Gaseous Fuels

Gaseous fuels are free from impurities such as ash, and are very easy to burn. Natural gas is the most common gaseous fuel burned in furnaces. The main constituents of natural gas are:

Methane (CH4): 80.1%

Ethane (C2H6): 14.7%

Nitrogen (N): 5.2%

Moisture: negligible

Sometimes, very small quantities of pentane and butane are also present.

Heating value of natural gas (High Heating Value): 1076 BTU/cu. ft. or 18,800 BTU per pound.

Combustion Air

In furnaces, air is used as the source for oxygen for combustion.

Air contains about 21% oxygen by volume. The other main component of air is nitrogen (about 78%). Only oxygen is used in the combustion process; nitrogen, on the other hand, serves no useful purpose. At high temperatures, nitrogen combines with oxygen and forms environmentally objectionable compounds (NOx).