US1920117A - Pulverized fuel burner - Google Patents

Description

July 25, 1933. a v I TENNEY 1,920,117

PULVERIZED FUEL BURNER Filed June 29 1929 5 Sheets-Sheet 1 I I V PULVER IZ E R \NVENTOR w W YMT MMWMM%&%;WI

. July 25, 1933. TENN 1,920,117

PULVERIZED FUEL BURNER Filed June 29, 1929 3 Sheets-Sheet 2 July 25, 1933. E. H. TENNEY 1, PULVERIZED F-UEL BURNER Filed June 29, 1929 s Sheets-Sheet 5 INVENTOR Patented July 25, 19.33

UNITED sures-PATENT OFFlCE EDW ABD H. TENNEY, 0F WEBSTER GROVES, MISSOURI 'rULvEcaIzEn. Fm BURNER Application men an. 29,

t This invention is primarily a novel pulverized fuel burner, that is, a device employed as at the entrance toa furnace for delivering for immediate combustion a stream of pulverized coal or similar fuel in suspension in air received at the burner from a transporting passage or pipe; the invention as illustrated being designed more especially for use with the so-called unit system wherein the coal is reduced ina pulverizer and thence conducted directly to the burner and furnace.

One of the principal objects of the present invention is to provide a separating action in the burner of such character that the coarser pulverized particles will be effectively separated out from the flowing stream while the finer particles and air are delivered, for example, for immediate combustion in the furnace. It has been ascertained that in practice, notwithstanding the efficiency of modern pulverizers a-substantial quantity or percentage of relatively coarse material is supplied or likel to be delivered along with the relatively ne material, either continuously or at intervals during the operation of the plant. To the extent that relatively large fuel particles are passed through to a burner and furnace there are decided disadvantages. These particles are incapableoftburning completely in the shot period of travel through the furnace. The particles that are carried up through the boiler and stack without complete combustion cause a substantial loss of fuel economy, while the portion that settles intothe ash pit tends to the increase ofslag formation and consequent trouble and expense in the operation of thefurnace and boiler.

I am aware that so-called classifiers or separators have been proposed, intended to be used at a point between a pulverizer and a burner for separating and returning coarser particles. These however have not been highly satisfactory, and they are bulky and expensive and cause complicationin the piping arrangements, as well as producing a substantial loss of pressure or head in the delivered stream of air and fuel, thus consuming excessive power in transporting thetream from the pulverizer to the furnace.

A particular object of the present invention therefore is to afford a burnerwhich will possess the functions of, first, separat- 1929. Serial No. 374,641.

ing out the coarse-particles from the stream so that they can be collected, forexam le for return to the pulverizer, and second, e

livering the fine particles with the carrying air so that they can be burned immediately at the delivery in the furnace and under the most advantageous conditions. It is believedto be new with this invention to pro vide' aburner having means for continuously separating out the coarser particles from the stream while delivering the finer particles with air for immediate combustion' inthe furnace.

Other objects of the invention include to make possible, in a furnace burning pulverized fuel, very high rates of complete combustion, and without production of smoke, and yet without the need of supplying unduly high percentages of excess air; also, to permit the production of a whirling flame of advantageous character, instantaneous combustion, and of small volume.

Other and further objects and advantages of the-present invention will be explained in the hereinafter following .description of an illustrative embodiment thereof or will be understood'to those skilled in the subject. To the attainment of such objects and advantages the present invention consists in the. novel pulverized fuel burner and the novel features of operation, combination, ar-

rangement and structure herein illustrated or escribed. 4

In the accompanying drawings 'Fig 1 is a more or less diagrammatic elevation of a classifying burner and cooperating elements, being supposedto be viewed from the furnace side.-

Fig. 2, on an enlarged scale, shows the. same elevation view of the burner detached, and partly broken away.

Fig. 3 is a vertical section taken substantially through the center of the burner and a portion of the furnace wall, being partly a-right elevation of the burner shown in Fig. 2.

Fig. 4 is a perspective view of the interior arrangement at that portion of the burner where the separated heavy particles are ejected and recovery'therefrom of finer particles is effected.

' Fig. 5 shows in elevation a modified form Fig. 6 is a central section similar to Fig. 3, but showing a modification in respect to the admission of secondary air.

Fig. 7 is a view similar to Fig. 2, but showing a modification in respect to the bafiling action in the burner.

Fig. 8 is a modification of the device shown in Fig. 5, in similar view.

Referring first to Fig. 1, facing toward the observer are the burner and associated elements of the present invention. A suitable motor 13 is shown direct-coupled to a pulverizer indicated at 14. This for example may be an impact type pulverizer having a fuel inlet or hopper 15 for crushed coal at one end and a delivery fan at the other end. A return pipe 16 from the burner may deliver the ejected heavy particles to the hopper 15 or directly to the pulverizer. At a suitable point, for example at the fan end of the pulverizer, there may be a damper 17 for admitting additional air under regula tion. The pulverizer may have a tangential delivery tube 18 which may be connccted'by an ample transport pipe 19 extending directly to the entrance passage of the classifying burner 20. The ejection of coarse particles by way of pipe 16 may be controlled or stopped by cutting off the pipe by damper or valve 16, which also may be closed when the burner is operated by fuel containing no coarse particles.

The burner or classifier 20 is shown as formed with what may be termed a curved passage or conduit 21 forming a continuation of the entrance passage of the burner, so that the fuel or material ascending through the transport pipe 19 will pass upwardly at high velocity and thence into the urner and around into the curved passage, with the results to be described. The cross sectional shape of the passage may vary, but for convenience is shown as having, 'a four-sided shape rather than circular. These passage walls are well illustrated in Fig. 3, and from Figs. 1, 2 and 3 the preferable arrangement will be seen in which the inside wall 22 is shaped as a hollow frustum of a cone and arranged flaringly toward the furnace. The passage is provided with a number of apertures 23 discharging fuel and air inwardly into what may be termed the central space 24. These apertures 23 are preferably elongated in a direction toward the furnace, since this construction increases the capacity and efliciency of the burner. The resultof the flared form of the wall 22 is that the jets discharged through the apertures or slots 23 converge in a direction toward the furnace, facilitating the delivery through the opening 12 in the furnace wall 12 to constitute a quick burning flame in the combustion chamber. By a curved passage is intended any passage extending around or substantially around the central space, and it may be spiral, or helical, and with less or more than a single turn, so long as the travel is along the passage and therefore around the central space. It will be noted that in the illustrated embodiment the curved passage 21 is in the form of an annular chamber, and the inner wall 22 of the chamber defines an axial passage 24. The openings 23 in this inner wall establish communication between the chamber and the axial passage. The fan and pulverizer l4 deliver air and pulverized fuel tangentially to the chamber through its outer wall.

The classifying or separating action within the passage 21 takes place by centrifugal force, tending to throw out to the peripheral or outside wall 25 the coarse and heavy particles, while the finer particles, being light enough to move along with the air flow are carried through the system of discharge apertures or slots 23 into the central space 24. The differentiation between material thrown outwardly and material drawn inwardly may of course be varied'by altering the character of the passage, the velocity of travel, etc. For pulverized fuel combustion, it is preferable to discharge into the central space only the very fine fuel particles, allowing all coarse and heavy particles to pass along the periphery to ejection. The finer particles discharged with air through the inside Wall apertures are referably directed at an angle as already described so as to assist carrying them to the place of use or disposal, for example directly to the whirling flame in a furnace. v

The heavy particles traveling around the periphery of the curved passage are sooner or later preferably the passage. As herein illustrated the heavy particles are carried clear around through the length of the passage, at the end of which is a space receiving the heavy particles and delivering them to the return pipe 16 as will be more particularly described, this pipe carrying the particles back, for example to the pulverizing' machine. In order to improve the separating action it is preferable that the velocity of flow through the curved passage shall be relatively high, to give effective centrifugal force, while the travel through the discharge slots or nozzles is relatively slow to prevent the forcible inward dragging of the heavy particles against their centrifugal force. For this purpose, the cross sectional area of the passage entrance is preferably less than the aggregate effective discharge area of all of the slots or nozzles 23; and as will be further described the curved passage preferably decreases or contracts in cross sectional area throughout its length so as. to prevent an undesirable decrease in velocity and pressure notwithstanding the disperipherally ejected from whirling flame is injected at high speed into the combustion chamber.

charge of substantial portions through the successive apertures. a As a burner it is highly desirable to provide for thorough mixlng and instantaneous combustion, with a turbulent flame occupying but a small volume. A whirling action is produced with this invention by the fact that the jets delivered into the central space through the apertures 23- depart from a radial direction, each jet being discharged at an incline to the radius on which it enters or tangential to an imaginary cylinder about which a whirl is thus set up. This ortex action may be obtained in different ways. In Figs. 1, 2 and 3 the action occurs with the use of simple discharge slots 23 due to the fact that 'the air and fuel before it is discharged through the slots is already traveling in tangential directions so that the jets issue from the apertures in the offset manner described, as .best indicated by the arrows in Fig. 2.

As already described the jets are delivered not only with the vortex action, but they are directed toward the furnace, so that a To produce the most effective and uniform whirling vortex of delivered fuel it is Y advantageous to provide for substantially uniform pressure and velocity in the-materials discharged through the apertures 23, or at least to arrange that the discharged velocities through the successive apertures are maintained sufliciently high to roduce an effective whirling action. For t is purpose, as clearly shown in Figs. 1 and 2, the

, curved passage 21 is shown as progressively contracting in size or cross sectional area, thus making possible a high static pressure throughout the extent of the passage, a high velocity therein for classification pur oses,i and a high discharge velocity throug the successive apertures. This progressive contraction of the curved passage 1s preferably provided by progressive reduction of its radial dimension, as shown, while maintaining its .axial depth substantially uniform, so that the discharge apertures 23 may be of uniform length. By this arrangementeach of the passage end walls 26 is progressively narrowed, giving the spiral conformation as shown in Figs. 1 and 2. The discharge apertures 23 are herein shown ascof uniform dimension both axially and transversely, which would generally be. satisfactory.

' As already indicated the fuel and primary air receive a supply of secondary air within the central space 24. The primary air may be regulable at the pulverizer or otherwise by damper, and the secondary air may be similarly regulable, so that the two may be coordinated in relation to each other to afford a total quantity of air as.may be required for the complete combustion of the fuel being delivered.

The secondary air may be drawn through the central space from the exterior. Coming toward-the observer in Figs. 1 and 2, and passin to the left in Fig. 3, the secondary air wi l intersect with the jets of fuel laden air so as to give a most intimate mixing action and consequent complete combustion. Instead of relying upon natural draft for secondary air it is preferred to forcibly deliver the air through the central space. The arrangement of the present burner is such that the secondary air can readily be provided by a rotary fan 27 of the propeller type, which has the additional advantage that it delivers the air forwardly with a whirling motion, which may be in the same direction as the whirl or vortex of delivered fuel, so as to accentuate the whirling motion and quick combustion. The fan 27 is shown mounted on brackets 28 within anair box 29. The fan may be driven mechanically in any desired manner, for example by a motor 30 which may be placed within or outside of the air box 29. The

supplied to the burner may be by a damper .31 of the louver "type, or otherwise.

A preferable adjunct to the curved passage consists 'of baffling or retarding means therein for obstructing or agitating the advancing materials so as to create eddies and assist the thorough extraction of the finer particles, to be carried forward with the air, and the centrifugal projection of the I eavier particles to the periphery. Thus in Fig. 2 is shown a system of bafiles 32 in the form of circular rods located at or near the periphery within the channel. The tendencfy of these is to cause disturbances in the orward flow of that the agitation gives the finer particles a better opportunity to be taken up in the air stream and discharged into the centralspace, the heavier particles returning toward the periphery following each ballie. It is not intended to limit the shape or position of the baffles 32, and they may for example be of angular shape spaced slightly from the peripheral wall, as indicated by the bafiies 33 in Fig. 7. It ma also be desirable to provide strips or afiies 34 as shown in Fig. 7 along the inside wall of the passage, these beingplaced for example at the entering edge of each discharge aperture, thus tending to deflect towardthe peulverized materials so ing space or Chamber preferably below the burner wall 22 and adjacent to the passage entrance, the ejected heavy particles passing from the collecting chamber into the return pipe 16 leading to the pulverizer. According to this invention one feature of improvement is the recovery at the ejection point of a substantial percentage of fine material which may have been carried around with the coarse material and wouldotherwise be ejected from the burner. This is herein effected by means of an upwardly flowing air stream which serves to pick up and elevate. any descending fine particles without preventing the gravity discharge of the heavy particles. The arrangement is indicated in Figs. 2 and 3 and in enlarged perspective in Fig. 4. The collecting chamber 35 is a generally triangular space heneath certain of the discharge apertures 23 and enclosed between the walls 22, 25 and 26 of the passage, the wall 25 being extended tangentially downward from the point where the passage contraction ceases. The tail chamber therefore is of the full axial depth of the burner, but, as shown in Fig. 4, it discharges downwardly through a relatively narrow ejection passage 36 communicating directly with the return pipe 16. At the .top of the ejection passage 36, at each side. is a I flat wall or shelf 37, each of these constituting the top wall of a triangular air box 38 exterior to the passage 36. Each of the air boxes 38 has an inward delivery opening 39 to the ejection passage 36, so that the pulverized matters passing from the collecting chamber to the ejection passage are subjected fine material for to the influence of the two opposite air streams coming through openings 39, which air effectively picks up a, large percentage of recovery and return to the burner.

The air supplied to the triangular air boxes 38 for recovery purposes may come from any source, but preferably from the ascending entrance to the curved passage 21. The elements 35 to 39 are shown adjacent to the interior wall 40 of the passage entrance.

As-indicated in Fig. 4 thiswall 40 has two openings 41 leading into the triangular air boxes 38', and for each opening isshown a damper or regulator 42, the two dampers mounted on a common rock shaft adjustable by an exterior handle 43, so that the quantity, pressure and velocity of air ascending through the air boxes maybe properly adjusted. The adjustment of air is to be such that there will be a constant upstream, which tends to draw only the finer particles from the ejected mass, and which then rises through the collecting chamber 35 carrylng the fine particles and discharging them through the lower apertures 23 into the central space 24. In this way a complete, circular system of discharge apertures is main the secondary air may flow taincd actively in operation. In some cases the dampers 42 may be operated in cooperation with damper 16 in the return pipe 16. Thus to throw all coal, coarse and fine, into the furnace, dampers 42 may be widely opened and damper 16 closed.

Certain modifications have been described in connection with Fig. 7. Among other modifications is the arrangement shown in Fig. 5 wherein the inside wall 22 of the curved passage 21 is flaring as in Fig. 2, but in which in place of simple discharge slots are a system of discharge nozzles 23 which may be tubular and are preferably slanted to give both the desired angular direction toward the furnace as well as'the tangential or vortex relation. These nozzles not only give more definite discharge action, but have the advantage that the whirling flow of fuel laden air is surrounded by a substantially clear or free space,

namely between the nozzles, through which so that the de livered flame will be surrounded by an envelop of secondary air. The wall 22 may be cylindrical as in Fig. 8, with nozzles 23 similar to nozzles 23.

Fig. 6 shows an arrangement wherein the secondary air instead of being drawn or forced endwise through the central space is injected with a vortex action similar to the injection of fuel. This may be accomplished by a substantial duplicate of the curved fuel passage 21, namely between the latter and the furnace. An air supply pipe 44 is shown delivering tangentially into a progressively contracting curved passage 45, which in turn delivers into the central space through a system of slots 46, the effect of which will be to give a whirling action to the air in the same direction as that of the fuel, the two combining in a forcible turbulent vortex of thoroughly mixed fuel and air. In this case the rear or outer end of the space 24 may be wholly closed by a wall 47, it being intended that all necessary air is admitted through the two passages 21 and 45; although the wall 47 might carry a regulable damper. This described modification is of especial utility where the secondary air is to be preheated, for example in the furnace walls, the preheating channels delivering to the air passage 45. 7

It will thus be seen that there has been described a combined burner and classifier embodying the principles and attaining the objects of the present invention. Since many matters of operation, combination, arrangement and structure may be variously modified without departing from the prin-' are ' coarse fuel particles,

, coarse fuel particles,

What is claimed is:

1. A burner for pulverized fuel comprising walls forming a curved conduit, the inner wall of the conduit defining an axial passage and being provided with an opening establishing communication between said conduit and passage, and the outer wall being provided with an outlet opening for coarse fuel particles, means for supplying air and pulverized fuel to saidconduit at a point circumferentially remote from said,

outlet opening in the direction .of travel, and walls forming a collecting chamber communicating with the outlet opening.

2. A burner forpulverized fuel comprising walls forming a curved conduit, the inner wall of the conduit defining an axial passage and being providedwith an opening establishing communication between said conduit and passage, and the outer wall being provided with an outlet opening for means for supplying air and pulverized fuel to said conduit at a point circumferentially remote from said outlet opening in the direction of travel, the conduit being shaped to provide a gradually decreasing cross sectional area throughout its extent, and walls forming a collecting chamber communicating with the outlet opening.

3. A burner for pulverized fuel comprising walls forming an annular chamber, the inner wall OftllQ chamber defining an axial passage and being provided with an opening establishing communication between said chamber and passage, and the outer wall being providedv with an outlet opening for means for supplying air and pulverized fuel tangentially to said chamber through its outer wall,and walls forming a collecting chamber communicat ing with the outlet opening. 1

' 4. A burnerfor pulverized fuel comprising walls forming an annular chamber, the inner wall of the chamber defining an axial passage and being provided with an open ing establishing communication between said chamber and passage, and the outer wall being provided with an outlet opening for coarse fuel particles, means for supplying air and pulverized fuel tangentially to said chamber through its outer wall, and means for admitting a current of air to the chamber through said outlet opening, thereby preventing ejection of fine fuel particles.

5. A burner for pulverized fuel comprising walls forming an annular chamber, the inner wall of the chamber defining an axial passage and being provided with spaced apertures establishing" communication between said chamber and passage, and the outer wall being provided with an-outlet opening for .ticles from the coarse chamber and coarse fuel particles, means for supplylng air and pulverized fuel tangentially to said chamber through its outer wall, and a set of bafiles adjacent to the entering edges of the apertures operating to dirlelct coarse fuel particles toward the outer wa 6. In combination -with a furnace wall having an opening, a burner for pulverized fuel-comprising walls forming a substantially circular chamber mounted adjacent to and substantially coaxial with said opening, means to introduce pulverized fuel and air into said chamber and cause the fuel to travel along the peripheral wall of the chamber, thereby separating the coarse particles of fuel by centrifugal force into an outer zone surrounding the fine, a passage communicating with the central portion of the chamber which delivers the fine particles through and an ejection passage communicating with the outer zone through which the coarse particles in the outer zone may escape from the burner.

7. A burner as in claim 6 and wherein a damper is provided to' open or close said ejection passage.

the opening in the furnace wall,

8. A burner for pulverized fuel comprising walls forming a substantially circular chamber, means for supplyingair and pulverized fuel to said chamber in a direction tangential to the peripheral wall of the chamber and thereby causing the fuel to ticles, and walls forming a collecting cham-.

ber communicating with said last-mentioned outlet opening.

9. A burner as in claim 8 and wherein a system of bafiles is provided adjacent the inner surface of the peripheral wall to retard or agitate the heavy material and thereby facilitate separation of the fine fuel par particles;

10. A burner for pulverized fuel comprising walls forming a substantially circular an axial outlet passage communicating therewith, the peripheral wall of the chamber being provided with an out let opening through which coarse fuel particles may pass and be separated from the stream of fine fuel, walls enclosing a space communicating with said opening into whicl thecoarse particles may escape from the burner, and means for supplying pulverizedfuel and air to the chamber m a direction

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