We have gas turbine of frame 7E. and MRK V is the controller.
Could you please tell me why the Exhaust temperature (TTXM) should not exceed 400 degree Celsius during unit warm-up period? On completion of warm-up why TTXM should not exceed 568 degree Celsius while the unit accelerates to 100% (360rev/min).

Note that I need this very urgent and very clear in the explanation.

 

If you have a Control Specification you can maybe refer to it. Simply during Warm-up there is a max. temp limit set during the warm-up period, once warm-up is released you are really using the maximum Exhaust temp. setting for the machine during the run up to make sure the temperature is not exceeded during Start-up. Start-up FSR control should normally be in control until FSNL, but, if for any reason the max. Temp. is reached, Temperature Control will take over and limit the FSR.

If you can give me an Email address, I can send you a few documents which should help.

 

568 deg C is called the isothermal limit and protects the gas turbine exhaust struts and diffuser from overheating and damage caused by excessive exhaust temperature.

If there is an actual limit during starting it was probably in response to some limit of a HRSG/boiler on the exhaust of the gas turbine.

 

Dear Sir;
this is my E-mail address [email protected]

 

why warm up period?

in this period hot gas path metals are cold and not acceptance high temp. so to avoid thermal stress need trip setting on 400 after warmup period metals temp. of thermal stress level will be beyond 400 c.

 

The original poster has never appropriately responded to indicate if there is an HRSG in the GT exhaust and/or if there is a limit in sequencing of 400 deg C during warm-up.

If there is an HRSG then it's possible the limit is to protect the HRSG components since air flow is very low during initial firing, warm-up and acceleration.

And precisely because any metal is "cold" (at ambient) is another reason for keeping the temperature spike during firing and warm-up to a minimum thereby reducing thermal stresses thereby extending the service life of the machine and the exhaust components.

I have heard people say there is an arbitrary limit of 400 deg C on the exhaust temp during firing and warm-up, and have actually seen it implemented in sequencing once. But, in ordrer for the GT to accelerate to rated speed it's necessary for the exhaust temperature to go, sometimes, as high as the isothermal limit--though that's not desirable. If the exhaust temp during acceleration reaches the isothermal limit that usually means the unit is being accelerated too quickly or that the torque assist from the starting means is lower than it should be.

And, as Bob Johnston has said, if the exh temp reaches the isothermal limit during acceleration then fuel will be limited to prevent the exh temp from increasing any further. Which will slow the acceleration rate and cause people to believe there is a problem of another sort, ignoring the real problem(s).

 

Hi Bob,

can you please send me TTXm related material?

Thanks
[email protected]