US3905751A

US3905751A - Gas burner

Info

Publication number: US3905751A
Application number: US453346A
Authority: US
Inventors: Klaus H Hemsath; Frank J Vereecke
Original assignee: Midland Ross Corp
Current assignee: Surface Combustion Corp; Grimes Aerospace Co
Priority date: 1974-03-21
Filing date: 1974-03-21
Publication date: 1975-09-16
Anticipated expiration: 1992-09-16
Also published as: CA1034479A; JPS50130031A

Abstract

An industrial gas burner especially suitable for operation with oxygen-enriched combustion air is constructed and arranged to discharge concentric and complementary spinning streams of gas and oxygen-enriched combustion air acting to create a recirculation and intermixing zone spaced outwardly from the burner mouth to provide aerodynamic flame stabilization in space. The burner flame is thus outwardly removed from and out of contact with the burner, thereby avoiding excessive heating of the burner.

Description

nited States Patent 1191 Hemsath et al.

[4 1 Sept. 16, 1975 GAS BURNER [75] lnventors: Klaus H. Hemsath, Sylvania, Ohio; Frank J. Vereecke, Palmyra, Mich.

[73] Assignee: Midland-Ross Corporation,

Cleveland, Ohio 22 Filed: Mar. 21, 1974 21 Appl. No.: 453,346

[52] U.S. Cl. 431/183; 431/9; 431/353 [51] Int. Cl. F23M 9/00 [58] Field of Search 431/9, 182, 183, 184, 185,

[56] References Cited UNITED STATES PATENTS 1,101,925 6/1914 Harris 122/2 2515845 7/1950 Van Den Bussche 431/115 X 2,675,068 4/1954 Gollus et a1 239/552 X 3,612,737 10/1971 Sharan 431/183 3,748,087 7/1973 Shular 431/182 Primary Examiner-Edward G. Favors Attorney, Agent, or Firm-Frank J. Nawalanic [57] ABSTRACT An industrial gas burner especially suitable for opera tion with oxygen-enriched combustion air is constructed and arranged to discharge concentric and complementary spinning streams of gas and oxygenenriched combustion air acting to create a recirculation and intermixing zone spaced outwardly from the burner mouth to provide aerodynamic flame stabilization in space. The burner flame is thus outwardly re moved from and out of contact with the burner, thereby avoiding excessive heating of the burner.

11 Claims, 5 Drawing Figures NATURAL GAS GAS BURNER This invention relates generally to a gas burner and, more particularly, to a gas burner of the industrial type.

The invention is particularly applicable to a burner which uses oxygen-enriched combustion air for high temperature applications and will be described with particular reference thereto. However, as will be appreciated by those skilled in the art, the invention has broader applications and may be used in any industrial burner application including those which do not operate at high temperature or those which do not use oxygen-enriched air.

Generally, burner design considerations require that a gaseous fuel be mixed with a predetermined percentage of oxygen, preferably in stoichiometric relationship, to achieve desired combustion characteristics. Accordingly, it has been known that an increase in the oxygen content of air, which by definition normally includes a somewhat fixed percentage of oxygen, will increase the fuel efficiency of the burner. That is, oxygen-enriched combustion air reduces the mass of air otherwise required for mixing with gaseous fuel to decrease the total volume or mass of the exhaust gases which in turn results in less heat loss in the flue prod ucts. Because of the additional amount of oxygen available and the resulting higher flame temperatures, burners operated with oxygen-enriched combustion air are ideally suitable for high temperature burner applications.

High temperature applications of oxygen-enriched burners, however, have not experienced widespread commercial success because of the inability of the burner construction to withstand such high temperature. More particularly, the burner must propagate the flame in a stable manner and flame stability has heretofore been achieved by originating or directing the flame from some fixed point in the burner construction, be it the burner tube, refractory material, baffles, or otherwise. Because the high temperature flame thus propagated must directly impinge against such burner parts, the parts eventually fail from thermal stress, thermal fatigue or both.

The prior art has recognized this problem and has attempted with varying degrees of success to alleviate same. Thus, exotic materials have been employed in burner constructions at the flame stabilization points therein. Besides the expensive cost of such materials, exotic type materials have generally not been satisfactory because of their unreliability to withstand temperature fluctuations to which they are subjected. To increase reliability of such material, complicated external cooling means such as cooling air or water jacket mechanisms have been employed in the burner design. As a practical matter, such designs are objectionable not only because of their high construction cost but also because of the operating and maintenance problems associated therewith.

In addition to the major problem of thermal stress failure of burner components as noted above, other problems have likewise plagued oxygen-enriched gas burners. One such problem may be defined as objectionably high operating noise levels attributed to the rapid oxidation of the burner gas discharged from the gas nozzle.

It is thus an object of the subject invention to provide a burner arrangement which aerodynamically'stabilizes the burner flame in space to prevent direct flame impingement against any part of the burner apparatus.

It is another object of the subject invention to provide a gas burner for operation with oxygen-enriched combustion air at high temperatures which apparatus is characterized as being comprised of conventional metallic and refractory burner components.

Yet another object of the invention is to provide in a gas burner for operation with oxygen-enriched combustion air, aerodynamic flame stabilization means which inherently direct oxygen-enriched combustion air along the burner components to cool same.

Still another object of the invention is to provide in a gas burner for operation with oxygen-enriched air, a design structure which permits the gas burner to operate at a sound level below or at most approximately equal to that of standard air-gas burners of equivalent capacity,

Still another object of the invention is to provide a gas burner for operation with oxygen-enriched combustion air which is constructed in such a manner so as to be interchangeable with standard air-fuel burners while possessing performance characteristics which are equal to or better than said standard air-fuel burners.

Briefly stated, in accordance with one aspect of the invention, an industrial gas burner suitable for operation with oxygen-enriched combustion air is provided with respective gas and combustion air spin generator means for creating a spinning annulus of combustion air from an annular air supply tunnel or passageway through the refractory burner block and concentrically enveloping a central column of burner gas which is discharged from a co-axial gas supply tube in the passageway into and spinning complementary with the core of the spinning annulus of combustion air. The air supply passageway in the burner block is abruptly widened to a substantial diameter out to its mouth end, from a location slightly downstream from the gas nozzle end, to cause the concentric complementary spinning columns of gas and air to spread laterally outward from the core or burner axis and thus create an underpressure (i.e., a pressure lower than atmosphere, a vacuum) at the core which then acts to draw the spinning gas and air columns back inwardly toward the burner axis to form a recirculation zone out in space, and removed from the burner block walls, where the gas and air columns thoroughly intermix to effect flame propagation thereat. Aerodynamic flame stabilization in space is thereby achieved so that the exceedingly high temperature burner flame, which is characteristic of gas burners operating with oxygen or oxygen-enriched combustion air, is outwardly removed from and out of contact with the refractory burner block and other burner parts, thereby avoiding the overheating and damage of these burner components.

In accordance with a further aspect of the invention, the oxygen-enriched combustion air is disposed axially of the gaseous fuel to effect a cooling of the burner components.

In accordance with yet another aspect of the invention, the aerodynamic propagation of the flame is accurately positioned within a cylindrical chamber in accordance with predetermined geometry considerations to reduce the noise level of the burner to acceptable limits.

The invention may take form in certain parts and arrangement of parts, a preferred embodiment of which will be described in detail herein and illustrated in the accompanying drawings which form a part hereof and wherein:

FIG. 1 is a longitudinal section of a gas burner comprising the invention;

FIG. 2 is a transverse section on the line 2--2 of FIG.

FIG. 3 is a fragmentary longitudinal section, on an enlarged scale, of the nozzle end of the gas burner tube of the gas burner shown in FIG. 1;

FIG. 4 is an end view, on an enlarged scale, of the nozzle end of the gas burner tube; and

FIG. 5 is a schematic longitudinal sectional view of the gas burner comprising the invention showing the flow pattern of the burner gas and combustion air emanating therefrom during the burner operation.

Referring now to the drawings wherein the showings are for purposes of illustrating a preferred embodiment of the invention only and not for the purpose of limiting same, there isshown in FIG. 1 a gas burner 10. Gas burner comprises an elongated burner block or housing 1 1 which may be of approximately square exterior cross section and made of a suitable heatrefractory material such as any of the conventional castable refractory materials commonly employed for the burner blocks of standard air-gas industrial burners and having a use limit of 2800F. or thereabouts. For definitionalpurposes high temperature as referred to herein shall mean temperatures resulting from direct combustion of natural gas and combustion air or oxygen-enriched combustion air having a flame temperature near or greater than the use limit of common refractory material. Furthermore, combustion air shall mean normal air at atmospheric pressure which by definition includes a sufficient, definable percentage of oxygen to support combustion and oxygen-enriched combustion air shall mean combustion air having a greater percentage of oxygen, supplied by external means, than that normally encountered in combustion air, and for purposes of explanation may contain total oxygen by volume of from around 21 to about 45 percent and preferably from 25 to 35 percent.

Burner block 1 l is formed with a tubular combustion air supply tunnel or first chamber 12 of circular cross section and extending longitudinally therethrough. Tunnel 12 is defined by refractory wall section 13 of a few inches in length, e.g., around 6 /2 to 9 /2 inches, extending from the upstream end of the tunnel. Wall section 13 may be either of plain cylindrical form throughout its length, or slightly flared out in the downstream direction as shown, for example, at a taper angle of around 1/z to 4 to the tunnel or burner axis A,,for manufacturing purposes. At its downstream outlet end 14, wall section 13 of tunnel 12 merges into an abrupt outwardly expanding throat or flared chamber section which may be of conical form as shown and flaring out in a downstream direction, e.g., at a flare angle in the range of about 30 to 55 to tunnel axis A, to a substantial diameter D,. relative to the diameter D, of wall section 13 at its outlet end 14. The flared or conical chamber section 15 terminates at its downstream end into a cylindrical chamber section or tunnel extension 16 terminating at the mouth end 17 of burner tunnel l2. Burner block or housing 11 is thus defined by a first chamber 12 contiguous with a second chamber defined by outward-expanding throat section 15 and a cylindrical chamber section 16. For the purposes of the inven tion, the diameter D of tunnel extension 16 should be so proportioned to the diameter D, of outlet end 14 of wall section 13 that the ratio D,./D, preferably lies within the approximate range of 1.8 to 2.1.

Burner block 11 is received and supported within a metallic holder 18 comprised of a backplate 19 with axially extending housing flanges 20 within which the burner block is received and mounted. Backplate 19 extends radially beyond housing flanges 20 and is provided with a central circular air passage opening 21 therein coaxially aligned with and of the same diameter as the adjacent circular upstream end of tubular wall section 13 of air passageway or tunnel 12. Backplate 19 is also formed with a plurality of outlying, circumferentially spaced threaded studs (not shown) which provide means for securing the burner to a furnace wall (not shown). Burner block 11 is securely held in place within holder 18 as by cement, for instance.

A metallic housing or burner casting 25 of circular cross section is secured to burner block 11 for supplying oxygen-enriched combustion air to air supply tunnel 12 of burner 10. Burner casting 25 is mounted to a mounting plate 19a by means of a group of fastening assemblies 26 extending from the back side of backplate 19 which clamp an annular flange 27 of the housing to mounting plate 19a and backplate 19, with suitable gasket means 28, 28a interposed therebetween. Housing 25 is provided with a radial air inlet 29 into the .opening 30 of which is connected an air supply pipe (not shown) through which oxygen-enriched combustion air is supplied to the housing under slight pressure from a known air supply source shown schematically and identified herein as 30a.

Extending into housing 25 through its back end wall 31 in a substantially air-tight. manner, as by being screw-threaded thereinto, is a gas supply tube or nozzle 32 suitably formed of stainless steel pipe and constituting the gas nozzle of burner 10. Gas nozzle tube 32 extends axially through cylindrical housing 25 and the axial opening 33 in its front end, and precisely axially into and through wall section 13 of air supply tunnel 12 in burner block 11 so as to form, in conjunction with the circular cross-section wall of wall section 13, an annular combustion air supply chamber 34 through the throat section of the burner block. To this end, the outer wall surface of gas nozzle tube 32 is of straight, i.e., continuous cylindrical form throughout its length, in the manner characteristic of conventional stainless steel or other like pipe. The axial centering of gas nozzle tube 32 in wall section 13 of combustion air tunnel 12 is one of the critical tolerance dimensions to proper operation of burner 10 in the manner according to the invention. Too great a misalignment of gas nozzle tube 32 in wall section 13 will cause burner flame attachment to thewall of burner block tunnel 12, or throat section 15 or cylindrical chamber section 16 resulting in severe hot spots thereon during burner operation. With the high flame temperature which is characteristic of gas burners operating with oxygen-enriched com bustion air, such flame contact against the walls of first 12 or

second chambers

15, 16 of burner block 11 would soon result in the destruction of most refractories employed for burner block 11.

Externally of housing 25, gas nozzle tube 32 is connected to a known suitable gas supply source shown schematically at 32a. Gas supply 32a could be natural gas or other conventional type burner gas at a relatively low pressure in the range of around 17 to 27 inches w.c, (water column), depending on the. design capacity of burner and on the oxygen concentration of the combustion air. Thus, for burners 10 having respective rated capacities of approximately 0.5, 1.0, 2.0 and 4.0 MM (million) Btu per hour. andoperating with combustion air having approximately .35 percent total oxygen content by volume, the pressure of the gas neces} sary to operate the burner at rated capacity is about 17 inches w.c. above atmospheric pressure. Operation of such burners 10 above rated capacity with higher oxygen content combustionair requires higher gas pressures Thus, operation of burners 10 with 45 percent total .oxygen contentcombustion air requiresa gas pressure of about 27 inches w.c,. over atmospheric pressure. Also, in the case of burners 10- having the above indicated approximate rated capacities of 0.5, 1.0, 2.0 and 4.0'MM Btu per hour, gas nozzletube 32 thereof may have respective pipe sizes of around 3%, A, 1 and Gas nozzle tube 32 extends into and through burner tunnel 12 nearly the full length of wall section 13 thereof but withits inner or nozzle end 35 setback or upstream from outlet'or downstream end 14 of wall section 13 a'predetermined slight distance L, (FIG. 1). The location of nozzle end 35 iscritical for the proper operation of burner 10 in the intended manner according to the invention inasmuch'as it greatly influences two very important initial design parameters. First is the proper mixing of the gas'fuel from gasnoz zl'e 32 with oxygen-enriched combustion air or oxidant from annular air supply passageway 34. That is, within relatively wide limits, if the nozzle end is placed too close to tunnel flare section 15, poor intermixing of the gas fuel with the oxidant results and if the nozzle end is placed too far upstream from outlet end 14 of wall sec tion 13 of burner tunnel 12 the oxidation or mixing rate of the fuel with the air is dangerously accelerated. This mixing effect, balanced against the second design parameter of burner sound or operating noise level (which is more critical), thus determines the proper location of gas nozzle end 35 for the purposes ofthe invention. The sound level design parameterfor burner 10 according to the invention is that it possess a'sound level no greater than and preferably below that of a standard air-gas burner of equal capacity. However, the attainment of this objectis particularly difficult in view of the well known fact that rapid. oxidation of the gas fuel with the oxygen-enriched combustion air producesv high operating noise levels Neverthele ss we haye determined that, for burners 10 of approximately 0.5, 1.0,

2.0 and 4.0 MM Btu per hour rated capa eity both of the above mentioned design parameters for. the burner are satisfied when nozzle end 35 of gas no qle tu ble 32 is set back distances L from outlet end 14 of wall sec tion 13 of approximately 1% inches for the 4.0 MM Btu per hourbumer 10 and approximately A inch for the other three rated capacity burners 10.

I a necessary condition to the operation of burner 10 the manner according to the invention, both the burner'gas forced through gas nozzle tube 32 and the oxygenated combustion air. forced through annular air supply passageway 34 are discharged therefrom in eomplementary spinning or swirling flow paths for the purpose of inducing a recirculation flow pattern of these gas and air streams at a region out in space, i.e., outwardly removed from the end of gas tube 32 (see FIG. 5). To this end, respective spin generator means such as known spin vanes may be employed for imparting the desired spinning motion to the gas and to the combustion air discharged into burner tunnel 12. In the preferred embodiment illustrated, the spinning motion of the burner gas discharged from noule end 35 of gas nozzle tube 32 may be suitably imparted thereto by a tube closure member in the form of an ordinary commercial metallic helical gear 36 (FIGS. 3 and 4) fitting tightly, axially within nozzle end 35 of gas nozzle tube 32 and fixedly secured therein as by welding, for example, The spaced helical teeth 37 of gear 36 form, in conjunction with the encasing cylindrical inner wall 38 of gas nozzle tube 32, a plurality of helical gas discharge or outlet passageways 39 (i.e., an annulus when viewed from the end) in gas nozzle tube end 35 corresponding in number to the number of gear teeth 37 on the gear. Thus, the burner gas forced under pressure through gas nozzle tube 32 isseparated, by the several helical gas passageways 39, into a corresponding number of individual high velocity gas streams which are discharged from nozzle end 35 in a helical path concentrically disposed about axis A of burner 10 and gas nozzle 32, as indicated by the arrows in FIG. 5.

The particular form of helical gear 36 employed for the gas spin generator means is selected first to have enough passages 39 as determined by gear teeth 37 to impart an effective spin motion to the gas. In this respect, two passages would not develop an efficient spin which would recirculate the gas in an effective pattern, four passages would probably be marginal and the preferred embodiment utilizes eight passages. After the number of passages have been determined, the area of same is determined by their total cross section which would produce the required pressure drop in gas spin gear 36 necessary to attain the rated burner capacity with the desired low operating gas'pressure of, for example, 17 inches w.c. above atmosphere. In the event thatt he passageway area is insufficient to develop this predetermined pressure drop, it has been found that an axial hole 41 through the center of the gear may be provided without adversely disturbing the circulatory mixing pattern developed by the spin generating means. Obviously there is an upper limit to the diameter of hole 41 which, if exceeded, would adversely affect burner operation and it is believed that this limit would be approximately 25-30 percent of the flow area through passageways 39. In the case of a burner 10 of a rated capacity of 1 MM Btu per hour and having the specific sizes mentioned hereinabove for gas nozzle tube 32 and wall section 13, a conventional helical gear 36 having eight helical gear teeth 37 will provide the required cross-sectional open area or helical gas passageway areas 39 therethrough necessary to enable the operation of burner 10 with the above mentioned relatively low gas operating pressure of around 17 inches w.c. above atmosphere. However, with burners 10 of 0.5, 2.0 and 4.0 MM Btu per hour rated capacity and having the specific sizes mentioned hereinabove for gas nozzle tube 32 and wall section 13, operation thereof with a gas pressure of around 17 inches w.c. requires the addition to such an eight-tooth helical gas spin gear 36 of a supplementary axial gas port or bore opening 41 therethrough having diameters, respectively, of around 0.154, 0.288, and 0.375 inch. 8

The spinning motion of the oxygenated burner combustion air passing through burner tunnel 12, in a spin direction complementary to that of the burner gas discharged from gas nozzle end 35, may be imparted thereto by spin generator means 42 located within burner housing 25 and comprising a group (four in the particular case illustrated) of spin vane members 43, as shown in FIGS. 1 and 2. Spin vanes 43 are disposed in a circular pattern concentrically about gas nozzle tube 32, and in correspondingly oriented and uniformly spaced apart position therearound, at the entrance of upstream end of burner tunnel 12. Spin vanes 43 are clamped, as by means of fastening bolts 44, flatwise to and between the back face of a mounting plate 19a adjacent backplate 19 (and sealed by rope gasket 28a) and a flat annular collar 45 fitted over gas nozzle tube 32 and suitably secured thereto, as by an annular weld therearound, to form an air-tight seal therewith. Thus, spin vanes 43 block off the annular space around gas nozzle tube 32 and being located between backplate 19 and collar 45 except for the spaces between'adjacent ones of spin vanes 43 thereby form air inlet slots or passageways 46 leading from the combustion air chamber 47 of burner housing 25 into backplate opening 21 and inlet end of air supply tunnel 12.

As shown in FIG. 2, each spin vane 43 is formed with an extended length flat inner side edge 48 and a shorter flat end or heel edge 49 extending generally perpendicular to one another. The group of spin vanes 43 are secured in place on mounting plate 19a with their flat side edges 48 extending approximately tangential to, and defining an imaginary square circumscribed by an imaginary circle concentric with gas nozzle tube 32 and corresponding in diameter to circular opening 21 in backplate 19 and to the circular inlet end of burner tunnel 12. In their mounted position on backplate l9, spin vanes 43 are further located with their flat heel edges 49 positioned opposite but spaced from and extending parallel to flat side edges 48 of the next adjacent spin vane 43. The spaced opposing side and end

edges

48, 49 of adjacent ones of spin vanes 43 thus form, in conjunction with the flat sides of mounting plate 19a and collar 45, the afore-mentioned combustion air slots or passageways 46 extending tangentially of the annular inlet end of the annular combustion air supply passageway 34 which extends through burner block 11 around gas nozzle tube 32 therein. In the case of burners 10 having respective rated capacities of approximately 0.5, 1.0, 2.0 and 4.0 MM Btu per hour, spin vanes 43 are formed with respective thicknesses T (FIG. 1) of approximately /2, /4, 1-1/16 and 1 /2 inches. Also, the width W, (FIG. 2) of combustion air slots 46 of such burners 10 is preferably so proportioned relative to the width W of the annular combustion air passageway formed by the circular outside wall of gas nozzle tube 32 and the rim of concentric circular air passage opening 21 in backplate 19 as to produce a ratio wu/ p in the range of approximately 1.2 to 1.7. The

length L of combustion air slots 46'also is preferably so proportioned relative to their width W, as to maintain the ratio L,,/W,, in the range of approximately 1.8 to 3.

In the operation of burner 10, the oxygenated combustion air in air supply chamber 47 of burner housing 25 is forced, by the pressure thereof, out of chamber 47 through air slots 46 of combustion air spin generator means 42 which slots, because of their extending tangentially to air passageway 34, then discharge the air into passageway 34 in the form of individual gas streams directed tangentially of such passageway, thereby imparting a spinning movement or flow of the combustion air thereinto and therethrough, as indicated by the arrows 50 in FIG. 5. The direction in which air slots 46 extend tangentially to annular air passageway 34 is the same, e.g., clockwise in the particular case shown in FIG. 2 and as viewed from its inlet end, as the downstream direction in which helical gas passageways 39 in gas spin generator gear 36 extend about burner axis A, in order to thereby spin the combustion air discharged into passageway 34 in the same, i.e., complementary, direction as that in which the gas stream from gas nozzle 32 is spun by gas spin generator gear 36.

In place of fabricating the combustion air spin generator means or assembly42 from a number of separate. parts, i.e., the several spin vanes 43, collar 45, fastening bolts 44 and plate 19a, the spin generator may be formed instead as a unitary structure with either burner housing 25 or backplate 19, as by being cast integral with one or the other of these members, for example.

In this way, simplification of the burner design and saving in burner manufacturing cost can be realized.

In order to provide ignition means for the combustible mixture formed by the mixing of the gas and the oxygenated combustion air from gas nozzle 32 and annular air passageway 34, burner block 11 and backplate 19 are provided with an angular opening 51 'therethrough which opens into flare section 15 0f burner tunnel 12 and receives the usual sparkplug (not shown) whose electrodes extend up to the mouth end of flare section 15. Additionally, a sight glass (not shown) may be provided on backplate 19 to provide visual examination of the burner flame, for supervision purposes, through a similar angular opening (not shown) extending through backplate l9 and burner block 11.

' As noted above and referred to throughout the specification, the operation of burner 10 of the present invention will be such that the oxygen-enriched combustion air will mix with the gaseous fuel in a recirculating manner as shown within a zone designated as F in FIG. 5 wherein a burner flame will be propagated. More particularly and as will be explained, recirculation zone F, herein defined as a flame stabilization zone, may be accurately positioned at any desired distance within the burner block and the flame developed thereby will occur out in space and be so directed so as not to impinge against any of the burner components while constantly recirculating a portion of the fuel-air mixture to insure stabilization. That this flame stabilization zone F will occur and can be regulated in the manner indicated will be explained first with reference to the burner block geometry and then with reference to the effect of the spin generating means on the burner construction.

Neglecting for the moment the spin generating means and viewing burner 10 from the right as shown in FIG.

5, it should be clear that at the intersection of wall section 13 with first annular chamber 12 there is a volume of air defined as an annulus which is axially moving by virtue of air supply means 30a. Similarly, at the outlet end of the tube 32 there is an annulus volume of gaseous fuel defined by passageways 39, which gaseous fuel is axially moving by virtue of gas supply means 32a. As the air and gaseous fuel move axially towards the right as viewed in FIG. and flow through throat section 15 and cylindrical chamber section 16, they will rapidly expand in a radially outward direction and entrain themselves within one another. The rate of radial expansion of the gaseous fuel and air is a function of their pressures from their respective supply sources, the cross-sectional flow areas involved hereinbefore expressed as D,/D,. and D,,/D,. and the radial component of the swirl angle as explained in detail hereinafter. The outwardly expanding throat section 15 is not critical to this radial expansion and its purpose is only to assure 'a smooth transition from a small area to a relatively large area. The entrainment or aspiration of the air and fuel will occur at the boundary line of the two mixtures. That is, the gas at the outer periphery of the fuel will mix at the inner periphery of the air annulus until a preferred mixture occurs (i.e., at or near stoichiometric) and combustion takes place. It should be clear that this entrainment will occur equally as well if the gaseous fuel surrounded the air instead of vice versa as shown. However, when the annulus of air surrounds the annulus of fuel, the outer periphery of air is available to cool the refractory material of the burner block, gas tube 32 and nozzle end 35, especially so when it is realized that the combustion will propagate radially outwardly as the boundary layer interactions increase. If the burner of the present invention were designed in this manner without anything more, the flame propagation would not be stable because of inefficient recirculation. It should also be noted that as the gases rapidly expand radially outward into second cylindrical chamber section 16, an underpressure or vacuum is created at the center of chamber 16 due to the outward suction of the gases. Thus there will be some backward recirculation motion imparted thereto. It has been found that this backward recirculating motion will not be sufficient to establish the aerodynamic stabilized flame of the subject invention.

With the problem thus defined, it has been particularly determined by the present invention that imparting a spin characteristic to either the air or the gaseous fuel will result in a utilization of the vacuum created by the radial expansion of the gases to cause a sufficient portion of said gases to recirculate and establish a stabilized flame in the recirculation zone F shown. That is, spinning either the air or the gass in a helix (as shown) or spiral or sinusoidal shape, at a predetermined angle imparts a tangential velocity component to the gas thus spun which in turn causes sufficient recirculation of that gas and importantly the portions of the other gas mixed therewith into the circular type recirculation path shown at zone F. The dimension of the recirculation path is believed to be a function of the angle of the tangential velocity of the spun gas in combination with the burner block design and fluid pressure. Furthermore, tests have indicated that the recirculation path defined at zone F will occur if only one of the gases is spun but that control or stabilization of the recirculation is more effective if both of the gases are spun. Con

trol will thus be improved if the gases are spun either complementary to one another as illustrated or countercurrent to one another. If the gases are spun countercurrent, there will be a more thorough mixing be tween the air and the gaseous fuel although eddy currents established at the boundaries between the air and the gas will not impart as good a stabilized flame as when the gas and air are spun complementary to one another. For this reason the gases are shown spinning complementary with one another in the embodiment illustrated. In particular, it has been determined that when oxygen-enriched combustion air and gaseous fuel are spun complementary to one another as described in detail above, an extremely stable flame is aerodynamically propagated in zone F and controlled to such limits whereby the flame thus propagated does not impinge against any part of burner 10.

Furthermore, in accordance with another feature of the invention, the noise formed by the combustion process in the present burner can be adequately controlled by positioning the flame stabilization zone Fin about the middle of second annular chamber 16. This positioning can be controlled by axially displacing the outward end 35 of gas tube 32 away from the intersection or line of demarcation between first annular chamber 12 and throat section 15 of the second chamber. Importantly, it should be noted that this displacement of gas tube 32 defined as L is nonlinear with respect to the other dimensions of the burner arrangement. All other dimensions giving rise to the ranges set forth above are believed to be linear. That is, given the capacity of the burner to establish the fuel and oxygenenriched combustion air volumes to be supplied to burner 10 and the pressures at which the air and fuel are to be supplied, the remaining dimensions of the ap paratus such as passageways 39, the air spin means, the relationships between the D,, D,, and D,. are all linear. Furthermore, the helix angle or tangential component of spin is believed to be associated with the diameter dimension D of cylindrical chamber section 16.

The invention has thus been described with reference to a preferred embodiment. It is apparent that modifications and alterations will occur to others upon a reading and understanding of the specification. It is our intention to include all such modifications and alterations insofar as they come within the scope of the present invention.

It is thus the essence of the invention to provide in a burner an orificing arrangement in combination with a mechanism for spinning at least one of the gaseous fluids supplied thereto to impart a tangential component to such gaseous fluid whereby the vacuum created by the orifice arrangement is efficiently utilized to aerodynamically propagate, in space, a stable flame.

Having thus described the invention, we claim:

1. A gas burner for operation with a mixture of natural gas and oxygen-enriched combustion air, said burner comprising:

a burner block of heat refractory material having an axial tunnel of circular cross section extending therethrough and comprised of a throat section terminating at its downstream end in an abruptly widening flare chamber section flaring out to a diameter appreciably greater than that of said throat section;

a gas nozzle tube of cylindrical outer contour extending axially through said tunnel from the inlet end thereof and in spaced relation to the wall thereof to form therebetween an annular combustion air passageway through the said throat section of the tunnel;

said gas nozzle tube having a nozzle end set back a slight distance upstream from the downstream end of said throat section;

means for supplying gas fuel under a slight positive pressure to the inlet end of said gas nozzle tube;

means for supplying oxygen-enriched combustion air under a slight positive pressure to the inlet end of said annular air passageway;

respective gas and combustion air spin generator means respectively associated with said gas nozzle tube and with said annular combustion air passageway for imparting spinning motion in complementary directions about the tunnel axis to the gas column discharged endwise from said gas nozzle and to the combustion air discharged endwise from said annular air passageway and enveloping the spinning gas column whereby to cause said gas and air columns to spread laterally outward from the tunnel axis on passage through the said flare chamber section of said tunnel and subsequently to be drawn back inwardly toward the tunnel axis to thereby create a gas and air recirculation and flame stabilization zone located entirely out in space and outwardly removed from the walls of said burner .block; and I the ratio of the diameter of the downstream end of said tunnel throat section to the outside diameter of said gas nozzle tube is within the approximate range of 1.9 to 2.2. ,2. A gas burner for operation with a mixture of natural gas and oxygen-enriched combustion air, said burner comprising:

a burner block of heat refractory material having an axial tunnel of circular cross section extending therethrough and comprised of a throat section terminating at its downstream end in an abruptly wid- .ening flare chamber section flaring out to a diameter appreciably greater than that of said throat section;

respective gas and combustion air spin generator means respectively associated with said gas nozzle tube and with said annular combustion air passageway for imparting spinning motion in complementary directions about the tunnel axis to the gas column discharged endwise from said gas nozzle and to the combustion air discharged endwise from said annular air passageway and enveloping the spinning gas column whereby to cause said gas and air columns to spread laterally outward from the tunnel axis on passage through the said flare chamber section of said tunnel and subsequently to be drawn back inwardly toward the tunnel axis to thereby create a gas and air recirculation and flame stabilization zone located entirely out in space and outwardly removed from the walls of said burner block; and

the nozzle end of said gas nozzle tube is set back upstream from the downstream end of said tunnel throat section a distance of at least approximately A inch.

3. A gas burner as specified in claim 2 wherein the ratio of the diameter of the downstream end of said tunnel throat section to the outside diameter of said gas nozzle tube is within the range of approximately 1.9to 2.2.

4. A gas burner as specified in claim 3 wherein the ratio of the diameter of the downstream end of the said flare chamber sectionof said tunnel to the diameter of the downstream end of the said throat section of said tunnel is within the range of approximately 1.8 to 2.1.

5. A gas burner as specified in claim 1 wherein the ratio of the diameter of the downstream end of the said flare chamber section of said tunnel to the diameter of the downstream end of the said throat section of said tunnel is within the range of approximately 1.8 to 2.1.

6. A gas burner for burning a mixture of natural gas with oxygen-enriched air, said burner comprising:

a burner block of heat refractory material having an axial tunnel of circular cross section extending therethrough and comprised of a generally cylindrical throat section terminating at its downstream end in an abruptly widening flare chamber section flaring out to a diameter appreciably greater than that of said throat section; holder supporting said burner block at its rearard end and including a backplate having a circular air supply opening therethrough coaxial with and approximately corresponding in diameter to the inlet end of said tunnel; combustion air supply housing mounted on said backplate for supplying a mixutre of oxygen and atmospheric air under slight positive pressure to the inlet end of said tunnel;

gas nozzle tube of cylindrical outer contour mounted on said housing and extending therethrough and axially into said tunnel from the inlet end thereof and in spaced relation to the wall therreof to form an annular combustion air supply passageway in said tunnel; said gas nozzle tube being connected to a source of burner gas under slight positive pressure and having its nozzle end set back a slight distance upstream from the downstream end of said throat secti0n,.g as spin generator means located within said gas nozzle tube at its nozzle end for imparting to the gas stream discharged therefrom a spinning motion concentrically about the said tunnel axis; and

combustion air spin generator means mounted in said housing for discharging the pressurized combustion air therein tangentially into the said annular combustion air passageway to impart thereto a spinning motion complementary in direction to that of said burner gas discharged from said gas nozzle end,

said combustion air generator means including a collar mounted on said gas nozzle tube with an airtight connection therearound and spaced rearwardly from said backplate, and a plurality of spin vanes clamped tightly between said backplate and said collar and positioned around said gas nozzle tube in spaced apart relation to define a plurality of combustion air outlet passageways extending tangentially to said annular combustion air supply passageway whereby to discharge the combustion air from said housing tangentially into said annular passageway to impart spinning motion to the combustion air entering and passing through said passageway.

7. A burner for operation with a mixture of gaseous fuel and combustion air comprising:

a housing, said housing having a generally cylindrical passage with an open inlet and open outlet end, and an abruptly flaring wall surface adjacent said passage outlet end, said flaring surface opening out into space;

a gas tube within said passage having an open outlet end generally adjacent said passage outlet end and concentric therewith;

gas supply means associated with said tube for supplying a source of axially moving gaseous fuel to said tube at a predetermined pressure;

air supply means for supplying a source of axially moving combustion air to said passage at a predetermined pressure;

air spin means associated with said air means and operable to form said combustion air injected into said passage into a plurality of swirling annular streams having a predetermined tangential velocity component;

gas spin means associated with said gas supply means and operable to form said gaseous fuel into a plurality of swirling annular gas streams at the outlet end of said tube, said streams having a predetermined tangential velocity component;

said air spin means and said gas spin means interacting with one another when said air and gas streams are injected into space to establish stable recirculation and mixing of air and gas streams in a flame stabilization zone to produce combustion located out in space and out of contact with said burner housing; and

ignition means including an open passage in said flaring surface for igniting a portion of said gaseous fuel as said air and fuel exit said passage and said tube.

8. The burner of claim 7 wherein said tangential velocity components of said gas and air spin means are complementary with one another.

9. The burner of claim .8 further including muffle 10. The burner of claim 9 wherein said burner further includes means for positioning said outlet end of said tube relative to said outlet end of said passage for positioning said stabilization zone within said cylindrical chamber.

11. A burner for operation with a mixture of gaseous fuel and combustion air comprising:

a housing, said housing having a generally cylindrical passage with an open outlet end, and an abruptly flaring wall surface adjacent said passage outlet end, said flaring surface opening out into space;

a gas tube within said passage having an open outlet end generally adjacent said pasage outlet end and concentric therewith;

said air spin means and said gas spin means interacting with one another when said air and gas streams are injected into space to establish stable recircula' tion and mixing of air and gas streams in a flame stabilization zone to produce combustion located out in space and out of contact with said burner housing;

ignition means including an open passage in said flaring surface for igniting a portion of said gaseous fuel as said air and fuel exit, said passage and said tube; and

said gas means includes ahelical gear inserted at said outlet end of said gas tube, said gear optionally including an axially extendingopening therethrough.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION PATENT NO. 3, 905, 751 DATED September 16, 1975 INVENTOR(S) Klaus I-l Hemsath, Frank J. Vereecke It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 9, line 54, change "gass" to gas Column 12, line 42., change "mixutre" to mixture Column 14, line 17, after "open insert inlet and open Signed and Scaled this twentieth D y f January 1976 [SEAL] Arrest:

RUTH C. MASON Attesring Officer C. MARSHALL DANN Commissioner of Pa rents and Trademarks

Claims

1. A gas burner for operation with a mixture of natural gas and oxygen-enriched combustion air, said burner comprising: a burner block of heat refractory material having an axial tunnel of circular cross section extending therethrough and comprised of a throat section terminating at its downstream end in an abruptly widening flare chamber section flaring out to a diameter appreciably greater than that of said throat section; a gas nozzle tube of cylindrical outer contour extending axially through said tunnel from the inlet end thereof and in spaced relation to the wall thereof to form therebetween an annular combustion air passageway through the said throat section of the tunnel; said gas nozzle tube having a nozzle end set back a slight distance upstream from the downstream end of said throat section; means for supplying gas fuel under a slight positive pressure to the inlet end of said gas nozzle tube; means for supplying oxygen-enriched combustion air under a slight positive pressure to the inlet end of said annular air passageway; respective gas and combustion air spin generator means respectively associated with said gas nozzle tube and with said annular combustion air passageway for imparting spinning motion in complementary directions about the tunnel axis to the gas column discharged endwise from said gas nozzle and to the combustion air discharged endwise from said annular air passageway and enveloping the spinning gas column whereby to cause said gas and air columns to spread laterally outward from the tunnel axis on passage through the said flare chamber section of said tunnel and subsequently to be drawn back inwardly toward the tunnel axis to thereby create a gas and air recirculation and flame stabilization zone located entirely out in space and outwardly removed from the walls of said burner block; and the ratio of the diameter of the downstream end of said tunnel throat section to the outside diameter of said gas nozzle tube is within the approximate range of 1.9 to 2.2.

2. A gas burner for operation with a mixture of natural gas and oxygen-enriched combustion air, said burner comprising: a burner block of heat refractory material having an axial tunnel of circular cross section extending therethrough and comprised of a throat section terminating at its downstream end in an abruptly widening flare chamber section flaring out to a diameter appreciably greater than that of said throat section; a gas nozzle tube of cylindrical outer contour extending axially through said tunnel from the inlet end thereof and in spaced relation to the wall thereof to form therebetween an annular combustion air passageway through the said throat section of the tunnel; said gas nozzle tube having a nozzle end set back a slight distance upstream from the downstream end of said throat section; means for supplying gas fuel under a slight positive pressure to the inlet end of said gas nozzle tube; means for supplying oxygen-enriched combustion air under a slight positive pressure to the inlet end of said annular air passageway; respective gas and combustion air spin generator means respectively associated with said gas nozzle tube and with said annular combustion air passageway for imparting spinning motion in complementary directions about the tunnel axis to the gas column discharged endwise from said gas nozzle and to the combustion air discharged endwise from said annular air passageway and enveloping the spinning gas column whereby to cause said gas and air columns to spread laterally outward from the tunnel axis on passage through the said flare chamber section of said tunnel and subsequently to be drawn back inwardly toward the tunnel axis to thereby create a gas and air recirculation and flame stabiLization zone located entirely out in space and outwardly removed from the walls of said burner block; and the nozzle end of said gas nozzle tube is set back upstream from the downstream end of said tunnel throat section a distance of at least approximately 1/4 inch.

4. A gas burner as specified in claim 3 wherein the ratio of the diameter of the downstream end of the said flare chamber section of said tunnel to the diameter of the downstream end of the said throat section of said tunnel is within the range of approximately 1.8 to 2.1.

6. A gas burner for burning a mixture of natural gas with oxygen-enriched air, said burner comprising: a burner block of heat refractory material having an axial tunnel of circular cross section extending therethrough and comprised of a generally cylindrical throat section terminating at its downstream end in an abruptly widening flare chamber section flaring out to a diameter appreciably greater than that of said throat section; a holder supporting said burner block at its rearard end and including a backplate having a circular air supply opening therethrough coaxial with and approximately corresponding in diameter to the inlet end of said tunnel; a combustion air supply housing mounted on said backplate for supplying a mixutre of oxygen and atmospheric air under slight positive pressure to the inlet end of said tunnel; a gas nozzle tube of cylindrical outer contour mounted on said housing and extending therethrough and axially into said tunnel from the inlet end thereof and in spaced relation to the wall therreof to form an annular combustion air supply passageway in said tunnel; said gas nozzle tube being connected to a source of burner gas under slight positive pressure and having its nozzle end set back a slight distance upstream from the downstream end of said throat section, gas spin generator means located within said gas nozzle tube at its nozzle end for imparting to the gas stream discharged therefrom a spinning motion concentrically about the said tunnel axis; and combustion air spin generator means mounted in said housing for discharging the pressurized combustion air therein tangentially into the said annular combustion air passageway to impart thereto a spinning motion complementary in direction to that of said burner gas discharged from said gas nozzle end, said combustion air generator means including a collar mounted on said gas nozzle tube with an air-tight connection therearound and spaced rearwardly from said backplate, and a plurality of spin vanes clamped tightly between said backplate and said collar and positioned around said gas nozzle tube in spaced apart relation to define a plurality of combustion air outlet passageways extending tangentially to said annular combustion air supply passageway whereby to discharge the combustion air from said housing tangentially into said annular passageway to impart spinning motion to the combustion air entering and passing through said passageway.

7. A burner for operation with a mixture of gaseous fuel and combustion air comprising: a housing, said housing having a generally cylindrical passage with an open inlet and open outlet end, and an abruptly flaring wall surface adjacent said passage outlet end, said flaring surface opening out into space; a gas tube within said passage having an open outlet end generally adjacent said passage outlet end and concentric therewith; gas supply means associated with said tube for supplying a source of axially moving gaseous fuel to said tube at a predetermined pressure; air supply means for supplying a source of axially moving combustion air to said passage at a predetermined pressure; air spin means associated with said air means and operable to form said combustion air injected into said passage into a plurality of swirling annular streams having a predetermined tangential velocity component; gas spin means associated with said gas supply means and operable to form said gaseous fuel into a plurality of swirling annular gas streams at the outlet end of said tube, said streams having a predetermined tangential velocity component; said air spin means and said gas spin means interacting with one another when said air and gas streams are injected into space to establish stable recirculation and mixing of air and gas streams in a flame stabilization zone to produce combustion located out in space and out of contact with said burner housing; and ignition means including an open passage in said flaring surface for igniting a portion of said gaseous fuel as said air and fuel exit said passage and said tube.

9. The burner of claim 8 further including muffle means for reducing the noise emitted and controlling the shape of the flame generated in said stabilization zone, said muffling means including said housing further having a generally cylindrical chamber adjacent and concentric with said flaring wall surface, said cylindrical chamber of sufficient length to surround at least a portion of said stabilization zone and appreciably greater in diameter than the outlet of said passage.

10. The burner of claim 9 wherein said burner further includes means for positioning said outlet end of said tube relative to said outlet end of said passage for positioning said stabilization zone within said cylindrical chamber.

11. A burner for operation with a mixture of gaseous fuel and combustion air comprising: a housing, said housing having a generally cylindrical passage with an open outlet end, and an abruptly flaring wall surface adjacent said passage outlet end, said flaring surface opening out into space; a gas tube within said passage having an open outlet end generally adjacent said pasage outlet end and concentric therewith; gas supply means associated with said tube for supplying a source of axially moving gaseous fuel to said tube at a predetermined pressure; air supply means for supplying a source of axially moving combustion air to said passage at a predetermined pressure; air spin means associated with said air means and operable to form said combustion air injected into said passage into a plurality of swirling annular streams having a predetermined tangential velocity component; gas spin means associated with said gas supply means and operable to form said gaseous fuel into a plurality of swirling annular gas streams at the outlet end of said tube, said streams having a predetermined tangential velocity component; said air spin means and said gas spin means interacting with one another when said air and gas streams are injected into space to establish stable recirculation and mixing of air and gas streams in a flame stabilization zone to produce combustion located out in space and out of contact with said burner housing; ignition means including an open passage in said flaring surface for igniting a portion of said gaseous fuel as said air and fuel exit said passage and said tube; and said gas means includes a helical gear inserted at said outlet end of said gas tube, said gear optionally including an axially extending opening therethrough.