New life of known technologies for desalination of sea water.The design of the classic solar still basin has exhausted its usefulness. Let's nam...
Published on by Arkady Levshin, Director
The design of the classic solar still basin has exhausted its usefulness. Let's name the main reasons:
1. Relatively low process temperature – below 70°C;
2. The evaporator and condenser are in the same volume, and the temperature gradient does not exceed 15°C;
3. Sedentary air interferes with the evaporation of water;
4. The flat interface between the media has a small area and reduces the intensity of water evaporation;
Therefore, from 1 m2 of such a pool you get approximately 1.5-2 liters of fresh water for the whole day. All the numerous attempts to improve the design over the past 30 years (porous objects thrown into the water, pools with cascades, fans inside, additional screens, additional solar water heaters placed outside the pool) make it possible to increase productivity to 3.5-4 liters per day from 1m2, but this is the limit. In addition, all this increases the cost of the device, and pumps and fans require electricity.
Therefore, the basin design cannot be used for emergency desalination of water during humanitarian crises (Haiti, Somalia etc.). In general, the world market of simple inexpensive and compact solar desalination devices for 10-15 l/day of fresh water without the use of electricity (even in the form of photovoltaic panels) and cheaper than $90 seems completely unfilled.
Let's look again at the design requirements for an autonomous and cheap solar seawater desalination plant:
- the evaporator and condenser should be as compact, cheap and separated from each other as possible;
- evaporation should be carried out in the volume of air in the smallest drops possible;
- spraying water without nozzles and pumps;
- heating (cooling) must be carried out quickly and efficiently;
- the temperature of the evaporation process should approach 95°C on a bright sunny day;
- salt should not remain in the evaporator;
- no electricity.
All these requirements are met by the evaporation of sea water in a highly turbulent flow of hot air with subsequent condensation of steam according to patent RU 2743173 C1. The desalination module is a corrugated tube made of thin stainless steel, half of which is heated by the sun, and the other half is cooled by the breeze. Salt deposits are eliminated with a simple and elegant technique. The air pump can be powered by wind and sea waves. The author of the patent used for full-scale testing a simple wind engine with a high-speed hollow propeller, which acts as a centrifugal air pump.
Laboratory tests showed a good result - 2 l/hour of fresh water. In terms of a day (10.00 – 16.00) approximately 12 liters.
The cost of a desalinator and a wave air pump of the simplest option does not exceed $50-60.
The size of the packaged desalination module with a simple solar concentrator is 120x100x7 cm, gross weight is 8-10 kg. Service life 10 years. Does not require maintenance. The air pump is packaged separately.
I am also pleased to inform you that a patent application is being prepared for another interesting autonomous compact desalination plant based on RO. This desalination machine does not require sun, electricity or high-pressure pumps, as it is based on the water hammer effect. Several stages (0.2 kg/cm2 - 4 kg/cm2, 4 kg/cm2 - 16 kg/cm2, 16 kg/cm2 - 59 kg/cm2) provide the necessary pressure for desalination of PO. An ingenious solution for stable operation of impact valves. You can use plastic tubes. The initial height of sea water accumulation at a height of 1-2 m is provided by a wind pump/wave pump/tide.
The pressure booster will not cost more than $80 and can be packaged in a box 100x100x10 cm.
If the task is to desalinate brackish water, you can get by with 2 stages and provide fresh water not only to places of humanitarian crises, but also to half of Africa and southern Asia.
Patents, know-how and research belong to LEK wind-water, which has a branch in Italy.
For contacts: levshin@lekw-w.com. We are ready to sell patents and know-how.