Patent Application
20150159877
The present invention relates to gas turbine engines, and more particularly, to a late lean injection manifold mixing system to inject a premixed fuel/air mixture into a combustion zone downstream of a primary combustion zone for a can-annular gas turbine combustor.
Multiple designs exist for staged combustion in combustion turbine engines, but most are complicated assemblies consisting of a plurality of tubing and interfaces. One kind of staged combustion used in combustion turbine engines is late lean injection. In this type of staged combustion, late lean fuel injectors are located downstream of the primary fuel injector. Combusting a fuel/air mixture at this downstream location may be used to improve NOx performance. NOx, or oxides of nitrogen, is one of the primary undesirable air polluting emissions produced by gas turbine engines that burn conventional hydrocarbon fuels.
Current late lean injection assemblies are expensive and costly for both new gas turbine units and retrofits of existing units. One of the reasons for this is the complexity of conventional late lean injection systems, particularly those systems associated with the fuel delivery. The many parts associated with these complex systems must be designed to withstand the extreme thermal and mechanical loads of the turbine environment, which significantly increases manufacturing expense. Even so, conventional late lean injection assemblies still have a high risk for fuel leakage into the compressor discharge casing, which can result in auto-ignition and be a safety hazard.
Gas fuel is typically transmitted from a supply manifold to the combustor injector using a tube assembly.
The injectors are typically connected with the combustor sleeve, while the fuel line may be connected to a different component of the combustor such as the mounting flange. A bellows may be used to accommodate thermal excursions during start-up and shut down. These separate sub-assemblies need to move relative to each other in operation. The components, however, are installed as a module, and it is undesirable for the sub-assemblies to move relative to each other during installation, which could result in damage to the bellows. Assembly thus requires an elaborate assembly tool, which must be used properly and requires operator experience. Moreover, gas fuel is transmitted from the supply manifold to the combustor injector using a tube assembly. When the gas turbine is fired, the relative thermal displacements between the supply manifold and the injector can create undesirable strains in the tube.
In an exemplary embodiment, a manifold mixing system for combustor of a gas turbine engine includes a fuel supply, a fuel injector coupled with the fuel supply, and a manifold mixer cooperable with the fuel injector and including mixing air inlets. The fuel injector is displaceable relative to the manifold mixer while being positioned to deliver fuel from the fuel supply to the manifold mixer. The manifold mixer is shaped to mix the fuel from the fuel supply with air input via the mixing air inlets for injection into the combustor.
In another exemplary embodiment, a combustor for a gas turbine engine includes a combustion chamber including a primary combustion zone downstream of a fuel nozzle and a liner and flowsleeve assembly delimiting the combustion chamber. A manifold mixing system is coupled between a combustor mounting flange and the liner and flowsleeve assembly and delivers pre-mixed fuel and air downstream of the primary combustion zone.
It will be appreciated that the flow sleeve 26 and impingement sleeve 27 typically have impingement apertures (not shown) formed therethrough which allow an impinged flow of compressed air from the compressor 12 to enter the flow annulus 27 formed between the flow sleeve 26/liner 24 and/or the impingement sleeve 67/transition piece 25. The flow of compressed air through the impingement apertures convectively cools the exterior surfaces of the liner 24 and transition piece 25. The compressed air entering the combustor 20 through the flow sleeve 26 is directed toward the forward end of the combustor 20 via the flow annulus 27 formed about the liner 24. The compressed air then may enter the fuel nozzles 21, where it is mixed with a fuel for combustion within the combustion zone 23.
As noted above, the turbine 16 includes turbine blades, into which products of the combustion of the fuel in the liner 24 are received to power a rotation of the turbine blades. The transition piece directs the flow of combustion products into the turbine 16, where it interacts with the blades to induce rotation about the shaft, which, as stated, then may be used to drive a load, such as a generator. Thus, the transition piece 25 serves to couple the combustor 20 and the turbine 16. In systems that include late lean injection, it will be appreciated that the transition piece 25 also may define a secondary combustion zone in which additional fuel supplied thereto and the products of the combustion of the fuel supplied to the liner 24 combustion zone are combusted.
As used herein, a “late lean injection system” is a system for injecting a mixture of fuel and air into the flow of working fluid at any point that is downstream of the primary fuel nozzles 21 and upstream of the turbine 16. In certain embodiments, a “late lean injection system 28” is more specifically defined as a system for injecting a fuel/air mixture into the aft end of the primary combustion chamber defined by the liner. In general, one of the objectives of late lean injection systems includes enabling fuel combustion that occurs downstream of primary combustors/primary combustion zone. This type of operation may be used to improve NOx performance, however, as one of ordinary skill in the relevant art will appreciate, combustion that occurs too far downstream may result in undesirable higher CO emissions. As described in more detail below, the present invention provides effective alternatives for achieving improved NOx emissions, while avoiding undesirable results.
With reference to
The fuel injector 30 includes one or more spike components 36 (three shown in
With continued reference to
The manifold mixer 32 may additionally include a ring of surface air inlet holes 44 substantially midway between ends of the manifold mixer. The surface air inlet holes 44 are oriented at a shallow angle to create a film of air on the manifold interior surface. The film of air keeps the fuel/air profile lean on the outside diameter of the manifold mixer 32. The air film surrounds the air/fuel mixture and further prevents the production of NOx emissions. At the transition 42, the film of air further mixes with the air/fuel mixture.
The length of the manifold mixer 32 in the configuration of the preferred embodiment is considerably longer than prior art mixing zones. NOx emissions are more effectively controllable when the fuel and air are highly pre-mixed before injection. The short lengths of existing systems require mixing in as little as two inches whereas the present design provides for mixing over a much greater distance, such as two feet or more.
The manifold mixing system injects a premixed fuel/air mixture into the combustion zone downstream of the primary combustion zone for a can-annular gas turbine combustor. The manifold mixer is preferably located outside a flow sleeve/unisleeve and extends aft to a combustor liner/unibody/transition piece injection point downstream of the primary combustion zone. The manifold mixer is attached or is transitioned to a late lean injector that turns the flow into the combustion zone as it passes through the flow sleeve/unisleeve and liner/unibody. The fuel injector and manifold mixer do not require a leak detection system, and the design is more robust and simpler than previous designs. The assembly also provides better premixing of the fuel/air mixture before being injected into the combustor. The structure provides for a combustor with better reliability, better emissions, and lower overall gas turbine cost.
While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiments, it is to be understood that the invention is not to be limited to the disclosed embodiments, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.
