Patent Publication Number: US-8123406-B2

Title: Externally adjustable impingement cooling manifold mount and thermocouple housing

Description:
BACKGROUND OF THE INVENTION 
     The subject matter disclosed herein relates to gas turbines and, more particularly, to an adjustable mount for an air impingement cooling manifold for a gas turbine. 
     Air impingement cooling is used to manage the casing temperature of a gas turbine and to reduce and maintain the clearances between rotating blades and accompanying interior casing surfaces. The cooling of the casing in general needs to be relatively uniform to avoid undesired non-roundness and local stress concentration. The efficiency of cooling is affected by various air impingement cooling configurations. One problem with air impingement cooling configurations on gas turbines is the difficulty in achieving a relatively uniform heat transfer coefficient across large, non-uniform, non-standard casing surfaces. On some gas turbines, small impingement holes and relatively short nozzle to surface distances are applied. While these features may produce the required higher heat transfer coefficients on the casing, a problem with the use of relatively small impingement cooling holes is the need for operating with a relatively high differential pressure drop across the holes. This results in the requirement for undesirable high cooling air supply pressures which negatively impacts net efficiency for gas turbines. Also, relatively smaller holes and shorter hole to surface distances have detrimental cross flow and an inadvertent effect on cooling efficiency of constant coolant flow rate. Consequently, a high pressure blower may be needed with added system capital and operational cost. 
     One known air impingement cooling configuration includes a plurality of manifolds affixed to the turbine casing directly above the target cooling area. The manifolds are typically affixed to the turbine casing using mounts. Cooling air is provided to the manifolds, which have a series of air impingement holes formed in a lower plate of each manifold. The size and positioning of the impingement holes on the lower plates are selected to produce a relatively uniform and desired heat transfer coefficient across the turbine casing targeted for cooling by the air impingement cooling system. With this type of manifold cooling system, the distance between the lower plate of each manifold and the turbine casing determines the cooling of the casing achieved by the manifolds. However, the mounts that affix the manifolds to the casing are problematic in that they do not allow for any adjustment of the gap distance between the lower plate of the manifold and the turbine casing while the manifold is mounted to the casing. The mount gap distance can only be adjusted with the manifolds removed from the casing. This results in an undesirable, time consuming trial and error method needed to achieve the desired gap distance between the lower plate and the casing. That is, typically the manifolds need to be placed on and off the casing several times until the desired gap distance and, thus, the proper amount of cooling of the casing is achieved. 
     BRIEF DESCRIPTION OF THE INVENTION 
     According to one aspect of the invention, a mount includes a mounting bolt attached to a casing; an internal bushing that engages the casing at a distal end of the internal busing; and an external bushing that engages a manifold and engages the internal bushing, the internal bushing being adjustable with respect to the external bushing thereby allowing the manifold to be adjustable with respect to the casing. 
     According to another aspect of the invention, a mount for mounting a manifold having a pair of spaced apart plates to a casing, one of the plates located closest to the casing having a plurality of cooling holes formed therein, the mount includes a mounting bolt attached to a casing; an internal bushing that engages the casing at a distal end of the internal bushing; and an external bushing that engages a manifold and threadably engages the internal bushing, the internal bushing being adjustable with respect to the external bushing thereby allowing the manifold to be adjustable with respect to the casing. 
     According to yet another aspect of the invention, a method includes attaching a mounting bolt to a casing; engaging an internal bushing with the casing; and engaging an external bushing with the manifold and with the internal bushing, the internal bushing being adjustable with respect to the external bushing thereby allowing the manifold to be adjustable with respect to the casing. 
     These and other advantages and features will become more apparent from the following description taken in conjunction with the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
       The subject matter which is regarded as the invention is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which: 
         FIG. 1  is a cross-section view of a gas turbine; 
         FIG. 2  is a detailed view of the turbine blade to shroud clearance in the gas turbine of  FIG. 1 ; 
         FIG. 3  is an impingement cooling system implemented on the gas turbine of  FIG. 1 ; 
         FIG. 4  is a cross-section view of an impingement cooling manifold that is part of the impingement cooling system of  FIG. 3 ; 
         FIG. 5  is a detailed cross-section view of the impingement cooling manifold of  FIG. 4 ; 
         FIG. 6  is a detailed view of a mount according to an embodiment of the invention for the impingement cooling manifold of  FIGS. 4 and 5 ; 
         FIG. 7  is a cross-section view of a mounting bolt and thermocouple holder that is part of the mount of  FIG. 6 ; 
         FIG. 8  is a cross-section view of an internal bushing that is part of the mount of  FIG. 6 ; and 
         FIG. 9  is a cross-section view of an external busing that is part of the mount of  FIG. 6 . 
     
    
    
     The detailed description explains embodiments of the invention, together with advantages and features, by way of example with reference to the drawings. 
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  illustrates an embodiment of a gas turbine  110 . The gas turbine includes a compressor section  112 , combustor section  114 , and a turbine section  116 . The turbine  110  also includes a compressor casing  118  and a turbine casing  120 . The turbine and compressor casings  118 ,  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. 
     Referring to  FIGS. 1 and 2 , the turbine casing  120  may include a shroud  126  affixed to the interior surface of the casing  120 . The shroud  126  may be positioned proximate to the tips of the rotating turbine blades  122  to minimize air leakage past the blade tip. The distance between the blade tip  123  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 and casing during operation of the gas turbine. 
     A contributor to the efficiency of gas turbines is the amount of air/exhaust gas leakage through the blade tip to casing clearance  128 . Due to the different thermal growth characteristics of the turbine blades  122  and turbine casing  120 , clearances  128  significantly change as the turbine 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 all operating conditions. Incorrect design and/or sequencing of the control system may lead to excessive rubbing of the turbine blade  123  tips with the casing shrouds  126 , which can result in increased clearances and reduced performance. 
     As illustrated in the exemplary embodiment of  FIG. 3 , an impingement air-cooling system may be used to reduce and maintain the clearances between the turbine shroud  126  and the accompanying blade tip  123 . The impingement air-cooling system may comprise a blower  130 , a flow control damper  132 , interconnect piping  134 , a distribution header  136 , and a series of impingement cooling manifolds  140 . The impingement cooling manifolds  140  are affixed to the turbine casing  120 . In the exemplary embodiment of  FIG. 3 , a plurality (e.g., eight) 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 , and into the impingement cooling manifolds  140 . The blower  130  may be any blowing device including a fan or a jet. The impingement cooling manifold  140  provides for a relatively uniform heat transfer coefficient to be delivered to the turbine casing  120 . It should be appreciated that the impingement air-cooling system is not limited to the components disclosed herein but may include any components that enable air to pass along the impingement cooling manifolds  140 . 
     Referring to the 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 an air feed pipe  144 , a lower plate  146  with multiple impingement holes  148 , side pieces, leveling legs  150 , and hold down supports or mounts  152 . The mounts  152  (and, thus, the manifolds  140 ) are externally adjustable according to an embodiment of the invention and the mounts  152  are described and illustrated in more detail hereinafter with respect to  FIGS. 6-9 . The impingement holes  148  permit the air to flow from the impingement cooling manifold  140  to the turbine casing to selectively cool the turbine casing. 
     The impingement holes  148  may be positioned in an array. In an exemplary embodiment, the impingement holes  148  may be spaced in the range from 1.25 to 2.5 inches, and the individual impingement holes  148  may be sized between 0.12 and 0.2 inches. The varying hole sizes and spacing are required to compensate for the non-uniformity of the geometry of the turbine casing  120 . The size and positioning of the impingement holes  148  on the lower plate  146  produce a uniform heat transfer coefficient across the casing  120  targeted by the impingement air-cooling system. 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 reduce internal pressure variations, which results in relatively more uniform cooling hole pressure ratios. 
     The gap distance between each impingement cooling manifold lower plate  146  and the turbine casing  120  affects the heat transfer coefficient. Too large of a gap can result in an undesirable heat transfer coefficient. Too little of a gap can result in both an undesirable and a non-uniform heat transfer coefficient. In an exemplary embodiment, a gap of between 0.5 and 1.0 inch provides a suitable heat transfer coefficient. However, the gap is not limited to this range and may be any distance that provides a suitable heat transfer coefficient. As described in greater detail hereinafter, the mounts  152 , according to embodiments of the invention, provide for an external adjustment of the gap distance between the manifold lower plate  146  and the turbine casing  120  while the manifolds  140  are mounted or affixed to the turbine casing  120 . 
     An exemplary embodiment of a gas turbine may include a plurality of impingement cooling manifolds  140 . The manifolds  140  may be affixed to the casing  120  of the turbine directly above the target cooling area on the casing  120 . The impingement cooling manifolds  140  may be 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 may be between 1 to 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 a horizontal split joint. 
     Referring to  FIG. 6 , the mount  152  according to an embodiment of the invention is illustrated in more detail. In embodiments of the invention, the mounts  152  function to hold or support the manifolds  140  (in particular, the impingement holes  148  formed in the lower plate  146  of the manifold  140 ) at a predetermined gap distance from the surface of the turbine casing  120 . The mounts  152  also function as a well or holder for a thermocouple  154  that monitors the temperature of the turbine casing  120 . Referring also to  FIGS. 7-9 , the mount  152  comprises an assembly of various components that include a mounting bolt  156  ( FIG. 7 ) that also holds the thermocouple  154 , an internal bushing  158  ( FIG. 8 ), and an external bushing  160  ( FIG. 9 ). 
     The mount  152  is located through a hole  164  in the upper plate  142  of the manifold  140  and a hole  166  in the lower plate  146  of the manifold  140 . The mounting bolt  156  includes a threaded distal end  168  that engages a threaded counter bore  170  formed in the turbine casing  120  to secure the mount  152  to the casing  120 . The thermocouple body  154  is threaded or affixed in a threaded or tapped well or bore  172  within a hex head  174  located at the proximal end of the mounting bolt  156 . The bore  172  continues unthreaded through the entire length of the mounting bolt  156 . The thermocouple  154  includes a thin rod or wire  155  disposed through the length of the bore  172 , where the rod  155  terminates in the counter bore  170  in the casing  120 . The rod  155  makes contact with the casing  120  in the counter bore  170  below the threaded engagement of the mounting bolt  156  with the casing  120 , thereby allowing for measurement of the temperature of the casing  120 . 
     The internal bushing  158  includes a flange  176  at a distal end that sits on a surface  178  of the casing  120 . The internal bushing includes external male threads  180  along a portion of its length. The threads  180  engage with internal female threads  182  along a portion of a bore  184 . The proximal end of the internal bushing  158  includes a flat portion  186  that is used to adjust the position or gap distance of the manifold  140  with respect to the casing  120 , in accordance with embodiments of the invention as described hereinafter. The flat portion  186 , which may take any other suitable shape besides flat, extends beyond the external busing  160  to allow access to the flat portion  186  by someone who desires to adjust the gap distance using, e.g., a wrench. 
     The distal end of the external bushing  160  includes a flange  188  that engages a surface  190  of the lower manifold plate  146  through use of a graphite gasket  192  and a sheet metal washer  194 . The proximal end of the external bushing  160  includes external male threads  196  along a portion of its length. The threads  196  engage with two jam nuts  198 ,  200  located next to one another and also next to a sheet metal washer  202  and a graphite gasket  204 . The graphite gasket  204  engages a surface  206  of the upper plate  142  of the manifold  140 . The external bushing  160  is located through the hole  164  in the upper plate  142 . The mounting bolt  156  passes through an internal bore  208  along the entire length of the internal bushing  158 . 
     In use, after the manifold  140  has been assembled or mounted to the turbine casing  120  using the mount  152  of embodiments of the invention, the gap distance of the lower plate  146  of the manifold from the casing  120  can be varied without having to remove the manifold  140  from the casing  120 , as mentioned above with known designs. Instead, the gap distance can be varied with the manifold  140  mounted to the casing  120  through use of a wrench or other suitable tool that grabs onto the flat portion  186  of the internal bushing  158  and then turning the internal bushing  158  in either a clockwise or counter-clockwise direction. As such, the external threads  180  of the internal bushing  156  “run” or are adjustable with respect to the internal threads  182  of the external bushing  160 , thereby adjusting the gap distance of the manifold  140  with respect to the turbine casing  120 . 
     The mount  152  according to embodiments of the invention described and illustrated herein provides for improved manifold to casing gap distance clearance control and reduces the installation time when the manifolds  140  are mounted to the casing  120  both during the initial fit-up and during subsequent manifold re-installations. Relatively improved and tighter tolerances during the re-installations may also be maintained by the mounts  152 . 
     While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.