CHAPTER XV
EXHAUSTING MACHINERY
Although the exhauster has only come into universal use during comparatively recent years its invention extends back to quite the early days of gas production, the scientific apparatus employed to-day having been gradually evolved from an exceed-ingly crude beginning. The necessity for some such apparatus first became apparent when the original cast-iron retorts began to give way to those made from more porous substances. The idea of drawing off the gas from the retorts by the creation of a vacuum seems to have first occurred to an engineer named Grafton, about the year 1839. The machine which. this investigator made use of was extremely inefii-cient, consisting of an ordinary wet-gas meter with. the inlet and outlet reversed and having the drum driven by power. The notion, liowever, paved the way for more suitable apparatus, with the result that ten years later the exhauster had. become a familiar feature of the larger works. Nowadays, this machine, in various forms, is to be found on all gasworks with the exception of the very smallest, where the cost of installing and operating it would not be commensurate with the saving entailed by its introduction. Where the limit, so far as the size of the works is concerned, should be placed is a matter for argument. It is frequently stated that any works making two million cubic f eet of gas or over per annum can profitably instal exhausting plant. When faced with. actual facts, however, such, a proposition does not bear examination. and, unless exceptional circumstances intervene, the use of the exhauster on works making less than four or five million cubic feet per annum is not to be recommended.
Consideration of an actual case is sufficient to emphäsize this point. For instance, consider a works making five million cubic feet per annum. When. working without an. exhauster the gas made per ton of coal would probably average 9,500 cubic feet, whilst the introduction of the exhauster might account for an increased yield of from 800 to 1,000 cubic feet. In consequence, the coal consumed annually would be reduced from 525 to 480 tons, i.e. a saving of 45 tons.
Capital Outlay£ s. d.
Engine, exhauster, valves, foundation ___________________________...... 200 0 0 N.B.—If no building is available for this plant, an additional outlay (say £80)
would be entailed.