Optical fiber Raman scattering sensing system for monitoring underground coal gasification temperature distribution

Abstract

The invention relates to an optical fiber Raman scattering sensing system for coal underground gasification temperature distribution monitoring, and the system comprises a distributed optical fiber temperature sensing host which is used for transmitting a laser pulse, enabling the laser pulse to generate Raman scattering with optical cable molecules in the transmission process of a temperature sensing optical cable, generating a Raman scattering signal, calculating a light intensity ratio, and transmitting the light intensity ratio to the optical cable molecules; obtaining temperature distribution along an optical cable path; and the data processing module is used for performing spatial interpolation, time sequence analysis and temperature gradient calculation on the received temperature distribution data, identifying a high-temperature region and a temperature sudden change point, and judging a combustion front position and an expansion speed in real time in combination with a coal seam geologic model and a gasification propulsion direction. The sensor has the advantages of intrinsic safety, electromagnetic interference resistance, corrosion resistance, capability of realizing kilometer-level continuous distributed temperature measurement and the like, and is particularly suitable for complex and severe environments such as underground coal mines and the like. Raman scattering signals are sensitive to temperature but not sensitive to strain, so that the method is very suitable for temperature monitoring of underground coal seam combustion areas.

Description

Technical Field

[0001] This invention relates to the field of temperature monitoring technology in underground coal gasification processes, and in particular to a fiber optic Raman scattering sensing system for monitoring temperature distribution during underground coal gasification. Background Technology

[0002] Underground coal gasification (UCG) is a clean energy utilization technology that converts underground coal seams into combustible gases through thermochemical reactions. This process involves complex physicochemical reactions such as high-temperature combustion, pyrolysis, and gasification. The temperature distribution and changes in the combustion zone are key parameters for judging the stability of the gasification reaction, controlling the combustion rate, and preventing thermal runaway.

[0003] Currently used temperature monitoring methods include thermocouples, infrared thermometry, and wireless sensors, but these methods have the following shortcomings: (1) Thermocouple wiring is complex and has limited high-temperature resistance, making it difficult to achieve long-distance distributed measurement; (2) Infrared thermometry is limited by line of sight, smoke and gas interference, and cannot obtain deep underground temperature information; (3) Wireless sensors have problems such as difficulty in power supply, signal attenuation, and weak anti-interference ability, and are not suitable for long-term deployment in underground environments with high temperature and high pressure. Summary of the Invention

[0004] To address the problems existing in the prior art, the present invention aims to provide a fiber optic Raman scattering sensing system for monitoring the temperature distribution during underground coal gasification. This system monitors the temperature distribution during the underground coal gasification process, enabling real-time sensing of the combustion zone range, combustion rate, and temperature gradient, thus providing data support for the safe control and optimization of the gasification process.

[0005] To achieve the above objectives, the present invention provides the following solution: A fiber optic Raman scattering sensing system for monitoring the temperature distribution of underground coal gasification includes: A distributed optical fiber temperature sensing host is used to emit laser pulses, and the laser pulses undergo Raman scattering with optical fiber molecules during the transmission of the temperature sensing optical cable to generate Raman scattering signals. The light intensity ratio is calculated to obtain temperature distribution data along the optical cable path. The data processing module is used to perform spatial interpolation, time series analysis, and temperature gradient calculation on the received temperature distribution data, identify high-temperature regions and temperature abrupt change points, and, in conjunction with the coal seam geological model and gasification propulsion direction, determine the location and expansion speed of the combustion front in real time.

[0006] Optionally, the distributed fiber optic temperature sensing host includes: A laser emitting unit is used to emit laser pulses of a specific wavelength; An optical receiving unit is used to collect the Raman scattering signal generated by the laser pulse interacting with the optical fiber molecules during the transmission of the temperature-sensitive optical fiber; A signal amplification unit is used to amplify the weak scattered signal in the Raman scattering signal; A data conversion unit is used to convert the amplified Raman scattering signal into a digital signal; and a light intensity ratio calculation unit is used to process the digital signal and calculate the light intensity ratio of Stokes light to anti-Stokes light, thereby obtaining temperature distribution data along the optical cable path.

[0007] Optionally, the temperature-sensing optical cable is laid along the borehole above the coal seam and maintains a target vertical distance from the coal seam, for sensing the temperature changes conducted to the surrounding rock during the combustion of the coal seam.

[0008] Optionally, the temperature-sensing optical cable adopts a multi-layer composite structure, consisting of a fiber core, cladding, coating layer, buffer layer, and metal armor layer from the inside out.

[0009] Optionally, the fiber core is made of germanium-doped quartz and forms an optical guide structure with the cladding, the coating layer is a high-temperature resistant polyimide coating, the buffer layer is made of ceramic fiber, and the metal armor layer is made of stainless steel.

[0010] Optionally, the system also includes: The remote monitoring platform is used to visualize the temperature distribution map, replay historical data, and further set alarm thresholds. When the high-temperature area exceeds the alarm threshold, an early warning signal is automatically issued.

[0011] Optionally, the system also includes: The calibration and maintenance module is used to set the maintenance cycle, and to perform system performance testing and optical cable loss testing according to the maintenance cycle.

[0012] The beneficial effects of this invention are as follows: 1. Distributed continuous temperature measurement: Enables continuous temperature monitoring at the kilometer level with high spatial resolution, allowing for precise location of the combustion zone.

[0013] 2. Intrinsically safe: The fiber optic sensing system is passive and electricity-free, making it suitable for flammable and explosive underground coal mine environments.

[0014] 3. Strong anti-interference ability: Raman scattering thermometry is not affected by electromagnetic interference, humidity, gas composition, etc., and is suitable for complex geological conditions.

[0015] 4. Strain immunity: Raman scattering signals are not sensitive to strain, avoiding measurement errors caused by formation movement and borehole deformation.

[0016] 5. Good long-term stability: The optical cable is resistant to high temperature and corrosion, suitable for long-term deployment, and supports full life cycle monitoring.

[0017] 6. High-precision temperature measurement: It has a high temperature resolution, meeting the requirements for high-precision temperature monitoring.

[0018] 7. Intelligent Analysis: The system integrates temperature gradient analysis, anomaly identification and trend prediction functions, supporting intelligent early warning and decision support. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 This is a schematic diagram of an optical fiber Raman scattering sensing system for monitoring the temperature distribution of underground coal gasification according to an embodiment of the present invention. Figure 2 This is a schematic diagram of the temperature-sensing optical cable layout according to an embodiment of the present invention; Figure 3 This is a DTS temperature measurement curve diagram of an embodiment of the present invention. Detailed Implementation

[0021] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0023] like Figure 1As shown in the figure, this embodiment discloses a fiber optic Raman scattering sensing system for monitoring the temperature distribution of underground coal gasification, including: a distributed fiber optic temperature sensing host, used to emit laser pulses, and the laser pulses undergo Raman scattering with the molecules of the optical cable during transmission of the temperature sensing optical cable to generate Raman scattering signals, and calculate the light intensity ratio to obtain temperature distribution data along the optical cable path; a data processing module, used to perform spatial interpolation, time series analysis and temperature gradient calculation on the received temperature distribution data, identify high-temperature regions and temperature abrupt change points, and, combined with the coal seam geological model and gasification propulsion direction, determine the position and expansion speed of the combustion front in real time.

[0024] Specifically, this embodiment discloses an optical fiber Raman scattering sensing system for monitoring the temperature distribution of underground coal gasification, including: (1) a distributed optical fiber temperature sensing host (DTS host); (2) a temperature-sensing optical cable laid along the borehole above the coal seam; (3) an optical cable protective sleeve and fixing device; (4) a data acquisition and processing module; (5) a remote monitoring platform; and (6) a description of the core component structure.

[0025] Raman scattering temperature measurement principle: When the laser pulse emitted by the DTS host is transmitted in the temperature-sensing optical cable, it undergoes Raman scattering with the optical cable molecules, producing Stokes light (no frequency shift) and anti-Stokes light (frequency shift). The intensity of anti-Stokes light increases significantly with increasing temperature, while the intensity of Stokes light is basically unaffected by temperature. By calculating the ratio of the two light intensities and combining it with the Boltzmann distribution law, the temperature value of the corresponding optical cable location can be obtained.

[0026] Combustion zone monitoring logic: The heat generated by coal seam combustion is transferred to the surrounding rock through heat conduction. The temperature-sensing optical cable detects the temperature change of the surrounding rock and converts it into Raman scattering signal. The data processing module locates the high-temperature concentrated area (combustion core area) by analyzing the spatial gradient and temporal trend of temperature distribution, and tracks the direction and speed of temperature gradient abrupt change (the expansion speed of the combustion front), providing data support for the adjustment of gasification process parameters.

[0027] Furthermore, the distributed fiber optic temperature sensing host includes: a laser emitting unit for emitting laser pulses of a specific wavelength; a light receiving unit for collecting Raman scattering signals generated by the laser pulses interacting with the fiber optic molecules during transmission through the temperature-sensing fiber optic cable; a signal amplification unit for amplifying the weak scattering signals in the Raman scattering signals; a data conversion unit for converting the amplified Raman scattering signals into digital signals; and a light intensity ratio calculation unit for processing the digital signals and calculating the intensity ratio of Stokes light to anti-Stokes light, thereby obtaining temperature distribution data along the fiber optic cable path.

[0028] Specifically, the Distributed Fiber Optic Temperature Sensing (DTS) host integrates a laser emitting unit, an optical receiving unit, a signal amplification unit, a data conversion unit, and a light intensity ratio calculation unit. The laser emitting unit uses a distributed feedback laser, capable of stably emitting laser pulses of specific wavelengths. The optical receiving unit employs an avalanche photodiode, efficiently collecting Raman scattering signals returned from the optical cable. The signal amplification unit is a low-noise operational amplifier, amplifying weak scattering signals and reducing signal interference. The data conversion unit uses a 16-bit high-speed ADC to convert analog signals into digital signals. The light intensity ratio calculation unit, based on the digital signals, calculates the intensity ratio of Stokes light to anti-Stokes light and, according to the Raman scattering temperature measurement principle, inversely calculates the temperature distribution data along the optical cable path. The entire host is encapsulated in an explosion-proof enclosure, whose protection level meets the safety standards for underground coal mines, allowing for safe operation in flammable and explosive environments.

[0029] The DTS host emits laser pulses into the temperature-sensing optical cable, collects the returned Raman scattering signals (Stokes and anti-Stokes light), and uses a built-in intensity ratio calculation unit to calculate the ratio and invert the temperature to obtain temperature distribution data along the optical cable path. Since Raman scattering signals are sensitive to temperature changes but not to strain changes, strain compensation is unnecessary, simplifying system design and data processing.

[0030] Furthermore, the temperature-sensing optical cable is laid along the borehole above the coal seam, maintaining a target vertical distance from the coal seam, to sense temperature changes conducted to the surrounding rock during coal combustion. The temperature-sensing optical cable adopts a multi-layer composite structure, consisting of a fiber core, cladding, coating layer, buffer layer, and metal armor layer from the inside out. The fiber core is made of germanium-doped quartz and forms a light-guiding structure with the cladding. The coating layer is a high-temperature resistant polyimide coating, the buffer layer is made of ceramic fiber, and the metal armor layer is made of stainless steel.

[0031] Specifically, the temperature-sensing optical cable is laid along a borehole above the coal seam, maintaining a certain vertical distance (usually 2m) between the cable and the coal seam to detect temperature changes transmitted to the surrounding rock during coal combustion. The optical cable adopts a metal armored structure, possessing excellent high-temperature resistance, corrosion resistance, and tensile strength.

[0032] Temperature-sensing optical cable: Utilizing a multi-layered composite structure, from the inside out, it consists of a fiber core, cladding, coating, buffer layer, and metal armor layer. The fiber core is made of germanium-doped quartz to ensure stable laser signal transmission; the cladding works in conjunction with the fiber core to form a light guide structure, reducing signal loss; the coating is a high-temperature resistant polyimide coating that can withstand high-temperature environmental corrosion; the buffer layer is made of ceramic fiber, providing both heat insulation and protection; the metal armor layer is made of stainless steel, possessing excellent high-temperature resistance, corrosion resistance, and tensile strength, enabling it to adapt to the complex and harsh geological and environmental conditions of underground coal mines, ensuring long-term stable operation of the optical cable.

[0033] Furthermore, the data acquisition and processing module receives temperature distribution data from the DTS host and performs spatial positioning, time series analysis, temperature gradient calculation, and anomaly area identification. Combined with the coal seam geological model and gasification propulsion direction, it determines the location and expansion speed of the combustion front in real time.

[0034] Specifically, spatial positioning: based on the principle of optical fiber time domain reflection, each temperature measurement point is bound to the precise physical distance on the optical cable to generate spatial profile data of "distance-temperature".

[0035] Time series analysis: For each fixed location point in the spatial profile, its temperature measurement values ​​are stored in chronological order to form temperature-time change curves for each point, which are used to analyze the heating rate and trend at that location.

[0036] Temperature gradient calculation and anomaly region identification: Calculate the rate of temperature change (spatial temperature gradient) between adjacent measurement points along the spatial profile. Set a temperature threshold and a gradient threshold; identify continuous optical cable segments where the temperature is consistently higher than the temperature threshold and the absolute value of the temperature gradient is greater than the gradient threshold as high-temperature anomaly zones; the points with the largest temperature gradient are marked as temperature abrupt change points.

[0037] Combustion status judgment: Combining the coal seam geological model and the gasification propulsion direction, the high temperature anomaly zone is determined as the combustion influence zone, and its core high temperature section is the combustion core zone; the trajectory of the temperature change point or the boundary of the high temperature anomaly zone moving forward over time is tracked, and the leading edge of the trajectory is determined as the combustion front, and its moving speed is the combustion front expansion speed.

[0038] Furthermore, the system also includes a remote monitoring platform for visually displaying temperature distribution maps and replaying historical data, and for setting alarm thresholds. When a high-temperature area exceeds the alarm threshold, an early warning signal is automatically issued.

[0039] Specifically, the remote monitoring platform enables the visualization of temperature distribution maps, playback of historical data, setting of alarm thresholds, and automatic early warning functions.

[0040] like Figure 2 As shown in the diagram, the temperature-sensing optical cable layout diagram illustrates the specific layout of the temperature-sensing optical cable in the borehole above the coal seam, including the relative position of the optical cable and the coal seam (usually 2m).

[0041] like Figure 3 As shown, the DTS temperature measurement curve displays the temperature distribution along the optical cable laying path. Based on the measured temperature data, the high-temperature concentration area (combustion core area) can be located, and the location of the combustion front can be determined.

[0042] This embodiment discloses a fiber optic Raman scattering sensing system for monitoring the temperature distribution of underground coal gasification, comprising: 1. Construct a row of monitoring boreholes above the coal seam, with a diameter of approximately 75 mm and a depth determined based on the coal seam burial depth; 2. Lower the metal-armored temperature-sensing optical cable along the borehole to a position 2m above the coal seam, and fix it using grouting or clamping methods; 3. Connect the optical cable to the DTS host through the outlet. Set the host to a sampling interval of 1m and a sampling period of 30s. 4. The DTS host processes the Raman scattering signal, calculates and acquires the temperature distribution data along the optical cable path, and transmits the data to the data processing module in real time; 5. The data processing module performs spatial interpolation, time series analysis, and gradient calculation on the received temperature distribution data to identify high-temperature regions and temperature abrupt change points; 6. The remote monitoring platform displays a temperature distribution map in real time. When the temperature in a certain area exceeds the set threshold (such as 80℃), the system automatically issues an early warning signal. 7. Based on the temperature distribution trend, determine the position and propulsion speed of the combustion front, providing a basis for adjusting gasification process parameters; 8. System Calibration and Maintenance: To eliminate system errors and ensure the accuracy and stability of temperature measurements, periodic calibration is necessary. Calibration utilizes a known temperature reference point (such as a constant temperature chamber) to calibrate the parameters of the inversion model between Raman scattering intensity ratio and temperature, ensuring the metrological traceability of the DTS system's measurement results. For maintenance, it is recommended to perform system performance testing and optical cable loss testing every six months.

[0043] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made to the technical solutions of the present invention by those skilled in the art without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A fiber-optic Raman scattering sensing system for monitoring temperature distribution in underground coal gasification, characterized in that, The system comprises: a distributed optical fiber temperature sensing host for emitting laser pulses, and the laser pulses are Raman scattered with optical cable molecules during the transmission process of the temperature sensing optical cable, Raman scattered signals are generated, and the optical intensity ratio is calculated to obtain temperature distribution data along the optical cable path; a data processing module for spatial interpolation, time series analysis and temperature gradient calculation on the received temperature distribution data, identifying high temperature areas and temperature mutation points, and combining with the coal seam geological model and the gasification direction, real-time judging the combustion front position and expansion speed.

2. The fiber-optic Raman-scattering sensing system for monitoring temperature distribution in underground coal gasification according to claim 1, characterized in that, The distributed optical fiber temperature sensing host comprises: a laser emission unit for emitting laser pulses of a specific wavelength; an optical receiving unit for collecting Raman scattered signals generated by Raman scattering of the laser pulses with optical cable molecules during the transmission process of the temperature sensing optical cable; a signal amplification unit for amplifying weak scattered signals in the Raman scattered signals; a data conversion unit for converting the amplified Raman scattered signals into digital signals; an optical intensity ratio calculation unit for processing the digital signals to calculate the optical intensity ratio of Stokes light and anti-Stokes light, thereby obtaining temperature distribution data along the optical cable path.

3. The fiber-optic Raman-scattering sensing system for monitoring temperature distribution in underground coal gasification according to claim 1, characterized in that, The temperature sensing optical cable is arranged above the coal seam along the borehole and maintains a target vertical distance with the coal seam, and is used for sensing the temperature change of the surrounding rock conducted during the combustion process of the coal seam.

4. The fiber-optic Raman-scattering sensing system for monitoring temperature distribution in underground coal gasification according to claim 1, characterized in that, The temperature sensing optical cable adopts a multi-layer composite structure, and from the inside to the outside, it comprises a core, a cladding layer, a coating layer, a buffer layer and a metal armor layer.

5. The fiber-optic Raman-scattering sensing system for monitoring temperature distribution in underground coal gasification according to claim 4, characterized in that, The core is made of germanium-doped quartz material, and cooperates with the cladding layer to form a light guide structure, the coating layer is a polyimide high temperature resistant coating layer, the buffer layer is made of ceramic fiber material, and the metal armor layer is made of stainless steel material.

6. The fiber-optic Raman-scattering sensing system for monitoring temperature distribution in coal underground gasification according to claim 1, characterized in that, The system further comprises: a remote monitoring platform for visualizing and displaying temperature distribution graphs, and playing back historical data, further setting an alarm threshold, and when the high temperature area exceeds the alarm threshold, an early warning signal is automatically sent.

7. The fiber-optic Raman-scattering sensing system for monitoring temperature distribution in coal underground gasification according to claim 1, characterized in that, The system further comprises: a calibration and maintenance module for setting a maintenance cycle, and performing system performance detection and optical cable loss test through the maintenance cycle.

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