Patent Application
20060000216
The present invention relates to a fuel injector for gas turbine combustors and particularly relates to a multi-venturi fuel injector for catalytic and dry low-NOx applications.
The main components of a combustor for a gas turbine, for example, a catalytic combustor, include (1) a pre-burner which may typically constitute a diffusion style combustor that burns a small fraction of the fuel to elevate air temperature sufficiently to activate the catalyst downstream; (2) a pre-mixer which includes the main fuel injector and accomplishes fuel and air mixing; (3) a catalyst which partially converts the fuel in a flameless reaction in which no NOx is produced; and (4) a burn-out zone which includes homogeneous combustion in a post-catalyst liner of the lean fuel/air mixture flowing from the catalyst which does not generate NOx due to the relatively reduced temperature of the combustion. This type of combustor is capable of generating very low emissions.
A multi-venturi tube has been used in a catalytic combustor as a main fuel injector. See, for example, U.S. Pat. Nos. 4,845,952 and 4,966,001. These arrangements are intended to provide a uniform fuel/air mixture at the catalyst inlet. It will be appreciated that tight uniformity of the fuel distribution must be maintained over the large cross-sectional area at the catalyst inlet. Fuel/air mixing is accomplished by distributing the fuel among the large number of venturis that fill up the cross-section of the combustor followed by aerodynamic mixing inside the venturi tube as well as in the downstream region between the venturi exit plane and the catalyst inlet. In addition to uniform fuel/air mixture, the catalyst requires a uniform temperature and a uniform velocity across the catalyst inlet plane. Absent either one of these factors, the catalyst does not function optimally. It will also be appreciated that multiple venturi tubes produce laminar flow which suppresses large scale mixing and preconditions the flow such that only local mixing can be accomplished between the diffuser exit and the catalyst inlet. That is, mixing in that cross-sectional region is limited. For example, if a region of flow has a high temperature or velocity in comparison to the remaining flow, the thermal or velocity mal-distribution will deleteriously appear at the catalyst inlet. Accordingly, there is a need for a fuel injector for a gas turbine combustor affording improved uniform fuel/air, temperature and velocity distributions to the catalyst inlet.
In accordance with the preferred aspect of the present invention, there is provided in combination in a combustor, a flow conditioner, a venturi configuration having a diffuser with multiple sides and an improved fuel circuit. The flow conditioner may be of the type described and illustrated in co-pending U.S. patent application Ser. No. 10/648,203 filed Aug. 27, 2003, the disclosure of which is incorporated herein by reference. In addition to the flow conditioner, multiple venturi tubes having a frustum-like cross-sectional configuration are provided to enhance fuel/air mixing, to afford uniform distribution of the fuel/air, velocity and temperature at the catalyst inlet, and to eliminate flame-holding issues. The venturi configuration eliminates recirculation regions, i.e., flow gaps between the venturis in the exit planes and downstream thereof, as well as the potential for flame-holding. The venturis have a three body construction to improve fuel distribution among the various venturis and also to improve mechanical durability by thermo-shielding of the brazed joints of the construction. The venturi fuel circuit provides a secondary plenum between the main fuel plenum surrounding the venturis defined between spaced axial forward and aft walls and fuel supply inlets to the converging inlet of the venturis. By providing a secondary plenum in each venturi, the plane of fuel intake into the plenum is separated from the plane of fuel injection into the venturi by a maximum available distance. Also cold fuel flow is directed along the cold side of the fuel plenum thereby minimizing thermal stress at the front and aft plate brazed joints.
In accordance with a preferred aspect of the present invention, there is provided a combustor for a gas turbine comprising a combustor housing including a flow liner for receiving compressor discharge air; a main fuel injector downstream of the flow liner for receiving the compressor discharge air and mixing air and fuel; a catalytic section downstream of the main fuel injector for receiving a mix of air and fuel from the main fuel injector; the main fuel injector including (i) an array of venturis each including a convergent inlet, a throat and a diffuser for flowing a fuel/air mixture therethrough in a generally axial direction for exit from said diffuser, (ii) a front plate and (iii) an aft plate surrounded by an enclosure defining a fuel supply plenum between the plates; each plate having a plurality of openings for receiving the venturis; and each venturi inlet having at least one fuel supply hole for supplying fuel from the fuel supply plenum into the venturi inlet at a location axially upstream from the throat.
In accordance with another aspect of the present invention, there is provided a combustor for a gas turbine comprising a combustor housing including a flow liner for receiving compressor discharge air; a main fuel injector downstream of the flow liner for receiving the compressor discharge air; a catalytic section downstream of the main fuel injector for receiving a mix of air and fuel from the main fuel injector; the main fuel injector including an array of venturis about a combustor axis, each venturi including a converging inlet, a throat and a diffuser for flowing the fuel/air mixture, each venturi including a fuel supply hole for flowing fuel into the venturi, said diffuser having multiple discrete angularly related side walls therealong, the array of venturis being arranged in circumferential side-by-side relation to one another about the axis and spaced radially from one another.
As will be appreciated a typical gas turbine has an array of circumferentially spaced combustors about the axis of the turbine for burning a fuel/air mixture and flowing the products of combustion through a transition piece for flow along the hot gas path of the turbine stages whereby the energetic flow is converted to mechanical energy to rotate the turbine rotor. The compressor for the turbine supplies part of its compressed air to each of the combustors for mixing with the fuel. A portion of one of the combustors for the turbine is illustrated in
Referring to
At the inlet to the multi-venturi tube arrangement 21 (hereinafter MVT) forming part of the main fuel injector 20, there is provided a perforated plate 24 to assist in conditioning the flow of fuel/air to obtain optimum mixing and uniform distribution of the flows and temperature at the inlet to catalytic section 22.
The main fuel injector 20 includes a pair of axially spaced perforated plates, i.e. a front plate 30 and an aft plate 32 (
The openings through the plates 30 and 32 are closed by venturis generally designated 42 and forming part of the MVT 21. Thus each pair of axially aligned openings 34 through the plates 30 and 32 receive a venturi 42. Each venturi includes a converging inlet section 44, a throat 46 and a diverging section or diffuser 48. Each venturi is a three part construction; a first part including the inlet converging portion 44, a second part comprising the throat and diffuser 46 and 48, and a third part comprising an annular venturi member or body 50. Body 50 extends between each of the axially aligned openings in the front and aft plates 30 and 32 and is secured thereto for example by brazing. The converging inlet section 44 of the venturi 42 includes an inlet flange 52 which is screw threaded to a projection 54 of the body 50. The integral throat and diffuser 46 and 48, respectively, has an enlarged diameter 56 at its forward end which surrounds the aft end of the inlet 44 and is secured, preferably brazed, thereto.
It will be appreciated that the space between the front and aft plates 30 and 32 and about the annular bodies 50 of each venturi constitutes a main fuel plenum 60 which lies in communication with the fuel inlets 40. The main fuel plenum 60 lies in communication with each inlet section 44 via an aperture 62 through the annular body 50, a mini fuel plenum 64 formed between the body 50 and the inlet 44 and supply holes 66 formed adjacent the leading edge of the inlet section 44. The fuel supply holes 66 are spaced circumferentially one from the other about the inlet 44 and preferably are four in number. It will be appreciated that the fuel inlet holes 66 to the venturi are located upstream of the throat 46 and in the converging section of the inlet section 44. Significantly improved mixing of the fuel/air is achieved by locating the fuel injection holes 66 in the converging inlet section of the venturi without flow separation or deleterious flame holding events.
Fuel from the fuel inlet plenum 38 circulates between the front and aft plates 30 and 32 and about the annular bodies 50 for flow into the venturis 42 via the fuel apertures 62, the mini plenums 64 between the inlet sections 44 and annular bodies 50 and the fuel inlet holes 66. With the fuel inlet holes located adjacent the inlets to the converging sections of the venturis, the fuel is injected in a region where the air side pressure is higher, e.g., compared to static pressure at the throat. It will be appreciated that the magnitude of the fuel/air mixing taking place in each venturi is directly related to the jet penetration which in turn depends on the pressure ratio across the fuel injection holes 66 and the jet momentum ratio, i.e., between the jets and the main flow stream. To increase the pressure ratio and decouple the fuel injection from airflow distribution, the fuel holes are located upstream of the throat. The fuel is therefore injected in a region where the air-side pressure is higher compared to the static pressure at the throat and therefore, for the same fuel side effective area, the pressure ratio is increased. An optimum pressure ratio-circumferential coverage is achieved. Air velocity is also lower than at the throat and therefore the jets of fuel adjacent the venturi inlet sections 44 develop under better conditions from a momentum ratio standpoint. Further, improved air fuel mixing due to this fuel inlet location is achieved also by the increased mixing length, i.e., the actual travel distance inside the venturi for the same overall length of tube. Additionally, the venturis 42 are fixed between the two plates 30 and 32 to form the main fuel plenum 60 between the plates and the outside surfaces of the venturis. Fuel is introduced into plenum 60 from the outside diameter. A general flow of fuel with some axial symmetry occurs from the outside diameter of the plenum toward the center of the MVT as the venturis are fed with fuel. Thus, a potential imbalance in fuel flow around the tubes and among the tubes with a penalty in mixing performance which occurs with fuel injection at the venturi throats is avoided since the fuel injection holes into the venturis are spatially displaced from a plane in which the general plenum flow occurs. Finally, because the fuel inlet injection holes 66 are located adjacent the venturi inlet section 44, the potential for fuel jet induced flow separation inside the venturis is greatly reduced.
Referring now to
Further, from a review of
While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.
