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  • Gas Turbine

    baja

    Member

    Updated: Oct 25, 2024
    Views: 1.1K
    I want to calculate the overall efficiency of a gas turbine coupled with generator in a co generation plant with HRSG (Heat Recovery Steam Boiler)...
    I need to make an performance evaluation..
    Need help with formulae... thanks..
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Replies

  • ISHAN TOPRE

    Member • Feb 18, 2011

    I think you want to calculate the "Over all" efficiency,right?
    So the block diagram basically consists of a compressor and a turbine which are connected by a shaft.The combustion chamber is bypassed an connected to gas turbine.
    So the cycle used in that turbine will actually define the process and ultimately affects its efficiency.
    Usually the cycle used is Brayton cycle,isn't it?
    So formula of efficiency for Brayton cycle(In our case gas turbine alone with no accessories)is:
    eff=1-(1/R)^[(y-1)/y]
    where eff=efficiency,
    R is pressure ratio,
    y is gamma i.e; Cp/Cv.
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  • A_87

    Member • Feb 23, 2011

    Hi
    I am looking to model a gas turbine that will be able to power an x amount of daily electricity load using Matlab.

    Using the basic Brayton cycle how can I work backwards i.e to input the daily load and thus be able to identify what specifications the most ideal gas turbine should have?
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  • ISHAN TOPRE

    Member • Feb 23, 2011

    I did't get your question.But one thing which I can tell for sure is that the most ideal conditions you can get is from a rankine cycle.You can try to improve your design by taking it near to ideal.
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  • A_87

    Member • Feb 23, 2011

    hi thanks for the reply

    basically i want to work with the Brayton since I think I will find it easier to get a real machine working on this (since I want to improve my model in the future for CHP).

    Do you know of any good sources that will give me the equations for pressure, temperature and flow rate (and any other variables needed) for each of the 4 stages of the cycle? That way I think I will be able to find the power delivered to the generator to then find how much electricity I can generate.
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  • ISHAN TOPRE

    Member • Feb 23, 2011

    See a Brayton cycle consists of following stages:
    1.Isentropic compression.


    2.Heating of compressed air.

    3.Air expands isentropically.

    4.Air is brought to initial condition.
    So from any reference book you can get these formulae.So you can easily calculate the work done in each case.
    If you don't then I will surely tell you those.😀
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  • baja

    Member • Feb 23, 2011

    @A 87: i am also trying to do the same.....

    but i am a newbie to matlab and also gas turbine...

    if u succeed please let me know how u did that....

    thank u
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  • TinaT

    Member • Feb 24, 2011

    Overall efficiency = energy out / energy in

    Energy out = power + steam
    Energy in = fuel to gas turbine

    You'll find the actual efficiency is a LOT different from the ideal Brayton cycle efficiency.
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  • baja

    Member • Feb 24, 2011

    coming around 30%... including combined cycle....
    because PLF ()Plant load factor is less than 10 percent....

    This is my problem...

    I am working in a sugar plant which is getting steam from HRSG (Heat Recovery Steam Boiler) where steam is produced from flue gas out of GT(Gas Turbine)

    We have 36MW gas power plant with gas consumption of 250000SCM (Standard Meter Cube)
    But we are allocated only 100000 SCM
    Which forces to reduce the load to home consumption of 2 MW
    Also not getting much money on power export ....

    Its all ok but 100000 SCM is not enough to run plant at 2 MW for 24 hours...
    is there any idea to reduce fuel consumption?????????

    We are ready to anything to reduce consumption...

    Thanks for all your views..
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  • TinaT

    Member • Feb 25, 2011

    I think you might be stuck.

    The only way to reduce absolute fuel consumtion is to lower the load on the gas turbine - but that makes the gas turbine very inefficient.

    The only other thing I can think of is to add an auxiliary / package boiler, so you could run the steam generator without the gas turbine. But, then you wouldn't get any power at all off the system.

    30 percent efficiency isn't all that bad for a small simple cycle gas turbine.

    If you went with an external boiler (significant capital investment) - would you be able to get some sugar cane waste / by-products to burn for fuel?? That would certainly help the economics work out.
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  • baja

    Member • Feb 25, 2011

    Sorry it was 20%.. on that 14% is steam energy.. 6% is in electrical energy..

    also no sugarcane here... only raw sugar refining...

    only source is fossil fuels...
    we r planning for external firing also
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  • TinaT

    Member • Feb 26, 2011

    Yikes. 6 percent on the electrical side, that is bad. The steam side should be better too. You might not be getting enough air flow with the heat to get good heat transfer (wrong residence times for the design of the HRSG). If you can increase the efficiency on the HRSG, you would be able to drop your fuel consumption down to get the same (or more) steam flow - if you had something other than that gas turbine burning the gas.

    I imagine running at that low of a load on the GT will impact maintenance, too. Things are probably running hotter than they would at base load, causing faster degradation of hot gas path parts.

    I'm not sure if anyone offers this, but what about a big fan (either Induced Dfraft on the stack or Forced Draft near the GT exhaust) to push ambient air through the HRSG, and add in some duct burners to the HRSG. I'm not a design engineer, so I don't know if that would work, but it might be less expensive than an external auxiliary boiler.

    The other thing I would look at is a completely separate steam / boiler package. Let the GT/HRSG sit idle unless power prices are good and you can run at higher loads.
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  • baja

    Member • Feb 27, 2011

    What u told is really valuable to me...
    i ll work out. but i guess fans wont work out...
    i ll do calc and inform u...
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