US1817911A - Pulverized fuel burner - Google Patents

Description

Aug.'11, 1931.

L. V. ANDREWS ET AL PULVERIZEID FUEL BURNER Filed May 19, 1927 2 Sheets-Sheet l WITNESS INVENTORS L. V. ANDREWS OLLISON CRAIG Q? m ATTOR EY 1931- L. v. ANDREWS ET AL 1,817,911

PULVERIZED FUEL- BURNER Filed May 19, 1927 2 Sheets-Sheet 2 INVENTORS L. V. ANDREWS OLLI-S'ON CRAIG WITNESS fl. f BY Patented Aug. 11, 1931 UNITED STATES PATENT OFFICE L. V. ANDREWS AND OLLISON CRAIG, 0F WORCESTER, MASSACHUSETTS, ASSIGNORS TO RILEY STOKER CORPORATION, OF WORCESTER, MASSACHUSETTS, A. CORPORA- TION OF MASSACHUSETTS PULVERIZED FUEL BURNER Application filed May 19,

This invention relates to fuel burners of the type in which pulverized fuel mingled with air is injected directly into a furnace.

Various types of burner have been pro- 5 posed for burning pulverized fuel and in these there is inherent the ever present problem of providing a uniform distribution of the coal around the periphery of the burner pipe andcausing it to mingle uniformly with the air which is supplied for combustion. The present invention relates to a burner of the type in which the pulverized fuel is ini tially mingled with a portion of the air required for its combustion, and is then projected into the furnace within an annulus of secondary air. One of the bothersome problems has been to keep the fuel and the primary air properly mixed so that there will be a uniform distribution of the fuel into the surrounding layer of secondary air within the furnace. It is ordinarily necessary to conduct the pulverized fuel within circuitous or tortuous passages extending from the storage bin or the pulverizer to the burner, because of the cramped space within the average furnace room. The Velocity in these passages has to be high in order to prevent the fuel from being deposited therein, and wherever the mixture of fuel and primary air passes around a bend in the conducting pipe, the coarser particles of fuel are necessarily segregated to some extent, because of the action of centrifugal force, and pass along that portion-of the pipe which has the curve of greater radius. Various devices have been proposed for mixing the coal and primary air but these have involved difiiculties in the matter ofproducing a satisfactory distribution of the material around the inner periphery of the burner pipe at the point fwhere it issues into the furnace combustion space. 1 1 Itis accordingly the main object of this 'inventionto provide a burner of this type for pulverized fuel which is of very simple construction and may be easily manufactured and readily installed in cramped quarters in a furnace room, which will serve efficiently to maintain the fuel and rimary air proper- 1y distributed within the liiurner pipe around 1927. Serial No. 192,635.

its periphery, and which will cause this fuel to mingle with the secondary air and be substantially uniformly distributed thereto.

With these and other objects in View, as will be apparentto those skilled in the art, our invention resides in the combination of parts set forth in the specification and covered by the claims appended hereto.

In accordance with this invention, we provide a furnace burner which has a burner pipe arranged to project the pulverized fuel and primary air through an opening in a furn'ace wall, and deflectors to distribute the secondary air around the outside of the primary burner pipe,- and we provide the burner pipe with a baffling structure so constructed that the fuel will be uniformly distributed around its inner periphery just before issuing into the furnace and into contact with the secondary air. The battle structure is so arranged in the pipe that it changes the direction of movement of the heavier particles of fuel which tend to segregate as they pass around bends in the pipe and so'causes the heavier and the lighter particles of fuel to mix with one another. This is accomplished closely adjacent to and in direct line with the end of the burner and preferably near distributing vanes which are provided to throw the fuel outwardly in every direction into the ring of secondary air surrounding the burner pipe. The deflectors for introducing the secondary air provide a uniform distribution and cause the air to whirl, thus aiding in the production of a thorough mixture and rapid combustion.

Referring more particularly to the drawings which illustrate one embodiment of our invention, and in which like reference numerals indicate like parts:

Fig. 1 is a vertical section through a burn I er, the section being taken on the line 1'1 of Fig. 2;

Fig. 2 is a'section on the line 2-2 1; and

Fig. 3 is a perspective view of a mixing baflle.

The embodiment of our invention illustrated in the drawings com rises a vertical furnace wall 10, constructed of suitable'reof Fig.

tractor-y material, and provided with an opening ll thercthrough which is preferably circular as shown. A. plate 14. may be suitably attached to the outside of the, wall, surrounding; the opening. and arranged to act as a support for other parts of the burner. A heavy no lo. with an internal diameter equal to nit of the opening 11, may be bolted to the .urnace side of the plate ll to ac as a stitfenr: nu-niher, and toform a ledge which brick mason in constructing the, circular refractory arch forming the opening.

EL horizontal cylindrical. fuel L zle 1S mounted adjacent to the furnace, wall arranged to project a stream of pulveriuel and primary air centrally through opening ll into the furnace. This n: is derived from any suitable source of such as a storage bin or a pulveriaer -callcd unit type, and is fed to the 'ough a connecting pipe. It is cuso wave a pipe elbow 2O bolted to the l e pipe 18, and this elbow may be "-n'ious angles about the axis of i as to provide a convenient cono the source of supply of fuel and in order to supply secondary air uniformly around the fuel nozzle to the opening 11, we provide a series of guide vanes or deflectors 25 spaced evenly around the nozzle, and preferably arranged tangentially as illustrated so as to cause a whirling motion of theentering air. These vanes may be conveniently constructed by lirst forming a hollow cylinder 26 of sheet metal, cutting three sides of each vane therein, and then bending the vanes inwardly to the angle desired. The cylinder 26 may be suitably at ched to the plate M by means of the angle shaped members 2S. ll'ith the burner illustrated, the air is drawn inwardly between the deflectors by the suction of the furnace, this suction being maintained either by the natural draft of the staclc or by the action of an induced draft fan. It is apparent that in case it is desired to utilize forced draft with this burner, it is merely necessary to provide a casing to form a pressure chamber around the outside of the detle rtors. is it is advisable to provide means for controlling the size of the openings between the deflectors and thereby permit operation at various ratings, we arrange outside the cylinder 26 a cylindrical damper 30, which may be rotated to the desired point by handles 31. This damper should be ar ranged to close in the direction of the arrows in Fig. 2, so as to cause the air to flow along the vanes and maintain its whirling motion even at the lower ratings.

A vertical closing plate 35 is mounted at the front of the burner and together with the cylinder 26 forms a casing to prevent the entrance of secondary air except between the deflectors. In order to prevent injury to this plate from the radiant heat of the furnace, we prefer to arrange a flat shield 36 on the furnace side of the closing plate. This shield may be constructed of any suitable material, such as cast iron, and it is provided with perforations 37 as illustrated to eliminate cracking due to expansion. If desired, a small door 38 may be provided to cover an opening through the plate and shield, thus permitting observation of the flame, or the insertion of a torch for igniting the fuel stream.

The deflectors bring about an even distribution of secondary air around the fuel nozzle 18, and in order to obtain uniform combustion conditions and a symmetrical flame it essential to deliver the fuel evenly to this secondary air. This problem is rendered difficult because of the segregation which invariably occurs in the pipe line lea ding to the burner. The coarse particles of fuel tend to separate from the lines by gravity even in a straight pipe, and when there are bends or elbows in the pipe line, as is usually the case. this separation is greatly aggravated by the action of centrifugal force. In order to eliminate this segregation, we provide within the fuel pipe a transverse plate or narrow annular battle -Ll5 having a circular orifice l6 therein substantially smaller in diameter than the pipe. This plate presents a deflecting surface to any segregated portion of the fuel traveling close to the pipe wall. l-l hile this orifice or battle plate may be flat. we prefer to construct it in the form of a hollow frustum of a cone, as illustrated, which produces less resistance to the flow. The presence of the plate 4-5 is thought to cause great turbulence and violent eddy currents in the fuel stream, whereby the coarse and fine particles are thrown together and a thorough mixture produced. If the plate is shaped as illustrated, the frustum is preferably arranged to converge towards the discharge end of the pipe in the direction of the stream travel, and serves as a sloping battle along which coarse particles may slide and so be thrown into the burner pipe at an angle to the axis thereof, thus causing them to be distributed more uniformly in the air current. This ballle is preferably located near the outlet or burner end of the pipe so that there will be no opportunity for the coarse particles to segregate again before they enter the furnace. This plate should on the other hand be spaced somewhat from the discharge end of the fuel nozzle, as illustrated, so that the mixing operation may take place fully before the fuel issues into the furnace, but this space should not be excessive nor should any pipe bends occur therein, for under those conditions all advantages obtained from the use of the plate will be lost. The plate 45 may be conveniently mounted, as shown, by providing thereon a flange 48 which is held between the elbowr20 and the closing plate 35. A hollow cylindrical extension 50 on the furnace side of the flange 48 provides a convenient arrangement for supporting the pipe 18, which is held therein.

As it is desirable to produce a rapid and thorough mixture-of fuel and secondary air within the furnace, resulting in complete combustion and a short flame, we provide adjacent to the discharge end of the fuel nozzle a suitable spreading device 55. In the embodiment illustrated, this comprises a sheet metal structure having a large number of sma'l inwardly extending vanes 56, each arranged at an angle to the fuel flow. The stream of primary air and fuel strikes these vanes, and is thrown outwardly in all direction-s'with a whirling motion into the surrounding secondary air, producing a condition of extreme turbulence. We have found that under most conditions the results obtained are better if the direction of whirl of the fuel is opposite to that of the secondary air, though under some circumstances it may be preferable to whirl them both in the same direction. In order to avoid impingement of the flame on the refractory surfaces of the opening 11 and the slagging condition which would result therefrom, we construct this opening so as to flare outwardly on the side toward the furnace as shown at 58.

The operation of our inventionwvill now be apparent from the above disclosure. A whirling stream of secondary air is delivered by the deflectors 25 to the opening 11. A stream of pulverized fuel and primary air is brought to the e'bow 20 from a pulverizer or storage bin, and the segregation in this stream is destroyed by the action of the oritice plate 45, which produces a uniform mixture within the pipe 18. This mixture strikes the vanes 56 nearthe exit end of the pipe, and is thrown outwardly with a whirling motion into the surrounding secondary air. Each vane 56 tends to produce asmall localized stream of a mixture rich in fuel,

These small streams have a rate of flame propagation much higher than that of the remaining mixture. and as a result they form a plurality of small pilot lights, which maintain ignition close to the burner and produce a short flame. Combustion is also acceleratezl by the heat which is reflected on to the present a deflecting surface to any segregated fuel traveling close to the pipe wall, and means adjacent to the discharge end of the pipe for throwing the fuel outwardly into the secondary air.

2. A burner for pulverized fuel comprising a central imperforate fuel pipe mounted adjacent to a furnace and arranged to discharge into said furnace a stream of pulverized fuel and primary air, means including a series of deflectors arranged uniformly around the pipe to direct a whirling stream of secondary air into the furnace, an annular orifice plate mounted within the pipe and spaced from its discharge end to present a narrow deflecting surface in the path of any segregated fuel traveling along the pipe wall, and a spreading device adjacent to the discharge end of the pipe and arranged to whirl the fuel stream and throw it outwardly into the secondary air.

3. In a furnace having a wall provided with a circular burner opening, a burner for pulverized fuel comprising a central cylindrical fuel pipe arranged to discharge a stream of pulverized fuel and primary air through the opening means including a series of deflectors arranged uniformly around the pipe and substantially parallel thereto so as to direct a whirling stream'of secondary air through the opening and outside the fuel fuel outwardly in a whirling stream into the secondary air.

Signed at Worcester, Mass, this sixteenth day 6f May 1927.

OLLISON CRAIG. L. V. ANDREWS.

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