US3405923A

US3405923A - Side wall firing system for multi-stand annealing covers

Info

Publication number: US3405923A
Application number: US578027A
Authority: US
Inventors: John D Nesbitt; Herbert M Kohn
Original assignee: Midland Ross Corp
Current assignee: Midland Ross Corp
Priority date: 1966-09-08
Filing date: 1966-09-08
Publication date: 1968-10-15
Anticipated expiration: 1985-10-15
Also published as: FR1529482A

Description

J. D. NEsBnT ET AL 3,405,923

SIDE WALL FIRING SYSTEM FOR MULTI-STAND ANNEALING COVERS 5 Sheets-Sheet l nvvmvmm.4 JUHN Z7. NESBJTT,

, HERBERTM. KUHN.

Cet. 15, 1968 Filed sept. e, 196e Oct. 15, 1968 J. D. NESBITT ET AL. 3,405,923

SIDE WALL FRING SYSTEM FOR MULTI-STAND ANNEALING CGVERS Filed Sept. 3, 1966 l 5 Sheets-Sheet 2 45 44 INVENTOR.;

Oct. 15, 1968 J. D. NESBITT ET AL 3,405,923

STAND ANNEALING COVERS SIDE WALL FIRING SYSTEM FOR MULTI- I5 Sheets-Sheet 5 Filed Sept. 8, 1966 INVENTORS JDHM Il. NE SEIT?,

HERBIH T M KUHN.

United States Patent O 3,405,923 SIDE WALL FIRING SYSTEM FOR MULTI-STAND ANNEALING COVERS `lohn D. Nesbitt and Herbert M. Kohn, Toledo, Ohio, as-

signors to Midland-Ross Corporation, Toledo, Ohio, a corporation of Ohio Filed Sept. 8, 1966, Ser. No. 578,027 21 Claims. (Cl. 263-40) ABSTRACT F THE DISCLOSURE A burner for distributing a flame along a furnace wall containing the burner. A swirling centrally enriched fuelair mixture flows from a fuel chamber of the burner into a fuel-air entry port where it intermixes with a surrounding swirling air stream. A diverging opening extends from the entry port through the wall. This opening is flared towards the wall section over which the flame is to be spread. The flared portion may take the form of a Coanda turn and have a baille cooperating therewith to urge the flame along the wall.

Background of the invention While the instant invention relates particularly to direct fired burner equipment, it has applicability in boilers, stills, reformers, strip heating furnaces and the like and the novelty and advantages of the instant burner equipment will be illustrated by describing its use in multistand coil annealing furnaces and the overcoming of problems that are associated with such furnaces.

A multi-stand coil annealing furnace includes a plurality of aligned pedestals, each of which supports a plurality of steel coils which are placed one on top of another. An inner cover is sealingly placed over each pedestal and the coils thereon, this combination of pedestal, coils and cover being referred to as a stand, and the sealing is accomplished by a bed of sand which receives the inner covers. A protective atmosphere is circulated within each of the covers by a fan located within the pedestal. An outer, refractory lined heating cover is placed over all the stands and during the heating portion of the annealing cycle, heat is supplied to the stands by burners located in the walls of the outer cover. Burners cannot supply heat to the stands by direct flame impingement on the inner cover, for this would adversely affect inner cover life; therefore, radiant heat is relied upon either by utilizing radiant tubes or direct fired burner equipment that transfers heat to the inside refractory surfaces of the outer cover and supplies heat to the stands primarily by radiation from the heated refractory surfaces and by direct ame radiation.

ln the heating cycle of the coil annealing furnace, which cycle may extend for a period of 2() to 30 hours, a common problem has beenl the attainment of uniform heat distribution. This problem is three-fold in that heat should be supplied uniformly from stand to stand, distributed uniformly along the vertical length of each coil stand, as well as uniformly about the circumference of each coil. The aforementioned vertical and circumferential heat distribution problems are associated with individual stands, and the fans located in each pedestal recirculate a protective atmosphere within each inner cover to distribute heat more uniformly. The problem of non-uniform temperature distribution from stand to stand is the only one that can be controlled completely by means external to the inner covers, whereas the other two heat distribution problems are associated with additional factors. Various types of burners have been used 3,405,923 Patented Oct. 15, 1968 ice in attempts to improve temperature uniformity among stands, but to date none of these attempts have proven entirely satisfactory.

During a coil annealing run, the heating rate is controlled first by a furnace thermocouple located between the stands and the outer cover and subsequently by a thermocouple that extends through one of the pedestals, this latter thermocouple being referred to as the load thermocouple. The maximum heating rate is supplied until tbe furnace thermocouple reaches a predetermined set point, for example, l550 F. and the input is then cycled to maintain the temperature between fixed limits, for example, between l500 F. and 1550" F. When the furnace thermocouple reaches the set point, all the stands will not be at the same temperature and it is preferable to have the load thermocouple in the stand that has the fastest heat rise. The cyclic operation continues until the load thermocouple attains a control point, for example, l250 F. At this time the temperature control switches from the furnace thermocouple to the load thermocouple and the heat input is cycled to maintain the predetermined load temperature. During this latter cycling, the colder coils within the furnace approach the control point temperature and the average thermal head decreases until all coils are substantially at the same temperature. When satisfactory temperature uniformity is reached within the furnace, the soak period is then begun and the annealing temperature will be maintained sufliciently long to obtain the metallurgical properties sought.

From the foregoing, it is apparent that non-uniform temperature distribution within the furnace adversely affects the control of metallurgical properties, for some stands will be at maximum temperature longer than others. lf the non-uniformity from stand to stand is sufficiently large, it would not be possible to obtain substantially equal temperature among the stands within a furnace and the metallurgical properties of the coils therewithin would vary widely.

Satisfactory heat distribution could be obtained by providing the inner walls of the outer heating cover with a multiplicity of relatively small, direct radiation burners providing complete wall coverage zoned both vertically and horizontally, whereby the inner refractory wall temperature can be controlled in accordance with local heat emission requirements. This arrangement, however, would require a prohibitive investment in burner equipment, piping and controls.

Objects and advantages It is, therefore, an object of this invention to provide a unique and economical wall heating means.

It is a further object of this invention to Aprovide direct red wall heating means useful for transferring heat to internal structures with minimum flame impingement on the surface to be heated.

lt is another object of this invention tov provide direct fired combustion means capable of rapidly heating multistand annealing furnaces without adversely affecting inner cover life and achieving small temperature differences between similarly oriented coils of steel located on such pedestals.

It is still another object of this invention to provide means for varying flame height as required by any specific geometry for local heat transfer requirements.

It is still a further object of this invention to provide a direct fired burner whose use in a coil annealing furnace results in better fuel eiciency and the maximum rate of temperature rise consistent with metallurgical limitations.

Brief description of the invention In a preferred embodiment of this invention, the burners are disposed longitudinally along the side walls of the outer cover, and each burner is positioned intermediate the axis of adjacent stands to minimize risk of ame irnpingement on the inner covers. The burners -are also lcated near the bottom of the side walls to provide maximum flame coverage over the vertical wall surface. Each burner comprises a slot or opening formed within a side wall of the outer cover, a pair of slot entry ports. also formed within the side Walls adjacent slot and a pair of annular, juxtaposed housings secured to the outside of the side wall in axial alignment with the slot entry ports,

The slots are generally rectangular but with inwardly diverg'ing lateral walls. The top surface of the slot curvesupwardly at the inner end thereof andthe bottom surface of the slot has an upwardly extending baffle tha-t cooperates with said curved portion to direct gases owing through the slot upwardly along the inside surface of the outer cover, while the diverging Walls tend to spread the gases longitudinally. Extending laterally intermediate the diverging Walls isa partition separating the slot into two compartments. Disposed at the rear of each slot is a pair of parallel, cylindrical slot entry ports that have diameters substantially equal to the height of the slot.

Variable air supply means is provided to introduce air under pressure into each housing. Secured to the outer end and extending coaxially into each housing is a generally cylindrical throat casting whose circumference is spaced relative to the circumference of the annular housing thereby forming an -annular plenum therebetween, which plenum communicates with the slot entry port. At the rear wall of the chamber formed yby the throat casting, tangential vair inlets are formed in the wall thereof to provide means for transferring air from the annular plenum to, and about, the inside perimeter of each throat casting. At the downstream end, each throat casting communicates with `a slot entry port. Disposed about the outside circumference of the throat castings, at a position downstream from the tangential air inlets, are a plurality of helical vanes that impart a spin to the air as it flows through the annular plenum and into the slot entry port, the pitch of the vanes being such that the spin of the air in adjacent slot entry ports `are counter to one'another. Intermediate the tangential air inlets and vanes, a plurality of openings is provided within the throat castings to allow air to ilow radially from the annular plenums into the throat casting.

Fuel is supplied at the rear of the cylindrical throat casting by regulated fuel supply means attached thereto. The fuel supply means directs fuel inwardly, or downstream, along the 'axis of each throat casting. Ignition means is provided 'to ignite that portion of the fuel stream which mixes with the air entering the throat casting through the tangential inlets. As the yair enters the vthroat casting tangentially, a ring of ame results within the inside periphery of the throat casting. The air that enters radially through the openings downstream of the tangential inlets provides -a continuous llame between the spinning pilot flame and the main combustion region starting in theV slot entry port. l

The -bulk of the air from the air supply means is directed axially downstream through the annular plenum and is given a spinning or rotating movement by the helical vanes attached to the circumference of the throat castings, the'spin imparted to the air being opposite in adjacent slot entry ports. The spinning air from the annular plenum and the burning fuel from the throat casting enter the slot entry port, but rapid mixing of the air and fuel is not achieved until they expand into the slot. In addition, expansion of the counter-rotating streams substantially reduces the axial velocity of the air-fuel mixture and causes the resulting flame to spread longitudinally along the diverging walls of the slot `and subsequently longitudinally along the inside wall of the outer cover. Thevbafe att'he downstream end of the slot oor and the upwardly curved position of the slot ceiling direct the llame issuing from the slot upwardly along the inside surface of the outer cover. Thus, the combination of expansion and counterrotating fuel-air gas streams, the baille, and upwardly curved ceiling provides means for directing a lblanket of llame along the inside surface of the outer cover.

i Description of the drawings In the drawings:

FIG. 1 is a View in perspective of va multi-stand coil annealing furnace with one end portion in transverse cross-section and with a port-ion of one inner'cover and a coil broken away; t

FIG. 2 is a view inV elevation of a yburner embodying the principles of this invention shown with a `portion ofv the bale memberbroken away from the interi-orof the furnace ofFIG. 1; t -f t v FIG, 3 is anv enlarged view of the burnertaken in vertical cross-section along the line 3-3 of FIG. 2;

FIG. 4 is a yView* in horizontal cross-section taken along the line 4 4 of FIG. 3;

FIG. 5 is a view in vertical cross-section taken along line 5 5 of FIG. 3; and Y FIG. 6 is an enlarged view in vertical cross-section of a modied form of the burner in FIG. 2-5 taken along the line 3 3 of FIG. 2.

Detailed description of preferred embodiments of the invention Referring to FIG. 1, a multi-stand annealing furnace 10 includes a hearth 12, a plurality of aligned pedestals 14 disposed on the hearth with each supporting one or more coils 16, an inner cover 18, and an outer heating cover 20. The combination of a pedestal, coils disposed thereon and the inner cover is referred to as a stand 19; The outer cover 20v is of rectangular horizontal crosssection and includes straight, parallel side walls 22 and a roof 24. A lprotective atmosphere is circulated around the coils within each of the inner covers 18, bya fan, not shown, located centrally in or below each pedestal 14, as is well known lin the art. The atmosphere is maintained within the inner cover by a `bottom seal 26 of any suitable design to minimize leakage of the atmosphere, yet enable the inner covers to Ibe removed. The space outside the inner cover 18 and within the outer cover 20 contains no special atmosphere, ybut only gaseous products of combustion and a relatively small amount of protective atmosphere that leaks through the said sealing means'26. These gases can escape through suitable flues 28 located in the roof 24. i

The furnace 10 employs direct fired burners 30 located in the lower portion of each side wall and which fire directly into the furnace chamber, there being no protective atmosphere therein which must be maintained separately from the products of combustion. As shown, the Aburners 30 in each side vwall 22 are staggered with respect to the inner covers 18 so that each is located intermediate the centers or axes of the covers 18, or between an end wall and center, thereby minimizing the possibility of local overheating. More specically, two of the burners 30 are positioned between adjacent inner covers, or more accu- -rately between their axes or centers, while one of the burners 30 is located at each end of the furnace Ibeyond the -axis of the inner covers 18 of the end stands. Thus, there are four burners 30 directly disposed about each of the inner covers 18. Preferablypthe ilues 28are`located along each lateral side of the roof 24, each flue beingv aligned between a paired set of burners 3 A Referring more particularly to FIGS. 2-5, the burner 30 includes a slot 32 which extends through the side wall 22 near the bottom of the wall and is bounded by a suitable high temperature refractory brick. The'slot 32V includes a ceiling 34 having a curved forward edge portion 36, FIG. 3, and a floor 38. The curved forward edge portion 36 of the upper wall 34 is preferably a Coanda turn, the reason for this preference to be explained hereafter. The slot 32 further includes

side Walls

40 and 42, FIG. 4, which diverge Vas they extend inwardly, i.e., toward the inner covers 18. A plurality of yblocks 44 form a forward baffle 46 at the front lower edge of the slots 32, and such block may be secured as by tongue in groove arrangement shown at 45. The bafiie 46 cooperates with the curve portion 36 of the upper wall 34 and, in conjunction with appropriate flue orientation, directs flame and products of combustion upwardly along the side wall 22, thereby minimizing tiame impingement on the inner cover 18.

Two cylindrical slot entry ports 48 and 50 (FIG. 4) are provided through a second wall member or refractory block 51 adjacent the slot 32 and have diameters substantially equal to the height of the slot 32. The outer edges of the slot side walls and 42 intersect the inner edges of the

slot entry ports

48 and 50, although the side walls can be spaced somewhat farther apart and still obtain effective expansion of gases within the slot. The said

ports

48 and 50 are spaced from one another in order to provide room for structural components of the burner. A partition 52 is centrally disposed between the

side walls

40 and 42 and serves to support the upper wall 34, which is a large area.

Behind and concentric with the slot entry ports 48 and are

metal housings

54 and 56 which are bolted to a plate 58 affixed to the side wall 22. Air is supplied to each

housing

54 and 56, in the proximity of the outer ends thereof, by air supply lines or

conduits

60 and 62 extending radially from each housing. Means (not shown) is provided for regulating the air supplied through

lines

60 and 62. Sealingly bolted to the outer end and extending concentrically into each

housing

54 and 56 is a generally cylindrical throat casting 64 and 66, each throat casting defining a cylindrical fuel chamber `68 and 70. Each throat casting 64 and 66 is spaced relative to its

respective housing

54 and 56 thereby forming an

annular plenum

72 and 74 therebetween. The

annular plenums

72 and 74 are couent with the air lines 60 `and 62, respectively, at their upstream ends and are confluent with the

slot entry ports

48 and 50 at their downstream ends.

The forward, or downstream, ends of the

throat castings

64 and 60 terminate at the

slot entry ports

48 and 50, respectively, while the upstream ends of the

fuel chambers

68 and 70 are defined by

rear walls

76 and 78. Adjacent to the

rear walls

76 and 78,

tangential air inlets

80 and 82 are formed Within the walls of the throat castings 64 and 66 (FIG. 5) to provide communication between the

annular plenums

72 and 74 and the

fuel chambers

68 and 70. The

tangential inlets

80 and 82 are diametrically opposed and project slightly beyond the periphery of the

throat castings

64 and 66. The corresponding

tangential air inlets

80 and 82 for each throat casting 64 and 66 extend in opposite directions so that air directed into the

chambers

68 and 70 will spin in opposite directions in each respective throat casting.

Disposed about the outside surface of the

throat castings

66 and 68 and projecting into the

annular plenums

72 and 74 are a plurality of peripherally spaced,

helical vanes

84 and 86. The direction of pitch to the

helical vanes

84 and 86 is in opposite directions on each respective throat casting 66 and 68 and corresponds to the direction of spin imparted to air entering the throat casting by the

tangential air inlets

80 and 82. Intermediate the

tangential air inlets

80 and 82 and the

helical vanes

84 and 86 are a plurality of radially extending ports 88 and 90 (FIG. 4) providing additional communication between the

fuel chambers

68 and 70 and the

annular plenums

72 and 74.

Fuel, specifically combustible gas, is supplied centrally through the

rear Walls

76 and 78 by short

fuel entry tubes

92 and 94 connected with

fuel supply pipes

96 and 98, which entry tubes are in substantially axial alignment with the

fuel chambers

68 and 70. The air supplied to the annular plenums 72 vand 74 and the fuel supplied to the

fuel chambers

68 and 70 are controlled to provide the proper air-fuel mixture.

In operation, air is supplied to the

annular plenums

72 and 74 by the

air supply lines

60 and 62 and a portion of the air enters the

fuel chambers

68 and 70 through the tangential air inlets and 82 as fuel enters through the

entry tubes

92 and 94. The air supplied to the

fuel chambers

68 and 70 by the

tangential air inlets

80 and 82 forms a spinning air stream that circumposes the axially owing fuel stream supplied by the

entry tubes

92 and 94, the spin imparted to the air being in opposite direction in adjacent fuel chambers. The combustible mixture of fuel and air formed at the interface of the lspinning air stream and the axially flowing fuel stream is ignited (the ignition means not shown) to establsh a spinning, slowly mixing pilot flame along'the inside perimeter of the

fuel chamber

68 and 70. Additional air is admitted radially to the

fuel chambers

68 and 70 by the ports 88 and extending through the throat casting 64 and 66. This additional air provides a continuous ame between the spinning pilot flame and the combustion region starting at the

slot entry ports

48 and 50. The major portion of air passes through the

plenums

72 and 74 and is given a spinning motion by the

helical vanes

84 and 86, the spin in each plenum being in the same direction as the spin imparted by the tangential air inlets to the air in the associated fuel chamber of each plenum. The spinning air from each annular plenum and the burning and combustible fuel from the throat castings enter the

slot entry ports

48 and 50 where further combustion takes place before the gases enter the slot 32. The percentage of overall combu-stion occuring in the

slot entry ports

48 and 50 is relatively small and the combustion therein is primarily for the purpose of promoting ame stability and high turn-down ratios.

As the spinning gases enter the slot 32 they tend to expand longitudinally, relative to the outer cover, because of the spin and the diverging

walls

40 and 42; however, the two streams emitted from the

slot entry ports

48 and 50 remain separated from one another within the slot due to the partition 52. This expansion of the gases results in increased mixing of the fuel and air as well as longitudinal direction. At the downstream end of the slot 32, each gas stream is directed upwardly by the curve 36 in the ceiling 34 and by the baffle 46. As the oppositely spinning gas streams from each burner 30 leave the slot 32, they meet each other and the counter spinning effects increased mixing of the air and fuel, further longitudinal expansion and a substantial decrease in axial velocity of the merging gas streams. The location of the flues 28 at the lateral edges of the roof 24 and at a location intermediate adjacent burners produces a draft for directing the ame and products of combustion upwardly.

Thus, as the gases emerge from each burner 30, a sheet of flame spreads longitudinally and upwardly along the inside surfaces of the side walls 22 to heat the same. Radiant heat is then emitted from the side Walls 22, as well as from the flame, to the stand-s 19 so that direct flame impingement on the inner covers 18 is avoided. In addition, the burners 30 are so located relative to one another that an overlapping of the ame from adjacent burners occurs and the stands 19 are exposed to radiant heat along the entire length of each side wall 22.

In another embodiment of this invention, FIG. 6, the downstream end of the slot 32 is modified. A dynamic bafe is disposed below the level of the slot oor 38 and adjacent to the exit of the slot 32. This dynamic bafile is in the form of an air line 102 having a plurality of longitudinally extending openings 104 formed within the upper portion thereof. The downstream end of the roof 34 has a Coanda turn 106 which comprises a series of straight segments 108. Air is provided under pressure within the-air lines 102 and directed upwardly through the openings 104. As the gases emerge from the slot 32, they are driven upwardly by the dynamic balile 100 and tend to hold fast along the inside surface of the side wall due to the characteristic nature of the Coanda curve 106. Since additional air is supplied by the dynamic bale 100, the air to the

annular plenums

72 and 74 should be reduced accordingly to maintain the proper airfuel ratio.

In the previously described embodiment of this invention, as air entered the

throat castings

64 and 66 through the

tangential air inlets

80 and 82, the Spin imparted to such air was in the same direction as the spin imparted to the air in the

plenums

72 and 74, respectively, by the

helical vanes

84 and 86. By having the spin of the gases the same in each throat casting plenum combination, the mixing of fuel and air is kept low so that the bulk of mixing takes place after the two, counter spinning streams of gases encounter one another as they exit from the slot 32. In this way, a long, wide flame is spread along the inside surface of the side walls 22. In some installations, it may be desirable to have a short ame and to have more combustion taking place within the slot 32. This may be accomplished by having the spin of the air in each throat casting 64 and 66 opposed to the spin of air in its associated

annular plenum

72 and 74 so that a greater amount of mixing of the fuel and air takes place within the

slot entry ports

48 and 50. In addition, the partition 52 that segregates the streams of gases emitted from the

slot entry ports

48 and 50 may be reduced in length, or removed, to effect substantial mixing of fuel and air within the slot 32.

Although only a few embodiments of this invention have been shown and described, changes and modifications can be made therein without departing from the scope of this invention, and it is understood that the preceding descriptions are illustrative only and not for the purpose of rendering this invention limited to the details illustrated or described except insofar as they are limited bythe terms of the following claims.

We claim:

1. A multi-stand annealing furnace including a floor, a plurality of platforms spaced along said floor for supporting a plurality of coils to be annealed, an inner cover positioned over each of said platforms, an elongated, removable outer cover positioned over all of said platforms, said outer cover having a pair of parallel side walls, a plurality of burners located in lower portions of said side walls, said burners being in staggered positions relative to said platforms, with at least two of said burners being directed to tire toward a space between vertical axes of two adjacent platforms, each of said burners comprising refractory wall means forming an elongated, horizontal slot in the sidewall, side portions of said slot being ared outwardly in a direction toward said platforms, means forming a pair of side-by-side slot entry ports located centrally of said slot and on the end of said slot away from the platforms, means forming a pair of cylindrical chambers, each chamber being coaxial with and adjacent to a slot entry port, said chambers having rear Walls, a central fuel tube concentric with each of said chambers and extending into said chambers from said rear walls, means for supplying fuel to each of said fuel tubes, said cylindrical chamber forming means having a pair of diametrically opposed, tangential air inlets for each of said cylindrical chambers adjacent the rear walls thereof and `behind the terminal ends of said fuel tubes, said chamber means also having a plurality of radial air ports for each of said cylindrical chambers near the ends of said fuel tubes, means forming yan annular air passage around each of said cylindrical chambers, a plurality of vanes at the forward end of each of said air passages near the ends of said cylindrical chambers, said vanes of each annular passage being disposed at common angles relative to the longitudinal axes of said annular passages, conduit means communicating with each of said `air passages and disposed generally radially of said chambers for supplying air to said annular passages, and a baie at the other end of said slot forming means for directing the fuel and air upwardly.

2. A multi-stand annealing furnace including a oor, a plurality of platforms spaced along said floor for supporting a plurality of coils to be annealed, an inner cover positioned over each of said platforms, an elongated, removable outer cover positioned over all of said platforms, said outer cover having a pair of parallel side walls, a plurality of burners located in lower portions of said side walls, said burners being in staggered positions relative to said platforms, each of said burners comprising refractory wall means forming an elongated horizontal slot in the side wall, means forming a pair of side-byside, cylindrical slot entry ports located centrally of said slot and on the end of said slot away from the platforms, means forming a pair of cylindrical chambers, each chamber being coaxial with and adjacent to slot entry port, -said chambers having rear walls, a central fuel tube concentric with each of said chambers and extending into said chambers from said rear walls, means for supplying fuel to each of said fuel tubes, said cylindrical chamber forming means having a pair of diametrically opposed, tangential air inlets in each of said cylindrical chambers adjacent the rear wall thereof and Ibehind the terminal end of said fuel tube, means forming an annular air passage around each of said cylindrical chambers, a plurality of vanes at the forward end of each of said air passages near the end of said cylindrical chamber, said vanes being disposed to direct air from one of said passages in a clockwise direction Iand air from the other of said passages in a counterclockwise direction, and conduit means communicating with each of said air passages for supplying air thereto.

3. The furnace of claim 2 wherein said elongated slot has side portions that diverge as they extend toward said platforms and a baille at the downstream end of said slot operative to direct the fuel and air upwardly.

4. A multi-stand annealing furnace including a floor, a plurality of platforms spaced along said floor for supporting coils to be annealed, an inner cover positioned over each of said platforms, an elongated, removable outer cover positioned over all of Said platforms, said outer cover having a pair of parallel side walls, a plurality of burners located in lower portions of said side walls, said burners being in staggered positions relative to said platforms, each of said burners comprising refractory wall means forming an elongated horizontal slot in the side wall, -means forming a pair of slot entry ports located centrally of said slot and on the end of said slot away from the platforms, means forming a pair of fuel chambers, each chamber being coaxial with and adjacent to a slot entry port, said chambers having rear walls, means for supplying fuel into each of said chambers, said fuel chamber forming means having a pair of diametrically opposed, tangential air inlets in each of said cylindrical chambers adjacent the rear wall thereof, means forming an air passage around each of said fuel chambers, a plurality of vanes at the forward end of each of said air passages, and means communicating with each of said air passages for supplying air thereto.

5. A multi-stand annealing furnace including a floor, a plurality of platforms spaced along said floor for supporting a plurality of coils to be annealed, an inner cover positioned over each of said platforms, an elongated, removable outer cover positioned over all of said platforms, said outer cover having a pair of parallel side walls, a plurality of burners located in lower portions of said side walls, said burners being in staggered positions relative to said platforms, each of said burners comprising means forming a pair of side-by-side, cylindrical chambers having rear walls, a central fuel tube concentric with each of said chambers and extending into said chambers from said rear walls, means for supplying fuel to each of said fuel tubes, said cylindrical chamber forming means having a pair of diametrically opposed, tangential air inlets in each of said cylindrical chambers adjacent the rear wall thereof and behind the terminal end of said fuel tube, means forming an annular air passage around each of said cylindrical chambers, a plurality of vanes at the forward end of each of said air passages near the end of said cylindrical chamber, said vanes being disposed to direct air from one of said passages in a clockwise direction and air from the other of said passages in a counterclockwise direction, and conduit means communicating with each of said air passages for supplying air thereto.

6. The furnace of claim wherein at least four of said burners are directed to fire into the space between the vertical axes of two adjacent platforms and each of said cylindrical chambers has a plurality of radial air ports adjacent to the ends of said fuel tubes.

7. In a burner, the combination comprising: wall means having a pair of side walls, a ceiling and a oor defining a slot having open ends; housing means attached to said wall means; a chamber forming member disposed within said housing means and defining a plenum in cooperation with said housing means; said chamber and said plenum communicating with said slot; means for supplying `air to said plenum; means for supplying air tangentially to said chamber; means disposed within said plenum for imparting a spin to air passing therethrough; means for supplying fuel to said chamber; and means disposed at the downstream end of said slot for directing gases upwardly as they exit therefrom.

8. In a burner having a high turndown ratio, the combination comprising: wall means defining a slot having spaced open ends; housing means attached to said wall means at one end of said slot; fuel chamber forming means for promoting flame stability during turned-down fuel-air input said chamber being disposed within said housing means and defining a plenum in conjunction with said housing; said chamber and said plenum Communicating with said slot; means for supplying air to said plenum, means for supplying air to said chamber; means for supplying fuel to said chamber; and means for imparting a spin to air within said plenum.

9. In a burner for distributing a flame along a wall containing said burner, the combination comprising: wall means defining a generally horizontally elongated slot having spaced open ends and `at least two sides which diverge asymmetrically from one another towards one end of said slot; chamber forming means disposed within said housing means and defining a plenum in conjunction with said housing; said chamber and said plenum communicating with said slot; means for supplying air to said plenum, means for supplying air to said chamber; means for supplying fuel to said chamber; and means for imparting a spin to air within said plenum.

10. The combination of claim 8 wherein said burner has means for directing upwardly gases that are emitted from said slot, said directing means being disposed at said end opposite said housing and including a bafiie means outside of said slot.

11. In a burner, the combination comprising: first wall means having a pair of side walls, a ceiling and a floor defining a slot having open ends; second wall means attached to said first wall means at one end of said slot and defining a slot entry port that communicates with said slot; housing means Vattached to said second wall means; a chamber forming member disposed within said housing means and defining a plenum in cooperation with said housing means; said chamber and said plenum communicating with said entry port; means for supplying air to said plenum; means for supplying air tangentially to said chamber; means disposed within said plenum for imparting a spin to air passing therethrough; means for supplying fuel to said chamber; and means disposed at the downstream end of said slot for directing gases upwardly as they exit therefrom.

12. In a burner, the combination comprising: first wall means having a pair of side walls, a ceiling and a fioor defining a slot having open ends; second wall means attached to said first wall means at one end of said slot and defining a pair of parallel, cylindrical slot entry ports that communicate with said slot; said side walls diverging from one another as they extend from said second wall means; housing means attached to said second wall means in alignment with said slot; a pair of chamber forming members disposed within said housing means and defining annular plenums between said housing means and said members, each member being severally aligned axially with one of said slot entry ports; each of said chambers and said plenums communicating severally with one of said slot entry ports; means for supplying air to said plenums; means for supplying air tangentially into said chambers; means for supplying air radially into said charnbers downstream from said tangential means; means disposed within said plenums for imparting a spin to air therein; means for supplying fuel to said chamber; and means disposed at the downstream end of said slot for directing gases upwardly as the same exit therefrom.

13. The burner of claim 12 wherein said means for directing gases upwardly as they exit from said slot comprises an air line having openings at the top thereof, said air line being disposed across the other end of said slot adjacent to said oor, whereby air emitted from said openings imparts an upward direction to gases exiting from said slot; and a Coanda turn formed in said first wall means at the exit end of said ceiling whereby said upwardly directed gases tend to flow adjacent to said first wall means.

14. The burner of claim 12 wherein a partition extends within said slot intermediate said side walls.

15. In a burner, the combination comprising; first wall means having a pair of side walls, a ceiling and a floor defining a slot having open ends; said ceiling curving upwardly at a first end of said slot and said licor having an upwardly extending baffle spaced relative to said curving portion; second wall means attached to said first wall means at the second end of said slot and defining a pair of parallel, cylindrical slot entry ports that communicate with said slot; said side walls diverging from one another as they extend from said sec-ond wall means; a pair of generally cylindrical housing means attached to said second wall means, each housing means being coaxial with a slot entry port; a pair of cylindrical chamber forming members, each disposed within a housing means and spaced relative to the inside surfaces of said housing means to define annular plenums therebetween; each of said chambers and said plenums communicating with one of said slot entry ports; means for supplying air to said plenums; tangential air inlets extending through the walls of said members whereby air fiows into said chambers with a spinning motion; said members having circumferentially spaced openings downstream of said tangential air inlets thereby providing means for air to flow radially from said plenums into said chambers; means for supplying fuel to said chambers; and helical vanes attached to the outside surfaces of said members in circumferentially spaced relationship and extending into said plenums to impart a spin to air moving through said plenums.

16. The burner of claim 15 wherein said tangential air inlets in a first member are directed in an opposite direction from the tangential air inlets in the second member and said helical vanes attached to said first member and extending into said first annular plenum have an opposite pitch to the helical vanes attached to said second member and extending into said second plenum.

17. The burner of claim 16 wherein the tangential air inlets tend to introduce air into said first chamber with a spin in the same direction as said helical vanes attached to said first member tend to spin air moving through said plenums.

18. In a burner, the combination comprising: first wall means defining a slot having open ends; second wall means attached to said rst wall means at one end of said slot and defining a pair of parallel, cylindrical slot entry ports that communicate with said slot; housing means attached to said second wall means in communication with said slot entry ports; means forming a pair of side by side cylindrical chamber members disposed within said housing means and defining a pair of annular plenums therebetween, said Chamber members and said annular members being in axial alignment with and communicating with said slot entry ports; means for supplying air to said plenums; means for supplying fuel t0 said chamber members, each of said chamber members having a pair of diametrically opposed tangential air inlets; .and means within said plenums for directing air from one of said plenums in a clockwise direction and air from the other of said plenums in a counterclockwise direction.

19. The burner of claim 18 wherein said tangential air inlets introduce air into each of said chamber members with a spin that coincides in direction to said directed air in each respective annular plenum.

20. The burner of claim 18 wherein said slot has at its end opposite said second wall means a baille forming 12A means for upwardly directing gases emitted from said slot.

21. The burner of claim 20 wherein said baille forming means comprises a Coanda turn formed at the upward portion of said opposite end and an air line having openings at the top thereof disposed adjacent to the lower portion of said opposite end.

References Cited UNITED STATES PATENTS 1,508,718 9/1924 Peabody 15S-1.5 1,576,537 3/1926 Peabody 15S-1.5 2,283,982 5/1942 Germany 266-5 2,436,024 2/ 1948 Smith 263-43 2,553,130 5/1951 Cadella 15S-1.5 XR 2,658,744 11/1953 Ipsen 263-42 3,042,105 7/ 1962 Bitterlich 158-15 3,049,173 8/1962 Costello et al. 15S-1.5 XR 3,283,802 11/1966 Farnham 15S-1.5

FREDERICK L. MATTESON, JR., Primary Examiner.

A. D. HERRMANN, Assistant Examiner.