Modern Gasworks Practice

PLANNING AND LAYING OUT OF GAS WORKS 17 In recent years tlie Capital expenditure on the district bas increased rapidly, owing to the development of the prepayment meter business and the greatly extended use of gas cookers, fires, circulators, etc. The first-named item of expense may now be considered as varying from £13 to £18 per house (including cooker), but excluding service, which is common to all classes of consumer. The consump-tion for this expense may be from 7,000 to 22,000 cubic feet per arniim ; and, aver-aging thesc figures, we get an expenditure of £850 per million on the gas sold through, this channel. There is, of course, an. increased receipt from this source, which may or may not give an adequate return on the Capital, after allo wing for extra cost of collection, repairs, and maintenance. The result is that, whereas twenty years ago the works usually cost more than the distributing plant, the reverse is now invariably the case. Keeping in mind, however, the general example we are considering, the cost of mains, meters, stoves, etc., comprising the distributing plant, may absorb 55 per cent, of the total, the works and equipment amounting to 38 per cent., whilst engineers’ fees, parlia-mentary and promotion expenses complete the total. A faet not generally realized with regard to works outlay is that the expense of gasholders in many cases accounts for one-fourth. or even one-third of the total, and is the most expensive individual item on the works. The remainder is apportioned somewhat as follows :— Land ____________________________...... 2-4 per cent, of works expenditure. Carbonizing plant (including buildings) . 20-27.'. „ „ Purifying plant. ..... 5-8 Exhausters, condensers, washers, etc.. . 3-4 „ „ „ GENERAL RULES FOR SIZE AND CAPACITY OF PLANT Gasworks are never designed by rule-of-thumb methods, and the details con-nected with. their construction are mostly the outcome of extended practical experi-ence. For all that, certain constants for the computation of the capacity of the various pieces of plant have come to be recognized, and are given here with the strict warning that they are merely a guide, exemplifying rules and their application. Varying circumstances alter cases, and in laying out the works all those circum-stances should be taken into account which would tend to vary sizes from the normal. Alth.ou.gh, in the main, tlie rules given will be found as occurring in general practice, the author wish.es to deter the aspiring designer, with little or no actual experience of gasworks erection, from drawing up specifications on such a basis alone. Land Allow at least 2J, and preferably 3J acres per million cubic feet per maximum day. Retort House Dependent upon the gas-making capacity of each “ unit,” i.e. the number of retorts set in each arch. The following table gives approximate figures for the make of straight coal gas per retort per day of twenty-four hours :— c