EP1141628A1

EP1141628A1 - Burner for heat generator

Info

Publication number: EP1141628A1
Application number: EP99959164A
Authority: EP
Inventors: Klaus DÖBBELING
Original assignee: Alstom Technology AG; Alstom Power Schweiz AG
Current assignee: General Electric Technology GmbH
Priority date: 1998-12-23
Filing date: 1999-12-21
Publication date: 2001-10-10
Anticipated expiration: 2019-12-21
Also published as: DE59912077D1; US6702574B1; DE19859829A1; AU1646000A; WO2000039503A1; EP1141628B1

Abstract

The invention relates to a burner for operating a heat generator. Said burner consists essentially of a swirl generator (100) for a combustion air flow (115) and means for injecting at least one fuel into the combustion air flow (115). Downstream of the swirl generator (100) a mixing section (20) is positioned which in a first part, in the direction of flow, presents a number of channels which are embodied in a transition piece (200) and serve to transfer a flow produced in the swirl generator (100) into a mixing tube (20) positioned downstream of the transition piece (200). A combustion chamber (30) is situated downstream of the mixing tube (20). The swirl generator (100) is integrated into a self-contained inflow cross-section (10) which is subjected to the combustion air flow (115).

Description

Burner for operating a heat generator

Technical field

The present invention relates to a burner for operating a heat generator according to the preamble of claim 1.

State of the art

In order to achieve high levels of efficiency and high power density, the principle of staged combustion is used for modern gas turbines. A hot gas is generated in a first high-pressure combustion chamber, preferably equipped with premix burners (cf. EP-0 321 809 B1), which flows after partial relaxation in a first high-pressure turbine into a second combustion chamber (reheat combustion chamber), in which the partially expanded hot gas is heated to the maximum turbine inlet temperature again, so that such a gas turbine is based on sequential combustion. Such a gas turbine is disclosed in US Pat. No. 5,454,220, US Pat. No. 5,577,378 and EP-0 620 362 A1, these publications forming an integral part of the present description.

The so-called reheat combustion chamber has a configuration which is shown and described in more detail in documents EP-0 745 809 A1 and EP-0 835 996 A1, these documents also forming an integral part of this description.

This combustion chamber is of an annular configuration, and it essentially has a number of individual, adjacent transition channels, which the Form single burners of this combustion chamber. These single burners have an almost rectangular cross-section, with the mixing of the fuel with the oxygen-containing partially released hot gas, hereinafter called combustion air, from the first turbine, via several longitudinal vortex generators, also called vortex generators, which are attached to the cooled walls of the mixing section and be cooled yourself. These longitudinal vortex generators (cf. EP-0 745 809 A1) generate a flow separation and deflection on their surface, which ultimately leads to the formation of longitudinal vortexes. The rectangular mixing channel is almost filled by several of these longitudinal vortices. It has been shown that such a configuration can lead to imperfections in the case of very specific operating modes and operating parameters: a) A considerable recooled air mass flow is required to cool the mixing section and the longitudinal vortex generators. b) The generated longitudinal vortices cannot completely capture the flow cross-section, particularly in the corners of the rectangle. c) In the generation of the longitudinal vortices, kinetic energy is dissipated in turbulence in the separation areas of the longitudinal vortices and only part of the kinetic energy is converted into the longitudinal vortical movement. d) After the step-like expansion into the combustion chamber, the flow does not touch the combustion chamber wall until after a considerable distance, ie undesired dead water and backflow areas arise after the step change.

Presentation of the invention

The invention seeks to remedy this. The invention, as characterized in the claims, is based on the object of eliminating the imperfections listed above in a premix burner of the type mentioned. According to the invention, the mixing of the combustion air, ie the partially relaxed hot gases and fuel, is accomplished in a round mixing section, which mixing section is filled by a single swirl flow. To generate swirl, a conical swirl generator or swirl generator blades consisting of several partial bodies are built into the still rectangular inlet cross-section, which swirl the combustion air. The entry slots formed by the swirl generator blades or present between the individual partial bodies of the swirl generator are preferably of constant slot width, but they can have a variable slot width along their length. Four inlet slots are preferably provided, but designs with a different number of slots are also possible. Such a swirl generation largely corresponds to that according to DE-44 35 266 A1. A difference to this swirl generation is that the swirl generator according to the invention is installed in an initially rectangular channel, which is converted over the length of the swirl generator into a channel with an approximately square or round cross-section, with care being taken to ensure a clean flow against the swirl generator inlet slots must, in order to avoid flow separation at best.

A fuel distribution system for gaseous and / or liquid fuels is integrated in the swirl generator, the fuel being distributed along the inlet slots, as can be seen from the last-mentioned publication, or through the trailing edges of the swirl generator blades or by axially injecting the fuel from the blade surface, whereby here is primarily about the injection of a low or medium calorific fuel (Lbtu, Mbtu). If necessary, the fuel can be enveloped in a cold carrier air stream or inert gas stream in order to avoid premature ignition of the fuel. Liquid fuels are advantageously injected at the upstream end of the swirl generator by means of several individual jets, it being shown here that it is extremely advantageous if the number of individual radiate with the number of inlet slots in the swirl generator or the number of swirl generator blades.

There is a free flow channel on the axis of the swirl generator, which prevents a backflow zone from forming in the mixing tube. Liquid fuel must therefore be supplied off-axis, preferably through the multiple nozzle system already mentioned above.

In order to protect the swirl generator blades against oxidation attacks due to the hot inlet temperatures, they can either be made of a ceramic material and / or can be provided with internal air cooling. The design and manufacture of the air-cooled swirl generator blades follows the rules known from the cooled turbine blades, but the heat transfer coefficients are significantly lower compared to rotor or guide blades in the turbine due to the lower flow velocities.

After the swirl generator, the flow is conducted in a cylindrical mixing tube. The transition from the swirl generator to the mixing tube is to be designed in such a way that the flow cross-sectional area is almost constant and no detachments occur. This can be done either by a specially shaped transition piece or by immersing the swirl generator blades in the cylindrical channel. Another possibility is to provide the swirl generator blades with a cut-free trailing edge in the axial direction. The length of the mixing tube is chosen so that the auto-ignition time of the selected fuels is not exceeded from the fuel injection to the end of the mixing tube. Depending on the size of the burner and depending on the selected burner pressure loss, the length of the mixing section can vary between zero and two burner diameters.

In order to prevent the flame from reigniting in the boundary layers of the transition piece and the mixing tube that are building up, flame reignition barrier films can be introduced at a suitable point. At the downstream end of the mixing tube a differently designed tear-off edge can be attached, which stabilizes the boundary layer via the Conda effect due to a convexly curved end part and deflects the entire flow outwards. On the one hand, this ensures that the flow in the combustion chamber is applied to the wall faster and decelerated faster, so that a turbulent flame front can occur. On the other hand, due to the delay at the end of the mixing tube, part of the dynamic pressure is recovered in the sense of a diffuser effect.

The swirl strength can be set to such an extent that a backflow area arises on the axis downstream of the mixing section, but preferably the swirl strength should be so large that the flow downstream of the mixing pipe within a mixing pipe diameter on the axis only decelerates to speeds lower than the cross-section-average combustion chamber speed becomes. The turbulent speed fluctuations generated during this lossy deceleration serve to stabilize the flame.

The fuel is supplied to the swirl generator by a fuel and cooling air supply that runs radially to the burner axis. The swirl generator can be attached to the fuel feed and can be removed radially from the gas turbine with it, without the housing having to be lifted off.

The main advantages of the invention can be seen in

a) that the design of the mixing section according to the invention as a cylindrical tube minimizes the surface sensitive to the flashback, this reduces the cooling and film air required for non-return check and for cooling the wall and thus optimizes the overall process; b) that the inventive design of the mixing section as a cylindrical tube makes it possible to optimally fill the entire mixing section with a single longitudinal vortex; c) that the injection of the fuel along the inlet slots enables a good fine distribution, thereby minimizing the required mixing distance after the swirl generator; d) that the swirl is generated with little loss, ie, no separation areas and total pressure loss zones are generated with an inventive design. As a result, the pressure loss coefficient of the burner is small in relation to the effective flow cross-section, and there is only little flame-stabilizing turbulence in the mixing section, so that a flashback is avoided even at lower flow velocities, e) due to the strong flow delay downstream of the mixing tube it is possible to increase the opening ratio, namely the mixing tube cross section to the proportionate combustion chamber cross section, to values> 4 to at least 10. As a result, a substantially shorter combustion chamber can be built with the same dwell time and thus still good burnout, f) that the swirl generator and the fuel injection can be designed in such a way that they can be removed radially outward without lifting off the housing of the gas turbine. This makes it easy to replace swirl generators that need to be replaced and to switch to other fuels or fuel injection systems.

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. The same elements are provided with the same reference symbols in the different figures. The direction of flow of the media is indicated by arrows. Brief description of the drawings

It shows:

1 shows a schematic section through a burner,

Fig. 2 shows a configuration of the built-in swirl generator in perspective and

Fig. 3 shows another embodiment of a swirl generator.

WAYS OF CARRYING OUT THE INVENTION, INDUSTRIAL APPLICABILITY

Fig. 1 shows the overall structure of a burner system for operating a combustion chamber. The burner system basically consists of four operating levels, each of which fulfills a specific function and is interdependent in a process flow. The first section consists on the one hand of an inflow cross section 10 for a combustion air flow, in which inflow cross section 10 a swirl generator 100 is arranged. The swirl flow formed in this swirl generator 100 is transferred without separation into a mixing tube 20 using a downstream transition geometry 200. Such a transition geometry 200 is shown and described in the document DE-44 35 266 A1, under FIG. 6, this document forming an integral part of the present description. On the outflow side of the mixing tube 20 there is the actual combustion chamber 30, which here is only symbolized by the flame tube. The mixing tube 20 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 20, furthermore enables loss-free flow guidance, so that no backflow zone can initially form even in operative connection with the transition geometry 200, so that the length of the mixing tube 20 can exert an influence on the quality of the mixture for all types of fuel. However, this mixing tube 20 also has another property, which consists in the fact that the axial velocity profile in the mixing tube itself has a pronounced maximum on the axis, so that the flame can not be re-ignited from the combustion chamber 30. However, it is correct that with such a configuration this axial speed drops towards the wall. To prevent re-ignition in this area, the mixing tube 20 is provided in the flow and circumferential direction with a number of regularly or irregularly distributed bores 21 of various cross-sections and directions through which an amount of air flows into the interior of the mixing tube 20 and along the wall in the In the sense of filming, an increase in the speed prevailing there is induced. Another possibility of achieving the same effect is that the flow cross section of the mixing tube 20 is narrowed on the outflow side of the transition geometry 200, as a result of which the overall speed level within the mixing tube 20 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 geometry corresponds to the narrowest flow cross-section of the mixing tube 20. The transition geometry 200 mentioned therefore bridges 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 20, this can be remedied by providing a diffuser, not shown in the figure, at the end of the mixing pipe 20. At the end of the mixing tube 20, the aforementioned combustion chamber 30 on, with a cross-sectional jump between the two flow cross-sections. Only here does a central backflow zone 50 form, which has the properties of a disembodied 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 return flow zone 50 flows directly into the cross-sectional jump, and there contributes lower 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 end of the tube, for example by means of tangential openings. It is assumed here that the amount of air required for this is about 5-20% of the total amount of air used to operate the combustion chamber. With regard to the more detailed configuration of the edge at the end of the mixing tube 20 to strengthen the backflow zone 50, reference is made to the documents DE-195 47 913 A1, FIG. 7 and DE-196 39 301 A1, FIGS. 8-11, whereby both documents in their entirety form an integral part of the present description.

Fig. 2 shows the head stage of the burner. The square inflow cross section 10 and the swirl generator 100 integrated therein are shown here. This inflow cross-section 10 per se forms an autonomous burner unit and, in conjunction with a number of further subordinate inflow cross-sections, an annular combustion chamber, preferably for operating gas turbines, in particular an afterburning chamber, as can be seen from EP-0 620 362 A1, FIG. 5. The inflow cross section 10 has a rectangular shape on the head side the run length of the swirl generator 100 changes into a square cross section.

The mode of operation of the swirl generator 100 shown here can be seen from the description of the documents DE-44 35 266 A1, Fig. 2-5; DE-19547 913 A1, Fig. 2-5; DE-196 39 301, Fig. 2-5, remove, these documents form an integral part of this description.

Briefly described here, the swirl generator (100) consists of at least two hollow, conical partial bodies 101 nested one inside the other in the direction of flow, the respective axes of longitudinal symmetry of which are offset such that the adjacent walls of the partial bodies 101 have tangential channels 102 in their longitudinal extension for the inflow of the combustion air 115 in have an interior 103 formed by the partial bodies 101. With effect on this interior, at least one fuel nozzle is provided.

FIG. 3 shows a further embodiment of a swirl generator, which can easily be integrated into the inflow cross section according to FIG. 2. This swirl generator 150 consists of a central body 151, which has a radial or quasi-radial line 152 for the supply of fuels 153, 154. Individual swirl blades 156, which extend in the axial direction, are anchored on this central body 151. These swirl blades are encased in a jacket-like manner by a pipe 155, which is open at the ends, on the head side for the inflow of the combustion air 115 (see FIG. 1) and on the outflow side for the onward flow of the swirled combustion air (see FIG. 1), with which he differs from that of the swirl generator according to FIG. 2 as far as the inflow of the combustion air is concerned. Interdependent on the swirling of the combustion air 115, fuel is added, which also results in a first premixing analogous to the swirl generator according to FIG. the final premixing then takes place downstream, on the one hand along the transition geometry (see FIG. 1, item 200) and then within the mixing tube (see FIG. 1, item 20). Liquid fuels 154 are on the top and central resp. quasi-centrally injected 154a; gaseous fuels 153, on the other hand, via a number of openings 153a integrated in the swirl blades 156. The number and degree of swirl of the swirl blades 156 vary depending on the particular requirements of the premixing process.

In the case of a decentralized fuel injection 154a of the liquid fuel 154, the injection angle of the fuel jet belonging to the fuel nozzle 154a with respect to the axis is preferably approximately set equal to the angle of attack of the swirl vanes 156. With this precaution a perfect premixing of the fuel used is guaranteed, while maintaining a reliable and optimal flame positioning, i.e. Enrichment of the central zone is thus permanently prevented, and the fuel drops are exposed to greater radial acceleration as the radius increases within the premixing section in such a way that they can mix well into the combustion air entering there.

In the case of a swirl generator of a burner consisting of several shells, as can be seen, for example, from EP-B1-0 321 809 or from the swirl generator according to FIG. 1 (cf. the documents cited there), the follow-up zones along the Leeward side of the corresponding shell, or the guide vanes or the swirl vanes of a correspondingly designed swirl generator. There, the drop spray is exposed to lower aerodynamic forces and, accordingly, it is better mixed radially into the combustion air.

The number of injection points is adapted to the burner design, at least one injection per bowl or scoop being provided.

Reference list

10 inflow cross section 20 mixing tube Holes combustion chamber, combustion chamber openings pipe flow backflow zone, backflow bubble burner axis swirl generator part body tangential channels interior combustion air, combustion airflow swirl generator central body fuel line fuel, gaseous fuel a fuel injection, fuel nozzle fuel, liquid fuel a fuel injection, fuel nozzle tube swirl vane transition piece, transition piece

Claims

claims

1. Burner for operating a heat generator, the burner consisting essentially of a swirl generator for a combustion air flow and of means for injecting at least one fuel into the combustion air flow, a mixing section being arranged downstream of the swirl generator, which is located within a first section part in the flow direction has a number of channels in a transition piece for transferring a flow formed in the swirl generator into a mixing tube downstream of this transition piece, a mixing chamber formed by a cross-sectional widening being arranged downstream of this mixing tube, characterized in that the swirl generator (100, 150) is in one is closed and integrated by a combustion air flow (115) inflow cross-section (10) is integrated.

2. Burner according to claim 1, characterized in that the swirl generator

(100) consists of at least two hollow, conical, part-bodies (101) nested one inside the other in the direction of flow that the respective longitudinal axes of symmetry of these part-bodies run offset from one another, in such a way that the adjacent walls of the part-bodies in their longitudinal extension are tangential channels (102) for the inflow of the combustion air flow (115) into an interior (103) formed by the partial bodies (101).

3. Burner according to claim 2, characterized in that with effect on the interior (103) at least one fuel nozzle is present.

4. Burner according to claim 2, characterized in that the partial body

(101) have a shovel-shaped profile in cross section.

5. Burner according to claim 1, characterized in that the swirl generator (150) consists of a number of swirl blades (156) which are integrated in a closed casing (155).

6. Burner according to claim 5, characterized in that the swirl generator has means for the injection (153a, 154a) of at least one fuel (153, 154).

7. Burner according to claims 5 and 6, characterized in that the swirl generator has at least one head-side fuel nozzle (154a), and that the fuel nozzle (154a) is directed approximately towards the burner axis (60) according to the angle of attack of the swirl vanes (156).

8. Burner according to claims 3 or 7, characterized in that the number of fuel nozzles (154a) corresponds at least to the number of swirl-forming elements (101, 156) of the swirl generator (100, 150).

9. Burner according to claims 1 and 2 or 1 and 5, characterized in that the number of channels in the transition piece (200) corresponds to the number of swirled partial flows formed by the swirl generator (100, 150).

10. Burner according to claim 1, characterized in that the inflow cross section (10) merges from a rectangular cross section on the head side over the barrel length of the swirl generator (100) into an approximately square or round cross section.

11. Burner according to claim 1, characterized in that the inflow cross section (10) is part of an annular combustion chamber.