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IGV Control On
Why does inlet air temperature increase? Is it because IGV control is on?

My Unit is the GE Frame 9E. I noticed that once the load is low IBH valve is energized, in effect inlet air temperature is increased. Why is this so since my country is already a hot region? Has it got to do with IGV control on?

On our 7FA.05's, inlet bleed heating (IBH), through the use of recirculated compressor discharge airflow, is necessary when operating with reduced IGV angles. Inlet heating protects the compressor from stall by relieving the discharge pressure and by increasing the inlet air stream temperature. Other benefits include anti-icing protection
due to increased pressure drop across the IGVs. (From GEK)

Although we're in Colorado, we do see some 100f summer temps now and then. Build a few trends off the inlet air screen, and you'll likely see some shenanigans with the "relative humidity" as well.

I'm curious, do you use direct fog injection or evaporator coolers?



DLN combustion requires that when operating at "lower" loads (that is, lower fuel flow-rates) the air flow be reduced in order to maintain flame stability. The only way to control (reduce; limit) air flow on a GE-design heavy duty gas turbine is to use the IGVs. So, most GE-design heavy duty gas turbines (regardless of whether they use DLN-I or DLN-2.0 or -2.6 or -2.6e) use the IGVs to reduce the air flow into the combustors (by reducing the air flow into the axial compressor) below the minimum air flow limit of the axial compressor design (which was always 57 DGA for most GE-design heavy duty gas turbines--until they started incorporating aircraft-derivative axial compressor designs into newer heavy duty gas turbines)

One of the effects of using the IGVs to reduce air flow is that it causes the gas turbine exhaust temperature to increase. And, the turbine control system will limit the IGV closure to keep the exhaust temperature from exceeding the CPD- or CPR-biased exhaust temperature control reference (limit): TTRX.

Another of the effects of using the IGVs to reduce air flow is that it can cause axial compressor instability under certain operating conditions. So, GE borrowed some hardware from their Inlet Air Heating (Anti-icing) systems, modified it slightly, and use it to recirculate air from the axial compressor discharge (which can be as much as approximately 750 deg F) into the axial compressor inlet. They gave this system the unfortunate name Inlet Bleed Heating (the bleed term comes from an English-language colloquialism for extraction ("bleeding" off a portion of the flow for some other purpose)). This further reduces the air flow into the combustors AND it also increases the axial compressor inlet air temperature by a few degrees.

Increasing the axial compressor inlet air temperature reduces the density of the air entering the axial compressor, which is a good thing when you're trying to limit axial compressor instability. (It also serves to help limit ice formation on the IGVs when the ambient temperature is low and the ambient air is humid.) Recirculating air from the axial compressor discharge also serves to reduce the "back-pressure" on the axial compressor which helps to further protect the compressor.

So, because it is necessary to limit air flow into the combustors at low loads (low fuel flow-rates) in order to maintain flame stability and because the only way to do so is to use the IGVs to control air flow and because it is necessary to close the IGVs further than the original design of the axial compressors it was necessary to find a way to protect the axial compressor when the IGVs were closed below the original design minimum angle (air flow-rate). And, using the IGVs presents another issue in that they can't just be closed to any angle because that will cause the gas turbine exhaust temperature to get too high.

The fortunate thing is that all of this is designed into the turbine control system and actually works very well. The unfortunate thing is that when operating at lower loads when it's necessary to use the IGVs and Inlet Bleed Heating the turbine efficiency isn't as great as it could be--but there's no way around that. (.05 technology is helping with that, though.) IGV exhaust temperature control is almost always active by default and can't nor shouldn't be deactivated--because it's necessary for flame stability at lower loads (fuel flow-rates).

You will see axial compressor inlet air temperature increase above ambient temperature (if there is no other inlet air cooling, such as evaporative cooling or fogging or chillers, etc.) when IBH (Inlet Bleed Heating) is active--again, it's taking hot air (as much as approximately 750 deg F, and usually no more than 5% of air flow)) from the axial compressor discharge and recirculating it back to the axial compressor inlet--and there is no cooling of that air before it is put back into the inlet air flow downstream of the inlet air filters--it's only "cooled" by passage of inlet air over the IBH manifolds and by dilution from the inlet air flow mixing with the air as it leaves the IBH manifolds.

By itself, IGV exhaust temperature control would not increase the axial compressor inlet air temperature above ambient; it only causes the gas turbine exhaust temperature to increase when limiting the inlet air flow to the axial compressor.

Hope this helps!

GT at low load and the IGV at minimum angle, the IBH valve will open around 5% flow rate, that is the logic for the IBH, even at hot region. The effect of closing IGV and open IBH valve to increase the inlet air temperature by axial compressor discharge air through IBH, to allows the DLN-1 equipped GT to extend the premix operation in a wider operating range.