Abstract:
A non-transitory computer-readable medium storing computer executable code that includes instructions to receive a signal representative of a gas turbine firing temperature. The code further includes instructions to convert the signal to an actuator signal to actuate a fuel valve supplying fuel to the gas turbine by following a first reference function. The first reference function includes a first boundary function, a second boundary function, or a combination thereof. The first boundary function maps a first value to a first temperature and the second boundary function maps a second value to a second temperature.

Description:
BACKGROUND 
     The subject matter disclosed herein relates generally to turbomachinery systems, such as gas turbines. Specifically, the subject matter relates to methods and systems for controlling a gas turbine system. 
     In a turbine system, the firing temperature is the temperature produced within the turbine&#39;s combustion system, e.g. flame temperature. Firing control algorithms may determine how to derive a desired firing temperature and then provide the actual firing temperature of the turbine by controlling, for example, an amount of fuel fed to the combustion system. The firing control algorithms may determine the desired firing temperature based on turbine parameters such as exhaust temperature, compressor pressure ratio, and compressor inlet temperature. 
     Current firing control algorithms incorporate static assumptions about the turbine&#39;s operating environment and component performance over time. They also consider the turbine&#39;s various operating states and constraints interdependent with each other. Because of such assumptions and state interdependency, the accuracy of the firing temperature control and the level of performance associated with these firing control algorithms may decreases as the turbine ages, and the algorithms may require seasonal tuning. 
     Certain firing control algorithms, such as model based control (MBC) algorithms, may incorporate variations in the turbine&#39;s operating environment and/or component performance over time. MBC firing control algorithms may treat the turbine&#39;s various operating states and constraints as independent states, leading to more accurate firing temperature control and increased levels of performance. However, implementing MBC firing control algorithms may require a complete overhaul of the turbine controller&#39;s software and/or hardware by a qualified technician, which can be slow and expensive. 
     BRIEF DESCRIPTION 
     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. 
     In a first embodiment, a system may include a controller configured to control a turbomachinery. The controller may include data relating to a first boundary function mapping a first value related to the turbomachinery to a first temperature and a second boundary function mapping a second value related to the turbomachinery to a second temperature. Further, the controller may receive a sensor signal representative of a fired temperature of the turbomachinery. The controller may subsequently transform the sensor signal to an actuator signal to actuate a fuel valve supplying fuel to the turbomachinery by following a first reference function that includes at least the first boundary function, the second boundary function, or a combination of the two. 
     In a second embodiment, a non-transitory computer-readable medium may store computer executable code that includes instructions to receive a signal representative of a gas turbine firing temperature. The computer executable code may also include instructions to convert the signal to an actuator signal to actuate a fuel valve supplying fuel to the gas turbine by following a first reference function. The first reference function may include a first boundary function, a second boundary function, or a combination thereof. The first boundary function may map a first value related to the gas turbine system to a first temperature and the second boundary function may map a second value related to the gas turbine system to a second temperature. 
     In a third embodiment, a method includes deriving a first boundary function mapping a first value related to a turbomachinery to a first temperature and deriving a second boundary function mapping a second value related to the turbomachinery to a second temperature. The method may also include collecting a sensor signal representative of a fired temperature of the turbomachinery and converting the sensor signal to a first actuator signal to actuate a fuel valve of a gas turbine system by following a first reference function. The first reference function may include the first boundary function, the second boundary function, or a combination thereof. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       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: 
         FIG. 1  a block diagram of an embodiment of a gas turbine system, in accordance with an embodiment of the present approach; 
         FIG. 2  is a block diagram of a control system of a gas turbine system, in accordance with an embodiment of the present approach; 
         FIG. 3  is a block diagram of a control flow of a gas turbine system, in accordance with an embodiment of the present approach; 
         FIG. 4  is a block diagram of a prior art firing control algorithm for a gas turbine system, in accordance with an embodiment of the present approach; 
         FIG. 5  is a block diagram of an enhanced firing control algorithm for a gas turbine system, in accordance with an embodiment of the present approach; 
         FIG. 6  is a block diagram illustrating the reference functions associated with various operating states, in accordance with an embodiment of the present approach; 
         FIG. 7  is a block diagram of the enhanced firing control algorithm of  FIG. 5  with a humidity correction, in accordance with an embodiment of the present approach; 
         FIG. 8  is a graph comparing embodiments of firing temperature profiles of the existing and enhanced firing control algorithms and the desired firing temperature for a specific set of operating characteristics; and 
         FIG. 9  is a graph comparing embodiments of firing temperature profiles of a variety of firing control algorithms and the desired firing temperature after 24K hours of operation. 
     
    
    
     DETAILED DESCRIPTION 
     One or more specific embodiments of the present subject matter 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. 
     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. The term “firing temperature” refers to the overall temperature of the combustion gases generated in the combustion system of a turbomachinery system or to the temperature of the combustion gases at specific locations in the turbomachinery system, such as combustor exit, turbine inlet or stage  1  nozzle trailing edge. A “firing control algorithm” refers to an algorithm that determines a desired firing temperature and then manipulates one or more actuators, such as fuel valves delivering fuel to fuel nozzles, to produce an actual firing temperature in a combustion system. The term “boundary function” refers to one or more reference functions mapping a measured turbine parameter to a temperature, such a temperature related to turbomachinery. 
     Present embodiments relate to systems and methods for controlling the firing temperature of a turbine combustion system based on one or more parameters associated with the turbomachinery system. Specifically, the present embodiments relate to a control process to determine the firing temperature of the turbine combustion system based on the one or more parameters and then determine control actions that may be applied to a fuel supply of the turbomachinery system to achieve the desired firing temperature. The control processes described herein may be provided as a software upgrade, such as by adding or updating a few lines of computer code (e.g., less than 500 lines of code) to an existing control system. The update control process may improve a full load firing control response and address performance degradation of the turbine system and components thereof. 
     Techniques described herein provide for a full (or partial) load firing control strategy where a singular exhaust temperature reference scheduled as a function of compressor pressure ratio may be used to implicitly manage a resultant firing temperature target that may be variable across a minimum to maximum ambient temperature range. These control strategies provide implicit control of firing temperature based on assumed component performance levels that reflect the average unit and the associated relationship between firing temperatures and exhaust temperatures. While other control strategies, such as model based control (MBC) may provide more direct control of firing levels by use of gas turbine cycle performance models within the control algorithm, there are a large number of gas turbine systems deployed in the field that currently use simpler control strategies. Such deployed systems might benefit from the upgrades to control algorithms described herein. 
     The desired firing temperature may be variable with ambient or compressor inlet condition, usually resulting in a suppression of the target temperature at cold ambient conditions to maintain combustor operability and emissions within desired limits. As noted above, tailoring of the firing profile with ambient temperature may be built into the singular exhaust temperature reference scheduled as a function of compressor pressure ratio. The singular exhaust temperature reference may be tuned to meet a target firing level with reasonable accuracy during a new unit installation performance characterization. However, as the gas turbine continues to operate and component performance levels degrade from the level demonstrated during performance characterization, the resultant firing temperature level may begin to trend off target to design intent. The degree to which the exhaust temperature control algorithm trends off target is a function of multiple effects but is most pronounced where the intended shaping of the firing profile with ambient condition is being suppressed relative to a maximum level. Where there is an intended suppression with ambient condition built in to the exhaust temperature reference, then the sensitivity of firing control to degradation effects is most pronounced. This trending of firing temperature off target relative to design intent can result in combustor operability and emissions issues, possibly leading to combustor operability re-tuning and periods of unavailability. The techniques described herein offer an approach to improving this tendency of firing temperature drift from design intent as the component performance degrades. 
     The control processes described herein may treat the turbine&#39;s operating states and constraints as independent states, increasing the accuracy of the firing temperature control and the overall performance of the turbine. The control process may also include a tuning element and adjustment functions to account for variation among individual turbomachinery systems as well as variation in the turbine&#39;s operating environment. Further, the control process may include some or all elements of existing control processes, and may be provided as a smaller and more efficient upgrade to the turbomachinery software and/or hardware. 
     With the forgoing in mind, it may be useful to describe an embodiment of a turbomachinery system, such as an example gas turbine system  10  illustrated in FIG.  1 . In certain embodiments, the gas turbine system  10  may include a gas turbine  12 , a control system  14 , and a fuel supply system  16 . These systems may operate in conjunction to determine the firing temperature in the gas turbine  12  and to adjust the fuel supply system  16 . As illustrated, the gas turbine  12  may include a compressor  18 , combustion system  20 , fuel nozzle  22 , turbine  24 , and exhaust section  26 . During operation, the gas turbine  12  may intake gas (e.g., air)  28  into the compressor  18 , which then compresses the air  28  and moves it to the combustion system  20  (e.g., a plurality of combustors). In the combustion system  20 , the fuel nozzle  22  (or a plurality of fuel nozzles  22 ) injects fuel that mixes with the compressed air creating an air-fuel mixture. The air-fuel mixture may combust in the combustion system  20  to generate hot combustion gases, which flow downstream into the turbine  24  to drive one or more turbine  24  stages. For example, the combustion gases move through the turbine  24  to drive one or more stages of turbine  24  blades, which in turn drive rotation of shaft  30 . The shaft  30  connects to a load  32 , such as a generator that uses the torque of the shaft  30  to produce electricity. After passing through the turbine  24 , the hot combustion gases may vent as exhaust gases  34  into the environment through the exhaust section  26 . 
     In certain embodiments, the control system  14  may include a controller  36 , a processor  38 , a memory  40 , and a hardware interface  45  suitable for interfacing with the actuators  42  and the sensors  44 , as shown in  FIG. 2 . Accordingly, the control system  14  may be communicatively coupled to sensors  44  such that the controller  36  may receive data from the sensors  44 . In response to the sensor  44  data, the processor  38  may then execute instructions stored on the memory  40  to control components of the gas turbine system  10  (e.g., fuel system  16 ) via the actuators  42 . The actuators  42  may include valves, pumps, positioners, inlet guide vanes, switches, and so on, useful in performing control actions. The sensors  44  may provide various data to the controller  36  including, for example, the amount of fuel  46  provided to the combustion system  22 , the temperature of the fuel  46 , the pressure ratio of the compressor  18 , and the inlet temperature of the compressor  18 . 
     The firing temperature of the combustion system  20 , as described above, may be determined in part by the ratio of fuel to air in the air-fuel mixture. As such a desired firing temperature graph  48 , as illustrated in  FIG. 3 , may reflect the desired firing temperature  51  of the combustion gases as a function of a turbine parameter  47 . Additionally, a plurality of other graphs  49  are provided as described in more detail below with respect to  FIGS. 4-8 , also useful in deriving control actions. In the embodiments described below, the graph  48  may be implicit within the definition a graph  49 , and the graphs  49  may be stored in the memory  40  and executed by the processor  38 . Further, the memory  40  may also contain instructions executable by the processor  38  that implement a firing control process, as described above. The processor  38  may execute the instructions of the firing control process to determine the actual firing temperature of the combustion system  20  based on a turbine parameter measured by the sensors  44 . The processor  38  may then execute instructions in the firing control process to compare the actual firing temperature to the desired firing temperature and determine the amount of fuel  46  to supply to move the actual firing temperature to the desired firing temperature. 
     With the foregoing in mind,  FIG. 4  is a block diagram that illustrates existing desired firing control process  50 . As mentioned above, the firing temperature graph  48  may be used to derive a desired firing temperature and associated control actions and may be implicit in the definition of graphs used in a firing control process, as described in more detail below. In the depicted embodiment, for example, a compressor inlet temperature (CTIM)  52 , as measured, for example, by sensors  44 , may be mapped to a desired firing temperature  51  via the graph  48 . As stated previously, this graph is notional or implicit in the definition of the actual Tx vs CPR control curve. It is the implicit or intended outcome that is used to produce the operative Tx vs. CPR curve but it is this translation from a boundary space as a function of CTIM to a boundary space that is a function of CPR that introduces the primary problem with respect to degradation. In this notional curve, the element shown as  64  is a constraint at or above ISO conditions that relates to hot gas path life and element  66  is at or below ISO constraint that relates to combustion system emissions and operability. A compressor pressure ratio (CPR) reference function or graph  56 , which may incorporate the desired firing temperature graph  48 , maps a measured CPR  58  to an actual firing temperature defined as an actual or current temperature Tx_Cur_A  60 . More specifically, the graph  56  may be used as a proxy for the graph  48  to derive the desired firing temperature  51  based on the exhaust temperature, as indicated by the dashed line in  FIG. 4 . Tx_Cur_A  60  may then be adjusted to account for the load  32 , ambient humidity and temperature, and other factors via corrections  61  that affect the gas turbine system  10 . The adjusted Tx_Cur_A  60  may then used to yield a fuel stroke reference FSR_A  62 . FSR_A  62  represents a fuel valve control action derived to achieve a target exhaust temperature representative of the desired firing temperature; based on fuel flow. The controller  36  may thus adjust the amount of fuel  46  provided to the combustion system  20 . 
     The firing control process  50  may include certain assumptions regarding the operating conditions of the gas turbine  12 . For example, levels of the compressor inlet pressure, exhaust back pressure, and specific humidity may be defined in the firing control algorithm  50 , for example, and incorporated as assumptions in a shape or curve provided by the reference function  56 . As such, deviations from the assumptions may be incorporated as corrections  61  into Tx_Cur_A  60 , as described above. The firing control process  50  may also include assumptions about desired performance levels of individual components of the gas turbine  12 . 
     The firing control process  50  may only contain one boundary function. Specifically, there are many operating states and sets of operating constraints in which the gas turbine system  10  may function. For example, the baseload operating state refers to the state at which the gas turbine system operates at its highest efficiency. Additionally, within the baseload operating state, there may be different constraints placed on the firing temperature based on whether the turbomachinery system  10  is operating at, above, or below international organization for standardization (ISO) conditions. The partload operating state refers to any state when the gas turbine system  10  does not operate at its highest efficiency, and may be further divided into other operating states. For example, the loading portion operating state may refer to a specific partload operating state in which the gas turbine system  10  is continually adjusted to move towards the baseload operating state. 
     The relationship between a measured turbine parameter and a firing temperature may change depending on the operating state and/or set of operating constraints of the gas turbine system  10 . Because the firing control process  50  may contain only one boundary function, all of the operating states and/or sets of operating constraints for the gas turbine system  10  may be expressed in a single reference function used to determine the actual firing temperature. For example, the desired firing temperature graph  48  illustrated in  FIG. 4  may correspond to a baseload operating state that may be divided into a section  64  that corresponds to the turbomachinery below ISO conditions and a section  66  that corresponds to the turbomachinery at or above ISO conditions. In other embodiments wherein the desired firing temperature graph  48  corresponds to a partload operating state, the sections  64  and  66  may correspond to various operating states and/or constraints and may establish the “best path” to base load. 
     As noted above, the CPR reference function  56  (e.g., a proxy for the graph  48  based on measuring the turbine exhaust temperature) is a singular boundary function  56  that may incorporate all types of operating states and/or sets of operating constraints. For example, the reference function  56  as depicted in  FIG. 4  may incorporate both sections  64  and  66  into its definition, wherein the point or turn  68  represents the change from one operating state and/or set of operating constraints to another. In short, during execution, the firing control process  50  considers the various operating states and/or sets of operating constraints of the gas turbine system  10  to be interdependent. 
     In one embodiment, an enhanced firing control process  70 , as illustrated in  FIG. 5 , is provided that incorporates the firing control process  50  as a first control process  50  and then subsequently adds a second and third control process, thus using multiple functions or graphs. Advantageously, a control process already implemented by the control system  14  may be reused, and modifications to the control system programming may be smaller. For example, the existing firing control process  50  may still function as described above and may not require any substantial modification, or any modifications. A second control process  59  maps a measured value of the CTIM  52  to a delta firing temperature via CTIM reference function  72 , and the output is defined as dTx_A  74 . That is, the CTIM reference function  72  may include an abscissa having a measured temperature of the compressor inlet valve and an ordinate having a delta firing temperature, and a shape similar to or the same as illustrated in the figure. In this process  59 , the delta firing temperature represents the difference between the actual firing temperature as determined by the measured CTIM value and the desired firing temperature. Similarly to the reference function  56 , the CTIM reference function  72  may incorporate the desired firing temperature graph  48  within its definition. 
     A tuning element  76  may be applied to dTx_A  74 , and the output is defined as dTfire  78 . The tuning element  76  is a constant that may be used during new unit installation and commissioning to shift the firing level up or down. For final settings, the tuning element  76  emerges as a calibration constant that may be employed to tune an individual gas turbine system  10  to the original intended design; it absorbs the unit to unit variation from the mean machine used in theoretical designs. 
     In a third control process  79 , as illustrated in  FIG. 5 , dTFire  78  is mapped to a delta exhaust temperature according to a transfer function  80  to produce the output dTx_B  82 . The transfer function  80  may include an abscissa having dTfire  78 , which, as mentioned above, may represent the result of applying the tuning element  76  to dTx_A  74 . The transfer function may also include an ordinate having a delta exhaust temperature, wherein the delta exhaust temperature represents the relationship between a specified change in firing temperature and corresponding change in exhaust temperature. Similarly to the reference functions  56  and  72 , the transfer function  80  may incorporate the desired firing temperature graph  48  within its definition. dTx_B  82  and Tx_Cur_A  60  are then combined to produce the output Tx_Cur_B  84 . Tx_Cur_B  84  may be adjusted using corrections  61  described above and may then be used to generate a fuel stroke reference FSR_B  86 . Based on FSR_B  86 , the controller  36  determines the amount of fuel  46  that may be supplied to the combustion system  20  to achieve the target exhaust temperature. 
     As the enhanced firing control process  70  may incorporate the control process  50  in its entirety, it may also incorporate other aspects related to the existing control process  50 . However, in certain embodiments departing from the existing control process  50 , the enhanced firing control algorithm  70  may include more than one boundary function. 
     In the enhanced firing control process  70 , the various operating states and/or sets of operating constraints may be divided into at least two boundary functions, or more. As noted above, the desired firing temperature graph  48  in  FIG. 3  may be divided into two boundary functions, one describing to a section  64  that corresponds to the turbomachinery in a baseload operating state and below ISO conditions and another describing a section  66  that corresponds to the turbomachinery in a baseload operating state and at or above ISO conditions. For example, the reference functions  56 ,  72 , and  80  illustrated in  FIG. 4  may correspond to a boundary function that describes section  64 , which corresponds to the turbomachinery in a baseload operating state and below ISO conditions. A second boundary function may describe section  66 . The reference functions  56 ,  72 , and  80  corresponding to the second boundary function describing section  66  may differ from the reference functions used that correspond to section  64 . In other embodiments, one version of a reference function may be associated with multiple boundary functions. 
     Because the reference functions may change as the current operating state and/or set of operating constraints of the gas turbine system  10  changes, the controller  36  may be configured to determine the appropriate boundary function and select the corresponding set of reference functions. To determine the desired boundary function, the enhanced firing control process  70  may include a boundary function selection input  88 . The controller  36  may include a user input device, such as a keyboard or mouse, through which an operator may manually select the current operating state and/or set of operating constraints and subsequently the correct boundary functions. Alternatively, the controller  36  may communicate with the sensors  44  to automatically determine the operating state and/or set of operating constraints and adjust the boundary functions accordingly. 
     For the enhanced firing control process  70 , the various operating states and/or sets of operating constraints may be divided into five boundary functions. For instance,  FIG. 6  illustrates the desired firing temperature graph  48  divided into sections  64 ,  66 ,  63 ,  65 , and  67 , each of which is associated with a particular operating state and/or set of operating constraints. Each of the sections may be described by a boundary function, which may correspond with a unique version of the reference function  56 , as illustrated and as described above. In one embodiment, incorporating more than five boundary functions into the enhanced firing control process  70  may introduce an amount of complexity similar to that of more sophisticated firing control algorithms. The increased complexity may lead to a significant overhaul of the instructions stored on the memory  40  and may also do a poor job of leveraging the existing firing control process  50 . 
     The enhanced firing control process  70  may include assumptions about the turbine&#39;s operating environment and component performance level, much like the existing firing control algorithm  50 . As such, it may also allow for adjustments to deviations from the assumptions. For example, if a sensor  44  produces an inlet humidity measurement, then a humidity correction  90  may be incorporated into the enhanced firing control process  70 , as illustrated in  FIG. 7 . 
     An actual inlet humidity  92 , as measured by one or more sensors  44 , may have an adjustment factor  94  applied to it, and an output may represent a humidity adjustment  96 . For example, a process  97  illustrated in  FIG. 7  has an assumed humidity level of zero, and so the adjustment factor  94  may be a constant gain factor. The humidity adjustment  96  may be combined with Tx_Cur_B  84  to produce Tx_Cur_C  98 , which may then be adjusted by other corrections  61  before being used to generate FSR_B  86  as described above. 
     Further, even if a humidity measurement is unavailable, it may be advantageous to set the assumed humidity profile of the enhanced firing control process  97  to the median humidity profile. Such an adjustment may reduce the error to the actual humidity, and may result in an outcome that is no worse than the uncompensated scenario and possibly better. As will be appreciated, the types of corrections for the enhanced firing control process  70  are not limited to the humidity correction  90  as shown in process  97 , but may focus on other aspects of a turbine&#39;s operating environment or component performance (e.g., compressor inlet pressure loss, exhaust back pressure). 
     As the enhanced firing control process  97  also incorporates the existing firing control process  50 , it may be easy to configure the controller  36  to use the enhanced firing control processes  70  and/or  97 . The enhanced firing control processes  70  and/or  97  may be provided as an update and, rather than overwriting the instructions for the existing firing control algorithm  50 , may only add additional instructions. 
       FIG. 8  is a graph illustrating embodiments of specific component performance degradation levels for both the existing and the enhanced firing control algorithms at 0K and 24K fired hours using a particular set of operating characteristics defined as “7FA.03” corresponding, for example, to a 7FA heavy duty gas turbine available from General Electric Company, of Schenectady, N.Y. The graph illustrates the relative accuracy of each of the firing control processes over time, and demonstrates the effect of performance degradation for various components, such as compressor efficiency and turbine efficiency.  FIG. 8  may be useful to compare performance of various processes, such as the processes described herein. The curve indicated by reference numeral  100  may correspond to the design intent of the gas turbine. The curves indicated by reference numerals  102  and  104  may correspond to the firing temperature profile associated with the existing process  50  after 0K hours and after 24K fired hours, respectively. Similarly, the reference numerals  106  and  108  may correspond to the firing temperature profile associated with the enhanced processes  70  and/or  97  after 0K hours and after 24K. The hot day maximum level of the gas turbine is depicted by the reference numeral  110 .  FIG. 8  includes an abscissa  112  having a measured compressor inlet temperature and an ordinate  114  having a derived firing temperature. 
     As shown, the existing firing control process  50  may result in an over-fire to the desired firing temperature when the desired firing temperature is below the hot day maximum level. Once the hot day maximum level has been reached, the existing firing control algorithm tends to under-fire, which may occur when using exhaust temperature control strategies due to turbine efficiency loss. 
     The enhanced firing control processes  70  and/or  97  minimize or eliminate the cold day over-fire exhibited by the existing firing control strategy 50, and exhibit a slight under-fire at or above ISO conditions, much less than the existing firing control algorithm. ISO conditions or ratings may be used to specify an expected turbine system  10  performance (e.g., power produced, fire temperature achieved) based on ambient conditions of a given geographic locality (e.g., latitude and longitude) of the turbine system  10 , such as altitude, ambient temperature, humidity, and other atmospheric conditions. The degree of under-fire increases with increasing levels of component performance degradation, as shown. Further, the “tilted profile” shaping as a function of compressor inlet temperature is largely maintained, unlike the more degraded characteristic of the existing firing control process  50 . Indeed,  FIG. 8  shows that performances for the processes  70  and/or  97  improve over performances for the process  50   
       FIG. 9  is a graph illustrating embodiments of specific component performance degradation levels for the existing and enhanced firing control processes as well as more sophisticated firing control algorithms CPC and MBC at 24K fired hours, for comparison purposes. The graph illustrates the relative accuracy of each of the firing control processes after a certain amount of time, and demonstrates the effect of performance degradation for various components, such as compressor efficiency and turbine efficiency.  FIG. 9  includes an abscissa  112  having a compressor inlet temperature, an ordinate  114  having a derived firing temperature, and a reference numeral  110  indicating the hot day maximum level of the gas turbine.  FIG. 9  also includes the firing temperature profiles associated with the existing process  50  after 24K fired hours and the enhanced processes  70  and/or  97  after 24K fired hours, numbered  104  and  108  respectively. The graph includes a firing temperature profile associated with a CPC firing control process, indicated by reference numeral  116 , and a firing temperature profile associated with an MBC firing control process, indicated by reference numeral  118 . While  FIG. 8  compares the existing process  50  and the enhanced processes  70  and/or  97  to themselves and each other over an extended period of time,  FIG. 9  compares the existing process  50  and the enhanced processes  70  and/or  97  to other firing control processes after an extended period of time. 
     As mentioned above, the existing firing control algorithm exhibits an over-fire at below ISO conditions and a slight under-fire at or above ISO conditions, which may lead to seasonal retunes. The enhanced firing control processes  70  and/or  97  exhibits characteristics similar to that of the CPC and MBC firing control algorithms. However, the enhanced firing control algorithm exhibits a hot day sensitivity to humidity variation much like the existing firing control algorithm, which may warrant a humidity correction as described above. 
     Technical effects of the disclosed embodiments include controlling the firing temperature of a combustion system of a gas turbine system. Certain embodiments may improve the accuracy of the firing temperature control and improve the performance level of the gas turbine system. For example, an enhanced firing control process organizes the various operating states into multiple boundary functions that may be used to determine the actions need to match an actual firing temperature to a desired firing temperature, which may lead to more accurate evaluations. The enhanced firing control process may be added to an existing firing control process, for example, by adding lines of computer executable code, which may minimize or eliminate the need for a significant overhaul of the gas turbine system&#39;s software and may require only a minimal amount of computer skills to implement. Further, the enhanced firing control process performs at levels not too dissimilar from more sophisticated firing control processes. By separating boundary functions, upgrades to firing control processes may not result in major changes to the gas turbine system&#39;s operation. The enhanced firing control process may also be implemented in older gas turbine systems not likely to be upgraded to more sophisticated firing control algorithms, for example, because of hardware constraints. 
     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.