WO2025080763A1 - Systems and methods for minimizing greenhouse gas emissions and eliminating carbon emissions from combustion turbine engines - Google Patents

Abstract

A combustion engine combustion control system or subsystem may comprise a pressure pulsation measurement subsystem configured to continuously measure amplitudes of greater than 0.2 psi, frequency pressure pulsations of less than 100 Hz adjacent to a combustion zone of a combustion engine to detect a precursor to a lean-blowout condition. The combustion engine combustion control system or subsystem may also comprise a control system comprising logic and an injector configured to adjust an air-to-fuel ratio based on the measured amplitude and the measured frequency of the pressure pulsations.

Description

Inventor: Richard L. Lopushansky

TITLE

SYSTEMS AND METHODS FOR MINIMIZING GREENHOUSE GAS EMISSIONS AND ELIMINATING CARBON EMISSIONS FROM COMBUSTION TURBINE ENGINES

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to U.S. Patent Application No. 63/543,381, filed on October 10, 2023, entitled “SYSTEMS AND METHODS FOR MINIMIZING GREENHOUSE FROM GAS EMISSIONS GAS TURBINES,” which is incorporated herein by reference in its entirety.

FIELD

[0002] The present disclosure relates to a combustion control system, and, more particularly, a combustion control system to minimize greenhouse gas emissions from combustion turbine engines fueled by fossil fuels and to eliminate carbon emissions from combustion turbine engines fueled by hydrogen.

BACKGROUND

[0003] The global reduction of greenhouse gas emissions from combustion turbine engines to near theoretical limits and the elimination of carbon emissions from combustion turbine engines has become a worldwide priority for jet engines and other combustion engines, including, without limitation, combustion turbine engines used for electrical power generation and other industrial applications. When combustion turbine engines operate with a too-rich air-to-fuel ratio, not all the fuel is consumed in the combustion process. But a too rich air-to-fuel ratio is deemed necessary because it provides for a very stable combustion process that results in a safe and highly reliable operation. Under a too-rich condition, the portion of the fuel that is not combusted is emitted into the atmosphere as unburned hydrocarbons (UHC). When that fuel is methane (CH4), the UHC is classified as greenhouse gas emissions. However, if the air-to-fuel ratio is changed to near ideal stoichiometric combustion, UHCs and greenhouse gas emissions are decreased to near the theoretical minimum. At ideal stoichiometric combustion, all the fuel is combusted and there are no greenhouse gas emissions or UHC. That is the ideal operating condition for a combustion turbine engine from an environmental perspective, i.e., an efficient use of fuel and minimal greenhouse gas emissions or UHC.

[0004] One of the most common fossil fuels used in power plant applications is methane (CH4) because it is cheap and plentiful. But methane is a very potent greenhouse gas and has 80 times the warming power of carbon dioxide during the first twenty years after it reaches the atmosphere. So, the less methane that is emitted from power plants the better it is for the environment.

[0005] However, for safety and reliability reasons, existing combustion controls are not designed to minimize emissions. They are designed to maximize safety and reliability consistent with practical technology limited emission standards. So, combustion turbine engines operate with richer than-necessary air-to-fuel ratios in a “safe mode” to provide safety and reliability margins, i.e., to reduce the possibility of lean-blowouts. But operating a gas turbine at those conditions (richer than ideal stoichiometry) is why gas turbines have much higher levels of greenhouse gas emissions than is theoretically possible. Western societies are demanding lower emissions and want to achieve carbon-free jet engines and combustion turbines.

[0006] It has not been practical to operate a combustion turbine engine at ideal stoichiometry continuously because there was no instrumentation available in the world that could be integrated into a combustion control system that could be used to achieve near ideal stoichiometry. So, combustion turbine engines have had to be operated with air-to-fuel ratios that are inherently too rich and emit more greenhouse gases into the atmosphere than is theoretically necessary. That is because conventional piezoelectric sensing systems are not capable of making the necessary measurements to keep the engine running in a safe and reliable manner.

[0007] If the engine is operated too close to ideal stoichiometry and the air-to-fuel ratio becomes too lean, the combustion process is starved for fuel and the combustion process becomes increasingly unstable. This is a very dangerous condition because when operating in a too-lean condition, the combustion flame begins to partially collapse and is subject to be extinguished instantaneously in what is defined as a lean-blowout or LBO. However, the physics of the combustion process provides a warning of an impending lean-blowout. That phenomenon is exhibited as continuous high amplitude pressure pulsations at a very low, almost infrasonic, acoustic frequency, e.g., 25Hz (within a band of about plus or minus 3-5 Hz), inside the combustor of a large-frame Siemens combustion turbine engine, for example. Under this too-lean operating condition, the combustion flame is subject to being extinguished immediately.

[0008] The partial collapse or flickering of the combustion flame acts much like a candle that flickers when the air flow around it is disrupted. The candle isn’t always extinguished immediately by a disruption of the air flow, but if the disruption of the air flow is too severe and the air-to-fuel ratio is too lean, even momentarily, the candle will be extinguished, e.g., this is analogous to when candles are deliberately blown out. In the combustion turbine, a too-lean condition can also result in an immediate lean-blowout just like a candle.

[0009] Of course, the opposite is also true. If the candle flame is covered by a glass jar and starved for air (oxygen), the air-to-fuel ratio will drop as the oxygen inside the glass jar is consumed until the flame is extinguished due to a lack of oxygen or a too-rich air-to-fuel ratio. So, there are two limits for sustained combustion. One limit is an air-to-fuel ratio that is too lean, and the other is an air-to-fuel ratio that is too rich. This zone in between is referred to as the “combustion slot” where a relatively wide range of air-to-fuel ratios of methane can reliably sustain combustion. In a combustion turbine engine that is fueled with hydrogen (H2), the “stable combustion slot” is much smaller and so these hydrogen-fueled engines also need more advanced combustion controls to operate safely and reliably.

[0010] It is not possible to design a combustion control system that can operate at near ideal stoichiometry using conventional piezoelectric-based sensors, because conventional piezoelectric sensors cannot measure the near infrasonic, low frequency pressure pulsations, e.g., less than 50Hz, due to the inherent limitations of the piezoelectric technology. Furthermore, piezoelectric sensors cannot be used in a close-coupled, direct measurement mode due to size constraints and temperature limitations which are far less than the required 1000°F. Conventional piezoelectric sensing systems are also sensitive to noise and signal distortion caused by shock and vibration, thermal transients from flashbacks, and electromagnetic interference (EMI). Conventional piezoelectric sensing systems are not intrinsically-safe and cannot fit into existing access ports. Accordingly, such instrumentation cannot not be used in continuous closed-loop control systems.

[0011] Because conventional piezoelectric-based sensors cannot survive the elevated temperatures at the core of the engine, they can only be used to make indirect measurements at the end of tubes (acoustic waveguides) that are welded to the combustors. These indirect measurements are prone to huge distortions of the acoustic signals due to the ever-changing resonance caused by condensation that settles inside the acoustic waveguides. In summary, the combination of the blind spot at low frequencies, the noise from a variety of sources, and the unpredictable distortion of the signals (false signals) make piezoelectric sensing systems completely unsuitable for use in advanced combustion control systems designed to operate the engine at near ideal stoichiometry. [0012] So, to reduce greenhouse gas emissions, and to accelerate the adoption of hydrogen as fuel for jet engines and combustion turbine engines to eliminate carbon emissions completely, more advanced instrumentation and advanced combustion controls are necessary. The present disclosure is concerned with advanced combustion control systems that are designed to achieve and maintain near ideal stoichiometric combustion within the “combustion slot” by reducing the combustion slot to near ideal stoichiometric combustion where theoretically all the fuel is consumed by the combustion process.

[0013] The key to achieving lower emissions is to operate the engines continuously at near ideal stoichiometry. This is only possible if the instrumentation used to monitor the combustion stability is capable of measuring low frequency pressure pulsations which are an indication of an impending lean-blowout. Those low frequency pressure pulsations are a physical phenomenon caused by the partial collapse of the combustion flame. Those low frequency pressure pulsations are indicative of a too-lean condition and are always a precursor signal prior to the extinguishing of the combustion flame. Instantaneous detection of that condition is the key to safe, reliable, low emission combustion turbine engines.

[0014] A lean-blowout of a combustion turbine engine is a very serious situation and requires that the combustion turbine engine be shut down immediately. Otherwise, unburnt fuel injected into the combustors will flow downstream into the turbine section where an uncontrolled ignition of the fuel and a resulting explosion could cause serious mechanical damage to the engine and/or loss of human life.

[0015] In addition to the safety considerations, the economic consequences of taking 200MW of power off the grid instantly are considerable. In addition, operating a combustion turbine engine with high amplitude pressure pulsations can severely damage critical components in a combustion turbine engine. Also, a lean-blowout results in the rapid cool down of the engine and this leads to thermal fatigue of critical engine components. So, for safety and economic reasons unexpected lean-blowouts are totally unacceptable in any aviation, power generation, or other industrial application.

[0016] In actual operations, the combustion control system must make continuous adjustments for many operating parameters that are constantly changing including the ambient temperature, humidity, air pressure, fuel quality, load, and wear and tear on the engine. These parameters and others all have an affect on the ideal air-to-fuel ratio, i.e., stoichiometric combustion, which cannot simply be locked in a set. In large-frame, canannular combustion turbine engines, there are typically several combustors, and each combustor has its own unique characteristics and its own unique ideal stoichiometry. So, highly responsive, high-resolution, low-frequency, pressure pulsation measurements integrated with very fine air-to-fuel ratio controls are needed on each combustor in a combustion turbine engine to keep the entire engine operating at near ideal stoichiometric combustion continuously. This systems architecture is necessary to maximize safety and reliability, minimize greenhouse gas emissions, eliminate carbon emissions, maximize fuel efficiency, and minimize wear and tear on the engine.

[0017] With increasing worldwide political pressure to minimize greenhouse gas and UHC emissions, and to eliminate carbon emissions completely, there is a need to develop advanced pressure measurement instrumentation and integrate such advanced instrumentation into advanced combustion control systems to minimize greenhouse gas and UHC to near theoretical lower limits and to accelerate the use of hydrogen as fuel to eliminate carbon emissions completely.

SUMMARY

[0018] The following presents a summary of this disclosure to provide a basic understanding of some aspects. This summary is intended to neither identify key or critical elements nor define any limitations of the disclosed embodiments or claims. This summary may provide a simplified overview of some aspects that may be described in greater detail in other portions of this disclosure. Furthermore, any of the described aspects may be isolated or combined with other described aspects without limitation.

[0019] The present disclosure relates to a combustion control system that overcomes all of the fundamental limitations of combustion control systems that are based on conventional piezoelectric sensing systems, including those described above. The present disclosure uses a temperature-tolerant, fiber-optic-based pressure pulsation measurement system that makes continuous, direct dynamic pressure measurements very close to the combustion zone in a combustion turbine engine to detect precursor indications of impending lean-blowouts. This optical instrumentation will enable the development of advanced combustion controls to enable reliable, safe, and continuous operation of combustion turbine engines at near ideal stoichiometric combustion. By operating the combustion turbine engines near ideal stoichiometric conditions, the combustion turbine engines will operate at reduced UHC and greenhouse gas emission levels while maintaining safety and reliability. The present system will also accelerate the adoption of hydrogen as fuel for combustion turbine engines that will eliminate carbon emissions entirely.

[0020] In some embodiments, the combustion control system comprises highly customized, temperature-tolerant, miniature Fabry -Perot interferometers (“fiber optic interferometers”) such as that shown in Figure 3. In such embodiments, the fiber optic interferometers operate at elevated temperatures exceeding l,000°F, are immune to significant shock and vibration, thermal transients from flashbacks, and electromagnetic interference (EMI). They are intrinsically-safe and are attached to long flexible transducer probes to fit into existing acoustic waveguides as shown in Figure 10. The fiber-optic interferometers of the present disclosure are safe to use in combustion turbine engines, including those fueled with hydrogen because the optical energy density within the optical fiber is so low that it cannot ignite the most volatile of gases. The very low optical power used in the fiber-optic interferometers allows this instrumentation to be classified as intrinsically-safe and suitable for use even in areas that are deemed Class I Division 1 explosion hazardous areas. This fiber-optic-based combustion control system can be certified as a Safety Integrity Level (SIL) 3 certified system.

[0021] These temperature-tolerant, fiber-optic interferometric pressure measurement instruments are uniquely capable of making low frequency pressure pulsation measurements below 100Hz. These instruments can also be used for making static pressure measurements or dynamic pressure measurements with a very wide frequency response from 0 to 10,000Hz. These fiber optic interferometric pressure sensing systems are small enough to fit into existing access ports. They are tolerant enough to survive the extremely high temperatures at the core of the engine. Accordingly, these fiber optic interferometric pressure sensing systems are suitable for continuous use in closed-loop control systems.

[0022] The fiber optic interferometers are coupled via ruggedized fiber optic cables to mating optical interrogators that make high-resolution dynamic pressure measurements, e.g., 0 to 10 psi at sampling rates exceeding 50 kHz, and with high-fidelity frequency responses ranging from static pressure, i.e., DC, to 10,000Hz. These unique instruments are ideally suitable for use in advanced combustion control systems to minimize greenhouse gas emissions and to eliminate all carbon emissions through the use of hydrogen as fuel instead of methane and other fossil fuels.

[0023] A microprocessor in the optical interrogator can be used to analyze the time series pressure pulsation measurements via a Fast Fourier Transform (FFT) function to provide pressure as a function of frequency as illustrated in Figure 4.

[0024] The resulting pressure versus frequency waveform is analyzed continuously, e.g., at 10Hz or higher, for indications of high amplitude, low frequency pressure pulsations, i.e., combustion instabilities, at particular frequencies that are unique for each specific engine/combustor design. When pressure pulsations created by combustion instabilities reach specific amplitudes at specific frequencies, the optical interrogator provides a signal to an advanced combustion control system to automatically take corrective measures to prevent lean-blowouts while maintaining near perfect stoichiometric combustion, which leads to the reduction in greenhouse gas and UHC emissions and the tighter control necessary for hydrogen-fueled combustion turbine engines.

[0025] The key to achieving continuous combustion in a combustion turbine engine at ideal stoichiometry and minimizing greenhouse gas and UHC emissions without risking an LBO is an advanced combustion control system integrated with such state-of-the-art low frequency pressure pulsation measurement systems that continuously measure the amplitude of low frequency pressure pulsations in each combustor. Then, whenever the amplitude of low frequency pressure pulsations at specified frequency bands exceeds the specified threshold for a specific combustion turbine engine, the controls are adjusted to slightly enrichen the air- to-fuel ratio to ensure there is no lean-blowout.

[0026] The advanced combustion control system may be operatively connected to the pressure pulsation measurement system for this purpose, continuously receiving operating data (in real time) corresponding to an amplitude and frequency, whereupon the controls are continuously adjusting the air-to-fuel ratio whenever the pressure pulsation measurement system observes high amplitude, low frequency pressure pulsations in the appropriate frequency band.

[0027] In some embodiments, the advanced combustion control system is configured to adjust the air-to-fuel ratio by sending signals to flow-control valves, e.g., to decrease the flow rate of air (oxygen) and/or increase the flow rate of fuel to attain a new target set point (e.g., a new air-to-fuel ratio) in real time. In some embodiments, it is contemplated that the advanced combustion control system comprises algorithmic instructions (e.g., embodied in a storage device or memory) to decrease the air-to-fuel ratio.

[0028] By continuously dithering the air-to-fuel ratio in each combustor in very fine increments at 10Hz or higher the combustion turbine engine can be operated at near ideal stoichiometry over a very wide range of operating conditions without risking a lean-blowout. A dithering algorithm can keep the air-to-fuel ratio at near ideal stoichiometry and remain in the low greenhouse UHC emission “combustion slot” under a wide range of operating conditions.

[0029] Combustion turbines operating on hydrocarbon-based fuels like methane (CH4) have very generous combustion slots but those engines operating on hydrogen (H2) have much smaller combustion slots and need this kind of advanced combustion control system to maintain reliable and safe operation of hydrogen-fueled combustion turbine engines.

[0030] The present disclosure can be designed to operate on any combination or mixture of hydrocarbon (methane) and hydrogen which should accelerate the adoption and commercialization of 100% hydrogen-fueled combustion turbine engines, for both land and air use.

[0031] The fundamental concept is to adjust the air-to-fuel ratio under any operating condition until the ratio is just slightly too lean. At that point in the tuning, the engine will exhibit very low frequency and very low amplitude pressure pulsations that are indicative of a too-lean operating condition. Once the too-lean condition is established, the advanced combustion control system will enrichen the air-to-fuel ratio ever so slightly until the amplitude of the low frequency pressure pulsations disappears into the noise floor of the system. Then the control system will dither the air-to-fuel ratio frequently and precisely to maintain combustion very near ideal stoichiometric combustion. [0032] This present disclosure is only possible because of the fiber-optic pressure pulsation measurement systems are now small enough and rugged enough to fit into existing acoustic waveguides and other access ports and are capable of operating continuously at temperatures in the range of 1000°F. These fiber optic interferometric sensors have pressure sensing diaphragms that are almost infinitely sensitive and instantaneously responsive to the slightest changes in pressure, i.e., 0.005 psi (280) as shown in Fig 8. The key though is the optical interrogator and the associated microelectronics that can sample and make frequency domain pressure measurements from static to 10 kHz so there is very high fidelity and no blind spots over that acoustic spectral range.

[0033] A combustion engine combustion control system or subsystem may comprise a pressure pulsation measurement subsystem configured to continuously measure amplitudes of greater than 0.2 psi, frequency pressure pulsations of less than 100 Hz adjacent to a combustion zone of a combustion engine to detect a precursor to a lean-blowout condition. The combustion engine combustion control system or subsystem may also comprise a control system comprising logic and an injector configured to adjust an air-to-fuel ratio based on the measured amplitude and the measured frequency of the pressure pulsations. The combustion engine combustion control system or subsystem may also include in any combination and in any order the following.

• the pressure pulsation measurement subsystem comprises a fiber optic interferometer.

• the fiber optic interferometer is coupled to a mating optical interrogator.

• the pressure pulsation measurement subsystem is configured to measure the amplitude pressure pulsations above 0.2psi in a range from 5 to-75Hz.

• the pressure pulsation measurement subsystem is configured to measure the amplitude of pressure pulsations in the range from 0 to 10,000Hz. a combustion turbine engine wherein the combustion turbine engine operates on any combination of fossil fuel and hydrogen.

[0034] A combustion turbine engine combustion control system may comprise a pressure pulsation measurement subsystem configured to periodically measure amplitudes of greater than 0.2 psi and frequency pressure pulsations of less than 100Hz, wherein a fiber optic interferometer within the pressure pulsation measurement subsystem is located near the combustion zone, makes a direct measurement, and detects a precursor to a lean-blowout condition. The combustion turbine engine combustion control system may also comprise a control system comprising logic and mechanism to adjust an air-to-fuel ratio based on the measurement of the amplitude and frequency of the pressure pulsations that are indicative of an impending lean-blowout condition.

[0035] A combustion turbine engine combustion control system may comprise a pressure pulsation measurement system configured to measure an amplitude of greater than 0.2 psi and a frequency pressure pulsation of less than 100Hz, wherein a fiber optic interferometer within the pressure pulsation measurement subsystem is located near the combustion zone and makes a direct measurement. The combustion turbine engine combustion control system may also comprise a control system comprising logic and mechanism to adjust an air-to-fuel ratio of the combustion turbine engine based on the measurement of the amplitude and frequency of the pressure pulsations that are indicative of an impending lean-blowout condition or indicative of other operating anomalies.

[0036] The following description and the drawings disclose various illustrative aspects. Some improvements and novel aspects may be expressly identified, while others may be apparent from the description and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS [0037] Operation of the present teachings may be better understood by reference to the detailed description taken in connection with the following illustrations. These appended drawings form part of this specification, and written information in the drawings should be treated as part of this disclosure. In the drawings:

[0038] Figure 1 is an example chart showing an acoustic frequency waveform for a gas turbine engine operating under a normal safe mode where a moderate level of greenhouse gas is emitted, and the low frequency pressure pulsations noise floor is less than 0.2 psi.

[0039] Figure 2 is an example chart showing an acoustic frequency waveform for a gas turbine engine operating under a too-lean air-to-fuel ratio, wherein the engine is experiencing high amplitude, low frequency pressure pulsations of 1.2 psi at 25Hz and well above the 0.5 psi alarm threshold which is representative of combustion instabilities that are a precursor to a lean-blowout.

[0040] Figure 3 shows a typical Fabry-Perot extrinsic interferometer that is simultaneously being subjected to pressure waves at multiple frequencies. The actual Fabry-Perot cavity is located inside a sealed chamber where it is not subjected to any fouling by the combustion process.

[0041] Figure 4 is an illustration showing the conversion of time series pressure measurements transformed into the frequency domain by the Fast Fourier Transform analyzer contained within the microelectronics complete with graphic displays of alarm thresholds for low, medium, and high frequency bands.

[0042] Figure 5 is an example of a combustion control system according to the present disclosure.

[0043] Figure 6 is a flowchart of an example of a method according to the present disclosure. [0044] Figure 7 is a schematic showing the entire combustion dynamics monitoring system including the transducer/interferometric sensor, the tactical cable, junction box, home run cable, rack mount optical interrogator/spectrum analyzer, and the monitor

[0045] Figure 8 shows a comparison between the fidelity of a laboratory grade calibration microphone with the fidelity of a 1000°F temperature-tolerant combustion dynamic pressure pulsation measurement system of the present disclosure in a controlled laboratory test.

[0046] Figure 9 shows how generous the stable combustion zone is when, for example, an antiquated oil-fired plant is grandfathered and not held to tight emissions standards as compared to the very narrow range of combustion stability when a modem low-NO_x plant is held to far more rigorous emissions standards.

[0047] Figure 10 shows a cut-away of a rugged, flexible, temperature-tolerant fiber optic transducer/sensor used to monitor combustion dynamics in an acoustic waveguide in a Siemens 50 IF combustion turbine engine.

[0048] The embodiments disclosed herein may be embodied in several forms without departing from their spirit or essential characteristics. The scope of the system is defined in the appended claims, rather than in the specific description preceding them. All embodiments that fall within the meaning and range of equivalency of the claims are therefore intended to be embraced by the claims.

DETAILED DESCRIPTION

[0049] Reference will now be made in detail to exemplary embodiments of the present disclosure through examples which are illustrated in the accompanying drawings. It is to be understood that the same acoustic phenomenon occurs regardless of whether the combustion turbine engine is operated with a fossil fuel, hydrogen fuel, or any combination of fossil fuel and hydrogen. It is also to be understood that other embodiments may be utilized, and structural and functional changes may be made without departing from the respective scope of the present disclosure. Moreover, features of the various embodiments may be combined or altered without departing from the scope of the present disclosure. As such, the following description is presented by way of illustration only and should not limit in any way the various alternatives and modifications that may be made to the illustrated embodiments and still be within the spirit and scope of the present disclosure.

[0050] As used herein, the words “example” and “exemplary” mean an instance, or illustration. The words “example” or “exemplary” do not indicate a key or preferred aspect or embodiment. The word “or” is intended to be inclusive rather an exclusive, unless context suggests otherwise. As an example, the phrase “A employs B or C,” includes any inclusive permutation (e.g., A employs B; A employs C; or A employs both B and C). As another matter, the articles “a” and “an” are generally intended to mean “one or more” unless context suggests otherwise.

[0051] Figure 1 is a chart showing an acoustic frequency waveform under normal moderate emission conditions, i.e., pressure amplitude (0 to 2 psi) versus frequency (0 to 500Hz), for a combustion turbine engine operating with a richer air-to-fuel ratio than ideal stoichiometry. Under these normal safe-mode operating conditions, there are by design moderate greenhouse gas emissions but with this too-rich air-to-fuel ratio the combustion turbine engine is able to operate safely without concern of a lean-blowout condition. Note, there is no indication of a high amplitude pressure pulsation alarm condition (170) at 25Hz on the chart in Figure 1 in either the instantaneous signal (150) or the peak signal (160). The peak pressure pulsations at 25Hz is about 0.2 psi and is well below the 0.5 psi alarm threshold (170) and that signal is buried in the noise floor.

[0052] Figure 2 is a chart showing an acoustic frequency waveform, i.e., pressure amplitude (0 to 2 psi) versus frequency (0 to 500Hz), for a combustion turbine engine operating under an air-to-fuel ratio that is too lean and where the engine is experiencing low frequency pressure pulsations from combustion instabilities that are a precursor warning of a leanblowout. This operating condition resulted in a 1.2 psi peak pressure pulsation at 25Hz (185), and that peak pressure signal was well above the 0.5 psi alarm threshold (175). Note also, the instantaneous signal at the second point in time (155) shows that the too-lean condition and the resulting pressure pulsations have already been corrected. But at some brief moment in time, perhaps only a few tenths of a second earlier, the peak pressure pulsation signal (165) was dangerously high at 1.2 psi. This is precisely the evidence that the system was in a dangerous too-lean condition. The whole concept of the combustion control system is triggered by the amplitude of the instantaneous signal (155). The air-to-fuel was enriched immediately avoiding a lean-blowout of the combustion turbine engine.

[0053] If the combustion turbine engine remains in the “too lean” air-to-fuel ratio condition for too long, e.g., a few seconds, the flame inside the combustor may be extinguished, resulting in a lean-blowout. The combustor may suffer severe mechanical damage from those low frequency pressure pulsations and that is another reason to avoid low frequency pressure pulsations from a too lean combustion condition. In addition to the immediate safety concerns, the engine life is degraded from the thermal fatigue as the engine cycles from a high operating temperature to an immediate shutdown and cool down.

[0054] A lean-blowout is a very serious condition and forces the engine into a shutdown condition for the safety of the plant and its personnel. If the fuel were to continue to enter the engine and if it were to ignite downstream of the combustor, it would create an uncontrolled explosion causing severe damage to the engine and potential loss of life. So, this is a very serious business, it requires very serious technology, and a very rigorous qualification.

[0055] FIG 9 shows a comparison of the stable combustion zone in a high emission engine (285) with the stable combustion zone in a modern low-NOx (low emission) engine (290). Operating the engine in this manner with a too-rich air-to-fuel mixture results in high reliability operation even with conventional piezoelectric instrumentation and conventional controls but also results in higher than necessary greenhouse gas emissions. The corollary is also true. High reliability with state-of-the-art fiber optic instrumentation integrated into advanced combustion controls can result in operation of the engine at almost perfect stoichiometry with minimal emissions, which is what this disclosure covers.

[0056] A pressure pulsation measurement system according to the present disclosure makes a discernible measurement of a high amplitude, e.g., greater than 0.2 psi, low frequency pressure pulsation at less than 100Hz. In a large-frame Siemens 50 IF engine, a signal above 0.2 psi between 20Hz and 30Hz is a precursor indication of a pending lean-blowout as illustrated in the example of FIG. 2). This is the key signal that indicates the air-to-fuel ratio is too lean to sustain combustion. For each unique engine design, there is a similar phenomenon with a pressure pulsation that exceeds 0.2 psi below 100Hz that is an indication of a lean-blowout condition. The present system intends to detect such, while operating under such difficult conditions, and provide feedback to the system to make appropriate adjustments to prevent such situation.

[0057] A fiber optic Fabry -Perot interferometric sensor assembly of the present combustion turbine engine combustion control system or subsystem is shown in FIG 3. The Fabry -Perot interferometric sensor comprises a pressure diaphragm (210) that deflects in response to acoustic pressure waves (190) at multiple frequencies simultaneously changing the interferometer gap (215). The Fabry-Perot sensor cavity (220) is encapsulated in a sealed structure so it cannot be fouled by the combustion process present in combustion engines. An optical fiber (225) transmits light and in one embodiment, it represents one partially mirrored surface of the Fabry-Perot interferometer.

[0058] A fiber optic Fabry-Perot transducer/probe assembly is shown in FIG 10. The cutaway photograph shows a rugged, flexible, temperature-tolerant fiber optic transducer/sensor used to monitor combustion dynamics in a Siemens 50 IF combustion turbine engine. The fiber optic interferometric sensor must be miniature, and the transducer probe must be flexible so the fiber optic interferometric fiber-optic interferometer can be positioned very close to the end of the 1 ” x .035” stainless steel tube (acoustic waveguide) in this specific Siemens engine - although the size and shape of such can be modified to fit with other engines of different sizes and shapes. In this location, the close-coupled direct measurement is essentially free of any resonance or electromagnetic noise that could degrade the acoustic signal quality.

[0059] The present disclosure contemplates a fiber optic Fabry-Perot transducer/probe assembly of any appropriate configuration. The appropriate configuration will depend upon the configuration of the combustion turbine engine combustion control system or subsystem. [0060] Further, the schematic in FIG 7 shows the combustion dynamics monitoring system including the transducer/interferometric sensor (240), the tactical cable (245), junction box (250), home run cable (260), rack mount optical interrogator/spectrum analyzer (265), and the monitor (270). These are components of the combustion turbine engine combustion control system or subsystem.

[0061] The optical interrogator/spectrum analyzer (265) shown in FIG 7 processes the raw optical signal through various stages of signal processing and generates a time-series pressure readings (230) at very high sampling rates as illustrated in FIG 4. Then, the electronics embedded in the optical interrogator/spectrum analyzer (265) transforms the time-series pressure readings into the frequency domain (235) as shown in FIG 4.

[0062] The fiber optic interferometric system of the combustion turbine engine combustion control system or subsystem has such high natural resonance that it instantly responds to the applied pressure in the applicable combustion engine and accurately measures the pressure amplitude of the pressure pulsations in frequency bins that are 1Hz wide (plus or minus 0.25 Hz). To appreciate the essentially perfect fidelity of the fiber optic pressure pulsation measurement system, see FIG 8 which compares the frequency response of a laboratorygrade calibration microphone (275) designed for use at room temperature at twelve selected frequencies from 25Hz to 950Hz to the fiber optic interferometric pressure pulsation measurement system (280) of the present combustion turbine engine combustion control system or subsystem, that is designed for continuous use at 1000°F. This testing was done in a controlled laboratory test at room temperature. Note the near perfectly flat response of the fiber optic interferometric pressure pulsation measurement system, which actually had a flatter frequency response than the reference calibration microphone. Note, also, the resolution of the pressure amplitude is in the range of 0.005 psi or less and the frequency resolution is in the range of 1Hz.

[0063] By continuously monitoring the low frequency pressure pulsations and adjusting the air-to-fuel ratio continuously in very fine increments the pressure measurement system, according to the present disclosure, enables the use of automated combustion controls to keep the air-to-fuel ratio at ideal stoichiometry under a very wide range of operating conditions, e.g., changes in ambient temperature, atmospheric pressure, humidity, fuel quality, engine wear and tear, etc. The air-to-fuel ratio is more accurately defined as the air mass flow vs the fuel mass flow. Ideal stoichiometric combustion with methane occurs at a ratio of 18.98: 1. Any lower ratio is fuel-rich and has excessive hydrocarbon emissions. Any higher and there is a risk of a lean-blowout. The actual ideal ratio, however, is a function of the composition of the fuel, i.e. pure methane versus other fossil fuels. This fuel quality index is called the Wobbe Index. It is a measure of the fuel’s heating value to its specific gravity (SG air) relative to air. In operation, the air to fuel ratio is not measured but air pressure and flow and fuel pressure and flow are measured. So the metrics for control are the interaction of those two parameters which are measured directly. [0064] In some embodiments, the pressure pulsation measurement system is comprised of a high-fidelity optical interferometric pressure measurement system as shown in Figure 7. In some embodiments, the pressure measurement system is comprised of a highly customized, miniature Fabry -Perot interferometer as shown in Figure 3.

[0065] Referring to FIG. 3, a fiber optic Fabry-Perot interferometric sensor assembly of the present system is shown. The Fabry-Perot interferometric sensor comprises a pressure diaphragm (210) that deflects in response to acoustic pressure waves (190) at multiple frequencies simultaneously changing the interferometer gap (215). The Fabry-Perot sensor cavity (220) is encapsulated in a sealed structure so it cannot be fouled by the combustion process. An optical fiber (225) transmits light and in one embodiment, it represents one surface of the Fabry-Perot interferometer.

[0066] Referring to FIG. 5, an example of a combustion turbine engine combustion control system or subsystem 100 according to the present disclosure is shown. The combustion turbine engine combustion control system or subsystem 100 may be comprised of a processor 102 and a storage device 104 (e.g., on which instructions are embedded). The processor 102 may embody any suitable processing device or set of processing devices such as but not limited to: a microprocessor, a microcontroller-based platform, a system on a chip, suitable integrated circuit, one or more field programmable gate arrays (FPGAs), and/or one or more application-specific integrated circuits (ASICs). The storage device 104 may be volatile memory (e.g., RAM, which can include non-volatile RAM, magnetic RAM, ferroelectric RAM, or any other suitable forms); non-volatile memory (e.g., disk memory, FLASH memory, EPROMs, EEPROMs, non-volatile solid-state memory, etc.), unalterable memory (e.g., EPROMs), read-only memory, high-capacity storage devices (e.g., hard drives, solid state drives, etc.) and/or a non-transitory computer readable medium. In some examples, the storage device 104 may comprise multiple kinds of memory, particularly volatile memory and non-volatile memory. The storage device 104 may also embody a computer-readable media on which one or more sets of instructions are embedded, including, without limitation a non-transitory computer readable medium. The instructions may embody one or more of the methods or logic as described herein.

[0067] In a particular embodiment, the instructions may reside completely, or at least partially, within any one or more of the storage devices 104, the computer-readable medium, and/or within the processor 102 during execution of the instructions. The combustion turbine engine combustion control system or subsystem 100 may be operatively connected to a pressure pulsation measurement system 120 that is configured to continuously monitor a pressure pulsation amplitude and frequency near the combustion zone (i.e., the critical operating data). In some embodiments, the pressure pulsation measurement system 120 may be integrated with the combustion turbine engine combustion control system or subsystem 100 (e.g., as a subcomponent thereof).

[0068] Upon detecting high amplitude, low frequency pressure pulsations (indicative of a lean air-to-fuel ratio susceptible to a lean -blowout), the pressure pulsation measurement system 120 is configured to transmit operating data (indicative of the lean air-to-fuel ratio) to the combustion turbine engine combustion control system or subsystem 100. In such embodiments, the combustion turbine engine combustion control system or subsystem 100 may transmit signals to flow control devices 140 to adjust the air-to-fuel ratio (e.g., to increase or decrease the flow rate of air).

[0069] Referring to FIG. 6, an example of a flowchart of a method to detect high-amplitude, low frequency pulsations in the combustion turbine engine combustion control system or subsystem 100 is shown. At step 200, the pressure pulsation measurement system 120 receives operating data, e.g., operating data indicative of a potential lean-blowout. At step 202, the pressure pulsation measurement system 120 transmits the operating data to the combustion turbine engine combustion control system or subsystem 100. At step 204, the combustion turbine engine combustion control system or subsystem 100 is configured to adjust the air-to-fuel ratio in real time, e.g., to attain a new air-to-fuel ratio setpoint, mitigating the possibility for a lean-blowout.

[0070] Referring to FIG. 7, a schematic shows the combustion dynamics control system 100 including the turbine enclosure 208, electrical package 272, transducer/interferometric sensor 240, the tactical cable 245, junction box 250, home run cable 260, rack mount optical interrogator/spectrum analyzer 265, and the monitor 270.

[0071] Referring to FIG. 8, a chart shows on the top the signal as measured by a room temperature high-fidelity calibration microphone at twelve selected frequencies from 25Hz to 950Hz compared to the present 1000°F temperature-tolerant combustion dynamic pressure pulsation measurement system of the combustion turbine engine combustion control system or subsystem in a controlled laboratory test. Note the near perfectly flat response of the pulsation measurement system which actually has a flatter frequency response than the reference calibration microphone. Note also the resolution of the pressure amplitude is in the range of 0.005 psi or less and the frequency resolution is in the range of 0.5Hz.

[0072] Referring to FIG. 9, an illustration shows how generous the stable combustion zone is when, for example, an oil-fired plant is not held to tight emissions standards as compared to the very narrow range of combustion stability when the plant is held to rigid emissions standards. The same principle applies with the present disclosure. When the air-to-fuel ratio is too rich, emissions of greenhouse gases are high but the reliability of the engine is high and the probability of a lean-blowout is low. Better measurement and more precise controls enables lower emissions, more stable combustion, higher engine reliability, and reduced maintenance costs. [0073] Referring to FIG. 10, a cut-away photograph shows a rugged, flexible, temperature- tolerant fiber optic transducer/ sensor 240 used to monitor combustion dynamics in a Siemens 50 IF combustion turbine engine. The fiber optic interferometric sensor must be miniature in size, and the transducer probe must be flexible so the fiber optic interferometric sensor can be positioned very close to the end of the ’ ” x .035” stainless steel tube 242 (acoustic waveguide). In this location, the close-coupled direct measurement is essentially free of any resonance or electromagnetic noise. The configuration of rugged, flexible, temperature tolerant fiber optic transducer/sensor 240 may be modified to fit the applicable combustion engine so as to be part of the combustion turbine engine combustion control system or subsystem and is not limited to the embodiment shown.

[0074] Although the embodiments of the present disclosure have been illustrated in the accompanying drawings and described in the foregoing detailed description, it is to be understood that the present disclosure is not to be limited to just the embodiments disclosed, but that the disclosure described herein is capable of numerous rearrangements, modifications and substitutions without departing from the scope of the claims hereafter. The terms “includes,” “including,” and “include” are inclusive and have the same scope as “comprises,” “comprising,” and “comprise” respectively. The claims as follows are intended to include all modifications and alterations insofar as they come within the scope of the claims or the equivalent thereof.

Claims

1. A combustion engine combustion control system or subsystem comprising: a pressure pulsation measurement subsystem configured to continuously measure amplitudes of greater than 0.2 psi and frequency pressure pulsations of less than 100 Hz adjacent to a combustion zone of a combustion engine to detect a precursor to a lean-blowout condition; and a control system comprising logic and an injector configured to adjust an air-to-fuel ratio based on the measured amplitude and the measured frequency of the pressure pulsations.

2. The combustion engine combustion control system or subsystem of claim 1, wherein the pressure pulsation measurement subsystem comprises a fiber optic interferometer.

3. The combustion engine combustion control system or subsystem of claim 2, wherein the fiber optic interferometer is coupled to a mating optical interrogator.

4. The combustion engine combustion control system or subsystem of claim 1, wherein the pressure pulsation measurement subsystem is configured to measure the amplitude pressure pulsations above 0.2psi in a range from 5 to-75Hz.

5. The combustion engine combustion control system or subsystem of claim 1, wherein the pressure pulsation measurement subsystem is configured to measure the amplitude of pressure pulsations in a range from 0 to 10,000Hz.

6. The combustion engine combustion control system or subsystem of claim 1 further comprising a combustion turbine engine wherein the combustion turbine engine operates on any combination of fossil fuel and hydrogen.

7. A combustion turbine engine combustion control system comprising: a pressure pulsation measurement subsystem configured to periodically measure amplitudes of greater than 0.2 psi and frequency pressure pulsations of less than 100Hz, wherein a fiber optic interferometer within the pressure pulsation measurement subsystem is located near the combustion zone, makes a direct measurement, and detects a precursor to a lean-blowout condition; and a control system comprising logic and mechanism to adjust an air-to-fuel ratio based on the measurement of the amplitude and frequency of the pressure pulsations that are indicative of an impending lean-blowout condition.

8. A combustion turbine engine combustion control system comprising: a pressure pulsation measurement system configured to measure an amplitude of greater than 0.2 psi and a frequency pressure pulsation of less than 100Hz, wherein a fiber optic interferometer within the pressure pulsation measurement subsystem is located near the combustion zone and makes a direct measurement; and a control system comprising logic and mechanism to adjust an air-to-fuel ratio of the combustion turbine engine based on the measurement of the amplitude and frequency of the pressure pulsations that are indicative of an impending lean-blowout condition or indicative of other operating anomalies.