US493854A - Furnace for burning coal-screenings - Google Patents

Description

(No Model.)

P. LpBARTLETT. FURNACE FOR BURNING COAL SCREENINGS No. 493,854-.

Patented Mar; 21, 1893.

wi p ss y tempts at burning such coals with a heavy 30,

UNITED STATES PATENT OFFlCEe FRANK L. BARTLETT, OF PORTLANDpMAINE.

FURNACE FOR BURNING COAL-SCREENINGS.

SPECIFICATION formiug part of Letters Patent No. 493,854, dated March 21, 1893.

Application filed March 25, 1892.

.To all whom it may ooncern:

Be it known that I, FRANK L. BARTLETT, a citizen of the United States, residing at Portland, in the county of Cumberland and State of Maine, have invented certain new and useful Improvements in Furnaces for Burning Coal-Screenings; and I do hereby declare the following to be a full, clear, and exact descri ption of the invention, such as will enable others skilled in the art to which it appertains to make and use the same. e

The objectof ny invention is to provide means for burning finely pulverized Waste coal under stean boilers and other furnaces. Waste coal from anthracite mines has heretofore been burned by mixing the fine coal with sawdust, spent tan bark or with bituminous coals. The problem of burning the waste from the soft lignite coals, such as are mined in Colorado, YVyoning, New Mexico and other Western States, has never been satisfactorily solved so far as I am aware. Such waste is extremely fine, fully one half being dust and often an impalpable powder,so that any device such as is economically used on the heavier and more dense coal slack of the Eastern or Middle States, fails to work on the lighter lignite coals of the Western States. All atblast, results in filling the flues of the boiler and the conduits of the furnace with fine half burned coal, or else when the blast is lightened the grates are packed with the fine coal so that the air cannot force its way through. Again, no method has been found, so far as I know, for burning the dense Volume of smoke which such coal gives off.

The object of the present invention is to overcome the difficulties mentioned and to efiect the complete and economical combustion of this kind of coal dust without filling the flues with dust, without the production of smoke and without destroying the grates and the walls of the furnace.

The various features of my invention will be described in the specification and set forth in the claims.

In the accompanying drawings, I illustrate my invention as applied to a horizontal tubular boiler.

Serial No. 426.330. (No model.)

In the drawings Figure l is a central longitudinal section. Fig. 2 is a cross section, half being on line :r w and half on the line y y of Fig. 1. Fig. 3 is a perspective view of one of the hollow perforated brick used in the bridge wall, and. Fig. 4: is a section through the same. v

A represents the stean boiler and B is a perforated inclined grate which I prefer to make of solid cast bars having one-fourth inch perforations.

C is the bridge wall which in this case extends the entire distance across the furnace and is made hollow to admit the blast 'which enters through the pipe L. This pipe as herein shown is connected with a blower P. The top of the bridge wall, as herein shown, is arched and it contains on each side of the arch a row of perforations d adapted to'discharge a hot air blast obliquely toward the front and rear of the furnace. These perforations d are formed in hollow bricks D pret erably of cast iron which are-set in the brick Work of the arch. The inner edgeof the brick D is open and allows the air to pass through the perforations.

In the front partitio of the bridge wall is an opening for admitting air beneath the grate. I prefer to use for this opening a pipe E which is fixed in the lower part of the Wall and points obliquely upward. This opening is controlled by a damper F which is opened and closed by means of a rod G. In rear of the bridge wall is an inclined surface H where the ashes collect as they come over the bridge wall and in rear of this is the ash collecting clamber I.

N is the ash door. p

K represents the stack and J is the damper which controls the draft in the stack.

In Operating the furnace a light blast 'from a fan or other device is delivered into the hollow bridge Wall at a low pressure, say two ounces to the square inch. The air will pass out of the' perforations d d in the top of the wall as a hot blast, being heated in its passage 5 The colder air will A fire havthrougl the bridge wall. be discharged through the pipe.

IOO

, The backward direction of the cold blast issuing from the pipe E beneath the grate and the hot blast through the front row of holes d d tend to hold back the smoke and light dust from the coal giving it a rotary motion, while the s'tack Ic tends to draw it slowly forward and through the flues of the boiler. The result is that the coal is burned in passing over the perforated bridge wall and meeting the heated air currents from the openings d d and the fine completely burned ash drops in the ash chamber I, accumulating at the bottom of the inclne II where it nay readily be removed through the ash door N( It will be observed that the chamber I growsgradually larger from the bridge wall backward to the rear erd of the boiler. This coustruction of the apparatus is of great importance for the reason that the combustion of the dust begins in the vicinity of the bridge wall and as it proceeds it requires an expanding chamber or flue in which to effect a complete combustion and to prevent counter currents. The fiue grows graduaily larger as the Volume of gas caused by the combustion of the dust expands.

In practice the light clinker which forms on the grate is not disturbed for several hours, the fuel being frequently spread over the hot clinkerthus formed, and burned ofi until the porous clinker has become too thick to allow the blast to penetrate, when it is broken up and removed.

It will be seen that the operation of this invention is nearly the reverse of ordinary firing,inasmuch as the finecoal is burned in the air and the ash deposited in the rear of the boiler instead of under the grates as is customary. By means of the cold blast under the grates and the hot blast through the perforations of the bridge wall, complete combustion is not only Secured, but the grates last much longer and the wear on the boiler and furnace is lessened, the smoke ceases to be a nuisance, the flues do not fill up and a very cheap and hitherto unutilized class of fuel can be burned. -For effective work under boilers and stills it is found necessary to have &93,854

the grate quite near the boiler to be heated, much nearer in fact than is customary with ordinary firing.

When this invention is applied to furnaces already set in the usual way, the rear ends of the grate are raised and a fire brick arch 'M turned at the front end near the charging door. The object of this arch is to prevent the cold air from the lower blast from passing through and impinging on the cooler surface of the boiler plates and thus reducing the temperature of the blast below the point of combustion. This device is not necessary when the grate is constructed to be within say eighteen or twenty inches.

I claim- 1. In a furnace for stean boilers and other like purposes, the conbination of a perforated grate, a lollow bridge wall forn'ing an air chamber, perforations at the top of said bridge Wall for supplyinga hot blast from the upper part of said air chamber, an opening through the lower portion of said bridge wall beneath said grate for discharging the cooler air from said air chamber, substantially as described.

2. The herein described method of burning fine coal under stean boilers consisting of Spreading the coal in a thin layer over a perforated grate, forcing an air blast beneath said grate sufficient 'to lift the fine coal dust from said grate, blowing jets of heated air into the Suspended coal dust immediately after it leaves said grate and burning it while held in suspension, and slowly drawing off the products of combustion through the stack, substantiall y as described.

3. In a furnace for steam boilers and other like purposes, the combination of a finely perforated grate, an air blast apparatus for delivering air under pressure beneath said grate, a bridge wall having air discharge openings therein and a gradualiy enlarging or expanding chamber in rear of said bridge wall extending without substantial diminution of section to the rear of the furnace, substantially as described.

In testimony whereof I affix my signature in presence of two witnesses.

FRANK L. BARTLETT. VVitnesses:

HENRY LLOYD, FRANK MCFARLANE.

IOO

Images