GB2360085A

GB2360085A - Annular heat exchanger with concentric cells for use in gas turbine engine

Info

Publication number: GB2360085A
Application number: GB0005691A
Authority: GB
Inventors: Richard Henry Barr; Frank Lawrence Burgess
Original assignee: Centrax Ltd
Current assignee: Centrax Ltd
Priority date: 2000-03-09
Filing date: 2000-03-09
Publication date: 2001-09-12
Also published as: AU3758601A; WO2001067018A1; GB0005691D0

Abstract

A heat exchanger in which heat is transferred from one fluid to another by conduction through stationary annular cells (108a) to (108d) with corrugated plates (112a) (112b) which are flattened at their axially outer ends (114a) (114b). The cells (108a) to (108d) have differing diameters with adjacent cells closely fitting inside one another to form an annular matrix between an outer (106) and inner (104) casing. Compressed air flowing to a gas turbine engine enters through inlet openings (110a), passes through a first fluid tight compartment and leaves through outlet openings (110b). While passing through the heat exchanger, the compressed air receives heat from the engine exhaust gas, which passes from inlet (117), through a second fluid tight compartment to outlet (118).

Description

2360085 ANNULAR HEAT =CEMGER This invention relates to annular heat

exchangers.

BACKGROUND OF THE INVENTION

Heat exchangers are used in gas turbine engines as a means of increasing efficiency by extracting heat from the exhaust gas and donating this heat to the compressed air leaving the compressor prior to its entering the combustion chamber. Such exchangers are of two general types, f irstly the rotating disc type, commonly known as a regenerator and secondly, the static plate type commonly known as a recuperator.

In designing gas turbines of less than about one megawatt in output power, but more especially for small turbines of less than about 300 kilowatts output, space and weight become important factors. For this reason, an elegant and compact technical solution to the problem of integrating the heat exchanger with the rest of the gas turbine can be provided by surrounding the exhaust region of the engine with a heat exchanger which is annular in cross section. Such heat exchangers have to withstand the considerable temperature experienced in the exhaust gases, which might be up to 7000C, and the high pressure of the compressed air which might be up to eight times atmospheric.

Our earlier Patent Application PCT/GB99/03456, describes a heat exchanger matrix in which the heat exchanger plates are arranged in a largely radial direction. It is also known to form a heat exchanger matrix by winding pairs of plates in a spiral on to an inner drum or casing and to attach various types of headers to the spirally wound plates so that the first and second gas streams flow in a largely axial and counterflow mode between pairs of plates. The problem with this concept is that the sealing of the pairs of is is plates at their edges and the interconnection with the header system, which may be accomplished by brazing or welding is extremely complicated owing to the spiral nature of the wound plates. This interconnection involves complicated forming techniques to ensure that on an ever increasing radius caused by the spiral, header openings or attachments suitable for fixation to the header system can be made to line up in a radial direction. However, it should be stated that if the process can be accomplished, the resulting system requires substantially less welding compared to systems with radial cells and for this reason may be considerably cheaper to produce. Also, it is argued that the spirally wound concept would lend itself to a more continuous manufacturing process for the annular heat exchanger although the inventors of the present patent believe that the other complexities caused by the spiral winding more than offset the gains caused by shorter welding distances and the concept of manufacturing continuity.

The present application seeks to embrace the shorter welding distances caused by the circumferential arrangement of plates, without involving the complexities of spiral winding and seeks to provide a method of construction of such an annular heat exchanger which is compact, light in weight and cheaper to manufacture than designs provided hitherto.

SUMMARY OF THE INVENTION

According to a first aspect of the present invention, there is provided a heat exchanger in which heat is extracted f rom a f irst f luid at a f irst temperature and donated to a second f luid at a second temperature lower than the f irst temperature by heat conduction through stationary heat exchanger plates, in which heat exchanger respective plates are f ormed into is a plurality of discreet annular cells of differing diameters such that the outer diameter of one cell substantially corresponds to the inner diameter of an adjacent cell, the various cells being stacked together to form an annular matrix and being linked together through a header system which permits the first fluid to enter the insides of the cells and flow through the cells and be separated from the second fluid which flows between adjacent cells.

Preferably, the first fluid comprises the compressed air of a gas turbine prior to entering the combustion chamber of the said turbine and the second fluid comprises the exhaust gases of the gas turbine.

In accordance with a preferred embodiment of the present invention, discreet annular cells formed by welding or otherwise fixing pairs of wavy corrugated plates together each fit snugly to their neighbour in a radial direction so that the whole heat exchanger matrix is formed by a multiplicity of such annular cells joined together by a suitable header system which flows one stream of gas in a radial direction, and enables this stream to enter respective cells in an axial direction and to pass axially along each of the cells of the matrix where it is led from the cells by similarly radially arranged headers. Meanwhile the second stream of gas is preferably led in a counter axial direction in between respective cells.

This concept enables the welding together of plates, to form cells, to be carried out with easy access to the individual cells before final assembly via the header system.

When the first and second streams of gas have entered segments of the matrix by means of the header system or the spaces in between the header system, the streams are enabled to spread out in a peripheral direction, to occupy the whole periphery of the is annulus, by virtue of the corrugations being of a wavy form criss- crossing on alternate plates of cells. This spreading out process can be better accomplished if the inlet headers are staggered circumferentially relative to the outlet headers.

In each case the extremities of the cells on the circumferential face and where the radial header system affixes to the cells have an edge formed by crushing the corrugations into a regular surface suitable for welding or otherwise fixing.

Preferably the corrugated plate from which each side of a cell is formed, is formed with corrugations of a wavy shape. Preferably the wave forms at each side of a cell will differ by around one half wave pitch so that the corrugations of a cell criss-cross.

Alternatively the corrugations forming each plate of a cell may be straight but set at an angle to the axis of the heat exchanger, the corrugations on one plate being set at an angle to one side of the axis and the corrugations on the other plate being set at a similar angle to the other side of the axis.

In one f orm of the invention, the inner plate of the innermost cell will not be corrugated but will comprise the inner cylindrical casing of the annulus and the outer plate of the outermost cell will not be corrugated but will comprise the outer cylindrical casing of the annulus. In another form the invention, the inner plate of the innermost cell will comprise the corrugated material and will snugly contact the inner cylindrical casing of the annulus, whilst the outer plate of the outermost cell will comprise the corrugated material and will snugly contact the outer cylindrical casing.

Any combination of the above two forms may also be employed.

Spacer bars may be used if required to facilitate the welding together of the crushed edges of cells.

BRIEF DESCRIPTION OF THE DRAWINGS is For a better understanding of the present invention and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which:- Figure 1 is a drawing of the basic cylindrically shaped matrix composed from a multiplicity of concentric cells, prior to the provision of header systems to the matrix; Figure 2a is an exploded view of the heat exchanger matrix of Figure 1; Figure 2b is a cross section X-X through two cells and the outer casing of the heat exchanger of Figure 2a and shows an arrangement of cells wherein the header system is formed by an arrangement of radial holes cut within the matrix itself and joined together by welding or other fixation; Figure 3a shows an arrangement of cells wherein the header system is formed by welding or otherwise fixing a series of radial ducts on to the face of the matrix formed by the circumferential stacking of cells; Figure 3b is a partial view. on arrow X in Figure 3a; Figure 3c is a partial cross-section Y-Y through the heat exchanger matrix of Figure 3a; Figure 4a shows an arrangement of cells wherein the header system is formed by cutting ports into the matrix in a way which is mid way between the above two methods, enabling entry gas to flow radially within the confines of the matrix annulus and at the same time permitting an external header duct to be fixed; Figure 4b, is a partial view on arrow X in Figure 4a; Figure 4c is a partial cross-section Y-Y through the heat exchanger matrix of Figure 4a; and Figure 4d is a partial view on arrow z in Figure 4c with the outer casing omitted.

is DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

Figure 1 shows an annular heat exchanger matrix 102 defined between a hollow cylindrical inner casing 104 and a hollow cylindrical outer casing 106. The heat exchanger matrix 102 is made up from a plurality of annular heat exchanger cells 108 which are received closely one within another.

Figure 2a is a simplified exploded view of the annular heat exchanger of Figure 1 showing only four heat exchanger cells 108a to 108d. In a commercial embodiment of the invention many more cells would normally make up the heat exchanger matrix. It will be appreciated that the radially outer and inner diameters of successive heat exchanger cells 108a to 108d decrease progressively such that the heat exchanger cells can be fitted one within the other. Each of the heat exchanger cells 108a to 108d and the inner casing 104 are provided with a plurality of inlet openings 110a and outlet openings 110b which are aligned when the heat exchanger matrix is assembled and thereby provide flow passages from the inner casing 104 to the outside face of the outermost heat exchanger cell 108a.

Figure 2b is an enlarged cross-sectional view of the outer casing 106 and the two nearest heat exchanger cells 108a and 108b. Towards the axially outer ends of the heat exchanger cells 108a and 108b are located the inlet openings 110a and outlet openings 110b which together define a header system for the heat exchanger matrix.

Each heat exchanger cell 108a, 108b comprises a pair of corrugated heat exchanger plates 112a, 112b is which are flattened at their axially outer ends in the regions 114a, 114b. These regions 114a and 114b are bent towards one another such that they abut and are welded, brazed, glued or otherwise connected together along their axially outer periphery 115. This method of construction ensures that each cell defines a first fluid tight compartment which is in fluid communication with the inlet openings 110a and the outlet openings 110b. Furthermore, respective pairs of cells 108a, 108b define the sides of a second compartment having an inlet end 117 and an outlet end 118.

In a preferred embodiment of the invention, the exhaust gas E from a gas turbine engine is forced into the inlet ends 117 of the second compartments defined between respective pairs of heat exchanger cells 108a to 108d and leave these compartments via the outlet ends 118. At the same time, compressed air C on its way to the combustion chamber of the gas turbine engine is forced into the inlet openings 110a and thereby through the first fluid tight compartments defined within respective heat exchanger cells 108a to 108d in a direction opposite to the direction of the exhaust gas E passing between the heat exchanger cells 108a to 108d and out through the outlet openings 110b. It will be appreciated that the exhaust gas E travelling in a first direction and the compressed air C travelling in the opposite direction are separated only by the thickness of the heat exchanger plates 112a, 112b. Consequently, in following a tortuous path between respective pairs of corrugated heat exchanger plates 112a, 112b the hot exhaust gas E donates a proportion of its heat to the colder compressed air C, so that the compressed air C is heated before it enters the combustion chamber. As the plates are corrugated, the surface area over which heat can be donated is increased and therefore the efficiency of the heat is exchanger is improved.

Figures 3a, 3b and 3c show an alternative embodiment of heat exchanger matrix in which the inlet openings 210a and outlet openings 210b through the heat exchanger cells 212a, 212b are replaced by externally mounted ducts 220, which extend radially outwardly from the inner casing 204 and terminate substantially at the level of the outer casing 206.

As best shown in Figure 3c, the ducts 220a, 220b are welded, brazed, glued or otherwise fixed directly to the heat exchanger plates 212a, 212b of respective heat exchanger cells 208a, 208b. In this embodiment, rather than the heat exchanger plates 212a, 212b of a heat exchanger cell 208a being welded together along the periphery of both axial ends, the adjacent heat exchanger cells 208a, 208b are welded together in the regions 222a, 222b adjacent each duct 220a, 220b so that the inner compartment defined by each heat exchanger cell is in fluid communication with the inlet duct 220a and the outlet duct 220b.

Thus, in a preferred embodiment, compressed air C, prior to entering the combustion chamber of a gas turbine engine, is directed into the inlet duct 220a through the first compartment defined within the heat exchanger cells 212a, 212b and into the combustion chamber of the gas turbine engine via the outlet duct 220b. At the same time, exhaust gas E from the gas turbine engine is forced through the second compartments defined between respective pairs of heat exchanger cells 208a, 208b which remain open between the respective inlet ducts 220a and outlet ducts 220b (as best shown in Figure 3a). In a preferred embodiment of the invention, a plurality of openings 210 are provided through the inner casing 204 so that the interior space enclosed by the inner casing 204 is in fluid communication with the interior of the ducts 1 is -g- 220a, 22ob. Thus the inner casing 204 effectively acts as a manifold by which compressed air C can be directed into the inlet ducts 220a and directed out of the outlet ducts 220b.

In this embodiment, the inlet ducts 220a are offset relative to the outlet ducts 220b, so that the compressed air C passing from the inlet ducts 220a to the outlet ducts 220b has to cross the heat exchanger matrix at an angle to the axis of the heat exchanger matrix. Therefore. compressed air C entering a particular inlet duct 220a has to travel further across the heat exchanger matrix to reach an outlet duct 220b. This has the effect of increasing the length of time over which heat can be donated f rom the exhaust gas E to the compressed air C.

Figures 4a, 4b, 4c and 4d show a further embodiment of the invention in which the inlet ducts 320a and outlet ducts 320b extend for a predetermined distance into the heat exchanger matrix. This embodiment of the invention is basically a combination of the two previous embodiments combining both an inlet duct 320a, an outlet duct 320b and openings 310a, 310b formed through the heat exchanger matrix.

Referring particularly to Figure 4d, it will be appreciated that as in the previous embodiment, the adjacent heat exchanger plates 312a, 312b of adjacent pairs of heat exchanger cells 308a, 308b are welded together adjacent inlet ducts 320a and outlet ducts 320b, so that the inlet ducts 320a and outlet ducts 320b are in fluid communication with the first compartments defined within each heat exchanger cell. The particular advantage of this final embodiment of the invention is that the flow passages defined by the inlet ducts 320a and outlet ducts 320b are larger than in the previous embodiments, so that the flow rate of compressed air C through the cells 320a to 320d of the 1 heat exchanger matrix is increased for the same number of inlet ducts 320a and outlet ducts 320b.

is

Claims

1. A heat exchanger in which heat is extracted from a first fluid at a first temperature and donated to a second fluid at a second temperature lower than the first temperature by heat conduction through stationary heat exchanger plates, in which heat exchanger the plates are formed into a plurality of discreet annular cells of differing diameters such that the outer diameter of one cell substantially corresponds to the inner diameter of an adjacent cell, the various cells being stacked together to form an annular matrix and being linked together through a header system which permits the first fluid to enter the insides of the cells and flow through the cells and be separated from the second fluid which flows between adjacent cells.

2. A heat exchanger as claimed in Claim 1 in which the first fluid comprises the compressed air of a gas turbine prior to entering the combustion chamber of the said turbine and the second fluid comprises the exhaust gases of the gas turbine.

3. A heat exchanger as claimed in Claim 1 or 2, in which the first fluid flows in the opposite direction, through the heat exchanger matrix, from the second fluid.

4. A heat exchanger as claimed in any one of the preceding claims in which the heat exchanger plates are corrugated in cross-section and the corrugations of the corrugated plates follow an oscillating path in the direction of the axis of the heat exchanger so that the corrugations define a wave pattern when viewed in a direction normal to the surface of the plate.

5. A heat exchanger as claimed in Claim 4, in which the wave pattern of the plates of each respective cell and/or the wave pattern of the corrugation of adjacent plates in adjacent cells criss-crosses.

is

6. A heat exchanger as claimed in Claim 4 or 5, in which the peaks of the corrugations of each plate are substantially aligned with the troughs of the corrugations of an adjacent plate in the heat exchanger matrix.

7. A heat exchanger as claimed in any one of the preceding claims, in which the circumferential edges of each cell are sealed by crushing the corrugations of the cell to a substantially flat surface.

8. A heat exchanger as claimed in Claim 7, in which the plates of each cell are spaced apart by means of spacer elements.

9. A heat exchanger as claimed in any one of the preceding claims in which the header system extends outwardly from a radially inner edge of the heat exchanger matrix.

10. A heat exchanger as claimed in Claim 9, which the header system comprises a plurality of circumferentially aligned openings formed through a plurality of the cells.

11. A heat exchanger as claimed in Claim 10, in which the openings are formed at or near an axial end of the cells.

12. A heat exchanger as claimed in Claim 10 or 11, in which the holes are elliptically shaped.

13. A heat exchanger as claimed in any one of Claims 10 to 12, in which each cell is crushed around the periphery of the said opening formed through that cell.

14. A heat exchanger as claimed in Claim 13, in which the corrugations of a respective cell are crushed to form a substantially planar region of the cell surrounding the opening in the cell such that adjacent cells can be joined together by welding, brazing or other means to form fluid inlets and fluid outlets whilst at the same time separating the first and second is fluids.

15. A heat exchanger as claimed in any one of the preceding claims, in which the header system comprises a duct which is connected to an axial end of the cells.

16. A heat exchanger as claimed Claims 15, in which the duct extends beyond the axial end of the cells.

17. A heat exchanger as claimed in Claim 15 or 16, in which the duct is in fluid tight communication with the interior of the cells.

18. A heat exchanger as claimed in any one of Claims 15 to 17, in which at least a part of the said duct comprises a pocket cut into the circumferential edges of the cells, the corrugations being crushed around the periphery of the pocket and adjacent cells being joined to the said duct by welding, brazing or other means.

19. A heat exchanger as claimed in any one of claims 15 to 18, in which a plurality of ducts are provided on both axial ends of the cells.

20. A heat exchanger substantially as described herein, with reference to and as shown in Figures 1, 2a and 2b or Figures 3a to 3c or Figures 4a to 4d of the accompanying drawings.

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