BURNER FOR A GAS TURBINE

Abstract

A burner for a gas turbine, wherein the burner has a combustion chamber, a preheating device adapted to preheat air before it enters the combustion chamber and a swirler adapted to guide a swirler air flow that has the preheated air to the combustion chamber, wherein the swirler has a base plate with a surface that confines the swirler air flow, wherein the surface has a hole adapted to inject a liquid fuel into the swirler air flow and the base plate has a channel for transporting the liquid fuel to the hole, wherein at least a part of the channel is oriented essentially parallel to the surface so that the liquid fuel streams essentially parallel to the surface and is preheated by the swirler air flow.

Description

FIELD OF INVENTION

The invention relates to a burner for a gas turbine.

BACKGROUND OF INVENTION

A burner for a gas turbine can be operated at certain operating conditions by injecting water into the combustion chamber in order to reduce the flame temperature and therefore reducing the emission of NO_x. An alternative approach for reducing the emission of NO_x lies in using dry low emission (DLE) burners that are operated without the injection of water and are based on premixing fuel and air prior to combustion. DLE burners emit low concentrations of NO_x and produce compact flames. However, the DLE burners are conventionally designed for a full load operation. In particular, the DLE burners comprise fuel lances for the injection of a liquid fuel into the combustion chamber, wherein the lances are sized such that an efficient atomisation of the liquid fuel and an efficient mixing of the fuel with air occurs at the full load operation.

However, when the burner is operated at a part load operation, the pressure drop over the lances is lower in comparison to the full load operation, which results in a less efficient atomisation than at the full load operation. This leads to a less efficient mixing of the fuel with air and can lead to the formation of fuel ligaments that are deposited on surfaces of the burner where it leads to the formation of a carbon build-up. When the carbon build-up is formed on the lances it can lead to an obstruction of the fuel and when this carbon build-up is formed at an igniter-port it can lead to a reduction in the efficiency of ignition. Furthermore, the less efficient mixing of the fuel with air can lead to the formation of soot that is emitted into the atmosphere.

Conventionally, at the part load operation the DLE combustor is operated such that compressed air is bled from the gas turbine so that less air enters the combustion chamber which raises the flame temperature. With this higher temperature the carbon build-up can at least be partly burned. However, this operation is disadvantageous since it reduces the efficiency of the gas turbine and can not be performed at a part load of less than 40% of the full load.

SUMMARY OF INVENTION

It is therefore an object of the invention to provide a burner that can be operated throughout the load range including a part load operation with an efficient atomisation of a liquid fuel and an efficient mixing of the fuel with air.

The burner according to the invention for a gas turbine comprises a combustion chamber, a preheating device adapted to preheat air before it enters the combustion chamber and a swirler adapted to guide a swirler air flow that comprises the preheated air to the combustion chamber, wherein the swirler comprises a wall with a surface that confines the swirler air flow, wherein the surface has a hole adapted to inject a liquid fuel into the swirler air flow and the wall has a channel for transporting the liquid fuel to the hole, wherein at least a part of the channel is oriented essentially parallel to the surface so that the liquid fuel can stream essentially parallel to the surface and can be preheated by the swirler air flow. The viscosity of the liquid fuel is reduced when its temperature is increased by the preheating. This leads advantageously to an efficient atomisation of the liquid fuel and therefore to an efficient mixing of the fuel with the air. The atomisation and the mixing will also be efficient at a part load operation of the burner when the pressure drop of the liquid fuel over the through hole is lower than at a full load operation of the burner. Furthermore, the hole requires a lower pressure drop for the atomisation of the liquid fuel in comparison to a fuel lance. Also for this reason an efficient atomisation of the liquid fuel can take place at low part loads.

It is advantageous that the part of the channel which is oriented essentially parallel to the surface has a distance to the surface from 2 mm to 10 mm. These values ensure an efficient heat transfer to the liquid fuel while maintaining the integrity of the wall. The diameter of the hole is advantageously from 0.5 mm to 3 mm. It is advantageous that the diameter of the channel in a plane perpendicular to the flow direction of the liquid fuel is from 0.5 mm to 3 mm.

The material of the wall advantageously consists of carbon steel and/or steel with 1 weight-% carbon. The carbon steel has a heat conductivity of 54 W/(m*K) and the steel with 1 weight-% carbon has a heat conductivity of 43 W/(m*K) which are much higher values than the heat conductivity of 16 W/(m*K) for the conventionally used stainless steel.

It is advantageous that the wall with the channel is formed by electronic discharge machining, selective laser sintering and/or selective laser melting. With these techniques it is advantageously possible to form channels with complex geometries with many curves. With these complex geometries it is possible to bring a long section of the channel close to the surface, hence making the heat transfer to the liquid fuel particularly efficient. The wall advantageously comprises two joint plates, wherein each plate comprises recesses that form a part of the channel. The recesses in the plates can be formed by milling that is advantageously a simple and cost-efficient technique. It is advantageous that the channel has the shape of a spiral. It is advantageous that the channel has a meandering shape. With both shapes it is possible to bring a long section of the channel close to the surface, hence making the heat transfer to the liquid fuel particularly efficient.

It is advantageous that the burner comprises a compressor for compressing the air before it enters the combustion chamber, whereby the temperature of the air raises and the compressor forms the preheating device. By preheating the air in this manner, it is advantageously achieved that the air is sufficiently hot for preheating the liquid fuel.

The burner comprises advantageously a further wall confining the swirler air flow on the same side as and upstream with respect to the swirler air flow from the wall and being displaced with respect to the wall in a direction towards the swirler air flow so that a step being able to cause a flow separation of the swirler air flow is formed by the wall and the further wall. The flow separation caused by the step causes the formation of a vortex downstream with respect to the swirler air flow. Since the liquid fuel is injected via the through hole into the swirler air flow and not by a lance that would protrude from the wall, the liquid fuel is directly mixed with the air when exiting the second wall and therefore interacts with the vortex. Together with the low viscosity of the liquid fuel this interaction leads to a particular efficient atomisation of the liquid fuel and a particular efficient mixing with air.

It is advantageous that the combustion chamber is essentially rotationally symmetric around a burner axis and the step is located at a radial distance from the burner axis which is from r₁+0.2*(r₂−r₁) to r₁+0.8*(r₂−r₁), wherein r₁ is the radial distance from the burner axis to the radial inner end of the swirler and r₂ is the radial distance from the burner axis to the radial outer end of the swirler. The lower boundary advantageously ensures an efficient interaction of the liquid fuel with the vortex. The upstream boundary advantageously ensures the formation of the vortex. The height of each step is advantageously from 0.2*L to 0.5*L, wherein L is the distance from the step to the hole. This height advantageously ensures the formation of the vortex that is efficiently interacting with the liquid fuel. It is advantageous the height of each step is maximum 15% of the swirler channel height, wherein the swirler channel height is the distance from the further wall to an opposite wall confining the swirler air flow and facing towards the wall. This maximum height advantageously avoids a large pressure drop of the swirler air flow when passing the step.

BRIEF DESCRIPTION OF THE DRAWINGS

The above mentioned attributes and other features and advantages of this invention and the manner of attaining them will become more apparent and the invention itself will be better understood by reference to the following description of embodiments of the invention taken in conjunction with the accompanying drawings, wherein

FIG. 1 shows part of a gas turbine in a sectional view and in which the present inventive burner is incorporated,

FIG. 2 shows a longitudinal section of the burner and a part of the combustor,

FIG. 3 shows a perspective view of a part of the a swirler of the burner,

FIG. 4 shows a sectional view of a part of the swirler with a first channel,

FIG. 5 shows a top view of the swirler,

FIG. 6 shows a perspective view of a part of the swirler with a second channel,

FIG. 7 shows a perspective view of a part of the swirler with a third channel,

FIG. 8 shows a sectional view of a part of the swirler with a fourth channel.

FIGS. 9 to 13 show different embodiments for holes of the swirler.

DETAILED DESCRIPTION OF INVENTION

FIG. 1 shows an example of a gas turbine engine 10 in a sectional view. The gas turbine engine 10 comprises, in flow series, an inlet 12, a compressor section 14, a combustor section 16 and a turbine section 18 which are generally arranged in flow series and generally about and in the direction of a longitudinal or rotational axis 20. The gas turbine engine 10 further comprises a shaft 22 which is rotatable about the rotational axis 20 and which extends longitudinally through the gas turbine engine 10. The shaft 22 drivingly connects the turbine section 18 to the compressor section 14.

In operation of the gas turbine engine 10, air 24, which is taken in through the air inlet 12 is compressed by the compressor section 14 and delivered to the combustion section or burner section 16. As part of the compression process, the air temperature is normally raised from ambient temperature to approximately 400-400° C., along with the raise in air pressure. The burner section 16 comprises a burner plenum 26, one or more combustion chambers 28 and at least one burner 30 fixed to each combustion chamber 28. The combustion chambers 28 and the burners 30 are located inside the burner plenum 26. The compressed air preheated through the compressor 14 enters a diffuser 32 and is discharged from the diffuser 32 into the burner plenum 26 from where a portion of the air enters the burner 30 and is mixed with a gaseous or liquid fuel. The air/fuel mixture is then burned and the combustion gas 34 or working gas from the combustion is channelled through the combustion chamber 28 to the turbine section 18 via a transition duct 17.

This exemplary gas turbine engine 10 has a cannular combustor section arrangement 16, which is constituted by an annular array of combustor cans 19 each having the burner 30 and the combustion chamber 28, the transition duct 17 has a generally circular inlet that interfaces with the combustor chamber 28 and an outlet in the form of an annular segment. An annular array of transition duct outlets form an annulus for channelling the combustion gases to the turbine 18.

The turbine section 18 comprises a number of blade carrying discs 36 attached to the shaft 22. In the present example, two discs 36 each carry an annular array of turbine blades 38. However, the number of blade carrying discs could be different, i.e. only one disc or more than two discs. In addition, guiding vanes 40, which are fixed to a stator 42 of the gas turbine engine 10, are disposed between the stages of annular arrays of turbine blades 38. Between the exit of the combustion chamber 28 and the leading turbine blades 38 inlet guiding vanes 44 are provided and turn the flow of working gas onto the turbine blades 38.

The combustion gas from the combustion chamber 28 enters the turbine section 18 and drives the turbine blades 38 which in turn rotate the shaft 22. The guiding vanes 40, 44 serve to optimise the angle of the combustion or working gas on the turbine blades 38.

The turbine section 18 drives the compressor section 14. The compressor section 14 comprises an axial series of vane stages 46 and rotor blade stages 48. The rotor blade stages 48 comprise a rotor disc supporting an annular array of blades. The compressor section 14 also comprises a casing 50 that surrounds the rotor stages and supports the vane stages 48. The guide vane stages include an annular array of radially extending vanes that are mounted to the casing 50. The vanes are provided to present gas flow at an optimal angle for the blades at a given engine operational point. Some of the guide vane stages have variable vanes, where the angle of the vanes, about their own longitudinal axis, can be adjusted for angle according to air flow characteristics that can occur at different engine operations conditions.

The casing 50 defines a radially outer surface 52 of the passage 56 of the compressor 14. A radially inner surface 54 of the passage 56 is at least partly defined by a rotor drum 53 of the rotor which is partly defined by the annular array of blades 48.

The present invention is described with reference to the above exemplary turbine engine having a single shaft or spool connecting a single, multi-stage compressor and a single, one or more stage turbine. However, it should be appreciated that the present invention is equally applicable to two or three shaft engines and which can be used for industrial, aero or marine applications. It should be appreciated that the invention is equally applicable to burners used in e.g. annular combustion chambers.

FIG. 2 shows that the burner 30 comprises an inner wall 101 that confines the combustion chamber 28 in a radial direction. Furthermore, the burner 30 comprises a pilot burner 104 and a main burner 105 that are arranged on an axial end of the burner 30 and confine an axial end of the combustion chamber 28. The main burner 105 is arranged radially outside from the pilot burner 104. The burner 30 comprises an outer wall 102 that is arranged radially outside of the inner wall 101. The inner wall 101 and the outer wall 102 are essentially rotationally symmetric around a burner axis 35 of the burner 30. In the operation of the burner, the air 24 is streamed in the space between the inner wall 101 and the outer wall 102 towards the pilot burner 104 and the main burner 105 as indicated by arrows 108, so that the inner wall 101 is cooled and the air 24 is preheated before it enters the combustion chamber 28. In this manner the inner wall 101 and the outer wall 102 form a preheating device for preheating the air.

The burner 30 comprises a swirler 107 located on the main burner 105 for swirling the air before it enters the combustion chamber 28. After passing the space between the inner wall 101 and the outer wall 102 the air 24 passes through the swirler 107 in a direction towards the burner axis 35 and enters the combustion chamber 28. The burner 30 is configured for dry operation only, i.e. it is not configured for the injection of water into the combustion chamber 28.

The swirler 107 comprises a first axial end 113 that coincides with the main burner 105 and a second axial end 114 being located opposite to the first axial end 113. As it can be seen in FIGS. 3 and 5, the swirler 107 furthermore comprises a multitude of swirler sectors or vanes 118 that are in contact with the first axial end 113 and the second axial end 114. The first axial end 113, the second axial end 114 and the swirler sectors 118 confine a swirler air flow 125. The swirler sectors 118 are shaped such that the air flow entering the combustion chamber 28 has a flow direction with respect to the burner axis 35, wherein the flow direction essentially consists of a radial inward component and a component in circumferential direction. The swirler 107 comprises an annular array of vanes 118 (swirler sectors) extending from a base plate or wall 116 which define an annular array of passages for the swirler airflow (125). The base plate 116 defines one of the surfaces of the passages over which the swirler air flow 125 flows.

FIGS. 2 to 8 show that the swirler 107 comprises a wall or base plate 116 with a surface that confines the swirler air flow 125 at the first axial end 113. The surface has a hole 103 adapted to inject a liquid fuel into the swirler air flow 125 and the wall has a channel 131 to 134 for transporting the liquid fuel to the hole 103, wherein at least a part of the channel 131 to 134 is oriented essentially parallel to the surface so that the liquid fuel can stream essentially parallel to the surface and is partly preheated by the swirler air flow 125. The swirler itself incurs temperature input directly from the combustion flame and the surrounding combustor or burner architecture. As it can be seen in FIGS. 3, 4 and 6 to 8, after leaving the hole 103 the liquid fuel is atomised and mixed with the swirler air flow 125 in an atomisation region 119.

It is conceivable that the part of the channel 131 to 134 which is oriented essentially parallel to the surface has a distance to the surface from 2 mm to 10 mm. It is furthermore conceivable that the diameter of the hole 103 is from 0.5 mm to 3 mm. It is conceivable that the diameter of the channel 131 to 134 in a plane perpendicular to the flow direction of the liquid fuel is from 0.5 mm to 3 mm. The wall 116 consists of a material with high heat conductivity, for example carbon steel and/or steel with 1 weight-% carbon. It is conceivable that the wall 116 with the channel 131 to 134 is formed by electronic discharge machining, selective laser sintering and/or selective laser melting.

As it can be seen in FIGS. 3, 4, and 6 to 8 the burner 30 comprises a further wall 115 confining the swirler air flow 125 on the same side as and upstream with respect to the swirler air flow 125 from the wall 116. The further wall 115 can be displaced with respect to the wall 116 in a direction towards the swirler air flow so that a step being able to cause a flow separation of the swirler air flow 125 is formed by the wall 116 and the further wall 115.

FIG. 4 shows the burner 30 with a first channel 131. The first channel 131 has a meandering shape, wherein a multitude of sections of the first channel 131 are arranged next to each other in the axial direction with respect to the burner axis 35. FIG. 6 shows the burner 30 with a second channel 132. The second channel 132 has a meandering shape, wherein the section of the second channel 132 with the meandering shape is arranged parallel to the surface of wall 116. FIG. 7 shows the burner 30 with a third channel 133. The third channel 133 has the shape of a spiral, wherein the hole 103 is located in the centre of the spiral. FIG. 8 shows the burner 30 with a fourth channel 134. The fourth channel 134 has a meandering shape, wherein a multitude of sections of the forth channel 134 are arranged next to each other in the axial direction with respect to the burner axis 35. The fourth channel 134 extends almost over the entire wall 116 for an effective heat transfer from the swirler air flow 125 to the liquid fuel.

FIG. 4 shows the swirler 107 with the second channel 132 according to FIG. 6 and and the third channel 133 according to FIG. 7. As it can be seen in FIG. 4 a single hole 103 can be arranged between two neighboured swirler sectors 108 or a multitude of holes can be arranged between two neighboured swirler sectors 108.

FIGS. 9 to 13 show possible geometries for the holes 103. The first hole 121 according to FIG. 9 has the shape of a circle with a missing sector having an angle of 90°. The second hole 122 according to FIG. 10 has the shape of a ring. The hole 123 according to FIG. 11 consists of a plurality of elongate holes that are arranged tilted with respect to each other. The hole 124 according to FIG. 12 has the form of a circle. FIG. 13 shows a perspective view of a plate 126 containing the hole 124 according to FIG. 12. The holes 103 can be formed as an assembly of several joint layers of metal.

Although the invention is described in detail by the preferred embodiment, the invention is not constrained by the disclosed examples and other variations can be derived by the person skilled in the art, without leaving the extent of the protection of the invention.

Claims

1. A burner for a gas turbine, wherein the burner comprises: a combustion chamber, anda swirler,wherein the swirler comprises an annular array of vanes extending from a base plate which define an annular array of passages for guiding a swirler airflow, the base plate defines a surface of the passage over which the swirler air flow flows,wherein the surface has a hole adapted to inject a liquid fuel into the swirler air flow and the base plate has a channel for transporting the liquid fuel to the hole,wherein at least a part of the channel is oriented essentially parallel to the surface so that the liquid fuel is streamed essentially parallel to the surface and is preheated.

2. The burner according to claim 1, wherein the part of the channel which is oriented essentially parallel to the surface has a distance to the surface from 2 mm to 10 mm.

3. The burner according to claim 1, wherein the diameter of the hole is from 0.5 mm to 3 mm.

4. The burner according to claim 1, wherein the diameter of the channel in a plane perpendicular to the flow direction of the liquid fuel is from 0.5 mm to 3 mm.

5. The burner according to claim 1, wherein the material of the base plate consists of carbon steel and/or steel with 1 weight-% carbon.

6. The burner according to claim 1, wherein the base plate with the channel is formed by electronic discharge machining, selective laser sintering and/or selective laser melting.

7. The burner according to claim 1, wherein the base plate comprises two joint plates, wherein each plate comprises recesses that form a part of the channel.

8. The burner according to claim 1, wherein the channel has the shape of a spiral.

9. The burner according to claim 1, wherein the channel has a meandering shape.

10. The burner according to claim 1, further comprising: a compressor for compressing the air before it enters the combustion chamber, whereby the temperature of the air raises and the compressor forms the preheating device.

11. The burner according to claim 1, further comprising: a further wall confining the swirler air flow on the same side as and upstream with respect to the swirler air flow from the base plate and being displaced with respect to the base plate in a direction towards the swirler air flow so that a step being able to cause a flow separation of the swirler air flow is formed by the base plate.

12. The burner according to claim 1, wherein the combustion chamber is essentially rotationally symmetric around a burner axis and the step is located at a radial distance from the burner axis which is from r1+0.2*(r2−r1) to r1+0.8*(r2−r1), wherein r1 is the radial distance from the burner axis to the radial inner end of the swirler and r2 is the radial distance from the burner axis to the radial outer end of the swirler.

13. The burner according to claim 1, wherein the height of each step is from 0.2*L to 0.5*L, wherein L is the distance from the step to the hole.

14. The burner according to claim 1, wherein the height of each step is maximum 15% of the swirler channel height (H), wherein the swirler channel height (H) is the distance from the further wall to an opposite wall confining the swirler air flow and facing towards the base plate.

15. The burner according to claim 1, further comprising: a preheating device adapted to preheat air before it enters the combustion chamber and the swirler adapted to guide the swirler air flow that comprises the preheated air to the combustion chamber.