Modern Gasworks Practice

WATER GAS 741 difficulty in the way of clinkering and ash removal, while the gas-producing capacity of the plant is rechiced by at least 5 per cent. As before mentioned, the liberation of a considerable amount of volatile matter from the coal is objectionable, for chn-ing the period of the “ blow ” this appears at the open stack-valve as smoke ; moreover, the increase in calorific power of the producer gas tends to result in overheating of and damage to the chequer brickwork of the carburettor and superheater. As would be expected, too, the free space for gas passage in the generator fuel is constantly fluc-tuating owing to the tendency of bituminous coals to form channels in the fuel-bed, an effect which is coiitributedto by the caked condition which the fuel assumes. It has to be remembered, of course, that the depth of fuel employed is primarily a function of its density, so that whereas a 7 ft. bed is used with coke as the fuel, with coal the depth will only be some four feet. The shallower bed is essential, in fact, to permit of the passage of the primary air from the blast. American experience tends to show that the quantity of steam used per 1,000 cubic feet of gas made is very much more with. coal than with coke ; a natural disadvantage, too, is that the crude gas from coal gasification contains considerably more sulphuretted hydrogen than does ordinary ‘ ‘ blue ’ ’ water gas. Thus purification costs are increased. However, in spite of the rather formidable list of disadvantages enumerated above, it is still found practicable to employ coal; and, as oil is unlikely to return to its pre-war price, there is no reason why an efEort should not be made in this country, not neces-sarily to utilize coal alone, but to ascertain the effect and practicability of employing a coal and coke mixture. As a matter of fact, the American, investigations in connection with the utiliza-tion of bituminous coal suggest that the only practicable way of producing a high quality uncarburetted gas is by means of some form of plant in which the volatile constituents of the coal are first removed, and the fixed residue isthcn subjected to gasification with steam. This, of course, merely brings one back again to the principle of complete gasification which, so long as a mixed town’s gas is provided, appears to be a scientific solution of the problem. Complete gasification, however, possesses the disadvantage that it cannot be reasonably conducted in water-gas plant of existing design, and thus the question of Capital expenditure is immediately opened up. On the other hand, the expenditure should be by no means excessive, for wrisfring blowers, steam plant, relief holders and purifiers could all be made use of, and the only new portion of plant to be introduced would be the special gas generators. EXHAUST STEAM FOR WATER-GAS MANUFACTURE The Substitution of exhaust steam for the live steam more commonly employed for water-gas production has been experimented with for a number of years. In the early experiments the wet steam taken direct from engine exhausts was used, the entrained moisture giving rise to a great deal of trouble. Various methods for removing the free water were tried, including very extensive trapping systems and separators of all styles. WliUc most of the free water was removed in this way the water in suspension still remained, due to the steam bcing saturated at a comparatively low temperature.