The Oil Drum

61 comments on The needs and use of water for power, industrial plants and people

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Stuart Staniford on November 6, 2007 - 2:35pm

I know next to nothing about power station engineering. However, I'm curious to know whether it would be possible to use a working fluid with a higher boiling point than water, thus having the overall system hot enough to boil the cooling water and implement HO's idea?

Also, some loss of efficiency could be tolerated if the value of the desalinated water was high enough (and that of the sea salt - which would have to be mechanically removed somehow).

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TJ on November 6, 2007 - 2:53pm

Quick answer: yes, it's possible, but very expensive in capital and loss of efficiency.

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geek7 on November 6, 2007 - 5:32pm

In power engineering there are 'topping' cycles, and 'bottoming' cycles.

Topping cycles are designed to use a fluid that can be handled effectively at temperature for which H2O offers serious difficulties. One fluid that I have heard of being used in this application is Mercury. It boils at higher temperature. The vapor maintains reasonably high density at very high temperatures. The condenser can be used to warm the H2O on its way to the main boiler. Condensing the Mercury is technically very easy. Keeping the piping absolutely leak free probably requires different gasket materials than H2O. Topping cycles have some importance in coal fired plants and less importance in nuclear plants because it is often hard to keep the reactor from melting at typical temperatures of topping.

Bottoming cycles are used in solar boiling water power stations. The fluid is one that boils at a lower temperature than H2O. Various fluids that have application in refrigeration systems also are used here. Boiling the fluid is done in the steam condenser. Recondensing the vapor is done in yet another condenser which itself requires either
cool air or cool water to carry away the reject heat. Bottoming cycles allow the use of a higher density vapor at low temperatures. This allow the use of physically smaller turbines.

I a physicist. I don't know much detail about these systems. There a lot of tricky ideas that have been tried to improve the efficiency of power plants. Part of the design process is figuring out how to build plants that have good survival under the stress of handling the nasty fluids and vapors. I suggest that great caution be exercised discussing this technology. A lot has been left out of THIS presentation. BEWARE!

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Heading Out on November 6, 2007 - 7:11pm

Sorry, but when I first went to the csp site I found a neat little video that showed that an oil was used to carry the heat from the collectors to the power plant, at several hundred degrees. It doesn't appear to be there now, though there is one at Youtube on the subject. Pity since it showed off the project quite well, and I had thought I had referenced it.