Modern Gasworks Practice

THE HORIZONTAL RETORT BENCH 67 of the air supplies, from bad design of the producers, from neglect to clean the fuel-bed, or from defective chimney draught. (6) The use of a poor quality fuel containing a high proportion of asli. (c) Ill-fitting cleaning doors or producer charging-lids. Also ill-fitting plugs in sight-holes, cleaning boxes, etc. (d) Faulty stoking, resulting in the depth of the fuel falling below the pre-scribed level. Also neglect to level off the surface of the fuel-bed as far as possible. (e) Poor heat transmission between waste gases and secondary air, re.snlf.ing in high temperature of main waste-gas flue and chimney. A considerable proportion of the loss-under this heading may be recovered by installing a waste-heat boiler system. (f) Abnormal radiation losses, arising from imperfect lagging of all external walls. (</) Extensive variation in the composition of the producer gas. It must be realized that secondary-air adjustment is made to conform with. average conditions. Thus the influences which give rise to tiiese conditions should be maintained as consistently as possible. Variation in producer-gas composition may chiefly be traced to fluctuation in the depth of the fuel-bed, probably resulting from too in-frequent charging of the producer. The average producer, having a depth of from 6 to 8 feet, should never be permitted to go unreplenished for a period of longer than four hours. The necessary operation of cliiikering has a temporary ill-efl'ect upon the producer gas ; for, during the time when this is being carried out, the cleaning doors are open ; and, therefore, air is passing through the fuel-bed in unrestricted quantities. The result is that temperatures in the retort setting are temporarily reduced by the excess of air, while the temperature of the fuel-bed is considerably increased o wing to the complete combustion which is taking place therein. This means extrava-gance in the direction of fuel consumption, apart from the dislocation of the normal conditions prevailing with gaseous firing. The effect may be considerably modified by substituting a special type of grate (such as the Grille Grate), and by precluding the formation of clinker. The old-fashioned type of horizontal bar-grate, with. its predisposition towards the formation of large masses of clinker, frequently entails a clinkering period of half an hour. With the modern sloping grate, however, removal of the friable ash can usually be eflected in less th.an ten minutes. In some instances at the present time it is customary to work with the producer cleaning doors removed. Primary-air adjustment is then effected by regulation of the main waste-gas dampers which are closed to about one-flfth. of the damper opening employed with. the doors in place. The method has its advantages, its chief merit being that the conditions remain. practically constant throughout, as there is no increase in the quantity of air passing through the fuel-bed during the process of cleaning the fire. Incidentally, expense is saved as no doors are required. The only defect of such a method of working is that it does not permit of so fine an adjust-ment of combustion as is given by the employment of primary-air slides. Again,