CA1065243A - Burner flameholder - Google Patents
Burner flameholderInfo
- Publication number
- CA1065243A CA1065243A CA253,045A CA253045A CA1065243A CA 1065243 A CA1065243 A CA 1065243A CA 253045 A CA253045 A CA 253045A CA 1065243 A CA1065243 A CA 1065243A
- Authority
- CA
- Canada
- Prior art keywords
- apertures
- flameholder
- velocity
- regions
- flame
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
- F23D—BURNERS
- F23D14/00—Burners for combustion of a gas, e.g. of a gas stored under pressure as a liquid
- F23D14/46—Details, e.g. noise reduction means
- F23D14/48—Nozzles
- F23D14/58—Nozzles characterised by the shape or arrangement of the outlet or outlets from the nozzle, e.g. of annular configuration
Abstract
Abstract A burner for air-fuel mixtures, having a flameholder provided with closely spaced apertures and means for forcing an air-fuel mixture under pressure through the apertures of the flameholder, has an improved flameholder characterized by structure which produces, in successive zones of the flameholder, a. progressive inhibiting of the velocity of flow of the air-fuel mixture from the apertures in a waveform differential velocity, which diminishes from a maximum velocity region inter-mediate the zone to minimum velocity regions at either side of it. In consequence, the mixture flowing through each zone at high flow rates and ignited forms a single flame of cor-responding waveform bridging the minimum velocity regions at each side of the zone, highest in the maximum velocity region and lowest in the minimum velocity regions, such wave-form flames being more stable and less noisy than individual flames opposite the individual apertures produced by uniform velocity of flow flameholders of the prior art.
Description
1~65Z43 This invention relates to burners for air-fuel mixtures, and particularly to the flameholders thereof.
In burners of the type concerned, a fuel in the form of gas, vapor or aerosol, substantially uniformly mixed with air, is forced through a flameholder beyond which it ignites and burns.
Such burners can be used for example as the heat source of heat exchangers and various energy conversion systems such as hot water heaters, boilers~ Rankine engine vapor generators, gas turbine engine combustors and other combustion systems where high efficiency, low pollutant emissions and small size are important.
Customarily, the flameholders used have been of the so-called "Meker" burner type comprising a plate with numerous approximately uniformly spaced apertures through which the fuel-air mixture passes to the ignition zone, the apertures usually being smaller than the critical quenching diameter, typically less than 0.065 inch (1.65 mm), to avoid accidental flame propa-gation back through the apertures, thus igniting the mixture upstream of the holder ("flashback"). Although otherwise satisfactory, at high velocities of the air fuel mixture forced through them, these flameholders have poor flame stability (re-sistance to "blow-off"). Also, such flameholders are subject to "hooting", a highly audible sound generated by vibration of the flameholder and driven by the flame. Thus such flameholders are not satisfactory at the high velocities required for use of lean fuel to air mixtures, desirable for low pollutant emission and fuel conservation, and for uses where quiet operation is desired.
The object of the invention is to provide a burner of the type concerned with a flameholder which retains the advan-tages of the Meker but has much greater flame stability at high - 30 fuel-air mixture velocities and is non-hooting,quiet in operation.
It has been discovered that the object of the invention can be achieved by modification of the Meker type flameholder to ~65Z43 change the substantially uniform velocity of flow of the fuel-air mixture therefrom to a waveform differential velocity of flow pattern across successive zones of the flameholder.
More specifically, the flameholder according to the in-vention utilizes closely spaced apertures but has structure which produces, in successive zones of the flameholder, a progressive inhibiting of the velocity of flow of the fuel-air mixture from the apertures in a waveform differential velocity of flow pattern which diminishes from a maximum velocity region intermediate the zone to minimum velocity regions at either side of the zone, so that the mixture flowing through the zone at high flow rates and ~ -ignited forms a single flame of corresponding waveform bridging .. . .
the minimum velocity regions, the flame in each zone being of maximum height in the maximum velocity of flow region and of minimum height in the minimum velocity of flow regions. Gener-ally, the apertures have a smallest dimension less than the criti-cal quenching diameter, although this dimension may be somewhat larger where flow rates of the combustible mixture are controlled -to avoid flashback velocity.
In the Meker type flameholder, at low and moderate vel-ocities of the combustible mixture, individual and distinct flames are anchored opposite each aperture. However, when lift-off flow velocity is reached at which the flames opposite the individual apertures merge and lift off the flameholder, blow-off (flame loss) occurs, since there is nothing to anchor the flame to the flameholder. With the flameholder according to the in-vention, when lift-off velocity is reached between the minimum velocity regions of the zones, the resultant waveform flames in the respective zones are anchored to the flameholder at the minimum flow velocity regions. In consequence, much higher throughputs can be obtained than with the Meker before lift-off - ., :. ~ ~ -. .
velocity is attained at the minimum velocity anchor regions and blow-off will occur. Hooting does not occur, and operation remains quiet at the flow velocities at which the Meker type flameholder is often extremely noisy.
Apparently, the relatively long and stable waveform flames cannot resonate with the flameholder, and so suppress hooting.
To produce the zonal differential flow inhibiting and consequent desired zonal waveform differential velocity of flow pattern, the invention provides in a Meker type flameholder having a plurality of apertures distri-- buted over substantially the entire wall of a thin-plate flame-supporting surface through which a combustible mixture is emitted for combustion at the surface thereof, said apertures comprising rows of apertures in alternating groups to form long wavelength flame regions bridged by intermediate short wavelength flame regions, said flameholder being formed with a corrugated surface, the apertures intermediate the crests thereof defining said long wavelength flame regions and the apertures at the crests thereof forming said short wavelength flame regions.
Desirably, the wavelength, or distance between minima, of the velocity of flow pattern is at least 10 times the minimum aperture dimension, and preferably is 10 to 20 times that dimension. Typically, all apertures have a minimum dimension less than the critical quenching diameter. The flameholder is of a size and shape suitable for the particular purpose for ~ which the burner is used, which may be most usually of circular cross-section, ; either cylindrical or frusto-conical.
~ -3-1~65243 In the accompanying drawings:
Fig. lA is a fragmentary plan view of typical plate used to form the surface of flameholders of the prior art Meker burner;
Fig. lB is a transverse cross-section view on line lB- lB of Fig. l;
Fig. 2 is a velocity vs. length diagram indicating flame wavelength in flameholders according to the invention;
Fig. 3A is a fragmentary plan view of one form of apertured plate that may be used to form the surface of flameholders according to the invention;
Fig. 3B is a cross-section view on line 3B-3B of Fig. 3A, diagrammatically indicating flame pattern;
Fig. 4A is a view similar to Fig. 3A of another form of such plate;
Fig. 4B is a cross-section view on line 4B- 4B of Fig. 4A, diagrammatically indicating flame pattern;
Fig. 5A is a view similar to Figs. 3A and 4A of another form of such plate;
Fig. 5B is a cross-section view on line 5B-5B o:E
Fig. SA, diagrammatically indicating flame pattern;
Fig. 6A is a view similar to Figs. 3A, 4A and 5A of another form of such plate;
Fig. 6B is a cross-section view on line 6B-6B of ; Fig. 6A, diagrammatically indicating flame pattern;
, Fig. 7A is a view similar to Figs. 3A, 4A, 5A and 6A
of another form of apertured material for the same purpose;
Fig. 7B is a cross-section view on line 7B-7B of ~ Fig. 7A, diagrammatically indicating flame pattern; and .. ~.
.', .
1~)6SZ43 Fig. 8 is a transverse cross-section view of a heat exchanger incorporating a flameholder according to the invention. `
Referring to the drawings, Fig. lA illustrates a fragmentary portion of typical plate used in making the flame- :
holders of prior art Meker burners. It will be observed that the metal plate 10 has apertures 12 which are of uniform size ~-and spacing. While plate 10 is shown as flat, it will be understood that it may be curved as in cases where the flame-holder is of circular cross-section. The flame pattern at moderate velocity of the combustible mixture is indicated by the broken line F in Fig. lB with the direction of flow of the fuel-air mixture shown by arrows at the opposite side of the plate. The flame pattern is a series of individual flames opposite and anchored to each aperture. As the velocity of the mixture is increased, these flames will more or less uni-formly lift off and merge and will then blow-off because there - is nothing to anchor them.
Fig. 2 illustrates the varying velocity of flow of the combustible mixture which is produced by the flameholder structure according to the invention. The line V-F, represent-ing variably inhibited velocity with distance in a repeat pattern, also represents the flame waveform pattern at moderate to high flow velocities, which follows rather precisely the velocity variation curve. While at low throughputs an in-dividual flame pattern may occur similar to that of Fig. lB, at moderate to high throughputs the flame lifts off between and bridging each pair of lowest velocity areas, peaking at the central region of maximum velocity and diminishing with reducing velocity toward each side area of lowest velocity.
.
' 1~;5243 Blow-off does not occur until flow rate of the mixture is increased to such extent that the throughput velocity at minimum velocity points reaches blow-off velocity of the relatively small flame anchored there. Since the flow-through velocity at these points is inhibited substantially below the mean flow-through velocity, it becomes possible to establish much higher rates of flow or throughput than with the prior art of Figs. lA and lB,or much fuel-leaner mixtures,before blow-off - will occur.
The wavelength, which as indicated in Fig. 2,corre-sponds to the distance between velocity minima and is a variable depending on such factors as aperture size and spacing. If the wavelength is too short, the full advantages of the invention will not be realized. If the wavelength is too long, the flame may blow-off between its anchored ends. In one preferred structure utilizing apertures of 0.033 inch ( mm) diameter spaced apart slightly more than their diameter, a wavelength of 0.45 inches (11.4 mm) in a uniform pattern has produced very satisfactory results. While a uniform wavelength is preferred it is not essential. Generally, the wavelength should be not ; less than one-half inch (12.7 mm) nor more than two inches (50.8mm).
Figs. 3A and B to 7A and B illustrate various modifi-cations of flameholder structure of the prior art which, together with their effects on aerodynamics, produce the desired velocity differential across the flameholder. In these Figures it should be understood that the flameholder plate may be curved in cross-section rather than straight as in the frag-mentary portions shown.
In Figs. 3A and 3B, these effects are produced in the flameholder-forming plate structure 20 having uniformly sized and spaced apertures 22 as in the prior art, by forming ` 1065243 generally parallel corrugations 24 in the plate spaced peak to - peak at the desired wavelength. As shown in Fig. 3B, the effect of the corrugations is to produce a velocity of flow through the plate which is progressively inhibited from a maximum in the valleys to a minimum at the peaks, with a ` corresponding flame maximum opposite the valleys and minimum opposite the peaks, as indicated by the broken line F. ~;
The reason why this effect is produced may not be ~ fully understood. However, it will be noted that apertures in 10 the opposed sides of successive corrugations 24 direct the combustible mixture somewhat laterally toward the center line between the corrugations which probably has a venturi effect of producing a pressure gradient, with the lowest pressure opposite the center,increasing toward the corrugation peaks.
- The velocity of flow from the flameholder is therefore at maximum centrally of the valleys between corrugations and is progressively relatively inhibited to a minimum at the corrugation peaks.
It will be appreciated that a similar effect could be produced by thickened areas of the plate, thicker at the middle than at their sides, corresponding to corrugations 24 of Figs.
3A and 3B, which could be on the inner or outer side of the ; plate. In such case, greater resistance to flow through : apertures from the sides to the middle of the thickened portions would largely produce the desired velocity of flow differential.
However, such structure is more costly and difficult to fabri-cate.
While the flame is indicated by a line F in Fig. 3B, it should be understood that the effect is substantially uni-formly produced longitudinally of the corrugations, with theresult that at medium to high throughputs a single flame forms ::
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' ~65Z43 .
between each pair of corrugations, bridging their peaks.
Similarly, in Figs. 4B, 5B, 6B and 7B the line F designates a flame which is continuous between and longitudinally of adjacent minimum velocity areas.
In Fig. 4A a like effect is produced by varying the spacing of apertures 26 in flameholder-forming plate structure 28. As shown, the apertures are arranged in rows closely spaced in zones 30 alternating with areas 32 each containing a single row of apertures relatively widely spaced from the zones 30 at either side of it. As will be seen from Fig. 4B, the flow velocity from the plate structure and the flame height of flame F are at minimum centrally of areas 32 and at maximum centrally of zones 30. Evidently, the effects of the aperture spacing variation are closely similar to those of the corruga-tions of the Figs. 3A and 3B embodiment.
Plate structure similar to Fig. 4A but with areas 32 somewhat narrower and without apertures has been tried. It is operative to produce a similar velocity of flow gradient across the zones 30 and individual corresponding flames like those of Fig. 4B coextensive with zones 30 but not joined across areas 32. However, these flames are not as resistant to blow-off as the flames produced by the aperture pattern of Fig. 4A. Ap-parently, the flames opposite the apertures in zones 32 have a substantial stabilizing effect on the flames opposite zones 30 and it is therefore preferred to provide such apertures. More than one row of apertures 26 could be provided in areas 32 but such is not needed. -Figs. 5A and 5B show a flameholder-forming plate structure 34 similar to plate structure 28 of Fig. 4A except that zones 36, corresponding to zones 30 of Fig. 4A, are provided with slots 38 extending the width of these zones; the ~065243 slots of successive zones 36 being arranged in herringbone fashion, and spaced apart slightly more than apertures 26 in zones 30 of Fig. 4A. The areas 40 between zones 36 correspond to areas 32 of Fig. 4A in that they are provided with a row of round apertures 42 spaced between the sides of the con-tiguous zones 36. The velocity of flow and flame patterns as shown in Fig. 5B are closely similar to those of Fig. 4B.
However, the slots, by providing greater frictional resistance . . .
~` to flow toward their ends, assist in providing the desired velocity of flow differential, and the slot structure permits more open area as may be desirable.
Figs. 6A and B show a flameholder-forming plate struc-; ture 44 of metal with relatively large and closely spaced aper-tures 45. Such a structure may be used to advantage where the apertures need not have a dimension less than the critical quenching diameter because flashback is prevented by other means, such as flow rate control. In accordance with the present in-vention, structure 44 is modified by attaching as by welding to a surface thereof, as shown the outflow surface, baffle strips 48 provided with apertures 50 considerably smaller than apertures 46, strips 48 being provided at substantially uniform spacing across the flameholder surface formed from structure 44 and spaced therefrom to permit lateral flow thereunder.
Baffle strips 48 serve the inhibit flow from the plate in the areas which they occupy. As can be seen from Fig. 6B, the velocity and flame patterns resultant from the baffles are very similar to those of preceding Figures, except that the two rows of apertures 50 shown provide two spaced minimum velocity areas with corresponding minimum height flames, these serving to anchor intervening large flame which has a profile of increasing height from ends to mid-portion.
~' . .
g 1~5z~3 Figs. 7A and B show flameholder-forming plate structure 52 of honeycomb formation formed of metal with apertures 54 and a thickness several times that of the structures shown in the previous Figures. Such honeycomb structure, which may also be made of ceramic material, makes an excellent flameholder, but because of its very poor flame stability its use has been con-fined to relatively low flow velocity, fuel-rich mixtures. The flame stability which this invention produces greatly increases the potential for use of this structure in flameholders.
As in Figs. 6A and 6B, the desired waveform velocity of flow and flame pattern is obtained by securing to a face of ~-the structure 52, the outflow face as shown, appropriately spaced baffle strips 56, having therein apertures 58 smaller than the honeycomb apertures 54, in this case only one row of such aper-tures being provided. Because of the flow-velocity-inhibiting effect of the baffle strips, a similar velocity and flame pattern ., :
results as in Fig. 6B, except for the single flame in the mini-mum velocity regions of the baffle strips, which are spaced across the flameholder surface as in Figs. 6A and 6B.
In all the foregoing figures illustrative of the inven-tion, the lowest velocity areas can be spaced in any direction over the surface of the flameholder;--i.e., vertically, horizon-tally or at an angle between vertical and horizontal. Where the flameholder is of frusto-conical shape, the arrangement is such as to allow for diminishing diameter while maintaining a fairly constant distance between the low velocity areas.
Fig. 8 shows a heat exchanger for converting water to steam, utilizing a burner with a flameholder according to the invention. As shown, the heat exchanger has an insulated housing 60 having at one end an exhaust outlet 61 connected to an - , - . ,.
. :
1~65243 exhaust stack (not shown). The housing may be disposed in any convenient position but for purposes of discussion will be deemed disposed as shown in the Figure, with outlet 61 at its upper end.
A stack of five coaxially wound, frusto-conical conduit coils 62a to 62e is supported in the upper part of the housing, and two additional such coils 62f and 62g are supported in the ; lower part of the housing. The coils 62a-62e are finned as indicated. Water is admitted to the lower end of coil 62a, after which the flow by connections indicated in the Figure, is through coil 62a to coil 62b at the top, through coil 62b to coil 62c at the bottom, through coil 62c to coil 62g at the top, through coil 62g to coil 62d at the bottom, through coil 62d to coil 62e at the top, through coil 62e to coil 62f at the bottom and through coil 62f to the steam outlet pipe 62h at its top.
A tubular duct 64 mounted in the upper end of the hous-ing has its upper end exposed through the housing to receive external air, and is also provided with ports 66 for receiving hot combustion products internally of the housing. An outer base portion 68 of the housing is bolted to a support ring 70 of the housing which supports the coiled tubing. Base portion 68 supports an extension 72 of duct 64, romovably fitting therewith.
A fuel ejector nozzle 74 is supported in the lower part of ex-tension 72 on,its three supply pipes 76 (two shown) which extend to a suitable source (not shown) of fuel under pressure. A
blower 78 immediately below nozzle 74 provided with vanes 80, is attached to a shaft 82 extending rotatably through a bearing 84 mounted on a removable plate 86 in base portion 68. Shaft 82 is adapted to be connected to a suitable mo~or (not shown) for rotating it and blower 78.
A throttle valve 88 provided with adjustable hinged shutters is mounted in stack 64, 72, as indicated by dash lines , --1~165243 Fig. 8, for adjustably confining the air flow toward the axis of the stack and nozzle 74. An external adjustment device (not ; shown), such as a rack and pinion, may be provided for operating the shutters of the valve. Air drawn into the open end of duct 64, 72 by the suction of blower blades 80 is mixed with heated combustion products from ports 66 to attain a temperature of the order of 300F. to 500F. (depending on fuel type) before it reaches nozzle 74, which charges the air with liquid or gaseous fuel. The air is then thoroughly intermixed with the fuel as it is driven by blades 80 of blower 74 under and about a fixed baffle member 90 supported on duct 64, 72 and between fixed dividers 92 which act to suppress the turbulence.
A flameholder 94 of frusto-conical shape has its large end supported on the housing and its small end secured to duct 64, 72. The flameholder may have any of the waveform velocity and flame producing structures of the invention, such as those previously described. The air-fuel mixture passes through a flow straightener 96 mounted in housing 60, which may be a honey-comb structure such as used in making flameholders according to Figs. 7A and 7B, and which acts further to suppress turbulence in the flow and direct it generally axially oE the flameholder.
The combustible mixture passes outwardly through the flameholder beyond which it ignites to form the flame pattern such as shown - in Figs. 3B to 7B (initial ignition may be by a suitable igniter such as a spark plug not shown). The heated air with products of combustion flows successively through heat exchange coils 62g to 62a to exhaust port 61 through duct space provided in housing 60 around the inlet to duct 64, 72.
: ':
..
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1~65Z43 It will be understood that Fig. 8 is illustrative of but one of the various advantageous uses of flameholders according to the invention.
~.
In burners of the type concerned, a fuel in the form of gas, vapor or aerosol, substantially uniformly mixed with air, is forced through a flameholder beyond which it ignites and burns.
Such burners can be used for example as the heat source of heat exchangers and various energy conversion systems such as hot water heaters, boilers~ Rankine engine vapor generators, gas turbine engine combustors and other combustion systems where high efficiency, low pollutant emissions and small size are important.
Customarily, the flameholders used have been of the so-called "Meker" burner type comprising a plate with numerous approximately uniformly spaced apertures through which the fuel-air mixture passes to the ignition zone, the apertures usually being smaller than the critical quenching diameter, typically less than 0.065 inch (1.65 mm), to avoid accidental flame propa-gation back through the apertures, thus igniting the mixture upstream of the holder ("flashback"). Although otherwise satisfactory, at high velocities of the air fuel mixture forced through them, these flameholders have poor flame stability (re-sistance to "blow-off"). Also, such flameholders are subject to "hooting", a highly audible sound generated by vibration of the flameholder and driven by the flame. Thus such flameholders are not satisfactory at the high velocities required for use of lean fuel to air mixtures, desirable for low pollutant emission and fuel conservation, and for uses where quiet operation is desired.
The object of the invention is to provide a burner of the type concerned with a flameholder which retains the advan-tages of the Meker but has much greater flame stability at high - 30 fuel-air mixture velocities and is non-hooting,quiet in operation.
It has been discovered that the object of the invention can be achieved by modification of the Meker type flameholder to ~65Z43 change the substantially uniform velocity of flow of the fuel-air mixture therefrom to a waveform differential velocity of flow pattern across successive zones of the flameholder.
More specifically, the flameholder according to the in-vention utilizes closely spaced apertures but has structure which produces, in successive zones of the flameholder, a progressive inhibiting of the velocity of flow of the fuel-air mixture from the apertures in a waveform differential velocity of flow pattern which diminishes from a maximum velocity region intermediate the zone to minimum velocity regions at either side of the zone, so that the mixture flowing through the zone at high flow rates and ~ -ignited forms a single flame of corresponding waveform bridging .. . .
the minimum velocity regions, the flame in each zone being of maximum height in the maximum velocity of flow region and of minimum height in the minimum velocity of flow regions. Gener-ally, the apertures have a smallest dimension less than the criti-cal quenching diameter, although this dimension may be somewhat larger where flow rates of the combustible mixture are controlled -to avoid flashback velocity.
In the Meker type flameholder, at low and moderate vel-ocities of the combustible mixture, individual and distinct flames are anchored opposite each aperture. However, when lift-off flow velocity is reached at which the flames opposite the individual apertures merge and lift off the flameholder, blow-off (flame loss) occurs, since there is nothing to anchor the flame to the flameholder. With the flameholder according to the in-vention, when lift-off velocity is reached between the minimum velocity regions of the zones, the resultant waveform flames in the respective zones are anchored to the flameholder at the minimum flow velocity regions. In consequence, much higher throughputs can be obtained than with the Meker before lift-off - ., :. ~ ~ -. .
velocity is attained at the minimum velocity anchor regions and blow-off will occur. Hooting does not occur, and operation remains quiet at the flow velocities at which the Meker type flameholder is often extremely noisy.
Apparently, the relatively long and stable waveform flames cannot resonate with the flameholder, and so suppress hooting.
To produce the zonal differential flow inhibiting and consequent desired zonal waveform differential velocity of flow pattern, the invention provides in a Meker type flameholder having a plurality of apertures distri-- buted over substantially the entire wall of a thin-plate flame-supporting surface through which a combustible mixture is emitted for combustion at the surface thereof, said apertures comprising rows of apertures in alternating groups to form long wavelength flame regions bridged by intermediate short wavelength flame regions, said flameholder being formed with a corrugated surface, the apertures intermediate the crests thereof defining said long wavelength flame regions and the apertures at the crests thereof forming said short wavelength flame regions.
Desirably, the wavelength, or distance between minima, of the velocity of flow pattern is at least 10 times the minimum aperture dimension, and preferably is 10 to 20 times that dimension. Typically, all apertures have a minimum dimension less than the critical quenching diameter. The flameholder is of a size and shape suitable for the particular purpose for ~ which the burner is used, which may be most usually of circular cross-section, ; either cylindrical or frusto-conical.
~ -3-1~65243 In the accompanying drawings:
Fig. lA is a fragmentary plan view of typical plate used to form the surface of flameholders of the prior art Meker burner;
Fig. lB is a transverse cross-section view on line lB- lB of Fig. l;
Fig. 2 is a velocity vs. length diagram indicating flame wavelength in flameholders according to the invention;
Fig. 3A is a fragmentary plan view of one form of apertured plate that may be used to form the surface of flameholders according to the invention;
Fig. 3B is a cross-section view on line 3B-3B of Fig. 3A, diagrammatically indicating flame pattern;
Fig. 4A is a view similar to Fig. 3A of another form of such plate;
Fig. 4B is a cross-section view on line 4B- 4B of Fig. 4A, diagrammatically indicating flame pattern;
Fig. 5A is a view similar to Figs. 3A and 4A of another form of such plate;
Fig. 5B is a cross-section view on line 5B-5B o:E
Fig. SA, diagrammatically indicating flame pattern;
Fig. 6A is a view similar to Figs. 3A, 4A and 5A of another form of such plate;
Fig. 6B is a cross-section view on line 6B-6B of ; Fig. 6A, diagrammatically indicating flame pattern;
, Fig. 7A is a view similar to Figs. 3A, 4A, 5A and 6A
of another form of apertured material for the same purpose;
Fig. 7B is a cross-section view on line 7B-7B of ~ Fig. 7A, diagrammatically indicating flame pattern; and .. ~.
.', .
1~)6SZ43 Fig. 8 is a transverse cross-section view of a heat exchanger incorporating a flameholder according to the invention. `
Referring to the drawings, Fig. lA illustrates a fragmentary portion of typical plate used in making the flame- :
holders of prior art Meker burners. It will be observed that the metal plate 10 has apertures 12 which are of uniform size ~-and spacing. While plate 10 is shown as flat, it will be understood that it may be curved as in cases where the flame-holder is of circular cross-section. The flame pattern at moderate velocity of the combustible mixture is indicated by the broken line F in Fig. lB with the direction of flow of the fuel-air mixture shown by arrows at the opposite side of the plate. The flame pattern is a series of individual flames opposite and anchored to each aperture. As the velocity of the mixture is increased, these flames will more or less uni-formly lift off and merge and will then blow-off because there - is nothing to anchor them.
Fig. 2 illustrates the varying velocity of flow of the combustible mixture which is produced by the flameholder structure according to the invention. The line V-F, represent-ing variably inhibited velocity with distance in a repeat pattern, also represents the flame waveform pattern at moderate to high flow velocities, which follows rather precisely the velocity variation curve. While at low throughputs an in-dividual flame pattern may occur similar to that of Fig. lB, at moderate to high throughputs the flame lifts off between and bridging each pair of lowest velocity areas, peaking at the central region of maximum velocity and diminishing with reducing velocity toward each side area of lowest velocity.
.
' 1~;5243 Blow-off does not occur until flow rate of the mixture is increased to such extent that the throughput velocity at minimum velocity points reaches blow-off velocity of the relatively small flame anchored there. Since the flow-through velocity at these points is inhibited substantially below the mean flow-through velocity, it becomes possible to establish much higher rates of flow or throughput than with the prior art of Figs. lA and lB,or much fuel-leaner mixtures,before blow-off - will occur.
The wavelength, which as indicated in Fig. 2,corre-sponds to the distance between velocity minima and is a variable depending on such factors as aperture size and spacing. If the wavelength is too short, the full advantages of the invention will not be realized. If the wavelength is too long, the flame may blow-off between its anchored ends. In one preferred structure utilizing apertures of 0.033 inch ( mm) diameter spaced apart slightly more than their diameter, a wavelength of 0.45 inches (11.4 mm) in a uniform pattern has produced very satisfactory results. While a uniform wavelength is preferred it is not essential. Generally, the wavelength should be not ; less than one-half inch (12.7 mm) nor more than two inches (50.8mm).
Figs. 3A and B to 7A and B illustrate various modifi-cations of flameholder structure of the prior art which, together with their effects on aerodynamics, produce the desired velocity differential across the flameholder. In these Figures it should be understood that the flameholder plate may be curved in cross-section rather than straight as in the frag-mentary portions shown.
In Figs. 3A and 3B, these effects are produced in the flameholder-forming plate structure 20 having uniformly sized and spaced apertures 22 as in the prior art, by forming ` 1065243 generally parallel corrugations 24 in the plate spaced peak to - peak at the desired wavelength. As shown in Fig. 3B, the effect of the corrugations is to produce a velocity of flow through the plate which is progressively inhibited from a maximum in the valleys to a minimum at the peaks, with a ` corresponding flame maximum opposite the valleys and minimum opposite the peaks, as indicated by the broken line F. ~;
The reason why this effect is produced may not be ~ fully understood. However, it will be noted that apertures in 10 the opposed sides of successive corrugations 24 direct the combustible mixture somewhat laterally toward the center line between the corrugations which probably has a venturi effect of producing a pressure gradient, with the lowest pressure opposite the center,increasing toward the corrugation peaks.
- The velocity of flow from the flameholder is therefore at maximum centrally of the valleys between corrugations and is progressively relatively inhibited to a minimum at the corrugation peaks.
It will be appreciated that a similar effect could be produced by thickened areas of the plate, thicker at the middle than at their sides, corresponding to corrugations 24 of Figs.
3A and 3B, which could be on the inner or outer side of the ; plate. In such case, greater resistance to flow through : apertures from the sides to the middle of the thickened portions would largely produce the desired velocity of flow differential.
However, such structure is more costly and difficult to fabri-cate.
While the flame is indicated by a line F in Fig. 3B, it should be understood that the effect is substantially uni-formly produced longitudinally of the corrugations, with theresult that at medium to high throughputs a single flame forms ::
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' ~65Z43 .
between each pair of corrugations, bridging their peaks.
Similarly, in Figs. 4B, 5B, 6B and 7B the line F designates a flame which is continuous between and longitudinally of adjacent minimum velocity areas.
In Fig. 4A a like effect is produced by varying the spacing of apertures 26 in flameholder-forming plate structure 28. As shown, the apertures are arranged in rows closely spaced in zones 30 alternating with areas 32 each containing a single row of apertures relatively widely spaced from the zones 30 at either side of it. As will be seen from Fig. 4B, the flow velocity from the plate structure and the flame height of flame F are at minimum centrally of areas 32 and at maximum centrally of zones 30. Evidently, the effects of the aperture spacing variation are closely similar to those of the corruga-tions of the Figs. 3A and 3B embodiment.
Plate structure similar to Fig. 4A but with areas 32 somewhat narrower and without apertures has been tried. It is operative to produce a similar velocity of flow gradient across the zones 30 and individual corresponding flames like those of Fig. 4B coextensive with zones 30 but not joined across areas 32. However, these flames are not as resistant to blow-off as the flames produced by the aperture pattern of Fig. 4A. Ap-parently, the flames opposite the apertures in zones 32 have a substantial stabilizing effect on the flames opposite zones 30 and it is therefore preferred to provide such apertures. More than one row of apertures 26 could be provided in areas 32 but such is not needed. -Figs. 5A and 5B show a flameholder-forming plate structure 34 similar to plate structure 28 of Fig. 4A except that zones 36, corresponding to zones 30 of Fig. 4A, are provided with slots 38 extending the width of these zones; the ~065243 slots of successive zones 36 being arranged in herringbone fashion, and spaced apart slightly more than apertures 26 in zones 30 of Fig. 4A. The areas 40 between zones 36 correspond to areas 32 of Fig. 4A in that they are provided with a row of round apertures 42 spaced between the sides of the con-tiguous zones 36. The velocity of flow and flame patterns as shown in Fig. 5B are closely similar to those of Fig. 4B.
However, the slots, by providing greater frictional resistance . . .
~` to flow toward their ends, assist in providing the desired velocity of flow differential, and the slot structure permits more open area as may be desirable.
Figs. 6A and B show a flameholder-forming plate struc-; ture 44 of metal with relatively large and closely spaced aper-tures 45. Such a structure may be used to advantage where the apertures need not have a dimension less than the critical quenching diameter because flashback is prevented by other means, such as flow rate control. In accordance with the present in-vention, structure 44 is modified by attaching as by welding to a surface thereof, as shown the outflow surface, baffle strips 48 provided with apertures 50 considerably smaller than apertures 46, strips 48 being provided at substantially uniform spacing across the flameholder surface formed from structure 44 and spaced therefrom to permit lateral flow thereunder.
Baffle strips 48 serve the inhibit flow from the plate in the areas which they occupy. As can be seen from Fig. 6B, the velocity and flame patterns resultant from the baffles are very similar to those of preceding Figures, except that the two rows of apertures 50 shown provide two spaced minimum velocity areas with corresponding minimum height flames, these serving to anchor intervening large flame which has a profile of increasing height from ends to mid-portion.
~' . .
g 1~5z~3 Figs. 7A and B show flameholder-forming plate structure 52 of honeycomb formation formed of metal with apertures 54 and a thickness several times that of the structures shown in the previous Figures. Such honeycomb structure, which may also be made of ceramic material, makes an excellent flameholder, but because of its very poor flame stability its use has been con-fined to relatively low flow velocity, fuel-rich mixtures. The flame stability which this invention produces greatly increases the potential for use of this structure in flameholders.
As in Figs. 6A and 6B, the desired waveform velocity of flow and flame pattern is obtained by securing to a face of ~-the structure 52, the outflow face as shown, appropriately spaced baffle strips 56, having therein apertures 58 smaller than the honeycomb apertures 54, in this case only one row of such aper-tures being provided. Because of the flow-velocity-inhibiting effect of the baffle strips, a similar velocity and flame pattern ., :
results as in Fig. 6B, except for the single flame in the mini-mum velocity regions of the baffle strips, which are spaced across the flameholder surface as in Figs. 6A and 6B.
In all the foregoing figures illustrative of the inven-tion, the lowest velocity areas can be spaced in any direction over the surface of the flameholder;--i.e., vertically, horizon-tally or at an angle between vertical and horizontal. Where the flameholder is of frusto-conical shape, the arrangement is such as to allow for diminishing diameter while maintaining a fairly constant distance between the low velocity areas.
Fig. 8 shows a heat exchanger for converting water to steam, utilizing a burner with a flameholder according to the invention. As shown, the heat exchanger has an insulated housing 60 having at one end an exhaust outlet 61 connected to an - , - . ,.
. :
1~65243 exhaust stack (not shown). The housing may be disposed in any convenient position but for purposes of discussion will be deemed disposed as shown in the Figure, with outlet 61 at its upper end.
A stack of five coaxially wound, frusto-conical conduit coils 62a to 62e is supported in the upper part of the housing, and two additional such coils 62f and 62g are supported in the ; lower part of the housing. The coils 62a-62e are finned as indicated. Water is admitted to the lower end of coil 62a, after which the flow by connections indicated in the Figure, is through coil 62a to coil 62b at the top, through coil 62b to coil 62c at the bottom, through coil 62c to coil 62g at the top, through coil 62g to coil 62d at the bottom, through coil 62d to coil 62e at the top, through coil 62e to coil 62f at the bottom and through coil 62f to the steam outlet pipe 62h at its top.
A tubular duct 64 mounted in the upper end of the hous-ing has its upper end exposed through the housing to receive external air, and is also provided with ports 66 for receiving hot combustion products internally of the housing. An outer base portion 68 of the housing is bolted to a support ring 70 of the housing which supports the coiled tubing. Base portion 68 supports an extension 72 of duct 64, romovably fitting therewith.
A fuel ejector nozzle 74 is supported in the lower part of ex-tension 72 on,its three supply pipes 76 (two shown) which extend to a suitable source (not shown) of fuel under pressure. A
blower 78 immediately below nozzle 74 provided with vanes 80, is attached to a shaft 82 extending rotatably through a bearing 84 mounted on a removable plate 86 in base portion 68. Shaft 82 is adapted to be connected to a suitable mo~or (not shown) for rotating it and blower 78.
A throttle valve 88 provided with adjustable hinged shutters is mounted in stack 64, 72, as indicated by dash lines , --1~165243 Fig. 8, for adjustably confining the air flow toward the axis of the stack and nozzle 74. An external adjustment device (not ; shown), such as a rack and pinion, may be provided for operating the shutters of the valve. Air drawn into the open end of duct 64, 72 by the suction of blower blades 80 is mixed with heated combustion products from ports 66 to attain a temperature of the order of 300F. to 500F. (depending on fuel type) before it reaches nozzle 74, which charges the air with liquid or gaseous fuel. The air is then thoroughly intermixed with the fuel as it is driven by blades 80 of blower 74 under and about a fixed baffle member 90 supported on duct 64, 72 and between fixed dividers 92 which act to suppress the turbulence.
A flameholder 94 of frusto-conical shape has its large end supported on the housing and its small end secured to duct 64, 72. The flameholder may have any of the waveform velocity and flame producing structures of the invention, such as those previously described. The air-fuel mixture passes through a flow straightener 96 mounted in housing 60, which may be a honey-comb structure such as used in making flameholders according to Figs. 7A and 7B, and which acts further to suppress turbulence in the flow and direct it generally axially oE the flameholder.
The combustible mixture passes outwardly through the flameholder beyond which it ignites to form the flame pattern such as shown - in Figs. 3B to 7B (initial ignition may be by a suitable igniter such as a spark plug not shown). The heated air with products of combustion flows successively through heat exchange coils 62g to 62a to exhaust port 61 through duct space provided in housing 60 around the inlet to duct 64, 72.
: ':
..
'~.
1~65Z43 It will be understood that Fig. 8 is illustrative of but one of the various advantageous uses of flameholders according to the invention.
~.
Claims (10)
PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. In a Meker type flameholder having a plurality of apertures distributed over substantially the entire wall of a thin-plate flame-supporting surface through which a combustible mixture is emitted for com-bustion at the surface thereof, said apertures comprising rows of apertures in alternating groups to form long wavelength flame regions bridged by intermediate short wavelength flame regions, said flameholder being formed with a corrugated surface, the apertures intermediate the crests thereof defining said long wavelength flame regions and the apertures at the crests thereof forming said short wavelength flame regions.
2. A flameholder according to claim 1 wherein the wavelength of said long wavelength flames is at least 10 times the minimum dimension of said apertures.
3. A flameholder according to claim 1 wherein the wavelength of said long wavelength flames is between 10 and 20 times the minimum dimension of said apertures.
4. A flameholder according to any of claims 1 and 3 wherein the minimum dimension of said apertures is less than 1.65 mm.
5. A flameholder according to claim 1 wherein said apertures are of substantially uniform size and spacing along the surface of said flameholder, and said corrugations provide an effective non-uniform distribution of apertures therefor.
6. A flameholder according to claim 1 wherein a substantially lower percentage of open area is provided by the apertures in said long wavelength flame regions than by the apertures in said short wavelength flame regions.
7. A flameholder according to claim 6 wherein said apertures are arranged in rows longitudinally of said regions, and a row thereof at each side of the region is spaced from the contiguous row of the region a distance substantially greater than the spacing between the remainder of the rows of the region.
8. A flameholder according to claim 6 wherein said short wavelength regions include apertures having substantially smaller cross-sectional areas than the apertures in the long wavelength region.
9. A flameholder according to claim 1 which includes baffles restricting flow velocity from apertures in the short wavelength flame regions.
10. A flameholder according to claim 9 of honeycomb structure.
Priority Applications (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA253,045A CA1065243A (en) | 1976-05-21 | 1976-05-21 | Burner flameholder |
| JP5928677A JPS52156426A (en) | 1976-05-21 | 1977-05-21 | Combustion device |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA253,045A CA1065243A (en) | 1976-05-21 | 1976-05-21 | Burner flameholder |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1065243A true CA1065243A (en) | 1979-10-30 |
Family
ID=4106015
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA253,045A Expired CA1065243A (en) | 1976-05-21 | 1976-05-21 | Burner flameholder |
Country Status (2)
| Country | Link |
|---|---|
| JP (1) | JPS52156426A (en) |
| CA (1) | CA1065243A (en) |
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4397631A (en) * | 1980-09-08 | 1983-08-09 | The Carlin Company | Pre-mix forced draft power gas burner |
| US5368476A (en) * | 1991-07-05 | 1994-11-29 | Tokyo Gas Company Ltd. | Low-NOx gas burner |
| US5490778A (en) * | 1990-04-12 | 1996-02-13 | Dru B.V. | Burner |
| WO2015196504A1 (en) * | 2014-06-27 | 2015-12-30 | 艾欧史密斯(中国)热水器有限公司 | Pre-mix gas burner |
Families Citing this family (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS58175335U (en) * | 1982-05-17 | 1983-11-24 | 株式会社ハ−マン | High load combustion burner |
| JPH01101030U (en) * | 1987-12-26 | 1989-07-06 | ||
| JPH01310217A (en) * | 1988-06-09 | 1989-12-14 | Rinnai Corp | Combustion plate |
| JPH0457020U (en) * | 1990-09-04 | 1992-05-15 | ||
| JP5191964B2 (en) * | 2009-07-16 | 2013-05-08 | リンナイ株式会社 | Burner equipment |
-
1976
- 1976-05-21 CA CA253,045A patent/CA1065243A/en not_active Expired
-
1977
- 1977-05-21 JP JP5928677A patent/JPS52156426A/en active Pending
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4397631A (en) * | 1980-09-08 | 1983-08-09 | The Carlin Company | Pre-mix forced draft power gas burner |
| US5490778A (en) * | 1990-04-12 | 1996-02-13 | Dru B.V. | Burner |
| US5368476A (en) * | 1991-07-05 | 1994-11-29 | Tokyo Gas Company Ltd. | Low-NOx gas burner |
| WO2015196504A1 (en) * | 2014-06-27 | 2015-12-30 | 艾欧史密斯(中国)热水器有限公司 | Pre-mix gas burner |
Also Published As
| Publication number | Publication date |
|---|---|
| JPS52156426A (en) | 1977-12-26 |
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