Modern Gasworks Practice

K> © MODERN GASWORKS PRACTICE It should be noted tliat the slight reduction in gas yield of the plant is nearly all accounted for by the CO2 which has been. eliminated. The policy of superheating the steam before its admission to the generator is one on. which much discussion has taken place. Certainly, by this means a greater store of heat is ensured in the generator. If the practice can be carried out without introducing structural complications, and by making use of heat which. would otlier-wise be wasted, it is, no doubt, to be commended. But in any case the effect will be limited. Glasgow has pointed out that even when superheated to 800° C. the steam carries scarcely 9,000 additional heat units, or but 2J per cent, of the energy absorbed in the manufacture of the carburetted product. The provision of a dry steam is, however, essential; and to this end the boilers should be adjacent to the Fig. 447.—Diagram showing Principle of Steam Metee. plant, the steam mains being adequately lagged, and, if necessary, trapped. Sufficient and uniform boiler pressure is essential, for if the steam pressure is permitted to fluctuate to any marked extent it will be followed by disastrous results on the output of the plant. Many installations are designed to operate with steam at 130 Ib. per square inch, though 100 Ib. pressure is, perhaps, more common. In the latter case, some appreciable improvement will frequently be followed by increasing the pressure to 110 Ib., if the boilers are capable of taking the increase. Steam meters are an undoubted asset to any plant, and enable accurate adjustment to be made. The factor of the quantity of steam admitted is of greater importance than miglit at first sight be supposed. Whilst a sufficiency of steam is imperative, an excess is to be rigidly avoided. In general, it will be foimd that for effective results the consumption of steam will arnoimt to from 27 to 30 Ib. per 1,000 cubic feét of gas. Thus, with a plant making 8,000 cubic feet per “ run ” of five minutes the steam should be set at