5.2 Hand Firing

Although hand firing is seldom used, it is included here to explain a simple application of combustion fundamentals. The grates serve the twofold purpose of supporting the fuel bed and admitting primary air. The front end of the grate was supported from the dead plate and the rear end by the bridge wall. The grate was not set level but was inclined toward the bridge wall. This was done to aid the operator in getting the fuel to the rear of the furnace and to carry a slightly heavier fire near the bridge wall, where the effect of the draft is greatest.

Hand-fired grates were made of cast iron. They varied in design to suit the type of fuel to be burned. The air openings in the grates varied from 1/8 to 1/2 in in width, and larger air openings were used for burning bituminous than for burning anthracite coal. The bridging action of bituminous coal prevented it from sifting through the grates. Grates designed to burn bituminous coal had air openings equal to 40 percent of the total grate area, while those intended for anthracite had air openings equal to about 20 percent.

The width of the boiler limited the width of the furnace. The length of the furnace was limited to 6 or 7 ft by the physical ability of the operator to handle the fire. The actual grate area required for a given installation depended on its heating surface, the capacity at which...