CA1269919A - Method of lengthening the flame from a gas burner - Google Patents

Abstract

ABSTRACT
A ribbon gas burner for use in a baking oven has a row of gas apertures disposed between two rows of air apertures through which air is forced under pressure. The streams of air issuing from the two rows of air apertures are inclined inwardly towards the gas stream, thereby lengthening the ribbon flame produced by the burner and improving the uniformity of heating within the band oven.

Description

12~j9~ ~

METHOD OF LENGTHENING THE FLAME FROM A GAS BURNER

Field of the Invention This invention relates to a method of lengthening the flame from a gas burner, particularly in a baking oven, and is a divisional of Canadian application Serial No.
506,928, filed April 17, 1986.

Background o~ the Invention In high-volume productlon of baked goods, for example cookies, crackers, bread, rolls etc., baking of the goods is conventionally effected using a band oven.
Such a band oven comprises an insulated housing enclosing a baklng chamber of considerable length;
chambers ln commercial ovens are typically around 300 feet (approximately 90 meters~ long. A belt conveyor formed Or a heat-reslstant material, ty`pically steel mesh, extends longltudinally through the baking chamber and extends beyond both ends oP the baklng chamber.
Goods to be baked are placed on the inlet end of the belt conveyor, which moves continuously and thus carries a continuous stream of goods through the baking chamber.
The speed of the conveyor is regulated so that the goods be'ng baked remain wlthln the baking chamber for the proper baklng tlme, and the baked goods are continuously ~4 1269~

discharged from the outlet end of the conveyor.
Heating of the baking chamber is conventionally effected by means of elongate gas burners which extend transversely across the conveyor at spaced intervals, each of these gas burners being provided with a row of apertureq through which gas isques to form either a large number of ind~vidual ~lame~ lylng cloqe to one another, or a single continuous ribbon-llke flame extending the full length of the row of apertures.
Either form oP flame will hereinafter be referred to as a "ribbon flame". To render supervlsion and maintenance of tne band oven as simple as possible, one side of the housing ls provided with a serles of removable plates, one ad~acent the end of each ga~ burner, these removable plates each bearlng a gas supply aperture through whlch gas ls supplled to the burner and a transparent wlndow through which an operator can observe the gas burner to ensure that proper combustion is taking place. The plate may also be provided with an lnlet for power connections to an ignlter placed ad~acent the gas burner to ignite the gas issuing from the burner.
A ma~or consideration in the operation of such band ovens ls to ensure uniformity of heating along the band, since if non-uniform distribution of heat occurs, wlth the development of hot zones on the band ad~acent each burner and cooler spots midway between ad~acent burners~

l~i9~

the baking of the goods may be deleteriously affected, and excessive gas consumption may occur. (References to non-uniformity of heating herein refer to such non-un ~ormity of heating over the relatively short distances between ad~acent gas burner~ and are not intended to refer to deliberate creation of zone~ of differing temperature along the length of the band oven which are often dellberately introduced, for example to ensure that the goods entering the oven are rapidly ralsed to a proper baking temperature.) Non-uniformlty of heating can be reduced by using a large number of burners spaced apart by relatively small distances. For example, in prior art band ovens burners may be spaced at intervals of 12 to 18 inches (305 to ~57 mm.) along the len~th of the band, the burners being dlsposed ln two row9 above and below the band.
Unfortunately, when such a lar~e number of burners are employed the rate at which gas needs to be burned at each burner to maintain the requisite baklng temperature within the insulated baking chamber is low, so that only a short flame ls produced at each burner, and the burner thus provides a concentrated heat source, thereby tending to produce non-uniformity of heating within the baking chamber. Thus, improvement in the uniformity of heating wlthin band oven~ is de~irable.
U.S. Patent 596,578 describes an acetylene burner 12~i9~3~9 in which gas is forced under pressure through a duct into a slot where it comes into contact with air contained within the slot and contacts a flat vertical wall of the slot opposite the qide to which the gas enters so that the column of gas is flattened. This flattened column Or gas, follow ng upwardly along the vertical face Or the wall of the slot, pas~es out of the slot, where it is ignited and a flat, uniform and smokeless blaze is produced.
U.S. Patent 1,213,675 to Maynard describes an oil burner having a slot like aperture through which the oil is discharged, and a steam conduit through which steam passes into a large number Or apertures, which emerge from the burner ad~acent the slot-like oil aperture, so that the steam is pro~ected from the burner in a substantially fan-shaped form contacting and mixing with oil pro~ected through the oil conduit to atomize the o~l.
U.S. Patent 1,400,024 to Caracristi describes a gas burner in which control of the gas/air ratio is effected by provldlng an air supply conduit, which is separate from the gas supply condult, and through which air is forced under pressure. The combustible gas emerges from the burner through a set of slot-like gas apertures arranged parallel to one another, while the air emerges through a set of slot-llke air apertures disposed ~Xf~9~19 between adJacent pairs of the gas apertures, so that parallel alternating flat streams of ga~ and air emerge from the burner. It is stated that the alternate layers of gas and air emerging Prom the slotted outlets form a stratified stream at the exit, the gas and air then becoming thoroughly intermixed so that the regulation of the air both as to velocity, pressure and volume enables a proper quantity of ai~ to be provided dependin~ upon the quality of the gas, thus providing maximum ro combustlon effeciency.
U.S. Patent 1,702,625 to Anderson et al. describes a gas burner having the form of an elongate trapezoidal prism. This prism is hollow, having an internal trapezoldal chamber open at both top and bottom, flanked by two almost t-iangular prlsmatlc gas chambers closed at their lower ends but having narrow, slot-llke apertures at their upper ends. The Jets of combustible gas emerging from the upper ends of these two ga3 chambers are angled inwardly towards one another so that they meet along a line lying above the central chamber of the gas burner. This arrangement allows air to be drawn up through the central chamber of the gas burner, thereby augmenting the air supply along the line at which the gas ~ets meet and, so the patent tates, producing an inten~ely hot flame tlp along this line.
U.S. Patent 2,418,533 to Walker describes a gas lZtj9~19 torch designed so that lt is capable of being operated very hot with no possibility of flashbacks and so that high velocity and highly oxidizing flame ~ets can be employed without danger of the flames blowing away from the tip or blowing out. This gas torch has a tip of elongate rectangular form having a slot of rectangular cross-section extending longitudinally therein.
Combustible gas is supplied to two gas conduits each of which communlcates with the base of the slot via a row of apertures, the two rows of apertures be!ng on opposed sldes of the slot. Oxygen ls ~upplled through a third conduit from which extend a row of branch condults, this row of branch conduits running parallel to the length of the slot. However, the oxygen branch conduits do not open into the slot, as do the gas conduits, but instead terminate in nozzles which extend upwardly along the central plane of symmetry of the slot and termlnate flush with the outer surface of the slot.
U.S. Patent 2,638,159 to Wlnkleman et al. describes a gas burner intended for producing very hlgh temperatures for use ln stripping coatings such as rust, scale, paint and other organic coatings from the surfaces of wood, metal and other bodies. In this burner, combustible gas emerges from a single row of apertures. Oxidizing gas is supplied via two rows of apertures, parallel to each other and to the row of i9~

apertures for the combustible gas, both rows of oxldizing gas apertures lying on the same side as the combustlble ga~ apertures. The two sets Or condult3 whlch terminate in the two rows of oxidlzing gas apertures are angled both with respect to each other and with respect to the set of conduits which terminate in the combustible gas aperture~, so that the stream Or combustible gas and the two streams of ox$dizing ga~
intersect along a single line. Thi 9 retards the velocity at whlch the oxidizing gas ls supplied to the surface coatlng to be treated, and thus causes the oxidation actlon Or the burner to be uniform over the width covered by the burner, rather than concentrated ln narrow paths correspondlng to separate Jets of oxidlzlng gas.
U.S. Patent 2,911,035 to Nleman et al. describes a gas burner ~or producing a soft, silent flame Or extremely hlgh temperature. In thl~ burner, a ~ingle casing is provided wlth a large number Or apertures, some belng connected to the combustlble gas supply and the remainder to the oxygen supply, the oxygen and combustible gas apertures belng intimately mlxed together 90 that mixlng of oxygen and combustible gas take~ place only after the gases have left the burner, thereby preventing flashback. However, the oxygen and combustible gas apertures are so close together that 126~319 'nt~mate mlxlng takes place almost at once and complete burnlng takes place with a very short dl3tance from the plate.
U.S. Patent 3,418,062 to Hovis et al. describes a substantially cyllndrlcal burner lntended for use ln a soaklng p1t. In thls burner, a central fluld fuel outlet ls surrounded by two consentric rings of combustion air outlets. The fuel outlet and the inner rlng Of 8a~ outlets direct fuel and air reRpectlvely parallel to the axis of the burner, while the outer ring of gas outlets proJects ~ets of air diverglng away from the axi3 of the burner.
U.S. Patent 3,706,520 to Grimm et al. describes a compllcated fuel gas burner for a vertical shaft furnaceO This burner includes a slngle shaft containing four concentric conduits, the conduits containing fuel, alr, fuel and air re~pectively reading from the lnnermo~t conduit. The three inner conduits terminate ln separate plena each prov'ded with a plurality of outlets arranged to d~rect the fuel or air ~ubstantlally perpendlcular to the axis of the shaft. The outermost conduit opens lnto a ~acket which directs the air backwards in the oppo~ite dlrectlon to the main fuel and alr flow, so that the outermost air is directed backwards parallel to the axis of the shaft.
U.S. Patent 3,850,571 to Zlnk et al. de~crlbes a 6~
g hlgh energy flame burner intended to produce a long, slender, rod-Jet of flame of small diameter. The flame burner has a substantially cylindrical tube the tip Or which is provided with a principal gas outlet orifice through which a combustible gas Jet flows axially of the burner. In the side wall~ of the burner are cut a plurallty Or 3econd~ry gas outlets, whlch i~sue lnto fl collar surrounding the burner. The forward end of this collar is provided with a forwardly-diverging frusto-conical flange, whlle the rear wall of the collar ls provided with a plurality of apertures. The flow of combustible gas through the secondary gas apertures draws air through the apertures in the rear wall of the collar and the resultant mlxture of gas and air is caused by the frusto-conical flange to ~ssue from the forward end of the collar as an outwardly diverging ring of flame encaslng the principal gas ~et so as to assist in the lgnltlon of the gas ln the princlpal Jet, and prevent it from being blown out due to the hlgh velocity of the ~et.
None of the above patents indicate any way in whlch the rlbbon gas ~et from a gas burner used in a band oven could be modlfled so a3 to lmprove the unlformity of heatlng within the band oven, and there ls thus 3till a need for a solution to the problem of non-uniformlty of heat distrlbution in band ovens. The present inventlon 12699~9 provides a way of improving the uniformity of heat distribution in a band oven.
Summary of the Invention This invention provides a method of lengthening the flame from a gas burner which produces an elongate flame, the method comprising directing two streams of air from opposed sides of the flame inwardly towards the flame, each stream of air being directed at an acute angle to the direction of the gas issuing from the gas burner, thereby causing the streams of air to impinge upon and lengthen the flame.
The burner used in a baking oven comprising a housing having walls defining a chamber, transport means for moving articles to be baked through the chamber, and a plurality of gas burners mounted within the chamber and spaced from one another. At least one of these gas burners comprises a gas supply conduit, and an elongate gas plenum communicating with the gas supply conduit, the gas plenum having walls defining a row of apertures spaced from one another along the length of the gas plenum and extending from the interior of the gas plenum to the external surface thereof, such that gas issuing from these apertures will burn to produce a flame extending along the length of the gas plenum. The burner or burners further comprises an air supply conduit and at least one air plenum communicating with the air supply conduit, this air ~:6991~

plenum or plena having walls defining two rows of apertures extending from the interior of the air plenum or plena to the external surface thereof, the two rows of apertures being disposed on opposed sides of the rows of apertures in the gas plenum and being directed towards the row of apertures in the gas plenum such that air issuing from the two rows in the air plenum will impinge upon the flame produced by the gas issuing from the row of apertures in the air plenum and lengthen the flame.
The lengthened flame may be used in a baking process comprising transporting the dough goods through a baking oven provided with a plurality of gas burners each having walls defining a row of gas apertures, supplying gas to the burners, whereby a stream of gas passes through the gas apertures and burns adjacent the gas burner, and, in at least one of the gas burners, directing two streams of air from opposed sides of the flame produced by the burning gas inwardly towards the flame, each stream of air being directed at an acute angle to the direction of the gas issuing from the gas apertures, thereby causing the streams of air to impinge upon and lengthen the flame.
The gas burner which is used comprises an ~Z~951~L~

elongate gas plenum having a row of gas apertures through whlch gas can issue and burn to produce a ribbon flame, and at least one alr plenum having walls definlng two rows of air apertures dlsposed on opposed sldes Or the row of gas apertures, the two rows of air apertures belng arranged to produce two streams of air incllned lnwardly toward the gas lssulng from the row Or gas apertures with the streams ot air being directed at acute angles to the stream of gas.

Brief Description Or the Drawin~s Flgure l ls a side elevation of part of a band oven of the lnvention wlth part of the houslng broken away to show the arrangement of the band, the gas burners, and associated parts o~ the oven;
Figure 2 is a vertlcal section through one of the gas burners shown in Figure 1, this sectlon being taken in a plane parallel to that of Figure 1 and perpendicular to the long axis Or the burner;
F_gure 3 is a plan vlew of the burner shown in Fi~ure 2 looking in the directlon of arrow A ln Figure l; .
Figure 4 is a section along the line 4-4 in Figure 3; and Figure 5 is a side elevation of the removable plate ln the wall Or the band oven associated with the burner

2 6 9 ~hown in Flgures 2, 3 and 4.

Detailed Description o~ the Drawing~
The baking oven (generally de~lgnated lO) shown ln Figure l comprises a housing having, at lts top and sides, an inner wall 12, an outer wall 14 and a layer of insulation 16 formed of, for example, fiberglass dlsposed between the inner and outer walls. The housing will typically be about 300 feet (90 meters) long, and only a small portion of the housing 1~ shown in Figure 1.
The houslng encloses an elongate cuboldal baking chamber 18 along the length of which runs a belt conveyor formed of a heat-resistant material, for example steel wire mesh. The upper land 20 of the belt conveyor is supported at intervals by idler rollers 22 and lies ln a horizontal plane approximately half-way up the baklng chamber 18. The upper land 20 of the belt conveyor transportq dough goods 24 being baked (from lert to right in Figure 1) longltudinally through ~he baking chamber 18, the speed of movement Or the conveyor and the temperatures within the chamber 18 being ad~usted so that the goods 24 are properly baked as they pass through the oven. The lower land of the belt conveyor runs longitudinally through the baking oven adJacent the bottom Or the chsmber 18 and is supported ~2~i9~19 by ldler rollers 26. Although for purpo~es of lllustra-tion the spacing between the rollers 26 has been made the same as that between the rollers 22 in Flgure 1, ln practice the spacing between the idler rollers 26, which support the non-load bearing lower land of the conveyor, can u~ually be greater than the space in between the rollers 22, which must support the upper land 20 Or the conveyor and the goods 24 resting thereon.
Although not shown ln Flgure 1, the belt conveyor proJects from both end~ of the baklng chamber 18 (the ends of the houslng are of course provided wlth appropriate apertures to allow entry and exit of the conveyor) and the belt conveyor 18 powered by driven rollers at either end. The baking oven i~ also provided wlth conventional exhaust ducts, fans and fan motors, these part3 being omitted from Figure 1 for ease of illustration.
The baking chamber 18 1~ heated by a large number of gas burners (generally deslgnated 28 and 30). The gas burners 28 and 30 are of elongate, substantially prlsmatic form and are arranged wlth thelr long axes horizontal and extending transversely across the baking chamber 18, these axe3 lying parallel to the horizontal surface of the upper land 20 of the conveyor but perpendicular to the direction of movement thereof. The gas burners are arranged ln two rows above and below the ~269919 upper land 20 Or the conveyor, the burner~ 28 in the upper row may be 3paced at interval~ of about 3 to 4 feet (0.91 to 1.22 m.) whlle the burners 30 ln the lower row may be ~paced at interval~ of about 18 to 24 inche~
(457 to 609 mm.). The burners 28 in the upper row are supported by U-ahaped hangerq 32 fixed to the top of the inner wall 12, whlle the burners 30 ~n the lower row are supported by sub~tantially H-shaped supports 34 re3tin~
on the base of the oven. Although not spparent from Flgure 1, the hangers 32 and support~ 34 do not extend the full wldth of the oven; in3tead, each hanger of ~upport has a width of only about 1 inch (25 mm.), two separate hangers or support~ being provided rOr each burner 28 or 30, one ad~acent each end of the burner.
Each of the burners 28 or 30 produces a flat ribbon flame 36 or 38 respectively, these flames extending the full width of the upper land 20 of the conveyor. The flames 36 from the upper burners 28 are dlrected downwardly toward the upper land 20 and down the direction of the movement of thi~ land. Simllarly, the flames 38 from the lower burners 30 are d~rected upwardly toward~ the upper land 20 and down the direction of movement of thi~ land.
For ease of operation, supervi~lon and main~enance, the baklng oven 10 is arranged so that all the ga~
supply conduit and other connectlon~ are arranged in 12~9~19 one slde wall of the housing, thls side wall being designated the "operating slde" of the oven. The oven ls viewed ln Flgure l from its non-operating slde. To provide the necessary gas and other connectlons to each burner, a removable plate 40 is provided in the side wall Or the housing on the operating side of the oven.
In addltion to the gas supply, the removable plate carrles power connectlons to an electric igniter 42 dispo~ed ad~acent each burner.
The con~truction of the burner is shown in more detail in Figures 2 and 3. Although as noted above, the burners 28 and 30 are arranged so that their flames 36 and 38 are dlrected tran~versely downwardly or transversely upwardly respec~ivelg within the baking chamber 18, for ease of reference ln Flgures 2 and 3 the burner ha~ been shown and will be described as though i~
produced a flame di~ected vertically upwardly.
As best seen in Figure 2, the burner 28 or 30 comprises a gas plenum (generally de~lgnated 50) having the form of an elongate hollow tube 52 bearlng on its uppermost part a substantially cuboidal extension 54.
The upper surface Or the extenslon 54 ls formed by a strip of teel mesh 56 running along the length of the tube 52. The apertures ln the mesh strip 56 constltute the row of gas apertures Or the burner. It wlll be apparent to those ~killed ln the art Or burner ~2~9~1~

technology that gas i3suing from the apertures in the mesh str~p 56 and burnlng adJacent these apertures will provide a contlnuous rlbbon flame extending the full length of the mesh strlp 56.
The burner 28 or 30 Purther compri~e~ an air plenum 58. The air plenum 58 has siX flat races 60, which form fou- complete sldewalls, and part of two further sidewalls of a regular nonagonal prlsm, two further flat faces 62 and 64 which lie in plane~ lncluding the superimposed axe~ of the tube 52 and the nonagonal prism and at an angle of 140 to one another, and a part-cylindrlcal section 66 which extends in contact with and surrounding the tube 52 over the 220 sector of the tube between the Pace~ 62 and 64.
As best seen in Figure 3, the two surfaces 62 and 64 each have provided therein a row of air apertures 68 and 70 respectively. These air apertures 68 and 70 are the outlets Or alr conduits whlch are drilled normally through the surfaces 62 and 64 into the hollow lnterlor Or the alr plenum 58. ~ecause of the 140 angle between the surface~ 62 and 64, and the ~ymmetrlcal dispo~tion o~ these surfaces about the extenslon 54 of the ga~
plenum 50, ~hen Jets of air (produced a~ explained below) emerge Prom the aperture~ in the surfaces 62 and 64 re~pectively, these Jet~ oP air converge inwardly towards a Jet of gas (al~o produced as described below) ~Z6~919 emerging from the apertures ln the mesh str~p 56, so that the gas and air Jets meet along a ~lngle llne 72 (Fig. 2). The convergence of the air ~ets from either side on to the flame produced by the burning gas increases the length of the flame, thereby lmproving the uniformity of heating of the baked goods on the upper land 2Q of the belt conveyor (Fig. 1). ~y proper adJustment Or the pressures Or the gas and air red to the gas and alr plena 50 and 58 respectlvely (such adJustment being easlly effected empirically by routine methods)the air streams allow very marked elongation of the flame. For example, it has been found that using a gas pressure of 6 psig gauge (41.5 kPaO), and alr apertures 0.125 inch (3.2 mm.) in diameter and spaced at 1 lnch (25 mm.) lnte-vals along the ~urfaces 60 and 62, wlth an alr pressure of 16 inches water gauge (4 kPa.) -esults ln a flame approxlmately 6 lnches (152 mm.) long, as compared to a flame approxlmately 1 1/2 lnches (38 mm.) long when no alr supply is used.
As shown in Figure 3, at the end Or the burner whlch lies ad~acent the non-operatlng slde wall of the oven (the rlght-hand end in Figure 3) the alr plenum is closed by a flat endplate 74. As best seen in Flgure 4, thls endplate 74 has a form correspondin6 to the cross-sectlon of the air plenum 58 except that it ls provlded with an axial cut-out surrounded by a collar 1~i9~19 76, whlch i3 integral wlth the endplate 74. the endplate 74 iq secured to the body of the alr plenum 58 by set screws 78. A blind nipple 80 extends axially from the adJacent end of the tube 52 and passes through the collar 76. The collar 76, and thus the gas plenum 58, is fixed in position relative to the tube 52 by set screws 82.
At the left-hand end (in FiB. 3) of the burner, whlch lies ad~acent the operating slde wall o~ the oven, the al. plenum extends axially beyond the end of the tube 52 to an endplate 84, which is integral with the side walls 60, 62 and 64 of the air plenum 58. The endplate 84 carrles an integral collar 86. Unllke the collar 76 already described, the collar 86 extends ax ally both inwardly and outwardly from the endplate 84; the part-cylindrical recess ln the air plenum provided by the section 66 terminates short of the endQlate 84 so that the hollow interior of the collar 86 ln effect forms a reduced-diameter contlnuation of this reces~. -A gas supply tube 88 extend~ axially from the tube 52 and pa~ses through the collar 86, which ls clamped to the gas supply tube 88 by set screw~ 90. The gas supply tube 88 communicates wlth the lnterlor of the tube 52 of the gas plenum and supplies combustible gas thereto.
The endplate 84 of the air plenum 58 also has an 9~L9 aperture provided thereln, but in thls case the aperture ~s spaced from the axls of the gas plenum and lle~
adJacent one of the side walls of the alr plenum. The aperture in the endplate 84 ls surrounded by a cyllndrical stub tu~e 92, whlch ls connected to a flexlble metal tube 94, through whlch alr is supplied under pressure to the air plenum. The electrlc lgnlter 42 ia provided at thi~ end Or the burner, but ln order to show the construction Or the burner at ~hls end of the burner more clearly, the lgniter 42, whlch serves to ign'te gas lsquing from the burner and whlch i8 of a conventional type, and lts assoclated power connectlon~
95 a-e lndlcated only schematlcally ln broken llnes ln Flgure 3.
Figure 5 show~ the removable plate 40 di~posed ln the operating side wall Or the oven adJacent each burner 28 or 30. The plate 40 ls circular and covers a somewhat smaller clrcular aperture ln the operat!ng slde wall Or the oven, be~ng releasably ~ecured to the slde wall by screws. The plate 40 has a central ga~ lnlet aperture 96, through which passes a tube whlch ls secured to the ga~ supply tube 88 shown in Figure 3.
The plate 40 is also provided wlth an orr-center alr inlet aperture 98 through which passe a tube whlch is secured to the flexlble metal tube 94 connected to the alr plenum 58. The use Or the flexlble metal tube 94 ~2~i99~9 enables the same plate 40 to be used ~or both the upper and lower rows of burners 28 and 30 respectively (Figure 1) despite the difference in the posltlons of the stub tube 92 because of the different orientations of the two rows of burners. A transparent window 100 is formed in the upper part of the plate 40; thls window is of course formed of a material reqlstant to the temperatures to which it will be exposed by vlrtue of its proximity to the flame issulng from the burner. The window 100 ls provided to enable an operator to check that a proper flame is being produced by the burner. Finally, the plate 40 is provided with an lgniter power inlet 102 through which pass wires connected to the power connections 95 of the igniter 42.
A~ will be apparent to those skilled ln the art, the tubeq passing through the apertures 96 and 98 in the plate 40 are connected to conventional gas an~
compre~sed air lines via appropriate pressure-reduction or metering valves in order to ensure that air and gaq are qupplled to the burner at the proper pressures, while the power connections to ~he lgniter 42 are connected to an appropriate power supply via a conventional switch.
To aqqemble the burnerq 28 and 30 the blind nipple 80 and the ga~ supply tube 88 are first lnser~ed into their respectlve apertures in the ga~ plenum 50;

1~69~1 ~22--although not shown in the drawings the appropriate ends of the nipple 80 and the tube 88, and the apertures into which they fitS are provided with cooperat'ng sc-ew threads. Apart from the separate nlpple 80 and tube 88, the gas plenum 50 is a single, integral casting.
The air plenum 58, with itq endplate 74 and aqqociated collar 76 removed, has its part-cyllndrlcal section 66 engaged with the left-hand end (in Figure 3) of the tube 52, and is slid along the tube 52, from left to ri8ht in Figure 3 until the end of the tube 52 carrying the gas supply tube 88 abuts the shoulder where the part-cylindrlcal sectlon 66 meets the collar 86.
The endplate 74 and it~ as~oclated collar 76 are slid over the nipple 80 to their correct positions relative to the air plenum 58, fastened to the air plenum by means of the set screws 78 and finally clamped to the nipple 80 by means of the set screws 82. Flnally~ the set screws 90 are inserted to clamp the collar 86 to the tube 88. The nipple 80 and the tube 88 can then be placed on the hangers 32 or supports 34 and the gas and air supplies connected.
It will be seen that, if either the gas plenum or the air plenum of the burner has to be replaced because of, for example, wear or mechanical fallure, either plenum can be replaced without the other, simply by disassembling the burner in precisely the reverse of the assembly operatlon descrlbed above.
From the foregolng de~crlption o~ the preferred burner shown ln the accompanylng drawings, lt wlll be apparent that the constructlon of thls burner allows for easy retrofltting of exlsting band ovens provided wlth conventional burners. Most conventional burners closely resemble the gas plenum 50 oP the preferred burner of the present invention, and hangers and supporters suitable for supportlng such a conventlonal burner can also be used wlth the preferred burner of the present invention, s~nce the rod 74 and the gaq supply tube 80 of the burner of the present inventlon can have dimensions identical to the cor-esponding parts of a conventlonal burner. Moreover, existlng burners can be mod~fled simply by sliding a gas plenum over the burner, as already described. It will of course be necessary to modlfy conventional plates correspondlng to the plate 40 shown in Figure 5 to provide for a pressurized alr inlet, but in many cases it may be possible to re-use plates already provided with a gas inlet aperture, window and igniter power inlet s~mply by bor~ng or otherwlse cutting an appropriate aperture 98 in the plate. The use of the flexible metal tube 94 allows considerable latitude ln the placing of the aperture 98 in the plate 40. The provision of the necessary compresYed air llne and appropriate branch lines l~t;9~

-24- .

involved to supply compressed air to the burners is well withln the capacity of those skilled in the art, and does not involve any difficult design considerations, especially in view of the very low (and consequently safe) air pressures involved.
It will be apparent to those skilled ln the art that numerous changes and ~odifications can be made in the preferred embodiment of the invention described above without departing from the scope of the lnvention.
For example, the 20 angle between the gas and air streams in the preferred burner can be varted. In fact, almost an acute angle can be used over the range of both (say) 5 to 80. However, a relatively small acute angle within the range of about 10 to about 30 is preferred, since it has been found that the use of an angle within thi range gives maxiumum lengthening of the flame ls~uing from the burner. Since it is desirable to avold deflecting the gas flame from the plane ln which it would lie if no forced air streams were pre~ent, it is desirable that the acute angles between the two air streamq and the gas stream be equal to one another.
The dimen~ions of the oven of the present invention and the burners therein can vary very widely~ and the following suggestions are given solely by way of general guidance. If the housing of the oven ls to be a typical l~9t319 commercial houslng having a length of approximately 300 feet (90 meters), a helght of approximately 5 feet (1.5 meters) and a belt conveyor having a width of 38 nches (965 mm.), it has been found appropriate to use a burner measuring 42 1/2 inches (1079 mm.) between the endplates 74 and 84, wlth a g;lp of 1 1/2 lnche.~ (3~ ~m.) h~tw~en the endplateq ô4 and the adJacent end o~ the tu ~e 52 .
In this burner, the surfaces 62 and 64 are each provlded with 39 holes 0.125 lnch (3.2 mm.) ln d ameter spaced at intervals of 1 inch (25 mm.) beginning 1 inch (25 mm.) from the endplate 74 and termlnating 2 inches (51 mm.) short of the opposed end of the tube 52. The tube 52 is 1 3/4 inches (44 mm.) ~n internal diameter, with the mesh 56 spaced 1 15/16 inch (49 mm.) from the axis of the tube 52. With the air stream~ angled at 20 to the gas stream, as shown in the drawings, a burner of these dimensions has the line 72 oP intersection of the air and gas streams ~paced 5 1/8 inches (130 mm.) from the axis of the tube 52. The air pressure used is desirably in the range of about 8 to about 32 inches water gauge (about 2 to about 8 kPa. gauge).
In view of the numerous possible changes and modificatlons ln the oven, baking process and method of the present inventlon (the~e changes and modifications not being limited to those already discussed), the whole of the foregoing descrlption is to be construed in an ~2~9~319 illustrative and not in a limitative sense, the scope of the invention being defined solely by the appended claims.

Claims

Claims:
l. A method of lengthening the flame from a gas burner which produces a substantially planar ribbon flame, the method comprising directing two streams of air symmetrically upon the flame from opposed sides thereof inwardly towards the flame, the two streams of air being directed at equal acute angles in the range of from about 10° to about 30° to the plane of the flame, thereby causing the streams of air to impinge upon and lengthen the flame.