A system to clean water from gas wells

Washington, Feb 6 (IANS) A new system developed by MIT engineers could clean water gushing out from natural wells relatively cheaply, while radically improving the functioning of desalination plants for the developing world.

Increased natural gas production is seen as an alternative to greenhouse gas emissions of coal plants.

But natural gas wells have problems: Large volumes of deep water, often heavily laden with salts and minerals, flow out along with the gas.

That so-called "produced water" must be disposed of, or cleaned.

The research is the work of a team including MIT postdoc Prakash Narayan, mechanical engineering professor John H. Lienhard V, and King Fahd University of Petroleum and Minerals (KFUPM), Saudi Arabia, report the International Journal of Heat and Mass Transfer, Applied Energy and the American Institute of Chemical Engineers' Journal.

The method is a variation of the standard distillation process, in which salty water is vaporized and then condenses on a cold surface; the salt separates out during evaporation.

But this process is energy-intensive - and therefore costly - because all the water must be heated to the boiling point, while the condensing surfaces must be kept cold, according to an MIT statement.

In the new process, water well below the boiling point is vaporized by direct contact with a carrier gas; the moist air is subsequently bubbled through cooler water where the purified vapour condenses.

Narayan focused on ways "to increase energy efficiency and thermal efficiency, and to reduce size and cost" for desalination plants.

Such facilities are a critical need in parts of the developing world - such as in southern India - that have limited fresh water but abundant seawater.

Conventional distillation plants have efficiencies of scale - the bigger they are, the more cost-effective - but for the MIT system, the optimum size is a plant that produces about 1,200 to 2,400 litres of clean water a day, about the capacity needed for a rural village.

Such plants can easily be made larger simply by adding more modules, Narayan said.

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