Steam tubine output on Combined cycle 2

[npower0073]

Dear all. On site we have a combined cycle power plant with gas turbine and steam turbine, in multiple shaft. I try to find a way to assess the output of Steam Turbine in relation with ambient temperature and condenser opearting status. What physical values should i check and how can i assess the operation of the cooling towers operation in order then to assess the condenser operation and the steam turbine output?

 

[rmw]

I assume that you have all the plant documentation which contains the operating data and curves for the major components that you mention.

If you do, check the cooling tower curves for the CW temperature that is to be expected at the ambient in question. If the CW is not as predicted, do the necessary cooling tower checks to get the tower in spec (or determine that it is not performing).

Next, with a known CW temperature, check your condenser curves for its performance at those conditions. The CW temperature rise is important, as is the approach temperature (condensate saturated temperature vs. CW outlet temperature.) These all give you clues as to the condenser's operation and condition and then give you a predicted back pressure for the CW conditions.

Then use your turbine heat balances to determine what your predicted performance should be with the back pressure that you have regardless if it is on spec of off spec due to the cooling tower or condenser variations. (It could be better.)

If you are an engineer, it should be a fun trip if you remember your thermo (most of the electricals that I ever knew hated thermo). If you have ME's or CHE's on site, ask for their help. If you aren't an engineer don't start because it will be way over your head.

rmw

 

[davefitz]

Most design outfits will use a cycle simulation program to estiimate the heat correction factors as a function of ambient temp. Howeer, there are a few practical effects that are ususally ignored by designers, including:

a) air inleakage to condenser and incomplete rremoval of noncondensibles leads to a higher than expected condenser backpressure

b)some cooling tower vendors had severely shortchanged the clients by providing 20-30% less tower fill than actually required for correct long term perfromance of the cycle. They got away with it because most specs for condenser specify the use of a 80% cleanliness factor, and the initial testing of the plant during the first month of service was with a 100% actual cleanliness, so the extra 20% of condenser tube surface area would offset the loss of 20% of cooling tower fill area. After the SS condenser tubes eventaully fouled, the long term cycle performance would suffer. The root cause is usually and undersized cooling tower, and adding some more fill and changing the fan blades is not always enough to correct it.

 

[EdStainless]

The more that you know the better. You should have a condenser data sheet and the data from the original plant trials as a base line.
At minimum you will need to have the design and actual data for all of the steam side and any air side info. that you have.

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Still trying to help you stop corrosion.
formerly Trent Tube, now Plymouth Tube
eblessman@plymouth.com
or edstainless@earthlink.net

 

[EdStainless]

OK, I posted too fast. Since this is water cooled you will need the flow (actual) and inlet temp and outlet temp. This is exact. We will then make sure that the steam side info matches, and then we will tackle the cooling tower capacity.

= = = = = = = = = = = = = = = = = = = =
Still trying to help you stop corrosion.
formerly Trent Tube, now Plymouth Tube
eblessman@plymouth.com
or edstainless@earthlink.net