solar desalination, 040324

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Solar Desalination

Prof. Moustafa Elsayed

16-Mar-12 2

Introduction

� WHO: 480 millions of human beings are suffering from acute lack of water

� 5 million died per year due to this

� 23 million m3 seawater is desalinated every day

� 46 000 m3 (0.02 %) is produced by means of

renweable energy

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Solar Desalination Methods

� Solar Thermal Methods

� Solar Power Methods

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Solar Thermal Methods

� Generation of heat energy from sun

� Use heat energy in a desalination process

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Solar Thermal Methods

� Solar still

� Solar diffusion still

� Multi-effect evaporation

� Multi stage flash evaporation

� Humidification-dehumidification

� Freezing using absorption cooling process

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Solar Power Methods

� Vapor compression

� Reverse osmosis

� Freezing

� Electro dialysis

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Energy Requirements

Method kJ/kg PR

Reserve Osmosis 30 77

Electrodialysis 50 46

Absorption vacuum freeze 63 37

Vacuum freeze/ vapor compression 102 25

Multi-effect, multistage distillation 125 19

Multistage, flash/vertical tube distillation 175 13

Vapor compression distillation 186 12

Vertical tube evaporator distillation 204 11

Multistage flash distillation 251 9

Single-effect roof-type solar still 4350 0.53

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Solar Still

A well-designed

solar still can

produce 2 to 4

liters (or quarts)

of water per

square meter of

basin area

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Arrangements of Solar Stills

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Productivity of Solar Still

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Output of a solar still

� Q = E x G x A/2.3

� Daily output = 0.30 x 18.0 x 1/2.3

= 2.3 liters (per square meter)

� yearly output: approximately one cubic meter

per square meter

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Heat Fluxes in Solar Still

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Greenhouse-Integrated Stills

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Greenhouse-Integrated Stills

� Solar still

– o Roof-integrated

– o Only partly light-transparent

� Greenhouse

– o Lowered temperature

– o Less water demand

� Production: 1 litre/m2day

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Double Basin Solar Still

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Wick-Type Solar Still

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Cascade-Type Solar Still

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Cover Cooling Solar Still

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Double Effect Solar Still

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Single Effect Diffusion Solar

Still

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Multi-Effect Diffusion Solar

Still

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Single Stage Evaporation

Desalination

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Multi-Effect Evaporation

Desalination

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Multi-Effect Evaporation

Desalination

�Water production > 100 m3/day

�Seawater evaporates stepwise by heat transfer

from tubes with condensing steam

�Primary steam source is produced externally

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Solar Multi-Effect

Humidification Unit

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Solar Multi-Effect

Humidification Unit

�Development: Technical University of Munich

(1999)

�Principle: the evaporation of water and the

condensation of steam to and from humid air,

that flows in a circuit driven by natural

convection between condenser and evaporator.

�Pilot plant: Canary Islands, Spain, operating

since 1992

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Abhu Dhabi Solar

Desalination Plant

�Location: the United Arab Emirates

�Purpose: demonstration unit.

�Commissioned in 1984, with an average

of 85 m3/day of fresh water using sea

water with a salinity of 55,000 ppm.

�Sub-systems: the solar collector field,

heat accumulator and evaporator.

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Abhu Dhabi Solar

Desalination Plant

�Multiple effect stack-type (MES) evaporator of a rated capacity of 120m3/day

�An array of evacuated tube, flat plate collectors with a total absorber area of 1,862 m2.

�A thermally stratified heat accumulator, with a capacity of 300 m3

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Abhu Dhabi Solar

Desalination Plant

�The main grid supplies electricity

required by the different pumps.

�The performance of the collector field

and evaporator sub-systems have not

suffered in performance decline to any

appreciable degree up to today.

�Water cost: US$7/m3 to US$10/m3

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Multi-Stage Flash

Evaporation

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Multi-Stage Flash

Evaporation

�Global water production ≈ 10 million

m3/day

�Heated seawater is flash-evaporated in

low-pressure chamber

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(MSF) driven by solar pond

�Combining solar pond technology with desalination technologies

�The reject concentrate from the primary desalination process provides make-up water to the salinity gradient

�Environmental issues: – Reusing the brine concentrate thereby negating the

need for disposal (zero discharge)

– Pollution-free renewable energy for the desalting process.

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(MSF) driven by solar pond

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Solar Single-Stage Flash

Evaporation Unit

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Solar Single-Stage Flash

Evaporation Unit

�Development: Technical University of

Munich (1999)

�Sections: pressurized section and an

ambient pressure section

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Humidification-

Dehumidification Desalination

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Humidification-


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Humidification-


�1st step

– Heating from 25°C to 50°C

– Humidified to saturation (20 g/kg),

temperature decreases to 23°C

�15th step

– Heating from 58°C to 78°C

– Humidified to saturation (148 g/kg),

temperature decreases to 60°C

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Humidification-


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Humidification-


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Humidification-


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Humidification-


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Freezing Desalination Using

Absorption Refrigeration

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Solar Power Desalination

Vapor Compression

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Vapor Compression

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Freezing Desalination

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Reverse Osmosis Desalination

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Reverse Osmosis Desalination

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Solar RO Desalination

� The plant was designed and constructed in1995 by Water Re-use Promotion Center(Japan)

� Heat and electricity by solar energy

� Solar collector: 3 units of evacuated-tubecollectors each 4 m wide by 1 m long.

� Photovoltaic power generation system

� Fresh water production: 40 liters/hour, onaverage.

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Cost of Desalination Methods

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Cost of Desalination Methods

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Conclusions-1

�Solar Desalination is a cheap way to

produce fresh water.

�There are several available solar systems

for the production of fresh water from

saline or brackish water.

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Conclusions-2

� The preference of one solar desalination

method over other methods depends on:

� Location

� Amount of water to be produced

� Quality of water to be desalinated

� Quality of water to be produced

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Thank you

solar desalination, 040324

Engineering