Abstract:
An air bypass band assembly includes a transition piece of a gas turbine, the transition piece having at least one opening therein to allow a flow of air to pass through the at least one opening. The air bypass band assembly also includes a band that is movable between at least two positions, a first one of the at least two positions being a closed position where the at least one opening is closed to prevent the flow of air from flowing through the at least one opening, a second one of the at least two positions being an open where the at least one opening is opened to allow the flow of air to flow through the at least one opening. The air bypass band assembly further includes a mechanism that moves the band between the at least two positions.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of Russian Patent Application No. 2010101978, entitled “GAS TURBINE TRANSITION PIECE AIR BYPASS BAND ASSEMBLY”, filed Jan. 15, 2010, which is incorporated herein by reference in its entirety. 
       BACKGROUND OF THE INVENTION 
       [0002]    The subject matter disclosed herein relates to gas turbine combustors, and, more particularly, to a gas turbine transition piece air bypass band assembly that allows for excess compressor discharge air to be bypassed during certain gas turbine operating conditions. 
         [0003]    Gas turbines can be somewhat limited as to the amount that the combustor exit temperature can be reduced by the allowed levels of carbon monoxide (CO) produced by the gas turbine. Typically, the combustor exit temperature remains relatively high to ensure that the gas turbine does not exceed permitted levels of CO emissions. To keep combustor exit temperatures high enough to remain at relatively low CO emission levels requires that the fuel the customer is consuming remain “on-line,” that is, synchronized to the electrical power grid. If a primary contributor to CO production in the individual combustor cans is reduced, this would allow the gas turbine customer to further turn down the load on the gas turbine and, thus, reduce fuel consumption during periods of reduced electricity demand. This can replace the method of shutting down the gas turbine during periods of reduced electricity demand and later turning the gas turbine back on when the demand returns. This method of frequently turning the gas turbine on and off may reduce the reliability of the gas turbine. 
         [0004]    In existing turndown regimes, the gas turbine still operates at the speed required to produce electricity at the desired frequency, and the flow rate of fuel and air to the combustors is reduced to reduce the amount of combustion gases generated in the combustors, thereby reducing the power produced by the gas turbine. However, the operating range of typical compressors limits the extent to which the air flow may be reduced, thereby limiting the extent to which the fuel flow may be reduced while maintaining the relatively preferred fuel to air ratio. When the fuel to air ratio is in the relatively preferred position, then the combustor emissions are relatively low and the combustion is stable. Bypassing excess air through the transition piece openings can allow for the preferred fuel to air ratio to be achieved at the combustor head end when the combustion process occurs, thereby reducing CO emissions. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0005]    According to one aspect of the invention, an air bypass band assembly includes a transition piece of a gas turbine, the transition piece having at least one opening therein to allow a flow of air to pass through the at least one opening. The air bypass band assembly also includes a band that is movable between at least two positions, a first one of the at least two positions being a closed position where the at least one opening is closed to prevent the flow of air from flowing through the at least one opening, a second one of the at least two positions being an open position where the at least one opening is opened to allow the flow of air to flow through the at least one opening. The air bypass band assembly further includes a mechanism that moves the band between the at least two positions. 
         [0006]    According to another aspect of the invention, an air bypass band assembly portion of a gas turbine includes a transition piece, the transition piece having a plurality of openings therein to allow a flow of air to selectively pass through the plurality of opening. The air bypass band assembly also includes a band that is movable between at least two positions, a first one of the at least two positions being a closed position where the plurality of openings are closed to prevent the flow of air from flowing through the plurality of openings, a second one of the at least two positions being an open position where the plurality of openings are opened to allow the flow of air to flow through the plurality of openings. The air bypass band assembly further includes a mechanism that moves the band between the at least two positions. 
         [0007]    According to still another aspect of the invention, an air bypass band assembly includes a transition piece of a gas turbine, the transition piece having at least one opening therein to allow a flow of air to pass through the at least one opening. The air bypass band assembly also includes a band located radially around at least a portion of the transition piece, the band being movable between at least two positions, a first one of the at least two positions being a closed position where the at least one opening is closed to prevent the flow of air from flowing through the at least one opening, a second one of the at least two positions being an open position where the at least one opening is opened to allow the flow of air to flow through the at least one opening. The air bypass band assembly further includes a mechanism that moves the band between the at least two positions. 
         [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 a cross section of a combustor and transition piece portion of a gas turbine in which embodiments of an air bypass band assembly of the present invention may be located; 
           [0011]      FIG. 2  is a perspective view of the forward end of the transition piece of  FIG. 1  having the air bypass band assembly of embodiments of the invention located therein and with a manifold cover removed for clarity; 
           [0012]      FIG. 3  is a perspective view of the air bypass band assembly of the embodiment of  FIG. 2  shown in an open position; 
           [0013]      FIG. 4  is a perspective view of the air bypass band assembly of the embodiment of  FIG. 2  shown in a closed position; 
           [0014]      FIG. 5  is a cross section view of the air bypass band assembly of the embodiment of  FIG. 2  shown in an open position; and 
           [0015]      FIG. 6  is a cross section view of the air bypass band assembly of the embodiment of  FIG. 2  shown in a closed position. 
       
    
    
       [0016]    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 
       [0017]      FIG. 1  shows a gas turbine  10  having a combustor  12  and a transition piece  14  in which embodiments of an air bypass band assembly  16  of the present invention may be located, as described in detail hereinafter. The gas turbine  10  may be for land-based use for, e.g., generation of electricity, although it is not limited as such. That is, the turbine portion of the gas turbine may be connected with a generator for generating electricity. The transition piece  14  is typically located downstream of the combustor  12  and upstream of the turbine (not shown). 
         [0018]      FIG. 2  shows the forward end  18  of the transition piece  14  of  FIG. 1 .  FIG. 2  also shows a portion of the air bypass band assembly  16  of embodiments of the invention located therein and with a bypass manifold cover  24  ( FIGS. 1 ,  3 - 6 ) removed for clarity. The air bypass band assembly  16  of embodiments of the present invention include a flexible band  20  and a mechanism  22  that moves the band  20  between at least two positions; for example, an open and closed positions with respect to a plurality of air bypass openings (e.g., circular) or holes  26  located in the transition piece  14  ( FIGS. 3-6 ). The band  20  may comprise a flexible material, such as, for example, a nickel alloy that retains its elasticity at relatively elevated temperatures. 
         [0019]      FIGS. 3 and 5  show the air bypass band assembly  16  of the embodiment of  FIG. 2  in an open position in which the plurality of air bypass openings are  26  uncovered by the band  20  (i.e., with the band  20  in a “relaxed” or loosened position as provided by the mechanism  16 ). In such an open position, a flow of bypass air as indicated by the line with an arrowhead  28  in  FIG. 5 , which may be provided as discharge air from the compressor of the gas turbine  10  or from some other air source within the gas turbine  10 , flows within a cavity  30  of a forward ring  32  surrounding the transition piece  14 . The flow of bypass air  28  then flows through the plurality of openings  26  located in the transition piece forward ring  32  and into a bypass manifold cavity  34  bounded by the bypass manifold cover  24 . One or more bolts  35  may be used to retain manifold cover  24  on forward ring  32 . The flow of bypass air  28  then flows through a plurality of floating tubes  36  and into an inner portion  38  of the transition piece  14 . The floating tubes  36  connect the bypass manifold (cavity)  34  with the internal cavity portion  38  of the transition piece  14 . 
         [0020]    The air bypass band assembly  16  of embodiments of the present invention being in the open position, as illustrated in  FIGS. 3 and 5 , typically occurs when it is desired to operate the gas turbine  10  in a relatively “low” part load operation or regime. Operation in this manner allows an excess amount of the flow of air  28  to be bypassed, thereby reducing fuel consumption in the combustor  12 . In this open position, it can be seen from  FIGS. 3 and 5  that the band  20  moves away from the openings  26  and up against or adjacent to the inside of a radially outer wall of the bypass manifold cover  24 . 
         [0021]      FIGS. 4 and 6  show the air bypass band assembly  16  of the embodiment of  FIG. 2  in a closed position. In this closed position, the plurality of air bypass openings  26  are covered by the band  20  (i.e., the band  20  is in a “tight” or closed position as provided by the mechanism  16 ). As such, the flow of air  28  flows through the cavity  30  in the transition piece forward ring  32  without being bypassed through the cavity  34  bounded by the bypass manifold cover  24 . The air bypass band assembly  16  of embodiments of the present invention being in the closed position, as illustrated in  FIGS. 4 and 6 , typically occurs when it is desired to operate the gas turbine  10  in a relatively “high” or “base” load operation or regime. In this closed position, it can be seen from  FIGS. 4 and 6  that the band  20  moves up against or adjacent to the inside of a radially inner wall of the bypass manifold cover  24  to block the openings  26 . As such, the pressure in the cavities  34  and  38  are relatively the same, but lower than the pressure within the cavity  30 . Then when the mechanism  16  starts to loosen the band  20 , a positive pressure differential helps to open the band  20  and press it up against the inside of the radially outer wall of the bypass manifold cover  24 . 
         [0022]      FIGS. 1 ,  3  and  4  show the mechanism  16  for moving the band  20  radially between the open and closed positions described hereinabove may comprise, in an embodiment, a pair of levers  40 ,  42  interconnected by corresponding gears  44 ,  46  at one end of the levers  40 ,  42 . The other end of each lever  40 ,  42  may connect to shackles  48 ,  50 , which may connect to corresponding ends of the band  20  for opening and closing of the band  20 . The gears  44 ,  46  may rotate on bearings  52 ,  54 . The mechanism  16  may be at least partially enclosed by a box-like device  56 , which itself may be a cap-like device or cover  57 , shown in phantom in  FIG. 3 . The cap or cover  57  serves as a barrier for air inside and outside the bypass manifold cover  24 . 
         [0023]      FIG. 1  shows that the mechanism  16  may connect by a rod  58  to a gearbox  60 , which may connect by another rod  62  to an actuator  64 , such as, for example, a pneumatic cylinder  64 . However, other suitable actuators may be utilized, such as motors. Also, other suitable mechanisms  16  may be utilized for moving the band  20  between open and closed positions, including those mechanisms that do not include gears. It suffices that the mechanism  16  used be able to move the band  20  between the at least two positions (i.e., the open and closed positions), as described hereinabove. Further, the band  20  may comprise between approximately 300-340 degrees of the overall 360-degree circumference of the transition piece  14 . However, other angular amounts of the band  20  may be utilized, as deemed suitable. 
         [0024]    Further, embodiments of the air bypass band assembly  16  of the present invention when utilized at the forward end  18  of the transition piece  14  may omit the transition piece forward ring  32 . The flow of bypass air  28  may then instead flow through some other suitable cavity or flow channel. 
         [0025]    Embodiments of the present invention allow for the reduction in the production of emissions, such as but not limited to, carbon monoxide (CO) in a gas turbine combustor (e.g., in the individual combustor cans). This allows the gas turbine load to be further turned down, thereby reducing the amount of fuel consumption by the gas turbine, during periods of reduced electricity demand, also providing for increased cost savings. Embodiments of the present invention also allow for a relatively good seal capability of the transition piece openings, thereby providing little or no sensitivity to thermal growth and little or no vibration-caused wear problems. This is because any expansion of the air bypass band is compensated for by actuator load and band spring force. 
         [0026]    Embodiments of the air bypass band assembly of the present invention have been described and illustrated herein as being located at the forward end of the transition piece of the gas turbine (i.e., at the forward ring  32  of the transition piece  14 ). However, embodiments of the air bypass band assembly of the present invention may be located at other gas turbine locations, such as, for example, the combustor head end or the combustor liner aft section. In addition, embodiments of the present invention may be utilized in a gas turbine to modulate cooling airflow through components such as a turbine nozzle and blades. Also, embodiments of the present invention may be utilized to “tune” the combustor exit temperature profile during low load regimes. 
         [0027]    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.