Modern Gasworks Practice

698 MODERN GASWORKS PRACTICE It has been suggested that the small proportion of methane (0’5 to 1 per cent.) found in blue water gas is due to interaction between carbon monoxide or dioxide and hydrogen promoted by the ash acting catalytically. The contention, however,. is open to considerable doubt, particularly in view of the faet that for such inter-action it would seem necessary for nickel to be present. The most feasible explana-tion of the presence of methane is that it appears as a distillation product from those portions of tacky coke which must inevitably find their way to the generators. WATER-GAS SYSTEMS The systems which have been introduced for the purpose of manufacturing water gas may be classifled under the following three headings:— (1) The Continuous System. (2) The Intermittent System. (3) The Neat-Oxygen Method. Of these, the intermittent method is the only one to which serious considera-tion is given to-day. The continuous system, in which it was sought to replace the lost heat by independent external firing, received much attention in the early days of water gas ; and was in one respect to be commended, in that it endeavoured to provide for the uninterrupted manufacture of the gas and obviated the periods of blowing. Practical difficulties, heat losses by radiation, and general inefficiency, however, soon. sounded its knell, with the result that there are no examples of the method now extant. The intermittent process, with “ run ” and “ blow ” succeeding each other at regulär intervals, has shown itself, by the test of time, to be the only practicable method. A scientific and by no means impracticable system is that embodying the use of neat oxygen. The process operates on continuous lines and results in a gas practically free from nitrogen, but containing from 65 to 70 per cent, of carbon monoxide. Steam is admitted to the base of the generator in the ordinary manner ; and, along with it, is passed a stream of pure oxygen. In this way, whilst steam is combining: with a portion, of the carbon to form water gas, the heat lost by the endothermic-nature of the reactions is replaced by the exothermic combination of the oxygen with part of the carbon. If steam and oxygen are regulated. in accordance with theoretical requirements the process will proceed with little trouble. The chief drawback, which has as yet prevented the system from making any great headway, is the impossibility of obtaining oxygen at a price which would permit the gas to compare in cost with that produced by the more general methods. Some mention should be made here of the distinction between carburetted water gas and oil gas, the latter misnomer being still in somewhat common use for the former product. Oil gas, in the true sense of the name, is the gaseous mixture of hydrocarbon vapours resulting from the direct conversion of oil into gas, in an iron. retort, such as takes place in the Peebles and Pintsch processes. In this way a. gas ha ving an illuminating power of from 60 to 70 candles is obtained. An important feature of such processes is the further washing of the gas in oil, whereby any vapours-