Dear all,
My plant is using GE 9FA single shaft machine (350MW) and recently we had our compressor offline water wash as the compressor blades has fouled.

After the offline washing done, we did our baseload test and found that the power output is not resume back to 350MW as per previous wash but only at 347MW (still lack of 3MW).

Parameters did not change obviously compare with previous wash cycle.

* TTRF remain the same = 1332'C, CPD = 14.4bar with ambient temperature=29'C, RH =65%, Exhaust Temp = 620'C, HP steam inlet pressure = 97 barg, IGV angle = 89' and inlet air filter dp = 40mmH20 flow gas consumption = 16.7kg/s

Anybody had experience this kind of weird phenomena and how you guys remedy it? Thanks for the help!

 

Dear Fai,
How long since your last combustion- or hot gas path inspection?

Did you borescope your axial compressor to ensure the compressor is as clean as after the previous wash?

What is the condition of the inlet air filters with respect to the previous wash? Are they the same inlet filters, or have they been changed since the previous wash?

Did you inspect the bellmouth and IGVs and R0 blades prior to the water wash and subsequent to the water wash to ensure they were as clean as possible? Some sites will manually wash the bellmouth, IGVs, and R0 blades if they are really dirty (expecially if they have an oily residue or a hard, caked-on coating), and then perform an off-line water wash.

Are you aware that in addition to compressor performance degradation that turbine nozzles and buckets can also experience performance degradation over time?

Are you certain that the rinse was completed as well as the previous wash? (This is where most sites fail as they use too much detergent and then don't rinse as much as they should because they run out of time or patience or both and fire the unit before it's clear of detergent.)

Did you use the same amount of detergent, or more, or less, than the previous wash? Was it the same manufacturer's product, or a different manufacturer's product?

Compared to the period prior to the previous wash, did the unit have more starts or fewer starts? More emergency trips or less emergency trips?

Are you certain that the steam is good quality steam and that there has been no carryover and that the steam turbine control valves are clean and the exhaust vacuum is exactly the same as before?

As a combustion turbine and it's hot gas path components age there will be some performance degradation. In my opinion F-class machines are particularly susceptible to "premature" performance degradation because they are designed to operate on the limit of the materials used for construction. If they are subjected to cyclic loading/unloading or "excessive" trips, this can cause hot gas path parts to degrade faster than would otherwise occur.

So, there could be lots of reasons why you failed to get back to 100% of rated. And most of them we can't know since we don't know how your machine is operated or the condition of the machine prior to each wash. During your next hot gas path or major inspection you will likely find some possible contributors to loss of performance other than compressor cleanliness.

 

Dear CSA,
We did our MI (Major Inspection on Jan 2010), that time we found cracks on our rotor (GT side) and change to the refurbish one, so whole GT and compressor blades has also changed that time.

We don't boroscope our compressor condition after offline wash but we just take the water sampling from the drain to determine whether the cleaning is sufficient or not (by color and "soapy" feeling)

We have change our inlet filter ( pre and fine) in Dec 2010 and the dP rising until now is still acceptable (total dP reading = 40mmH20)

Yes, We did manual wash for our bellmouth, IGV blades first before rolling our shaft to compressor offline wash. Found traces of lube oil on the inlet plenum floor ( this is suspected from acoustic filter which we had previous lube oil leaks from bearing no.1) but now the leaks from bearing no.1 has been rectified, still we experience the gt compressor isentropic efficiency degradation is too fast. (1% drops in just 20days)

Same amount (mixture of detergent and water) was used during performing the compressor offline wash. the detergent brand remain the same also

Our unit now was in cyclic operation (most of the days we will be instructed to shut down our machine at midnight and start back in early morning tomorrow). So machine now is on higher number of starts.

Exhaust vacuum (or condenser vacuum pressure is still good/remain the same) MW losses from ST is not so obvious than GT MW losses. I have monitor the ST HP, IP, LP efficiency and the degradation is not as bad as GT compressor efficiency.

So, CSA, there might be a possibility that the component like hot gas path and gas turbine bucket aging contributes to the losses of MW without giving any indication on the daily monitoring device? (such as exhaust temp, TTRF, fuel gas flow etc...) as you were saying,

any more reasons or experience you found out during your days in combine cycle plant on how to look for when you can't gain back the MW?

thanks for the sharing.

 

Dear CSA,

We did our MI (Major Inspection on Jan 2010), that time we found cracks on our rotor (GT side) and change to the refurbish one, so whole GT and compressor blades has also changed that time.

We don't boroscope our compressor condition after offline wash but we just take the water sampling from the drain to determine whether the cleaning is sufficient or not (by color and "soapy" feeling)

We have change our inlet filter (pre and fine) in Dec 2010 and the dP rising until now is still acceptable (total dP reading = 40mmH20)

Yes, We did manual wash for our bellmouth, IGV blades first before rolling our shaft to compressor offline wash. Found traces of lube oil on the inlet plenum floor (this is suspected from acoustic filter which we had previous lube oil leaks from bearing no.1). but now the leaks from bearing no.1 has been rectified, still we experience the gt compressor isentropic efficiency degradation is too fast. (1% drops in just 20 days)

Same amount (mixture of detergent and water) was used during performing the compressor offline wash. the detergent brand remain the same also

Our unit now was in cyclic operation (most of the days we will be instructed to shut down our machine at midnight and start back in early morning tomorrow). So machine now is on higher number of starts.

Exhaust vacuum (or condenser vacuum pressure is still good/remain the same) MW losses from ST is not so obvious than GT MW losses. I have monitor the ST HP, IP, LP efficiency and the degradation is not as bad as GT compressor efficiency.

So, CSA, there might be a possibility that the component like hot gas path and gas turbine bucket aging contributes to the losses of MW without giving any indication on the daily monitoring device? (such as exhaust temp, TTRF, fuel gas flow etc...) as you were saying,

any more reasons or experience you found out during your days in combine cycle plant on how to look for when you can't gain back the MW?

thanks for the sharing.

 

I had a similar problem with my GE Frame 6 and invented a new way to address the problem. Check out www.inside-out-cleaner.com and see what I did to fix it. I know this is a year after you posted but compressor fouling is a continuing problem in all gas turbine power plants not to mention it has a huge impact on the bottom line.

 

Thanks Jeff for the info. May I know your GT power output is back to your baseload value after you cleaned your compressor blades with butler engineering company? How many % did you regain back your GT power and Compressor efficiency is better than previous wash? It would better if I could have some data to convince my management here using butler services. Do email me [email protected] for my reference. Thanks in advance