Handbook of Railroad Construction; For the use of American engineers. / Containing the necessary rules, tables, and formulæ for the location, construction, equipment, and management of railroads, as built in the United States.

by George L. Vose

Now let A be the number of lbs. of coke per foot of water evaporated.

B the number of lbs. of coal per foot of water evaporated.

C the number of lbs. of wood per foot of water evaporated.

Call d the depth at which if is the most economical to burn coke; d′ the same depth for coal, and the depth for wood d″. Then will the area of a coke grate be

A
d;

Of a coal grate

B
d′;

And of a wood grate

C
d″.

To be able to fix the proper grate area for any fuel, we must know its evaporative power, and a depth of a layer in the furnace. Knowing the absolute value for coke, it remains only to obtain the relative value for any other. Thus far we have disregarded the difference in time of burning wood and coke. To produce a given amount of heat, we burn a certain chemical value of fuel; a much larger bulk of wood than of coke is needed. If we burn wood and coke at the same depth and in the same time, the grate areas would be proportional to the bulks of fuel to produce the same heat; but, first, we burn fuel in a depth proportioned to the economic stowage bulk, or as 2.5 to 1.9, which decreases the wood area; and, second, a layer of coke 1.9 feet deep burns in one hour, while a layer of wood 24 feet deep burns in fifteen minutes; whence 60 m. divided by 15 m. = 4 layers of 2½ feet deep each, or in all ten feet, which into the bulk (equal to a mass of coke 1 foot square × 1.9 high) or 1 foot square by 14 high, gives 14 ÷ 10 = 1.4; or, finally, the area of the wood grate should be 1.4 times that of a grate to burn coke.