Modern Gasworks Practice

VERTICAL RETORTS AND CHAMBER OVENS 169 are usually set fifteen to a bed, are 16 feet 6 inches long and each. carbonizes 25 cwts. of coal per diem. THE DEMPSTER-TOOGOOD SYSTEM The retorts in this system are 25 feet in length, and are charged by means of a gastight valve arranged with. two miets. One of these miets is for the ordinary pur-pose of charging in coal, the otter is for use in the case of those retorts which have undergone scurfing, and which first receive a charge of coke. As will be seen from Kg. 88, the coal is fed on the centre line of the retort. The taper of the retort is greater at the top than at the bottom ; this is to accommodate for expansion of th.e coal on. first heating. There are no stationary inclines or curved parts to support the charge, which during its downward travel meets successively larger cross-sections, until the extractor gear is reached. This actually supports the maximum cross-section of the charge, hence bridging or hanging-up is prevented. At the base of the retort is an inclined plate supporting the whole charge at the natural angle of repose, and the coke is gradually pushed ofE by the reciprocating motion of the plate, which makes one complete stroke in about seven minutes. The coke is cooled by circulating primary and secondary air around the base of the retorts, which are heated on their broad sides only. Each retort is provided with an independent secondary-air supply, producer-gas and waste-gas dampers, and with separate supply of superheated steam for steaming the charge. Thus every facility is provided for individual control of the heats. The retorts are built up from special moulded blocks to form round-cornered retorts, each of which. is rated to carbonize 5 tons of coal per day. Four retorts are laid in each bed. The retorts are approximately 5 feet wide by 18 inches broad at the bottom, this being reduced to 4 feet by 7 inches at the top. A consideration of importance in this system is that the active combustion. zone is neither at the top nor at the bottom. This, it is claimed, has some considerable effect on the life of the refractories, which are most liable to corrosive influences in the upper and lower portions of the retort. THE GLASGOW SYSTEM This system, designed by Mr. Alexander Wilson, was introduced for the purpose of dealing with the non-caking or semi-caking Scotch coals, which under ordinary circumstances give a particularly small and friable coke. In order thai the charge may have ampie time to consolidate, the coke is not drawn out continuously, but at intervals of about four hours. In this way a fairly large coke of good appearance is obtained. The quantity of coke extracted at each period of discharging is governed by the size of the wagon or shoot into which it is delivered ; this is due to the faet that as the receiving wagon filis up it supports the whole weight of the charge in the retort, the bottom mouthpiece when being closed cuttmg through, the coke column and sealing the base of the retort. No constantly moviug machinery is required, and the coke is cooled in the bottom cast-iron