At present immense quantities of fuel are left at the mines, in the form of culm and slack, which, in quality, are much below the average output. Such fuel is considered of little or no value, chiefly because there is no apparatus in general use which can burn it to good advantage. The heat value of this fuel is often from 50 to 75% of that of the fuel marketed, and if not utilized, represents an
immense waste of natural resources. Large quantities of low-grade fuel are also left in the mines, simply because present conditions do not warrant its extraction, and it is left in such a way that it will be very difficult, if not practically impossible, for future generations to take out such fuel when it will be at a premium. Again, there are large deposits of low-grade coal in regions far remote from the sources of the present fuel supply, but where its successful and economic utilization would be a boon to the community and a material advantage to the country at large. The great importance of the successful utilization of low-grade fuel is obvious. Until within very recent years little had been accomplished along these lines, and there was little hope of ever being able to use these fuels successfully.
The development of the gas producer for the utilization of ordinary fuels,[19] however, indicates that the successful utilization of practically all low-grade fuel is well within the range of possibility. It is notable that, although all producer-gas tests at the Government testing stations, at St. Louis and Norfolk, were made in a type of producer[20] designed primarily for a good grade of anthracite coal, the fuels tested included a wide range of bituminous coals and lignites, and even peat and bone coal, and that, in nearly every test, little serious difficulty was encountered in maintaining satisfactory operating conditions.[21] It is interesting to note that in one test, a bone coal containing more than 45% of ash was easily handled in the producer, and that practically full load was maintained for the regulation test period of 50 hours.[22]
It is not expected that all the fuels tested will prove to be of immediate commercial value, but it is hoped that much light will be thrown on this important problem.
The equipment for this work consists of a single gas generator, rated at 150 h.p., and a three-cylinder, vertical gas engine of the same capacity. The producer is a Loomis-Pettibone, down-draft, made by the Power and Mining Machinery Company, of Cudahy, Wis., and is known as its “Type C” plant. The gas generator consists of a
cylindrical shell, 6 ft. in diameter, carefully lined with fire-brick, and having an internal diameter of approximately 4 ft. Near the bottom of the generator there is a fire-brick grate, on which the fuel bed rests. The fuel is charged at the top of the producer through a door (Fig. 1, [Plate XX]), which may be left open a considerable time without affecting the operation of the producer, thus enabling the operator to watch and control the fuel bed with little inconvenience. As the gas is generated, it passes downward through the hot fuel bed and through the fire-brick grate. This down-draft feature “fixes,” or makes into permanent gases, the tarry vapors which are distilled from bituminous coal when it is first charged into the producer. A motor-driven exhauster with a capacity of 375 cu. ft. per min., draws the hot gas from the base of the producer through an economizer, where the sensible heat of the gas is used to pre-heat the air and to form the water vapor necessary for the operation of the producer. The pre-heated air and vapor leave the economizer and enter the producer through a passageway near the top and above the fuel bed. From the economizer the gas is drawn through a wet scrubber where it undergoes a further cooling and is cleansed of dirt and dust. After passing the wet scrubber, the gas, under a light pressure, is forced, by the exhauster, through a dry scrubber to a gas-holder with a capacity of about 1,000 cu. ft.
All the fuel used is carefully weighed on scales which are checked from time to time by standard weights; and, as the fuel is charged into the producer, a sample is taken for chemical analysis and for the determination of its calorific power. The water required for the generation of the vapor is supplied from a small tank carefully graduated to pounds; this observation is made and recorded every hour. All the water used in the wet scrubber is measured by passing it through a piston-type water meter, which is calibrated from time to time to insure a fair degree of accuracy in the measurement. Provision is made for observing the pressure and temperature of the gas at various points; these are observed and recorded every hour.
From the holder the gas passes through a large meter to the vertical three-cylinder Westinghouse engine, which is connected by a belt to a 175-kw., direct-current generator. The load on the generator is measured by carefully calibrated switch-board instruments, and is regulated by a specially constructed water rheostat which stands in front of the building.
Careful notes are kept of the engine operation; the gas consumption and the load on the engine are observed and recorded every 20 min.; the quantity of jacket water used on the gas engine, and also its temperature entering and leaving the engine jackets, are recorded every hour. Indicator cards are taken every 2 hours. The work is continuous, and each day is divided into three shifts of 8 hours each; the length of a test, however, is determined very largely by the character and behavior of the fuel used.
A preliminary study of the relative efficiency of the coals found in different portions of the United States, as producers of illuminating gas, has been nearly completed under the direction of Mr. Alfred H. White, and a bulletin setting forth the results is in press.[23]