Modeling Power Plant Water Use in a River Basin in Texas [On Location]


By: Sarah Widder

Went to an interesting talk today about modeling power plant water use in a river basin in Texas. The talk discussed the trade-offs between open-loop cooling, closed-loop cooling, and dry cooling. Open loop withdraws the most water, which can be an issue is water scarce regions, but consumes very little of that water.

Closed loop cooling, such as with a cooling tower decreases the water withdrawal, but increases the water consumption and concentrates pollutants because of the use of evaporative cooling in cooling towers. Dry cooling uses no cooling water, but has a significant decrease in energy efficiency because of the much lower heat capacity of air.

What is the proper trade-off between increased energy use & decreased water use in this context?

Does it change based on the power generation technology?

image: United States Army Corps of Engineers via Wikimedia Commons

Comments

Robert S's picture

Not a simple question (or set of questions). Like you mentioned, a lot would be dependent on the location - what kind of water and how much are available. The answer will vary greatly depending on your priorities (cost, energy, sensitive aquatic life in the area) and what questions you ask. Without a detailed analysis, I would think that closed loop cooling would be better with the possibility of dry cooling being effective depending on the technology and demand level. You mentioned concentration of pollutants in closed loop cooling - any consideration of these contaminates being washed into the environment untreated in open loop? Or the temperature effects on the body of water used for discharge?

Sarah WIdder's picture

Thanks for responding Robert! You are right, this is not a simple question. As to the questions of contamination from open loop cooling, the main concern is thermal pollution and it's effect on the local river ecosystem. The reason increased pollutant concentrations is more of a concern for closed loop cooling is because the contaminants that may be in the water will not evaporate during the cooling process and so will build up in the water as it cycles through. Although make-up water is added, the pollutants will continue to increase. This is not as much a problem for the environment as it is for the plant compntents, with may erode more quickly due to high salinity or other contaminent concentrations. To deal with this, power plants usually must purge some fraction of the water and supply a larger fraction of make-up water. This both leads to increased consumption from the water resource and a significant amount of "purge" water that is more polluted than in the once through process. If you have further questions, I encourage you to look up the speaker of this talk from and in Water-Energy-Climate Nexus session to follow up! Here is the link to her paper: http://aiche.confex.com/aiche/2010/webprogram/Pap...

jvasko's picture

Thanks for the posts Sarah and all the interaction here. For a while, the images were appearing twice but I fixed that.