CPD Step Decrease/Increase at Constant Conditions

In GE 9E frame gas turbine, there is repeating decrease in compressor CPD and then restores back to same level. considering GT Base load and constant (GT inlet, IGV, Frequency) conditions only

analysis include values of CPD and GT output, only taken for GT base-load operations at constant (GT inlet temperature, IGV angle and Frequency) and plotted for the period of two years.

* Significant fall in CPD and hence in GT output for six months, and then CPD restores and remains unaffected for 11 months. and then again a step-fall of similar magnitude.

* Step fall in CPD is about 0.25 and 4 MW in GT output.

* Same trend is repeated at all GT inlet temperature bands (18°C, 19°C, 20°C and so on).

* No work has been done on the compressor or its auxiliary systems such as cooling air, sealing air during the periods of CPD fall.

* No conclusive leakage from bleed valves was observed in results of Thermographs.

* Impact of water washing is for only few following days and does not contribute to prolonged CPD trend.

* CTD increases marginally with decrease in CPD at constant GT inlet temperature.

* What can be probable reasons for this trend?
* Recommendation to avoid this loss in CPD/GT output.
What have you done to check out the instrumentation and control system--including the tubing connected between the compressor discharge casing and the transmitter(s)?

You can check Mark V/VI, but that doesn't tell us if you have a Mark V or a Mark VI, or even a Mark VIe (and many, MANY people call a Mark VIe a Mark VI, and they are two different control systems which share a portion of a name--not very good marketing or branding...). So, when posting for help the more information you can provide in the original post the better the initial responses will usually be.

PC Load Letter


The main reason for fall in CDP is compressor fouling & mass flow reduction due to inlet air filter chocking. Again I am assuming that the instruments are working fine which they usually are. couple of quick questions here

A. Is you plant located near a heavy industrial area or near the sea shore?

B. You say it gradually increased back? do you see the reduction in CDP during summer months and increase back in CDP in winter months?

C. Its not very clear what happens before the CDP increases from your explanation do you do a offline waterwash when the CDP reduces?

D. Do you monitor the inlet air filter DP? does your plat have a history of filter choking up pretty quickly. Does the filter DP increase with the lowering of the CDP.

Anyway enough questions for now. Hope you write back to the community here.

bye for now.