Abstract:
A turbine cooling system is provided, having a compressor for supplying cooling air, a forward turbine rotor wheel space, a high-pressure packing seal (HPPS) bypass cavity, and a metering device. The forward turbine rotor wheel space is cooled by the cooling air supplied by the compressor. The HPPS bypass cavity is in fluid communication with and receives a portion of the cooling air from the compressor, and is in fluid communication with and supplies the cooling air to the forward turbine rotor wheel space. The metering device is in operable communication with the forward turbine rotor wheel space and the HPPS bypass cavity to modulate the cooling air supplied to the forward turbine rotor wheel space from the HPPS bypass cavity. The metering device modulates the cooling air based on at least one operating condition of the turbine.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The subject matter disclosed herein relates to a turbine cooling system system, and more specifically to a turbine cooling system having a metering device for modulating cooling air to a forward turbine rotor wheel space. 
         [0002]    Gas turbines generally include a compressor, a combustor, one or more fuel nozzles, and a turbine. Air enters the gas turbine through an air intake and is pressurized by the compressor. The pressurized air is then mixed with fuel supplied by the fuel nozzles. The air-fuel mixture is supplied to the combustors at a specified ratio for combustion. The combustion generates pressurized exhaust gases, which drive blades of the turbine. 
         [0003]    The turbine includes a rotor assembly having a plurality of turbine blades installed on a rotating disk. During operation the turbine blades, the rotating disk, and other components in the turbine are subjected to elevated temperatures. In an effort to maintain the temperature of the internal components of the turbine at acceptable levels, cooling air is introduced. For example, cooling air may be supplied from the combustor plenum and is used to cool a forward turbine rotor wheel space. The forward turbine rotor wheel space is located between a nozzle assembly and a compressor exit diffuser of the turbine, and may be subjected to some of the highest temperatures experienced by the turbine. Cooling air is supplied to the forward turbine rotor wheel space in order to operate in a temperature range, which is suitable for long term component durability. Under certain operating conditions, such as high ambient temperatures, the volume of cooling air may be insufficient to maintain the forward turbine rotor wheel space within the desired temperature range for long term component durability. 
         [0004]    In one approach, the amount of cooling air supplied to the forward turbine rotor wheel space is increased by removing bore plugs from a compressor discharge casing. Removal of the bore plugs results in a portion of the high pressure air exiting the compressor to be diverted to the forward turbine rotor wheel space. However, this approach allows for cooling air to enter the forward turbine rotor wheel space at all operating conditions with no flow control. Therefore, removing the bore plugs results in a reduction in overall performance of the turbine, as more cooling air is supplied than needed during less demanding operating conditions. Moreover, this approach also requires the gas turbine to be shut down and the combustion system removed for access to the bore plugs, which can be troublesome and inconvenient. In another approach, an orifice may be provided to bypass some of the cooling air to the forward turbine rotor wheel space. However, the orifice is typically sized to provide adequate cooling to the forward turbine rotor wheel space during worst case conditions. Therefore, the orifice also results in a reduction in overall performance of the turbine, as more cooling air is supplied than needed during less demanding operating conditions. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0005]    According to one aspect of the invention, a turbine cooling system is provided having a compressor for supplying cooling air, a forward turbine rotor wheel space, a high-pressure packing seal (HPPS) bypass cavity, and a metering device. The forward turbine rotor wheel space is cooled by the cooling air supplied by the compressor. The HPPS bypass cavity is in fluid communication with and receives a portion of the cooling air from the compressor, and is in fluid communication with and supplies the cooling air to the forward turbine rotor wheel space. The metering device is in operable communication with the forward turbine rotor wheel space and the HPPS bypass cavity to modulate the cooling air supplied to the forward turbine rotor wheel space from the HPPS bypass cavity. The metering device modulates the cooling air based on at least one operating condition of the turbine. 
         [0006]    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 
         [0007]    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: 
           [0008]      FIG. 1  is a schematic view of an exemplary gas turbine system; and 
           [0009]      FIG. 2  is a cross-sectioned view of a portion of a compressor and a turbine section shown in  FIG. 1 . 
       
    
    
       [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]    As used herein the terms module and sub-module refer to an application specific integrated circuit (ASIC), an electronic circuit, a processor (shared, dedicated, or group) and memory that executes one or more software or firmware programs, a combinational logic circuit, and/or other suitable components that provide the described functionality. 
         [0012]      FIG. 1  illustrates a schematic diagram of an exemplary power generation system indicated by reference number  10 . The power generation system  10  is a gas turbine system having a compressor  20 , a combustor  22 , and a turbine  24 . Air enters the power generation system  10  though an air intake  30  located in the compressor  20 , and is compressed by the compressor  20 . The compressed air is then mixed with fuel by a fuel nozzle  34  located in an end cover (not shown) of the combustor  22 . The fuel nozzle  34  injects an air-fuel mixture into the combustor  22  in a specific ratio for combustion. The combustion generates hot pressurized exhaust gases that drives blades (not shown) that are located within the turbine  24 . In one exemplary embodiment, the turbine  24  is configured into three stages having six rows of airfoils (not shown) disposed axially for channeling the hot pressurized exhaust gases. In one embodiment, the turbine  24  includes a first stage stator vane (not shown) that defines a nozzle assembly (not shown). 
         [0013]      FIG. 2  is an enlarged view of a portion of the compressor  20  and the turbine  24  illustrating one exemplary embodiment of a metering device  46 . High pressure compressor discharge air or cooling air is supplied from the compressor  20 , and is located within and flows through a plenum  48 . A forward turbine rotor wheel space  50  is located between the nozzle assembly (not shown) and a compressor exit diffuser (not shown). The temperature of the cooling air in the plenum  48  is lower than the temperature of the air located in the forward turbine rotor wheel space  50 . Specifically, the forward turbine rotor wheel space  50  tends to experience some of the highest temperatures of the turbine  24  due to the specific location of the forward turbine rotor wheel space  50  in relation to some of the other components of the power generation system  10 , such as the combustor  22 . Therefore, the cooling air located in the plenum  48  is used to provide cooling to the forward turbine rotor wheel space  50 . The metering device  46  is used to modulate the amount of cooling air supplied to the forward turbine rotor wheel space  50 . 
         [0014]    Continuing to refer to  FIG. 2 , the cooling air from the plenum  48  flows through a cooling channel  52 . A portion of the cooling air from the cooling channel  52  leaks past a pressure packing seal (HPPS)  56  to create a HPPS leakage flow  58 . The HPPS leakage flow  58  flows to the forward turbine rotor wheel space  50 , and is employed to provide cooling to the forward turbine rotor wheel space  50 . The remaining cooling air that does not leak past the HPPS  56  flows into a HPPS bypass cavity  60 . The metering device  46  is employed to modulate the amount of cooling air supplied to the forward turbine rotor wheel space  50  from the HPPS bypass cavity  60 . 
         [0015]    The metering device  46  is typically any type of variable orifice that is able to modulate the amount of cooling air that is supplied to the forward turbine rotor wheel space such as, for example, a valve or a solenoid. In the exemplary embodiment as shown in  FIG. 2 , the metering device  46  is a pintle-type valve  62 , however it is understood that other metering devices may be used as well. The valve  62  includes a needle or pintle  64  that is an elongated member that cooperates with an orifice  66  located in a wall  68  of the HPPS bypass cavity  60  to modulate the amount of cooling air supplied to the forward turbine rotor wheel space  50 . Specifically, in the exemplary embodiment as shown, the pintle  62  includes an angular outer surface  70 , and the orifice  66  also includes a corresponding angular surface  72 . The pintle  62  is selectively actuated by a valve portion  74  of the pintle-type valve  62  in the directions D 1  and D 2 . In one embodiment, the valve portion  74  is a piezoelectric device that actuates the pintle  62  based on electrical current, however it is understood that other approaches may be used as well. 
         [0016]    The angular outer surface  70  of the pintle  62  cooperates with the corresponding angular surface  72  of the orifice  66  to modulate the amount of cooling air supplied to the forward turbine rotor wheel space  50 . That is, when the pintle  62  is actuated in the first direction D 1 , the pintle  62  is actuated towards the orifice  66 , and decreases the amount of cooling air supplied to the forward turbine rotor wheel space  50 . When the pintle  62  is actuated in the second direction D 2 , the pintle  62  is actuated away from the orifice  66  and the amount of cooling air supplied to the forward turbine rotor wheel space  50  increases. 
         [0017]    The modulation of the metering device  46  is controlled by a control module  80  that is in communication with the metering device  46  through a data link  82 . The data link  82  could be a hard-wired or a wireless radio frequency (RF) data link used to communicate control signals to the metering device  46 . The control module  80  includes control logic for sending a control signal to the metering device  46  to either increase or decrease the amount of cooling air supplied to the forward turbine rotor wheel space  50  based on specific operating conditions. For example, in the exemplary embodiment as shown in  FIG. 2 , the control module  80  includes control logic for sending a control signal to the metering device  46  to actuate the pintle  62  in the directions D 1  and D 2 . Specifically, the control module  80  either increases or decreases the amount of cooling air based on at least one of the following operating conditions which include but are not limited to ambient temperature, overall back flow margin of the turbine  24 , bulk metal temperature of the turbine blades, forward turbine rotor wheel space temperature, turbine emissions requirements, and compressor discharge pressure. 
         [0018]    In one embodiment, the control module  80  is connected to and receives temperature data from an ambient sensor (not shown). As the ambient temperature changes, the control module  80  includes control logic for sending a control signal to the metering device  46  to either increase or decrease the amount of cooling air to the forward turbine rotor wheel space  50 . For example, as the ambient temperature increases, the control module  80  includes control logic for sending a control signal to the metering device  46  to increase the amount of cooling air supplied to the forward turbine rotor wheel space  50 . 
         [0019]    The control module  80  may also include control logic for modulating the amount of cooling air supplied to the forward turbine rotor wheel space  50  based on the overall back flow margin of the turbine  24 . The overall back flow margin is the difference between the cooling air pressure and the gas flow pressure of the turbine  24 , where a positive overall back flow margin is typically maintained. The back flow margin may be a calculated or measured value. In one example, if the back flow margin is not sufficient, then the control module  80  includes control logic for sending a control signal to the metering device  46  to increase the amount of cooling air supplied to the forward turbine rotor wheel space  50 . 
         [0020]    The control module  80  may include control logic for modulating the cooling air to the forward turbine rotor wheel space  50  based on the bulk metal temperature of the turbine blades (not shown). Specifically, in one embodiment if the bulk metal temperature of the turbine blades exceeds a pre-defined temperature limit, then the control module  80  includes control logic for sending a control signal to the metering device  46  to increase the amount of cooling air supplied to the forward turbine rotor wheel space  50 . 
         [0021]    The control module  80  may include control logic for modulating the cooling air to the forward turbine rotor wheel space  50  based on the air temperature of the forward turbine rotor wheel space  50 . For example, in one embodiment, if the temperature of the forward turbine rotor wheel space  50  exceeds a pre-defined temperature limit, then the control module  80  includes control logic for increasing the amount of cooling air to the forward turbine rotor wheel space  50 . 
         [0022]    The control module  80  may also include control logic for modulating the amount of cooling air to the forward turbine rotor wheel space  50  based on emissions requirements. For example, in one embodiment, during a turndown mode of the power generation system  10 , increased airflow extraction out the plenum  48  is utilized to by-pass the primary combustion zone during load rejection resulting in a reduction in the mass flow rate of air entering the combustor  22  (shown in  FIG. 1 ); which in turn results in a lower combustion temperature resulting in reduced emissions. Thus the metering device  46  is modulated to increase the amount of cooling air supplied to the forward turbine rotor wheel space  50 . 
         [0023]    The control module  80  may also include control logic for modulating the amount of cooling air to the forward turbine rotor wheel space  50  to provide compressor surge protection. Specially, as the power generation system  10  operates at relatively high compressor pressure ratios, the pressure ratio of the compressor  20  may eventually exceed a critical value, which results in a rapid reduction of compressor discharge pressure. The decrease in compressor discharge pressure results in flow separation, which is known as compressor surge. Thus, the amount of cooling air to the forward turbine rotor wheel space  50  is modulated to provide a compressor discharge ratio that is a specified margin away from a surge boundary of the compressor  20 . Modulating the amount of cooling air supplied to the forward turbine rotor wheel space  50  reduces or substantially reduces or eliminates the need to recirculate a portion of the compressor discharge air back to the compressor inlet by an inlet bleed valve. Recirculating a portion of the compressor discharge air back to the compressor inlet is referred to as inlet bleed heat. 
         [0024]    The amount of cooling air is modulated to the forward turbine rotor wheel space  50  in an effort to manage turbine rotor cooling and enhance the part-life of the internal turbine components. Actively modulating the amount of cooling air to the forward turbine rotor wheel space  50  also increases the overall performance of the power generation system  10  when compared to some of the other approaches that are currently being used to increase cooling air to the forward turbine rotor wheel space  50 . For example, one approach for increasing cooling air involves removing the bore plugs from the compressor discharge casing. However, this results in cooling air entering the forward turbine rotor wheel space at all operating conditions with no flow control, and reduces the overall performance of the turbine. In contrast, actively modulating the amount of cooling air to the forward turbine rotor wheel space  50  allows for the amount of cooling air to be adjusted depending on specific operating conditions, which in turn increases overall performance of the power generation system  10 . 
         [0025]    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.