DIRECTIONS FOR FIRING WITH VARIOUS FUELS.
Firing Boilers Newly Set, etc.—Boilers newly set should be heated up very slowly indeed, and the fires should not be lighted under the boilers for at least two weeks after setting, if it is possible to wait this length of time. This two weeks enables all parts of the mason work to set gradually and harden naturally; the walls will be much more likely to remain perfect than when fires are lighted while the mortar is yet green.
When fire is started under a new boiler the first time, it should be a very small one, and no attempt should be made to do more than moderately warm all parts of the brick work. A slow fire should be kept up for twenty-four hours, and on the second day it may be slightly increased. Three full days should elapse before the boiler is allowed to make any steam at all.
When the pressure rises, it should not be allowed to go above four or five pounds, and the safety valve weight should be taken off to prevent any possibility of an increase. Steam should be allowed to go through all the pipes attached for steam, and blow through the engine before any attempt is made to get pressure on them. The object of all these precautions and this care is to prevent injury by sudden expansion, which may cause great damage.
Firing with Coke.
Coke, in order to be completely consumed, needs a greater volume of air per pound of fuel than coal. Theoretically it needs from 9 to 10 lbs. of air to burn a pound of coal, and 12 to 13 lbs. of air to burn a pound of coke.
Coke, therefore, requires a more energetic draft, which is increased by the fact that it can only burn economically in a thick bed. It is also necessary to take into account the size of the pieces.
The ratio between the heating and grate surface should be less with coke than with coal; that is to say, the grate should be larger.
The difference amounts to about 33 per cent. In fact, about 93⁄4 lbs. of coke should be burned per hour on each square foot of grate area, while at least 141⁄2 lbs. of coal can be burned upon the same space.