Modern Gasworks Practice

WATER GAS 725 up in the generator effective distribution is impossible. Thus the air blast will find its way through certain portions only of the bed, which portions will be raised to an abnormally high temperature, whilst the remainder of the bed is in a condition of comparative coolness. . Local steaming of the bed may, in the same way, be due to the formation of clinker, although it frequently occurs from the steam supply nozzle being non-central, partly choked, or broken. Owing to the gradual reduction in temperature of the fuel-bed during the “ run ” it has become essential that the steam supply should undergo reduction as the period of gasmaking proceeds. In this way a much better quality gas will be obtained. The gradual diminution of the steam is unfortunately the exception rather than the rille, although it is now becoming more general. (4) Periods of “ Run ” and “ Blow.” The duration of the “ run ” and “ blow ” differs in accordance with the type of plant. The following show the average conditions of working :— “ Run.” “ Blow.” Lowe Plant .......................................... 5 minutes and 3 minutes. or 6 minutes and 4 minutes, “ K. & A.” Plant . . . . . . ■ . 5 minutes and 70 seconds. Dellwik Plant ____________________________________....... 6 minutes and 60 seconds. With the Standard type of carburetting plant the author has found that the most favourable results are obtained by working on the five-minutes’ “ run ” and three-minutes’ “ blow ” cycle, but that the “ run ” immediately prior to recharging the generator may be prolonged to six minutes. At such stages the fire is moderately shallow and exceedingly hot, and there appears to be a good yield of gas during the extra minute. After coking up, moreover, it is as well to prolong the “ blow ” to four minutes. Clinkering on water-gas plants must be carried out at frequent intervals, for if once the mass is allowed to grow it will gradually arch over in the generator until the latter is almost completely choked. With the Lowe plants it is advisable to perform the operation at intervals of four hours, although in cases where a good quality coke is procurable the period may be prolonged to six hours. In many of the “ blue ” gas plants with double generators clinkering takes place only once in ten or twelve hours. In recent years mechanical grates, which obviate the greater portion of the labour entailed in clinkering, have been introduced, but they are as yet confined to generators of the larger capacities. Briefly, they consist of specially designed firebars which are caused to rotate and scrape out both clinker and ashes. A generator fitted with such a grate, designed by Humphreys and Glasgow, is seen in Fig. 450. The Kerpely producer, which is built with a specially revolving ash-extracting grate, has already been referred to in Chapter III. (6) Carburatwn. In the original plants employed for the manufacture of car-buretted water gas it was usual to spray the oil direct on to the fuel in the generator. This procedure, however, proved decidedly wasteful, with the result that a separate vessel was soon introduced for purposes of carburation. The duty obtained from the carburetting medium employed will largely depend upon the männer in which