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CSP and THE desalination of sea water

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Click the picture for a larger image showing how waste heat from CSP can be used for the desalination of sea water. The diagram also shows how melted salt may be used to store solar heat so that electricity generation may continue through the night.

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One of the most interesting aspects of CSP is that the waste heat from the turbines may be used for the desalination of sea water. This is shown schematically in the diagram on the right.

The basic idea is that spent steam from the turbines is used to raise the temperature of sea water (via a heat exchanger) causing it evaporate. The water vapour that comes off is then condensed as fresh water. This is normally done in a succession of stages ("multi-effect distillation") to improve overall efficiency. A vacuum is applied at all stages to promote evaporation.

A neat feature of this process is that it also has the effect of cooling the spent steam, something that is in any case needed in all thermal power stations. Without the cooling effect of the desalination process, the spent steam would normally be cooled by means of a cooling tower that sheds the waste heat into the atmosphere—a scandalous waste of energy that has been a feature of traditional power stations for many years, and is still widespread.

A team of researchers at the German Aerospace Center has produced a study called 'AQUA-CSP' (which may be downloaded from our Reports page) about using waste heat from CSP plants for the desalination of sea water.

Clouds near the coast

The AQUA-CSP report from the DLR confirms that coastal regions can be cloudy but suggests that, in that case, CSP plants may be located away from the cloudy regions and may supply power for desalination plants on the coast. This means that it is not possible to take advantage of waste heat from power generation for the desalination of sea water. But in coastal regions that are not too cloudy, that option is still open.

Disposal of brine

One potential problem with any process for the desalination of sea water is what to do with the brine which is created as a by-product. Clearly, the brine should be disposed of in a safe manner to minimise any possible damage to the environment. This issue is discussed in the AQUA-CSP report.

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Last updated: 2012-05-14 (ISO 8601)