modeling and simulation of multistage flash distillation pr

8/12/2019 Modeling and Simulation of Multistage Flash Distillation Pr

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MODELING AND SIMULATION OF MULTISTAGEFLASH DISTILLATION PROCESS 1

Dr. Osman Ahmed Hamed, Mohammad AK. Al-Sofi , Ghulam M Mustafa

Monazir Imam, Khalid Ba-Mardouf and Hamed Al-Washmi

Saline Water Conversion CorporationP.O.Box 8328, Al-Jubail -31951, Saudi ArabiaTel: + 966-3-343 0012, Fax: + 966-3-343 1615

Email: [email protected]

SUMMARY

The Saline Water Conversion Corporation (SWCC) is currently producing around

15.4% of the total worldwide capacity of desalted water. The majority of SWCC

desalination plants employ the multistage flash (MSF) process which produces

93% of SWCC's total desalinated water. SWCC various MSF distillers are

characterized by a wide range of operating and design conditions.

This research work is intended to perform comprehensive simulation studies to

evaluate the thermodynamic behavior of SWCC MSF plants. Operational

parameters of seven MSF distillers representing Jeddah, Al-Jubail, Al-Khobar and

Al-Khafji desalination plants have been collected and effectively utilized to analyze

and simulate their thermal performance.

A commercial computer program has been acquired for the simulation study. The

algorithm and overall logic of the program were firstly analyzed and developed to

suit the examined MSF distillers. The program was validated by comparing its

the simulated and design temperature profiles and stage brine vapor flow rates

was obtained and it has been verified that the MSF simulation model predicts the

operation of the selected MSF distiller as closely as possible. The program was

developed to predict the average heat transfer coefficients and fouling factor as

well as those of individual stages.

1 Issued as Technical Report No. TR-3808/APP97002 in December 1999.


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Concepts of both the first and second laws of thermodynamics are used for

thermal analysis. Variations in performance ratio, specific exergy losses and

exergy rational efficiency with time are evaluated for the seven distillers. It has

been found that all distillers operate at performance ratios within the range or incertain cases even higher than the design values. The specific exergy losses of

the seven distillers vary between 50 and 80 kJ/kg which are seven and eleven

times higher than that required for an ideal reversible MSF process. Design and

operating features of Jeddah phase II (high number of stages, high TBT and long

tube configuration) materialized in an improved thermal performance in spite of its

low specific condensing area. The exergy losses are highly influenced by the

number of stages, specific condensing area, TBT as well as the steamtemperature. The distribution of exergy losses among the various subsystems of

each examined distiller is determined. The brine heater is primarily responsible

for the largest exergy destruction flux and is highly influenced by heating steam

temperature.

The heat transfer simulation study revealed that both the clean overall heat transfer

coefficient (U C) and fouling factors are stage dependent while the operating overallheat transfer coefficient (U D) is to a great extent less stage dependent.

Exergy utilization is only part of the technoeconomic story. Economic and

thermodynamic considerations are to be merged (exergoeconomics) to

determine the optimum design and operating parameters of the MSF

configuration. A detailed study based on exergy cost accounting have to be

performed.

1. INTRODUCTION

The Saline Water Conversion Corporation (SWCC) is currently producing around 15.4% of

the total worldwide capacity of desalted water. The majority of SWCC desalination plants

employ the multistage flash (MSF) process which produces 93% of SWCC's total

desalinated water. SWCC various MSF distillers are characterized by a wide range of

operating and design conditions. Accumulated experience obtained from the operation of


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these plants can be effectively utilized to analyze and simulate the thermal performance of

these distillers. Steady and unsteady state simulation models are normally used for parametric

studies of MSF plants in order to determine the performance of an existing plant under wide

range of process parameters. They also give relevant guidance for process improvement andsimulate for short-term changes in the operating conditions. Furthermore, they provide design

parameters for new projects of desalination plants. Steady state models are mainly used for

design purposes as well as for parametric studies of existing plants to evaluate their

performance and adjust or optimize operating conditions.

A number of simulation studies on the performance of MSF plants which were based on the

first law of thermodynamics were published. Simulation studies based on simplified models

were reported [1-3]. These studies were based on simplifying assumptions which in most

cases are not sufficiently accurate since they generate a large discrepancy of the model's

results when compared to actual operating and design data.

Rigorous analytical studies have been reported in the literature [4-8]. The majority of these

references are proprietary and are based on the first law of thermodynamics. Although the

first law is an important tool in evaluating the overall performance of the desalting plant, such

analysis seldom takes into account the quality of energy which is being transferred. Thus, the

differentiation between high and low grade energy are not clearly evident in the majority of

such research work. The main drawback of the first law analysis is that it can not show where

the maximum loss of available energy takes place and would lead to the conclusion that the

energy losses to the surroundings and the blowdown are the only significant ones. On the

other hand, second law analysis (exergy) places all the energy interactions on the same basis

thus giving relevant guidance on process improvement. In this approach all losses are

calculated in terms of available energy (exergy) which would be a true measure of these

irreversible processes. Exergy is defined as the maximum achievable mechanical energy and is

a measure of the value of energy. It is the upper limit of the share of energy which is

transferable to mechanical work in bringing a system from its present thermodynamic state to

a stable equilibrium with the environment. The exergy method will give information on the

process details which are mainly responsible for the energy losses and thus can identifylocations were losses of useful energy occur within the process. Reported research work on


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exergy analysis of the MSF process is limited [9-11]. Sulaiman and Ismail reported a simple

scheme to evaluate overall exergy losses in Al-Khobar II, Al-Jubail II and Shoibah-I [12].

The study was limited to the design conditions and no actual test data was used in the thermal

analysis.

2. OBJECTIVES

i) To carry out a comprehensive simulation study on the performance of the multistage

flash distillation process under steady state conditions.

ii) To compare the thermal performance of SWCC commercial MSF plants under a wide

range of operating conditions using simulation programs.

3. METHOD OF ANALYSIS

A commercial program for MSF process simulation is used to analyze the thermal

performance of seven distillers of varying features representing Al-Jubail, Al-Khobar, Al-

Khafji and Jeddah MSF desalination plants. The acquired program has the capability to

perform two main functions:

i) Prediction of physical and thermodynamic properties such as density, heat capacity,

enthalpy, entropy and exergy of all liquid and vapor streams involved in the process.

ii) Simulation of MSF process and computation of operating parameters for optimum

operation under various conditions as well as calculation of energy, exergy and heat

transfer surface area requirements.

Mass, energy and exergy balance equations are firstly formulated to mathematically describe

the whole MSF process as well as its major subsystems. The formulated set of equations are

then solved using a specific solution procedure. The MSF physical and thermodynamic

models, algorithm and overall logic of the acquired program which are written in True Basic

language, were reviewed and analyzed thoroughly. The program was altered in order to

achieve the required output with the desired input such as calculation of heat transfer


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coefficients with the input values of heat transfer surface areas of brine heater, heat recovery

and heat reject section. A new subroutine of the program was developed for calculation of

heat transfer coefficients with various correlation available in literature. The overall input and

output data formatting were revised to make the program more user's friendly. Moreover, thelimitation of the program for simulation of the plants with more than 30 stages was also

relaxed to simulate plants with high number of stages such as Jeddah Phase II.

3.1 Physical and Thermodynamic Model s and Solution Scheme

Physical and thermodynamic models developed for simulation of MSF process are described

in the computation flow chart shown in Figure 1. The solution scheme of the models isexplained below in several steps:

1. Design and boundary parameters such as number of stages, top brine temperature

(TBT), surface area of the condensers, temperature and salinity of sea water and brine

reject, pump efficiency, pressure drop etc. are input parameters to the program.

2. Thermodynamic properties such as enthalpy (H), entropy (S) and saturation pressure

(Psat) of seawater feed, steam and its condensate are calculated at the known input

values by using appropriate correlation.

3. Uniform stage to stage temperature difference (DTn) is assumed in this simulation

program and is calculated by dividing flash range by total number of stages. The initial

values of makeup and recycle flows are assumed.

4. It is assumed that the flashing brine in all stages are homogeneous and at saturation

temperature. Flashing brine temperature(T B) of each stage is computed by using the

assumed equal temperature difference, while stage vapor temperatures (Tv) are

calculated by determining boiling point elevation(BPE) of brine in each stage.

5. All thermodynamic properties of the flashing brine, vapor and distillate are calculated

with the known fluid temperatures determined in step 4. Stage to stage mass and energy

balances are then performed to determine the amount of vapor generated in each stage

as well as salinity and flow rate of flashing brine.


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6. Thermo-mechanical and chemical exergy of flashing brine, vapor and product distillate

in every stage of an MSF unit are calculated with the known properties of step 5.

7. Total distillate production is calculated by adding distillates of all stages. Revised brine

recycle and makeup flows are then calculated based on the new value of distillate

production. The new value of brine blowdown salinity, X(N) is then compared with the

targeted input blowdown salinity, Xtarget.

8. Steps 5 to 7 are repeated until (X(N) - Xtarget) converges to 0.02. Convergence

which is normally achieved within 3-4 iterations, gives complete properties and process

information of flashing brine, vapor and product water.

9. The final makeup flow rate is calculated by mass balance using X(N). Temperature of

brine leaving last stage of recovery section is used to determine the number of recovery

stages.

10. Temperature and pressure of recycle brine at each recovery stage are calculated using

flashing brine temperature, BPE, terminal temperature difference(TTD) and pressure

drop across brine heater and heat recovery section. With the known temperature,

pressure and salinity of recycle brine in each stage, the thermodynamic properties

including exergy of all brine recycle streams in the upper part of the stages are

calculated.

11. With the known parameters of heat recovery section, log mean temperature

difference(LMTD), total heat transfer (Q) and overall heat transfer coefficients(OHTC)

in all recovery stages are calculated.

12. Temperature difference across brine heater is calculated by (DTn + BPE + DTT) while

LMTD, Q and OHTC in brine heater are calculated by appropriate correlations using

the above calculated parameters. The mass flow rate of the steam is calculated by

dividing Q by latent heat of vaporization( ).

13. With the known parameters in the heat rejection section, LMTD, Q and OHTC of the

tubes in all heat rejection stages are calculated. Total heat transfer and average HTC in

rejection section are also calculated.


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14. Seawater flow in rejection section is calculated by equating heat input in brine heater

and heat rejected through seawater. The thermo-mechanical and chemical exergy of all

seawater streams in the heat rejection stages are also calculated.

15. Rise in pressure (head) developed by different pumps of the system such as recycle,

makeup, distillate, blowdown and cooling seawater pump put certain amount of exergy

which are lost in the system. These exergies are determined in this step.

16. Exergy destruction in upper and lower part of all stages are calculated by solving exergy

balances in each part.

17. Exergy destruction in brine heater, heat recovery section and heat rejection section are

calculated by balancing exergy of various inlet and outlet streams to the system. Net

useful output exergy is also calculated by determining chemical exergy of the product.

18. Water-side and steam-side heat transfer coefficients of heat input and heat recovery

sections are calculated using Sieder & Tate and Kern equations respectively. The

calculated overall heat transfer coefficient gives the clean value. The fouling factor is

also calculated using the plant observed and clean values of heat transfer coefficients.

All thermal properties have been calculated separately for each stage of the distiller.

3.2 Calculation of H eat Tr ansfer Coeff icients and F ouli ng Factors

The overall heat transfer coefficients and fouling factors are one of the most important process

parameters since they have major influence on the thermal efficiency. Low heat transfer

coefficients caused by deposits (scaling and fouling) on the heat transfer surfaces and/or poor

overall heat transfer coefficients for different sections of MSF plant are estimated from the

existing heat transfer areas and flow temperature data extracted from the heat and mass

balances provided by the contractor. Designers normally use very conservative fouling factors.

It is thus worth while to calculate heat transfer coefficients and fouling factors from actual

operating data.


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Based on obtained operating brine and vapor temperatures and flow rates, the overall heat

transfer coefficient of the brine heater and heat recovery section are calculated from the

appropriate capacity equations.

In literature a number of equations are proposed for the calculation of the individual heat

transfer coefficients for turbulent liquid flow and for condensation of vapor [13]. In this study,

-side

and steam-side heat transfer coefficients of MSF condenser tubes respectively.

3.3 Program Validation

The program was first validated by comparing its re

design values. Design and operating data of SWCC major MSF plants were collected. Table

1 shows the general design characteristics of six MSF plants. The main design features are top

brine temperature (90 to 121 oC), rated capacity of the distillers (2.5 to 6.61 MIGD), number

of stages (16 to 34), performance ratio (2.95 to 4.566 Kg/1000kJ), and feed water salinity

(42000 to 53000 ppm). Condenser tube bundle configuration are cross flow in most plants

except Jeddah phase II and IV which are of long tube configuration. Materials of construction

are also included in Table 1 [15].

results for four MSF plants that include Al-Jubail II, Al-Khobar II, Al-Khafji and Jeddah II

plants. These plants were designed by different contractors and characterized by a wide

range of design and operating variables. Taweelah plant of Abu Dhabi which has a distiller of

unique rated capacity up to 12.8 MIGD [16] is also included in the list for comparison.

Table 2 shows the input design data for the simulation program and Table 3 shows the

comparison between the design and simulated values for the five examined plants. The

difference between the two compared values never exceeded 5% and in general below 1%.

The simulation program can also predict the behavior of MSF distillers. That is to predict the

temperature profiles of different vapor and flashing brine streams as well as stage distillate

production. As an illustration, comparison between the design and simulated temperature


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profiles, recycle & flashing brine and distillate flow rates for Al-Jubail II is shown in Figures 2

to 5. A reasonably good agreement between the design and simulated values was observed.

Figure 6 shows that there is a very close agreement between the design and simulated

performance ratios when the TBT is varied between 75 to 1120

C. From the foregoingcomparison it can be deduced that the MSF simulation model predicts the operation of the

examined MSF distiller as closely as possible.

4. RESULTS & DISCUSSION

The validated simulation program is used to predict the operational performance of a number

of SWCC MSF desalination plants. A total number of seven distillers which are of different

design configurations and covering a wide range of operation conditions, were selected. They

included two distillers of Al-Jubail Plant Phase II, one distiller from each of Al-Khobar Phase-

II and Al-Khafji Phase II and three distillers from Jeddah plants representing Phase-II, III and

IV. Field visits were arranged to these plants to collect design and operational data. For each

distiller, the operational data collected include temperature, pressure, flow-rate and salinity of

all streams. Frequency of data collection ranged between 1 and 3 weeks.

The selected seven MSF distillers are subjected to simulation model analysis. The results

obtained through simulation depict thermal performance of each distiller. Concepts of the first

and the second laws of thermodynamics are used in this simulation study. Performance ratio

was used as first law evaluation criterion while specific exergy losses due to process

irreversibility and exergy rational efficiency were used as the second law performance criteria.

These are defined as follows:

Performance ratio, kg/2326 kJ PR =Distillate water production x

Rateof heat added to brine heater

2326

(exergy required to produce = Total exergy lossesDistillate production

S ecific exer losses, kJ/k

1 kg of distillate)


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Exergy (Rational) efficiency =Useful chemical exergy output

Thermomechanical exergyinput

The inlet thermo-mechanical mass exergy input is supplied by brine heating steam, ejector

steam and pumping power while the useful exergy output represents the chemical exergy of

the product water with respect to that of seawater feed.

4.1 M acro Thermal Analysis

For each distiller the variation of performance ratio, specific exergy losses and exergy

efficiencies with time are evaluated. The impact of short-term changes in the operating

conditions such as, TBT, seawater inlet temperature and temperature of steam entering the

brine heater on the distiller thermal behavior are examined.

4.1.1 Jeddah MSF Plants Jeddah desalination plants incorporate three different groups of distillers. Phase-II group

consists of four distillers each of 34 stages long tube arrangement and design production

capacity of 10,800 m 3/day at a top brine temperature of 115 oC with acid treatment. Phase-

III group consists also of four distillers each of 16 stages cross tube arrangement and design production capacity of 22,000 m 3/day at TBT of 108 oC using polyphosphonate scale

inhibitor at 3 ppm. Phase-IV group consists of 10 distillers, each of 24 stages long tube

arrangement and design production capacity of 22,000 m 3/day at TBT of 110 oC using

polymaleic acid with 1.8 ppm dose rate. One distiller from each group was selected to

analyze its thermal performance. For each distiller, the variation of performance ratio, heat

transfer coefficient, fouling factor, specific exergy losses and exergetic efficiency as well as

operating temperatures with time is shown in Figure 7, 8 and 9. During the period of

performance analysis, seawater salinity was within the range of 40500 to 41000 ppm while its

temperature within 28 to 30 oC.

Figure 10 shows a comparison of the thermal performance of the three distillers of Phase II,

III and IV respectively. It shows that Jeddah II distiller which was working with a TBT of 115oC, did yield the highest performance ratio (PR) of around 11.5. This higher PR value is

expected because of the higher number of stages as well as the operation with a relatively


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higher TBT compared to other groups. The specific exergy losses of the distiller are relatively

low and ranging between 54 to 58 kJ/kg product, which is reflected in the relatively high

rational exergy efficiencies which range between 5.8 and 6.4 percent.

Although Jeddah Phase IV distiller has higher number of stages compared to phase-III distiller

and is operating with a higher TBT, it is yielding a lower thermal performance. The unit

performance ratio ranges between 7.1 to 8 and rational exergy efficiencies between 4.3 to 4.7

which are relatively lower than those of phase-III. The decrease in thermal performance is

attributed to its low specific condensing area (1.78 m 2/m3/day) which is 20 % lower than that

of the phase-III unit (2.25 m 2/m3/day). Both Jeddah III and IV are generating higher exergy

losses and hence higher irreversibility compared to Jeddah-II which incorporates high number

of stages.

4.1.2 Al-Juba il Plant

Two distillers of different design characteristics have been selected from Al-Jubail Phase-II

plant. One distiller (unit 8) is having 22 stages and specific condensing area of 3.55

m2/(m3/day) while the other distiller (unit 21) has 19 stages and 3.7 (m 2/m3/day) condensing

area. Figures 11 and 12 show the operating conditions and thermal performance of units 8

and 21 respectively. Unit 8 was operating mostly at a TBT of 90.5 oC and after 200 days of

operation the unit was shut down for acid cleaning and the TBT was increased to 95 oC. The

unit performance ratio during the first 200 days of monitoring was ranging between 7.7 and

8.4 which is within the range of the design performance ratio of 8.01 at 90 oC. During this

period, the unit specific exergy losses varied between 57 and 63 kJ/kg and the rational exergy

efficiency varied between 5.5 and 6.3 %. After acid cleaning, the thermal performance of theunit improved remarkably. The performance ratio increased to above 9 and the specific

exergy losses dropped to around 54 kJ/kg which is reflected in an increase of exergy

efficiency to 6.6 percent. Figure 11 shows that the impact of acid cleaning is most pronounced

in the heat recovery section compared to the brine heater. The overall heat transfer coefficient

in the heat recovery increased by 30 percent which resulted in very low fouling factor of about

0.05 (m 2K/kW) compared to a design value of 0.175 (m 2K/kW).This can be attributed to the

acid cleaning.


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Figure 12 shows the performance of unit 21, which was mostly operating at TBT of 98 oC.

PR varied between 8.5 and 8.9 and was comparable to the design performance ratio of 8.7.

The exergy losses ranged between 53 and 62 kJ/kg and the exergy efficiency varied between

5.6 and 6.6. The operating overall heat transfer coefficient of the brine heater is varying

between 3700 to 3000 kW/m 2K and which is consistently above the design value.

4.1.3 Al-Khobar Plant Phase-II

Figure 13 shows the variation of the operation performance of Al-Khobar Phase II distiller.

The TBT of the monitored distiller was maintained between 82 and 91 oC while the steam

temperature varied between 91 and 107oC. The unit which is only a 16 stage distiller was

yielding low performance ratios ranging between 6.7 and 7.6 and relatively high specific

exergy losses which varied between 64 to 75 kJ/kg while the rational exergy efficiency varied

between 5.6 and 7.0. The interdependence of the performance ratio, specific exergy losses

and exergetic efficiency is quite evident. During the period in between 40 to 120 days, where

the steam temperature is relatively high, the unit is experiencing low performance ratio, high

specific exergy losses and low exergetic efficiency. Increase of steam temperature resulted in

an increase of the specific exergy losses which in turn is inducing low performance ratio and

exergetic efficiency. This is because the thermal energy supplied to the brine heater has a high

exergy value which is eventually dissipated due to phase change. Although the distiller was

experiencing relatively high specific exergy losses, it was not reflected in the magnitude of

rational exergy efficiency. This is due to the fact that the unit was subjected to a make up of

relatively high salinity exceeding 50,000 ppm. In other words, the unit was producing a useful

product output with a relatively elevated chemical exergy related to the seawater make up.The overall heat transfer coefficients of the brine heaters and recovery sections as well as their

fouling factors are within the range of the design values.

4.1.4 Al-Khafji Plant

Distillers of Al-Khafji plant consist of twenty two stages and is of production capacity of

around 460 m 3/hr. Figure 14 shows the time dependence of the unit thermal performance.

During one year operational period, the top brine temperature was fluctuating between 87


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and 78 oC and the distiller performance ratio ranged between 7.7 and 9.4 kg/2326kJ and was

in most cases above the design value (8.2 kg/2326kJ) except for the case when the unit was

not operating at full load. The simulated values of fouling factors of the brine heater and heat

recovery section indicate that the plant was operating satisfactorily throughout the test periodand ensuring the effectiveness of polyphosphonate inhibitor with a dose rate of 1.0 ppm.

Operation above the design performance ratio could be attributed to the high specific

condensing area of the distiller which is 3.84 m 2/m3/day. The distiller specific exergy losses

(SEL) ranged between 51 and 61 kJ/kg and its exergetic efficiency ranged between 5.6 and

7.4. Both the specific exergy losses and the exergetic efficiency are influenced by the

operating temperature.

4.2 Micro -Thermal Analysis

4.2.1 Subsystem exergy analysis

Summary of the comparison of the plants' overall thermal performance is shown in Table 4.

The exergy losses of the examined distillers varied between 50 and 82 kJ/kg which are much

larger than the necessary for the infinitely slow reversible desalination process which is only

around 7.2 kJ/kg [17]. The excess exergy introduced in the various distillers is dissipated as a

result of the irreversibilities. It is essential to determine the distribution of the overall exergy

losses among the various subsystems of the MSF distiller. Information will be obtained about

the process details which are mainly responsible for exergy losses and this can identify

locations where losses of useful exergy occur within the process. Subsystems which are

responsible for exergy losses include brine heater, heat recovery section, heat rejection

section, leaving streams and the ejector system. The magnitude of the exergy losses in each

subsystem is calculated for each investigated distiller. As an illustration the break down of the

exergy losses among the major subsystems are shown in Figures 15 and 16 for Al-Khobar

and Al-Jubail plants respectively. The major exergy destruction has occurred in heat recovery

section which accounts for more than 50 percent. The exergy destruction in the brine heater,

heat rejection and losses through leaving streams are to some extent comparable. The exergy

losses due to ejector steam in Al-Khobar unit is high compared to Al-Jubail unit.


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Figure 17 shows summary of the break down of the exergy losses for the seven examined

MSF distillers. Al-Khobar distiller was presented by two bar charts where in both cases all

the operating parameters are kept constant except the temperature of steam entering the

brine heater. Increase of steam temperature from 95o

C to 105 resulted in 130 % increase ofexergy losses in the brine heater while exergy losses in the other subsystems were largely

unchanged. The influence of steam temperature on the overall exergy destruction is thus very

significant. The performance of Al-Khobar distiller when operating at TBT of 90 oC and

steam temperature of 95 can be compared with al Al-Jubail unit 8 which is operating under

similar conditions. The latter unit is generating less exergy losses than the former and this can

be attributed to the high exergy losses of ejector steam in Al-Khobar unit as well its low

specific condensing area and high salinity of seawater feed. This can also be due to lower

number of stages in Al-Khobar unit compared to Al-Jubail. Al-Khafji distiller is also having a

similar exergy destruction pattern as those of Al-Jubail units and with a lesser exergy

destruction in the recovery section which is characterized by a large condensing surface area.

This similarity supports number of stages as a good reason for variation of exergy destruction

in Al-Jubail and Al-Khafji compared to Al-Khobar.

Three units of Jeddah plants are operating at high top brine temperatures. The exergy losses

exhibited by the recovery and rejection section of Phase III and IV are 25 and 33 percent

higher than those of phase II, respectively. This is attributed due to the large difference in the

number of stages. Increasing number of stages decreases the temperature drop in each stage

which in turn reduces the exergy losses.

Figure 17 shows that the major exergy losses occurs in the recovery section. The exergy

destruction in the recovery section is the result of exergy losses in feed heaters and those

caused by flashing of brine and distillate in stages. The recovery section represents the largest

part of the distiller and its condensing area is several times higher than that of both the

rejection section and brine heater. Thus the high exergy losses in the recovery section is

primarily due to its large condensing area. To make a rational comparison between the

irreversibility associated with the recovery section to that associated with the brine heater and

reject section, it is essential to determine the exergy destruction flux (exergy per unit


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condensing area) for each subsystem. Figure 18 shows that the recovery section in most cases

is exhibiting the lowest exergy destruction flux. The only exceptions are Jeddah III and IV

which are having comparable values of exergy flux in the recovery and brine heater. This is

because both units are operating at high TBT and are having less number of stages comparedto Jeddah II which is also operating at a high TBT. Increase of TBT causes an increase of

both condenser and flashing exergy losses due to increase of temperature drop per stage. This

is not the case when comparing units 8 and 21 of Al-Jubail Phase II due to the design

philosophy of back pressure turbine whereby the recycle flow is reduced to maintain steam

flow rate as TBT is increased.

4.2.2 Simulates stage-wise heat transfer coefficients and fouling factors

Very little information is published on the fouling factors of individual stages [18] and in most

cases an average value for the entire recovery section is calculated. The simulation program

has been modified to enable the calculation of the overall heat transfer coefficient and the

fouling factor of each individual stage. As an illustration the simulated heat transfer results of

Al-Jubail II and Al-Khobar distillers are shown in Figures 19 and 20 respectively. Both

figures show that the operating overall heat transfer coefficient of each individual stage (U D) is

consistently higher than the design overall heat transfer coefficient. The clean overall heat

transfer coefficient (U C) of each stage which is calculated from the individual heat transfer

coefficients of each recycle brine and condensing vapors inside and outside the tubes

respectively, is highly dependent on the number of recovery stage. The highest value of Uc is

obtained in the first stage and is progressively decreasing towards the low temperature stages.

This is due to the fact that the individual heat transfer coefficients of the recycle brine and the

condensing vapors are dependent on their physical properties which are highly influenced bystage operating pressure and temperature. Although the high temperature stages of the

recovery section are having higher clean overall heat transfer coefficients compared to the low

temperature stages, the operating overall heat transfer coefficients (U D) of the different stages

remain virtually constant. This is due to the fact that stages of higher temperature are

experiencing high fouling factors which is offsetting the advantages gained by the clean heat

transfer coefficients. High values of fouling factors in the high temperature stages is due to the


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combined effect of the increase of scaling potential inside the tubes and the blanketing effect

induced by the non-condensable gases released from the flashing brine.

Comparison of the simulated fouling factors with the design values revealed that for Al-Jubail

value while the remaining recovery stages are exhibiting lower values as shown in Figure 19.

Figure 20 shows that Al-Khobar distiller is having a design clean heat transfer coefficient

which is almost equal to the simulated clean heat transfer coefficient of the first stage and

consequently the simulated fouling factors of all stages are lower than the design value and the

gap between the two values widens towards the low temperature stages.

5. CONCLUSIONS

1. The comparative thermal analysis of SWCC MSF distillers revealed that after more

than 16 years of continuous operation, their performance ratios are equal to or higher

than the design values. This is attributed to SWCC strict requirements of operation and

maintenance which could result in extending the plants life to more than 30 years.

2. Second law of thermodynamic analysis showed that specific exergy losses of distillers

are found to varying between 50 and 82 kJ/kg distillate. These losses are much higher

than that necessary for an ideal reversible process which is only 7.2 kJ/kg distillate [17].

The rational exergy efficiency of the examined distillers ranged between 4.3 to 7.0

percent.

3. Design and operating features of Jeddah phase II (high number of stages, high TBT and

long tube configuration) materialized in an improved thermal performance in spite of its

low specific condensing area.

4. Al-Jubail and Al-Khafji distillers were having comparable exergy destruction which was

similar to that in Jeddah II. Both the distillers are characterized by large condensing

surface area, especially that they were operated at TBTs less than 100 oC compared to

maximum design value of 112.8o

C.


17/44

17

5. Distillers which were generating high exergy losses, are Jeddah III and IV and both are

operating at high TBT and of relatively low number of stages compared to Jeddah II.

Al-Khobar distiller which is also of limited number of stages and subjected to seawater

of high salinity exhibited high exergy destruction.

6. Subsystems exergy analysis revealed that the brine heater in most cases is responsible

for the highest exergy destruction flux. Brine heater exergy losses are highly influenced

by steam temperature, and its associated exergy contents.

7. The heat transfer simulation study revealed that both clean overall heat transfer

coefficients and fouling factors are stage dependent and conversely the operating overall

heat transfer coefficient is to a great extent less dependent.

6. RECOMMENDATIONS FOR FURTHER WORK

1. A detailed parametric study using the simulation program has to be performed to

determine the impact of variation of the different process design and operating

condition on the thermal behavior of the MSF process.

2. A thermal performance simulation study has to be performed to selected MSF

distillers representing Yanbu, Shugaig, Shoaiba, Al-Jubail I and Al-Khobar III

desalination plants.

3. By present state of art, arguments favoring the brine recycle mode are no longer

valid for Middle East Installation [19-20] and it is thus essential to perform a

second law thermal analysis for a once-through configuration and is to be

compared with the results obtained with the recirculation flow system.

4. Exergy utilization is only part of the technoeconomic story [21-23]. Economic and

thermodynamic considerations are to be merged (exergoeconomics) to determine

the optimum design and operating parameters of the MSF configuration. A

detailed study based on exergy cost accounting have to be performed.


18/44

18

5. Thermodynamic analysis of the whole co-generation cycle has to be performed.

Since all the major multistage flash (MSF) distillers are allied to steam turbine

plant for power production.


19/44

19

Table -1: Design Specification of SWCC MSF Plants

1 2 3 4 5 6 7 8 9 10

S. No. SWCC-MSF plants Production, MIGD(max)

No. of Stages SW TDS SWT TBT BBT F. Range Steam in BH Design PR GOR

No. ofDistiller

s

MIGD/Distiller

H Rec.

H Rej. Total x1000 ppm 0C, 0C (max) 0C, 0C Temp.0C

Press.Kg/cm 2

Kg./1000 kJ Kg/Kg

1. Al-Jubail Phase I

Phase II C2

C3C4

C5

610

101010

5.036.29

6.296.296.11

1919

191719

33

323

2222

221922

46.546.5

46.546.546.5

3535

353535

90.6112.8

112.8112.8112.8

4143.3

43.345.242.8

49.669.5

47.367.669.9

100121.1

121.1121.1121.1

1.0352.05

2.052.052.05

3.454.09

4.094.094.09

7.879

999

2. Jeddah Phase II

Phase III

Phase IV

44

10

2.555

311421

323

341624

424245

313131

115108110

4040

39.5

7568

72.5

122115

117.1

1.750.980.82

3.983.053.02

9.287.077.02

3. Al-Khobar Phase II 10 6.61 13 3 16 57 35 115 43 71.5 130 2.25 2.39 6.5

4. Yanbu Phase I 5 5 21 3 24 45 30 121 40 81 127 1.47 4.57 10

5. Shugayg Phase I 4 5 16 3 19 45 33 90 39.5 50.5 97.3 0.94 3.55 8

6. Khafji Phase II 2 2.5 19 3 22 45 35 112.8 43.5 69.3 126.9 1.91 3.52 9.5

11 12 13 14S. No. SWCC-MSF PLANTS Chemical Treatment,

ppmHTC (clean), W/m 2K HTC (design) , W/m 2K FF (design), m 2K/W x 10 -3

Acid Antiscalant

BH H. Rec. H. Rej. BH H. Rec. H. Rej. BH H. Rec. H. Rej.

1. Al-Jubail Phase I

Phase II C2

C3

C4

C5

-----

-----

3105----

26502182225825052483

26502650

---

-2350

---

0..2640.1760.1760.1760.176

0.17610.1760.1760.1760.176

0.20.1760.1760.1760.176

2. Jeddah Phase II

Phase III

Phase IV

618057035500

494355864777

4314-

4179

403519991994

346828002770

274318861839

0.0860.3250.325

0.08610.1780.176

0.1320.3440.299


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20

3. Al-Khobar Phase II 4359 4374 3437 2568 2868 2037 0.160 0.12 0.204. Yanbu Phase I H2SO4 5347 4882 3925 3253 3390 23421 0.1204 0.1504 0.1765. Shugayg Phase I 3395 4145 3356 1885 2539 2219 0.300 0.17 0.26. Khafji Phase II 2049 2800 2300 0.279 0.279 0.279

Table 1: Design Specification of SWCC MSF Plants (Continued)

15 16 17 18

S. No. SWCC -MSFPLANTS

CR CR Max. Flow Rate, ton/hr. Brine Velocity, m / sec.

(BR) (BB) SW MU BR BB BH Cond BH H Rec. H Rej.

1. Al-Jubail Phase IPhase II C2

C3C4C5

1.441.351.351.391.4

1.561.391.39

-1.51

11267.58762876267348340

26313514351435413505

1200010745107451093010365

168223202320

2355.22342

116.01131.42131.42131.42128.22

2.01.981.981.981.58

1.871.981.981.981.58 2.03

2. Jeddah Phase IIPhase IIIPhase IV

1.281.3

1.32

1.491.361.46

310077958346

160027002900

344281427970

95018501900

130137

2.12.011.79

1.541.711.75

1.832.061.6

3. Al-Khobar Phase II 1.32 1.196 11872 5670 11000 4420 192 2.0 2.0 1.9

4. Yanbu Phase I 1.33 1.528 6522 2640 7095 1726 89.5 1.91 1.81

5. Shugayg Phase I 1.35-1.4 1.45-1.5 11558 3233 12948 2245 125.55 1.83 1.8 2.08

6. Khafji Phase II 1.7 4378 1418 5267 835 63.5 1.56 1.55 1.95

20 21

S. No. SWCC -MSF

PLANTS

Surface Area (m 2) Tube Dimension

BH H Rec. H Rej. BH H Rec. H Rej.number length

(m)ID (mm) t w (mm) number length(m

)OD(mm) t w, mm

(BWG)numbe

rlength

(m)OD(mm

)t w, mm(BWG)

1. Al-Jubail Phase IPhase II C2

C3C4C5

3013.313225.73225.733302920

6593077314.877314.88312476525

8738.47919.17919.11033510066

22221463146318521665

13.7216.8716.87

14.31214.5

30.7339.510839.5108

35.6139

0.6351.24461.24461.244618BWG

4451729298292983301431635

14.7320.020.020.0

19.92

32.042.042.04039

0.635(18)(18)(18)(18)

62943501350161605562

14.73220.020.021.0

19.934

30.036.036.025.029.0

0.635(22)(22)(22)(22)

2. Jeddah Phase II 819.3 15574.8 2198.1 2059 6.802 19 0.9 11036 24.54 20.8 0.9 1983 18.66 19 0.9


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21

Phase IIIPhase IV

46034660.8

3847231457.2

11036.3

7872.25

41865400

12.414.65

26.74717.2

0.9140.914

3369821600

12.81725.0

28.57519.2

0.9141.0

76445000

12.81725.0

17.2217.2

0.9141.0

3. Al-Khobar Phase II 3586.1 52872 10809 4415 10.58 22 1.22 56732 12.186 22 1.22 3687 12.184 23.86 0.77

4. Yanbu Phase I 1847 51534 3859 3147 8.125 23 1.2 67473 10.570 23 1.2 5490 10.650 21 0.7

5. Shugayg Phase I 4262 77662 10552 2760 15.6 29.35 1.2 44160 17.8 31.75 1.2 6201 17.8 31.75 0.7

6. Khafji Phase II 2165 38644.5 3742 2278 12.013 22.9 1.25 43282 11.2 25.4 - 4491 25.4 -

Table -1: Design Specification of SWCC MSF Plants (continued)

S. No. SWCC-MSF Plants Material of construction [15]Brine Heater Heat Recovery Heat Rejection

She ll Tube Tube plate Tube Tube plate Tube Tube plate

Evaporator Shell

Al-Jubail I CS Titan ium Al-Bronze Titanium Ni Al Bronze Titanium A l-Bronze CS (1,2,3,22 cladded with 316L)

Al-Jubail II C2 CS Cu/Ni70/30

CS claddedwith 70/30

Cu/Ni90/10


Titan ium Ni. Al-Bronze



Cu/Ni90/10





Cu/Ni90/10





Cu/Ni90/10



CS (1,2 cladded with 316L)

Jeddah II CS Cu/Ni90/10

Cu/Ni90/10

Cu/Ni90/10

Cu/Ni90/10

Cu/Ni90/10

Cu/Ni90/10

CS (Module 1 SS 316)

Jeddah III CS Cu/Ni90/10

Al-Bronze Cu/Ni90/10

Al-Bronze Cu/Ni90/10

Al-Bronze CS (1,2 SS)

Jeddah IV CS Cu/Ni90/10/Fe

CS Cu/Ni90/10/Fe

CS Cu/Ni90/10/Fe

CS CS (1,2 ( SS 316L))


22/44

22

Al-Khobar II CS Cu/Ni70/30

Cu/Ni70/30

Cu/Ni90/10

Cu/Ni90/10

Titan ium Al-Bronze CS (1to 16 (90/10Cu-Ni0)

Yanbu I CS 66/30/2/2 CS Cu/Ni70/30(1-10)

90/10(11-21)

CS Titanium CS CS [1 to 13 (316) epoxy coated]

Shugayg I CS Cu/Ni70/30

Cu/Ni90/10

Cu/Ni90/10/Fe

Al-Bronze Titan ium Al-Bronze CS (1 to 19 (316L &317L)]

6 khafji II CSCu/Ni70/30

SS 90/10 Cu/Ni66/30/2/2(9-19)

CuNiFeMn(1-8)

Cu/Ni90/10 &70/30

Titanium CS Claddeed CS [ 1 to 3 (316)

Table -2: Program input data

Input data design Al-Jubail,C2/C3 Al-Khobar II Al-Khafji Jeddah-II Taweelah

Sea water temperature 0C 23.9 35 35 31 32

Seawate r salt conten t ppm 46,500 57,000 46,000 45,000 45,000

Number of stages 22 16 22 34 20

Steam temperature 0C 98.9 107 102.4 113.3 120

Top brine temperature 0C 90.6 90 87.8 110 112

Bottom brine temperature 0C 32.2 42 43.4 37.7 40.5

Bot tom brine sal t content ppm 69,950 68,200 78,200 66,090 63,600

Product Flow ton/hr 1,035.3 896 485 289.3 2,258.4

Table -3: Comparison

Output data Al-Jubail Al-Khobar Al-Khafji Jeddah Taweelah

Dgn. Sim. %Diff Dgn. Sim. %Diff Dgn. Sim. %Diff Dgn. Sim. %Diff Dgn. Sim. %Diff

Recycle brine flow t/hr 10817 10732.5 0.78 12265 11678 4.78 6854 6892.7 0.56 2598 2520.8 2.97 19850 19734 0.58

Make up flow t/hr 2932 2923.9 0.28 5670 5456.7 3.76 1177 1178 0.08 936 906.4 3.16 7721.7 7723.2 0.02


23/44

23

Blowdown flow t/hr 1936.5 1935.8 0.04 4739 4557.8 3.82 691 692.76 0.25 637 616.2 3.18 5464 5461.8 0.04

Steam flow t/hr 126.77 126.52 0.20 145.27 143.13 1.47 61.27 60.75 0.849 30.78 30.44 1.1 296.1 296.22 0.04

TDS, brine recyc le, ppm 63700 63760 0.09 63.0 62.977 0.04 - 72,710 - 58500 58530 0.05 - 56334 -

Performance ratio 8.01 8.02 0.12 6.41 6.37 0.62 8.18 8.13 0.611 9.55 9.95 4.19 8.0 8.05 0.625

Gain output ratio 7.79 7.8 0.13 6.14 6.26 1.96 7.92 7.98 0.758 9.4 9.5 0.1 7.63 7.62 0.131


24/44

24

Table -4: Summary of the Overall Operational Thermal Performances of SWCC MSF Distillers

Plant

ParameterTBT oC

Flashrange, oC

Specificcond. aream2/m3/day

Number ofstages

Averageproduction

m3/dayPR

Sp. exergylosses, kJ/kg

product

Rational exg.efficiency (%)

Exergydestructionflux, kW/m 2

Al-Jubail Unit 8- C2 90-97 48-59oC 3.55 22 24000 7.8-9.4 53-63 5.5-6.6 0.185

Unit 21-C4 88 - 98 48 - 59 3.7 19 25200 8.5-8.9 53 - 62 5.6 - 6.6 0.175

Al-Khobar - 82 - 91 48-50 2.85 16 22320 6.7-7.6 64-74 5.7-7.0 0.263

Al-Khafji - 87-74 45-50 3.84 22 11000 7.7-9.4 50-61 5.6-7.4 0.162

Jeddah Phase II 107-115 64-75 1.646 34 10000 10.2-11.5 55-58 5.8-6.4 0.379

Phase III 106-108 62-67 2.25 16 21000 7.4-8 67-76 4.5-5.2 0.360

Phase IV 110-108 65-71 1.78 24 22000 7.1-8 72-82 4.3-4.7 0.50


25/44

21

Figure -1: Mathematical Models and Computation Flow Chart

Start

Perform unit conversion (SI FPS)Set natural seawater properties

Calculation of properties of steam and condensate

Stage to stage computation

Calculation of properties of brine in brine heaterTemperature, pressure, flow and thermal properties

Input parameters

Calculation of properties of flashing brine , vapor and distillate in stages Temperature, pressure, flow and thermal properties ( Cp, BPE, Latent heat, Enthalpy,

Sp. Heat, Dynamic Viscosity etc.) of flashing brine, vapor & condensate

For Stage(L) = 1 to N

ABS(DEV) < 0.02OR NRUN = 4

NO

YES

Calculation of total distillate, brine recycle per unit distillate and make-up feedDeviation in Salinit calculation

RevisedMakeup andRecycle Flows

Calculation of Exergy of flashing brine in all stages

Calculation of heat transfer coefficient (U D) in brine heaterheat recovery and heat rejection section

Calculation of Heat transfer to brine, LMTD and HTC ,

Calculation of Exergy input to pumps

Calculation of exergy destruction in upper and lower parts of the flash chamberand in liquid path due to friction

Calculation of Net exergy destruction in brine heater, heat recovery and heatrejection sections


26/44

22

Properties of brine at film temperature in brine heaterTw = Tw 0.05 ; Film temperature of brine in brine heater, Tf

Calculation of brine properties such as f, C pf, Hf, Kf, f, at film temperature

Properties of brine at bulk temperature in brine heaterBulk temperature (Tb) and pressure (Pb) of brine in brine heater;

Calculation of brine properties such as b, C p b, Hb, Kb, b, at bulk temp. & p ress.;Brine heater tube wall temperature, Tw; Brine velocity in Brine Heater tubes, Vbh

Calculation of Reynolds No. Rebh; Calculation of Prandtl No. Prbh

For L = 1 to Nrec

Calculation of Clean Heat Transfer Coefficient (U C )& Fouling Factor

STOP

Calculation of heat transfer coefficient (clean value) in brine heaterLiquid side heat transfer coefficient, h i; Vapor side heat transfer coefficient, h O;

Overall heat transfer coefficient, U C and Fouling Factor in brine heater, FF

Check the convergence of wall temperature, CKTwDeviation in Wall temp., DEV = Tw CKTw

ABS(DEV) < 0.02

Properties of brine at bulk temperature in heat recovery sectionBulk temperature of brine in Stage L, Tb(L); Bulk Pressure of brine in Stage L, Pb(L)

Calc. of brine properties such as b, C p b, Hb, Kb, b at bulk temp. T R (L) & press.P R (L);Calculation of Latent heat of condensation in stage L, (L); Velocity in tubes, Vrec(L) ;

Calculation of Reynolds No. Rerec(L) and Prantl No. Prrec(L)Calculation of heat recovery tube wall temperature, Tw (L)

Calculation of Overall HTC (Clean Value) in Heat Recovery Section

Liquid side heat transfer coefficient, h i(L); Vapor side heat transfer coefficient, h O(L)Overall heat transfer coefficient, U C(L) and Fouling Factor in brine heater, FF

For L = 1 to Nrec

Check the convergence of wall temperature, CKTw(L)Deviation in Wall tem ., DEV(L) = Tw(L) CKTw(L)

DEVMAX = MAX(DEV(L))IF DEVMAX > 0.5 THEN

Properties of brine at film temperature in heat recovery sectionTw = Tw 0.05 ; Film temperature of brine in heat recovery, Tf

Calculation of brine properties such as f, C pf, Hf, Kf, f, at film temp


27/44

23

Figure -2: Comparison of Simulated and Design Vapor TemperatureProfiles of Al-Jubail Phase II Unit # 8

Figure -3: Comparison of Simulated and Design Recycle Brine Temperature

Profiles of Al-Jubail Phase II Unit # 8

25

35

45

55

65

75

85

95

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22

No. of Stages

V a p o r

T e m p e r a t u r e

( o C

)

Vapor Temperature (Design)

Vapor Temperature (Simulation)

0

10

20

30

40

50

60

70

80

90

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22

No. of Stages

R e c y c l e

B r i n e

T e m p . (

o C )

RB Temperature (Desgin)RB Temperature (Simulation)


28/44

24

Figure -4: Comparison of Simulated and Design Flashing Brine FlowProfiles of Al-Jubail Phase II Unit # 8

Figure -5: Comparison of Simulated and Design Flashing Brine FlowProfiles of Al-Jubail Phase II Unit # 8

Figure -6: Comparison of Simulated and Design Performance Ratio

9600

9800

10000

10200

10400

10600

10800

11000

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 1 7 18 19 20 21 22

No. of Stages

F l a s h

i n g

B r i n e

F l o w

( T o n

/ h r

)

Brine Flow Rate Design

Brine Flow Rate Simul.

0

200

400

600

800

1000

1200

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22

No. of Stages

D i s t i l l a t e F l o w

( T o n

/ h r

)

Disstilate flow Rate Design

Distilate Flow Rate Simul.

7

7.5

8

8.5

9

9.5

70 75 80 85 90 95 100 105 110 115

TBTO

C

P . R . (

k g / 2 3 2 6 k J )

PR Simul.

PR Design


29/44

25

Profiles of Al-Jubail Phase II Unit # 8

Fig.# 7 Operation Performance of Jeddah II Plant


30/44

26


31/44

27

Fig # 8 Operation Performance of Jeddah III Plant

0

20

40

60

80

100

T e m p e r a t u r e SW Temp-3 TBT ( c)-3 Steam Temp.( c)-3 Flash Range( c )-3

60

70

80

90

100

S p e c

i f i c E x e r g y

L o s s e s

4

4.5

5

5.5

6

0 2 0

4 0

6 0

8 0

1 0 0

1 2 0

1 4 0

1 6 0

1 8 0

2 0 0

2 2 0

2 4 0

2 6 0

2 8 0

3 0 0

3 2 0

3 4 0

3 6 0

3 8 0

E x e r g y

E f f

0

1

2

3

4

5

6

B r i n e

H e a

t e r

H T C & F F

Fouled HTC of BH Clean BH FF of BH

00.5

1

1.5

22.5

33.5

44.5

H e a

t R e c o v e r y

H T C & F F

Av HTC of HRC Clea n HRC FF of HRC

6.2

6.7

7.2

7.7

8.2

P R

(K g

2 3 3 0 K J

(PR )d = 7.0

(U)d = 200 0(FF)d = 0.32 5

(U)d = 2800 , (FF)d= 0.178


32/44

28

Fig # 9 Operation Performance of Jeddah IV Plant

10

30

50

70

90

110

130

T e m p e r a

t u r e

SW Temp TBT ( c) Steam Temp. Flash Range( c)

6.4

6.9

7.4

7.9

8.4

P R

(K g

2 3 3 0 k J

70

75

80

85

90

S p e c i

f i c E x e r g y

(K J

3 .5

4

4 .5

5

0 2 0

4 0

6 0

8 0

1 0 0

1 2 0

1 4 0

1 6 0

1 8 0

2 0 0

2 2 0

2 4 0

2 6 0

2 8 0

3 0 0

3 2 0

3 4 0

3 6 0

3 8 0

E x e r g y

E f f i c i e n c y

0

1

2

3

4

5

6

B r i n e

H e a

t e r

H T C & F F


0

1

2

3

4

5

H e a

t R e c o v e r y

H T C & F F

Av HT C of HRC Clea n HRC FF of HRC

Ud=2000 , (FR)d=0.325

U d=2769.6 , (FR) d =.176

(PR)d=7.0


33/44

29

Fig. # 10 Comparison of the Thermal Performance of JeddahII, III and IV

98

100

102

104106

108

110

112

114

116

T B T

Jeddah-IIJeddah-IIIJeddah-IV

102104106

108110112114116118120122124

S t e a m

T e m p

Jeddah-II Jeddah-III Jeddah-IV

4

6

8

10

12

P e r

f o r m a n c e

(K g

2 3 3 0 k J

Jeddah-II

Jeddah-III

Jeddah-IV

010

20

3040

50

6070

8090

S p e c i

f i c E x e r g y

(K J

Jeddah-II

Jeddah-III

Jeddah-IV

0123

4567

0 2 0

4 0

6 0

8 0

1 0 0

1 2 0

1 4 0

1 6 0

1 8 0

2 0 0

2 2 0

2 4 0

2 6 0

2 8 0

3 0 0

3 2 0

3 4 0

3 6 0

3 8 0

Days

E x e r g y

E f f i c i e n c y

Jeddah-IIJeddah-III

Jeddah-IV


34/44

30


35/44

35

Fig # 12 Operation Performance of Al -Jubail Plant Unit 21

0

20

40

60

80

100

T e m p e r a

t u r e SW Temp( c) TBT ( c) Steam Temp( c) Flash Range( c)

8.48.58.68.7

8.88.9

9

P R

(K g

2 3 3 0 K J

52545658

606264

S p e c i

f i c E x e g y

L o s s e s

5.5

6

6.5

7

0 2 0

4 0

6 0

8 0

1 0 0

1 2 0

1 4 0

1 6 0

1 8 0

2 0 0

2 2 0

2 4 0

2 6 0

2 8 0

3 0 0

3 2 0

3 4 0

3 6 0

3 8 0

4 0 0

Days

E x e r g y

E f f i c i e n c y

0

1

2

3

4

5

B r i n e

H e a

t e r

H T C & F F

Fouled HTC of Brine Heater Clean HTC of Brine Heater Fouling F. of Brine Heater

00.5

11.5

22.5

33.5

4

H e a

t R e c o v e r y

H T C & F F

Av. HT C of H.Recovery Sec. Av. Cl ean HTC of H. Rec . Sec. Av. Fou ling F. of H.Rec. Sec .


36/44

36

Fig. # 13 Operation Performance of Al -Khobar Phase II Plant

20

30

40

5060

70

80

90

100

110


SW Temp. TBTSteam Temp. Flash Range

66.4

6.87.27.6

8

P R

(K g

2 3 2 6 K J

60

64

68

72

76

80

S p e c

i f i c

E x e r g y

( K J

55.4

5.86.26.6

77.4

0 2 0

4 0

6 0

8 0

1 0 0

1 2 0

1 4 0

1 6 0

1 8 0

2 0 0

2 2 0

2 4 0

2 6 0

2 8 0

3 0 0

3 2 0

3 4 0

3 6 0

Days

E x e r g y

E f f i c i e n c y

0

1

2

3

4

5

6

A v

. H.T R e c o v e r y

S e c

t i o n

0

0.5

1

1.5

2

F o u l

i n g

F a c t o r

(m 2 K

Av HTC of H . Recovery Section Clean HTC of H .Rec . Section Fouling Factor of H .RecSection

0

1

2

3

4

5

6

F o u l e d

& C l e a n

H .T. H e a

t e r

2 K

0

0 .5

1

1 .5

2

F o u l

i n g

F a c t o r

(m 2 K/

Fouled HTC of Brine Heater Clean HTC of Brine Heater Fouling F of Brine Heater


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37

.

Fig-14 : Operational Performance of Al -Khafji Plant

7 .58

8 .59

9 .510

10.5

P R

(K g

2 3 3 0 K J

40

46

52

58

64

S p

. E x e r g y

l o s s e s

5 .5

6

6 .5

7

7 .5

8

8 .5

9

0 50 100 150 200 250 300 350 400Days

E x e r g y

E f f i c i e c y

0

20

40

60

80

100

T e m p e r a

t u r e

SW Temp ( c) TBT ( c) Steam Temp ( c) Flash Range ( c)

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

B r i n e

H e a

t e r

H T C & F F

2 K


0

1

2

3

4

5

H e a

t R e c o v e r y

H T C & F F

( k W

2 K

Av HTC of HRC Clean HRC FF of HRC

Design PR =8.2


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38

Fig # 15 Breakdown of Exergy Destruction in Al -Khobar Plant

20

30

40

50

60

70

80

90

100

110

120


SW Temp . TBT

Steam Temp . Flash Range

0

10

20

30

40

50

60

70

80

0 20 40 60 80 100 120 140 160 180 200 220 240 260 280 300 320 340 360

Days

E x e r g y

D e s

t r u c t

i o n

Destruction In Brine Heater Destruction in Recovery

Destruction In Rejection Wasted in Leaving Streams

Wasted in Ejector Total losses


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39


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40

0

10

20

30

40

50

60

70

80

90

S p . E

x e r g y

L o s s e s

( k J / k g )

Destruction in Brine HeaterWasted in Ejector Wasted in Leaving StreamsDestruction In RejectionDestruction in Recovery

Plant Al-Khobar Al-Khobar Al-Jubail Al-Khafji Jeddah 2 Jeddah 3 Jeddah 4

Uni t No. 2 2 8 1 5 10 19TBT, oC 90 90 90.6 87 115 108 110

No. of S tages 16 16 22 22 34 16 24PR 6.8 7.1 8.1 9.2 11.2 7.6 8.7Ad/Md,(m2/m3/day)

2.85 2.85 3.56 3.84 1.646 2.25 1.7

Figure : Comparison of Breakdown of Exergy Destruction

0

0.1

0.2

0.3

0.4

0.5

0.6

Al-Khobar Al-Jubail II Al-Khaf ji Jeddah II Jeddah II I Jeddah IV

E x e r g y

D e s

t r u c t

i o n

F l u x

( k W / m

2 )

Recovery Section Rejection SectionBrine Heater

Figure : Breakdown of Exergy Flux Among Major Subsystems


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41

Fig # 19 : Variation of Heat Transfer Coeff . and Fauling Factor with Recovery Stage Number in Jubail Unit, 8 Distiller.

1000

2000

3000

4000

5000

0 2 4 6 8 10 12 14 16 18 20

O v e r a

l l H e a

t T r a n s

f e r

C o e f

f

2 K

UDUcUD(design)

Uc(design)

0

0.04

0.08

0.12

0.16

0.2

0 2 4 6 8 10 12 14 16 18 20

Recovery Stage Numbe

F o u

l i n g

F a c

t o r

2 K/

FF

FF(design)

Fig # 20 : Variation of Heat Transfer Coeff . and Fauling Factor with Recovery Stage Number in Alkhobar Distill .

2000

3000

4000

5000

0 2 4 6 8 10 12 14

O v e r a

l l H e a

t T r a n s f e r

C o e f

f

2 K

UD UcUD (design ) Uc (design )

0

0.04

0.08

0.12

0.16

0 .2

0 2 4 6 8 10 12 14

Recovery Stage Number

F o u

l i n g

F a c

t o r

2 K/

FF

FF(design)


42/44

42


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43

9. REFERENCES

1. Burley, M.J., (1967), Analytical comparison of the mutistage flash and long tube verticaldistillation, Desalination, 2, 81-88.

2. Darwish, M.A. and El-Hadik, A.A., (1986), The multieffect boiling desalting system and itscomparison with the multistage flash system, Desalination , 60 , 251-265.

3. Tanios, B.Z., (1984), Marginal operation field of existing MSF distillation plants,Desalination, 51 , 201-212.

4. El-Dessoukey, H., Shaban, H.I. and Al-Ramadan, H., (1995), Steady state analysis ofmultistage flash desalination process, Desalination , 103 , 271-287.

5. Hamed, O.A. and Aly, S., (1991), Simulation and design of MSF desalination processes,Desalination , 80 , 1-14.

6. Helal, A.M., Medani, M.S. and Soliman, M.A.,(1986), A Tridiagonal matrix model formultistage flash desalination plants, Computers and Chemical Engineering , 10 , (4), 327-342.

7. Hussain, A., Woldai, A., Al-Radif, A., Kesou, A., Borsani, R., Sultan, H. and Deshpandey,P.B., (1994), Modelling and simulation of a multistage flash (MSF) desalination plant,Desalination, 97, 555-586.

8. Rasso, M., Beltramini, A., Mazzotti, M and Morbidelli, M., (1996), Modelling multistageflash desalination plants, Desalination, 108 , 335-364.

9. Darwish, M.A., Al-Najem, N.M. and Al-Ahmed, M.S., (1993), Second law analysis ofrecirculating multistage flash desalting system, Desalination , 89, 289-309.

10. El-Nasher, A.M.,(1994), An MSF evaporator for the UANW 9 and 10 power station.Design consideration based on energy and exergy, Desalination ,107 , 253-279.

11. Koot, L.W., (1968), Exergy losses in a flash evaporator, Desalination, 5, 331-348.

12. Sulaiman, F.A. and Ismail,B.,(1995), Exergy analysis of major recirculating multistage flashdesalting plants in Saudi Arabia, Desalination, 103, 265-270.

13. Henning, S. and Wangnick, K, (1995), Comparison of Different Equations for the calculationof heat transfer coefficients in MSF multistage flash evaporators, IDA World Congress, AbuDhabi, Vol III, 515.

14. Kern, D.Q., (1987), Process heat transfer, McGraw Hill, London 20th

education, 313-374.


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15. Malik, A.U. and Kutty, P.C.M., (1992), Corrosion and material Selection in desalinationPlants. Proceeding of the seminar on Operation and Maintenance of Desalination Plants.,Saline Water Conversion Corporation, Al-Jubail, 274-307

16. Honburg, C.D. and Walson, B.M., (1993), Operational Optimization of MSF Systems,Desalination, 92 , 331-351.

17. Spiegler, K.S. and El-Sayed, Y.M., (1994), A Desalination Primer, Balaban DesalinationPublications, 185-190.

18. Rautenbach, R. and Schafer, S., (1997),. Calcculation of stagewise fouling factors from process data of large MSF distillers, IDA World Congress Proceedings, Madrid, Vol. 1,165-177.

19.Desalination Symposium, 2, Al Ain, UAE, 597-610.

20. Genthner, K., Wangnick, K., Bodendieck, F. and Al-Gobaisi, M.K., (1997), The Next SizeGeneration of MSF Evaporator: 100,000 m 3/hr, IDA, Proceedings, Madrid, Vol. 1, 271.

21. Barclay, F. J., (1995), Combined Power and Process an Exergy Approach, MechanicalEngineering Publications Limited, London, 27-40.

22. El-Sayed, Y. M., (1997), The Thermoeconomics of Sea-Water Desalination Systems, IDAProceedings, Vol. 1V, 149-166.

23. Geoge Tsatsaronics, (1994), Invited papers on exergoeconomics, Exergy, Pergamon, 19 , (3),279-381.

modeling and simulation of multistage flash distillation pr

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