Premixer assembly for mixing air and fuel for combustion

Abstract

Premixer arrangement (20) for mixing air and fuel for combustion, comprising: several tubes (32, 50) arranged at a head end (28) of a combustion chamber arrangement (14); a tube (50) of the several tubes (32, 50), wherein the tube (50) has a longitudinal axis; an inlet section of the tube (50) located at an inlet end (44) of the tube (50) and having a non-circular section, wherein the non-circular section has a non-circular inner cross-section perpendicular to the longitudinal axis of the tube (50); an outlet section of the pipe (50) located at an outlet end (46) of the pipe (50) and having a substantially circular inner cross-section perpendicular to the longitudinal axis of the pipe (50); and at least one fuel injection port (48) which is arranged in a fuel injection plane which is located between the inlet end (44) of the tube (50) and the outlet end (46) of the tube (50); wherein the inlet end (44) is arranged such that air enters the tube (50) through the inlet end (44) in order to mix with the fuel entering the tube (50) through the at least one fuel injection opening (48); and wherein the non-circular section extends to a point between the fuel injection plane and the outlet end (46) of the pipe (50).

Description

STATEMENT ON US FEDERAL RESEARCH

[0001] This invention was created with support from the U.S. Government under Contract No. DE-FC26-05NT42643 awarded by the U.S. Department of Energy. The U.S. Government has certain rights in this invention. BACKGROUND TO THE INVENTION

[0002] The subject matter disclosed herein relates to turbine systems and, more particularly, to a premixer assembly for mixing air and fuel for combustion within a combustor assembly of a gas turbine.

[0003] The primary air pollutant emissions typically produced by gas turbines burning conventional hydrocarbon fuels are nitrogen oxides, carbon monoxide, and unburned hydrocarbons. It is well known in the art that the oxidation of molecular nitrogen in air-breathing engines is highly dependent on the maximum hot gas temperature in the reaction zone of the combustion system. One method for controlling the reaction zone temperature of a heat engine combustor below the level at which thermal NOx is generated is to premix fuel and air to a lean mixture prior to combustion.

[0004] The efficiency of premixing fuel and air is an important factor in emissions levels. The length of the tubes used to mix the fuel with the air is determined by the mixing efficiency. Although longer tubes result in better mixing, increasing the length of the tube undesirably requires additional costs associated with tube manufacturing and increases the overall size of the combustor and gas turbine.

[0005] JP 2013-234836 A describes a premixer assembly for mixing air and fuel for combustion, comprising a plurality of tubes arranged at a head end of a combustion chamber assembly. The tubes each have an inlet end through which air enters the tubes, an outlet end, and fuel injection ports arranged in a fuel injection plane between the inlet end and the outlet end of the tube. An inlet plate with a mixing and introducing device is arranged at the inlet end of each tube. The inlet plate is located at the inlet end of the tube upstream of the fuel injection ports and has a plurality of projections projecting into the interior of the tube to swirl the air entering the tube to promote mixing of the air flow with the fuel flow entering through the fuel injection ports.

[0006] JP 2013-190201 A describes a premixer arrangement of a gas turbine having a plurality of premixing tubes for mixing air and fuel for combustion, wherein air enters through an inlet end of each premixing tube and fuel is supplied through a fuel inlet downstream of the inlet end of the premixing tube, and wherein the fuel inlet has a projection which projects radially into the premixing tube in a transverse direction relative to a longitudinal axis of the premixing tube. SUMMARY OF THE INVENTION

[0007] According to one aspect of the invention, a premixer assembly for mixing air and fuel for combustion includes a plurality of tubes disposed at a head end of a combustor assembly. Also included is a tube of the plurality of tubes, the tube having a longitudinal axis. Further included is an inlet portion of the tube located at an inlet end of the tube and having a non-circular portion, the non-circular portion having a non-circular internal cross-section perpendicular to the longitudinal axis of the tube. Further included is an outlet portion of the tube located at an outlet end of the tube and having a substantially circular internal cross-section perpendicular to the longitudinal axis of the tube. Further included is at least one fuel injection port disposed in a fuel injection plane located between the inlet end of the tube and the outlet end of the tube.The inlet end is arranged such that air enters the tube through the inlet end to mix with fuel entering the tube through the at least one fuel injection port. The non-circular portion extends to a point between the fuel injection plane and the outlet end of the tube.

[0008] In the premixer assembly of any type mentioned above, the at least one non-circular section of the tube may comprise a first non-circular section and a second non-circular section, the first non-circular section being located near the inlet end of the tube and having a first geometric cross-section, the second non-circular section having a second geometric cross-section different from the first geometric cross-section.

[0009] In the premixer assembly of any type mentioned above, a cross-sectional area of ​​the pipe may remain substantially constant over an entire length of the pipe.

[0010] In the premixer assembly of any type mentioned above, the at least one non-circular portion of the tube may have a geometry comprising at least one of oval, triangular, quadrilateral, and a pair of semicircular ends connected by a pair of parallel walls, wherein corners of a substantially triangular and a substantially quadrilateral geometry have fillets at an edge interface.

[0011] Alternatively, the at least one non-circular portion of the tube may have a geometry comprising a cardioid shape, wherein a tip of the cardioid shape has a fillet.

[0012] According to another aspect of the invention, a gas turbine includes a compressor, a turbine, and a combustor assembly having a premixer assembly as described above.

[0013] These and other advantages and features will become more apparent from the following description taken in conjunction with the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The subject matter regarded as the invention is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features and advantages of the invention will become apparent from the following detailed description taken in conjunction with the accompanying drawings, in which: Fig. 1 a schematic representation of a gas turbine from the centerline to the outer circumference; Fig. 2 a schematic representation of a combustion chamber arrangement of the gas turbine; Fig. 3 is a perspective view of a premixer assembly of the combustion chamber assembly; Fig. 4 is a schematic diagram comparing the geometry of an inlet end and an outlet end of a tube of the premixer assembly according to a first embodiment; Fig. 5 is a schematic diagram comparing the geometry of the inlet end and the outlet end of the tube of the premixer assembly according to a second embodiment; Fig. 6 is a schematic diagram comparing the geometry of the inlet end and the outlet end of the tube of the premixer assembly according to a third embodiment; Fig. 7 is a schematic diagram comparing the geometry of the inlet end and the outlet end of the tube of the premixer assembly according to a fourth embodiment; Fig. 8 is a schematic diagram comparing the geometry of the inlet end and the outlet end of the tube of the premixer assembly according to a fifth embodiment; Fig. 9 is a schematic representation of fuel injection into various geometric configurations of the premixer assembly tube; Fig. 10 is a perspective view of the tube illustrating a region of substantially constant cross-section along the length of the tube.

[0015] The detailed description explains embodiments of the invention together with advantages and features by way of example with reference to the drawings. DETAILED DESCRIPTION OF THE INVENTION

[0016] Referring to Fig. 1 illustrates a schematic representation of an exemplary gas turbine 10. The gas turbine 10 includes a compressor 11 and a combustor assembly 14. The combustor assembly 14 includes a combustor assembly wall 16 that at least partially defines a combustion chamber 12. A premixer assembly 20 extends from the combustor assembly wall 16 and into the combustion chamber 12. The premixer assembly 20 may also be referred to herein as a "premixer assembly." As explained in more detail below, the premixer assembly 20 receives a first fluid, such as a fuel, through a fuel inlet 22 and a second fluid, such as compressed air, from the compressor 11.The fuel and compressed air are then mixed together, transferred to the combustor 12, and ignited to produce a high-temperature, high-pressure combustion product or combustion gas stream. Although only a single combustor assembly 14 is illustrated in the exemplary embodiment, the gas turbine 10 may include multiple combustor assemblies 14. In any event, the gas turbine 10 also includes a turbine 24 and a shaft 26 operatively connecting the compressor 11 and the turbine 24. The turbine 24 is connected to the shaft 26 in a manner known in the art and drives the shaft 26, which in turn drives the compressor 11.

[0017] During operation, air flows into the compressor 11 and is compressed into a high-pressure gas. The high-pressure gas is delivered to the combustor assembly 14 and mixed with a fuel, e.g., process gas and / or synthetic gas (syngas), in the premixer assembly 20. The fuel / air or combustible mixture is directed into the combustor 12 and ignited to produce a high-pressure, high-temperature combustion gas stream. Alternatively, the combustor assembly 14 may combust fuels, including, but not limited to, natural gas and / or fuel oil. The combustor assembly 14 then directs the combustion gas stream to the turbine 24, which converts thermal energy into rotational mechanical energy.

[0018] By now on Fig. 2, an annular tubular array of combustor assemblies is arranged in a circumferentially spaced manner about an axial centerline of the gas turbine 10. For clarity of illustration, a partial view of a single combustor assembly of the annular tubular array is illustrated, and includes the combustor 12 and a head end 28. The head end 28 is disposed at an adjacent upstream location of the combustor 12 and includes the premixer assembly 20. The premixer assembly 20 includes a plurality of tubes 32 or conduits that may be divided into individual sections that mate together. In one exemplary embodiment, the premixer assembly 20 includes six sections, with each section having from about 20 to about 200 tubes.It should be understood, however, that the actual number of sections and number of tubes within each section may vary depending on the specific application. Each of the plurality of tubes 32 may vary in size. Although referred to throughout the specification as the plurality of tubes 32, it should be understood that a monolithic arrangement utilizes multiple passages. Therefore, for clarity of description, the term "tube" or "pipeline" is used herein for reference, but it should be understood that the term is to be used synonymously with passage.

[0019] The combustion chamber 12 is defined by a flame tube 34, such as a liner disposed further inwardly. A sleeve 38, such as a flow sleeve, is spaced radially outward from the flame tube 34 and enclosingly surrounds the flame tube 34. An air flow 40 flows in an upstream direction within an annulus 42 defined by the flame tube 34 and the sleeve 38 toward the head end 28 of the combustor assembly 14. The air flow 40 makes a 180-degree turn into inlets of the plurality of tubes 32 to mix with a fuel before the mixture is delivered to the combustion chamber 12.

[0020] Referring to Fig. 3, the premixer assembly 20 is illustrated in greater detail. Each of the plurality of tubes 32 of the premixer assembly 20 includes an inlet end 44 and an outlet end 46. Between the inlet end 44 and the outlet end 46 is at least one fuel injection port 48 for directing fuel from a plenum 45 disposed around the tubes 32 to an interior region of each of the plurality of tubes 32. The at least one fuel injection port 48 is located in a fuel injection plane between the inlet end 44 and the outlet end 46. As the airflow 40 of compressed air approaches the head end 28 of the combustor assembly 14, it is then redirected toward the inlet end 44 of each of the plurality of tubes 32 and into the inlet end 44.The fuel entering through the at least one fuel injection port 48 and the air flow 40 of compressed air entering through the inlet end 44 are mixed within the plurality of tubes 32.

[0021] Referring to the Fig. 4-8, several embodiments of a tube 50 of the plurality of tubes 32 are schematically illustrated. In particular, the inlet end 44 of the tube 50 and the outlet end 46 of the tube 50 are illustrated in a stacked arrangement for clarity. The tube 50 of each embodiment includes a non-circular portion 52. The non-circular portion 52 has a non-circular cross-sectional geometry that extends along at least a portion of the tube 50. The fuel injection ports 48 are shown at the inlet for illustrative purposes, however, it should be recognized that the fuel injection ports are not necessarily located at the outermost inlet end, but rather may be located anywhere downstream of the inlet end 44.

[0022] The non-circular section 52 is located near the inlet end 44 and extends downstream through the fuel injection plane, which includes the at least one fuel injection port 48. The non-circular section 52 then gradually transitions to either a circular cross-section geometry or another non-circular geometry upstream of the outlet end 46 of the tube 50. As such, the region of the tube 50 near the outlet end 46 is circular.

[0023] In one embodiment, tube 50 includes a first non-circular section located near inlet end 44 and a second non-circular section located near outlet end 46. The first non-circular section and the second non-circular section have different cross-sectional geometries. It is contemplated that more than two cross-sectional geometries may be included along the longitudinal extent of tube 50.

[0024] As will be appreciated from the description below, it is usually advantageous to position the non-circular portion 52 near the fuel injection plane.

[0025] Regardless of the precise location of the non-circular portion 52 or portions, it should be recognized that the non-circular geometry may be any non-circular shape. Illustrative embodiments of the non-circular portion 52 are shown in the Fig. 4-8. In particular, a substantially square or rectangular shape ( Fig. 5), an essentially triangular shape ( Fig. 6), an oval shape ( Fig. 7) or a “racetrack” or “stadium”-shaped figure ( Fig. 8). In each shape shown, the corners of the quadrilateral or triangle are rounded to a fillet. The shapes shown and described above are merely exemplary and not intended to be limiting. It should be understood that any non-circular shape may be used. One particular embodiment that has proven particularly advantageous for mixing fuel and compressed air is shown in Fig. 4. The illustrated non-circular shape is referred to as an essentially cardioid shape. A cardioid is a type of epicycloid with a single apex. The apex is rounded to a fillet.

[0026] As expressly mentioned above, any non-circular shape may be used for the non-circular portion 52 of the tube 50. Regardless of where the non-circular portion(s) are located along the longitudinal extent of the tube 50, a gradual transition from one particular geometry (e.g., circular or non-circular) to another is created. In other words, abrupt or rapid transitions are typically avoided to reduce or eliminate flow separation and / or significant secondary flows within the tube 50. While it is contemplated that any conventional manufacturing process may be used to create the plurality of tubes 32, one manufacturing process category for creating the gradual shape transitions along the longitudinal extent of the tube 50 is particularly useful. In particular, additive manufacturing may be used to create the tube 50.The term "additively manufactured" should be understood to describe components built by forming and solidifying successive layers of material one upon another. Specifically, a layer of a powder material is deposited on a substrate and melted by applying heat, a laser, an electron beam, or some other process, and then allowed to solidify. Once solidified, a new layer is deposited, solidified, and fused to the previous layer until the component is created. An exemplary additive manufacturing process includes direct metal laser sintering (DMLS).

[0027] In all of the above-described embodiments of the tube 50, a substantially constant cross-sectional area is maintained over the majority of the tube 50. In particular, the cross-sectional area is constant over substantially the entire length of the tube 50. Maintaining a constant cross-sectional area over the length of the tube 50 maintains the average velocity of the fluid(s) within the tube, thereby reducing the likelihood of flashback or flame holding with certain highly reactive fuels. The constant cross-sectional area is in Fig. 10, where A1, A2, and A3 represent cross-sectional areas at three locations along the length of the tube 50. A1, A2, and A3 are substantially equal to each other, with A1 representing the cross-sectional area at the inlet end 44, A2 representing the cross-sectional area at the fuel injection plane, and A3 representing the cross-sectional area at the outlet end 46 in the illustrated embodiment.

[0028] According to the invention, the region of the tube 50 near the fuel injection plane has a non-circular cross-sectional geometry. By avoiding a circular geometry at the fuel injection plane, more efficient mixing between the fuel and the compressed air can be achieved. In particular, more efficient use of the available internal area of ​​the tube 50 is achieved by injecting fuel closer to the center of the tube or by orienting the fuel injection jets 49 ( Fig. 9) are distributed over the inner area, thereby resulting in a faster spread and / or more turbulent mixing of the fuel with the air flowing within the tube 50. A comparison between a circular cross-sectional area and exemplary non-circular cross-sectional areas at the fuel injection plane is shown in Fig. 9. The non-circular configurations reduce or avoid coalescence of fuel injection jets where fuel injection jets 49 are directed toward each other. Furthermore, the fuel injection jets 49 are not injected directly into a wall. This combination results in a more balanced and / or more centered injection of fuel to mix with the compressed air therein. This type of filling of the tube 50 results in more efficient mixing and may result in lower emissions of nitrogen oxides or, alternatively, may assist in achieving a shorter tube required for a given emission level, which includes the advantage of smaller, lower-cost components and lower pressure drop.

[0029] As illustrated, one or more than one fuel injection port 48 may be associated with each tube. The exact number of fuel injection ports depends on the particular cross-sectional geometry of the tube 50. In some embodiments, such as the substantially cardioid-shaped tube ( Fig. 4), a single fuel injection port positioned at the apex of the cross-sectional shape is advantageous. The other illustrated configurations may benefit from strategic positioning of multiple fuel injection ports to efficiently utilize the available internal area of ​​the tube 50. Regardless of which non-circular shape is used along a portion of the tube 50, it should be understood that one or more fuel injection ports may be accommodated and that the positioning of the fuel injection port(s) may vary. For example, although the fuel injection ports may be positioned at the fillets of the shapes according to the Fig. 5 and Fig.6, some or all of the fuel injection ports may be positioned along the longitudinal extent of one of the sides of the shapes, such as mid-span thereof. Another advantage of the tube configurations is that the fuel injection ports are better positioned within the fuel plenum chamber, with more clearance between adjacent tubes. Numerical analysis has shown that when the fuel port inlets are located near an "open" space within the plenum chamber and not facing the opening of an adjacent tube, fuel distribution (and emissions) can be improved.

[0030] Advantageously, the above-described embodiments achieve more efficient and / or faster mixing of fuel and air in the premixer assembly 20, as well as better distribution of fuel in the fuel injection ports. As a result, the overall length of the premixer assembly 20 can be reduced while maintaining the same or better NOx emission levels. A shortened assembly is also typically less expensive and easier to install within the combustor assembly 14 and can result in a lower combustion chamber pressure drop, which can provide an advantage in gas turbine efficiency.

[0031] While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention may be modified to incorporate any number of changes, modifications, substitutions, or equivalent arrangements not described hereinabove, which are nevertheless within the spirit and scope of the invention. Furthermore, it should be understood that although various embodiments of the invention have been described, aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be considered limited by the foregoing description, but is limited only by the scope of the appended claims.

[0032] A premixer assembly for mixing air and fuel for combustion includes a plurality of tubes disposed at a head end of a combustor assembly. Also included is a tube of the plurality of tubes, the tube including an inlet end and an outlet end. Also included is at least one non-circular portion of the tube extending along a length of the tube, the at least one non-circular portion having a non-circular cross-section, and the tube having a substantially constant cross-sectional area along its length. Parts list: 10 gas turbines 11 compressors 12 Combustion chamber 14 Combustion chamber arrangement 16 Combustion chamber arrangement wall 20 Premixer arrangement 22 Fuel inlet 24 turbines 26 Wave 28 headboard 32 Multiple pipes 34 Flame tube 38 sleeve 40 Air flow 42 annular space 44 Admitting 45 Collection chamber 46 omitted 48 Fuel injection opening 50 pipe 52 Non-circular section

Claims

[1] Premixer arrangement (20) for mixing air and fuel for combustion, comprising: a plurality of tubes (32, 50) arranged at a head end (28) of a combustion chamber assembly (14); a tube (50) of the plurality of tubes (32, 50), the tube (50) having a longitudinal axis; an inlet portion of the tube (50) located at an inlet end (44) of the tube (50) and having a non-circular portion, the non-circular portion having a non-circular internal cross-section perpendicular to the longitudinal axis of the tube (50); an outlet portion of the tube (50) located at an outlet end (46) of the tube (50) and having a substantially circular internal cross-section perpendicular to the longitudinal axis of the tube (50); and at least one fuel injection port (48) disposed in a fuel injection plane located between the inlet end (44) of the tube (50) and the outlet end (46) of the tube (50); wherein the inlet end (44) is arranged such that air enters the tube (50) through the inlet end (44) to mix with fuel entering the tube (50) through the at least one fuel injection opening (48); and wherein the non-circular portion extends to a location between the fuel injection plane and the outlet end (46) of the tube (50). [2] A premixer assembly (20) according to any one of the preceding claims, wherein the at least one non-circular section of the tube comprises a first non-circular section and a second non-circular section, the first non-circular section being located near the inlet end of the tube and having a first geometric cross-section, the second non-circular section having a second geometric cross-section different from the first geometric cross-section. [3] Premixer assembly (20) according to claim 1 or 2, wherein an inner cross-sectional area of the tube (50) remains substantially constant over an entire length of the tube (50). [4] The premixer assembly (20) of any preceding claim, wherein the at least one non-circular portion of the tube (50) has a geometry comprising at least one of the following: oval, triangular, quadrilateral, and a pair of semi-circular ends connected by a pair of parallel walls, wherein corners of a triangular and a quadrilateral geometry have fillets at an edge interface; or wherein the at least one non-circular portion of the tube (50) has a geometry comprising a substantially cardioid shape, wherein an apex of the substantially cardioid shape has a fillet. [5] Gas turbine (10) comprising: a compressor (11); a turbine (24); and a combustion chamber arrangement (14) with a premixer arrangement (20) according to any one of the preceding claims.

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