Patent Publication Number: US-2017356344-A1

Title: Systems and Methods to Control Combustion Dynamic Frequencies

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority, as a continuation application, to co-pending U.S. patent application Ser. No. 13/777,724, filed Feb. 26, 2013, the disclosure of which is hereby incorporated by reference in its entirety. 
    
    
     TECHNICAL FIELD 
     Embodiments of the present disclosure relate generally to a gas turbine engines and more particularly to systems and methods to control combustion dynamic frequencies. 
     BACKGROUND 
     Combustors are commonly used in industrial and commercial operations to ignite fuel to produce combustion gases having a high temperature and pressure. For example, gas turbines and other turbomachines typically include one or more combustors to generate power or thrust. A typical gas turbine used to generate electrical power includes an axial compressor at the front, multiple combustors around the middle, and a turbine at the rear. Ambient air enters the compressor as a working fluid, and the compressor progressively imparts kinetic energy to the working fluid to produce a compressed working fluid at a highly energized state. The compressed working fluid exits the compressor and flows through one or more fuel injectors in the combustors where the compressed working fluid mixes with fuel before igniting to generate combustion gases having a high temperature and pressure. The combustion gases flow to the turbine where they expand to produce work. For example, expansion of the combustion gases in the turbine may rotate a shaft connected to a generator to produce electricity. 
     At particular operating conditions, combustion dynamics at specific frequencies and with sufficient amplitudes, which are in-phase and coherent, may produce undesirable sympathetic vibrations in the turbine and/or other downstream components. Typically, this problem is managed by combustor tuning. Combustor tuning to protect the turbine buckets, however, may impose severe restrictions on the function and operability of the combustor. Thus, there is a continued desire to improve the ability to separate the combustion dynamic frequencies and the turbine bucket natural frequencies. 
     SUMMARY 
     Some or all of the above needs and/or problems may be addressed by certain embodiments of the present disclosure. According to an embodiment, there is disclosed a method for frequency separation in a gas turbine engine. The method may include determining a hot gas path component natural frequency. The method may also include determining a combustion dynamic frequency. Moreover, the method may include modifying a compressor discharge temperature to separate the combustion dynamic frequency from the hot gas path component natural frequency. 
     According to another embodiment, there is disclosed a system for frequency separation in a gas turbine engine. The system may include a compressor, a combustor in communication with the compressor, and a turbine in communication with the compressor and the combustor. The system may also include a controller in communication with at least one of the compressor, the combustor, or the turbine. The controller may be configured to modify a compressor discharge temperature to separate a combustion dynamic frequency from a hot gas path component natural frequency. 
     Further, according to another embodiment, there is disclosed a system for frequency separation. The system may include a gas turbine engine and a controller in communication with the gas turbine engine. The controller may include at least one memory that stores computer-executable instructions and at least one processor configured to access the at least one memory. The at least one processor may be configured to execute the computer-executable instructions to: determine a hot gas path component natural frequency; determine a combustion dynamic frequency; and modify a compressor discharge temperature to separate the combustion dynamic frequency from the hot gas path component natural frequency. 
     Other embodiments, aspects, and features of the disclosure will become apparent to those skilled in the art from the following detailed description, the accompanying drawings, and the appended claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Reference will now be made to the accompanying drawing, which is not necessarily drawn to scale. 
         FIG. 1  is a schematic of an example diagram of a gas turbine engine system configured to control combustion dynamic frequencies, according to an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Illustrative embodiments will now be described more fully hereinafter with reference to the accompanying drawing, in which some, but not all embodiments are shown. The present disclosure may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Like numbers refer to like elements throughout. 
     Illustrative embodiments are directed to, among other things, systems and methods for frequency separation in a gas turbine engine. For example, in certain embodiments, a combustion dynamic frequency may be actively separated (or shifted) from a hot gas path component natural frequency by modifying a compressor discharge temperature. That is, the combustion dynamics frequencies associated with a combustor in a gas turbine engine may be modified by adjusting a compressor discharge temperature. In some instances, the compressor discharge temperature may be modified by adjusting one or more inlet guide vanes associated with a compressor. In other instances, the compressor discharge temperature may be modified by adjusting inlet bleed heat associated with a compressor. In yet other instances, the compressor discharge temperature may be modified by adjusting the temperature of the air entering the compressor section by evaporative cooling, heat exchangers, or other temperature-altering devices known in the art. Also, the compressor discharge temperature may be modified by a combination of adjusting one or more inlet guide vanes and/or adjusting inlet bleed heat and/or adjusting the temperature of the air entering the compressor. 
     The hot gas path component natural frequency may include a single frequency of interest or a range of frequencies of interest. In some instances, the hot gas path component may be a turbine bucket (such as, for example, a stage one turbine bucket) or other turbine component. The hot gas path component may include any turbine component at any stage in the turbine. Similarly, the combustion dynamic frequency may include a single frequency of interest or a range of frequencies of interest. 
     As noted above, the compressor discharge temperature can be adjusted by regulating an inlet guide vane angle and/or a flow of inlet bleed heat to a compressor and/or adjusting the temperature of the air entering the compressor. For example, in some embodiments, a controller may be configured to monitor a frequency and amplitude of a combustor tone in real time by way of one or more dynamic pressure sensors or the like. In this manner, active control can be implemented via the controller to regulate the frequency of interest of the combustor in real time, separating (or shifting) it from a hot gas path component natural frequency. The frequency of interest of the combustor can be modified in order to maintain frequency separation between the turbine buckets and the combustor, preventing unacceptable turbine bucket response due to frequency overlap. 
     In certain embodiments, the compressor discharge temperature may be adjusted to control combustion dynamics frequencies of interest to maintain separation from hot gas path component natural frequencies. The role of compressor discharge temperature in affecting the combustion dynamics frequencies is twofold. First, changing the temperature of the air entering the combustion system changes the speed of sound and therefore, the acoustic natural frequency of the combustor. Second, a change in compressor discharge temperature can be accompanied by, or result from, a change in airflow through the compressor, and therefore through the combustion system. Changing the airflow through the combustion system affects the coupling between the heat release fluctuation inherent to the combustion process and the acoustic resonant frequencies of the combustor. One specific mechanism known in the art to play a significant role in this coupling of heat release and combustor acoustic resonances occurs when acoustic pulsations driven by the heat release fluctuations cause mass flow fluctuations through the fuel ports, which then result in the fuel/air ratio of the flame zone to fluctuate. When the resulting fuel/air ratio fluctuation and the acoustic pressure pulsations are in-phase, a self-excited feedback loop results. This mechanism is a function of the time it takes for the fuel/air ratio disturbance to reach the flame zone, known in the art as convective time (Tau), and is therefore inversely proportional to the flow rate through the combustor. As the convective time increases, the frequency of the combustion instability decreases and when the convective time decreases, the frequency of the combustion instability increases. Therefore, by changing the compressor discharge temperature by changing the inlet guide vane, the flow of inlet bleed heat, and/or the temperature of the air entering the compressor, the natural acoustic frequency and/or the convective time of the combustor will change. By shifting the combustion dynamic frequency away from hot gas path component natural frequencies, operation of the gas turbine engine can continue without risk of damage to the turbine buckets due to high cycle fatigue. 
     Turning now to  FIG. 1 , which depicts a schematic view of an example embodiment of a gas turbine engine system  100  as may be used herein. For example, the gas turbine engine system  100  may include a compressor  102 . The compressor  102  may compress an incoming flow of air  104 . The compressor  102  may deliver the compressed flow of air  104  to a combustor  106 . The combustor  106  may mix the compressed flow of air  104  with a pressurized flow of fuel  108  and ignite the mixture to create a flow of combustion gases  110 . Although only a single combustor  106  is shown, the gas turbine engine system  100  may include any number of combustors  106 . The flow of combustion gases  110  in turn may be delivered to a turbine  112 . The turbine  112  may include a number of buckets  132  arranged in stages, such as stage 1, stage 2, stage 3, etc. The flow of combustion gases  110  may drive the buckets  132  within the turbine  112  so as to produce mechanical work. The mechanical work produced in the turbine  112  may drive the compressor  102  via a shaft  114  and an external load  116  such as an electrical generator or the like. 
     The gas turbine engine system  100  may use natural gas, various types of syngas, and/or other types of fuels. The gas turbine engine system  100  may have different configurations and may use other types of components. Moreover, other types of gas turbine engines also may be used herein. Multiple gas turbine engines, other types of turbines, and other types of power generation equipment also may be used herein together. 
     Still referring to  FIG. 1 , the gas turbine engine system  100  may include an inlet bleed heat system  120  associated with the compressor  102 . The inlet bleed heat system  120  may be configured to remove hot air from an aft portion of the compressor  102  and to subsequently deliver the hot air back to the compressor  102  for recirculation therethrough. In certain embodiments, the inlet bleed heat system  120  may include a valve  124  or other control means for regulating the inlet bleed heat system  120 . The amount of the inlet bleed heat may have an effect on the compressor discharge temperature and/or the flowrate of the air through the compressor. 
     In certain embodiments, the gas turbine engine system  100  may include an inlet guide vane system  118  associated with the compressor  102 . The inlet guide vane system  118  may include a number of fixed and/or adjustable vanes therein. The angle of the inlet guide vanes may have an effect on the compressor discharge temperature and/or the flowrate of the air through the compressor. 
     In certain embodiments, the gas turbine engine system  100  may include one or more sensors positioned at various locations about the gas turbine engine system  100 . The sensors may be associated with various components of the gas turbine engine system  100  for monitoring thereof. For example, a dynamic pressure sensor  128  may be associated with the combustor  106  for monitoring a combustion dynamic frequency and a combustion dynamic amplitude of the combustor  106 . A temperature sensor  130  may be positioned downstream of the compressor  102  for monitoring a compressor discharge temperature and/or a combustor inlet temperature. An accelerometer, a strain gage, or an optical sensor  134  may be associated with the turbine  112 , such as a stage 1 bucket  132 , for monitoring the vibratory response of the bucket  132 . Other sensors may also be used. The sensors may be of conventional design. Other types of operational parameters may be monitored herein. Moreover, any stage may be monitored in the turbine  112 . 
     In certain embodiments, the gas turbine engine system  100  may include one or more controllers  122  in communication with the various components of the gas turbine engine system  100  for monitoring and/or controlling thereof. For example, the controller  122  may be in communication with, among other things, the compressor  102 , the combustor  106 , the turbine  112 , the inlet guide vane system  118 , the valve  124  of the inlet bleed heat system  120 , the temperature sensor  130 , the dynamic pressure sensor  128 , and/or the vibration sensor  134 , etc. The controller  122  may include at least a memory  124  and one or more processing units (or processors)  126 . The processors  126  may be implemented as appropriate in hardware, software, firmware, or combinations thereof. Software or firmware implementations of the processors  126  may include computer-executable or machine-executable instructions written in any suitable programming language to perform the various functions described. Moreover, the processors  126  may be associated with a network, a server, a computer or a mobile device. 
     In some instances, the controller  122  may be configured to actively separate (or shift) a combustion dynamic frequency from a hot gas path component natural frequency by controlling a compressor discharge temperature. In some instances, the hot gas path component may be a stage one bucket  132 ; although any bucket stage may be used herein. For example, the controller  122  may be configured to determine, predict, monitor, identify, or the like a hot gas path component response amplitude and/or frequency, a combustion dynamic amplitude and/or frequency, and/or a compressor discharge temperature. The controller may also be configured to separate (or shift) the combustion dynamic frequency from the hot gas path component natural frequency by controlling/regulating the compressor discharge temperature. For example, the compressor discharge temperature may be controlled by adjusting the angle of the inlet guide vanes  118  associated with the compressor  102 , by adjusting the inlet bleed heat system  120  associated with the compressor  102 , by adjusting the temperature of the air entering the compressor, or a combination thereof. For example, the controller may open or close the valve  124  to increase or decrease the inlet bleed heat. 
     The algorithms associated with the controller  122  to separate (or shift) the combustion frequency can vary significantly, and will depend on the combustion architecture among other things. Although embodiments have been described in language specific to structural features and/or methodological acts, it is to be understood that the disclosure is not necessarily limited to the specific features or acts described. Rather, the specific features and acts are disclosed as illustrative forms of implementing the embodiments.