Smoke-con-sum′ing Fur′nace.
Smoke has been defined as the visible effluvium or sensible exhalation of anything burning.
So far as our subject is concerned, it may be considered as particles of finely divided carbon or pellicles of carbon containing inflammable gas. The object of the devices to be cited is to so apply the fuel that the escaping combustible matters shall be exposed to incandescent fuel and a due supply of vital air, which conjunction of agents will consume the combustible gases and the particles of carbon suspended therein.
In 1819, the
British House of Commons appointed a commission to “enquire how far it might be practicable to compel persons using
steam-engines and furnaces to erect them in a manner less prejudicial to public health and comfort, and report their observations thereupon to this House.”
A large number of practical and scientific men were examined, and, the commission becoming satisfied that “the reduction of smoke from furnaces might be practically accomplished,” a bill was brought forward and passed which made the avoidable production of smoke from furnace-chimneys an indictable and finable offense.
Complaints against the smoke nuisance are of very old date.
Great prejudice was felt in former times in
England against the burning of coal, known then as sea-coal, because it was brought from the Tyne to the
Thames by sea. It was supposed to be injurious to trade, health, the complexion, and a whole catalogue of evils was feared from its use. In 1306, the king of
England issued a proclamation against its use, and a commission was issued for the purpose of ascertaining who burned seacoal within the city and its neighborhood, and to punish them by fine for the first offense and by the demolition of their furnaces if they persisted; but even these severe proceedings failed to put down the nuisance.
A law was therefore passed, making the burning of sea-coal within the city a capital offense, and permitting its use only in the forges in the neighborhood.
In the reign of the first Edward a man was tried, convicted, and executed for burning sea-coal in
London.
Much has been written on this branch of the subject [consuming smoke]. The principles concerned are extremely simple and easily applied.
The volume of air supplied must be neither greatly in excess nor greatly deficient of that necessary for perfect combustion.
If it be seriously deficient, the fuel, if bituminous, is partly only distilled or sublimed into black smoke and tarry soot, the adherence of which to the boiler surfaces becomes a cause of farther loss of effect.
If the fuel be carbonaceous only, as coke, anthracite, etc., its gases are only oxidized to the state of carbonic oxide in part; and if the fuel be wood or peat, the last result occurs with the distillation of various tarry and acid products (pyroligneous acid), highly destructive to iron boilers.
If the volume of air be greatly in excess, the heat of the furnace is reduced, and may be so to an extent to cause even imperfect combustion, and a great volume (or weight) of air is uselessly heated and discharged by the chimney.
Non-bituminous fuel is more easily burned perfectly than bituminous; with either, but especially with the latter, if combustion is to be practically perfect, there must be a sufficient draft to carry the air-current steadily through the fuel.
The layer of this upon the dead-plate and grate should never exceed 10 to 15 inches, and is best not to reach 6 or 7; but thin firing requires very careful stoking, or bare patches of grate are exposed, occasioning much loss.
With coke or anthracite, and especially with a blast, a much greater depth of fuel may be practicable.
The air is best admitted partly beneath and through the fuel, and partly in adjustable volumes, at or just behind the bridge, where it should be so arranged that the air and combustible gases shall mingle as completely as possible.
This is the plan so much and so justly insisted on by Mr. C. W. Williams, Mr. Prideaux, and several others.
The air admitted should be heated; and this is best of all done by the use of Mr. C. Siemens' regenerator, applied to the flues of the boiler between the latter and the chimney-stack.
If the air be cold, the combustible gases are chilled more or less, and below a red heat these cannot burn perfectly or without the production of smoke.
The area of air aperture at the bridge is fixed by Mr. Williams at 1 square foot for every 36 square feet of grate, when the latter burns 25 pounds of coal per foot per hour, and in like proportion for larger consumption.
The maximum of economy will, in perhaps all boilers, be effected by the regenerative principle; and in this case the air passed into the flues above the fuel or at the bridge may be admitted at even 800° or 900° Fah.
When the proportioning and arrangements of the furnacegrate and draft are such as to insure the conditions for complete combustion, the next great point to be attended to is, that the rate of passage through the flues, or past the heat-receptive surfaces of the boiler, must be such that the combustion of gases shall have been perfected before they have been robbed of so much heat by the boiler as to fall in temperature below that for complete oxidation; if not, smoke, soot, or tarry products may be still formed in the remoter ends of the flues.
Where the regenerative system cannot be applied to the airsupply, Mr. Fairbairn's double furnace cylindrical boiler, for alternate firing, is the next best arrangement.
It is one that practically works well with the ordinary amount of stoker's attention, which alone can be reckoned on. — Armstrong.
One principal difficulty has arisen from the usual practice of placing the coals on top of the incandescent fuel, so that as the smoke is evolved it has free passage to escape by means of the chimney.
This is the simplest way of feeding a fire, but is evidently wasteful, unless secondary means be employed to consume the matters thus escaping.
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To obviate this, and cause the smoke to pass over a mass of burning fuel, various contrivances have been invented for introducing the fresh fuel beneath that which is already burning; among these may be mentioned
Cutler's; and
Dr. Arnott's, which is an improvement upon it. These and others are adapted for open grates.
See grate, smoke-consuming; base-burning stove.
Watt, in his specification of 1785, claims “constructing furnaces so that the smoke or flame of the fresh fuel is caused to pass, together with a current of fresh air, through, over, or among fuel which has already ceased to smoke, or which has already been converted into charcoal, coke, or cinders, and which is intensely hot.”
Several ways of effecting this are described by him. The introduction of fresh air, to consume the carbonaceous particles which have escaped the action of the air originally admitted to the furnace, is a very important element in producing a successful result, and appears to have been original with
Watt.
It has been introduced into most, if not all, subsequent devices of value.
Among the plans suggested and practiced for securing the perfect combustion of the fuel and its resulting valuable gases, may be cited:—
1. Introducing the fuel into the fire in such manner that the smoke and gases evolved pass through a bed of red-hot matter.
To this class belong:—
a. The
Athanor or constant furnace of the alchemists, used for keeping up a constant heat for many consecutive days, in their patient and laborious attempts to transmute base metals into gold, or produce the elixir of life.
Alongside the fireplace was a hollow containing charcoal, and closed above by a tight lid. As the fire consumed the fuel, the charcoal descended and replenished it.
b.
Delasme's baseburning furnace, exhibited by him at St. Germain's, in 1685.
It was in the form of an inverted siphon: the shorter leg
c contained a grate
o, and served as the fire-chamber, the longer leg
i constituting the chimney; the smoke was thus caused to pass through the incandescent fuel, and more or less perfectly burned.
The fire was kindled at the top, and the chimney
i was heated by a lamp to originate the draft.
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Watt's base-burning furnace. |
c.
Watt's base-burning furnace, in which a body of coal is supplied in a hopper, the coal gradually falling into the fire as the substance of the lower layer is consumed.
The coal-chamber may be covered in by a tight lid, so as to prevent the draft of hot air through it; or the inlet draft of air may be conducted through it. The former is perhaps the preferable mode, and the coal should be discharged through a throat of such capacity as, on the one hand, not to choke, and on the other, not to encourage, the access of fire to the contents of the supply-chamber.
In its character as a smoke-consuming furnace, it will be noticed that the fresh coal is constantly in contact with the incandescent fuel, and that all the gases evolved by the combustion are obliged to pass
through a body of hot coals, whereby the hydrogen and carbon which constitute the valuable portion of the smoke are consumed.
This feature is to be found in some stoves in which a body of coal is brought into contact with the fuel in such a manner that the volatile products of the fresh coal are compelled to pass
through the incandescent mass of fuel.
d. Stoves of the base-burner class, in which the fuel is introduced beneath the fire.
See stove, base-burner; magazine.
e. A furnace in which the escaping smoke from one fire is burnt at a second fire; also found in
Watt's patent, 1785.
This is thus described in the words of the inventor: “I place the fresh fuel on a grate as usual, as at
a, and beyond that grate, at or near the place where the flame passes into the flues or chimneys, I place another small grate
b, on which I maintain a fire of charcoal, coke, or coals, which have been previously burned, until they have ceased to smoke, which, by giving intense heat and admitting some fresh air, consumes the smoke of the former fire.”
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Watt's double-fire furnace. |
A modification of the Watt furnace, by
a Mr. Thompson, patent 1796, had an extension of the grate bars and arched bridge, about 2/3 the distance from the front end. Beneath this bridge the volatile products of the first part of the furnace were carried, and deflected upon a mass of incandescent fuel, which occupied the rear portion of the furnace, where they were met by a current of air admitted back of the bridge.
This backward portion was kept supplied with red-hot coals from the former fire, or by coke or charcoal separately introduced.
Gregson's patent, 1815 (also
English), depended upon the exposure of the volatile and inflammable results of combustion, to intense heat at an aperture at the back of the fire and passing through the firebridge.
Losh's double-fireplace furnace, 1815, is another example of this class.
This furnace has two fires, which are alternately replenished with fuel.
The fireplaces are connected, and either is thrown in connection with the chimney by means of suitable flues and dampers.
The fireplace which has just received coal pours its smoke and gases into the mass of red-hot coals of the other fire, from whence the volatile matters, deprived of their inflammable gases and carbon, pass to the chimney.
When the time comes to replenish the fire, the one which has acted as the secondary furnace receives the coal and delivers the smoke under the arch of the division wall to the other fire, which is connected to the chimney, by change of dampers.
The
City Flour Mills, Upper Thames Street,
London, are fitted with boilers consuming their own smoke, generating steam for an engine of 220 nominal horse-power.
The boilers are 7 in number, and the engine is on the marine principle.
The engine was formerly one of the stationary engines on the
Blackwall Railway, when the carriages were drawn by a rope.
The furnaces are arranged in a row, with communicating flues guarded by dampers.
When one fire has received fresh coals, its immediate connection with the chimney is closed, and the smoke is discharged into the adjoining furnace, whose fire is burning red.
2. The plan of admitting a second body of air to inflame the unconsumed combustible matters which pass away from the fire.
John and
James Robertson, of
Glasgow, patented a furnace in 1801, in which, by means of a pipe, air was admitted directly into the body of the fuel while burning, — the first practically successful contrivance of the kind.
In other cases, the air is admitted at or near the fire-bridge or in a chamber behind the fire-bridge.
Evett's reverberatory furnace (English patent, 1812) has a
conductor which introduces a body of air through the bridgewall, and ejects it upon the eddying volumes of smoke and gas which occupy the dome of the metal-chamber.
The size of the aperture in the air-tube was regulated by a valve.
This is, perhaps, an advance upon
Watt's patent of 1785, in which the accessory body of air passes through the grate-bars of a supplementary fire, which assists in the combustion of the smoke.
Chapman's furnace (1824) had hollow grate-bars, forming a series of parallel tubes opening into two boxes, one in front and the other behind the grate.
The rear one connected with a hollow fire-bridge, which discharged heated air in jets into the volume of smoke passing over the bridge, thereby causing the heated gases to ignite.
C. Wye Williams' furnace depends for its action on the thorough intermingling of the gas evolved by fuel with atmospheric air before the temperature of the carbon contained in the gas, then in the state of flame, be reduced below that necessary for sit ignition, — about 800°, according to
Sir Humphry Davy.
This is effected by admitting the proper proportion of air through several hundred half-inch orifices in and above the door-box.
According to
Mr. Williams, it is immaterial in what part of the furnace the air is introduced, provided that the above condition be attended to. In the experimental furnace at the
Newcastle trial, the area of the openings for the admission of air was equal to four inches square for each square foot of gratebars.
This received the prize of £ 500 offered by the Colliers' Association of
Newcastle for the best furnace of the kind.
3. The
dead-plate system.
Also described in the specification of
Watt's smoke-consuming furnace, 1785.
It had a grate with a slight descent to the rear, to enable the fuel to be pushed back from time to time, to give room for fresh coal.
The fresh supply is laid on a plate called the
dead-plate, at the front part of the grate.
The fuel being
coked by the heat, the gases and particles of carbon which form smoke are caused to pass over the incandescent fuel, and are thereby consumed.
The plan, to be successful, requires frequent feeding of the
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furnace, and necessitates the opening of the furnace doors.
To avoid this, self-feeders have been used, being hoppers by which the coal is introduced from time to time or continuously in small quantity.
Stanley's feed-apparatus for furnaces consists of a hopper at the front upper part of the furnace, containing a supply of small coals equal to a couple of hours' consumption.
Through an aperture at the lower end of the hopper the coal drops between two grooved rollers, which crush it and allow it to fall upon the
dead-plate, whence it is blown by air from a revolving fanner, which wafts it upon the burning fuel on the grate.
Other feed-apparatus consists in a hopper similarly situated, and having a counterpoised valve at bottom, which opens to allow the coal to fall upon the fire.
Another feed will be described in connection with the
revolving grate.
A feed-apparatus adapted to furnaces in which the fuel is burnt under pressure is illustrated in air-engines,
Bennett's patent, 1838.
4. The
revolving-grate furnace was introduced in
England by Steel, about 1818, and afterward improved by Brunton and
Murray.
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Steel's revolving-grate furnace. |
The fireplace is of circular form, and the grate is made to revolve on an upright axis by means of a cog-wheel on its lower extremity.
The coal is placed in a hopper on the upper front end of the furnace, and is delivered in regular and graduated quantities by a roller so situated as to command the throat of the hopper.
This roller rotates, so as to crush the coal to a proper size.
The comminuted fuel traverses the inclined chute and falls upon the surface of the incandescent fuel on the grate, which revolves beneath.
The illustration shows a tubular highpress-ure boiler set in masonry.
The rim of the rotary grate revolves in a trough with sand to prevent the passage of air around the edge of the grate.
Brunton added a revolving scraper, which gathered up the ashes as they fell upon the ash-plate, and devices by which the rotation of the feed-wheel may be regulated to give a greater or less amount of coal, according to the requirements.
It is not understood that a thermostatic arrangement was attached to graduate the amount of coal according to the heat of the furnace or the tension of the steam, or a device from the governor, which might also control the air-induction opening at the ash-pit.
In Juckes' furnace the fire-bars form an endless grate, which advances so that the fuel is gradually carried from the front to the back of the fireplace.
Coal in regulated quantities is dropped from a hopper upon the front of the grate, and the air for burning the fuel passes between the bars.
The whole area of the grate is covered with fuel, but, as the portion last laid on is always nearest the front, the smoke from that portion is compelled to pass over the more thoroughly ignited portion behind, where it undergoes thorough combustion, very little finding its way into the chimney.
5. Yet another method for attaining the perfect combustion of the smoke consists in injecting jets of steam into the furnace.
Evans, in
England, 1824, patented a method in which the steam was to be decomposed by passing through the hot fuel.
In 1844,
Christian Burckhardt, of
Cincinnati, consumed the smoke of a steamboat furnace by projecting fine jets of steam into its upper part.
Economy of fuel being a secondary consideration on the
Western waters, contrivances of this kind have met with but little attention.
