Compressor Discharge Temperature


Thread Starter


Hi all,

Need your expertise explanation out there for the above matter. I have a GE 9FA single shaft unit, during previous days, when compressor blades fouled, our CTDA or compressor discharge temperature will be at 426'C and CPD will be at 13.9barg during BASELOAD. while cleaned compressor blades (after offline wash) will shows around 398'C, CPD around 14.4barg. Lately this year, I observed that although compressor blades fouled - CPD at 14.0 barg and alarm backup temp curve active, the CTDA only at 410'C only. Can anyone experienced this problem before? Any related with air leakage from compressor?

Have you multiple sets of data relating increased compressor discharge temperature to fouled compressor conditions, or is this just a one-time occurrence?

I have never successfully related CDT to compressor fouling over time. It seems at times to be a good indicator, but it doesn't always seem to relate proportionally.

Was the data taken at the same inlet temperature?

Were the CDT T/Cs recently removed/replaced during a maintenance outage? If so, the different insertion depths could explain the differential.

Back-up temperature control active is not normally an indication of a fouled compressor. It's more an indication of a very tight "deadband" between the CPD-biased exhaust temperature control curve and the load-biased, back-up exhaust temperature control curve (I'm presuming the back-up exhaust temp control reference is load-biased since the unit most likely has DLN combustors). However, you stated the unit is single-shaft, and I take that to mean the gas turbine is directly connected to a steam turbine and they both directly connected to a generator. Sometimes, when the efficiency of the steam turbine is high and the gas turbine is low, I have seen the back-up exhaust temp active alarm but it's not always a function of a fouled compressor. It could be the condenser conditions or steam temperature or low extraction flow, lots of things, but not always fouled compressors.

Compressor leakage? There aren't too many ways for the compressor to "leak". Along the horizontal joint and vertical joints, but that's not very common and should be detectable. The compressor bleed valves of F-class units are known to leak from time to time, and infra-red heat guns have been successfully used to determine if they are leaking. But, that's about it. Internal seals might be a problem, but you have to take the unit apart to inspect those.

Again, if this is just a one-time observance, I suggest you make note and continue to gather data over the next few years. If it's a one-time difference compared to data from several years prior, then you might be looking at some other potential issues.
Thanks CSA for your reply.

Over the years since 2007, I have keep all the trending related to compressor fouling and it's efficiency drops due to this issue. But since last year somewhere in Oct 2010, the trending seems like mismatch with previous trending, when the compressor efficiency drops, normally the CPD will be lowered and the CTDA will be higher than cleaner compressor (Data is filtered with CTIM temperature between 29'C to 30'C). The CTDA transmitters (3 of them) just calibrated during July this year together with all the instruments related to performance monitoring tools. AFQ (total air flow) always reduced whenever compressor blades are fouled. I'm wondering whether the air leakage from the compressor might be problem or is there anything else that could lead to this problem? Anyway, I will check the compressor bleed valves to eliminate the valve passing possibilities. Can I check the Compressor bleed valves during Unit online?
It would be easiest to use an infrared heat gun to check the temperature of the piping on both sides of the bleed valve when the unit has been on line for some time. If the valve is fully closed the temperatures should be relatively low and equal. And if the valve is leaking it's pretty likely the temperatures are higher, especially on the upstream side, depending on how much the valve is leaking.

You still haven't said if the unit has recently undergone a maintenance outage.