BOILER ACCESSORIES: FUEL There are various kinds of fuel used in steam production, location, cost, and the exigencies of the case being the deciding factors. Usually the kind of fuel is determined upon, and the boiler designed with that end in view. Sometimes, however, the fuel must be adapted to the boiler.
Coal.Coal is not only the most important fuel, but in many localities the only one available. It is of vegetable origin, being the long-decayed product of ancient forests. Frequently it occurs so mixed with earthy matter as to be of little value; but the supply of good coal is still abundant, and likely to be so for some time to come.
The most important elements in coal are hydrogen, producing 62,000 B. T. U. per pound, and carbon, producing 14,500 B. T. U. per pound. Although several coals may have the same total percentage of combustible material and ash, the heat values may not be the same, because heat value depends upon the amounts of hydrogen and carbon they contain. The heat value of fuels is determined by chemical analysis, or by calorimetric test, and varies for coal from different localities. The following table is compiled from several sources: Analysis and Heat Value of Various Kind of Coal % of ash Theoretical Pounds of Water B.T.U per lb Evaporated Per Pound (Theoretical)BTU Per LbPenn. Anthracite 3.49 14,199 14.70 Penn. Anthracite 2.90 14,221 14.72 Penn. Cannel 15.02 13,143 13.60 Penn. Connellsville 6.50 13,368 13.84 Penn. Semi-bituminous 10.70 13,155 13.62 Penn. Brown 9.50 12,324 12.75 Kentucky Caking 2.75 14,391 14.89 Kentucky Cannel 2.00 15,198 16.76 Kentucky Lignite 7.00 9,326 9.65 Indiana Caking 5.66 14,146 14.64 Indiana Cannel 6.00 13,097 13.56 Maryland Cumberland 13.88 12,226 12.65 Arkansas Lignite 5.00 9,215 9.54 Colorado Lignite 9.25 13,569 14.04 Texas Lignite 4.50 12,962 13.41 Washington Lignite 3.40 11,551 11.96 In practice, no fuel gives its theoretical evaporation value. On account of several losses that are inevitably incurred, heat is radiated from, and conducted away by, the boiler setting. The admission of
too much air into the furnace, either through the doors or through cracks in the setting, reduces the theoretical evaporation value. Improper firing causes considerable loss; and errors in design, construction, or setting reduce the efficiency.
The different kinds of coal are too numerous to be easily named, but in general they may be classified as anthracite or bituminous, commonly called hard or soft respectively, of which there are various subdivisions.
Anthracite.Anthracite coal consists almost entirely of carbon, but has a small amount of hydrocarbon. Good anthracite is lustrous, hard, flinty, but breaks up easily under high temperature. It burns with very little flame and smoke, and gives an intense heat. It does not ignite so readily as the softer varieties of coal; but once started, the fire requires less attention. It is an excellent fuel where the production of smoke is a decided objection.
Semi-Anthracite.This is a coal between pure anthracite and semi-bituminous. It is not so hard as anthracite, and burns more freely. It is not so compact as anthracite, and burns with a short flame, the anthracite having practically no flame.
Semi-Bituminous.This is the next softer grade of coal. It burns more freely than either anthracite or semi-anthracite, contains more volatile hydrocarbon, and is a valuable coal for steaming purposes.
Bituminous.Bituminous coal forms by far the larger portion of steam coal. It contains a large but varying amount of hyrocarbon or bituminous matter. Unless fired with care, it will produce a considerable amount of smoke and clinkers.
Dry Bituminous.This is a black coal with a resinous luster. It burns freely, and kindles with much less difficulty than the anthracites. It is hard, but is easily splintered. When burning, it gives a moderate amount of flame, with but little smoke, and does not cake. It is found chiefly in Maryland and Virginia.