Turbine Power Generation Reduced


Thread Starter


Our Gas turbine model GE PG9171E power generation reduced from 125MW to 117-119 MW after cleaning the inlet air filters as they clogged during heavy fog. After cleaning, turbine reached the load of 123-125 MW, but after 2 days its load remain constantly in limit of 117-119 MW.

Is this power generation is linked with damaged air filters? If yes please explain.

Can you tell us what kind of filters you have, self cleaning (Donaldson Type) or standard triple element? Do you have CPD readings and Filter Diff. pressure readings before and after?

From experience, high humidity (fog, etc) will cause much bigger pressure drops across the filters hence less CPD and less performance. Your drops in performance look typically like wet filters.
I am glad you replied sir.

We have self cleaning (donaldson type) and we have CPD readings, and also we have DP readings before and after filters.

DP reading is normal but still power generation decreased.

Can a moisture carry over could be a cause?
Yes, high humidity can be the problem, especially on Donaldson filters, that's why I asked. What exactly was the CPD readings, was it the same at the reduced output or a bit less. I've seen humidity getting the filters wet and losing around 10% output until the filters dry out when the air gets dryer. The dirtier the filters are, the worse will be the problem. There is nothing much you can do about it. It is an unfortunate feature of self cleaning filters although they are still the best filter type.
thank you sir.... Its being quite informative.

One thing more, What would happen if gas pressure inside combustion chamber exceeds from its set limit? In our turbine GE PG9171E its around 15-16 bars.

Do you mean P3 pressure/GCV Discharge pressure? This is really demand related and will constantly change depending on load output and Air Inlet Temp. When you say the pressure increased, did the load increase?
There is continuous monitoring on that set value. And there is no load increase rather if it exceeds above its set value, we immediately call our gas supplier to reduce gas pressure.

But I did not know what sort of effect it would have on combustion either NOx emission affected, or im-mature combustion or is it related to the length of flame inside combustion chamber?
This is getting kind of scary....

What glenmorangie is saying is that load is proportional to fuel flow-rate. Increase the fuel flow-rate, and the load increases. Decrease the fuel flow-rate and the load decreases.

P3 is Gas Control Valve discharge pressure--the pressure of the gas in the manifold after it leaves the Gas Valve skid and before it enters the ring manifold(s) around the compressor casing, not Gas Fuel Supply Pressure. Usually, as P3 pressure increases that is because the gas fuel flow-rate is increasing. Gas Fuel Supply pressure fluctuations should be kept in check by the SRV (Stop-Ratio Valve) which is upstream of the Gas Control Valve(s)--unless they are very high or very low pressure excursions. The SRV should never be at 100% position (stroke) as that would indicate the Gas Fuel Supply Pressure was too low.

glenmorangie is also trying to get you to provide the before- and after CPD readings. Before the fog, after the filters were cleaned, and when the load dropped.

Base Load for a DLN-I combustor-equipped unit is not just a function of CPD--it's a function of CPR (Compressor Pressure Ratio), which includes ambient (barometric) pressure as well as CPR. Many units have experienced problems reaching Base Load because the 96AP transmitters were either not calibrated correctly, or, more commonly, the sensing port is somehow blocked. I've even found the manual isolation valve(s) in the wrong position at more than one site.

Have you checked the feedback from the 96AP transmitters (usually signal name AFPAP) to see if it has changed significantly since the fog event?

How about CPR--how has it changed since before the event?

Are you certain that Base Load is enabled and active? (Does the HMI indicate 'Exhaust Temperature Control'? Does TTXM equal TTRX?)

There was an interesting characterization used on an earlier post by the original poster: " ... its load remain constantly in <i><b>limit</i></b> of 117-119 MW."

What alarms (Process- and Diagnostic) are being annunciated when the load is "limited"? You know--those nuisance things that pop up on the Alarm Window screen from time to time that no one pays attention to until the turbine trips?

But, this line of questioning is just deteriorating--and badly. Talk of a limit of gas fuel pressure in the combustor.... Is this something new from GE-Belfort? Or, is this some imagined limit? And, how does that relate to Gas Fuel Supply pressure (sometimes called P1)? How much has "... gas pressure inside combustion chamber..." increased since before the fog event?

There have been a couple of posts on other Internet forums about fog causing problems with filters of gas turbines. Is this fog unusual for the area--or is it normal?

Hmmmm..... But, the best way to get help is to provide actionable data--provide the requested information (CPD, CPR and AFPAP--before the fog, after the filters were cleaned (which won't dry them, by the way! it just helps to remove dirt which can cause an even higher DP when the filter elements get wet from fog), and when the load dropped; the Process- and Diagnostic Alarms which are active and annunciated when the load is "limited"; and, if possible, what the "limit" of gas fuel pressure inside the combustor is.
Very comprehensive answer sir. Thanks for that.

The gas pressure issue was not linked with fog issue ( I wanted to clear that).

I was interested in getting information on "What will be the effect of high gas pressure inside combustion chamber." e.g. our gas normal pressure after GCV is 15 bar and somehow it gets to 19 bar (suppose) then what will be its affect on combustion.
Strange questions.

GE-design fuel nozzles are usually designed to be operated in a particular range of pressure, and operation outside that range can result in some problems.

But, as simple as possible: High gas pressure inside the combustor will result when the gas fuel flow-rate is high--and when the gas fuel flow-rate is high the load will be high. And, also when the gas fuel flow-rate is high the exhaust temperature will be high--and if the exhaust temperature gets too high, <b>the turbine will TRIP on exhaust overtemperature.</b>

Glad to be of help!

For me, it's very confusing when questions in a thread differ from the original topic/subject without some kind of clarification. It makes it appear (to me) that the questioner is implying some kind of relationship to the original topic/subject and, as in this case, I have difficulty in understanding if the questioner is implying some kind of relation or not.

Muhammad Asim Khan


We are facing similar issues with our Frame 9E i.e. low output and CDP with dirty inlet filters with high DP in foggy season. We suspected the same problem with the filters hence replaced our air inlet filters and did offline washing. This resulted in recovery of lost CDP and turbine output but the improvement lasted for only a couple of days and the compressor parameters and output has gone to the state prior to filter replacement and offline washing. Can you help us understand why would the turbine performance go down just after two days of operation while the recommended offline washing frequency is 4 months?
Muhammad Asim Khan,

Recommended off-line water wash frequencies are just that: recommendations. Site conditions <b>ALWAYS</b> determine actual off-line water wash frequencies. And, that can change depending on time of year and type of contaminants.

If the heavy fog condition continued after the filters were replaced it's most likely that the filter material swells when wet--and that can cause high differential and low power output. Unless the filters were replaced with filters which are less susceptible to swelling when wet, they're going to behave just like the filters they replaced, though if cleaner they will eventually dry (when the humidity goes down) and have a lower differential.

Filters don't remove all contaminants nor every particle size. The condition of the inlet duct and the way filters are installed when replaced can also allow unfiltered air to enter the axial compressor. Some operators have been appalled to stand inside the inlet filter house and walk through the inlet duct work and see all of the places where sunlight shines through welded seams, cracks, and betwee poorly installed filters. It surprises many people to learn that many seams in inlet filter houses are not fully welded; the manufacturer's assembly instructions only called for stitch welds to be used. Pick a bright sunny day once a year and inspect the inside of the duct; you may be very surprised.

The type of contaminants in the air can also be very difficult to remove. Cement dust, for example, can be a real problem--especially when there are leaks in the filters and/or inlet duct.

Hope this helps.