The removal of the ashes and clinkers should be accomplished as infrequently as possible, since opening the doors of the ash-pit and of the combustion-chamber necessarily causes an inward suction of cold air which is harmful.
As a rule with generators employing anthracite coal, it is sufficient to empty the ash-pit twice daily; this should be preferably done during stoppages. However, the cleaning of the grate by means of a poker passed between the grate-bars or over them in order to bring about the falling of the ashes, should be attended to every two to four hours, according to the type of the generator and the nature of the fuel. In order that this cleaning may be done without opening the doors, the latter should be provided with apertures having closing devices.
This cleaning has for its chief object to allow the free passage of the air for supporting combustion and to keep the incandescent zone in the apparatus at the proper height. The accumulation of ashes and clinkers at the bottom of the retort will shift this zone upward and impair the quality of gas.
=Stoppages and Cleaning.=--After closing the gas-inlet to the engine, the damper in the gas-outlet flue of the generator should be opened and the cocks controlling the feed of water to the scrubber and to the vaporizer should be closed.
If it is desired to keep up the fire of the generator during the stoppage so as to be able to start again quickly, the ash-pit door should be opened so as to produce a natural draft which will maintain combustion. While the door is open, the clinkers which have accumulated above the grate may be removed, as they are much more easily taken off the grate when they are hot.
At least once a week the fire in the generator should be put out and the generator completely cleaned--that is, when ordinary fuel is employed. For this purpose, as soon as the apparatus is stopped, a portion of the incandescent fuel is withdrawn through the doors of the combustion-chamber, and the retort is allowed to cool before it is emptied entirely. Too sudden a cooling of the retort may injure its refractory lining. In order to prevent explosions caused by the entrance of air, the feed-hopper should remain hermetically closed during the removal of the incandescent fuel through the doors of the combustion-chamber.