Solar Thermal Technologies for Seawater Desalination

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Solar Thermal Technologies for Seawater
Desalination
Jenny Lindblom, Luleå Technical University, Sweden
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Seawater desalination

• 23 million m3 seawater is desalinated every day
• 46 000 m3 (0.02 ) is produced by means of
  renweable energy

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Direct Solar DesalinationSingle-effect
StillsWater production lt 6 litres/m2,day

• Active stills
• Stills with solar collectors
• Stills with solar concentrators
• Stills with waste heat

• Passive stills
• Basin stills
• Wick stills
• Greenhouse integrated stills

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Basin still with radiative cooling

• Condenser
• Packed Bed
• Cooled during night
• Evaporator
• Solar still
• Natural Convection
• Production
• 5-6 litres/m2,day

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Greenhouse-Integrated Stills

• Solar still
• Roof-integrated
• Only partly light-transparent
• Greenhouse
• Lowered temperature
• Less water demand
• Production
• 1 litre/m2,day

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Direct Solar DesalinationMulti-effect
StillsWater production lt 20 litres/m2,day

• Still with preheating of feed water

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Double-glazed still with preheating

• Feed water
• Serpentine tube
• Tilted wick
• Air
• Humidified over tilted wick
• Condenses on serpentine tubes
• Production
• 1 litre/m2,day

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Direct Solar Desalination Humidification -
Dehumidification Water production 1 - 20
litres/m2,day

• HD with open-air cycle
• HD with step-wise humidification

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HD with open-air cycle

• Humidification
• Water heating by solar collector
• Dehumidification
• Ambient air
• Production
• 6 litres/m2,day

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HD with Stepwise Humidification

• Humidification
• Air is warmed and humidified in several steps
• Dehumidification
• Warm air condenses on incoming air and water

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HD with Stepwise Humidification

• 1st step
• Heating from 25C to 50C
• Humidified to saturation (20 g/kg), temperature
  decreases to 23C
• 15th step
• Heating from 58C to 78C
• Humidified to saturation (148 g/kg), temperature
  decreases to 60C

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Indirect Solar DesalinationMulti-EffectWater
production gt 100 m3/day

• Seawater evaporates stepwise by heat transfer
  from tubes with condensing steam
• Primary steam source is produced externally

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Indirect Solar DesalinationMulti-Stage
FlashWater production gt 100 m3/dayGlobal
water production ? 10 million m3/day

• Heated seawater is flash-evaporated in
  low-pressure chamber

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Indirect Solar DesalinationSalinity-gradient
Solar Ponds

• Utilization
• Heat storage
• Steam generation
• 3 zones
• Upper convective
• Gradient
• Lower convective

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Indirect Solar DesalinationParabolic trough
collectors

• Reflector concentrates sun irradiation up to 60
  times
• Used for steam production