Patent Publication Number: US-9903218-B2

Title: Turbine shroud assembly

Description:
FIELD OF THE INVENTION 
     The present invention is directed to turbine components. More particularly, the present invention is directed to turbine components having an inner shroud loaded to an outer shroud. 
     BACKGROUND OF THE INVENTION 
     In gas turbines, certain components, such as the shroud surrounding the rotating components in the hot gas path of the combustor, are subjected to extreme temperatures, chemical environments and physical conditions. Inner shrouds are subjected to further mechanical stresses from pressures applied to load the inner shroud to the outer shroud, pushing against the pressure of the hot gas path. Pressurizing the space between the inner shroud and the outer shroud leaks high pressure fluid into the hot gas path, decreasing efficiency of the turbine. Further, mechanisms for mechanically loading the inner shroud against the outer shroud, such as springs, exhibit decreased effectiveness at high temperatures, and the springs themselves may creep over time, leading to insufficient loading pressure. Inner shrouds which are insufficiently biased toward the hot gas, for example due to insufficient loading pressure, have increased clearance between the bucket/blade tips and the inner shroud, which decreases the efficiency of the gas turbine. 
     BRIEF DESCRIPTION OF THE INVENTION 
     In an exemplary embodiment, a turbine shroud assembly includes an inner shroud having a surface adjacent to a hot gas path, an outer shroud, a damper block disposed between the inner shroud and the outer shroud, a first biasing apparatus, and a second biasing apparatus. The first biasing apparatus provides a first biasing force to the inner shroud, biasing the inner shroud a first deflection distance in a direction toward the hot gas path and away from the outer shroud. The second biasing apparatus provides a second biasing force to the damper block, biasing the damper block a second deflection distance in a direction toward the hot gas path and away from the outer shroud. The second deflection distance is greater than the first deflection distance, loading the damper block to the inner shroud. 
     In another exemplary embodiment, a turbine shroud assembly includes an inner shroud having a surface adjacent to a hot gas path, an outer shroud, a damper block disposed between the inner shroud and the outer shroud, a first springless biasing apparatus driven by a pressurized fluid, a second springless biasing apparatus driven by a pressurized fluid, and an adjustable deflection limiter. The first springless biasing apparatus provides a first biasing force to the inner shroud, biasing the inner shroud a first deflection distance in a direction toward the hot gas path and away from the outer shroud. The first springless biasing apparatus includes at least one bellows, at least one thrust piston, or a combination of at least one bellows and at least one thrust piston. The second springless biasing apparatus provides a second biasing force to the damper block, biasing the damper block a second deflection distance in a direction toward the hot gas path and away from the outer shroud. The second springless biasing apparatus includes at least one bellows, at least one thrust piston, or a combination of at least one bellows and at least one thrust piston. The adjustable deflection limiter is arranged and disposed such that the first deflection distance does not exceed a predetermined deflection. The predetermined deflection is alterable by adjustment of the deflection limiter. The second deflection distance is greater than the first deflection distance, loading the damper block to the inner shroud. 
     In another exemplary embodiment, a method for loading a turbine shroud assembly includes applying a first biasing force exerted by a first biasing apparatus to an inner shroud, biasing the inner shroud a first deflection distance in a direction toward a hot gas path and away from an outer shroud, and applying a second biasing force exerted by a second biasing apparatus to a damper block disposed between the inner shroud and the outer shroud, biasing the damper block a second deflection distance in a direction toward the hot gas path and away from the outer shroud. The second deflection distance is greater than the first deflection distance, loading the damper block to the inner shroud. 
     Other features and advantages of the present invention will be apparent from the following more detailed description, taken in conjunction with the accompanying drawings which illustrate, by way of example, the principles of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a sectioned view of turbine shroud assembly including at least one bellows, according to an embodiment of the disclosure. 
         FIG. 2  is a sectioned view of turbine shroud assembly including at least one thrust piston, according to an embodiment of the disclosure. 
         FIG. 3  is a sectioned view of turbine shroud assembly including at least one spring, according to an embodiment of the disclosure. 
         FIG. 4  is a sectioned view of turbine shroud assembly including at least two different biasing apparatuses, according to an embodiment of the disclosure. 
         FIG. 5  is a perspective view of the inner shroud of  FIGS. 1-4 , according to an embodiment of the disclosure. 
     
    
    
     Wherever possible, the same reference numbers will be used throughout the drawings to represent the same parts. 
     DETAILED DESCRIPTION OF THE INVENTION 
     Provided is a turbine shroud assembly. Embodiments of the present disclosure, for example, in comparison to concepts failing to include one or more of the features disclosed herein, reduce blade/bucket tip clearance, increase efficiency, increase durability, increase temperature tolerance, reduce the possibility of loss of load, reduce overall cost, eliminate the need for pressurizing the shroud, produce other advantages, or a combination thereof. 
     Referring to  FIG. 1 , a turbine shroud assembly  100  includes an inner shroud  102 , an outer shroud  104 , a damper block  106 , a first biasing apparatus  108  and a second biasing apparatus  110 . The inner shroud  102  includes a surface  112  adjacent to a hot gas path  114 . The damper block  106  is disposed between the inner shroud  102  and the outer shroud  104 . The first biasing apparatus  108  provides a first biasing force  116  to the inner shroud  102 . The first biasing force  116  biases the inner shroud  102  a first deflection distance  118  in a direction  120  toward the hot gas path  114  and away from the outer shroud  104 . The second biasing apparatus  110  provides a second biasing force  122  to the damper block  106 . The second biasing force  122  biases the damper block  106  a second deflection distance  124  in a direction  120  toward the hot gas path  114  and away from the outer shroud  104 . The second deflection distance  124  is greater than the first deflection distance  118 , loading the damper block  106  to the inner shroud  102 . 
     In one embodiment, the first biasing apparatus  108  includes a deflection limiter  126 . The deflection limiter  126  is arranged and disposed such that the first deflection distance  118  does not exceed a predetermined deflection  128 . In a further embodiment, the deflection limiter  126  is adjustable. Adjusting the deflection limiter  126  alters the predetermined deflection  128 . The deflection limiter  126  may threaded into the outer shroud  104  such that rotating the deflection limiter  126  will increase or decrease the predetermined deflection  128 . 
     In one embodiment, the turbine shroud assembly  100  includes a third biasing apparatus  130 . The third biasing apparatus  130  provides a third biasing force  132  to the damper block  106 . The third biasing force  132  biases the damper block  106  a third deflection distance  134  in a direction  120  toward the hot gas path  114  and away from the outer shroud  104 . The third deflection distance  134  is greater than the first deflection distance  118 , loading the damper block  106  to the inner shroud  102 . The turbine shroud assembly  100  may include any suitable number biasing apparatuses, including, but not limited to, more than three biasing apparatuses. 
     The first biasing apparatus  108  may be connected to the inner shroud  102  by any suitable attachment, including, but not limited to, a pin  136 , a hook, a dovetail, a t-slot, or combinations thereof. 
     In one embodiment, the damper block  106  exerts a dampening pressure on the inner shroud  102  sufficient to dampen vibrations of the inner shroud  102  under operating conditions. The damper block  106  may be formed from any suitable material, including, but not limited to, a steel alloy, a stainless steel alloy, a nickel alloy, or a combination thereof. The damper block  106  may also include a thermal barrier coating which protects the damper block  106  from exposure to hot gas path  114  gasses. The damper block  106  may maintain alignment of the turbine shroud assembly  100  by moving only in the direction  120  due to the interface of the damper bloc  106  with the outer shroud  104 . Without being bound by theory, it is believed that the vibrations of the inner shroud  102  are caused in part by the varying pressure field resulting from buckets/blades rotating in close proximity to the inner shroud  102 . In another embodiment, contact between the inner shroud  102  and the damper block  106  reduces ingestion of hot gasses from the hot gas path  114  into the turbine shroud assembly  100 . 
     In one embodiment, one of, two of, or all of the inner shroud  102 , the outer shroud  104 , and the damper block  106  includes a ceramic matrix composite, a metal, a monolithic material, or a combination thereof. As used herein, the term “ceramic matrix composite” includes, but is not limited to, carbon-fiber-reinforced carbon (C/C), carbon-fiber-reinforced silicon carbide (C/SiC), and silicon-carbide-fiber-reinforced silicon carbide (SiC/SiC). 
     In one embodiment, the surface  112  includes an environmental barrier coating (EBC) which protects the surface  112  from water vapor, heat, and other combustion gases. In another embodiment, the surface  112  includes a thermal barrier coating (TBC) which protects the surface  112  from heat. In yet another embodiment, at least one of the EBC and the TBC coats the exterior  138  of the inner shroud  102 , including both the surface  112  as well as the distal surface  140 . 
     In one embodiment, the turbine shroud assembly  100  includes a springless first biasing apparatus  108 . In another embodiment, the turbine shroud assembly  100  includes a springless second biasing apparatus  110 . As used herein, “springless” indicates that a biasing force, such as the first biasing force  116  applied to the inner shroud  102  or the second biasing force  122  applied to the damper block  106 , is not generated by a spring. In certain embodiments, a springless first biasing apparatus  108  or a springless second biasing apparatus  110  may include a spring provided that any included spring does not generate a biasing force applied to the inner shroud  102  or the damper block  106 . 
     In one embodiment, the first biasing apparatus  108  is driven by a pressurized fluid  142 . In another embodiment, the second biasing apparatus  110  is driven by a pressurized fluid  142 . The pressurized fluid  142  may be any fluid, including, but not limited to, air. Suitable sources for pressurized air include air from a gas turbine compressor. The first biasing force  116  and the second biasing force  122  are proportional to the pressure of the pressurized fluid  142  and the sectional area of the first biasing apparatus  108 . In a further embodiment, the pressurized fluid  142  is sourced at a fixed location in the gas turbine compressor, and the first biasing force  116  and the second biasing force  122  vary with the pressure generated by the gas turbine compressor. In another embodiment, the first biasing force  116  and the second biasing force  122  may be controlled by adjusting the pressure of the pressurized fluid  142 . 
     In one embodiment, the first biasing apparatus  108  includes at least one bellows  144  connecting to or contacting the inner shroud  102 . In a further embodiment, the at least one bellows  144  includes a first end  146  attached to the outer shroud  104  and a second end  148  configured to expand toward the hot gas path  114  in response to an increased internal pressure within the at least one bellows  144 . The expansion of the at least one bellows  144  exerts the first biasing force  116  on the inner shroud  102 . The second end  148  of the at least one bellows  144  may be attached to at least one pin  136  which connects to at least one projection  150  of the inner shroud  102 . In one embodiment, the second end  148  is attached to the at least one pin  136  by a stanchion  152 . 
     In one embodiment, the second biasing apparatus  110  includes at least one bellows  144  connecting to or contacting the damper block  106 . In a further embodiment, the at least one bellows  144  includes a first end  146  attached to the outer shroud  104  and a second end  148  configured to expand toward the hot gas path  114  in response to an increased internal pressure within the at least one bellows  144 . The expansion of the at least one bellows  144  exerts the second biasing force  122  on the damper block  106 . The second end  148  of the at least one bellows  144  may contact, directly or indirectly, the damper block  106 . 
     In one embodiment, the at least one bellows  144  hermetically caps a pressurized fluidic supply line  154 . As used herein, “hermetically caps” indicates that there is little or no leakage of pressurized fluid  142  from the region where the at least one bellows  144  joins with the pressurized fluidic supply line  154 , and that there is also little or no leakage of pressurized fluid  142  from the at least one bellows  144 . 
     Referring to  FIG. 2 , in one embodiment, the first biasing apparatus  108  includes at least one thrust piston  200  connecting to or contacting the inner shroud  102 . The at least one thrust piston  200  may include a piston head  202  and at least one piston seal  204 . In a further embodiment, the at least one thrust piston  200  is configured to urge the stanchion  152  in a direction  120  toward the hot gas path  114  in response to an increased pressure from the pressurized fluid  142 . The movement of the at least one thrust piston  200  exerts the first biasing force  116  on the inner shroud  102 . The piston head  202  may be attached to at least one pin  136  which connects to at least one projection  150  of the inner shroud  102 . In one embodiment, the piston head  202  is attached to the at least one pin  136  by a stanchion  152 . 
     In another embodiment, the second biasing apparatus  110  includes at least one thrust piston  200  connecting to or contacting the damper block  106 . The at least one thrust piston  200  may include a piston head  202  and at least one piston seal  204 . In a further embodiment, the at least one thrust piston  200  is configured to urge the stanchion  152  in a direction  120  toward the hot gas path  114  in response to an increased pressure from the pressurized fluid  142 . The movement of the at least one thrust piston  200  exerts the second biasing force  122  on the damper block  106 . The stanchion  152  may contact, directly or indirectly, the damper block  106 . 
     Referring to  FIG. 3 , in one embodiment, the first biasing apparatus  108  includes at least one spring  300  connecting to or contacting the inner shroud  102 . The at least one spring  300  may include a pressure screw  302 . The pressure screw  302  may be tightened to increase the compression of the at least one spring  300  or loosened to reduce the compression of the at least one spring  300 . In a further embodiment, the at least one spring  300  is configured to urge the stanchion  152  in a direction  120  toward the hot gas path  114 . The compression of the at least one spring  300  exerts the first biasing force  116  on the inner shroud  102 . The at least one spring  300  may be attached to at least one pin  136  which connects to at least one projection  150  of the inner shroud  102 . In one embodiment, the at least one spring  300  is attached to the at least one pin  136  by a stanchion  152 . 
     In another embodiment, the second biasing apparatus  110  includes at least one spring  300  connecting to or contacting the damper block  106 . The at least one spring  300  may include a pressure screw  302 . The pressure screw  302  may be tightened to increase the compression of the at least one spring  300  or loosened to reduce the compression of the at least one spring  300 . In a further embodiment, the at least one spring  300  is configured to urge the damper block  106  in a direction  120  toward the hot gas path  114 . The compression of the spring  300  exerts the second biasing force  122  on the damper block  106 . The at least one spring  300  may contact, directly or indirectly, the damper block  106 . 
     Referring to  FIG. 4 , the turbine shroud assembly  100  may include combinations of bellows  144 , thrust pistons  200  and springs  300 , or a sub-set thereof. By way of example (shown), the first biasing apparatus  108  may include at least one bellows  144 , the second biasing apparatus  110  may include at least one thrust piston  200 , and the third biasing apparatus  130  may include at least one spring  300 . These elements may be combined in any suitable combination, including in turbine shroud assemblies  100  having any number of biasing apparatuses. 
     Referring to  FIG. 5 , in one embodiment the at least one projection  150  of the inner shroud  102  includes an insertion aperture  500 . The insertion aperture  500  is arranged and disposed such that the at least one pin  136  may be inserted through the insertion aperture  500  to reversibly attach the inner shroud  102  to the first biasing apparatus  108 . 
     Referring to  FIGS. 1-4 , a method for loading a turbine shroud assembly  100  includes applying a first biasing force  116  exerted by a first biasing apparatus  108  to the inner shroud  102 , biasing the inner shroud  102  a first deflection distance  118  in a direction  120  toward a hot gas path  114  and away from an outer shroud  104 , and applying a second biasing force  122  exerted by a second biasing apparatus  110  to a damper block  106  disposed between the inner shroud  102  and the outer shroud  104 , biasing the damper block  106  a second deflection distance  124  in a direction  120  toward the hot gas path  114  and away from the outer shroud  104 . The second deflection distance  124  is greater than the first deflection distance  118 , loading the damper block  106  to the inner shroud  102 . In one embodiment, the first biasing apparatus  108  may be any suitable mechanism, including, but not limited to, at least one spring  300 , at least one bellows  144 , at least one thrust piston  200 , or a combination thereof. In another embodiment, the second biasing apparatus  110  may be any suitable mechanism, including, but not limited to, at least one spring  300 , at least one bellows  144 , at least one thrust piston  200 , or a combination thereof. 
     In one embodiment, loading a turbine shroud assembly  100  by biasing the inner shroud  102  in a direction  120  toward the hot gas path  114  and away from the outer shroud  104 , and biasing the damper block  106  in a direction  120  toward the hot gas path  114  and away from the outer shroud  104 , wherein the second deflection distance  124  is greater than the first deflection distance  118 , loading the damper block  106  to the inner shroud  102 , reduces damaging vibrations in the inner shroud  102 , in comparison to a turbine shroud assembly  100  lacking the damper block  106 . Without being bound by theory, it is believed that such damaging vibrations may be exacerbated in a turbine shroud assembly  100  in which the space between the inner shroud  102  and the outer shroud  104  is not pressurized by a fluid, such as, by way of example only, pressurized fluid  142 . 
     Each turbine shroud assembly  100  in a turbine may be individually adjusted to account for out of roundness of a turbine stator assembly as well as individualized blade/bucket tip clearance, optimizing turbine efficiency. Additionally, the first biasing apparatus  108  and the third biasing apparatus  130  may be individually adjusted within a turbine shroud assembly  100  to adjust the first biasing force  116  and the third biasing force  132  in order to optimize loading under conditions where the pressure of the hot gas path  114  varies across the surface  112  of the inner shroud  102 . Without being bound by theory, it is believed that such variations in the hot gas path  114  varies across the surface  112  of the inner shroud  102  may be caused by the operation of blades/buckets in close proximity to the inner shroud  102 , which may cause higher pressure at a leading edge of an inner shroud  102  in comparison to a trailing edge. Adjustment of the first biasing apparatus  108  and the third biasing apparatus  130  may also account for natural frequencies of the inner shroud  102 . 
     While the invention has been described with reference to one or more embodiments, it will be understood by those skilled in the art 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.