128
MODERN GASWORKS PRACTICE
WORKING UNDER PRESSURE
Until comparatively recent years the prevailing fashion was to work the retort-beuch under a slight vacuum throughout the whole of the setting. It is now recog-nized, however, that more effective results are ensured by maintaining a pressure in certain portions of the bed. Every endeavour should be made to maintain a slight pressure in the combustion chamber, and this will depend to a large extent upon the position of the waste-gas damper. The latter should be opened to the least possible extent, and if adjustment must be made the primary slides should be turned to, when by further opening them matters will be improved, owing to the velocity of air through the fuel-bed being reduced. All producers are, unfortunately,. affected to no little extent by the varying conditions of the fire, such, as clinkering, “ pricking-up,” fluctuation in depth of fuel-bed, etc. ; but the mtroduction of the automatic damper slide (such as Brooke’s) has gone some way towards remedy-ing this annoyance. The objects of such slides are :— («) To reduce fuel con-sumption.
(b) To maintain a more regulär temperature in furn-ace and setting.
(c) To avoid excessive formation of clinker.
The apparatus (Fig. 65)-consists of a vane A attached to a rod on which moves an adjustable balance weight C.
The vane is supported from two small hook bolts on which it swings A flat spring E presses on the spindle, the intensity of the pressure being regulated by the adjustable screw F. There is also provided a damper plate H for use when shutting down, and a shield piece G. The regulators are made to fit into existing secondary-air flues, or to bolt on. to the front of clinkering doors for the regulation of primary air. The fuel saving by the introduction of these slides is said in certain cases to be about 3 1b. of coke per 100 1b. of coal carbonized.
A similar type of regulator is also made for use with cliimney skafts, which, owing to variations in atmospheric conditions, account for considerable fluctuations in draught. In this case the swing damper is balanced by means of a counterweight until it is just closed, when the desired draught is given. Any alteration of the main damper will then be accompanied by a movement of the regulator, which will open and admit cold air until the draught is reduced to the set amount. Variations due to atmospheric conditions will be similarly counteracted. It must be rememberecL however, that devices of the kind are of a comparatively delicate nature, and care-