Non-contact Remote Ammonia Leak Detection System and Measurement Method using Raman LiDAR

Abstract

The present invention relates to an ammonia Raman scattering spectrum-based leak detection system and measurement method that combines Raman scattering spectrum and LiDAR optical technology to detect and quantitatively analyze ammonia gas leaked at a distance in real-time in a non-contact manner. The remote ammonia leak detection system using a non-contact Raman LiDAR according to the present invention comprises: a light source unit that irradiates light onto a detection target area; a beam splitter that passes the light irradiated from the light source unit and reflects backscattering light from the ammonia gas in the detection target area to align the light path coaxially; a variable focus optical system disposed between the beam splitter and the detection target area and composed of a combination of multiple lenses arranged to face each other, which varies the focal length of the light by adjusting the spacing between the lenses; and a signal detection unit that selectively separates a Raman signal band corresponding to ammonia gas from the light received through the variable focus optical system and the beam splitter and converts it into an electrical signal. and may include an analysis module that receives spectrum data obtained from the electrical signal of the signal detection unit and calculates the concentration of ammonia gas.

Description

Technology Field

[0001] The present invention relates to an ammonia gas leak detection system and method, and more specifically, to a leak detection system and measurement method based on a scattered light spectrum by an ammonia Raman spectrometer that combines Raman spectrometer and LiDAR optical technologies to detect and quantitatively analyze ammonia gas leaked at a distance in real time in a non-contact manner. Background Technology

[0002] Ammonia (NH₃) is widely used throughout industry, but it is a toxic gas that poses an explosion risk in the concentration range of 15–28% and is harmful to the human body.

[0003] Conventional ammonia gas measurement technologies mostly rely on laboratory-based or proximity measurement methods, which have inherent limitations in detecting ammonia leaks occurring in large spaces in real-time from a distance.

[0004] The indophenol spectrophotometry method is a traditional analytical technique that measures absorbance by converting ammonium ions into indole compounds; however, it has structural limitations, such as the necessity of sample collection and pretreatment, and the difficulty of real-time measurement in the field. While portable gas detectors offer the advantage of enabling rapid response in the field, their measurement range is extremely limited and they only capture localized concentration changes, making it impossible to determine the overall concentration distribution in large-scale leak situations.

[0005] FT-IR-based infrared absorption analyzers also utilize the unique absorption characteristics of ammonia, but the gas cell method is limited to analyzing the transmittance of light penetrating the interior of a cell within a certain section, making it difficult to grasp the entirety of a wide-ranging situation, such as a large-scale leak. Open-path FT-IR equipment introduced to compensate for this uses an open optical path structure, but it requires large lenses and heavy hardware for long-distance measurements and is vulnerable to external light interference, resulting in low operational effectiveness.

[0006] All of these technologies commonly fail to provide the ability to detect ammonia leaks with high precision in a long-distance, large-space, and non-contact manner. Furthermore, despite ammonia being a high-risk gas with an explosion risk in the 15–28% range, there was a lack of technology capable of detecting changes in the overall concentration at the leak site in real time.

[0007] Therefore, it was difficult to rapidly and accurately detect ammonia leaks occurring in large-scale facilities or wide workspaces with existing technological systems, and fundamental technical limitations existed, such as external optical interference, signal degradation due to increased distance, and difficulties in selective spectral separation. Prior art literature

[0008] Korean Registered Patent No. 10-1848439 (Registered Apr. 06, 2018) Korean Published Patent No. 10-2024-0073478 (Published May 27, 2024) International Published Patent WO 2012 / 226347 A1 (Published Nov. 11, 2021) European Published Patent EP 2 420 823 A1 (Published Feb. 22, 2012) The problem to be solved

[0009] The present invention aims to solve the aforementioned problems, and the objective of the present invention is to provide a non-contact ammonia leak detection system and method capable of efficiently collecting the intrinsic Raman signal of ammonia backscattered from a distance using a lidar optical system and precisely calculating the concentration through a Partial Least Squares (PLS) algorithm. means of solving the problem

[0010] A remote ammonia leak detection system using a non-contact Raman lidar according to the present invention for achieving the above objective may include: a light source unit that irradiates light onto a detection target area; a beam splitter that passes the light irradiated from the light source unit and reflects backscattering light from the ammonia gas in the detection target area to align the light path coaxially; a variable focus optical system disposed between the beam splitter and the detection target area and configured to vary the focal length of the light by adjusting the spacing between the lenses, the combination of a plurality of lenses arranged to face each other; a signal detection unit that selectively separates a Raman signal band corresponding to ammonia gas from the light received through the variable focus optical system and the beam splitter and converts it into an electrical signal; and an analysis module that receives spectrum data obtained from the electrical signal of the signal detection unit and calculates the concentration of ammonia gas.

[0011] The above variable focus optical system may include a first plano-convex lens and a second plano-convex lens stacked and arranged to face each other.

[0012] The above variable focus optical system further includes a lens holder having screw threads formed on its inner surface, wherein the convex surface of the first plano-convex lens and the convex surface of the second plano-convex lens are arranged to face in opposite directions, and screw threads that spirally engage with the screw threads of the lens holder are formed on the outer surfaces of the first plano-convex lens and the second plano-convex lens, thereby allowing the distance between the first plano-convex lens and the second plano-convex lens to be varied through the screw thread structure, so that the distant focus can be adjusted.

[0013] The light source unit may include a UV-COB (Chip on Board) LED light source that irradiates light in the ultraviolet band to the detection target area on an area-by-area basis.

[0014] The signal detection unit may include: a bandpass filter that blocks the Rayleigh scattering wavelength band among the backscattered light received through the variable focus optical system and the beam splitter, and transmits the Raman shift wavelength band inherent to ammonia; and a photodetector that receives the optical signal passed through the bandpass filter and converts it into an electrical signal.

[0015] The above bandpass filter is composed of an optical interference filter with a center wavelength (CWL) of 514.5 nm and a bandwidth of ±5 nm, which can remove Rayleigh scattering signals and selectively transmit ammonia Raman scattering signals in the 520 nm band to the detector.

[0016] The above photodetector may be configured to include a silicon photodiode having a predetermined light-receiving area and an amplification element (OP-Amp) having a variable gain of 0 dB to 70 dB.

[0017] The beam splitter above can adjust the light reception efficiency of backscattered signals by setting the ratio of transmittance to reflectance from the light source to any one of 5:5, 3:7, or 6:4.

[0018] The above analysis module can quantitatively calculate the concentration of ammonia gas by using the entire spectrum data in the 400 nm to 600 nm wavelength band obtained through the signal detection unit as an input variable and applying a regression analysis algorithm based on Partial Least Squares (PLS).

[0019] The method for measuring distant ammonia using a leak detection system based on a distant ammonia Raman scattering spectrum according to the present invention described above may include the following steps.

[0020] (S1) A step of irradiating light emitted from a light source unit into a detection target area through a beam splitter;

[0021] (S2) A step of adjusting the lens spacing of the variable focus optical system to focus the irradiated light at a distant measurement position;

[0022] (S3) A step of receiving backscattered light from the ammonia gas in the detection target area through the variable focus optical system and beam splitter to the signal detection unit;

[0023] (S4) A step of selectively separating a Raman signal band corresponding to ammonia gas from the received light and converting it into an electrical signal;

[0024] (S5) A step of calculating the ammonia concentration from the spectrum data of the converted electrical signal.

[0025] The above step (S2) allows the focus for a distant measurement point to be adjusted by physically varying the distance between the first plano-convex lens and the second plano-convex lens through the rotation of the lens holder having screw threads formed on its inner surface and the first plano-convex lens and the second plano-convex lens spirally coupled to the lens holder.

[0026] The above step (S4) may include a process of removing Rayleigh scattering signals from the received optical signal and selectively transmitting only ammonia Raman scattering signals in the 520 nm band using a bandpass filter having a center wavelength (CWL) of 514.5 nm and a bandwidth of ±5 nm.

[0027] The above step (S5) can quantitatively calculate the concentration through correlation with previously stored ammonia standard concentration data by using the entire spectrum data of the acquired wavelength band of 400 nm to 600 nm as input variables and applying a Partial Least Squares (PLS) regression analysis algorithm. Effects of the invention

[0028] According to the present invention, by combining a lidar optical design capable of high selectivity based on a Raman scattering spectrum, long-range detection based on backscattering, and long-range focus adjustment, ammonia leaks occurring in large spaces can be detected with significantly higher speed and accuracy than existing technologies.

[0029] In particular, thanks to its non-contact structure, workers do not need to be directly exposed to high concentrations of toxic and flammable gases, and it can be utilized as a practical safety management technology to prevent explosion risks at industrial sites at an early stage.

[0030] In addition, by using an area-type COB light source and silicon photodetectors, system configuration costs can be significantly reduced, and it provides scalability for application to various platforms, including portable, fixed, and drone-mounted types.

[0031] In addition, since real-time concentration prediction is possible based on quantitative analysis algorithms, it can be utilized as an early warning system across high-risk facilities, such as smart plants, digital safety monitoring systems, ports, chemical plants, and refrigerant facilities.

[0032] In particular, this technology can function as an essential safety diagnostic technology in future eco-friendly energy infrastructures that utilize ammonia as fuel or energy carriers, and can significantly contribute to enhancing the safety of national infrastructure by remotely detecting potential leaks during ammonia storage, transportation, and bunkering processes. Brief explanation of the drawing

[0033] FIG. 1 is a schematic diagram showing the overall configuration of a non-contact Raman lidar system according to one embodiment of the present invention. FIG. 2 is an illustrative diagram explaining the configuration of a variable focus optical system, which is a component of the non-contact Raman lidar system of the present invention. FIG. 3 is an example of quantitative analysis at a distance of 1m using a non-contact method utilizing an ammonia Raman scattering spectrum and a long-distance measurement method. Specific details for implementing the invention

[0034] A leak detection system and measurement method based on a long-distance ammonia Raman scattering spectrum using a non-contact Raman lidar according to an embodiment of the present invention will be described in detail with reference to the attached drawings.

[0035] The present invention is capable of various modifications and may take various forms, and specific embodiments are illustrated in the drawings and described in detail in the text. However, this is not intended to limit the invention to the specific disclosed forms, and it should be understood that the invention includes all modifications, equivalents, and substitutions that fall within the spirit and scope of the invention.

[0036] In describing each drawing, similar reference numerals have been used for similar components. Additionally, terms such as "first," "second," etc., may be used to describe various components, but said components should not be limited by said terms. These terms are used solely for the purpose of distinguishing one component from another.

[0037] Meanwhile, unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meaning as generally understood by those skilled in the art to which the present invention pertains. Terms such as those defined in commonly used dictionaries should be interpreted as having a meaning consistent with their meaning in the context of the relevant technology, and should not be interpreted in an ideal or overly formal sense unless explicitly defined in this application.

[0038] To aid understanding, the direction in which light is irradiated in the system according to the present invention is defined as the forward or target area direction, and the direction in which it is reflected back is defined as the rear or detection unit direction.

[0039] FIG. 1 is a schematic diagram showing the overall configuration of a non-contact Raman lidar system according to one embodiment of the present invention, and FIG. 2 is an illustrative diagram explaining the configuration of a variable focus optical system, which is a component of the non-contact Raman lidar system of the present invention.

[0040] Referring to FIGS. 1 and 2, a remote ammonia Raman scattering spectrum-based leak detection system (100) using a non-contact Raman lidar according to the present invention comprises a light source unit (110), a beam splitter (120), a variable focus optical system (130), a signal detection unit (140), and an analysis module (150).

[0041] The light source unit (110) is a component that emits light for ammonia gas detection. The light source unit (110) includes a UV-COB (Chip on Board) LED that emits light in the ultraviolet (UV) band. Unlike a general point source laser, by adopting a surface-emitting COB LED, light can be evenly irradiated in area units onto the detection target area. This has the advantage of maximizing backscattering efficiency by increasing the probability of collision with ammonia gas particles spread in the atmosphere.

[0042] The beam splitter (120) is positioned between the light source unit (110) and the variable focus optical system (130) and serves to align the light path coaxially. Specifically, light irradiated from the light source unit (110) passes through (or reflects) the beam splitter (120) and heads toward the target area, and light that is backscattered from the ammonia gas in the target area is reflected (or transmitted) by the beam splitter (120) and its path is changed toward the signal detection unit (140). At this time, the ratio of transmittance to reflectance of the beam splitter (120) can be set to 5:5, 3:7, or 6:4, etc., depending on the measurement environment to optimize light reception efficiency.

[0043] The variable focus optical system (130) is positioned in front of the beam splitter (120) (in the direction of the target area) to focus the irradiated light or convert it into collimating light, and to collect the returning scattered light. The variable focus optical system (130) has a structure in which a combination of multiple lenses, preferably a first plano-convex lens (131) and a second plano-convex lens (132), are stacked to face each other. More specifically, the first plano-convex lens (131) and the second plano-convex lens (132) are positioned so that their respective convex surfaces face in opposite directions (outward) or face each other, thereby performing the function of a single high-performance composite lens. The first plano-convex lens (131) and the second plano-convex lens (132) are coupled inside a lens holder (133) having screw threads (134) formed on its inner surface. Screw threads are formed on the outer surface of the first plano-convex lens (131) and the second plano-convex lens (132) and are screw-coupled with the screw threads (134) of the lens holder (133). Therefore, when the first plano-convex lens (131) and the second plano-convex lens (132) are rotated, the first plano-convex lens (131) and the second plano-convex lens (132) move in the axial direction of the lens holder (133). By finely adjusting the distance between the first plano-convex lens (131) and the second plano-convex lens (132) through this screw thread structure, a LiDAR function capable of accurately focusing on various distant locations of more than 1m can be implemented. This solves the distance limitation problem of existing fixed-focus equipment.

[0044] The signal detection unit (140) extracts only the signal necessary for analysis from the backscattered light and converts it into an electrical signal. To this end, the signal detection unit (140) includes a bandpass filter (141) and a photodetector (142). The received light contains not only Raman scattered light caused by ammonia but also Rayleigh scattered light, which is much stronger. The bandpass filter (141) is composed of an optical interference filter with a center wavelength (CWL) of 514.5 nm and a bandwidth of ±5 nm, which effectively cuts off the strong Rayleigh scattered signal and selectively passes only the Raman shift signal unique to ammonia that appears in the band of about 520 nm.

[0045] The above photodetector (142) receives a weak light signal that has passed through a filter. At this time, a silicon photodiode having a predetermined light receiving area (e.g., 10 mm × 10 mm) may be used to secure the amount of light received in a surface area. In addition, an amplification element (OP-Amp) (143) capable of adjusting the gain from 0 dB to 70 dB is combined to amplify the fine Raman signal and improve the signal-to-noise ratio (SNR).

[0046] The analysis module (150) converts the analog signal transmitted from the signal detection unit (140) into digital data and analyzes it to calculate the ammonia concentration. Conventional simple linear regression analysis has the disadvantage that it is difficult to fully reflect the characteristics of the complex Raman scattering spectrum. Accordingly, the present invention applies a machine learning regression analysis algorithm based on Partial Least Squares (PLS) that utilizes the entire spectrum data of the wavelength band from 400 nm to 600 nm as input variables.

[0047] In selecting the wavelength, the entire ammonia Raman scattering spectrum is selected. Since the spectrum is measured from 400 nm to 600 nm, if this entire portion is selected, there are 1064 to 2094 data points between 400 nm and 600 nm. However, since it is impossible to create a calibration curve using a linear equation with slope values ​​of 1030 data points as shown in Figure 3, the value calculated using the linear equation created at this time (also known as the predicted value) is represented on the Y-axis, and the X-axis represents the actual ammonia gas value used.

[0048] As a result of using the calibration curve, the linear relationship between the actual ammonia gas value and the calculated ammonia value was found to be 0.99, and the SEC (standard error between the two values) was confirmed to be very low at 105 ppm. Thus, since the non-contact optical system confirmed the correlation with ammonia gas in measuring ammonia, it was proven that measurement is sufficiently possible using this method.

[0049] This calibration curve relationship

[0050] ,

[0051] is the regression coefficient, and ε is the error that occurs when measuring the dependent variable Y. The estimation of a regression model involves the regression coefficients

[0052]

[0053] It refers to finding.

[0054] The analysis module (150) builds a calibration curve model by learning spectrum data obtained for ammonia standard gases of various concentrations (e.g., 1,000 ppm to 20,000 ppm) in advance, and quantitatively calculates the concentration of ammonia by inputting spectrum data input in real time into this model. Experimental results showed that when this algorithm is applied, it exhibits high linearity with a coefficient of determination (R²) of 0.99 or higher and a low standard error (SEC), confirming that high-reliability concentration analysis is possible despite being a non-contact remote measurement.

[0055] The measurement process using the system of the present invention configured as described above is as follows.

[0056] First, when a light source unit (110) including a UV-COB LED light source is turned on under the control of a microprocessor, the emitted light passes through a beam splitter (120) and enters a variable focus optical system (130) (S1). At this time, the user optimizes the focus by adjusting the distance between the first and second plano-convex lenses (131, 132) to match the distance to be measured (e.g., 1.5m) (S2).

[0057] Light irradiated into the target area through the first and second plano-convex lenses (131, 132) strikes the ammonia gas present in the target area, and the backscattered light is collected again through the variable focus optical system (130) and then transmitted to the signal detection unit (140) through the beam splitter (120) (S3).

[0058] The bandpass filter (141) of the signal detection unit (140) removes noise components from backscattered light and extracts only the ammonia Raman signal, and the photodetector (142) converts this into an electrical signal (S4).

[0059] The analysis module (150) analyzes spectrum data through the PLS algorithm to finally calculate the ammonia concentration and provides it to the user through a display, etc. (S5).

[0060] Although the detailed description of the present invention described above has been explained with reference to preferred embodiments of the invention, those skilled in the art or those with ordinary knowledge in the art will understand that various modifications and changes can be made to the invention without departing from the spirit and technical scope of the invention as set forth in the claims below. Explanation of the symbols

[0061] 100: Raman LiDAR System 110: Light Source 120: Beam splitter 130: Variable focus optical system 131: First plano-convex lens 132: Second plano-convex lens 140: Signal detection unit 141: Bandpass filter 142 : Photodetector 143 : Amplifying element 150 : Analysis Module

Claims

Claim 1 A system for detecting gas leakage and concentration from a distance using the Raman scattering spectrum of ammonia gas comprises: a light source unit that irradiates light onto a detection target area; a beam splitter that passes the light irradiated from the light source unit and aligns the path of backscattering light from the ammonia gas in the detection target area coaxially; a variable focus optical system disposed between the beam splitter and the detection target area and configured to include a first plano-convex lens and a second plano-convex lens arranged in a line facing each other, thereby varying the focal length of the light by adjusting the distance between the first plano-convex lens and the second plano-convex lens; and a signal detection unit that selectively separates only the ammonia gas from the light received through the variable focus optical system and the beam splitter into a Raman signal band and converts it into an electrical signal. The system includes an analysis module that receives spectrum data obtained from the electrical signal of the signal detection unit and calculates the concentration of ammonia gas; wherein the light source unit includes a UV-COB (Chip on Board) LED light source that irradiates light in the ultraviolet band onto the detection target area in an area unit, and the signal detection unit includes a bandpass filter that blocks the Rayleigh scattering wavelength band among the backscattered light received through the variable focus optical system and the beam splitter, and transmits the Raman shift wavelength band inherent to ammonia; and a photodetector that receives the light signal passed through the bandpass filter and converts it into an electrical signal; wherein the bandpass filter has a center wavelength (CWL) of 514.A remote ammonia Raman scattering spectrum-based leak detection system using a non-contact Raman lidar, characterized by being composed of an optical interference filter having a wavelength of 5 nm and a bandwidth of ±5 nm to remove Rayleigh scattering signals and selectively transmit ammonia Raman scattering signals in the 520 nm band to a detector, wherein the optical detector comprises a silicon photodiode having a predetermined light-receiving area and an amplification element (OP-Amp) having a variable gain of 0 dB to 70 dB. Claim 2 delete Claim 3 A remote ammonia Raman scattering spectrum-based leak detection system using a non-contact Raman lidar, wherein, in claim 1, the variable focus optical system further comprises a lens holder having screw threads formed on its inner circumference and arranged such that the convex surface of the first plano-convex lens and the convex surface of the second plano-convex lens face in opposite directions, and screw threads formed on the outer surfaces of the first plano-convex lens and the second plano-convex lens to spirally engage with the screw threads of the lens holder, thereby adjusting the remote focus by varying the distance between the first plano-convex lens and the second plano-convex lens through the screw thread structure. Claim 4 delete Claim 5 delete Claim 6 delete Claim 7 delete Claim 8 A far-distance ammonia Raman scattering spectrum-based leak detection system using a non-contact Raman lidar according to claim 1, characterized in that the beam splitter is set to one of 5:5, 3:7, or 6:4 in the ratio of transmittance to reflectance from a light source to control the light reception efficiency of a backscattered signal. Claim 9 A remote ammonia Raman scattering spectrum-based leak detection system using a non-contact Raman lidar, characterized in that, in claim 1, the analysis module uses the entire spectrum data in the 400 nm to 600 nm wavelength band obtained through the signal detection unit as an input variable and applies a regression analysis algorithm based on Partial Least Squares (PLS) to quantitatively calculate the concentration of ammonia gas. Claim 10 A method for measuring ammonia at a distance using a leak detection system based on a long-distance ammonia Raman scattering spectrum according to claim 1, comprising: (S1) a step of irradiating light emitted from a light source unit onto a detection target area through a beam splitter; (S2) a step of adjusting the lens spacing of a variable focus optical system to focus the irradiated light at a measurement location at a distance; (S3) a step of receiving backscattered light from the ammonia gas in the detection target area by passing it through the variable focus optical system and the beam splitter to a signal detection unit; (S4) a step of selectively separating a Raman signal band corresponding to the ammonia gas from the received light and converting it into an electrical signal; (S5) a step of calculating ammonia concentration from spectrum data of a converted electrical signal; wherein the step (S4) includes a process of removing Rayleigh scattering signals from a received optical signal and selectively transmitting only ammonia Raman scattering signals in the 520 nm band using a bandpass filter having a center wavelength (CWL) of 514.5 nm and a bandwidth of ±5 nm. A method for detecting leakage based on a far-distance ammonia Raman scattering spectrum. Claim 11 A method for detecting leakage based on a distant ammonia Raman scattering spectrum according to claim 10, wherein the above step (S2) is characterized by adjusting the focus for a distant measurement point by physically varying the distance between the first plano-convex lens and the second plano-convex lens through the rotation of a lens holder having screw threads formed on its inner surface and the first plano-convex lens and the second plano-convex lens spirally coupled to the lens holder. Claim 12 delete Claim 13 In claim 10, the above step (S5) is characterized by using the entire spectrum data of the acquired wavelength band of 400 nm to 600 nm as an input variable and applying a Partial Least Squares (PLS) regression analysis algorithm to quantitatively calculate the concentration through the correlation with the previously stored ammonia standard concentration data, thereby providing a method for detecting leaks based on a distant ammonia Raman scattering spectrum.

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