Patent Application
20120167544
The present application relates generally to gas turbine engines and more particularly relates to a combustor with fuel staggering and/or fuel injector staggering for flame holding mitigation due to local flow obstructions and other types of flow disturbances.
In a gas turbine engine, operational efficiency generally increases as the temperature of the combustion stream increases. Higher combustion stream temperatures, however, may produce higher levels of nitrogen oxides (“NOx”) and other types of emissions. Such emissions may be subject to both federal and state regulation in the United States and also subject to similar regulations abroad. A balancing act thus exists between operating the gas turbine engine in an efficient temperature range while also ensuring that the output of NOx and other types of regulated emissions remain below the mandated levels.
Several types of known gas turbine engine designs, such as those using Dry Low NOx (“DLN”) combustors, generally premix the fuel flows and the air flows upstream of a reaction or a combustion zone so as to reduce NOx emissions via a number of premixing fuel nozzles. Such premixing tends to reduce overall combustion temperatures and, hence, NOx emissions and the like.
Premixing, however, may present several operational issues such as flame holding, flashback, auto-ignition, and the like. These issues may be a particular concern with the use of highly reactive fuels. For example, given an ignition source, a flame may be present in the head-end of a combustor upstream of the fuel nozzles with any significant fraction of hydrogen or other types of fuels. Any type of fuel rich pocket thus may sustain a flame and cause damage to the combustor.
Other premixing issues may be due to irregularities in the fuel flows and the air flows. For example, there are several flow obstructions that may disrupt the flow through an incoming pathway between a flow sleeve and a liner. With a combustor having fuel injector vanes that inject fuel into the airflow upstream of the head-end, these flow disturbances may create flow recirculation zones on the trailing edge of the vanes. These recirculation zones may lead to stable pockets of ignitable fuel-air mixtures that can in turn lead to flame holding or other types of combustion events given an ignition source.
There is thus a desire for an improved combustor design. Such a design should accommodate flow disturbances upstream of the fuel injectors so as to avoid flame holding, flashback, auto-ignition, and the like. Moreover, an increase in the flame holding margin may allow the use of higher reactivity fuels for improved performance and emissions.
The present application thus provides a combustor. The combustor may include an air flow path with a flow of air therein. A flow obstruction may be positioned within the air flow path and cause a wake or a recirculation zone downstream thereof. A number of fuel injectors may be positioned downstream of the flow obstruction. The fuel injectors may inject a flow of fuel into the air flow path such that the flows of fuel and air in the wake or the recirculation zone do not exceed a flammability limit.
The present application further provides a combustor. The combustor may include an air flow path with a flow of air therein. A flow obstruction may be positioned within the air flow path and cause a wake or a recirculation zone downstream thereof. A number of fuel injectors may be positioned downstream of the flow obstruction. The fuel injectors may be positioned outside of the wake or the recirculation zone.
The present application further provides a combustor. The combustor may include an air flow path with a flow of air therein. A flow obstruction may be positioned within the air flow path and cause a wake or a recirculation zone downstream thereof. A number of fuel injectors may be positioned downstream of the flow obstruction. One or more of the fuel injectors may be downstream fuel injectors positioned downstream of but in line with the wake or the recirculation zone.
These and other features and improvements of the present application will become apparent to one of ordinary skill in the art upon review of the following detailed description when taken in conjunction with the several drawings and the appended claims.
Referring now to the drawings, in which like numerals refer to like elements throughout the several views,
The gas turbine engine 10 may use natural gas, various types of syngas, and/or other types of fuels. The gas turbine engine 10 may be anyone of a number of different gas turbine engines offered by General Electric Company of Schenectady, N.Y., including those such as a heavy duty 9FA gas turbine engine and the like. The gas turbine engine 10 may have different configurations and may use other types of components. Other types of gas turbine engines also may be used herein. Multiple gas turbine engines, other types of turbines, and other types of power generation equipment also may be used herein together.
The flow of air 20 may enter the combustor 25 from the compressor 15 via an incoming air path 75. The incoming air path 75 may be defined between a liner 80 of the combustion chamber 50 and an outer casing 85. The flow of air 20 may travel along the incoming air path 75 and then reverse direction about the fuel nozzles 55. The flow of air 20 and the flow of fuel 30 may be ignited downstream of the fuel nozzles 55 within the combustion chamber 50 such that the flow of the combustion gases 35 may be directed towards the turbine 40. Other configurations and other components may be used herein.
The combustor 25 also may have a lean pre-nozzle fuel injection system 90 positioned about the incoming air path 75 between the liner 80 and the casing 85. The lean pre-nozzle fuel injection system 90 may have a number of fuel pegs or fuel injectors 92. The fuel injectors 92 may have an aerodynamic airfoil or streamline shape. Other shapes may be used herein. The fuel injectors 92 each may have a number of injector holes 94 therein. The number and positioning of the fuel injectors 92 and the injection holes 94 may be optimized for premixing. A premix fuel or other types of fuel flows 30 may be used therein.
As described above, a number of flow obstructions 96 also may be positioned within the incoming air path 75. These flow obstructions 96 may be structures such as a number of crossfire tubes 98. Other types of obstructions 96 may include liner penetrations, liner stops, and the like. These flow obstructions 96 may create a low velocity wake or a low or negative velocity recirculation zone. The wake or the recirculation zone may envelop one or more of the fuel injectors 92 and/or create other types of local flow disturbances. A flow of the fuel 30 from the holes 94 of the fuel injectors 92 thus may be pulled upstream within the wake or recirculation zone. Although these flow obstructions 96 may cause these flow disturbances, the structures are otherwise required for efficient combustor operation.
The air path 110 also may include one or more flow obstructions 170 therein. The flow obstructions 170 may be a crossfire tube 180 or any other type of flow obstruction including liner penetrations, liner stops, and the like. The flow obstruction may be any structure that may create a flow disturbance in the flow of air 20. The flow disturbance may be a wake or other type of region with a reduced or negative velocity that may serve as a wake or a recirculation zone 190 and the like.
In this example, the fuel injectors 140 may include a number of unfueled fuel injectors 200 positioned downstream of the flow obstruction 170 in the wake or the recirculation zone 190 thereof. The remaining fuel injectors 140 may be fueled fuel injectors 210. By removing the flow of fuel 30 in the fuel injectors 140 within the wake or the recirculation zone 190, the possibility of fuel entrainment therein that may lead to flashback and the like may be reduced. To the extent that the flow of fuel 30 enters the wake or the recirculation zone 190, the maximum fuel-air mixture may never exceed a flammability limit for a number of given conditions because of the unfueled fuel injectors 200 therein. A position outside or downstream or otherwise out of the wake or the recirculation zone 190 thus means that the position of the fuel injector 140 is in an acceptable velocity range with respect to an overall bulk velocity in the air path 110. Other configurations and other components may be used herein.
In use, the combustors described herein thus reduce the possibility of fuel entrainment downstream of the flow obstructions 170 so as to reduce the possibility of flame holding and other types of combustion events about the fuel injectors 140. The fuel injectors 140 may vary the fuel-air ratio that could feed a wake or a recirculation zone caused by the flow obstructions 170. The fuel injectors 140 also may have an increased flame holding margin such that the overall gas turbine engine 10 may be able to use higher reactivity fuels.
It should be apparent that the foregoing relates only to certain embodiments of the present application and that numerous changes and modifications may be made herein by one of ordinary skill in the art without departing from the general spirit and scope of the invention as defined by the following claims and the equivalents thereof.
