Abstract:
A method of recovering heat energy from a cooling medium used to cool hot gas path components in a turbine engine includes cooling one or more hot gas path components with the cooling medium; supplying spent cooling medium used to cool the one or more hot gas path components to a heat exchanger; supplying air (e.g., compressor discharge air) to the heat exchanger so as to be in heat exchange relationship with the spent cooling medium and thereby add heat to the compressor discharge air; and supplying the air heated in the heat exchanger to at least one combustor.

Description:
The present invention relates generally to steam-cooled turbine engines and, specifically, to a manner in which heat energy can be recovered from spent cooling steam in a gas turbine engine. 
     BACKGROUND OF THE INVENTION 
     There have been many efforts focused on the cooling of hot gas path components of gas turbine engines, typically resulting in some loss of efficiency. Closed-loop steam cooling of, for example, stator vanes of the first-stage nozzle in a gas turbine engine extracts heat from the vanes which is transferred to the cooling steam. During this heat energy exchange process, turbine heat energy given up to the steam as a result of cooling the vanes is manifest as a parasitic penalty or loss to combined cycle efficiency. 
     It would therefor be desirable to provide a cooling circuit for steam-cooled gas turbine components that recovers at least a portion of the heat energy otherwise lost to the cooling process. 
     BRIEF SUMMARY OF THE INVENTION 
     In one exemplary but nonlimiting embodiment, the invention relates to a method of recovering heat energy from a cooling medium used to cool hot gas path components in a turbine engine comprising: (a) cooling one or more hot gas path components with the medium; (b) supplying spent cooling medium used to cool the one or more hot gas path components to a heat exchanger; (c) supplying air cooler than the spent cooling medium to the heat exchanger so as to be in heat exchange relationship with the spent cooling medium and thereby add heat to the air; (d) supplying the air heated in the heat exchanger to at least one combustor. 
     In another exemplary but nonlimiting embodiment, the invention provides a method of recovering heat energy from a cooling medium used to cool a plurality of stator vanes in a nozzle stage of a gas turbine engine comprising: (a) passing the cooling medium through the plurality of stator vanes; (b) supplying spent cooling medium used to cool the plurality of stator vanes to a heat exchanger; (c) supplying compressor discharge air to the heat exchanger so as to be in heat exchange relationship with the spent cooling medium to thereby extract heat from the spent cooling medium and add heat to the compressor discharge air; (d) supplying the compressor discharge air heated in the heat exchanger to each of a plurality of combustors arranged in an annular array about a rotor of the gas turbine engine; and (e) recycling the spent cooling medium exiting the heat exchanger to step (a) in a closed loop cooling circuit. 
     In still another aspect the invention provides a an energy reclaiming system adapted to recover heat energy from a medium used to cool stator vanes in a first stage nozzle of a gas turbine engine comprising: a manifold for collecting spent cooling medium exiting the stator vanes, the manifold arranged to supply the spent steam through at least one conduit to a heat exchanger; a compressor adapted to supply compressor discharge air to each of a plurality of combustors arranged in an annular array; the heat exchanger arranged to receive a portion of the compressor discharge air upstream of the plurality of combustors, and to pass the portion of the compressor discharge air in heat exchange relationship with the spent cooling medium; and a second manifold arranged to receive discharge air exiting the heat exchanger and to distribute the discharge air exiting the heat exchanger to each of the plurality of combustors. 
     The invention will now be described in greater detail in connection with the drawings identified below. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a simplified sectional view of a gas turbine combustor and stage one nozzle with a simplified schematic illustration of a heat recovery circuit for recovering heat energy from a cooling medium in accordance with a first exemplary but nonlimiting embodiment of the invention; 
         FIG. 2  is an enlarged detail of location A in  FIG. 1 ; 
         FIG. 3  is a first enlarged detail of location B in  FIG. 1 ; 
         FIG. 4  is a second enlarged detail of location B in  FIG. 1 ; 
         FIG. 5  is an enlarged detail of location C in  FIG. 1 ; 
         FIG. 6  is an enlarged detail of location D in accordance with a first exemplary embodiment; and 
         FIG. 7  is an enlarged detail of location D in  FIG. 1  in accordance with a second exemplary embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     With reference to  FIG. 1 , a conventional combustor  10  of the type employed in a can-annular arrangement of similar combustors in a gas turbine is illustrated. A compressor  12 , represented by a compressor outlet diffuser  14  supplies discharge air to the combustor  10  for mixing with fuel at the head end  16  of the combustor where one or more fuel nozzles (not shown) are supported. Fuel and air are ignited in the combustion chamber  18  and the hot combustion gases are supplied via transition piece  20  to the first stage nozzle represented by stator vane  22 . It will be understood that there are several combustors arranged in an annular array about the turbine rotor (not shown), each supplying hot combustion gases to the turbine first stage. 
     Cooling medium, preferably steam, is supplied to the stator vanes  22  via inlet conduit  24  which introduces the cooling steam into an annular manifold (not shown) which, in turn, supplies cooling steam to the internal cooling circuit(s) of each vane via an outer ring  26  which supports a plurality of like vanes in an annular array in the first stage of the turbine section of the engine. The cooling steam, at temperature T 1 , passes through the internal cooling circuit in each of the stator vanes which, in this first stage, are exposed to the highest-temperature gases exiting the combustor. The vane internal cooling circuit, which may be of any known, suitable design, is not part of this invention, and therefor need not be described in detail. 
     The cooling steam exiting the individual vanes or groups of vanes via exemplary pipe sections  28 , is collected in a second manifold  30  as shown in the enlarged detail of location A in  FIG. 2 , and supplied via pipe section  32  to a heat exchanger  34 . The temperature T 2  of the cooling medium or steam exiting the first stage stator vanes is higher than the temperature T 1  of the cooling medium or steam in the inlet conduit  24 , the steam having absorbed heat from the cooling circuits of the collective array of vanes. 
     The “spent”, i.e., heated, cooling steam entering the heat exchanger  34  passes in heat-exchange relationship with a portion of the compressor discharge air (or air from another suitable source) that bypasses the combustor  10 . Specifically, while a major portion of the compressor discharge air is reverse-flowed to the head end  16  of each combustor where it is introduced into the fuel nozzles for mixing with fuel and subsequent combustion in the combustion chamber  18 , a smaller portion of the compressor discharge air bypasses the combustion process by exiting the combustor case  36  and entering a bypass conduit  38  at location B, and specifically B 1  as shown in  FIG. 3 . The bypass conduit  38  is provided with a bypass valve  40  that enables control of air flow (On/Off and amount) that enters an air manifold  42  at location B 2  ( FIG. 4 ) noting that the air manifold  42  receives bypass air in multiple pipes or conduits  38  from the various respective combustors in the can-annular array. As noted above, air from the manifold  42  is supplied to the heat exchanger  34  via pipe or conduit  43  where it passes in heat exchange relationship with the “spent” cooling steam. 
     The compressor discharge air absorbs heat in the heat exchanger  34  from the spent cooling steam and is distributed via pipe section  44  to a return-air manifold  46  (see the detail of location C in  FIG. 5 ) surrounding the respective combustors  10 , with individual pipes  48  branching off the manifold  46  and extending through their respective combustor cases  36  where they are coupled to a respective internal manifold  50  surrounding the combustor liner  52 . 
     In an exemplary implementation, temperatures of the cooling medium on both sides of the stator vanes (i.e., at inlets and outlets) range from about 700 F to about 1100 F, respectively. Similarly, compressor discharge air temperatures on both sides of the heat exchanger (i.e., at the inlets and outlets) may be in a range of about 800 F to about 950 F, respectively. It will be appreciated that the above temperatures are exemplary only, and may change depending on turbine frame size, operating conditions, and the like. 
     Accordingly, the temperature of the compressor discharge air exiting the heat exchanger  34  and entering the the combustor (Tc IN) at location D as described below is higher than the temperature of the compressor discharge air (Tc OUT) exiting the combustor at location B and entering the heat exchanger  34 , and thus, the difference Tc IN−Tc OUT represents the heat energy recovered from the cooling steam. In the above example, the difference, or recovered heat energy, would be about 150 F. 
       FIGS. 6 and 7  illustrate variants in the return of the heated air at temperature Tc IN to the combustor at manifold  50 . Thus,  FIG. 6  illustrates a combustion system without Late Lean Injection (LLI) also known as Axial Fuel Staging (AFS), such that, at location D 1 , air from the heat exchanger is supplied alone as dilution air to mix with the combustion products in the combustor  10 , downstream of the combustion chamber  18 , or in the transition piece  20  ( FIG. 1 ) that carries the hot combustion gases to the first turbine stage  22 . 
       FIG. 7  illustrates a combustion system with LLI (or AFS), where fuel is supplied to the pipe  48  via fuel injectors  54  for mixing with air in the pipe  48  at the combustor liner interface and injection into the hot gas path for additional combustion. The air in pipe  48  used for the axial fuel staging characteristic of LLI can be actively or passively controlled. 
     The spent cooling steam, having been cooled in the heat exchanger  34 , may be recycled via pipe section(s)  56  to the first-stage nozzle vane cooling circuit(s) in a closed-loop system (see  FIG. 1 ). 
     It will be appreciated that the invention as described herein has applicability to both open and closed loop cooling systems using steam, fuel, N2 or other cooling medium, and in cooling circuits used to cool any turbine hot gas path components that typically require cooling. 
     While various embodiments are described herein, it will be appreciated from the specification that various combinations of elements, variations or improvements therein may be made by those skilled in the art, and are within the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.