A Small And Simple Plastic Desalination Device Junko TAJIMA*, Kosuke SAITO, Haruki SATO Faculty of Science and Technology Keio University
Introduction Water shortage in the world Large scale plants is not possible to be used for the areas having not enough infrastructure easily-obtainable, self-sustained, small and simple distillation device would be required in many areas in the world 1
Objective Development of Desalination Device which has following characteristics Small and light Easier maintenance and long durability Cheap and lower running cost High availability including energy supply Self-sustained 2
Device Main materials of device are Plastic pipe and Membrane H I G A 50 cm P B D J C 20 cm P E P F A trap F heater B raw water G cooler C membrane of heat exchanger H thermostat bath D distilled water bottle I circulation pump E vacuum pump J pressure sensor one stage system Plastic is cheap and light but corrosion resistance even for sea water 3
Principle Decompression Boiling and Multi-Effect Distillation decompress the equipment and lower the boiling point around 30 at 4 kpa enables the distillation more effective Less heat loss from surface of the equipment Less energy for heating the raw water Energy for decompression can be managed by battery and photovoltaic cells 4
Principle Decompression Boiling and Multi-Effect Distillation reuse latent heat from vapor into heating raw water Nth stage cooler vapor distillated water The latent heat is used to heat raw water in next stage raw water Cool the steam and collect latent heat 2nd stage 1st stage heater Input heat into raw water and get steam This Multi-effect enables distillation more effective and can make the device much smaller 5
Discussion Material of the membrane Boiling on the top surface Condensing on the bottom surface Material should have corrosion resistance even for sea water be clean have high heat transfer Titanium is usually used to desalinate sea water however its thermal conductivity is low oxidized and carbon doped Titanium Fresh Green 6
Fresh Green Fresh Green has following characteristics Hard surface Corrosion resistance Easier and lower cost for hardening treatment Photocatalytic Hydrophilic effect Hard to be scratched Sea water resistance Mass production and cost reduction More sanitary Effective for water collection Main maintenance is just washing the membrane and it enables it more durable 7
average amount of water (ml h -1 m -2 ) Membrane 4600 4500 4400 4300 4255 4499 Hydrophilic differences of materials 4200 4100 4076 4000 3900 3800 Copper (t=0.5) Titanium (t=0.3) Fresh Green (t=0.3) material (thick[mm]) Titanium : hydrophobic Average amount of distilled water for each membrane Thermal conductivity Copper 398 W m -1 K -1 Titanium 21.9 W m -1 K -1 Fresh Green : hydrophilic Fresh Green as a membrane can distill water more than Copper 5.8 % and than Titanium 10.4 % 8
total amount of distilled water [ml h -1 ] Number of distillation stages Experiment from 2 to 4 stages in each input heat power 4000 3500 2 stages 3 stages 4 stages 3000 2500 2000 1500 area of a membrane = 0.19625 m 2 1000 500 0 300 400 500 600 700 800 900 input heat power [W] Average amount of water for each stage Increasing is 30 % from 2 to 3 stages 9.8 % from 3 to 4 stages 9
Solar power Heat pump can be used for heating and cooling Energy for Heat pump and Vacuum pump can be managed by solar energy <Energy consumption> Heat pump 25 W Vacuum pump 150 Wh / 5 hours = 30 W Solar energy of summer in Yokohama 1 kw m -2 Assuming Conversion efficiency 15 % (25 + 30) W / 150 W m -2 = 0.37m 2 solar panel is enough for this equipment 10
Conclusion Small and simple self-sustained distillation device has been developed Simple Small and light using just Plastic pipe for the equipment Unnecessary of frequent maintenance Long durability Decompression-boiling and Multi-effect principle Hydrophilic surface of membrane Can be managed by only Solar energy Can supply 3.5 kg fresh water per hour with this device 11