[daf44]

Dear all,

I've made some calculations for gas consumption for a steam boiler, could you perhaps check these numbers?

I require 7,2 ton of steam (@ 6 bar g) per hour
6 bar g equals to a latent heat of evaporation of 2066 kJ/kg (steam tabels)
Total amount of energy required = 7200 * 2066 = 14875000 kJ/h or 14875,2 MJ/h
The lower heating value of natural gas is 31,65 MJ/m3 gas
Amount of gas needed (assuming 85% efficiency of the boiler) = (14875,2 / 31,65) / 85% = 552,9 m3 gas per hour

This sounds like a lot of gas to me, am I making wrong calculation/wrong assumption?

[Enthalpy]

Hi, the approximate amounts are correct.

You describe a 4MW boiler, it does need some fuel. Consuming 1kg gas for 17kg vapour is normal. It's nearly the ratio between 2MJ/kg vaporization and 34MJ/kg burning.

The heating value of your natural gas is in the lower portion of the spectrum. It depends on the location.

Your estimate forgets the heat needed to bring the liquid water to its boiling point.

At 4MW, most designers would thrive to condense the combustion water. 11% of 500m³/h pay quickly for a better design. Or do you consider that the condensation compensates the liquid preheating? If burning at 1atm, condensation would provide heat at 100°C only, not 160°C.