Modern Gasworks Practice

392 MODERN GASWORKS PRACTICE by blowing water gas into the retort towards the end of the charge. This scheme has been tried on several works but has now been discontinued, preference now being shown for admitting the water gas to the hydraulic or foul mains. J. G. Aarts 1 proposes that the hot mass of coke, after its discharge from the carbonizing chamber, should be exposed over its whole length and at both sides to jets of superheated steam directed towards the middle of the mass under constant conditions of quantity, velocity, and temperature. In this way advantage is taken of the usual fissures in the longitudinal direction of the mass to allow of the rapid escape of the gases containing ammonia, so that dissociation of the latter is avoided as far as possible. Aarts’ invention provides for the glowing mass of coke, as it leaves the carbonizing chamber, to be moved past tubes arraiiged transversely to the direction of movement, and provided with. steam nozzles. The velocity and quantity of the steam should, the patentee says, be regulated in accordance with the velocity, mass, and temperature of the coke, so that “ a sufficient quantity of nascent hydrogen is formed to give.the maximum yield of ammonia, and that the temperature of the coke is reduced sufficiently to prevent as far as possible decom-position of the ammonia formed.” So far as gasworks are concerned the many suggestions for recovering a greater proportion, of the nitrogen of coal have as yet led to no very satisfactory result; but the problem is of deep concern to the gas engineer, and should not be allowed to rest. It has been solved in part by the introduction of the vertical retort and the process of steaming the coal charge (see page 424). Details of the working of vertical retorts collected over a considerable period show that, with steaming carried out continuously, the .normal yield of 35 gallons of 8 oz. ammoniacal liquor per ton of coal may be enhanced to something between 50 and 60 gallons. Tlie reason why this appreciable increase occurs has not as yet been definitely explained, but as ammonia begins to decompose at a temperature of 500° C., and is almost completely broken down if it comes into contact with hot surfaces at 800°, it would seem that the steam, involving as it does an absorption of heat, exercises a cooling action in the retort, and also acts as a shield to the ammonia vapours. In this respect it may be noted that the continuous vertical retort, unlike the horizontal pattern, is not subject to a stage in the distillation period when the temperature of the charge approaches that of the retort, and thus the chief dis-integrating influence is eliminated. Again, the work of Tervet and Beilby throws a good deal of light on the question. Tervet, in fact, succeeded in obtaining a yield of ammonia equivalent to 571b. of sulphate of ammonia per ton of coal, and he showed that, if a stream of hydrogen is passed through the incandescent coke remaining after carbonization, ammonia is formed by combination of the hydrogen with the residual nitrogen of the coke. This work was corroborated by Beilby, who employed a mixture of air and steam in lieu of hydrogen, so that the vertical retort process of to-day may be looked upon as a partial application to the gas retort of the principles made use of in the manufacttire of Mond gas. A later development which should also 1 Eng. Pat. 11,202, 1916.