396
MODERN GASWORKS PRACTICE
formed at the higher temperatures, due to the combination of part of the sulphur with. carbon. The higher the temperature of distillation the greater will be the quantity of sulphur driven off from the coke, and extended travel of the gas through heated coke or in contact with hot surfaces accounts for the decomposition of sulphur-•etted hydrogen and the subsequent formation of carbon disulphide. Accordingly, when secondary reaction at high, temperatures is permitted to take place, the easily removable sulphuretted hydrogen gives place, in part, to undesirable compounds, such, as carbon disulphide, which are only eliminated from the gas with great trouble. Sulphuretted. hydrogen is usually present in the crude gas in the proportion of about 1-5 per cent., whilst the other sulphur compounds together total no more than 0-05 per cent.
The influence of yield of gas per ton (therefore, temperature) on the production ■of sulphur compounds other than sulphuretted hydrogen has been shown by figures given by Lewis T. Wright:—
Gas made per ton. Cubic feet. 6,896 8,370 9,431 10,772 11,620 Sulphur other than H2S. Grains per 100 cubic feet. 13-91 19-16 26-75 36-93 44-17
Again, the influence of the duration of the carbonizing period is illustrated by the folio wing results given by Ferguson Bell1:—
Duration of charges. CO2 per cent, by volume. H2S per 100 cubic ’feet. CS2 per 100 cubic feet.
Hours. Grains. Grains.
6 3-20 736 43-40
8 3-19 996 60-20
10 3-10 814 56-10
12 3-25 020 47-40
■Some investigators have given the opinion that the distribution of the sulphur ■ of the coal amongst the products of carbonization depends largely on the character of the constituents forming the ash. J. R. Campbell,2 for instance, found that wlien the coke ash is rieh in oxides of iron, calcium, and magnesium, a coke free from sulphur cannot be obtained. In this respect the figures below, given by Percy, are .of interest:—
Trans. Inst. Gas Engineers, 1909.
Chemiker Zeitung, Feb. 10, 1917.