Abstract:
A turbine includes: a plurality of turbine blades arranged within a casing, the arrangement including a clearance between tips of the blades and the casing; a plurality of manifolds disposed proximate to the casing opposite the clearance, wherein each of the manifolds includes a plurality of impingement holes in the surface thereof; a source of clearance information; and a source of cooling air for supplying cooling air through a plurality of flow control devices to selected ones of the manifolds according to the clearance information. A system and a method are also provided.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     The subject matter disclosed herein is generally related to U.S. patent application Ser. No. 11/548,791, entitled “Turbine Case Impingement Cooling for Heavy Duty Gas Turbines,” filed Oct. 12, 2006. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The teachings herein relate to reducing eccentricity and out-of-roundness in a turbine, and, in particular, to techniques for controlling cooling. 
     2. Description of the Related Art 
     Air impingement cooling has been used to manage the casing temperature of small gas turbines and to reduce and maintain the clearances between rotating blades and accompanying interior casing surfaces. One problem for air impingement cooling systems on gas turbines is the ability to achieve a uniform heat transfer coefficient across large non-uniform non-standard casing surfaces. On small gas turbines, small impingement holes and short nozzle to surface distances are normally applied. These factors produce the required higher heat transfer coefficients on the casing. One detrimental impact of applying small impingement cooling holes is the need for operating with high differential pressure drop across the holes. This results in the requirement for undesirable high cooling air supply pressures which negatively impacts net efficiency. 
     Impingement cooling has been applied to aircraft engines as a method of turbine clearance control. However, the impingement systems used on aircraft engines cannot be used in some turbine applications. The systems applied to aircraft engines use air extracted from the compressor as the cooling medium. It is not feasible to use compressor extraction air on some other gas turbines because the design heat transfer coefficients require cooler air temperatures. For example, some other gas turbines have a significantly larger, non-uniform casing surface that requires an intricate manifold design as compared to aircraft engines. Also, the casing thickness and casing thickness variations are considerably greater on such gas turbines. 
     A problem with eccentricity and out-of-roundness for the gas turbine casing is rub between the rotor and the stator and other mechanical problems. This decreases efficiency of the power output. The problem is primarily addressed by increasing the cold built clearance of the gas turbines, which does not address the problem, but further lowers the efficiency. 
     Some apparatus are known that provide cooling with impingement air. For example, one system includes an impingement cooling manifold affixed to a casing of the turbine, wherein the impingement cooling manifold includes a plurality of impingement holes in the surface of the impingement cooling manifold; and a blower that provides air flow across the plurality of impingement holes of the impingement cooling manifold to cool the casing of the turbine to control the clearance between a tip of a turbine blade and a shroud of the turbine. While such a system has certain advantages, it is desirable to provide greater control over cooling to further improve performance. 
     Thus, there is a need for an impingement cooling system that can provide clearance control on gas turbines. Preferably, this system delivers the required heat transfer coefficient to the targeted casing surface, and provides a high degree of control over the flow of air to the casing. Such a system is disclosed herein. 
     BRIEF DESCRIPTION OF THE INVENTION 
     In one embodiment, a gas turbine is disclosed and includes: a plurality of turbine blades arranged within a casing, the arrangement including a clearance between tips of the blades and the casing; a plurality of manifolds disposed proximate to the casing opposite the clearance, wherein each of the manifolds includes a plurality of impingement holes in the surface thereof; a source of clearance information; and a source of cooling air for supplying cooling air through a plurality of flow control devices to selected ones of the manifolds according to the clearance information. 
     In another embodiment, a flow regulated impingement air cooling system for a gas turbine engine, is disclosed and includes: a plurality of manifolds for being disposed proximate to a casing of the gas turbine and opposite to a clearance between tips of turbine blades therein, wherein each of the manifolds includes a plurality of impingement holes in the surface thereof; at least one clearance measuring device for providing clearance information; a plurality of flow control devices for controlling air cooling flow to the plurality of manifolds; and a source of cooling air for supplying cooling air through the plurality of flow control devices to selected ones of the manifolds according to the clearance information. 
     In a further embodiment, a method for controlling clearance between tips of turbine blades and a casing of a gas turbine, is disclosed and includes: receiving clearance information; determining an amount of cooling air to be supplied to sections of the casing; and regulating flow from a source of cooling air to each section of the casing to reduce the clearance. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Referring now to the drawings wherein like elements are numbered alike in the several Figures, wherein: 
         FIG. 1  depicts aspects of a cross-sectional view of a heavy duty gas turbine; 
         FIG. 2  depicts aspects of a close-up view of the turbine blade to shroud clearance; 
         FIG. 3  depicts aspects of an impingement cooling system; 
         FIG. 4  is an orthographic view of a impingement cooling manifold; 
         FIG. 5  is a cross-section view of an impingement cooling manifold; 
         FIG. 6  is an orthographic view of installed impingement cooling manifolds on a turbine casing; 
         FIG. 7  depicts aspects of the impingement cooling system including clearance probes and regulators. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Disclosed are methods and apparatus for active clearance control using cooling manifolds in a gas turbine engine. The cooling flow of each individual manifold is regulated by devices such as tuning valves or orifices. Clearance control makes use of information of overall eccentricity and out-of-roundness and local clearance in sectors. The information may be collected in a variety of ways, including with the use of clearance probes. Prior to discussing the methods and apparatus in greater detail, certain aspects of a gas turbine are discussed for perspective. 
     Turning now to  FIG. 1 , there is illustrated therein an exemplary embodiment of a gas turbine  110 . The gas turbine  110  includes a compressor section  112 , a combustor section  114  and a turbine section  116 . The gas turbine  110  also includes a compressor casing  118  and a turbine casing  120 . The turbine casing  118  and the compressor casing  120  enclose major parts of the gas turbine  110 . The turbine section  116  includes a shaft and a plurality of sets of rotating and stationary turbine blades  122 . 
     Referring also to  FIGS. 2 and 3 , the turbine casing  120  may include a shroud  126  affixed to an interior surface of the casing  120 . The shroud  126  may be positioned proximate to tips  123  of the rotating turbine blades  122  to minimize air leakage past the tip  123 . The distance between the tip  123  of the blade  122  and the shroud  126  is referred to as the clearance  128 . It is noted that the clearances  128  of each turbine stage are not consistent due to the different thermal growth characteristics of the blades  122  and casing  120 . 
     A key contributor in the efficiency of gas turbines is the amount of air and exhaust gas leakage through a clearance  128  between the blade tip  123  and the casing  120  or shroud  126  (as shown in  FIG. 2 ). Due to the different thermal growth characteristics of the turbine blades  122  and turbine casing  120 , clearances  128  may significantly change as the turbine  110  transitions through transients from ignition to a base-load steady state condition. A clearance control system, including its operating sequence may be implemented to address the specific clearance characteristics during operating conditions. Incorrect design and/or sequencing of the control system may lead to excessive rubbing of the tips  123  with respective casing shrouds  126 , which can result in increased dimensions for clearances  128  and reduced performance. 
     As illustrated in the exemplary embodiment of  FIG. 3 , a flow regulated impingement air cooling system  200  may be used to reduce and maintain a desired clearance  128  between the turbine shroud  126  and the respective set of blade tips  123 . Referring to  FIG. 3 , the flow regulated impingement air cooling system  200  includes a source of cooling air  131 . The source of cooling air  131  may include, for example, a compressor  112  ( FIG. 1 ), and/or the illustrated blower  130  and flow control damper  132 . The source of cooling air  131  may further include electro-mechanical components for providing an interface and operating with control components, such as controller  160 . 
     Further included in the flow regulated impingement air cooling system  200  are interconnect piping  134 , a distribution header  136 , flow metering valves or orifices  138  and a series impingement cooling manifolds  140 . Each of the impingement cooling manifolds  140  may be affixed to the turbine casing  120 . In the exemplary embodiment of  FIG. 3 , a plurality of impingement manifolds  140  are affixed about the circumference of the turbine casing  120 . The impingement cooling blower  130  takes suction from ambient air and blows the air through the flow control damper  132 , interconnect piping  134 , distribution header  136 , flow metering valves or orifices  138  and into the impingement cooling manifolds  140 . The blower  130  may be any blowing device including a compressor, a fan or a jet. The impingement cooling manifold  140  insures a uniform heat transfer coefficient is delivered to the turbine casing  120 . It should be appreciated that the flow regulated impingement air cooling system  200  is not limited to the components disclosed herein but may include any components that enables air to pass along the impingement cooling manifolds  140 . 
     Further shown in  FIG. 3  are aspects of control components. In the embodiment depicted, included with the control components are the controller  160  and control lines  161 . The control lines  161  provide for communication between the controller  161  and a plurality of clearance probes  701  (only a portion of which are illustrated in  FIG. 3 ). The clearance probes  701  communicate clearance information to the controller  160  via the communication lines  161 . The controller  160  males use of the clearance information to generate instructions and provide commands to a plurality of flow regulators  702 . Although only one of the flow regulators  702  in  FIG. 3  is illustrated as receiving a signal from the controller  160  in response to a signal from one of the clearance probes  701 , other flow regulators  702  may be similarly controlled in response to signals from one or more of the probes  701  and/or other data. For example, the flow regulators  702  may be in the form of control valves and/or secondary equipment such as positioners, transformers, regulators, actuators, manual operators, snubbers, limit switches and other such devices. The flow regulators  702  adjust the flow metering valves  138  according to the instructions. Thus, a flow of cooling air for each manifold  140  is separately regulated, and cooling of the casing  120  is accomplished in sections (where each section generally corresponds to a manifold  140 ). 
     The controller  160  may be implemented in any mechanical, electrical and or optical form, including in the form of conventional P-I-D control and/or computer control with a computer program. The computer program, which comprises an ordered listing of executable instructions for implementing logical functions, can be embodied in any computer-readable medium for use by or in connection with an instruction execution system, apparatus, or device, such as a computer-based system, processor-containing system, or other system that can fetch the instructions from the instruction execution system, apparatus, or device and execute the instructions. In the context of this document, a “computer-readable medium” can be any means that can contain, store, communicate, propagate, or transport the program for use by or in connection with the instruction execution system, apparatus, or device. The computer readable medium can be, for example but not limited to, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, device, or propagation medium. More specific examples (a nonexhaustive list) of the computer-readable medium would include the following: an electrical connection (electronic) having one or more wires, a portable computer diskette (magnetic), a random access memory (RAM) (electronic), a read-only memory (ROM) (electronic), an erasable programmable read-only memory (EPROM or Flash memory) (electronic), an optical fiber (optical), and a portable compact disc read-only memory (CDROM) (optical). Note that the computer-readable medium could even be paper or another suitable medium upon which the program is printed, as the program can be electronically captured, via for instance optical scanning of the paper or other medium, then compiled, interpreted or otherwise processed in a suitable manner if necessary, and then stored in a computer memory. In addition, the scope of the certain embodiments of the present invention includes embodying the functionality of the preferred embodiments of the present invention in logic embodied in hardware or software-configured mediums. 
     As may be surmised, the flow regulated impingement air cooling system  200  may include a variety of components generally used for signal collection, processing and component control. These include at least one of a processor, a memory, a storage, a power supply, a set of machine readable instructions stored on machine readable media (i.e., software), a wire, a cable, an optical fiber, a connection, a couplings, an interface (including wireless implementations) and other such components. Accordingly, embodiments of the flow regulated impingement air cooling system  200  include software for receiving clearance information and controlling each of the flow regulators  702 . The controlling may be performed on a real time basis (that is, as quickly as desired by a user or designer for production of clearance control during operation of the turbine  110 ). Other input data besides clearance information may also be used, including local casing temperature, vibration data and other process parameters. 
     A technical effect is that the flow regulated impingement air cooling system  200  may include machine executable instructions stored on machine readable media, where the instructions provide for operation of the flow regulated impingement air cooling system  200  and components thereof. 
     Referring to exemplary embodiment illustrated in  FIGS. 4 and 5 , the impingement cooling manifolds  140  may be designed to the contours of the target area of the turbine casing  120 . Each impingement cooling manifold  140  may include an upper plate  142  with feed pipe  144 , a lower plate  146  with multiple impingement holes  148 , side pieces  154 , support legs  150  and hold-down supports  152 . The impingement holes  148  permit air to flow from the impingement cooling manifold  140  to the turbine casing  120  to selectively cool the turbine casing  120 . 
     The impingement holes  148  are generally positioned in an array. In an exemplary embodiment, the impingement holes  148  may be spaced in the range from about 1.25 inches to about 2.5 inches. In an exemplary embodiment, the individual impingement holes  148  may be sized between about 0.12 inches and about 0.2 inches. The varying hole sizes and spacing are required to compensate for the non-uniformity of the turbine casing geometry. The size and positioning of the impingement holes  148  on the lower plate  146  produce a uniform heat transfer coefficient across the casing targeted by the flow regulated impingement air cooling system  700 . However, the impingement holes are not limited to these sizes or spacings. The distance between the upper  142  and lower plates  146  also may be dimensioned to minimize internal pressure variations, which results in uniform cooling hole pressure ratios. 
     The gap distance between impingement cooling manifold lower plates  146  and the turbine casing  120  effects the heat transfer coefficient. Too large of a gap can result in a non-optimum heat transfer coefficient. Too little of a gap can result in both non-optimum and a non-uniform heat transfer coefficient. In an exemplary embodiment, a gap of between about 0.5 inch and about 1.0 inch provides a suitable heat transfer coefficient. However, the gap in not limited to this range and may be any distance that provides a suitable heat transfer coefficient. 
     As illustrated in  FIG. 6 , the multiple impingement cooling manifolds  140  are affixed to the casing  120  of the turbine directly above target cooling area (i.e., opposite to the clearance  128 ). The impingement cooling manifolds  140  are positioned such that there is ample spacing between their edges and any protrusions off of the casing. This provides a free path for the air passing through the impingement holes  148  to exhaust from under the impingement cooling manifold  140  to the environment. In an exemplary embodiment, the spacing between two adjacent impingement cooling manifolds  140  may be between about 1 inch to about 30 inches and is dependent on casing protrusions and flanged joints. The spacing is not limited to these dimensions and may be spaced at any suitable distance. The impingement cooling manifolds  140  also may provide impingement cooling to any of the axial flanges, including the horizontal split joint. 
     Now with reference to  FIG. 7 , another embodiment of the flow regulated impingement air cooling system  700  is shown. In  FIG. 7 , the flow regulated impingement air cooling system  700  includes devices for measuring clearance during operation (i.e., online measurement). In this embodiment, the devices for measuring clearance include the plurality of clearance probes  701 . Exemplary embodiments of clearance probes  701  include probes operating by use of at least one of mechanical, electrical, electromechanical, magnetic, electromagnetic, optical as well as other technologies. The clearance probes  701  are generally evenly distributed to provide for sensing aspects of the clearance  128 , such as by determining proximity of the turbine casing  120 . The devices for measuring clearance provide clearance information for each of the impingement cooling manifolds  140 . 
     Also included in the flow regulated impingement air cooling system  700  is a plurality of flow control devices. In the embodiment depicted, the flow control devices include flow regulators  702 . Each of the flow regulators  702  is adapted for regulating flow of cooling air from the feed pipe  144  to the respective impingement cooling manifold  140 . By use of the flow regulators  702 , it is thus possible to finely regulate flow of cooling air to selected portions of the turbine casing  120 . 
     In another embodiment of the flow regulated impingement air cooling system  700 , the amount of cooling needed for each of the impingement cooling manifolds  140  may be known. This may be the case when the pattern of eccentricity and out-of-roundness is known (as may be the case for some gas turbines  110 ). Accordingly, in this embodiment, the devices for measuring clearance are not directly incorporated into the gas turbine  110 . That is, for example, the devices for measuring clearance (i.e., a source of clearance information) may include devices used for performing measurements during design, assembly or maintenance (i.e., offline measurement). Non limiting examples include optical devices (for example, an optical sensing system), radiofrequency devices (for example, a microwave sensing system), magnetic devices (for example, a magnetic sensing system), and mechanical devices such as micrometers, calipers, feeler gauges and digital or analog embodiments thereof. 
     Further, the flow control devices may be a plurality of appropriately sized orifices, instead of or in addition to the flow regulators  702 . As used herein, the term “orifice” makes reference to a flow restriction exhibiting predetermined properties for restricting flow to a desired amount. 
     Further, in some instances, software may be included which provides for adjusting flow configurations based upon operational conditions. 
     Accordingly, advantages over prior solutions to the problem of eccentricity and out-of-roundness, primarily addressed by increasing the cold built clearance of the gas turbines, are provided. The advantages include reduced possibility of rubbing as well as increased efficiency. 
     In some embodiment, the flow regulated impingement air cooling system  700  is provided as a kit. For example, the flow regulated impingement air cooling system  700  can be provided as a retro-fit option for an existing gas turbine. In some instances, the retro-fit kit includes, as a non-limiting example, clearance measuring devices for measuring clearance during operation (such as the clearance probes  701  discussed above), flow control devices for controlling air cooling flow during operation (such as the flow regulators  702  discussed above), a plurality of impingement cooling manifolds  140 , and the source of cooling air  131 . Other equipment as necessary may be included. For example, the kit may include processing components, such as a controller, a processor, storage, memory, a communications component, an interface, an electromechanical unit (such as servos for operating the flow regulators  702 ) and machine executable instructions stored on machine readable media, where the instructions provide for governing operation of the flow regulated impingement air cooling system  700 . 
     Although the technology described herein has been exemplified with respect to a gas turbine, it may also be used in connection with a wide variety of other turbine machinery including oil, coal-fired, steam and other types of turbines and compressors. 
     While the invention has been described with reference to an exemplary embodiment, it will be understood that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.