Patent Application
20160281979
Not applicable.
The present invention relates generally to an apparatus and method for directing a flow of compressed air into a fuel nozzle assembly. More specifically, a fuel nozzle assembly is provided with a flow directing device at an air inlet region.
In an effort to reduce the amount of pollution emissions from gas-powered turbine engines, governmental agencies have enacted numerous regulations requiring reductions in the amount of oxides of nitrogen (NOx) and carbon monoxide (CO) produced. Lower combustion emissions can often be attributed to a more efficient combustion process, with specific regard to fuel injector location, airflow rates, and mixing effectiveness.
Early combustion systems utilized diffusion type nozzles, where fuel is mixed with air external to the fuel nozzle by diffusion, proximate the flame zone. Diffusion type nozzles historically produce relatively high emissions due to the fact that the fuel and air burn essentially upon interaction, without mixing, and stoichiometrically at high temperature to maintain adequate combustor stability and low combustion dynamics.
An enhancement in combustion technology is the concept of premixing fuel and air prior to combustion to form a homogeneous mixture that burns at a lower temperature than a diffusion type flame and thereby produces lower NOx emissions. Premixing can occur either internal to the fuel nozzle assembly or external thereto, as long as it is upstream of the combustion zone. An example of a premixing combustor has a plurality of fuel nozzle assemblies, each injecting fuel into a premix chamber where fuel mixes with compressed air from a plenum before entering a combustion chamber. Premixing fuel and air together before combustion allows for the fuel and air to form a more homogeneous mixture, which, when ignited will burn more completely, resulting in lower emissions. However, the thoroughness and completeness of the mixing and resulting burning of the fuel-air mixture depends on the effectiveness of the mixing.
The present invention discloses an apparatus and method for improving the air supply for mixing with fuel being injected through a fuel nozzle assembly. More specifically, in an embodiment of the present invention, a fuel nozzle assembly is disclosed comprising a plurality of concentric tubes forming first, second and third passageways. The fuel nozzle assembly also comprises a premix tube coaxial to and radially outward of a third tube, the premix tube having a plurality of swirler vanes contained therein for inducing a swirl into a passing flow of air and fuel. The fuel nozzle assembly further comprises a hemispherically-shaped dome extending around an inlet end of the premix tube positioned towards a base of the fuel nozzle assembly, and having a plurality of openings oriented in both an axial and radial component.
In an alternate embodiment of the present invention, an air conditioning screen for use in a fuel nozzle assembly is disclosed. The air conditioning screen comprises a generally hemispherically-shaped dome positioned about an air inlet region of a fuel nozzle assembly. The hemispherically-shaped dome has a plurality of openings, or holes, extending from an outer wall through to an inner wall and angled downstream having both an axial and radial component. The hemispherically-shaped dome also has a plurality of pins positioning the hemispeherically-shaped dome relative to a premix tube of the fuel nozzle assembly.
In yet another embodiment of the present invention, a method of conditioning an incoming air stream entering a fuel nozzle assembly is disclosed. The method generally comprises providing a flow of compressed air to a region surrounding the fuel nozzle assembly, the fuel nozzle assembly having a hemispherical dome at an air inlet region. A first portion of the compressed air is directed through a plurality of cooling holes, or openings, in the hemispherically-shaped dome portion and while a second portion of the compressed air through an annular opening at a region between the hemispherically-shaped dome and a premix tube of the fuel nozzle assembly.
Additional advantages and features of the present invention will be set forth in part in a description which follows, and in part will become apparent to those skilled in the art upon examination of the following, or may be learned from practice of the invention. The instant invention will now be described with particular reference to the accompanying drawings.
The present invention is described in detail below with reference to the attached drawing figures, wherein:
The present invention discloses a fuel nozzle assembly for use in a gas turbine combustion system for use in a premix combustion system to help reduce emissions from the combustion system as shown in detail in
Emissions from a combustion system are based in part on how completely the fuel and air mix and then burn, or combust. In order to minimize the emissions and maximize the burning of the fuel that is being injected, it is preferable that the fuel and air are thoroughly mixed. To ensure thorough mixing, one factor considered is the condition of the air mixing with the fuel.
Referring specifically to
An improved way of treating the incoming air flow to a fuel nozzle assembly is discussed below with respect to
Coaxial to and radially outward of the first tube 202 is a second tube 206. A second passageway 208 is formed between the first tube 202 and the second tube 206. The second passageway 208 extends coaxial to the first passageway 204 to within approximately the swirler vanes 220, as discussed below. The second passageway 208 contains a gas fuel, air, or mixture thereof, directed to the swirler vanes 220, as discussed below.
The fuel nozzle assembly 200 also comprises a third tube 210 which is coaxial to and radially outward of the second tube 206, thereby forming a third passageway between a portion of the second tube 206 and the third tube 210 as well as between a portion of the first tube 202 and the third tube 210. That is, the third passageway is split into two portions, 212A and 212B, which do not communicate with each other. A first portion 212A extends from a base 224 of the fuel nozzle assembly 200 to proximate the swirler vanes 220. A second portion 212B extends from proximate the swirler vanes 220 to the tip region 205 of the fuel nozzle assembly 200. A gas flows through the first portion 212A, where the gas initially travels axially through the first portion 212A and then radially outward through the swirler vanes 220, where it is injected into a surrounding air stream. The second portion 212B flows air, fuel, or a mixture thereof, which is drawn into the second portion 212B at the region adjacent to the swirler vanes 220, through air inlet holes 221. The air, fuel, or mixture thereof then passes axially through the second portion 212B to the tip region 205 of the fuel nozzle assembly 200, where it serves to mix with the diffusion gas from the first passageway 204 proximate the tip region 205.
In an alternate embodiment of the present invention, a fuel-air mixture can be provided to second portion 212B for injection through the tip of the fuel nozzle assembly. This is shown in
Referring to
Referring back to
The fuel nozzle assembly 200 also comprises a hemispherically-shaped dome 222 extending from approximately the inlet end 216 of the premix tube 214 towards the base 224 of the fuel nozzle assembly 200. The hemispherically-shaped dome 222 provides an improved way of conditioning the incoming air flow into the fuel nozzle assembly 200, compared to the prior art. More specifically, as shown in
Referring to
Referring now to
For the embodiment depicted in
Coupled to the hemispherically-shaped dome 222, between the dome 222 and the premix tube 214, is an annular plate 228. The annular plate 228 has a curved and cylindrical cross sectional shape and may be secured to the generally hemispherically-shaped dome 222 at one end and positioned within the inlet end 216 of the premix tube 214 at an opposing end. The annular plate 228 may be held in place in part due to a plurality of generally radially-extending pins 230 positioned between the cylindrical portion of the annular plate 228 and the premix tube 214. In an alternate embodiment of the present invention, the annular plate 228 is not secured to the hemispherically-shaped dome 222, but instead the hemispherically-shaped dome 222 is secured to the base 224. The annular plate 228 provides an alternate air inlet region for a portion of the compressed air into the fuel nozzle assembly 200. Furthermore, the annular plate 228 serves to split the compressed air between an outer region 232 and an inner region 234. However, as it can be clearly seen from
Additional details regarding the fuel nozzle assembly 200 can be seen in
The present invention provides a hemispherically-shaped dome 222 for use with an improved fuel nozzle assembly 200. However, it is envisioned that the hemispherically-shaped dome 222 can be used with a variety of fuel nozzle assemblies. The fuel nozzle assembly 200 of the present invention is configured to operate at least within a Dry-Low Nox (DLN) combustion system. However, the DLN combustion system can operate with alternate fuel nozzle assemblies. The hemispherically-shaped dome 222 can be used with alternate fuel nozzles, such as the fuel nozzle depicted in
Referring now to
In a step 804, a first portion of the compressed air is directed through a plurality of cooling holes, or openings, in the hemispherically-shaped dome portion. The openings in the hemispherically-shaped dome are arranged in a plurality of axially-spaced rows and oriented at an angle relative to the center axis A-A of the fuel nozzle assembly so as to direct the flow of compressed air in a generally axial direction upon exiting the hemispherically-shaped dome and entering the premix tube.
In a step 806, a second portion of the compressed air is directed through a region between the hemispherically-shaped dome and a premix tube of the fuel nozzle assembly. More specifically, an annular plate having a cylindrical portion and a curved cross section is spaced axially and radially from the inlet end of the premix tube to direct a portion of the compressed air through an annular opening into the fuel nozzle assembly. However, as discussed above, the majority of the compressed air is directed into the fuel nozzle assembly by way of the openings in the hemispherically-shaped dome.
While the invention has been described in what is known as presently the 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 within the scope of the following claims. The present invention has been described in relation to particular embodiments, which are intended in all respects to be illustrative rather than restrictive.
From the foregoing, it will be seen that this invention is one well adapted to attain all the ends and objects set forth above, together with other advantages which are obvious and inherent to the system and method. It will be understood that certain features and sub-combinations are of utility and may be employed without reference to other features and sub-combinations. This is contemplated by and within the scope of the claims.
