GE Gas turbine NOx & CO was fluctuated and opposite reading on off-peak load(@21 Mw)

Dear Sir,

I am engineer for power plant (GE PG6581B-Gas turbines), I found problem of exhaust emission (CEMs) 1 unit for NOx and CO relation of off-peak load time(@21Mw) are fluctuated and opposite (CO increase will NOx decrease and CO decrease will NOx increase) and On peak load time(@30 Mw) was normal, and exhaust temperature was normal same on-peak & off-peak load.

I would like for suggestion for fix it.

Best regards,
Can you give some more data, What DLN version are you using ? What TTRF are these results from and what TTRF transfer points do you have(Check Control spec) Yes, there is an interface between CO and NOx, that is what DLN Tuning sets.
Please read attached Doc. on DLN-1 (I'm sure that is what you are using, if DLN-2 let me know and I can send you another document)



WHEN did this problem start?

One presumes it has been working fine for some time and has just begun exhibiting these problems. If this just started after a recent maintenance outage, this would be helpful to know. If this started after ambient conditions have changed (warming; cooling; rains started; rains diminished; etc.) this would be helpful to know. If the source of the fuel has changed (for example, the unit burns LNG and the source of the LNG has recently changed), this would be helpful to know.

When was the last maintenance outage and what was it (Combustion Inspection; Hot Gas Path Inspection; Major Inspection)? What components were replaced at the last maintenance outage (fuel nozzles; combustion liners; turbine nozzles; etc.)?

Is the unit actually operated in Peak Load mode? Or by "peak" are you referring to high loads (such as when ambient temperatures are very high or some nearby process plant is running at high output

When was the last time the unit was tuned--DLN tuning?

Have the gas control valves recently been "calibrated"?

Has one or more of the gas control valves had its servo-valve changed?

Have the IGVs recently been worked and/or "calibrated"?

Does the unit have IBH (Inlet Bleed Heat)? If so, is it in operation when this change in emissions was experienced? If it was in operation, was it stable?

What Process and Diagnostic Alarms are present when this change in emissions was experienced?

Is this a change in the operating mode of the unit (that is, does it normally run consistently at Base Load and not very often at Part Load, or is this normal operations, switching to Part Load at some period(s) during the day)?

Does the unit exhaust into an HRSG ("boiler") or just to the atmosphere? If it exhausts into an HRSG, has the exhaust duct back-pressure changed recently?

When was the last off-line axial compressor water wash performed?

Actual emissions values (including O2 (oxygen)) would be very helpful.

The intent of the questions IS NOT to cause aggravation or extra work on your part. The intent of the questions is to try to understand the operating conditions of the machine and any recent changes. Almost always, when a problem like this is noticed on a unit which has been running fine for some time it can usually be traced to some recent outage work or parts replacement or "calibration." Or a change in fuels, or a change in operations from previous practices. Problems don't normally just appear on their own.

AND, many times it's found that there are alarms (Process and/or Diagnostic) which can point to some problems which aren't thought to be relevant but may well be.

Knowing more about the machine (like the type of turbine control system) and the conditions of operation are very helpful when trying to troubleshoot problems like this. This type of problem, while not typical, does happen from time to time--but it's almost always after some kind of change has been experienced. Or, the unit is close to a maintenance outage and the hot gas path parts are worn and need replacement. Or the axial compressor is dirty and needs to be cleaned. Or, there is an oil leak in the #1 turbine bearing and the oil is contaminating the compressor and the hot gas path (causing the formation of carbonized oil deposits). Or the fuel constituency has changed.

So, the more information you can provide the more suggestions we can offer--and we can eliminate some possibilities. Emissions problems can be caused by MANY things; have a read of the document glenmorangie attached to his post.

We look forward to getting more information from you!

The answer is simple. More and more people think that all they have to do is provide a snippet of information about a perceived problem and an experienced person will just intuitively know precisely what the answer is and can tell them exactly what to do to resolve the issue. They don't have to understand what they are working on because the information provided is sufficient to get a detailed answer to their dilemma.

Ask them for actionable data (not anecdotal data) and they disappear back where they came.

And, many people are looking for validation of their perceived cause for some issue. And, when they don't get the validation they want they just don't know what to do, and also disappear back from where they came.

The world is changing--actually, it has changed and continues to change. Remember what our buddy Jack Welch was so fond of saying: "The only constant is change."

Anyway, Happy New Year, sir! Be safe, and stay healthy!!!


A better year without a pandemic would be very welcome.

And greatly reduced inflation.

And a return to more normal supply chain and logistical issues.

And a gentler, more civil and graceful existence.

And a meaningful reduction in greenhouse gases.

And an increase in critical thinking.

But I don’t want much.