EMBEDDED ELECTRICAL HEATING CIRCUITRY

[0001] BACKGROUND

[0002] 1. Field

[0003] Disclosed embodiments are generally related to internal combustion engines, such as gas turbine engines and, more particularly, to a system for controlling clearances between stationary and rotating components in a gas turbine engine.

[0004] 2. Description of the Related Art

[0005] A gas turbine engine generally includes a compressor section, a combustor section, and a turbine section. In operation, the compressor section ingests ambient air and compresses it. The compressed air from the compressor section enters one or more combustors in the combustor section. The compressed air is mixed with fuel in the combustors, and an air-fuel mixture is combusted in the combustors to form a hot working gas. The hot working gas is routed to the turbine section where it is expanded through alternating rows of stationary airfoils and rotating airfoils and used to generate power that can drive a rotor. The expanded gas exiting the turbine section may then be exhausted from the engine via an exhaust section.

[0006] The compressor and turbine sections may include several locations in which there may be gaps or clearances between the rotating and stationary components. During engine operation, fluid leakage through clearances in the compressor and turbine sections can contribute to system losses, making the operational efficiency of a turbine engine less than a theoretical maximum. For example, flow leakage can occur across a clearance between the tips of rotating blades and a surrounding stationary structure or boundary, such as an outer shroud or a vane carrier. [0007] Small clearances are desired to keep air leakage to a minimum; however, it is important to maintain at least some minimum clearance between the rotating and stationary components at all times. Rubbing of any of the rotating and stationary components can lead to substantial component damage, performance degradation, and extended outages. The size of the clearances can change during engine transient operation due to, for example, differences in thermal inertia of the rotor supporting the rotating blades compared to the thermal inertia of the stationary structure, such as the outer casing or the vane carrier. Because the thermal inertia of the vane carriers is substantially less than the thermal inertia of the rotor, the vane carrier has a faster thermal response time and can respond (through expansion or contraction) more quickly to a change in temperature than the rotor. Disclosed embodiments offer improvements relating to a clearance control system. See patent application publication WO 2016064389 for one example of a system using a radiant heater for controlling clearances in a gas turbine engine.

[0008] BRIEF DESCRIPTION

[0009] One disclosed embodiment is directed to a clearance control system for controlling a clearance between rotating blades and a boundary adjacent to tips of the rotating blades in a gas turbine engine. In one disclosed embodiment, the clearance control system may include electrical heating circuitry embedded in the vane carrier and a controller may be configured to energize the electrical heating circuitry to provide selectable heating to the vane carrier.

[0010] In accordance with a further disclosed embodiment, electrical heating circuitry may be configured to transfer thermal energy directly to the vane carrier, and a controller may be configured to energize the electrical heating circuitry to provide selective heating to the vane carrier. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] FIG. 1 is an elevational, cross sectional view of one non limiting example of a combustion turbine engine, such as a gas turbine engine that can benefit from disclosed embodiments of a clearance control system for controlling a clearance between rotating blades and a boundary adjacent to tips of the rotating blades.

[0012] Fig. 2 is a zoomed-in, cross-sectional view of a vane carrier, which is a component of the gas turbine engine shown in FIG. 1, and illustrates a non limiting example of electrical heating circuitry, as may be embedded within or otherwise disposed onto the vane carrier;

[0013] FIG. 3 is a top view of a portion of the vane carrier shown in

FIG. 2 illustrating a non-limiting example of one arrangement of grooves that may be constructed within the vane carrier for accommodating electrical heating circuitry in the form of a heating wire.

[0014] FIG. 4 is a non-limiting example of another arrangement of grooves that may be constructed within the vane carrier for accommodating electrical heating circuitry in the form of a heating wire.

[0015] FIG. 5 in part shows a cross-sectional view of electrical heating circuitry in a non-limiting form of a heating blanket, as may be disposed onto the vane carrier;

[0016] FIG. 6 shows an isometric, exploded view of electrical heating circuitry in another non-limiting form of heating electrical boxes, as may be disposed onto the vane carrier. [0017] FIG. 7 is a simplified schematic illustration of a gas turbine engine including a controller that may be a part of a disclosed clearance control system.

[0018] DETAILED DESCRIPTION

[0019] The inventors of the present invention have recognized that a practical limitation of certain known systems for controlling clearances in a gas turbine engine may be somewhat detrimental effects in connection with bleed air cavities in the compressor and/or turbine sections of the gas turbine. For example, the footprint of protruding heating elements may reduce the volume available in the bleed air cavities and/or may introduce aerodynamic distortion to air flow passing through the bleed air cavities. Additionally, such known systems for controlling clearances in a gas turbine engine may lack appropriate zonal-control in connection with the electrical heating applied to casing components.

[0020] In view of such a recognition, the present inventors propose an innovative system for controlling clearances in a gas turbine engine in a reliable and cost-effective manner. In one non-limiting embodiment, electrical heating circuitry may be configured to transfer thermal energy directly to casing components, e.g., vane carriers, which is conducive to a more efficient transfer of thermal energy to such components. In one non-limiting embodiment, electrical heating circuitry may be embedded in the vane carriers, which is conducive to preserving the volume available in the bleed air cavities and/or is further conducive to avoid introducing aerodynamic distortion to air flow passing through the bleed air cavities.

[0021] In the following detailed description, various specific details are set forth in order to provide a thorough understanding of such embodiments. However, those skilled in the art will understand that disclosed embodiments may be practiced without these specific details, that aspects of the present invention are not limited to the disclosed embodiments, and that aspects of the present invention may be practiced in a variety of alternative embodiments. In other instances, methods, procedures, and components, which would be well-understood by one skilled in the art have not been described in detail to avoid unnecessary and burdensome explanation. [0022] Furthermore, various operations may be described as multiple discrete steps performed in a manner that is helpful for understanding embodiments of the present invention. However, the order of description should not be construed as to imply that these operations need be performed in the order they are presented, nor that they are even order dependent, unless otherwise indicated. Moreover, repeated usage of the phrase“in one embodiment” does not necessarily refer to the same embodiment, although it may. It is noted that disclosed embodiments need not be construed as mutually exclusive embodiments, since aspects of such disclosed embodiments may be appropriately combined by one skilled in the art depending on the needs of a given application.

[0023] The terms“comprising”,“including”,“having”, and the like, as used in the present application, are intended to be synonymous unless otherwise indicated. Lastly, as used herein, the phrases “configured to” or“arranged to” embrace the concept that the feature preceding the phrases “configured to” or “arranged to” is intentionally and specifically designed or made to act or function in a specific way and should not be construed to mean that the feature just has a capability or suitability to act or function in the specified way, unless so indicated.

[0024] FIG. 1 shows a combustion turbine engine 10, such as a gas turbine illustrating aspects of disclosed embodiments. Engine 10 includes a compressor section 12 including an outer compressor casing 26 that encloses various compressor components, such as vane carriers 28 supported from an interior structure defined on an inner side of outer casing 26. Stationary vanes 30 are supported from vane carriers 28, and rotating blades 32 are supported on a rotor assembly 34 and may be located in alternating relation to vanes 30 to form compressor stages. Vanes 30 and blades 32 extend radially across a flow path 36 extending from an inlet 38 at an upstream end of compressor section 12 to an exhaust manifold 20. [0025] Engine 10 further includes a combustor section 14 including a plurality of combustors 16 (only one shown), and a turbine section 18. It is noted that the engine 10 illustrated herein includes an annular array of combustors 16 that are disposed about a longitudinal axis 24 of the engine 10 that defines an axial direction of the engine 10. Such a configuration is typically referred to as a“can-annular” combustion system.

[0026] As may be better appreciated in FIG. 2, blades 32 include radially outer blade tips 32a that rotate proximate inner surfaces 28a of vane carriers 28. Inner surfaces 28a of vane carriers 28 define a radially outer boundary 29 (FIG. 1) for flow path 36 within compressor section 12. As shown in FIG. l, bleed air cavities 40 are defined between at least some of vane carriers 28 and outer casing 26, and comprise annular plenum or cavities extending circumferentially within outer casing 26. In the illustrated embodiment, three bleed air cavities are shown, and are located at axially downstream locations within compressor section 12. Respective bleed air passages connect bleed air cavities 40 in fluid communication with flow path 36. The bleed air passages may be defined by radially-extending gaps formed between adjacent vane carriers 28 for bleeding off a portion of the compressed air from flow path 36 into bleed air cavities.

[0027] In one non-limiting embodiment, as may be appreciated in FIG.

2, electrical heating circuitry 62 may be configured to transfer thermal energy directly to vane carriers 28. Without limitation, electrical heating circuitry 62 may be embedded in the vane carrier or otherwise disposed onto vane carriers 28. For example, as shown in FIG. 5, in one non-limiting embodiment, the electrical heating circuitry may take the form of one or more heating blankets 98 disposed onto vane carriers 28. For example, a relatively thin heating blanket would allow providing a low-profile electrical heating circuitry with reduced volumetric intrusion into the bleed air cavities. This low profile would also avoid introducing undesirable aerodynamic distortion to air flow passing through the bleed air cavities. [0028] In another non-limiting embodiment, as shown in FIG. 6, the electrical heating circuitry may take the form of one or more heating electrical boxes 102 (e.g., pre-assembled heating electrical boxes) that can be bolted down or otherwise attached onto vane carriers 28. Depending on the needs of a given application, pockets 104 or similar subsurface voids may be constructed (e.g., machined, milled, etc.) on the vane carriers to receive a respective heating electrical box. Alternatively, in certain applications heating electrical boxes 102 may be disposed onto respective outer surfaces of the vane carriers.

[0029] In one non-limiting embedment, as may be appreciated in FIGs.

2 and 3, at least one subsurface void, e.g., one or more grooves 94, may be constructed within vane carriers 28 to receive electrical heating circuitry 62, such as an electrical conductor in the form of a heating wire 95 (e.g., a high-temperature resistant wire). In one non-limiting embodiment, grooves 94 may comprise spaced apart grooves, which may be transversely arranged relative to a longitudinal axis 96 of the vane carrier.

[0030] In one non-limiting embodiment, depending on the needs of a given application, grooves 94 may comprise an undulated arrangement of grooves, e.g., a plurality of undulated grooves. This arrangement may be conducive to covering a relatively larger surface area and may also be conducive to, for example, accommodating different thermal expansions between casing and cables. It will be appreciated that such an arrangement should be construed in an example sense and not in a limiting sense since other arrangements may be tailored based on the needs of a given application. For example, as may be appreciated in FIG. 4, in one non-limiting embodiment, the heating wires may be arranged in linearly- arranged grooves 94, e.g., practically straight grooves other than at turning locations. It will be appreciated that regardless of the specific geometric arrangement of the heating wires, such heating wires may be embedded within vane carriers 28 and/or such heating wires may be optionally disposed onto respective outer surfaces of the vane carriers. [0031] Referring to FIG. 1, combustor section 14 includes a combustor shell 44 defined within a combustor casing 46 that receives compressed air from compressor section 12, referred to herein as“shell air”. The shell air passes into the individual combustors 16 for combustion with a fuel to produce hot combustion gases. The hot combustion gases are conveyed through a transition duct 48 associated with each combustor 16 to turbine section 18.

[0032] Conceptually similar to compressor section 12, turbine section

18 includes vane carriers 50 supported within an outer turbine casing 52. Accordingly, based on the specific needs of a given application, such vane carriers can similarly benefit from electrical heating circuitry, as described above.

[0033] In one non-limiting embodiment, outer compressor casing 26, outer combustor casing 46, and outer turbine casing 52 collectively define an outer casing 53 of engine 10. Stationary turbine vanes 54 are supported on vane carriers 50 and extend radially inward across flow path 36. Vane carriers 50 additionally support outer shrouds or ring segments 55 located in an axially alternating arrangement with outer end walls of vanes 54 to define a turbine portion of the radially outer boundary 29 of flow path 36. Rotating turbine blades 56 are supported on respective turbine rotor disks 58 in an alternating arrangement with the vanes 54 to form stages of the turbine section 18. The rotating blades 56 extend radially outward across flow path 36, and radially outer tips 56a of blades 56 may be located adjacent to inner surfaces 55a of ring segments 55. The hot combustion gases are expanded through the stages of turbine section 18 to extract energy, and at least a portion of the extracted energy from the combustion gases causes the rotor 34 to rotate and produce a work output during a power producing mode of operation of the engine 10, referred to herein as a “first mode of operation”. [0034] It should be noted that the vane carriers 28 of the compressor section 12 may comprise multiple pieces, such as two semi-cylindrical halves defining a ring around the path of the blade tips 32a. Similarly, the vane carriers 50 of the turbine section 18 may comprise multiple segments defining a ring around the path of the blade tips 56a. Accordingly, aspects of disclosed embodiments may be applied to any structure that constitutes the vane carriers 28, 50 or equivalent structure that either defines or supports an outer boundary forming a static structure located proximate the tips of rotating blades 32, 56 extending in the flow path 36. Therefore, disclosed embodiments are not intended to be limited by the particular terminology used to describe such disclosed embodiments. For example, the term“vane carrier” may be understood to encompass“blade segment” or“blade ring” and that such structure may be incorporated as a support for“ring segments”,“shrouds”,“shroud segments”, and similar structure.

[0035] In one non-limiting example, the respective diameters of vane carriers 28, 50 and the respective lengths of blades 32, 56 are designed so that during engine startup, the tips 32a, 56a of the blades 32, 56 do not contact the inner surfaces 28a, 55a of the static structure defined by the vane carriers 28, 50 or equivalent structure, e.g., the ring segments 55. However, as is described in greater detail below, the gap between the blade tips 32a, 56a and the static vane carrier 28, 50 can increase during transient operation due to the vane carrier temperature increasing.

[0036] During an initial engine startup (cold startup), the turbine blades 56 radially expand quickly due to a rapid increase in the temperature as a result of the hot working gases impinging on the blades 56 and centrifugal forces acting on the blades 56. Also during start-up, the respective vane carriers 28 and 50 of the compressor 12 and turbine 18 expand radially outward away from the blade tips of the respective blades 32, 56 as the temperature of the vane carriers 28, 50 increases, typically creating a gap at the blade tips 32a, 56a that is larger than optimal for preventing or limiting secondary gas flows across the tips 32a, 56a.

[0037] During an engine startup that does not incorporate a pre-heating operation as described below, the respective vane carriers 28, 50 may expand at a slower rate than the radial outward expansion of the blades 32, 56, substantially reducing the gap or clearances between blades 32, 56 and the respective inner surfaces 28a, 55a of the vane carrier 28 and ring segment 55. Also, during a warm restart of the engine, the reduction in the blade to vane carrier clearances is exacerbated by the relatively high thermal inertia of the rotor assembly 34, with an associated higher temperature, in comparison to the vane carriers 28, 50 in that the rotor assembly 34 can retain heat longer with an associated greater thermal expansion of the blades 32, 56 than the surrounding vane carriers 28, 50, causing the clearance gap to substantially decrease and be smaller than the cold gap. Hence, warm restarts represent a limiting transient clearance gap condition when the clearance gaps between blade tips 32a, 56a and inner surfaces of the outer flow boundary 29 are at a minimum. The clearance between the blade tips 32a, 56a and inner surfaces of the outer flow boundary 29 will hereinafter be referred to as“clearance gap”.

[0038] In one non-limiting embodiment, the respective vane carriers 28,

50 or equivalent structure, e.g., ring segments 55, may be heated by electrical heating circuitry 62 embedded in the vane carrier or otherwise disposed onto vane carriers 28, 50 or equivalent structure and avoid interference, i.e., contact between adjacent rotating blade tips 32a, 56a and the boundary (e.g., structures) adjacent to the tips of the rotating blades.

[0039] In certain disclosed embodiments, additional control of the clearance gap between respective blade tips 32a, 56a and outer boundary 29 during a warm restart can be implemented by controlling the air flow through the engine 10 during a turning gear operation. As may be understood from the following description, heating of respective vane carriers 28, 50 can be performed independently of the availability of warm air or the air flow conditions in the engine 10.

[0040] Referring to FIG. 1, in one non-limiting embodiment, an air duct system 74 may be provided extending outside of outer casing 53 of the engine 10 between compressor section 12 and turbine section 18. Air duct system 74 can include one or more bleed air ducts extending from compressor section 12 to an axially downstream location on the engine 10, as is illustrated in FIG. 1 by bleed air ducts 76a, 76b, 76c. The bleed air ducts 76a, 76b, 76c extend axially between respective first ends connected to respective bleed air ports extending through the compressor outer casing 26 and associated with the bleed air cavities in the compressor section. The bleed air ducts 76a, 76b, 76c may include respective second ends connected to ports associated with respective turbine cooling air plenum or cavities defined between turbine casing 52 and vane carriers 50. In this non-limiting embodiment, air duct system 74 may be operable in the first mode of operation, i.e., powered turbine engine operation, to provide cooling air from the compressor section 12 to such turbine cooling air cavities.

[0041] Air duct system 74 can also include a valve structure including control valves 82a, 82b, 82c located in bleed air ducts 76a, 76b, 76c, respectively. Valves 82a, 82b, 82c are adjustable between fully open and fully closed positions, and can include a plurality of partially open positions between the fully open and fully closed positions, wherein valves 82a, 82b, 82c may be configured to provide a range of continuously variable partially open positions to control the amount of flow through the respective bleed air ducts 76a, 76b, 76c. Valves 82a, 82b, 82c can be operated during a non-power producing mode of operation of the engine 10, referred to herein as a“second mode of operation”, as will be described further below. The positions of the valves 82a, 82b, 82c may be controlled by a controller 92, which may also comprise a controller for controlling other operations of the engine 10 including operation of electrical heating circuitry 62 (see FIG. 7). In one non-limiting embodiment, controller 92 may be configured to energize electrical heating circuitry 62 to provide selectable zonal heating to the vane carrier.

[0042] In certain disclosed embodiments, electrical heating circuitry 62 may comprise a plurality of individually controlled electrical heating circuitries, such as may be controlled by controller 92, located at different circumferential positions within one or more stages of the compressor section 12 and/or turbine section 18. Electrical heating circuitries 62 located at different circumferential positions can be controlled and/or configured to selectively provide heat to particular circumferential locations within a stage, such as to heat a circumferential section of the stage to selectively increase/decrease the clearance gap at such locations.

[0043] During standard turning gear operation (e.g., after engine has shut down), due to natural convection, a top section of the engine is warmer than a bottom section of the engine. Hence, during this condition, relatively more heat should be supplied to the bottom section to equalize the temperatures circumferentially. Accordingly, in one non-limiting example, more thermal energy (e.g., more heating) may be applied to the bottom section of the engine, e.g., by way of respective vane carriers 28, 50 located at the bottom section of the engine, as opposed to respective vane carriers 28, 50 located to the top section of the engine. This would be effective to achieve any desired circumferentially-asymmetric tip gap clearance or to offset a circumferentially-asymmetric heat distribution within the stage and maintain a substantially equalized clearance gap around the circumference of the vane carrier 28, 50.

[0044] In operation, disclosed embodiments may be effective to transfer thermal energy directly to casings and/or casing components, e.g., vane carriers, which is conducive to a more efficient transfer of thermal energy to such components. Additionally, disclosed embodiments, as may involve electrical heating circuitry embedded within or otherwise disposed onto the vane carriers, may be conducive to preserving the volume available in the bleed air cavities and/or may be further conducive to avoid introducing aerodynamic distortion to air flow passing through the bleed air cavities. Additionally, in operation disclosed embodiments may be effective to avoid or at least reduce casing ovalisation. That is, avoid or reduce the deviation of casing roundness (“ovalisation”) that otherwise would be caused by uneven temperature distribution within one or more stages of the compressor section 12 and/or turbine section 18, which can lead to increased and unequal radial clearances between rotating components and adjacent stationary components.

[0045] It will be appreciated that any of the above-disclosed embodiments of electrical heating circuitry could be optionally installed within and/or onto inner and/or outer casings of the engine. For example, based on the needs of a given application, electrical heating circuitry within and/or onto inner and/or outer casings of the engine could be installed alone or in combination with disclosed embodiments embedded in the vane carrier or otherwise disposed onto the vane carriers. [0046] While embodiments of the present disclosure have been disclosed in exemplary forms, it will be apparent to those skilled in the art that many modifications, additions, and deletions can be made therein without departing from the scope of the invention and its equivalents, as set forth in the following claims.