Modern Gasworks Practice

THE HORIZONTAL RETORT BENCH 65 the temperature of the gases has, in the modern regenerator, been reduced to 530°-650° C. before their escape is permitted, this accounting for a saving in fuel of from 6 to 11 per cent, compared with the generator setting. In the ordinary way the secondary air approaches a temperature of 950° C. before combustion. THEORY OF REACTIONS The exact nature of the reactions occurring in the fuel-bed during the formation of producer gas is still open to doubt. Argument is chiefly waged round the ques-tion as to whether the carbonic oxide is formed by direct combination between carbon and oxygen, or whether the greater proportions of it is the outcome of the reduction of carbon dioxide to the monoxide. Some valuable research, on the subject has been carried out by Rhead and Wheeler,1 who foimd strong evidence of the faet that neither carbon dioxide nor carbon monoxide is formed at the outset, but that both. oxides are produced simultaneously as a result of the decomposition of a complex CxOy, which they regarded as the primary product of the combination of oxygen and solid carbon. Bone 2 regards this as being the best available hypo-thesis, and states that the production of the oxides of carbon in such, a manner would be accompanied by a rapid attainment and adjustment of a mobile equilibrium in the reversible system— 2 CO C + C02 in consonance with the temperature in each successive layer as the mixture of gases ascends through the fire. The whole theory, however, is complicated by the faet that, during the combustion of solid carbon, the above reversible reaction beging to manifest itself at approximately the same temperature as that at which oxidation begins. Thus, whilst CO2 may be reduced to CO, the CO may in turn be dissociated into carbon and CO2, an equilibrium being eventually established. Rhead and Wheeler, however, have recorded that the velocity of the reduction of carbon dioxide to carbon monoxide is invariably very mueh greater than the velocity at which carbon monoxide is dissociated. Perhaps the whole case cannot be better summed up than by quoting Bone,3 who says that we are justified in concluding that in the lower layers of the furnace, where the incoming primary air meets the incandescent coke, there probably results very rapidly a mixture of CO and CO2 in nearly the equilibrium proportions corresponding to the prevailing temperature, and to the partial pressures of these gases, and that at 1,200° C. (2,192° F.) and upwards CO will constitute nearly 99 per cent, of the total oxides of carbon present. From the practical point of view of the gas engineer, however, it is perhaps as well to regard the finer considerations outlined above as chiefly of academic interest. With the modern appliances at his disposal the gas engineer judges the situation from its practical results, and he knows füll well that when the depth of his fuel-bed falls below a minimum of some 4 feet, be obtains a high, proportion of carbon dioxide in his producer gas, foliowed by greater heat in the producer than in the combustion 1 Trans. Chem. Soc., 1912, 101, 846, also 1913, 103, 461. 2 Cool and its Scientific Uses, p. 171. 3 Loo. cit.