Fuel mas flowrate claculation 1

[dianad]

Hi, i have another question related to the fact of founding 2 different values, for the same thing, if we use 2 different methods.

PROBLEM: I want to know the fuel (Natural Gas) mass flowrate with the following known values:
Boiler power (P): 6500 kW
Boiler efficiency (E): 87,8%
Natural gas HHV: 64606 kJ/kg
Air flowrate (Q(Air)): 4265,4 kg/h
Air fuel ratio (AF): 18 kgAir/kgFuel

METHOD 1)
Burner input=P/E = 6500/0,878 = 7403,2 kW
Q(NaturalGas)=Burner input/HHV = 0,1146 kg/s = 412.5 kg/h

METHOD 2)
Q(Air)=AF*Q(NaturalGas) <=> Q(NaturalGas)=4265,4/18=237 kg/h

What is the correct method?

Thanks!

 

[Feric]

dianad:

Yes, your both assumptions are valid and correct -- there is nothing wrong with them.

Thanks,

G. Feric, PE

http://engware.i-dentity.com

 

[dianad]

Thank you all, specially Feric!!

Hope that this helps someone!