Abstract:
An exhaust gas diffuser for a turbomachine includes a diffuser supported on a turbine rotor, aligned with an axis of said turbine rotor. The diffuser is configured to re-direct turbine exhaust gas substantially ninety degrees from a first direction of flow along the rotor axis. A plenum chamber is in fluid communication with and surrounds an outlet end of the diffuser. The plenum chamber is in fluid communication with a transition duct adapted to supply the exhaust gas to another turbomachine. The plenum chamber expands in volume between the diffuser and the transition duct.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    This invention relates generally to integrating heat recovery steam generation (HRSG) systems with gas turbine exhaust components, and more specifically, to a turbine exhaust gas plenum designed to promote uniform flow of combustion gases into the HRSG. 
         [0002]    In combined cycle power generation systems, heated exhaust gas discharged from gas turbines may be used by HRSG systems as a source of heat which may be transferred to a water source to generate superheated steam. In turn, the superheated steam may be used within steam turbines as a source of power. The heated exhaust gas from a gas turbine may be delivered to the HRSG system through, among other things, an exhaust plenum and diffuser, which may help convert the kinetic energy of the heated exhaust gas exiting the last stage of the gas turbine into potential energy in the form of increased static pressure. Once delivered to the HRSG system, the heated exhaust gas may traverse a series of heat exchanger elements, such as superheaters, re-heaters, evaporators, economizers, and so forth. The heat exchanger elements may be used to transfer heat from the heated exhaust gas to the water source to generate superheated steam. It is a design objective to promote uniform flow through the exhaust gas plenum without negatively impacting diffuser performance, i.e., enabling flow diffusion without appreciable total pressure loss. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0003]    In one embodiment, there is provided an exhaust gas diffuser for a turbomachine comprising a diffuser supported in a turbine rotor, aligned with an axis of the turbine rotor, the diffuser configured to re-direct turbine exhaust gas substantially ninety degrees from a first direction of flow along the axis; a plenum chamber in fluid communication with and surrounding an outlet end of the diffuser, the plenum chamber in fluid communication with a transition duct adapted to supply the exhaust gas to another turbomachine; wherein the plenum chamber expands in volume in a direction toward the transition duct. 
         [0004]    In another embodiment, there is provided a turbomachine comprising a gas turbine section including a turbine rotor; a radial diffuser disposed along a first axis of the turbine rotor; an exhaust plenum comprising an inlet receiving a portion of the radial diffuser, the exhaust plenum extending along a second axis substantially perpendicular to the first axis, the plenum chamber expanding in volume along the second axis. 
         [0005]    In still another embodiment, there is provided a combined cycle system comprising: a gas turbine including a turbine rotor extending along a first axis; a heat recovery steam generator; a steam turbine adapted to receive steam from the heat recovery steam generator; a radial diffuser disposed along the first axis; and an exhaust plenum comprising an inlet receiving a portion of the radial diffuser, the exhaust plenum extending along a second axis substantially perpendicular to the first axis, the plenum chamber expanding in volume along the second axis and communicating with the heat recovery steam generator. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]    These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein: 
           [0007]      FIG. 1  is a schematic flow diagram of an embodiment of a combined cycle power generation system having a gas turbine, a steam turbine, and an HRSG; 
           [0008]      FIG. 2  is a detailed but partial side section view of an embodiment of the gas turbine of  FIG. 1  having heat exchanger elements of the HRSG of  FIG. 1  integrated with components of an exhaust diffuser of the gas turbine; 
           [0009]      FIG. 3  is a cut-away perspective view of an exhaust gas plenum of the type which could be employed in the gas turbine of  FIG. 2 ; 
           [0010]      FIG. 4  is a partially cut-away top view of the exhaust plenum shown in  FIG. 3 ; 
           [0011]      FIG. 5  is a perspective view of an exhaust gas diffuser and plenum in accordance with an exemplary but nonlimiting embodiment of the invention; 
           [0012]      FIG. 6  is another perspective view of the exhaust gas diffuser and plenum shown in  FIG. 5 ; and 
           [0013]      FIG. 7  is a top plan view of the exhaust gas diffuser and plenum shown in  FIGS. 5 and 6 . 
           [0014]      FIG. 8  illustrates HRSG inlet profiles at the plenum exit and at the downstream edge of the transition section. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0015]    One or more specific embodiments of the present invention will be described below. In an effort to provide a concise description of these embodiments, all features of an actual implementation may not be described in the specification. It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation-specific decisions must be made to achieve the developers&#39; specific goals, such as compliance with system-related and business-related constraints, which may vary from one implementation to another. Moreover, it should be appreciated that such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure. 
         [0016]    When introducing elements of various embodiments of the present invention, the articles “a,” “an,” “the,” and “said” are intended to mean that there are one or more of the elements. The terms “comprising,” “including,” and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements. Any examples of operating parameters are not exclusive of other parameters of the disclosed embodiments. 
         [0017]      FIG. 1  is a schematic flow diagram of an embodiment of a combined cycle power generation system  10  having a gas turbine, a steam turbine, and an HRSG. Specifically, the system  10  may include a gas turbine  12  for driving a first load  14 . The first load  14  may be, for instance, an electrical generator for producing electrical power. The gas turbine  12  may include a turbine  16 , a combustor  18 , and a compressor  20 . The system  10  may also include a steam turbine  22  for driving a second load  24 . The second load  24  may also be an electrical generator for generating electrical power. It will be understood, however, that both the first and second loads  14 ,  24  may be other types of loads capable of being driven by the gas turbine  12  and steam turbine  22 . In addition, although the gas turbine  12  and steam turbine  22  may drive separate loads  14  and  24 , as shown in the illustrated embodiment, the gas turbine  12  and steam turbine  22  may also be utilized in tandem to drive a single load via a single shaft. In the illustrated embodiment, the steam turbine  22  may include one low-pressure section  26  (LP ST), one intermediate-pressure section  28  (IP ST), and one high-pressure section  30  (HP ST). However, the specific configuration of the steam turbine  22 , as well as the gas turbine  12 , may be implementation-specific and may include any combination of sections and/or stages. 
         [0018]    The system  10  may also include a multi-stage HRSG  32 . The simplified depiction of the HRSG  32  and its components are not intended to be limiting. Rather, the illustrated HRSG  32  is shown to convey the general arrangement of such systems. Heated exhaust gas  34  from the gas turbine  12  may be transported into the HRSG  32  and used to heat steam used to power the steam turbine  22 . Exhaust from the low-pressure section  26  of the steam turbine  22  may be directed into a condenser  36 . Condensate from the condenser  36  may, in turn, be directed into a low-pressure section of the HRSG  32  with the aid of a condensate pump  38 . 
         [0019]    The condensate may then flow through a low-pressure economizer  40  (LPECON), which is a device configured to heat feedwater with gases, may be used to heat the condensate. From the low-pressure economizer  40 , the condensate may either be directed into a low-pressure evaporator  42  (LPEVAP) or to an intermediate-pressure economizer  44  (IPECON). Steam from the low-pressure evaporator  42  may be returned to the low-pressure section  26  of the steam turbine  22 . Likewise, from the intermediate-pressure economizer  44 , the condensate may either be directed into an intermediate-pressure evaporator  46  (IPEVAP) or to a high-pressure economizer  48  (HPECON). In addition, steam from the intermediate-pressure economizer  44  may be sent to a fuel gas heater (not shown) where the steam may be used to heat fuel gas for use in the combustor  18  of the gas turbine  12 . Steam from the intermediate-pressure evaporator  46  may be sent to the intermediate-pressure section  28  of the steam turbine  22 . 
         [0020]    Finally, condensate from the high-pressure economizer  48  may be directed into a high-pressure evaporator  50  (HPEVAP). Steam exiting the high-pressure evaporator  50  may be directed into a primary high-pressure superheater  52  and a finishing high-pressure superheater  54 , where the steam is superheated and eventually sent to the high-pressure section  30  of the steam turbine  22 . Exhaust from the high-pressure section  30  of the steam turbine  22  may, in turn, be directed into the intermediate-pressure section  28  of the steam turbine  22 , and exhaust from the intermediate-pressure section  28  of the steam turbine  22  may be directed into the low-pressure section  26  of the steam turbine  22 . 
         [0021]    An inter-stage attemperator  56  may be located in between the primary high-pressure superheater  52  and the finishing high-pressure superheater  54 . The inter-stage attemperator  56  may allow for more robust control of the exhaust temperature of steam from the finishing high-pressure superheater  54 . 
         [0022]    In addition, exhaust from the high-pressure section  30  of the steam turbine  22  may be directed into a primary re-heater  58  and a secondary re-heater  60  where it may be re-heated before being directed into the intermediate-pressure section  28  of the steam turbine  22 . The primary re-heater  58  and secondary re-heater  60  may also be associated with an inter-stage attemperator  62  for controlling the exhaust steam temperature from the re-heaters. 
         [0023]    In combined cycle systems such as system  10 , hot exhaust may flow from the gas turbine  12  and pass through the HRSG  32  and may be used to generate high-pressure, high-temperature steam. The steam produced by the HRSG  32  may then be passed through the steam turbine  22  for power generation. In addition, the produced steam may also be supplied to any other processes where superheated steam may be used. The gas turbine  12  generation cycle is often referred to as the “topping cycle,” whereas the steam turbine  22  generation cycle is often referred to as the “bottoming cycle.” By combining these two cycles as illustrated in  FIG. 1 , the combined cycle power generation system  10  may lead to greater efficiencies in both cycles. In particular, exhaust heat from the topping cycle may be captured and used to generate steam for use in the bottoming cycle. 
         [0024]    Therefore, one aspect of the combined cycle power generation system  10  is the ability to recapture heat from the heated exhaust gas  34  using the HRSG  32 . As illustrated in  FIG. 1 , components of the gas turbine  12  and the HRSG  32  may be separated into discrete functional units. In other words, the gas turbine  12  may generate the heated exhaust gas  34  and direct the heated exhaust gas  34  toward the HRSG  32 , which may be primarily responsible for recapturing the heat from the heated exhaust gas  34  by generating superheated steam. In turn, the superheated steam may be used by the steam turbine  22  as a source of power. The heated exhaust gas  34  may be transferred to the HRSG  32  through ductwork, which may vary based on the particular design of the combined cycle power generation system  10 . 
         [0025]    A more detailed illustration of how the gas turbine  12  functions may help illustrate how the heated exhaust gas  34  may be transferred to the HRSG  32  from the gas turbine  12 . Accordingly,  FIG. 2  is a detailed side view of an embodiment of the gas turbine  12  of  FIG. 1  having heat exchanger elements of the HRSG  32  of  FIG. 1  integrated with components of an exhaust diffuser of the gas turbine  12 . As described with respect to  FIG. 1 , the gas turbine  12  may include the turbine  16 , the combustor  18 , and the compressor  20 . Air may enter through an air intake  64  and be compressed by the compressor  20 . Next, the compressed air from the compressor  20  may be directed into the combustor  18  where the compressed air may be mixed with fuel gas. The fuel gas may be injected into the combustor  18  through a plurality of fuel nozzles  66 . The mixture of compressed air and fuel gas is generally burned within the combustion chamber of the combustor  18  to generate a high-temperature, high-pressure combustion gas, which may be used to generate torque within the turbine  16 . A rotor of the turbine  16  may be coupled to a rotor of the compressor  20 , such that rotation of the turbine rotor may also cause rotation of the compressor  20 . In this manner, the turbine  16  drives the compressor  20  as well as the load  14  (not shown in  FIG. 2 ). Exhaust gas from the turbine  16  section of the gas turbine  12  may be directed into an exhaust diffuser  68 . In the embodiment of  FIG. 2 , the exhaust diffuser  68  may be a radial exhaust diffuser, whereby the exhaust gas may be re-directed by exit guide vanes  70  to exit the exhaust diffuser  68  through a 90-degree turn outwardly (i.e., radially) through an exhaust plenum (not shown) and a transition inlet to the HRSG  32 . 
         [0026]    Another aspect of certain components of the exhaust diffuser  68 , in addition to directing the heated exhaust gas  34  to the HRSG  32 , may be to ensure that certain aerodynamic properties of the heated exhaust gas  34  are achieved. For instance, an exhaust frame strut  72 , illustrated in  FIG. 2 , may be cambered with an airfoil wrapped around it. The exhaust frame strut  72  may also be rotated such that swirling of the heated exhaust gas  34  may be minimized and flow of the heated exhaust gas  34  may generally be more axial in nature until flowing through the exit guide vanes  70 . In addition, the exit guide vanes  70  may also be designed in such a way that, when the heated exhaust gas  34  is turned toward the exhaust plenum at a 90-degree angle, the exit guide vanes  70  minimize the aerodynamic loss incurred in turning the flow 90 degrees radially. Therefore, proper aerodynamic design of the exhaust frame strut  72 , exit guide vanes  70 , as well as other components of the exhaust diffuser  68  within the flow path of the heated exhaust gas  34 , may be a design consideration. 
         [0027]      FIG. 3  is a cut-away perspective view of an embodiment of a diffuser that may be similar to the diffuser  68  in  FIG. 2 , but for convenience, it will be appreciated that the diffuser is not shown to the same scale as in  FIG. 2 . The diffuser  68  connects to a plenum  74  which, along with guide vanes  46 , redirects the exhaust gas substantially ninety (90) degrees and into the transition duct  76  which connects to the HRSG inlet (not shown). The radial guide vanes  46  may be circular (e.g., tapered annular or conical structures) and disposed concentrically about the x-axis  31 . The plenum  74  then gradually guides the combustion gases along the z-axis  35 , into the expanding transition section  76  which is connected to the inlet to the HRSG. 
         [0028]    The plenum  74  in the known configuration shown in  FIGS. 3 and 4  is generally square or rectangular in shape, but with a slanted end wall portion  78  extending from the top wall  80  to a side wall  82 . Walls  80  and  82  are substantially perpendicular to each other, while upstream and downstream sides  84 ,  86 , respectively, are parallel as best seen in  FIG. 4 . The bottom wall  88  is parallel to the top wall  80 , but may have a slanted component  90  between the bottom wall  88  and the side wall  82 . 
         [0029]      FIGS. 5-7  illustrate a modified plenum  100  in accordance with an exemplary but nonlimiting embodiment of the invention. The radial diffuser  101  is received within the plenum inlet, concentric to the turbine rotor axis  114  ( FIG. 7 ). In this example, the plenum  100  is formed with a radiused end defined by a curved end wall  102  merging with top and bottom walls  104 ,  106 . The curved end wall  102  and top and bottom walls  104 ,  106  collectively form a peripheral edge wall upstream and downstream side walls  108 ,  110 , respectively, which extend from the radiused end wall  102  to the expanding transition section  112 . The curved end wall  102  is drawn on the center axis  114  of the diffuser  101  (here again, not drawn to scale), and the top and bottom walls  104 ,  106  extend tangentially, in parallel, from opposite ends of the radiused end wall. Note that the straight top and bottom walls  104 ,  106  cross the axis  114  of the diffuser/turbine rotor. 
         [0030]    It will be understood that the internal vane components of the diffuser may be similar to the arrangement shown in  FIG. 3 . 
         [0031]    Significantly, the upstream and downstream side walls  108  and  110  are not parallel. As best seen in  FIG. 7 , the downstream side wall  110  is perpendicular to the center axis  114 , but the upstream side wall  108  extends at an angle of between 20 and 50 degrees (and preferably between 35 and 45 degrees) relative to the downstream side wall  110 . This expansion of the flow path from the plenum  100  to the transition section  112  promotes a redistribution to uniform flow of gases to the HRSG inlet without impact on diffuser performance. In fact, the uniform flow not only benefits HRSG performance, but also simplifies the design of the HRSG silencer located in the HRSG inlet. The plenum design described herein also enables relatively flat inlet profiles across operating conditions, and across a range of last stage turbine bucket exit profiles. 
         [0032]      FIG. 8  illustrates HRSG inlet profiles at the plenum exit plane  116  and at the downstream edge  118  of the transition section  112 . The Y-axis “% Span” refers to the height of the plenum, from bottom to top. It can be seen that the “total Velocity” of air flow through the plenum is relatively uniform across the height of the plenum. 
         [0033]    While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.