Modern Gasworks Practice

182 MODERN GASWORKS PRACTICE into the lower end of a chamber, and the gas is removed at the base of the chamber, which. is the coolest part. In this way it is claimed that it is possible to obtain high gas, tar, tar oils, and by-product yields, and provide a coke of good quality. Definite quantiti.es of oxygen or air, and steam or water are in-troduced into the top of the retort. The oxygen, or air, and steam pass down the retort, and at the hottest zone combustion takes place, the temperature consider-ably increasing, whereby the well-known water-gas reaction takes place from the steam admitted. The hot gases thus generated descend through the retort and through the incoming coal, giving up their heat and assisting carbonization, and pass to an exit in the bottom of the retort, which. is the coldest zone within the retort. As the heat is gradually applied (from the base of the retort upwards) and owing to the hot gases passing through. the incoming coal, the “rieh.” gases evolved do not pass over any hot surfaces and do not become subject to deterioration. The retort is heated in a customary mariner by means of producer gas and in such a way that the incoming coal is first subject to a low temperature ; and the temperature increases towards the top, which is the hottest zone. Steaming in Vertical Retorts The principle of steaming the coal charge in vertical retorts - has within recent years assumed considerable importance. The subject is fully dealt with in Chapter XII on Carbonization (see p. 424), CARBONIZATION IN COKE OVENS The coke-oven. industry has now assumed such immense importance that th.e methods and apparatus employed would, to be fully described, demand a volume to themselves. It is not proposed, therefore, to deal with the subject in anything more than in outline. There can be no question that there is a considerable field for the employment of surplus coke-oven gas for admixture with town’s gas, more especially now that thermal standards of quality have at last come to be appreciated. In composition there is practically no difference between straight coal-gas as yielded by the retort and unstripped coke-oven gas. In faet, the one point in which. the two systems differ is that of the size of the coal charge. This distinction does certainly affect the gas composition slightly, büt essentially the product remains the same. It is, of course, for the future generation of engineers to decide whether it is prefer-able, from the economic standpoint, to segregate the carbonization of coal in industrial and mining centres and pipe the gas for long distances, or whether it is more feasible to operate on the present system of local gasworks and distribute the coal over a considerable area. From the point of view of transport the super-carbonizing station has its merits; but it must not be forgotten that such a principle entails segregation of coke supplies, and. coke is a fuel which. is in constant demand in all parts of the country. Thus, what is gained in one direction is partly lost in another. There are those, too, who argue that efficiency will best be obtained not only by Segregation of plant, but by effecting carbonization entirely on the mass principle