how do I calculate BTU of gas 3

[sspence]

how do I calculate BTU of gas, with composition of CH4, C2H6, CO2, N2, etc.

 

[macmet]

you have to have more information then that

?

 

[sspence]

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?

 

[mbeychok]

sspence:

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

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

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

If your percentages are weight perecents, then:

HV_n = 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 www.air-dispersion.com)
.

 

[sspence]

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]

sspence:

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 www.air-dispersion.com)
.

 

[25362]

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