Abstract:
A method and apparatus are disclosed for a gas turbine power plant with a variable area turbine nozzle and an integrated motor/alternator device for starting the gas turbine and power extraction after starting.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the priority benefit under 35 U.S.C. § 119(e) of U.S. provisional patent application No. 60/927,342 filed May 3, 2007. The aforementioned provisional application is herein incorporated by reference in its entirety. 
     
    
     BACKGROUND 
       [0002]    The present development relates generally to turbo machines and, more particularly, multi-spool intercooled recuperated gas turbine systems and methods. The system and method are particularly adapted for use as a power plant for a vehicle, especially a truck, bus or other overland vehicle. However, it will be appreciated that the present disclosure has broader applications and may be used in many different environments and applications, including as a stationary electric power module for distributed power generation. 
         [0003]    Vehicular bus or truck applications demand a very wide power range of operation. The multi-spool configuration described in this disclosure creates opportunities to control the engine to a very low power range. 
         [0004]    Typical multistage gas turbine engines incorporate a coaxial stack of turbines and compressors, thereby making a compact axial machine, with minimized frontal area. 
         [0005]    A conventional gas turbine may be composed of two or more turbo compressor rotating assemblies to achieve progressively higher pressure ratio. A turbo machine composed of three independent rotating assemblies or “spools,” including a high pressure turbo compressor spool  10 , a low pressure turbo compressor spool  9 , and a free turbine spool  12  appears in  FIG. 1 . As seen in  FIG. 1 , the high pressure spool  10  is composed of a compressor  22 , a turbine  42 , and a shaft  16  connecting the two. The low pressure spool  9  is composed of a compressor  45 , a turbine  11 , and a shaft  18  connecting the two. The free turbine spool  12  is composed of a turbine  5 , a load device  6 , and a shaft  24  connecting the two. Said load device is normally a gearbox, generator, or a transmission for a vehicular application. A combustor  41  is used to heat the air between the recuperator  44  and high pressure turbine  42 . 
         [0006]    A common method for starting a turbo machine is seen in  FIG. 2  and provides electro-mechanical motive power to the high pressure spool  10 . A motor/clutch  13  is engaged to provide rotary power to the high pressure spool  10 . Once the high pressure spool  10  is supplied with power, air flow within the cycle occurs, enabling the fuel to be admitted into the combustor and the subsequent initiation of combustion. Hot pressurized gas from the high pressure spool  10  is delivered to the low pressure spool  9  and the free turbine spool  12 . The present apparatus contemplates new methods for starting a turbo machine and efficiently operating at low power levels. 
       SUMMARY 
       [0007]    The present disclosure describes an apparatus and method for starting and/or extracting power from a gas turbine engine and a turbo machine employing the same. In certain embodiments the introduction of a pressurized motive fluid such as air or hydraulic fluid to a starter turbine on the high pressure spool provides the starting power for the gas turbine. The starter turbine can be a separate turbine on the high pressure spool or may be provided by buckets or blades machined into or otherwise formed or provided on the rotor of the compressor. In other embodiments, a motor/alternator combination is incorporated with the high pressure spool. The addition of a motor/alternator combination to the gas turbine&#39;s high spool  10  provides the means for both starting the gas turbine and extracting a small amount of power during engine operation. For example, the combined motor alternator device may be coupled to the electrical system of a vehicle such that the vehicle power supply may be used to operate the motor/alternator device for starting the gas turbine and, after the gas turbine has been started, for converting a portion of the rotational power of the high pressure spool to electrical power. 
         [0008]    In certain embodiments, efficiency is also increased by the addition of a variable area turbine nozzle between a low pressure turbo compressor spool and a free turbine spool. The variable area turbine nozzle allows the user to have control over the level of fuel consumption enabling the user to lower the fuel consumption by the gas turbine. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    The invention may take form in various components and arrangements of components, and in various steps and arrangements of steps. The drawings are only for purposes of illustrating the preferred embodiments and are not to be construed as limiting the invention. 
           [0010]      FIG. 1  depicts a turbo machine composed of three independent spools, two nested turbo compressor spools and one free turbine spool connected to a load device. 
           [0011]      FIG. 2  illustrates an apparatus and method for starting the turbo machine, providing electro-mechanical motive power to the high spool turbo compressor. 
           [0012]      FIG. 3  illustrates an apparatus and method for starting the gas turbine by providing pneumatic power to the high spool turbo compressor. 
           [0013]      FIG. 4  illustrates an apparatus and method of integrating an air starter turbine into the back face of the compressor impeller. 
           [0014]      FIG. 5  illustrates an electric motor/generator combination, connected to the highest pressure turbo compressor spool. 
           [0015]      FIG. 6  illustrates yet another variation on the integrated high spool motor generator. 
           [0016]      FIG. 7  illustrates an apparatus and method for combining a high speed permanent magnetic alternator into the shaft of a turbo compressor spool. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0017]    Referring to the drawings, wherein like reference numerals refer to like or analogous components throughout the several views,  FIG. 3  illustrates an apparatus and method of starting a multi-spool gas turbine which may generally be of the type appearing in  FIG. 1 , by providing pneumatic or hydraulic power to the high spool turbo compressor  10 . In certain embodiments, a vessel  20  contains a high pressure gas such as air, which is delivered through conduits  23  and  21 , having a control valve  25  therebetween, to a starter turbine  4 , which may be a gas turbine affixed to the shaft  16  of the turbo compressor spool  10 . 
         [0018]    In alternative embodiments, the conduit  23 , valve  25 , and conduit  21  may supply hydraulic fluid as the motive fluid to the starter turbine  4 , which may alternatively be a hydraulic turbine affixed to the shaft  16  of the turbo compressor spool  10 . It is preferable to employ air as the motive fluid for the turbine  4  rather than hydraulic fluid in those embodiments wherein the turbine  4  is supported on air bearings. Likewise, it is preferable to employ conventional, oil lubricated bearings in place of air bearings when the motive fluid is a hydraulic fluid. 
         [0019]    The valve  25  may have a controller for selectively opening the valve to permit passage of the pressurized fluid in the container  20  to the starter turbine  4  in response to a control signal, such as a signal to start the gas turbine engine. When the valve  25  is opened, e.g., in response to a control signal from the valve controller, the motive fluid travels via the conduit  21  to the starter turbine  4 . The turbine  4  may be affixed or integrated with the turbo compressor spool  10  without the need for additional bearings or couplings. The motive fluid delivered to the turbine  4  imparts angular momentum to rotate the high spool turbo compressor  10 . As the turbo compressor spool  10  rotates, it creates flow within the low pressure turbo compressor spool  9  and the turbo alternator spool  12  of the turbo machine. 
         [0020]    Referring now to  FIG. 4 , there is shown a fragmentary view of an exemplary embodiment of the present development wherein the turbine  4  is and air or gas turbine supported on a shaft  31  which, in turn, is rotatably supported on air bearings  32 . The turbine  4  may be integrated with a compressor impeller  35  of the compressor  22  by milling or otherwise forming or providing small turbine buckets  30  on or in the back face of the compressor impeller  35 , as shown in  FIG. 4 . The addition of the turbine buckets  30  enables the compressor  35  to more productively use the high pressure air supplied from the air supply  20  and air nozzle  33 . As the air enters the compressor  35 , the turbine buckets  30  catch the air and turn the turbo compressor shaft  31  to start the gas turbine. 
         [0021]      FIG. 5  illustrates a further embodiment wherein an electric motor/alternator combination  17  is combined with a high pressure turbo compressor spool  10 , which may otherwise be as described above. The motor/alternator combination  17  provides a means for starting the gas turbine as well as the option of extracting a small amount of power (for example, less than about 5% of the power output of the gas turbine) during engine operation. This small amount of extracted power provides a means of controlling the speed of high spool turbo compressor  10  while the engine operates at minimum power near the idle point. The relatively small amount of electric power generated is well suited for vehicular auxiliary electric system loads, independent of drive power needed for the vehicle. 
         [0022]    Also shown in  FIG. 5 , is an exemplary method of power take off for a single spool gas turbine engine, which requires the coupling of the motor/alternator  17  at the inlet end of the compressor shaft. Single spool gas turbines, configured as a turbo compressor alternator assembly require a mechanical coupling to connect the turbo compressor  10 , operating on its main bearings  91 , to the alternator load, operating on its bearings  32 . In such an embodiment the turbo compressor  10  and the alternator  17  are installed on their own bearings  91  and  32 , respectively, with a coupling  90  employed to connect the two rotating machines. In certain configurations, the coupling  90  may incorporate a mechanical clutch or mechanism typically used to engage and disengage the starting device. 
         [0023]    In the present disclosure, referring to  FIG. 6 , due to the small fraction of the turbine power devoted to the load, the size of the alternator  27  is relatively small when compared to alternators driven by gas turbines. For this reason, a compact shaft-speed alternator may be installed on the turbine alternator spool  10  without separate bearings and couplings. For example, a samarium-cobalt type permanent magnet alternator is small enough to fit within a hollow portion of the shaft, either between the compressor  22  and turbine  42  or overhung from the compressor inlet.  FIG. 6  illustrates a variation on the integrated high spool motor/generator device, incorporating a compact motor/alternator combination  27  between the turbine  42  and the compressor  22 . The terms “generator” and “alternator” are used interchangeably herein unless specifically stated otherwise. 
         [0024]      FIG. 7  shows an alternative embodiment integrating a magnetized motor/alternator  38  into the high spool turbo compressor  10 . A hollow shaft  31 , which connects a compressor rotor  35  and a turbine rotor  39 , rotates on main bearings  91 . Due to the small accessory load absorbed by the alternator rotor  38  and small starting power required from the motor  38 , the magnetized rotor  38  is contained inside the hollow shaft  31 . Electrical stator components  37  surround the magnetized alternator/motor rotor  38  assembly. In an alternative embodiment, an alternate mechanical configuration, employing theses same components, may be arranged with the alternator rotor  38  and the alternator stator  37  in front of or integral with compressor  35 , employing a single pair of main bearings  91 . 
         [0025]    Exemplary embodiments of the present invention showing the location of a variable area turbine nozzle  40  are seen in  FIGS. 3 ,  5  and  6 . Although the gas turbine embodiments herein may operate with a conventional fixed geometry turbine nozzle, the use of a variable area turbine nozzle  40  is advantageous in that it enables an additional control feature to lower fuel consumption by controlling the rate of flow of air to the turbine  5  of the free turbine spool  12 . The ability to lower fuel consumption makes the present development more efficient. 
         [0026]    The invention has been described with reference to the preferred embodiments. Modifications and alterations will occur to others upon a reading and understanding of the preceding detailed description. It is intended that the invention be construed as including all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.