Modern Gasworks Practice

14 MODERN GASWORKS PRACTICE residential and agricultural. As a general rule it may be said that the smaller the population the less will be the consumption per consumer, this being partly due to the faet that in such districts gas is mainly employed for ligliting, and is not generally used for cooking, etc., owing to its cost necessarily being higlier th.au in the large towns. From the estimating standpoint, the second column, of figures is the most use-ful, for, taking all considerations into account, the number of consumers and their probable average can be fairly closely approached by one of experience. In the above calculations the gas employed for public ligliting has been included in the consumers’ quantity. In a general way, a very good idea of the total probable output can be gleaned from an analysis of the situation on lines such as the following:__ Say the district contains 17,500 to 18,500 liouses, of whicli the mains to be laid would permit of access to 17,000 or so. In the circumstances, 90 per cent, of these may be expected, or 15,500. Then the estimated amount of gas to be sold per annum would be:— Cubic Feet. ,, , .. Millions. 6,500 consumers through ordinary meters at 42,000 .................. 273 s’500 » „ “slot” „ 15,000 . ... . 127 For industrial purposes extra (say 500 consumers) .... 60 For public lighting (1,200-1,500 lamps), ...........................20 480 In addition to this sale, about 6 per cent, must be allowed for gas lost by leak-age and gas used on the works. This brings the annual production up to 50S millions or, in round figures, 500 millions. The sale per head then works out at nearly 5,500 cubic feet, or 30,000 cubic feet per consumer, excluding public lighting; which, on reference to the table, is seen to be normal, and satisfactory for estimating purposes. AMOUNT OF LAND REQUIRED In considering ground area required, mucli depends on the manufacturing system it is proposed to employ, but a good guide is to allow a minimum of 2 g-, and preferably acres per million cubic feet per diem. So far as the maximum day’s send out is concerned, this is now found to amount to 1/230 to 1/260 of the whole year’s consumption. That is in normal cases, apart from health resorts or towns having a double heavy season. Ten years ago this ratio varied from 1/185 to'1/210 ; so that it is now possible to seil from 10 to 15 per cent, more gas with. identical plant, owing to the Welling up of the daily load curve. In the same männer the liourly load curve has also been appreciably straightened out, thus saving many undertakings considerable expense in gasholder construction. In the example taken we get a maximum day’s production of 500/240 millions per day=2 1 millions. So that land and plant must be at least equal to this production.