CHAPTER XIX
THE STORAGE OF GAS
Of the various portions of apparatus commonly found on gasworks, that made use of for storing the finish ed gas prior to its delivery to the supply area accounts for the greatest individual outlay. In normal instances, from one-quarter to one-third of the total Capital expenditnre on the works will be absorbed by the storage plant, whilst the ground area cover ed by this plant will amount roughly to some 20 per cent, more than that required for retort houses and coal stores com-bined.
Since the introduction of gas as an illummant the same principle, that of a floatmg vessel rising and falling in a seal of water, has been embodied in all storage appara-tus ; and although suggestions for replacing the gasholder by some less cumbersome contrivance liave, from time to time, been brouglit forward, they have not as yet materialized in practice.
The quantity of gas which it is desirable to hold in reserve at the works is chiefly dependent upon the fluctuation of the daily load curve. During recent years the hourly consumption has tended to become more and more regulär, witli a consequent levelling out of the curve. For this reason, the necessary holder capacity has under-gone reduction ; and it has been suggested that, in the future, storage will be practically uimecessary, once the daily curve of consumption has been straightened out altogether. It must be remembered, however, that one of the most important functions of the gasholder is the provision it affords against breakdown, and it would seem that the day of gasworks without this familiar apparatus is still far distant. With present-time conditions it may be assumed that the maximum hourly consump-tion is approximately arrived at by dividing the maximum daily output by 22. The amount of storage provided will not only be influenced by the nature of the supply, that is, whether chiefly lig'hting, power or cooking, but by the facilities at the works for meeting fluctuating demands with a similar variation in the quantity of gas produced.
It is in the latter respect that a water-gas plant, capable of being started up or dropped at short notice, proves of value. Accordmgly, in instances where the daily load curve is moderately constant, and where the peak of the load may occur during the daytime, the storage provided may be safely reduced to 16 or 18 Iiours maximum production. On works in which no surplus water-gas plant (or no water-gas plant at all) is available the capacity of the holders should be increased to from 21 to 24
621