“A moderately thick and hot fire with rapid draft uniformly gave the
best results.
“Combustion of black smoke by additional air was a loss.
“In all experiments the highest result was always obtained when all the
air was introduced through the fire bars.
“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.
TO DETERMINE THE TEMPERATURE OF A FURNACE FIRE the following table is
of use. The colors are to be observed and the corresponding degrees of
heat will be approximately as follows:
Faint red 960° F.
Bright red 1,300° F.
Cherry red 1,600° F.
Dull orange 2,000° F.
Bright orange 2,100° F.
White heat 2,400° F.
Brilliant white heat 2,700° F.
That is to say, when the furnace is at a “white heat” the heat equals
2,400 degrees Fahrenheit, etc.
Another method of finding the furnace heat is by submitting a small
portion of a particular metal to the heat.
Tin melts at 442° F.
Lead „ „ 617° F.
Zinc „ „ 700° F. nearly.
Antimony melts at 810 to 1,150° F.
Silver melts at 1,832 to 1,873° F.
Cast Iron melts at 2,000° F. nearly.
Steel „ „ 2,500° F. „
Wrought Iron melts at 2,700° F. „
Hammered Iron melts at 2,900° F. „