Modern Gasworks Practice

WATER GAS 697 The possibilities of the process are well illustrated by the following results cbtained from laboratory experiments — CONVERSION OF CO INTO METHANE h2 CO ch4 CO2 ' Na .B.Th.U per cu. ft. Mixture used for reduction . 80-9 16-3 — — 2-8 298 Mixtures after reduction: (a) 64-8 — 28-3 — 6-9 466 (6) . 60-6 0-2 31-8 14 5-8 488 (c) . 614 — 31-8 0-6 6-2 490 Ash Constituents as a Catalyst Considerable study has been given to the effect of catalysts in the reversible reaction known. as the water-gas equilibrium— CO +h2o^co2 +h2. In Connection with hydrogen manufacture a number of processes are based on the faet that in the presence of suitable catalysts steam and carbon monoxide react to give hydrogen and carbon dioxide as shown above, and at temperatures above 600° C. equilibrium is quickly established. It has been shown that iron and lime (constituents of ash) tend to promote the attainment of equilibrium, and for this reason it has been suggested that the ash. content of coke is operative in facilitating equilibrium. Gwosdz 1 has pointed out that over a range of 560°-855° C. a con-siderable proportion of carbon dioxide (up to 29 per cent.) is always fonned with coke containing 8-5 per cent, of ash ; whereas with pure carbon (lampblack with 0-1 per cent, of ash) even at 600° C. the water gas contained only 8-6 per cent, of carbon dioxide. The opinion of this investigator is that, in the primary reaction between coke and steam, carbon dioxide is not formed, but only carbon monoxide and hydrogen. This is followed by the establishment of the water-gas equilibrium in the upper layers of the fuel-bed, followed by catalysis promoted by the ash. in the fuel. Fürther experiments show that if steam is passed through coke the gas resulting •contains a comparatively high proportion of carbon dioxide. On tlie other hånd when, under the same conditions, retort carbon is substituted for coke the carbon dioxide content of the gas is extremely small, in faet under 1 per cent. Both theory and practice, therefore, point to the faet that the final gas mixture obtained and the proportion of incombustible gas present are a ffe et ed by the proportion of ash present in the fuel. As, therefore, equilibrium in the above-quoted reaction is most probably established in the upper layer of the fuel, there is every need to ensure that the steam flow to the generator is so regulated (particularly during the later minutes of the “run”) that the least possible excessshall pass through to the top portions of the fuel-bed. 1 Z. Angew. Chem., 1918, p. 137.