CO
MODERN GASWORKS PRACTICE
for steaming th.e charge in the retorts, the pressure being reduced to from 25 to 30 Ib. The steam tlien passes through a l|-inch pipe to superheaters. The temperature of the waste gases at the inlet of the boiler is approximately 850° C. (1,560° F.), and at the outlet 400° C. (752° F.). The water evaporated per ton of coal carbonized is 600 1b. Tests have shown that about 240 1b. of steam per ton of coal was actually
used in the retorts, although slightly more th.an this may be required. The surplus steam, therefore, is turned to assist the ordinary works boilers. It will be noted, however, that the outlet temperature of the waste gases appears to be abnor-mally high as they leave the setting and enter the boiler.
Waste-heat boilers are particularly suitedto installations of vertical retorts, and as an example of the saving which. may be effected, the case may be quoted of a vertical bench of the Woodall-Duckham type now in operation, the chimney gases from which are evapo-rating approximately 6,000 1b. of water per hour at a pressure of 130 1b. The retort bench in question is carbonizing about 200 tons of coal daily.
Steam raising on gas-works is usually compara-tively cheap owing to the fact that on such establishments
Fig. 40.—Glovbb-Wbst Waste-Hbat Bojler. ig invariably a fair
proportion of low-grade fuel available which in some instances would be difficult to dispose of in any other way. The position as regards coke breeze, however, is not what it was a year or so ago, and there would now be little difficulty in fmding a reasonable market for it. Incidentally, there is also a demand for tar-breeze briquettes; and, no doubt, a large quantity of the available breeze might be disposed of in this form. If consideration is given