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HRSG Efficiency
How to calculate efficiency of HRSG?

Our HRSG receive exhaust flue gas from GT at 560 Deg C & exhaust temp from final stack after CPH is 170 Deg C. Steam is generated at a rate of 75 TPH at 37 KG/CM2 and 350 Deg. C. CPH inlet feed water temp is @ 45 Deg.C and outlet temp to deaerator is @ 80 ~ 85 Deg C. How to calculate efficiency of HRSG ?

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> Our HRSG receive exhaust flue gas from GT at 560 Deg C & exhaust temp from
> final stack after CPH is 170 Deg C. Steam is generated at a rate of 75 TPH
> at 37 KG/CM2 and 350 Deg. C. CPH inlet feed water temp is @ 45 Deg.C and outlet
> temp to deaerator is @ 80 ~ 85 Deg C. How to calculate efficiency of HRSG ?

Calculating the HRSG Efficiency

you have not written a important parameter required in the calculation, the exhaust flow rate. i will give the variables in the standard form and you can do the calculations. i am assuming a unit GT-HRSG configuration.

HRSG Efficiency = heat content of output steam + heat gain in CPH / Flue gas Heat energy


a. heat content of the output steam = steam flow (t/hr) * enthalpy of steam (kcal/kg) * 1000 (unit Kcal)
(steam enthalpy can be calculated form steam tables,
for your steam temp and pressure, 37kg/cm2 and 370 deg it works out to be 741kcal)

b. Heat gain in CPH = water flow (t/hr) (enthalpy of water at inlet (kcal/kg) - enthalpy of water at outlet (kcal/kg)) *1000 (unit kcal)

for water the enthalpy will be the same as its temp (approx)
so you can take it to be 45 and 85 respectively.

c. Flue gas heat energy = exhaust flow (t/hr) * Cp (kcal/deg kg) * inlet temp * 1000 (deg) (unit kcal)
(this will give you the efficiency inclusive of the stack losses)
= exhaust flow * Cp * (inlet temp - stack temp)
(this will give you the HRSG heat exchanger efficiency, ie non inclusive of the stack losses)


read a good text on basic thermodynamics to know more about efficiency calculations.

where I can get the information referring to the formula in order to seek more information. if you could help me please.

> where I can get the information referring to the formula in order to
> seek more information. if you could help me please.

er .. are you asking to suggest a few text books??
well i use the following for reference

Basic and applied thermodynamics - PK Nag
Thermal engineering - Bilani
Power plant engineering - PK Nag , Black and Vetach
BEE (beaureu of energy efficiency) exam text books.

i am no great shakes in mechanical , i am a electrical engineer , there might be better books but the above are simple , easy to read and understand.and yes they are from Indian authors.

if I meant books did you get the formula to get the efficiency of the HRSG, and try to use the formula but data is not clear to me why I would like to know where you got the formula because of heat exchangers that are not much. Thanks for your support

Can someone give me a ballpark estimate of what their efficiency is for the HRSG? I'm doing some calculations but getting roughly 11%. This doesn't seem right to me. Also if you have a better equation to use than what is already posted here that would be great.