Modern Gasworks Practice

HIGH TEMPERATURE CARBONIZATION OF COAL 411 ring benzene compounds to benzene, but at the same time to preserve the benzene nuclei intact. A similar action of hydrogen on the attached groups of more com-plicated ring compounds most probably accounts for the production of naphthalene and anthracene. Hence the formation duriug high temperature conditions of the horizontal retort of a considerable quantity of the aromatic hydrocarbons and naphthalene, with. a corresponding decrease in the yield of paraffins and phenols. THE MODERN REQUIREMENTS OF CARBONIZATION There can be no question that in comparing the relative merits of various systems of carbonization too much importance has been attached to considerations of “ yield of gas per ton of coal.” During the past fifteen years a notable advance has certainly been made in the process of carbonization, the volume of gas obtained from coal having been increased by some 40 per cent, as a result of the introduction of improved carbonizing apparatus and methods. It has now to be borne in mind, however, that with. the introduction of the Gas Regulation Act, the question of volume has lost much of its former significance, and the true criterion at the present day must necessarily be the yield of gaseous thermal units per ton of coal. In discussing the advances made duriug the past fifteen years it is not possible to neglect the factor of gas volume obtained per ton of coal, and it is of interest to follow out the means whereby the yield has been enhanced from some 10,000 cubic feet to upwards of 14,000 cubic feet. Primarily, the introduction of the modem form of regenerative setting composed of material ha ving greatly improved refractory qualities has rendered the first essential—the employment of high distillation temperatures—possible. The prolonged heating of the solid residue at temperatures of about 1,100° C. is followed by the evolution of practically the last traces of volatile matter, with the result that the constituents of present-day coke are almost wholly of a “ fixed ” nature. It must be realized, however, that the procurement of high, makes of combustible gas does not in any way depend solely upon the efficient burning-ofE of the charge, but is due to a combination of small influences, each. of wliich requires expert and detailed supervision. On the average gasworks there are many insignificant items, probably unnoticed in the general way, which may account for some slight disorganization of working, and it is the suppression of these and the maintenance of the whole machine up to conoert pitch which teils its tale m the end. In addition to the higher heats of distillation now in use, the increased volume of gas may be ascribed largely to the following :— (a) More complete gasification of tarry vapours, so that otherwise condeusible products yield permanent gas. (S) Increase of volume obtained by over-cracking the primary gas within the economical limit. (c) The use of light seals, or no seals, in the “ hydraulic ” mains, and the strict avoidance of tar seals.