Apparatus and method for mixing fuel in a gas turbine nozzle   

This invention was made with Government support under Contract No. DE-FC26-05NT42643, awarded by the Department of Energy. The Government has certain rights in the invention.

FIELD OF THE INVENTION

The present invention generally involves an apparatus and method for supplying fuel to a gas turbine. Specifically, the present invention describes a nozzle that may be used to supply fuel to a combustor in a gas turbine.

BACKGROUND OF THE INVENTION

Gas turbines are widely used in industrial and power generation operations. A typical gas turbine includes an axial compressor at the front, one or more combustors around the middle, and a turbine at the rear. Ambient air enters the compressor, and rotating blades and stationary vanes in the compressor progressively impart kinetic energy to the working fluid (air) to produce a compressed working fluid at a highly energized state. The compressed working fluid exits the compressor and flows through nozzles in the combustors where it mixes with fuel and ignites to generate combustion gases having a high temperature, pressure, and velocity. The combustion gases expand in the turbine to produce work. For example, expansion of the combustion gases in the turbine may rotate a shaft connected to a generator to produce electricity.

It is widely known that the thermodynamic efficiency of a gas turbine increases as the operating temperature, namely the combustion gas temperature, increases. However, if the fuel and air are not evenly mixed prior to combustion, localized hot spots may form in the combustor near the nozzle exits. The localized hot spots increase the chance for flame flash back and flame holding to occur which may damage the nozzles. Although flame flash back and flame holding may occur with any fuel, they occur more readily with high reactive fuels, such as hydrogen, that have a higher burning rate and wider flammability range. The localized hot spots may also increase the production of nitrous oxides, carbon monoxide, and unburned hydrocarbons, all of which are undesirable exhaust emissions.

A variety of techniques exist to allow higher operating temperatures while minimizing localized hot spots and undesirable emissions. For example, various nozzles have been developed to more uniformly mix higher reactivity fuel with the working fluid prior to combustion. The higher burning rate of higher reactivity fuel, however, still creates an environment conducive to flame flash back and/or flame holding events. As a result, continued improvements in nozzle designs that can support increasingly higher combustion temperatures and higher reactive fuels would be useful.

Aspects and advantages of the invention are set forth below in the following description, or may be obvious from the description, or may be learned through practice of the invention.

One embodiment of the present invention is a nozzle that includes a fuel plenum and an air plenum downstream of the fuel plenum. A plurality of fuel channels radially outward of an axial centerline of the nozzle includes an inlet and an outlet downstream of the inlet and allows an air to flow through the inlet. A fuel port in the plurality of fuel channels provides fluid communication between the fuel plenum and the plurality of fuel channels. An air port in the plurality of fuel channels downstream of the fuel port provides fluid communication between the air plenum and the plurality of fuel channels.

Another embodiment within the scope of the present invention is a nozzle that includes a shroud circumferentially surrounding the nozzle. A plurality of barriers inside the shroud extends radially across the nozzle and define a fuel plenum and an air plenum, wherein the air plenum is downstream of the fuel plenum. A plurality of fuel channels radially outward of a centerline of the nozzle wherein the plurality of fuel channels are defined as a fluid passage and include an inlet and an outlet downstream of the inlet, a fuel port in fluid communication with the fuel plenum, and an air port in fluid communication with the air plenum, wherein the air port is downstream of the fuel port.

The present invention also includes a method for mixing fuel and air in a nozzle prior to combustion. The method includes flowing air through inlets of a plurality of fuel channels, flowing fuel to a fuel plenum, and flowing air to an air plenum downstream of the fuel plenum. The method further includes injecting fuel from the fuel plenum through fuel ports in the plurality of fuel channels, wherein the plurality of fuel channels is radially outward of an axial centerline of the nozzle and injecting air from the air plenum through air ports in the plurality of fuel channels, wherein the air ports are downstream of the fuel ports.

Those of ordinary skill in the art will better appreciate the features and aspects of such embodiments, and others, upon review of the specification.

BRIEF DESCRIPTION OF THE DRAWINGS

A full and enabling disclosure of the present invention, including the best mode thereof to one skilled in the art, is set forth more particularly in the remainder of the specification, including reference to the accompanying figures, in which:

FIG. 1 is a simplified cross-section of a combustor according to one embodiment of the present invention;

FIG. 2 is an enlarged cross-section of a nozzle according to one embodiment of the present invention;

FIG. 3 is an enlarged cross-section of a portion of the combustor shown in FIG. 1;

FIG. 4 is a plan view of a nozzle according to one embodiment of the present invention;

FIG. 5 is a plan view of a combustor top cap according to one embodiment of the present invention; and

FIG. 6 is a plan view of a combustor top cap according to an alternate embodiment of the present invention.

DETAILED DESCRIPTION

Reference will now be made in detail to present embodiments of the invention, one or more examples of which are illustrated in the accompanying drawings. The detailed description uses numerical and letter designations to refer to features in the drawings. Like or similar designations in the drawings and description have been used to refer to like or similar parts of the invention.

Each example is provided by way of explanation of the invention, not limitation of the invention. In fact, it will be apparent to those skilled in the art that modifications and variations can be made in the present invention without departing from the scope or spirit thereof. For instance, features illustrated or described as part of one embodiment may be used on another embodiment to yield a still further embodiment. Thus, it is intended that the present invention covers such modifications and variations as come within the scope of the appended claims and their equivalents.

Embodiments of the present invention include a nozzle having multiple fuel channels that mix fuel and air prior to combustion. In general, the fuel flows into a fuel plenum in the nozzle. The air, generally comprising a compressed working fluid from a compressor, flows into a separate air plenum downstream of the fuel plenum. Fuel from the fuel plenum then flows or is injected into the fuel channels located radially outward of an axial centerline of the nozzle. Similarly, air from the air plenum flows or is injected into the fuel channels to flow along the surface of the fuel channels and mix with the fuel therein before exiting the nozzle. Air flowing outside of the nozzle and outside of the air plenum may also flow into the fuel channels to mix with the fuel therein before exiting the nozzle. In this manner, the fuel channels provide more evenly mixed and possible leaner mixture of fuel and air downstream of the nozzle.

FIG. 1 shows a simplified cross-section of a combustor 10 according to one embodiment of the present invention. As shown, the combustor 10 generally includes one or more nozzles 12 radially arranged in a top cap 14. A casing 16 may surround the combustor 10 to contain the air or compressed working fluid exiting the compressor (not shown). An end cap 18 and a liner 20 may define a combustion chamber 22 downstream of the nozzles 12. A flow sleeve 24 with flow holes 26 may surround the liner 20 to define an annular passage 28 between the flow sleeve 24 and the liner 20.

As shown in FIG. 2, the nozzle 12 generally includes a shroud 30 that circumferentially surrounds a plurality of fuel channels 32. The shroud 30 may include one or more divider plates or barriers that define discrete chambers or sections inside the nozzle 12. For example, as shown in FIG. 2, top, middle, and bottom barriers 34, 36, 38 inside the shroud 30 may extend radially across the width or diameter of the nozzle 12. In this manner, fuel may enter the nozzle 12, for example through a fuel conduit 40, and flow into a fuel plenum 42 defined by the top and middle barriers 34, 36. Similarly, air or compressed working fluid from the compressor may flow through the inlet of fuel channels and one or more air ports 44 in the shroud 30 into an air plenum 46 defined by the middle and bottom barriers 36, 38.

The fuel channels 32 are aligned radially outward of an axial centerline 48 of the nozzle 12 and generally extend parallel to one another through one or more barriers 34, 36, 38 along the axial length of the nozzle 12. For example, as shown in FIGS. 2 and 3, each fuel channel 32 generally extends from the fuel plenum 42 through the air plenum 46 to the downstream exit of the nozzle 12. In this manner, the fuel channels 32 are able to provide a mixture of fuel and air to the combustion chamber 22. The fuel channels 32 generally comprise a tube or passage 50, an inlet 52, an outlet 54, one or more fuel ports 56, and one or more air ports 58. The tube or passage 50 may be round, oval, square, triangular, or any known geometric shape. The inlet 52 and outlet 54 may simply comprise openings at the upstream and downstream ends of the fuel channels 32 that permit air to freely flow through the fuel channels 32 and mix with fuel injected into the fuel channels 32 through the fuel ports 56.

The fuel ports 56 provide fluid communication between the fuel plenum 42 and the fuel channels 32. Depending on the design needs, some or all of the fuel channels 32 may include fuel ports 56. The fuel ports 56 may simply comprise openings or apertures in the tube or passage 50 that allow the fuel to flow or be injected from the fuel plenum 42 into the fuel channel 32. The fuel ports 56 may be angled with respect to the axial centerline 48 of the nozzle 12 to vary the angle at which the fuel enters the fuel channels 32, thus varying the distance that the fuel penetrates into the fuel channels 32 before mixing with the air. For example, as shown in FIG. 2, the fuel ports 56 may be angled between approximately 30 and approximately 90 degrees with respect to the axial centerline 48 of the nozzle 12.

The air ports 58 similarly provide fluid communication between the air plenum 46 and the fuel channels 32. Air or compressed working fluid from the compressor may thus flow into the air plenum 46 through the air ports 44 in the shroud 30. The air may then flow from the air plenum 46 through the air ports 58 into the fuel channels 32. The air ports 58 may simply comprise openings or apertures in the tube or passage 50 that allow the air to flow or be injected from the air plenum 46 into the fuel channel 32. As shown in FIG. 2, the air ports 58 may be angled less than approximately 30 degrees with respect to the axial centerline 48 of the nozzle 12 to vary the distance that the air penetrates into the fuel channels 32 before mixing with fuel.

In this manner, the fuel channels 32 provide three separate fluid flow paths there through, as shown by the arrows in FIG. 2. The first flow path is simply air that enters through the inlet 52 and flows completely through the tube or passage 50 before exiting the nozzle 12 at the outlet 54. Approximately 60 to approximately 90 percent of the air from the compressor may flow through this first path. The second flow path is fuel that enters through the fuel ports 56 and mixes with the air passing from the inlet 52 to the outlet 54. The third flow path is air that enters through the air ports 58 and forms an air layer very close to the surface of the tube 50 to prevent flashback and flame holding inside the tube 50 or mixes with the fuel/air mixture previously described before exiting the nozzle 12. Approximately 2 to 30 percent of the air from the compressor may flow through this third path.

FIGS. 2 and 3 provide an enlarged cross-section of a portion of the combustor 10 shown in FIG. 1 with arrows to illustrate the various flow paths of the air or compressed working fluid from the compressor. As shown in FIG. 3, the air may flow between the flow sleeve 24 and liner 20 toward the nozzles 12. As the air reaches the nozzles 12 and passes along the outside of the shroud 30, some of the air may flow through the air ports 44 into the air plenum 46, as shown in FIG. 2. Once in the air plenum 46, the air may flow through the air ports 58 into the fuel channels 32 where it mixes with the fuel before exiting the nozzle 12 into the combustion chamber 22. Returning to FIG. 3, the remainder of the air passing along the outside of the shroud 30 reaches the end cap 18 where it reverses direction and flows into the inlet 52 of the fuel channels 32. Once in the fuel channels 32, the air mixes with fuel entering through the fuel ports 56 before exiting the nozzle 12 into the combustion chamber 22.

FIGS. 4, 5, and 6 provide various plan views of the top cap 14 looking upstream from the combustion chamber 22. For example, FIG. 4 provides a plan view of the nozzle 12 previously described and illustrated. As shown in FIG. 4, the fuel channels 32 appear as circles radially outward of the axial centerline 48 of the nozzle 12. As shown in FIGS. 5 and 6, the nozzles 12 may be circular, triangular, square, oval, or virtually any shape and may be arranged in various geometries in the top cap 14. For example, the nozzles 12 may be arranged as six nozzles surrounding a single nozzle, as shown in FIG. 5. Alternately, a series of pie shaped nozzles 60 may surround a circular nozzle 12, as shown in FIG. 6. One of ordinary skill in the art should understand that the present invention is not limited to any particular geometry of individual nozzles or nozzle arrangements or number of fuel channels, unless specifically recited in the claims.

The various embodiments of the present invention may provide several advantages over existing nozzles. For example, the use of fuel channels 32 allows for faster flow of fuel through the nozzle 12, thus reducing the time it takes for the fuel to flow through the nozzle 12. In addition, the nozzles 12 within the scope of the present invention may be installed in existing combustors, allowing for less expensive modifications of existing nozzles.

This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other and examples are intended to be within the scope of the claims if they include structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.