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MODERN GASWORKS PRACTICE
It will be appreciated that the principle of water-gas production depends upon the heat which is available in the fuel-bed and generator for raising the reacting substances to a temperature sufficient to complete those reactions which yield combustible gases.
In reality the blow reaction is as follows :—
C + 02 + 4 N2 = CO2 + 4 N2 + 14,600 B.Th.U. per Ib. of carbon.
It has been shown by experiment that in the water-gas process the reaction mainly predominating at 600° C. is
C +2H2O = CO2 + 2H,
At such temperatures only a small proportion of the water vapour is decomposed, but as the temperature is raised carbon dioxide gives way almost entirely to carbon monoxide. An indication of the efiiect of temperature is given by the following table :—1
Effect of Tempbratube on Water-Gas Reactions
Temp. Cent. Per cent, of steam decomposed. Per cent, by Volume.
Hydrogen. CO. COs.
674 8-8 65-2 4-9 29-8
758 25-3 65-2 7-8 27-0
838 41-0 61-9 151 22-9
954 70-2 63-3 39-3 6-8
1,010 94-0 48-8 49-7 1-5
1,060 93 0 50-7 48-0 1-3
1,125 994 50-9 48-5 0-6
As a matter of faet, at the lower temperatures the proportion of undecomposed steam would, in practice, be considerably greater than the percentages given in the above table.
Other figures 2 show the variation of the products to be as follows :—
Temp. of Carbon. Cent. Per cent, by Volume.
Hydrogen. CO. CO".
600 66 4 30
700 65 6 29
800 62 15 23
900 54 39 7
1,000 50 48 2
Clearly, therefore. the temperature of the fuel-bed should be maintained as far as possible above 1,000° C., even towards the end of the run.
1 Bunte.
Thorpe’s Diet. Applied Chem.