Modern Gasworks Practice

WATER GAS 727 factor is the time taken to inj eet the oil. The quantity sprayed in must not be so apportioned that oil is running in during the whole of the gasmaking period. Such procedure would lead to inevitable waste, for the carburettor and superheater would not be swept clean from oily matter before the commencement of the “ blow.” Generally, it may be said that it is as well to arrange for the desired quantity of oil to be sprayed in during the first half of the “ run ” or thereabouts. For instance, with a five-minutes’ “ run ” the oil may be got rid of in the first three minutes, leaving two minutes for the mamifacture of “ blue ” gas, which will perform the necessary scavenging of the remaining vessels. The oil spray is a matter of importance, and tliorougli atomization should be aimed at. It would seem that rather th.an the oil should be injected under a pressure of 401b. per squäre inch it is preferable to employ higher pressures of. from 80 to 100 1b. Such pressure in conjunction with. a spray of the Brighton type (Fig. 451) gives the most effective mechanical subdivision and uniform distribution. The extremely fine distribution of the oil in this männer tends towards maintaining the chequer-work of the carburettor in a more cleanly condition, whilst patchiness in heating is avoided. It is customary on gasworks in arriving at an indication of the efliciency obtained from the oil to note from day to day the yie]d of “ candles per gallon.” This figure is arrived at by taking the average candle power of the gas, and dividing it by the oil used per 1,000 cubic feet of gas made over the same period. In practice -the result varies betwecn 7 and 8 candles per gallon, but the latter figure should be easily obtainable when the sei is worked on effective lines. To-day, however, little oil, if any, is used for enrichment, so tliat a criterion based on candle power has lost the significance it had in pre-war days. It may be stated. here that the amount of gas yielded per gallon of American gas oil varies from 70 to 90 cubic feet. A rough-and-ready test which. may be applied to the superlieater in Order to determine whether the most is being made of the oil is merely thai; of holding, during the “ run,” a piece of clean blotting paper to a small jet of the gas taken off from the Fig. 451.—Details of “ Beighton ” Oil Spray. down pipe from the superlieater. If the oil is being subjected to too great a heat a small black deposit of free carbon will be found on the paper; if, on the other liand, it is insufficiently cracked, a slight deposit of an oily nature will result. In