Patent Publication Number: US-2007095069-A1

Title: Power generation systems and method of operating same

Description:
BACKGROUND OF THE INVENTION  
      This invention relates generally to wind turbines, and more specifically to a combined wind turbine and gas turbine system.  
      In at least one known system, a plurality of wind turbines, commonly referred to as wind energy farms are installed in various geographic locations to facilitate harvesting wind energy when it is available.  
      The power output of the wind turbine is limited by either the mechanical load on the turbine blades and/or the mechanical load on the generator or the availability of wind. Accordingly, the electrical output of each wind farm varies depending on the various wind conditions and the mechanical load on the wind turbine. More specifically, although wind energy farms provide a clean and renewable source of energy, the power output generated by each wind turbine varies based on the wind, and thus reduces the usefulness of the energy generated by the wind energy farm. For example, producing wind energy during the night, when demand is relatively low, may result in reduced local marginal pricing of the electricity generated by the wind energy farms and/or increased cycling of the baseload plants. cl BRIEF SUMMARY OF THE INVENTION  
      In one aspect, a method for operating a power generation system including a wind turbine and a turbine assembly is provided. The method includes operating the wind turbine, storing the energy generated by the wind turbine as compressed air, and channeling the compressed air to the turbine assembly when it is economically viable.  
      In another aspect, a power generating system is provided. The power generating system includes a wind turbine, a storage device configured to store energy generated by said wind turbine as compressed air, and a turbine assembly configured to receive the compressed air when it is economically viable.  
      In a further aspect, a power generating system is provided. The power generating system includes a wind turbine, an air compressor operationally coupled to the wind turbine, a turbine assembly including a combustor, a turbine, a recuperator coupled in flow communication with the wind turbine, and a generator operationally coupled to the turbine. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a perspective view of an exemplary power system;  
       FIG. 2  is schematic illustration of an exemplary gas turbine assembly that can be used with the power system shown in  FIG. 1 ;  
       FIG. 3  is perspective view of an exemplary wind turbine that can be used with the power system shown in  FIG. 1 ;  
       FIG. 4  is a perspective view of a portion of the wind turbine shown in  FIG. 3 ;  
       FIG. 5  is schematic illustration of an exemplary turbine assembly that can be used with the wind turbine shown in  FIG. 3 ;  
       FIG. 6  is perspective view of an exemplary wind turbine that can be used with the turbine assembly shown in  FIG. 5 ;  
       FIG. 7  is a perspective view of a portion of the wind turbine shown in  FIG. 6 ; and  
       FIG. 8  is an exemplary temperature/entropy chart.  
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
       FIG. 1  is a perspective view of an exemplary power system  6 . Power system  6  includes a turbine generator assembly  8  and a wind turbine assembly  100  that is configured to channel compressed air  9  to the gas to the turbine generator assembly  8 .  
       FIG. 2  is a schematic illustration of an exemplary gas turbine generator assembly  8  that can be used with power system  6 . Gas turbine generator assembly  8  includes a gas turbine engine  10  including, in serial flow relationship, a high-pressure compressor  16 , a combustor  18 , a high-pressure turbine  20 , and a low-pressure or power turbine  24 . High-pressure compressor  16  has an inlet  30  and an outlet  32 . Combustor  18  has an inlet  34  that is substantially coincident with high-pressure compressor outlet  32 , and an outlet  36 . In one embodiment, combustor  18  is an annular combustor. In another embodiment, combustor  18  is a dry low emissions (DLE) combustor. In a further embodiment, combustor  18  is a can-annular combustor.  
      High-pressure turbine  20  is coupled to high-pressure compressor  16  with a first rotor shaft  40  that is substantially coaxially aligned with respect to a longitudinal centerline axis  43  of engine  10 . Engine  10  may be used to drive a load, such as a generator  44 , which may be coupled to low-pressure turbine  24  using a power turbine shaft  46 . Alternatively, the load may be coupled to a forward extension (not shown) of rotor shaft  42 . Gas turbine engine assembly  8  also includes a heat exchanger  50  that has a first fluid path  52  to facilitate channeling compressed air from high-pressure compressor  16  through heat exchanger  50 , a second fluid path  54  to facilitate channeling heated air discharged from heat exchanger  50  to combustor  18 , and a third fluid path  56  to facilitate channeling exhaust gases from low-pressure turbine  24  through heat exchanger  50 . In the exemplary embodiment, heat exchanger  50  is a recuperator  50 .  
       FIG. 3  is a perspective view of exemplary wind turbine  100  that can be used with power system  6 .  FIG. 4  is a perspective view of a portion of wind turbine  100  shown in  FIG. 3 . In the exemplary embodiment, wind turbine  100  includes a nacelle  102  that is mounted atop a relatively tall tower  104 . Wind turbine  100  also includes a rotor  106  that includes a plurality of rotor blades  108  that are each coupled to a rotating hub  110 . Although wind turbine  100  is shown including three rotor blades  108 , it should be realized that wind turbine  100  can include any number of rotor blades to facilitate operating wind turbine  100 .  
      Moreover, wind turbine  100  includes a storage tank  140  that is configured to receive compressed air generated using a compressor assembly  120 . In the exemplary embodiment, at least a portion of tower  104  is utilized to form storage tank  140 , and thus at least a portion of tower  104  is utilized to store compressed air generated using compressor assembly  120 . More specifically, at least a portion of tower  104  is substantially hollow such that compressed air generated by compressor assembly  120  can be stored within a cavity  142  defined by the exterior walls  144  of tower  104 . Accordingly, the height and volume of tower  104  may be selectively sized to store a predetermined quantity of air discharged from compressor assembly  120 .  
      In some configurations and referring to  FIG. 4 , various components of wind turbine  100  are housed in nacelle  102  atop tower  104  of wind turbine  100 . In one embodiment, wind turbine  100  includes one or more microcontrollers coupled within a control panel  112  that are used for overall system monitoring and control such as, but not limited to, pitch and speed regulation, high-speed shaft and yaw brake application, yaw and pump motor application and fault monitoring. In an alternative embodiment, wind turbine  100  utilizes a distributed or centralized control architecture (not shown) to perform system monitoring and control.  
      In the exemplary embodiment, the control system, i.e. control panel  112 , transmits control signals to a variable blade pitch drive system  114  that includes at least one of an AC or DC pitch drive motor (not shown) to control the pitch of blades  108  that drive hub  110  as a result of wind. In some configurations, the pitches of blades  108  are individually controller by blade pitch drive system  114 .  
      Wind turbine  100  also includes a main rotor shaft  116  (also referred to as a “low speed shaft”) connected to hub  110  and a gearbox  118  that, in some configurations, utilizes a dual path geometry to drive a high speed shaft enclosed within gearbox  118 . The high speed shaft (not shown in  FIG. 4 ) is used to drive compressor assembly  120  that is supported by a main frame  132 . Optionally, compressor assembly  120  is driven utilizing a low-speed shaft (not shown) and the high-speed shaft is utilized to drive an electric generator.  
      Yaw drive  124  and yaw deck  126  provide a yaw orientation system for wind turbine  100 . In some configurations, the yaw orientation system is electrically operated and controlled by the control system in accordance with information received from sensors used to measure shaft flange displacement, as described below. Either alternately or in addition to the flange displacement measuring sensors, some configurations utilize a wind vane  128  to provide information for the yaw orientation system. The yaw system is mounted on a flange provided atop tower  104 .  
      During operation, wind is channeled through blades  108  thus causing main rotor shaft  116  to rotate. The rotational forces generated by blades  108  are transmitted to compressor assembly  120  via gearbox  118 , thus causing compressor assembly  120  to compress air. The compressed air generated by compressor assembly  120  is channeled to storage device  140 , i.e. tower  104 , wherein the compressed air is stored for future use. Although the exemplary embodiment illustrates a single wind turbine  100  that is utilized to compress and store compressed air, it should be realized that a plurality of wind turbines  100  can be utilized to compress and store air to be utilized by a single gas turbine engine. Optionally, a single wind turbine  100  may be utilized to compress and store air that is then channeled to a plurality of gas turbine engine generator assemblies.  
      Accordingly, system  6  facilitates producing power and storing the wind energy generated by wind turbine  100  in the compressed air, i.e. storage tank  140  whenever wind energy can be harvested. In the exemplary embodiment, compressed air stored within storage tank  140  is channeled to at least one gas turbine engine  10  when the electricity demand exceeds a predetermined threshold.  
      Referring to  FIG. 2 , more specifically, air is drawn into high-pressure compressor inlet  30  from wind turbine storage tank  140 , i.e. the compressed air stored within cavity  142  of tower  104 . High-pressure compressor  16  compresses the air and delivers the compressed air to recuperator  50  via first fluid path  52 . The compressed air is then heated within recuperator  50  utilizing low-pressure turbine  24  exhaust gases that are channeled through recuperator  50  utilizing third fluid path  56 . Channeling exhaust gases through recuperator  50  facilitates increasing an operational temperature of the air channeled therethrough. Accordingly, air discharged from low-pressure compressor  24  is channeled through recuperator  50 , wherein an operating temperature of the compressed air is increased from a first operational temperature to a second operational temperature that is greater than the first operational temperature utilizing exhaust gases discharged from low-pressure turbine  24 . The heated compressed air is then channeled from recuperator  50  to an inlet  34  of combustor  18  via second fluid path  54  where it is mixed with fuel and ignited to generate high temperature combustion gases. The combustion gases are channeled from combustor  18  to drive turbines  20  and  24 .  
       FIG. 5  is another exemplary turbine generator assembly  200  that can be utilized with wind turbine  100  shown in  FIG. 1 ,  FIG. 3 , and  FIG. 4 . Turbine generator assembly  200  is substantially similar to gas turbine engine generator assembly, shown in  FIG. 2 , and components in assembly  200  that are identical to components of assembly  10  are identified in  FIG. 5  using the same reference numerals used in  FIG. 3 .  
      Assembly  200  includes a combustor  18  and a high-pressure turbine  20  that is substantially coaxially aligned with respect to a longitudinal centerline axis  43  of assembly  200 . Combustor  18  has an inlet  34  and an outlet  36 . In one embodiment, combustor  18  is an annular combustor. In another embodiment, combustor  18  is a dry low emissions (DLE) combustor. In a further embodiment, combustor  18  is a can-annular combustor.  
      Assembly  200  may be used to drive a load, such as a generator  44 , which may be coupled to high-pressure turbine  20  using a power turbine shaft  46 . Alternatively, the load may be coupled to a forward extension (not shown) of high-pressure turbine  20 . Assembly  200  also includes a recuperator  50  that has a first fluid path  52  to facilitate channeling compressed air received from storage tank  140 , i.e. tower  104  through recuperator  50 , a second fluid path  54  to facilitate channeling heated air discharged from recuperator  50  to combustor  18 , and a third fluid path  56  to facilitate channeling exhaust gases from high-pressure turbine  20  through recuperator  50 .  
      In the exemplary embodiment, assembly  200  does not include a high pressure compressor to supply compressed air to combustor  18 . Rather, the total quantity of air utilized within combustor  18  to generate power to drive turbine  20  is supplied from at least one wind turbine tank  140 . Accordingly, wind turbine storage tank  140  is selectively sized to store a predetermined quantity of compressed air such that assembly  200  can be operated without utilizing a high-pressure compressor to supply additional air to supplement the combustion process.  
      During operation, wind is channeled through blades  108  thus causing main rotor shaft  116  to rotate. The rotational forces generated by blades  108  are then transmitted to compressor assembly  120  via gearbox  118 , thus causing compressor assembly  120  to compress air. The compressed air generated by compressor assembly  120  is channeled to storage device  140 , i.e. tower  104 , wherein the compressed air is stored for future use. Although the exemplary embodiment illustrates a single wind turbine  100  that is utilized to compress and store compressed air, it should be realized that a plurality of wind turbines  100  can be utilized to compress and store air to be utilized by a single gas turbine engine. Optionally, a single wind turbine  100  may be utilized to compress and store air that is then channeled to a plurality of gas turbine engine generator assemblies.  
      More specifically, air is drawn into recuperator  50  along first fluid path  52  from wind turbine storage tank  140 , i.e. the compressed air stored within cavity  142  of tower  104 . The compressed air is then heated within recuperator  50  utilizing high-pressure turbine  20  exhaust gases that are channeled through recuperator  50  utilizing third fluid path  56 . Channeling exhaust gases through recuperator  50  facilitates increasing an operational temperature of the air channeled therethrough. Accordingly, air discharged from storage tank  140  is channeled through recuperator  50 , wherein an operating temperature of the compressed air is increased from a first operational temperature to a second operational temperature that is greater than the first operational temperature utilizing exhaust gases discharged from high-pressure turbine  20 . The heated compressed air is then channeled from recuperator  50  to an inlet  34  of combustor  18  via second fluid path  54  where it is mixed with fuel and ignited to generate high temperature combustion gases. The combustion gases are channeled from combustor  18  to drive turbine  20 .  
       FIG. 6  is a perspective view of an exemplary wind turbine assembly  300  that can be utilized with assembly  200  shown in  FIG. 5 .  FIG. 7  is a portion of wind turbine  300  shown in  FIG. 6 . Wind turbine  300  is substantially similar to wind turbine  100 , shown in  FIG. 1 , and components in wind turbine  300  that are identical to components of wind turbine  100  are identified in  FIGS. 6 and 7  using the same reference numerals used in  FIG. 1 .  
      In the exemplary embodiment, wind turbine  300  includes a nacelle  102  that is mounted atop a relatively tall tower  104 . Wind turbine  100  also includes a rotor  106  that includes a plurality of rotor blades  108  that are each coupled to a rotating hub  110 . In some configurations and referring to  FIG. 7 , various components of wind turbine  300  are housed in nacelle  102  atop tower  104  of wind turbine  300 . The height of tower  104  is selected based upon factors and conditions known in the art. In one embodiment, wind turbine  300  includes one or more microcontrollers coupled within a control panel  112  that are used for overall system monitoring and control such as, but not limited to, pitch and speed regulation, high-speed shaft and yaw brake application, yaw and pump motor application and fault monitoring. In an alternative embodiment, wind turbine  300  utilizes a distributed or centralized control architecture (not shown) to perform system monitoring and control.  
      In the exemplary embodiment, the control system, i.e. control panel  112 , transmits control signals to a variable blade pitch drive system  114  that includes a DC pitch drive motor (not shown) to control the pitch of blades  108  that drive hub  110  as a result of wind. In some configurations, the pitches of blades  108  are individually controller by blade pitch drive system  114 .  
      Wind turbine  300  also includes a main rotor shaft  116  (also referred to as a “low speed shaft”) connected to hub  110  and a gearbox  118  that, in some configurations, utilizes a dual path geometry to drive a high speed shaft enclosed within gearbox  118 . The high speed shaft (not shown in  FIG. 6 ) is used to drive a first generator  320  that is supported by a main frame  132  as shown in  FIG. 7 . In some configurations, rotor torque is transmitted via a coupling  122 . First generator  320  may be of any suitable type, for example and without limitation, a wound rotor induction generator. Another suitable type by way of non-limiting example is a multi-pole generator that can run at the speed of the low speed shaft in a direct drive configuration, without requiring a gearbox.  
      Yaw drive  124  and yaw deck  126  provide a yaw orientation system for wind turbine  300 . In some configurations, the yaw orientation system is electrically operated and controlled by the control system in accordance with information received from sensors used to measure shaft flange displacement, as described below. Either alternately or in addition to the flange displacement measuring sensors, some configurations utilize a wind vane  128  to provide information for the yaw orientation system. The yaw system is mounted on a flange provided atop tower  104 .  
      In the exemplary embodiment, wind turbine  300  also includes a compressor assembly  330  that includes an air compressor drive  332  and an air compressor  334  that is coupled to air compressor drive  332 . In one embodiment, compressor drive  332  is an impeller or fan that is coupled to air compressor  334  such that when compressor drive  332  is rotated, a rotational force is transmitted to air compressor  334  to facilitate rotating air compressor  334  thus generating compressed air. For example, and in one embodiment, compressor assembly  330  is coupled within nacelle  102  such that the inlet of compressor drive  332  is approximately coaxial with the airstream channeled through blades  108  thus causing compressor drive  332  to also rotate.  
      In another embodiment, compressor assembly  330  is coupled to wind turbine  100  utilizing a shaft (not shown) such that wind moving through blades  108  causes the shaft to rotate thus rotating air compressor  334  to generate compressed air. For example, in on embodiment, the shaft is coupled to gearbox  118  such that gearbox  118  drives the shaft and thus drives air compressor  334 . Optionally, generator  320  is utilized to supply power to air compressor  334  to facilitate operating air compressor  334 . Although the exemplary embodiment illustrates a single wind turbine  100  and a single air compressor  334  configured to channel compressed air to a single air storage device  336 , a plurality of wind turbines  300  may be coupled to a plurality of compressors  334  that are each configured to channel compressed air to a single air storage device  336 . Optionally, a plurality of air storage devices  336  may be coupled together in a series arrangement to a single wind turbine  300 .  
      At least one wind turbine  300  is coupled to air compressor  334  such that wind turbine  300  drives air compressor  334  to generate compressed air. The compressed air is then channeled to air storage device  336  wherein the compressed air is stored until the compressed air is utilized by assembly  200 . Accordingly, wind turbine  300  facilitates producing power and storing the wind energy generated by wind turbine  300  in the compressed air, i.e. storage device  336  whenever wind energy can be harvested. In the exemplary embodiment, compressed air stored within storage device  336  is channeled to assembly  200  when the electricity demand exceeds a predetermined threshold.  
      More specifically, air is drawn into recuperator  50  along first fluid path  52  from wind turbine storage tank  336 . The compressed air is then heated within recuperator  50  utilizing low-pressure turbine  24  exhaust gases that are channeled through recuperator  50  utilizing third fluid path  56 . Channeling exhaust gases through recuperator  50  facilitates increasing an operational temperature of the air channeled therethrough. Accordingly, air discharged from storage tank  336  is channeled through recuperator  50 , wherein an operating temperature of the compressed air is increased from a first operational temperature to a second operational temperature that is greater than the first operational temperature utilizing exhaust gases discharged from low-pressure turbine  24 . The heated compressed air is then channeled from recuperator  50  to an inlet  34  of combustor  18  via second fluid path  54  where it is mixed with fuel and ignited to generate high temperature combustion gases. The combustion gases are channeled from combustor  18  to drive turbine  24 .  
       FIG. 8  is a temperature (T) and entropy (S) chart illustrating the systems described herein during normal operation. More specifically,  FIG. 8  illustrates that the working fluid, i.e. compressed air temperature is raised in the recuperator followed by further temperature rise in the combustor. Additionally, energy is extracted from the air flow in the turbine and the hot exhaust flow returns to the recuperator to preheat the incoming air.  
      Accordingly, as the pressure of the air flow from the compressed air storage device drops, temperature extraction from the turbine is reduced, thus increasing the turbine exhaust temperature. The temperature of the air entering the recuperator rises as a result and this also results in a corresponding increase in the temperature of the preheated air. The resulting efficiency characteristic is relatively insensitive to changes in the compressed air pressure although the highest power may be produced when the density of the air i.e. the pressure is highest.  
      Accordingly, the power generation system described herein facilitates storing energy produced by a wind farm, which can be harvested whenever the wind is available. Moreover, the stored energy from the wind can be utilized when the power demand is highest. In addition, the power generation system described herein provides a higher net conversion of gas energy to electricity using a recuperated gas turbine engine. Specifically, described herein is a system that includes at least one wind turbine system that is utilized to compress and store compressed air in a storage tank. The compressed air is discharged from the storage tank into a recuperator wherein a temperature of the compressed air is increased. The compressed air is then channeled from the recuperator into a combustor where fuel is ignited to further increase the temperature of the compressed air. The compressed air is then channeled to a turbine to produce power. Additionally, turbine exhaust is channeled through the recuperator to facilitate increasing the operational temperature of the compressed air channeled from the wind turbine.  
      While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims.