1002 - Method of saltwater solar distillation for obtaining freshwater and apparatus for making the same

Ing. Zátopek

Patent 305 255

The invention is a device that uses solar energy to turn sea water into drinking water by simulating the natural water cycle. The solution is unique in it‘s very high effectivity which  is achieved by limiting heat loss to a minimum. The top cover consists of two layers of glass. The space between the layers contains braces and is a vacuum chamber. That prevents heat loss by convection, which is in this case about 10 times lower than of a standard window. Just under the cover, a pool of water on a black solar energy absorption layer is warmed up. The resulting vapor is moved by a fan through a countercurrent heat exchanger located under the pool. The vapor saturated warm air transmits heat to the air moving in the opposing direction and as it cools, the ability to hold vapor is lost. The vapor condensates and leaves the system as the final product. The warmed up countercurrent air is reused and continues to the top pool to collect vapor and thus completing the cycle. The device therefore utilizes solar energy very effectively and only a small amount is lost through the top and bottom (the effectivity of the countercurrent heat exchanger can be up to 95%). This large amount of solar energy allows for all the state of matter changes needed to desalinate water.  The actual performance of the device is based on the amount of solar energy available. The avarage annual amount of solar energy recieved is around 250 W/m2 (W = J/s). About 2.5 MJ of energy is needed to vaporize a liter of water. This means a theoretical maximum performance of 9.3 l/m2/day. In reality it is lower due to glass not being perfectly transparent (11% loss) and the combined heat loss of the device. This device can be slightly altered into a version where the solar collector is placed in the focal point of several reflectors made from polished aluminum. The device can be applied in combination with a wind pump and greenhouse as a system to support desert agriculture. Fast-growing plants like bamboo or seaweed can be turned into charcoal and compost by pyrolysis and composting respectively. Mixing these materials with sand creates soil. Bamboo can also be used as a construction material for parts of the desalination device, the greenhouse structure, wind pumps, water reservoirs and piping used to distribute water for irrigation. A greenhouse lower the water requirement from 5-10 liters/m2/day to 1-2 liters/m2/day. A wind pump can be used to cycle cold sea water through piping inside the greenhouse to create condensation useful in returning the water from air back to the soil. This complete strategy has only minimal requirements for materials, and energy input that is obtained from renewable sources (Sun, wind). It leads to storing atmospheric carbon, which is bound by photosynthesis and turned into a stable form – charcoal, which is then user to fertilize, which is also an attractive aspect. The strategy is related to  the problems of climatic change which has many aspects, is geographically inconsistent and consequently lowers the global food production. Related is also the problem of environmental refugees. Ideally this strategy would also impact and lessen the agricultural pressure we today put on rainforests, one of the most valuable habitats on Earth.

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