This question's been bugging me from past 2 days. If you consider at typical gas turbine, which has a axial compressor and rotates at 3600 rpm., and at a particular IGV position., then will the compressor discharge pressure be independent of the changes to the turbine vane angle?

Other way of asking the same question is: How is the compressor discharge pressure dependent on the design changes made to the downstream like inside a combustion chamber or turbine section.

Thanks in advance.

 

No, compressor discharge pressure of an axial compressor will depend on the turbine vane angle and type of first stage nozzles and a lot more other things.

When a compressor is rotating in a constant speed and at a fixed IGV angle, if fuel is increased for increasing load, CPD also increases. It happens because of the increased fuel burning in the combustion chamber which produces more exh gas which restricts the flow of the compressor discharge downstream. The turbine nozzles, buckets etc are a kind of obstruction for the compressor discharge to flow downstream(as like an orifice in between a free flowing pipeline).

So look at the loading of your GT from full speed no load up to the load when IGV begins to open, you can see CPD is increasing (with constant speed and fixed IGV angle), because of more exh gas pressure being present in the combustion chamber for increased fuel burning there.

Hope this will help.

 

Thank you Mr. Ahsan for the guidance, but can you please discuss on what are the ‘Lot more things’ that can effect the CPD.
Can the HGP components (undergone in multiple RF cycle) could have more contribution to CPD ?

Thank You

 

Dear Sir,

I have read your explanation, It is very useful for me.

Basically I am a Electrical engineer But I know something that "Amount of flue gas entering into the turbine at part load is less as compare to the base load operation".

Amount of Air entering into the combustion chamber at part load is less as compare to full load.

While increase the GT load, Fuel flow also will increase to maintain the speed-droop(at part load FSR will concentrate to maintain the GT load, At base load it will maintain the Exhaust temperature of the gas turbine). At the same condition(GT load improvement) IGV will open to maintain the exhaust temperature of the Gas turbine.(This is at part load, In the full load it will not control any thing, but it will monitor the protection).

As per the compressor characteristics,

Quantity of air flow is proportional to speed, pressure is proportional to the square of the speed and power is proportional to the cube of speed.

So, At a constant speed(Synchronized to grid) amount of air flow compressed by the compressor is constant but it will depends on the opening of IGV.

Basically IGV is designed fro following control to regulate the quantity of air flow to the compressor.

IGV basically designed for 3 controls.

1. Compressor pressure control(Surge control)
2. turbine exhaust pressure control
3. Turbine exhaust temperature control.

First 2 conditions only for machine protections and 3rd one is operating protections.

While operating IGV to maintain the exhaust temperature, it will monitor protection also.

So, without IGV opening, compressor discharge pressure will not improve unless the machine is operating with very low Net calorific value fuel, Very less frequency and extremely high ambient conditions.

Normally in our DCS screen unable to find out the minute variation of IGV angle(2nd and 3rd digit), If you go for logic, you are able to find out 3rd digit variation also.

I hope it is useful for u,

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