GB1601687A - Gas turbine engines - Google Patents

Description

(54) IMPROVEMENTS IN AND RELATING TO GAS TURBINE ENGINES (71) We, JOHNSON, MATTHEY & CO., LIMITED, a British Company of 43 Hatton Garden, London, EC1N SEE, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to gas turbines and to improved methods of operation of gas turbines in which catalytic oxidation of a major proportion of the fuel takes place and produces a considerable reduction in the quantity of pollutant present in the exhaust gases.

At present it is unusual for a gas turbine to utilize catalytic combustion for even a proportion of the inlet fuel. The main difficulty confronting designers of gas turbines utilizing catalytic combustion is the very high throughputs of air or oxygen and fuel involved. The volume of catalyst required to ensure effective surface reaction of a major proportion of the combusting gases is totally unrealistic in relation to the designs for turbines currently in use.

An object of the present invention is to produce a gas turbine in which a major proportion of the fuel undergoes catalytic combustion within the confines of a combustion chamber having a volume of similar order to that of turbines presently operating.

According to the present invention a gas turbine engine comprises a gas turbine engine comprising: (a) a compressor for producing a supply of hot compressed air; (b) means for dividing the said compressed air so that a major proportion thereof by-passes a combustor section which includes a pilot burner; (c) means for injecting fuel into the pilot burner which is adapted to consume not more than approximately 5% of the total fuel consumption of the engine at full power; (d) a chamber for combining the hot gas effluent from the pilot burner with a proportion of the hot compressed air by-passed at stage (b); (e) an injector capable under full power conditions of injecting a major portion of the total fuel requirement into the effluent hot gases exiting from chamber (d);; (f) a catalytic combustor section comprising a temperature stable and oxidation resistant metallic monolith, the said metallic monolith having walls possessing a thickness within the range 0.002 to 0.004 inches and providing catalytic channels for contact with and passage therethrough of the combustible gases combined with injected fuel at stage (e) such that combustion of a substantial proportion of the uncombusted fuel takes place; (g) a reaction chamber subsequent to the catalytic combustor section in which combustion continues, and (h) a gas generator turbine which may be engaged in a mechanically rigid manner to the compressor (a) and which is driven by expansion of the hot combusting gases produced by the engine.

In section (a) the temperature of air leaving the compressor is preferably within the range 25"C to 600"C and at a pressure within the range 1 atm to 20 atm. In section (b) up to approximately 60% of the compressed air is taken off. The quantity of air taken off is preferably within the range 10% to 80% by volume.

In section (c) the pilot burner burns up to approximately 5% by weight of the total fuel consumption of the engine at full power. The proportion of fuel utilised by the pilot burner during normal running may range from 0.1% by weight to 50% or 6623% by weight. The fuel injector for the pilot burner (c) is able to control the quantity of fuel and is adjusted primarily to give a temperature within a specified preferred range in chamber (d). A typical preferred temperature range in chamber (d) is 200"C to 500"C. Pilot burner (c) is normally adjusted for the combustion of a fuel-air mixture ranging approximately from stoichiometric to rich. It utilizes the remaining compressed air not taken off at stage (b).

In a preferred embodiment 4 separate fuel injectors are used in the pilot burner stage (c) spaced from each other at angles of YO"C in the vertical plane in Figure 2 at position I,.

Similarly a multi-injector array may be used in place of the single injector illustrated at I2 in Figure 2.

In section (g) which preferably contains a bluff body, the combustion commenced in contact with the metallic monolith of section (f) continues and combustion also commences of virtually all of the remainder of the uncombusted fuel.

Preferablv the metallic monolith in section (f) is formed from one or more metals selected from the group comprising Ru, Rh, Pd, Ir and Pt. However base metals may be used or base metal alloys which also contain a platinum group metal component may be used.

The walls of the metallic monolith have a thickness within the range 2-4 thousandths of one inch. The preferred characteristics of the metallic monolith having catalyst deposited thereon are (i) that it presents low resistance to the passage of gases by virtue of its possession of a high ratio of open area to blocked area and (ii) that it has a high surface to volume ratio.

A typical 200 cells per square inch ceramic monolith has walls 0.008 - 0.011 inches thick, a 71who open area and a 15% pressure drop. A typical 400 cells per square inch metallic monolith of the present invention has walls 0.002 inches thick, a 91 - 92% open area and a 4% pressure drop. A 200 cell per square inch metallic monolith still has a 95% open area and a pressure drop of 4% of less.

Suitable platinum group metals for use in fabrication of the metallic monolith are platinum, 10% rhodium-platinum and dispersion strengthened platinum group metals and alloys as described in British Patent Specifications Nos. 1280815 and 1340076 and United States Patent Specifications Nos. 3689987, 3696502 and 3709667.

Suitable base metals which may be used are those capable of withstanding rigorous oxidising conditions. Examples of such base metal alloys are nickel and chromium alloys having an aggregate Ni plus Cr content greater than 20% by weight and alloys of iron including at least one of the elements chromium (3-40) wt.%, aluminium (1-10) wt.%, cobalt (trace) wt.%, nickel (trace-72) wt.% and carbon (trace-0-5) wt.%. Such substrates are described in German DOS 2450664.

Other examples of base metal alloys capable of with-standing the rigorous conditions required are iron-aluminium-chromium alloys which may also contain yttrium. The latter alloys may contain 0.5-12 wt.% O/o Al, 0.1-3.0 wt.% Y, 0-20 wt.% Cr. and balance Fe. These are described in United States Patent No. 3298826. Another range of Fe-Cr-Al-Y alloys contain 0.5 - 4 wt.% Al, 0.5 - 3.0 wt. % Y, 20.0 - 95.0 wt.% Cr and balance Fe and these are described in United States Patent No. 3027252.

Base metal alloys which also contain a platinum group metal component are useful as a catalytic metallic monolith in very fierce oxidising conditions, for example in catalysis of the combustion in gas turbine engines. Such alloys are described in German DOS 2530245 and equivalent BP 1520630 and contain at least 40 wt.% Ni or at least 40 wt.% Co, a trace to 30 wt.% Cr and a trace to 15 wt.% of one or more of the metals Pt, Pd, Rh, Ir, Os and Ru.The alloys may also contain from a trace to the percentage specified of any one or more of the following elements: % by weight Co 25 Ti 6 Al 7 W 20 Mo 20 Hf 2 Mn 2 Si 1.5 V 2.0 Nb 5 B 0.15 C 0.05 Ta 10 Zr 3 Fe 20 Th and rare earth metals 3 or oxides Where the metallic substrate is composed either substantially or solely of platinum group metal it may be in the form of an interwoven wire gauze or mesh or corrugated sheet or foil.

Where the metallic substrate is composed substantially of base metal it is preferably in the form of corrugated sheet or foil. These types of base metal monoliths are also described in German DOS 2450664 and they may be used in turbines according to the present invention.

Such base metal monoliths may have deposited thereon a first layer comprising an oxygen containing coating and a second and catalytic layer. The oxygen containing coating is usually present as an oxide selected from the group consisting of alumina, silica, titania, zirconia, hafnia, thoria, beryllia, magnesia, calcium oxide, strontium oxide, barium oxide, chromia, boria, scandium oxide, yttrium oxide and oxides of the lanthanides. Alternatively, the oxygen in the first layer is present as an oxygen containing anion selected from the group consisting of chromate, phosphate. silicate and nitrate. The second catalytic layer may, for example, comprise a metal selected from the group consisting of Ru, Rh, Pd, Ir, Pt, Au. Ag, an alloy containing at least one of the said metals and alloys containing at least one of the said metals and a base metal. The first and second layers may be deposited or otherwise applied to the monolith as described in German DOS 2450664.

Alternative catalytic monoliths for use in section (f) are the structures defined in British Patent Application 51219/76 dated 8th December, 1976.

In British Patent Application 51219/76 there is described a catalyst comprising a metallic substrate having deposited thereon a surface coating consisting of one or more intermetallic compounds of the general formula A B where A is selected from the group consisting of Ru, Rh, Pd, Ir, and Pt and B is selected from the group consisting of Al, Sc, Y, the lanthanides, Ti, Zr, Hf, V, Nb, and Ta and x and y are integral and may have values of 1 or more.

In British Patent Application 51219/76 the surface coating of intermetallic compound is, preferably in the form of a thin film ranging in thickness from 2 to 15 microns.

Many compounds of the type AxBy are miscible with one another and structures in which the surface coatings deposited upon the said metallic substrate contains more than one compound of the type AxBy are within the scope of this invention.

When the intermetallic compound is deposited in the form of a coating not more than 15 microns thick upon the surface of a metallic substrate, excessive brittleness is absent and the coated substrate may be handled normally.

A number of different techniques may be employed to produce a coating in the form of a thin film of intermetallic compound upon the surface of the metal metallic monolith. For example, aluminium may be deposited onto the surface of rhodium-platinum gauzes by a pack-aluminising process. In this process the gauzes are packed into a heat-resistant container in an appropriate mixture of chemicals such that aluminium is transferred via the vapour phase to the gauze surface. At the aluminising temperature, typically 800-900"C, interaction between the platinum and aluminium occurs to give the required intermetallic compound.

Alternatively, chemical vapour deposition from ZrCl4 can be used to form a layer of Pt3Zr, or electrodeposition may be used either from aqueous or fused salt electrolysis to give the requisite compound.

Whichever method is adopted the objective is to form a layer of a firmly adherent, intermetallic compound on the wires of the gauze pack or other substate.

In another technique, the metals forming the intermetallic compound are prepared as an appropriate solution in water or an organic solvent. The compound is caused to deposit upon the metallic substrate or gauze by the addition of a reducing agent.

The metallic substrate is placed in the solution whilst the precipitation is taking place and becomes coated with a uniform, microcrystalline layer of the intermetallic compound.

Preferably the reaction chamber (g) contains a bluff body which has the effect of stabilizing the gas phase reaction initiated in the catalytic combustor section (f).

Suitable bluff bodies are fabricated from the same material as the temperature stable and oxidation resistant metallic monolith of section (f). The composition of such alloys are detailed in full above and examples of alloys we have found to be useful are Inconel 600 and 601. The Nimonic alloys, Incoloy 800 and the Nichrome alloys (Registered Trade Marks), stainless steels and platinum group metals may also be used.

The invention will now be described by way of example with reference to Figure 1 which is a diagrammatic cross section of a preferred embodiment including an optional variable vane fluid (air) control system. A number of different engine geometries may be devised, for example that shown in Figure 2. In Figure 2 a fluid flow control system in which variable vanes are not used is shown.

In Figure 1 a compressor (which is not shown) produces hot compressor feed air indicated by and moving in the direction indicated by arrow F.

Section (b) of the turbine as defined above may include a variable vane system for controlling the flow of Fl (preburner air) F2 (preburner dilution air) and F3 (by-pass air).

From Figure 1 it will be seen that the flow Fl is directed to a preburner injector I1 and the ingnitor L1 whereas the flows F2 and F3 by-pass Il, and L1. During start up flows F2 and F3 are quite low and nearly all of the incoming hot compressor feed air F passes the preburner I, and igniter L1. On ignition the flow F2 and/or the fuel injector I can be adjusted to produce temperatures of the flow F4 (i.e. F1 + F2) suitable for main burner ignition by igniting by igniting 12 and, consequently, optimum performance. When these conditions are achieved, the main burner in section (e) may be started and the flow F2 will be unrestricted.

In these conditions, a flow F6 (which is controlled by operation of variable vanes V2) is also permitted and the quantity of fuel injected by main injector I2 is adjusted such that diluted power turbine feed F8 is at the desired gas temperature for optimum performance. The start up will normally reach ignition prior to the end of "engine-cranking", but self-sustaining speed may not yet be achieved and "engine-cranking" may be continued to that speed. The flow F3 provides wall cooling and blade cooling contact air if required.

Heated gas from diluted preburner (pilot burner) exhaust is mixed with air in chamber (d) as defined above and fed at sufficient temperature to the main catalytic combustor (f) where it mixes with fuel from injector I2 (e) and passes over the catalyst monolith C. The catalyst C burns some or all of the fuel and any remainder is burnt by free radical reaction immediately downstream of the catalyst. Further dilution is available by introduction of air from the flow F3 if necessary. Further, a large flow F6 ignited by an emergency igniter I3 provides emergency power as required.

Throttle response is achieved by control of fuel injection and by sequenced operation of igniters Il and 12.

A variable vane system is not essential and in Figure 2 (where the same reference symbols are used) an alternative geometry is depicted in which division of the air flow is accomplished by geometric fluidic control. T1 is a temperature probe which is connected via a feedback circuit to control injector I1, In Figures 1 and 2 an optional bluff body is indicated by reference B.

Example The turbine used was a Rover/Lucas 60 b.h.p. simple cycle turbine on a Heenan and Froude G type dynamometer. The analytical equipment used was the following: Gas Detector Method.

CO, CO2 Non-dispersive infra red (Analytical Development Ltd.) HC Flame ionisation detector (IPM) NOX Luminox 201 (BOC) 2 Servomex.

Chromel-Alumel thermocouples linked to an MBM high speed data logger and punch unit were used for temperature measurement. Fuel consumption was determined by gravimetric systems and air consumption by venturi depression metering. Commercially available diesel fuel (DERV) was used.

The engine was run initially with the production flame combustor to determine the normal parameters. The results are given in Table 1. The exhaust gas analyses obtained for these runs are given in Table 2. On the basis of the idle and emergency power settings, the emission index for each gas was calculated and these figures are given in Table 3.

The standard combustor was then replaced by the catalytic system described above and shown in diagrammatic form in Figure 2. An idle test was performed under the same conditions as for the flame combustor. The exhaust analysis for the catalytic combustor is given in Table 4. together with the emission index figures.

During this catalyst test it was observed that the fuel injection system was delivering a mixture to the catalyst which was too rich. Despite this, however, the emission index is considerably below that recorded for the flame combustion engine.

The catalyst used was a 400 cell per square inch Fecralloy (Registered Trade Mark) metallic monolith substrate having a wall thickness of 0.002 inches. Washcoat used was 5 parts Kaiser "SAM" alumina to 1 part barium stabilized "Sol-Gel" alumina (UKAEA) at a loading of lg per cubic inch of monolith. Platinum was deposited on the washcoat by known techniques at a loading of 150g per cubic foot of washcoated monolith.

A Kanthal D (Registered Trade Mark) metallic monolith substrate also having a wall thickness of 0.002 inches may replace the Fecralloy substrate in this test.

TABLE 1 Data from gas turbine running with production flame combustor Test Condition * 1 2 3 4 5 Brake load (relative) 10 40 70 95.2 10 Time to consume 21. fuel (sec) 230 201 167 145 230 Impellor tip press. (p.s.i.g) 3.4 3.6 3.7 3.8 3.5 Compressor delivery press. (p.s.

i.g.) 26 26.6 27.9 28.1 26 Compressor delivery press. (p.s.

i.a.) 41 41.6 42.9 43.1 41 Combustor back press. (cm. Hg) 15.5 15.7 14.4 14.0 15.7 Exhaust press. (cm.H2O) 5.3 3.2 2.0 -2.3 4.3 Air venturi depression (cm. H2O) 24.6 22.4 22.0 20.5 24.5 Air temp. ("F) 68 68 68 68 68 Jet Pipe temp ("C) 385 453 535 594 378 W 1 = sustaining idle; 2 = mid-power, 3 = baseline power; 4 = emergency power; 5 = idle.

TABLE 2 Exhaust Analysis Test No. 1 2 3 4 5 HC ppm 350 180 150 140 360 NO ppm 13 22 33 44 17 NOX ppm 22 24 42 58 18 CO ppm 1450 150 97 112 1560 C02% 2.5 3 3.7 4.5 2.4 02% 18 17.5 16.7 15.7 18.2 TABLE 3 Emission indices in glkg fuel Test No. 1 4 HC 53.4 12.26 NO 1.5 2.82 NOX 2.3 3.72 CO 150.0 6.24 TABLE 4 Exhaust analysis and emission index figures for catalytic combustor Exhaust Analysis Emission Index (glkg. fuel) HC 30 ppm 4.5 NO 1 0.11 NOX 1 0.11 CO 150 15.5 CO 4% O2 17 WHAT WE CLAIM IS: 1.A gas turbine engine comprising: (a) a compressor for producing a supply of hot compressed air; (b) means for dividing the said compressed air so that a major proportion thereof by-passes a combustor section which includes a pilot burner; (c) means for injecting fuel into the pilot burner which is adapted to consume not more than approximately 5% of the total fuel consumption of the engine at full power; (d) a chamber for combining the hot gas effluent from the pilot burner with a porportion of the hot compressed air by-passed at stage (b) (e) an injector capable under full power conditions of injecting a major portion of.the total fuel requirement into the effluent hot gases exiting from the chamber (d);; (f) a catalytic combustor section comprising a temperature stable and oxidation resistant metallic monolith, the said metallic monolith having walls possessing a thickness within the range 0.002 to 0.004 inches and providing catalytic channels for contact with and passage therethrough of the combustible gases combined with injected fuel at stage (e) such that combustion of a substantial proportion of the uncombusted'fuel takes place; (g) a reaction chamber subsequent to the catalytic combustor section in which combustion continues. and (h) a gas generator turbine which may be engaged in a mechanically rigid manner to the compressor (a) and which is driven by expansion of the hot combusting gases produced by the engine.

2. A gas turbine according to claim 1 wherein the metallic monolith of (f) is formed from one or more metals selected from the group comprising Ru, Rh, Pd, Ir and Pt.

3. A gas turbine according to claim 2 wherein the metallic monolith is made from 10% rhodium/platinum alloy.

4. A gas turbine according to claim 1 wherein the metallic monolith is made from a nickel/chromium alloy having an aggregate Ni plus Cr content greater than 20% by weight.

5. A gas turbine according to claim 1 wherein the metallic monolith is made from an alloy of iron. chromium and aluminium and optionally one or more of the elements cobalt, nickel, carbon and yttrium.

6. A gas turbine according to claim 5 wherein the alloy of iron contains from 3-40% by wt CR, from 1-10% by wt Al, from a trace -5% by wt Co, from a trace -72% by wt Ni, from a trace to 0.5% by wt carbon and balance Fe.

7. A gas turbine according to the claim 5 wherein the metallic monolith is made from an alloy comprising 0.5-12 wt% Al, 0-20 wt % Cr, 0.1 - 3.0 wt % Y and balance Fe.

8. A gas turbine according to claim 5 wherein the metallic monolith is made from an alloy comprising 0.5-4 wt% Al, 0.5-3.0 wt %Y, 20.0-95 wt % Cr and balance Fe.

9. A gas turbine according to claim 1 wherein the metallic monolith is made from an alloy comprising at least 40 wt % Ni or at least 40 wt % Co, a trace to 30 wt % Cr and a trace to 15 wtYc of one or more of the metals Pt, Pd, Rh, Ir, Os and Ru 10. A gas turbine according to claim 9 in which the said alloy may also contain from a trace to the percentage specified of any one or more of the following elements:

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (19)

1. **WARNING** start of CLMS field may overlap end of DESC **.

   TABLE 4 Exhaust analysis and emission index figures for catalytic combustor Exhaust Analysis Emission Index (glkg. fuel) HC 30 ppm 4.5 NO 1 0.11 NOX 1 0.11 CO 150 15.5 CO 4% O2 17 WHAT WE CLAIM IS: 1.A gas turbine engine comprising: (a) a compressor for producing a supply of hot compressed air; (b) means for dividing the said compressed air so that a major proportion thereof by-passes a combustor section which includes a pilot burner; (c) means for injecting fuel into the pilot burner which is adapted to consume not more than approximately 5% of the total fuel consumption of the engine at full power; (d) a chamber for combining the hot gas effluent from the pilot burner with a porportion of the hot compressed air by-passed at stage (b) (e) an injector capable under full power conditions of injecting a major portion of.the total fuel requirement into the effluent hot gases exiting from the chamber (d);; (f) a catalytic combustor section comprising a temperature stable and oxidation resistant metallic monolith, the said metallic monolith having walls possessing a thickness within the range 0.002 to 0.004 inches and providing catalytic channels for contact with and passage therethrough of the combustible gases combined with injected fuel at stage (e) such that combustion of a substantial proportion of the uncombusted'fuel takes place; (g) a reaction chamber subsequent to the catalytic combustor section in which combustion continues. and (h) a gas generator turbine which may be engaged in a mechanically rigid manner to the compressor (a) and which is driven by expansion of the hot combusting gases produced by the engine.
2. 2. A gas turbine according to claim 1 wherein the metallic monolith of (f) is formed from one or more metals selected from the group comprising Ru, Rh, Pd, Ir and Pt.
3. 3. A gas turbine according to claim 2 wherein the metallic monolith is made from 10% rhodium/platinum alloy.
4. 4. A gas turbine according to claim 1 wherein the metallic monolith is made from a nickel/chromium alloy having an aggregate Ni plus Cr content greater than 20% by weight.
5. 5. A gas turbine according to claim 1 wherein the metallic monolith is made from an alloy of iron. chromium and aluminium and optionally one or more of the elements cobalt, nickel, carbon and yttrium.
6. 6. A gas turbine according to claim 5 wherein the alloy of iron contains from 3-40% by wt CR, from 1-10% by wt Al, from a trace -5% by wt Co, from a trace -72% by wt Ni, from a trace to 0.5% by wt carbon and balance Fe.
7. 7. A gas turbine according to the claim 5 wherein the metallic monolith is made from an alloy comprising 0.5-12 wt% Al, 0-20 wt % Cr, 0.1 - 3.0 wt % Y and balance Fe.
8. 8. A gas turbine according to claim 5 wherein the metallic monolith is made from an alloy comprising 0.5-4 wt% Al, 0.5-3.0 wt %Y, 20.0-95 wt % Cr and balance Fe.
9. 9. A gas turbine according to claim 1 wherein the metallic monolith is made from an alloy comprising at least 40 wt % Ni or at least 40 wt % Co, a trace to 30 wt % Cr and a trace to 15 wtYc of one or more of the metals Pt, Pd, Rh, Ir, Os and Ru
10. 10. A gas turbine according to claim 9 in which the said alloy may also contain from a trace to the percentage specified of any one or more of the following elements:

    % by weight Co 25 Ti 6 Al 7 W 20 Mo 20 Hf 2 Mn 2 Si 1.5 V 2 Nb 5 B 0.15 C 0.05 Ta 10 Zr 3 Fe 20 Th and rare earth metals or oxides 3
11. 11. A gas turbine according to claim 1 wherein the metallic monolith is in the form of an interwoven wire gauze, mesh, corrugated sheet or foil.
12. 12. A gas turbine according to any one of claims 4 to 11 wherein the metallic monolith has a first layer of an oxygen containing material and a second catalytic layer.
13. 13. A gas turbine according to claim 12 wherein the said first layer is one or more oxides selected from the group consisting of alumina, silica, titania, zirconia, hafnia, thoria, beryllia, magnesia, calcium oxide, strontium oxide, barium oxide, chromia, boria, scandium oxide, yttrium oxide and oxides of the lanthanides.
14. 14. A gas turbine according to claim 12 wherein the said first layer is an oxygen containing anion selected from the group consisting of chromate, phosphate, silicate, and nitrate.
15. 15. A gas turbine according to claims 12, 13 or 14 wherein the said second catalytic layer is a metal selected from the group consisting of Ru, Rh, Ir, Pt, Au, Ag, an alloy containing at least one of the said metals and alloys containing at least one of the said metals and a base metal.
16. 16. A gas turbine according to claims 12, 13 or 14 wherein the said second catalytic layer comprises one or more intermetallic compounds of the general formula AxBx where A is selected from the group consisting of Ru, Rh, Pd, Ir, and Pt and B is selected from the group consisting of Al, Sc, Y, the lanthanides, Ti, Zr, Hf, V, Nb, and Ta and x and y are integral and may have values of 1 or more.
17. 17. A gas turbine according to claim 1 wherein the hot compressed air at (a) is at a pressure within the range 1-20 atmospheres.
18. 18. A gas turbine according to any preceding claim which includes a power output turbine also driven by expansion of the hot combusting gases produced by the engine thus producing shaft or thrust power.
19. 19. A gas turbine engine constructed and arranged substantially as hereinbefore described with reference to and as shown in the accompanying drawings.