Into The Sea For Fresh Water

Press, Volume CVI, Issue 31143, 20 August 1966, Page 5

Into The Sea For Fresh Water

(Specially written for "The Press’’ by

TERRY McGOVERNE)

IAESALINATION—getting fresh water from the sea—is a U new word for a process which has been going on as long as human beings have been drinking water and probably thousands of years longer. But as a principle, desalination is becoming increasingly important as supplies of fresh water throughout the world diminish and fail to meet the requirement of industry and human consumption.

Every drop of fresh water on earth is, in fact, derived from the sea either by desalination in a natural cycle or by an artificial process.

In the natural cycle, water evaporates from the oceans and moves over the land in clouds falling as rain, hail, snow or sleet. Much of this soaks into the soil and when trapped in underground basins provides drinkable water. Some of it returns to the surface in springs which add up to produce rivers which in turn go back to the sea.

The artificial cycles of which there are dozens, range from the simple boiling and condensing process to the highly specialised gas cooled nuclear reactor and multi-stage flashdistillation processes. The significant of desalination today is the need to get more water to the right places than the natural processes provide. It must come at the right time in a controlled way and unaffected by the whims of the weather.

Getting fresh water to parched inland areas of the world may not be a great mechanical problem but keeping it there is. In Central Australia, huge Inland lakes lose as much as 600 million gallons of water a day in evaporation during the long hot summers. All the discussion now going on and the experiments being undertaken in many places aim at getting salt out of sea water or brackish water. Interest in the problem is greater now than ever because the population of the world is expanding so rapidly, industry is booming in the well-to-do and developing countries, and in most industrial plants enormous quantities of water are needed either for cooling or chemical processing.

There are some countries where there is no real water shortage, even though there is an uneven distribution. England and New Zealand are such countries. But in the United States and Australia there are shortages not only because of drought, but because agriculture and industry cannot expand for want of water. Obvious Source The need for more water which so many people take for granted and use in vast quantities every day, is already a serious problem in some places and will become one in others within the foreseeable future. We are, however, no longer content to leave it to nature and hope for the best. Man intends to be in control and as in so many other endeavours the United States has provided the greatest technological drive. The first and obvious way to get the salt out of sea water is to do what nature does only more quickly. The technique is to evaporate the pure water from the salt and then condense it. The most obvious way of doing this is to boil the sea water. The vapour or steam is then condensed.

This is the distillation process, and is the most widely used today from the China Seas to Persian Gulf and the West Indies. In this process, heat must be supplied whether from

oil, coal or any other source and the question arises whether the energy put in is being efficiently used. In essence anyone could desalinate sea water with a simple glass condenser and a flask but when the process is boosted to engineering size and the output measured in millions of gallons, all the difficulties appear. Salt is corrosive, pipes get covered in scale, the cost of energy is high. Difficulties such as these have led to notable developments in large-scale distillation. British Invention One of the most significant is the use of multi-flash distillation in which successive reductions of air pressure enable boiling to take place at a lower temperature. This has made a great difference to the economics of distillation and was invented by two British engineers in two concerns now combined to form Weir-Westgarth responsible for so many distillation plants throughout the world. Other devices in the use of tubular boilers whether vertical or horizontal have also come into the distillation picture.

Indeed, probably more engineering effort is being put into distillation technology than any other at present.

As a source of heat, nuclear fission comes into the picture. Nuclear power stations now can be cited in remote places near the sea and where there is no coal oil or gas. Nuclear Station As nuclear energy becomes competitive in price with that from older fuels so nuclear power stations using some of their heat for distillation becomes an attractive proposition. A full scale study of the possibilities of a large dual purpose nuclear station has already been done in Britain and the United States. The nuclear heat could also be used alone without the generation of power in places where such power is not needed. The distillation technique is still the main one for getting fresh water from the sea. It is hardly worth the trouble for brackish water which can be made pure by a number of physical processess the most noteworthy of which is known as reverse osmosis. Matter Of Cost The great question always is the cost and are the methods economic. These questions are not always valid for no-one in dire need would count the cost. Kuwait is exceedingly rich, but has no natural water except the sea. Nevertheless every system has to be paid for and considerable research

is being done in sorting out the claims made for various systems. Other Methods At the same time more fundamental research is going on into the physical chemistry of solutions and liquids so that it is not too late for some entirely new system of desalination to be invented. Outside the distillation process there are only three real contenders for extracting fresh water from salt. Of these, only electrodialysis is in commercial use. Where distillation takes fresh water from salt electrodialysis takes away the salt until the water is drinkable. The cost involved depends on the amount of salt in the water. For sea water which is three per cent salt, the cost is high but with brackish water, 0.6 per cent salt or less the process is very cheap. Electro-dialysis employs specially prepared membranes which hold the water while an electric current takes away the salt. Outlook In Israel The process was developed about 15 years ago, but suffered severe development troubles from which it has only recently emerged. Manufacturers of the plants fell out, but the British Government is now supporting further development aimed at simplifying the apparatus and reducing costs. The reverse osmosis process still in the pilot stages is yet regarded as unreliable. It too works on the membrane principle. When subjected to very high pressure the membrane allows water to pass but retains the salt In Israel, a process of partly freezing the salt water has been used successfully to get pure water from the ice, but the costs are high. However, in a country where water is nationalised and

strict rationing enforced, the cost is considered only in terms of its limiting influence on the economy as a whole. Israeli authorities look to artificial methods of obtaining fresh water as the key to national development. In the United States, a huge desalination programme is in operation. Like most countries, the United States has enough water for everyone, but much of it is in the wrong places. The authorities are tackling the problem on four fronts—by conservation, pollution control, redistribution and desalination. U.S. Experiments The Department of Interior set up the Office of Saline Water to experiment and develop new techniques in obtaining fresh water. In 1961, the O.S.W. set up a plant at Freeport, Texas, and by using the vertical tube falling-film process produced fresh water from brackish at a cost of about 10s a 1000 gallons. The office then set up a multi-flash distillation plant at San Diego which achieved fame in 1964 when it was dismantled and shipped to the American Base at Guantanamo Bay, Cuba, where it replaced the Cuban-controlled fresh-water supply. At Rosswell, New Mexico, is the largest vapour-compres-sion plant in the world which turns out 1,000.000 gallons a day of fresh water at a cost of about 12s a 1000 gallons. Plant For Kuwait The big industrial enterprise Westinghouse has won the huge contract for desalting water for Kuwait. The plant will have a capacity of 6,000,000 gallons a day. The United States Atomic Energy Commission is aiding desalination with the organic liquid-cooled reactor which will first be used to supply 150,000,000 gallons a day for

Los Angeles as well as 1800 megawatts of electricty. With the present world market for desalination plant doubling every two or three years, American industry is likely to be well placed to supply a considerable proportion of the world's requirements.