WO2007128963A1

WO2007128963A1 - A fuel burner and a method of manufacturing a fuel burner

Info

Publication number: WO2007128963A1
Application number: PCT/GB2007/001236
Authority: WO
Inventors: Philip David Butler; John Robert Hill; Nicholas James Vanter
Original assignee: Rolls-Royce Fuel Cell Systems Limited
Priority date: 2006-05-05
Filing date: 2007-04-04
Publication date: 2007-11-15
Also published as: GB0608862D0

Abstract

A fuel burner (10) comprises a plurality of sealed fuel ducts (12). Each fuel duct (12) has at least one open end, a first sealed edge (18) and a second open edge (20). The fuel ducts (12) are arranged substantially parallel to each other and the fuel ducts (12) are spaced apart to form a plurality of parallel oxidant passages (24) therebetween. A fuel supply supplies fuel to the at least one open end of each fuel duct (12). The fuel ducts (12) are arranged such that the second open edges (20) face in substantially the same direction to discharge fuel in said direction. An oxidant supply supplies oxidant to the parallel oxidant passages (24) between the fuel ducts (12) in substantially the said direction to mix with the fuel discharged from the second open edges (20) of the fuel ducts (12).

Description

A FUEL BURNER AND A METHOD OF MANUFACTURING A FUEL BURNER

The present invention relates to a fuel burner, and in particular to a fuel burner for fuel cells.

Conventionally, gas turbine engine fuel burners use a relatively high-pressure drop across the fuel and/or airflow to provide mixing of the fuel and air prior to burning in the combustion chamber. Good mixing of the fuel and air is required in order to minimise flame temperature and thus the emissions of nitrous oxides (NOx) . A fuel burner for a solid oxide fuel cell system is required to burn any small amounts of fuel left over by the solid oxide fuel cells . The principal flammable component of the fuel is hydrogen. The key properties of hydrogen, which affect the design of the fuel burner, are that hydrogen has a very high diffusivity making the design susceptible to leakage and hydrogen has a very short auto- ignition time and thus the hydrogen will ignite rapidly in an oxidising environment when that environment is above the auto-ignition temperature of hydrogen. The leakage of fuel within a fuel burner is particularly important because it is likely to result in combustion within the structure of the fuel burner because solid oxide fuel cells operate in a high temperature environment. Any combustion of fuel within the structure of the fuel burner would compromise the integrity, and operational life, of the fuel burner and effect the performance of the whole solid oxide fuel cell system.

However, in fuel burners used for some solid oxide fuel cell systems there is insufficient pressure drop available to provide mixing of the fuel and air. In some solid oxide fuel cell systems oxidant and fuel is recycled to the cathode electrodes of the solid oxide fuel cells using a fuel burner and ejector pumps. As a consequence of the use of the ejector pumps, the fuel burner must have a low-pressure drop. A fuel burner with a high-pressure drop would compromise the performance of the ejector pumps, reducing the gas mass flow that may be recycled. Accordingly the present invention seeks to provide a novel fuel burner, which reduces, preferably overcomes, the above-mentioned problem.

Accordingly the present invention provides a fuel burner comprising a plurality of sealed fuel ducts, each fuel duct having at least one open end, a first sealed edge and a second open edge, the fuel ducts being arranged substantially parallel to each other, the fuel ducts being spaced apart to form a plurality of parallel oxidant passages therebetween, means to supply fuel to the at least one open end of each fuel duct, the fuel ducts being arranged such that the second open edges face in substantially the same direction to discharge fuel in said direction, means to supply oxidant to the parallel oxidant passages between the fuel ducts in substantially the said direction to mix with the fuel discharged from the open edges of the fuel ducts .

Preferably each fuel duct having a first open end and a second open end, means to supply fuel to the first open end and the second open end of each fuel duct .

Preferably each fuel duct comprising a first plate and a second plate, a first edge of the first plate being sealed to a corresponding first edge of the second plate to form the first sealed edge of the fuel duct and a second edge of the first plate being sealed to a corresponding second edge of the second plate adjacent the ends of the fuel duct.

Preferably the first plate and the second plate of each fuel duct being pressed plates, the first and second plates having bent over first and second edges.

Preferably adjacent fuel ducts being spaced apart by spacer members sealed to the fuel ducts to define the oxidant passages.

Preferably the spacer members being arranged adjacent the ends of the fuel ducts.

Preferably each parallel oxidant passage having a corrugated member, or a porous member, to control the direction of flow of oxidant. Preferably each fuel duct having a corrugated member, or a porous member, adjacent the open edge of the fuel duct to control the direction of the flow of fuel from the open edge of the fuel duct . Preferably the corrugated member having longer corrugations at the ends of the fuel duct than at the centre of the fuel duct .

Preferably the fuel ducts being bent between the ends. Preferably the means to supply fuel comprising a fuel manifold sealed to the at least one open ends of the fuel ducts.

Preferably the means to supply fuel comprising a first fuel manifold sealed to the fuel ducts to supply fuel to the first open ends of the fuel ducts and a second fuel manifold sealed to the fuel ducts to supply fuel to the second ends of the fuel ducts.

Preferably the first fuel manifold comprising plates. Preferably the second fuel manifold comprising plates. Preferably the first and second plates are metal sheets .

Preferably the first and second plates are high temperature oxidation resistant metal sheets for example steel, nickel, nickel alloy or an alloy of iron, chromium and aluminium. Preferably the sealed edges of the first and second plates of the fuel ducts comprising laser welded sealed edges .

Preferably the spacer members being sealed to the fuel ducts by laser welded seals and/or brazed seals. Preferably the fuel manifolds being sealed to the ends of the fuel ducts by laser welded seals and/or brazed seals .

The present invention also seeks to provide a novel method of manufacturing a fuel burner. Accordingly the present invention provides a method of manufacturing a fuel burner comprising the steps of (a) forming a plurality of sealed fuel ducts, each fuel duct having at least one open end, a first sealed edge and a second open edge, (b) arranging the fuel ducts substantially parallel to each other,

(c) spacing the fuel ducts apart to form a plurality of parallel oxidant passages therebetween, (d) providing means to supply fuel to the at least one open end of each fuel duct,

(e) arranging the fuel ducts such that the second open edges face in substantially the same direction to discharge fuel in said direction, (f) providing means to supply oxidant to the parallel oxidant passages between the fuel ducts in substantially the said direction to mix with the fuel discharged from the open edges of the fuel ducts.

Preferably the method comprising forming each fuel duct with a first open end and a second open end, means to supply fuel to the first open end and the second open end of each fuel duct .

Preferably the method comprising forming each fuel duct from a first plate and a second plate, sealing a first edge of the first plate to a corresponding first edge of the second plate to form the first sealed edge of the fuel duct and sealing a second edge of the first plate to a corresponding second edge of the second plate adjacent the ends of the fuel duct . Preferably the method comprising pressing the first plate and the second plate of each fuel duct such that the first and second plates have bent over first and second edges .

Preferably the method comprising spacing adjacent fuel ducts apart by sealing spacer members to define the oxidant passages .

Preferably the method comprising arranging the spacer members adjacent the ends of the fuel ducts.

Preferably the method comprising positioning a corrugated member, or a porous member, in each parallel oxidant passage to control the direction of flow of oxidant .

Preferably the method comprising positioning a corrugated member, or a porous member, adjacent the open edge of each fuel duct, to control the direction of the flow of fuel from the open edge of the fuel duct.

Preferably the corrugated member having longer corrugations at the ends of the fuel duct than at the centre of the fuel duct .

Preferably the method comprising bending the fuel ducts between the ends.

Preferably the method comprising sealing a fuel manifold sealed to the at least one open ends of the fuel ducts.

Preferably the method comprising sealing a first fuel manifold sealed to the fuel ducts to supply fuel to the first open ends of the fuel ducts and sealing a second fuel manifold to the fuel ducts to supply fuel to the second ends of the fuel ducts .

Preferably the first fuel manifold comprising plates.

Preferably the second fuel manifold comprising plates.

Preferably the first and second plates are metal sheets . Preferably the first and second plates are high temperature oxidation resistant metal sheets for example steel, nickel, nickel alloy or an alloy of iron, chromium and aluminium .

Preferably the sealing of the edges of the first and second plates of the fuel ducts comprising laser welding the sealed edges .

Preferably the sealing of spacer members to the fuel ducts comprising laser welding and/or brazing.

Preferably the sealing of the fuel manifolds to the ends of the fuel ducts comprising laser welding and/or brazing.

The present invention will be more fully described by way of example with reference to the accompanying drawings in which: - Figure 1 is a perspective view of a fuel burner according to the present invention.

Figure 2 is an end view of a fuel burner according to the present invention. Figure 3 is a side view of a fuel burner according to the present invention.

Figure 4 is a plan view of a fuel burner according to the present invention. Figure 5 is an enlarged cross-sectional view in the direction of arrows X-X in figure 2.

Figure 6 is an exploded view showing a second sub assembly for a fuel burner according to the present invention. Figure 7 is a perspective view of a fuel duct of a fuel burner according to the present invention.

A fuel burner 10 according to the present invention is shown in figures 1 to 7 and comprises a plurality of sealed fuel ducts 12. Each fuel duct 12, as shown more clearly in figure 7, has a first open end 14 and a second open end 16. Each fuel duct 12 has a first sealed edge 18 and a second open edge 20. The fuel ducts 12 are arranged substantially parallel to each other. Each fuel duct 12 defines a passage 22 for the flow of fuel. The fuel ducts 12 are spaced apart to form a plurality of parallel oxidant passages 24 therebetween, as shown in figure 5. The fuel ducts 12 are arranged such that the second open edges 20 face in substantially the same direction A to discharge fuel in the direction A. A fuel supply 26 is arranged to supply fuel to the first and second open ends 14 and 16 of each fuel duct 12. An oxidant supply 28 is arranged to supply oxidant to the parallel oxidant passages 24 between the fuel ducts 12 in substantially the direction A to mix with the fuel discharged from the open edges 20 of the fuel ducts 12.

Each fuel duct 12, as shown in figure 7, comprises a first plate 30 and a second plate 32, a first edge 34 of the first plate 30 is sealed to a corresponding first edge 36 of the second plate 32 to form the first sealed edge 18 of the fuel duct 12 and a second edge 38 of the first plate 30 is sealed to a corresponding second edge 40 of the second plate 32 adjacent the first and second open ends 14 and 16 of the fuel duct 12. The first plate 30 and the second plate 32 of each fuel duct 12 comprise pressed plates, the first and second plates 30 and 32 have bent over first and second edges 34, 36 and 38 and 40 respectively, as shown in figures 5 and 7. Adjacent fuel ducts 12 are spaced apart by spacer members 42, as shown in figure 6, which are sealed to the fuel ducts 12 to define the parallel oxidant passages 24. The spacer members 42 are arranged adjacent the first and second open ends 14 and 16 of the fuel ducts 12. At least one corrugated member, or a porous member, 44 is arranged in each oxidant passage 24 to control the direction of flow of oxidant through the oxidant passage 24. The corrugations of the corrugated members 44 may be arranged substantially parallel or alternatively the corrugations of the corrugated members 44 may be arranged at different angles. The porous member may be a ceramic foam or a metal foam, the metal foam is preferably a high temperature oxidation resistant metal for example steel, nickel, nickel alloy or an alloy of iron, chromium and aluminium. The high temperature oxidation resistant metal sheets preferably contain aluminium, such that they are alumina formers and preferably they do not loose chromium, because chromium poisons the solid oxide fuel cells.

Similarly a corrugated member, or a porous member, 46 is arranged in each fuel duct 12 adjacent the second open edges 20 of the fuel ducts 12 to control the direction of the flow of fuel from the second open edges 20 of the fuel ducts 12. The corrugated members 46 have longer corrugations at the first and second open ends 14 and 16 of the fuel ducts 12 than the corrugations at the centre of the fuel ducts 12 to produce a uniform distribution of fuel. However, the corrugated members 46 may have longer corrugations at different positions to produce the uniform distribution of fuel. The porous member may be a ceramic foam or a metal foam, the metal foam is preferably a high temperature oxidation resistant metal for example steel, nickel, nickel alloy or an alloy of iron, chromium and aluminium. The high temperature oxidation resistant metal sheets preferably contain aluminium, 'such that they are alumina formers and preferably they do not loose chromium, because chromium poisons the solid oxide fuel cells.

A notable feature is that the fuel ducts 12 are bent between the first and second ends 14 and 16 and preferably the bends 43 are substantially at the middle of the fuel ducts 12.

The fuel supply 26 comprises a first fuel manifold 46 sealed around the first open ends 14 of the fuel ducts 12 to supply fuel to the first open ends 14 of the fuel ducts 12 and a second fuel manifold 48 sealed around the second open ends 16 of the fuel ducts 12 to supply fuel to the second open ends 16 of the fuel ducts 12. The first fuel manifold 46 is defined by and comprises a number of plates 50, 52 and 54 sealed together. Similarly the second fuel manifold 48 comprises a number of plates 50, 52 and 56 sealed together. The plates 50 and 54 extend perpendicularly to the fuel ducts 12 and the plates 50 and 52 extend parallel to the fuel ducts 12.

The first and second plates 30 and 32 of the fuel ducts 12 are metal sheets and the first and second plates 30 and 32 are high temperature oxidation resistant metal sheets for example steel, nickel, nickel alloy or an alloy of iron, chromium and aluminium. The high temperature oxidation resistant metal sheets preferably contain aluminium, such that they are alumina formers and preferably they do not loose chromium, because chromium poisons the solid oxide fuel cells.

The sealed edges 34, 36 and 38, 40 of the first and second plates 30 and 32 of the fuel ducts 12 comprise laser welded sealed edges or seam welded sealed edges. The spacer members 42 are sealed to the fuel ducts 12 by laser welded seals or seam welds and/or brazed seals.

The first and second fuel manifolds 46 and 48 are sealed to the first and second open ends 14 and 16 of the fuel ducts 12 by laser welded seals or seam welded seals and/or brazed seals. The plates 50, 52, 54 and 56 of the first and second fuel manifolds 46 and 48 are sealed together by laser welded seals or seam welded seals and/or brazed seals. The plates 50 and 52 are also the end plates for the fuel burner 10. The plates 50, 52, 54 and 56 are also metal sheets and the plates 50, 52, 54 and 56 are preferably high temperature oxidation resistant metal sheets for example steel, nickel, nickel alloy or an alloy of iron, chromium and aluminium. Also the plates 50 and 52 are bent between the ends, in a similar manner to the fuel ducts 12, and preferably the bends are substantially at the middle of the plates 50 and 52. The end fuel ducts 12 are spaced from the end plates 52 and 54 by spacer members 42, which are sealed to the fuel ducts 12 to define further parallel oxidant passages 24. The spacer members 42 are again arranged adjacent the first and second open ends 14 and 16 of the fuel ducts 12. Thus the fuel burner 10 comprises a series of alternate fuel passages 22 and oxidant passages 24 for the flow of fuel and oxidant through the fuel burner 10 and for the subsequent combustion at an outlet plane 58 of the fuel burner 10. In operation oxidant flows from an inlet plane 60 through the parallel oxidant passages 24 between the fuel ducts 12 and through the corrugated members 44, or porous members, which control the pressure drop, smooth out the oxidant flow and provide a directional component to the oxidant flow. Fuel flows from the fuel supply 26 through fuel pipes 62 to the first and second fuel manifolds 46 and 48. The fuel flows from the first and second fuel manifolds 46 and 48 through the first and second open ends 14 and 16 respectively of the fuel ducts 12 into the fuel passages 22. The fuel flows from the first and second open ends 14 and 16 of the fuel ducts 12 towards the centre of the fuel ducts 12 and through the corrugated members 46, or porous members, which provide a uniform distribution of fuel at the open edge 20 and a directional component to the fuel flow. The corrugated members, or porous members, 44 and 46 control the pressure drop through the fuel burner 10 and promote mixing of the fuel and oxidant at the outlet plane 58 by directing the oxidant flow and promoting shear mixing. It is to be noted that the fuel flowing from the open edges 20 of each of the fuel ducts 12 is flowing in substantially parallel directions, in direction A. Thus, the fuel is supplied/discharged, from the open edges 20 of the fuel ducts 12 as a plurality of parallel layers, or laminae, of fuel. It is also to be noted that the oxidant flowing from the parallel oxidant passages 24, between the parallel fuel ducts 12, is supplied as a plurality of parallel layers, or laminae, of oxidant. The oxidant flow is not directed to flow into, or across, the fuel flow and the fuel flow is not directed to flow into, or across, the oxidant flow and thus the fuel burner operates in laminar flow regions with parallel laminae of fuel and oxidant . Thus, there are alternate parallel layers, or planes, of fuel and oxidant discharged from fuel ducts 12 and oxidant passages 24 respectively.

The length and/or widths of the fuel ducts 12 are selected to match the aerodynamic requirements for the flame taking into account the oxidant/fuel ratio, velocities of the fuel and oxidant etc. The dimensions of the fuel burner are configured to suit the flame conditions i.e. outlet area, flame velocities and profiles, spacer member thickness, total area and pressure drop.

The advantages of the present invention are that leakage of fuel is minimised, preferably avoided, in the fuel burner in a cost effective manner by edge sealing with laser welding or seam welding and brazing the interface between the fuel ducts and the spacer members. The corrugated members, or porous members, control the pressure drop through the fuel burner. The oxidant flow pressure drop is minimised by ensuring the oxidant flow is not turned and any pressure drop is small, known and controllable. The surface area of fuel to oxidant mixing is maximised to provide relatively small flames and therefore a short residence time, and hence low emissions, this is beneficial where mixing is important and a pressure drop is not available.

The fuel burner 10 is manufactured by forming a plurality of sealed fuel ducts 12. Each fuel duct 12 is formed from a first plate 30 and a second plate 32. A first edge 34 of the first plate 30 is sealed to a corresponding first edge 36 of the second plate 32 to form the first sealed edge 14 of the fuel duct 12 and a second edge 36 of the first plate 30 is sealed to a corresponding second edge 38 of the second plate 32 adjacent the first and second open ends 18 and 20 of the fuel duct 12 to form the second open edge 16 of the fuel duct 12. The first plate 30 and the second plate 32 of each fuel duct 12 are initially pressed such that the first and second plates 30 and 34 have bent over first and second edges 34, 36 and 38, 40. The sealing of the first and second edges 34, 36 and 38, 40 of the first and second plates 30 and 34 of the fuel ducts 12 comprises laser welding, seam welding or other suitable welding process. A corrugated member, or a porous member, 46 is preferably positioned in each fuel duct 12, adjacent the second open edge 16 of each fuel duct 12, before the first and second plates 30 and 32 are welded together. 12. The corrugated member 46 is preferably spot welded to one of the first and second plates 30 and 32 at suitable positions.

It may be possible to form the second open edge 16 of the fuel ducts 12 by laser welding the whole of the second edges 38 and 40 of the first and second plates 30 and 32 together and then cutting out a slot to form the second open edge 16. Alternatively, it may be possible to form the second open edge 16 of the fuel ducts 12 by cutting out slots in the second edges 38 and 40 of the first and second plates 30 and 32 and then laser welding the uncut portions of the second edges 38 and 40 of the first and second plates 30 and 32.

It is to be noted that the first plates 30 are provided with apertures 70 and 72 adjacent the first and second open ends 14 and 16 and that the second plates are provided with apertures 74 and 76 adjacent the first and second open ends 14 and 16. The apertures 70 and 72 and the apertures 74 and 76 become coaxial when the first and second plates 30 and 32 are welded together. The apertures 70, 72, 74 and 76 allow the fuel ducts 12 to be positioned upon dowels/bolts 78 and 80 extending from the first end plate 50.

The fuel ducts 12 are positioned on the dowels/bolts 78 and 80 such that the second open edges 16 face in substantially the same direction to discharge fuel in the direction A.

The spacer members 42 are also provided with apertures 82 and 84 to allow the spacer members 42 to be positioned on the dowels/bolts 78 and 80. The spacer members 42 are provided with slots 86 to receive the ends of the corrugated members 44. The corrugated member 42 is preferably spot welded to both of the associated spacer members 42. The spacer members 42 are arranged adjacent the first and second open ends 14 and 16 of the fuel ducts 12. The ends of the corrugated members 44 are also provided with apertures 45 to allow oxidant to flow into the passages of the corrugated members 44.

Thus, the fuel ducts 12 and spacer members 42 together with the corrugated members 44 are placed alternately on the dowels/bolts 78 and 80 to build up a stack of fuel ducts 12 and spacer members 42 and corrugated members 44 to build up the fuel burner 10. Thus, the adjacent fuel ducts 12 are spaced apart by spacer members 42 to define the oxidant passages 24. The second end plate 52 is positioned on the dowels/bolts 78 and 80 to finish the fuel burner 10 and nuts 82 are positioned on the bolts 78 and 80 and tightened to compress the assembly. The spacer members 44 are then brazed to the open ends of the fuel ducts 12 to form seals around the open ends of the fuel ducts 12.

The edges 84 and 86 of the plates 56 and 58 are sealed by laser welding, seam welding, other suitable welding, and/or by brazing to both of the edges of the first and second open ends 14 and 16 of the fuel ducts 12 and the edges of the spacer members 42. The ends 88 and 90 of the plates 56 and 58 are sealed to the plates 52 and 54 by laser welding, seam welding or other suitable welding.

In an alternative method it is possible to sequentially position a first plate 30, a corrugated member 46, a second plate 32 and two spacer members 42 with associated corrugated member 44 on the dowels/bolts 78 and 80. Then when the plate 54 is positioned on the dowels/bolts 78 and 80 and the nuts 82 tightened the first edges 34 and 36 of the first and second plates 30 and 32 are sealed by laser welding etc and the second edges 38 and 40 if the first and second plates 30 and 32 are sealed by laser welding, seam welding etc. Then the manufacturing process follows the same sequence as before. In a preferred manufacturing process a pair of spacer members 42 and a corrugated member 44 are spot welded to a first plate 30 to produce a first sub-assembly. The first sub-assembly is placed on the dowels/bolts 78 and 80 with the spacer members 42 between the end plate 50 and the first plate 30. A number of second sub-assemblies are produced. A corrugated member 46 is spot welded to one side of a second plate 32, a pair of spacer members 42 and a corrugated member 44 is spot welded to the other side of the second plate 32 and a first plate 30 is spot welded to the other side of the spacer members 42 to produce a second sub-assembly. The second sub-assembly is placed on the dowels/bolts 78, 80 with the corrugated member 46 between the first plate 30 of the first sub-assembly and the second plate 32 of the second sub-assembly. The remaining sub- assemblies are placed on the dowels/bolts 78, 80 with the corrugated member 46 between the first plate 30 of the previous second sub-assembly and the second plate 32 of that second sub-assembly. A third sub-assembly is produced. A corrugated member 46 is spot welded to one side of a second plate 32 and a pair of spacer members 42 and a corrugated member 44 are spot welded to the other side of the second plate 32 to form the third sub-assembly. The third sub-assembly is placed on the dowels/bolts 78, 80 with the corrugated member 46 between the first plate 30 of the previous second sub-assembly and the second plate 32 of the third sub-assembly. Then the second end plate 54 is placed on the dowels/bolts 78, 80.

The edges of the first and second plates 30 and 32 of the first and second plates 14 and 16 are then laser welded or seam welded. Then the manufacturing process follows the same sequence as before .

The first and second plates 30 and 32 may be pressed to provide features on the surfaces of the first and second plates 30 and 32 to aid the flow of braze material between the first and second plates 30 and 32 and the spacer members 42. Braze material is placed between the first and second plates 30 and 32 and the spacer members 42 during assembly of the sub-assemblies. It may be possible to supply fuel to a single fuel manifold and then supply to only one open end of the fuel ducts. In this case the corrugated member will be altered accordingly, e.g. the lengths of the corrugations at different positions altered, to redistribute the fuel to obtain a uniform fuel distribution at the open edges of the fuel ducts. It may be possible to use other shapes of fuel manifold to that shown and with the fuel pipes connecting to the fuel manifolds at different positions.

It may be possible to use plates, e.g. pressed metal sheets for the spacer members.

In an alternative method of manufacturing the corrugated member 44 may be spot welded to an adjacent second plate 32 and the corrugated member 46 may be spot welded to a second plate 32. In another method the corrugated member 44 may be spot welded to an adjacent second plate 32 and the corrugated member 46 may be spot welded to a first plate 30.

The fuel burner of the present invention is suitable for use in a solid oxide fuel cell system in which oxidant and fuel are recycled to the cathode electrodes of the solid oxide fuel cells using a fuel burner and one or more ejector pumps. As a consequence of the use of the ejector pumps, the fuel burner must have a low-pressure drop. The fuel principally comprises hydrogen. The fuel supplied to the fuel burner is supplied from the anodes of the solid oxide fuel cells, the oxidant supplied to the fuel burner is supplied from the cathode electrodes of the solid oxide fuel cells and the product gases of the fuel burner are supplied to the cathode electrodes of the solid oxide fuel cells .

It is to be noted that the fuel burner of the present invention is a low-pressure drop fuel burner, and is suitable for sue with a solid oxide fuel cell system, and is specifically arranged to reduce pressure drop and suit laminar flow regimes. The corrugated members, or porous members, control the outlet velocity profile by controlling frictional losses along its length and do not change the direction of flow of the fuel. The present invention provides a continuous diffusion flame thereby maximising exposure of the fuel to oxidants in a restricted space and achieves low NO_x, less than 5ppm at atmospheric conditions and off gas, in laminar flow regimes with low turbulence and minimal micro turbulent mixing. This allows simple joining techniques with high integrity and low cost.

It may be possible to use the fuel burner in other circumstances where a low-pressure drop exists and where hydrogen is the fuel. The oxidant may be oxygen or air or oxygen depleted air.

In a further method of manufacture it may be possible to cast the fuel ducts from a suitable metal, or alloy, preferably together with corrugated members, porous members or other members to control the flow of the fuel . The cast fuel ducts may then be brazed, bonded, diffusion bonded or welded together, preferably with spacers and corrugated members, porous members or other members to control the flow of the oxidant .

Claims

Claims : -

1. A fuel burner (10) comprising a plurality of sealed fuel ducts (12) , each fuel duct (12) having at least one open end (14, 16), a first sealed edge (18) and a second open edge (20) , the fuel ducts (12) being arranged substantially parallel to each other, the fuel ducts (12) being spaced apart to form a plurality of parallel oxidant passages (24) therebetween, means (26) to supply fuel to the at least one open end (14, 16) of each fuel duct (12), the fuel ducts (12) being arranged such that the second open edges (20) face in substantially the same direction to discharge fuel in substantially parallel layers, means (28) to supply oxidant to the parallel oxidant passages (24) between the fuel ducts (12) , the parallel oxidant passages (24) being arranged to supply oxidant in substantially parallel layers between layers of fuel to mix with the fuel discharged from the open edges (20) of the fuel ducts (12) .

2. A fuel burner as claimed in claim 1 wherein each fuel duct (12) having a first open end (14) and a second open end (16) , means to supply fuel to the first open end (14) and the second open end (16) of each fuel duct (12) .

3. A fuel burner as claimed in claim 1 or claim 2 wherein each fuel duct (12) comprising a first plate (30) and a second plate (32) , a first edge (34) of the first plate (30) being sealed to a corresponding first edge (36) of the second plate (32) to form the first sealed edge (18) of the fuel duct (12) and a second edge (38) of the first plate (30) being sealed to a corresponding second edge (40) of the second plate (32) adjacent the ends of the fuel duct (12) .

4. A fuel burner as claimed in claim 3 wherein the first plate (30) and the second plate (32) of each fuel duct (12) being pressed plates, the first and second plates (30, 32) having bent over first and second edges (34, 36, 38, 40).

5. A fuel burner as claimed in claim 1, claim 2, claim 3 or claim 4 wherein adjacent fuel ducts (12) being spaced apart by spacer members (42) sealed to the fuel ducts (12) to define the oxidant passages (24) .

6. A fuel burner as claimed in claim 5 wherein the spacer members (42) being arranged adjacent the ends (14, 16) of the fuel ducts (12) .

7. A fuel burner as claimed in any of claims 1 to 6 wherein each parallel oxidant passage (24) having a corrugated member (44) , or a porous member, to control the direction of flow of oxidant.

8. A fuel burner as claimed in any of claims 1 to 7 wherein each fuel duct (12) having a corrugated member (46) , or a porous member, adjacent the open edge (20) of the fuel duct (12) to control the direction of the flow of fuel from the open edge (20) of the fuel duct (12) .

9. A fuel burner as claimed in claim 8 wherein the corrugated member (46) having longer corrugations at the ends (14, 16) of the fuel duct (12) than at the centre of the fuel duct (12) .

10. A fuel burner as claimed in any of claims 1 to 9 wherein the fuel ducts (12) being bent (43) between the ends (14, 16) .

11. A fuel burner as claimed in any of claims 1 to 10 wherein the means (26) to supply fuel comprising a fuel manifold (46, 48) sealed to the at least one open ends (14, 16) of the fuel ducts (12) .

12. A fuel burner as claimed in claim 2 wherein the means (26) to supply fuel comprising a first fuel manifold (46) sealed to the fuel ducts (12) to supply fuel to the first open ends (14) of the fuel ducts (12) and a second fuel manifold (48) sealed to the fuel ducts (12) to supply fuel to the second ends (16) of the fuel ducts (12) .

13. A fuel burner as claimed in claim 12 wherein the first fuel manifold (46) comprising plates (50, 52, 54) .

14. A fuel burner as claimed in claim 12 or claim 13 wherein the second fuel manifold (48) comprising plates (50, 52, 56) .

15. A fuel burner as claimed in claim 3 or claim 4 wherein the first and second plates (30, 32) are metal sheets.

16. A fuel burner as claimed in claim 15 wherein the first and second plates (30, 32) are high temperature oxidation resistant metal sheets.

17. A fuel burner as claimed in claim 16 wherein the first and second plates (30, 32) comprise steel, nickel, nickel alloy or an alloy of iron, chromium and aluminium.

18. A fuel burner as claimed in claim 3 or claim 4 wherein the sealed edges (18) of the first and second plates (30,

32) of the fuel ducts (12) comprising laser welded sealed edges .

19. A fuel burner as claimed in claim 5 wherein the spacer members (42) being sealed to the fuel ducts (12) by laser welded seals and/or brazed seals.

20. A fuel burner as claimed in claim 11, claim 12, claim 13 or claim 14 wherein the fuel manifolds (46, 48) being sealed to the ends (14, 16) of the fuel ducts (12) by laser welded seals and/or brazed seals.

21. A fuel cell system comprising a fuel burner as claimed in any of claims 1 to 20.

22. A method of manufacturing a fuel burner (10) comprising the steps of

(a) forming a plurality of sealed fuel ducts (12) , each fuel duct (12) having at least one open end (14, 16) , a first sealed edge (18) and a second open edge (20) ,

(b) arranging the fuel ducts (12) substantially parallel to each other,

(c) spacing the fuel ducts (12) apart to form a plurality of parallel oxidant passages (24) therebetween,

(d) providing means (26) to supply fuel to the at least one open end (14, 16) of each fuel duct (12),

(e) arranging the fuel ducts (12) such that the second open edges (20) face in substantially the same direction to discharge fuel in said direction,

(f) providing means (28) to supply oxidant to the parallel oxidant passages (24) between the fuel ducts (12) in substantially the said direction to mix with the fuel discharged from the second open edges (20) of the fuel ducts (12) .

23. A method as claimed in claim 22 comprising forming each fuel duct (12) with a first open end (14) and a second open end (16) , means (26) to supply fuel to the first open end (14) and the second open end (16) of each fuel duct (12) .

24. A method as claimed in claim 22 or claim 23 comprising forming each fuel duct (12) from a first plate (30) and a second plate (32) , sealing a first edge (34) of the first plate (30) to a corresponding first edge (36) of the second plate (32) to form the first sealed edge (18) of the fuel duct (12) and sealing a second edge (38) of the first plate

(12) to a corresponding second edge (40) of the second plate (32) adjacent the ends of the fuel duct (12) .

25. A method as claimed in claim 24 comprising pressing the first plate (30) and the second plate (32) of each fuel duct (12) such that the first and second plates (30, 32) have bent over first and second edges (34, 36, 38, 40).

26. A method as claimed in any of claims 22 to 25 comprising spacing adjacent fuel ducts (12) apart by- sealing spacer members (42) to define the oxidant passages (24) .

27. A method as claimed in claim 26 comprising arranging the spacer members (42) adjacent the ends (14, 16) of the fuel ducts (12) .

28. A method as claimed in any of claims 22 to 27 comprising positioning a corrugated member (44) or a porous member, in each parallel oxidant passage ( 24 ) to control the direction of flow of oxidant.

29. A method as claimed in any of claims 22 to 28 comprising positioning a corrugated member (46) or a porous member, adjacent the open edge (20) of each fuel duct (12) , to control the direction of the flow of fuel from the open edge (20) of the fuel duct (12) .

30. A method as claimed in claim 29 wherein the corrugated member (46) having longer corrugations at the ends (14, 16) of the fuel duct (12) than at the centre of the fuel duct

(12) .

31. A method as claimed in any of claims 22 to 30 comprising bending (43) the fuel ducts (12) between the ends (14, 16) .

32. A method as claimed in any of claims 22 to 31 comprising sealing a fuel manifold (46, 48) to the at least one open ends (14, 16) of the fuel ducts (12) .

33. A method as claimed in claim 32 comprising sealing a first fuel manifold (46) to the fuel ducts (12) to supply fuel to the first open ends (14) of the fuel ducts (12) and sealing a second fuel manifold (48) to the fuel ducts (12) to supply fuel to the second open ends (16) of the fuel ducts (12) .

34. A method as claimed in claim 33 wherein the first fuel manifold (46) comprising plates (50, 52 54) .

35. A method as claimed in claim 33 or claim 34 wherein the second fuel manifold (48) comprising plates (50, 52, 56) .

36. A method as claimed in claim 24 or claim 25 wherein the first and second plates (30, 32) are metal sheets.

37. A method as claimed in claim 36 wherein the first and second plates (30, 32) are high temperature oxidation resistant metal sheets.

38. A method as claimed in claim 37 wherein the first and second metal plates (30, 32) comprise steel, nickel, nickel alloy or an alloy of iron, chromium and aluminium.

39. A method as claimed in claims 24 or claim 25 wherein the sealing of the edges (18) of the first and second plates (30,32) of the fuel ducts (12) comprising laser welding the sealed edges.

40. A method as claimed in claim 24, claim 25 or claim 38 wherein the sealing of spacer members (42) to the fuel ducts (12) comprising laser welding and/or brazing.

41. A method as claimed in claim 32 to 35 wherein the sealing of the fuel manifolds (46, 48) to the ends (12, 14) of the fuel ducts (12) comprising laser welding and/or brazing.