HIGH TEMPERATURE CARBONIZATION OF COAL 420
swept from the retort by the scouring action of the steam, while the state of dilution existing affects the position of gaseous equilibrium. Cobb has suggested that ammonia is formed by the action of steam in breaking down complex nitrogen compounds. It should be understood that in the above table the figures given for coke yield represent the total coke made. In this instance the retorts were heated by surplus coal gas, thus no coke was employed as fuel.
The effect of various degrees of steaming on the ultimate composition of the gas is well illustrated by the analyses which accompany the five tests already quoted.
Effect of Steaming on Composition of Gas
Test No. I. II. III. IV. V.
Steam, per cent, on coal used Nil 13-3 22-1 32-7 44-8
Analysis of gas (per cent, by vol.):
Hydrogen 49-5 49-5 48-9 48-8 48-3
Methane 28-5 23-5 19-0 16-8 14-5
Unsaturated hydrocarbons .... 2-3 1-8 1-8 1-8 1-6
Carbon monoxide 10-3 13-8 16-4 17-4 17-9
Carbon dioxide 2-2 3-3 3-6 5-1 6-6
Nitrogen 6-8 7-5 9-4 9-2 10-1
Oxygen 0-4 0-6 0-9 0-9 1-0
Total inert constituents 9-4 11-4 13-9 15-2 17-7
Calorific power, B.Th.U. gross 544 482 447 436 410
If the above percentages are converted into cubic feet of each constituent per ton of coal it will be observed that not only have hydrogen and carbon monoxide been generated but the hydrocarbons have also been augmented. Thus :—
Cubic Feet per Ton of Coal Cabbonized
Test No. I. II. III. IV. • V.
Methane Unsaturated hydrocarbons 2,669 215 2,976 228 2,892 274 2,992 320 2,841 313
It will be observed that the quality of the extra gas tends to fall with increasing quantities of steam, and the problem arises as to what percentage steaming may be carried before the desirable limit is passed. Much must depend upon. the dass of coals employed, but it should be noted that with steaming at 32-7 per cent, not only has the calorific power of the mixture fallen to 436, but inerts are present in the proportion of over 15 per cent. To conform, therefore, with present-day ideas as to the most economic gas to supply, it would appear that it is not advisable to exceed 30 per cent, of steam on the weight of coal used.
The main difficulty when steaming is carried out on a high percentage basis