Flex-fuel injector for gas turbines

This application claims benefit of the 26 Sep. 2008 filing date of U.S. provisional application No. 61/100,448.

Development for this invention was supported in part by Contract No. DE-FC26-05NT42644, awarded by the United States Department of Energy. Accordingly, the United States Government may have certain rights in this invention.

This invention relates to a combustion engine, such as a gas turbine, and more particularly to a fuel injector that provides alternate pathways for gaseous fuels of widely different energy densities.

In gas turbine engines, air from a compressor section and fuel from a fuel supply are mixed together and burned in a combustion section. The products of combustion flow through a turbine section, where they expand and turn a central shaft. In a can-annular combustor configuration, a circular array of combustors is mounted around the turbine shaft. Each combustor may have a central pilot burner surrounded by a number of main fuel injectors. A central pilot flame zone and a main fuel/air mixing region are formed. The pilot burner produces a stable flame, while the injectors deliver a stream of mixed fuel and air that flows past the pilot flame zone into a main combustion zone. Energy released during combustion is captured downstream by turbine blades, which turn the shaft.

In order to ensure optimum combustor performance, it is preferable that the respective fuel-and-air streams are well mixed to avoid localized, fuel-rich regions. As a result, efforts have been made to produce combustors with essentially uniform distributions of fuel and air. Swirler elements are used to produce a stream of fuel and air in which air and injected fuel are evenly mixed. Within such swirler elements are holes releasing fuel supplied from manifolds designed to provide a desired amount of a given fluid fuel, such as fuel oil or natural gas.

Fuel availability, relative price, or both may be factors for an operation of a gas turbine, so there is an interest not only in efficiency and clean operation but also in providing fuel options in a given turbine unit. Consequently, dual fuel devices are known in the art.

Synthetic gas, or syngas, is gas mixture that contains varying amounts of carbon monoxide and hydrogen generated by the gasification of a carbon-containing fuel such as coal to a gaseous product with a heating value. Modern turbine fuel system designs should be capable of operation not only on liquid fuels and natural gas but also on synthetic gas, which has a much lower BTU (British Thermal Unit) energy value per unit volume than natural gas. This criterion has not been adequately addressed. Thus, there is a need for a flex-fuel mixing device that provides efficient operation using fuels with low energy density, such as syngas, as well as higher energy fuels, such as natural gas.

The invention is explained in the following description in view of the drawings that show:

FIG. 1 is a side sectional view of a prior art gas turbine combustor.

FIG. 2 is a conceptual sectional view of prior art can-annular combustors in a gas turbine, taken on a plane normal to the turbine axis.

FIG. 3 is a side sectional view of a prior art injector using injector swirler vanes.

FIG. 4 is a transverse sectional view of a prior art injector vane.

FIG. 5 is a side sectional view of a flex-fuel injector per aspects of the invention.

FIG. 6 is a transverse sectional view of a flex-fuel injector vane of FIG. 5 .

FIG. 7 is a side sectional view of a flex-fuel injector second embodiment.

FIG. 8 is a transverse sectional view of a flex-fuel injector vane of FIG. 7 .

FIG. 9 is a transverse sectional view of flex-fuel injector vanes in a third embodiment.

FIG. 10 is a conceptual side sectional view of a flex-fuel pilot nozzle per aspects of the invention.

FIG. 11 is a side sectional view of a flex-fuel injector fourth embodiment.

FIG. 1 shows an example of a prior art gas turbine combustor 10 , some aspects of which may be applied to the present invention. A housing base 12 has an attachment surface 14 . A pilot fuel delivery tube 16 has a pilot fuel diffusion nozzle 18 . Fuel inlets 24 provide a main fuel supply to main fuel delivery tube structures 20 with injection ports 22 . A main combustion zone 28 is formed within a liner 30 downstream of a pilot flame zone 38 . A pilot cone 32 has a divergent end 34 that projects from the vicinity of the pilot fuel diffusion nozzle 18 downstream of main swirler assemblies 36 . The pilot flame zone 38 is formed within the pilot cone 32 adjacent to and upstream of the main combustion zone 28 .

Compressed air 40 from a compressor 42 flows between support ribs 44 through the swirler assemblies 36 . Within each main swirler assembly 36 , a plurality of swirler vanes 46 generate air turbulence upstream of main fuel injection ports 22 to mix compressed air 40 with fuel 26 to form a fuel/air mixture 48 . The fuel/air mixture 48 flows into the main combustion zone 28 where it combusts. A portion of the compressed air 50 enters the pilot flame zone 38 through a set of vanes 52 located inside a pilot swirler assembly 54 . The compressed air 50 mixes with the pilot fuel 56 within pilot cone 32 and flows into pilot flame zone 38 where it combusts. The pilot fuel 56 may diffuse into the air supply 50 at a pilot flame front, thus providing a richer mixture at the pilot flame front than the main fuel/air mixture 48 . This maintains a stable pilot flame under all operating conditions.

The main fuel 26 and the pilot fuel 56 may be the same type of fuel or different types, as disclosed in US Pre-Grant Pub No. 20070289311, of the present assignee, which is incorporated herein by reference. For example, natural gas may be used as a main fuel simultaneously with dimethyl ether (CH 3 OCH 3 ) used as a pilot fuel.

FIG. 2 is a schematic sectional view of prior art combustors 10 installed in a can-annular configuration in a gas turbine 11 with a casing 17 . This view is taken on a section plane normal to the turbine axis 15 , and shows a circular array of combustors 10 , disposed about a shaft 13 , each having swirler assemblies 36 with swirler vanes 46 on main fuel delivery tubes 20 . The present invention deals with a flex-fuel design for a swirler assembly 36 and to a pilot fuel nozzle 18 . The invention may be applied to the configuration of FIG. 2 , but is not limited to that configuration.

FIGS. 3 and 4 illustrate basic aspects of a prior art main fuel injector and swirler assembly 36 such as found in U.S. Pat. No. 6,832,481 of the present assignee. A fuel supply channel 19 supplies fuel 26 to radial passages 21 in vanes 47 A that extend radially from a fuel delivery tube structure 20 A. Combustion intake air 40 flows over the vanes 47 A. The fuel 26 is injected into the air 40 from apertures 23 open between the radial passages 21 and an exterior surface 49 of the vane. The vanes 47 A are shaped to produce turbulence or swirling in the fuel/air mixture 48 .

The prior design of FIGS. 3 and 4 could use alternate fuels with similar viscosities and energy densities, but would not work as well for alternate fuels of highly dissimilar viscosities or energy densities. Syngas has less than half the energy density of natural gas, so the injector flow rate for syngas must be at least twice that of natural gas. This results in widely different injector design criteria for these two fuels.

Existing swirler assemblies 36 have been refined over the years to achieve ever-increasing standards of performance. Altering a proven swirler design could impair its performance. For example, increasing the thickness of the vanes 47 A to accommodate a wider radial passage for a lower-energy-density fuel would increase pressure losses through the swirler assemblies, since there would be less open area through them. To overcome this problem, higher fuel pressure could be provided for the low-energy-density fuel instead of wider passages. However, this causes other complexities and expenses. Accordingly, it is desirable to maintain current design aspects of the swirler assembly with respect to a first fuel such as natural gas as much as possible, while adding a capability to alternately use a lower-energy-density fuel such as synthetic gas.

FIGS. 5 and 6 illustrate aspects of a fuel injector according to the invention. First and second fuel supply channels 19 A and 19 B alternately supply respective first and second fuels 26 A, 26 B to respective first and second radial passages 21 A, 21 B in vanes 47 B that extend radially from a fuel delivery tube structure 20 B. The fuel delivery tube structure 20 B may be formed as concentric tubes as shown, or in another configuration of tubes. Combustion intake air 40 flows over the vanes 47 B. The first fuel 26 A is injected into the air 40 from first apertures 23 A formed between the first radial passages 21 A and an exterior surface 49 of the vane. Selectably, the second fuel 26 B is injected into the air 40 from second apertures 23 B formed between the second radial passages 21 B and the exterior surface 49 of the vane. The vanes 47 B may be shaped to produce turbulence in the fuel/air mixture 48 , such as by swirling or other means, and may have a pressure side 49 P and a suction side 49 S as known in aerodynamics.

The first fuel delivery pathway 19 A, 21 A, 23 A provides a first flow rate at a given backpressure. Herein “backpressure” means pressure exerted on a moving fluid at an exit of a fluid conduit. In order to accommodate fuels with dissimilar energy densities, the second fuel delivery pathway 19 B, 21 B, 23 B provides a second flow rate at approximately the given backpressure. The first and second flow rates may differ from each other by at least a factor of two. This difference may be achieved by having a reduced pressure loss in the second fuel delivery pathway 19 B, 21 B, 23 B when compared to a pressure loss in the first fuel delivery pathway 19 A, 21 A, 23 A. This may be accomplished by having different cross-sectional areas in one or more respective portions of the two fuel delivery pathways, as known in fluid dynamics, and may be enhanced by differences in the shapes of the two pathways. For example, it was found that a rounded or gradual transition area 25 between the second fuel supply channel 19 B and the second radial passages 21 B substantially increases the second fuel flow rate at a given backpressure, due to reduction of turbulence in the radial passages 21 B. Such transition area may take a curved form as shown, or may take a graduated form, such as a 45-degree transitional segment. Rounding or graduating of the transition 25 area may be done in an axial plane of the injector as shown and/or in a plane normal to the flow direction 40 (not shown).

FIG. 6 shows a sectional view of a fuel injector vane 47 B as in FIG. 5 , with a pressure side 49 P, a suction side 49 S, a front portion F and a back portion B. The front portion F may extend parallel to the flow direction of the intake air supply 40 to accommodate the second radial passage 21 B and apertures 23 B in the vane 47 B. By extending the front portion F in-line with the airflow, differential pressures between the pressure and suction sides 49 P, 49 S occur downstream of the apertures 23 A, 23 B. This allows approximately equal fuel injection rates from the apertures of a given radial passage 21 A, 21 B on both sides 49 P, 49 S of the vane 47 B. Extending the vane in this way can be done without increasing the vane width, thus maintaining known design aspects for the first fuel elements 21 A, 23 A and minimizing pressure loss on the fuel/air mixture 48 through the swirler assembly 36 .

FIGS. 7 and 8 illustrate aspects of a second embodiment of the invention. A first fuel supply channel 19 A provides a first fuel 26 A to a first radial passage 21 A in vanes 47 C that extend radially from a fuel delivery tube structure 20 B. Alternately, a second fuel supply channel 19 B provides a second fuel 26 B to second and third radial passages 21 C, 21 D in the vanes 47 C. The fuel delivery tube structure 20 B may be formed as concentric tubes as shown, or in another configuration of tubes. Combustion intake air 40 flows over the vanes 47 C. The first fuel 26 A is injected into the air 40 from first apertures 23 A formed between the first radial passages 21 A and an exterior surface 49 of the vane. Selectably, the second fuel 26 B is injected into the air 40 from second and third sets of apertures 23 C, 23 D formed between the respective second and third radial passages 21 C, 21 D and the exterior surface 49 of the vane. The vanes 47 C may be shaped to produce turbulence in the fuel/air mixture 48 , such as by swirling or other means, and may have pressure and suction sides 49 P, 49 S.

The first fuel delivery pathway 19 A, 21 A, 23 A provides a first flow rate at a given backpressure. In order to accommodate fuels with dissimilar energy densities, the second fuel delivery pathway 19 B, 21 C, 21 D, 23 C, 23 D provides a second flow rate at the given backpressure. The first and second flow rates may differ by at least a factor of two. This difference may be achieved by providing different cross-sectional areas of one or more respective portions of the first and second fuel delivery pathways, and may be enhanced by differences in the shapes of the two pathways. It was found that contouring the transition area 31 between the fuel supply channel 19 B and the second and third radial passages 21 C, 21 D increases the fuel flow rate at a given backpressure, due to reduction of fuel turbulence. A more equal fuel pressure between the radial passages 21 C and 21 D was achieved by providing an equalization area or plenum 31 in the transition area, as shown. This equalization area 31 is an enlarged and rounded or graduated common volume of the proximal ends of the radial passages 21 C and 21 D. A partition 33 between the radial passages 21 C and 21 D may start radially outwardly of the second fuel supply channel 19 B. This creates a small plenum 31 that reduces or eliminates an upstream/downstream pressure differential at the proximal ends of the respective radial passages 21 D, 21 C. Rounding or graduating of the equalization area 31 may be done in an axial plane of the injector as shown and/or in a plane normal to the flow direction 40 (not shown).

FIG. 8 shows a sectional view of a fuel injector vane 47 C as used in FIG. 7 . It has a pressure side 49 P, a suction side 49 S, a front portion F and a back portion B. The front portion F extends parallel to the flow direction of the intake air supply 40 to accommodate the second and third radial passages 21 C, 21 D and apertures 23 C, 23 D. Since the front portion F is in-line with the airflow 40 , differential pressures between the pressure and suction sides 49 P, 49 S occurs downstream of the apertures 23 A, 23 C, 23 D. This allows approximately equal fuel flows to exit the apertures of a given radial passage 21 A, 21 C, 21 D on both sides of the vane 47 C. Extending the vane in this way can be done without increasing the vane width, thus maintaining known design aspects with respect to the first fuel elements 21 A, 23 A, and minimizing pressure loss on the fuel/air mixture 48 through the swirler assembly 36 .

FIG. 9 shows a third embodiment of the invention. A first flex-fuel injector vane 47 A has a first radial passage 21 A and apertures 23 A. The first radial passage 21 A communicates with a first fuel supply channel as previously described. A second vane 47 D has a second radial passage 21 E and apertures 23 E. The second radial passage 21 E communicates with a second fuel supply channel as previously described. The first set of vanes may each comprise a trailing edge 41 that is angled relative to a flow direction 40 of an intake air supply. The second vane 47 D may be positioned directly upstream of the first vane 47 A. The first and second fuel delivery pathways may differ by at least a factor of two in fuel flow rate at a given backpressure as previously described, thus providing similar features and benefits to the previously described embodiments. Flex-fuel capability is provided for alternate fuels of highly different energy densities, without reducing the area of the intake air flow path between the vanes.

Main injector assemblies embodying the present invention may be used with diffusion or pre-mixed pilots. FIG. 10 shows a pilot fuel diffusion nozzle 18 that may be used in combination with the main flex-fuel injector assemblies 36 herein. A pilot fuel delivery tube structure 16 B has first and second pilot fuel supply channels 35 A, 35 B for respective first and second alternate fuels 26 A and 26 B. Diffusion ports 37 for the first fuel have less area than diffusion ports 39 for the second fuel, thus providing benefits as discussed for the main flex-fuel injector assemblies 36 previously described. The first and second fuels 26 A and 26 B in the pilot supply channels may be the same fuels used for the main flex-fuel injector assemblies 36 .

FIG. 11 illustrates aspects of a fourth embodiment of the invention, in which the arrangement of the fuel supply channels 19 A, 19 B and the relative positions of the respective radial passages is reversed from previous figures. A first fuel supply channel 19 A provides a first fuel 26 A to a first radial passage 21 A in vanes 47 E that extend radially from a fuel delivery tube structure 20 C, 20 D. Alternately, a second fuel supply channel 19 B provides a second fuel 26 B to second and third radial passages 21 F, 21 G in the vanes 47 E. The fuel delivery tube structure 20 C, 20 D may be formed as concentric cylindrical tubes, or in another configuration of tubes. Combustion intake air 40 flows over the vanes 47 E. The first fuel 26 A is injected into the air 40 from first apertures 23 A formed between the first radial passage 21 A and an exterior surface 49 of the vanes. Selectably, the second fuel 26 B is injected into the air 40 from second and third sets of apertures 23 F, 23 G formed between the respective second and third radial passages 21 F, 21 G and the exterior surface 49 of the vanes. The vanes 47 E may be shaped to produce turbulence in the fuel/air mixture 48 , such as by swirling or other means.

The first fuel delivery pathway 19 A, 21 A, 23 A provides a first flow rate at a given backpressure. In order to accommodate fuels with dissimilar energy densities, the second fuel delivery pathway 19 B, 21 F, 21 G, 23 F, 23 G provides a second flow rate at the given backpressure. The first and second flow rates may differ by at least a factor of two. This difference may be achieved by providing different cross-sectional areas of one or more respective portions of the first and second fuel delivery pathways, and may be enhanced by differences in the shapes of the two pathways. It was found that contouring the transition area 41 between the second fuel supply channel 19 B and the second and third radial passages 21 F, 21 G increases the fuel flow rate at a given backpressure, due to reduction of fuel turbulence. Fuel pressure differences between the radial passages 21 F and 21 G may be equalized by providing an equalization area or plenum 41 in the transition area, as shown. This equalization area 41 is an enlarged and rounded or graduated common volume of the proximal ends of the radial passages 21 F and 21 G. A partition 33 between the radial passages 21 F and 21 G may start radially outwardly of the second fuel supply channel 19 B. For example, it may start radially flush with an inner diameter of the first fuel supply tube 20 C. This creates a small plenum 41 that reduces or eliminates an upstream/downstream pressure differential at the proximal ends of the respective radial passages 21 F, 21 G. Rounding or graduating of the equalization area may be done in an axial plane of the injector as shown and/or in a plane normal to the flow direction 40 (not shown).

The vanes 47 B, 47 C, 47 D, 47 E of the present invention may be fabricated separately or integrally with the fuel delivery tube structure 20 B, 20 C, 20 D or with a hub (not shown) to be attached to the fuel delivery structure 20 B, 20 C, 20 D. If formed separately, the radial passages 21 A, 21 B, 21 C and transition areas 25 , 31 , 41 may be formed by machining. Alternately, the vanes may be formed integrally with the fuel delivery tube structure 20 B or a hub. For example, the fuel channels and/or radial passages may be formed of a high-nickel metal in a lost wax investment casting process with fugitive curved ceramic cores or by sintering a powdered metal or a ceramic/metal powder in a mold with a fugitive core such as a polymer that vaporizes at the sintering temperature to leave the desired internal void structure.

The embodiment of FIG. 11 may be alternately formed by casting and machining, as follows:

1) Cast the overall injector assembly 36 without forming the fuel channels 19 A, 19 B or radial passages 21 A, 21 F, 21 G in the casting process; 2) Machine the radial passages 21 A, 21 F, 21 G; 3) Machine the apertures 23 A, 23 F, 23 G; 4) Machine the outer fuel channel 19 A with an end mill up to a channel end 43 ; 5) Use a cutter or abrasive wheel to round the proximal ends of the radial passages 21 A, 21 F, 21 G, at least in a plane normal to the flow direction 40 ; 6) Fabricate the inner fuel tube 20 D separately, insert it into the outer fuel tube 20 C, and braze the inner fuel tube in place; 7) Seal the distal ends of the radial channels with plugs 45 .

In any of the embodiments herein, any of the injector “vanes” may be aerodynamic swirlers as shown, or they may have other shapes, such as the non-swirling vane 47 D of FIG. 9 , or twisted vanes. Non-swirler injection vanes may be used in combination with swirler airfoils upstream or downstream of the non-swirler injector vanes. The radial passages for the first and second fuels 26 A, 26 B may be in the same set of vanes, such that one or more radial passages for each fuel 26 A, 26 B are disposed in each vane, as in FIGS. 5 , 7 , and 11 . Alternately different radial passages for different fuels 26 A, 26 B may be in different injector vanes, as in FIG. 9 .

In any of the embodiments of the invention herein, the first and second fuels 26 A, 26 B may be supplied from two or more independent supply facilities, such as storage tanks, supply lines, or an on-site integrated gasification facility. For example, the first fuel 26 A may be natural gas supplied from a storage tank or supply line, while the second fuel 26 B may be a synthetic gas supplied from on-site gasification of coal or other carbon-containing material. The first and second fuels 26 A, 26 B are selectively supplied alternately to the first main fuel supply channel 19 A or to the second main fuel supply channel 19 B respectively. The same first and second fuels 26 A, 26 B may also be selectively supplied alternately to the first pilot fuel supply channel 35 A or to the second pilot fuel supply channel 35 B respectively. The selection and switching between alternate fuels may be done by valves, including electronically controllable valves. Embodiments where more than two (such as three for example) radial passages may be fed by a central fuel supply channel may be envisioned.

The present invention provides alternate fuel capability in a fuel/air mixing apparatus, and allows the fuel/air mixing apparatus to maintain a predetermined and proven performance for a first fuel while adding an optimized alternate fuel capability for a second fuel having a widely different energy density from the first fuel.

While various embodiments of the present invention have been shown and described herein, it will be obvious that such embodiments are provided by way of example only. Numerous variations, changes and substitutions may be made without departing from the invention herein. For example, while exemplary embodiments having two radial passages for a lower BTU fuel are discussed, other embodiments may have more than two radial fuel passages fed by a single fuel supply, such as three radial passages in one embodiment. Accordingly, it is intended that the invention be limited only by the spirit and scope of the appended claims.