EFFECTIVE THERMAL VALUE OF LIGNITES Some excellent grades of lignite as purchased at the mine, at mine weights, contain as high as 4o per cent., by weight, of moisture (water). If a pound of such lignite is dried (that is, all of the moisture ex pelled), only 6—io of a pound of lignite will be left and available for use as a fuel.
A pound of this dried lignite may contain as high as 10,500 B. T. U., but since each pound as originally purchased at the mine contained only 6—io of a pound of lignite and 4-10 of a pound of water in saturation, it is evident that a pound of such lignite as purchased contained 6—io of io,5oo, or only 6,30o B. T. U.
This 6,30o B. T. U. value is reduced by the heat re quired to evaporate and superheat the moisture present in the lignite when fired in a boiler furnace. Assuming the lignite to contain when fired 25 per cent. of moisture (the difference between 25 per cent. per cent. having been evaporated in transit), then there will be required to evaporate and superheat 25-too of a pound of moisture, 312 B. T. U., which
deducted from 6,300 leaves 5,988 as the effective B. T. U. value of one pound of such lignite as pur chased, when used under boilers.
Little is generally known of these characteristics of lignite fuel, and many misleading reports of analyses and B. T. U. values of dried lignite are published, which make no comments on the difference between lignite as purchased, as fired under boilers, and as artificially dried for analytical purposes. We accord ingly deem it advisable to call the attention of our readers to these, in order that those comparing the efficiencies of lignite and oil fuel when burned under boilers can secure, from those mining and selling lignites, a correct statement of the actual heat value of a pound of such lignite as purchased at the mine, instead of basing their comparisons on B. T. U. values as published from time to time.