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 9-3/4 lbs.
of coke should be burned per hour on each square foot of grate area,
while at least 14-1/2 lbs. of coal can be burned upon the same space.
The high initial temperature which is developed by the combustion of
coke requires conducting walls. Therefore the furnace should not be
entirely surrounded by masonry; and the plates of the boiler should
form at least the crown of the fire-box. In externally fired boilers,
the furnace should be located beneath and not in front of the boiler.
Internal fire-boxes may be used, but the greatest care should be
exercised to avoid any incrustation of the plates, and in order that
this may be done, only the simplest forms of boilers should be used.
With coke it is not essential that long passages should be provided for
the passage of the products of combustion, since the greater part of
the heat developed is transmitted to the sheets in the neighborhood of
the furnace.
Since coke contains very little hydrogen, the quick flaming combustion
which characterizes coal is not produced, but the fire is more even and
regular. And, finally, the combustion of coal is distinguished by the
fact that in the earlier phases there is usually an insufficiency of
air, while in the last there is no excess.
The advantage of coke over raw soft coal as a fuel is that otherwise
useless slack can be made available by admixture in its manufacture,
and especially that it can be perfectly and smokelessly burnt without
the need of skilled labor. And we cannot doubt that the public demand
for a clear and healthy atmosphere will finally result in the almost
complete substitution of coke fuel for soft lump coal.
SIXTEEN STEAM BOILERS in a large mill in Massachusetts of 54 and 60
inches in diameter are fired as follows:
There are three separate batteries; one of five boilers, one of eight
and one of three. Each boiler is fired every five minutes. There are
two firemen for the battery of twelve and one for each of the others.
A gong in each fire-room is operated by electricity in connection with
a clock. The duty of the fireman is this, that when the gong strikes he
commences at one end of his fire-room and fires as rapidly as possible,
opening one-half of each furnace door. The coal is thrown only on
one-half of the grate space as he rapidly fires each boiler, the
other half is covered at the next sounding of the gong. The old style
of straight grate is used. The fires are kept six inches thick or a
little thicker. No slicing is done. It is, of course, to be understood
that the firemen arrange the quantity of coal fired according to the
apparent necessity of the case. Bituminous coal is used, and it is
broken into small pieces, so as to distribute well. Accurate account
is kept of the quantity of coal used and the engines are frequently
indicated.
TWENTY HORSE POWER.—An old engineer says the way he handled his boiler
of this size, burning 800 lbs. of screenings per day, is as follows:
My method is to run as heavy a fire as my fire-box will allow to be
kept under the bridge wall, and not to disturb it more than once in a
ten-hours run, then clean out with care and as speedily as possible,
dress light and let it come up and get ready to bank. In banking I make
sure to have an even fire, as deep as the bridge wall will allow. Then
I shut my dampers and let it lie. In the morning I open and govern by
the dampers. I do not touch my fire until 3.30 or 4 o’clock in the
afternoon, and then proceed to clean as before.
FIRING WITH COAL TAR.—The question of firing retort benches with tar
instead of coke has engaged the attention of gas managers for many
years, and various modes have been adopted for its management. The
chief difficulty has been in getting a constant flow of tar into the
furnace, uninterrupted by stoppages caused by the regulating cock or
other appliance not answering its purpose and by the carbonizing of
the tar in the delivery pipe, thus choking it up and rendering it
uncertain in action. To obviate these difficulties various plans have
been resorted to, but the best means for overcoming them are thus
described; fix the tar supply tank as near the furnace to be supplied
as convenient, and one foot higher than the tar-injector inlet. A cock
is screwed into the side of the tank, to which is attached a piece
of composition pipe 3/8-inch in diameter, ten inches long. To this a
1/2-inch iron service pipe is connected, the other end of which is
joined to the injector. By these means it is found that at the ordinary
temperature of the tar well (cold weather excepted) four gallons of
tar per hour are delivered in a constant steam into the furnace. If
more tar is required, the piece of 3/8-inch tube must be shortened,
or a larger tube substituted, and if less tar is required it must
be lengthened. The risk of stoppage in the nozzle of the injector
is overcome by the steam jet, which scatters the tar into spray and
thus keeps everything clear. Trouble being occasioned by the retorts
becoming too hot, in which case, on shutting off the flow of tar
for a while, the tar in the pipe carbonized and caused a stoppage,
a removable plug injector is fitted and ground in like the plug of
a cock, having inlets on either side for tar and steam. This plug
injector can be removed, the tar stopped in two seconds and refixed in
a similar time. The shell of the injector is firmly bolted to the top
part of the door frame. The door is swung horizontally, having a rack
in the form of a quadrant, by which it is regulated to any required
height, and to admit any quantity of air.
FIRING WITH STRAW.—The operation of burning straw under a boiler
consists in the fuel being fed into the furnace only as fast as needed.
When the straw is handled right, it makes a beautiful and very hot
flame and no smoke is seen coming from the stack. The whole secret
of getting the best results from this fuel is to feed it into the
furnace in a gradual stream as fast as consumed. When this is done
complete combustion is the result. A little hole maybe drilled in the
smoke-box door, so that the color of the fire can be seen and fire is
handled accordingly. When the smoke comes from the stack the color of
the flame is that of a good gas jet. By feeding a little faster the
color becomes darker and a little smoke comes from the stack; feeding a
little faster the flame gets quite dark and the smoke blacker; faster
still, the flame is extinguished, clouds of black smoke come from the
stack, and the pressure is falling rapidly.
FIRING WITH OIL.—Great interest is now manifested in the use of oil as
fuel. There are various devices used for this purpose, most of them
depending upon a steam jet to atomize the oil, or a system of retorts
to first heat the oil and convert it into gas, before being burned.
Another method in successful operation is the use of compressed air
for atomizing the oil—air being the element nature provides for the
complete combustion of all matter. The cleanliness of the latter system
and its comparative freedom from any odor of oil or gas and its perfect
combustion, all recommend it. Among the advantages claimed for the use
of oil over coal are 1, uniform heat; 2, constant pressure of steam;
3, no ashes, clinkers, soot or smoke, and consequently clean flues; 4,
uniform distribution of heat and therefore less strain upon the plates.
FIRING ON AN OCEAN STEAMER like the “_Umbria_.”—The men come on in
gangs of eighteen stokers or firemen and twelve coal passers, and
the “watch” lasts four hours. The “_Umbria_” has 72 furnaces, which
require nearly 350 tons of coal a day, at a cost of almost $20,000 per
voyage. One hundred and four men are employed to man the furnaces, and
they have enough to do. They include the chief engineer, his three
assistants, and ninety stokers and coal passers.
The stoker comes to work wearing only a thin undershirt, light trousers
and wooden shoes. On the “_Umbria_” each stoker tends four furnaces.
He first rakes open the furnaces, tosses in the coal, and then cleans
the fire; that is, pries the coal apart with a heavy iron bar, in order
that the fire may burn freely. He rushes from one furnace to another,
spending perhaps two or three minutes at each. Then he dashes to the
air pipe, takes his turn at cooling off, and waits for another call
to his furnace, which comes speedily. When the “watch” is over, the
men schuffle off, dripping with sweat from head to foot, through long,
cold galleries to the forecastle, where they turn in for eight hours.
Four hours of scorching and eight hours sleep make up the routine of a
fireman’s life on a voyage.
The temperature is ordinarily 120°, but sometimes reaches 160°; and the
work is then terribly hard. The space between the furnaces is so narrow
that when the men throw in coal they must take care when they swing
back their shovels, lest they throw their arms on the furnace back of
them.
In a recent trial of a government steamer the men worked willingly
in a temperature of 175°, which, however, rose to 212° or the heat
of boiling water. The shifts of four hours were reduced to 2 hours
each, but after sixteen men had been prostrated, the whole force of
thirty-six men refused to submit to the heat any longer and the trial
was abandoned.
There is no place on ocean or land where more suffering is inflicted
and endured by human beings than in these h——holes, quite properly so
called; it is to be hoped that the efforts towards reform in the matter
will not cease until completely successful.
FIRING OF SAWDUST AND SHAVINGS.—“The air was forced into the furnace
with the planer shavings at a velocity of about 12 feet per second, and
at an average temperature of about 60 degrees Fahrenheit. The shavings
were forced through a pipe 12 inches in diameter, above grate, into the
combustion chamber. The pipe had a blast gate to regulate the air in
order to maintain a pressure in the furnace, which a little more than
balanced the ascending gases in the funnel or chimney. All the fireman
had to do was to keep the furnace doors closed and watch the water in
the gauges of his boiler. The combustion in the furnace was complete,
as no smoke was visible. The shavings were forced into the combustion
chamber in a spray-like manner, and were caught into a blaze the moment
they entered. The oxygen of the air so forced into the furnace along
with the shavings gave full support to the combustion. The amount of
shavings consumed by being thus forced into the furnace was about fifty
per cent. less than the amount consumed when the fireman had to throw
them in with his shovel.”
[Illustration: Fig. 9.]
It is an important “point” when burning shavings or sawdust with a
blast, to keep the blower going without cessation, as there have been
disastrous accidents caused by the flames going up the shutes, thence
through the small dust tubes leading from the bin to the various
machines.
[Illustration: Fig. 10.]
In firing “shavings” by hand it is necessary to burn them from the top
as otherwise the fire and heat are only produced when all the shavings
are charred. To do this, provide a half-inch gas pipe, to be used as a
light poker; light the shaving fire, and when nearly burned take the
half-inch pipe and divide the burning shavings through the middle,
banking them against the side-walls, as shown in Fig. 9. Now feed a
pile of new shavings into the centre on the clean grate bars, as shown
in Fig. 10, and close the furnace doors. The shavings will begin to
burn from above, lighted from the two side fires, the air will pass
through the bars into the shavings, where it will be heated and unite
with the gas, making the combustion perfect, generating heat, and no
smoke, and the fire will last much longer and require not half the
labor in stoking.