Modern Gasworks Practice

HIGH TEMPERATURE CARBONIZATION OF COAL 395 coal as calcium sulphate, whilst the volatile sulphur is chiefly derived from pyrites and certain organic sulphur compounds. Coals as commonly used for gasmaking contain a percentage of sulphur varying from 0-6 to 1-2, and that remaining behind. in the coke, under modem conditions of carbonization, seldom exceeds 0-8 to 1 per cent. Powell and Pair 1 suggest that sulphur occurs in coal in four characteristic forms, two of which are organic and two inorganic. The classification is made as follows:— (a) If the resinic organic type is shown. to be organic sulphur by its lack of an asli, its presence in the portion of the organic material soluble in phenol indicates its association with. that substance. (b) The humus organic sulphur is shown to be organic by the very small amount of ash in the compounds in which it occurs. These compounds are shown to be closely related to humus substances by their Chemical action. (c) The pyritic or marcasitic sulphur is present as FeS2 as indicated by the iron-sulphur ratio when the pyrites is oxidized and taken into solution. (d) The sulphate sulphur is shown to be such by the faet that it dissolves in dihite hydrochloric acid as sulphate without preliminary oxidation. All four forms were definitely proved to be present, and free sulphur was not found in any of the coal samples tested. The experimental data suggest that when. coal is coked the sulphate sulphur is retained by the coke, but in some form other than inorganic sulphate, that the pyritic sulphur is partially volatilized and a portion is also left in the coke, probably as sulphide. All the pyrites are decomposed. The resinic sulphur is left in the coke, but in a form different from that existing in the coal, and the humus sulphur volatilizes partly, but some remains in the coke in a changed form. The forms of sulphur in the coke were also studied, but could not be identified. A small part of the sulphur exists as sulphide, and the remainder is probably m combination with carbon. This last form is extremely stable to strong acids, oxidizing agents, and heat, but readily gives up its sulphur as hydrogen sulphide when subjected to the action of nascent hydrogen. During the coking process, secondary reactions between constituents of the coal and the decomposed sulphur compounds affeet the quantity of sulphur retained by the coke. As previously pointed out, sulphuretted hydrogen is a primary product of dis-tillation, and is one of the first products to be evolved. Colman says that the sulphur probably comes off in the first place as volatile compounds of carbon and hydrogen, and that these, when more strongly heated, yield sulphuretted hydrogen. A small quantity of sulphur, hydrogen and carbon compounds are, however, ultimately obtained, as an instance of which may be mentioned thiophen (C4H4S). This is freqnently found in the tar, although. traces of it are usually present in the small percentage of sulphur compounds in the finished gas. The sulphur compounds, as distinet from sulphuretted hydrogen, are chiefly Univ. Illinois Experimental Station, 1919.