Simple Cycle CT power plant water use

[chadl]

My company is working on the design of a fire protection system for a new development located near a 680 megawatt simple cycle power plant. The plant consists of 4 170 megawatt CT's, fueled by natural gas or fuel oil.

A flow test was conducted on the water system near the site to determine the available water supply. We are concerned that intermittent water use at the plant could effect the water supply in the area.

I have some experience with power plant design, but it's been a few years ago, and mainly with combined cycle type plants, which have a substantial water demand for cooling tower make up and other uses. A simple cycle plant would not seem to require that much. I do know that some plants utilize evaporative cooling on the intake air for the CT's, and if my (very) rough (but conservative) calculations are correct, that is limited to under 100 gpm for a plant this size.

Are their any other process in a plant like this that would require a significant amount of water (ie greater than a couple hundred gpm)?

Also, I understand this is a very vague questions, we do not know any details about this plant other than basic size and type (mainly pulled from internet press releases). I'm mainly trying to determine if it could be an issue, if so, we will try to get the water department to provide use with more detailed information regarding their water usage.

Thanks for any help

Chad

 

[ScottyUK]

The plant I work at is CCGT, not OCGT, but we use a fair bit of water in the auxiliary cooling system which provides coolant to the heat exchangers on the lube oil system and distillate fuel pump skids. At our site this is a hybrid system running a closed loop water circuit from the LO cooler's and fuel skids to a secondary heat exchanger which itself is cooled by water from the cooling tower. I'm not sure of the heat rejection from the system but it is significant. I guess a big fin-fan assembly could also carry out this duty, but that's a little out of my field or expertise.

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I don't suffer from insanity. I enjoy it...

 

[GaryDCarr]

Chad,
Most simple-cycle power plants will have very little water usage compared to a combined-cycle plant. Presumably the combustion turbine generators (CTG's) in the plant near your development have DLN (dry low NOx) combustors and don't have need for combustion water injection to control NOx.

As you pointed-out, they may have evaporative cooling on the CTG inlet. If they have evaporative cooling, the total water usage for evap cooling could be variable depending on ambient temperature (AT) and relative humdity (RH). As an example, for a 90 °F AT and 60% RH a total of approximately 60 GPM of water would be consumed. However, for the same AT but at 20% RH, the total water consumption for evaporative cooling of all four machines would be about 140 GPM. If the plant is located in a hot, dry region, it is quite likely that it will have evaporative cooling or fogging on the CTG inlets. However, if the plant is located in the midwest or the east, where the relative humidities are much higher, then evaporative cooling or fogging is not very effective and quite possibly the CTG's would not be equipped with inlet conditioning. Of course, any inlet conditioning would be seasonal and would typically only be used in hot weather.

The other possible water usage in the plant would be for auxiliary cooling for such things as lube oil cooling, gas compressor cooling (if the plant is equipped with compressors), etc. However, if the plant does not have a wet auxiliary cooling tower, then most likely, the auxiliary cooling is performed by dry fin-fan type coolers, which don't use any water.

If the power plant uses ground water for make-up water, the plant developer presumably would have performed draw-down tests as part of their fatal flaw analysis for plant siting prior to deciding to build the plant. It is unlikely that they would have sited a plant in a location where any water supply needed for their plant would be marginal.

 

[chadl]

Thanks for the reply guys,

The plant is actually located on the east coast of Florida (probably should have mentioned that), so evaporative cooling for inlet air seems unlikely, and would most likely not pull significant amounts of water. I do not see any evidence of cooling towers, so I’m thinking you are correct with the closed loop cooling on lube oil and other small cooling loads. According to people we talked to at the water department, (we questioned their reliability hence the post) there water usage is not very significant, so it looks like we should be fine.

Thanks again for all the replies