Abstract:
Disclosed is a steam turbine including a turbine rotor, a generator end having a generator end first stage with a first reaction, and a turbine end having a turbine end first stage with a second reaction not equal to the first reaction. The steam turbine includes a tub section disposed between the generator end and the turbine end, the turbine rotor and the tub section defining an annulus therebetween. A difference between the first reaction and second reaction is capable of urging a steam flow through the annulus for reducing a temperature of the turbine rotor. A method of cooling the turbine rotor is also disclosed.

Description:
BACKGROUND 
       [0001]    The subject invention relates to steam turbines. More particularly, the subject invention relates to cooling a tub region of a double-flow steam turbine. 
         [0002]    Double-flow steam turbines typically include two parallel flow turbine ends arranged on a common shaft. A tub section is often located between the turbine ends and disposed around the shaft. Steam flows into the steam turbine radially inwardly toward the tub section, and the steam flow then divides, turns axially, and flows in opposing directions to enter each of the two parallel flow turbine ends. 
         [0003]    Steam flow may become stagnant between the rotor and the tub section of the double-flow steam turbine resulting in a high temperature on the rotor due to windage heating of the stagnant steam. High rotor temperature potentially shortens the useful life of the rotor and may lead to failure of the steam turbine. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0004]    A steam turbine is provided which includes a turbine rotor, a first generator end having a generator end first stage with a first reaction, and a turbine end having a turbine end first stage with a second reaction not equal to the first reaction. The steam turbine includes a tub section disposed between the generator end and the turbine end, the turbine rotor and the tub section defining an annulus therebetween. A difference between the first reaction and second reaction is capable of urging a steam flow through the annulus for reducing a temperature of the turbine rotor. A method for cooling a tub section of the steam turbine includes urging a steam flow into the steam turbine including a turbine rotor, a generator end having a generator end first stage with a first reaction, a turbine end having a turbine end first stage with a second reaction less than the first reaction, and a tub section disposed between the generator end and the turbine end, the turbine rotor and the tub section defining an annulus therebetween. The method further includes flowing the steam flow through the generator end first stage and urging at least a portion of the steam flow through the annulus, by a difference between the second reaction and the first reaction for reducing the temperature of the turbine rotor. The portion of the steam flowed is then flowed from the annulus into the turbine end. 
         [0005]    These and other advantages and features will become more apparent from the following description taken in conjunction with the drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]    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 objects, features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which: 
           [0007]      FIG. 1  is a schematic view of an example of a double-flow steam turbine; 
           [0008]      FIG. 2  is a cross-sectional view of an example of a double-flow steam turbine having a cooling flow through a tub section; and 
           [0009]      FIG. 3  is a cross-sectional view of another example of a double-flow steam turbine having a cooling flow through a tub section. 
       
    
    
       [0010]    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 
       [0011]    Shown in  FIG. 1  is a schematic representation of a double-flow steam turbine  10 . Steam turbine  10  includes a generator end  12  disposed nearest to a generator (not shown) and a turbine end  14  disposed farthest from the generator, and the generator end  12  and turbine end  14  may be disposed in an outer case  16 . A double flow tub section  18  is disposed axially between the generator end  12  and the turbine end  14  and radially outboard of a rotor  20 . The rotor  20  may comprise, for example, a drum rotor or at least one rotor disk disposed on a rotor shaft. The rotor  20  and the tub section  18  are configured and disposed to define an annulus  22  between the rotor  20  and the tub section  18 . Steam enters the steam turbine  10  at an inlet  24  which is disposed radially outboard of the rotor  20  and the tub section  18 . Steam entering the steam turbine  10  at the inlet  24  flows toward the tub section  18 , divides, and then enters either of the generator end  12  or the turbine end  14 . 
         [0012]    Referring now to  FIG. 2 , the generator end  12  includes a generator end first stage  26  which comprises a plurality of generator end nozzles  28  which in some embodiments are disposed in the tub section  16 , and a plurality of generator end buckets  30 . The generator end buckets  30  are mounted on the rotor  20 . In some embodiments, the rotor  20  may include a plurality of generator end balance holes  32  which may include wheel holes and/or dovetail holes located radially inboard from the generator end buckets  30 , or alternatively in the generator end buckets  30 . Similarly, the turbine end  14  includes a turbine end first stage  34  which comprises of a plurality of turbine end nozzles  36  and a plurality of turbine end buckets  38 . The turbine end buckets  38  are on the rotor  20 . In some embodiments, a plurality of turbine end balance holes  40  may be located radially inboard from the turbine end buckets  38 , or alternatively in the turbine end buckets  38 . 
         [0013]    The generator end  12  and turbine end  14  are configured to produce a pressure differential between a first annulus end  42  and a second annulus end  44  so that a cross-flow  46  through the annulus  22  is created by the pressure differential. In some embodiments, this is achieved by configuring one of the generator end first stage  26  or the turbine end first stage  34  to have a negative reaction and the other of the generator end first stage  26  or the turbine end first stage  34  to have a positive reaction. “Reaction”, as used herein, refers to a ratio of a static pressure drop over the buckets to a total pressure drop across both the nozzles and buckets for the particular stage. In a stage having negative reaction, a bucket exit pressure is greater than a nozzle exit pressure. 
         [0014]    In the embodiment of  FIG. 2 , the generator end first stage  26  is configured with a negative reaction, and the turbine end first stage  34  is configured with a positive reaction. Further, an exit pressure of the generator end buckets  30  is greater than an exit pressure of the turbine end buckets  38 . Configuring the steam turbine  10  to include a negative reaction at the generator end first stage  26  and a positive reaction at the turbine end first stage  34  initiates a flow pattern to cool the rotor  20  in the annulus  22 . When the steam turbine  10  is operating, this results in a steam flow as shown by arrows  46 . The steam flow  46  passes through the generator end nozzles  28  and through the corresponding generator end buckets  30 . A portion of the flow proceeds to a generator end second stage  48  while another portion flows through the generator end balance holes  32 , or other through holes or pathways, through rotor  20  and proceeds to the annulus  22  between the tub section  18  and the rotor  20 . The steam flow  46  proceeds through the annulus  22  to turbine end  14 . The steam flow  46  flows through the turbine end balance holes  40 , or other holes or pathways, and to a turbine end second stage  50 . The steam flow  46  through the annulus  22  provides cooling to rotor  20  adjacent to the annulus  22  thereby limiting exposure of the rotor  20  to temperatures that would shorten the useful life of the rotor  20  and potentially damage the steam turbine  10 . Similarly, it is to be appreciated that configuring the generator end first stage  26  to have a positive reaction and the turbine end first stage  34  to have a negative reaction would establish a similar steam flow  46  through the annulus  22  but in the opposite direction. 
         [0015]    In some embodiments, generator end balance holes  32  and/or turbine end balance holes  40  may not be provided. In a steam turbine  10  with such a configuration, a portion of the steam flow  46  passes between the generator end nozzles  28  and generator end buckets  30  and into the annulus  22 . The steam flow  46  proceeds through the annulus  22  to turbine end  14 , and between turbine end nozzles  36  and the turbine end buckets  38  and then through the turbine end buckets  38 . 
         [0016]    In some embodiments, the steam turbine  10  is configured such that both the generator end first stage  26  and turbine end first stage  34  have positive reactions, but the reaction of one of the generator end first stage  26  and turbine end first stage  34  is greater than the other of the generator end first stage  26  and turbine end first stage  34 . Referring to  FIG. 3 , this configuration produces a cooling flow  52 . The cooling flow  52  proceeds through the generator end nozzles  28 , a portion continuing through the generator end buckets  30  and another portion proceeding between the generator end nozzles  28  and generator end buckets  30  and into the annulus  22 . The cooling flow  52  proceeds through the annulus  22  and to the turbine end  14  where it passes between the turbine end nozzles  36  and the turbine end buckets  38  and then through the turbine end buckets  38 . The cooling flow  52  has a higher temperature than the steam flow  46  since the cooling flow  52  does not have energy removed by, and thus temperature lowered by, passing through the generator end buckets  30  prior to entering the annulus  22 . 
         [0017]    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.