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NATURAL GAS

The combustion of natural gas is a bit more complex. Although methane typically is the major constituent, natural gas often contains a number of other combustible organic materials, depending on the gas field from which it was obtained. In St. Louis, the local gas supplier delivers natural gas with the following major constituents:

• Methane, 94.8 percent by weight.

• Ethane, 2.5 percent by weight.

• Carbon dioxide, 1.4 percent by weight.

• Nitrogen, 0.6 percent by weight.

• Propane, 0.6 percent by weight.

• Trace hydrocarbons, 0.1 percent by weight.

The higher heating value is 1,032.2 Btu per cubic foot. The specific gravity is 0.5934.

As with coal, analysis of the combustion of natural gas begins with consideration of the reaction of carbon, hydrogen, and, if it is present, sulfur with oxygen:

• Methane combustion: CH₄ + 2 O₂ = CO₂ + 2 H₂O

• Ethane combustion: C₂H₆ + 3.5 O₂ = 2 CO₂ + 3 H₂O

• Propane combustion: C₃H₈ + 5 O₂ = 3 CO₂ + 4 H₂O

The carbon dioxide produced by each of the combustion reactions can be calculated for each pound of natural gas burned:

• Carbon dioxide produced from methane: 0.948 lb x (44 �÷ 16) = 2.607 lb

• Carbon dioxide produced from ethane: 0.025 lb x(88 �÷ 30) = 0.073 lb

• Carbon dioxide produced from propane: 0.006 lb x(132 �÷ 44) = 0.018 lb

• Carbon dioxide in original constituents: 0.014 lb

The total is 2.712 lb of carbon dioxide.