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Can anyone shed some light on base load limit temp calculations for Frame 6B gas turbines running with mark 4 speedtronic control systems? We have two identical machines both running with HRSGs and both running with TX control on. At the same loading (31MW) with IGVs at 84deg, one machine has reached the base load limit while the other still has 20deg C to go. The machine with some to go has an exhaust temp median (TTXM1) roughly 5 degrees higher than the one which has reached base load. The CPD for the machine with some to go is 800KPa and the one which has reached base load is up around 970KPa.
Going off previous experience, a lower CPD normally indicates a dirty compressr or fouling inlet filters and results in a decrease in base load, but this is not the case this time.
Doing some research I found the base temp exhaust limit calculation from CPD is as follows:
A=(CPD/1380)-0.5434
B=0.5298-(0.5298-(A/0.1613))
IF B<0 then C = 0.5298
IF B>0 then C = 0.5298-(A*0.1613)
Base load temp limit = (1138*C)-18
This seems to be following pretty closely to what is actually happening.
My question is, how and at what stage does the exhaust temperature bias start effecting the limit and are there any other factors which can come into it?
Going off previous experience, a lower CPD normally indicates a dirty compressr or fouling inlet filters and results in a decrease in base load, but this is not the case this time.
Doing some research I found the base temp exhaust limit calculation from CPD is as follows:
A=(CPD/1380)-0.5434
B=0.5298-(0.5298-(A/0.1613))
IF B<0 then C = 0.5298
IF B>0 then C = 0.5298-(A*0.1613)
Base load temp limit = (1138*C)-18
This seems to be following pretty closely to what is actually happening.
My question is, how and at what stage does the exhaust temperature bias start effecting the limit and are there any other factors which can come into it?