Modern Gasworks Practice

146 MODERN GAS WORKS PRACTICE It iS difficult to draw comparisons between the continuous and ihtermittent systems. In most cases the engineer must take into consideration the prevaiKiig conditions, and select his system accordingly. In comparison with. horizontal systems the following advantages are claimed for vertical retorts :— (1) Greater yield of gas on a given area. For horizontals the average yield of straight coal-gas is 200 to 250 cubic feet per square foot of ground area. For verticals this figure may be increased to as much. as 475 feet per square foot of area—according to the system. (2) Better conditions in retort house and no very arduous labour. Less clinkering. (3) Low consumption of fuel (see p. 61). This claim, although invariably made for vertical systems of the continuous type, must be viewed with a certain amount of reserve. As yet it is not possible to say definitely that the vertical retort shows any superiority over the latent types of horizontal retort in this direction. (4) Control of heats as regards various sections of the retort. In the modern horizontal setting the multiple control of secondary air ensures almost as perfect adjustment. (5) Each particle of coal is subjected to exactly similar treatment. This means that all coal passes in turn through the various temperature zones prevailing in the retort, and t liere is no trouble with uncarbonized portions of coal, as is often the case near the mouthpieces of horizontal sp.t,tings (6) With continuous systems the gas is certainly produced in more uniform quality. (7) The heat in the coke is in most systems utilized, and not wasted as in horizontals. (8) The gas is not subjected to degradation by long contact in a large free space. The gas evolved from the lower portions of the vertical charge travels to the outlet pipe partly through red-hot coke and partly against the sides of the retorts (see p. 435). (9) “ Make per ton ” may be appreciably increased by steaming the base of the charge, when the coal is sufficiently good to allow of this. (10) Heavy and complicated charging and discharging machmery is eliminated —thus wear and tear expenditure is reduced. (11) Labour costs per ton of coal per diem are from one-half to one-third less than with. horizontal retorts. The Claims of the horizontal bench may be sat down as follows :— (1) The coke in vertical retorts has occasionally a tendency to “ jam ” up. This particularly refers to the intermittent types. (2) The retorts are more difficult to repair during operation, and as the continn-ous retort is only cleared at long intervals a leak may go undetected for some time. (3) The Capital cost per ton of coal per maximum day is in general higher for the vertical systems. Inclusive of complete bench and foundations, coal-handling plant, power-operating plant, coke-handling plant, but exclusive of retort house, a vertical installation (according to size) will cost from about £450—£600 per ton of coal. The