US3414362A

US3414362A - Burner for firing a combustion chamber

Info

Publication number: US3414362A
Application number: US630580A
Authority: US
Inventors: Schoppe Fritz
Original assignee: F SCHOPPE DR ING
Current assignee: Dr-Ing F Schoppe; F SCHOPPE DR ING
Priority date: 1966-04-15
Filing date: 1967-04-13
Publication date: 1968-12-03
Anticipated expiration: 1985-12-03

Description

Dec. 3, 1968 F. SCHOPPE BURNER FOR FIRING A COMBUSTION CHAMBER 3 Sheets-Sheet, 1

Filed April 13, 1967 INVENTOR.

FR/TZ SCHOPPE' JWWMfM/dug ATTORNEYS Dec. 3, 1968 F. SCHOPPE FOR FIRING A COMBUSTION CHAMBER BURNER 3 Sheets-Sheet 2 Filed April 13, 1967 INVENTOR.

FRITZ .S'CHOPPE ATTORNEYS Dec. 3, 1968 F. SCHOPPE 3,414,362

BURNER FOR FIRING A COMBUSTION CHAMBER Filed April 13, 1967 3 Sheets-Sheet 3 IN V EN TOR.

F R/ 7' Z SCHOPPE JMVMMWMW ATTORNEYS United States Patent 18 Claims. (31. 431 5s ABSTRACT OF THE DISCLOSURE A burner for firing a combustion chamber having a flame tube which widens conically in the direction of the main flow of the throughput flow, to which the fuel can be fed in through a central injection port at the intake end of the flame tube, where the combustion air also is fed in partly via a twisting device with predominantly radially directed guide vanes and also partly through the injection port, and with an accelerating nozzle connected with the outlet end of the flame tube for the production of a flame gas jet whose velocity at the outlet end of the accelerating nozzle has a dynamic pressure value amounting to 510 times the pressure in the combustion chamber acting on the flame gas jet (this latter pressure is the result of buoyancy per unit area exerted on the flame jet by gases within the combustion chamber). The twisting device and the dimensions of the flame tube are designed to provide a negative pressure formed in the center of the intake end of the flame tube whose numerical value is at least to 20 times greater than the average stagnation pressure of the throughput flow measured at the half length of the flame tube at the site of the highest velocity of the velocity profile at that location.

Background of the invention A burner of the type to which this invention pertains is the subject of applicants copending application Ser. No. 630,581, filed Apr. 13, 1967, and is characterized in that it is capable of generating a flame gas jet of an extremely high velocity with high stability of the flow pattern in the burner. The pressure conditions are independent of the size of the burner. Dimensions determined as correct for one output, upon transition to another output are changed in proportion to the root of the throughputs corresponding to the output. This is so, because the flow in the burner is independent of the Reynolds number. For this reason, such a burner can also be designed for relatively small outputs, such as are customary for firing of central heating boilers for example. It has been found, however, that such burners develop exhaust gases at low outputs which result in substantially deviation from the ideal soot curve.

By the soot curve is understood the plotting of the soot content according to Bacharach for the CO content of the exhaust gases. While a theoretically ideal burner produces a soot-free exhaust gas at all CO contents below the stoichiometric limit, practically designed burners show an increasing soot content on approaching this limit. The CO content at which the soot content exceeds certain limit values (the so-called soot limit) is a measure of the excess air needed for the combustion and also of the efficiency of the mixing of air and fuel. The boundary layer influence that is present especially in small burners and manufacturing inaccuracies are plainly represented by the soot curve, the latter giving the specialist an unequivocal measure of the extent and kind of the mixing error. The smaller the burner is, the more important are the measures for improving the soot curve according to the invention as described hereinafter.

Patented Dec. 3, 1968 Accordingly, deviations from the ideal soot curve mean that the burner has more soot in the exhaust gas than should be necessary under consideration of the type of fuel and the actual air conditions.

Summary of the invention A primary object of the invention is to provide a further development of the inventive 'bumer of the other application to the effect that it will produce a soot curve closely approximating the ideal soot curve in the layout for smaller combustion outputs suitable for the heating of central heating boilers and the like. This is achieved according to the invention in that an equalizing device for the distribution of the air over the periphery of the twisting device and for the equalization of the flow is provided in the path of the combustion air upstream from the intake, that this intake to the twisting device and the injection port originates in a common chamber free from combustion and that a baffle, shutter or deflector is arranged at the outlet end of the flame tube to disrupt the boundary layer.

As practical experiments have shown, the soot curve for burners according to the invention deviates only very little from the ideal soot curve. The burner also assures optimal combustion at small outputs. This is to be attributed to the following influences:

In a burner of the present kind, the combustion air flows with a twist from the intake end to the outlet end of the tube. Thereby a pressure drop is produced at the burner axis from the outlet to the intake end due to the reduction of the tangential component of the spiral flow caused by the conical widening of the flame tube and the resultant reduction of the centrifugal forces acting on the combustion air. A part of the combustion air at the outlet end of the burner flame tube thereupon tumbles over inward and flows back along the burner axis. The rest of the combustion air arrives in the accelerating nozzle. A zone of intense turbulence within the flame tube develops between the inner zone of return flow and the other zone of spiral flow that moves forward, in which turbulence zone the combustion air is mixed with the fuel.

In the burner according to the invention, the equalizing device ensures a uniform entry of the combustion air over the periphery of the flame tube. Thereby a symmetrical flow in rotation is obtained, which leads to a uniformly intensive turbulence, so that the mixing likewise takes place to a uniform degree in the entire turbulence zone. In small output burners, manufacturing tolerance in the fuel injection system can have the effect that injection will be temporarily wispy or asymmetrical. The danger arising therefrom of a throwing out of fuel particles by the rotating flow is offset by the burner according to the invention in that combustion air enters through the injection port together with the fuel, which combustion air is under the same static pressure as the air entering through the twisting device. This air flow prevents a throwing out of fuel particles in the area of the intake system. Finally, with small burner sizes, boundary flow along the inner wall of the tube can no longer be ignored. Inasmuch as it cannot enter directly into the combustion process, surplus air can become greater than desired. As to the boundary flow problem, the invention brings relief through the arrangement of a bafile just before the accelerating nozzle at the outlet end of the flame tube. The baflle causes the boundary layer to separate and become mixed with the general flow.

The design characteristics of the burner according to the invention also have the combined effect of producing an optimal soot curve. It is true that the construction cost is somewhat higher than for the usual burners, but for that it is possible with such a burner to increase the heating efliciency of the fired objects to almost double that of comparable known burners, with the same exhaust gas temperature. This increase in efficiency more than compensates for the extra construction expenditure.

In conjunction with the aforedescribed objectives and inventive structure, the uniformity of the flow to the twisting device can be improved further by arranging a restrictor between the equalizing device and the intake to the twisting device.

Further objects reside in the provision of novel strucetural devices needed for the desired effect and made as simply as possible. To this end, it is provided in the preferred embodiment of the invention that the flame tube, at least over a part of its length, is arranged in a cylindrical housing concentric with said tube and surrounding it at a distance, that the intake end of the flame tube is closed by a face wall and that a combustion air feed opens at a distance upstream from the intake end, that the equalizing device is arranged in the annular space between the flame tube and the housing and that the twisting device has a plate-like guide vane support whose periphery together with the housing encloses an annular slot constituting a restrictor. With such a design, the equalizing device is located in the annular channel between the flame tube and the housing. At this location a flow equalization can be achieved with relatively simple means, for examle, a perforated metal sheet or a circular collar. The guide vane support of the twisting device has the additional function of forming a restrictor in combination with the housing. Thus no special structural means are needed to form the restrictor.

Another object resides in a further novel structural simplification wherein the twisting device is closed on the side that is turned away from the guide vane support by an annular cover plate in whose center the injection port is located. The cover plate of the twisting device, at the same time, forms the closure of the intake side of the flame tube with the injection port.

Still further objects reside in the novel provisions that the "rearward part of the flame tube together with the guide vane support, the guide vanes and possibly the perforated plate are made as one casting, which at the front merges into a tight wall that is sealed at its periphery against the housing, and that the front part of the flame tube the accelerating nozzle and the baflle, consist of refractory sheet metal or of ceramic material. By this construction the number of parts is reduced to a minimum and can result in savings in the cost of manufacturing and installation.

Still another object resides in the novel provision of a very slender burner design made with a combustion air feed coaxial with the flame tube and arranged behind the intake end of the flame tube, with a perforated metal plate between the feed on the one hand and the injection port of the twisting device on the other hand.

Further novel improvements and other objects of the invention and advantageous characteristics as well as exemplary dimensions which can be utilized for the achievement of a stable flow are apparent from the following detailed description, discussion and the appended claims taken in conjunction with the accompanying drawings showing various embodiments in which:

FIGURE 1 is a schematic longitudinal section of a combustion chamber burner incorporating various features of the invention: and

FIGURES 2-5 are also schematically represented longitudinal sections of burners incorporating the basic principles of the invention but utilizing modifications in various detals of structure for achieving such principles, FIGURE 2 showing details for burning gas as a fuel, FIGURE 3 illustrating simplified casting of a group of burner components, FIGURE 4 illustrating how a portion of the flame tube can be made from refractory material, and FIGURE 5 illustrating an axial flow air inlet construction.

Specific description The burner shown in FIGURE 1 has a flame tube 1, which from its intake end In to the outlet end 1b widens conically. An accelerating nozzle 2 adjoins it at the outlet end. A twisting device 3 with predominantly radial guide vanes 4 is located at the intake end. At the axis of the burner at the flame tube intake end 1a is located an injection port through which fuel, for example, oil, can be introduced by means of a nozzle system 6.

The guide vanes 4 are mounted on a plate-like guide vane support 7 advantageously made integral therewith. On the opposite side of the guide vane support 7, the twisting device is closed off by a likewise plate-like cover plate 8 which incorporates the injection port 5 in its center.

Flame tube 1 is surrounded over a part of its length by a cylindrical housing 9 which can be secured by flanges 10 onto the combustion chamber (not shown) that is to be fired. An air feed conduit 11 opens into the housing at its front end, in which conduit the combusion air flows in the direction of arrow A. Behind and at a distance from the intake end 1a of the flame tube 1, the cylindrical housing 9 is closed by face wall 12, which supports the accessory components of the burner, such as the injection system 6, the ignition device 22 and the flame control 24 (the latter two not shown in FIGURE 1 but shown, e.g., in FIGURE 2). Between the intake 13 to the twisting device 3 and the combustion air feed 11 there is mounted an equalizing device for the flow, in FIGURE 1, a perforated metal sheet 14 which extends as a ring around the flame tube 1 within the annular space 15 between flame tube 1 and housing 9. The guide vane support 7 is placed so close to the housing 9 that only a narrow entry slot 16 constituting a restrictor for the combustion air remains. Behind the restrictor 16 the

housing

9, 12 forms an air collecting chamber 17, in fluid flow communication with both the intake 13 of the twisting device 3 and with the injection port 5. Between intake 13 and injection port 5 there is no restrictor, so that the static pressure at these locations in the air collecting chamber 17 is the same. Housing 9 is closed at its front end by an annular sealing membrane or plate 18.

In the flame tube 1 immediately adjacent its outlet end there is mounted an annular batfle 19 of conical form in the direction of accelerating nozzle 2.

The guide vane support 7 which forms the ring slot 6 is secured to cylindrical wall 9 by spacers 20 that are dihtributed around the periphery of support 7.

In the burner thus described, the combustion process occurs as follows:

The combustion air enters in the direction of arrow A through feed 'pipe 11 into housing 9. It flows through the perforated plate 14, and by being obstructed briefly, it is distributed there evenly over the periphery of the flame tube and arrives flowing calmly at the annular slot 16 which forms a restrictor. Then a further calming of the flow takes place. The major part of the combustion air then arrives from the air collecting chamber 17 through the twisting device 3 at the intake end 1a of the flame tube. A part of the air also flows through the injection port 5, however, through which the fuel is injected in the direction of the burner axis 0. As a result of the twisting imparted by device 3, air moves in a helical path to'the flame tube outlet end 1b. However, because of the widening of the flame tube, the tangential component of the helical flow diminshes and therewith also the centrifugal force acting on the combustion air diminishes. From point P in the outlet cross section to point Q in the intake cross section there is therefore a pressure drop which imparts a flow of a part of the combustion air back along the axis and opposite to the direction of the main flow. Between the flow next to the wall and the return flow along the axis, a turbulence zone develops in which the fuel is intensively mixed with the combustion air. The unrecycled part passes through the open cross section of the baffle 19 into the accelerating nozzle 2 and leaves the burner in the form of a flame gas jet of very high velocity. Behind baflle 19 vortices W are formed, which disrupts the laminar boundary layer of air flow and causes it to mix with the flame jet. From joint P to point R, there is also a pressure drop as velocity increases.

The portion of the combustion air flowing through injection port 5 carries the fuel into the interior of the flame tube 1 and keeps the space around the injection port 5 free from the elfect of the flame.

The burner permits the propagation of a flame gas jet of a velocity that corresponds to a dynamic pressure that is at least 5 to times the buoyancy force per unit area within the combustion chamber which is acting on the flame gas jet, and which also permits the achievement of a stable flow pattern in spite of the pressure drops PQ and PR, working contrary to each other, and also the obtaining of an optimal smoke curve, if with a combustion output of 100,000 kcal./hr. and a preliminary pressure of the combustion air of 100 mm. water column, the following dimensions are adhered to:

Intake diameter of flame tube, d 84 mm.;

Outlet diameter of flame tube, D :175 mm.;

Outlet diameter of accelerating nozzle equals throughpass diameter of baffle, D 80 mm.;

Length of flame tube, L =approx. 240 mm.;

Length of accelerating nozzle, L =13O mm.;

Axial length of guide vanes, b =30 mm.;

Spiral angle of air intake with direction of periphery,

=7-l5 mm.;

Thickness of guide vanes, :5 mm.;

Diameter of injection port, d =25 mm.;

Diameter of housing, d =250 mm.;

Width of slot, s=7.5 mm.;

Intake of diameter of combustion air feed, d =100 mm.;

Distance between restrictor and face Wall of housing,

b =62 mm.

Through pass area of perforated plate corresponds to 364 holes each of 4 mm. diameter.

If the burner is to be laid out for other outputs, then the indicated dimensions, or at least the dimensions d D D L L b and d are to be changed, such changes should be in the same proportions as the ratio between the square root of the throughput or air flow for 6,000,000 kcal./hr. and the square root of the throughput for the desired different combustion output. In addition, changes can be made with the indicated dimensions of the intake diameter d of the flame tube, the width b of the guide vanes and the spiral angle, such changes of these values being determined in substantially linear proportion relating to each other.

With the foregoing exemplary values, there occurs in the center of the intake end a negative pressure that is 10 to 20 times greater than the average dynamic pressure of the flow in the flame tube, measured at the half length L of the flame tube, at the site of the highest velocity of the velocity profile at that location. This pressure ratio guarantees the stability of the flame flow.

The embodiments according to FIGURES 2 to 5 are in principle and in most structural parts identical with that according to FIGURE 1. To avoid repetitions, the identical structural parts are not mentioned again in the following, but they are provided with the same identification numbers.

The embodiment according to FIGURE 2 serves to fire a boiler which is indicated by 21. The cylindrical fire box 22 of boiler 21 has an extension 9' which forms the housing for the burner, representing a substantial structural simplification.

The fuel used in the burner according to FIGURE 2 is gas, and is fed in centrally through a pipe 6'. Further accessory components of the burner can be seen in the form of an ignition device 23 and a flame control 24. The said

accessory components

6', 23, and 24 are mounted in the face wall 12.

A further peculiarity of the burner according to FIG- URE 2 consists in the support of the front end 1b of flame tube 1 in the housing 9'. For this purpose, the accelerating nozzle 2 is extended backward beyond the outlet end lb of the flame tube and thereby forms a conical plate 2' whose outer edge is supported against the inner wall of housing 9 with interposition of a sealing ring 25.

Finally, in the embodiment according to FIG. 2, an nular equalizer collar 14" is provided, spaced from wall 9 and flame tube 1 and disposed between the combustion air feed 11 and the flame tube 1. This collar 14" breaks the momentum of the 'air and distributes the air uniformly over the periphery of the space remaining between the said collar and the flame tube.

While in the embodiments according to FIGS. 1 and 2, the flame tube, the accelerating nozzle and the baffie are made of heat-resistant sheet metal throughout, this is not the case with embodiments according to FIGS. 3 and 4. In the burner according to FIG. 3, a flame tube 1' consisting of two

parts

10 and 1d is provided. The rearward part 1d is made together with the perforated disk 14', forming the equalizing device, the guide vane support 7 and the guide vanes 4' as a single cast piece. The tube section 1d has at its front end a sealing wall 26, which is sealed against the inner wall of housing 9 through a seal-ing ring 27. The front section 1c of the flame tube, which again like the accelerating nozzle 2 and the baffle 19 consists of heat-resistant sheet metal, is secured by a flange to the sealing wall 26.

In the embodiment according to FIG. 4, a ceramic or otherwise refractory piece 28 which forms both the nozzle 2' and the baflie 19 adjoins the outlet end of the flame tube. This embodiment is suitable when the fuel contains corrosive contaminants which would destroy a nozzle made of sheet metal.

Finally in the embodiment according to FIG. 5, an air feed tube 11' is provided, which opens into the housing coaxially with housing 9 and flame tube 1. Before the combustion air can enter into the air collecting chamber 17, it flows through the perforated plate 14', which forms the equalizing device. In this case, the perforated plate 14' can also support the accessory organs of the burner.

The invention is not limited to the embodiments shown in the drawings. Especially the shown structural characteristics of the individual burners can be mutually exchanged. Furthermore, instead of a conical baffle with a cone base angle 01:30", a different conicity or a flat annular baffle can be chosen. Furthermore, all burners can optionally be operated with oil, gas or powdered coal.

The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

What is claimed and desired to be secured by Letters Patent is:

1. A burner for firing into a heating zone comprising: a diverging frusto-conical flame tube having a length greater than its maximum diameter; separate inlet passage means at and coaxially disposed with the intake end of said flame tube for feeding fuel and a partial supply of combustion air into said intake end from separate sources; a major combustion air supply inlet device coaxially disposed about and in fluid communication with said flame tube intake and including flow guide vanes having a spiral configuration; a convergent nozzle device connected with the large outlet end of said flame tube and having an outlet cross-section area less than the flame tube inlet cross-section area for accelerating the exiting burning gases from said flame tube and generating a flame gas jet with a velocity at the outlet end of the accelerating nozzle having a dynamic pressure corresponding to a pressure which is at least to 10 times the buoyancy force acting on the flame jet in the combustion chamber, per unit of area; said spiral vane inlet device and said flame tube being relatively dimensioned to constitute means for utilizing a high pressure source of combustion air and therewith generating a negative pressure in the center of the intake end of said flame tube which is at least 10 to times greater than the average dynamic pressure of the flame tube throughput flow at the site of the highest velocity of the flame tube velocity profile taken at the half length location in said flame tube; a combustion air chamber providing a common source of combustion air connected to said partial air inlet passage means and to said inlet device and having an inlet means; an equlizing device disposed in said common chamber to enable equalizing of the distribution and flow of the combustion air around the periphery of the inlet device; and a baffle at the outlet end of said flame tube acting on the flame gas flow stream passing from said flame tube through said accelerating nozzle.

2. A burner as defined in claim 1, wherein a restrictor means is disposed between said equalizing device and the intake to said flame tube inlet device.

3. A burner as defined in claim 1, wherein a cylindrical housing is disposed concentric with and surrounding said tube in spaced relationship over at least a part of the length of said tube; a face wall closes the end of said housing adjacent and spaced away from the intake end of said tube; said equalizing device is arranged in the annular space formed between said flame tube and said housing; and said inlet device has a plate-like guide vane support, the periphery of which together with said h0us ing comprises an annular slot restrictor means.

4. A burner as defined in claim 3, wherein spacers secure said guide vane support to said housing to form said annular slot restrictor means.

5. A burner as defined in claim 3, wherein said inlet device includes an annular cover plate on the opposite side of its vanes from said guide vane support and an injection port is loacted in the center of said cover plate.

6. A burner as defined in claim 3, wherein said equalizing device includes a perforated annular metal plate.

7. A burner as defined in claim 3, wherein said equalizing device consists of an annular collar disposed in the space between said chamber inlet and said flame tube.

8. A burner as defined in claim 3, wherein accessory components are provided for said burner and are mounted on said face wall.

9. A burner as defined in claim 3, wherein a flanged joiner means is provided and couples said housing with said flame tube.

10. A burner as defined in claim 3, wherein an annular diaphragm seals said flame tube against said housing.

11. A burner as defined in claim 3, wherein a pcripheral plate is secured to said flame tube adjacent its outlet end and a sealing ring seals the outer edge of said plate against said housing.

12. A burner as defined in claim 11, wherein said peripheral plate is conical and is formed by a rearward extension of said accelerating nozzle.

13. A burner as defined in claim 1, wherein said bafiie comprises a frusto-conical shape extending toward outlet end of said accelerating nozzle.

14. A burner as defined in claim 1, wherein said flame tube, accelerating nozzle and battle are made from heatresistant sheet metal.

15. A burner as defined in claim 1, wherein the rearward part of said flame tube together with one side of said air inlet device and said guide vanes are made as one casting the front of which has tight wall, and seal means are provided at the tight wall periphery to seal against said housing; and the front part of said flame tube, said accelerating nozzle and said bafile consist of a single piece made from high heat resistant material.

16. A burner as defined in claim 1, wherein said combustion air feed chamber inlet is disposed coaxial with and behind the intake end of said flame tube; and a perforated metal plate is secured in said chamber between said inlet and the partial air inlet passage means.

17. A burner as defined in claim 16, wherein accessory devices are provided for said burner and are mounted on said perforated plate.

18. A burner as defined in claim 1, having the following dimensions:

Intake diameter of said flame tube, d =84 mm.;

Outlet diameter of flame tube and intake diameter of accelerating nozzle, D =l mm.;

Outlet diameter of accelerating nozzle and throughpass diameter of the baflie, D mm.;

Length of flame tube, L =240 mm.;

Length of accelerating nozzle, L =130 mm.;

Axial length of intake guide vanes, b =30 mm.;

Spiral angle of air intake with direction of periphery,

Thickness of guide vanes, :5 mm.;

Diameter of injection port, d =25 mm.;

Diameter of housing, d =250 mm.;

Width of slot, s=7.5 mm.;

Intake diameter of combustion air feed, d mm.;

Distance between restrictor and face wall of housing,

b :62 mm.

Throughpass area of perforated plate corresponds to 364 holes, each of 4 mm. diameter; a burner constructed with the foregoing dimensions, when used with an air source under a pressure of 100 mm. water column being capable of a combustion output of 100,000 kcaL/hr. (400,000 B.t.u./hr.).

References Cited UNITED STATES PATENTS 2,901,032 8/1959 Brola 158-15 X 2,927,632 3/1960 Fraser 158-4 3,255,802 6/1966 Browning 158-49.1

FREDERICK L. MATTESON, 111., Primary Examiner E. G. FAVORS, Assistant Examiner.