High Discharge Temperature of Gas Turbine Atomizing Air Compressor


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we are operating two frame 5 gas turbines having power output of 18MW (base output of each turbine). Few years back we removed the atomizing air compressor from both the turbines due to maintenance issues. Recently we restored the compressor on one of our turbine. This new AA compressor proposal and installation kit was procured from GE including engineering of piping. Piping modification only includes the orientation and modification of suction and discharge nozzles. After startup, the discharge temperature of AA compressor reached to 190 degree C. While this temperature used to be 75 degree C before the removal of old compressor. CPD inlet pressure and temperature are the same. The major difference in new and old AA compressor is the type of compressor. the old compressor was screw type, while new compressor is centrifugal compressor.

Please advise the reason of high discharge temperature of new AA compressor.

Have you asked GE this question? If so, what was their response?

Is there a cooler in the inlet air piping to the atomizing air compressor? If so, is there a temperature regulating valve to control the flow of water to the cooler?

I've not seen a screw-type AA compressor, but I've seen lots of Accessory Gear-driven centrifugal compressors. The centrifugal compressors manufactured by Atlas-Copco have a maximum inlet temperature of 300 deg F, and since the inlet air comes from the axial compressor discharge where the temp can be more than 500 deg F the AA compressor inlet air must be cooled to protect the compressor. It's very common for the temperature regulating valve of the cooler to be misadjusted or broken.

Further, the discharge temperature of the centrifugal compressor is not typically measured since the discharge goes into the combustors to atomize the liquid fuel (or to purge/coll the AA passages when running on gas fuel).

So, I'm not familiar with the need to measure AA compressor discharge temperature--only AA compressor inlet temperature since it must be limited to protect the centrifugal compressor.

I presume the discharge temperature of a screw-type AA compressor might have been monitored to detect problems with the screw-type compressor but I can't think of why excessive AA compressor discharge temperature would be a problem for fuel nozzles or for AA temperature since, again, the AA goes into the combustors where the temperature is very high from the flame anyway.

Without being able to see the P&iD for the original system and the new system--including the cooler, if present--and to know more about the new centrifugal compressor and its operating limits and -design it's not really possible to say much more. There are a couple of contributors to control.com that have probably seen screw-type AA compressors and may be able to add more to the discussion; hopefully they'll add the benefit of their knowledge and experience shortly.

Please write back to let us know what determine from discussing this with GE Andy/or from reviewing the AA manufacturer's instruction book. You might also try contacting the compressor manufacturer for assistance.

Hope this helps!