Modern Gasworks Practice

WATER GAS 731 As regards the heat units obtained in the gas per gallon of oil used, it was found that the highest results were given by the hydrogen atmosphere, this being accounted for by an abnormal prodnetion of saturated hydrocarbons. On the other Land, the most effective illuminating power results were obtained with. a methane atmosphere, the Suggestion being that methane lias a preservative influence on the illuminants, since its presence introduces equilibrium conditions which prevent the more valuable light-giving hydrocarbons from reacting with. hydrogen to form saturated hydrocar-bons. Methane, in faet, is shown to behave more or less like an inert atmosphere, such as nitrogen, which generally brings about a considerable yield of tar and free carbon. A remarkable faet is that when the oil is cracked in a nitrogen atmosphere there is an. appreciable evolution of hydrogen, whereas when the atmosphere consists solely of hydrogen there is actually an absorption of this element. As regards the efEect of carbon dioxide, it is shown that when oil is cracked in an atmosphere of particularly poor gas the loss in illuminating power is 5-5 per cent, for each per cent, difference in carbon dioxide in the finished gas, or 3-6 per cent, loss for each per cent, difference in carbon dioxide in the “ blue ” gas. As regards carbon monoxide, it is shown that this gas is instrumental in preserving the illuminants from decomposition, although it appears to be a direct cause of the prodnetion of tar—a greater quantity of tar being produced in this atmosphere than in any of the others experimented with. The explanation is that carbon monoxide exerts a tendency towards the prodnetion of the lighter olefines which. enhance the proportion of illuminants in the gas, while a certain proportion of the heavier olefines go to swell the tar yield. Experiments conducted with an atmosphere of typical “ blue ” gas as obtained direct from the water-gas generator led to the conclusion that no advantage is to be gained over “ blue ” gas by the substitution of any single atmosphere. With “ blue ” gas generally the most favourable results were obtained in all directions. As regards temperatures, the light-giving constituents formed from a gallon of oil reach. a maximum at 700° to 730° C., and higher temperatures than these are followed by iineconomical degradation. This point is one of extreme importance, and should prove a useful illustration to those who still contimie to operate their carburettor and superheater on the old-fashioned principle which advocated a temperature ap-proacliing 1,000° C. At the lower temperatures it seems very probable that the oil is cracked without the formation of hydrogen, for the American investigators fotind less of this element in the finished gas than in the “ blue ” gas. At temperatures above 800° C., however, the reverse was the case, and there can be little doubt that methane decomposes into hydrogen and free carbon. The outlet gas from the generator invariably contains a small proportion of undecomposed steam, which must always be looked upon as detrimental because of its tendency to react with carbon monoxide, with the formation of carbon dioxide. In addition, this steam has an injurious effeet upon candle power, and its presence is followed by a lower yield of tar and larger deposits of free carbon. The reduction noticeable in illuminating power is attributed to the reaction of the steam with hydro-carbons, such as et hylene, which are decomposed into carbon monoxide and hydrogen.