Patent Publication Number: US-7713023-B2

Title: Steam turbine nozzle box and methods of fabricating

Description:
BACKGROUND OF THE INVENTION 
   This invention relates generally to steam turbines and, more particularly, to a nozzle box for use with a steam turbine. 
   At least some known steam turbines include a nozzle box that facilitates channeling fluid towards a first stage of a turbine. At least some known nozzle boxes each include a plurality of inlets, an annular region, and a plurality of discharge nozzles. The inlets channel steam into the annular region. Because the steam discharged from each inlet typically varies in pressure, the annular region facilitates mixing the steam discharged from the various inlets to provide a substantially evenly distributed pressure of steam throughout the region. The steam is discharged from the annular region through the plurality of nozzles towards the first stage of turbine rotors. 
   The annular regions of at least some known nozzle boxes have a circular cross-section. Moreover, at least some known nozzle box inlets are oriented such that steam is discharged into the annular region in a direction that is substantially perpendicular to a line extending tangentially to the region. However, the circular cross-section of the annular region and the orientation of the inlets may result in an uneven flow distribution throughout the annular region such that portions of the annular region may be deprived of steam flow. Such uneven flow may create an uneven steam pressure distribution which may induce vibrations within the turbine when the steam is discharged through the nozzles at uneven pressures. Continued operation with such vibrations may decrease the useful life of the turbine and/or increase maintenance costs associated with the turbine. 
   BRIEF DESCRIPTION OF THE INVENTION 
   In one aspect, a method of fabricating a steam turbine nozzle box is provided, wherein the method includes forming an annular chamber defined by a radially outer wall and a radially inner wall and coupling a plurality of inlets in flow communication with the annular chamber such that steam is discharged from each of the plurality of inlets into the chamber at an oblique discharge angle with respect to an inlet axial centerline. 
   In another aspect, a steam turbine nozzle box is provided, wherein the nozzle box includes an annular chamber defined by an outer annular wall and an inner annular wall that is radially inward from the outer annular wall and a plurality of inlets coupled in flow communication with the annular chamber. The inlets are positioned to facilitate discharging steam into the annular chamber at an oblique discharge angle with respect to an inlet axial centerline. 
   In a further aspect, a steam turbine is provided, wherein the steam turbine includes a turbine and a nozzle box configured to channel steam into the nozzle box for use with the turbine. The nozzle box includes an annular chamber, a plurality of inlets, and a plurality of nozzles. The annular chamber is defined by an outer annular wall and an inner annular wall that is radially inward from the outer annular wall. The plurality of inlets are coupled in flow communication with the annular chamber such that the inlets discharge steam therefrom into the annular chamber at an oblique discharge angle with respect to an inlet axial centerline. The plurality of nozzles are coupled in flow communication with the annular chamber and are configured to discharge steam towards the turbine. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a cross-sectional schematic illustration of an exemplary opposed-flow steam turbine engine; 
       FIG. 2  is a perspective view of a nozzle box that may be used with the engine shown in  FIG. 1 ; 
       FIG. 3  is a partial cross-sectional view of the nozzle box shown in  FIG. 2 ; 
       FIG. 4  is a side view of a portion of a known flowpath through a nozzle box; 
       FIG. 5  is a perspective view of the flowpath shown in  FIG. 4 ; 
       FIG. 6  is a side view of a portion of a flowpath through the nozzle box shown in  FIGS. 2 and 3 ; 
       FIG. 7  is a perspective view of the flowpath shown in  FIG. 6 ; and 
       FIG. 8  is a schematic cross-sectional view of the flowpaths shown in  FIGS. 4 and 5  superimposed on a cross-sectional view of the flowpaths shown in  FIGS. 6 and 7 . 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1  is a cross-sectional schematic illustration of an exemplary opposed-flow steam turbine engine  100  including a high pressure (HP) section  102  and an intermediate pressure (IP) section  104 . An HP shell, or casing,  106  is divided axially into upper and lower half sections  108  and  110 , respectively. In the exemplary embodiment, shells  106  and  108  are inner casings. Alternatively, shells  106  and  108  are outer casings. A central section  118  positioned between HP section  102  and IP section  104  includes a high pressure steam inlet  120  and an intermediate pressure steam inlet  122 . A nozzle box (not shown in  FIG. 1 ) is fluidly coupled between each of high pressure steam inlet  120  and high pressure section  102 , and intermediate pressure steam inlet  122  and intermediate pressure section  104 . 
   During operation, high pressure steam inlet  120  receives high pressure/high temperature steam from a steam source, for example, a power boiler (not shown in  FIG. 1 ). Steam flows from high pressure steam inlet  120  through a first nozzle box (not shown in  FIG. 1 ), through an inlet nozzle  136 , and through HP section  102 , wherein work is extracted from the steam to rotate a rotor shaft  140  via a plurality of turbine blades, or buckets (not shown in  FIG. 1 ) that are coupled to shaft  140 . 
   In the exemplary embodiment, steam turbine  100  is an opposed-flow high pressure and intermediate pressure steam turbine combination. Alternatively, the present invention may be used with any individual turbine including, but not being limited to low pressure turbines. In addition, the present invention is not limited to being used with opposed-flow steam turbines, but rather may be used with steam turbine configurations that include, but are not limited to single-flow and double-flow turbine steam turbines. 
     FIG. 2  is a perspective view of a steam turbine nozzle box  200  that may be used with steam turbine engine  100 . In the exemplary embodiment, nozzle box  200  includes an annular chamber  202  and two inlets  204  coupled in flow communication with annular chamber  202 , wherein each inlet  204  has an axial centerline C 1 .  FIG. 3  is a partial cross-sectional view of nozzle box  200  and annular chamber  202 . In the exemplary embodiment, only a semi-circular half of annular chamber  202 , is illustrated. In the exemplary embodiment, nozzle box  200  includes a vertical centerline C 1  spaced equidistant between each inlet  204 . In alternative embodiments, nozzle box  200  may include more or less than two inlets  204 . 
   Annular chamber  202  includes a first section  206 , a second section  208 , and a center section  210  extending integrally therebetween. In an embodiment having more or less than two inlets  204 , annular chamber  202  may include more or less than three sections. Annular chamber  202  also includes a flowpath  212  defined by an inner annular wall  214  and an outer annular wall  216  that is radially outward from inner annular wall  214 . Flowpath  212  includes a flowpath first section  218 , a flowpath second section  220 , and a flowpath center section  222 . Specifically, in the exemplary embodiment, flowpath first section  218  is defined within chamber first section  206 , flowpath second section  220  is defined within chamber second section  208 , and flowpath center section  222  is defined within chamber center section  210 . Furthermore, each inlet  204  includes a flowpath  224  formed therethough that is coupled in flow communication with flowpath  212 . Specifically, a first inlet flowpath  226  is coupled in flow communication with flowpath first section  218 , and a second inlet flowpath  228  is coupled in flow communication with flowpath second section  220 . 
   During operation steam flows through inlets  204  into annular chamber  202 . Specifically, steam is channeled through inlet flowpaths  226  and  228  and is discharged into annular chamber  202 , wherein steam discharged from inlet flowpath  226  enters flowpath first section  218 , and steam discharged from inlet flowpath  228  enters flowpath second section  220 . Within annular chamber  202  flowpath first section  218  and flowpath second section  220  are coupled in flow communication with flowpath center section  222 , such that annular chamber  202  facilitates providing a unitary flowpath  212  having an evenly distributed pressure therethrough. Specifically, steam channeled through inlet flowpaths  226  and  228  is mixed within annular chamber  202  such that steam discharged from nozzle box  200  has an even temperature and pressure. Steam is discharged from nozzle box  200  through a plurality of nozzles (not shown in  FIG. 2 ) into a first stage of a turbine. The mixture of steam within annular chamber  202  facilitates discharging steam through each of the plurality of nozzles at an equal temperature and pressure. As such, vibrations within the first stage of the turbine are facilitated to be reduced. 
     FIG. 4  is a side view of a portion of a known flowpath  250  as defined by a portion of a known nozzle box.  FIG. 5  is a perspective view of flowpath  250 . Specifically,  FIGS. 4 and 5  illustrate only a quarter-section of an annular flowpath  250 . Flowpath  250  includes an inlet flowpath  252 , a flowpath first section  254 , and a flowpath center section  256 . Flowpath sections  254  and  256  have substantially circular cross-sectional areas A 1  and A 2 , respectively, defined at their intersection with inlet flowpath  252 . Furthermore, in the exemplary embodiment, inlet flowpath  252  also has a circular cross-sectional area A 3 . Moreover, flowpath center section  256  tapers to a triangular cross-sectional area A 4  at a distance D 1  from inlet flowpath  252 . 
   During operation, steam channeled through inlet flowpath  252  is discharged into the known annular chamber through a discharge path P 1  that is substantially parallel to an inlet flowpath centerline C 3 . Steam discharged from inlet flowpath  252  is channeled through flowpaths  254  and  256 . However, because steam is discharged along path P 1  into a spherical terminus S 1 , the steam does not mix evenly throughout flowpaths  254  and  256 . Moreover, the cross-sectional areas A 1  and A 2  of flowpaths  254  and  256  limit the flow of steam throughout flowpaths  254  and  256 , such that steam is not dispersed into an upper area  258  of center section flowpath  256 . 
   Because steam flow dispersement is limited, steam-deprived pockets may form within the known annular chamber. For example, at least one steam-deprived pocket may form in area  258 . The steam-deprived pockets result in an uneven distribution of steam pressure and temperature within the known annular chamber, which further results in an uneven distribution of steam pressure discharged from the known nozzle box. Specifically, the nozzles of at least some known nozzle boxes discharge steam at varying temperatures and pressures. However, discharging steam into a turbine at uneven pressures and temperatures may cause vibrations within the turbine, which may result in increasing maintenance costs of the turbine and/or may decrease the life-span of the turbine. 
     FIG. 6  is a side view of a portion of nozzle box flowpath  212  as defined by annular chamber  202 .  FIG. 7  is a perspective view of flowpath  212 . Furthermore,  FIGS. 6 and 7  illustrate only a quarter-section of annular flowpath  212 . In the exemplary embodiment, inlet flowpath  226  is defined by inlet  204 , flowpath first section  218  is defined by chamber first section  206 , and flowpath center section  222  is defined by chamber center section  210 . 
   Both flowpath first section  218  and flowpath center section  222  have respective elliptical cross-sectional areas A 5  and A 6  as defined by their intersection with inlet flowpath  226 . Cross-sectional area A 6  transitions to a rectangular cross-sectional area A 7  a distance D 1  from inlet flowpath  226 . Inlet flowpath  226  includes a circular cross-sectional area A 8 , and a radius portion  300 . Radius portion  300  is defined at an inlet flowpath end  302  positioned at an intersection between inlet flowpath  226 , first section flowpath  218 , and center section flowpath  222 . 
   During operation, steam channeled through inlet flowpath  226  is discharged into annular chamber  202  in a discharge path P 2  that is defined at an oblique angle θ 1  with respect to inlet centerline C 1  and at a tangent to the inner wall of flowpaths  218  and  222 . More specifically, in the exemplary embodiment, path P 2  is oriented such that steam is discharged towards the second nozzle box inlet  204 . As such, in the exemplary embodiment, steam discharged from the first inlet  204  is discharged towards the second inlet  204 , and stream discharged from the second inlet  204  is discharged towards the first inlet  204 . In alternative embodiments, steam may be discharged in any other suitable direction that is oblique with respect to inlet centerline C 1 . 
   The combination of the orientation of path P 2  and cross-sectional areas A 5  and A 6  facilitates mixing steam discharged through inlet flowpath  226 . Specifically, steam mixes within flowpaths  218  and  222 . Moreover, cross-sectional areas A 5  and A 6  of flowpaths  218  and  222  provide a larger torodial area within which steam can mix, enabling the steam to fill the entirety of flowpaths  218  and  222 . More specifically, steam is enabled to fill steam-deprived pockets, such as a pocket  304  that may be formed in flowpath  222  near vertical centerline C 2 . Furthermore, the greater tordial area in combination with steam flow along path P 2  facilitates an enhanced mixing of steam within annular chamber  202 . As such, pressure and temperature throughout annular chamber  202  is facilitated to distribute evenly. Resultantly, steam discharged through each nozzle of nozzle box  200  is facilitated to have an even pressure and temperature distribution when discharged into a turbine. As such, vibrations within the turbine are facilitated to be reduced, enabling greater turbine efficiency and life-span. 
     FIG. 8  is a cross-sectional view of flowpath  212  superimposed on a cross-sectional view of flowpath  250 . Specifically,  FIG. 8  is a comparison of circular cross-sectional areas A 1  and A 2  compared to elliptical cross-sectional areas A 5  and A 6 . Flowpath  250  is indicated by dashed lines  350 , and flowpath  212  is indicated by solid lines  352 . 
   The above-described methods and apparatus facilitate improving turbine efficiency by evenly distributing the pressure and temperature of steam discharged from a nozzle box. Specifically, the nozzle box includes an elliptical cross-sectional area and an inlet flowpath that discharges steam into the nozzle box at an oblique angle with respect to the nozzle box inlets. The elliptical cross-sectional area and the enhanced flowpath facilitate evenly distributing steam throughout the nozzle box. As such, steam-deprived pockets within the nozzle box are prevented, and steam pressure and temperature throughout the nozzle box is facilitated to be evenly distributed. By evenly distributing steam pressure and temperature throughout the nozzle box, the pressure and temperature of steam discharged into the turbine is likewise evenly distributed, facilitating fewer vibrations within the turbine, and, thus, increasing the useful life of the turbine and decreasing maintenance costs associated with the turbine. 
   As used herein, an element or step recited in the singular and proceeded with the word “a” or “an” should be understood as not excluding plural said elements or steps, unless such exclusion is explicitly recited. Furthermore, references to “one embodiment” of the present invention are not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the recited features. 
   Although the apparatus and methods described herein are described in the context of a nozzle box for a steam turbine, it is understood that the apparatus and methods are not limited to nozzle boxes or steam turbines. Likewise, the nozzle box components illustrated are not limited to the specific embodiments described herein, but rather, components of the nozzle box can be utilized independently and separately from other components described herein. 
   While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims.