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Posted by Boiler Guy on October 04, 2004 at 10:55:12:

In Reply to: Gas usage of boilers posted by Kerry on October 04, 2004 at 10:26:19:

The calculation is pretty easy:

((enthalpy of water/steam exiting boiler - enthalpy of water entering boiler) * mass flow rate of boiler) / (1 - efficiency)

Let's say you have a 10,000 lb/hr 150 psig saturated steam boiler with feedwater at 212 deg F and the boiler is 82.0% efficient

enthlpy 150 psig saturated steam = 1195 btu/lb

enthalpy feedwater at 212 deg F = 180 btu/lb

delta differential is 1195-180 or 1,015 btu/lb

Multiply 1,015 btu/lb by 10,000 lbs/hr gives 10,150,000 btu/hr NET to transfer inside of boiler

Divide that by 0.820 for fuel-to-steam efficiency provides a gross input of 12,378,000 btu/hr input required at full fire condition.

Basic calculations above will work for any type of boiler. Good luck with your studies.

Boiler Guy

: I'm doing a class project and would like to know if there's a way to figure out how much gas a natural gas boiler will use. I've been looking at specifications, but I can only find efficiencies and the energy output. For the project I know the temperature and pressure of the water coming in, and am looking for how much gas the boiler will use while operating. Any help is much appreciated. Thanks!