Three quarters of the surface of our planet is covered with water, but unfortunately with salt water. Nevertheless, these inexhaustible reservoirs that are the oceans are dreaming: and if it was possible to transform this salt water into fresh water?
This would indeed resolve all the difficulties of water scarcity experienced by many countries, because many of them have access to the oceans, when they do not have a substantial maritime coastline.
In fact, desalinating seawater to make it consumable is possible. Many systems are even available today, many of which have reached the industrial stage. The two most commonly used processes are distillation and reverse osmosis. Their principle is simple.
Distillation consists in evaporating the sea water, either by using the heat of the sun's rays, or by heating it in a boiler. Only the water molecules escape, leaving in deposit the dissolved salts and all the other substances contained in sea water. It is then enough to condense the water vapor thus obtained to obtain a consumable fresh water.
Reverse osmosis requires treating the seawater beforehand by filtering and disinfecting it in order to rid it of suspended elements and the micro-organisms it contains. The process then consists in applying sufficient pressure to this salt water to pass it through a semi-permeable membrane: only the water molecules pass through the membrane, thus providing potable fresh water.
The major drawback of these systems is that they are very expensive. The installations are not very profitable:
the amounts of energy required for heating or compressing the water are too high, and the volumes of water produced are too low Indeed to transform one kg of liquid water into 1 kg of steam water at the same temperature it takes about 2250 kilojoules (if the change of state is at 100 ° C). The use of this drinking water production technique therefore remains very marginal. Only some countries with very low but sufficiently rich water resources, such as Kuwait and Saudi Arabia, use desalination of seawater to produce fresh water for human consumption. Be that as it may, this question, which is a major issue, has already been the subject of much research which is continuing.
So-called "multiple effects" evaporators have thus been developed which aimed to limit the energy expenditure of previous systems by using the heat produced during the condensation of water vapor to evaporate sea water. But, technically very complex, these systems required the presence of highly qualified personnel. However, an improvement has just been made to them which makes it possible to further reduce energy losses while gaining in simplicity. Inexpensive, modular, very simple to install and maintain, and capable of producing, at a lower energy cost, 20 to 30 liters of fresh water from 100 liters of seawater, these new systems should appeal to countries most interested in desalination than are many developing countries.
See n ° 377 of CNRS Info (Sept. 1999):
Desalinate seawater without salting the bill
source:
http://www.cnrs.fr/cw/dossiers/doseau/d ... alEau.html
