Practical Hand Book of Gas, Oil and Steam Engines / Stationary, Marine, Traction; Gas Burners, Oil Burners, Etc.; Farm, Traction, Automobile, Locomotive; A simple, practical and comprehensive book on the construction, operation and repair of all kinds of engines. Dealing with the various parts in detail and the various types of engines and also the use of different kinds of fuel.

by John B. Rathbun

(9) Gasifying Coal.

Coal Gas or Illuminating Gas is generated by baking the coal in a closed retort or chamber out of contact with the air so that no combustion takes place either complete or incomplete. The hydrocarbon gases and tars are set free from the coal as permanent gases and are then piped to a gas holder after going through various purifying processes to remove the tars, oils, moisture and dust. The free or solid part of the coal remains in the retort in the form of coke, which is again burned for fuel.

Because of its high carbon content, coal gas burns with a yellowish-white flame and is extensively used for lighting purposes, hence the name illuminating gas. In many ways coal gas is an ideal fuel for power purposes as it has a high calorific value (650–750 B.T.U. per cubic ft.), is supplied by the illuminating company at practically a constant pressure, and is uniform in quality. Its only drawback is its comparatively high cost.

This gas is always obtained from the city service mains as its preparation is too expensive and complicated for the gas engine owner. Because of its cost, the use of coal gas is restricted to small engines.