Modern Gasworks Practice

612 MODERN GASWORKS PRACTICE 2. There must be a sufficiency of surface area of catalytic material exposed per unit volume of gas passed. 3. The reaction is affected by the porosity, specific heat and thermal conductivity of the porous carrier of the catalyst, and also by the volume of free space allowed between the contact surfaces. 4. The presence of sulphuretted hydrogen in the gas before treatment decreases the efficiency of the process, which cannot, therefore, be advantageously applied to crude gas. It seems probable that carbon oxysulphide is produced by conducting gas containing carbon monoxide and sulphuretted hydrogen over the catalyst— (2) H,S = H2 + S. (2) CO + S = COS. It is possible, in faet it has been found in practice, that the small quantity of carbon oxysulphide formed may give trouble in the way of sulphuretted hydrogen stains. This may probably be explained by the fact that wheu the gas enteis the Station meters the carbon oxysulphide combines with the water as follows— COS + H2O = CO2 + H2S. Ammonia is to be found at the outlet of the plant, and results from the hydrolysis of hydrocyanic acid, which occurs on the lines described in the previous ch apter (see page 564). The inventors point out that although this ammonia is too small in quantity to represent a financial asset, it serves a useful purpose in mamtaining the oxide of iron used to remove the sulphuretted hydrogen (formed by the decom-position of the CS2) in a strongly alkaline condition. Practically the whole of the oxygen is removed by the process, but there is ueithcr increase nor decrease in the volume of gas. So far as the effect on the general composition of the gas is con-cerned, Dr. Carpenter1 has given the following figures:— Analysis of Gas. CO 2, per cent, by volume . Unsaturated hydrocarbons . Oxygen .... Carbon monoxide Methane .... Hydrogen .... Nitrogen .... Illuminating power Calorific power, B.Th.U. gross Before Treatment. 1-44 3-55 0-33 8-16 26-85 54-19 5-48 14-7 . 590-0 After Treatment. 1-45 3-63 0-06 8-03 27-26 54-25 5-32 14-7 594-4 A complete view of the plant, with explanation of the working, is shown in Fig. 375. The plant illustrated is that in operation at the East Greenwich works of the South Metropolitan Gas Company and consists of five units each capable of dealing with three million cubic feet of gas per day. Each unit is provided with a producer (zt) and a combustion chamber (B). On either side of the combustion chamber are the heating chambers (C), which contain the reaction tubes (F). The gas (purified 1 Proc. Inst. Gas Eng., June, 1914.