The =CALORIFIC VALUE= of a fuel may be calculated from its analysis, or may be determined by means of the =CALORIMETER= from a sample of the coal; the latter method is the most reliable. Table gives approximately the calorific values, and the proximate analysis of several representative coals from various sections of the country. The values given in the table are not exact, as the coal from each locality varies considerably in quality, but the figures will indicate what may be expected from each type of coal.
Connellsville, Pa., Coke has a calorific value of approximately 13,000 B.T.U.’s per pound, contains no volatile matter, and has an approximate content of 10% ash. Coke is a valuable fuel for the gas producer, but is rather expensive. It is clean and the absence of volatile matter reduces the “scrubbing” problem to a minimum.
Small coal such as buckwheat and pea contain a much higher percentage of moisture than given in the table, running from 5% to 10% higher than the given values.
Bituminous coal is high in hydrocarbons or volatiles which condense easily and form tar. If the tar is not removed or converted into a permanent gas, it will clog the passages of the producer and the engine and cause trouble.
The removal of the tar and ash from a gas is called =SCRUBBING=, and is performed by a device much resembling a filter. Anthracite coal and coke are low in volatiles or hydrocarbons, and therefore do not cause trouble with tar deposits.
A high percentage of volatile matter also causes trouble by the tar cementing the particles of fuel together. This interferes with the proper action of the producer.
Fuels having a high percentage of ash call for perfect filtering or “scrubbing” as such fuels will fill the gas passages with dust. Dust should be kept out of the engine at all costs, for the dust even in a quantity will cause wear in the cylinder.
Depending on the quality of the fuel, bituminous coal will produce about 4½ pounds of ammonia and 12 gallons of tar with about 5% of sulphur.
Anthracite coal will produce approximately six pounds of tar, and two pounds of ammonia with traces of sulphur.
Loose Anthracite coal requires approximately 40 cubic feet of storage space per ton of 2240 pounds and weighs about 56 pounds per cubic foot (market sizes).