Heating Value of Gaseous Fuels—The method of computing calorific values from an ultimate analysis is particularly adapted to solid fuels, with the exceptions already noted. The heating value of gaseous fuels may be calculated by Dulong’s formula provided another term is added to provide for any carbon monoxide present. Such a method, however, involves the separating of the constituent gases into their elementary gases, which is oftentimes difficult and liable to simple arithmetical error. As the combustible portion of gaseous fuels is ordinarily composed of hydrogen, carbon [Pg 175] monoxide and certain hydrocarbons, a determination of the calorific value is much more readily obtained by a separation into their constituent gases and a computation of the calorific value from a table of such values of the constituents. [Table 37] gives the calorific value of the more common combustible gases, together with the theoretical amount of air required for their combustion.

[TABLE 37]
WEIGHT AND CALORIFIC VALUE OF VARIOUS GASES
AT 32 DEGREES FAHRENHEIT AND ATMOSPHERIC PRESSURE
WITH THEORETICAL AMOUNT OF AIR REQUIRED FOR COMBUSTION
GasSymbolCubic Feet of
Gas per Pound		B. t. u. per
Pound		B. t. u. per
Cubic Foot		Cubic Feet of
Air Required
per Pound of
Gas		Cubic Feet of
Air Required
Per Cubic Foot
of Gas
HydrogenH177.9062000 349428.25 2.41
Carbon MonoxideCO 2.81 4450 347 30.60 2.39
MethaneCH4 22.37235501053214.00 9.57
AcetyleneC2H2 13.79214651556164.8711.93
Olefiant GasC2H4 12.80214401675183.6014.33
EthaneC2H6 11.94222301862199.8816.74

In applying [this table], as gas analyses may be reported either by weight or volume, there is given in [Table 33][36] a method of changing from volumetric analysis to analysis by weight.

Examples:

1st. Assume a blast furnace gas, the analysis of which in percentages by weight is, oxygen = 2.7, carbon monoxide = 19.5, carbon dioxide = 18.7, nitrogen = 59.1. Here the only combustible gas is the carbon monoxide, and the heat value will be,

0.195 × 4450 = 867.75 B. t. u. per pound.

The net volume of air required to burn one pound of this gas will be,

0.195 × 30.6 = 5.967 cubic feet.

2nd. Assume a natural gas, the analysis of which in percentages by volume is oxygen = 0.40, carbon monoxide = 0.95, carbon dioxide = 0.34, olefiant gas (C2H4) = 0.66, ethane (C2H6) = 3.55, marsh gas (CH4) = 72.15 and hydrogen = 21.95. All but the oxygen and the carbon dioxide are combustibles, and the heat per cubic foot will be,

From CO = 0.0095 × 347 = 3.30
C2H4 = 0.0066 × 1675 = 11.05
C2H6 = 0.0355 × 1862 = 66.10
CH4 = 0.7215 × 1050 = 757.58
H = 0.2195 × 349 = 76.61
–––––––––––
B. t. u. per cubic foot = 914.64