WO2005078348A1

WO2005078348A1 - Premixing burner arrangement for operating a burner chamber and method for operating a burner chamber

Info

Publication number: WO2005078348A1
Application number: PCT/EP2005/050579
Authority: WO
Inventors: Elena De Marcos; Christian Steinbach; Nicolas Ulibarri; Martin Andrea Von Planta
Original assignee: Alstom Technology Ltd
Priority date: 2004-02-12
Filing date: 2005-02-09
Publication date: 2005-08-25
Also published as: MXPA06008994A; MY141577A; CN1942710A; EP1714081A1; ATE391887T1; DE502005003648D1; BRPI0507640A; CA2555481A1; US20070042307A1; EP1714081B1

Abstract

The invention relates to a premixing burner arrangement for operating a burner chamber with a gaseous and/or liquid fuel. Said premix burner comprises a swirl generator (2) for a combustion air influx for forming a swirl and means (5) for jetting in fuel into the swirl. The swirl generator (2) comprises at least two partial conical shells (1) that complement each other to give a flow-type body and that together include a conical swirl chamber having a cone angle η and air inlet slots (4) that are tangential relative to the longitudinal extension of the cone. The invention is characterized in that at least in the flow-distal end zone of the swirl generator (2) a shaped element (7) enclosing the partial conical shells (1) and having an inner wall (6) facing the partial conical shells (1) is provided and in that the partial conical shells (1) run flush into the inner wall (6) thereby keeping the shape of the structure.

Description

Premix burner arrangement for operating a combustion chamber and method for operating a combustion chamber

Technical field

The invention relates to a premix burner for operating a combustion chamber with a gaseous and / or liquid fuel with a swirl generator for a combustion supply air flow to form a swirl flow and means for injecting fuel into the swirl flow, the swirl generator having at least two partial cone shells which complement one another to form a flow body which together enclose a conical swirl chamber with a cone angle y and tangential air inlet slots in the longitudinal direction of the cone.

State of the art

Premix burners of the aforementioned type are known from a large number of previously published documents, for example from EP 0210462 A1 and EP 0 321 809 B1, to name just a few. Premix burners of this type are based on the general principle of operation, within a swirl generator, which is usually designed as a cone and which provides at least two partial cone shells with corresponding mutual overlap, to produce a swirl flow consisting of a fuel-air mixture, which is formed within a combustion chamber following the premix burner under formation a premixing flame which is as stable as possible is ignited becomes. The spatial position of the premixing flame is determined by the aerodynamic behavior of the swirl flow, the swirl number of which increases with increasing propagation along the burner axis, so that it becomes unstable and ultimately bursts due to an unstable cross-sectional transition between burner and combustion chamber into an annular swirl flow with the formation of a backflow zone in the latter , the premixing flame forms in the direction of flow at the front.

The aerodynamic stability of the backflow zone that forms is of particular importance, but depends in a highly sensitive manner on the design, shape and size of the swirl generator. If, for example, it is not possible to spatially stabilize the foremost front of the backflow zone that is formed in the direction of flow, thermoacoustic oscillations or pulsations occur increasingly within the combustion system, which significantly impair the entire combustion and the heat release.

In view of this fact, the previously known and used premix burner systems are limited to sizes whose maximum burner diameter at the burner outlet is only 180 mm. Such premix burners also have a relatively pointed, i.e. small cone angle of less than or equal to 18 °, so that the burner length is rather large in relation to the downstream burner diameter, but is still quite manageable for assembly and maintenance purposes.

However, if it is necessary to fire large combustion chambers, so-called multiple burner arrangements have been used so far, which provide for the use of the above premix burners. Such multiple burner arrangements can be found, for example, in DE 4223 828 A1 or DE 44 12 315 A1. In order to operate such multiple burner arrangements, which are suitable, for example, for firing a silo combustion chamber, a sophisticated arrangement of the large number of premix burners, each serving as a main or pilot burner, is required in order to ultimately be able to operate the combustion chamber with the lowest possible emission values in the entire load range. However, there is a desire to reduce the complexity and thus also the number of individual premix burners that are required for firing large-sized combustion chambers without having to accept any loss of quality in the combustion process itself. In addition, for reasons of ever stricter environmental standards with regard to the reduction of emission values, it is necessary to replace the single diffusion burners that have been in operation until now, which are mainly used to fire large-sized silo combustion chambers, with more modern, more environmentally friendly burner systems. In particular with a view to avoiding high retrofitting and new procurement costs, it is desirable to provide premix burners with the largest possible dimensions in order, for example, to be able to continue to operate such large dimensioned silo combustion chambers with only a single premix burner.

Theoretical considerations as well as tests have shown that simple scaling, for example of a double-cone burner known from EP 0321 809 B1, does not lead to the goal, especially since, as already mentioned above, the burner length would increase disproportionately. In addition, the width of the air inlet slots running tangentially in the burner axis, through which the combustion air flows in to generate the desired swirl flow into the swirl generator, would also increase proportionally, so that good mixing of fuel and combustion air can no longer be guaranteed in sufficient quality.

Another very important and at the same time critical aspect in the case of a desired increase or increase in performance of the previously known premix burner systems relates to the downstream end of the partial cone shells which enclose the swirl chamber of the swirl generator and which, in the example of the double-cone burner described in EP 0321 809 B1, end in axially directed obstructions , These blockages contribute to the formation of undesired detachment vortices, which, as coherent vortex structures, lead to combustion instabilities and, as a result, to thermoacoustic vibrations or pulsations. Premix burner arrangements are also known (for example US 5,588,826) which, in contrast to the premix burner described above, have a transition geometry interposed between the swirl generator and the combustion chamber, for example in the form of a hollow cylindrical mixing tube. However, such transition geometries are extremely aerodynamically sensitive, since flow separations in this zone can lead to a flashback or self-ignition. Such transition geometries also make a decisive contribution to the production costs due to their complex production.

Presentation of the invention

The invention is based on the object of developing a premix burner in accordance with the features of the preamble of claim 1 in such a way that, despite enlarging the burner dimensions, the burner properties which have been optimized in previously known premix burners are to be maintained almost unchanged. It is therefore necessary to increase the burner size of previously known premix burner systems in order to reduce the number of burners in multiple burner arrangements, as described at the beginning, and also to reduce the system costs associated therewith. It should also be possible with the larger premix burner systems to replace previously known diffusion single burners, such as those used for firing silo combustion chambers, by a single premix burner.

The solution to the problem on which the invention is based is specified in claim 1. Features which advantageously further develop the inventive concept are the subject matter of the subclaims and the description, in particular with reference to the exemplary embodiments.

According to the invention, a premix burner is developed in such a way that, at least at the downstream end region of the swirl generator, a shaped element enclosing the partial cone shells with a Partial conical shells facing inner wall is provided, and that the partial conical shells run out flush with the shape of the inner wall.

A large number of theoretical considerations, as well as experiments carried out experimentally, to enlarge the previously known design of premix burners, which usually have a maximum burner outlet-side burner diameter of 180 mm, led to the realization that the downstream end structure of the partial cone shells has a significant influence on the stability of the forming premix burner flame, in particular in the endeavor to make the premix burner as large as possible.

This shows that in most cases of the premixing burners in use, the end regions of the partial cone shells merge into a hollow cylindrical flow channel in the flow direction, which is either directly connected to the combustion chamber or an additional mixing section in the form of a mixing tube. In order to avoid the swirling vortices directly adjoining the partial cone shells in the direction of flow, it has been recognized according to the invention that the swirl flow is able to spread directly after exiting the swirl generator largely without the swirl flow becoming unstabilized, if the individual partial cone shells retain their shape with the inner wall of the flow duct adjoining the swirl generator nestle. In the sense of the invention, the term “shape-preserving” means that the part-conical shape of the partial cone shells remains unchanged in the region of contact with the inner wall of the shaped element surrounding the partial cone shells, as if the partial cone shells penetrated the shaped element radially outward unhindered.

The inner wall of the shaped element also serves to form a flow channel downstream of the partial cone shells. Depending on the shape and size of the shaped element, this is also used as a mixing tube or as a joining element, in the sense of a flange piece, by means of which the swirl generator is connected to an in Direction of flow downstream combustion chamber, such as a silo combustion chamber, or another channel structure can be connected.

To make the premix burner as compact as possible, i.e. To be able to achieve the smallest possible burner length, cone angles of at least 11 °, but preferably in the range of 20 ° and larger, are used, under which the partial cone shells surround the swirl space in a conically widening manner. This enables burners with a burner diameter in the outlet area of, for example, greater than 500 mm to be made possible, which have a burner length well below one meter. To ensure thorough mixing of the fuel-air mixture within the swirl generator, it is also advantageous to increase the number of partial cone shells and the associated number of air inlet slots in order to achieve the smallest possible slot width per air inlet slot.

Brief description of the invention

The invention is described below by way of example with reference to the drawings, without restricting the general idea of the invention. Show it:

1 + 2 perspective view of a premix burner with a cylindrical shaped element,

3 + 4 perspective view of a premix burner with a frustoconical shaped element,

Fig. 5 sectional view through a premix burner with a frustoconical shaped element and

Fig. 6 + 7 perspective view of a premix burner with a funnel-shaped inlet area having a shaped element. WAYS OF IMPLEMENTING THE INVENTION, INDUSTRIAL APPLICABILITY

1 shows a perspective illustration of a premix burner, looking in the direction from the downstream side into the swirl space of a swirl generator 2 spanned by a plurality of partial cone shells 1. 2 shows the same premix burner, but from a different angle, namely from the outside onto the swirl generator 2, which is spanned by eight partial cone shells 1 in the exemplary embodiment shown. The further external guides with respect to the exemplary embodiment shown in FIGS. 1 and 2 are made uniformly, so that no further distinction is made between FIGS. 1 and 2.

The premix burner shown has a central receiving unit 3, which is designed in the form of a receiving sleeve and is provided for inserting and holding a central fuel supply unit, for example in the form of a fuel nozzle for liquid fuels or a fuel lance for a pilot flame (not shown). The partial cone shells 1 connected with their upstream ends to the receiving unit 3 mutually enclose air inlet slots 4 and are positioned relative to a burner axis A running centrally through the premix burner in such a way that they limit a swirl space that widens conically in the direction of flow at a cone angle y. Each individual partial cone shell 1 also has, depending on the type of fuel, at least one fuel feed line 5, via which fuel can be mixed into the combustion air supply stream passing through the air inlet slots 2.

The individual partial cone shells 1 open with their downstream end to maintain shape on an inner wall 6 of a cylindrical shaped element 7 surrounding the partial conical shells 1. The individual partial cone shells 1 are connected to the inner wall 6 of the shaped element 7 along a cutting line 8, which is defined by a virtual penetration each individual partial cone shell 1 with the inner wall 6 of the cylindrical shaped element 7 results. In this way, the swirl flow formed in the interior of the swirl generator 2 does not experience any disturbance after overflowing the individual partial cone shells 1. Upstream of the shaped element 7, for the purpose of an improved supply air flow through the air inlet slots 4 of the swirl generator 2, a second shaped element 9 is provided, which is also hollow-cylindrical and has a larger inner diameter than the first shaped elements 7. The inner diameter transition between the shaped elements 7 and 9 takes place via a discontinuous stage 10, on which the fuel supply lines 5 of each individual partial cone shell 1 adjoin.

The downstream contour of the shaped element 7 is cylindrical and offers the possibility of a structurally simple connection, for example with a combustion chamber (not shown) arranged according to the premix burner shown in the flow direction.

3 and 4 show a perspective view of a further embodiment of a premix burner designed according to the invention, in which, in contrast to the embodiment shown in FIGS. 1 and 2, the area of the shaped element 7 as a truncated cone section which tapers conically in the direction of flow is trained. In order to avoid repetition, the description of the reference symbols already introduced is omitted. The exemplary embodiment shown in FIGS. 3 and 4 has in the region of the shaped element 7 an inner wall 6 shown hatched in the perspective representations, on which the downstream ends of the partial cone shells 1 adjoin in a shape-maintaining manner. A hollow cylindrical shaped element 11, which serves as a coupling or flange piece for a subsequent combustion chamber, adjoins the inner wall 6 of the shaped element 7 downstream. Due to the inner wall 6 positioned in relation to the partial cone shells 1, the cutting lines 8 of the partial cone shells 1, with which they adjoin the inner wall 6, are smaller or shorter in the flow direction than in the case of the above exemplary embodiment, in which the partial cone shells are cylindrical in shape along a coaxial to the burner axis Adjoin the inside wall. A cross-sectional drawing of the embodiment shown in FIGS. 3 and 4 can be seen in FIG. 5. The shape-preserving abutment of each individual partial cone shell 1 on the inner wall 6 of the shaped element 7, which tapers conically in the flow direction and transitions into a straight-cylindrical region 11 in the flow direction, can be clearly seen.

FIGS. 6 and 7 show a further exemplary embodiment of a premix burner with a shaped element 7 which provides an upstream region, the so-called inflow region 12, which has an inner wall 6 which tapers in the direction of the flow in a funnel shape. The curvature of the inner wall 6 in this inflow region 12 corresponds approximately to the contour of a quarter ellipse. In the flow direction to the inflow region 12, a flow region 12 ′ adjoins within the frame of the shaped element 7 with a largely constant flow cross section, to which an inlet flange of a combustion chamber can ultimately be attached (not shown). As in the variants described above, the partial cone shells 1 of the swirl generator 2 run flush with the adjacent inner wall 6 of the shaped element 7 while maintaining their partial cone shell shape, as if the partial cone shells penetrated the inner wall 6 unhindered, but the partial cone shells 1 each connect via the cutting lines 8 the inner wall 6 from. In the case of the inflow region 12 designed as a quarter ellipse, the downstream end regions of the partial cone shells 1 nestle against the ellipse curvature of the inner wall 6 in this region 12. Reference is made to the above figures for the meaning of the reference symbols already introduced, which are additionally provided in FIGS. 6 and 7.

The connection according to the invention of each individual partial cone shell with its downstream end region maintaining shape with an inner wall of a shaped element surrounding the partial cone shells leads to the slightest irritation of the swirl flow passing through the partial cone shells. In contrast to the previously known premix burners, there are no blocking effects in the axial direction Direction connected by the burner axis with the shape-retaining runout of the partial cone shells according to the invention into the corresponding inner wall.

LIST OF REFERENCE NUMBERS

Cone shell

swirl generator

recording unit

Air inlet slots

Fuel supply line

inner wall

forming element

cutting plane

forming element

Step hollow cylindrical shaped element

inflow

Claims

claims

1. premix burner for operating a combustion chamber with a gaseous and / or liquid fuel with a swirl generator (2) for a combustion supply air flow to form a swirl flow and means (5) for injecting fuel into the swirl flow, the swirl generator (2) being at least two Partial conical shells (1) complementing a flow body, which together enclose a conical swirl chamber with a conical angle y and tangential air inlet slots (4) in the longitudinal direction of the cone, characterized in that at least on the downstream end region of the swirl generator (2) encloses the partial conical shells (1) Shaped element (7) with an inner wall (6) facing the partial cone shells (1) is provided, and that the partial cone shells (1) end flush into the inner wall (6) in a shape-retaining manner.

2. premix burner according to claim 1, characterized in that the shaped element (7) surrounds the partial cone shells (1) at their downstream end region in a ring-like manner such that the inner wall (6) of the shaped element (7) each has a cutting line (8) through the respective Partial cone shell (1), which along which the partial cone shell (1) penetrates the inner wall (6) virtually in a shape-retaining manner, is connected to the latter.

3. premix burner according to claim 1 or 2, characterized in that the inner wall (6) is frustoconical and has a tapered contour in the flow direction.

4 premix burner according to claim 1 or 2, characterized in that the inner wall (6) immediately downstream of the swirl generator (2) adjacent an inflow region (12) in which the inner wall (6) is funnel-shaped in the direction of flow.

5. premix burner according to claim 4, characterized in that the inner wall (6) in the inflow region (12) has a curvature contour formed in longitudinal section as a quarter ellipse.

6. premix burner according to claim 4 or 5, characterized in that downstream of the inflow region (12) the inner wall (6) merges into a flow section (12 ') which has a flow cross-section which remains constant in the flow direction.

7. premix burner according to claim 1 or 2, characterized in that the inner wall (6) is cylindrical.

8. premix burner according to claim 3 or 7, characterized in that in the flow direction a further shaped element (11) adjoins the first shaped element (7) with a further inner wall which has a constant flow cross-section axially.

9. premix burner according to one of claims 1 to 10, characterized in that the cone angle y is greater than 11 °, preferably greater than 20 °.

10. premix burner according to one of claims 1 to 9, characterized in that at least four, preferably eight, partial cone shells (1) are provided to form the swirl chamber.

11. premix burner according to one of claims 1 to 10, characterized in that the swirl generator (2) has a downstream burner diameter of greater than 180 mm.

12. Use of the premix burner according to one of claims 1 to 12 for firing a silo combustion chamber.