US3322180A

US3322180A - Burner apparatus

Info

Publication number: US3322180A
Application number: US463584A
Authority: US
Inventors: Walter M Perry
Original assignee: Johns Manville
Current assignee: Johns Manville Corp; Johns Manville
Priority date: 1965-06-14
Filing date: 1965-06-14
Publication date: 1967-05-30
Anticipated expiration: 1984-05-30

Description

May 30, 1967 w. M. PERRY 3,322,180

BURNER APPARATUS Filed June 14, 1965 sa 45 fum BYZQ /VM ATTORNEY United States Patent Nfice 3,322,180 Patented May 3U, i967 This invention relates generally to burner apparatus for generating a high velocity stream of hot products of combustion. More specifically, this invention relates to a refractory tunnel burner for generating a relatively wide and flat hot gaseous blast of high temperature and high velocity.

In the gaseous heating art, there are applications which require the use of burners which develop a high temperature and high velocity generally wide flat blast of heating gases and most particularly in the local heating of work which is being continuously advanced in planar array in relation to the blast such as in flame hardening and flame drawing or attenuating processes. In order to obtain generally uniform heating conditions, it is necessary to produce the heating gases at a rate at least as great as that at which the work is advanced. Consequently, it is most desirable to use a premix fuel to accelerate the combustion process. However, certain difficulties have been experienced in the ignition of such fuels in regard to flash back (backfire), and to blow off (isolation of flame from emitting port).

The problem of uniform heat distribution across the blast is particularly acute in those applications where it is desired to employ a wide relatively flat blast of products of combustion because of the natural tendency of gaseous mixtures to burn and expand radially as they are propagated in an axial stream. This same phenomena makes it difcult to achieve uniform distribution, velocity and temperature of the products of combustion across the width of the blast. If the distribution, velocity and temperature are not closely and uniformly maintained across the width of the blast, the work subjected to the blast will not be uniformly heated unless sufficient time is provided for the heat to soak through the work. In some continuous processes it is economically unfeasible to so extend the time during which the work is exposed to the blast.

Another problem which has plagued the industry in the use of hot velocity gas flow is the stabilization of the flame. It has been heretofore suggested to provide auxiliary pilot flames to envelope and stabilize the main flame. It has also been suggested to use metal bluff bodies in burners to create an area of turbulence and low velocity to stabilize burning. However, certain disadvantages are attendant with these arrangements, such as more complex construction, use of additional fuel in operating the pilot flames, and substantial reduction in velocity of the moving stream, which reduction and velocity materially reduces the attenuating force.

One of the advantages of burners incorporating the features of this invention is the ability to effectively burn airgas mixtures which are richer than stoichiometric. Rich mixtures are usually difficult to burn with stability. With stoichiometric and lean mixtures combustion of the fuel occurs relatively fast and a short flame is produced. With a rich mixture, the flame temperature is considered to be higher and the rate of heat transfer from the burning mixture to the object being heated is faster. Consequently, with stoichiometric or lean mixtures complete combustion is easy to attain in a relatively short tunnel but complete combustion of rich mixtures is difiicult to attain in such a short tunnel. If complete combustion is not attained, external burning of the gaseous mixture occurs and the flame velocity, effectiveness are reduced.

A primary object of this invention is to provide an improve temperature, and heating It is another object of this invention to provide means for stabilizing the flame in the refractory tunnel of a burner without the need of separate pilot flames or metal bluff bodies.

burner adapted to discharge the products of combustion stream with preferred velocity and temperature distribution patterns within the stream.

To accomplish the stated objects, the novel burner of this invention is designed to deliver a plurality of streams of premix fuel from a plenum chamber through the passages o-f a refractory burner block or grid for discharge into a refractory lined tunnel, wherein said streams are preferably delivered in a substantially uniform distribution pattern corresponding to the cross-sectional configuration of the tunnel, and wherein some of said streams are discharged from their respective passages upstream of where other of said streams are discharged. The streams which are discharged upstream are preferably discharged into a recessed portion of said refractory grid, said recessed portion preferably having an elongated distribution pattern corresponding to said cross-sectional configuration of the tunnel and defining laterally extending refractory surfaces. Refractory burner tunnels are usually designed so that the combustible mixture, on issuing from the burner block, expands and cornes in contact with the refractory wall(s) of the tunnel. The refractory offers some resistance and friction to the combustible mixture flowing over it, and sets up numerous eddy currents which slow down the mixture to a point where the flow is much slower than the rate of propagation of the flame. The refractory tunnel wall at this point incandescent and tends to increase the speed of combustion and to stabilize and hold the flame. However, sometimes a condition results where the central portion of the combustible mixture will not impinge upon the wall and due to the high velocity the flame will have no tendency to hold on but will burn a considerable distance away from the tunnel entrance and sometimes will not stay lit but will blow off. Also, the gases immediately adjacent to the tunnel wall will tend to burn at a faster rate than the gases at the interior of the stream. The provision of sub-tunnels or recessed portions within the refractory burner block provides additional catalytic surfaces and edges on which the interior portion of the gaseous stream may be heated by incandescence and thus obviate the above-recited disadvantages. The refractory grid is preferably of relatively high density refractory, which facilitates the fabrication of the orices. Because of the increased strength of the highdensity refractory smaller and more uniformly accurate orifices may be provided than with low density refractory. To further enhance the ignition and combustion processes within the tunnel, surface catalyst zones on walls of the tunnel are provided immediately adjacent to the grid plate and are preferably defined by relatively low density refractory. The low density refractory presents a relatively porous surface defining a series of interstices in which the gaseous mixture may burn and thus heat the surface to incandescence to facilitate ignition of additional gases.

The invention will be more fully understood, and further objects and advantages thereof will become apparent by reference to the following detailed description in conjunction with the accompanying drawing, in which like references designate like parts.

immediately becomes To facilitate the description, variations of like parts in different embodiments are designated with letter suffixes and variations of like parts within an embodiment are further designed with number suffixes.

FIG. l is a plan view of one form of the burner of this invention;

FIG. 2 is an elevational view of the burner of FIG. 1, with the burner tunnel shown in cross section taken along the longitudinal center line 2-2 thereof, and illustrating in more detail the sub-tunnel or recessed portion of the burner grid;

FIG. 3 is a cross-sectional elevational View of the burner taken along line 3-3 of FIG. 2;

FIG. 4 is a fragmentary cross-sectional elevational view, similar to FIG. 2 but of an alternate embodiment wherein a plurality of sub-tunnels are employed;

FIG. 5 is a fragmentary cross-sectional elevation view, similar to FIG. 2, but of a further embodiment wherein a plurality of interconnected sub-tunnels are employed;

FIG. 6 is a fragmentary cross-sectional elevational view, similar to FIG. 2 but of a still further alternate embodiment wherein the sub-tunnels are defined intermediate non-perforated portions of the burner block and which portions extend slightly downstream of the perforated portions of the burner block; and

FIG. 7 is a fragmentary cross-sectional elevational view of another embodiment wherein the sub-tunnels are in staggered relation to each other.

The burner 10, as shown in FIGS. 'l-3, preferably and generally comprises `an elongated refractory body defining a burner grid plate or block 12, a tunnel defined by refractory walls, upper wall 16, lower wall 18 and

side walls

20 and 22, and a metal housing 24 encasing the refractory walls. It will be understood that, in all of the illustrated embodiments, the grid plate 12 may be fabricated from a single block of refractory or a plurality of blocks in laminate fashion. A plenum chamber 30, which may be generally described as a manifold, is suitably connected through supply pipe 34 to a source of an admixture of combustible fuel and air (not shown). The plenum chamber 30 facilitates the uniform distribution of the fuel across the lateral Width of back face 36 of the burner block 12. To further facilitate such distribution, a diffuser screen 26, shown to be in the form of metal mesh, may be provided intermediate the entrance 28 of supply pipe 34 and the back face 36.

The burner block 12 is provided with a group of passages 40 extending straight therethrough parallel to the longitudinal axis of block 12, to front face 42. The front face 42 of burner block 12 defines a sub-tunnel or recess portion 44 to which some of the passages 40 discharge prior to discharging into the main tunnel 14. It is preferred that the recess portion 44 have a cross-sectional configuration corresponding substantially to the cross-sectional configuration of the main tunnel 14 and also define a distribution pattern for the passages 40A discharging into recess portion 44, which corresponds to the cross-sectional configuration of the tunnel 14. Where ya single sub-tunnel or recess 44 is employed, it is also preferred that the recess portion 44 be centrally located so as to provide a maximum amount of stabilization for the interior portion of the overall gaseous stream being discharged from the passages 40 into the tunnel 14.

The axial extent of the refractory grid 12 is such that the passages 40 extending therethrough are of sufficient axial extent in relation to the diameters thereof, preferably a length equal to at least 5 diameters, to quench any flame tending to travel backwardly and flash back. Although the major extent of the side walls 50 and 52 defining the recesses of sub-tunnels 44 may be considered to be relatively cold during operation, the edges 46 and 48 become heated to incandescence more quickly and maintain temperatures which are substantially higher than other portions of the gaseous streams emanating from the burner block 12. The edges 46 and 48 are primarily heated to incandescence by heat radiated from the

walls

16 and 18 and by eddies of gases burning at the portions of face 42, contiguous to the edges 46 and 48, where the gas velocity is relatively low. Consequently, edges 46 and 48 define surface catalyst zones 45 which facilitate and maintain ignition of the central portion of the overall stream emitted into the main tunnel 14.

In preferred embodiments, surface catalyst zones 60 are also provided in the main portion of tunnel 14 irnmediately adjacent to grid 12 in at least the top wall 16 and -bottom wall 18, and in the most preferred embodiments also in the lsidewalls 2G and 22.

The surface catalyst zones 60 and the grid 12 are preferably defined by low density and highly porous refractory, in the general range of 45470 ylb./ft.3, such as highly pure kaolin clay marketed by the Babcock-Wilcox Company and known as K-SO. The remainder of the tunnel walls, defining a main refractory Zone, is preferably of castable refractory of relatively higher density, in the range of 71-165 lb./ft.3.

The feature of providing a surface catalyst zone interiorly of the side walls of the main combustion tunnel is particularly adaptable and useful in burners having relatively elongated tunnels wit-h elongated -gas inlet openings or discharge openings, in which case the problem of maintaining uniform distribution, velocity, and ternn perature is very acute. However, this feature, as well as other features of this invention, will be of advantage in burners having tunnels of other cross-sectional configurations. The elongated pattern of the surface catalyst zone facilitates the achievement of uniform distribution of burning gases across the cross-sectional area of the inlet opening and of the tunnel. The combination of the interior surface catalyst zones and the surface catalyst zones of the main tunnel provides a proper balance of heat distribution, in the area where ignition is started, throughout the stream of the combustible admixturei emitted from the ports 38 without materially disrupting the flow of the burning gases within the tunnel, and `without subdividing the tunnel into separate compartments.

In FIG. 4 is illustrated an alternate embodiment of grid block, designated by the reference numeral 12A, wherein a pair of sub-tunnels or recesses 44A are incorporated. The recesses 44A are shown to be laterally displaced from each other in a vertical direction. Such an arrangement increases the areas of the catalytic surfaces 45 two-fold over that of the grid 12 shown in FIG. 2 and positions more of the discharge ports 38 of the passages 40 in closer adjacent relation with a catalytic surface 45, if the dimensions of the grid 12 and the

passages

40 and 40A are otherwise maintained. Thus the arrangement in FIG. 4 may be described as one which there is increased catalytic grid surface available. v

In FIG. 5 is illustrated an alternate grid block, designated by the reference numeral 12B, in which catalytic lgrid surface is increased by providing two recesses 44B and 44E-1 which may be described as being axially displaced from each other. Also, the lateral vertical dimension of recess 44B is `greater than that of recess 44E-1. In such arrangement the gases emanating from-the most interior passages 40C are subjected to the heat `radiating from the catalytic surfaces 45B as well as that from surfaces 45.

In FIG. 6 is illustrated a further alternate grid block, designated by the reference numeral 12C, in which all the passages 40A terminate at a face S4 of a recess 44C which face 54 is displaced from the front face 42 of grid 12C. The `catalytic surfaces 45 are defined by portions of the grid 12C which are not perforated with passages.

In FIG. 7 is illustrated a still further alternate grid block, designated by the reference numeral 12D, in which the axial displacement of the recesses 44D is progressively increased in descending vertical order, i.e., recess 44D-1 is the least axially displaced from the front face 42 of the grid block 12D and consequently recess 44D-1 has the least axial extent of the recesses 44D. Recess 44D-3 has the most axial extent. An advantage of this arrangement is that each of the catalyst edge zones 45 looks at the bottom wall 18 and receives radiant heat therefrom.

The structure and operation of the yburner may be distinguished from the tunnel burners having dividing walls therein as disclosed in U.S. Patent Nos. 2,489,244 and 3,- 048,217. In these patents, dividing walls are provided to divide the main tunnel portions into individual compartments. In Patent No. 2,489,244, the dividing walls are in alignment with the discharge opening of the tunnel so that the discharge opening is offset in respect to each of the compartments and turbulence of the burning gases is increased. In Patent No. 3,048,217, the dividing walls extend from the grid plate substantially the length of the chamber and serve as vertical partitions to divide the chamber into three separate horizontally spaced chambers.

The present invention is concerned with the initiation of ignition of gases emanating from relatively interior port-s at the earliest possible moment in a manner whereby initial ignition of gases emanating from other ports and stabilization of the flame are enhanced to provide an undivided and uniform flame pattern within the combustion tunnel. Ignition of combustion of the gases discharging from the ports terminating at the recessed portions of the grid plate is initiated at the recessed portions. These burning gases diffuse with and provide ignition points for the other gases. All of the gases are burned and uniformly distributed across the width of the tunnel and across the discharge opening. The surface catalyst zones dened by the recessed portion of the grid plate refractory tend to increase the speed of combustion and to stabilize and hold the flame without materially resisting, particularly in a frictional sense, the flow of the gas-air mixture through the tunnel.

What I claim:

1. Burner apparatus, comprising:

(a) a refractory lined tunnel having a laterally elongated inlet opening and a laterally elongated discharge opening; and

(b) a grid of refractory material positioned across said inlet opening having generally parallel front and rear faces and defining a plurality of passages extending generally axially therethrough,

(c) said grid also having therein a laterally elongated recessed portion of rectangular cross-section in its front face extending transversely substantially across the grid face from one tunnel side wall to the other tunnel side wall,

(d) said recessed portion defining a surface catalyst zone within said grid in an area laterally displaced from the top and bottom walls of said tunnel, and

(e) at least a portion of said passages discharging into said recessed portion.

2. Burner apparatus as defined in claim 1 wherein:

(a) said tunnnel comprises a main refractory zone and a surface catalyst refractory zone,

(b) said surface catalyst Zone of said tunnel being adjacent said grid,

(c) and wherein the refractory of said tunnel catalyst zone is of relatively low density, in the range of 45-70 lbs/cu. ft., and refractory of the main zone is of a density in the range of 71-165 lbs/cu. ft.

3. Burner apparatus as defined in claim 1, wherein:

(a) a first group of said passages have terminal discharge ports at the front face of said grid, and

(b) a second group of said passages have terminal discharge ports at said recessed portion.

4. Burner apparatus as defined in claim 1, wherein:

said grid defines at least two recessed portions which are laterally displaced from each other in a vertical direction.

5. Burner apparatus as defined in claim K1, wherein:

6. Burner apparatus as defined in claim 1, wherein:

said grid defines at least two recessed portions which are displaced from each other in a direction corresponding to the axial extent of said grid.

7. Burner apparatus as defined in claim 1, wherein:

said grid defines interconnected recesses comprising two contiguous portions with one of said portions being of greater late-ral extent than the other of said portions.

8. Burner apparatus, comprising:

(a) a refractory tunnel having a laterally elongated and generally rectangular crosssectional configuration throughout its axial extent;

(b) a plenum chamber adjacent to the inlet of said tunnel; and

(c) a refractory grid positioned across the tunnel separating said plenum chamber from said tunnel having generally parallel front and rear faces and defining a plurality of discharge orifices for emitting a combustible mixture from said plenum chamber to said tunnel,

(d) said discharge orifices being arranged in a pattern generally corresponding to the cross-sectional configuration of said tunnel, and

(e) a laterally elongated and rectangular cross-section portion of said refractory grid being recessed in its front face extending transversely substantially across the grid face from one tunnel side wall to the other tunnel side wall and at least some of said orifices discharging into the recessed portion.

9. Burner apparatus, comprising:

(a) a laterally elongated refractory tunnel of generally rectangular cross-section having an inlet, a main portion, and a discharge opening, said inlet, main portion and discharge opening having a generally rectangular cross-section,

(b) said discharge opening having a cross-sectional area less than the corresponding cross-sectional area of the main portion of said tunnel;

(c) a plenum chamber adjacent said inlet; and

(d) a refractory grid separating said plenum chamber from said main portion positioned across said inlet having generally parallel front and rear faces,

(e) said grid defining a plurality of orifices adapted to discharge a plurality of streams in a direction generally co-axial with the axial extent of said main portion,

(f) said grid also defining a laterally elongated recessed portion of rectangular cross-section on the `ront face thereof extending transversely substantially across the grid face from one tunnel side wall to the other rtunnel side wall, and

(g) at least a portion of said orifices discharging into said recessed portion.

10. Burner apparatus as defined in claim 9, which further comprises a diffuser screen within said plenum chamber to facilitate distribution of gases across the lateral extent of said grid.

11. Burner apparatus as described in claim 9 wherein said grid is of relatively low density refractory in the range of 45-70 lbs./ cu. ft.

12. Burner apparatus as described in claim 9 wherein:

(a) said tunnel comprises a main refractory zone and a surface catalyst refractory zone,

(b) said surface catalyst zone of said tunnel being adjacent said grid,

(c) and wherein the refractory of said tunnel catalyst zone is of relatively low density, in the range of 45-70 lbs./cu. ft., and the refractory of the main zone is of a density in the range of 7l-165 lbs/cu. ft.

(References on following page) 7 8 References Cited 3,002,224 10/1961 Stalego et a1 158--99 X UNITED STATES PATENTS 3,048,217 8/1962 DenlSOIl 158-116 7/ 1919 Lucke 158-99 FOREIGN PATENTS 6/1950 Stadlef- 5 558,007 6/1957 Belgium. 7/1951 I-Ienwood 158-109 X 9/1953 Morck, et a1 158-116 JAMES W. WESTHAVER, Primary Examiner.

Claims

1. BURNER APPARATUS, COMPRISING: (A) A REFRACTORY LINED TUNNEL HAVING A LATERALLY ELONGATED INLET OPENING AND A LATERALLY ELONGATED DISCHARGE OPENING; AND (B) A GRID OF REFRACTORY MATERIAL POSITIONED ACROSS SAID INLET OPENING HAVING GENERALLY PARALLEL FRONT AND REAR FACES AND DEFINING A PLURLITY OF PASSAGES EXTENDING GENERALLY AXIALLY THERETHROUGH, (C) SAID GRID ALSO HAVING THEREIN A LATERALLY ELONGATED RECESSED PORTION OF RECTANGULAR CROSS-SECTION IN ITS FRONT FACE EXTENDING TRANSVERSELY SUBSTANTIALLY ACROSS THE GRID FACE FROM ONE TUNNEL SIDE WALL TO THE OTHER TUNNEL SIDE WALL, (D) SAID RECESSED PORTION DEFINING A SURFACE CATALYST ZONE WITHIN SAID GRID IN AN AREA LATERALLY DISPLACED FROM THE TOP AND BOTTOM WALLS OF SAID TUNNEL, AND (E) AT LEAST A PORTION OF SAID PASSAGES DISCHARGING INTO SAID RECESSED PORTION.