Use seas more to get drinking water
Updated: 2008-04-25 07:27
When there is an acute shortage of water both for drinking and for industry and agriculture, the technology of desalination which turns seawater or brackish water into fresh drinking water becomes very important.
Even drinking water is in short supply in urban areas. If one were to adopt a ration of 2.5 liters of drinking water per person, a 100,000 cu m plant would relieve 40 million people with a daily necessity at a capital cost of $3 per person.
China has a coast line of 32.647 km and there are more than 100 cities with an extreme scarcity of water. In 2006, the construction of the largest seawater desalination factory in Asia was started in Dagang district, Tianjin. When finished it could provide up to 150,000 tons per day.
At present the cost of running water is relatively low because of public subsidies - about 1.5 to 2 yuan per cu m. The price of desalinated water will be higher, around 4.5 to 8 yuan per cu m depending on the price of electricity.
The principle of desalination is based on Reverse Osmosis (RO) by which water diffuses across a semi-permeable membrane by applying high pressure with electric pumps. Water thus diffuses across the membrane and salt is left behind.
This process is electricity-intensive, in the range of 3-6 kwh for a cu m.
Nuclear desalination is the technology of the future, pushed by shortages of clean fresh water and high energy costs. Here we combine the generation of electricity with fresh water production.
Small and medium sized nuclear reactors are suitable for desalination, often with cogeneration of electricity using low-pressure steam from the turbine and hot sea water feed from the final cooling system for fresh water output.
The capacities of nuclear plants have been identified to be in the range of 80,000 - 100,000 cu m per day to 200,000 -500,000 cu m per day, suitable for medium sized cities.
The feasibility of integrated nuclear desalination plants has been proven in Kazakhstan, India, Japan and other countries. There are more then 50 new plants in the planning or feasibility stage today in the world.
According to IAEA, the cost of nuclear-generated water in China would be quite competitive with the costs of fossil fuel generated water - around 5.25 yuan per cu m. There is also another great advantage - nuclear power does not produce Green House Gases to pollute the atmosphere.
According to Helmut Kaiser Consultancy, Japan and China have the highest research and development spending in nuclear desalination reactors to lead the future markets, which are booming.
The author is a senior fellow of American Center for International Policy Studies amcips.org
(China Daily 04/25/2008 page9)
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