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

Question

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

MedicineEng (Industrial)

(OP)

5 Apr 19 07:14

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.

Assumptions:
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

georgeverghese (Chemical) · Answer 1 · 2019-04-05 09:24:32

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 ?

Come Join Us!

Posting Guidelines

Related Projects

Jobs

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