“Difference in mode of firing only may produce a difference of 13 per cent. (in economy).”
The thickness of the fire under the boiler should be in accordance with the quality and size of the fuel. For hard coal the fire should be as thin as possible, from three to six inches deep; when soft coal is used, the fire should be thicker, from five to eight inches deep.
If it is required to burn coal dust without any change of grates, wetting the coal is of advantage; not that it increases its heat power, but because it keeps it from falling through the grates or going up the chimneys. The same is true of burning shavings; by watering they are held in the furnace, and the firing is done more easily and with better results.
Stirring the Fire should be avoided as much as possible; firing should be performed evenly and regularly, a little at a time, as it causes waste fuel to disturb the combustion and by making the fuel fall through the grates into the ash pit; hence do not “clean” fires oftener than absolutely necessary.
The slower the velocity of the gases before they pass the damper, the more nearly can they be brought down to the temperature of the steam, hence with a high chimney and strong draft the dampers should be kept nearly closed, if the boiler capacity will permit it.
No arbitrary rule can be laid down for keeping fires thick or thin. Under some conditions a thin fire is the best, under others a thick fire gives best economy. This rule, however, governs either case: you must have so active a fire as to give strong radiant heat.
One of the highest aims of an expert fireman should be to keep the largest possible portion of his grate area in a condition to give great radiant heat the largest possible part of the day—using anthracite coal by firing light, quick and often, not covering all of the incandescent coals. Using bituminous coal, hand firing, by coking it very near the dead plate, allowing some air to go through openings in the door, and by pushing toward the bridge wall only live coals—when slicing, to open the door only far enough to work the bar; this is done with great skill in some cases.
Regulating the Draft.—This should be done so as to admit the exact quantity of air into the furnace, neither too much nor too little. It should be remembered that fuel cannot be burned without air and if too much air is admitted it cools the furnace and checks combustion. It is a good plan to decrease the draft when firing or cleaning out, by partly closing the damper or shutting off the air usually admitted from below the grates; this is to have just draft enough to prevent the flame from rushing out when the door is opened.
By luminous flame is generally meant that which burns with a bright yellow to white color. All flame under a boiler is not luminous, sometimes the whole or a part of it will be red or blue. The more luminous the flame, that is to say, the nearer white it is, the better combustion.