Abstract:
A system includes a controller communicatively coupled to a compressor. The controller is configured to sense an exhaust temperature of a gas turbine system fluidly coupled to the compressor and derive a setpoint based on the sensed exhaust temperature. The controller is also configured to actuate an inlet bleed heat valve based on the derived setpoint and an ambient temperature. The inlet bleed heat valve directs a compressor fluid from the compressor into a fluid intake system fluidly coupled to the compressor upstream of the compressor and configured to intake a fluid.

Description:
BACKGROUND 
       [0001]    The subject matter disclosed herein relates to power generation systems. Specifically, the embodiments described herein relate to controlling a turbine system in low ambient temperatures. 
         [0002]    In a power generation system, such as a gas turbine system, a compressor may be used to compress a fluid (e.g., air) prior to mixing the fluid with fuel for combustion. In low ambient temperatures, the power generation system may be configured to observe and maintain the operating limit of the compressor, particularly when the power generation system uses a low British Thermal Unit (BTU) fuel. Low BTU fuels include fuels that may have large concentrations of inert gases, synthetic gases, waste gases, and biomass gases. 
         [0003]    To maintain the operating limits of the compressor in low ambient temperature conditions, the power generation system may be configured to intentionally under-fire. That is, the fuel flow is often reduced to account for reduced compression due to the design limits of the compressor in low ambient temperatures. Reducing the fuel flow may in turn lead to lower firing temperatures for the power generation system. However, intentionally under-firing the power generation system may also result in output loss, in terms of the power generated by the power generation system as well as a loss of exhaust energy which may be captured and used by other components, such as a heat steam recovery generator (HSRG). It would be beneficial to operate power generation systems in low ambient temperatures, particularly when utilizing low BTU fuels, such that the system maintains the compressor limits while minimizing intentional under-fire. 
       BRIEF DESCRIPTION 
       [0004]    Certain embodiments commensurate in scope with the originally claimed invention are summarized below. These embodiments are not intended to limit the scope of the claimed invention, but rather these embodiments are intended only to provide a brief summary of possible forms of the invention. Indeed, the invention may encompass a variety of forms that may be similar to or different from the embodiments set forth below. 
         [0005]    In a first embodiment, a system includes a fluid intake system configured to intake a fluid and a compressor system fluidly coupled to the fluid intake system and configured to compress the fluid. The system also includes a combustor system fluidly coupled to the compressor and configured to combust a fuel mixed with the fluid, as wells as a turbine system fluidly coupled to the combustor and configured to rotate a shaft mechanically coupled to a load. Further, the system includes an inlet bleed heat system fluidly coupled to the compressor and to the fluid intake system and configured to direct a compressor fluid from the compressor into the fluid intake system. The system also includes a controller operatively coupled to the inlet bleed heat system and configured to sense an exhaust temperature of the turbine system. The controller is configured to adjust the compressor fluid flow via the inlet bleed heat system based on the exhaust temperature. 
         [0006]    In a second embodiment, a system includes a controller communicatively coupled to a compressor. The controller is configured to sense the exhaust temperature of a gas turbine system, wherein the gas turbine system is fluidly coupled to the compressor. The controller is also configured to derive a setpoint based on the sensed exhaust temperature. Further, the controller is configured to actuate an inlet bleed heat valve based on the derived setpoint and an ambient temperature. The inlet bleed heat valve directs a compressor fluid from the compressor into a fluid intake system which is fluidly coupled to the compressor upstream of the compressor and configured to intake a fluid. 
         [0007]    In a third embodiment, a non-transitory, computer-readable medium includes executable code having instructions. The instructions are configured to receive an input corresponding to an exhaust temperature of a turbine system and retrieve a baseload control function for a compressor system coupled to the turbine system. The instructions are also configured to retrieve data corresponding to a design limit of the compressor system and determine the difference between the operating level of the compressor system and the design limit of the compressor system. Further, the instructions are configured to calculate an exhaust temperature bias based on the baseload control function and the exhaust temperature. The instructions are configured to actuate an inlet bleed heat valve based on the exhaust temperature bias and the difference between the operating level of the compressor system and the design limit of the compressor system. The inlet bleed heat valve directs a compressor fluid from the compressor system into a fluid intake system fluidly which is coupled to the compressor system upstream of the compressor system and configured to intake a fluid. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    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: 
           [0009]      FIG. 1  is a schematic view of a power generation system, in accordance with an embodiment of the present approach; 
           [0010]      FIG. 2  is a block diagram of a control system within the power generation system of  FIG. 1 , in accordance with an embodiment of the present approach; 
           [0011]      FIG. 3  is a cross-sectional view of a compressor within the power generation system of  FIG. 1 , in accordance with an embodiment of the present approach; 
           [0012]      FIG. 4  is a schematic view of a cold day system included in the power generation system of  FIG. 1 , in accordance with an embodiment of the present approach; and 
           [0013]      FIG. 5  is a flow chart illustrating a process for operating the cold day system of  FIG. 4 , in accordance with an embodiment of the present approach. 
       
    
    
     DETAILED DESCRIPTION 
       [0014]    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. 
         [0015]    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. When a set of guide vanes is described as “closed,” it is intended to mean that the blades of the guide vanes are positioned at a relatively small angle. When a set of guide vanes are described as “open,” it is intended to mean that the blades of the guide vanes are positioned at a relatively large angle. 
         [0016]    Present embodiments relate to systems and methods for maintaining compressor operating limits and system output in power generation systems, such as gas turbine systems. Specifically, the techniques described herein use inlet bleed heat to maintain compressor operating limits in low ambient temperatures. More specifically, the techniques described herein relate to using inlet bleed heat to operate a compressor in low ambient temperatures, as well as adjusting the fuel schedule of the power generation system containing the compressor based on, for example, the inlet bleed heat adjustments. By utilizing inlet bleed heat to operate the compressor and adjusting the fuel schedule accordingly, the compressor may operate at the design limits during low ambient temperatures without a reduction in compression. As such, the power generation system may operate without intentionally under-firing (e.g., reducing the fuel flow) to account for reduced compression due to low ambient temperatures. As a result, the power generation system may remain at the desired firing temperature levels, increasing the output and exhaust energy of the power generation system in low ambient temperatures. 
         [0017]    With the foregoing in mind,  FIG. 1  illustrates a power generation system  10  that may be used to provide power to a load, such as an electric generator, a mechanical load, and so on. The power generation system  10  includes a fuel supply system  12 , which includes a fuel repository  14  and a fuel control valve  16  that controls the amount of fuel supplied to the power generation system  10 . The power generation system  10  further includes a fluid intake system  18  coupled to a fluid source  20  and a fluid control valve  22  that controls the amount of fluid supplied to the power generation system  10 . The power generation system  10  also includes a turbine system  24  which in turn includes a compressor  26 , a combustion system  28  containing one or more fuel nozzles  30 , a turbine  32 , and an exhaust section  34 . As shown in  FIG. 1 , the exhaust section  34  may include a heat recovery steam generator (HRSG)  36 . Further, a control system  38  oversees certain aspects of the power generation system  10 . In particular, the control system  36  may work in conjunction with sensors  40  and actuators  42  to monitor and adjust the operation of the power generation system  10 . For instance, the sensors  40  may include temperature sensors, oxygen sensor, pressure sensors, speed sensors, fuel flow sensors, fuel type sensors, and the like, while the fuel control valve  16  and the fluid control valve  22  are examples of actuators  42 . The control system  38  may also include a cold day system  44  to monitor and adjust the performance of the power generation system  10  based on the design limits of the compressor  26  and which is described in further detail below. 
         [0018]    During operation of the power generation system  10 , the fuel supply system  12  may provide fuel to the turbine system  24  via the fuel control valve  16 . Similarly, the fluid intake system  18  may provide oxidant fluid (e.g., air) to the compressor  26  via the fluid control valve  22 . The fluid is then compressed before being sent to the combustion system  28 . Within the combustion system  28 , the fuel nozzle(s)  30  inject fuel that mixes with the compressed fluid to create a fluid-fuel mixture that combusts before flowing into the turbine  32 . The combusted fluid-fuel mixture drives one or more stages of the turbine  32 , which may in turn drive a shaft connected to a load  46 . For example, the load  46  may be a generator to produce electricity. The combusted gases exit the turbine  32  and vent as exhaust gases through the exhaust section  34 . In the depicted embodiment, the exhaust gases pass through the HRSG  36 , which recovers the heat from the exhaust gases to produce steam. That is, the depicted power generation system  10  may be a combined cycle or co-generation system, such that the steam is used to drive a downstream steam turbine (i.e., a combined cycle system) or for a co-generation process. Additionally or alternatively, the exhaust gases may pass through other components within the exhaust section  34 , such as catalytic converter systems. 
         [0019]    As mentioned above, the control system  38  may control certain aspects of the operation of the power generation system  10 . The control system  38  includes memory  48 , a processor  50 , and a hardware interface  52  for interacting with the sensors  40  and the actuators  42 , as depicted in  FIG. 2 . As depicted, the processor  50  and/or other data processing circuitry may be operably coupled to memory  48  to retrieve and execute instructions for managing the power generation system  10 . For example, these instructions may be encoded in programs or software that are stored in memory  48 , which may be an example of a tangible, non-transitory computer-readable medium, and may be accessed and executed by the processor  50  to allow for the presently disclosed techniques to be performed. The memory  48  may be a mass storage device, a FLASH memory device, removable memory, or any other non-transitory computer-readable medium. Additionally and/or alternatively, the instructions may be stored in an additional suitable article of manufacture that includes at least one tangible, non-transitory computer-readable medium that at least collectively stores these instructions or routines in a manner similar to the memory  48  as described above. The control system  38  may also communicate with the sensors  40  and the actuators  42  via the hardware interface  52 , as stated above, including through wired and wireless conduits. 
         [0020]    In some embodiments, the control system  38  may be a distributed control system (DCS), such that each component or a group of components may include or be associated with a controller for controlling the specific component(s). In these embodiments, each controller may contain memory, a processor, and a hardware interface similar to that of the control system  38  as described above. Further, in such embodiments, the controllers may include a communicative link to other controllers to coordinate decision-making. 
         [0021]    Turning now to  FIG. 3 , the compressor  26  may include several sets of blades  54  that are arranged in stages or rows around a rotor or shaft  56 . The compressor  20  is coupled to the fluid intake system  18  via an intake shaft  58 , and to the combustion system via an output shaft  60 . A set of inlet guide vanes  62  controls the amount of fluid (e.g., air) that enters the compressor  26  at any given time, in contrast to the fluid control valve  22 , which controls the amount of fluid delivered from the fluid intake system  18  to the compressor  26 . In particular, the angles of the blades of the inlet guide vanes  62  may determine the amount of fluid that enters the compressor  26 . When the angles of the blades are relatively small (i.e., “substantially closed”) less fluid is received, but when the angles of the blades are relatively large (i.e., “substantially open”) more fluid is received. The angles of the inlet guide vanes  62  may be controlled by the control system  38 , or, as described in further detail below, by the cold day system  44 . 
         [0022]    During operation, the fluid travels through the compressor  26  and becomes compressed. That is, each set of blades  54  rotatively moves the fluid through the compressor  26  while reducing the volume of the fluid, thereby compressing the fluid. Compressing the fluid generates heat and pressure. In the present embodiments, the compressor  26  may be configured to re-circulate the compressor discharge (e.g., discharge fluid) back into the intake shaft  58  via an inlet manifold  64 . The re-circulated compressor discharge fluid is commonly referred to as “inlet bleed heat,” and may be used for a variety of functions, such as reducing icing on various inlets on the compressor  26  due to low ambient temperatures and protecting the compressor  26  when the inlet guide vanes  62  are closed. Accordingly, there are several commercially available inlet bleed heat systems that can be added to compressors such as the compressor  26  and incorporated into the operating software (e.g., control system  38 ) of the power generation system  10 . Advantageously, the techniques described herein apply the inlet bleed&#39;s temperature and pressure characteristics to more efficiently operate in certain environments, such as low ambient temperatures, for example, without a substantial reduction in compression. 
         [0023]    As mentioned above, the control system  38  oversees the operation of the power generation system  10 , and ensures that each component operates within its design limits. To do so, the control system  38  may have different components and processes for monitoring each component, similar to the scheme for a distributed control system as described above. One such aspect of the control system  38  may be the cold day system  44 . The cold day system  44  may monitor the operation of the compressor  38  and, in some embodiments, the fuel system  12 , when the power generation system  10  operates during low ambient temperatures, and may control certain aspects of the system  10  based on the monitoring. In particular, the cold day system  44  may redirect a portion of the inlet bleed heat generated by the compressor  26  to be added to the intake fluid for the compressor  26 , and may control the fuel scheduling based on the amount of inlet bleed heat fed into the compressor  26 . 
         [0024]    As will be described in further detail below, utilizing the inlet bleed heat as part of the intake fluid and adjusting the fuel scheduling may enable the compressor  26  to operate at desired margins (e.g., safety margins) of the design limits during low ambient temperatures. This, in turn, may reduce the amount of intentional under-firing of the power generation system  10  to account for compressor safety margins during low ambient temperatures, which subsequently improves the output of the power generation system  10  during low ambient temperatures. Particularly, the embodiments described herein may also improve the output of power generation systems  10  that utilize low BTU fuels during low ambient temperatures. Further, as noted above, because there are several commercially available inlet bleed heat systems, the embodiments described herein may be applied retroactively to power generation system  10  by utilizing a commercially available inlet bleed heat system and making modifications to the control system  38  as necessary. In some power plants having the system  10 , the modifications may be software only, while in other power plants, the modifications may include hardware and software modifications. 
         [0025]    In present embodiments, the cold day system  44  is part of the control system  38 , and thus uses the sensors  40 , actuators  42 , memory  48 , and processor  50 , as described above. In other embodiments, the cold day system  44  may be configured on a controller as part of a distributed control system. In still other embodiments, the cold day system  44  may be separate from the control system  38 , and may communicate and work in conjunction with the control system  38  as necessary. 
         [0026]    Turning now to  FIG. 4 , the figure illustrates a schematic diagram of embodiments of the cold day system  44  communicatively coupled to the compressor  26  and combustor  28 . As stated above, the cold day system  44  oversees the operation of the compressor  26 , as well as other components of the system  10 . The cold day system  44  may utilize a baseload control curve  66  (or similar derivation) that represents normal operating procedures for the compressor  26  (i.e., no inlet bleed heat addition at low ambient temperatures). In present embodiments, the baseload control curve  66  corresponds to a compressor pressure ratio function, which compares the pressure of the fluid exiting the compressor  26  to that of the fluid entering the compressor  26 . Alternately or additionally, other baseload control curves  66  that quantify the operation of the compressor  26  may be used. The baseload control curve  66  may be stored or generated during operation by either the cold day system  44  or the control system  38 . In other embodiments, the baseload control curve  66  may be calculated offline and uploaded to the cold day system  44  or the control system  38 . 
         [0027]    The cold day system  44  then determines an operating difference  68  between the design limits  70  of the compressor  26  and the current operating level  72  of the compressor  26 . The data representing the design limits  70  (e.g., pressures, flows, temperatures, speeds, compression ratios) may be stored on the memory  48  in embodiments in which the cold day system  44  is part of the control system  38 . Alternately, in embodiments in which the cold day system  44  is a controller within a distributed control system or separate from the control system  38 , the cold day system  44  may be configured to retrieve the design limits  70  from the control system  38 , or from memory in the cold day system  44 . In still further embodiments, either the cold day system  44  or the control system  38  may be configured to retrieve the design limits  70  from another component or system, such as a data repository containing information about the various components of the power generation system  10 . The current operating level  72  may be determined based on data received from the sensors  40  disposed in or around the compressor  26 , such as the temperature or pressure of the fluid exiting the compressor  26 . In some embodiments, the cold day system  44  may determine the operating difference  68  only when activated by a control signal. For instance, the cold day system  44  may only determine the operating difference  68  if the cold day system  44  or the control system  38  has determined that the ambient temperature is below a pre-set threshold. 
         [0028]    Based on the operating difference, the cold day system  44  may control an inlet bleed heat valve  74  to add inlet bleed heat to the intake fluid of the compressor  20 . By adding the inlet bleed heat, which, as mentioned above, is included in a portion of the fluid generated by compressing fluid, the temperature of the intake fluid increases as a whole. This temperature increase, in turn, increases the amount of compression of the fluid, regardless of the operating level of the compressor  26 . That is, if the compressor  26  receives a fluid at a first temperature and then a second fluid at a second higher temperature, the compression at the lower temperature will be less than the compression the higher temperature, regardless of any change in the operation of the compressor  20 . 
         [0029]    Adding inlet bleed heat enables the compressor  26  to more closely adhere to the desired compressor pressure ratio function, even when the compressor  26  operates at a reduced rate due to low ambient temperatures. Further, because the compressor  26  still may adhere to the desired compressor pressure ratio, the control system  38  does not need to reduce fuel flow in order to account for a decrease in compression. Accordingly, the power generation system  10  can then maintain the desired firing temperatures during low ambient temperatures. As such, the power generation system  10  may have increased output compared to other power generation systems in which firing temperature suppression is used to maintain compressor operating limits during low ambient temperatures. The power generation system  10  may also have increased exhaust energy, which may be used by downstream components, such as the HRSG  30 . 
         [0030]    Once inlet bleed heat is added to the fluid intake, the temperature of the compressed fluid rises, as mentioned above. Subsequently, the compressor pressure ratio function, and other types of baseload control curves  66 , shift based on the inlet bleed heat addition. Additionally, the exhaust gas temperature of the turbine system  24  changes relative to the exhaust gas temperature of the turbine system  24  when no inlet bleed heat is added. Based on the shifted baseload control curves  66 , the cold day system  44  then calculates an exhaust temperature bias  76  that represents the change in the exhaust gas temperature due to the inlet bleed heat addition. The cold day system  44  then adjusts the inlet bleed heat addition or the fuel schedule for the turbine system  24  to maintain the desired firing temperature of the turbine system  24  while observing the design limits  70  of the compressor  26 . 
         [0031]    Turning now to  FIG. 5 , the figure depicts a flow chart of an embodiment of a process  80  suitable for adding inlet bleed heat during low ambient temperature conditions. The process  80  may be implemented as computer instructions stored in memory and executable by the cold day system  44 . The cold day system  44  may execute for the instructions to better maintain the design limits  70  of the compressor  26  during operation. Although the process  80  is described below in detail, the process  80  may include other steps not shown in  FIG. 5 . Additionally, the steps illustrated may be performed concurrently or in a different order. The process  80  may be stored in the memory  40  and executed by the processor  42 , as described above. 
         [0032]    Beginning at block  82 , the cold day system  44  may retrieve the baseload control curve  66 , which may correspond to the compressor pressure ratio function, or any other control function that quantifies the operation of the compressor  26 . As mentioned above, the cold day system  44  may retrieve the baseload control curve  66  from the memory  40 , the control system  38 , or an external system such as a data repository. Further, in other embodiments, the cold day system  44  may be configured to generate the baseload control curve  66  when the power generation system  10  is offline or during operation, or the curve  66  may be generated by the manufacturer and stored for use during system  10  operations. 
         [0033]    At block  84 , the cold day system  44  compares the design limits  70  of the compressor  26  to the current operating level  72  of the compressor  26  to generate the operating difference  68 . Again, as mentioned above, the cold day system  44  may retrieve the design limits  70  from the memory  40 , the control system  38 , or an external system such as a data repository. The current operating level  72  (e.g., pressure, temperature, flow, speed, compression ratio) may be determined based on the data from the sensors  40 . In some embodiments, the current operating level  72  may be determined by the control system  38 , and the data passed to the cold day system  44 . Further, as mentioned above, the cold day system  44  may be configured to determine the operating difference  68  only upon receipt of an activation signal. 
         [0034]    Next, at block  86 , the cold day system  44  determines whether to adjust the amount of inlet bleed heat addition to the fluid intake of the compressor  26  or adjust the fuel schedule of the turbine system  24  based on the baseload control curve  66 , the operating difference  68 , and the exhaust temperature bias  76 , if available. Further, in some embodiments, the cold day system  44  may also determine whether to adjust the inlet guide vanes  62  instead. If the cold day system  44  decides to adjust one of the three parameters, then it may proceed to block  88 , which is described in detail further below. If not, then the cold day system  44  returns to generating the operating difference  68  at block  84 . 
         [0035]    At block  88 , the cold day system  44  adjusts the inlet bleed heat addition, the fuel schedule, and/or the inlet guide vanes  62  as determined in block  86 . To do so, the cold day system  44  actuates the inlet bleed heat valve  74 , the fuel control valve  16 , or the inlet guide vanes  62 . In some embodiments (e.g., in a distributed control system), the cold day system  44  may send a control signal to the control system  38  to actuate any of the inlet bleed heat valve  74 , the fuel control valve  16 , or the inlet guide vanes  62 . 
         [0036]    Once the cold day system  44  adjusts the inlet bleed heat addition, the fuel schedule, or the inlet guide vanes  62 , the cold day system  44  then determines any changes to the control functions or parameters. That is, at block  90 , the cold day system  44  may determine any shifts in the baseload control curve  66 , the new operating level  72  of the compressor  26  and, subsequently, the operating difference  68 , or the exhaust temperature bias  76 . The cold day system  44  may then return to determining adjustments for the inlet bleed heat addition, the fuel schedule, or the inlet guide vanes at block  86 . 
         [0037]    Technical effects of the invention include systems and methods for operating a power generation system during low ambient temperatures. Certain embodiments may enable components of the power generation system to operate at design limits during low ambient temperatures without reducing the output of the power generation system. For example, the present cold day system may add inlet bleed heat from the compressor to the fluid intake of the compressor, which may allow the compressor to operate at design limits during low ambient temperatures while producing the desired amount of compression. Accordingly, the present power generation system does not have to intentionally under-fire to account for reduced compression, which subsequently increases the output of the power generation system during low ambient temperatures. Further, in certain embodiments, the present cold day system may be applied retroactively to power generation systems by utilizing commercially available inlet bleed heat systems and modifications to the control system of the power generation system. The technical effects and technical problems in the specification are exemplary and not limiting. It should be noted that the embodiments described in the specification may have other technical effects and can solve other technical problems. 
         [0038]    This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal language of the claims.