WATER GAS
709
the gas superheated ; finally it makes its way through, the second generator, m which the carbon dioxide is reduced to carbon monoxide. For the next “ nm ” the
direction of the steam is reversed, that is, the final generator now becomes the first.
This system combines a shallow fuel-bed for the biast, together with a deep fire and long contact with the incandescent coke during the “ nm.” The fact that while during the “ blo w’ ’ a shallow bed of
fuel is required and during the “ run ” a deep fire is desirable has proved a difficulty to many designers of water-gas plant, but the introduc-
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Fig. 439.—Dellwik “ Blue ” Gas Plant.
tion of the split generator has efiectively over-come this.
It is interest-ing to note that in the large hy-drauEcally con-trolled installation at the Beckton works the units are fitted with generators on the
“ twin ” principle and that by the movement of a lever the generators may be set during the “ run,” for operating either in series or in parallel. In this case the generators are no more shallow than is the ordinary single generator, and the chief advantage lies in the fact that when tliey are operated in parallel during the “ run ” the capacity of the plant is increased by some 25 to 30 per cent. On the other hånd, when the demand for gas may be less they can be steamed in series when arather better quality gas containing a smaller percentage of CO2 will be obtained.
The Dellwik blue-gas plant (Fig. 439), while yielding a gas very similar to that produced in the “ K. & A.” apparatus, materially difEers from it in construction. In this case there is a single generator preceded by a superheater through which the steam passes before entering the generator. It will be noticed that the door at the top of the generator performs the double duty of a stack valve and charging door for replenishing the coke. The gas passes direct from the generator to the superheater, and thence through a coke scrubber. As in the other plants, an inter-locking valve-gear precludes the possibility of any danger which. might arise from ■carelessness on the part of the operator.