Abstract:
A steam turbine includes a rotor having a plurality of early stages and a stator portion surrounding a portion of the rotor and arranged such that a leakage region exists between the stator portion and the rotor and having a cooling steam channel that passes cooling steam from one portion of the stator portion to the leakage region. The turbine also includes at least one cooling steam transmission channel axially displaced about the rotor that receives the cooling steam from the leakage region and provides it to at least a portion of the early stages.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The subject matter disclosed herein relates to steam turbines and, in particular, to providing cooling to rotors of the turbine during operation. 
         [0002]    In power generation systems where waste heat from one portion is used to heat steam in a steam turbine (e.g., a combined cycle power plant (CCPP), or multi-stage steam turbine), the first portion generates waste heat and the steam turbine recovers that heat to produce electricity. For example, in a CCPP a gas turbine generator generates electricity and the waste heat is used to make steam to generate additional electricity via a steam turbine. Utilizing the waste heat to make steam for use in a steam turbine enhances the efficiency of electricity generation. 
         [0003]    An increase in temperature of the steam passing into an inlet throttle of a steam turbine has been shown to have a direct effect on the efficiency of entire CCPP. Indeed, an increase in the steam inlet temperature of around 50° F. attributes to a considerable increase in the plant efficiency. Experience has shown, however, that even 50° F. increase in the steam temperature may affect the steam turbine&#39;s rotor life. 
         [0004]    The problem is usually overcome by using more temperature resistant rotor material. Such a solution, however, typically increases costs. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0005]    According to one aspect of the invention, a steam turbine that includes a rotor having a plurality of early stages is provided. The turbine includes a stator portion surrounding a portion of the rotor and arranged such that a leakage region exists between the stator portion and the rotor and having a cooling steam channel that passes cooling steam from one portion of the stator portion to the leakage region. The turbine also includes at least one cooling steam transmission channel axially displaced about the rotor that receives the cooling steam from the leakage region and provides it to at least a portion of the early stages. 
         [0006]    According to another aspect of the invention, a method of cooling one or more early stages in a steam turbine is provided. The method includes providing high-pressure low-temperature steam through cooling steam channels formed in a stator component that surrounds at least portion of a rotor to a leakage region; passing the high-pressure low-temperature steam provided to the leakage region through cooling steam transmission channels formed in a rotor; and passing the high-pressure low-temperature steam through holes in the cooling steam transmission channels to contact the one or more early stages. 
         [0007]    According to yet another aspect, a power plant including a steam turbine is provided. The steam turbine includes a rotor having a plurality of early stages and a stator component surrounding a portion of the rotor and arranged such that a leakage region exists between the stator component and the rotor and having a cooling steam channel that passes cooling steam from one portion of the stator component to the leakage region. The steam turbine also includes at least one cooling steam transmission channel axially displaced about the rotor that receives the cooling steam from the leakage region and provides it to at least a portion of the early stages. 
         [0008]    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 
         [0009]    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: 
           [0010]      FIG. 1  is shows a block diagram of a combined cycle power plant; 
           [0011]      FIG. 2  is cut-away front view of a portion of steam turbine that may be utilized in a combined cycle power plant; 
           [0012]      FIG. 3  is a more detailed depiction of the portion of a steam turbine shown in  FIG. 2 ; 
           [0013]      FIG. 4  is a cut-away front view of a portion of steam turbine according to one embodiment; 
           [0014]      FIG. 5  shows possible steam paths for the portion of the steam turbine shown in  FIG. 4 ; 
           [0015]      FIG. 6  shows one manner in which a cooling steam path may be created in a stator portion according to one embodiment; and 
           [0016]      FIG. 7  shows a side view of a stator portion having a cooling steam transmission channel passing there through. 
       
    
    
       [0017]    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 
       [0018]    As discussed above, the increased temperatures that allow for greater combined cycle efficiency may not be beneficial to rotors in a steam turbine portion of a combined cycle power plant. Of course, the same problem could exist in stand-alone steam turbines. Embodiments disclosed herein may reduce or eliminate these problems by providing a cooling steam to a few initial stages of the rotor. This cooling steam may help keep these initial stages cool and, therefore, help avoid the need to replace the entire rotor with higher temperature capability material. In one embodiment, the cooling steam need only be provided to an initial few stages of the rotor through which the main steam temperature drops enough to be withstood by lower temperature resistant material. 
         [0019]      FIG. 1  shows a block diagram of a combined cycle power plant  100  coupled to an electrical substation  102 . The combined cycle power plant  100  creates electricity and provides it to the electrical substation  102 . 
         [0020]    The combined cycle power plant  100  may include a gas turbine portion  104  and a steam turbine portion  106 . The gas turbine portion  104  includes a compressor  108  that includes an air intake  107 . The compressor  108  is coupled to a combustor  109  that combusts a gas or fuel oil in a stream of compressed air. The combustor  109  is coupled to a turbine  110 . The turbine  110  extracts energy from a flow of hot gas produced by combustion of gas or fuel. In one embodiment, the extracted energy is converted to electricity by a first generator  112 . 
         [0021]    The output  113  of the gas turbine  110  is an exhaust gas that may be used in other cycles of the combined system  100 . The exhaust gas may be used, for example, to heat steam for use in the steam turbine portion  106 . To that end, the system combined cycle power plant may include a heat recovery steam generator (HRSG)  118  coupled to the output  113 . 
         [0022]    The HRSG  118  receives the exhaust gas and uses it to heat steam/water to an elevated temperature. The high temperature steam is provided via steam channel  120  to the steam turbine portion  106 . 
         [0023]    The steam turbine portion  106  includes a steam turbine  114 . The steam turbine  114  receives steam from the HRSG  118 . The steam is passed over rotors in the steam turbine  114  causing portions of the steam turbine  114  to rotate. This rotational energy is converted to electricity by the second generator  116  and the electricity is provided to the electrical substation  102 . 
         [0024]      FIG. 2  shows a cut-away front view of a portion of a steam turbine  114 . The portion of the steam turbine  114  shown in  FIG. 2  includes a stator component  202 . The stator component  202  is typically cylindrical and surrounds a portion of a rotor  204 . The rotor  204  includes early stages  206  to which high-pressure high-temperature steam is passed via one or more steam channel(s)  208 . The high-pressure high-temperature steam causes the rotor  204  to turn and, thereby, the steam turbine  114  may be used to create electricity. Another portion of the rotor  204  and at least a portion of stator component  202  are surrounded by a casing  210 . The steam channel(s)  208  typically pass through the casing  210 . 
         [0025]    As discussed above, the initial few stages (shown in dashed boxes  212 , also referred to herein as “early stages”) of the rotor  204  may be damaged if the temperature of the incoming high-pressure high-temperature steam (received, for example, from HRSG  118  ( FIG. 1 )) is too high. One approach has been to cool a portion of the steam separately from the remainder of the steam and to recombine the steam to create cooler steam before it is provided to the rotors. Such an approach may be effective but it means that heat is lost and requires the use of a heat exchanger to reduce the temperature of cooled steam. 
         [0026]      FIG. 3  shows a more detailed depiction of a portion of the steam turbine  114  shown in  FIG. 2 . The portion of the steam turbine  114  shown in  FIG. 3  includes a stator component  202 . The rotor  204  includes early stages  206  to which high-pressure high-temperature steam is passed via one or more steam channel(s)  208 . The early stages  206  include inlet nozzles  302 ,  304 ,  306  and  308 . Of course the early stages  206  could include more or fewer inlet nozzles shown in  FIG. 3 . The early stages  206  also include rotor blades  303 ,  305 ,  307  and  309 . Of course the early stages  206  could include more or fewer rotor blades than those shown in  FIG. 3 . The steam channel(s)  208  typically pass through the casing  210 . Steam enters the steam channel(s)  208  as indicated by arrow A and passes down the length of the rotor  204  (through the early stages  206 ) as indicated by arrow B. 
         [0027]    As discussed above, in some cases the steam that enters the early stages  206  via the steam channels  208  (as indicated by arrow A) may be at a temperature that damages the early states  206 . Embodiments disclosed herein may alleviate such a problem by providing cooling steam in form of a relatively high-pressure low-temperature steam to the initial few stages of the steam turbine rotor. The steam may be admitted through a channel in the stator and passed through axial displaced cooling steam transmission channels that pass through the rotor and are close to an outer edge of the rotor. The steam may be from an external source or from an internal source such as exhaust or intermediate stages of a high pressure turbine and passed through the cooling steam channels provided in the stator. The steam is released near the stage 1 nozzle. A portion of the admitted steam passes through the end packing seals, a portion joins back to the main flow and the rest passes through the cooling steam transmission channel. The steam passing through the cooling steam transmission channels cools the rotors and reduces the amount of heat penetrating into the rotor further. 
         [0028]      FIG. 4  shows an example of a portion of a steam turbine  400  according to one embodiment. In this embodiment, the shown portion of the steam turbine  400  includes a stator component  402  that surround at least a portion of a rotor. A casing  404  surrounds at least a portion of the stator component  402 . The casing  404  may also surround a portion of the rotor  405 . The stator component  402  includes a cooling steam channel  406 . The cooling steam channel  406  may provide high-pressure low-temperature steam through the stator component  402 . The cooling steam channel  406  may, in one embodiment, also pass through the casing  404 . 
         [0029]    The cooling steam channel  406  may be coupled to a steam source  420 . The steam source  420  may be a high-pressure low-temperature steam source in one embodiment. High-pressure is a term known in the steam turbine art and shall be so interpreted herein. Low-temperature, as used herein with respect to steam, shall refer to steam that is of a lower temperature than steam provided through steam channel  208 . In one embodiment, the low temperature steam is at least 50° C. cooler than the steam provided through the steam channel  208 . Of course, the low temperature steam could be more or less than 50° C. cooler than the steam provided through the steam channel  208 . 
         [0030]    In one embodiment, the cooling steam channel  208  may provide steam through the casing  404  and the stator component  402  to an inlet of a packing flow leakage region  422  which is located near the first stage nozzle  410 . The packing flow leakage region  422  may be in fluid communication with one or more cooling steam transmission channels  408 . Each cooling steam transmission channel  408  is an axial fluid (or steam) transport mechanism such as, for example, a pipe. The cooling steam transmission channel  408  is arranged such that it may provide steam to one or more initial stages (e.g. rotors  411  and  414 ) of the rotor  405 . In one embodiment, holes are formed in the cooling steam transmission channel  408  such that steam passing there through may cool the rotors. The steam passes through the cooling steam transmission channel  408  in the direction indicated by arrow D. In general, radial slots may be provided on the bucket shanks of the last stage intended to be cooled. For example, the last stage is shown by rotor blade  424  of  FIG. 4 . This allows the high-pressure lower-temperature steam to return to the main flow path A thereby avoiding the high temperature main flow path steam entering into the cooling holes of further downstream stages. 
         [0031]      FIG. 5  shows a detailed depiction of the paths that may be taken by the high-pressure low-temperature steam (also referred to as “cooling steam”) in a portion of a steam turbine. The cooling steam is provided to the inlet  502  of the packing flow leakage region  422  as indicated by arrow C. Some of the cooling steam flows into the main flow path A as indicated by arrow F. Another portion of the cooling steam flows in the packing flow leakage region  422  as indicated by arrow E. The majority of the steam, however, passes through cooling steam transmission channel  408  as indicated by arrow D. The cooling steam transmission channel  408  has radial holes in either bucket shank or the rotor or both. These radial holes allow the low temperature high pressure steam to flow back into the high pressure high temperature steam flow shown by arrow A. It shall be understood that the inlet  502  may provide an inlet into an annulus to which multiple cooling steam transmission channels  408  are in fluid communication. 
         [0032]    In one embodiment, the cooling steam channel(s)  406  may be formed in the stator component  402  when it is constructed. In another embodiment, the cooling steam channel(s)  406  may be provided to a previously formed stator component  402 . 
         [0033]      FIG. 6  shows a cut-away front view of two portions,  402   a  and  402   b,  of a stator component  402 . The two portions may have been cut from a pre-formed stator component  402 . The second portion  402   b  has a groove  602  formed therein. This groove  602  allows steam to pass through the stator component  402  when portions  402   a  and  402   b  are joined together as indicated by arrow Z. Of course, the groove  602  could be formed in the first portion  402   a  rather than the second portion  402   b,  or in both. 
         [0034]      FIG. 7  shows a side view of stator component  202  according to one embodiment. The stator component  202  surrounds at least a portion of a rotor  204 . The stator component  202  includes a cooling steam channel  406  as described above. In this embodiment, the cooling steam transmission channel  406  includes a first portion  702  and an angled portion  704 . The angled portion  704  may be at any angle relative to the first portion  702  so long as it provides a path form the first portion  702  to the transmission holes (not shown) in the rotor  204 . In general, the angled portion cooling stream channel  406  may reduce the pressure drop of the steam while entering the transmission channels in the rotor. 
         [0035]    It should be noted that the cross section of the cooling steam transmission channel in any of the embodiments described above, may take one a variety of different shapes without departing from the teachings herein. For instance, the cooling steam channel may be round or elliptical in cross section. 
         [0036]    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.