Modern Gasworks Practice

780 MODERN GASWORKS PRACTICE The furnace is arranged to support the fuel in a vertical column in such, a männer tliat the fuel may be continuously advanced through it, while gas is being inter-mittently procluced and coal in the fuel is being carbonized. The furnace e.nnsists of a cylindrical gas-tight metal Shell provided with. a refractory lining, and having a top cover in which is the charging opening, and a coke-discharging hopper at its lower end. The upper end of the lining is constructed to form a restricted opening for the passage of fuel through the coal-carbonizing zone ; and the restricted passage extends down to the upper end of the hot combustion zone. Below this the lining conforms to the shape of the stell, so as to increase the cross-sectional area of the fuel column, in order that the coal may expand and be in an open condition to assist the cross blast in penetrating through, the column. Arches are arranged to form the lower portion of each side of the restricted passage immediately in front of the blast flues, and serve to direct the blast downwardly into the hot mid-zone. These arches confine the cross blast to the mid-zone and prevent a direct application of the cross blast into the coal-carbonizing zone, so that the temperature of this zone may be accurately controlled. The fuel here consists mainly of coke ; and when the blast gases pass through the mid-zone, the coke is bumed to produce carbon dioxide. The temperature of the coke in the mid-zone is very high, and the fuel-bed usually Jias such a thickness that the differential pressures which. may be practically used for driving the blast will not entirely prevent the formation of some carbon monoxide by the decom-position of carbon dioxide within the fuel-bed. This carbon, monoxide, therefore, passes out through, one of the cross flues into the corresponding regenerator. To ensure that all the heat in the exhaust gases leaving the fuel-bed (heat of combustion as well as sensible heat) may be removed in the regenerators, sufficient secondary air is led around the fuel column to bum the carbon monoxide carried out of the fuel column with. the blast gases. The generator illustrated is said to be well adapted for use in conjunction with coal carbonizing plant, used for producing coke ; while the coke would be used for making water gas. If the fuel column consists entirely of coke, only three distinct zones would be maintained in the fuel column—namely: (1) the hot mid-zone through which the cross blast is forced ; (2) the coke-cooling zone extending from the hot mid-zone to the bottom of the column ; and (3) a coke-preheating zone extending from the hot mid-zone to the top of the column. Steam alone would be used as the heat-transferring medium for making gas from the coke-fuel column; but it is preferable to use a mixture of water gas or otier combtistible gas and water vapours absorbed in the gas, sin.ce the gas acts as a carrying medium for mtroducing the water vapours into the fuel column without the necessity of heating water sufficiently high to generate steam. Further, the gas of the mixture would act as a heat-ti ans-ferring medium for maintaiiiing the distinct zones in the coke column and rp.Hnr.ing the partial pressures at which. the formation of gas takes place. When coal is carbonized, coal (or a mixture of coal with coke—the mixture, depending upon the amount of volatile material in the coal) is charged into the generator, and the four distinct zones above refened to are maintained in the fuel