I am a operator of Combined cycle power plant.

I wonder IGV Full Open is more effective or not during on-line water washing?

another question:

How could I calculate the compressor efficiency? (what is the formula?)
Is the formula different on the type of GT (Compressor)?

 

Hello, operator of a Combined cycle power plant,

On-line water washing is not as effective as off-line water washing. In fact, there comes a time after several on-line washes there is little or no benefit derived from performing an on-line wash, and at that point it's best to shut down and perform an off-line water wash.

On-line water washing is only effective on the first few stages of the axial compressor because at rated speed the water/detergent vaporizes as the air and moisture is heated by compression. Off-line water washing can only hope to clean the IGVs and first few stages of the axial compressor before the effectiveness is considerably reduced because of vaporization due to the heat of compression.

I would estimate it would be best to have the IGVs fully open when performing any water washing--off-line or on-line. However, I have no data to support that belief.

As for calculating compressor efficiency, you would need to be able to measure the air flow through the compressor and turbine, and that requires additional instrumentation that is not typically provided with many gas turbines. What most people do is try to gather data (compressor discharge pressure, compressor discharge temperature, power output) at similar loads and similar operating conditions. One of the best conditions is at Base Load, which by definition, means the IGVs are fully open. If the data can be gathered at approximately the same ambient temperature each day, that is even better. By plotting this information daily one can usually begin to see a drop-off in performance (power output; compressor discharge pressure) over time. After a water wash (on-line or off-line) one should see an increase in performance at the same operating condition (i.e., Base Load).

However, with on-line washing the performance increase achieved after each successive washing will decrease to near zero and at that point it's necessary to shut down and perform an off-line compressor wash/rinse to regain as much lost performance as possible.

Hope this helps!

 

thanks for all, CSA