Frame 7 rated at 65MW produces 66MW on base load after a major overhaul on the unit. The turbine buckets were completely changed. The unit produced 70MW on recommissioning. The exhaust temperature TX is 1032 deg F. The temperature reference temp is 1040 deg F. I would like to know why the unit does not try to produce more power, since its present exhaust temp is 1032.

 

Your post is unclear. First you seem to say a unit rated at 65 MW produced 66 MW after a major in which the turbine buckets were changed.

Then you seem to say that it produced 70 MW on recommissioning.

What is the "recommissioning"?

We have no idea what kind of turbine control system the unit has. If it has a Speedtronic Mark IV or Mark V or Mark VI, then the Exhaust Temperature Reference (TTRX) is the lower of either the primary exhaust temperature reference (TTRXP) which is usually CPD-biased exhaust temperature control or the secondary exhaust temperature reference (TTRXS) which is usually FSR- or MW-biased exhaust temperature control.

So, we need to understand:

1) What is the difference between the start-up of the unit after the major overhaul and the "recommissioning"?

2) If the turbine control system is one of the above, we need to know the values of the Primary- (TTRXP) and Secondary (TTRXS) Exhaust Temperature Control References, the value of the Exhaust Temperature Control Reference (TTRX), the value of FSR and the load (DW) when the unit appears to running below some exhaust temperature control reference. In other words, we need the data from operation while at Base Load for all of the above values when the unit has been operating at Base Load for at least 1 hour (to allow internal temperatures to stabilize).

If it turns out that the TTRXS is greater than TTRXP and TTRX is equal to TTRXS during Base Load operation, then we would need to know the values and their engineering units for the secondary exhaust temperature control curve. Without knowing what turbine control system you have it's impossible to tell you what Control Constant values might be the ones which would need to be provided for the analysis.

Power output is a function of many parameters: ambient temperature, compressor cleanliness, hot gas path part integrity, inlet filter cleanliness and efficiency, exhaust duct back pressure, etc. The proper calibration of the compressor discharge pressure sensor(s) is also critical, as is the calibration of the Gas Control Valve LVDTs.

Also, if something was done to actually greatly improve the power output of the unit (such as new design turbine buckets and shrouds and other new combustion (hot gas path) hardware) and a good compressor water wash and new inlet filters, etc., then it's possible the secondary exhaust temperature control curve might need to be recalculated. That should be done by the provider of the new hardware if it can be determined that all the instrumentation is working correctly and the unit is, in fact, producing more power more efficiently with the improved operating conditions and hardware.

But, again, the post is unclear and this is just speculation based on what *might* be the cause of a sudden increase in power output (which is suspect given the information provided). Most times, it's discovered that some instrumentation has not been properly calibrated, or if a new turbine control system has been installed (which could result in a "recommissioning") that some parameters have not been properly calculated or set. But, again, this is all speculation because we don't have a clear understanding of the sequence of events and what might have occurred.

We have tried to provide some possible causes for something like what was described in the original post, but that's about all we can do given the information provided.