how can we keep the firing temperature constant on increasing or decreasing of fuel flow. As compressor discharge pressure increases the fuel needed also increases. can we maintain the same firing temperature when CPD decreases and fuel flow decreases

 

surya,

What are you trying to understand or wanting to do?

What operating condition are you talking about: Part Load or Base Load?

Firing temperature is <b>NOT</b> the same as exhaust temperature.

At Part Load "firing" temperature isn't important. I'm referring to the definition of firing temperature that refers to the temperature of the combustion gases leaving the first stage turbine nozzle.

Because *by definition* at Part Load the firing temperature is less than rated (which is "maximum").

At Part Load as fuel flow increases, firing temperature and exhaust temperature increase. As fuel flow decreases, firing temperature and exhaust temperature decrease. (Presuming the unit is not operating on IGV Exhaust Temperature Control while at Part Load.)

You stated that the fuel needs to increase as the CPD increases. That's NOT true while running on Part Load. As fuel flow increases, CPD increases while on Part Load. As fuel flow decreases while on Part Load, CPD will decrease. But, CPD <b>does not dictate fuel</b> flow while on Part Load, <b>CPD follows fuel flow</b> while on Part Load (regardless of whether the unit is operating on IGV Exhaust Temperature Control or not).

At Base Load, as compressor discharge pressure changes with ambient and machine conditions, fuel is adjusted to maintain <b>constant firing temperature</b> which, by definition, is Base Load: constant firing temperature.

When at Base Load, as CPD increases fuel flow increases. But, that's to maintain a constant <b>firing</b> temperature (NOT exhaust temperature!) while operating at optimum output, which is defined to be Base Load. <b>As CPD increases, more fuel can be burned *for the SAME (constant) firing temperature* when operating at Base Load</b>.

When a unit is operating at Base Load and CPD decreases, then fuel flow must decrease *for the SAME (constant) firing temperature (NOT exhaust temperature!).

CPD increases and decreases while operating at Base Load based on a lot of parameters, the biggest one being ambient temperature. As ambient temperature changes during the day, CPD will change and Base Load will vary. So, will exhaust temperature. BUT, <b>firing temperature will remain constant while operating at Base Load!</b>.

You mention combustion dynamics in the title of your post. Combustion dynamics are usually only a problem for units with DLN combustors and other things are adjusted to mitigate combustion dynamics, not just the over-all fuel flow (the fuel flow-rates to the various nozzles and combustion zones).

So, I'm <b>VERY</b> confused by this post and what is is you're trying to understand.

If by "firing temperature" you mean exhaust temperature, then at Part Load conditions many machines have something called IGV Exhaust Temperature Control which can be used to increase exhaust temperature at Part Load to help with maximizing steam production when the turbine is exhausting into a "boiler" (heat recovery steam generator or waste heat recovery boiler).

So, please be clear about your terms and what it is you're trying to understand or accomplish.