US3202196A

US3202196A - Method and apparatus for burning fuel

Info

Publication number: US3202196A
Application number: US194841A
Authority: US
Inventors: John M Rackley; Musat George; John H Kidwell
Original assignee: Babcock and Wilcox Co
Current assignee: Babcock and Wilcox Co
Priority date: 1962-05-15
Filing date: 1962-05-15
Publication date: 1965-08-24
Anticipated expiration: 1982-08-24
Also published as: GB1034826A; ES288042A1

Description

Aug. 24, 1965 l. M. RACKLEY ETAL METHOD AND APPARATUS FOR BURNING FUEL 2 Sheets-Sheet 1 Filed May l5, 1962 FIG.1

INVENTORS John M. R ackle{ By John H. Kldwel ATTORNEY llg- 24, 1955 J. M. RACKLEY ETAL 3,202,196

METHOD AND APPARATUS FOR BURNING FUEL Filed May l5, 1962 2 Sheets-Sheet 2 Ge e Musar ATTQRNEY United States Patent O METHUD AND APPARATUS FR BURNlNG FUEL John M. Racirley, Alliance, George Musat, Canton, and

.lohn H. Kidwell, Alliance, Ohio, assignors to rEhe Babcock it Wilcox Company, New York, NSY., a corporation of New .iersey Filed May l5, 1962, Ser. No. 194,841 Ciairns. (Cl. 15s- 1.5)

The present invention relates generally to the construction and operation of fuel burners, and more specically to fuel burners capable of burning a plurality of fuels separately or simultaneously in a furnace.

In recent years, the general trend in the design of vapor generating units for use in the field of electrical power generation has been toward higher capacity units; hoW- ever, for reasons of cost, an attempt is simultaneously being made to limit the physical size of these high capacity installations. As a result of this trend, greater heat input rates are required for any given furnace, but the furnace wall space available for mounting the fuel burning equipment has become proportionally less than with the lower capacity furnaces previously used. The high heat input rates cannot satisfactorily be attained by increasing the number of burners used since this would tend to further crowd the available wall space, introduce flame impingement problems, and increase the cost of the furnace walls and associated fuel burning equipment. One solution to the problem might be to increase the physical size and thus the rated capacity of existing burners; however, there are definite restrictions to this approach. The usual type of circular burners have definite size limitations because of furnace wall support and tubular wall construction complications, While the majority of the rectangular or slot burners in use are subject to ignition instability unless supported by auxiliary lighters `or mutually by the flames from other burners. This iustability greatly limits the possible arrangements and applicability of the present rectangular burners even though the furnace wall construction with these burners would be considered generally acceptable.

The equal distribution of hot combustion gases over i the cross-sectional area of the furnace of a large vapor generating unit is primarily a function of the fiame shape of individual burners and the heat release patterns of the burners mounted in the furnace walls. Many of the present large capacity burners produce bushy irregularly shaped flames having uneven heat release patterns that do not readily lend themselves to arrangement in furnace walls to effect equal distribution of heat within the fur nace.

In accordance with the present invention, we provide, for efficiently burning fuel, an apparatus that is simple in design and comparatively inexpensive to construct. We further provide an apparatus and method for burning various fluent fuels, either singly or in combination, characterized by positive ignition and flame stability over a wide load range with desirable arne shape and heat distribution pattern, and that effectively lends itself to the compact arrangement of multiple fuel buners in the fur nace walls of a modern, high capacity vapor generating unit. We further provide a high heat input burner that may be sized and arranged in modules or cells for high heat release rates to the furnace, and that occupies a small amount of furnace wall area in relation to its capacity.

In the present invention, fuel is introduced into a furnace with a portion of the necessary combustion air at velocity conditions which promote the establishing of a semi-quiescent zone within the furnace and in front of the fuel introduction elements. Ignition is established and maintained in this zone. The low velocity burning fuel and air stream, as it issues from the semi-quiescent zone, comes into direct contact with higher velocity streams of additional combustion air introduced to intersect the fuelair stream at a location downstream of the semi-quiescent zone.

The burner of the present invention is made up of one A or more burner cells, each cell Containing the basic elements of a burner, namely, fuel introduction elements and ports for introducing and directing the air streams. The burner may be constructed as a single cell, and as such will have all the desirable operating and construction characteristics herein described for the present in-` vention,

For higher capacities, two or more burner cells may be combined into a single multi-cell burner unit. In such a burner, the dividing walls between adjacent cells may advantageously be eliminated for ease and simplicity of construction so that the burner and air ports extend throughout the height of the burner zone. The unitary multi-cell burner advantageously utilizes-all of the desirable construction features and operating characteristics of the subject invention.

To attain the functional objectives in the present invention, fuel and a portion of the necessary combustion air are introduced in at least one location along the vertical axis of a rectangular main burner port. Additional air is separately introduced between the outer boundary of the fuel introduction elements and the inner boundary of the burner port to `surround and cool the burner parts and to prevent the back iiow of hot combustion gases past the ends of the fuel introduction elements. The fuel and air velocities leaving the main burner port `are sufficiently low to permit the establishment of a stable ignition zone within the furnace directly in front of the fuel `introduction elements. The remainder of the necessary combination air, or secondary air, is introduced directly into the furnace through separate narrow rectangular openings at the sidesof the main burner port at a relatively high velocity so that the air impinges on and mixes with the burning fuel issuing from the stable ignition zone established semi-quiescent zone defined by the main burner port and the intersecting secondary air streams. `Beyond the semiquiescent zone, the burning fuel is intimately mixed with the remaining necessary combustion air, and intense combustion commences.

The oblique, impinging sheets of secondary air tend to control the resulting flame shape, advantageously producing a stable and predictable pattern. Admitting air in this manner tends to produce a slower burning flame which results in more even heat transmission over the majority of the llame length; the combustion :of the fuel in this manner thus resulting in a regular predictable liame shape having an even heat release pattern. In addition, the liame shape obtained with this burner results in a greater degree of penetration in the furnace. This not only results in a more uniform furnace flow pattern, but also provides a greater degree of furnace mixing between opposed and adjacently mounted burners. p

The various features :of novelty which characterize our invention are pointed out with particularity in the claims annexed'to and forming a part of this specification. For a better understanding of the invention, its operating advantages and specific objects attained by its use, reference should be had to the accompanying drawings and descriptive matter in which we have illustrated and described an embodiment of our invention.

` Of the drawings:

FIG. 1 is a horizontal sectional view of an embodiment of the present invention taken on line 1-1 of FIG. 2;

FlG. 2 is an elevation of the burner of the present invention;

FG. 3 is a sectional side view of the burner taken on line 3-3 of FIG. 2;

FIG. 4 is a horizontal sectional View of an embodiment of the present invention taken on line 4-4 of FIG. 5;

FlG. 5 is an elevation of another embodiment of the burner of the present invention; and

PEG. 6 is a schematic cross-section of a furnace showing .a possible arrangement for a group of burners of the present invention and the resulting composite llame patterns.

In the drawings, FIGS. l, 2 and 3, like reference numerals refer to like parts in the several views. An embodiment of the burner 1@ of the present invention is shown including a pair of symmetrically arranged burner cells 11, one of which is superposed on the other end which are symmetrically disposed on either side of the horizontal line 7 7, combined t0 form a single multicell burner unit. It will be understood that a plurality of burner cells may be combined to form burner units of various sizes and capacities.

The burner 10 is shown installed in a tubular watercooled wall 12 of a funace 9, the wall being arranged to :accommodate an elongated vertically disposed rectangular main burner port 13 and two adjacent relatively narrow elongated secondary air ports 14 displaced from and parallel `to the vertical sides of the main burner port 13.

A housing associated with each burner 10 is provided Vto add structural rigidity to the furnace wall, to support additional burner parts, and to direct fuel and air flows through the burner into the furnace.

A housing 15, disposed in spatial relation to the main burner port 13 as disclosed in FIGS. l, 2 and 3 land suitably attached to the furnace wall 12, is arranged with the side which is in the plane of the furnace wall 12 opening into the furnace 9. The fuel introduction elements 16 are received through and attached to the back-plate A of the housing `15. The back-plate 15A cooperates with the vertical side plates 15B to form rectangular openings 17 in the side plates 15B which are perpendicular to the plane of the furnace wall 12 as shown in FIG. 1. Forwardly curved vertical baille members 18, suitably attached to the housing 15 by'horizontal support plates 20 are used to divide the flow area of the openings 17 to effect distribution of air without the main burner port 13,.

The axially inclined plate members 21 cooperate with the inclined portions of the side plates 27 to form the secondary air ports 14, which are symetrically disposed on either side of the main burner port 13. These rearwardly extending open-ended ports have the forward ends opening into the furnace 9 while the rearward ends open to the internal chamber 22 of the burner lll. The secondary ports 14 thus formed are attached to the tubular furnace wall with the acute angle a as shown in FlG. 1 dening the angularity of the ports with respect to the vertical plane of the burner centerline. Horizontal divider plates 23 are spaced within the secondary Vair ports 14 to rprovide structural rigidity to the housings and to direct the how of air horizontally through the ports.

During operation, the velocity of the air entering the furnace 9 from the main burner port 13 is lower than the velocity :of the air exiting the ports 14, and the openings 17 and ports 14 are sized to effect this velocity relationship. It should further be noted that the ports 14 are of larger cross-sectional flow area than are the openings 17 so that the air passing into the furnace 9 through the ports 14 constitutes a major portion of the total combustion :air entering the furnace 9 from the burner 1d.

Displaced to the rear of and at the sides of the burner 1i) are burner shut-off dampers 25 within the windbox 24 and mounted vertically in a plane substantially parallel to the furnace wall 10. They are suitably framed by structural members 26. Sides plates 27, ltop cover plate 23, bottom cover plate 30, and rear cover plate 31 are provided between the frame of the shut-off dampers 25 and the lateral and vertical extremities of the burner, thus requiring the air that enters the furnace 9 through the secondary air ports 14 or through the vertical openings 17 within the main burner port housing 15 to pass through the burner shut-off dampers 25.

The furnace wall tubes in line with the burner port openings are suitably bent out of the plane of the furnace wall 12, and into locations behind and parallel to the furnace wall at the vertical extremities of the burner ports to thus provide the space required for the ports within the furnace wall. These tubes assume their normal positions in the plane of the wall upon having formed the burner ports. For example, the wall tubes 32 in line with the main burner port opening 13 are bent into a plane parallel to and on the outside boundary of the main burner port housing side plates r[he wall tubes 33, in line with the secondary air port openings 14, are bent into a plane parallel to and on the outside `boundary of plate 211. ft will be noted that all of the bends in any of these tubes lie in a single plane, thus minimizing the cost of the tubular wall construction associated with this burner installation.

The burner of the present invention is capable of burning pulverized solid fuel, liquid fuel or gaseous fuel either separately or in combination. The combination fuel introduction elements 16 are spaced along the central axis of the main burner port 13 in the embodiment shown in FlGS. l, 2 and 3.

Gaseous fuel is supplied under pressure to the doublewalled cylindrical gas element 3S in the burner through a supply pipe 34 and thence into the annular space between the concentric walls of the gas element 3S; the space between the walls being sealed at the ends by annular members 35C attached, as by welding, between the inner wall 35A and the outer wall 35B of the gas element 35. Each cylindrical gas element is received in, extends through, is attached to and supported by the rear wall 15A of the main burner port housing 1S and the rear cover plate 31. Each gas element 3S extends forwardly toward the, 'furnace 9 through the main burner port housing 15, terminating substantially in the plane of the furnace Wall 12. Gaseous fuel is introduced into the furnace 9 through openings 35D in the forward end of the cylin-V drical gas element 35.

Pulverized coal entrained in air is supplied to the burner 1h directly from a pulverizer (not shown) or from a storage bin (not shown) through a coal pipe 3e to the furnace 9. Each coal pipe is received in and supported by the windbox casing 37 (see FIG. 4) and is positioned concentrically with respect to the cylindrical gas element 35, the coal pipe 3o terminating within the cylindrical gas element. The coal pipe is additionally centered and supported by radial struts 35 installed within the space between the exterior of the coal pipe 36 and the inner wall 35A of the cylindrical gas element. The annular opening 4t? between the coal pipe 36 and the gas element 35 is open to the windbox 24, and air passes through this annular space to the furnace 9 whenever the air pressure in the windbox 24 is higher than in the furnace QQ A coal dispersing impeller 41 is provided at the forward end of each coal pipe, and is held in place by an axially adjustable tubular member 42 which extends rearwardly and axially through the coal pipe to the outside of the windbox casing 37. Thev tubular member 42 is positioned and supported within the coalr pipe by radial struts 43 permanently affixed to the tubular member 42 and extending radially therefrom to the inner wall of the coal pipe 36. When not in use, the impeller 41 may be retracted within the coal pipe 36 by moving the tubular member 4Z rearwardly. v

Liquid fuel to be red is supplied to an atomizer barrel (not shown) which is contained within and extends through the tubular member 42. The iiuid fuel is introduced into the furnace 9 through an appropriate atomizerV head (not shown) that is aifixed to the forward end of the atomizer barrel and terminates substantially ush with the forwardmost portion of the coal dispersing impeller 4l. The particular atomizer assembly used may be any one of the many standard designs presently used in large fluid fuel burners, and it may preferably be removed from the `tubular member 42 from outside the windbox casing 37 when not in use.

A tubular lighter housing 44, substantially aligned with respect to the burner cells, extends through and is supported by the back plate 15A of the main burner port housing 15, the rear cover plate 31, and the windbox casing 37. A lighter (not shown) of any suitable type may be installed or inserted in the tubular lighter housing 44 for use during start-up and low load operation of the burner lil.

If the burner consists of more than two cells, a lighter should be installed adjacent to the main fuel element of each cell.

In the drawings, FIGS. 4 and 5, another embodimen-t of the burner of the present invention is shown, with like reference numerals in these figures indicating similar parts of the burner shown in FIGS. 1, 2 and 3.

In this embodiment, gaseous fuel is supplied under pressure to elongated tubular spuds 45 which are here arranged substantially equally spaced in two vertical rows within the main burner port housing I5. The spuds 45 extend forwardly through sleeves 46 in the windbox casing 37, through the rear cover plate 31, through the bac1 `plate 15A of the main burner port housing, and terminate within the main burner port housing 15 adjacent the forward end of coal pipe 35. The forward ends 45A of the spuds 45 are sloped backwardly toward the central axis of the burner, these sloped ends being provided with a plurality of orifices through which gaseous fuel is emitted.

The gas spuds may be retracted rearwardly when not being used, and a seal (not shown) is provided between the spuds 45 and the sleeves 46 to prevent leakage of the air from the windbox 24.

The firing of pulverized solid fuel and liquid fuel is accomplished in the same manner as was previously described with reference to FIGS. l, 2 and 3.

In this embodiment, the rear cover plate 31 is litted snugly to the coal pipe 36 to prevent air from by-passing the shut-off dampers 25 as shown in FIG. 4,

As a modification to the embodiment shown in FIGS. 4 and 5, the gas supply to the spuds 45 may be through a manifold system (not shown) within the windbox 24. The spuds 45 would be permanently aiiixed to this manifold, and would extend through the rear cover plate 31 and terminate adjacent the coal pipe 36.

It should be recognized that the above described embodiments of the present invention could advantageously be simplified in instances where all three types of fuel are not to be fired, and the inventive features of this fuel burner are retained if only one or two main types of l fuel are to be utilized.

For example, in the embodiment shown in FIGURES l, 2 and 3, if only liquid and gaseous fuels are to be used, the coal pipe 36 and the coal dispersing irnpeller 41 could be eliminated. If this were done, in order to afford maximum stability when firing liquid fuel, the axial air flow through the cylindrical gas element 35 should be restricted and a stationary spinner, mounted axially on the tubular member 42 within and near the forward end of the cylindrical gas element 35, should be utilized to impart rotation -to the air passing through the cylindrical gas element 35.

In the drawing, FIG. 6, a schematic horizontal crosssectional view of a furnace 47 is shown bounded by walls 48. The burners 49 are supplied with air from a source (not shown) through the windbox S0. The burners 49 are installed in a staggered pattern on opposite walls and the slender burner flames 51 are shown as being interlacing and substantially filling the cross-sectional area of the furnace 47.

The slender flame shape produced by this burner is a result of the control afforded by the irnpinging secondary air streams, and is readily used in conjunction with llames of similar shape to produce an even furnace flow pattern. In addition, the control of the sides of the ame by the secondary air streams affords a greater degree of penetration of the flame into the furnace, which results in a greater degree of furnace mixing and therefore more uniform temperature distribution and more complete combustion.

As an indication of the operativeness of the present invention, but not to be construed as any limitation to the size or capacity of the particular burner design disclosed in this invention, a burner was built according to the invention and tested. The subject test burner, installed at the laboratory facilities of the assignee of theI present invention, was a single burner having two multifuel burner cells of million Btu. per hour capacity each for a total heat input capacity of 200 million B.t.u. per hour. The test burner was similar to the embodiment shown in FIGS. l, 2 and 3. The openings provided for the burner in the furnace wall consisted of a main burner porthaving its major dimension in the vertical direction, and rectangular secondary air ports arranged along and spaced from each side of the main burner port and being the same height as the burner port.` The overall height of the` burner port opening in the furnace wall was 62 inches and the distance between the lateral extremities of the secondary air ports was 54 inches. The main port was 22 inches wide, and the secondary air openings were lll/z inches wide. Each secondary air port was constructed to introduce its air stream into th-e furnace at an angle of intersection a of 30 degrees with the central axis of the main burner port perpendicular to the furnace wall. A housing 16% inches deep was constructed around the main burner port on the outside of the furnace. A17

`inch wide rectangular opening was provided on each side of the housing for air admission. Fuel was introduced into the furnace through a pair of fuel elements equally spaced along the central vertical axis of the main burner port.

While in accordance with the provisions of the statutes j we have illustrated and described herein the best form and mode of operation of the invention now known to us, those skilled in the art will understand that changes may be made in the form of the apparatus disclosed without departing from the spirit of the invention covered by our claims, and that certain features of our invention `may sometimes be used to advantage without a correspondin g use of other features.

What is claimed is:

1. The method of burning fuel in a furnace which comprises the steps of introducing fuel into the furnace in a plurality of parallel streams uniformly spaced along the vertical axis of a single burner port, introducing low velocity air in surrounding relationship to the streams of fuel to form a semi-quiescent stable ignition Zone, and introducing a pair of higher velocity continuous vertical sheets of combustion air into said furnace at equal and opposite angles to the streams of fuel so that each of said sheets of combustion air intersects all of said streams of fuel downstream of said ignition zone within said furnace.

2. In combination with a boundary wall of a furnace, a fuel burner comprising means forming a vertically disposed rectangular burner port in said boundary wall, a housing disposed outside of said wall, said housing dening a chamber having an open end coincident with said port and an oppositely disposed closed end, means for introducing a minor portion of the necessary combustion air through said housing into said furnace, a plurality of horizontally disposed burner elements spaced apart along the vertical axis of said port for introducing streams of fuel and an additional minor portion of the necessary combustion air into said furnace, said burner elements having their discharge ends within said chamber, means forming additional ports vertically disposed along the sides of said port in said boundary wall, said additional ports being arranged for the introduction of the remaining portion of the necessary combustion air into said furnace at a higher velocity than either of said minor portions of air in impinging directions to said streams of fuel.

3. In combination with a boundary wall of a furnace, a fuel burner comprising means forming a vertically elongated rectangular burner port in said boundary wall, a housing disposed outside of said wall defining a substantially rectangular chamber having an open end coincident with said burner port, said housing including an oppositely disposed closed end plate and side walls formed with openings therein, a plurality of fuel introduction elements spaced along the `vertical axis of said burner port and terminating in said chamber, said fuel introduction elements passing through said end plate, means for introducing streams of fuel and a minor portion of the necessary combustion air into said furnace through said fuel introduction elements, means for introducing an additional minor portion of the necessary combustion air through said openings into said chamber for passage through said chamber into said furnace, means forming a pair of narrow air ports displaced from and parallel to the vertical sides of said burner port and having substantially the same vertical height as said .burner'port, said narrow air ports being arranged for the introduction of the remaining portion of the necessary combustion air into said furnace at a higher velocity than either of said minor portions of air in impinging directions to said streams of fuel to intersect said streams of fuel at a point displaced outwardly from said boundary wall.

""4. In combination with a boundary Wall of a furnace, a fuel burnercomprising means defining an elongated rectangular burner port in said boundary wall, a plurality of fuel introduction elements spaced within said burner port, means for introducing streams of fuel from said fuel introduction elements through said burner port into said furnace, means forming continuous narrow rectangular air introduction ports disposed along each of the longer sides of and spaced from said burner port, the discharge end of each of said ports being inclined only in a direction toward said burner port to project all of the air passing therethrough in a continuous uniform sheet of air in an intersecting direction with all of said streams of fuel so as to intersect therewith along their entire heights at a location displaced a substantial distance within said furnace, and means for separately introducing ,air in surrounding relationship with said streams of fuel so as to mix therewith and form a stable ignition zone between said boundary wall and the location of intersection of said she-ets of air with said streams of fuel.

5. ln combination with a fluid cooled boundary wall of a furnace, a fuel burner comprising means defining a vertically elongated rectangular burner port in said boundary wall, a plurality of fuel introduction elements uniformly spaced along the vertical axis of said burner port for the introduction of streams of fuel through said burner port into said furnace, a housing disposed outside of said boundary wall and defining a chamber containing the terminal ends of said fuel introduction elements and having an open end coincident with said burner port, means for passing air through said chamber in surrounding relationship to said fuel introduction elements to effect cooling thereof and to establish a stable ignition zone immediately downstream of the terminal ends of said fuel introduction elements, means defining a pair of continuous rectangular air introduction ports formed in said boundary wall and disposed on opposite vertical sides of and spaced from said burner port and having substantially the same vertical dimension as said burner port, the discharge ends of said air introduction ports being inclined only in directions toward said burner port to project all of the air passing therethrough in a pair of continuous uniform Vertical sheets of air intersecting with each other and with all of the streams of fuel along the entire height thereof after the streams of fuel have passed through said burner port and said ignition zone.

References Cited by the Examiner UNlTED STATES PATENTS 1,994,443 3/35 Bailey 110-22 X 2,011,026 8/35 Bailey et al. 122-235 2,025,066 12/35 Millar 122--235 2,242,797 5/4l Luclie l58-l.5 2,363,942 ll/44 Campbell 15S- 1.5 X 2,397,793 4/46 Leach 11G-28 2,480,459 8/ 49 Fletcher 122-235 2,823,628 2/58 Poole et al. 1l0-22 X 3,074,361 l/63 Huge et al. 110-28 i FOREIGN PATENTS 847,570 7/39 France. Y

331,555 7/30 Great Britain.

375,275 12/30 Great Britain.

845,702 8/ 60 Great Britain.

100,711 3/ 62 Netherlands.

JAMES w. wEsTHAvER, Primary Examiner.

FREDERICK L. MATTEsoN, JR., Examiner.

Claims

4. IN COMBINATION WITH A BOUNDARY WALL OF A FURNACE, A FUEL BURNER COMPRISING MEANS DEFINING AN ELONGATED RECTANGULAR BURNER PORT IN SAID BOUNDARY WALL, A PLURALITY OF FUEL INTRODUCING ELEMENTS SPACED WITHIN SAID BURNER PORT, MEANS FOR INTRODUCING STREAMS OF FUEL FROM SAID FUEL INTRODUCTION ELEMENTS THROUGH SAID BURNER PORT INTO SAID FURNACE, MEANS FORMING CONTINUOUS NARROW RECTANGULAR AIR INTRODUCTION PORTS DISPOSED ALONG EACH OF THE LONGER SIDES OF AND SPACED FROM SAID BURNER PORT, THE DISCHARGE END OF EACH OF SAID PORTS BEING INCLINED ONLY IN A DIRECTION TOWARD SAID BURNER PORT TO PROJECT ALL OF THE AIR PASSING THERETHROUGH IN A CONTINUOUS UNIFORM SHEET OF AIR IN AN INTERSECTING DIRECTION WITH ALL OF SAID STREAMS OF FUEL SO AS TO INTERSECT THEREWITH ALONG THEIR ENTIRE HEIGHTS AT A LOCATION DISPLACED A SUBSTANTIAL DISTANCE WITHIN SAID FURNACE, AND MEANS FOR SEPARATELY INTRODUCING AIR IN SURROUNDING RELATIONSHIP WITH SAID STREAMS OF FUEL SO AS TO MIX THEREWITH AND FORM A STABLE IGNITION ZONE BETWEEN SAID BOUNDARY WALL AND THE LOCATION OF INTERSECTION OF SAID SHEETS OF AIR WITH SAID STREAMS OF FUEL.