Modern Gasworks Practice

-q üt >4- MODERN GASWORKS PRACTICE struction, will be largely determined by the system of draught adopted, whether “ natural,” “ induced,” or “ forced.” The apparently beneficial effect of a limited supply of steam on the combustion of coke warrants due consideration of the steam-jet impelled system, applied either on the closed ash-pit or hollow firebar principle. Various types of steam-jet forced draught furnaces, permitting a comparatively short chimney shaft to be used, have been employed in conjunction with coke and breeze burning for some years, but in many cases the alterations have been cumber-some and expensive. The blower introduced by the London Coke Committee may best be described as providing an “ impelled ” draught, which is admitted beneath the firebars by either two or three delivery pipes fashioned somewhat on the lines of a Venturi tube. The whole can be fitted to a coal-burning boiler in a few hours, and requires for its operation only two to three per cent, of the steam raised. Mechänical Stoking In the larger works the possibility of automatically stoking and cleaning boiler furnaces has led to the adoption of mechanical stokers of the travelling-grate or “ sprinkler .” type. The latter are applicable to either water-tube or Lancashire boilers, but so far the application of the travelling-grate of the “ underfeed ” or Babcock type has been limited to water-tube boilers of fairly high capacity. These generally operate in conjunction with some system of forced draught. Rates of 30 1b. of fuel per square foot per hour are.said to be maintained, so that the full normal capacity of the boiler with this equipment may be realized with coke fuel. Superheat All steam engines are essentially heat engin.es, and the manufacture of water gas is essentially a heat process. Accordingly, the use of steam superheaters, either as an integral part of the boiler unit or separately fired, is the trend of modern practice. Economizers, etc. The development of the economizer has followed the recognition of the inef-ficiency of coal as a boiler fuel, with which fuel as much as 20 per cent, saving may be effected by installing a suitably proportioned economizer betwecn a coal-fired boiler and its chimney shaft. The same would not, of course, apply in the case of coke-fired boilers, in which the heat of combustion. appears to be largely trans-mitted to the water and steam inside by radiation, and consequently there is a smaller proportion of heat carried off in the waste gases. Moreover, as the proportion of excess air necessaiy for the complete combustion of coke is so much less than that required with coal, a relatively smaller volume of gas comes iii contact with the economizer tubes. Reliable tests show that where an average increase of 108° F. in feed temperature was obtained with a coal-fired boiler fitted with an economizer of the ordinary type, an average increase of only 78°F. was main-tained when the same boiler was working with coke fuel on a forced draught grate. For each 10° F. increase in feed temperature, a saving in fuel of about one per