€2 MODERN GASWORKS PRACTICE
from actual tests carried out with continuous verticals subjected to steaming, are appended:—
Coke sold per ton of coal. Per cent, used as fuel and in steaming.
(a) Beresford Seam Coal .... (ö) Haigh Moor (c) Lanark Washed Nuts .... 10 cwts. 11 9-25 „ 1042 „ 37-5 per cent, of total coke made-18'8 » „ „ „ 29-6 (approximate). 22-0 (approximate).
The above tests would seem to indicatc tliat there is a good deal of divcrgence in fuel results obtained with verticals. It must be remembered, however, that the figures for coke sold exclude that portion of the coke utilized in making blue water gas in situ.
An interesting illustration of the quantity of coke sold per ton of coal carbon-ized is obtained by a consideration of the average figure of the three metropolitan gas undertakings. These undertakings employ horizontal retorts almost exclusively.
Average Coke Sold per Ton of Coal (Metropolitan Gas Companies).
Year. Sold. Per cent, used as fuel.
1895 9-65 cwts. 22 per cent, of total coke made.
1905 9-55 „ 23
1915 9-71 „ 21
1916 9-91 „ 20
1917 9-98 „ 18
1918 10-05 „ 17-5 „
The above figures indicate that the proportion of coke employed for carboniza-tion of the coal shows a gradual tendency to decrease as improved methods of firing are introduced.
THEORY OF COMBUSTION
An elementary scientific fact which must be realized at the outset is that a definite amount of coke, wh.eth.er burnt at once to CO2 in the direct fire, or in two stages, as in the gaseous furnace, in each instance yields a similar number of heat units. This may be simply illustrated as follows:—
(1) 1 Ib. of carbon bumt direct to CO2 evolves (approximately) . 14,600 B.Th.U.
(2) 1 Ib. of carbon burnt to CO evolves ____________________.... 4,400
1 Ib. of CO bumt to CO2 evolves . 4,371
Ist stage. 1 Ib. of carbon—
C + i (O2) = CO
1 Ib. C = 2-333 1b. CO = 4,400 B.Th.U.
2nd stage . . 2-333 1b. CO = 2-335 X 4,371 = 10,200 „
Total 14,600