 408105022.8 mg = 408 kg/h

30 days storage is required for the acid, therefore total amount of acid to be stored = 408 × 24 × 30 =

293836 kg. Price5 of H2SO4 per ton = £ 77. Monthly cost =

Density at storage conditions = 1832.9 kg/m3 therefore storage tank volume =

= 160 m

3

H2SO4 pump power requirement = 0.0041 kW

5.2.2.4 Carbon dioxide consumption and storage

CO2 required at a rate = 18.5 mg/l 6 of product water. Total seawater going through post treatment

section = 6278538 l/h. Total CO2 required = 6278538 × 18.5 = 116152968 mg/h = 116 kg/h

Storage for 30 days = 116 × 24 × 30 = 83630 kg. Price7 of CO2 per ton = £ 96. Monthly cost =

. Carbon dioxide will be stored at -17.8 ⁰C and at 21 bars, at these conditions,

density of carbon dioxide = 1020 kg/m3, therefore, volume of CO2 storage =

82 m

3

5.2.2.5 Calcite Dissolution Step

Calcite dissolution processes are cost effective in places where calcite abounds in nature and can be

easily extracted (as is the case in Israel) (BIRNHACK, L. ET. AL., 2008). Calcite is calcium

carbonate, commonly with some impurities of iron, magnesium, manganese and occasionally with

zinc and cobalt (WWW.MINERALS.NET)

The calcite bed is used for alkalinity and supply of calcium ions. The acidified water enters the calcite

reactors and CaCO3 is dissolved. Calcite reactor effluent will have the following characteristics:

Alk = 85 and [Ca2+

] = 126 mg/l as CaCO3

H2SO4 → 2H+ + SO4

2−

4 (Birnhack,Liat; Oren,Shaul; Lehmann,Orly; Lahav,Ori, 2010)





28


H+ + CaCO3(s) ↔ Ca

2+ + HCO3

−

CO2 (aq) + H2O + CaCO3(s) ↔ Ca2+

+ 2HCO3−

5.2.2.6 Design of calcite reactor

Calcite8: Bulk density = 90 lbs/cu.ft= 1442 kg/m

3 Composition: CaCO3 0.95%, MgCO3

0.03%. Amount of CaCO3 required = (126 mg/l product water)9 = 791 kg/h

Total amount of calcite required =

= 833 kg/h

The calcite will be toped up every 15 days, total calcite required for 15 days = 833 × 24 × 15 =

299747 kg. Price10

of calcite per ton = £19.2. Monthly cost = (

Volume of Calcite required =

= 208 m

3. Number of Calcite reactors selected = 20, therefore

volume of Calcite in each reactor = 10 m3. Reactor diameter selected = 3 m; therefore reactor cross

sectional area = 7 m2, reactor length = 2.2 m. Calcite bed length = 1.5 m. Flow rate of product water

to each bed = 314 m3/h Pressure drop across calcite bed = 0.15 bar. Pressure drop was calculated

using Figure 56 in Appendix A.

5.2.2.7 Ion Exchange Step

The ion exchange process is divided into three steps: an exchange step, load step and drain step.

(Birnhack,Liat; Oren,Shaul; Lehmann,Orly; Lahav,Ori, 2010)

In the exchange step, Mg2+

ions loaded resin is brought to contact with calcite effluent water that

contains a high Ca+2

concentration and virtually no Mg2+

. As a result, Mg+2

ions are released to the

water. Following the exchange step a “load” step is initiated, in which Mg2+

ions are preferentially

separated from seawater onto the resin.

The final step is the “drain” step, in which seawater which remains in the resin‟s pores at the end of

the load step is drained from the bed, using pressurised air.

5.2.2.8 IX reactor

Product water through resin beds = 6279 m3/h

Manufactures given maximum flow = 40 BV/h. Maximum flow taken for this design= 38 BV/h

Required bed volume of resins =

= 165 m

3

8 (clackcorp)




29


Volume of resin required for both load and exchange step = 165 × 1.08 = 178 m3

Resin density = 755 kg/m3, therefore total weight of resin = 755 × 178 = 134724 kg

Number of IX columns selected = 35, therefore volume of resin in each column = 5 m3

Diameter of column selected = 2.5 m, therefore Cross sectional area of column= 4.9 m2

Height of column = 1.039 m, Column height considering any bed expansion = 1.35 m

Linear velocity across bed = 36.5 m/h. Pressure drop across bed = 0.8 bar, pressure drop was designed

to be as low as possible across both the calcite reactor and ion exchange beds. The graph used to

calculate the pressure drop across the IX beds can be found in Appendix A, Figure 57.

5.2.2.9 Calcite pump

Calcite pump is required to increase the pressure of the product water going to the post treatment

section. As the above calculations show, the sum of the pressure drops across the calcite reactors and

IX columns is around 1 bar. Therefore the pressure of the product water has to be increased by 1 bar.

q= 6279 m3/h, Density of seawater = 1022 kg/m

3, Gravity = 9.81 m/s

2, Differential head = 15 m

Ph =

= 262 kW, η = 0.75, Ps =

= 350 kW

5.2.2.10 Addition of Sodium Hydroxide

Sodium hydroxide is dosed to the water with the aim of raising the calcium carbonate precipitation

potential (CCPP value) from around −50 to +3 mg/l as CaCO3, but its addition also raises both the pH

and Alk values (BIRNHACK, L. ET. AL., 2010).

5.2.2.11 Sodium hydroxide consumption, storage and pump

NaOH required at a rate = (19.7 mg/l)11

of product water, therefore NaOH flow rate = 12557078 ×

19.7 = 247374429 mg = 247 kg/h. Storage for 30 days = 247 × 24 × 30 = 178109 kg.

Price12

of NaOH per ton = £ 257 Monthly cost =

Density of NaOH at storage Conditions = 1913 kg/m3, therefore volume required for 1 month storage

= 93 m3

5.2.2.12 Product water storage and pump

The intermediate product storage is used for the two feeds to mix; it is designed to hold the product

water for up to 10 minutes at the designed volumetric flow rate of 12557 m3/h=

× 10 = 2093 m

3

Product pump power requirement = 467 kW




30


5.3 Total operating cost and equipment cost for the pre and post

treatment sections

5.3.1 Total operating Cost

Table 1: Cost of chemicals used in pre and post treatment sections

Pre-treatment Chemicals

kg/month

required

Price per

Ton £

Cost Per

Month £

Cost Per

Year £

Ferric Chloride 7030 474 3333 40000

Sodium Hypochlorite 6416 139 892 10702

Post treatment Chemicals

Sodium Hydroxide 178110 257 45713 548557

Sulphuric Acid 293836 77 22624 271494

Carbon Dioxide 83630 96 7244 86930

Calcium Carbonate 569589 19 21928 263140

Resin Annual Replacement Cost = 91370

TOTAL = 1312194

The above table shows the total annual cost for chemicals used in both the pre-treatment section and

post treatment section.

5.3.2 Cost of resin replacement

The resin will be replaced at a rate of 10% per year. The total volume of resin required = 178 m3 total

cost of 1 litre of resin is at $813

total annual replacement cost of resin = 178 × 1000 × 0.10 × 8 = $

142400, the conversion rate used = 0.6416426, therefore price in UK pound = £91370

5.3.3 Cost of UF membrane Replacement

Table 2: UF Membrane Replacement Cost

Membrane life time 5 years

Cost to replace all membrane£ = 10235858

Its reported that membrane will last 8 years

Average life time of membrane = 6.5 Years

Number of replacements required = 3.4

Total cost during plant operational time £ = 34644442

The above calculation is based on the assumption that membrane will last an average age of 6.5 years.

However if the 5 years quoted by manufacturer is used then total replacement costs during the life

time of the plant = £ 40943432



31


5.3.4 Total Equipment Cost

Installation sub-factors method was used to determine the installed cost of all the equipments in the

pre and post treatment sections this can be found on the next page. This method is taken from GUIDE

TO CAPITAL COST ESTIMATING fourth edition by A.M. Gerard.

Most of the equipment prices were at year 2000 value, because the source used gave the equipment

values at that year so the price had to be inflated to this year‟s value. When that was done the final

capital employed had to be calculated by calculating the following

Engineering Design and supervision (15%), Management overheads (10%), Commissioning costs

(5%) and Working capital provision (15%)

Table 3: Total Capital Employed For Pre and Post Treatment section

The total cost of all equipments in the pre and post treatment section of this desalination plant totalled

up to £ 59969964. The full individual cost of the equipments in both sections is listed in Section 20.1,

Appendix A.

Total Cost of installed equipments Year 2000 £ 38750631

Total Cost of installed equipments year 2010 £ = 41358596

Engineering Design and supervision (15%) = 6203789

Management overheads (10%) = 4135860

Commissioning costs (5%) = 2067930

Working capital provision (15%) = 6203789

Total Capital employed £ = 59969964


32

Section 5 Author: PS

5.4 Multi Stage Flash Distillation (MSFD)

5.4.1 Process description

Desalination by MSFD operates based on the principle of flash evaporation. An MSFD unit is

comprised of a heat rejection section, a heat recovery section and a heat input section (Belessiotis and

Delyannis, 2006). Typically, there are 3 heat rejection stages (Hussain, 2009), with the remainder of

the stages being termed “heat recovery stages”. The brine heater, wherein heat is supplied to the

process, is the heat input section (Hussain, 2009).

Seawater is fed into the last stage of the evaporator at ambient temperature. It flows in tubes, through

all the stages of the evaporator, gaining heat from condensing steam in each stage. After gaining heat

from the 3 heat rejection stages, a major portion of the flow is rejected as cooling seawater, whilst the

remainder is used as make-up and combined with the concentrated brine stream from the last stage

(Khawaji et al., 2008). This combined stream, called the recycle brine stream, is then fed through

tubes into the heat recovery section, where it continues to rise in temperature as a result of the heat

transferred by condensing steam (Khawaji et al., 2008).

Following an incremental temperature rise in the heat recovery section, the recycle brine stream flows

into a heat exchanger, called the brine heater. In the brine heater, low pressure steam (2.0 – 3.0 bar)

(Darwish et al., 2008) transfers its latent heat to the recycle brine stream. The additional heat input

raises the temperature of the recycle brine stream to a maximum value. This temperature is called the

top brine temperature (TBT). The pressure at the brine heater is maintained such that it is always

above the corresponding saturation temperature. This ensures that the recycle brine stream remains

liquefied (Sommariva et al., 2010). Generally, waste heat from conventional power plants or boilers

act as the source of low pressure steam (Serra et al., 2006). The advantage of this is two-fold; firstly,

the waste heat produced by the power plant provides the process with energy that the MSFD plant

would otherwise have to purchase, thereby reducing the operating expense and secondly, this method

helps curtail the harmful effects that power plant exhausts have on the environment.

The MSFD stages are maintained at successively lower pressures to enable flash evaporation of the

brine stream (Khawaji et al., 2008). An orifice device placed at the inlet of each stage reduces the

pressure of the incoming brine stream to the value maintained in that stage (Khawaji et al., 2008).

Following heat addition in the brine heater, the recycle brine stream, now at its highest temperature

and pressure, is made to flow back into the first stage of the MSFD unit through the orifice device.

The lower pressure of the stage initiates spontaneous flashing of the recycle brine stream (Khawaji et

al., 2008). Flashing continues until an equilibrium is established between the liquid and the vapour.

This equilibrium is set by the saturation temperature of the stream at the stage pressure (Serra et al.,

2006). At this temperature, both the liquid and the vapour streams co-exist.

The flashed vapour, steam in this case, has a lower density than the liquid and therefore, flows up the

column and through demisters to remove entrained brine droplets (Serra et al., 2006). The steam flows


33


around the tubes, located towards the top of the stage, and transfers its latent heat to the recycle brine

stream flowing through the tubes. On transferring its latent heat, the steam condenses and forms water

droplets (Krishna, N.D.), which are collected in troughs, located below the tubes. The condensed

steam, collected in troughs, is the fresh water product. MSFD plants produce fresh water, containing

only 2-50 ppm of total dissolved solids (TDS) (Sommariva et al., 2010). This value is distinctly lower

than corresponding values from other technologies such as reverse osmosis (RO).

The liquid stream that remains at the bottom of the stage is unvapourised brine. It flows through the

orifice device into the next stage, where flashing occurs again. This process is repeated until the last

stage, with the unvapourised brine stream increasing in concentration with every stage due to the

vapour flashing. The fraction of the brine stream flashed reduces with every stage down the

evaporator. This is attributed to an increase in the latent heat of vapourisation and a decrease in the

specific heat capacity of seawater at lower temperatures. In the last stage, a portion of brine is

disposed of as brine blowdown (Sommariva et al., 2010), whilst the remainder is combined with the

make-up seawater stream and recycled through the process.

5.4.2 Key variables affecting process operation

Top brine temperature (TBT) is the maximum temperature of the recycle brine stream

at any point in the process. TBT is achieved at the outlet of the brine heater. Increasing

TBT while keeping the number of stages constant will increase the performance ratio

(Amount of distillate produced (kg/s) for every 2326 KJ of heat input) and decrease the

specific condensing area. It also results in a higher inter-stage temperature drop, which

increases the irreversibility of the system due to an increase in condenser and flash

exergy losses (Hamed and Ba-Mardouf, N.D.). Too low a TBT can result in a low

performance ratio (PR).

Steam temperature is the temperature of the low pressure saturated steam, which

transfers its latent heat to the recycle brine stream in the brine heater. It leaves the brine

heater as saturated liquid at the same temperature and pressure as the inlet steam. For

heat transfer to occurs, the steam temperature must be higher than that of the recycle

brine stream entering the brine heater. However, introducing the steam at too high a

temperature is also not advisable. Firstly, higher temperature steam implies higher

pressure steam, which is more expensive to generate (Hussain, 2009). Secondly, there are

higher specific exergy losses associated with steam that is at too high a temperature. This

is because the steam supplied to the heater is of high quality (high exergy value) and the

resultant phase change is responsible for dissipating this energy (Hamed et al., 2000).


34


Therefore, as a compromise, a steam temperature 8°C greater than the TBT, has

been chosen.

Flash range is the difference in temperature between the TBT and the concentrated brine

stream temperature in the last stage. The effect of flash range on exergy losses is similar

to that of TBT on exergy losses.

Number of stages (n) is a very key parameter in ensuring efficient process operation.

Increasing the number of stages while maintaining a constant TBT reduces the inter-

stage temperature drop, increases the specific condensing area and has an effect on

exergy losses similar to that of flash range and lowering the TBT (Hamed et al., 2000).

The upper limit on the number of stages is set by the pressure drop required to move the

brine from one stage to the next, particularly at the cold end (Hamed and Ba-Mardouf,

N.D.). A greater number of stages also mean greater capital expenditure.

Specific condensing area: This refers to the stage area required to condense 1 kg of

water vapour. It is governed by the main heat transfer equation, .

A larger specific condensing area results in better performance and lower specific exergy

losses due to a terminal temperature difference. However, the financial downside of a

larger specific condensing area is increased capital cost.

5.4.3 Calculation procedure

A detailed calculation procedure has been presented in Appendix A, Section 20.7.

5.4.4 Varying MSFD energy requirements

Figure 10 and Figure 11 shows how the energy requirement of an MSFD unit varies with number of

stages (TBT = Constant at 90°C) and TBT (Number of stages = Constant at 40) respectively.

Table 28, presented in Appendix A, Section 20.9, summarises the key parameters obtained on

varying the TBT (and thus the steam temperature) and number of stages.

It was decided that an investigation into desalination by reverse osmosis was required as, on perusing

through literature, it was evident that reverse osmosis yielded lower specific energy requirements.

Section 5.5 describes reverse osmosis and presents the associated calculations.


35


Figure 10: Variation of energy requirement of an MSFD unit with number of stages at a TBT of 90°C

Figure 11: Variation of energy requirement of a 40 stage MSFD unit with TBT

5.5 Reverse osmosis (RO)

5.5.1 Process description

Unlike MSFD, which operates on the basis of flash evaporation, RO is a membrane process that uses

high pressure to achieve separation of salts from the feed by forcing water through a semi-permeable

membrane (Krishna, N.D.). A semi-permeable membrane allows the passage of water whilst rejecting

the passage of salts through it based on selectivity and pore size (Sommariva et al., 2010). Water has a

tendency to diffuse through the membrane more easily than salts.

High pressure operation is necessary to overcome the naturally occurring phenomenon of osmosis. If

solutions of varying concentration are present on either side of a semi-permeable membrane, the

natural tendency is for water to flow through the membrane from a region of low solute concentration

to a region where there is a high concentration of solute (BenJemaa and Karajeh, 2007). This process

is called osmosis and it continues until a state of equilibrium is established. The equilibrium pressure

20

24

28

32

36

40

45 50 55 60 65 70 75 80 85 90 95 100

To

tal n

um

be

r o

f s

tag

es

Energy requirement (kWh/m3 of distillate)

Variation of energy requirements of an MSFD unit with number of stages at a TBT of 90°C

90.00

95.00

100.00

105.00

110.00

49.65 49.70 49.75 49.80 49.85 49.90 49.95

TB

T (°C

)

Energy requirement (kWh/m3 of distillate)

Variation of energy requirements of a 40 stage MSFD unit with TBT


36


difference between the two solutions is termed as the osmotic pressure (Belessiotis and Delyannis,

2006). To prevent the permeation of water into the region of high solute concentration, feed pressure

in excess of the osmotic pressure is applied to the side with the high solute concentration (Fritzmann

et al., 2007). This concept is known as reverse osmosis. The high pressure forces water out of the

saline solution and through the semi-permeable membrane, resulting in the production of fresh water

(permeate). The energy consumption of RO desalination plants is comparatively lower than MSFD

desalination plants. Estimates values range from 6-8 kWh/m3 of fresh water produced. However,

facilities equipped with an energy recovery device consume energy in the region of 4-5 kWh/m3 of

fresh water produced (Khawaji et al., 2008).

Typically, the 1st pass receives feed at a pressure between 50-80 bar (Khawaji et al., 2008). The

maximum limit on this pressure is set by the maximum operating pressure of the membrane. Studies

show that operation above this limit results in rapid membrane deterioration. Figure 58 in Appendix

A, Section 20.10, illustrates the difference between osmosis and reverse osmosis.

5.5.2 RO membranes

Membranes are the most vital components of a RO desalination plant. In most cases, the effectiveness

of the membrane usually dictates process performance and energy requirements (Li and Wang, 2010).

Different membranes have been used with varying degrees of success. Each membrane is unique in

assembly, configuration and effectiveness. The most widely used membrane, for desalination

purposes (Sommariva et al., 2010) is detailed below:

Spiral wound membranes (SWM): A SWM (also called spiral wound element), shown in Figure 59

in Appendix A, Section 20.11, is made up of several flat sheet membranes that are glued together

with a permeate spacer installed in between (Fritzmann et al., 2007) to constitute a membrane

envelope.

The membranes are made of cellulose acetate polymers or thin film composite polymers (Belessiotis

and Delyannis, 2006). Each membrane envelope is wound spirally around a porous central permeate

collector tube, with feed spacers installed between each envelope. Feed enters the membrane

assembly through the open end and leaves through the other end as concentrate (retentate) (Fritzmann

et al., 2007).

5.5.3 Main process parameters

The performance of an RO plant is characterised by certain key parameters, described below.

Optimisation of these parameters increases plant efficiency and performance.

Energy requirement: The energy requirement of an RO plant is considerably lower than

an MSFD plant. Energy is required by the high pressure pumps to pressurise the feed to


37


achieve separation and thereby produce fresh water. The amount of energy consumed

depends on a variety of factors, described in Section 5.5.6.1.

Recovery ratio: This is the amount of fresh water recovered from the feed. The

following equation can be used to determine the recovery ratio (Belessiotis and

Delyannis, 2006):

Over the years, designers have tried to maximise this value. Typical values range from

35-40% (Von Gottberg, 2005). The Ashkelon RO plant, the largest seawater RO plant in

the world, uses a 1st pass recovery ratio of 45% (Sauvet-Goichon, 2007). However, there

are operational issues which limit the maximisation of this value. An increase in the

recovery ratio increases the concentration of the brine stream in the pass. This increases

the osmotic pressure and therefore the feed pressure must be increased as well.

Membranes are only designed to operate up to a certain pressure. The upper limit on

spiral wound membranes is 82.7 bar (Von Gottberg, 2005) at seawater temperatures

below 29°C. Feed pressure in excess of the membrane design pressure will result in

premature membrane damage.

Rejection ratio: Like any removal system, membranes are not 100% efficient at salt

removal. The efficiency of salt removal, termed rejection ratio, varies from membrane to

membrane. Advances in membrane technology have meant rejection ratios as high as

99.80% are now possible (Fritzmann et al., 2007). The remainder of the salts are

entrained in the fresh water (permeate) flow through the membrane. Further treatment

may be required if the salt concentration in this stream is above acceptable levels.

Membrane permeate flux: The permeate flux is defined as the flow rate of permeate per

unit area of membrane. It is inversely proportional to thickness (Belessiotis and

Delyannis, 2006) and a high flux is desirable, as it enables the membrane to allow as

much of the water through as possible. The water flux at a given temperature is

represented by the following equation; (Kirkby, 2009). The thin

membranes, a requirement for high permeate flux, are comprised of an ultra thin active

non-porous layer and a porous support layer. The support layer prevents membrane wear

and tear whilst the active layer provides a barrier to mass transport and is responsible for

membrane selectivity (Fritzmann et al., 2007).


38


5.5.4 Energy recovery device

Energy recovery devices are vital in improving plant performance. Principally, they reduce the plant‟s

energy requirement by up to 40% (Avlonitis et al., 2003) by extracting energy from the reject

concentrate stream and transferring it to the incoming feed stream (Fritzmann et al., 2007). The

pressure of the reject concentrate stream is around 1-4 bar lower than the feed pressure (Khawaji et

al., 2008). Like membranes, there are a variety of types, each one unique in its own way. Energy

recovery devices can be grouped into two categories, namely turbine devices and pressure exchangers

(Fritzmann et al., 2007). Turbine devices have efficiencies in the order of 90% (Fritzmann et al.,

2007), and operate by extracting the pressure energy from the reject concentrate stream and

converting it to mechanical energy (Liberman, N.D.), which is transferred to the high pressure feed

pump. Pressure exchangers, shown in Figure 60 in Appendix A, Section 20.12, extract pressure

energy from the reject concentrate stream and transfer it directly to a portion of the feed. They either

use ceramic rotors or a set of valves and closed cylinders (Serra et al., 2006). Direct connection

between the feed and the reject concentrate stream results in these systems possessing efficiencies in

the region of 98% (ERI, N.D.) . Energy savings are achieved by means of the high pressure pump

only pressurising a percentage of the feed (Avlonitis et al., 2003). The remainder is pressurised by the

pressure exchangers. This project will use pressure exchangers, due to the highly superior

efficiency it possesses over turbine devices.

5.5.5 Boron treatment

5.5.5.1 The problem

The overall make-up of an RO desalination facility is determined to a huge extent by the amount of

boron present in the feed and the 1st pass permeate. 80-90% of the boron in the wastewater effluent

stream that is eventually discharged into the sea is accounted for by detergents (Bick and Oron, 2005).

Although boron concentration in the seawater vary from place to place, the typical value is around 4.5

mg/L (Fritzmann et al., 2007). A high concentration of boron in drinking water can pose serious

issues in humans, some of which are foetal abnormalities, birth defects (Fritzmann et al., 2007),

nausea and diarrhoea (LennTech, N.D). Although plants require boron for their growth, an excess can

result in negative impacts such as loss of photosynthetic capacity and plant productivity (Kabay et al.,

2010). Due to the deleterious effect that boron has on human beings, the WHO established a boron

limit of 0.5 mg/L in drinking water (Abdulraheem et al., 2010). There are plenty of methods of

removing boron from seawater.

5.5.5.2 Treatment methods

Some of these are reverse osmosis, ion exchange resins, electrodialysis reversal and adsorption

membrane filtration (Kabay et al., 2010). This project will explore the reverse osmosis method for

boron removal.


39


5.5.5.3 Boron chemistry

Essentially boron is present either as boric acid (H3BO3) or in its dissociated form as borate ions

(H3BO2-). The dominant form of boron is pH-dependent. The dissociation of boric acid is represented

by (Trussell, 2005):

Boric acid is a weak acid with a pKa of 9.2 at 25°C (Kabay et al., 2010). This means that boric acid is

the dominant form of boron until a pH of 9.2. Thus, boron in seawater, which has a pH of 8, is

predominantly in the form of boric acid.

5.5.5.4 Treatment by RO

The removal of boron by RO membranes depend on the dominant form of boron. Membranes reject

the borate ions better, as these ions are negatively charged and fully hydrated. The hydration results in

a larger radius, whilst the negative charge on the ion is repelled by the negatively charged membrane

(Kabay et al., 2010). Meanwhile, boric acid is smaller in size and neutrally charged, making it harder

for the membranes to reject it (Fritzmann et al., 2007). The pH of the feed is increased by caustic soda

injection (Kabay et al., 2010) to convert the dominant form of boron from boric acid to borate ions.

However, this addition is not performed upstream of the 1st pass in a multi pass RO plant as a high pH

in the 1st pass can result in excessive caustic soda consumption, as well as precipitating the scaling

layers (Kabay et al., 2010). The addition is performed between the 1st and 2

nd pass.

Generally, the percentage of boron removed from the 1st pass is membrane dependent. The most

efficient 1st pass membranes removes 93% of the boron (Toray, N.D.). However, this is insufficient to

reduce the boron concentration below desired levels. Thereby, a 2nd

pass is required to reduce the

boron content to below 0.5 mg/L.

5.5.6 Calculations

5.5.6.1 Key decisions

Deciding on the number of passes/stages: This decision rests of the recovery ratio

desired and permeate (desired product) purity required. Recovery ratio can be increased

by treating the concentrate stream in treatment stages whereas permeate can be further

purified by treating it in passes. Due to time constraints, this project focuses on

producing pure water by treating permeate from the 1st pass in a 2

nd pass, rather

than treating the concentrate in additional stages.

Deciding on the number of membranes: Membranes are housed in a pressure vessel,

with each pressure vessel containing between 6 to 8 spiral wound membranes (Fritzmann


40


et al., 2007). The calculations in this project assume 6 spiral wound membranes per

pressure vessel.

Type of membrane chosen: It is important that the membrane chosen provides optimum

performance. Membranes that have high area, high salt rejection, high flux, high boron

rejection and the ability to perform at high pressures, are highly desirable. 1st pass

membranes are usually seawater membranes, as they exhibit most of the qualities

required of a good membrane. 2nd

pass membranes are usually of the brackish water type,

as they are cheaper. For this project, the 1st pass membrane chosen in Toray’s

TM820C-400 and the 2nd

pass membrane chosen is Toray’s TML20-400.

Type of energy recovery device chosen: As mentioned previously, pressure exchangers

have been chosen as the energy recovery device for this project. More specifically, the

PX-300 has been chosen, as it exhibits up to 98% energy transfer efficiency, whilst

being able to handle flows of up to 68 m3/hr (ERI, N.D.).

5.5.6.2 Water permeability

The first step in being able to carry out calculations is to determine the water permeability. The

assumption of constant permeability for all 6 membranes in a pressure vessel is a safe one (Sharif,

2010). This calculation requires key information, provided by the membrane manufacturer. This data

was obtained in the form of a data sheet. For the 1st pass membrane,

The feed pressure based on which the results were obtained was 800 psi (=55.17 bar), with a permeate

pressure of 1 atmosphere (=0.987 bar)

, the reflection coefficient, is the fraction of pores too small to let salt through. This fraction is

assumed to be 1, since the vast majority of pores will be too small to let salts through. The

membrane manufacturers quote their results based on a feed salinity of 32,000 mg/L. However,

to avoid the complication of dealing with minor quantities of several ions, they have made the

simplification that the feed water contains only Na+ and Cl

- ions. This enables the osmotic pressure, π,

presented in the water permeability equation, to be calculated. The equation requires the knowledge of

the Van‟t Hoff factor (i, which in this case is 2, NaCl dissociates into 2 ions), the molarity of the

solution (M), the universal gas constant (R) and the temperature (T, which in this case is 25°C or 298


41


K). The molarity, M, is the number of moles per litre. The number of moles of NaCl is calculated by

dividing the mass of NaCl (=32,000 mg or 32 g) by the RMM (58.44 g/mol).

Since all the quantities of the water permeability equation have been found, the water permeability

can be found:

The 2nd pass membrane produces 38.6 m

3/day of permeate and has an area of 37 m

2. The results

quoted are based on a feed pressure of 225 psi and a feed salinity of 2,000 mg/L NaCl. A water

permeability calculation similar to the one above, for the first pass, yield a 2nd

pass water permeability

of

5.5.6.3 Feed flowrate

Each membrane is designed to process a maximum flow rate. This value is determined during the

design stage. For the 1st pass membrane, the permeate flow rate, as mentioned previously, was 24.6

m3/d at 8% recovery (from membrane specifications). For the 2

nd pass membrane, the permeate flow

rate was 38.6 m3/d at a recovery of 15%. Therefore, the maximum design feed rate processed by the

membranes can be calculated using the following equation:

Carrying this calculation through for the 1st and 2

nd pass membranes yield feed rates into the 1

st

membrane in the pressure vessel of 307.50 m3/d and 257.33 m

3/d.

5.5.6.4 Salt rejection and salt concentrations

Every membrane rejects a certain percentage of salt. The higher the rejection, the cleaner the

permeate. The membranes chosen for this process are characterised by extremely high salt rejection

values. The 1st pass membranes reject 99.75% of the salts whilst the 2

nd pass membranes discard

99.70% of the salts. A sample calculation is presented below for the 1st membrane in a 1

st pass

pressure vessel.


42


Figure 12: A simplified RO membrane (Source: Self)

MASS OF SALTS IN = MASS OF SALT IN PERMEATE + MASS OF SALT IN RETENTATE

It was stated in Section 20.7, Appendix A that a feed salinity of 35,000 mg/L NaCl and a feed

temperature of 30°C were assumed for the MSFD process. However, on extensive research it was

found that this was not true of Israeli waters. The feed salinity assumed is an average of the value

listed on the LennTech website of 38,600 mg/L and the Ashkelon case study value of 40,679 mg/L

(Sauvet-Goichon, 2007). This yields an average value for the feed salinity of 39,640 mg/L. The

RO design also assumes a feed temperature of 25°C. Combining the feed salinity with the

membrane feed rate allows the salt content in the feed to be calculated:

The 1st pass membrane rejects 99.75% of the salts. Therefore,

To express these salt masses in terms of a concentration requires the calculation of retentate and

permeate flow rates. The value presented below is for the 1st membrane in a 1

st pass pressure vessel.

Firstly, the osmotic pressure must be calculated, using . If it assumed that the feed

contains 100% NaCl, the osmotic pressure is:

Using the permeability calculated previously, the flux can be calculated. The trans-membrane

pressure, can be calculated, given that the feed pressure is set at 70 bar and the permeate pressure

is 1 atm (=0.987 bar). Thus,

Permeate

Retentate

Feed Membrane (99.75%

salt rejection)


43


Knowing the area of the membrane (=37 m2), this value for the flux can be substituted in the

equation, to obtain the permeate flow rate.

Obtaining the permeate flow rate from the 1st membrane allows the retentate flow rate from the 1

st

membrane to be calculated.

Having deduced the flow rates of the permeate and retentate stream from the 1st membrane, the salt

concentrations can be calculated by dividing the mass of salt by the flow rates of the respective

streams.

The retentate stream from the 1st membrane forms the feed to the second membrane. It can

immediately be seen that the salt concentration of this stream has increased. This has consequences in

the effectiveness of downstream membrane operation. The trend of increasing retentate salinity is

expected, as a major portion of the salt is rejected into that stream. Theory states that an increased

salinity results in increased osmotic pressure (Rybar et al., 2010). This reduces the term in

the equation, , which results in progressively lower fluxes and permeate rates

from the membranes downstream.

5.5.6.5 Boron calculation

The issue of boron in water was documented in Section 5.5.5. This section presents the associated

calculations. Values for boron concentration in seawater feed were not readily available. Sources

indicate that it is likely to lie in the range 4-6 mg/L (Bick and Oron, 2005). Therefore, an average


44


value of 5 mg/L was assumed.

Boron concentration in the permeate and retentate are calculated in exactly the same way as the salt

concentration calculations, presented in Section 5.5.6.4. The 1st pass membrane rejects 93% of the

boron in the feed (Toray, N.D.), whilst the 2nd

pass membrane rejects 99% of the boron at a pH of 11

(Fritzmann et al., 2007). WHO guidelines require drinking water to contain less that 0.5 mg of

boron/litre of water (Kabay et al., 2010).

5.5.6.6 Split partial second pass: An efficient solution

Under normal circumstances, all the permeate collected from a pressure vessel, in the central

collecting tube, would be sent to the 2nd

pass to reduce permeate salinity and boron content. This is the

conventional set-up of an RO plant.

However, a very novel design to increase RO plant recovery and thereby lower capital and operating

costs, is to treat only a part of the permeate in the 2nd

pass. This design, illustrated in Figure 61 in

Appendix A, Section 20.13, is called split partial second pass (SPSP). It takes advantage of the fact

that the membranes at the front end (the first 2 or 3 membranes) of the pressure vessel produce better

quality permeate than the membranes at the back end of the pressure vessel (Sauvet-Goichon, 2007).

This design has been implemented successfully at Ashkelon. It is deemed that the boron concentration

of the front end membranes are much lower compared to the boron emanating from the rear end

membranes (Sauvet-Goichon, 2007). Due to the unavailability of an advanced software to model the

design, in this project, the boron from the front end permeate is assumed to be minimal. To enable

SPSP operation, a permeate plug is installed. The location of the plug is determined by process

calculations. In an eight membrane pressure vessel, the plug is installed after the 3rd

or 4th membrane

(Rybar et al., 2010). Therefore, it is indicative that in a six membrane pressure vessel, the plug would

be best located after the 2nd

or 3rd

membrane.

Calculations were performed to explore both these options (i.e. installing the plug after the 2nd

membrane and installing the plug after the 3rd

membrane). The final decision was based on the

blended permeate salinity of the 1st pass front end permeate stream and the 2

nd pass permeate stream

(which treats the rear end permeate of the 1st pass). A blended permeate salinity of 500 mg/L was

deemed low enough to satisfy drinking water quality requirements (Oram, N.D.). The option that best

satisfied this criterion involved installing the plug after the 2nd

membrane.

5.5.6.7 Summary of results of 1st pass operation

Calculations, using the procedure detailed in Section 5.5.6.4, were carried out on the remaining 5

membranes in the pressure vessel. Table 4 presents a summary of the results obtained from those

calculations:


45


Table 4: Summary of results of a 1st pass pressure vessel containing 6 membranes

Element

number

Element

feed

Boron in

feed to

element

(mg/L)

Element

feed

salinity

Osmotic

pressure

(kPa)

Flux

(m3/m

2/d)

Permeate

(m3/d)

Boron in

permeate

Permeate

salinity

FRONT

END 1 307.50 5.0 39,640 3,361 0.87 32.22 Minimal 946

2 275.28 5.6 44,168 3,745 0.78 28.72 Minimal 1058

REAR

END

3 246.56 6.2 49,190 4,171 0.67 24.84 4.3 1221

4 221.72 6.4 54,564 4,627 0.56 20.69 4.8 1462

5 201.03 6.6 60,030 5,090 0.45 16.47 5.7 1832

6 184.56 6.7 65,224 5,531 0.34 12.46 6.9 2415

Exit from PV 172.10 69,772 135.40

5.5.6.8 1st pass recovery ratio

The recovery ratio of the 1st pass is defined as fraction of permeate obtained for every m

3 of feed.

Since the feed rate to all 1st pass pressure vessels are the same, the 1

st pass recovery ratio is the same

as a 1st pass pressure vessel recovery ratio. This equation below can be used:

5.5.6.9 2nd pass calculations

As mentioned previously, the 2nd

pass uses brackish water membranes. These membranes treat the 1st

pass permeate to the desired specification, at a cost lower than the seawater membranes. Key

parameters associated with the 2nd

pass membranes are listed in Table 5:

Table 5: Key parameters associated with 2nd pass membranes

Parameter Value

Feed flow rate into each pressure vessel (m3/day) 257.33

Permeability to water (m3/m

2/s/kPa)

Membrane area (m2) 37

Salt rejection (%) 99.70

Boron rejection at pH 11 (%) 99.00

To carry out calculations associated with the 2nd

pass, the feed characteristics must be obtained. This

relates to the salinity and boron concentrations.

It is known that each membrane can process a maximum feed of 257.33 m3/day. This is the amount of

feed that will be processed by the first membrane in every pressure vessel and is therefore the quantity

of feed that each pressure vessel (PV) receives. From Table 4, it can be seen that each 1st pass

pressure vessel produces 74.47 m3/day of rear end permeate (sum of permeates from the last 4


46


membranes), which is fed to 2nd

pass pressure vessels. However, each 2nd

pass pressure vessel can

process 257.33 m3/day of 1

st pass rear end permeate. Therefore, it can be seen that each 2

nd pass PV

processes rear end permeate from more than 1 1st pass PV. The exact number (ratio of 1

st pass PV to

2nd

pass PV) of 1st pass PVs feeding rear end permeate to 1 2

nd pass PV is calculated by the following

equation:

This means that it requires rear end permeate from 3.46 1st pass PVs to feed 1 2

nd pass PV. This

number is greatly increased by SPSP operation, implying reduced need for 2nd

pass PVs, which

reduces capital and operating expenditure.

The salinity and boron concentration of the feed to every 2nd

pass PV is calculated by evaluating the

individual contents in the permeate of the rear end membranes from 1st pass PVs. The individual

contents are obtained using the same procedure as that detailed in Section 5.5.6.4. These individual

contents are culminated to obtain the boron and salt contents in the combined rear end permeate

stream from the 1st pass. This is then divided by the rear end permeate stream flow rate to obtain the

feed salinity and boron concentration of the combined rear end permeate stream from the 1st pass.

Table 6 summarises the results:

Table 6: Rear end permeate feed salinity and boron concentration from the 1st pass

Membrane element

Permeate

flow rate

(m3/day)

Boron

concentration

in permeate

(mg/L)

Boron

content in

permeate

(mg)

Salt

concentration

in permeate

(mg/L)

Salt content

in permeate

(mg)

3 24.84 4.33 107,625 1221

4 20.69 4.84 100,091 1462

5 16.47 5.65 93,085 1832

6 12.46 6.95 86,569 2415

Combined stream 74.47 ? 387,370 ?

It was noted above that the rear end permeate from 3.46 PV feed 1 2nd

pass PV. This alters the boron

and salt content in the feed to the 2nd

pass PV, as shown below:

Having calculated the 2nd

pass salt and boron content in the feed to each PV, the concentrations can be

obtained by dividing the quantities by the feed rate to each 2nd

pass PV:


47


Combining this information with the values presented in Table 5, an amicable 2nd

pass design can be

completed. A feed pressure of 17.50 bar was chosen for the 2nd

pass. This was found to yield a

good compromise in terms of blended permeate salinity, energy requirements and 2nd

pass recovery

ratio. Table 7 shows the results obtained from 2nd

pass calculations:

Table 7: Summary of results of a 2nd pass pressure vessel containing 6 membranes

Element

number

Feed to

element

Boron in feed

to element

(mg/L)

Element

feed

salinity

Osmotic

pressure

(kPa)

Flux

(m3/m

2/d)

Permeate

(m3/d)

Boron in

permeate

(mg/L)

Permeate

salinity

(mg/L)

1 257.33 5.2 1,623 138 1.23 45.55 0.29 27

2 211.78 6.3 1,966 167 1.21 44.68 0.30 28

3 167.10 7.9 2,484 211 1.17 43.35 0.30 29

4 123.75 10.5 3,344 284 1.11 41.15 0.32 30

5 82.60 15.6 4,995 424 1.00 36.93 0.35 34

6 45.66 27.9 9,008 764 0.72 26.68 0.48 46

Exit from PV 18.99 21,598 238.35

The 2nd

pass recovery ratio is calculated in the same way that the 1st pass recovery ratio was calculated

in Section 5.5.6.8.

5.5.6.10 1st and 2nd stage calculation

From Table 7, it can be seen that every 2nd

pass PV produces 238.35 m3/day of permeate. Every 2

nd

pass PV receives feed from the rear end of 3.46 1st pass PVs. At the same time, the 3.46 PVs also

produce front end permeate, which is blended with the permeate from the 2nd

pass, upstream of the

product tank.


48


This value includes permeate from1 2nd

pass PV and 3.46 1st pass PVs. However, the objective of the

plant is to produce 110 million m3 of fresh water annually. This amounts a production rate of

301369.86 m3 of fresh water every day. Thus,

It was established above that the ratio of the 1st pass PVs to 2

nd pass PV was 3.46:1. Thus

Each PV has 6 membranes. Therefore, the 1st pass contains 13,920 membranes whilst the 2

nd pass

contains 4,032 membranes, culminating in a total of 17,952 membranes.

5.5.6.11 Blended permeate salinity

Table 8 summarises the results of the blended permeate salinity calculation:

Table 8: Table to calculate blended permeate salinity

Membrane element

Permeate

flow rate

from 1 PV

(m3/day)

Salt concentration

in permeate from

1 PV (mg/L)

Salt content in

permeate from 1

PV (mg)

Permeate flow rate

from 3.46 1st pass

PVs (m3/day)

Salt content in

permeate from

3.46 1st pass PVs

(mg)

1st pass 1

st element 32.22 946 111.34

1st pass 2

nd element 28.72 1,058 99.25

2nd

pass 1st element 45.55 27 - -

2nd

pass 2nd

element 44.68 28 - -

2nd

pass 3rd

element 43.35 29 - -

2nd

pass 4th element 41.15 30 - -

2nd


2nd


The salt content of the blend is the sum of the individual salt contents, highlighted in grey in Table 8.

The salt content of the blend is .The flow rate of the blend is the sum of the individual

permeate flow rates from the membranes, highlighted in yellow in Table 8. As mentioned in Section

5.5.6.11, the flow rate of the blend is 448.94 m3.

5.5.6.12 Overall RO plant recovery

Calculating the number of 1st pass PVs enables the calculation of the total feed rate into the RO part of

the desalination facility. The exact number of 1st pass PVs is 2319.84, each processing a feed of

307.50 m3/day. Thus,


49


5.5.6.13 Energy recovery calculation

The importance of the energy recovery device cannot be understated. Essentially, the energy recovery

device (ERD), pressure exchanger, PX-300, in this case, reduces the amount of energy required by

the high pressure pump by recovering energy from the 1st pass retentate stream and transferring it to a

portion of the RO plant feed. This means the high pressure pumps only pressurise some of the feed,

with the remainder pressurised by the energy recovery device and a booster pump. The following

section details the calculation of the portion of the feed pressurised by the energy recovery deice.

The amount of brine treated in 1 ERD was assumed to be an average of values quoted by the ERD

manufacturer. The values quoted were 45-68 m3/hr (ERI, N.D.).

In Section 5.5.4, it was stated that the retentate enters the ERD at a pressure 1.5-4.0 bar lower than the

1st pass operational pressure of 70.0 bar. This implies that the retentate stream pressure could lie

anywhere between 66.0 bar and 68.5 bar. An average value of 67.25 bar (6,725,000 Pa) was

assumed for the purpose of calculations. It is also assumed that the retentate leaves the ERD at

atmospheric pressure (101,325 Pa). The energy contained in the retenate stream from the 1st pass,

entering each ERD is the difference in pressure (Pa) between the retentate entering and leaving the

ERD multiplied by the flow rate of retentate (m3/s) into each ERD.

Due to ERD limitations, only 98% of this power is transferred to the RO plant feed (called Bypass

(B/P) feed from here on in). Thus,


50


Upstream of the RO plant, the seawater is stored at atmospheric pressure in a storage tank. Therefore,

the RO plant feed to the high pressure (HP) pump and the ERD is at atmospheric pressure (101,325

Pa). The B/P feed pressurised in the ERD is assumed to leave the ERD at 65.0 bar (6,500,000 Pa).

This allows for the calculation of the amount of RO plant feed pressurised in the ERD.

Expressed as a percentage, this is equivalent to 56.89%.

5.5.6.14 Power consumption

The RO plant consumes power in the form of electricity required by the high pressure (HP) pump, the

booster pump and the 2nd

pass pumps.

5.5.6.14.1 HP pump power consumption

14

14 http://www.ksbusa.com/WAndWW/desal.html


51


HP pump inlet pressure = Atmospheric (101,325 Pa); HP pump outlet pressure = 70 bar (7,000,000

Pa); HP pump efficiency = 85% (Sinnott, 1999).

5.5.6.14.2 Booster pump and 2nd stage pump power consumption

Using the same procedure as Section 5.5.6.14.1, Table 9 was produced:

Table 9: Booster pump and 2nd stage pump power consumption

Parameter Booster pump 2nd stage pump

Total flow to be processed by pump (m3/day) 405,804.4 172,759.815

Capacity (gpm) 21,13416 6,00017

Capacity (m3/s) 1.601 0.455

Number needed 3 (+1 spare) 5 (+1 spare)

Pressure at pump inlet (Pa) 6,500,000 101,325 (Atmospheric)

Pressure at pump outlet (Pa) 7,000,000 1,750,000

Pump efficiency 85% 85%

Power consumed by 1 pump (kW) 941.932 881.768

Total power consumed by pump type (kW) 2,826 4,409

5.5.6.14.3 Total power consumption

This is sum of the power consumption of the HP, booster and 2nd

stage pumps.

5.5.6.15 Specific energy consumption of plant

The specific energy consumption is obtained by dividing the total energy consumption (calculated by

multiplying total power consumption by 24, the number of hours in a day, to obtain the amount of

energy consumed by the pumps in a day) by the amount of water produced in a day (301,369.86 m3).

15 Number of 1

st stage PVs (2320) multiplied by sum of rear end permeate from each PV (74.47 m

3/day)

16 http://www.ksbusa.com/WAndWW/desal.html

17 http://www.sulzerpumps.com/portaldata/9/Resources//brochures/water/SP_Desalination_E00551.pdf


52


Therefore, the specific energy consumption of the RO part of the desalination facility is 3.06 kWh per

m3 of fresh water produced.

5.5.7 Cost of RO trains and pumps (excluding pre- and post-treatment)

Table 10: Cost of the RO trains and pumps

Equipment Quantity

Nominal

power, kW

Cost of 1 in

Jan 2000 (£)

Cost of 1 in

2009 (£)

Cost of 1

($) Cost of all

TM820C-400 13920 $603 $8,400,581

TML20-400 4032 $476 $1,919,192

HP pumps 11 3113 £468,396 £585,495 $912,963 $10,042,594

Booster pumps 4 942 £145,944 £182,430 $284,462 $1,137,849

2nd stage pumps 6 882 £137,032 £171,290 $267,092 $1,602,555

1st stage PV 2320 $5,575 $12,934,000

2nd stage PV 672 $5,575 $3,746,400

ERD 295 $25,000 $7,375,000

TOTAL $47,158,170

5.5.8 RO process schematic

The RO part of the desalination plant is illustrated in Figure 62 in Section 20.14, Appendix A.

Desalination: Group 2 Structure

53

Section 6 Author: KK

6 Structure

6.1 Reverse Osmosis Process Plant

6.1.1 Introduction

From the process diagram, Figure 53, Appendix A, it is clear that the plant must shelter the

Ultra Filtration (UF) trains, the Reverse Osmosis (RO) trains, pumps and the energy recovery

devices, all of which require fully adaptable spaces. The plant must also be designed to

provide a measure of flexibility to allow for changes, improvements or extension. High

strength to weight ratio and speed of erection of steel makes it the only economical solution

for a large scale RO plant.

Steel portal frames are very efficient and economical when used for single-storey buildings,

provided that the design details are cost effective and the design and analysis assumptions are

well chosen. Low cost, rapid fabrication and the wide range of possible exteriors make portal

frame the dominant form of single-storey structures used for industrial buildings. These

structures offer a flexible internal layout, which can be easily adaptable for future use by

installing additional bays. A typical portal frame building consists of rafters and purlins,

which are supported by the column. Figure 13 shows a typical single-bay portal frame

arrangement.

Figure 13: Typical single-bay portal frame (PRIMECON.CO.ZA, 2009)

Most economic form of portal frame, using hot rolled sections, is usually achieved by plastic

design of a frame with pinned column bases. This allows he engineer to analyse frames easily

and design it to use maximum capacity of each sections. However, due to the fact that the


54


plant may require expansion in the near future, the building was analysed elastically with the

aid of LUSAS and individual elements were designed to their plastic moment capacity with

the key structural stability parts of the structure remaining elastic at all times. This chapter

highlights the design of portal frame structure

6.1.2 Floor Design and Layout

The reverse osmosis plant must comprise of RO pressure vessels and UF units. Additional

space must also be available to house high-pressure pumps and energy recovery devices. The

units within the structure must be integrated effectively both internally as well as externally

(e.g. to storage tanks) for maximum efficiency.

The pre-treatment section contains 95 ultra filtration units, each of which requires a floor area

of 1.9m × 7m (including horizontal spacing) and height of 2.4 m. The units will be arranged

with a 12 × 1 train configuration, with a spacing of 5m between each train, as shown in floor

plan, Figure 14. Similarly, the 1st and 2

nd pass of the RO process constitute a total of 2992 RO

pressure vessels. Each pressure vessel is 6.734 m in length and has a diameter of 0.225 m.

The pressure vessels will be arranged in trains of 15 × 12; thus there will a total of 17 PV

trains. In addition to the filters, the pumps and a chlorine storage tank will also be sheltered in

the portal frame. Physical dimensions of the high-pressure pumps are obtained from the

Uminokakamichi Nata seawater desalination as reported by (FDWA, 2007). A floor area of

2.5m×3m was allocated for each of 31 high-pressure pumps, and each pump is separated by a

spacing of 0.6 m, as highlighted in Figure 14. Further space was required for 295 P-300 ERD

(ENERGY RECOVERY INC, 2009). Additional space was allocated for chlorine storage,

part of the pre-treatment section.

Consequently, a rectangular double-bay portal frame structure, each with a floor area of 56m

× 70m, was chosen to shelter the membranes and pumps. The shelter will be integrated to

inflow and outflow storage tanks placed outside the structure. The layout of various elements

in the plant is highlighted in Figure 14.The location of desalination plant is highlighted in

Figure 17.

In addition to the process plant, two additional structures are required to house the intake and

discharge pumps, as well as for control centre as illustrated in Figure 18. Both structures will

be connected to the additional storage tanks for intermediate storage.


55


Figure 14: RO plant layout

Figure 15: Structural diagram


56


Figure 16: RO plant site layout

Water Intake

Desalination

Plant

Main Access


57


Figure 17: Location of Desalination Plant

Figure 18: 3D Illustration of Desalination Plant

6.1.3 Quantification of actions, load combinations and general safety criteria

The portal frame is 70 m long, has a span (centre to centre) of 56m, a height of 6m, a rafter slope

of α = 60 and a spacing between frames of 7m, as illustrated in Figure 19. The rafter includes 5.6

m long eaves haunches and 1.5 m long haunches close to the apex connection. The column bases

are assumed to be pinned. The purlins will be installed at 1.4 m spacing. The steel used is S275

and a basic wind load of 14.4 m/s is assumed (SAARONI, H et al., 1998).

Figure 19: Portal frame

The quantification of the actions and their combinations is made in accordance with EN 1990

(2002), EN 1991-1-1 (2002) and EN 1991-1-4 (2005), considering the permanent actions that

corresponds to the self-weight of the structure and non-structural members, the variable actions

Column

Gable post

Bracing

Rafter


58


corresponding to imposed loads and wind action in accordance with reported Easterly wind

velocities.

6.1.3.1 Permanent actions

Permanent action corresponds to the self-weight of structural members, including sheeting and

frame. The estimated unfactored permanent loads of the structural members are as follows:

Sheets & installations = 0.22 kN/m2

Purlins = 0.07 kN/m2

Frame = 0.15 kN/m2

Total unfactored permanent action is 0.44 kN/m2, and since γG = 1.35 (EN 1990), the design

permanent action = 1.35 × 0.44 kN/m2 = 0.594 kN/m

2.

6.1.3.2 Imposed loads

According to EN 1991-1-1, the unfactored characteristic value of imposed load for roofs not

accessible except for normal maintenance and repair (category H), can be selected within the

range of 0 kN/m2 to 1.0 kN/m

2 (clause 6.3.4.2). An unfactored uniformly distributed characteristic

imposed load, qk, of 0.6 kN/m2 was chosen, as the roof must be accessible for maintenance. For

each frame, considering the spacing between frames of 7 m:

qk = 0.6 kN/m2 × 7 m = 4.2 kN/m

As γQ = 1.5 (EN 1990), the design imposed load for each frame is:

Qk = 1.5 × 4.2 kN/m = 6.3 kN/m

6.1.3.3 Wind Actions

The force exerted on the structure by wind is determined in accordance with EN 1991-1-4.

Assuming a wind velocity of 14.4 m/s, reported to be the maximum easterly windstorm velocity

experienced in the region, wind actions on the structure are determined. The calculations in

deriving the wind forces have been highlighted in the Appendix. Figure 20 summarizes the wind

forces applicable to this design.


59


Figure 20: Transverse and longitudinal wind loads

6.1.4 Loads Summary

Table 11 summarises the resulting actions for this design.

Table 11: Summary of actions

Description Type Value Safety Factor

(favorable/ unfavorable)

Design Load

Self weight

of structural

elements

Permanent

action

3.08 kN/m

1.0 or 1.35 4.20 kN/m

Imposed

access load

Variable

action

4.20 kN/m 1.0 or 1.5 6.30 kN/m

Longitudinal

wind action

Variable

action

See figure

xx

0 or 1.5 See Figure

20

Transverse

wind action

Variable

action

See figure

xx

0 or 1.5 See Figure

20

6.1.5 Design of Members

The design values of the applied forces are obtained from the fundamental combinations, given in

(EN 1990).

Thus Ed = (1.5×7m×0.6) + (1.35×0.44×7) = 10.458 kN/m

The values of γG,I and γg are taken as 1.35 and 1.5 respectively. The combination of permanent

and imposed load, applied on the roof, dictates the worst case load as illustrated in Figure 21. It is

achieved by considering the unfavorable imposed and permanent loads, with values of wind

action reduced to zero.


60


Figure 21: Worst Load case

Considering the load case shown in Figure 21, the bending moments can be achieved, using

LUSAS. The appropriate section sizes can be selected accordingly. Figure 22 summarizes the

bending moments.

Figure 22: LUSAS BM Diagram

Consequently the following sections were chosen to carry the axial load to the foundations (see

Section 20.16 for details):

Rafter: 914 x 305 x 224 UB

Column: 356 x 406 x 551 UC

6.1.6 Bracing and Gable post

In portal frame design, the standard method of transferring longitudinal forces (e.g. wind loads)

from the eave line to the foundation is by reinforcing the structure with roof and side bracings

(CECO BUILDING, N/A). Roof bracings along with the purlins provide stability to the structure

by preventing buckling of the rafter. In this case, the bracings must be designed such that they

will be located at each end of the building as illustrated in Figure 15. Side bracings on the other

hand acts to resist and transfer wind forces to the foundation. Gable posts should be designed to

support both the purlins and the bracings.

The following sections were chosen (see Section 20.16 for details):

Bracing: 114.3 × 5 × 13.5 CHS

Gable post: 254 × 102 × 28 UC


61


6.1.7 Future Expansion

As stated earlier, steel portal frames with steel cladding are very adaptable for future extensions

because the steel frame is easy to modify and the cladding can either be modified or removed. The

structure can be adapted to fit the future needs in one of two ways:

Incorporating additional frames to lengthen the building

Incorporating additional bays to increase the width of the building

In this design, the ends of the building comprises of gable posts that support the purlins. In order

to increase the length of the portal frame, the gable posts will have to be replaced, in which case

the economical aspects has carefully considered. Addition of further bays serves as the most

economical in this design. The bending on most of the columns would be reduced and thus

smaller sections may be used. In general it is recommended to use the configuration of the

original building, however checks must be preformed to ensure the stability of the structure as a

whole (KING, C M, 2001).

6.1.8 Cost summary

The bill of quantities is compiled in accordance to (LANGDON, Davis, 2009). Table 31 indicates

the cost summary for the portal frame. As highlighted, the portal frame structure is estimated to

cost approximately £452,000. It is worth noting that the cost of the pumping station and labour

costs are excluded in the estimation.


62


6.2 Foundation design

6.2.1 Choice of foundation:

The choice of foundation is governed by two conditions, firstly the ground conditions

(specifically the strength of the soil) and secondly the type of structure including its layout and

level of loading. In consideration of the foundations for the portal frame structure, the ground

conditions are alluvium (see Appendix A, Figure 69), which is typical for the area of Rishon

Lezion which will house the reverse osmosis plant. Alluvium is made up of loose, unconsolidated

matter, typically silt, sand, clay, gravel and often contains a good deal of organic matter. Due to

the fact that alluvium is not very good at withstanding large loads, and considering the layout of

the portal frame structure, a raft foundation is the best choice for the structure‟s base.

Raft foundations can be used to help distribute the loads from the structure over a larger area; in

this case it will be over the entire floor plan for the reverse osmosis plant. A raft foundation is a

shallow foundation, which consists of concrete slab extending over the entire area of the plant.

They also have the added advantage of reducing any differential settlement from various loading

position, which is particularly appropriate for soils, such as alluvium where there bearing capacity

of the soil is low.

6.2.2 Bear Capacity of the Soil:

Bearing capacity refers to the capacity of a soil to support the loads applied through the

foundation to the ground beneath it. This capacity is the maximum average contact pressure

between the foundation and soil, which will not cause a shear failure. In addition due to the

conditions in which the foundation will exist, attention has to be paid to ensure that the foundation

will not „float‟. Foundation floatation occurs when the hydrostatic pressure created from the

groundwater is greater than the weight of the building, thus causing it to effectively „float‟. If this

were the case, the foundation would have to be anchored to prevent this failure from occurring.

By consideration of the safe bearing capacity, which is shown further on in this calculation, the

design checks to ensure that floatation does not occur can be satisfied.

For the checking of the bearing capacity of the soil:

Dead and live loads are unfactored.

Water table is assumed to be at ground level, this is the worse case scenario.

The concrete shall be grade C40 (fcu = 40 N/mm2)

The raft will be designed as a flat slab with column and middle strips.

The foundation will sit at ground level, thus enabling easy access.

Assume a slab depth of 500mm.


63


The main loadings on the base of the foundation will be from the reverse osmosis units, with the

worse (i.e. the heaviest loadings) coming from the pressure vessel units. In order to derive a

loading, a typical m2 floor area of the plant was considered. Typical uniformly distributed

loadings for the reverse osmosis plant are as follows (for full derivation, see Section 20.18.2,

Appendix A):

Dead Load = 55.9 kN/m2

Live Load = 7.5 kN/m2

Column Loads:

The loads from the portal frame are carried through the columns and into the portal frame base.

They will therefore have to be considered in the design of the raft foundations for the structure.

The load (q), which the footing will experience, is equivalent to the uniformly distributed load

(UDL) plus the loads exerted on the footing by the column, i.e. Total load = Dead load (55.9

kN/m2)+ live load (7.5 kN/m

2)+ column loads (as a UDL, 1.5 kN/m

2, thus giving a load, q of

64.9kN/m2.

Calculating the safe bearing capacity of the soil in accordance with BS 8004:1986

Before the raft foundation is analysed, the safe bearing capacity of the soil underneath the

foundation should be calculated. Adopting the approach by Terzaghi and modifying the equation

for rectangular footings by Skempton gives the following (full calculations are outlined Section

20.18.3, Appendix A (WOODS, R., 2009):

Net ultimate bearing capacity (Terzaghi):

q f = c ' IcNc + po ' Iq Nq -1( ) +1

2Bg IgNg + po

The following data is correct for alluvium (GHOSH, K., 2009):

Smallest dimension of raft, B= 72m and L=104m

c‟=0 as the soil has no cohesion due to it‟s grainy nature, this is a worse case scenario

estimation.

Ic, Iq and I are empirical correction factors.

Shape Correction Factor: (For a rectangular footing)

Sq= 1 + (B/L)tan ‟ = 1 + (70/104)tan 25 = 1.31

S=1 – 0.4 B/L = 1 – 0.4 (70/104) = 0.73


64


Depth Correction Factors:

D/B =0.5/104 = 0.004 0 Therefore can ignore depth correction factor

Ic=1.0, Iq=1.31 and Iγ=0.73

bulk = 18kN/m2

‟=25 for alluvium (GHOSH, K, 2009)

Therefore:

Nc (Praddtl, 1920) = 20.72

Nq (Reissner 1924) = 10.66

N (Hansen 1961) = 8.11

P0‟ = initial effective overburden pressure = p0 – u0

As the Ground water level is assumed to be at the surface, i.e. <1.5B, the submerged unit

weight has to be used:

sub = sat - water

sub = 18 – 10 = 8 kN/m2

p0= (0.5 x 18) = 9 kN/m2

uo= (0.5 x 10) = 5 kN/m2

p0‟ =4kN/m2

This gives the ultimate bearing capacity as 1717kN/m2. In order to compensate for any

uncertainties such as non-homogeneity of the soil, or incomplete soil exploration, the safe bearing

capacity (qs) is calculated through the following equation:

qs =q f - po( )F

+ po

Using a safety factor (F) of 4.0 which is assuming that the structure is likely to reach its maximum

design load and it helps to compensate for the fact that the soil exploration is incomplete

(WOODS, R., 2009). The safe bearing capacity is calculated as 436kN/m2.

Therefore, q<qs meaning that the soils bearing capacity is suitable and piles or a thicker slab are

not necessary.


65


6.2.3 Raft analysis

Method of analysis:

The slab may be analysed as an inverted flat slab by an empirical method subjected to an

upwards-contact soil pressure when the columns are equally spaced in either directed. This

however is not the case for this frame as the columns along the x and y plane have different

spacing, it is therefore appropriate to use the frame analysis method outlined in BS 8110. The

following considerations were made in the design of the flat slab:

The frame is split into a series of transverse and longitudinal strips along column lines in

either direction; the strips are equal to the spacing of the columns (see Figure 70, Appendix

A for illustration).

The net ultimate upwards pressure is equal to 88.74 kN/m2 (1.4DL + 1.6LL

The depth of the slab is 500mm.

For 90 minutes of fire protection (BS 8110, Fig. 3.2) and cover of 30mm- a suitable value for

an assumed exposure condition of XS1 (Exposed to airborne salts but not permanently

submerged- BS 8500) the effective depth of the slab is 450mm.

By dividing the structure into a number of equivalent frames, these frames can be analysed and

the moments for each frame derived. This can either be done by a computer or through a

simplified method outlined in BS 8110, which uses moment coefficients to calculate moments

within the frame, this is the method that will be adopted.

The frame analysis method assumes that the slab is continuous beneath the columns and that the

ends are hinged. Between the column and end the slab connection is assumed to be hinged also.

This means that no column stiffness is taken into account in the analysis.

The following details the sizes column and middle strips within the structure. Running along the x

axis are the transverse strips and along the y axis are the longitudinal strips, within each there are

column and middle strips, a diagram of the arrangement can be found in Figure 70, Appendix A.

The width of the column strips is calculated through the equation:

Ws = column width + effective depth x 4

The width of the panel is the spacing between supports, thus allowing the middle strip to be the

difference in size between these two values, which gives the following:


66


Longitudinal Strip Transverse Strip

Panel Width = 5.3m Panel Width = 7.78m

Column Strip = 2.25m Column Strip = 2.25m

Middle Strip = 3.35m Middle Strip = 5.53m

For the analysis of the slab, firstly the moments were calculated. Due to the fact that the spans are

of equal spacing, the moments can be calculated as follows, using the coefficient (0.086), the net

upwards contact pressure and the panel width (BS 8100:1 table 3.12):

Firstly, considering the edge Transverse Strip:

Panel Width = 7.78m

Column Strip = 2.25m

Middle Strip = 5.53 m

Net upwards contact pressure per m = 88.7 kN/m2 x 7.78m = 690.4 kN/m

-ve BM @ first interior support= -0.086 x 690.4 x 7.78 m2 = -3593.8 kNm

+ve BM @ middle of edge span = +0.086 x 690.4 x 7.78 m2 = 3593.8kNm

These output results can be distributed into column and middle strips as a percentage of the total

positive and negative moment in accordance with BS 8110:1, table 6.1:

For the column strip:

-ve BM @ support = 75% of 3593.8 = 2695.4 kNm

+ve BM @ midspan = 55% of 3593.8 = 1976.6 kNm

For the middle strip:

-ve BM @ support = 25% of 3593.8 = 898.5kNm


The strips are then designed per meter run. Firstly, a check is carried out as to determine if the

section should be doubly or singly reinforced:

Column Strip:

At support –ve moment = -2695.4 kNm

Width of column strip = 2.25m


67


BM/m = -2695.4/2.25 = 1198.0 kNm/m run

Assuming that the depth of the slab is 500mm and therefore that the effective depth is 450mm:

K =M

bd2 ´ fcu=

1198 ´106

1000 ´ 4502 ´ 40= 0.148

K‟= 0.156 since K<K‟ no compressive reinforcement is required.

From this, the lever arm (or „z‟) of the section can be calculated:

z = d 0.5 +0.25 -K

0.9

æ

è ç

ö

ø ÷

0.5é

ë ê

ù

û ú

\z = d 0.5 +0.25 - 0.148

0.9

æ

è ç

ö

ø ÷

0.5é

ë ê

ù

û ú = 0.84

This, in turn is used to calculate the amount of reinforcement that is required in that part of the

section:

Asrequired=

Mu

(0.95 ´ fy ´ z)=

1198 ´106

0.95 ´ 460 ´ 0.84 ´ 450( )= 7252mm2

This is then expressed in terms of a bar diameter and spacing of reinforcement, ensuring that the

area of reinforcement provided is greater than that required.

Therefore adopt T32 @ 100mm c/c bottom spacing (Asprovided = 8040mm2)

Shear reinforcement checks show that the section‟s depth is sufficient and shear reinforcement is

not necessary:

Shear should be checked along the perimeter at a distance of 1.5d from the face of the support.

Therefore, the ultimate shear is derived as follows:

At the column perimeter (Most critical position):

Critical perimeter= column perimeter + 8x1.5d

= 400 x 4 + 8 x 1.5 X 450 = 7000mm


68


Shear force=

V = F -Õ

41.22n

Where:

F is the load on the panel= 56m2 x 92.4kN/m

2 = 5174.4kN

n is the equivalent distributed load = 92.4 kN/m2

V = 5174.4 -Õ

41.22 ´ 92.4

é

ë ê ù

û ú = 5069kN

Maximum permissible shear force:

Max. permissible shear force=

Vmax .permis. = 0.5ud 0.6 1-fck

250

æ

è ç

ö

ø ÷

é

ë ê

ù

û ú fck

1.5

Where:

u is the critical perimeter

d is the effective depth

Vmax .permis. = 0.5 ´ 7000 ´ 450 0.6 1-40

250

æ

è ç

ö

ø ÷

é

ë ê

ù

û ú

40

1.5´10-3 = 21168kN

Vmax.permissible (21162kN)> V (5069kN) OK, shear reinforcement is not required.

This method is followed for both the transverse and longitudinal frames. For the full outline of

calculations, see Section 20.18.8, Appendix A. A summary of the results is shown below:

Transverse Strip:

Column Strip:

8400mm

T32@100 mm c/c

0 c/c

!" #$%&' ( !)*)!

T32@150 mm c/c T32@150 mm c/c

T32@100 mm c/c

0 c/c

!" #$%&' ( !)*)!

T32@100 mm c/c

0 c/c

!" #$%&' ( !)*)!

56000mm 56000mm

8400mm 33600mm

BM

01

BM

02 BM

03

BM

04

BM

05


69


¢

Figure 23 : Transverse strip reinforcement

Longitudinal Strip:

Column Strip:

Middle Strip:

Figure 24 : Longitudinal strip reinforcement

Curtailment of reinforcement:

T20@150 mm c/c

T20@250 mm c/c

T20@175 mm c/c

0 c/c

!" #$%&' ( !)*)!

T20@175 mm c/c

0 c/c

!" #$%&' ( !)*)!

T20@250 mm c/c

0 c/c

!" #$%&' ( !)*)!

T20@250 mm c/c

0 c/c

!" #$%&' ( !)*)!

T20@250 mm c/c

0 c/c

!" #$%&' ( !)*)!

Middle Strip:

BM 01

70000mm

T20@175 mm c/c

T20@125 mm c/c

70000mm

BM 02


70


The following figure details the rules for the curtailment of reinforcement for a continuous slab.

Here, „l‟ refers to the distance between supports and ø refers to the diameter of the reinforcement

(AYRA, C., 2003).

This information has been used in order to quantify the amount of reinforcement that will be

required in order to construct the raft foundation in a bar bending schedule, which can be found in

Appendix A, Section 20.19. The bar bending schedule was calculated using BS 8666:2000.

6.3 Base plate design

Base plates connect the steel column to its concrete footing to transfer to loads to the foundations.

Through use of BS 5950:1 and the design procedure, which is outlined in clause 4.13, a suitable

base plate connection can be designed.

Assuming that the column is axially loaded and looking specifically at the central columns in

the portal frame:


71


Figure 25: Column dimensions and arrangement

Area of the baseplate:

Effective area: The applied load acts over a proportion of the base plate known as the „effective

area‟, which has the following equation:

Abe =axial load

bearing strength=

590.94 ´103

0.6 ´ 40= 24622.5mm2

Bearing strength must be taken at 0.6 times the characteristic cube strength of the concrete base,

which in this case is 40 N/mm2.

Actual area: This is the actual size of the „effective‟ area, which is derived through both knowns

(column dimensions) and unknowns (c), which are then equated in order to give a base plate size.

B=418.5 mm D=455.7mm T=67.5 mm t=42mm c= unknown

Abe = B + 2c( ) D+ 2c( ) - 2 D - 2 T + c[ ]( ) B + 2c[ ] - t + 2c[ ]( ){ }

24622.5 = 418.5 + 2c( ) 455.7 + 2c( ) - 2 455.7 - 2 67.5 + c[ ]( ) 418.5 + 2c[ ] - 42.0 + 2c[ ]( ){ }\c =15.3mm

Therefore the minimum length of the base plate = D+2c = 455.7 + (2 x 15.3)

= 486.3mm

And the minimum width of the base plate = B + 2c = 418.5 + (2 x 15.3)

= 449.1 mm

Therefore provide a base plate of 550 x 450mm base plate.

Base plate thickness:


72


Assuming a base plate thickness of less than 40mm the design strength will be pyp = 265 N/mm2,

the actual thickness, tp is:

tp = c3w

pyp

é

ë ê

ù

û ú

0.5

=15.33 ´ 0.6 ´ 40( )

265

é

ë ê

ù

û ú

0.5

= 21.6mm

Where:

ω is the pressure on the underside of the plate, for this assumes to be the bearing capacity.

Therefore a plate of 500mm x 450 mm x 10 mm in grade S275 steel would be suitable.


73


6.4 Monopole Design

6.4.1 Introduction

This section will provide design for an individual monopole to EC3 which will be used to support

the solar receiver at the centre of an individual solar field. This design can be repeated as with the

rest of the field so that manufacturing costs can be lowered as well as keeping other overheads

down such as structural design fees.

6.4.2 Tower Requirements

From the solar field design (Section 7.1) the receiver is required to be at a height of 65m above

ground level, therefore the monopole will be designed to 65 m. It will have to resist all actions on

it in particular the strong winds present in the Negev Dessert.

6.4.3 Choice of Structural Material & Design

When selecting a material to construct the tower out of a number of different factors impact on the

choice. The effects of external climactic actions on the structures durability and corrosion have a

large bearing on an appropriate material, however if these can be mitigated the choice is a simple

economical decision. The two most appropriate choices were that of either a steel monopole

design similar to that used in the wind turbine industry or a reinforced concrete structure.

Concrete has the advantage of being more resistant to sand scaling and thermal actions whilst

steel can be constructed off site, reducing site labour and quality created issues from on-site

construction. The weight and windage area of the receiver are the most important none adjustable

factors when designing the tower as these effect the imposed loads and moments generated over

the tower. Battleson has made calculations of cost for increased tower heights in both steel and

concrete with fixed external parameters for different receiver size. This cost analysis indicated

that steel towers are less expensive for heights of less than about 120 m and that concrete towers

are less expensive above this (Battleson, 1981). This analysis must be taken as an approximate

guide due to the sources age. It is evident however at these heights in the commercial market steel

is still being chosen for towers below 100 m. Therefore a steel monopole design has been chosen

due to its strong economical position. It also has advantages when considering its ease of factory

fabrication. In all probability utilisation of wind turbine monopoles would be likely and would

reduce costs considerably as this market is already far more developed with component parts

having a lower associated costs.


74


Figure 26: Figure showing the economical advantage steel towers have below 120m when

compared to concrete towers

6.4.4 Design Method

The design will be carried out to EC3 and in particular chimney design will be used for

considering the overall structural design. Further analysis of buckling will be considered by taking

a representative section at the worst case location between horizontal stiffeners and ensuring

buckling of this element will not take place. Due to the height of the structure special care must be

maintained when calculating the wind loads on the structure and their increase with height.

Fatigue of the structure is also of concern and will be addressed later in the section.

The use of finite elements within analysis of the structure could have been used if more time and

resources had been available. This would be strongly recommended if the design was taken

further.

6.4.5 Design Requirements

The design requires and will include the following:

Monopole: Height - 65 m

Sufficient internal space for the following; 2 steam pipes of 200 mm diameter,

electrical and control wiring and ladder access with partition floors every 4 - 7 m


75


Receiver: weight – 45,360 kg, height - 5 m, width – 4.25 m

Steam pipes to run into foundation base turning through 90 degrees and exiting

through side (see Figure 27)

Cut-out at raised height for man access where loads are reduced but not at significant

height for safety

Structure required in multiple connecting sections due to transport and manufacturing

constraints (suggested 2 – 4 sections ideal).

Figure 27: Cross section showing foundation connection and pipe detailing.

6.4.6 Quantification of Actions, Load Combinations and General Safety Criteria

The quantification of the actions and their combinations are made in accordance with EN 1990

(2002), EN 1991-1-1 (2002) and EN 1991-1-4 (2005), considering permanent actions that

correspond to the self-weight of the structure and non-structural members and the variable actions

which correspond to imposed loads and wind action in accordance with reported wind velocities.

Geometry of structural sections

The following are the geometric dimensions associate with the structure:

Hollow Section; external diameter – 2500 mm, wall thickness – 40 mm, cross sectional area –

0.309 m2

Vertical Stiffeners; No. 25, thickness - 40 mm, length (taken later as web length) - 120 mm


76


Horizontal Stiffeners; No. 10, thickness - 40 mm, spacing between - 6500 mm.

Permanent actions

Permanent action corresponds to the self-weight of the structure, including horizontal and vertical

stiffeners. The unfactored permanent loads from the structural members are as follows:

Circular hollow section = 1587.4 kN

Vertical stiffeners = 616.2 kN

Horizontal stiffeners = 27.4 kN

Reciever weight = 444.8 kN

x2 200 mm steam pipes = 70.9 kN

Total unfactored permanent load is 2746.7 kN, and since γG = 1.35 (EN 1990 n.d.), the design

permanent load = 1.35 × 2746.7 kN = 3708.0 kN.

Imposed loads

An unfactored uniformly distributed characteristic imposed load, qk, of 0.6 kN/m2 was chosen, as

the receiver must be accessible for maintenance. It will be assumed that the maximum load

applied at any one time during maintenance will be that covering an area twice that of the receiver

plan area, 36.1m2. Unfactored maintenance load for receiver = 0.6 kN/m

2 x 36.1m

2 = 21.6kN.

The steam pipes are assumed to contain 100% water, even though in reality it is likely often one

will contain water vapour, however on maintenance and shut down periods this may not be the

case. Due to the variable nature of the load it has been classed as an imposed load. Unfactored

water load = 4.3 kN. Assumed water in pipes travels full length of tower and within receiver so

full height of 70 m used to calculate load.

Total unfactored imposed load is 25.9 kN, and since γQ = 1.5 (EN 1990 n.d.), the design imposed

load = 1.5 × 25.9 kN = 38.9 kN.

Wind Actions

The force exerted on the structure by wind is determined in accordance with EN 1991-1-4.

Assuming a wind velocity of 20.6 m/s (Vb), reported to be the maximum windstorm velocity

experienced in the region, wind actions on the structure are determined.

The structure has been spilt up into strips so that the wind force can be better approximated due to

wind pressures changing at greater heights. These strips are as follows:


77


Strip 1: 0 – 2.5 m

Strip 2: 2.5 – 22.5 m

Strip 3: 22.5 – 42.5 m

Strip 4: 42.5 – 62.5 m

Strip 5: 62.5 – 65 m

Strip 6 (receiver section): 65 – 70 m

The following will first explain the different equations required to calculate the wind loadings,

stating variables which are fixed across all sections. The majority of calculations however will be

laid out in a table to compress and simplify reading of the data.

– Calculations Required

The force exerted on the structure by wind is determined in accordance to EN 1991-1-4. Clause

5.3 (2) states the wind force Fw acting on a structure or a structural component may be

determined as follows;

Fw = cscd * cf * qp (ze) * Aref

where; cscd is the structural factor defined in cause 6.2 (1). This structure does not conform to any

of these standard cases so a value of 1.1 was derived for cscd by interpreting Figure D.3 in Annex

D specifically designed for chimneys. Note, that the roughness category was required as well as

the basic geometry of the chimney to interpret D.3. Cat I was chosen after consulting Table 4.1

(Lakes or flat and horizontal area with negligible vegetation and without obstacles).

cf is the force coefficient for the structure or structural element and was found to be 0.6 for the

monopole section (Edinburgh, 1973) and 1.67 for the receiver in worst case (that being wind

normal to the square face) (www.struware.com), [accessed 02/01/11]).

Aref is the reference area of the individual surfaces and can be taken simply by calculating the area

normal to the wind (for the monopole section this would be the diameter multiplied by the strip

height. THIS VARIES DEPENDING ON THE STRIP BEING CONSIDERED AND

THEREFORE WILL BE DEFINED LATER.

qp (ze) is the peak velocity pressure and is given by clause 4.5(1). Expression 4.8 states how it is

calculated with the relevent section being:

qp(z) = ce(z) qb

http://www.struware.com/


78


where; ce(z) is the exposure factor and is a function of the terrain category and the height above

the terrain, z. It can be found by interpreting Figure 4.2. THIS VAIRES WITH HEIGHT AND

THEREFORE WILL BE DEFINED LATER.

qb is the basic velocity pressure given in Expression (4.10) which states:

qb = ½ Vb2

in which ρ is the density of the wind air and is taken to be the recommended value of 1.25 kg/m3.

The basic wind velocity, vb is calculated according to clause 4.2. Expression (4.1) of EN 1991-1-4

states:

vb = cdircseasonvb,0

where; cdir and cseason are directional and seasonal factors respectively, which are recommended to

be taken as 1. For this location, the basic wind velocity vb,o is taken as 20.6 m/s, which is the

maximum monthly average Easterly storm wind velocity for Yattir. Thus, from expression 4.1 vb

= vb,0 = 20.6 m/s. Hence the basic velocity pressure is:

qb = 0.5 * 1.25 * 20.62 = 265.23 kg/ms

2

Since 1 N = 1 kg.m/s2, the basic velocity pressure can also be expressed as:

qb = 0.27 kN/m2


79


– Calculated Data

Table 12 : Calculated data

Strip No. 1 2 3 4 5 6

Strip height hstrip m 2.5 20 20 20 2.5 5

Height from base to

top of strip

ze m 2.5 22.5 42.5 62.5 65 70

Height from base to

centre of strip

zb-centre m 1.25 12.5 32.5 52.5 63.75 67.5

Basic velocity

pressure

1/2 * ρ * Vb2

qb kN/m2 0.27 0.27 0.27 0.27 0.27 0.27

Exposure factor from figure 4.2 ce(z) 1.95 3.3 3.7 3.95 4 4.05

Peak velocity

pressure

c(z) * qb qp kN/m2 0.52 0.88 0.98 1.05 1.06 1.07

Reference area hstrip*d Aref m2

6.25 50 50 50 6.25 21.25

Wind force,

Newtons

cscd*cf*qp(ze)*Are Fw N 2.13 28.88 32.38 34.57 4.38 41.93

Factored wind

force, Newtons

(Saftey Factor, 1.5) Fw N 3.20 43.32 48.58 51.86 6.56 62.90

Factored wind

force, Kilo

Newtons

Fw kN 0.00 0.04 0.05 0.05 0.01 0.06

Moment generated

at base due to wind

force

Fw * zb-centre M kNm 0.00 0.54 1.58 2.72 0.42 4.25

Therefore the total moment generated by the wind load at the base of the monopole is 9.51 kNm

Stress created at base

Due to the greatest stress being created at the base of the monopole at the extreme fibers this

stress should be considered to ensure it does not beyond the yielding point of the steel used, 275

N/mm2. As:


80


M / I = σ / Y, so, σ = MY / I

where; M is the moment, I is the second moment of area, σ is the stress and Y is the distance from

the neutral axis.

As well as:

σ = p / A

where; p is the load and A is the cross sectional area., assuming that only the hollow section is

loaded with the stiffeners not taking axial load.

From these an overall stress can be calculated from all the loads applied on the structure.

σ = M*Y/I = 9.51 kNm x 1.25 m ( x 10-3

) / 0.23 = 0.05 N/mm2

and,

σ = p/A = (3708.0 kN + 38.9 kN) ( x 10-3

) / 0.309 = 12.13 N/mm2

Total stress created by all actions at extreme fiber of monopole base = 12.18 N/mm2

Therefore structure satisfies check for ultimate material failure. This is to be expect and it more

likely that this type of structure will fail through a local buckling or rupture failure mode.

Stiffeners have been applied to the hollow section to limit this and prevent buckling of areas by

stiffening them.

Buckling failure check

An individual T-section has been examined which consists of part of the hollow section bound

vertically by two horizontal stiffeners and connected to a vertical stiffener which makes up the

web. This is then analyzed as a T-shaped column for longitudinal buckling.


81


Figure 28: Cross section showing how local section split away for buckling analysis, also shows

vertical stiffener layout.

Assuming all the T-section has the maximum stress applied across its complete cross section, this

being 12.18 N/mm2 and has a cross sectional area of 17366.4 mm

2

P = NEd = σ * A = 12.18 * 17366.4 = 211.5 kN

First Check Compression resistance of cross-section

The following must be satisfied:

NEd / Nc,Rd ≤ 1.0

where;

Nc,Rd = A*fy / γM0 = 17366.4 * 265 / 1.00 = 4602.1 kN > NEd = 211.5 kN :. OK

Note: fy is found in Table 3.1.

Now check buckling resistance of member

As both ends are connected fully with rest of hollow section the effective length is to be taken as

0.65L where both ends are fully fixed.

The following must be satisfied:

NEd / Nb,Rd ≤ 1.0


82


where;

Nb,Rd = X*A*fy / γM1 = X * 17366.4 * 265 / 1.00

where;

X is the reduction factor for the relevant buckling mode, and can be found:

X = 1 / (Φ + √(Φ2 – λ

2)) <= 1.0

where;

Φ = 0.5[1 + α(λ – 0.2) + λ2]

where;

α is the imperfection factor and is found in Table 6.1 and Table 6.2 for a T-section as 0.49

following buckling curve, c.

λ = √(A*fy/Ncr) = Lcr / ix x 1 / λ1

where;

λ1 = π * √( E / fy ) = π * √( 210x10^3 / 265 ) = 88.44

:. λ = Lcr / ix x 1 / λ1 = 6500*0.65 / 154.4 x 1 / 88.44 = 0.309

:. Φ = 0.5[1 + α(λ – 0.2) + λ2] = 0.5[1 + 0.49(0.309 – 0.2) + 0.309

2] = 0.574

:. X = 1 / (Φ + √(Φ2 – λ

2)) = 1 / (0.574 + √(0.574

2 – 0.309

2)) = 0.945

so,

Nb,Rd = 0.945 * 17366.4 * 265 / 1.00 = 4348.9 kN > NEd = 211.5 kN :. OK

This satisfies both the buckling and compression checks for the individual section. Therefore the

structure as a whole should not fail with local buckling.

6.4.7 Discussion on validity of design & other considerations

This is an extremely large monopole and so will require 5 separately fabricated 13 m sections to

be connected on site to aid manufacture, delivery and craning. Connection flanges will be

required to couple adjoining sections which will coincide with the location of horizontal stiffeners

to increase the moment transfer between the two sections. These horizontal and vertical stiffeners

are to be welded during fabrication to the hollow section with vertical stiffeners taking priority


83


and the horizontal ones being welded around them, maintaining the rigidity of the vertical

sections.

Figure 29: Cross section showing stiffeners and flange connection detailing which will be present

at each of the 5 mid connections (note gap between flange plates is only present for clarity).

The design is quite a complex one when considering the different mechanisms of failure. It is

probable that local failure will occur due to the scale of the structure so a finite element model

should be used so that stress build up points can be analysed to ensure no failure will occur

because of these. The design of structural connections should also be carefully considered as these

areas create weaknesses which therefore must be over designed to in fact make them stronger than

the main structural section. This however will increase the loading on the local main structure so

checks should be made. Additional reinforcement around the man access opening will be

required. This opening should be at a sufficient height so that the loading on the local section is

reduced and so a reduced the amount of additional reinforcement is required around the cut-out,

compared to that required at the base where stresses are larger.


84


Figure 30: Figure showing detailing required around Man Access with additional stiffener

sections being indicated in red.

A painting system will be applied to protect the tower from sand scaling and should be maintained

to ensure that erosion of the structural steel does not occur. This will require a routine inspection

programme.

6.4.8 Fatigue of Structure

Fatigue of the structure is also of concern due to evidence of these types of modern monopoles

having structural related issues as a direct result of fatigue. Fatigue results from cyclic loading

often brought about by wind gusting in varied directions. Stress concentration areas such as holes

in the plate (i.e man access panel) and connection flanges must be looked at closely when

considering fatigue. When the load is repeatedly applied or the load fluctuates between tension

and compression, these points experience a higher range of stress reversal than the applied

average stress. These fluctuations involve high stress ranges and cause minute cracks at these

points, which open up progressively and spread with each application of the cyclic load,

ultimately leading to rupture. Therefore fatigue induced rupture should be designed against

especially with new evidence that this is a problem in modern monopoles is known. Further

assessment of this should be made if the design was continued.

Desalination: Group 2 Solar fields

85


7 Solar fields

7.1 Solar Field

7.1.1 Introduction

Concentrated solar power (CSP) represents a key technology of the 21st century. CSP has

amazing potential and the market is expected to grow rapidly in the next century as more

sustainable energy generation methods are sought. CSP theory is based on system which is able to

focus and concentrate the power of the sun to a single point where the energy is intense enough to

be efficiently transferred into a heating liquid, creating steam, which can be used to generate

commercialised power. This whole process has the ability to be completely „green‟ and has

advantages over other methods of solar power due to its supplies consistency and predictability. A

key requirement of this system is enough suitable land in which a field of controllable mirrors or

heliostats can be situated in great number to direct and focus the sun light falling on the earths

surface towards a single point.

7.1.2 System concept

Many companies and research groups have worked on creating efficient and optimum systems to

harness this power taking a variety of different routes. Some have used „super towers‟ around

165m18 in height whilst others have chosen to miniaturise the process and utilise repetition in

manufacture and design to simply construction and reduce overall costs.

18 http://earthobservatory.nasa.gov/IOTD/view.php?id=40204

http://earthobservatory.nasa.gov/IOTD/view.php?id=40204


86


Figure 31 : Single system consisting of one tower with a duel cavity receiver and two heliostat

fields (North and South).

After analysis of the different approaches it was seen that duplicated small systems would provide

a better solution to the needs presented for this project both reducing the costs associated and

allowing for a far more expandable system to meet future needs, see Table 13 for a comparison of

different CSP systems. This system would utilise towers which raise the receivers to about 70m

above the ground. In total 32 towers would be required to provide sufficient electricity

production, with 512,000 1.5m2 individually tracking heliostats redirecting the required sunlight.


87


Table 13: A comparison of different CSP systems

LARGE TOWER, SINGLE FIELD SCALABLE SOLUTION

Key Values

Tower Height 110 - 170 m 40 - 80 m

Number of Towers

Required

1 - 2 20+ (approx. 32)

Size of Individual

Heliostat (area of

reflective surface)

140 m2 1.5 m2

Number of Heliostats

per Tower

2000 - 5000 1200

Tower Construction Concrete, jump formed Steel, Monopole

Advantages

Less components to monitor, inspect and maintain

> Less things to go wrong.

Modular design

> Simple plant expansion.

Turbine can be located near solar receiver

> All steam produced only needs to travel short

distance to large turbine which increases efficiency.

Repeatable design elements

> Factory fabrication appropriate.

> Reduced costs due to repetition.

Can be situated on smaller site than modular system More flexible with failures

> A receiver failure does not effect

supply greatly.

Predictability advantages with

component failure

> Replacement or monitoring can take

place if failure of single component is

seen to reduce loss to overall system.

More cost effective

Disadvantages

Large tower requires high outlay and increased time

to construct on site.

> Greater capital cost associated.

Less efficient

> Shadowing losses due to repeatable

shape of fields.

Critical system must be kept operational

> Receiver failure would result in total loss in power

output.

Takes up more space

Requires more pipework as individual

receivers will not be all close in

proximity to turbine

> Losses associated with heat transfer

through pipe wall.


88


7.1.3 Geometrical Positioning

The geometric positioning of a heliostat field has a significant effect on its efficiency both in the

amount of space it takes up and the amount of losses experienced through shadowing19

, blocking20

and the cosine effect21

. These losses combined with the choice of receiver height and relative

costs create a multifaceted problem. This is very complicated and is best calculated using

computer driven algorithms. It is clear however that an optimisation based on reducing both

shadowing, blocking and the cosine effect creates a large heliostat field with a complex pattern, as

can be seen at PS10 and PS2022

. This is clearly shown in taken from Figure 32 (Zhang, et al.,

2007) which shows a heliostat system which provides the most energy output for a single tower

with an unspecified area available, costs have been considered. Whilst this optimises the

production of energy it means that the field is extremely complex, very tailored to the specific

location deigned for and of a shape which does not fit well with other fields in close proximity.

Figure 32: Example of heliostat field providing optimum energy output

In fact, when considering this efficiency based field it leads to a design which is unsuited to a

scalable solution of multiple fields and towers. It is impossible for every mirror to in the most

efficient location as there is normally a hot spot of maximum efficiency which decreases as

19 Shadowing; Where one heliostat blocks another‟s sun and so reduces the amount of flux

generated by that given heliostat. 20

Blocking; Where one heliostat blocks another‟s reflection to the receiver reducing the amount

of flux received at the central point. 21

Cosine Effect; An efficiency dependent on both the sun‟s position and the location of the

individual heliostat relative to the receiver. The angle in which the light is reflected effects how

efficient the heliostat is. 22

PS20 solar power tower - eNotes.com Reference [accessed 28/12/10]

http://www.enotes.com/topic/PS20_solar_power_tower


89


you move away from the centre of this. The major losses which characterise the fields

efficiency are largely geometry based but also include losses associated with atmospheric

attenuation23

and spillage24

due to light not being utilised by the receiver to heat the medium.

Therefore the field will always be a compromise between efficiency, possible power

production, area used and cost. When considering cost, the capital expenditure for heliostats

and there set up is high. To reduce these a rectangular field will be used with its centre being

the area of best solar flux transfer and optimum efficiency. Figure 9.6 represents how the field

will have optimum efficiency at the centre but also maintain the characteristics which make it

cost effective, simple and easily repeatable in close proximity.

7.1.4 Heliostat System

The heliostat system will be made up of a number of repeating interlocking bases which gain

there rigidity through this and house two rows of mirrors. These will be aligned in straight rows

running across the solar field. This has the result of making the field very easily set out and makes

the process of constructing the field much more straight forward. The bases and mirror units

themselves will be small and light enough to be moved and placed by hand removing the

necessity for lifting machinery. The base elements utilise light truss members in order to both

reduce weight and reduce the amount of steel used in order to lower the price per unit. This

heliostat structure due to it lightness and utilisation of rigidity above ground means that no

dedicated foundations are required. By means of ground preparation and placing the heavy motor,

gearing and drive system in an enclosed base container supporting the truss structure and mirror

unit above the system is able to remain stable. A basic schematic of this can be seen in Figure 9.7,

with components highlighted in different colours. Figure 9.8 shows how the system acts in larger

groupings, note foot access can be gained in space between paired rows.

Design requirements due to field selection:

Receiver 70m above ground level

Each receiver requires a North and South field of prepared ground, 170m by 100m.

32 receivers required to fulfill necessary electricity production.

23 Attenuation; A loss caused as the light beam travels through the atmosphere between the

heliostat and the receiver, a problem when heliostats are at a large distance away from the

receiver. 24

Spillage; loss when energy directed toward the receiver does not fall on the absorbing area.


90


Figure 33: Rectangular heliostat field efficiency, red indicates most efficient location

Figure 34: Schematic showing heliostat system


91


Figure 35: Schematic showing heliostat system


92


7.1.5 Receiver Design

The solar receiver fundamentally is a simple heat exchanger built to convert the solar radiance

directed at it from the heliostats into a heating liquid (water to steam). They do this by creating

the maximum transfer surface from input source to heating liquid. For solar receivers this is done

by splitting the flow into thousands of small pipes so as to create the maximum surface area.

Different designs have there own advantages the main two being cavity and external receivers.

External receivers are of simple construction, where as cavity receivers have the advantage of

being capable of collecting more energy due to there focusing and capturing of reflected light.

They do this by allowing the light through a narrow opening into a reflective surfaced cavity.

Here the light is directed at the multiple liquid carrying pipes where the energy is transferred into

heating the liquid. Any light which does not heat the liquid and is reflected away is then

rebounded back towards the pipes by the reflective surface and the geometric shaping of the

cavity. This allows for reduced losses and a performance increase. Cavity receivers have been

chosen due to there improved performance and are not expected to be significantly more

expensive.


93


Photo showing large solar towers as seen from space, even here they are clearly visible with there

large heliostat fields.

esolar, 2007. [online] http://www.esolar.com/ [accessed 05/10/10]

Zhang, H., Juchli, I., Favrat, D., and Pelet, X., 2007. Multi-objective thermoeconomic

optimisation of the design of heliostat field of solar tower power plants, Infoscience,

EPFL.

enotes, 2010. PS20 solar power tower, [photograph]

http://www.enotes.com/topic/PS20_solar_power_tower [accessed 20/12/10]

Figure 36: Photo showing complex arrangement of heliostat fields in arced configuration at PS10

and PS20 in Seville, Spain.

http://www.esolar.com/

http://www.enotes.com/topic/PS20_solar_power_tower


94


7.2 Energy generation calculation The number of heliostats required will depend directly, on the amount of energy required by the

desalination plant. The energy consumed by the high pressure, booster and 2nd

stage pumps totals

38,369 kW, whilst the pre- and post-treatment pumps consume 4,485 kW. This is culminated in

the desalination plant, therefore consuming a total of 42,854 kW.

However, it was thought that the solar facility should be designed for a specific energy

consumption of 4 kWh/m3 of fresh water produced. This will increase the absolute energy

consumption of the desalination plant, which allows for more water to be produced in the future.

It also implies that more energy will have to be generated by the solar plant, and this increase

accounts for the energy needed to operate the solar plant itself.

Assuming a turbine efficiency of 40%,

If an 80% heliostat efficiency is assumed,

If the fluid absorbs 92% of the energy reflected by the heliostats, each having an area of 1.5 m2,


95


If each tower can accommodate 16,000 heliostats around it;

To fully utilise the power provided by 32 towers requires the installation of 512,000 heliostats,

instead of the 498,188 stated above. This allows the provision of desalination 51,621 kW of

power to the desalination facility, which amounts to a specific energy consumption of 4.11

kWh/m3. The important parameters are presented in


96


Table 14.

Table 14: Solar plant parameters

RO plant pump power

required (kW) 51621

Amount of water

produced per year (m3) 1.10E+08

Solar plant energy

generation

requirement (kWh/yr) 1.13E+09

Energy required

(kWh/year) 4.52E+08

Solar plant energy

generation requirement

(kWh/m3) 10.28

Solar plant energy

generation

requirement (J/yr) 4.07E+15

Energy required by RO

(kWh/m3) 4.11

Solar irradiance

(kWh/m2) 2000 Energy supplied by

sun (J/m2/year) 7.20E+09

Turbine efficiency 40%

Sunlight hours in a day

(average) 9 Energy reflected by

heliostats (J/m2/year) 5.76E+09

Solar process energy

generation (kWh/year) 1.13E+09 Solar irradiance (W/m2) 673.40 Energy absored by

fluid (J/m2/year) 5.30E+09

Energy generated by solar

process (kWh/year/m3) 10.28 Heliostat efficiency 80% Heliostat area

required (m2) 768000

Fluid absorption

efficiency (transfer to

fluid) 92%

Number of heliostats

required 512000

Surface area of each

heliostat (m2) 1.5 Number of towers

required 32


97


Note: This calculation suggests that the desalination plant requires . The

quantities of heliostats are tailored towards providing the desalination plant with this amount of

energy. An energy consumption of corresponds to a specific energy

requirement of 4.11 kWh/m3.

If the desalination plant consumes 3.41 kWh/m3 of energy, as is the case now, an energy

consumption of is sufficient to produce nearly 148 million m3 of fresh

water per year, which translates to an additional 38 million m3 of fresh water being produced.


98


7.3 Sizing of Solar Plant Process Equipments

Process equipments in the solar plant consist of a turbine, condenser, pump and the receiver. The

turbine used is a condensing turbine type with a power output of 138.4 MW.

7.3.1 Turbine

The selected turbine exhaust pressure is at 0.05 bar and this will be the design outlet pressure

selected in an attempt to extract the maximum possible energy from the steam.

Steam design conditions

Inlet: Temperature: 440⁰C, Pressure: 60 bar

At the inlet conditions maximum available energy = 3277 kJ/kg, and since an ideal turbine

expansion is associated with constant entropy, using Mollier diagram the available energy at the

end of the expansion can be found by knowing the final pressure to be 0.05 bar. Therefore the

final available energy taken from Mollier diagram at constant entropy = 2040 kJ/kg.

Available energy = 3277 – 2040 = 1237 kJ/kg

Theoretical steam rate=

2.9 kg/kWh

Typical turbines have efficiencies between 80 to 70%25

, selected efficiency for the propose of this

design is 75%, therefore the actual steam flow rate =

= 3.9 kg/h

Total energy required by the desalination plant =

Solar plant total operational days per year = 360 days

Average day light hours in Israel26

= 9

Solar plant power output excluding pump power consumption and generator efficiency

=

= 136 MW

Electrical generator efficiency = 98.94 % .Therefore

= 137 MW

25 Invalid source specified.



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Pump in solar plant power requirement = 1.19 MW

Total solar plant output including pump power consumption = 138 MW = 138447 kWh

Therefore total steam flow rate = 3.9 × 138447 = 537225 kg/h

7.3.2 Condenser

The condenser is required to condense the exhaust steam leaving the turbine. The steam is at very

low pressure below atmospheric at 0.05 bar and condensation will be at vacuum.

Q=UA∆Tm, will be used to find the area required for condensation.

∆Tm= Ft∆Tlm, Ft the temperature correction factor will be assumed to be 1 and therefore the

logerthemic mean temperature difference will be calculated.

∆Tlm =

, where T1 is the inlet temperature of the steam, and T2 is the outlet

temperature of the steam. t1 and t2 are the inlet and outlet temperature of the cooling fluid and in

this design is water.

T1 =T2 = 32.806 ⁰C 27

this is a phase change and temperature does not change.

t1= 22 ⁰C, and t2 =31⁰C. Therefore ∆Tlm = 5 ⁰C, Q for phase change = 330346000 W, and the

overall heat transfer coefficient U 28

= 350 (W/m2 °C).

Area required for phase change =

187614 m

2

Total amount of cooling water required =

31564484 kg/h

7.3.3 Solar plant Pump

The pump is required to increase the condensate pressure from 5 kPa to 6000 kPa.

Power = q ∆P/η

P1 = 5 kPa

P2 = 6000 kPa

q = 0.15 m3/s

27 ChemCad simulation (included in appendix A)



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η = 0.75

Power =

1.2 MW

7.3.4 Solar tower receiver

The receiver is designed as a heat exchanger, so similar condenser design steps are followed.

There are two areas required, 1st is the area required for sensible heating and 2

nd the area required

for phase change.

Area required for phase change = 4973 m2

Area required for sensible heating = 3706 m2

Total area required = 8679 m2

7.4 Cost of solar plant process equipment

The total installed cost of the turbine, condenser, pump and heat exchanger = £ 49263480

Desalination: Group 2 Electrical systems

101

Section 8 Author: NJ

8 Electrical systems

8.1 Introduction of Power Usages for Solar-RO Desalination Plant

Beersheba is a sunny place and has the highest solar energy potential in Israel in comparison to

the other places in Israel. It enjoys over 3000 hours of sunlight every year (BECKER, S., 1997),

with a daily average of 9 hours. The energy required for the RO plant must therefore be generated

during the day.

270MVA power is produced by generator of the solar thermal power system to support the whole

process of reverse osmosis. The power will be sent to the national grid, which is located at the

Rutenberg power station, by a high voltage transmission. The RO plant will obtain the supply

power directly from the grid.

8.2 Active, Reactive, and Apparent Power

The concept of active, reactive and apparent power plays an important role in electrical systems.

The terms Watt (W), Volt-Ampere (VA) and Volts-Amps- Reactive (VAR) are often

misinterpreted. The voltage and current for active, apparent and reactive power, is an AC signal,

in steady sinusoidal form (WILDI, Theodore, 2000).

Active power, P, is a real power that always flows from generator, and is delivered to the load. It

can also be expressed as the product of voltage across AC current and the load, which is in phase

with the voltage; the unit of active power is Watt (W), (kW) or (MW). The unit for reactive power

is VAR, which is affected by a reactive load, such as capacitor or inductor. Components such as

capacitors or inductors are used to store energy. They are referred to as reactive power when the

waves of the AC signal return to the source in a repeating cycle of the line frequency (WILDI,

Theodore, 2000).

The apparent power can be defined as the combination of active and reactive loads, or VRMS*IRMS.

The apparent power is used to ensure that all equipment being used is within the standards of the

jurisdiction. The unit of apparent power is Volts-Amps (VA); it is used in calculating the loads

and line voltage, and to design the single line diagram. The apparent power is a product of real

power and power factor multiplied by 85%.

8.3 Transferring Power to National Grid Power Station

Rutenberg Power Station is situated on the Mediterranean Coast in Ashkelon, south of Tel Aviv,

Israel. This power plant is the second largest power generation plant in Israel; it is coal-powered,

and possesses a generation capacity of 2250MW (CORP., Israel Electric, 2009). It was built under

the Israel Electric Corporation and 98.5% of it belongs to the State of Israel (CORP., Israel


102


Electric, 2009). This power plant is chosen due to its ability to receive high power from the

thermal solar power station. Rutenberg is the power station nearest Beersheba, with an

approximate distance of 50.2 km between the two. The proximity of this plant aids in reducing the

line losses and in reducing the skin effect along the transmission line.

The design production capacity of RO Plant is 110 million cubic meters per year, which translates

to 305,600m3 per day. On average, the RO plant requires 6.65 kWh to produce 1m

3 of water. Thus

the power required to produce 305,600m3 of water on a 24-hour basis is 2.04MW, all of which

must be produced during the day.

Approximately, the power required to run the RO process is 85MW. This comprises of the power

consumption of high-pressure pumps, pre-treatment pumps, water intake pumps, booster pumps

and other electrical appliances. On average, 1.8MW of power is required by solar thermal system

and 22.5MW for general purposes. All these values are summed and then divided by the power

factor, to convert the unit from watt “real power” to VA “apparent power”. This is important, in

order to determine the energy produced by generator and to select the appropriate power

transformer. The total energy calculated is equivalent to 100MVA (The calculation for power

production by a generator is shown in Section 20.20, Appendix A), with an excess energy,

corresponding to 20% of this value, being sold to the grid.

According to the calculation from Section 20.20, Appendix A, the rating power generated is

270MVA. Almost 90% of the power produced will be transferred to the Rutenberg grid, at the

rate of 16kV (Y) to 500kV () (KOPF, Rick, 2010). Thus, the overhead transmission system is

most appropriate from a design point of view, as it is economical and efficient for high voltage

transmission compared to underground power lines. Moreover, the cost for burying cables is 2 to

4 times more expensive than the overhead power line constructions (EEI, 2010).

There are two ways of transferring the large energy; High Voltage Alternating Current (HVAC)

and High Voltage Direct Current (HVDC). Both technologies have their own pros and cons.

However, it is also important to know the type of conductor used for the transmission. There are

several types of conductor used for transmission lines, namely copper, aluminium, alloy, ACSR,

ACAR. For high voltage transmission, the bare wire is made from an aluminium conductor, with

reinforced steel (composite material). Currently, copper is used on a less frequent basis due to its

limited supplies and price rise.

8.4 Comparing HVDC versus HVAC Power Transmission

The key aspect of transmission that has to be taken into account once the power plant is

established. With the development of power transmission technology, HVDC has been used in

place of HVAC, especially when transferring bulk power for long distances (Transmission and


103


Distribution Theory 2, 2010). The growth in use of HVDC is also affected by technical benefits

and economics.

HVDC is the only alternative that uses direct current to transfer the high voltage AC electrical

power for long distances. This is in contrast with the typical AC power transmission. HVDC is

known to be reliable, inexpensive and it consists of less electrical losses. The system requires two

converter stations and a cable for direct current (DC) (BAHRMAN, Michael, 2006).

Typical power lines in Israel oscillate at a frequency of 50Hz, carrying the alternating current

mostly in high voltage transmission and distribution systems. To minimise the losses and reduce

cost, the transmission line is connected in series. In this region, AC transmission is used to

transfer bulk power instead of DC transmission line. The positive aspects of an AC system can

transform a voltage into various voltage levels by using a transformer (2.7, WP, 2006). Although

the AC power transmission is widely used and seems to be working well, some aspects of the

system need to be tackled. Inefficiencies in the system and installation of components are some

aspects that need particular attention.

Direct cost comparisons between DC and AC alternatives should be considered as well. HVAC is

proposed for this project although HVAC system will cause line losses due to the “skin effect”.

The cost of the terminal equipment for the DC system is much higher than for an AC system.

More than 50% of the transmission costs are related to the converters. This is due to the AC-DC

to DC-AC conversion. If the travel distance is longer, >500km; the HVDC cost per unit length

will be cheaper than HVAC line of the same power capacity (KALA MEAH; SADRUL ULA,

2008). Figure 37 shows the typical HVDC and HVAC transmission cost per distance. The

breakeven distance is measured at 500km. In addition, above the distance concerned, HVDC will

always be at the lowest cost. Finally, the HVAC technology is proposed to maximise the benefits

towards this project. Figure 38 shows the HVDC system, with 2000km of transmission distance

yielding real benefits to the system with long distance.


104


Figure 37: HVDC and HVAC Transmission system cost. Breakeven shows at 500km between

HVAC and HVDC

Figure 38: Comparison of AC transmission line (purple line) over the ultra-Higher Voltage DC

(green line). The graph shows the cost approximation in million USD versus the percentage of

line losses. Picture on the right shows one line of 800kV DC and seven line of 500kV AC.

Source: Video of HVDC (ABB, 2004).

8.5 The Electrical Distribution System

In this project, an extensive electrical distribution system will be utilised to accommodate all

equipment and components used with reliable power, in order to run the reverse osmosis (RO)

plant on a 24 hour basis. The thermal solar power plant cannot store energy economically and the

RO plant cannot be shut down completely. Therefore, the RO plant cannot get power directly

from the thermal solar. In addition to this, the RO plant is located in Palmachim, which is about

32 miles away from the solar plant and there will be line losses resulting from a long

transmission. To ensure the reliability of the RO plant, the power source is provided from


105


national grid. The solar plant will transfer the energy through HVAC transmission line to

Rutenberg power station to cover the energy used by the RO plant, day and night. The diagram

below describes the energy flow to the RO plant.

Solar Generator National Grid

(Rutenberg PS)

RO PlantHVACAC transmission

98.2MVA/400kV

160kV/4.16kV80.32MVA

13.8kV/4.16kV

Figure 39: Basic diagram for AC transmission line

Figure 40 and Figure 41 show the one line diagram of all equipment used in the solar power

plant and the process plant. The electricity was generated from thermal energy that arises from

high-pressure steam, which turns the turbine, generating power.

The output of the main generator from Figure 41 is connected with the input of two different

types of transformer. The first connection, to the step-up transformer, directly transfers the AC

power to the Rutenberg power station, without converting to DC. Another branch of output is

connected to the auxiliary transformer and finally fed to the load.

The function of step-up transformer is to increase the generator voltage. The output voltage from

the generator is approximated to be 100MVA and 97.78% of which will be transferred to

Rutenberg Power Station through the step-up transformer. A further 2.3% will be sent to auxiliary

transformer unit (AUT) or the step down transformer of the solar thermal plant to provide power

during the daytime (CASTLEBERRY, Gerry W., 2008). Three winding forms part of the

auxiliary transformer; one of the windings, the primary winding, is used to connect to the main

generator. This winding is rated at 16kV is connected to the generator by the isolated phase bus

duct. The secondary winding, which is rated at 4.16kV, provides sufficient power to the power

station through the non-isolated phase bus duct.


106


To Transmission Rutenberg Substation

4.2kV Bus 2A

From Transmission Rutenberg Substation

480V Bus 3A

SUS Transformer 3A

2500kVA

ONAN

4160V/480V

Start-up Transformer

2.12MVA (3MVA)

OA/FA/FOA

160kV / 4.12kV

Auxiliary

Transformer

2.12MVA (3MVA)

OA/FA/FOA

16kV / 4.16kV

Step Up Transformer

98.2MVA

OA/FA/FOA

16kV / 400kV

Main Generator

100MVA

16kV

Spare Pumps

House

1.5MW

Spare Spare

Low power load for general

purposes

Isolated Phase

Busduct

Non-isolated

Busduct

Figure 40: SLD for Solar Thermal power plant system. Solar Grid


107


To Transmission

Rutenberg SubstationFrom Transmission Rutenberg

Substation To RO Plant

SUS Transformer

3000kVA

ONAN

4160V/480V

13.8kV

480V Bus 3A

240V

High Voltage

Medium Voltage

Low

Voltage

4.16kVHigh Voltage

Auxiliary Transformer

80.32MVA

OA/FA/FOA

400kV / 13.8kV / 4.16kV

High

Pressure

Pumps

House

8 Units

33MW

Spare Spare Booster

Pumps

House

10 units

2.70MW

Product

Water

Pump

2 Units

470W

Calcite

Pump

2 Units

350W

Backwash

Pump

3 Units

120kW

Lo

w P

ow

er P

um

p

Spare SpareSecond

Pass

Pumps

House

3 Units

4MW

Spare

SpareSpare

Coagulant

Pump

0.1mW

Chlorine

Pump

0.1mW

H2SO4

Pump

5mW

NaOH

Pump

2mW

SpareSpare

Spare Spare

SUS Transformer 3A

3000kVA

ONAN

4160V/480V

480V Bus 4ALow

Voltage

SpareSpare

240V

Low power load for general

purposes

Spare

240V

Low power load for

general purposes

Seawater

Pumps

House

4 Units

4.40MW

Spare

Spare

Single Phase Transformer

2500kVA

4160V/240V

Single Phase Transformer

2500kVA

4160V/240V

Low

Voltage

Phase Busduct

Figure 41: SLD of three stages of the system. GridRO


108


From Figure 40, it can be seen that there is another AUT or step down transformer, shown on the

top right of the drawing; it is used to power the plant equipment during system start up from cold

conditions (CASTLEBERRY, Gerry W., 2008). This is because the sunlight takes some time to

heat the water. Figure 41 illustrates a single line diagram for RO system in Parmachim.

Normally, the load power is measured according to the range of voltage connection to limit the

current for safety and economic reasons (AMOTT, Prof. Nick, 2010).

Table 15: Range of voltage (AMOTT, Prof. Nick, 2010)

Power Range Voltage Range

Normal Usage 120 V

Small Pumps to 150 kW 480V

150 kW - 3MW 4.16 kV

More than 3MW 13.8 kV

This classification is not standardized but the loads given are simply typical divisions of power

plant loads. Since the load power classification information is hard to get from the Israel Electric

Corporation, the information presented above might be useful in deciding the voltage range for

each power load.

8.6 System Description

8.6.1 Main Generator

The main generator is an important element in the power plant design. The typical generator could

be rated at 500kV, 230kV and etc (GONYEAU, Joseph, 2001). In this design, the main generator

will produce electricity by extracting thermal energy from the steam turbine, to support the whole

system. From the calculations shown in Section 20.20, Appendix A, the total power requirement,

including the excess energy, is 85MW. This is equal to 100MVA, with a power factor of 0.85.

Therefore,

Generator power rating

= 266.67MVA ≈270MVA

The main generator is normally delivered from the supplier. Siemens generator, S Gen -1000A,

for example, offers a comprehensive generator with a 98.94% efficiency that provides ratings

between 165MVA to 350MVA for the steam turbine. The line voltage that could feed this power

is between 10.5kV to 20kV (SIEMENS, 2010).

8.6.2 Bus Duct

The phase bus duct in Figure 40 is used to carry high voltage current (13.8kV) from the generator

to the main transformer at the power plant, and from AUX transformer to switch board (4.16kV).

The bus duct is comprised of large aluminium tubes. The diameter of the tube is around 18 inches


109


and forms an enclosed protection to the energized bus bar, which is mounted with polymer

insulator. There are three phases in the system and each phase is isolated from each other. This is

to avoid faulty or short circuits involved in the three phases (CASTLEBERRY, Gerry W., 2008);

it gives a high degree of protection to the generator and to the main step-up transformer.

8.6.3 Step-up Power Transformer

The step-up transformer is a device that increases the primary voltage (that comes from the

generator) to secondary voltage, for the transmission of power to the grid (Rutenberg Power

Station). There are two types of step-up transformers:

Single three phase transformer

Three single phase transformer

The single three-phase transformer is appropriate to use for the step up process. This type of

transformer offers many advantages, particularly to the industrial sector. The only advantage of

the three single-phase transformer is that it is easy to maintain in case of a failure. Whenever there

is a winding failure in one of the three single-phase units, only that particular unit needs to be

replaced (MAHARANA, Suman, 2010). Although the maintenance cost is cheaper, the

installation cost is much more expensive compared to the single three phase transformer.

Delta () wye (Y) configuration is connected in the three-phase transformer; it is commonly

applied in industry because it serves several useful functions. If there is a large amount of

unbalanced loads supplied from the secondary transformer, the delta, which is the primary source,

provides a better current balance. The delta connection is provided with a high level of reliability.

The wye (Y) provides multiple voltages and can be used over long distances transmission.

This is a liquid oil type of step-up power transformer. A liquid type transformer was chosen for

this project because of the higher standard of energy efficiency that they possess over the dry

transformer. The dry transformer is environmentally safe and does not require any fire proofing

but they need a larger space for ventilation and tend to be more costly, with great losses.

Moreover, the lifespan for a dry transformer is 15 to 25 years. The transformer replacement every

15 years is a bit challenging with extended delivery since Beersheba is in the middle of Negev

desert and the transportation cost is expensive (REPS, RM, 2008). On the other hand, the liquid

filled transformer has a superior operating life time, ranging between 25 and 35 years. “Because it

has a longer lifespan, we can save on the labour and material cost of a new transformer

replacement and operational impact due to outage replace”; taken from –ORNL-6847.pdf

(SYSTEM, Cooper Power, 2008)


110


8.6.4 Auxiliary Transformer

Liquid auxiliary transformer or step down transformer is used to step down a high voltage coming

from the generator through the isolated phase bus duct. The three phase transformer has three

windings, allowing it to have two different voltage levels, 13.8kV and 4.16kV. For example,

higher voltage equipment such as large pumps or motors will fit under 13.8kV windings and the

4.16kV winding for lower devices. Finally, the primary winding is designed to carry 16kV to

match the generator output.

8.6.5 Start-up Transformer

The high voltage start up transformer or step down transformer will be installed to supply power

when the plant is being started. It is termed as a standby transformer to supply power to 13.8kV

and 4.16kV unit boards. The power is taken from the grid if the auxiliary transformer is broken

down or not in operation.

8.6.6 Voltage Switchgear

Switch gear is essentially a combination of electric disconnects or circuit breakers with fuses to

protect equipment from damage (CASTLEBERRY, Gerry W., 2008). Medium voltage switchgear

is used in this system. Switch gear refers to the line up load as shown in Figure 40. This is also

due to safety that prevents user or any equipment coming in direct contact with high voltages of

13.8kV and 4.16kV.

8.6.7 Secondary Unit Substations

The secondary unit represents the slightly lower voltage configuration in this system but it has the

same configuration as the high voltage system. The supply power comes from the medium

voltage of circuit breaker and connects to a low voltage step down transformer to reduce the

voltage to 480V of switchgears. 480V is a three phase source that is used for light machines.

Finally, a single phase is used when the voltage is dropped to 240V for normal electrical

appliances such as computer, telephone, photostat machine (Three Phase Transformer ).

8.7 Business in Selling the Excess Energy

Apart from the power usage, any excess or unused energy will be sold to the grid. This

application is quite similar to a scheme called Feed-In-Tariffs (FITs), which is applicable in the

UK. The following paragraph explains the FITs scheme in Israel.

In Israel, the regulations are recently published by the Israel government regarding the purchase

of surplus power from private producers. “With a solar power system will be eligible from NIS

2.04 per kilowatt-hour (kWh) rebate on electricity produced”, taken from Globes [online], Israel

business news - (ANKORI, Merav, 2008) www.globes-online.com - on July 3, 2008.

http://www.globes-online.com/


111


From the power calculation in Section 20.20, Appendix A, the excess electricity is 16.731MWatt.

Therefore:

1kWh = 1 Unit, if 16.731MWatt is used in 9 hours daily:

16.731MWatt for 9 hours =

Assume NIS 2.04 (£ 0.371) per kilowatt-hour/unit;

per day!

To conclude, this project not only relies on the profitability of selling water but also on the power

generation, as the electricity sold also contributes to the profitability of the project

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9 Infrastructure

9.1 Introduction

Infrastructure plays a vital role in ensuring the plant can run as efficiently as possible by allowing

maintenance, deliveries and general process activities to take place through varied weather

conditions. Infrastructure includes but is not limited to; access and maintenance roads, facilities

for operational staff and chemical and other storage. Israel has a fairly developed national

infrastructure within the Middle East and so allows for developed plant operations to take place

within the country. In this section the role infrastructure plays both on the site and the local area

will be considered, how this has affected the infrastructure design for the project and then

schematic layouts of this will be given.

9.2 The Importance of Infrastructure on the Operational Success of a

Plant

One of the fundamentals to a successful plant, whether it is a local refuse site or large scale

industrial activity, is the ability for the overall plant to operate as efficiently as possible. This

requires infrastructure in the form of transport links both to site and around site that enable

activities to be undertaken as smoothly as possible. The problems that can occur can clearly be

seen when driving around a poorly designed supermarket car park when the design does not fit the

requirement. Not only do transport links need to be provided but also provision for any

operational staff. This includes on site facilities for night staff, etc. Without these crucial services

a plant cannot be run day and night throughout the year, which would severely impact the

facilities output.

Provision and consideration must also be given for maintenance and plant upgrades. This includes

their delivery and fitting. Therefore thought has to be made not only as to how new membranes

will be moved into the plant room and fitted but how delivery vehicles will move on site.

Introducing how this is an important factor to both the success of the project and how it is the

main interface with local community.

9.3 Impact Infrastructure has on Location Choice

Whilst it was critical to choose locations for both the RO and CSP plants in which variables like

sun light and availability of sea water were critical to their success the location of near by services

and infrastructure were also important. Consideration to how roads will be connected has to be

made at this initial stage. Urban areas are not ideal to connect into as these often have small roads

suitable only for cars and not able to deal with large delivery lorries. Therefore close proximity to

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main roads and highways was sought for the location of both plants. When considering other

infrastructure the availability of both suitable potable water pipes to connect the supply into as

well as power lines need to be considered. This is difficult to do with limited resources and

information and so these were approximated using engineering judgement to where these

resources would likely be, linking the likelihood of these services with light industry in the area

and population centres.

9.4 The Plant’s Requirements

The plants will have differing levels of traffic due to there different purposes and operations. The

RO plant will have the following during normal operation and maintenance periods:

Operation staff traffic with parking required

Chemical and membrane replacement deliveries

Quality control visiting made to ensure water quality.

The CSP plant will have the following requirements:

Operation staff traffic with parking required

Heliostat repair and delivery vehicles

Both would be considered to have a light demands on the local infrastructure with minimal

noticeable impact during operational periods. Both plants however during the construction are

likely to have heavy traffic both in number and delivery size. Therefore the requirement the plants

will have on the local infrastructure during this period is very important. The CSP plant will have

deliveries of very large monopole sections which will be delivered likely on low loaders. Both

sites will also have deliveries of structural steel and numerous concrete deliveries, which mean

heavy vehicles, will be using the local roads. The turning circles of such plant, there likely

transport routes should be considered so that deliveries can be carried out as smoothly as possible.

9.5 Integration Considerations

When new access roads are joined to the local road network the works to achieve this and any part

or full road closures must be accounted for and communications made with local businesses to

ensure their activities are not affected. The increased traffic from the RO plant will have an

impact on local infrastructure; it is unlikely that this will be great enough to require improvement

of the local infrastructure however more considerations may be made by local authorities when

considering any road junctions to ensure that delivery vehicles are accommodated for. The impact

on damaging road surfaces should be considered and minimised where ever possible.

See Figure 72 in Section 20.26, Appendix A for a detailed illustration of the CSP plant.

Desalination: Group 2 Integration

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10 Integration

10.1 Introduction

The success of this project depends on providing the population of Israel with regular and reliable

supply of drinking water. This can only be achieved by integrating the desalination plant into the

national and regional water supply system. In addition the plant must have a regular supply of

electricity, to ensure continuous water production. This section discusses the considerations and

factors that require to be analysed in order to utilise the existing infrastructure to produce and

supply potable water.

10.2 The national water carrier (NWC)

The National Water Carrier (NWC) is Israel‟s main water distribution network. It collects fresh

water from various sources to supply potable water to its population. It is considered the largest

water related project in Israel, with the construction taking over two decades to complete.

Eventually achieving completion in 1964, it was originally intended to supply the central and

southern parts of Israel with water for irrigation purposes. However, it has been utilised to supply

more than half of the country‟s potable water needs since the 1990s. Although the NWC was

intended to integrate Israel‟s three main fresh water sources (Sea of Galilee, Mountain aquifers

and coastal aquifers), more potable water sources have been added to the system over the years in

an attempt to bridge the gap between demand and supply (MEKOROT, 2007).

Over the years the Sea of Galilee has become Israel‟s main natural water source. Annually, over

400 million m3 of water is pumped from the Sea of Galilee to the south of Israel, making it the

single largest potable water source in the country. The water from Sea of Galilee is also used to

recharge aquifers and groundwater sources. This is done in order to reduce significant loss of

water through evaporation of the surface reservoirs (Mekorot, 2007). Currently, an annual amount

of approximately 315 million m3 of water is supplied to population centres via the NWC and the

capacity is expected to increase to 500 million m3/year in 2015 and 650 million m

3/year in 2020

(DREIZIN, Y et al., 2008).


115


Figure 42: National water carrier (Mekorot, 2007)


116


The path of the NWC covers mountains, streams and rocky terrains, as highlighted in Figure 42.

The construction challenges were overcome by digging tunnels and incorporating advanced

pumps, mechanised devices and sophisticated control centres. The water from the Sea of Galilee

first enters the NWC through pipes, submerged under the northern part of the lake. It then flows

into the Eshed-Kinerot water pumping station, located in mountain cavern (NGIA, 1993). The

pumping station contains 30,000 HP pumps that force the water into pressure pipes. The pressure

pipes raise the water from 213 m below sea level to 44 m above sea level as highlighted in Figure

43 (MEKOROT, 2007). The water is then discharged into the 17 km Jordan Canal, following

which it is discharged into the Tsalmon Canal, which is an operational reservoir with a capacity of

1 million m3. The water is then elevated by further 115m by the Tsalmon pumping station before

it is brought to the Eshkol reservoir via the BeitNetofa canal. Eshkol reservoir includes the Eshkol

Water Filtration Plant, a state of the art water treatment plant that has the capacity to supply 1.7

million m3 of water on a 24 hour basis (WATER-TECHNOLOGY.NET, 2009). The potable

water, which is regularly analysed for quality, is regulated before it enters an 86 km pipeline that

transports the water to the Yarkon-Negev system at Rosh Ha‟ayin (MEKOROT, 2007). Several

pumping stations, namely Menasche and Tnuvot, are constructed along the way to increase the

capacity of NWC. The NWC consumes a significant amount of energy, particularly to raise the

water from 213m below sea level to an elevation of 150m above sea level. The NWC requires

over 100 MW of power to operate. This amounts to about 4% of Israel‟s electricity production

(MEKOROT, 2007).

Figure 43: NWC - Longitudinal section

The NWC supplies potable water to the South of Israel by transferring water from various sources

in North of the country. Since the desalination plant is situated in the South, the potential


117


consumers are limited, since the potable water produced by the desalination plant can only be

consumed by the southern part of the country. The desalination plant will be supplying water to

the regions of Tel Aviv, Ashdod and Ashkelon, all of which have higher population growth rates

than anywhere else in the country (POPULATION REFERENCE BUREAU, 2010). Thus, it is

reasonable to assume that there is sufficient demand for water to utilize the NWC.

The closest pumping station connected to the NWC is located in Rash Ha‟ayin, approximately 34

km from the desalination plant. It would be economically beneficial to integrate the desalination

plant to the NWC via a pumping station that is closer. The long-term benefits include a significant

reduction of energy required to pump the water to the integration point, and a greater flexibility in

case of expansion. It is best to integrate so as to provide water to Tel Aviv, one of the major

population centers in the South. Figure 44 highlights the possible integration position.

Figure 44: Integration to NWC

A post treatment facility including a laboratory to monitor the water quality of the inflow and

outflow will have to be installed at the integration point. This allows the water quality to be

monitored before it enters the NWC. The inflow will go through the post-treatment before being

deployed to the pumping station, where the high-pressure pumps will raise the pressure, enabling

the water to enter the NWC.

10.3 Power

As stated earlier, the reverse osmosis process requires a constant supply of electricity. The

functions of the plant include pumping of raw seawater, membrane desalination and disposal of

brine, all of which require significant amount of energy. Furthermore, for the processes to be

RO Process

Plant

Integration

Point


118


efficient, they must operate continuously, without interference. The desalination plant will utilize

the national electrical grid network to transfer the power generated at the dedicated solar thermal

power plant, installed near Be‟er Sheva, to the desalination plant, some 50 km away. The power

plant is designed such that it will supply all of the desalination plant‟s power requirements to the

national electrical grid during the daytime and allow the desalination plant to extract the energy

off the grid during night.

In general, the energy demand is higher during the day than it is at night. This is particularly true

in Israel, as operating air conditioning units during the day accounts for a major proportion of the

energy consumed in the country. It is economically beneficial to supply power to the grid during

the day and to use it during the night when the demand is lower. Furthermore, supplying

electricity to the grid eliminates the need for a storage medium, thereby reducing the overall cost.

The power plant will generate 226.667 MW of power during 9 hours of sunlight, of which 37.5%

will be used during the day and 62.5% will be used later during the night. As reported in the

Section 8, approximately 20% of the total electrical production will be sold off to the grid for

profit.

A step up transformer must be used to connect the power plant to the national grid in order to

minimize energy losses. Electricity loses energy as it travels through wire cables, but high voltage

electricity loses less energy than low voltage electricity. The overall efficiency can be improved

by elevating the voltage, using step up transformers before transmitting electricity through the

grid. A step down transformer must be used at the desalination plant to reduce the voltage to the

appropriate level. The voltage must be raised to 400 kV at the power plant before it goes into the

national grid, and reduced to a final value of 4.16 kV at the RO plant.

Desalination: Group 2 Finance

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11 Finance

11.1 Introduction

The main objective of this section is to address the business appraisal of the project, associated

with producing water and electricity for the following 20 years. The total cost of this project is

proposed at £ 334,619,897, which is recommended to be financed by the bank at an interest of

7.02% and shareholder equity in the rate of 70:30 with respect to the over total cost. This is a new

project, established with a combination of Solar-RO technologies. The cost is calculated to

appraise the financial position for this project, particularly the cash flow, profit and loss and

operating cost for twenty years.

11.2 Price of Water

Through the advances of reverse osmosis (RO) system over the last twenty years, the cost of

desalinated water has greatly reduced in places like the U.S.A and the Middle East, but not in

Israel. Uri Shani, the director of Water Authority in Israel has mentioned that the country faces

“the worst water crisis in 80 years, and ever since they started keeping records” (RATZLAV-

KATZ, Nissan, 2008). The price of water in Israel is expected to increase by 10% for domestic

consumption and for other uses, it will increase from 3.90NIS/m3 to 7.40NIS/m

3 (£0.68/m

3 to

£1.29/m3) (RATZLAV-KATZ, Nissan, 2008)

The Ashkelon RO desalination plant that has been fully operational since 2006 is the largest plant

in Israel. It can produce 110million cubic meter per year and produces water at $0.53/m3

(£0.34/m3), which is cheap. It still not meet high demand in the south of Israel where the price of

water is still high (WATER-TECHNOLOGY.NET, 2010). Therefore, increasing the number of

desalination plant in Israel will decrease the price per cubic metre. In this section, finance flow of

the project is analysed.

11.3 Carbon Offset Arrangement

Solar-RO Desalination is producing water with zero carbon emission of green house gasses

(GHG). In this design, the solar thermal system is built to provide sufficient energy for the RO

plant. The desalination plant was constructed to provide adequate clean water to local residents

and this indirectly lowers the price of water. Essentially, this means that although the construction

of the power plant will be slightly higher, the cost operating for 20 years will be much lower since

the energy to run the RO unit is renewable.


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11.4 Project risk

There are a number of uncertainties involved in the design of the desalination plant, namely those

associated with the projection of specific data, for example, population growth, supply and

demand. The financial risk involved with this speculation is a reduction of demand in the

consumer sector, which may be incurred as a result of a reduced population growth. Financially,

this would mean a reduction in revenue, resulting in a higher priced source of potable water. This

would be catastrophic for the shareholders and investors, as well as the Israeli government who

would have invested in such a flagship scheme. Further to issues that could arise from a change in

demand, the solar power plant is sensitive to changes in weather; therefore global climate change

could cause detrimental changes affecting the power production.

11.5 Financing Source

There are several sources of finance available for this project, such as government sources, shares

(equity), retained earnings, bank loan, franchise etc. A huge project involving two plants, reverse

osmosis and solar power plant were proposed to be financed by equity and bank borrowing.

Equity or shares are normally issued to the owners of a company. The interest rate from the Bank

of Israel (year 2000 – 2009) fluctuates every year. In 2005, the lowest interest rate recorded was

6.6% and in 2009 the highest interest rate recorded was 7.5% (ISRAEL, Bank of, 2009).

Therefore, 7.02% is being used in this account as the average interest rate.

The cost of the project is estimated at £ 334,619,896.50. It is assumed that 70% of this amount is

financed by the bank loan, with the other 30% financed from equity. The bank loan to equity ratio

break up is calculated in Table 16.

Table 16: Debt to equity ratio breaks up

Sources of funding Cost in (£)

Bank Loan (Debt) 70% capital cost 234,233,927.55

Equity 30% from capital cost 100,385,968.95

Total Capital Cost 334,619,896.50

Ratio 2.33

To summarise:

The debt to equity ratio is 7:3;

The average interest rate is counted at 7.02%; and the

Repayment period for £ 234,233,92,8 borrowed from the bank is 13 years.

The next point is the cost estimation reported by all engineering sections.


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11.6 Project Main Cost

The project main cost has been calculated to estimate how much funding will be required to

develop this project. The total cost is estimated at £ 334,619,896.50. In Table 17, the third

column is recorded as the original cost without investment tax.

Table 17: The project main crust

Fixed Capital Israel Grant Tax Cost Cost after finance and tax

Land & Site Development

Beersheba 25% 25,074,673.31 31,343,341.64

Land & Site Development

Permachime 0% 316,344.00 316,344.00

Building & Civil Works 0% 912056.35 912,056.35

Plant and Machinery- RO unit 0% 104,564,750.20 104,564,750.20

Power Plant 24% 32,811,950.08 40,686,818.10

Solar Plant Equipment 24% 71,432,046.00 88,575,737.04

Solar System 24% 52,786,350.03 65,455,074.04

Miscelaneous cost 2% 2,765,775.13 2,765,775.13

Total 265,272,927.79 334,619,896.50

The Israel government has introduced the investment incentives grant scheme program for any

investment project that gains the qualification enterprise status (PKF, 2009). The grant program

is assembled by the government according to the region division and total main cost of the whole

project. There are several regions in Israel that have been declared in National Priority Regions of

Israel and classified in three priority areas:

Table 18: Percentage is calculated from the original cost of land development, buildings,

installation of equipment, machinery and any other related to the project cost. Taken from PKF

Israel Tax Guide 2009 (PKF, 2009).

Priority Area Percentage (%)

Industrial project up to (NIS

140M @ £ 25.34M)

Industrial project above

(NIS 140M @ £ 25.34M)

A Galilee, Negev, Jordan

Valley, Jerusalem

24 % 20 %

B South Galilee, Northern

Negev

10 % 10 %

C The rest of the country - -

Reference in Table 18 states that Beersheba is included in Priority Area A, for which tax is

charged at 24%. Palmachim, which is located in southwest of Israel is included in Priority Area C,

which has no tax grant. The new Israel government grant scheme is calculated as the percentage

from the original cost of all equipment and machinery that are used; installation cost, buildings,

land and site development and also other core expenses that relate to the project.


122


The cost from Table 17 is divided into two parts, the soft cost and the hard cost. Preliminary

expenses which is a part of miscellaneous cost, belongs to soft cost. The land and site

development, civil works, plant and machinery, miscellaneous fixed assets and plant and

machinery are all included in the hard cost.

11.6.1 Land and site development

The proposed Solar-RO project will be located in two separate places, Palmachim and Beersheba.

The total area needed for the RO plant is 3920 m2 in Palmachim and the power plant in Beersheba

requires 1,557,675 m2. This land in Palmachim is used to build only the power plant and excludes

the administrative building and the car park. Palmachim is classified as Priority Area C and

Beersheba as Priority Area A. This means that the land price is taxed at a rate of 24% of the

original price paid in Priority Area A, culminating in the total price is 24% greater than the

original price.

11.6.2 Civil works

Buildings and other civil structures are estimated to cost £912,056.35. This total includes:

Portal frame substructure for RO unit

Portal frame structure for RO unit

Pumping station structure

11.6.3 Plant & Machinery for RO unit

Plant and machinery cost include all kind of pumps used in the process; this costs

£104,564,750.20.

11.6.4 Power Plant Cost

The cost of the 85MW thermal solar power plant to be built in Beersheba, Negev is estimated at

£40,686,818.10. This cost includes the core of electrical equipment for electrical generation, and

other auxiliary components.

11.6.5 Solar System

The cost for solar system includes 512000 heliostats, 32 receivers, control building, and power

substation, the sum of which is estimated at £65,455,074.04.

11.7 Soft cost

11.7.1 Miscellaneous Fixed Assets

Miscellaneous fixed assets are considered to be the preliminary expenses; these are quantities

such as the interest during construction (IDC), transportation, permit, contingency, advance fee,

which is estimated at £2,765,775.13.


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11.8 Appraisal Analysis

The Reverse Osmosis plant is proposed to produce 110 million cubic meters per year at a design

life of 20 years. Two types of plants will be established to meet green goals; the Reverse Osmosis

Plant and the Solar Thermal Power Plant. This analysis assumes that the cost of selling 1m3 of

clean water is £ 0.47 and the price to sell 1 unit of electricity is £0.10. The appraisal analysis is

used to value the project and understand the risk involved when the “green gadget” is applied.

Figure 45 shows the scenario when 100% of the energy is purchased from the grid (no green

gadget).

Figure 45: Graph shows the different between Revenues – Operating cost with no green gadget

and Revenues –Operating Cost with green gadget

Figure 46: The net cumulative cash flow for 20 years operation

Figure 45 shows that with no green gadgets applied, the operating cost will be extremely high

and no revenues can be achieved in ten years of operation. This is because the energy required to

produce 110 million cubic meter of water from RO plant is slightly high. The cost of the energy is

1.00E+00

1.00E+01

1.00E+02

1.00E+03

1.00E+04

1.00E+05

1.00E+06

1.00E+07

1.00E+08

1.00E+09

1.00E+10

1.00E+11

1.00E+12

0 1 2 3 4 5 6 7 8 9 10

Co

st (

£)

Year

Revenues versus Operating Cost

-2.00E+13

-1.50E+13

-1.00E+13

-5.00E+12

0.00E+00

0 2 4 6 8 10 12 14 16 18 20

Co

st (

£)

Year

The Net Cash FlowNet cash flow after finance and tax

Cumulative cash flow


124


38% of the capital cost. The representative from the Ashkelon plant states that “… the provision

of a dedicated power plant is a major factor in both safeguarding operational reliability and

reducing energy costs. (WATER-TECHNOLOGY.NET, 2010)” Therefore, a new (WATER-

TECHNOLOGY.NET, 2010) power plant was built to accommodate the energy required by the

Ashkelon RO plant in 2005. Thus, the importance of incorporating a self sufficient power plant

cannot be overemphasised.

Table 19 shows the assumptions made for the base case scenario, on the basis that the green

gadget is chosen. The energy saved is 57%, meaning the excesses energy produced from the

power plant will be sold directly. Moreover, this will generate 28% of additional revenue.

Table 19: Shows the base case scenario of the energy save percentage based on the application of

green gadget

Subject Value

Initial Cost of Solar Power Plant £ 160,605,896.8

Solar Power Plant Lifespan 25 years

Annual electricity required for RO plant (kWh) 385,166,828 kWh/year

Price of electricity (price/unit) yearly with £ 0.1 kWh/unit £ 38,516,682.82

Annual Electricity can be produce by solar power plant 673,200,000 kWh/year

Energy saved percentage 57%

Additional profit by selling the excess electricity 28%

The cash flow graph highlighted in Figure 47 is the cost when the solar power plant is included.

From year 1 onwards, the cumulative cash flow has a negative value. This is due to the high

capital cost that is used to set up the main project. As highlighted there is no profit generated in

the first eight years but the money is still raised gradually over time until it reaches the break-even

point in the 8th year. Following this, the project begins to generate profit and accumulates up to

+500 million pounds after year 20. This indicates that the scheme is a profitable.


125


Figure 47: Shows the net and cumulative cash flow from starting year until 20 years later

11.9 Net present value (NPV) Net present value (NPV) is usually used to evaluate a new project or business to be undertaken. It

is used to decide whether it worth investing in the project, by looking at the current cash flow.

Sometimes NPV is also called the liable sensitivity for the future cash flow.

Where t=the time of the cash flow; i = discount rate

893,250,816.15

500,870,867.7

-4.00E+08

-2.00E+08

0.00E+00

2.00E+08

4.00E+08

6.00E+08

8.00E+08

1.00E+09

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

Co

st (

£)

Year

Net cash flow before and after finance and tax


126


Legend:

Figure 48: NPV for 8%, 12%, 15% and 17% of discount rate for 20 years

According to Figure 48, this project (8% discount rate case) will not make any profit from year 0

until year 10 because the graph shows that the cash flows is negative. After year 11, there is a

benefit in investing in the project; the overall profit after 20 years is £137,349,423. According to

Figure 48, the cumulative cash flows for the 12% discount rate case shows that the breakeven

point is at year 14. This project should make profit from year 14 onwards. Finally, it is not worth

investing in the project if the discount rate is 17% because no profit will be made even after 20

years of operation.

137,349,423.0

52,932,205.2

14,435,324.8

-11,546.3

-1.50E+08

-1.00E+08

-5.00E+07

0.00E+00

5.00E+07

1.00E+08

1.50E+08

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20Co

st (

£)

Year

Net Present Value

Desalination: Group 2 Future demand

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12 Future demand

12.1 Introduction

Forecast of future potable water requirement is an important element in this project, as it is crucial

to meet the demand of an ever-growing population. It is essential to take future potable water

needs into consideration in the design phase, as the plant will have to be expanded to meet the

demand. Water and economic planners often find it difficult to make precise predictions with

regards to water use. The water use in a country is affected by many unknown or poorly defined

variables, such as population growth and quality of life, all of which are difficult to predict

without there being a degree of uncertainty.

This section details the projected water requirement over the next 25 years. The following factors

need to be carefully analyzed to predict the total desalinated water requirements (DREIZIN, Y et

al., 2008):

Total projected water supply capacities over the period, of all sources and all qualities

including brackish water, flood water catchments, wastewater reuse/ recycle etc.;

Domestic water demand, based on projected population and per capita demand growth rates;

Agricultural allocations, including treated municipal wastewater and, where possible,

brackish water;

Demand by other users e.g. nature conservation, aquifer rehabilitation and neighbouring

entities.

Water demand projections

Table 39 in Appendix A illustrates the latest demand projections, last updated in 2004

(DREIZIN, Y et al., 2008). As of 2005, the total water consumed in Israel (including portable

water, recycled wastewater and brackish water) was 2060 million m3/year and it is expected to

rise to 2805 million m3/year by 2020. This section attempts to; (i) further extrapolate the

projections up to the year 2035, and, (ii) detail the expected desalination water capacity required

to identify and meet potential gaps between demand and supply.

12.2 Population Growth

Population growth is one of the major factors driving the potable water demand. In case of

completely unforeseeable events, the population is likely to or is equally likely to decline very


128


rapidly. Unless precautions are taken early on, it will be impossible to maintain a sustainable

supply of potable water quality and quantity. This will increase the water stress in the country.

Historically, the population of Israel has been on the rise since records were maintained.

However, as Figure 73 indicates, although the population has been increasing, the rate of growth

has been slow since 1990 (THE WORLD BANK, 2010). Assuming an average annual population

growth rate of 1.8%, the total population for the year 2035 can be estimated. Whilst these

projections are not meant to predict the future, they provide the framework that can be used in

development of socio-economic policies. The annual population projection is summarized in

Figure 49. As indicated in the figure, Israel is expected to have 11.8 million inhabitants in year

2035.

Figure 49: Total projected population of Israel

12.3 Standard of Living

In a broader sense, the quality of life and the lifestyle of a nation is reflected by the country‟s

water consumption habits. A country that has a high gross national income, such as the USA,

tends to have a high water footprint compared to countries such as Israel (CHAPAGAIN, A.K.

and Hoekstra, A.Y., 2004). This is due to the fact that in the Most Economically Developed

Countries (MEDC), people consume more goods and services, which translates to a greater water

footprint. Additionally, economic growth entails higher water requirements for production (e.g.

for agriculture).

0.00

2.00

4.00

6.00

8.00

10.00

12.00

14.00

1960 1970 1980 1990 2000 2010 2020 2030

Tota

l Po

pu

lati

on

(×1

06

pe

op

le)

Year

Total Projected Population of Israel


129


Israel‟s water footprint is expected to increase as its economy grows. Comparing the country‟s

population (THE WORLD BANK, 2010) to that of domestic water demand (ISRAEL WATER

COMMISSION, 2002), it is possible to determine the per capita consumption. Analyzing the data

provided in Table 20 indicates that the water consumption in Israel per person can increase to 121

m3/year, by the year 2035. This is further illustrated in Figure 50.

Table 20: Water consumption per person

Year Population Potable Domestic

Water Demand

Per capita consumption

m3/cap/year

2005 6.93 720 103.9

2010 7.58 840 110.9

2015 8.28 960 115.9

2020 9.06 1080 119.3

Figure 50: Consumption per person per year

12.4 Total Demand Projections

The water consumers can be categorized into four sectors: domestic, industrial, agricultural and

aquifer rehabilitation. The consumption forecast of each of these sectors is estimated periodically.

The most recent water demand projections extend up to the year 2020 (ISRAEL WATER

COMMISSION, 2002) (DREIZIN, Y et al., 2008). This section of the chapter aims to estimate

the water demand in the year 2035, with the information available.

102.0

104.0

106.0

108.0

110.0

112.0

114.0

116.0

118.0

120.0

122.0

2005 2010 2015 2020 2025 2030 2035 2040

Co

nsu

mp

tio

n (

m3 /

pe

rso

n/y

r)

Year

Consumption per person

Actual

Projected


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12.4.1 Agricultural consumption forecast

Israel‟s water policy regarding agricultural use is to reduce as much fresh water consumed by the

sector as possible. Instead, Israel has adapted a recycle/reuse water policy. Their revised policy

aims to prevent hazards to the environment and the potable water sources, by utilizing the

effluents for irrigation instead of uncontrolled discharge. This also minimises the fresh water

demand of the agricultural sector, which can be diverted, to urban uses (ISRAEL WATER

COMMISSION, 2002).

Following the drought years experienced by Israel over the past decade, the government decided

to limit the amount of potable water available for agriculture to 530 million m3/year. The rest of

the agricultural water demand will be fulfilled by low-grade water, which comprises of

wastewater effluents, brackish water and storm water (ISRAEL WATER COMMISSION, 2002).

The total estimated demand for the agriculture is 1780 million m3/year, of which 530 million

m3/year is potable water and 140 million m

3/year is brackish water. The Israel Water Commission

should develop the capacity to supply up to 1110 million m3/year of water by the year 2035, as

depicted in Figure 50.

12.4.2 Industrial consumption forecast

The basis for the forecast of industrial water consumption is the historical data reported

(DREIZIN, Y et al., 2008). The total industrial consumption in the year 2035 is estimated to be

187.1 million m3/year, as highlighted in Figure 75. The industrial sector will use both fresh and

low-grade water, including brackish and treated water. A total of 32.1 million m3 of treated water

will be consumed by the sector, as indicated in Figure 76. Historically 40 million m3 of brackish

water is consumed by the sector annually, and the remainder is fulfilled by fresh water:

Potable water required = 187.1×106 – (40 + 32.1) ×10

6 = 115 million m

3/year

12.4.3 Domestic consumption forecast

As indicated earlier, the domestic and the public water consumption is dependent on two main

factors: population and specific per capita consumption. The current population in Israel is about

7.58 million people and this figure is expected to rise to 11.83 million by the end of 2035 (Figure

49 ). As highlighted in Section 12.3, the consumption per capita by 2035 is expected to grow

to121 m3/year. This is a reflection of the expected rise in the standard of living of the population

and implementation of water saving policy (ISRAEL WATER COMMISSION, 2002). Thus, the

domestic potable water consumption is:

Potable water required = 11.83×106 × 121 = 1431.9 million m3/year


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12.4.4 Aquifer rehabilitation and neighboring entities

Located on the edge of the desert, Israel attached ecological importance to the preservation of

moist habitats for unique fauna and flora (ISRAEL WATER COMMISSION, 2002). Constant

water shortages have led to the neglect of water needs for nature and this has led to a significant

deterioration of water quality and quantity in aquifers. As reported by the Israel Water

Commission, from 2002, the environment and nature is defined as a consumer, and will receive an

allocation of the fresh water. Figure 77 highlights the projection of annual allocation for this

sector. As indicated, the aquifer rehabilitation and neighbouring entities will require 199 million

m3/year by the year 2035.

12.4.4.1 Total demand

Table 21 summarizes the total demand outlined in this chapter:

Table 21: Projected total potable water demand

Year Projected portable water demand (×106 m

3/year)

2005 2010 2015 2020 2025 2030 2035

Agricultural 530 530 530 530 530 530 530

Industrial 85 90 95 100 166.5 176.8 187.1

Domestic 720 840 960 1080 1197.9 1309.7 1431.9

Aquifer-

rehabilitation

200 210 230 150 165 182 199

Total

Demand

1535 1670 1815 1860 2059.4 2198.5 2348.0

12.4.5 Total Supply Projections

As stated earlier, efforts must be take to meet Israel‟s future needs and to preserve non-renewable

water resources. In order to ensure sustainability of the water supplying system, the gap between

demand and supply must be assessed. This section analyses Israel‟s current water supply sources

reported by (DREIZIN, Y et al., 2008) and attempts to estimate the total additional water

requirement in the year 2035. The results are summarized in Table 22. As indicated, the total

additional desalination water requirement in the year 2035 is 150 million m3/year.

Table 22: Projected total water supply

Year Projected total water supply (×10

6 m

3/year)

2005 2010 2015 2020 2025 2030 2035

Natural sources 1470 1470 1470 1470 1470 1470 1470

Desalinated

brackish water

30 50 80 80 80 80 80

Desalinated

seawater

50 315 500 650 650 650 800

Total 1550 1835 2050 2200 2200 2200 2350

Desalination: Group 2 Sustainability

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13 Sustainability

13.1 Introduction

Desalination creates many sustainability issues both positive and negative, which if managed

appropriately can make desalination a truly sustainable method of producing fresh water, but can

make it a very expensive and wasteful in terms of natural resources usage. Whilst the source of

the input water is near endless and so sustainable, the methods used are very energy intensive and

therefore the way in which energy is created for any chosen process heavily affects the true

sustainability of the solution. The salinity of the waste stream is also a concern with high levels of

chemicals added through the processing stages with little or none of these being removed. This

highly saline and chemically contaminated water often then can find its way into the local

environment. Can this be a sustainable waste disposal solution? The following will attempt to

explain the relevant issues and discuss what the thought process was when coming to a final plant

design and elucidate how our plant is attempting to be one of the most sustainable methods of

creating drinkable water in the world.

13.2 The Energy Intensiveness of Desalination and its Implications

When desalination is compared to other methods of producing potable water, it is found to be

extremely energy intensive. It is clear however, that in certain circumstances where no other input

water supply is available, desalination provides an important and vital alternative solution. It can

be seen that desalination compared to large scale indirect potable wastewater recycling is around

twice as energy intensive (Knights, MacGill and Passey, 2007). This must be put into context

however, as one of the reasons for using desalination is because other more cost effective sources

have already been utilised or are under threat of over-use (See Section 13.6). Therefore the

validity of using such energy intensive methods may be justified due to the simple fact no other

methods are available. This does not however negate the fact that desalination is a very energy

intensive form of supplying drinking water.

The amount of energy required to power desalination varies depending on the method adopted

and surrounding conditions; for example the input water temperature or type of input (brackish or

sea water) however all methods are fairly energy intensive. Multi Stag Flash Distillation (MSFD)

is the most intensive method using predominantly thermal energy often taped from sources such

as waste heat in industrial coal and gas power stations. Various sources suggest the energy

intensiveness can vary from as little as 12kWh/m3 up to 80kWh/m3 of thermal energy and

3kWh/m3 to 5kWh/m3 of electrical energy required. This is a huge variance and after detailed

process design, it was found that with the most efficient energy recovery system this value could

only get as low as around 50 kWh/m3 of thermal energy (See Table 28). This variance is due to


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the rapid developments of the technology and some impugnable assumptions made by bias

sources. Other thermal process such as Multi Effect Distillation (MED) utilise less energy but are

still highly intensive. Similarly varied figures are associated with MED, but a more realistically

achievable value in real life situations is around 40kWh/m3. Reverse Osmosis (RO) holds one of

the most energy efficient desalination methods however it should be noted this is still an

extremely intensive method for generating drinkable water and so all attempts to reduce this

energy consumption must be sought. Values around 3kWh/m3 to 7kWh/m3 are most common

with RO. Estimates for the energy used in Australia for a Large Scale Indirect Potable Wastewater

Recycling system are about 2.8 to 3.8 kWh/m3 (NSW LC, 2006).

13.3 Power Source, the Key to Sustainability

This energy intensiveness associated to desalination means that the power source used for supply

is where a lot of the environmental and sustainability issues propagate. Whilst technological

advancements enable a reduction in the energy required for desalination these would never be at a

point where this process becomes energy free and so there will always be a high energy bill for

this activity.

The choice of either a thermal or membrane process will impact on what power source must be

chosen. Thermal process can utilise steam already produced and remove the electrical conversion

stages where efficiency is around 40% (Electropaedia, 2005) due to Carnot's law. This is when

considering common thermally functioning power plants. It must be understood however that if

these thermal processes are over 15 times more energy intensive the loss provided at conversion

to electricity still puts membrane treatment at a less energy intensive overall position and so all

means of power supply become useable within desalination.

It is important for desalination to be run consistently as this is how a system can be optimised and

a consistently high quality product can be produced. Therefore the power source used be able to

provide a continued supply of power 24 hours a day 365 days a year. This supply has to be

dependable as a failure to supply the plant could cause the system to be down for weeks whilst

optimisation process takes place to prevent the system being damaged. This is especially the case

for membrane technologies as these can easily be fowled and damaged irreversibly.

The following table draws together information regarding different power supply options

including their sustainability, emissions and applicability to desalination within Israel. Equivalent

CO2 levels are given in column two and have been calculated considering the full life cycle of the

plant, including; construction, running emissions and mining and transportation of the fuel source.


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Table 23: Applicability of power source for sustainable desalination in Israel

Plant Type Emissions Sustainable

Source

Ability to

Provide

Consistent

Supply

Applicable

for

Sustainable

Desalination

Applicable

in Israel CO2

eq

(kg/M

Wh)

SO2

(kg/

MWh

)

NOx

(kg/

MWh

)

H2S

(kg/

MWh

)

Oil 893 814 No Yes No Yes

Natural Gas 751 550 No Yes No Yes

Coal 863 -

941

4.71 1.95 0 No Yes No No

Nuclear 60 - 65 Yes Yes Yes Yes

Geothermal

Low

Temperature/c

losed circuit

0 - 1 0.16 0 0.08 Yes Yes Yes No

High

Temperature/o

pen circuit

91 -

122

0.16 0 0.08 Yes Yes Yes No

Conc. Solar

thermal

25 - 55 Yes No No Yes

Conc. Solar

thermal with

grid

connection

25 - 55 Yes Yes Yes Yes

Hydro-electric 15 Yes Yes Yes No

Wind 21 Yes No No Yes

Wind with

grid

connection

21 Yes Yes Yes Yes

Photovoltaic 106 Yes No No Yes

Photovoltaic

with grid

connection

106 Yes Yes Yes Yes

(Fridleifsson, et al., 2008.. Lund, John W, 2007.. Bilek et al., 2008)

From Table 23, it can be seen that only a few power supply options are applicable for sustainable

desalination within Israel. These are limited to: Nuclear, Concentrated Solar Thermal, Wind, and

Photovoltaic. The Last three “green” energies need to be linked to the grid so that energy can be

stored due to the lack of a consistent supply.

It can be seen that whilst renewable energy sources have considerably lower effective carbon

emissions compared to fossil fuels they do actually have relatively considerable level of emissions


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due to their construction phases. Therefore all measures in reducing these can produce a large

reduction in effective emissions of CO2.

13.4 Desalination Across the Globe; are there any lessons to be learnt?

77% of desalination plants are located in the Middle East, mainly in the Arabian Gulf. Of these

plants 90% use thermal processes (MSFD & MED) (Lattemann and Höpner, 2008). This is due to

the relative in-expense of oil and gas within these nations and their large amounts of waste

thermal heat in the form of steam being available from power generation. This has enabled them

to use the more energy intensive thermal methods due to a surplus of an energy source, which

would have been wasted otherwise. This still means that a huge amount of harmful green house

gases are emitted due to the desalination of seawater in these Arab states from cogeneration power

plants. Clearly however where a supply of otherwise wasted energy in the form of secondary

steam from power plants is available; an effective energy supply for desalination may be found.

This cannot be seen as a purely sustainable solution for power generation though as the fossil

fuels used are a finite resource. When considering this for use in other countries with higher fuel

prices this cannot be not be seen as either an environmentally or economically sustainable option.

Figure 51: Desalination breakdown, globally and in Israel (Lattemann and Höpner, 2008)


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Figure 52 : Installed desalting capacity by process and raw water quality (Zhou and Tol,

2004)

The only way that this may become a sustainable solution is if another industrial process had the

ability to produce secondary steam that a desalination plant could use. Of course this process

would have to be of a scale that could provide large volumes of steam that a desalination plant

requires. One such option especially applicable for Israel and other nations known to have nuclear

capabilities is that of nuclear power. Whilst these power plants have their own environmental

issues their ability to produce energy is thought to be fairly sustainable (with a huge supply of

nuclear material found in the world) and with their use of a conventional thermal steam process to

generate electricity the production of wasted secondary steam is clear. Such thermal desalination

may become a practical solution if this energy source became available. Care would have to be

taken to protect against radiation contamination of the water but this may be a key way in which

thermal desalination could be sustainably implemented.

When considering the rest of the world in particular the Mediterranean membrane technologies

are far more commonly used. Spain is the largest producer of desalinated water in the

Mediterranean area (producing 7% of the worlds desalinated water) 95% of this is done through

RO processes. This is due to their need for a desalination method with as smaller energy demands

as possible. In nations where energy is not abundant, this generally being all outside of the Middle

Eastern oil producing countries, the lowest energy intensive methods are most viable.

13.5 Other Factors

Other factors, which make a design sustainable, are to do with the chemicals used in the

desalination process either as pre treatment to protect the membranes or to aid in the membranes

removal efficiencies. These make up nearly a third of the cost to desalination and so are important

areas to consider when designing a sustainable solution to desalination (Thames Water


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representative, 2010). The type and quantities of chemicals used depends heavily on the

desalination method and the stages chosen within this.

13.6 Sustainable Power in Israel; possibilities and current technologies

Israel whilst not a world leader in all green technologies does have a lot of experience especially

with harnessing solar power mainly for export however and not large scale national deployment

(Mor, et al., 2005). They have however in recent years understood the benefits green energies

hold and with the contracting of a number of wind farms on the Golan Heights in the North of the

country there aim is to have 5% of the nations energy supply come from wind technology by 2012

(Kloosterman, 2008). Other areas such as the Negev desert, Galilee and the Arava Valley (the last

one in cooperation with Jordan) are possible suited locations. Israel however is much more

knowledgeable in the field of solar technology and are considered one of the worlds leading

authorities on the subject. Extensive research has been carried out at a number of institutes, the

for-most being that at Ben-Gurion University of the Negev. Here they have experimented with

both photovoltaic cells and thermal processes and with a number of companies set up within the

growing market Israel is perfectly placed to capitalise on this form of energy (Solar Energy in

Israel, 2008). With a large amount of suitable dessert area, which cannot be cultivated into arable

land the country has good prospects in this field.

Another form of sustainable energy is that of nuclear. This requires high levels of both capital and

technological expertise however it is considered that Israel does have this potential even if not

officially recognised internationally (Rabinovitch and Balmer, 2010). It has been thought that

Israel has nuclear capabilities since around the 1960‟s (Aftergood and Kristensen, 2007). It would

be likely that any new plant constructed would have to be done with technical help from a more

experienced nation, Israel having close ties with France therefore being the most likely.

13.7 Sea Water; a limitless supply?

The availability of seawater can be seen as limitless in respect to quantity however the quality of

this is less clear. As more desalination takes place the ability for the natural mixing of ocean

currents and tides to take place before influent is taken back from the sea will become more and

more critical to the desalination process. This is especially the case for enclosed seas for example

the Arabian Gulf and the Mediterranean Sea. Here natural mixing is less effective and the overall

salinity of the sea could be put at harm. This would of course have effects on desalination, as an

increase in salinity would require an increase in the rigorousness of the process.

This would not to mention have an effect on the oceanic environment but would also pull the

efficiencies of desalination up to possibly much higher levels. Research has been carried out by

Tettelbach and Rhodes (1981) in where marine embryos were subjected to increased salinity. It


138


showed that this negatively effected their development. When considering a sustainable source of

drinking water the immediate area around the source has an effect on the desalination process.

Means to reduce the salinity of the waste stream should be looked at, for instance mixing it with

some other sea outfall allows a proportion of the salinity to be balanced out; E.g. treated sewage

effluent, as found at the Thames Water Gateway Water Treatment Works. This plant actually has

combined effluent lower in salinity than the environment it is discharged into.

Desalination of seawater within Israel is more sustainable than the desalination of other sources

such as brackish aquifers. This is due to them being already over utilised, which could cause them

to become highly salinified and also increase the saline intrusion on fresh aquifer supplies so

valuable to Israel‟s overall water supply network. The best solution is to reduce the demand on

these resources by providing a different source, which can account for the increase in demand

over time and satisfy the current demand at an acceptable pumping level.

13.8 The Benefits of a Sustainable Solution

Sustainability is defined by the United States Environmental Protection Agency (2010) as “social

and environmental practices that protect and enhance the human and natural resources needed by

future generations to enjoy a quality of life equal to or greater than our own.” Whilst this is the

case there are also other benefits to creating a sustainable solution for water production. Whilst it

is expected that the capital expenditure on such a project will be higher to ensure its sustainability

the operational costs are extremely low and this is often of financial benefit for investors as it

likely means a high rate of return on their investment. It can also have carbon offsetting

advantages. These advantages are currently taking place in countries such as the US however

other countries are sure to follow suit in a bid to increase the sustainability of power production

and also reduce their dependency on oil rich states. Finally in a time where considering the

environment and the impact things have on society and the future are popular the PR that this can

have on the business are great, increasing the value of products and services.

13.9 The Schemes Sustainability Credential

The scheme design chosen combines the most energy efficient desalination method closest to

where the water needs to be and as close to the source as possible with a completely sustainable

source of energy situated for the most optimum efficiency possible.

Reverse osmosis has been chosen as any other form of desalination were considered too energy

intensive. This combined with the exciting continued development in membrane technology,

which can be utilised though retro fitting and thus increasing efficiency is highly desirable.


139


The process will aim to use as little chemical treatment as possible to be both economically and

environmentally sustainable as possible. This will be done by the use of careful pretreatment

systems, which at the same time protect the expensive RO membranes.

Concentrated Solar Thermal Power will be utilised within the Negev desert where sunlight

efficiency is highest and where a number of test facilities are situated. This geographical split with

the desalination plant being located by the coast means that the electricity produced in the solar

plant can be transferred through connection to the national grid. This also gives the ability for the

desalination section of the scheme to operate 24hours a day allowing for plant optimisation and

water output predictability. This will also allow storage of large amounts of electricity generated

throughout the day by the solar pant and provide Israel with peak electricity when it is required

through the day (for energy intensive activities such as air conditioning). This will not only create

a sustainable energy source but also allow the plant through input and output from the grid to earn

capital due to electricity price day/night fluctuations.

Desalination: Group 2 Environmental impact

140

Section 14 Author: SA & KK

14 Environmental impact

Seawater intake and pre-treatment, as well as, brine discharge are those that could pose a risk to

the environment depending on the method selected and amount of chemicals required and

discharged.

14.1 Intake

The major risk associated with intake systems are loss of aquatic life when they collide with the

intake system if the open intake system is used. Marine life can be trapped or entrained by the

intake system. The intake system could also affect water structures and sediment transport, act as

artificial reefs for organisms or could interfere with shipping routes or other maritime uses

(LATTEMANN,SABINE; HÖPNER,THOMAS, 2008).

Seabed filtration intake eliminates any risk of impingement and entrainment of marine life and

impact to marine environment. Another important aspect about this method of intake is the fact

that there are no structures above the seabed and so there are absolutely no risks of affecting water

exchange and sediment transport, also shipping routes are unaffected and there are no structures to

act as artificial reefs for organisms. More importantly the impact of seawater intake systems on

the poseidonia prairies, that are highly protected by the environmental legislation in the

Mediterranean sea will be avoided (PETERS, T. ET. AL., 2008).

The system once installed will not require additional work or rehabilitation and it can withstand

earthquakes. The only possible impact is during the construction of the filtration beds because it

requires the seabed to be excavated and undersea pipes installed. This impact can be minimised

by constructing and excavating small sections of the seabed at a given time and doing so while

ensuring that all methods employed does not harm or cause permanent damage to seabed and

marine life. It‟s worth noting that, there is a potential of increasing the infiltration rate which will

reduce the area required for the filtration bed significantly, hence minimising any problems

related to excavation.

14.2 Pre-treatment

Pre-treatment method selected will have an impact on the environment, as well as, the overall

process. Chemicals used in pre-treatment vary considerably between the conventional and non-

conventional pre-treatment. In the membrane pre-treatment method selected, use of chlorine as

bio-fouling control and use of antiscalnt chemicals are avoided, more importantly coagulant

dosage is significantly lower than the dosage required for conventional pre-treatment. All this

contribute to create a process less dependent on chemicals and one that has low to no impact on

marine life and marine environment.


141


14.3 Chemicals used in pre-treatment: Coagulant as FeCl3 and NaOCl

Coagulant: Coagulants get to the marine environment when the UF membranes are backwashed,

however levels of coagulant are very low and the actual chemical have a very low toxic potential

(LATTEMANN,SABINE; HÖPNER,THOMAS, 2008). The only real issue related to using this

type of coagulant is the fact that it causes an intense colouration of the reject stream. The intensity

of the colouration will depend on concentration levels and whether or not the stream is diluted

before being discharged.

Sodium hypochlorite: NaOCl is the only other chemical used in the pre-treatment section of this

desalination plant, its use is mainly limited to membrane cleaning and there is a potential of using

even less chemicals due to the way pre-treatment is designed. The cleaning chemicals, may be

harmful to aquatic life if discharged to surface water (LATTEMANN,SABINE;

HÖPNER,THOMAS, 2008) so there is no real danger associated with discharging such small

concentration which will be even more dilute if mixed with other rejected streams.

14.4 Post-treatment

The post-treatment section of the desalination plant poses no risk to environment as all chemicals

used are to stabilise the product water and produce water that is safe for drinking.

14.5 Brine Disposal

The production and disposal of brine is a fundamental aspect of the desalination process. Great

care and caution must be exercised in the discharge of the brine as it may impose adverse effects

on the environment. It has been devised that a flowrate of 412,000 m3/day must be disposed and

through critical analysis, it is deemed that discharge through an ocean outfall equipped with

diffuser nozzles is the most environmentally friendly approach that has minimal impact on the

marine fauna and flora.

The outfall system is designed to reject the by-product of RO process into the sea. After thorough

consideration of the environmental conditions, an outfall system consisting of submarine pipelines

installed on the ocean floor a few hundred meters offshore is selected as the most sustainable

solution. The length of the offshore pipeline is dictated by the location of the tidal zones in the

ocean. To ensure the design thoroughly disperses the brine economically, the brine stream must

be discharged at the tidal zone. As discussed in the Inception report, this is not possible for this

scheme as the brine stream discharge load is likely to be greater than the transport capacity of the

tidal zone. Thus brine discharge beyond the tidal zone is more suitable.

Due to the reasons outlined before an outfall design consists of T-shaped diffusers installed at the

end of a length of pipe was chosen to aid in diluting the salt concentration of the brine. The


142


diffusers are equipped with a nozzle, which accelerates the brine flow prior to the discharge,

greatly improving the dilution of the effluent (FRIOCOURT, Yann et al., 2009). The diameter of

the nozzle can be optimised to comply with the environmental regulations as well as to minimise

the amount of energy for operation. Careful consideration must be given to the location of the

tidal zones to ensure that the concentration of brine does not exceed acceptable levels.

In addition to the brine, the by-products of pre-treatment (e.g. backwash) will all be discharged

into the sea. By mixing the treated backwash with the brine, concentration of the brine can be

reduced.

Desalination: Group 2 Durability of design

143


15 Durability of design

The durability of the design within this project refers to the plant‟s ability to endure over time.

Due to the complex nature of the various schemes that have a part in the process, there are many

factors, which have an influence on durability. For example, careful consideration has to be paid

to the environment in which the plant will operate, so that it can have a longer operational life. As

the desalination plant incurs high capital costs, through having a longer operative life, the costs of

the potable water produced can be reduced.

15.1 Reliability of the system & technological advances:

One of the main reasons why desalination and in particular reverse osmosis is the most suitable

method for providing Israel‟s potable water is its reliability. Desalination is however, a rather

energy intensive process. This along with the effects that the process, brine disposal and water

intake methods may have on the environment tends to give the impression that the process has the

scope to be unsustainable. The project shows that through careful consideration and selection of

new and green technologies this does not need to be the case. By careful consideration of new

technologies that become available, such as those utilised in the solar power plant, the process

becomes more environmentally friendly thus negating any sustainability issues associated with

the design.

As mentioned previously, in order to accommodate technological advances in the industry the

design has to have scope for retrofitting. Such technological advances are expected within the

three main areas or sub-systems of the reverse osmosis process i.e. the pre-treatment, membrane

technology and the pumping and energy recovery device. These will not only aid in the durability

of the system through continual improvement to the process in place but it will also help to

improve the reliability of the system and reduce costs through increased efficiencies. Through

increasing the efficiency of the plant and in turn it‟s capacity, there will be an extension to it‟s

working life due to the fact that it will be able to continually provide a cost-effective source of

water. The importance is therefore shown of a durable design, as it needs to endure potentially

unpredictable changes to the technology which the system may utilise. The following outlines the

technological advances and the possible effects that they may have on the durability, reliability

and cost effectiveness of the system:

Improvements to the RO membranes: Through improvements being made to the RO membranes there can be increased performance and

durability in regards to the membrane‟s permeability and salt rejection. This, alongside increased

modular capacity, will aid in the reduction of costs. Through development of fouling resistant

membranes, the system‟s reliance on prefilters can be reduced as well as a reduction in chemical


144


cleaning which has a direct effect on the plant‟s availability through it‟s operating hours and

therefore operational costs.

Advanced Pre-filters: In this field, there is a trend for improvements to disinfection methods as well as more efficient

filtration aids. Improvements to bio-fouling control, membrane cleaning and restoration will also

aid in the reduction of costs and increasing of reliability.

Better Construction Materials: Through the use of cheaper and newer construction materials specifically high pressure pumps,

energy recovery devices and piping, improvements to both the durability of the design as well

reductions in costs can be achieved.

One of the main advantages of the technological advances mentioned above is that they will aid in

increasing the operational life of the plant. Through these improvements to reliability and

efficiency, the plant will be able to produce more water in a cost-effective manner. In turn, this

will increase the number of people that the system is able to provide water for at the same cost of

operation. This means that the price of potable water will be greatly reduced. Due to the fact that

there is plenty of scope for retrofitting this is easily facilitated. This is mainly facilitated through

the large expanse of land that is available at both the process plant and the solar power plant. In

addition to this, the modular nature of the design means that extra modules can be added easily to

the plant and be introduced systematically.

15.2 Structural Design

Through consideration of the structure, care has to be taken to follow the correct design

procedures, which should ensure that sufficient durability is achieved. This involves a detailed

review of the exposure conditions in order to determine the extent to which the structure will be

exposed to abrasive chemicals or conditions. Specifically, with consideration of the concrete

within the structure, care has to be taken in order to protect the steel reinforcement, which carries

the tensile forces within the structure. A lack of protection can lead to premature failure of the

structure. In order to help prevent this, the design must use:

A detailed consideration of the exposure conditions, the construction methods and the

operational procedures as inputs to corrosion assessment.

Durability modelling can take place in order to assess the various design options (this is

however, beyond the scope of this project.)

Concrete mix design trials in order to provide information for the placing, corrosion

assessment and crack control of the design.


145


A vigorous, well-defined and followed method for inspection and maintenance of the

structure. This should check both the state of the structure itself as well as ensuring that the

proper specifications are being followed.

Maintenance management should be both long and short term.

For the consideration of the exposure class of the concrete, which is used in order to detail

features such as the depth of concrete cover, there is a lack of specification for the case of a

desalination plant. This is mainly due to the fact that the concrete has the potential to be exposed

in many situations e.g. in tanks, channels, pipes and pits. It is therefore appropriate to take a

conservative approach in estimating these conditions.

The steel within the structure will be used in a number of situations, for example in the pipelines

and for the portal frame structure. The importance of selecting the correct grade of steel is vital in

order to create enhanced corrosion resistance and therefore a prolonged durability. Considering

the buried intake, there are a number of advantages, which aid in the maximisation of the

durability of the structure. Firstly, it is a more environmentally friendly option, as there is no

direct contact between the intake and aquatic life. In addition, they require very little maintenance

and they act as in intake pre treatment, thus protecting the pre-filters from any „heavy‟ materials.

Due to the nature and quality of seawater that the intake pipe will be in contact with, it will be

constructed from corrosion-resistant steel, thus aiding in its durability. Stainless steel is also used

for the pumps, pressure vessels, for heat exchangers, tanks and pipes that transport the high-

temperature and high-pressure seawater. These components will require good corrosion

resistance, durability and pressure resistance, all of which can be provided through stainless steel

piping.

The coastal location and application of the portal frame structure makes it‟s durability a critical

part of the design. In order to create a superior corrosion protection system, which will require

minimum maintenance, a galvanised steel option will be utilised for the majority of the structural

and associated steel work. This not only protects the steel but also allows the manufacture of the

sections and the galvanisation to occur offsite, thus allowing for fast and non-energy intensive

fabrication. All of such adds to the cost effective nature of the material.

Desalination: Group 2 Construction programme

146

Section 15 Author: PB & KK

16 Construction programme

The construction process of the CSP and RO plants is where the majority of capital cost is

consumed. Considerable expense is associated with the length of time taken for project

completion, thus it is important to manage the construction programme to minimise this and

reduce costs.

The construction programme Gantt charts are highlighted in Error! Reference source not

found. and Error! Reference source not found.Error! Reference source not found.. These

show the construction sequence for the CSP and RO plants separately. It has been noted that

the construction of the CSP plant must be completed before the RO plant to ensure there is

sufficient power available to run the RO processes. The duration for these programmes has

been estimated and is based on engineering judgement. The expected timeframe for the CSP

is extremely aggressive. It is likely that individual sections will have larger timeframes

associated with them due to management and implementation of resources, such as labour,

plant and materials.

The duration for construction programme of the desalination plant on the other hand has been

estimated conservatively. Time allowance for the limited availability of resources such as

labour and materials has been given to give a construction programme that is both realistic

and manageable. It is notable that the CSP plant may take longer for completion than the

desalination plant as the project is larger in scale. Consideration for the availability of

equipment, persons and materials should be given for a more precise estimate of the duration.


147



148


Construction programme - RO Plant


149


Construction programme - Power plan

Desalination: Group 2 Conclusion

150

Section 17 Author: KK, SA, ED & PS

17 Conclusion

The aim of this project is to design a desalination plant, giving particular attention to providing a

green and sustainable solution to Israel‟s water crisis. Desalination, coupled with a green energy

source is deemed to be the most economical and long-term solution. Various aspects and

challenges in introducing a comprehensive desalination plant to the Israeli population are

discussed. This section concludes the general findings giving an indication of where further

design and detailed study is required.

Desalination, whilst being widely used, is a relatively new and developing technology. As

concluded in the inception report, the two feasible desalination processes appropriate for this

region are Multistage Flash Distillation and Reverse Osmosis. Comprehensive study on the two

process indicated that Reverse Osmosis is by far the most energy efficient with MSFD requiring

more than ten times the energy. The specific energy requirement of RO is 3.41 kWh/m3, whilst

the MSFD options investigated had specific energy requirements ranging from 49.66 kWh/m3-

99.74 kWh/m3. Hence, RO with a green source of energy was chosen to be the solution to the

problem.

As part of the sustainable agenda, a renewable source of energy source required to be chosen.

After giving critical consideration to Israel‟s energy sources, solar power was deemed to be the

most appropriate choice. On evaluation of new and innovative power producing technologies,

concentrated solar power (CSP) was selected. It operates by exploiting the vast amount of solar

radiance Israel receives on a daily basis. An integral part of this project is the physical location of

both the solar power and desalination plant.

A design choice was made to separate the reverse osmosis plant and the power production plant.

By doing this, the scheme can benefit from the use of Israel‟s natural resources, namely it‟s

abundant solar capacity and access to the Mediterranean Sea. When considering the choice of

location for the solar power plant, the most important factor was optimising the sunlight that the

plant will receive. The best location was therefore Beersheba in the Negev desert, where both

sunlight hours and strength are at a maximum whilst the rain and cloud cover are minimised. In

addition to this, there are advantageous affects such as the fact that readily available land.

The process plant has a different set of criteria. It needs to be close to the sea in order to minimise

both the disruption and costs of the project. It should also be close to the National Water Carrier,

which will be used as a means of integrating the source into Israel‟s existing water supplies. By

consideration of the current locations of desalination plants, the area of Palmachim was chosen.

The site is close to the sea, local industries and infrastructure and yet is far enough away from

Desalination: Group 2 Conclusion

151

Section 17 Author: KK, SA, ED & PS

existing desalination plants to minimise any detrimental effects that the plant may have on the

local environment. Palmachim is also well connected to the national power grid, which will be

utilised to transfer the energy from the solar power plant to the reverse osmosis plant.

The National Water Carrier is a complex pipe network that distributes water from the wetter

Northern region to the drier regions of the South. It is located approximately 10 km from the

desalination plant and is the ideal infrastructure to be used to distribute the potable water to the

Israeli population. Problems involved with the integration of large-scale desalination plant to the

NWC have been clearly addressed in this report.

The financial feasibility of the project is limited by the cost of the water, which has been

calculated to be £0.47 per cubic meter. To put this into context the Ashkelon desalination plant

produces water at £0.34. Whilst the price of water may appear to be expensive, the design is both

innovative and sustainable, making great use of Israel‟s abundant solar potential. The break-even

point of the project with 7.02% tax and NPV discount rate of 8% is 12 years, which appears to be

at a critical level. Considering the fact that desalination is a developing technology which is

becoming more efficient and cost effective on daily basis, the design has the potential to be long-

standing. Modification in the design is necessary if the scheme is to be attractive to the investors.

This project has been mainly been focused on the RO plant the power tower design, giving

particular attention to the portal frame, raft foundation and the solar receiver tower. It has been

concluded that this scheme is economic and feasible. Durability of the structures has been assured

for the 20-year life span of the project, as well as beyond. Further attention needs to be given for a

comprehensive design, which includes pumping station, heliostat design, tower pad foundation,

pipe network and turbine control room.

For a more comprehensive design, an RO plant that treats concentrate in downstream treatment

stages would be incorporated. This would yield a higher recovery ratio, implying lower seawater

intake thereby reducing operating costs in the long term.

This plant is designed for a life of 20 years; an initial investment of £300 million yields a profit of

£500 million at the end of the project life. The break-even point is found to be after 8.5 years from

the start of the project. Solely based on these numbers, this can be considered an attractive

investment. However, a major downside to this is to do with the price of water, which is

calculated to be £0.47/m3. This is in stark contrast to the price of water produced by Ashkelon,

which is quoted as £0.33/m3. As a result, the water produced by the plant is not at a marketable

price, thereby losing favour with the customers. If the water is priced at £0.33/m3 (Ashkelon‟s

price), the NPV is negative, presenting an unattractive option for investment.

Desalination: Group 2 Nomenclature

152

Section 18

18 Nomenclature

Table 24 : List of abbreviations

HDD Horizontal Directional Drilling

HDPE High Density Polyethylene

MF Microfiltration

NF Nanofiltration

PP Polypropylene

RO Reverse Osmosis

SDI Silt Density Index

SS Stainless steel

SWRO Seawater Reverse Osmosis

TSS Total suspended solids

TOC Total Organic Carbon

UF Ultrafiltration

Alk alkalinity (H2CO3*) = 2[CO32−] + [HCO3

−] + [OH−]–[H+]

BV Bed volume

WHO World Health Organization

MGD Mega Gallons per Day

Ph Power (kW)

q Flow capacity (m3/h)

ρ Density of fluid (kg/m3)

g Gravity (9.81 m/s2),

h Differential head (m)

Ps Shaft power (kW)

η Pump efficiency

PESM Polyethersulfone

Jw Flux

Lw Permeability

∆P Transmembrane pressure


153

Section 18

Table 25 : List of symbols

Symbol/Abbreviation Quantity Units Value (if

constant)

MSFD Multi Stage Flash Distillation

TBT Top brine temperature °C

ppm Parts per million

TDS Total dissolved solids ppm or mg/L

RO Reverse osmosis

KJ Kilo Joules

PR Performance ratio Dimensionless -

n Total number of stages Dimensionless

QHT Rate of heat transfer W -

U Overall heat transfer coefficient W.m-2

.°C-1

-

AHT Heat transfer/condensing area m2 -

ΔTLM Log-mean temperarture difference °C -

NaCl Sodium Chloride

BPE Boiling point elevation

ΔTBPE Boiling point elevation °C -

Kb Ebullioscopic constant °C. molal-1

-

MLsoln Molality of solution molal -

SW Seawater

RMMSW Relative molar mass of seawater g. mol-1

58.50

R Molar gas constant J. mol-1

. °C-1

8.3143

TBP Boiling point/saturation temperature °C -

ΔHv Latent heat of vapourisation J. mol-1

of solvent -

Msolute Moles of solute mol

MLsolute Molality of solute molal or mol.kg-1

-

iNaCl Van‟t hoff factor for sodium chloride Dimensionless 2

Qreq Energy required J

Lsteam Latent heat of saturated steam J.kg-1

msteam Mass flow rate of steam kg.s-1

Tbn Last stage brine temperature °C 40

Tcw Inlet seawater temperature °C 30

Tb,i Temperature of brine at stage i °C

ΔTstage Temperature drop per stage °C

i Stage number Dimensionless

ΔTheat rej Temperature increase of seawater in heat rejection

section

°C 3.33

j Number of stages in heat rejection section Dimensionless 3

Trb Recycle brine temperature (flowing through tubes) °C

mrb Mass flow rate of recycle brine stream kg.s-1

Trb,stage 1exit Recycle brine temperature at stage 1 exit (flowing

through tubes to the brine heater)

°C

Cp, SW Specific heat capacity of seawater J.kg-1

.°C-1

4053.53

mcw Inlet seawater mass flow rate kg.s-1

mcw,rej Mass flow rate of reject cooling seawater stream kg.s-1

mm/u Mass flow rate of make-up seawater stream kg.s-1

CR Conversion ratio Dimensionless 0.462

Xm/u Salinity of make-up seawater stream ppm or mg/L 35,000

Xbn Salinity of unvapourised brine in the last stage ppm or mg/L 65,000

Xf Salinity of feed seawater stream ppm or mg/L 35,000

mwater, prod Mass flow rate of freshwater stream produced kg.s-1

3858


154

Section 18

yi Fraction of brine vapourised at stage i Dimensionless

Cp brine, i-1 Specific heat capacity of brine at previous stage i-1 kJ.kg-1

.°C-1

Lbrine, i Latent heat of vapourisation of brine at stage i kJ.kg-1

y1 Fraction of brine vapourised at stage 1 Dimensionless

mb,1 Mass flow rate of brine stream in stage 1

(Shellside fluid)

kg.s-1

mwater, 1 Mass flow rate of freshwater produced in stage 1 kg.s-1

mwater, i Mass flow rate of freshwater produced in stage i kg.s-1

mb,i-1 Mass flow rate of brine stream in stage i-1

(Shellside fluid)

kg.s-1

mwater, i-i Mass flow rate of freshwater produced in stage i-1 kg.s-1

mb,2 Mass flow rate of brine stream in stage 2

(Shellside fluid)

kg.s-1

mb,n,new Mass flow rate of brine stream in the last stage

after goalseeking (Shellside fluid)

kg.s-1

mrb,new Mass flow rate of recycle brine stream in the last

stage after goalseeking (Tubeside fluid)

kg.s-1

mb B/D Mass flow rate of brine blowdown stream kg.s-1

Xrb Salinity of recycle brine stream entering heat

recovery section

ppm or mg/L

Xi Salinity of unvapourised brine in stage i ppm or mg/L

SWM Spiral wound membrane

Jw Water (Permeate) flux m3.m

-2.s

-1

Lw Water permeability m.Pa-1

.s-1

ΔP Trans-membrane pressure Pa

σ Reflection coefficient Dimensionless

π Osmotic pressure Pa

P Permeate flow rate m3.day

-1

A Membrane area m2

iRO Van‟t Hoff factor (used in RO calculations) Dimensionless

MSW Molarity of seawater mol.m-3

TSW Seawater temperature in RO design K 298

SPSP Split partial second pass

WHO World Health Organisation

PV Pressure Vessel

ERD Energy recovery device

B/P Bypass

HP High pressure

Desalination: Group 2 References

155

Section 19

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Desalination: Group 2 Appendix A

166


20 Appendix A

20.1 Cost of pre and post treatment sections

Table 26 : Total cost of equipment in pre- and post-treatment sections

Pumps Vessels Membranes Material of construction

Equipment Cost (year 2000

UK £)

Total Installed Cost £ year

2000

Equipment kW m3 m

2 CFC

Intake system 182000 4300456 11337016*

Seawater intake well - 6448 RC/Anticorrosion coating 921120 1228303

Seawater intake pumps × 4 4310 - A351 SS 560256 1996864

Ultrafiltration membrane - - 450378 12666874 20087871*

Filtrate Tank - 5307 CS 758212 1046332

Backwash Pump × 3 120 - A351 SS 40000 209733

Coagulant storage Tank - 2.43 CS 10000 31100

Coagulant Pump × 1 8.32E-05 - 316 SS 500 3395

Sodium hypochlorite Storage - 1.1 Titanium 15000 64590

Sodium hypochlorite × 1 9.57E-05 - 316 SS 500 3480

IX Columns - 232 CS 60714 134179

Calcite reactors - 312 CS 67143 148386

Calcite Pump × 2 350 - A351 SS 75714 430057

H2SO4 Storage - 160 Mild steel 44286 90343

H2SO4 Pump × 1 0.004125 - 316 SS 600 4944

CO2 Storage 82 SS 550000 863500

NaOH Storage - 93 CS 32857 73271

NaOH Pump × 1 0.001914 - 316 SS 600 4392

Product water storage 2093 CS 298978 475375

Product water pump × 2 466 - A351 SS 90000 517500

Total Cost Year 2000 UK £ = 38750631

* 2010 prices and are not inflated with costs


167


20.2 Israel reverse osmosis desalination plant

Seawater feed pump

FeCI3

Storage

Backwash Pump

UF UNIT

Filtrate Tank

NaOCl

Storage Pump

CoagulantPump

2.5 bar

Seawater 25° C3 bar

Filtrate1 bar

3 bar

Seawater Storage

2 bar

Seawater

High Pressure

Pump

RO UNIT

Filtrate 70 bar

Booster Pump

ERD

Brine

67.25 barFiltrate 65 bar

Filtrate70 bar

ISRAEL REVERSE OSMOSIS PLANT

IX Columns

PressurisedAir

Waste

Brine discharged to sea

Calcite Bed

1.8 bar

CO2Storage tank

ProductWater

50%

Product water Storage

18.5 mg/l

1 bar

2 bar

NaOH 19.7 mg/l

NaOH Storage

Product water

04/12/2010BD 1.1

Israel Reverse Osmosis Plant

RO UNIT

17.5 bar

Brine to IX Columns

Pump

2 bar

Pump

H2SO4Storage

65 mg/l

65 mg/l

Pump

Pump

Figure 53: Israel Reverse Osmosis Desalination Block Diagram


168


20.3 Solar plant simulation

Figure 54: Solar plant Simulation

Desalination: Group Appendix A

169


20.4 ChemCad stream report

Figure 55: ChemCad stream report

Desalination: Group Appendix A

170


20.5 Calcite bed pressure drop

Figure 56: Calcite bed pressure drop

20.6 Resin bed pressure drop

Figure 57: Resin bed pressure drop


171


20.7 MSFD detailed calculations

The following section details out a calculation procedure for an MSFD unit with 40 stages, TBT

of 110°C and a steam temperature of 118°C. Calculations in the MSFD design are based on an

inlet salinity of 35,000 mg/L NaCl and an inlet temperature of 30°C.

20.7.1 Boiling point elevation (BPE)

When a solute is added to a solvent, the boiling point of the solution is different to that of the pure

solvent. Boiling occurs when the vapour pressure of a solution is equal to the surrounding

pressure. Addition of the solute lowers the vapour pressure of the solution. Thus the solution

requires to be heated to a higher temperature in order for the vapour pressure to equal the

surrounding pressure (Purdue, N.D.). In the case of desalination, the solution is seawater, which is

comprised of water (solvent) and the dissolved solids (solute). Typically, the total dissolved solids

in seawater range from 20,000 ppm–50,000 ppm (Belessiotis and Delyannis, 2006). The

predominant solid dissolved is Sodium Chloride (NaCl). Therefore, for the purposes of

calculation, an average value of 35,000 ppm NaCl, shall be used. Thus, seawater comprises of

3.5% dissolved solids, in the form of NaCl, and 96.5% water.

The BPE, ΔTBPE, is calculated using (Aus-e-Tute, N.D.)

The constant, Kb, also called the molal boiling point elevation constant, is calculated using the

following formula (Chaplin, 2009). For example, the boiling point temperature, TBP, of water at a

pressure of 1.304 bar is around 107.13°C. The BPE is calculated below. Mw, SW refers to the

molecular weight of seawater (SW) (assumed to be 58.50 g/mol).

Thus, it can be seen that the ebullioscopic constant, Kb, is a strong function of the boiling point

temperature, TBP. Boiling point temperature is dependent on the pressure that the stages operate at.

Going down the MSFD unit, since the pressure of the stages decrease progressively, so will the

boiling point temperatures. Thus, different values of Kb and thus ΔTBPE will be obtained at the

different boiling point temperatures.

The brine solution, as it passes down the MSFD evaporator, will increase in concentration as a

result of water vapour evaporating at each stage. This concentration, expressed in ppm, affects the

molality of the solute and solution. If the concentration of the solution before under these

conditions is 57,490 ppm (5.749 wt%), and if seawater is assumed to consist of 100% NaCl, the

molalities can be calculated as follows (ChemTeam, N.D.):


172


Since molality of solute, MLsolute, has units of mol.kg-1

(molal), the moles of solute are divided by

the kg of solvent per 100 grams of solution.

The molality of the solution, is obtained by multiplying the solute molality by the Van‟t factor, i.

The Van‟t factor accounts for the degree of solute dissociation in the solvent. For NaCl, the Van‟t

factor, iNaCl is 2.

Thus, the boiling point of the solution is the boiling point of pure solvent at a given pressure

plus , calculated from the equation above, at that pressure.

20.7.2 Process parameters and energy consumption calculation

It is known that the plant is to produce 100 million m3/year of fresh water. A 10% contingency is

added, to ensure that the plant is not running at 100% capacity at all times, as this would result in

premature damage of equipment. Israel receives 330 days of sunlight a year. This, coupled with a

110 million m3/year of fresh water production equates to a flow rate, mwater, prod, of 3858 kg s

-1 and

an MSFD plant operation of 330 days per year.

An arbitrary value for the energy requirement, x, expressed in kWh.m-3

is chosen and this value is

multiplied by the annual amount of freshwater produced (110 million m3 year

-1). This yields the

energy required by the plant in one year. The energy required, Qreq, in 1 second can be calculated

by:

If the arbitrary value chosen is 80 kWh/m3,


173


The number of stages, n, and top brine temperature (TBT) are set in accordance with conditions

laid out in Section 5.4.2.

Latent heat of this saturated steam, Lsteam, is obtained (Rogers and Mayhew, 1995) at the

saturation pressure. The TBT chosen for this example is 110°C and the steam temperature is

118°C. At this temperature, the latent heat of vapourisation is 2207765 J/kg. Thus, the steam flow

rate can be calculated using:

The brine temperature leaving the last stage, Tbn is set at 40°C, 10°C above the inlet seawater

temperature, Tcw, of 30°C (Sommariva et al., 2010).

The flash range (TBT – Last stage brine temperature) and therefore, the temperature drop per

stage can be computed using (Darwish et al., 1997):

A low value is desirable to minimise specific exergy losses.

Stage-wise brine temperatures (shellside fluid) are calculated using the formula (Hussain, 2009):

As mentioned in Section 5.4.1, there are 3 heat rejection stages (j). The temperature of seawater

(SW) exiting the heat rejection is set equal to the last stage brine temperature as a result of the

formula shown below (Hussain, 2009):

Recycle brine temperature, Trb in the heat recovery section is calculated, courtesy of the following

equation, which involves the number of stages in the heat rejection section, j (Hussain, 2009):

Table 27, presented in Appendix A, Section 20.7, illustrates how the temperature of the recycle

brine (tubeside fluid) and the temperature of the brine (shellside fluid) vary as it passes from one


174


stage to another. The table also shows the pressure that each stage is set at, so as to initiate flash

evaporation.

The recycle brine flowrate, mrb, is calculated using the following equation:

The required inlet seawater feed rate, mcw, is computed using (Darwish et al., 1997):

On exiting the heat rejection section, the inlet seawater feed splits into two streams, namely the

reject cooling seawater flow, mcw,rej and the make-up seawater flow, mm/u. To work out these

quantities, the conversion ratio (CR) requires to be calculated. Xm/u, the salinity of the make-up

seawater stream is the same as the intake seawater. This value is fixed at 35,000 ppm. Xbn, the

salinity of the unvapourised brine in the last stage, is found to be 1.8 times that of the feed stream

(Sommariva et al., 2010). Thus, a value of 65,000 ppm is assumed. This yields a CR of 0.462,

courtesy of the equation below (Al-Sahali and Ettouney, 2007):

Dividing the freshwater flow rate by the CR yields the mass flow rate of the make-up seawater

stream.

The reject cooling seawater flow is then represented by:

It is expected that mcw,rej> mm/u (Khawaji et al., 2008).

The stage pressures are set such that the brine entering a stage flashes instantly due to being a

superheated liquid. Flashing reduces the temperature of the incoming brine stream, to the

saturation temperature at the pressure of the stage. The pressure of the brine solution at the brine

heater is set by the steam pressure.

The brine temperatures computed above for the different stages, Tb,i are used to set the stage

pressures. The GOAL SEEK function in MS Excel matches the boiling point of the solution,


175


calculated in Section 20.7.1, to the brine temperature at each stage, Tb,i, by varying the stage

pressure, which affects the solvent boiling point and latent heat of vapourisation.

The next very key quantity calculated is the fraction of brine vapourising to steam in each stage

(Hussain, 2009). The steam eventually condenses over the tubes, through which recycled brine

flows, producing distillate/fresh water.

Calculating this enables the calculation of the amount of distillate vapour produced at each stage

and the brine flowing through each stage using the following equations:

The amount of brine flowing to stage 1 from the brine heater is the same as the recycle brine flow

through the tubes. Therefore,

For the first stage,

The general formula can be written as

The brine flow to stage i is given as

Brine flow to stage 2,

If

, the arbitrary energy requirement chosen

earlier, should be varied such that

. This can be

performed either manually or via GOAL SEEK.

Performing this function yields a specific energy requirement of 49.91 kWh/m3 of fresh

water produced. Goalseeking alters the values; therefore all the flow rates presented above will

change as well. The results after goal seeking are presented in Appendix A, Section 20.7, as

Table 27.

The brine exiting the MSFD unit is either combined with make-up seawater and circulated around

the process as recycle brine or is disposed of as brine blowdown. The brine blowdown flow rate,

mb,B/D is calculated using the following equation:

It was previously mentioned that the intake seawater salinity was assumed to be 35,000 ppm and

the salinity of the brine in the last stage was 65,000 ppm. The recycle brine salinity is a


176


combination of the make-up seawater salinity, Xm/u and the salinity of the brine in the last stage. It

is flowrate dependent.

This is the salinity of the recycle brine stream until it enters the 1st stage. On entering the first

stage, some of the water vapourises. Therefore, an increase in salinity is expected. The salinity of

the brine in stage i, after vapourisation is calculated by:


177


20.8 MSFD calculation summary

Table 27: Summary of an MSFD unit with 40 stages and a TBT of 110°C

Section

Stage

number

Stage

pressure

(bar)

S/S

fluid

(Brine)

temp

exiting

each

stage

(°C)

T/S fluid

(Seawater)

exit temp

(°C)

Specific

heat

capacity

(J kg-1

K-1)

Latent heat

of

vaporisation

(J kg-1)

Fraction

vapourised

Amount

of brine

entering

stage

(kg s-1)

Amount

vapourised/distillate

produced (kg s-1)

Brine

salinity

at

stage

(ppm)

Entry/Ext atm 30.00 28714 65000

Heat

rejection

40 0.068 40.00 33.33 4006.80 2321760.72 0.003020567 28801 86.99 65000

39 0.076 41.75 36.67 4007.45 2317721.66 0.003026328 28888 87.43 64804

38 0.085 43.50 40.00 4008.11 2313676.96 0.003032126 28976 87.86 64607

Heat

recovery

37 0.094 45.25 41.75 4008.78 2309626.23 0.003037963 29064 88.30 64412

36 0.103 47.00 43.50 4009.46 2305569.07 0.003043841 29153 88.74 64216

35 0.113 48.75 45.25 4010.16 2301505.07 0.003049761 29242 89.18 64020

34 0.124 50.50 47.00 4010.88 2297433.83 0.003055726 29332 89.63 63825

33 0.135 52.25 48.75 4011.62 2293354.95 0.003061737 29422 90.08 63630

32 0.146 54.00 50.50 4012.37 2289268.00 0.003067797 29512 90.54 63435

31 0.158 55.75 52.25 4013.15 2285172.57 0.003073908 29603 91.00 63241

30 0.171 57.50 54.00 4013.95 2281068.24 0.003080071 29695 91.46 63046

29 0.185 59.25 55.75 4014.77 2276954.59 0.003086289 29787 91.93 62852

28 0.200 61.00 57.50 4015.62 2272831.20 0.003092563 29879 92.40 62658

27 0.216 62.75 59.25 4016.50 2268697.63 0.003098897 29972 92.88 62464

26 0.233 64.50 61.00 4017.41 2264553.46 0.003105292 30066 93.36 62271

25 0.251 66.25 62.75 4018.34 2260398.27 0.003111751 30159 93.85 62077


178


24 0.271 68.00 64.50 4019.31 2256231.60 0.003118275 30254 94.34 61884

23 0.292 69.75 66.25 4020.31 2252053.04 0.003124867 30349 94.84 61691

22 0.315 71.50 68.00 4021.35 2247862.13 0.003131529 30444 95.34 61499

21 0.340 73.25 69.75 4022.43 2243658.45 0.003138264 30540 95.84 61306

Heat

recovery

(continued)

20 0.367 75.00 71.50 4023.54 2239441.55 0.003145074 30636 96.35 61114

19 0.396 76.75 73.25 4024.69 2235210.99 0.003151961 30733 96.87 60921

18 0.428 78.50 75.00 4025.88 2230966.34 0.003158927 30830 97.39 60729

17 0.461 80.25 76.75 4027.12 2226707.15 0.003165976 30928 97.92 60538

16 0.496 82.00 78.50 4028.40 2222432.98 0.003173109 31027 98.45 60346

15 0.532 83.75 80.25 4029.73 2218143.39 0.00318033 31126 98.99 60154

14 0.570 85.50 82.00 4031.10 2213837.95 0.00318764 31225 99.53 59963

13 0.610 87.25 83.75 4032.53 2209516.21 0.003195043 31325 100.09 59772

12 0.651 89.00 85.50 4034.00 2205177.75 0.00320254 31426 100.64 59581

11 0.694 90.75 87.25 4035.53 2200822.12 0.003210135 31527 101.21 59390

10 0.739 92.50 89.00 4037.11 2196448.90 0.00321783 31629 101.78 59199

9 0.786 94.25 90.75 4038.74 2192057.66 0.003225628 31731 102.35 59009

8 0.836 96.00 92.50 4040.44 2187647.98 0.003233531 31834 102.94 58819

7 0.890 97.75 94.25 4042.19 2183219.43 0.003241543 31938 103.53 58628

6 0.948 99.50 96.00 4044.00 2178771.61 0.003249665 32042 104.13 58438

5 1.012 101.25 97.75 4045.87 2174304.09 0.003257902 32147 104.73 58248

4 1.081 103.00 99.50 4047.81 2169816.49 0.003266254 32252 105.34 58059

3 1.155 104.75 101.25 4049.81 2165308.40 0.003274727 32358 105.96 57869

2 1.229 106.50 103.00 4051.88 2160779.43 0.003283321 32465 106.59 57680

1 1.302 108.25 104.75 4054.02 2156229.20 0.003292041 32572 107.23 57490

Heat input

Brine

heater 2.000 110.00 4056.23 2151657.33 57301

TOTAL 3858


179


20.9 MSFD energy requirement

Table 28: MSFD desalination energy requirement

Number

of

stages

Brine

temperature

entering

brine heater

(°C)

Top

brine

temp

(°C)

Steam

temp

(°C)

Steam

flow

rate

(kg.s-1

)

Mass flow rate

of recycle brine

stream (kg.s-1

)

Flash

range

(°C)

Temp

drop

per

stage

(°C)

Cooling

seawater

(inlet)

flowrate

(kg s-1

)

Cooling

seawater

(reject)

flowrate

(kg s-1

)

Energy

requirement

(kWh/m3)

40 86.25 90.00 98.00 304.83 45372 50.00 1.25 17015 8656 49.66

40 95.50 100.00 108.00 309.31 37909 60.00 1.50 17059 8700 49.79

40 104.75 110.00 118.00 313.96 32572 70.00 1.75 17100 8741 49.91

35 85.71 90.00 98.00 348.35 45369 50.00 1.43 19444 11085 56.75

35 94.86 100.00 108.00 353.47 37905 60.00 1.71 19494 11135 56.89

35 104.00 110.00 118.00 359.72 32568 70.00 2.00 19541 11182 57.03

30 85.00 90.00 98.00 406.37 45365 50.00 1.67 22682 14323 66.20

30 94.00 100.00 108.00 412.33 37901 60.00 2.00 22740 14381 66.37

30 103.00 110.00 118.00 418.52 32564 70.00 2.33 22795 14436 66.53

25 84.00 90.00 98.00 487.58 45358 50.00 2.00 27215 18856 79.43

25 92.80 100.00 108.00 494.72 37894 60.00 2.40 27284 18925 79.63

25 101.60 110.00 118.00 502.12 32557 70.00 2.80 27348 18989 79.82

20 82.50 90.00 98.00 609.35 45349 50.00 2.50 34012 25653 99.26

20 91.00 100.00 108.00 618.24 37885 60.00 3.00 34096 25737 99.51

20 99.50 110.00 118.00 627.47 32548 70.00 3.50 34175 25816 99.74


180


20.10 Reverse osmosis illustration

Figure 58: Osmosis and reverse osmosis ((Smith and Shaw, N.D.), Pg.1)

20.11 RO membrane

Figure 59: A Spiral Wound Membrane element ((Fritzmann et al., 2007), Pg. 24)

20.12 Pressure exchanger

Figure 60: Pressure Exchangers ((Fritzmann et al., 2007), Pg. 32)


181


20.13 SPSP

Figure 61: A typical SPSP set up (Source: (Rybar et al., 2010), Pg. 189)


182


20.14 RO process schematic

Feed from pre-

treatment

storage tank

(713,351 m3/day)

(Pressure = atm) HP pumps

(Quantity = 10)

(Flow = 307,546 m3/day)

(Outlet pressure = 70 bar)

ERD

(Quantity = 295)

(Energy transfer efficiency =

98%)

Booster

pumps

(Quantity = 3)

(Flow = 405,804 m3/day)

(Inlet pressure = 65 bar)

Seawater bypass feed

stream

(Flow = 405,804 m3/

day)

(Inlet pressure = atm)

Seawater bypass feed

stream

(Flow = 405,804 m3/

day)

(Pressure = 70 bar)

2nd

stage pumps

(Quantity = 5)

(Flow = 172,760 m3/day)

(Outlet pressure = 17.50 bar)

1st

pass rear end

permeate

(Flow = 172,760 m3/

day)

(Pressure = atm)

2nd

pass RO

(Number of pressure

vessel = 672)

(Salt rejection = 99.70%)

2nd

pass permeate

(Flow = 160,169 m3/day)

(Pressure = atm)

1st

pass front end

permeate

(Flow = 141,380 m3/day)

(Pressure = atm)

RO plant blended

permeate to storage

(Flow = 301,369 m3/day)

(Pressure = atm)

1st

pass brine to

ERD

(Flow = 399,262

m3/day)

(Pressure = 67.25

bar)

1st

pass brine to

disposal

(Flow = 399,262

m3/day)

(Pressure = atm)

2nd

pass brine to

disposal

(Flow = 12,759 m3/

day)

(Pressure = 67.25

bar)

1st

pass RO

(Number of pressure

vessel = 2320)

(Salt rejection = 99.75%)

Figure 62 : RO process schematic


183


20.15 Wind Actions

The force exerted on the structure by wind is determined in accordance to EN 1991-1-4. Clause

5.3 (3) states the wind force Fw acting on the structure or structural component can be determined

by vertical summation of the internal, Fw,i, and external forces Fw,e;

and

Where cscd is the structural factor defined in cause 6.2 (1), and for buildings with height, h≤15 m,

may be taken as 1. Aref is the reference area of the individual surfaces and We and Wi are external

and internal pressures on the individual surface at reference heights ze and zi expressed in clause

5.2:

and

qp(z) is the peak velocity pressure and cpe and cpi are the pressure coefficients for the external and

internal pressures, respectively.

20.15.1 Peak velocity pressure qp(z)

Peak wind velocity pressure wind is given by clause 4.5(1). Expression 4.8 states:

ce(z) is the exposure factor and is a function of the terrain category and the height above the

terrain, z. For flat terrain where c0(z) = 1.0 (clause 4.3.3), the exposure factor can be determined

using Figure 4.2 of EN 1991-1-4. Since z = 9 m, considering a flat category 0 (sea or coastal area

exposed to the open sea) terrain, the value of ce(z) is equals to 3. Basic velocity pressure of wind,

qb, is a function of density of air and basic wind velocity:


184


in which ρ is the density of the wind air and is taken to be the recommended value of 1.25 kg/m3.

The basic wind velocity, vb is calculated according to clause 4.2. Expression (4.1) of EN 1991-1-4

states:

where cdir and cseason are directional and seasonal factors respectively, which are recommended to

be taken as 1. For this location, the basic wind velocity vb,o is taken as 14.4 m/s, which is the

maximum monthly average Easterly storm wind velocity for Dorot, located 65 km from Tel Aviv

(H, Saaroni et al., 1998). Thus, from expression 4.1 vb = vb,0 = 14.4 m/s. Hence the basic velocity

pressure is:

Since 1 N = 1 kg.m/s2, the basic velocity pressure can also be expressed as:

Thus the peak velocity pressure can be determined using the following expression:

20.15.2 External Pressure coefficients (cpe)

The external pressure coefficients give the effect of the wind on the external surfaces of buildings

and change according to the direction of the wind and the area of the wall or roof as illustrated in

figure 7.8 of EN 1991-1-4. Clause 5.2(2) indicates different pressure zones on the walls and roofs

of this portal frame respectively.

The external pressure coefficients (clause 7.2.2) depend on the relation between the height, h, of

the building and the length, b. In this case, with h = 6 m < b = 70 m, the reference height ze is

equal to h and, as the ration between the height of the building and the width, d = L = 56 m, h/d ≤

0.25, the pressure coefficients indicated in Table 29 are obtained:

Table 29: External pressure coefficients (cpe) on the walls (Clause 7.2.2 (EN 1991-1-4))

A B C D E

Cpe -1.2 -0.8 -0.5 +0.7 -0.3

The external pressure coefficients on duo-pitch roofs are given by clause 7.2.5 and depends on the

slope α = 60 of the roof. The pressure coefficients are obtained by interpolation (of values given


185


in tables 7.4 of (EN 1991-1-4)) and are indicated in table 2 for the transverse wind direction (θ =

00) and for the longitudinal wind direction (θ = 90

0)

Table 30: External pressure coefficients (cpe) on the roofs (Clause 7.2.5 (EN 1991-1-4))

α = 60 F G H I J

Θ = 00 -1.62/0.2 -1.16/0.2 -0.57/0.2 -0.58/0.54 0.08/-0.54

Θ = 900 -1.57 -1.3 -0.69 -0.59 -1.57

From Table 30, there are two possible situations for transverse wind, which are illustrated in

Figure 63. For the longitudinal wind, consider a current frame in zone I (b).

Figure 63: Pressure coefficients for transverse and longitudinal wind actions

The internal pressure coefficients (cpi) depend on the dimensions of the openings in the building

and on the distribution of those openings along the building (clause 7.2.9 (2)). Assuming a

uniform distribution of the openings, according to clause 7.2.9, we can assume for the value of cpi,

and for any direction of the wind, the most unfavourable situation between the value of +0.2 and -

0.3. The external and internal pressures must act simultaneously. From the analysis of the

previous coefficients the most unfavorable situation is considered for each direction of the wind,

leading to the final coefficients given in Figure 64.

(a) Transverse coefficients

(b) Longitudinal coefficients


186


Figure 64: Final external coefficients

Consequently the wind action on the structure is determined:

Figure 65: Transverse and longitudinal wind actions on the structure

20.16 Rafter and Column Design

Figure 66: Members

Design outer column A

From BM diagram, Figure 22:

MEd = 2509.2 kNm


187


NEd = 10.458 × 28 = 292.8 kN

Lcr 1.5 x 7 = 10.5 m

Use 356 x 406 x 551 Class 1 S275 UC

Mb,Rd = 2810 kNm So OK; Nb,Rd = 2960 kN So OK.

Use the same section for the inner column.

Design rafter B

Md = 2509.2 kNm; L = 1.4 ≈ 2 m

Use 914 x 305 x 224 S275 UB Class 1

Mc,y,Rd = 2530 kNm (Md ≤ Mc,y,Rd); Mb,Rd = 2509.2 kNm so OK.

Design bracing C

Figure 67: Wind load carried by the bracing

Fw,Ed = 2.16 kN/m

Assume the force acts perpendicularly on the bracing:

Mw,Ed = (2.16 × 7.542)/8 = 15.35 kNm

Assume both ends are fixed: Lcr = 7.54 × 0.7 = 6 m

Use 114.3 × 5 × 13.5 S355 hot finished circular hollow section

Mc,Rd = 21.2 kNm

Design gable post D


188


Figure 68: Load carried by the gable post

Ned = 5.6 × (10.458/2) = 29.3 kN

LA = 6 + (2.94) = 8.94 m; Lcr = 8.94 × 1.5 = 14 m

Use 254 × 102 × 28 UC

20.17 Bill of Quantities

Table 31: Portal frame cost summary

Ref Description quanitty units Rate

(£/unit) Cost

A Frame

1 Columns (356×406×551 UC) 33 tonne 1,775.00 193,648.95

2 Gable post (152x152x23 UC) 42 item 100.00 4,200.00

3 Roof bracing (172x76x13 UB) 80 tonne 1,550.00 14,508.00

4 Horizontal bracing 4 item 120.00 480.00

Cladding

5 External metal cladding to structure 1130 m3 17.00 19,210.00

6 Painting of cladding 2 coats 1130 m3 13.00 14,690.00

External Doors

7 External door 1 (7.3m x 4.8 m) 1 m2 295.00 10,336.80

8 2nd Main Entrance (5.4m x 4.8m) 1 m2 295.00 7,646.40

9 Back Entrance (3m x 4.8m) 2 m2 295.00 8,496.00

10 Panic Bolts 2 nr 40.48 80.96


189


11 Heavy Bolts 4 nr 6.44 25.76

12 Door Frame 4 nr 62.26 249.04

13 Mortice Dead Lock 4 nr 16.56 66.24

Roof Structure

14 S275 Steel Rafters (356×127×39 UB ) 44 tonne 1,700.00 17,503.20

15 Steel Purlins 21 m 11.13 16,361.10

16 Crane Hire c/w operator 80T mobile 5 days 700.00 3,500.00

17 MEWP 2 wk 250.00 500.00

Roof Covering

18 Corrigated Steel with cutouts for

skylights 7883.12 m2 16.20 127,706.54

19 Rainwater guttering to include fittigns 364 m 17.00 6,188.00

20 Rainwater downpipes to include

fittings 24 m 12.57 301.68

21 Install skylights into roof covering 216 m2 20.00 4,320.00

Roof finishing

22 Fascia Boards 33.6 m2 40.66 1,366.18

23 Roof Ridge Capping 80 m 10.00 800.00

452,184.85


190


20.18 Foundation design

20.18.1 Ground Conditions:

Figure 69 : Geological Data For Rishon Lezion- Process Plant Location (Geological survey of

Israel, 2010)

20.18.2 Loads on the structure

Dead load = Load from pressure vessels + self weight of foundations + finishes

Loading from Pressure vessels:

20.18.2.1 Dead Load

Typically the pressure vessels will be a maximum of 3 per meter width and a height of 12 units.

Each unit is approximately 120mm wide with a tubing thickness of 8mm.

The loadings of the pressure vessels will consist of 6 membranes (typically 14.5 kg each) plus the

mass of the steel tubing and the mass of the water within the unit, this equates to the following:

Mass of Membranes: 6 x 14.5kg = 87 kg/m

Mass of steel =ρsteel x wall thickness x wall circumference

= 7850 kgm-3

x 8 x 10-3

x Π x 120 x 10-3

= 23.7 kg/m

Mass of water = ρwater x inner area of pipe

Alluvium


191


= 1000kgm-3

x Π x ((0.5(120-16) x 10-3

))2)

= 8.5 kg/m

Mass of 1 pressure vessel = 87 kg + 23.7 kg + 8.5 kg = 119.2 kg/m

Loadings per m2 = 3 unit wide x 12 unit high

= 119.2kg/m x 3 units/m x 12 units

= 4291.2 kg/m2

Weight per m2 = 4291.2 kg/m

2 x 10 ms

-1

= 42912 N/m

2 ve Load

=42.9 KN/m2

Self weight of slab, assuming a slab thickness of 500mm

= 0.5 m x 24 kN/m3 = 12 kN/m

2

Finishes, approximately = 1 kN/m2

Total dead load = 42.9 + 12 +1 = 55.9 kN/m2

20.18.2.2 Live Load

According to BS EN 1991-1-1:2002

For industrial uses (category E) qk = 7.5 kN/m2

Qk = 7.0 kN

20.18.2.3 Column Loads

Converting Column loads to a UDL: 11776kN/7840m2 = 1.5kN/m

2

20.18.3 Bearing capacity

Assuming that the soil type is alluvium, thus meaning that „drained‟ bearing capacity must be

considered for both the long and short-term stability of the structure.

(Calculations in terms of effective stresses) The bearing capacity (qf) is as follows:

qf c'IcNc po'Iq(Nq 1)1

2BIN po

Where:


192


Smallest dimension of raft, B= 72m and L=104m

c‟=0 as the soil has no cohesion due to it‟s grainy nature, this is a worse case scenario

estimation.

Ic, Iq and I are empirical correction factors.

Shape Correction Factor: (For a rectangular footing)

Sq= 1 + (B/L)tan ‟ = 1 + (70/104)tan 25 = 1.31

S=1 – 0.4 B/L = 1 – 0.4 (70/104) = 0.73

Depth Correction Factors:

D/B =0.5/104 = 0.004 0 Therefore can ignore depth correction factor

Ic=1.0, Iq=1.31 and Iγ=0.73

bulk = 18kN/m2

‟=25 for alluvium (GHOSH, K, 2009)

Therefore:

Nc (Praddtl, 1920) = 20.72

Nq (Reissner 1924) = 10.66

N (Hansen 1961) = 8.11

P0‟ = initial effective overburden pressure = p0 – u0

As the Ground water level is assumed to be at the surface, i.e. <1.5B, the submerged unit

weight has to be used:

sub = sat - water

sub = 18 – 10 = 8 kN/m2

p0= (0.5 x 18) = 9 kN/m2

uo= (0.5 x 10) = 5 kN/m2

p0‟ =4kN/m2

2/1717

911.873.08702

131.1166.1040

mkNq

q

f

f

20.18.4 Safe Bearing Capacity

Safe Bearing Capacity:


193


qs (q f po)

F p0

Where:

F= Load Factor- assuming a category A structure where the maximum design load is likely

to occur and the consequences of failure would be disasterous and the soil exploration is

limited, thus F=4.0

qs 1717 9

49 436kN /m2

Total load =q = (55.9 + 7.5 + 1.5) = 64.9 kN/m2

q < qs OK, Soil‟s bearing capacity is suitable

20.18.5 Load combination and arrangement

According to BS EN 1990, Table 8.7:

1.35DL + 1.5 LL = (1.35 x 57.4) + (1.5 x 7.5) = 88.74 kN/m2


194


Figure 70 : Raft Foundation Layout for Process Plant including Column and Middle Strip Details

20.18.6 Fire Resistance

For a fire resistance of 90 minutes (REI 90) a minimum slab thickness of 200mm and a minimum

axis distance of 25mm is required (BS 8110 Fig. 3.2). Thus meaning that a 500mm deep slab is

acceptable in this respect.

20.18.7 Cover

Cnom= cmin +cdev


195


Where:

Cmin= max [cmin,b ;; Cmin, dur; 10mm]

o Cmin.b=20mm, assuming a 20mm bar diameter

o Cmin, dur = 30 mm (XS1 exposure class: Exposed to air bourne salt but not

permenantly submerged: BS EN 205)

o +cdev = 10mm

Cnom= 30 + 10 mm = 40 mm

20.18.8 Raft Analysis

Effective depth of slab:

Deff = Depth of slab – cover – rebar diameter/2

= 500 – 40 – 20/2 = 450 mm

Column strip width:

Ws = 0.45 + (4 x 0.45) = 2.25 m

Firstly, considering the edge Transverse Strip:

Panel Width = 7.78m


Middle Strip = 5.53 m

Net upwards contact pressure per m = 88.7 kN/m2 x 7.78m = 690.4 kN/m

-ve BM @ first interior support= -0.086 x 690.4 x 7.78 m2 = -3593.8 kNm

+ve BM @ middle of edge span = +0.086 x 690.4 x 7.78 m2 = 3593.8kNm


-ve BM @ support = 75% of 3593.8 = 2695.4 kNm



-ve BM @ support = 25% of 3593.8 = 898.5kNm



196


Secondly, considering Longitudinal Strip:

Panel Width = 5.6m


Middle Strip = 2.25m

Net upwards contact pressure per m = 88.74kN/m2 x 5.6m = 496.9kN/m

As before:

-ve BM @ first interior support= -0.086 x 496.9 x 5.6 m2 = -1340 kNm

+ve BM @ middle of edge span = +0.086 x 496.9 x 5.6 m2 = 1340.1 kNm


-ve BM @ support = 75% of 1340 = 1005.0 kNm

+ve BM @ midspan = 55% of 1340 = 737.2 kNm


-ve BM @ support = 25% of 1340 = 335.0 kNm

+ve BM @ midspan = 45% of 1340 = 603.0 kNm

Design of the Transverse strip:

Column Strip:

At support –ve moment = -2695.4 kNm


BM/m = -2695.4/2.25 = 1198.0 kNm/m run

Assuming that the depth of the slab is 500mm and therefore that the effective depth is 450mm:

K M

bd2 fcu

1198106

1000 4502 40 0.148

K‟= 0.156 since K<K‟ no compressive reinforcement is required.


197


z d 0.50.25 K

0.9

0.5

z d 0.50.25 0.148

0.9

0.5

0.84

Area of steel required:

Asrequired=

Mu

(0.95 fy z)

1198106

0.95 460 0.84 450 7252mm2

Therefore adopt T32 @ 100mm c/c bottom spacing (Asprovided = 8040mm2)

Near Mid-span:

At the midspan +ve moment = 1976.6kNm


BM/m = 1976.6/2.25 = 1198.0 kNm/m run

K=0.108

z = 0.90

Asrequired=4982 mm2

Adopt T32 @150 mm c/c top spacing (Asprovided = 5360mm2)

Middle Strip:

At support: Moment/strip width = 898.5/5.53 = 162.5 kNm/m

At midspan: Moment/strip width = 1617.2/5.53 = 292.4 kNm/m

Considering the midspan:

(Using the approach outlined in BS 8110: Part B, using chart 2)

Mu

bd2292.4 106

1000 45021.44

FromChart :100As

bd 0.38

As 0.38 1000 450/100 1710mm 2

Provide T20@175mm c/c top spacing (Asprovided = 1800mm2)


198


At the support:

From Chart 2: Asrequired = 1125mm2

Provide T20@250mm c/c bottom spacing (Asprovided = 1260 mm2)

Design of the Longitudinal Strip:

Column Strip:

At support: –ve moment = 1005 kNm


BM/m = 1005/3.35 = 300 kNm/m run

From chart 2: Asrequired= 2310mm2

Adopt T20 @ 125mm c/c bottom spacing (Asprovided = 2510mm2)

At mid span: BM/m = 737.1/3.35 = 220 kNm/m run

From chart 2: Asrequired=1610mm2

Adopt T20 @ 175 mm c/c top spacing (Asprovided = 1800mm2)

Middle Strip:

At support: BM/m = 335/2.25 = 148.9 kNm/m run

From chart 2: Asrequired=1120mm2

Adopt T20 @ 250mm c/c bottom spacing (Asprovided = 1260 mm2)

At mid span: BM/m = 603/2.25 = 268 kNm/m run

From chart 2: Asrequired = 2030 mm2

Adopt T20 @ 150 mm c/c top spacing (Asprovided = 2090mm2)

20.18.9 Shear Reinforcement

Shear should be checked along the perimeter at a distance of 1.5d from the face of the support.

Therefore, the ultimate shear is derived as follows:

At the column perimeter (Most critical position):

Critical perimeter= column perimeter + 8x1.5d


199


= 400 x 4 + 8 x 1.5 X 450 = 7000mm

Shear force=

V F

41.22n

Where:

F is the load on the panel= 56m2 x 92.4kN/m

2 = 5174.4kN

n is the equivalent distributed load = 92.4 kN/m2

V 5174.4

41.22 92.4

5069kN

Maximum permissible shear force:

Max. permissible shear force=

Vmax .p ermis. 0.5ud 0.6 1fck

250

fck

1.5

Where:

u is the critical perimeter

d is the effective depth

Vmax.permi s. 0.5 7000 450 0.6 140

250

40

1.5103 21168kN

Vmax.permissible (21162kN)> V (5069kN) OK, shear reinforcement is not required.


200


20.19 Bar bending

Figure 71 : Barbending schedule

Member

Bar

Mark

No.

Type

Size

No.

of

Memb.

No.

in

Each

Total

Length

per bar

(mm)

Shape

Code

A*

B*

C*

D*

E/R*

Weight

(kg)

REV

Transverse:

Col. Strip BM 01 N 32 10 15 150 56000 00 56000 53,029.2

BM 02 N 32 10 15 150 56000 00 56000 53,029.2

BM 03 N 32 10 23 230 8400 11 8400 350 12,196.7

BM04 N 32 10 23 230 33600 00 33600 48,786.9

BM 05 N 32 10 23 230 8400 11 8400 350 12,196.7

Middle Strip BM 01 N 20 10 32 320 56000 00 56000 44,190.7

BM 02 N 20 10 32 320 56000 00 56000 44,190.7

BM 03 N 20 10 37 370 8400 11 8400 350 7,664.3

BM 04 N 20 10 37 370 33600 00 33600 30,657.3

BM 05 N 20 10 37 370 8400 11 8400 350 7,664.3


201


Longitudinal:

Col. Strip: BM 01 N 20 20 13 260 70000 00 70000 44,881.2

BM 02 N 20 20 18 360 10500 21 10500 350 350 9,321.5

Middle Strip: BM01 N 20 20 23 460 70000 00 70000 79,405.2

BM 02 N 20 20 13 260 10500 21 10500 350 350 6,732.2

* note: dimensions shown underlined are the free dimensions typically shown in parenthesis

Type, Shape Code and Bending Dimensions are in accordance with BS 8666:2005

Diameter mm 6 8 10 12 16 20 25 32 40 50

ALL BARS

THIS SHEET

Weight

kg

274,707

179,239

TOTAL

(kg)

453,946


202


20.20 Power system

Table 32 : Power system calculation

Plant

Energy

(W)

Energy

(kW)

Voltage Range

(kV)

Energy/0.85

(kVA)

Percentage

(%)

Current

(kA)

Solar Plant

Total power for pumps 1500000.00 1500.00 4.16 1764.71 360.58

Other Utilities (20%) 300000.00 300.00 4.16 352.94 72.12

Total Solar Plant Power 1800000.00 1800.00 2117.65 2% 432.69

Seawater intake pumps 4310000.00 4310.00 13.80 5070.59 312.32

Backwash Pump 120000.00 120.00 0.48 141.18 250.00

Coagulant Pump 0.00 0.00 0.12 0.00 0.00

Chlorine Pump 0.00 0.00 0.12 0.00 0.00

H2SO4 Pump 0.00 0.00 0.12 0.00 0.00

NaOH Pump 0.00 0.00 0.12 0.00 0.00

Calcite Pump 350.00 0.35 0.12 0.41 2.92

Product water pump 466.00 0.47 0.12 0.55 3.88

RO Plant High pressure pumps 32941000.00 32941.00 13.80 38754.12 2387.03

Booster pumps 2672000.00 2672.00 4.16 3143.53 642.31

Second pass pumps 3925000.00 3925.00 13.80 4617.65 284.42

Total RO Plant Power 43968816.01 43968.82 N/A 51728.02 52% 3882.88

General Purpose Standard Industry 22500000.00 22500.00 N/A 26470.59 26%

Excess energy To be sold 16731183.99 16731.18 N/A 19683.75 20%

Total 85000000.00 85000.00 100000.00 100000.00

Total net power

required: 100000.00 100%


203


N/b: Other utilities might be more than 20% which include regulators, switchgears, phase bus duct, and light equipment such control/computer systems.

Power units are in VA ~ normally PF = 0.85. This is important to deal with the transformers

20.21 Power generation calculation

Calculation for power generator rating:

Table 33 : Power generation calculation

Plant Power in kWatt Power in kVA Power in MVA

Solar Thermal 1800.00 2117.65 2.12

Reverse Osmosis 43968.82 51728.02 51.73

General Purpose 22500.00 26470.59 26.47

Excess energy to be sold 16731.18 19683.75 19.68

Total Power 85000.00 100000.00 100.00

0.00 0.00

Power for 1 day 2040000.00 2400000.00 2400.00

Power generator rating 226666.67 266666.67 266.67

Rounded number 230000.00 270588.24 270.59

Power calculation for 1 day = =

Power generator rating for 9 hours =

=

Power generator rating in apparent power =

=


204


20.22 Engineering sections costing

Table 34 : Costing for RO plant and power plant

Sales Revenues

Revenues Unit/year Price/m3 (£) Total Price (£) Total annual price (£)

Sales volume water 110000000.00 0.47 51700000.00 51700000.00

kWh/unit Price/kWh (£) Total price (£) Total annual price (£)

Excess electricity 16730.00 0.10 1673.00 14655480.00

Man Power

Position Number Monthly salary/person (£) Annual salary/person (£) Total annual cost (£)

Manager 5 3,020.00 36,240.00 181,200.00

Supervisor 10 2,130.00 25,560.00 255,600.00

Skilled 25 1,610.00 19,320.00 483,000.00

Semi skilled 20 1,300.00 15,600.00 312,000.00

Total 60 8,060.00 96,720.00 1,231,800.00

Government Land and Site Cost

Waste Land Type m2 Quantity Price/m

2 Total price

RO Plant 56 x 70 3920 2.0 32.28 253,075.20

Solar Plant 1,557,675.0 12.88 20,059,738.7

Land betterment cost 25% 5,078,203.46

Total land and site development 25,391,017.31

Government Land and Site Cost

Waste Land Type m2 Quantity Price/m

2 Total price

RO Plant 56 x 70 3920 2.0 32.28 253,075.20

Solar Plant 1,557,675.0 12.88 20,059,738.7

Land betterment cost 25% 5,078,203.46

Total land and site development 25,391,017.31

Building and Civil Structures

Materials kg/unit price/kg total cost (price/unit)

Portal frame 452,184.9

Substructure 459,871.5

Total 912,056.4


205


20.23 Plant and machinery costs

Table 35 : Plant and machinery costs

a) Electrical Instrumentation

Equipments Model Unit Price/ Unit Total Price

Installed

Price/unit Installed Price Total

Generator SGen1000A 1 8,017,492.99 8,017,492.99 10358601 10,358,600.9

Step-up Transformer 100MVA 1 2,329,122.21 2,329,122.21 3009226 3,009,225.9

Star-up Transformer 1 1,219,814.66 1,219,814.66 1866316 1,866,316.4

Aux Transformer 2 730,051.23 1,460,102.46 934466 1,868,931.1

SUS Transfomer 3 8,746.36 26,239.08 26974 80,921.4

Single Phase Transformer 2 9,634.71 19,269.42 18723 37,446.9

Phase Bus Duct Isolated 1 0.00 0 0.0

Phase Bus Duct

Non-

isolated 2 0.00 0 0.0

Switch Gear 3 1,007,586.70 3,022,760.10 1289711 3,869,132.9

Transmission Control & Power

Cables HT & LT 1 287,881.91 287,881.91 430383 430,383.5

Adjustable Freq Drives 1 431,822.87 431,822.87 557915 557,915.1

Lighting 1 143,940.96 143,940.96 167691 167,691.2

PLC/ SCADA automation

system 1 1,151,527.65 1,151,527.65 2063538 2,063,537.5

Miscellaneous 1 719,704.78 719,704.78 929859 929,858.6

Total 18,829,679.09 21,653,403.02 25,239,961.6

Total cost installed 25,239,961.60

Overhead (10%) 2,523,996.16

Working capital (15%) 3,785,994.24

Comission (5%) 1,261,998.08


206


Total capital employed 32,811,950.08

b) Solar Plant Mechanical

Equipment

Equipment Equipment Cost (£) year 2000 Total Installed Cost year

2000

Turbine 20,000,000.0 29,000,000.0

Pump 200,000.0 360,000.0

Condenser 4,000,000.0 6,280,000.0

Heat exchanger as a receiver 500,000.0 690,000.0

Total cost installed 2000 36,330,000.00

Total cost installed 2010 49,263,480.00

Engineering Design and supervision (15%) 7,389,522.00

Management Over heads (10%) 4,926,348.00

Commissioning (5%) 2,463,174.00

Working capital provision (15%) 7,389,522.00

Total capital employed 71,432,046.00

c) Solar System

Equipments Model Unit Price/ Unit Total Price (£)

Solar Array System

Total 52,786,350.0

d) Ultrafiltration Pre-treatment and

Post treatment

Cost

Total Cost Installed 41,358,596.0

Engineering Design and supervision (15%) 6,203,789.4

Management overheads (10%) 4,135,859.6


207


Commissioning costs (5%) 2,067,929.8

Working capital provision (15%) 6,203,789.4

Total Capital employed (£) 59,969,964.20

e) Reverse Osmosis

Quantity Power (kW) Total cost Installed cost

TM820C-400 13920 603.0 8,393,760.0 33,155,352.0

TML20-400 4032 476.0 1,919,232.0 7,580,966.4

HP pumps 11 3113 468,396.0 730,370.0 8,034,070.0 21,712,087.9

Booster pumps 4 942 145,944.0 227,570.0 910,280.0 2,460,030.2

2nd stage pumps 6 882 137,032.0 213,674.0 1,282,044.0 3,464,723.1

1st stage PV 2320 5,575.0 12,934,000.0 41,388,800.0

2nd stage PV 672 5,575.0 3,746,400.0 11,988,480.0

ERD 295 25,000.0 7,375,000.0 19,101,250.0

Total 44,594,786.0 140,851,689.7


208


20.24 Variable costs

Table 36 : Variable costs

Variable Cost

Material

kg/month

required Price/ Ton Price/ month Cost per year

Ferric Chloride 7,030 474.00 3,333.00 40,000.0

Sodium Hypochlorite 6,416 139.00 892.00 10,702.0

Sodium Hydroxide 178,110 257.00 45,713.00 548,557.0

Sulphuric Acid 293,836 77.00 22,624.00 271,494.0

CO2 83,630 96.00 7,244.00 86,930.0

Calcium Carbonate 569,589 19.00 21,928.00 263,140.0

Resin Annual Replacement Cost = 91,370.0

Total 1,312,193.0

20.25 Main crust of the project

Table 37: Main crust of the project

Main Crust of the Project

Fixed Capital Israel Grant Tax Cost Cost after finance and tax

Land & Site Development Beersheba 25% 31,343,341.64

Land & Site Development Permachime 0% 316,344.00

Building & Civil Works 0% 912056.35 912,056.35

Plant and Machinery 0% 104,564,750.20 104,564,750.20

Power Plant 24% 32,811,950.08 40,686,818.10

Solar Plant Equipment 24% 71,432,046.00 88,575,737.04

Solar System 24% 52,786,350.03 65,455,074.04

Miscelaneous cost 2% 2,765,775.13 2,765,775.13

Total 265,272,927.79 334,619,896.50


209


20.26 CSP Plant annotation

Figure 72: CSP plant


210


20.27 Israel population growth

Table 38: Population growth (actual and projected) of Israel (THE WORLD BANK, 2010)

Year

Population

growth

(annual %)

Total

Population

(x10^6)

1960 3.75 2.11

1965 3.49 2.56

1970 3.32 2.97

1975 2.28 3.46

1980 2.40 3.88

1985 1.76 4.23

1990 3.09 4.66

1995 2.67 5.55

2000 2.64 6.29

2005 1.76 6.93

2010 1.8 7.58

2015 1.8 8.28

2020 1.8 9.06

2025 1.8 9.90

2030 1.8 10.82

2035 1.8 11.83


211


20.28 Water demand projections

Table 39: Official water demand projections (DREIZIN, Y et al., 2008)

20.29 Annual population growth rate

Figure 73: Annual population growth rate of Israel (THE WORLD BANK, 2010)

20.30 Agriculture treated water requirement

0.00

1.00

2.00

3.00

4.00

5.00

6.00

7.00

1960 1970 1980 1990 2000 2010

Gro

wth

rat

e (

%)

Year

Annual population growth rate (%)


212


Figure 74: Total treated water requirement – agriculture

20.31 Total industrial water consumption projection

Figure 75: Total annual industrial consumption projection


213


20.32 Treated water industrial consumption projection

Figure 76: Total treated water consumption for industrial sector

20.33 Aquifer rehabilitation and landscaping water demand

Figure 77: Aquifer rehabilitation and landscaping water demand