Sir,
In our one GT temperature spread increased by nearly 10 degree after CIBI done. It is also observed that for a particular load exhaust temperature reduced by nearly 30-35 Degree, providing GT is running on NG. For a particular instance following are exhaust temperatures
443,464,465,468,474,462,471,458,463,450,431,442,441

Kindly explain what may be possible reason

 

Soumitra,

This is not a controls-related issue. It is most likely the result of improper ordering of fuel nozzles, or improper reassembly of combustors or transition pieces. (Fuel nozzles (what you might be referring to as "burners"???) are usually flow-tested by the manufacturer/refurbisher, and each nozzle's flow-rate is documented. When installing a set of nozzles it is important to ensure the nozzle with the highest flow-rate and the nozzle with the lower flow-rate are NOT installed side-by-side--as it automatically creates a spread. This is just one reason for spread increases after a maintenance outage (of any type involving combustors and "burners" (fuel nozzles)). Again, improper reassembly of everything from cross-fire tubes to transition pieces can result in higher-than-anticipated spreads.

If the exhaust thermocouples were removed and reinstalled, and that was not done properly that can cause artificial spreads. If people working in the exhaust duct were "fingerizing" the exhaust thermocouple tips in the radiation shields that can cause artificial spreads.

But, this is most likely NOT a controls-related issue.