Modern Gasworks Practice

138 MODERN GASWORKS PRACTICE without admixture with that already in the holder. The remedy for this is, of course, to avoid working both in and out of the same holder. FÜEL ECONOMY It is merely necessary to turn to the prevailing figures of a decade or so ago to realize that fuel waste has been curtailed to an even more striking extent than the make of gas per ton has been augmented, so that, instead of having for disposal only about 55 per cent, of the coke made, to-day, with the modern type of producer, it is possible, with careful working, to put on to the market (including sales to other departments of the works) no less than' 85 per cent. The true facts of the case are, perhaps, better exemplified by comparing the heat units expended with those ob-tained for such an outlay in the form of gas ; for whereas about 80,000 B.Th.U. used to be necessary to yield 6,000,000 B.Th.U., we now require something less than 26,000 B.Th.U. to give a yield of nearly 7,000,000 B.Th.U. in the gaseous state. That is to say, a reduction of 66 per cent, in the B.Th.U. required has been accompanied by a rise of about 17 per cent, in the B.Th.U. obtained in thé gas. Even now it must be remembered that the apparently effective producers of the present day have by no means reached perfection ; but, comparatively, the amount of the total heat utilized is a notably small percentage of that contained in the original fuel. For the most efficient producers the loss in heat still amounts to about 40 per cent, of the total contained in the fuel. This figure was in the neighbourhood of 65 per cent, before the introduction of regeneration. Some considerable gain in efficiency results, of course, from the utilization of the sensible heat in the waste gases for the generation of steam. HEAT BALANCES The question of the heat balance of a retort setting receives but meagre attention on the ordinary gasworks. Results can never be considered more than very approximate, owing to the difficulties with which the investigator is faced and the assumptions necessary ; hence the practical gas engineer finds no great use for them. Of the total heat due to the combustion of fuel in non-regenerative retort settings the greatest individual portion is accounted for by that passing away with. the waste gases—this amounting to nearly 50 per .cent, of the whole. By the employment of regeneration, however, the loss from this source has been reduced by almost exactly one-half. The main sources of thermal losses in a setting may be briefly summarized as follows :— (a) Carried away in waste gases. (&) Carbonization of coal, and carried away by evolved gases and vapours, and in hot coke. (c) Radiation and convection from brickwork. (d) Lost in ashes, clinker, etc. (e) Decomposition of water in fuel and moisture in inflowing air. Also vaporiza-tion of water in ash-pan. and on firebars. (f) Reduction of CO2 to CO in producer.