Patent Application
20130125549
This invention relates to gas turbine combustors generally, and more specifically, to a novel endcover assembly for the forward or upstream end of a gas turbine combustor.
In certain gas turbines, a plurality of combustors are arranged in an annular array about the turbine rotor to provide for the combustion of fuel and guide the energized combustion products into the turbine section to drive the turbine. Each combustor typically includes an outer casing which defines the external boundary of the combustor; a flow sleeve for distributing compressor discharge air to the head end of the combustor while also cooling a liner which encloses the combustion chamber; and a transition piece for flowing the combustion products into the turbine section. The combustor also includes a plurality of fuel nozzles coupled to an endcover. Air and fuel is supplied through the endcover to the fuel nozzles for combustion within the liner. The endcover thus functions to close the combustor forward end, to support the fuel nozzles, and to distribute air and fuel to the fuel nozzles.
Endcover designs for turbine combustor systems typically have included a plate mounting each fuel nozzle individually. In prior endcover assemblies of this type, the internal passages for the air and fuel were located in the fuel nozzle, separate and apart from the endcover. A follow-on generation of endcovers provided air and fuel passages internal to the endcover. This was done to accommodate a plurality of nozzles for each endcover rather than one fuel nozzle per endcover as in prior conventional combustors. While that change simplified the fuel nozzles and enabled the mounting of a plurality of fuel nozzles onto the endcover, the complexity of the endcover was increased in order to provide the integrated air and fuel manifolds and necessary multiple passages for the fuel nozzles carried thereby. Extra parts were necessary, such as inserts, to render complex passages in the endcovers possible. Brazed joints were also included to seal these extra parts, including inserts in the endcovers. A further generation of endcovers for turbine combustors followed. These endcovers employed even more complicated brazed joints between the endcovers and their various parts. However, cracking of the brazed joints was observed on these more recent endcovers.
In addition, certain turbine model endcover assemblies formed with internal passages as noted above also require premix gas flow orifices (also referred to herein as “flow restrictors”, or “flow restrictor inserts”) pressed and staked into place on the “hot side” of the combustor endcover plate (that side exposed to combustion in the combustion chamber). The location of the flow restrictor within the passageway in the endcover defines the acoustic length from the fuel nozzle gas exit holes at the cold-side of the endcover to the orifice restriction proximate the hot side of the endcover. The acoustic length has a natural frequency that can be negatively impacted by combustor dynamics which vary with site conditions and fuel variation. Accordingly, there is a need to provide endcovers with orifice restrictors that can accommodate acoustic length adjustments (preferably on site), favorable to combustor dynamics.
In a first exemplary embodiment, the invention provides an endcover for a turbine combustor adapted to support one or more combustor nozzles, the endcover comprising a plate having one side which in use, faces a combustion chamber and an opposite side which, in use, faces away from the combustion chamber; at least one fuel cavity in the substantially flat plate; a fuel restrictor insert formed with at least one flow orifice located within the at least one fuel cavity for supplying fuel to at least one combustor nozzle, the fuel restrictor insert adjustable along a length dimension of the at least one fuel cavity.
In another exemplary embodiment, the invention provides an endcover for a turbine combustor adapted to support one or more combustor nozzles, the endcover comprising an endcover plate having one side which in use, faces a combustion chamber and an opposite side which, in use, faces away from the combustion chamber; at least one premix fuel cavity in the endcover plate; a premix fuel supply passage in communication with said at least one premix fuel cavity; and a fuel restrictor insert formed with multiple flow orifices secured within each of the plural premix fuel cavities, the fuel restrictor insert within said at least one premix fuel cavity configured for adjustment is opposite axial directions within said at least one premix fuel cavity.
In another aspect, the invention provides a method of tuning an acoustic length property of a premix fuel cavity in an endcover of a turbine combustor adapted to support one or more combustor nozzles, wherein the endcover includes a plate having one side which in use, faces a combustion chamber and an opposite side which, in use, faces away from the combustion chamber; and a fuel restrictor insert formed with multiple flow orifices secured within the premix fuel cavity, the method comprising a) adjusting the fuel restrictor insert within the premix fuel cavity along a length dimension of the premix fuel cavity, and; b) locking the fuel restrictor insert at a predetermined location within the premix fuel cavity.
The invention will now be described in connection with the drawings identified below.
In operation, air flows through compressor 12 and compressed air is supplied to combustor 14. Specifically, a substantial amount of the compressed air is supplied to the endcover assembly 18 secured to the head end of the combustor 14. The fuel nozzles supported by the endcover assembly 18 channel fuel and air to combustion region 16 where the fuel/air is ignited. Combustion gases are supplied to the turbine section 2022 where the gas stream thermal energy is converted to mechanical rotational energy.
The passage 28 communicates with a cavity or chamber 32 formed in the plate 26. The cavity 32 is closed at its forward or upstream end by a cover 34 on the cold side 36 of the plate. A flow restrictor insert (or flow restrictor) 38 is secured adjacent the hot side 40 of the plate 26. The flow restrictor insert 38 may also be referred to as fuel restrictor or fuel restrictor insert. The fuel restrictor or insert 38 may be made of a suitable metal material such as brass or stainless steel, with or without plating such as silver, gold or aluminum. The cavity 32 may be a bore drilled through the plate, and with at least a portion of its length threaded. The peripheral edge of the flow restrictor 38 is also threaded, thereby allowing the restrictor 38 to be adjusted toward or away from the hot and cold sides of the plate 26 via rotation of the flow restrictor. To enable such axial adjustment of the restrictor 38, an Allen key feature (e.g., a hexagonal recess) 42 may be provided on the interior side of the restrictor, so that, with the cover 34 removed, an Allen wrench may be employed to rotate and thus axially adjust the location of the flow restrictor 38 within the bore or chamber 32.
When the restrictor 38 is located as desired, a threaded lock nut 44 may be tightened against the restrictor to prevent further movement of the restrictor. Movement of the lock nut 44 may be implemented via engagement of a second tool (not shown) engageable with an inner suitably shaped surface 46 of the lock nut 44. The inner diameter of lock nut should lie radially outward of the flow restrictor orifices 48.
It will be appreciated that any suitable mechanism may be employed to rotate (i.e., apply torque to) both the insert 38 and the lock nut 44.
By “tuning” the acoustic length property of the cavity within the endcover plate, the fuel restrictor insert more effectively dampens any imbalanced fuel feed that can otherwise result in reduced air flow and reduced combustor performance.
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.
