EP0780629A2 - Burner for a heat generator - Google Patents

Abstract

The burner has a mixer section and a swirl generator. The mixer section (220) is positioned downstream from the swirl generator (100) and has, within a first part of the section (200) transfer ducts (201) running in the direction of flow for transmitting a current (40) formed in the swirl generator into a pipe situated downstream from the transfer ducts. The outlet plane of the pipe to the combustion chamber (30) has a break edge (A) for stabilising and enlarging a reverse current zone (50) formed downstream. The number of transfer ducts in the mixed section matches the number of art currents formed by the swirl generator. The pipe situated after the transfer ducts has openings (21) for injecting an air current into the pipe.

Description

Technical field

The present invention relates to a burner according to the preamble of claim 1.

State of the art

From EP-B1-0 321 809, a cone-shaped burner, known as a double-cone burner, consisting of several shells, is known for generating a closed swirl flow in the cone head, which becomes unstable due to the increasing swirl along the cone tip and changes into an annular swirl flow with backflow in the core. Fuels, such as gaseous fuels, are injected along the channels formed by the individual adjacent shells, also called air inlet slots, and mixed homogeneously with the air before the combustion starts by ignition at the stagnation point of the backflow zone or backflow bubble, which is used as a flame holder. Liquid fuels are preferably injected via a central nozzle on the burner head and then evaporate in the cone cavity. Under typical gas turbine conditions, the ignition of these liquid fuels takes place early in the vicinity of the fuel nozzle, which is unavoidable that the NOx values rise sharply precisely because of this lack of premixing, for example it is necessary to inject water. In addition, it had to be determined that the attempt to burn hydrogen-containing gases similar to natural gas led to pre-ignition problems at the gas wells with subsequent overheating of the burner. This has been remedied by introducing a special injection method for such gaseous fuels at the burner outlet, but the results of which have not been entirely satisfactory.

Presentation of the invention

The invention seeks to remedy this. The invention, as characterized in the claims, is based on the object of proposing, in a burner of the type mentioned, precautions by which a perfect premixing of fuels of different types is achieved and by which an operationally reliable and optimal flame positioning is achieved.

The proposed burner has a swirl generator on the head side and upstream of a mixing section, which can preferably be designed such that the basic aerodynamic principles of the so-called double-cone burner according to EP-A1-0 321 809 are used. In principle, however, the use of an axial or radial swirl generator is also possible. The mixing section itself preferably consists of a tubular mixing element, hereinafter referred to as the mixing tube, which permits perfect premixing of fuels of various types.

The flow from the swirl generator is introduced seamlessly into the mixing tube: this is done by means of a transition geometry which consists of transition channels which are excluded in the initial phase of this mixing tube, and which transfer the flow into the subsequent effective flow cross-section of the mixing tube. This low-loss flow introduction between the swirl generator and the mixing tube initially prevents the immediate formation of a backflow zone at the outlet of the swirl generator.

First, the swirl strength in the swirl generator is selected via its geometry so that the swirl does not burst in the mixing tube, but further downstream at the combustion chamber inlet, the length of this mixing tube being dimensioned such that there is sufficient mixing quality for all types of fuel. If, for example, the swirl generator used is constructed according to the basic principles of the double-cone burner, the swirl strength results from the design of the corresponding cone angle, the air inlet slots and their number.

In the mixing tube, the axial speed profile has a pronounced maximum on the axis and thus prevents reignitions in this area. The axial speed drops towards the wall. In order to prevent reignitions in this area as well, various precautions are provided: For example, the entire speed level can be raised by using a mixing tube with a sufficiently small diameter. Another possibility is to only increase the speed in the outer region of the mixing tube, in that a small part of the combustion air flows into the mixing tube via an annular gap or through filming holes downstream of the transition channels.

As for the transition channels mentioned for introducing the flow from the swirl generator into the mixing tube, it can be said that the course of these transition channels can be designed to narrow or widen in a spiral fashion, in accordance with the effective subsequent flow cross-section of the mixing tube.

Part of the pressure loss that may be generated can be compensated for by attaching a diffuser to the end of the mixing tube. A venturi section can also be provided in this area or upstream.

At the end of the mixing tube, the combustion chamber connects with a cross-sectional jump. A central backflow zone is formed here, the properties of which are those of a flame holder.
The generation of a stable backflow zone requires a sufficiently high number of swirls in the mixing tube. However, if this is initially undesirable, stable return flow zones can be created at the end of the pipe by supplying small, strongly swirled air volumes, 5-20% of the total air volume.

• a) Stabile Flammenposition;
• b) Tiefere Schadstoff-Emissionen (Co, UHC, NOx);
• c) Minimierung der Pulsationen;
• d) Vollständiger Ausbrand;
• e) Grosse Betriebsbereich-Abdeckung;
• f) Gute Querzündung zwischen den verschiedenen Brennern, insbesondere bei gestufter Lasterstellung, bei welcher die Brenner untereinander interdependent betrieben werden;
• g) Die Flamme kann der entsprechenden Brennkammergeometrie angepasst werden;
• h) Kompakte Bauweise;
• i) Verbesserte Mischung der Strömungsmedien;
• j) Verbesserter "Patternfaktor" der Temperaturverteilung in der Brennkammer (= ausgeglichener Temperaturprofil der Brennkammerströmung).

In connection with the mentioned cross-sectional jump, the end of the mixing tube is formed with a tear-off edge, which gives the backflow zone a high spatial stability. In general, the measures mentioned can achieve the following advantages:

• a) Stable flame position;
• b) Lower pollutant emissions (Co, UHC, NOx);
• c) minimization of pulsations;
• d) complete burnout;
• e) Large operating area coverage;
• f) Good cross-ignition between the different burners, especially with stepped load position, in which the burners are operated interdependently with one another;
• g) The flame can be adapted to the corresponding combustion chamber geometry;
• h) compact design;
• i) Improved mixing of the flow media;
• j) Improved "pattern factor" of the temperature distribution in the combustion chamber (= balanced temperature profile of the combustion chamber flow).

Advantageous and expedient developments of the task solution according to the invention are characterized in the further claims.

Exemplary embodiments of the invention are explained in more detail below with reference to the drawings. All features which are not essential for the direct understanding of the invention have been omitted. Identical elements are provided with the same reference symbols in the various figures. The direction of flow of the media is indicated by arrows.

Brief description of the drawings

Fig. 1

einen Brenner mit anschliessender Brennkammer,

Fig. 2

einen Drallerzeuger in perspektivischer Darstellung, entsprechend aufgeschnitten,

Fig. 3

einen Schnitt durch den 2-Schalen-Drallerzeuger, nach Fig. 2,

Fig. 4

einen Schnitt durch einen 4-Schalen-Drallerzeuger,

Fig. 5

einen Schitt durch einen Drallerzeuger, dessen Schalen schaufelförmig profiliert sind,

Fig. 6

eine Darstellung der Form der Uebergangsgeometrie zwischen Drallerzeuger und Mischrohr und

Fig. 7

eine Abrisskante zur räumlichen Stabilisierung der Rückströmzone.

It shows:

Fig. 1

a burner with subsequent combustion chamber,

Fig. 2

a swirl generator in a perspective view, cut open accordingly,

Fig. 3

3 shows a section through the 2-shell swirl generator, according to FIG. 2,

Fig. 4

a section through a 4-shell swirl generator,

Fig. 5

a step through a swirl generator, the shells of which are profiled in a scoop shape,

Fig. 6

a representation of the shape of the transition geometry between swirl generator and mixing tube and

Fig. 7

a tear-off edge for spatial stabilization of the backflow zone.

Ways of carrying out the invention, commercial usability

Fig. 1 shows the overall structure of a burner. Initially, a swirl generator 100 is effective, the design of which is shown and described in more detail in the following FIGS. 2-5. This swirl generator 100 is a conical structure which is acted upon tangentially several times by a tangentially flowing combustion air flow 115. The flow formed here is seamlessly transferred to a transition piece 200 using a transition geometry provided downstream of the swirl generator 100, in such a way that no separation areas can occur there. The configuration of this transition geometry is described in more detail in FIG. 6. This transition piece 200 is extended on the outflow side of the transition geometry by a tube 20, both parts forming the actual mixing tube 220, also called the mixing section, of the burner. Of course, the mixing tube 220 can consist of a single piece, that is to say then that the transition piece 200 and tube 20 are fused into a single coherent structure, the characteristics of each part being retained. If the transition piece 200 and the tube 20 are created from two parts, they are connected by a bushing ring 10, the same bushing ring 10 serving as an anchoring surface for the swirl generator 100 on the head side. Such a bushing ring 10 also has the advantage that different mixing tubes can be used. The actual combustion chamber 30 is located on the outflow side of the tube 20 and is here only symbolized by the flame tube. The mixing tube 220 fulfills the condition that a defined mixing section is provided downstream of the swirl generator 100, in which a perfect premixing of fuels of different types is achieved. This mixing section, that is to say the mixing tube 220, furthermore enables loss-free flow guidance, so that it is also in operative connection cannot initially form a backflow zone with the transition geometry, which means that the length of the mixing tube 220 can influence the quality of the mixture for all types of fuel. However, this mixing tube 220 has yet another property, which consists in the fact that in the mixing tube 220 itself the axial speed profile has a pronounced maximum on the axis, so that the flame cannot be re-ignited from the combustion chamber. However, it is correct that with such a configuration this axial speed drops towards the wall. In order to prevent re-ignition in this area, the mixing tube 220 is provided with a number of regularly or irregularly distributed bores 21 of various cross-sections and directions in the flow and circumferential direction, through which an amount of air flows into the interior of the mixing tube 220 and along the wall in the Inducing an increase in speed in the sense of filming. Another possibility of achieving the same effect is that the flow cross section of the mixing tube 220 is narrowed on the downstream side of the transition channels 201, which form the transition geometry already mentioned, as a result of which the overall speed level within the mixing tube 220 is increased. In the figure, these bores 21 run at an acute angle with respect to the burner axis 60. Furthermore, the outlet of the transition channels 201 corresponds to the narrowest flow cross-section of the mixing tube 220. The transition channels 201 mentioned therefore bridge the respective cross-sectional difference without adversely affecting the flow formed. If the selected precaution triggers an intolerable pressure loss when guiding the pipe flow 40 along the mixing pipe 220, this can be remedied by providing a diffuser (not shown in the figure) at the end of the mixing pipe. A combustion chamber 30 adjoins the end of the mixing tube 220, a cross-sectional jump occurring between the two flow cross sections. Only here does one form central backflow zone 50, which has the properties of a flame holder. If a flow-like edge zone forms in this cross-sectional jump during operation, in which vortex detachments arise due to the prevailing negative pressure, this leads to an increased ring stabilization of the backflow zone 50. At the end, the combustion chamber 30 has a number of openings 31 through which an air quantity flows directly into the cross-sectional jump flows, and there contributes the others below that the ring stabilization of the backflow zone 50 is strengthened. In addition, it should not go unmentioned that the generation of a stable backflow zone 50 also requires a sufficiently high number of twists in a pipe. If this is initially undesirable, stable backflow zones can be created by supplying small, strongly swirled air flows at the pipe end, for example through tangential openings. It is assumed here that the amount of air required for this is about 5-20% of the total amount of air. With regard to the configuration of the tear-off edge at the end of the mixing tube 220, reference is made to the description under FIG. 7.

In order to better understand the structure of the swirl generator 100, it is advantageous if at least FIG. 3 is used at the same time as FIG. 2. Furthermore, in order not to make this FIG. 2 unnecessarily confusing, the guide plates 121a, 121b shown schematically according to FIG. 3 have only been hinted at in it. In the description of FIG. 2, reference is made below to the figures mentioned as required.

The first part of the burner according to FIG. 1 forms the swirl generator 100 shown in FIG. 2. It consists of two hollow, conical partial bodies 101, 102, which are nested one inside the other. The number of conical partial bodies can of course be greater than two, as shown in FIGS. 4 and 5; this depends on how each further will be explained in more detail below, depending on the mode of operation of the entire burner. In certain operating constellations, it is not excluded to provide a swirl generator consisting of a single spiral. The offset of the respective central axis or longitudinal symmetry axes 201b, 202b of the conical partial bodies 101, 102 to one another creates a tangential channel, that is to say an air inlet slot 119, 120 (FIG. 3), through which the combustion air 115 in Interior of the swirl generator 100, ie flows into the cone cavity 114 of the same. The conical shape of the partial bodies 101, 102 shown in the flow direction has a specific fixed angle. Of course, depending on the operational use, the partial bodies 101, 102 can have an increasing or decreasing cone inclination in the direction of flow, similar to a trumpet or. Tulip. The last two forms are not included in the drawing, since they can be easily understood by a person skilled in the art. The two tapered partial bodies 101, 102 each have a cylindrical starting part 101a, 102a, which, similarly to the conical partial bodies 101, 102, also run offset from one another, so that the tangential air inlet slots 119, 120 are present over the entire length of the swirl generator 100. In the area of the cylindrical initial part, a nozzle 103 is preferably accommodated for a liquid fuel 112, the injection 104 of which coincides approximately with the narrowest cross section of the conical cavity 114 formed by the conical partial bodies 101, 102. The injection capacity and the type of this nozzle 103 depend on the given parameters of the respective burner. Of course, the swirl generator 100 can be designed in a purely conical manner, that is to say without cylindrical starting parts 101a, 102a. The conical sub-bodies 101, 102 each further have a fuel line 108, 109, which are arranged along the tangential air inlet slots 119, 120 and are provided with injection openings 117, through which a gaseous fuel is preferably provided 113 is injected into the combustion air 115 flowing through there, as is to be symbolized by the arrows 116. These fuel lines 108, 109 are preferably placed at the latest at the end of the tangential inflow, before entering the cone cavity 114, in order to obtain an optimal air / fuel mixture. As mentioned, the fuel 112 brought in through the nozzle 103 is normally a liquid fuel, and it is readily possible to form a mixture with another medium. This fuel 112 is injected into the cone cavity 114 at an acute angle. A cone-shaped fuel spray 105 is thus formed from the nozzle 103 and is enclosed by the rotating combustion air 115 flowing in tangentially. In the axial direction, the concentration of the injected fuel 112 is continuously reduced by the inflowing combustion air 115 to mix in the direction of evaporation. If a gaseous fuel 113 is introduced via the opening nozzles 117, the fuel / air mixture is formed directly at the end of the air inlet slots 119, 120. If the combustion air 115 is additionally preheated or, for example, enriched with a recirculated flue gas or exhaust gas, this provides lasting support the vaporization of the liquid fuel 112 before this mixture flows into the downstream stage. The same considerations also apply if liquid fuels should be supplied via lines 108, 109. When designing the conical partial bodies 101, 102 with respect to the cone angle and the width of the tangential air inlet slots 119, 120, strict limits must be observed per se so that the desired flow field of the combustion air 115 can be set at the outlet of the swirl generator 100. In general, it can be said that reducing the tangential air inlet slots 119, 120 already favors the faster formation of a backflow zone in the area of the swirl generator. The axial speed within the swirl generator 100 cannot be changed by a corresponding one change the supply of an axial combustion air flow shown. A corresponding swirl generation prevents the formation of flow separations within the mixing tube downstream of the swirl generator 100. The design of the swirl generator 100 is furthermore excellently suitable for changing the size of the tangential air inlet slots 119, 120, with which a relatively large operational bandwidth can be recorded without changing the overall length of the swirl generator 100. Of course, the partial bodies 101, 102 can also be displaced relative to one another in another plane, as a result of which an overlap thereof can even be provided. It is also possible to interleave the partial bodies 101, 102 in a spiral manner by counter-rotating movement. It is thus possible to vary the shape, size and configuration of the tangential air inlet slots 119, 120 as desired, with which the swirl generator 100 can be used universally without changing its overall length.

3 now shows the geometric configuration of the guide plates 121a, 121b. They have a flow introduction function, which, depending on their length, extend the respective end of the tapered partial bodies 101, 102 in the direction of flow relative to the combustion air 115. The channeling of the combustion air 115 into the cone cavity 114 can be optimized by opening or closing the guide plates 121a, 121b about a pivot point 123 located in the region of the entry of this channel into the cone cavity 114, in particular this is necessary if the original gap size of the tangential air inlet slots 119, 120 should be changed dynamically. Of course, these dynamic arrangements can also be provided statically, in that guide baffles as required form a fixed component with the tapered partial bodies 101, 102. Likewise, the swirl generator 100 can also be operated without baffles, or other aids can be provided for this.

4 shows that the swirl generator 100 is now composed of four partial bodies 130, 131, 132, 133. The associated longitudinal symmetry axes for each partial body are marked with the letter a. Regarding this configuration, it should be said that, due to the lower swirl strength generated in this way and in cooperation with a correspondingly enlarged slot width, it is ideally suited to prevent the vortex flow from bursting in the mixing tube on the downstream side of the swirl generator, so that the mixing tube can best fulfill the role intended for it .

FIG. 5 differs from FIG. 4 in that the partial bodies 140, 141, 142, 143 have a blade profile shape which is provided to provide a certain flow. Otherwise the mode of operation of the swirl generator has remained the same. The admixture of the fuel 116 in the combustion air flow 115 takes place from the inside of the blade profiles, i.e. the fuel line 108 is now integrated in the individual blades. Here, too, the longitudinal axes of symmetry to the individual partial bodies are identified by the letter a.

6 shows the transition piece 200 in a three-dimensional view. The transition geometry is constructed for a swirl generator 100 with four partial bodies, corresponding to FIG. 4 or 5. Accordingly, the transition geometry as a natural extension of the upstream partial body four transition channels 201, whereby the conical quarter surface of the partial body is extended until it the wall of the tube 20 or. of the mixing tube 220 cuts. The same considerations also apply if the swirl generator is constructed from a principle other than that described under FIG. 2. The surface of the individual transition channels 201 which runs downward in the direction of flow has a shape which runs in a spiral in the direction of flow and which describes a crescent shape, corresponding to FIG The fact that in the present case the flow cross section of the transition piece 200 widens conically in the flow direction. The swirl angle of the transition channels 201 in the flow direction is selected such that the pipe flow then still has a sufficiently large distance up to the cross-sectional jump at the combustion chamber inlet in order to achieve a perfect premixing with the injected fuel. Furthermore, the above-mentioned measures also increase the axial speed on the mixing tube wall downstream of the swirl generator. The transition geometry and the measures in the area of the mixing tube bring about a significant increase in the axial speed profile towards the center of the mixing tube, so that the risk of early ignition is decisively counteracted.

Fig. 7 shows the tear-off edge already mentioned, which is formed at the burner outlet. The flow cross-section of the tube 20 receives a transition radius R in this area, the size of which basically depends on the flow within the tube 20. This radius R is selected so that the flow is applied to the wall and the swirl number can increase sharply. The size of the radius R can be quantitatively defined so that it is> 10% of the inner diameter d of the tube 20. Compared to a flow without a radius, the backflow bladder 50 now increases enormously. This radius R extends to the exit plane of the tube 20, the angle β between the beginning and end of the curvature being <90 °. The tear-off edge A runs along one leg of the angle β into the interior of the tube 20 and thus forms a tear-off step S with respect to the front point of the tear-off edge A, the depth of which is> 3 mm. Of course, the edge running parallel to the exit plane of the tube 20 can be brought back to the exit plane level using a curved course. The angle β ', which extends between the tangent of the tear-off edge A and perpendicular to the exit plane of the tube 20, is the same size as the angle β. On the Advantages of this training have already been discussed in more detail above under the chapter "Presentation of the Invention".

Reference list

10th

Beech ring

20th

pipe

21

Holes, openings

30th

Combustion chamber

31

Openings

40

Flow, pipe flow in the mixing pipe

50

Backflow zone, backflow bubble

60

Burner axis

100

Swirl generator

101, 102

Partial body

101a, 102b

Cylindrical starting parts

101b, 102b

Longitudinal symmetry axes

103

Fuel nozzle

104

Fuel injection

105

Fuel spray (fuel injection profile)

108, 109

Fuel lines

112

Liquid fuel

113

Gaseous fuel

114

Cone cavity

115

Combustion air (combustion air flow)

116

Fuel injection from lines 108, 109

117

Fuel nozzles

119, 120

Tangential air inlet slots

121a, 121b

Baffles

123

Pivot point of the guide plates

130, 131, 132, 133

Partial body

131a, 131a, 132a, -133a

Longitudinal symmetry axes

140, 141, 142, 143

Vane-shaped partial body

140a, 141a, 142a, 143a

Longitudinal symmetry axes

200

Transition piece

201

Transition channels

220

Mixing tube

d

Inner diameter of the tube 20

R

Transition radius

T

Tangent line of the tear-off edge

A

Tear-off edge

S

Demolition level

β

Transition angle from R

β '

Angle between T and A

Claims (14)

Burner for a heat generator, essentially consisting of a swirl generator for a combustion air flow and means for injecting a fuel into the combustion air flow, characterized in that a mixing section (220) is arranged downstream of the swirl generator (100) and is located within a first section part (200 ) has transition channels (201) running in the flow direction for transferring a flow (40) formed in the swirl generator (100) into a pipe (20) connected downstream of the transition channels (201), and that the outlet plane of this pipe (20) to the combustion chamber (30) with a tear-off edge (A) for stabilizing and enlarging a downstream backflow zone (50) Burner according to claim 1, characterized in that the number of transition channels (201) in the mixing section (220) corresponds to the number of partial flows formed by the swirl generator (100). Burner according to Claim 1, characterized in that the tube (20) connected downstream of the transition channels (201) is provided with openings (21) in the flow and circumferential direction for injecting an air stream into the interior of the tube (20). Burner according to claim 3, characterized in that the openings (21) run at an acute angle with respect to the burner axis (60) of the tube (20). Burner according to claim 1, characterized in that the tear-off edge (A) consists of a transition radius (R) in the region of the exit plane of the tube (20) and a tear-off step (S) offset from the exit plane of the tube (20). Burner according to claim 5, characterized in that the transition radius (R) is> 10% of the inner diameter of the tube (20) and that the tear-off step (S) has a depth> 3 mm. Burner according to claim 1, characterized in that the flow cross-section of the tube (20) downstream of the transition channels (201) is smaller, equal or larger than the cross-section of the flow (40) formed in the swirl generator (100). Burner according to claim 1, characterized in that a combustion chamber (30) is arranged downstream of the mixing section (220), that between the mixing section (220) and the combustion chamber (30) there is a cross-sectional jump which corresponds to the initial flow cross section of the combustion chamber (30) induced, and that a backflow zone (50) is effective in the area of this cross-sectional jump. Burner according to claim 1, characterized in that upstream of the tear-off edge (A) there is a diffuser and / or a venturi section. Burner according to claim 1, characterized in that the swirl generator (100) consists of at least two hollow, conical, part-bodies (101, 102; 130, 131, 132, 133; 140, 141, 142, 143) nested one inside the other in the flow direction, that the respective longitudinal symmetry axes (101b, 102b; 130a, 131a, 132a, 133a; 140a, 141a, 142a, 143a) of these partial bodies are offset with respect to one another in such a way that the adjacent walls of the partial bodies form tangential channels (119, 120) for a combustion air flow (115) in their longitudinal extent, and that at least in the cone cavity (114) formed by the partial bodies a fuel nozzle (103) is arranged. Burner according to Claim 10, characterized in that further fuel nozzles (117) are arranged in the region of the tangential channels (119, 120) in their longitudinal extent. Burner according to claim 10, characterized in that the partial bodies (140, 141, 142, 143) have a blade-shaped profile in cross section. Burner according to claim 10, characterized in that the partial bodies have a fixed cone angle in the flow direction, or an increasing cone inclination, or a decreasing cone inclination. Burner according to claim 10, characterized in that the partial bodies are nested spirally one inside the other.

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