WATER GAS
743
escaping through.the seal. In the event of the amoimt of exhaust steam being insufficient to maintain the gasmaking requirements of the plant, a supplementary supply is taken from the boilers.
THE RECOVERY OF WASTE HEAT
The thermal losses which. occur on water-gas plants have assumed very much. more importance lately owing to the faet that, as the use of oil has beeil greatly curtailed or discontinucd altogether, the hot products and combustible gases leaving the generator during the “ blow ” have practically no function to perform. It will be readily appreciated that in the “blue ” water-gas plant the sensible heat of the waste
gases and the carbon monoxide they con-tain are lost. In order that this waste heat may be turned to useful account, suitably designed boilers have been attached at the outlet of the generator. These boilers have for some time been extensively employed in America, and have recently been installed in this country with considerable success. The majörityof water-gas plants in operation in this country are of the Lowe type fitted with carburettor and superheater, in which. case the boiler (of the vertical multitubular type with separate steam drum) is placed im-mediately following the superheater. All combustibles remaining in the “blow ” gases are burnt, by the admission of secondary air, during the “blow,” and the heat evolved, together with the sensible heat in. the “ blow ” products, is sufficient to raise all the steam reqiiired for gasmaking in addition to a surplus which. may be employed for driving part of the auxiliary machinery. When a Lowe-type plant is being employed for making “blue” gas, the latter is also taken through the boiler, so that the sensible heat of the “ blue ” gas gives rise to an additional quantity of steam. In fact, imder
Fig. 454.—Waste-Heat Boheb for Watek-Gas Plant.
efficient conditions a “blue ” gas plant may be made practically “ self-steaming.” The Humphreys and Glasgow waste-heat boiler (Fig. 454) consists of a slightly inclined cylinder provided with gas chambers at top and bottom. The middle portion of tlie cylinder forms the water chamber, from top to bottom of wliich tun 3-incli tubes about 200 in number. The water circrdates around the tubes, the
“ blow ” gases passing through them. The steam drum is connected to the multi-tubular boiler by means of two branches. Steam is usually raised at a pressure of