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sspence (Electrical) (OP)
9 Dec 05 14:36
how do I calculate BTU of gas, with composition of CH4, C2H6, CO2, N2, etc.
macmet (Materials)
9 Dec 05 14:55
you have to have more information then that

sspence (Electrical) (OP)
9 Dec 05 15:17
was looking for how to calculate if I know individual gas compositions and properties of the gas.
in a simple formula, if I have 99.5% CH4, 0.5% CO, what would the btu level be?
Helpful Member!(3)  mbeychok (Chemical)
9 Dec 05 18:08

HV of gas = Sum [ (x1) (HV1) + (x2) (HV2) + (x3) (HV3) + ... ]

If your percentages are volume percents or mole percents (which are completely equivalent), then:

HVn = heating value of gas component n, in kJ/m3
x = (percentage/100) of gas component n

If your percentages are weight perecents, then:

HVn = heating value of gas component n, in kJ/kg
x = (percentage/100) of gas component n

If you would rather use USA units than metric units, then:

Use Btu/ft3 and Btu/lb instead of kJ/m3 and kJ/kg

Also, be consistent. If you want the higher (or gross) heating value of the gas, then use the higher (or gross)  heating value of each gas component. If you want the lower (or net) heating value of the gas, then use the lower (or net) heating value of each gas component.

Milton Beychok
(Visit me at

sspence (Electrical) (OP)
9 Dec 05 18:58
Much appreciated!
I was under a mis-impression that some inerts (like CO2) had a negative impact to the Btu (i.e. if CO2=10%, CH4=90%) and drive the BTU to much less than the calculated 910Btu/Lb.
mbeychok (Chemical)
9 Dec 05 19:16

Inerts such as carbon dioxide or nitrogen simply have a heating value of zero.  They should be included in the formula I gave you. Hence, they dilute the combustibles and do lower the heating value of the overall gas.

In other words, a gas containing 10% carbon dioxide and 90% methane will indeed have a lower overall heating value than a gas which is 100% methane. I guess you might consider that to be "negative impact", but that terminology really has no objective meaning.

Milton Beychok
(Visit me at

25362 (Chemical)
19 Dec 05 2:26

Sspence, don't confuse heating values with flame cooling effects which inert diluents may cause.

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