Patent Document

BACKGROUND OF THE INVENTION 
     The subject matter disclosed herein relates to a controller for a gas turbine. 
     Industrial and power generation gas turbines may have a control system, also referred to as a controller, that monitors and controls turbine operation. These controllers govern the combustion system of the gas turbine based on information and data sensors located at various positions in and around the gas turbine. Control scheduling algorithms are executed by the controller to operate the combustion system of the gas turbine based on the sensor data. Combustion systems for gas turbines are generally sensitive to ambient conditions, such as outside ambient humidity or temperature. In particular, seasonal variations in humidity or temperature may affect the operation of the combustion system. 
     The gas turbine may create environmental pollutants such as nitrogen oxides (NOx) during operation, which may be emitted as part of the turbine exhaust. Levels of NOx emissions by the gas turbine may be affected by ambient conditions. For example, a high ambient inlet temperature may drive NOx emissions relatively low; high ambient humidity may also lower NOx emissions. Periods of high ambient temperature or high ambient humidity may coincide with periods of high power demand, during which the combustion system of the gas turbine may be operated at a peak firing temperature to meet the high power demand. However, NOx emissions levels may increase as the firing temperature of the combustion system increases. Emissions of NOx from the gas turbine must be maintained below mandated levels in order to comply with emissions regulations. 
     BRIEF DESCRIPTION OF THE INVENTION 
     According to one aspect of the invention, a gas turbine comprises a plurality of target exhaust temperature determination modules, the plurality of target exhaust temperature modules comprising a nitrogen oxide (NOx) compliance module configured to determine an exhaust temperature at which an exhaust of the gas turbine complies with a maximum permitted level of NOx; at least one bias module, the at least one bias module configured to apply a bias to an output of at least one of the plurality of target exhaust temperature determination modules; and a controller configured to operate the gas turbine to produce the exhaust temperature determined by the NOx compliance module. 
     According to another aspect of the invention, a method for controlling a gas turbine comprises determining whether conditions are appropriate for peak operation, and in the event that conditions are determined to be appropriate for peak operation: determining a first peak exhaust temperature for the gas turbine at which nitrogen oxide (NOx) emissions of the gas turbine are below a maximum permitted level; applying a bias to a second determined exhaust temperature; and operating the gas turbine at the first determined peak exhaust temperature. 
     These and other advantages and features will become more apparent from the following description taken in conjunction with the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       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: 
         FIG. 1  is an embodiment of a gas turbine having a controller. 
         FIG. 2  is an embodiment of a gas turbine controller comprising NOx compliant peak. 
         FIG. 3  is an embodiment of a method for NOx compliant peak. 
         FIG. 4  is an embodiment of a computer that may be used in conjunction with embodiments of a controller for a gas turbine controller comprising NOx compliant peak. 
     
    
    
     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 
     Embodiments of systems and methods for NOx compliant peak for a gas turbine are provided. When ambient temperature, humidity, and power demand conditions are determined to be appropriate, gas turbine combustors may be operated at a peak firing temperature, up to a limit of NOx emissions compliance, resulting in high energy production to meet high demand levels. 
       FIG. 1  illustrates an embodiment of a gas turbine  100 . Gas turbine  100  comprises a compressor  104 , combustors  106  and  107 , a turbine  108  drivingly coupled to the compressor  104 , and a controller  101 . Two combustors  106  and  107  are shown in gas turbine  100  for illustrative purposes only; embodiments of a gas turbine  100  may comprise any appropriate number of combustors. Inlet duct  102  feeds ambient air and possibly injected water via inlet guide vanes  103  to the compressor  104 . The inlet duct  102  may have ducts, filters, screens, and sound absorbing devices that each may contribute to a pressure loss of ambient air flowing through the inlet  102  into the inlet guide vanes  103  of the compressor  104 . Exhaust duct  109  directs combustion gases from the outlet of the turbine  108  through ducts having, for example, emission control and sound absorbing devices. The exhaust duct  109  applies a back pressure to the turbine. The amount of back pressure may vary over time due to the addition of components to the exhaust duct  109 , and to dust and dirt clogging exhaust passages. The turbine  108  may drive a generator  110  that produces electrical power. The inlet loss to the compressor  104  and the turbine  108  exhaust pressure loss tend to be a function of corrected flow through the gas turbine  100 . Accordingly, the amount of inlet loss and turbine back pressure vary with the flow through the gas turbine  100 . 
     The operation of the gas turbine may be monitored by sensors  111 - 114 . Sensors  111 - 114  detect conditions at the inlet duct  102 , exhaust duct  109 , turbine  108 , compressor  104 , and ambient conditions surrounding gas turbine  100 . For example, temperature sensors may monitor ambient temperature surrounding the gas turbine, compressor discharge temperature, turbine exhaust gas temperature, and other temperature measurements of the gas stream through the gas turbine. Pressure sensors may monitor ambient pressure, and static and dynamic pressure levels at the compressor inlet and outlet and turbine exhaust, as well as at other locations in the gas stream. Further, humidity sensors, e.g., wet and dry bulb thermometers, may measure ambient humidity in the inlet duct of the compressor. The sensors  111 - 114  may also comprise flow sensors, speed sensors, flame detector sensors, valve position sensors, guide vane angle sensors, or the like that sense various data pertinent to the operation of gas turbine  100 . Sensors  111 - 114  are shown for exemplary purposes only; any appropriate number or type of sensors may be placed at any appropriate location on gas turbine  100 . 
     Embodiments of controller  101  may regulate the operation of combustors  106  and  107  via fuel control module  105  using the information provided by sensors  111 - 114  to produce exhaust having a target temperature at exhaust duct  109 . The target exhaust temperature is determined based on considerations including but not limited to emissions levels of carbon monoxide (CO) and NOx, and temperature tolerances of the physical components of gas turbine  100 . Controller  101  may be embodied in any appropriate hardware or software. Fuel control module  105  regulates the rate of fuel flowing from a fuel supply (not shown) to the combustors  106  and  107 , thereby determining the combustion temperature and levels of emissions of combustors  106  and  107 . The fuel control module may in some embodiments be a separate unit  105 , or may in other embodiments be an internal component of controller  101 . 
       FIG. 2  illustrates an embodiment of a gas turbine controller  200  comprising NOx compliant peak. Modules  201 - 204  may use any relevant data from sensors  111 - 114 , including but not limited to ambient humidity, ambient pressure, compressor pressure ratio, specific humidity, inlet pressure loss, exhaust backpressure, or compressor exit temperature, to determine a maximum temperature based on considerations including but not limited to emissions levels of CO or NOx, or temperature tolerances of the physical components of the gas turbine  100 . A maximum rated exhaust temperature for the gas turbine  100  is supplied to minimum selector module  209  at input  205 . NOx limiting module  201  determines a maximum exhaust temperature at which emissions levels of NOx are compliant with regulatory levels, and supplies the determined NOx compliant temperature to minimum selector module  209 . CO limiting module  202  determines a maximum exhaust temperature at which emissions levels of CO are compliant with regulatory levels. TFire target module  203  determines a target exhaust temperature reflecting an optimal firing temperature at which the gas turbine  100  is designed to operate. Each of these determined temperatures are supplied to maximum selector module  208 , which supplies the maximum of its two inputs to minimum selector module  209 . TFire limiting module  204  also determines a target exhaust temperature reflecting a maximum temperature for optimal firing of the gas turbine, which in some embodiments may be higher than the TFire target exhaust temperature, and supplies the determined temperature to minimum selector module  209 . Minimum selector module  209  selects the minimum value from maximum operating temperature  205 , NOx limiting module  201 , maximum selector module  208 , and TFire limiting module  204 , and outputs the minimum value as an overall target exhaust temperature at output  210 . The controller  200  then regulates the operation of combustors  106  and  107  to achieve the target exhaust temperature given at output  210  at exhaust duct  109 . 
     An operator of gas turbine  100  may determine that conditions of high ambient temperature and humidity exist at inlet duct  102 , and turn on NOx compliant peak operation if necessary to meet high power demand levels. Alternatively, NOx compliant peak may be turned on automatically if conditions are determined to be appropriate. When NOx compliant peak mode is turned on, bias module  206  for TFire target module  203  and bias module  207  for TFire limiting module  204  are enabled. Bias modules  206  and  207  raise the outputs of TFire target module  203  and TFire limiting module  204  such that the outputs of TFire target module  203  and TFire limiting module  204  are higher than the output of NOx limiting module  201 , resulting in NOx limiting module  201  supplying the controlling input to minimum selector module  209 . This allows the gas turbine  100  to raise power output to the limit of NOx compliance. 
     If conditions of relatively high ambient humidity and temperature exist, the temperature determined by NOx limiting module  201  may be higher than maximum exhaust temperature  205 . Under such conditions, the maximum exhaust temperature input  205  may be the controlling input to minimum selector  209 , and the gas turbine  100  will operate at the maximum exhaust temperature  205 , which may result in NOx levels below the compliance limit. 
       FIG. 3  illustrates an embodiment of a method  300  for NOx compliant peak. In block  301 , it is determined whether conditions are appropriate for NOx compliant peak operation. The conditions may include high ambient humidity, high ambient temperature, and high power demand. The determination may be made by an operator of the gas turbine, or may be made automatically. If conditions are appropriate, NOx compliant peak operation is enabled. In block  302 , a peak firing temperature at which NOx emissions levels are below maximum permitted levels is determined. In block  303 , a bias is applied the TFire target temperature and the TFire limiting temperature, raising the TFire target temperature and the TFire limiting temperature so that they are higher than the peak firing temperature determined in block  302 . In some embodiments, the TFire target temperature and TFire limiting temperature may be pegged to a maximum rated exhaust temperature of the gas turbine. In block  304 , the gas turbine operates at the peak firing temperature determined in block  302 , limiting NOx emissions to permitted levels while enhancing power production. 
       FIG. 4  illustrates an example of a computer  400  having capabilities, which may be utilized by exemplary embodiments of a controller for a gas turbine comprising a NOx compliant peak as embodied in software. Various operations discussed above may utilize the capabilities of the computer  400 . One or more of the capabilities of the computer  400  may be incorporated in any element, module, application, and/or component discussed herein. 
     The computer  400  includes, but is not limited to, PCs, workstations, laptops, PDAs, palm devices, servers, storages, and the like. Generally, in terms of hardware architecture, the computer  400  may include one or more processors  410 , memory  420 , and one or more input and/or output (I/O) devices  470  that are communicatively coupled via a local interface (not shown). The local interface can be, for example but not limited to, one or more buses or other wired or wireless connections, as is known in the art. The local interface may have additional elements, such as controllers, buffers (caches), drivers, repeaters, and receivers, to enable communications. Further, the local interface may include address, control, and/or data connections to enable appropriate communications among the aforementioned components. 
     The processor  410  is a hardware device for executing software that can be stored in the memory  420 . The processor  410  can be virtually any custom made or commercially available processor, a central processing unit (CPU), a data signal processor (DSP), or an auxiliary processor among several processors associated with the computer  400 , and the processor  410  may be a semiconductor based microprocessor (in the form of a microchip) or a macroprocessor. 
     The memory  420  can include any one or combination of volatile memory elements (e.g., random access memory (RAM), such as dynamic random access memory (DRAM), static random access memory (SRAM), etc.) and nonvolatile memory elements (e.g., ROM, erasable programmable read only memory (EPROM), electronically erasable programmable read only memory (EEPROM), programmable read only memory (PROM), tape, compact disc read only memory (CD-ROM), disk, diskette, cartridge, cassette or the like, etc.). Moreover, the memory  420  may incorporate electronic, magnetic, optical, and/or other types of storage media. Note that the memory  420  can have a distributed architecture, where various components are situated remote from one another, but can be accessed by the processor  410 . 
     The software in the memory  420  may include one or more separate programs, each of which comprises an ordered listing of executable instructions for implementing logical functions. The software in the memory  420  includes a suitable operating system (O/S)  450 , compiler  440 , source code  430 , and one or more applications  460  in accordance with exemplary embodiments. As illustrated, the application  460  comprises numerous functional components for implementing the features and operations of the exemplary embodiments. The application  460  of the computer  400  may represent various applications, computational units, logic, functional units, processes, operations, virtual entities, and/or modules in accordance with exemplary embodiments, but the application  460  is not meant to be a limitation. 
     The operating system  450  controls the execution of other computer programs, and provides scheduling, input-output control, file and data management, memory management, and communication control and related services. It is contemplated by the inventors that the application  460  for implementing exemplary embodiments may be applicable on all commercially available operating systems. 
     Application  460  may be a source program, executable program (object code), script, or any other entity comprising a set of instructions to be performed. When a source program, then the program is usually translated via a compiler (such as the compiler  440 ), assembler, interpreter, or the like, which may or may not be included within the memory  420 , so as to operate properly in connection with the O/S  450 . Furthermore, the application  460  can be written as (a) an object oriented programming language, which has classes of data and methods, or (b) a procedure programming language, which has routines, subroutines, and/or functions, for example but not limited to, C, C++, C#, Pascal, BASIC, API calls, HTML, XHTML, XML, ASP scripts, FORTRAN, COBOL, Perl, Java, ADA, .NET, and the like. 
     The I/O devices  470  may include input devices such as, for example but not limited to, a mouse, keyboard, scanner, microphone, camera, etc. furthermore, the I/O devices  470  may also include output devices, for example but not limited to a printer, display, etc. Finally, the I/O devices  470  may further include devices that communicate both inputs and outputs, for instance but not limited to, a NIC or modulator/demodulator (for accessing remote devices, other files, devices, systems, or a network), a radio frequency (RF) or other transceiver, a telephonic interface, a bridge, a router, etc. The I/O devices  470  also include components for communicating over various networks, such as the Internet or intranet. 
     If the computer  400  is a PC, workstation, intelligent device or the like, the software in the memory  420  may further include a basic input output system (BIOS) (omitted for simplicity). The BIOS is a set of essential software routines that initialize and test hardware at startup, start the O/S  450 , and support the transfer of data among the hardware devices. The BIOS is stored in some type of read-only-memory, such as ROM, PROM, EPROM, EEPROM or the like, so that the BIOS can be executed when the computer  400  is activated. 
     When the computer  400  is in operation, the processor  410  is configured to execute software stored within the memory  420 , to communicate data to and from the memory  420 , and to generally control operations of the computer  400  pursuant to the software. The application  460  and the O/S  450  are read, in whole or in part, by the processor  410 , perhaps buffered within the processor  410 , and then executed. 
     When the application  460  is implemented in software it should be noted that the application  460  can be stored on virtually any computer readable medium for use by or in connection with any computer related system or method. In the context of this document, a computer readable medium may be an electronic, magnetic, optical, or other physical device or means that can contain or store a computer program for use by or in connection with a computer related system or method. 
     The application  460  can be embodied in any computer-readable medium for use by or in connection with an instruction execution system, apparatus, or device, such as a computer-based system, processor-containing system, or other system that can fetch the instructions from the instruction execution system, apparatus, or device and execute the instructions. In the context of this document, a “computer-readable medium” can be any means that can store, communicate, propagate, or transport the program for use by or in connection with the instruction execution system, apparatus, or device. The computer readable medium can be, for example but not limited to, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, device, or propagation medium. 
     More specific examples (a nonexhaustive list) of the computer-readable medium may include the following: an electrical connection (electronic) having one or more wires, a portable computer diskette (magnetic or optical), a random access memory (RAM) (electronic), a read-only memory (ROM) (electronic), an erasable programmable read-only memory (EPROM, EEPROM, or Flash memory) (electronic), an optical fiber (optical), a USB drive, and a portable compact disc memory (CDROM, CD R/W) (optical). Note that the computer-readable medium could even be paper or another suitable medium, upon which the program is printed or punched, as the program can be electronically captured, via for instance optical scanning of the paper or other medium, then compiled, interpreted or otherwise processed in a suitable manner if necessary, and then stored in a computer memory. 
     In exemplary embodiments, where the application  460  is implemented in hardware, the application  460  can be implemented with any one or a combination of the following technologies, which are each well known in the art: a discrete logic circuit(s) having logic gates for implementing logic functions upon data signals, an application specific integrated circuit (ASIC) having appropriate combinational logic gates, a programmable gate array(s) (PGA), a field programmable gate array (FPGA), etc. 
     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.

Technology Category: 2