70. In general, the process of generating gas by means of producers consists in passing air, or a mixture of air and steam, through a bed of burning coal, coke, charcoal, or wood contained in a suitable receptacle known as a generator. The combustion of this fuel taking place in the lower part of the producer generates carbon dioxide, the greater percentage of which, in traveling up through the bed of highly heated carbon, is decomposed, one unit of the oxygen of the carbon dioxide uniting with a unit of carbon to form carbon monoxide. The steam entering the producer with the air is decomposed by the high temperatures into hydrogen and oxygen, the former passing through as free hydrogen, while the latter unites with the carbon just as does free oxygen from the air.
71. The formation of carbon dioxide from carbon and oxygen evolves heat, and that portion of the fuel bed where this takes place will be hottest. The two operations oi decomposing steam and reducing carbon dioxide to carbon monoxide, however, absorb heat, so that the combined result of the three operations tends to effect a temperature balance more or less controllable through variation of the amounts of steam supplied.
72. If the fuel beds contain holes, then air, composed of free oxygen and the inert element nitrogen, will pass through the producer and affect the final composition of the gas. The resulting gas will then contain carbon monoxide, carbon dioxide, free hydrogen, small percentages of illuminants, and nitrogen.
73. Description of Gas Producer. — The following explanation of the Koerting producer applies in most particulars to all of its kind. The apparatus is shown, somewhat simplified, in Fig. 4. The plant consists essentially of a generator a, an evaporator b, a scrubber or purifier c, and a sawdust purifier d. The generator is simply a vertical steel shell, cylindrical in form, and lined with firebrick. It is fitted at the bottom with grates e, and when in operation is kept nearly full of fuel. At the top is a hopper f having an air
