The constitution of producer gases from various fuels as made in a pressure plant is as follows : Coke — carbon monoxide, 27.6 per cent; hydrogen, 7 per cent; methane, 2 per cent; carbon dioxide, 42 per cent; nitrogen, 58.6 per cent placed as shown, while the hot water issuing from the top of the producer is carried by suit able pipes to the holder.
In the pressure systems all of the following named or similar materials may be used for fuel: Anthracite and bituminous coals, lignites, coke, charcoal, wood, peat and tanbark. Good anthracite coal is the best when convenience of operation is the primary consideration. When bituminous coals are used, preference should be given to those of the semi-bituminous class. According to general experience, soft-coal plants appear to be more expensive than those operated with hard coal, and when the price of anthracite does not exceed that of soft coal more than $1 per ton, it is advisable to em ploy a hard-coal plant. When coke is used it should be in small pieces of about one cubic inch; as the tendency of large-size coke is to give a weak gas. When coke is used instead of anthracite, one-third more, by weight, of the former should be taken as the fuel consumption.
A variation of the pressure producer is the down-draught apparatus, used for lignite and similar low-grade fuels. The tarry gases are driven down through the incandescent fuel, and Lignite — carbon monoxide, 18.90 per cent; hydrogen, 15.13 per cent; methane, 3.65 per cent; carbon dioxide, 9.43 per cent; nitrogen, 52.50 per cent.
Peat—carbon monoxide, 28.6 per cent; hydrogen, 8.5 per cent ; methane, 2.2 per cent; carbon dioxide, 6.9 per cent; nitrogen, 53.8 per cent.
Wood—carbon monoxide, 9.86 per cent; hydrogen, 54.14 per cent; methane, 3.45 per cent; carbon dioxide, 21.30 per cent; nitrogen, 10.53 per cent.
Fuel oil — carbon monoxide, 11.40 per cent; hydrogen, 5.37 per cent; 5.87 per cent; carbon dioxide, 4.10 per cent; nitrogen, 67 per cent.
The by-product gas producers used in the manufacture of illuminating gas separate and accumulite the tar, which is 38 per cent oil, and reclaim a large part of the nitrogen as ammonia. The latter passed through a sul phuric acid bath yields 80 to 90 pounds am monia sulphate per ton of coal.
Suction Gas Producer Fig. 4 shows the general arrangement of the several organs of a suction plant: A, represents the producer; B, the evaporator; C, the scrubber; and D, the receiver. The plant operates as follows: The gases generated in the producer pass through the evaporator, which is simply a small multitubular boiler, and serves to utilize the sensible heat of the gases for evaporating the water used as steam in the producer. The vapor thus obtained is conducted through the pipe E, to the ash-pit of the producer, by the suction of the engine piston, while at the same time the gases pass from the evaporator to the scrubber filled with coke. As these gases rise through the interstices of the coke they come in contact with the descending washing water, which not only takes up and thus removes the dust brought over from the producer, but also purifies the gases of ammonia and any other Impurities which water will absorb. From the scrubber, the purified gas passes into the re ceiver. The diameter of the receiver is rela tively large as compared with that of the suc tion pipe of the engine, and thus prevents the pulsations which would otherwise be caused by the strokes of the engine piston, between the receiver and the producer.
Usually, in the smaller plants, the producer is provided with a charging hopper of sufficient capacity for holding enough fuel for several hours' operation, and permits the admission of coal to the combustion chamber without allow ing air to enter it, during the charging opera tion.
To operate the plant a fire is first kindled upon the grate of the producer; the fuel bed then built thereon, and the air necessary for starting combustion is supplied by means of a hand- or belt-driven fan. At first, the poor or lean gases produced at starting are allowed to escape into the open air through the vent pipe G, until the test-cock shows that good gas of the desired quality is being generated. Then the vent-pipe is closed and the scrubber and receiver brought into the gas circuit. The engine is now brought into operation, and as the suction caused by the strokes of its piston thereafter performs the function of the fan, the latter is stopped.