HIGH TEMPERATURE CARBONIZATION OF COAL 435
The Travel of Gas in Vertical Retorts
So far as the path by which the gas finds its exit from the horizontal retort is concerned, when once a ring of hot coke has been formed around the cool coal core the only way of escape for the products is through this heated zone. In both types of vertical retorts, however, matters are different, and the volatile constituents may leave either by way of the cool central core, or by evolution from the outer layers of the pasty envelope they may travel upward through the heated coke. The former, owing to the absence of excessive degradation, is, of course, the most desirable outlet, and Bueb is of the opinion that with intermittent vertical systems the gas takes this course. Colman, however, holds the view that Bueb’s hypothesis is only true to a very limited extent, except in cases where no pasty envelope is formed— as with shales and non-caking coals. Colman corroborated his views by analysing the gas from various portions of the retort, with the following results :—
Gas drawn from coal core. Gas drawn from coke zone. Final gas obtained.
Hydrogen 45-3 per cent. 59'0 per cent. 53-5 per cent.
Methané 37-2 20-2 28-0
Carbon monoxide 8-8 12-9 11-9
Carbon dioxide 5-9 3-0 3-2
Unsaturated hydroearbons .... 2-0 1-9 2-3
Oxygen. , nil nil nil
Nitrogen 0-6 3-2 1-3 „
The marked resemblance of the final gas to that obtained from the coke zone will be noticed.
Vertical retorts, thougli having fully established their claims in many directions, are still passing through a stage more or less of evolution, and therefore it is inopportune to discuss their relative merits as carbonizing agents compared with. the time-honoured horizontal retorts. One cannot do better than quote the views of an authority who has had every opportunity of experimenting with all kinds of plant. His opinion is that “ on summing up the respective balance-sheets, very little difference may be found between the two competitive systems, and local circumstances may settie the question one way or the other.”