System and method for differentiating gas sources based on temperature

Abstract

A method for differentiating gas sources based on temperature includes transmitting an optical beam through a plume emitted by a combustion system. The method includes detecting the optical beam, after propagating through the plume, to obtain an absorption spectrum. The method includes determining, based on the absorption spectrum, a first path-integrated concentration of a gas species, a first temperature of the first path-integrated concentration, a second path-integrated concentration of the gas species, and a second temperature of the second path-integrated concentration. The second temperature is different from the first temperature. The method may further include performing an inversion to obtain a sampled quantity of the gas species within the plume. The method may be implemented with dual-comb spectroscopy, in which case the optical beam is formed from two frequency combs having slightly different repetition rates.

Description

PATENT Client Ref. CU6372B-02 Attorney Docket No. UOCO.P2089WO / 00623502 SYSTEM AND METHOD FOR DIFFERENTIATING GAS SOURCES BASED ON TEMPERATURE RELATED APPLICATIONS

[0001] This application claims priority to U.S. Provisional Patent Application No. 63 / 547,062, filed November 2, 2023, which is incorporated herein by reference in its entirety. BACKGROUND

[0002] A gas flare (also known as a flare stack, flare boom, ground flare, or flare pit) is a device that combusts, or “flares,” one or more flammable gases that are unwanted, unusable, or cannot be otherwise captured and reused. Such gases are referred to as “waste gases.” Gas flares are typically used in remote or offshore facilities that lack pipelines and other infrastructure for storing and transporting waste gases. Sometimes gas flares are used to burn waste gases in situations where it is not economically feasible or practical to collect and reuse these gases. Gas flares are commonly used at chemical plants, oil and natural gas facilities (e.g., refineries), well heads, rigs, and offshore platforms. Gas flares are also sometimes used to combust biogas generated at landfills.

[0003] Waste gases are typically hazardous (e.g., toxic). The combustion uses oxygen in the atmosphere to destroy the waste gases via thermal oxidation, thereby converting these waste gases into primarily carbon dioxide (CO2), which is non-toxic and therefore much safer for the environment and human exposure. Carbon dioxide is also a less potent greenhouse gas than many types of waste gas. Carbon dioxide has, by definition, a global warming potential (GWP) of 1 for all time scales. For comparison, methane (CH4), a common waste gas, has a GWP of 83 over 20 years, 30 over 100 years, and 10 over 500 years. The reduction in GWPwith time scale is due to the shorter atmospheric lifetime of methane (12 2 years), as comparedto carbon dioxide. Many other types of waste gas have an even greater warming effect than methane, with GWPs of tens of thousands, or more, over 100 years.

[0004] The “flare efficiency” of a gas flare is the fraction of carbon in the initial waste- gas stream that is emitted from the gas flare as carbon dioxide. The flare efficiency is also referred to as the “carbon conversion efficiency” and “combustion efficiency.” A related performance metric is the “destruction and removal efficiency” (DRE), or simply the “destruction efficiency.” The DRE is the fraction of carbon in a particular gas species (e.g.,PATENT Attorney Docket No. UOCO.P2089WO / 00623502 methane) of the initial waste-gas stream that is converted to carbon dioxide by the gas flare. It is possible to operate gas flares with flare efficiencies and methane DREs of 98%, or more. SUMMARY

[0005] The present embodiments include a laser-based sensor for stand-off detection of methane (CH4) emissions for real-time monitoring and optimization of gas flares. In some embodiments, the sensor uses optical-frequency-comb technology for detecting methane at part-per-billion (ppb) sensitivities level over a beam path of 1 km, or more. By using an optical frequency comb, the sensor can be adapted for the high sensitivity detection of additional warming agents and hazardous compounds across the molecular fingerprint spectrum. The sensor can be used to help achieve a “net-zero” carbon economy by providing a straight-forward scheme for measuring non-trivial emissions from oil and gas supply chains.

[0006] Flaring is the practice of combusting waste gas (typically a mixture of methane and higher hydrocarbons) that is associated with the oil extraction process. Flaring under optimal conditions reduces harmful gas emissions to carbon dioxide (CO2) and water vapor (H2O) through combustion. However, the oil-field environment rarely offers perfect conditions for the combustion process. Incomplete or non-optimal combustion (e.g., too rich, too hot, etc.) can allow methane and other hydrocarbons to escape from the flare, as well as generating a host of volatile and potentially harmful compounds, such as volatile organic compounds (VOCs), sulfur oxides (SOx), and nitrogen oxides (NOx).

[0007] Because flaring occurs under a range of temperatures, associated gas flow rates, and wind conditions that are constantly changing, it is challenging to maintain optimal flare operating parameters over extended periods of time. Current diagnostics available in the field include flare temperature measurements with thermocouples, upstream flare pressure measurements, and periodic assessment by “pumpers” (i.e., oilfield workers moving from site to site to maintain operations). Direct flare temperature measurements are unreliable because of vast changes in environmental conditions. Therefore, pumpers are primarily relied upon to determine if a flare is unlit. Assessment by pumpers is done through audio, visual, and olfactory (AVO) inspection, typically involving the minimization of soot emissions (black smoke). Assessment can be highly variable depending on pumper visit schedules and experience.

[0008] Some of the present embodiments combine a dual-comb laser spectrometer with data analysis to determine the concentrations of methane (and other types of gases) directly from flare streams. By adding real-time, quantitative monitoring capabilities for flare slip and incomplete combustion, the present embodiments may advantageously help operators remotelyPATENT Attorney Docket No. UOCO.P2089WO / 00623502 monitor and improve flare efficiency. By measuring the concentrations of these harmful gases quickly and reliably, counter measures to reduce their emissions can be implemented sooner and longer periods of accidental release of these harmful substances can be avoided.

[0009] Some prior-art, real-time, methane emissions monitoring systems use dual- frequency-comb spectroscopy from distances of up to 2.5 miles (or more) to provide real-time feedback to operators [1]. These prior-art monitoring systems measure methane emissions from all the oil and gas infrastructure components within the monitoring region (typically dozens of square miles), including flares. While these prior-art monitoring systems are capable of differentiating where, at a facility, emissions are originating from, they do not explicitly distinguish between high-temperature flare emissions and other types of emissions at the facility. The present embodiments advantageously have this capability. BRIEF DESCRIPTION OF THE FIGURES

[0010] FIG. 1 is a functional diagram of a gas-sensing system that can detect and differentiate gas sources based on temperature, in embodiments.

[0011] FIG.2 illustrates dual-comb spectroscopy.

[0012] FIG.3 shows the difference in the near-infrared absorption signature of 2 ppm of background methane (e.g., atmospheric methane) at 300 K over a pathlength of 1 km and 2% methane at 1000 K over a pathlength of 1 m.

[0013] FIG. 4 is a flowchart of a method for differentiating gas sources based on temperature, in embodiments. DETAILED DESCRIPTION

[0014] FIG.1 is a functional diagram of a gas-sensing system 100 that can detect and differentiate gas sources based on temperature. The system 100 uses laser spectroscopy to measure both amounts (e.g., concentrations) and temperatures of one or more gas species in a plume 114 emitted from a stack 108. As an alternative to the stack 108, the plume 114 may be emitted from a vent, exhaust, pipe, or other type or orifice or opening. The system 100 includes an optical transceiver 104 that transmits a free-space optical beam 116 towards the stack 108. The optical beam 116 propagates a distance through a first region 160 of space that is primarily the atmosphere, after which it propagates a distance through a second region 162 of space that is filled primarily with the plume 114. For clarity in FIG.1, it is assumed that theoptical beam 116 propagates horizontally in the direction of a right-handed Cartesiancoordinate system 120. For reference, gravity is assumed to point in the - direction.PATENT Attorney Docket No. UOCO.P2089WO / 00623502

[0015] The stack 108 may be a combustion device that generates at least part of the plume 114 via combustion. Examples of such combustion devices include, but are not limited to, enclosed combustors, incinerators, flare stacks, and flare pits. In the example of FIG.1, the stack 108 is an open-air gas-flare system that uses a flame 112 to combust flammable waste gas 150 that is injected into the stack 108 and drawn upward to the flame 112. The plume 114 is then dispersed into the surrounding atmosphere. Such gas flares are typically found at oil and natural gas wells, offshore oil and natural-gas platforms, oil and gasoline refineries, and landfills. In these examples, the plume 114 may contain a combination of various by-products generated from the combustion of the waste gas 150. The plume 114 may also contain a portion of the waste gas 150 that was not combusted by the flame 112. The plume 114 may also contain other gas species, such as atmospheric gases (e.g., O2and N2) and water vapor (H2O).

[0016] Alternatively, the stack 108 may not itself be a combustion device, but part of a larger combustion system. For example, the stack 108 may be a flue-gas stack, or chimney, that transports flue gases generated by combustion that occurs elsewhere (e.g., in a burner). Thestack 108 transports these flue gases vertically upward (i.e., in the + direction) for dispersalinto the surrounding atmosphere. Accordingly, the gas-sensing system 100 may be used with industrial furnaces, ovens, boilers, and other systems that use flue-gas stacks.

[0017] The gas-sensing system 100 also includes a retroreflector 118 that retroreflects the optical beam 116 into a retroreflected optical beam 126 that propagates back to the optical transceiver 104. The retroreflected optical beam 126 first propagates through the second region 162 (and therefore the plume 114), after which it propagates through the first region 160 (i.e., the atmosphere). The optical transceiver 104 receives the retroreflected optical beam 126 as received light 128 and couples the received light 128 to a spectrometer 130 (e.g., via a fiber- optic cable 122, as shown in FIG.1). The spectrometer 130 processes and detects the received light 128 to generate a measured absorption spectrum 132. A signal processor 134 processes the absorption spectrum 132 to determine one or more properties of gas within the plume 114.

[0018] The retroreflector 118 may be a corner-cube retroreflector, cat’s-eye retroreflector, hollow roof prism, or other type of optic that retroreflects an incident light beam regardless of the direction of the incident light beam. The retroreflector 118 may alternatively be a flat mirror or another type of optic off of which the optical beam 116 can reflect, diffract, or scatter. In some embodiments, the retroreflector 118 is affixed to the stack 108. In other embodiments, the retroreflector 118 is affixed to a motorized stage that is, in turn, affixed to the stack 108. In these embodiments, the angles of the retroreflector 118 can be adjusted to steerPATENT Attorney Docket No. UOCO.P2089WO / 00623502 the retroreflected optical beam 126 back toward the optical transceiver 104. It is assumed that the retroreflected optical beam 126 is spatially overlapped with the optical beam 116.

[0019] In other embodiments, the retroreflector 118 is not affixed to the stack 108. For example, the retroreflector 118 may be mounted on an unmanned aerial vehicle (UAV) that is controlled to hover near the top of the stack 108. These embodiments advantageously do not require the retroreflector 118 to be affixed to the stack 108, which can be a time consuming and dangerous procedure. Furthermore, the same retroreflector 118 can be reused for different stacks. Reuse of the retroreflector 118 also allows it to be easily cleaned between uses. The optical transceiver 104 may similarly be affixed to a UAV that is controlled to move upward such that the optical transceiver 104 and retroreflector 118 are at similar elevations.

[0020] While FIG. 1 shows the optical beam 116 and retroreflected optical beam 126 passing directly through the flame 112, the optical beam 116 and retroreflected optical beam 126 may alternatively pass below the flame 112 (e.g., to sample more of the waste gas 150before it is combusted), to the side of the flame 112, or above the flame 112 (i.e., in the +direction). Alternatively, the optical beam 116 and retroreflected optical beam 126 may pass through the waste gas 150 below the top of the stack 108. In this case, the stack 108 may be outfitted with windows through which the optical beams 116 and 126 can pass.

[0021] In some embodiments, the gas-sensing system 100 includes an optical source 102 that generates probe light 110 and couples the probe light 110 to the optical transceiver 104 (e.g., via a fiber-optic cable 124, as shown in FIG.1), which in turn couples the probe light 110 into free-space as the optical beam 116. The optical source 102 may include one or more lasers, in which case the probe light 110 is coherent. Each of the one or more lasers may generate single-frequency laser light or multi-frequency laser light. When the optical source 102 includes two or more lasers, the outputs of these lasers may be combined such that the probe light 110 has a plurality of optical frequencies or spectral components.

[0022] The optical transceiver 104 may be mounted on a gimbal mount 144 that can be controlled to change one or both of the azimuthal and elevation angles along which the optical beam 116 propagates. Thus, the gimbal mount 144 can be controlled to steer the optical beam 116 such that it strikes the retroreflector 118. Examples of the gimbal mount 144 are known in the art (e.g., see International Publication Number WO 2022 / 217039 and U.S. Patent No. 11,686,622). As an alternative to the fiber-optic cable 122, the optical transceiver 104 may include a photodetector that detects the retroreflected optical beam 126 and generates a resulting electrical signal that is transmitted to the spectrometer 130. As an alternative to the fiber-optic cable 124, the optical source 102 may be affixed to the optical transceiver 104, in which casePATENT Attorney Docket No. UOCO.P2089WO / 00623502 the optical source 102 rotates with the optical transceiver 104. While FIG.1 shows the optical transceiver 104 acting as both an optical transmitter and optical receiver, the gas-sensing system 100 may alternatively be implemented with a separate optical transmitter and optical receiver.

[0023] In FIG. 1, the spectrometer 130 and optical source 102 are advantageously located separate from the optical transceiver 104 such that the spectrometer 130 and optical source 102 are not affixed to the gimbal mount 144. Since the spectrometer 130 and optical source 102 contain lasers and optical locks that are sensitive to vibrations and temperature fluctuations, the spectrometer 130 and optical source 102 may be located in a vessel or room within which they are environmentally isolated from unnecessary mechanical motion (e.g., movement of the gimbal mount 144), wind, precipitation (e.g., wind, ice, snow), and debris (e.g., branches, leaves, insects, etc.), thereby helping to improve robustness and reliability of the gas-sensing system 100. For example, the spectrometer 130 and optical source 102 may be located in a van, building, or mobile office trailer near the gimbal mount 144. Alternatively, the fiber-optic cables 122 and 124 may be several kilometers long, in which case the spectrometer 130 and optical source 102 may be located several kilometers away from the gimbal mount 144.

[0024] In the example of FIG.1, the optical source 102 includes a first frequency-comb generator 106(1) that generates a first optical frequency comb 148(1) and a second frequency- comb generator 106(2) that generates a second optical frequency comb 148(2). Each of the optical frequency combs 148(1) and 148(2) has a spectrum formed from a plurality of discrete and equally-spaced frequency components, or “teeth.” Each of the frequency-comb generators 106(1) and 106(2) may be, for example, a fiber-based femtosecond laser (e.g., based on Yb-, Nd-, or Er-doped fiber), a solid-state femtosecond laser (e.g., Ti:Al2O3), or a microresonator- based frequency-comb source. When the frequency-comb generators 106(1) and 106(2) operate at slightly different repetition rates, the optical frequency combs 148(1) and 148(2) may be combined to create, as the probe light 110, a double-pulse train. In this case, the gas-sensing system 100 performs dual-comb spectroscopy (DCS). However, the system 100 may perform another type of absorption spectroscopy without departing from the scope hereof. Examples of such absorption spectroscopy include, but are not limited to, tunable diode laser absorption spectroscopy, Fourier transform spectroscopy, cavity ring-down spectroscopy, noise-immune cavity-enhanced optical-heterodyne molecular spectroscopy, wavelength modulation spectroscopy, and frequency modulation spectroscopy. Additional examples of the frequency- comb generators 106(1) and 106(2), optical source 102, and spectrometer 130 can be found in U.S. Patent Application Pub. No.2021 / 0080324.PATENT Attorney Docket No. UOCO.P2089WO / 00623502

[0025] The spectra of the optical frequency combs 148(1) and 148(2) cover absorption features of one or more gas species within the plume 114. In particular, several gas species of interest have absorption features in the near-infrared (IR) region of the electromagnetic spectrum. For example, the optical frequency combs 148(1) and 148(2) may have frequency components between 176 and 184 THz (i.e., wavelengths between 1.63 μm and 1.70 μm) for measuring methane. Alternatively, the optical frequency combs 148(1) and 148(2) may have spectral components between 193 and 198 THz (i.e., wavelengths between 1.52 μm and 1.55 μm) for measuring acetylene. Other gas species with absorption features in the near-IR include water vapor and carbon dioxide. Additional gas species that can be measured with the gas- sensing system 100 include, but are not limited to, hydrocarbons, VOCs, hydrogen (H2), carbon monoxide (CO), NOx, and SOx.

[0026] While the above examples describe absorption features in the infrared region of the electromagnetic spectrum, the optical frequency combs 148(1) and 148(2) may be configured to measure gases with absorption features in other parts of the electromagnetic spectrum, such as the ultraviolet, visible, near-infrared, mid-infrared, and far-infrared regions. Thus, the term “optical,” as used herein, is not limited to the visible part of the electromagnetic spectrum, and may refer to another region or regions of the electromagnetic spectrum.

[0027] Each spectral component of the optical beams 116 and 126, when detected by the spectrometer 130, indicates a path-integrated absorption value at the optical frequency or wavelength of the spectral component. Thus, the spectrometer 130 measures a plurality of path- integrated absorption values that form a one-to-one correspondence with the plurality of spectral components. This plurality of path-integrated absorption values is the absorption spectrum 132. As known by those trained in the art, concentration and temperature of a gas species can be obtained from the various features of the absorption spectrum 132.

[0028] For a single gas species, the absorption spectrum 132 will exhibit features (e.g., the relative sizes of different absorption lines, the presence and absence of certain absorption lines, etc.) indicative of two different temperatures. The first temperature is that of the atmosphere (i.e., the first region 160) while the second temperature is that of the plume 114 (i.e., the second region 162). Specifically, the absorption spectrum 132 can be expressed as the superposition of a first sub-spectrum and a second sub-spectrum. The first sub-spectrum exhibits features of the single gas species at the first temperaturewhile the second sub- spectrum exhibits features of the single gas species at the second temperature . Due to this superposition, any of several data-processing techniques (e.g., nonlinear regression) may be used to decompose the measured absorption spectrum 132 into the first sub-spectrum and thePATENT Attorney Docket No. UOCO.P2089WO / 00623502 second sub-spectrum. The first sub-spectrum may then be processed to extract a first path- integrated concentration and the first temperature of the single gas species in the first region 160. Similarly, the second sub-spectrum may be processed to extract a second path- integrated concentration and the second temperature of the single gas species in the second region 162. This data processing may be performed by the signal processor 134 of FIG.1.

[0029] The first temperature and second temperature are likely to be very different. For example, the first temperature , which is just the ambient temperature of the atmosphere in the example of FIG.1, may range from -20°C to +35°C, depending on various geographical and environmental conditions (e.g., season, time of day, location, altitude, etc.). By contrast, the plume 114 may have a second temperature up to 1000°C. Enclosed flares burn at even higher temperatures, typically between 1000°C and 1200°C, to ensure a high destruction efficiency and to avoid the formation of NOx. Due to these different temperature ranges, the first and second sub-spectra will have significantly different features, or “fingerprints,” which simplifies the process of decomposing the absorption spectrum 132 into the first and second sub-spectra (e.g., see FIG.3).

[0030] Gas sensing based on laser absorption is a well-known and powerful technique that allows for long integration paths, as opposed to point sensors, and can be used in remote stand-off detection schemes for environments that deny the placement of physical sensors such as combustion chambers or open flames [2–4]. Optical frequency combs based on mode-locked lasers are widely used spectroscopy tools [5]. The advantages of frequency combs include high brightness, excellent spatial beam quality, and broad spectral bandwidths. Frequency combs provide a large number of ultra-narrow frequency lines in the optical spectrum. The nearly perfect spacing between these lines can be used to accurately determine absorption features and to extract trace gas concentrations over a broad wavelength regime. Since the frequencies of these optical lines cannot be directly measured with high accuracy, a second frequency comb is used to down-convert the optical frequencies into easy-to-measure microwave frequencies. This method is commonly known as dual-comb spectroscopy (DCS) [6].

[0031] FIG. 2 illustrates DCS. Individual spectral components (also referred to as “lines” or “teeth”) of a first frequency comb are absorbed by quantum energy-level transitions of a gas in the sample. A second frequency comb with a slightly different repetition rate serves as the reference and down-converts the optical frequency components of the first frequency comb into the RF or microwave domain. When the light of the first and second frequency combs are guided through a sample of a molecular species that absorbs light in a spectral range that overlaps that of the frequency combs, certain comb lines are attenuated due to absorption.PATENT Attorney Docket No. UOCO.P2089WO / 00623502 Which spectral components get absorbed and by how much depends on the species of molecules in the sample as well as their concentration. By referencing the measured absorption against a known database [7], it is possible to extract the individual gaseous species and their concentrations.

[0032] Many optical frequency combs have a spectrum that overlaps with several methane absorption lines [8, 9] and are therefore suitable to detect methane trace gas concentrations. While the near-IR spectral region accesses strong absorption signatures of methane, CO2, H2O, and other small molecular compounds, the mid-infrared spectral region opens up the possibility to sense SOx, NOx, polycyclic aromatic hydrocarbons (PAH) and VOCs. The mid-IR region may be accessed, for example, by implementing difference frequency generation with near-IR frequency combs.

[0033] One way to measure flare inefficiency is to measure gas concentrations in situ to the flares. Placing point sensors in these harsh environments is challenging, especially for long- term operation. With the present embodiments, the laser beam can penetrate the flare from a distance. The laser beam may be retroreflected to return the beam to the detector in a safe environment away from the flare. With reference to FIG.1, the distance may be significantly longer than the distance . For example, the distance may be up to 1 km, or more (e.g., several kilometers) while the distance may be as short as a few meters, or less.

[0034] Accurately measuring waste gas escaping combustion adds another layer of complexity (and opportunity). Specifically, the temperature of methane and other gases slipping past the flare is much higher than the ambient temperature. The presence of high-temperature methane is an indicator of slipping, one that is accessible via near-IR spectroscopy. FIG. 3 shows the difference in the near-IR absorption signature of 2 ppm of background methane (e.g., atmospheric methane) at 300 K over a pathlength of 1 km (approximate ambient conditions) and 2% methane at 1000 K over a pathlength of 1 m (example flare conditions with slippage). As can be seen in FIG.3, the relative magnitudes of the different absorption feature peaks are very different for these two cases. This signal difference makes high-temperature methane slip discernable in a broadband frequency-comb measurement over a 1-m open path passing directly through an inefficient flare.

[0035] The advantages of using a dual-comb spectrometer to directly probe methane temperature and concentration within a flare include: (i) high accuracy in detecting methane gas concentrations from leaks and combustion processes, ultimately reducing the risk of harm to human health and the environment, (ii) suitability as an early warning system to alert relevantPATENT Attorney Docket No. UOCO.P2089WO / 00623502 personnel or machinery to prevent the spread and uncontrolled release of methane gas, (iii) remote monitoring for quick response times and effective mitigation measures, and (iv) integration with existing monitoring and control systems to provide a comprehensive solution.

[0036] FIG.4 is a flow chart of a method 400 for differentiating gas sources based on temperature, in accordance with some of the present embodiments. The method 400 may be performed, for example, by the gas-sensing system 100 of FIG. 1. In some embodiments, the method 400 starts with the step 403, in which an optical beam is transmitted through a plume emitted by a combination system. In one example of the step 402, the optical transceiver 104 of the gas-sensing system 100 of FIG.1 transmits the optical beam 116 to propagate through the plume 114 emitted by the stack 108. The optical beam 116 may propagate only through the plume 114 (e.g., above the flame 112). Alternatively, the optical beam 116 may propagate through the flame 112 generating the plume 114. Alternatively, the optical beam 116 may propagate through the waste gas 150 prior to the waste gas 150 reaching the flame 112 (e.g., below the top of the stack 108).

[0037] The method 400 also includes the step 404, in which the optical beam is detected, after the optical beam has propagated through the plume, to obtain a plurality of path-integrated absorption values corresponding to a plurality of spectral components of the optical beam. The optical beam may be detected with a spectrometer (e.g., a dual frequency-comb spectrometer). In one example of the step 404, the spectrometer 130 of the gas-sensing system 100 of FIG.1 detects the optical beam 116 as the retroreflected optical beam 126. The spectrometer 130 then generates the measured absorption spectrum 132. In other examples, the optical beam 116 is detected without retroreflection. In this case, the spectrometer 130 and optical transceiver 104 may be physically separated and located on opposite sides of the stack 108. Since the optical transceiver 104 does not receive in these examples, it may be replaced with an optical transmitter while the spectrometer 130 may be equipped with an optical receiver.

[0038] The method 400 also includes the step 406, in which four quantities are determined based at least in part on the plurality of path-integrated absorption values. These four quantities are: (i) a first path-integrated concentrationof a gas species, (ii) a first temperature of the first path-integrated concentration , (iii) a second path-integrated concentration of the gas species, and (iv) a second temperature of the second path- integrated concentration . The second temperature is different from the first temperature . In one example of the step 406, the signal processor 134 of the gas-sensing system 100 of FIG.1 processes the measured absorption spectrum 132 to obtain values for , , , and .PATENT Attorney Docket No. UOCO.P2089WO / 00623502

[0039] In some embodiments, the method 400 further includes the step 408, in which one or more of the values for , , , and are outputted. In one example of the step 408, the signal processor 134 of the gas-sensing system 100 of FIG. 1 outputs one or more of the values , , , and . These values may be transmitted, for example, to another component, computer, or sub-system for additional processing, data logging, monitoring of the combustion system, control of the combustion system, or a combination thereof.

[0040] In some embodiments, the step 406 of the method 400 further includes the step 410, in which an inversion is performed based at least on the second path-integrated concentration and an emission model of the combustion system. The inversion generates a sampled quantity of the gas species within the plume. This inversion may be performed, for example, by the signal processor 134 of the gas-sensing system 100 of FIG.1. In some of these embodiments, the method 400 further includes the step 412, in which the sampled quantity is outputted. The sampled quantity may be transmitted, for example, to another component, computer, or sub-system for additional processing, data logging, monitoring of the combustion system, control of the combustion system, or a combination thereof. In one embodiment, an indication is generated in response to the combustor efficiency falling below a threshold. For example, a warning message may be generated and displayed on a screen to notify a technician or engineer that the combustion system is not running optimally.

[0041] FIG.4 shows one example of how the sampled quantity may be used to control the combustion system. In this case, the method 400 further includes the step 414, in which a combustion efficiency is determined based on the sampled quantity and a total quantity of the gas species in the plume. The method 400 further includes the step 416, in which the combustion system is controlled based on the combustion efficiency. For example, a flare of the combustion system may be deactivated. In another example, one or more values connected to the combustion system may be opened or closed to alter the operating conditions of the combustion system. More generally, one or more parameters of the combustion system may be adjusted to increase the combustor efficiency.

[0042] In some embodiments, the method 400 further includes the step 402, in which the optical beam is generated prior to transmission via the step 403. In one example of these embodiments, the optical source 102 of the gas-sensing system 100 of FIG.1 generates probe light 110 that is subsequently transmitted by the optical transceiver 104.

[0043] In some embodiments, the optical beam is transmitted through a region of space adjacent to the plume such that the optical beam, when propagating through the region of space, does not propagate through the plume. The region of space, which may have a length of 1 kmPATENT Attorney Docket No. UOCO.P2089WO / 00623502 or more, may be located in front of the plume (with respect to the optical transceiver 104 of FIG.1) such that the optical beam propagates through the region of space before propagating through the plume. In one example of these embodiments, the optical beam 116 of FIG. 1 propagates through the first region 160 of space prior to propagating through the second region 162 of space that is filled primarily with the plume 114. In this example, the first path-integrated concentration represent the concentration of the gas species in the atmosphere adjacent to the plume (i.e., the first region 160 of space) while the second path-integrated concentration represents the concentration of the gas species with the plume.

[0044] In some embodiments, the method 400 further includes retroreflecting the optical beam into a retroreflected optical beam. In this case, the retroreflected optical beam is detected during the step 404. In one example of the step 404, the retroreflector 118 of the gas- sensing system 100 of FIG.1 retroreflects the optical beam 116 into the retroreflected optical beam 126. The spectrometer 130 then detects the retroreflected optical beam 126. The retroreflected optical beam may be detected after propagating through the plume.

[0045] In some embodiments, the method 400 may further include receiving the optical beam after the optical beam has propagated through the plume. For example, the optical transceiver 104 of the gas-sensing system 100 of FIG.1 receives the retroreflected optical beam 126 after propagating through the plume 114. In this case, the spectrometer 130 detects the retroreflected optical beam 126, as received by the optical transceiver 104. Combinations of Features

[0046] Features described above as well as those claimed below may be combined in various ways without departing from the scope hereof. The following examples illustrate possible, non-limiting combinations of features and embodiments described above. It should be clear that other changes and modifications may be made to the present embodiments without departing from the spirit and scope of this invention:

[0047] (A1) A method for differentiating gas sources based on temperature includes transmitting an optical beam through a plume emitted by a combustion system. The method also includes detecting the optical beam, after the optical beam has propagated through the plume, to obtain a plurality of path-integrated absorption values corresponding to a plurality of spectral components of the optical beam. The method also includes determining, based at least in part on the plurality of path-integrated absorption values, a first path-integrated concentration of a gas species, a first temperature of the first path-integrated concentration, a second path-PATENT Attorney Docket No. UOCO.P2089WO / 00623502 integrated concentration of the gas species, and a second temperature of the second path- integrated concentration, the second temperature being different from the first temperature.

[0048] (A2) In the method denoted (A1), the method also includes outputting one or more of the first path-integrated concentration, the second path-integrated concentration, the first temperature, and the second temperature.

[0049] (A3) In either of the methods denoted (A1) and (A2), the gas species is combustible.

[0050] (A4) In any of the methods denoted (A1) to (A3), the gas species is selected from the group consisting of: methane, hydrogen, carbon monoxide, hydrocarbons, and volatile organic compounds.

[0051] (A5) In any of the methods denoted (A1) to (A4), the first path-integrated concentration represents a concentration of the gas species in the atmosphere adjacent to the plume.

[0052] (A6) In any of the methods denoted (A1) to (A5), the second path-integrated concentration represents a concentration of the gas species within the plume.

[0053] (A7) In any of the methods denoted (A1) to (A6), said determining further includes performing an inversion, based at least on the second path-integrated concentration and an emission model of the combustion system, to obtain a sampled quantity of the gas species within the plume.

[0054] (A8) In the method denoted (A7), the method further includes outputting the sampled quantity.

[0055] (A9) In either of the methods denoted (A7) and (A8), the method further includes determining a combustor efficiency based on the sampled quantity and a total quantity of the gas species in the plume.

[0056] (A10) In the method denoted (A9), the method further includes outputting the combustor efficiency.

[0057] (A11) In either of the methods denoted (A9) and (A10), the method further includes generating an indication in response to the combustor efficiency falling below a threshold.

[0058] (A12) In any of the methods denoted (A9) to (A11), the method further includes measuring the total quantity of the gas species.

[0059] (A13) In any of the methods denoted (A9) to (A12), the method further includes controlling the combustion system based on the combustor efficiency.PATENT Attorney Docket No. UOCO.P2089WO / 00623502

[0060] (A14) In the method denoted (A13), said controlling includes deactivating a flare of the combustion system.

[0061] (A15) In either of the methods denoted (A13) and (A14), said controlling includes actuating one or more valves connected to the combustion system.

[0062] (A16) In any of the methods denoted (A13) to (A15), said controlling includes adjusting one or more parameters of the combustion system to increase the combustor efficiency.

[0063] (A17) In any of the methods denoted (A1) to (A16), the method further includes retroreflecting the optical beam into a retroreflected optical beam. Said detecting includes detecting the retroreflected optical beam.

[0064] (A18) In the method denoted (A17), the retroreflected optical beam propagates through the plume. Said detecting the retroreflected optical beam occurs after the retroreflected optical beam has propagated through the plume.

[0065] (A19) In any of the methods denoted (A1) to (A18), said detecting the optical beam includes detecting the optical beam with a spectrometer.

[0066] (A20) In the method denoted (A19), the spectrometer is a dual frequency-comb spectrometer.

[0067] (A21) In any of the methods denoted (A1) to (A20), the method further includes generating the optical beam.

[0068] (A22) In any of the methods denoted (A1) to (A21), said transmitting the optical beam includes transmitting the optical beam through a region of space adjacent to the plume such that the optical beam, when propagating through the region of space, does not propagate through the plume.

[0069] (A23) In the method denoted (A22), the optical beam propagates through the region of space prior to propagating through the plume.

[0070] (A24) In either of the methods denoted (A22) and (A23), the region of space has a length of 1 km or more.

[0071] (A25) In any of the methods denoted (A1) to (A24), the method further includes receiving the optical beam after the optical beam has propagated through the plume.

[0072] (A26) In the method denoted (A25), said receiving the optical beam includes receiving the optical beam with an optical receiver. Said detecting includes detecting the optical beam, as received by the optical receiver.

[0073] (A27) In any of the methods denoted (A1) to (A26), said transmitting the optical beam includes transmitting the beam with an optical transmitter.PATENT Attorney Docket No. UOCO.P2089WO / 00623502

[0074] (B1) A system for differentiating gas sources based on temperature includes an optical transmitter configured to transmit an optical beam through a plume emitted by a combustion system. The system also includes spectrometer configured to detect the optical beam, after the optical beam has propagated through the plume, to obtain a plurality of path- integrated absorption values corresponding to a plurality of spectral components of the optical beam. The system also includes a signal processor configured to determine, based at least in part on the plurality of path-integrated absorption values, a first path-integrated concentration of a gas species, a first temperature of the first path-integrated concentration, a second path- integrated concentration of the gas species, and a second temperature of the second path- integrated concentration, the second temperature being different from the first temperature.

[0075] (B2) In the system denoted (B1), the signal processor is configured to output one or more of the first path-integrated concentration, the second path-integrated concentration, the first temperature, and the second temperature.

[0076] (B3) In either of the systems denoted (B1) and (B2), the gas species is combustible.

[0077] (B4) In any of the systems denoted (B1) to (B3), the gas species is selected from the group consisting of: methane, hydrogen, carbon monoxide, hydrocarbons, and volatile organic compounds.

[0078] (B5) In any of the systems denoted (B1) to (B4), the first path-integrated concentration represents a concentration of the gas species in the atmosphere adjacent to the plume.

[0079] (B6) In any of the systems denoted (B1) to (B5), the second path-integrated concentration represents a concentration of the gas species within the plume.

[0080] (B7) In any of the systems denoted (B1) to (B6), the signal processor is configured to perform an inversion, based on the second path-integrated concentration and an emission model of the combustion system, to obtain a sampled quantity of the gas species within the plume.

[0081] (B8) In the system denoted (B7), the signal processor is configured to output the sampled quantity.

[0082] (B9) In either of the systems denoted (B7) and (B8), the signal processor is configured to generate an indication in response to the combustor efficiency falling below a threshold.

[0083] (B10) In any of the systems denoted (B7) to (B9), the system further includes a meter configured to measure the total quantity of the gas species. The meter may be a thermalPATENT Attorney Docket No. UOCO.P2089WO / 00623502 gas flow meter, one or more pitot tubes, an ultrasonic flow meter, a flare gas analyzer, or a combination thereof.

[0084] (B11) In any of the systems denoted (B7) to (B10), the system further includes a controller configured to control the combustion system based on the combustor efficiency.

[0085] (B12) In the system denoted (B11), the controller is configured to deactivate a flare of the combustion system.

[0086] (B13) In either of the systems denoted (B11) and (B12), the controller is configured to actuate one or more values connected to the combustion system.

[0087] (B14) In any of the systems denoted (B11) to (B13), the controller is configured to adjust one or more parameters of the combustion system to increase the combustor efficiency.

[0088] (B15) In any of the systems denoted (B1) to (B14), the system further includes a retroreflector configured to retroreflect the optical beam into a retroreflected optical beam. The spectrometer is configured to detect the retroreflected optical beam.

[0089] (B16) In the system denoted (B15), the spectrometer is configured to detect the retroreflected optical beam after the retroreflected optical beam has propagated through the plume.

[0090] (B17) In either of the systems denoted (B15) and (B16), the retroreflector is configured to be affixed to a stack of the combustion system.

[0091] (B18) In any of the systems denoted (B1) to (B17), the spectrometer is a dual frequency-comb spectrometer.

[0092] (B19) In any of the systems denoted (B1) to (B18), the system further includes an optical source configured to generate the optical beam.

[0093] (B20) In the system denoted (B19), the optical source is a dual frequency-comb source.

[0094] (B21) In any of the systems denoted (B1) to (B20), the system further includes an optical receiver configured to receive the optical beam after propagating through the plume. The spectrometer is configured to detect the optical beam received by the optical receiver.

[0095] Changes may be made in the above methods and systems without departing from the scope hereof. It should thus be noted that the matter contained in the above description or shown in the accompanying drawings should be interpreted as illustrative and not in a limiting sense. The following claims are intended to cover all generic and specific features described herein, as well as all statements of the scope of the present method and system, which, as a matter of language, might be said to fall therebetween.PATENT Attorney Docket No. UOCO.P2089WO / 00623502 References [1] S. Coburn et al., Optica 5, 320–327 (2018). [2] C. S. Goldenstein, R. M. Spearrin, J. B. Jeffries, and R. K. Hanson, Prog. Energy Combust. Sci.60, 132–176 (2017). [3] A. M. Zolot, F. R. Giorgetta, E. Baumann, W. C. Swann, I. Coddington, and N. R. Newbury, J. Quant. Spectrosc. Radiat. Transfer 118, 26–39 (2013). [4] P. J. Schroeder et al., Proc. Combust. Inst.36, 4565–4573 (2017). [5] G. B. Rieker et al., Optica 1, 290–298 (2014). [6] I. Coddington, N. Newbury, and W. Swann, Optica 3, 414–426 (2016). [7] I. E. Gordon et al., J. Quant. Spectrosc. Radiat. Transfer 203, 3–69 (2016). [8] J. Chen, X. Zhao, Z. Yao, T. Li, Q. Li, S. Xie, J. Liu, and Z. Zheng, Opt. Express 27, 11406–11412 (2019). [9] D. I. Herman et al., Sci. Adv.7, eabe9765 (2021).

Claims

PATENT Attorney Docket No. UOCO.P2089WO / 00623502 CLAIMS What is claimed is:

1. A method, comprising: transmitting an optical beam through a plume emitted by a combustion system; detecting the optical beam, after the optical beam has propagated through the plume, to obtain a plurality of path-integrated absorption values corresponding to a plurality of spectral components of the optical beam; and determining, based at least in part on the plurality of path-integrated absorption values, a first path-integrated concentration of a gas species, a first temperature of the first path-integrated concentration, a second path-integrated concentration of the gas species, and a second temperature of the second path-integrated concentration, the second temperature being different from the first temperature.

2. The method of claim 1, further comprising outputting one or more of the first path- integrated concentration, the second path-integrated concentration, the first temperature, and the second temperature.

3. The method of claim 1, the gas species being combustible.

4. The method of claim 1, the gas species being selected from the group consisting of: methane, hydrogen, carbon monoxide, hydrocarbons, and volatile organic compounds.

5. The method of claim 1, the first path-integrated concentration representing a concentration of the gas species in the atmosphere adjacent to the plume.

6. The method of claim 1, the second path-integrated concentration representing a concentration of the gas species within the plume.

7. The method of claim 1, wherein said determining further comprises performing an inversion, based at least on the second path-integrated concentration and an emission model of the combustion system, to obtain a sampled quantity of the gas species within the plume.

8. The method of claim 7, further comprising outputting the sampled quantity.PATENT Attorney Docket No. UOCO.P2089WO / 00623502 9. The method of claim 7, further comprising determining a combustor efficiency based on the sampled quantity and a total quantity of the gas species in the plume.

10. The method of claim 9, further comprising outputting the combustor efficiency.

11. The method of claim 9, further comprising generating an indication in response to the combustor efficiency falling below a threshold.

12. The method of claim 9, further comprising measuring the total quantity of the gas species.

13. The method of claim 9, further comprising controlling the combustion system based on the combustor efficiency.

14. The method of claim 13, wherein said controlling comprises deactivating a flare of the combustion system.

15. The method of claim 13, wherein said controlling comprises actuating one or more valves connected to the combustion system.

16. The method of claim 13, wherein said controlling comprises adjusting one or more parameters of the combustion system to increase the combustor efficiency.

17. The method of claim 1, wherein: the method further comprises retroreflecting the optical beam into a retroreflected optical beam; and said detecting comprises detecting the retroreflected optical beam.

18. The method of claim 17, wherein: the retroreflected optical beam propagates through the plume; and said detecting the retroreflected optical beam occurs after the retroreflected optical beam has propagated through the plume.

19. The method of claim 1, wherein said detecting the optical beam comprises detecting the optical beam with a spectrometer.PATENT Attorney Docket No. UOCO.P2089WO / 00623502 20. The method of claim 19, the spectrometer comprising a dual frequency-comb spectrometer.

21. The method of claim 1, further comprising generating the optical beam.

22. The method of claim 1, wherein said transmitting the optical beam comprises transmitting the optical beam through a region of space adjacent to the plume such that the optical beam, when propagating through the region of space, does not propagate through the plume.

23. The method of claim 22, the optical beam propagating through the region of space prior to propagating through the plume.

24. The method of claim 22, the region of space having a length of 1 km or more.

25. The method of claim 1, further comprising receiving the optical beam after the optical beam has propagated through the plume.

26. The method of claim 25, wherein: said receiving the optical beam comprises receiving the optical beam with an optical receiver; and said detecting comprises detecting the optical beam, as received by the optical receiver.

27. The method of claim 1, wherein said transmitting the optical beam comprises transmitting the beam with an optical transmitter.

28. A system, comprising: an optical transmitter configured to transmit an optical beam through a plume emitted by a combustion system; a spectrometer configured to detect the optical beam, after the optical beam has propagated through the plume, to obtain a plurality of path-integrated absorption values corresponding to a plurality of spectral components of the optical beam; and a signal processor configured to determine, based at least in part on the plurality of path-integrated absorption values, a first path-integrated concentration of a gasPATENT Attorney Docket No. UOCO.P2089WO / 00623502 species, a first temperature of the first path-integrated concentration, a second path-integrated concentration of the gas species, and a second temperature of the second path-integrated concentration, the second temperature being different from the first temperature.

29. The system of claim 28, the signal processor being configured to output one or more of the first path-integrated concentration, the second path-integrated concentration, the first temperature, and the second temperature.

30. The system of claim 28, the gas species being combustible.

31. The system of claim 28, the gas species being selected from the group consisting of: methane, hydrogen, carbon monoxide, hydrocarbons, and volatile organic compounds.

32. The system of claim 28, the first path-integrated concentration representing a concentration of the gas species in the atmosphere adjacent to the plume.

33. The system of claim 28, the second path-integrated concentration representing a concentration of the gas species within the plume.

34. The system of claim 28, the signal processor being configured to perform an inversion, based on the second path-integrated concentration and an emission model of the combustion system, to obtain a sampled quantity of the gas species within the plume.

35. The system of claim 34, the signal processor being configured to output the sampled quantity.

36. The system of claim 34, the signal processor being configured to determine a combustor efficiency based on the sampled quantity and a total quantity of the gas species in the plume.

37. The system of claim 36, the signal processor being configured to output the combustor efficiency.

38. The system of claim 36, the signal processor being configured to generate an indication in response to the combustor efficiency falling below a threshold.PATENT Attorney Docket No. UOCO.P2089WO / 00623502 39. The system of claim 36, further comprising a meter configured to measure the total quantity of the gas species, the meter comprising a thermal gas flow meter, one or more pitot tubes, an ultrasonic flow meter, a flare gas analyzer, or a combination thereof.

40. The system of claim 36, further comprising a controller configured to control the combustion system based on the combustor efficiency.

41. The system of claim 40, the controller being configured to deactivate a flare of the combustion system.

42. The system of claim 40, the controller being configured to actuate one or more values connected to the combustion system.

43. The system of claim 40, the controller being configured to adjust one or more parameters of the combustion system to increase the combustor efficiency.

44. The system of claim 28, wherein: the system further comprises a retroreflector configured to retroreflect the optical beam into a retroreflected optical beam; and the spectrometer is configured to detect the retroreflected optical beam.

45. The system of claim 44, the spectrometer being configured to detect the retroreflected optical beam after the retroreflected optical beam has propagated through the plume.

46. The system of claim 44, wherein the retroreflector is configured to be affixed to a stack of the combustion system.

47. The system of claim 28, the spectrometer comprising a dual frequency-comb spectrometer.

48. The system of claim 28, further comprising an optical source configured to generate the optical beam.

49. The system of claim 48, the optical source comprising a dual frequency-comb source.

50. The system of claim 28, wherein:PATENT Attorney Docket No. UOCO.P2089WO / 00623502 the system further comprises an optical receiver configured to receive the optical beam after propagating through the plume; and the spectrometer is configured to detect the optical beam received by the optical receiver.

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