Modern Gasworks Practice

22 MODERN GASWORKS PRACTICE Governors Dependent entirely on the nature and conditions of tlie district to be supplied. Absolutely no rules can be given attempting to cover more than the simplest possible case, i.e. a level district, with the gas sold in one centre, in which instance the one necessary governor is of the same size as the main outlet pipe from the works. Storage Capacity The levelling up of the hourly load curve in recent years has had a marked effect on the amount of storage necessary. In spite of considerable increases in annual sales, none of the three metropolitan. Companies has built a gasholder for many years, and as the South Metropolitan Company is here included, the question of storage cannot be due entirely to the use of carburetted water gas, although it is naturally influenced by the presence and capacity of the water-gas plant. The other factor affecting the storage required is the nature of the supply, wliether chiefly ligliting, or power, or cooking ; the last two, if in large quantities, causing the peak to be from 11.30 a.m. to 1.30 p.m., or thereabouts, instead of during the evening. Where the load curve is assisted in this männer and surplus water gas is available, the storage can safely be reduced to 18 hours’ maximum make. Otherwise 21-24 hours’ should be provided for. It is as well not to rely on the surplus water-gas plant other than as a means for meeting emergencies, such as fogs or breakdown in coal-gas plant. With. reference to ground space occupied, it may be mentioned that gasholders require, roughly, 20 per cent, more room than the combined retort liouses and coal stores, under normal conditions. It will be understood that the storage capacity on the daily make basis is very elastic, as the newest holder is almost invariably the largest; consequently before this is put into operation the storage is deficient, whilst immediately afterwards it may be excessive, provision being made for the future. A common method of providing for future devélopment is to build the tank and one or more lifts with all arrangements for adding a further (outer) lift in the future. Thus the capacity of such a holder may be increased from 50 to 100 per cent, with a comparatively small expenditure. It must be remembered, however, that this method cannot be adopted where one holder is relied upon, or where the other storage is so small that it cannot be reduced even in the slackest season of the year ; for the holder must necessarily be out of action for some weeks during the alterations. Albeit, many undertakings have gone through this ordeal on 12 hours’ storage, even when based on the minimum day (8-9 hours of maximum dav). The proportions of gasholders are discussed in Chapter XIX, but for single lift holders allow height equal to 0-3 to 0-4 of the diameter, and for multiple lift holders 0-6 to 1-0 of the diameter. This excludes tanks in both cases. Tar and Liquor Storage Ampie tar storage is ad visable, as it assists the manager in times of low prices, in addition to which the demand is a fluctuating one.