Modern Gasworks Practice

s IC MODERN GASWORKS PRACTICE A certain amount of succ'ess has more recently been achieved by the intro-duction of means for superheating the steam, the tougher grades of coke and breeze usually being employed for firing the superheater. In practice it is found that the most effective results are obtained if the steam is raised to a temperature of about 230° C The method has been operated on a fairly large scale at Chicago, where all the exhaust steam from the engines, turbines, pumps, etc., was gathered into one common header wliich led into the miet of the superheater, the size of the miet pipe m this case being 20 inches. At two points, preferably some distance from the superheater, 18-inch back-pressure atmospheric valves were installed, with exhaust heads leading to the air. They were kept away from the superheater to avoid unnecessary fluctua-tions in pressure near the latter, because the auxiliary live steam admission valve was very sensitive to any sudden changes in pressure. The back-pressure valves were usually set at about 3| 1b. Each superheater was capable of superheating 33,000 1b. of steam per hour to a temperature of 240° C., at 5 1b. maximum piessure. They were made of any desired capacity, and with grates for solid fuel or with tar bumers. The latter type of firing seemed to be the most economical. The following figures give a comparison between the actual results obtained when using live steam and. superheated exhaust steam. Live and Exhaust Steam. Compabative Figuees Live Steam. Superheated Exhaust. Total gas made per 24 hours on 412-foot machines, Pounds of carbon per thousand cubic feet of gas Boiler fuel per thousand, including superheater Total water used in boilers, pounds per thousand 10,954,000 28-37 13-56 97-5 11,807,000 27-09 9-67 70-0 The tests show that the steam used per thousand cubic feet of gas made is reduced by from 25 to 35 per cent., or approximately the whole of the live steam necessary for gas making is saved. H. E. Smith 1 points out that in the usual intermittent water-gas plant the fan is keptrunning continuously during both “blow” and “run.” Moreover, the quantity of exhaust steam from turbo-blowers is frequently in excess of the amount required for gasmaking. He proposes, therefore, to bring all available exhaust steam to a collecting main and to utilize it for gasmaking, the pressure in the collecting main being controlled by an adjustable relief valve. A liquid seal is provided between the collecting main and the inlet valves of the generators, so that the steam pressure may be readily adjusted by the depth of liquid in the seal pot, any excess of steam 1 B.P. 23052/14.