J
We just came out of a month long outage to repair the dreaded Frame 7EA bucket rock. All three rows of turbine buckets were repaired/recoated. the 2nd and 3rd stage turbine nozzles were repaired/recoated and we put in a new/used (2055F rated) 1st stage nozzle. We also put in refurbished fuel nozzles, TP's and liners that were in the machine a few years ago. The turbine is early 90's vintage, steam injected, 2035F firing temperature with MARK IV controls in combined cycle. Since coming out of the outage we have been unable to meet full load NOx emissions and have been reduced to 90% load to maintain emissions compliance. In addition to this our exhaust temperature is 20F higher than design for this ambient temperature and our compressor discharge pressure has jumped up (pressure ratio went from 11.3 to 12.9). All of the wheelspace spreads are within limits and steam injection is running at pre-outage levels. Has anyone experienced this before? How can the machine appear to be over-firing when it should be running on the MARK IV exhaust curves?