Modern Gasworks Practice

68 MODERN GASWORKS PRACTICE the conditions are more easily influenced by the effect on chimney draught of changes in the direction and in the velocity of the wind. (Å) Insufficiency of producer gas. While, from the standpoint of analysis, regulation of the air supplies may be perfect, indifferent heats are none the less found. This is due to insufficiency of furnace gas. The most ready practical means of ascertaining whether the requisite quantity of gas is passing through, the setting is to remove the inspection plug from the combustion chamber and to note, by holding a piece of lighted yarn to the open hole, whether conditions of vacuum or pressure are prevailing in the chamber. If the gas is deficient in quantity a vacuum will be found, and this should be transformed into a slight pressure By increasing the primary air-supply, with, of course, a corresponding increase of secondary air. On the other h.and, the vacuum may be caused by excessive pull through, the waste-gas dampers. Such conditions, however, are usually accompanied by roaring at the damper, and excessive heat of the base of the flue. (i) Charging with “ tacky ” coke. A warning is necessary with regard to replenishing producers with. badly carbonized or “ tacky ” coke ; and if the charges in the retort are not fully burnt-off, their discharge into the furnaces should be post-poned. The effect of sticky coke is to form a distillation zone on the top of the fuel-bed, thus a certain proportion of the heat of the fuel is absorbed in driving of? the volatile constituents. Moreover, as the supply of secondary air h.as not been adjusted to deal with the extra volume of combustibles thus yielded, the result is that complete combustion of the furnace gas is not obtained. The defect shows itself in the form of black smoke issuing from the retort-house chimneys, or by the appearance of a red flame after dark. (/) Short-circuiting. A general loss of efficiency results from short-circuiting, which most usually occurs when furnace linings are badly eroded and require removal. Accordingly, air from the secondary flues is passing into the fuel-bed and is followed by oxidation of the CO to CO2. If leakage is severe, the only satisfactory manner of putting matters right is to let the beuch down and to renew completely the brickwork forming the furnace cheeks. When the old brickwork is removed, the precaution should be taken of stopping up all tile joints in the exposed wall of the regenerator. With a properly constructed regenerator it is very seldom that leakage occurs between the secondary-air and waste-gas duets. Moreover, as the vacuum in each of these duets is almost identical, th.e effect of slight cracks, bad joints, etc., in the parting wall is not particularly serious. THE EFFECT OF STEAM Some precaution is necessary in the procedure of steaming the fuel. It is still in some cases the practice to provide water-sealed ash-pans for the producer, so that ashes falling through the firebars are quenched, with the formation of steam. At the same time, a longer life is ensured for the firebars by the provision of a con-tinuous trickle of water—this giving rise to further quantities of steam. The primary duty of the steam is that of keeping the base of the fuel-bed cool in comparison with the remainder, so that excessive fluxing of the ash is prevented, and the formation