The turbine in question is a 1990 dual fuel steam injected MS7001EA 2035F machine running MARK IV controls. I posted about this same unit a few months ago when we came out of a major/CI outage to correct bucket rock and were unable to meet our stack NOx on nat gas and kero when the machine is above 88MW/IGV's above 80 degrees . We have since done numerous test and calibrated every meter on the machine. The only wild card we have left are the combustion liners in the machine which we had to buy in an emergency (the outage was a borescope inspection that became a major...). Raw NOx out of the machine is 24 ppm which is below the 25 guarantee and it stays around 24 from 83-93 MW. The issue is the %O2 in the exhaust rises from 14.5-15.2 which then increases our corrected stack NOx value above our air permit limit of 9ppm after the SCR. In addition to this we are seeing very high CPD when we attempt to get to baseload (~185-190 psig @ 27 degree CIT). The field service folks said they have seen liners cause this before when the dillusion holes are improperly sized, space or were coated over with TBC. Has anyone ever had an experience like this before and found it to be the liners?

Note: During the outage we did not pull the compressor casing but we did replace the fuel nozzles and tp's with our spares then bought a set of liners. We also overhauled all three rows of buckets and nozzles in the turbine section.

 

By no means am I turbine combustion expert, but I've had to troubleshoot emissions problems before on various units (boilers, GT, diesels).

I'm speaking in very general terms. To me it sounds like you have too much air going into the unit. The main driver of NOx is peak combustion temp. Having high CPD would mean needlessly hot air going into the combustor, right?

Do you measure CO? How does it look compared to past trends. CO or unburnt hydro carbons tend to go down as NOx goes up (and vice versa). Do you have water injection? Can you increase the amount of water injection slightly to see if that affects your NOx? That's just an experiment. If your O2 is higher than in the past, and CPD is high, maybe it's an IGV problem? (I'll have to defer to the more experienced in that regard).

What type of SCR? Is it ammonia injection or just a dry SCR? Don't want to rule out the SCR, but if this emission exceedence occurred overnight, it probably isn't catalyst related.