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Natural gas consumption to produce 10m3 steam from room temperature water

Natural gas consumption to produce 10m3 steam from room temperature water

Natural gas consumption to produce 10m3 steam from room temperature water

Hi guys:
I confess that I'm not at ease with thermodynamic calculations regarding steam production and I need some help checking my calculations

I am trying to calculate how much natural gas a boiler would consume to produce 10m3 of 8 bar steam from room temperature water and I am reaching values that seem odd to me but still couldn't nail where is my mistake.

Water quantity: 10m3
Room Water temperature: 20C
Final Steam temperature: 170C
Water Sensible Heat: 1.2 kJ/Kg.C
Enthalpy liquid :720.9kJ/Kg
Enthalpy evaporation:2047 kJ/kg
Natural Gas Calorific value: 41,868.00 kJ/m3
Boiler efficiency: 85%

Total energy needed: 10,000*((150*1.2)+2047)=22,270,000.00kJ
Natural gas consumption:22,270,000.00/41,868*0.85=625.78 m3

I think that this is an absurd amount of natural gas and my gut feeling was expecting a much lower natural gas volume.
What am I doing wrong?

Thanks for the help

RE: Natural gas consumption to produce 10m3 steam from room temperature water

10m3 of saturated steam at 8barg has a specific volume of 0.235m3/kg, so this converts to 10/0.235 = 42.5kg of steam, so you'd start off with 42.5kg of liquid water, which translates to 42.5e-3m3, not 10m3. Else calc looks good.
The sensible heat to raise liq water from 20degC to 170degC should be based on a Cp value of 4.2kJ/kg/degC, not 1.2kJ/kg/degC - think you've quoted the Cp value of sat steam.
Nat gas calorific value seems high at 42MJ/sm3, usually it is approx 35MJ/sm3 (LHV), but maybe this is some rich nat gas ?

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