GB2269764A - A catalytic combustion chamber - Google Patents

Abstract

A catalytic combustion chamber (22A) comprises a first catalyst coated ceramic honeycomb monolith (30) which forms a first catalytic reaction zone. Fuel supplied from fuel injectors (28) is burnt in air supplied from inlet (24) in the first catalytic reaction zone. The first catalyst coated ceramic honeycomb monolith (30) is provided with a plurality of high conductivity beryllium copper heat conductors (40) which extend from the downstream end (42) to the upstream end (44) of the first catalytic reaction zone. The heat conductors (40) transfer heat from the downstream end (42) to the upstream end (44) of the first catalytic reaction zone to prevent over cooling of the upstream end (44) of the first catalytic reaction zone in order to minimise the possibility of the catalytic combustion process being extinguished at high mass flow rates. The heat conductors may extend downstream of the first catalytic reaction zone and may extend through the second catalytic reaction zone (32) to a third monolith, Figs 3 - 5 (not shown). A heat pipe may be used in place of each of the heat conductors. The arrangement of the invention may be used with a radial flow combustion chamber, Figs 8 - 10 (not shown). A catalyst coated metallic matrix may be used in place of the coated ceramic honeycomb monolith. <IMAGE>

Description

A CATALYTIC COMBUSTION CHAMBER The present invention relates to catalytic combustion chambers, and is particularly concerned with catalytic combustion chambers for gas turbine engines.

The use of catalytic combustion chambers in gas turbine engines is a desirable aim, because of the benefits in the reductions of combustion chamber emissions, particularly nitrogen oxides (NOx). The reductions in NOx is due to the lower operating temperatures. In catalytic combustion chambers it is known to use either metallic or honeycomb monoliths which are coated with a suitable catalyst. It is also known to arrange several of the honeycomb monoliths in flow series such that there is a progressive reduction in the cross-sectional area of the cells from one honeycomb monolith to an adjacent honeycomb monolith, in the direction of flow. The smaller cross-sectional area cells have the benefit of reducing emissions of unburned hydrocarbons.

In catalytic combustion chambers hydrocarbon fuel and air are mixed and supplied to the catalyst coated honeycomb monoliths. The hydrocarbon fuel and air mixture diffuses to the catalyst coated surface of the honeycomb monoliths and reacts on the active sites at, and within, the surface.

Near the entrances of the cell assembly where most of the fuel and air mixture is at a low temperature, gas phase chemical reactions are unimportant. At the entrance of the cells, heat release is controlled by catalytic wall chemical reactions. This heat is transferred by conduction, radiation and convection. Further down the cell assembly where the gas has been preheated to a high temperature, gas phase reactions occur. In this region fuel is rapidly consumed by a "flame type" phenomenon which reduces the amount of unburned hydrocarbons emitted such that under normal operating conditions very little unburned hydrocarbons are emitted from the Combustion chamber.

Within the honeycomb monolith the amount of unreacted hydrocarbon depends on the mass flow rate, such that above a certain mass flow rate, there is an increase in the emissions of unreacted hydrocarbons. The increase in the emissions of hydrocarbons is caused by the upstream end of the catalyst coated honeycomb monolith becoming cooled by the incoming fuel/air mixture. Further increases in mass flow rate cause the cool region to spread further downstream. If the whole of the axial length of the catalyst coated honeycomb monolith becomes too cool, all wall reactions are extinguished, and this is known as "blowout".

The present invention seeks to provide a catalytic combustion chamber which at least reduces, or overcomes, the above mentioned problems.

Accordingly the present invention provides a catalytic combustion chamber comprising a catalytic reaction zone, means to supply fuel to the catalytic reaction zone, means to supply air to the catalytic reaction zone, means to transfer heat from the downstream end of the catalytic reaction zone or from a region of the catalytic combustion chamber downstream of the catalytic reaction zone to the upstream end of the catalytic reaction zone or to a region of the catalytic combustion chamber upstream of the catalytic reaction zone such that an air and fuel mixture or the surfaces of the catalytic reaction zone at the upstream end of the catalytic reaction zone are preheated to a temperature at which combustion of the fuel and air mixture occurs in the catalytic reaction zone.

The means to transfer heat may comprise at least one heat conductor extending at least the length of the catalytic reaction zone.

The means to transfer heat may comprise at least one heat pipe extending at least the length of the catalytic reaction zone.

The means to transfer heat may comprise a rotary heat exchanger.

The at least one heat conductor or the at least one heat pipe may extend into a region of the combustion chamber downstream of the catalytic reaction zone.

The at least one heat conductor or the at least one heat pipe may extend into a second catalytic reaction zone positioned downstream of the catalytic reaction zone.

The at least one heat conductor or the at least one heat pipe may extend into a third catalytic reaction zone positioned downstream of the second catalytic reaction zone.

The rotary heat exchanger may incorporate the catalytic reaction zone.

The present invention will be more fully described by way of example, with reference to the accompanying drawings in which: Figure 1 is a partially cut-away view of a gas turbine engine having a catalytic combustion chamber according to the present invention.

Figure f is a cross-sectional view through a first embodiment of the catalytic combustion chamber shown in Figure 1.

Figure 3 is a cross-sectional view through a second embodiment of the catalytic combustion chamber shown in Figure 1.

Figure 4 is a cross-sectional view through a third embodiment of the catalytic combustion chamber shown in Figure 1.

Figure 5 is a cross-sectional view through a fourth embodiment of the catalytic combustion chamber shown in Figure 1.

Figure 6 is a cross-sectional view through a fifth embodiment of the catalytic combustion chamber shown in Figure 1.

Figure 7 is a cross-sectional view through a sixth embodiment of the catalytic combustion chamber shown in Figure 1.

Figure 8 is a cross-sectional view through a radial flow catalytic combustion chamber.

Figure 9 is a cross-sectional view through an alternative radial flow catalytic combustion chamber.

Figure 10 is a cross-sectional view through a further radial flow catalytic combustion chamber.

A gas turbine engine 10, which is shown in Figure 1, comprises in flow series an intake 12, a compressor section 14, a combustion section 16, a turbine section 18 and an exhaust 20. The gas turbine engine 10 operates conventionally in that air is compressed as it flows through the compressor section 14, and fuel is injected into the combustor section 16 and is burnt in the compressed air to provide hot gases which flow through and drive the turbines in the turbine section 18. The turbines in the turbine section 18 are arranged to drive the compressors in the compressor section 14 via shafts (not shown).

The combustion section 16 comprises one or more catalytic combustion chambers 22A as shown more clearly in Figure 2. The catalytic combustion chamber 22A has an inlet 24 at its upstream end for the supply of compressed air, from the compressor section 14, into the catalytic combustion chamber 22, and a fuel pipe 26 and fuel injectors 28, for the supply of fuel into the upstream end of the catalytic combustion chamber 22.

A first catalyst coated ceramic honeycomb monolith 30, positioned downstream of the fuel injectors, forms a first catalytic reaction zone. A second catalyst coated ceramic honeycomb monolith 32, positioned downstream of the first catalyst coated ceramic honeycomb monolith 30, forms a second catalytic reaction zone.

The catalytic combustion chamber 22A has an outlet 34 at its downstream end, for discharging the hot gases produced in the combustion process to the turbine section 18.

The first catalyst coated ceramic honeycomb monolith 30 has a plurality of cells 36 which extend therethrough. The second catalyst coated ceramic honeycomb monolith 32 has a plurality of cells 38 which extend therethrough. The cross-sectional area of individual cells 36 in the first honeycomb monolith 30 is greater than the cross-sectional area of the individual cells 38 in the second honeycomb monolith 32.

The first catalyst coated ceramic honeycomb monolith 30 has at least one heat conductor 40 which extends from the downstream end 42 to the upstream end 44 of the first catalyst coated ceramic honeycomb monolith 30. Preferably there are a plurality of heat conductors 40 suitably spaced throughout the first catalyst coated ceramic honeycomb monolith 30. The heat conductors 40 preferably comprise high conductivity beryllium copper or other suitable materials.

In operation the fuel and air supplied into the catalytic combustion chamber 22 is premixed before it enters the first catalytic reaction zone formed by the first catalyst coated ceramic honeycomb monolith 30. The temperature oX the surface of the first catalytic coated 0 ceramic honeycomb monolith has to be of the order of 350 to 4000C, or greater, for combustion of the fuel to be maintained.As discussed previously, even if the combustion process has become self sustaining it is possible that at very high flow rates the temperature at a region at the upstream end of the catalyst coated ceramic honeycomb monolith may fall below 35O0C, and this region, of the catalyst coated ceramic honeycomb monolith, which is at a temperature below 3500C may spread to the downstream end and extinguish the reaction process in the first catalytic reaction zone.

The provision of the heat conductors 40 in the first catalyst coated ceramic honeycomb monolith 30, allows heat to be transferred from the downstream end 42 to the upstream end 44 of the first catalyst coated ceramic honeycomb monolith 30 by conduction. This minimises the reduction in temperature at the upstream end 44 of the first catalyst coated ceramic honeycomb monolith 30 with increasing flow rates. The quantity of heat needing to be transferred is fairly small, because only the boundary layer of the fuel and air mixture at the upstream end of the first honeycomb monolith 30 needs to be heated, not all of the fuel and air.

Once the boundary layer of the fuel and air mixture equals or exceeds 350-4000C the catalytic reaction process takes place on the surface and heat is liberated which in turn assists combustion of the remainder of the fuel. Thus the heat conductors 40 transfer sufficient heat to maintain the surface temperature of the catalyst coated ceramic honeycomb monolith 30 sufficiently high to maintain combustion of the fuel and air mixture in the first catalytic reaction zone.

The heat transferred by the heat conductors 40 to the upstream end 44 of the first catalyst coated ceramic honeycomb monolith 30 allows operation of the catalytic combustion chamber 22A over a greater fuel to air ratio range, over a greater power range or over a greater range of compressor air outlet temperatures.

The catalytic combustion chamber 22B shown in Figure 3 is similar to that shown in Figure 2, but differs in that the heat conductors 40 extend in a downstream direction from the downstream end 42 of the first catalyst coated ceramic honeycomb monolith 30 into the region 50 of the catalytic combustion chamber 22 between the first and second catalyst coated honeycomb monoliths 30 and 32 respectively. The heat conductors 40 extend from the region 50 to the upstream end 44 of the first catalyst coated ceramic honeycomb monolith 30, to transfer heat from hot gases in the region 50 to the upstream end 44 of the first catalyst coated ceramic honeycomb monolith 30.

The catalytic combustion chamber 22C, shown in Figure 4 is similar to that shown in Figure 2, but differs in that the heat conductors 40 extend in a downstream direction from the downstream end 42 of the first catalyst coated ceramic honeycomb monolith 30 through the region 50 and into the second catalyst coated ceramic honeycomb monolith 32. The heat conductors 40 extend to the downstream end 46 of the second catalyst coated ceramic honeycomb monolith 32. The heat conductors 40 transfer heat from the downstream end 46 of second catalyst coated ceramic honeycomb monolith 32 to the upstream end 44 of the first catalyst coated ceramic honeycomb monolith 30.

The catalytic combustion chamber 22D, shown in Figure 5, is similar to that shown in Figure 2, but differs in that a third catalyst coated ceramic honeycomb monolith 78 forms a third catalytic reaction zone. The heat conductors 40 extend in a downstream direction from the downstream end 42 of the first catalyst coated ceramic honeycomb monolith 30 through the region 50, through the second catalyst coated ceramic honeycomb monolith 32, through the region 80 between the second and third catalyst coated honeycomb monoliths 32 and 78 and into the third catalyst coated ceramic honeycomb monolith 78. The heat conductors 40 extend to the downstream end 82 of the third catalyst coated ceramic honeycomb monolith 78.The heat conductors 40 transfer heat from the downstream end 82 of the third catalyst coated ceramic honeycomb monolith 32 to the upstream end 44 of the first catalyst coated ceramic honeycomb monolith 30.

The catalytic combustion chamber 22E, shown in figure 6, is similar to that shown in Figure 2, but differs in that at least one heat pipe 96 is arranged in the first catalyst coated ceramic honeycomb monolith 30. The heat pipes 96 extend from the downstream end 42 to the upstream end 44 of the first catalyst coated ceramic honeycomb monolith 30 to transfer heat from the downstream end 42 to the upstream end 44 of the first catalyst coated ceramic honeycomb monolith 30. It would be possible to use heat pipes instead of heat conductors in Figures 3,4 and 5.

The catalytic combustion chamber 22F, shown in Figure 7 is similar to that shown in Figure 2 and this is enclosed by a wall 98. An annular wall 100 encloses the catalytic combustion chamber 22F and defines an annular passage 102 therebetween A fuel pipe 104 is arranged to supply fuel to a plurality of fuel injectors 106 arranged in the annular passage 102 such that the fuel mixes with air flowing through the annular passage 102. The fuel and air mixture leaving the downstream end of the annular passage 102 mixes with the hot gases leaving the outlet 34 of the catalytic combustion chamber 22F in the region 108 downstream of the catalytic combustion chamber 22F. In operation at power settings less than or equal to about 25-33% of full power all the fuel is supplied to the fuel injectors 28 in the catalytic combustion chamber 22F.At power settings greater than 25-33* of full power, the fuel flow to the injectors 106 is gradually increased and the fuel injected by the injectors 106 is burnt in a homogeneous reaction at approximately 1300 C in the region 108.

The catalytic combustion chamber 22G, shown in Figure 8, is similar to that shown in Figure 2, but differs in that the catalytic combustion chamber 22F is a radial flow combustion chamber. The catalytic combustion chamber 22G has a plurality of apertures 118 therethrough to allow a portion of the fuel and air mixture to flow into the region 48 between the first and second catalyst coated honeycomb monoliths 30 and 32 respectively. A ring 120 is movable to control the flow of the fuel and air mixture through the apertures 118. In operation the ring 120 closes the apertures 118 at low power settings so that the fuel and air flows through the first catalyst coated ceramic honeycomb monolith 30.At high power settings, when the air supplied by the compressor is at a temperature greater than 0 350-400 C, the ring 120 moves to open the apertures 118 to allow a portion of the fuel and air mixture to bypass the first catalyst coated ceramic honeycomb monolith 30.

The catalytic combustion chamber 22H, shown in Figure 9 is similar to that shown in Figure 2, but differs in that the catalytic combustion chamber 22H is a radial flow combustion chamber. The catalytic combustion chamber 22H has an inner annular wall 122 which encloses the second catalyst coated honeycomb monolith 32. An intermediate annular wall 124 is arranged coaxially with and is spaced from the inner annular wall 122 by a helical wall 134. An outer annular wall 126 is arranged coaxially with and is spaced from, the intermediate annular wall 124 by a helical wall 128.

The downstream end of the intermediate annular wall 124 is secured to an annular wall 123, and an annular aperture 142 is defined between the downstream end of the inner wall 122 and the annular wall 123.

A third catalyst coated ceramic honeycomb monolith 33 is enclosed by the annular wall 123.

A first helical passage 130 is defined between the outer annular wall 126, the intermediate annular wall 124 and the helical wall 128 for the flow of the fuel and air mixture to a chamber 132. A second helical passage 136 is defined between the intermediate annular wall 124, the inner annular wall 122 and the helical wall 134 for the flow of the fuel and air mixture from the chamber 132 to the region 48 through the apertures 142. The surfaces of the outer annular wall 126, the intermediate annular wall 124 and the helical wall 128 defining the helical passage 130 and the surfaces of the intermediate annular wall 126, inner annular wall and helical wall 134 are coated with a catalyst to effectively form a first catalyst coated honeycomb monolith 30.

The upstream end of the inner annular wall 122 has an opening 138 for the flow of the fuel and air mixture into the second catalyst coated ceramic honeycomb monolith 32. A control member 140 is movable to control the flow of fuel and air mixture through the opening 138.

In operation the fuel and air mixture flows through the first helical passage 130 of the first catalyst coated honeycomb monolity 30 to the chamber 132. At low power settings the control member 140 restricts the flow of the fuel and air mixture through the opening 138 such that substantially all the fuel and air mixture flows through the second helical passage 136 of the first catalytic coated honeycomb monolith 30 from the chamber 132 to the region 48 in the opposite direction to the flow through first helical passage 130 of the first catalyst coated honeycomb monolith 30.Thus heat produced in the downstream end, ie second helical passage 136, of the first catalyst coated ceramic honeycomb monolith 30 by the catalytic combustion of the fuel in the air is conducted through the intermediate annular wall 124 to the upstream end, ie first helical passage 130, of the first catalyst coated ceramic honeycomb monolith 30. At high power settings, when the air supplied by the compressor is at a higher temperature, the control member 140 moves away from the opening 138 to allow substantially all the fuel and air mixture to flow through the opening 138 and bypass the second helical passage 136.

The catalytic combustion chamber 221, shown in Figure 10, is similar to that shown in Figure 2, but differs in that the catalytic combustion chamber 22I is a radial flow combustion chamber. The catalytic combustion chamber 22I includes a first annular wall 142 which encloses the second catalyst coated ceramic honeycomb monolith 32. An outer annular wall 144 is arranged coaxially with and is spaced from the inner annular wall 142. A corrugated wall member 146 extends between the inner annular wall 142 and the outer annular wall 144 and has chutes which alternately form first passages 148 and second passages 150.The first catalyst coated ceramic honeycomb monolith 30 is arranged between the inner annular wall 142 and the outer annular wall 144 at one end of the corrugated wall member 146. The first catalyst coated ceramic honeycomb monolith 30 is rotatably mounted coaxially with the axis of the inner and outer annular walls 142 and 144 and a shaft 154 is arranged to drive the first catalyst coated ceramic honeycomb monolith 30. The inner annular wall 142 has a plurality of apertures 156 to interconnect the second passages 150 and the region 48.

In operation the fuel and air mixture flows through the first passages 148 formed by the corrugated wall member 146 and through the rotating first catalyst coated ceramic honeycomb monolith 30 to a chamber 152 formed at the closed end of the combustion chamber. The fuel and air mixture is heated by the surface of the first catalyst coated ceramic honeycomb monolith 30. The fuel and air mixture in the chamber 152 then flows in the opposite direction through the rotating first catalyst coated ceramic honeycomb monolith 30 and burns to generate heat. The hot gases from the first catalyst coated ceramic honeycomb monolith 30 then flow through the second passages 150 formed by the corrugated wall member 146 and through the apertures 156 to the region 48. Further catalytic combustion of the hot gases then occurs in the second catalyst coated ceramic honeycomb monolith 32.

In all the arrangements discussed the quantity of heat to be transferred from the downstream end of the catalytic reaction zone, or from a region of the combustion chamber downstream of the catalytic reaction zone, to the upstream end of the catalytic reaction zone, or to a region of the combustion Chamber upstream of the catalytic reaction zone is relatively small, because only the surface layer of the upstream end of the catalytic reaction zone has to be heated. Once the surface layer at the upstream end of the catalytic reaction zone is in the region of 3500C to 4000C, the catalytic combustion process takes place on the surface and heat is liberated which in turn assists combustion of the remainder of the fuel.

The pressures at the upstream and downstream ends of the catalyst coated ceramic honeycomb monolith are substantially the same, and thus there is less likelihood of leakage of fuel and air or hot gases between the two ends.

Any leakage will not effect the catalytic combustion process significantly.

Although the description has referred to catalyst coated ceramic honeycomb monoliths it is equally possible to use a catalyst coated metallic matrix for example a metallic matrix comprising one or more corrugated metal strips interleaved with one or more smooth metal strips which are wound into a spiral or are arranged concentrically. A suitable metal for forming the metallic matrix is an iron-chromium-aluminium alloy which may contain yttrium for example Fecralloy (Registered Trade Mark). The catalyst may be platinum or 10% rhodium - platinum.

Claims (20)

Claims:

1. A catalytic combustion chamber comprising a catalytic reaction zone, means to supply fuel to the catalytic reaction zone, means to supply air to the catalytic reaction zone, means to transfer heat from the downstream end of the catalytic reaction zone or from a region of the catalytic combustion chamber downstream of the catalytic reaction zone to the upstream end of the catalytic reaction zone or to a region of the catalytic combustion chamber upstream of the catalytic reaction zone such that an air and fuel mixture or the surfaces of the catalytic reaction zone at the upstream end of the catalytic reaction zone are preheated to a temperature at which combustion of the fuel and air mixture occurs in the catalytic reaction zone.

2. A catalytic combustion chamber as claimed in claim 1 in which the means to transfer heat comprises at least one heat conductor extending at least the length of the catalytic reaction zone.

3. A catalytic combustion chamber as claimed in claim 1 in which the means to transfer heat comprises at least one heat pipe extending at least the length of the catalytic reaction zone.

4. A catalytic combustion chamber as claimed in claim 1 in which the means to transfer heat comprises a rotary heat exchanger.

5. A catalytic combustion chamber as claimed in claim 2 or claim 3 in which the means to transfer heat extends into a region of the catalytic combustion chamber downstream of the catalytic reaction zone.

6. A catalytic combustion chamber as claimed in claim 5 in which the means to transfer heat extends into a second catalytic reaction zone positioned downstream of the catalytic reaction zone.

7. A catalytic combustion chamber as claimed in claim 6 in which the means to transfer heat extends into a third catalytic reaction zone positioned downstream of the second catalytic reaction zone.

8. A catalytic combustion chamber as claimed in claim 4 in which the rotary heat exchanger includes the catalytic reaction zone.

9. A catalytic combustion chamber as claimed in claim 1 in which the catalytic reaction zone comprises a first portion and a second portion arranged in side by side abutting relationship, means to direct the fuel and air mixture leaving one end of the first portion into the second portion such that the flow of fuel and air through the second portion is opposite to the direction of the flow of fuel and air through the first portion whereby heat is transferred from the second portion to the first portion of the first catalytic reaction zone.

10. A catalytic combustion chamber as claimed in claim 9 in which the first and second portions are annular and concentric.

11. A catalytic combustion chamber substantially as hereinbefore described with reference to and as shown in Figure 2 of the accompanying drawings.

12. A catalytic combustion chamber substantially as hereinbefore described with reference to and as shown in Figure 3 of the accompanying drawings.

13. A catalytic combustion chamber substantially as hereinbefore described with reference to and as shown in Figure 4 of the accompanying drawings.

14. A catalytic combustion chamber substantially as hereinbefore described with reference to and as shown in Figure 5 of the accompanying drawings.

15. A catalytic combustion chamber substantially as hereinbefore described with reference to and as shown in Figure 6 of the accompanying drawings.

16. A catalytic combustion chamber substantially as hereinbefore described with reference to and as shown in Figure 7 of the accompanying drawings.

17. A catalytic combustion chamber substantially as hereinbefore described with reference to and as shown in Figure 8 of the accompanying drawings.

18. A catalytic combustion chamber substantially as hereinbefore described with reference to and as shown in Figure 9 of the accompanying drawings.

19. A catalytic combustion chamber substantially as hereinbefore described with reference to and as shown in Figure 10 of the accompanying drawings.

20. A gas turbine engine comprising a catalytic combustion chamber as claimed in any of claims 1 to 19.