In 9FA (GE machine), can somebody tell me what are the impacts to the Gas Turbine when PTG1 (G1 Manifold Temperature) reduced or increased during baseload? Is there any temperature limits for G1 manifold?

Thanks

 

It's not clear if you're asking about some condition that's causing the gas manifold temperature to change (increase or decrease) or if you are trying to understand the effects of applying heating or cooling to affect a change to the manifold temperature (and hence the gas temperature inside the manifold).

It's normal for the temperatures of the gas manifolds to be lower than the gas fuel supply temperature. That's because of the pressure drop--and temperature drop--which occurs as the gases flow through control valves. It's not unusual to see moisture condensing on gas manifolds when the unit is running on unheated gas, especially if the ambient air being used to cool the turbine compartment is humid.

If you're talking about applying heating or cooling to a particular manifold in some kind of attempt to affect performance, you should really talk this over with the supplier of the turbine. I would suspect that heating or cooling one gas fuel manifold would not have the desired effect; in fact it might have the exact opposite effect to the one desired.

 

Dear CSA,

Thanks for the reply, May I know what can cause this PTG1 temperature to increase or reduce? Before Major Inspection, this PTG1 temperature is at 386'C, after MI the temperature drops to 338'C. I'm sure PTG1 temperature is always hotter than gas suppy temperature as gas temperature for my unit is just at 183'C. Will the machine perform better (produce more load) with higher PTG1 temperature? Any affect to the D5 or(G1) combustor can if the PTG1 temperature is lower than gas supply temperature?

regards
Fai

 

Fai,

You are using symbols and terms I am not familiar with at all. You said "gas manifold" which to me means the ring manifolds around the axial compressor case for the various gas fuel nozzles. The outlets of the control valves directly feed the ring manifolds and "pigtails" connect the ring manifolds to the fuel nozzles. That's what "gas manifold" means to me.

If you're using heated fuel, that's usually heated before it enters the fuel control valves (at least on all the units I've ever worked on with heated gas fuel). The Belfort Boys are always doing something different so without being able to see the P&IDs and the actual installation anyone's guess is as good as mine. And, they're always using different signal names, just because they can.

You might be referring to the gas fuel supply piping upstream of the control valves as a "manifold", and depending on the construction of the assembly it may very well qualify as a manifold. But, to most people familiar with GE-design heavy duty gas turbines a gas manifold is a piping assembly in the turbine compartment which surrounds the axial compressor (sometimes completely; sometimes not) which directs the output of a gas control valve to the fuel nozzles.

If you mean some manifold other than that, then we have a misunderstanding.

Are you absolutely certain that the RTD(s) or T/C(s) that's measuring the gas temperature is(are) inserted in the thermowell at exactly the same depth, and that all the wire connections were made correctly?

Again, I've never seen fuel come from the supply, through a control valve then to a heater then to the manifold(s) around the axial compressor case.

So, I take back everything I said. It's completely non-applicable.

Heated fuel (fuel that's heated before it enters the control valves) is said to improve performance because when the gas fuel is cold it has something of a quenching effect on the combustion gas temperature, so by heating it the gas fuel doesn't cool the combustion gas temperature as much. And, it therefore takes slightly less fuel to maintain the same combustion gas temperature.

And on the F-class machines, where the machines are running virtually on the limit of the materials in the hot gas path and nothing much can be done to increase performance via any methods there, GE has resorted to fractional percentage increases, like heated gas fuel, to try to squeeze a little more performance out of the machine. A fraction of a percent on a 200+ MW machine can be a lot of savings over a period of time. So, it's not an insignificant amount--over a period of time.

Some also feel that heated gas fuel can affect combustion dynamics, also. Sometimes it negatively affects dynamics; sometimes it positively affect dynamics.