In the suction systems only anthracite coal, and the so-called carbonized fuels such as gas house coke and charcoal, have been satisfactor ily used up to the present time. When anthra cite is used it should not be less than °pea)) size, clean and of good quality. It is evident that the finer the size of the fuel and the greater its tendency to clinkering, the greater will be the amount of work required of the engine to draw the air current through the fuel bed. There fore, if continuous action and easy operation are desired, the use of anthracite of the ordi nary size will give the most satisfactory results.
In either case the gas produced is of good quality, when good fuel is used, the pressure producer gas averaging about 125 B.T.U.'s per cubic foot, and the suction-producer gas about 145 B.T.U.'s per cubic foot, with variations ac cording to the method of operation, and the proportion of hydrogen and carbon monoxide present.
In the power-plant operation, the fuel con sumption will average one and one-half pounds of coal per brake horse-power hour for small powers, and decrease in relative amount with the increase in the size of the engine until a rate of one pound per brake horse-power hour is at tained, thus giving a higher efficiency than that of the best marine steam engine or the largest steam pumping engine in the world.
Quality of Gas for Power In sidering the quality of a gas suitable for the production of power or for use in gas engines it is necessary to inquire into the amount and quality of gas obtainable from various kinds of fuels.
The following table gives an approximate index to the difference of yield of gas for the different materials available for this purpose.
The actual yield of gas varies, however, within wide limits, according to the composi tion of the fuel, its general character and the method of classification, and in the care of coal, as already stated, according to the proportion of steam used in the producing operations. It may be assumed, however, that on the average, one ton of anthracite buckwheat coal will yield about 170,000 cubic feet of gas, having a calorific value of 138,000 B.T.U.'s per 1,000 cubic feet; with an average composition as follows: Advantage of Using Producer The advantage to be derived from the use of pro ducer gas may be briefly stated as follows: The combined efficiency attainable in the best steam engines and boilers, operating under the most favorable conditions, is about 12 per cent of the intrinsic heat energy of the fuel used. On the other hand, the modern gas
engine, even in small powers, will give an efficiency much higher, but if it be supplied with illuminating gas for fuel, a large amount of the economy due to the higher efficiency is lost in the cost of the gas. Heat energy in the form of coal gas at a dollar per thousand feet, costs 13 times as much as an equiva lent amount of energy in the form of coal at $3 per ton; therefore, in order to utilize a gas engine to its full advantage, the gas used must be produced as economically as possible. This is exactly the function of the gas producer, and by its use a good gas engine with a theoretical thermal efficiency of 75 or 80 per cent, or a practical thermal efficiency of 25 or 30 per cent, will readily convert into actual work, or available power, 25 per cent of the heat energy of the gas delivered to it. The gas producer of such a plant will transfer to the gas about 80 per cent of the intrinsic en ergy of the coal, so that a gas-producer engine operating on an inferior grade of coal will show an efficiency of 20 per cent, as against the 12 per cent of a steam engine and boiler plant using the best steaming coal. Producer gas is used to great advantage in many industrial operations, among which may be mentioned the manufacture of high degree sulphuric acid; the regeneration of bone black ;•in the enameling processes; in making lime, cement, glass, brick, china and porcelain; in reverbatory furnaces, especially for small castings; in puddling fur naces in the steel industry; in reheating and annealing furnaces, etc.
Consult Askling, C. W., and Roesler, E., Combustion Engines and Gas Pro ducers' (London 1912) ; Hirshfeld, C. F., and Barnard, W. N., 'Elements of Heat-Power Engineering' (New York 1915) ; Jones, F. R., 'The Gas Engine' (New York 1909) ; Miller, J. C., (Power Gas and the Gas Producers' (Chicago 1910) ; Nagel, 0., (Producers Gas Fired Furnaces' (New York 1909) ; Robson, P. W., 'Power Gas Producers: their Design and Application' (London 1908) ; United States Mines Bureau Technical Paper 20, (The Slag ging Type of Gas Producer' (Washington 1912) ; Wimperis, H. E., 'Internal Combustion Engines' (London 1915).
Revised by RICHARD FERRIS. GAS TAR. See COAL TAR.