Coal Mine Natural Fire Monitoring Device Based on Fiber Bragg Grating Sensor

Abstract

This invention discloses a coal mine natural fire monitoring device based on fiber Bragg grating sensors, belonging to the field of fiber Bragg grating sensors. It includes an optical cable and a unit box deployed in a coal mine roadway. The unit box includes multiple fiber Bragg grating temperature sensors connected in series on a single optical cable using wavelength division multiplexing (WDM) technology. The cable is laid along the coal mine roadway or goaf. An installation device is mounted on the coal mine roadway using an anchor bolt machine. The installation device includes a supporting anchor bolt, which penetrates the coal mine roadway and extends into the soil layer. The supporting anchor bolt has a hollow rod structure, with a sharp end at one end. Multiple grouting holes are also provided on the surface of the supporting anchor bolt, distributed along its length. This invention offers high measurement accuracy, strong environmental adaptability, convenient maintenance, high system reliability, high functional integration, and a safe, passive design with zero false alarms and zero missed alarms. It is particularly suitable for fire monitoring in coal mine roadways.

Description

Technical Field

[0001] This invention relates to the field of fiber Bragg grating sensors, and particularly to a coal mine natural fire monitoring device based on fiber Bragg grating sensors. Background Technology

[0002] Currently, coal mine natural fire monitoring mainly relies on point thermocouples and distributed fiber optic temperature measurement (DTS) systems. Point thermocouples suffer from problems such as monitoring blind spots, complex wiring, and susceptibility to electromagnetic interference; while traditional DTS systems, although capable of distributed monitoring, face three major pain points when deployed underground in coal mines:

[0003] 1. Insufficient installation reliability: When fixed with expansion screws or simple clamps, the sensor is prone to loosening and falling off under mining vibration, mine pressure (pressure can reach 5-10MPa), and water corrosion environment, resulting in poor contact and temperature measurement error exceeding ±5℃, which cannot meet the accuracy requirement of ±1℃ for cable temperature monitoring.

[0004] 2. Limited functionality and low integration: Traditional installation components only provide support and cannot simultaneously support and reinforce roadways while integrating multi-parameter monitoring. In high-risk fire areas such as goaf and coal pillar areas, anchor bolts and sensor supports need to be constructed separately, which is time-consuming, costly, and excessive drilling can damage the integrity of the surrounding rock and exacerbate the risk of roof collapse.

[0005] Therefore, it is necessary to propose a coal mine natural fire monitoring device based on fiber optic grating sensors to solve the above problems. Summary of the Invention

[0006] The purpose of this invention is to provide a coal mine natural fire monitoring device based on a fiber optic grating sensor to solve the problems mentioned in the background art.

[0007] To achieve the above objectives, the present invention provides the following technical solution: a coal mine natural fire monitoring device based on fiber optic grating sensors, comprising an optical cable and a unit box arranged on a coal mine roadway. The unit box includes multiple fiber optic grating temperature sensors, which are connected in series on a single optical cable using wavelength division multiplexing technology and laid along the coal mine roadway or goaf. An installation component is installed on the coal mine roadway using an anchor bolting machine. The installation component includes a support anchor bolt, which penetrates the coal mine roadway and extends into the soil layer. The support anchor bolt is a hollow rod structure, with a sharp end at one end. The surface of the support anchor bolt is also provided with grouting holes, and multiple grouting holes are provided. The multiple grouting holes are distributed along the length of the support anchor bolt and penetrate both the inner and outer surfaces of the support anchor bolt.

[0008] The mounting component also includes a mounting plate, which is a hexagonal plate structure. The mounting plate has a grouting hole in the middle, which is connected to the interior of the support anchor. The mounting plate is integrally set at the end of the support anchor away from the sharp end. The surface of the mounting plate is provided with reserved holes. There are multiple reserved holes, which are distributed in a circular array.

[0009] The unit box is installed in the corresponding reserved hole using screws.

[0010] Preferably, an annular rubber pad is provided between the reserved hole and the inner wall of the coal mine roadway, and the annular rubber pad is movably sleeved on the outer ring of the supporting anchor rod.

[0011] Preferably, a connecting pipe is fixedly installed on the side of the reserved hole near the supporting anchor rod. The connecting pipe is a hollow tubular structure with an external thread on the outer ring and an internal thread on the inner ring of the supporting anchor rod. The connecting pipe is connected to the end of the supporting anchor rod away from the sharp end by threaded connection.

[0012] Preferably, the connecting pipe is connected to the supporting anchor rod by a threaded connection, and the annular rubber pad is compressed between the reserved hole and the inner wall of the coal mine roadway.

[0013] Preferably, the grouting holes on the mounting plate are sealed by plugs.

[0014] Preferably, a micro-vibration sensor, a gas sensor, and a stress sensor are installed on the corresponding reserved hole.

[0015] This invention also discloses a method for arranging a coal mine natural fire monitoring device based on a fiber optic grating sensor, including the coal mine natural fire monitoring device based on a fiber optic grating sensor, and further comprising:

[0016] S1: Drilling and anchor installation;

[0017] Use an anchor bolting machine to drill holes in the sidewalls or roof of coal mine roadways, with a hole diameter of Φ32mm and a hole depth of 2.0-2.5m; align the sharp end of the support anchor bolt with the hole position, and use a pneumatic anchor bolting machine with an air pressure of 0.5MPa and a rotation speed of 600r / min to screw the support anchor bolt into the drill hole until the installation plate is tightly attached to the roadway wall;

[0018] S2: Grouting reinforcement;

[0019] A mining grouting pump is connected to the grouting hole. The grout is a two-component grout of cement and water glass, and the initial setting time is controlled at 30-60 seconds. The grout flows through the grouting hole, the inner cavity of the support anchor, and the grouting hole in sequence, and seeps into the surrounding rock fissures.

[0020] S3: Unit box installation and sealing;

[0021] M6 threaded holes are machined on the back of the unit box. Stainless steel hexagonal screws are passed through the pre-drilled holes to fix the unit box to the mounting plate.

[0022] S4: Optical cable laying and splicing;

[0023] The optical cable is suspended along the top of the tunnel, with a unit box installed every 50m. Inside the unit box, a fiber optic fusion splicer is used to fusion the temperature-sensing fiber in the optical cable with the fiber Bragg grating temperature sensor inside the unit box. The fusion loss is <0.05dB, and the splice is encapsulated with a protective sleeve. At the same time, a micro-vibration sensor or a gas sensor is installed on the reserved hole.

[0024] S5: System debugging and calibration;

[0025] Start the ground demodulator and calibrate the initial center wavelength of each fiber Bragg grating sensor; record the temperature-wavelength curves under three operating conditions: cable no-load, rated load, and overload, and establish a temperature compensation database.

[0026] The controller automatically corrects the measurement deviation caused by the contact thermal resistance based on the real-time clamping force change of the metal sheet temperature control clamp, ensuring an accuracy of ±0.5℃ under all working conditions.

[0027] Preferably, the grouting pump has a working flow rate of 5-10 L / min and a pressure of 1-2 MPa.

[0028] Preferably, the volume ratio of the cement and water glass slurry is 1:0.5.

[0029] Preferably, during installation, the annular rubber gasket is placed over the connecting pipe, and the rubber gasket is compressed by tightening the threads, with a compression of 2-3 mm.

[0030] The technical effects and advantages of this invention are as follows:

[0031] 1. This invention has high measurement accuracy, strong environmental adaptability, and is easy to maintain. It also has high system reliability, high functional integration, and a safe passive design with zero false alarms and zero missed alarms. It is particularly suitable for fire monitoring in coal mine roadways.

[0032] 2. The multiple pre-drilled holes on the mounting plate can be used to install micro-vibration sensors, gas sensors, stress sensors, etc., to build an integrated monitoring network for multiple hazards such as fire, mine pressure and gas, and reduce redundant investment. Attached Figure Description

[0033] Figure 1 This is a schematic diagram of the coal mine natural fire monitoring device based on a fiber optic grating sensor according to the present invention.

[0034] Figure 2 This is a schematic diagram of the support anchor rod structure from one perspective of the present invention.

[0035] Figure 3 This is a schematic diagram of the supporting anchor rod of the present invention from another perspective.

[0036] Figure 4 This is a schematic diagram of the reserved hole structure of the present invention.

[0037] Figure 5 This is a cross-sectional view of the coal mine natural fire monitoring device based on a fiber optic grating sensor according to the present invention.

[0038] Figure 6 For the present invention Figure 5 Enlarged schematic diagram of the structure at point A in the middle.

[0039] In the diagram: 1. Coal mine roadway; 2. Optical cable; 3. Unit box; 4. Installation component; 401. Supporting anchor bolt; 402. Grouting hole; 403. Sharp end; 404. Reserved hole; 405. Installation plate; 406. Annular rubber pad; 407. Connecting pipe; 408. Plug. Detailed Implementation

[0040] This invention provides, for example Figures 1-6 The image shows a coal mine natural fire monitoring device based on a fiber optic grating sensor.

[0041] refer to Figure 1 As shown, the fiber Bragg grating sensor includes a unit box 3, which contains multiple fiber Bragg grating temperature sensors connected in series on an optical cable 2 using wavelength division multiplexing (WDM) technology. This cable is laid along a coal mine roadway 1 or a goaf area. When the ambient temperature rises, the period and refractive index of the fiber Bragg grating change, causing a shift in the reflection center wavelength. The wavelength shift Δλ is linearly related to the temperature change ΔT. When the system detects an abnormal temperature rise at a certain point (such as exceeding a preset threshold of 40-60℃) or an abnormal heating rate, an alarm is immediately triggered. Through WDM and optical time-domain reflectometry (OTDR) technology, the location of the abnormal point can be accurately pinpointed with a positioning accuracy of ±0.5 meters.

[0042] The advantages of fiber Bragg grating sensors include:

[0043] First: High safety. The fiber optic sensor is passive, non-electric, explosion-proof and flame-proof, and suitable for gas environments.

[0044] Second: It is resistant to interference, unaffected by electromagnetic interference, humidity, or dust, and adaptable to harsh underground environments;

[0045] Third: Real-time monitoring with fast response time (<5 seconds), enabling 24-hour uninterrupted monitoring;

[0046] Fourth: Quasi-distributed, a single optical fiber can connect dozens of sensors in series, covering an area of ​​several kilometers;

[0047] Fifth: High sensitivity; the temperature sensitivity of the packaged sensor is 1.75-2.34 times that of the bare grating.

[0048] refer to Figures 1 to 3 As shown, an installation component 4 is installed on a coal mine roadway 1 using an anchor bolting machine. The installation component 4 includes a support anchor bolt 401, which penetrates the coal mine roadway 1 and extends into the soil layer. The support anchor bolt 401 is a hollow rod structure, and one end of the support anchor bolt 401 is provided with a sharp end 403. The sharp end 403 makes it easy for the support anchor bolt 401 to be driven into the coal mine roadway 1. The surface of the support anchor bolt 401 is also provided with grouting holes 402. There are multiple grouting holes 402, which are distributed along the length of the support anchor bolt 401. The grouting holes 402 penetrate both the inner and outer surfaces of the support anchor bolt 401.

[0049] refer to Figure 4 As described above, the mounting component 4 also includes a mounting plate 405, which is a hexagonal plate structure. The mounting plate 405 has a grouting hole in the middle, which is connected to the interior of the supporting anchor rod 401. The mounting plate 405 is integrally set on the end of the supporting anchor rod 401 away from the sharp end 403. The surface of the mounting plate 405 is provided with reserved holes 404. There are multiple reserved holes 404, which are arranged in a circular array. The unit box 3 in this invention can be fixedly installed on the reserved holes 404 at the corresponding positions by screws. Similarly, since there are multiple reserved holes 404, vibration sensors and other devices can also be connected to the reserved holes 404 at the corresponding positions to facilitate integrated monitoring and convenient installation and use according to actual needs.

[0050] Furthermore, when a grouting mechanism (grouting pump) is connected to the grouting hole, the grout can be discharged into the soil layer through the grouting hole, the hollow inside the support anchor 401, and the grouting round hole 402 in sequence, thereby anchoring the support anchor 401. This replaces the method of installing the unit box 3 using expansion bolts. The method of installing the unit box 3 using the support anchor 401 can both strengthen the inner wall of the coal mine roadway 1 and replace the anchor, achieving a dual purpose and being highly practical.

[0051] When the reserved hole 404 is attached to the inner wall of the coal mine roadway 1, it can also seal the drilling position. In other words, the reserved hole 404 can simultaneously achieve the purpose of sealing the drilling position and providing space for the installation of the unit box 3, replacing the traditional technology where the support of the unit box 3 can only support the destination.

[0052] refer to Figure 5 and Figure 6As shown, to enhance the sealing effect, an annular rubber pad 406 is installed between the reserved hole 404 and the inner wall of the coal mine roadway 1. The annular rubber pad 406 is movably fitted onto the outer ring of the supporting anchor rod 401. A connecting pipe 407 is fixedly installed on the side of the reserved hole 404 near the supporting anchor rod 401. The connecting pipe 407 is a hollow tubular structure. The outer ring of the connecting pipe 407 has external threads, and the inner ring of the supporting anchor rod 401 has internal threads. The connecting pipe 407 is connected to the end of the supporting anchor rod 401 away from the sharp end 403 by threaded engagement, which facilitates connection. When the connecting pipe 407 is connected to the supporting anchor rod 401 by threaded engagement, the annular rubber pad 406 is compressed between the reserved hole 404 and the inner wall of the coal mine roadway 1, thereby achieving sealing.

[0053] After grout is injected through the grouting hole on the mounting plate 405, the plug 408 is engaged in the grouting hole to achieve a seal.

[0054] In practice:

[0055] Example 1: Multifunctional grouting anchoring installation

[0056] Step 1: Drilling and installing anchor bolts;

[0057] Use an anchor bolting machine to drill holes in the sidewall or roof of the coal mine roadway, with a diameter of Φ32mm and a depth of 2.0-2.5m (determined according to the stability of the surrounding rock). Align the pointed end 403 of the support anchor bolt 401 with the hole position, and use a pneumatic anchor bolting machine to screw the support anchor bolt 401 into the drill hole with an air pressure of 0.5MPa and a rotation speed of 600r / min until the mounting plate 405 is tightly attached to the roadway wall. During this process, the threaded structure on the pointed end 403 will self-cut the hole wall, forming an initial anchoring force (about 5-10kN).

[0058] Step 2: Grouting reinforcement;

[0059] A mining grouting pump (flow rate 5-10L / min, pressure 1-2MPa) is connected to the grouting hole. The grout is a cement-water glass two-component grout (volume ratio 1:0.5), and the initial setting time is controlled at 30-60 seconds. The grout flows sequentially through the grouting hole → the inner cavity of the support anchor 401 → the grouting hole 402, and seeps into the surrounding rock fissures. After 28 days, the anchoring force increases to 80-120kN, while reinforcing the roadway side / top surrounding rock and reducing the roof subsidence by more than 30%.

[0060] Step 3: Unit box installation and sealing;

[0061] M6 threaded holes are machined on the back of unit box 3. Stainless steel hexagonal screws are passed through the reserved hole 404 to fix unit box 3 to mounting plate 405. During installation, the annular rubber gasket 406 is put on the outside of the connecting pipe 407 and the rubber gasket is compressed by tightening the threads. The compression amount is 2-3mm to achieve IP68 level sealing, prevent water and coal dust from entering the reserved hole 404, avoid corrosion of sensor wiring terminals, and also prevent grout leakage during grouting.

[0062] Step 4: Fiber optic cable laying and splicing;

[0063] The optical cable 2 is suspended along the top of the tunnel 1, and a unit box 3 is set up every 50m. Inside the unit box 3, the temperature sensing fiber in the optical cable 2 is fused with the fiber optic grating temperature sensor in the unit box 3 using an optical fiber fusion splicer. The fusion loss is <0.05dB, and the splice is encapsulated with a protective sleeve. At the same time, a micro-vibration sensor (fixed by M6 screws) or a gas sensor (connected through a 4-20mA signal interface) can be installed on the reserved hole 404 to achieve "one hole for multiple uses and one rod for multiple functions".

[0064] Step 5: System debugging and calibration;

[0065] Start the ground demodulator and calibrate the initial center wavelength of each fiber optic grating sensor (e.g., 1528.000nm); record the temperature-wavelength correspondence curves under three operating conditions: cable no-load, rated load (e.g., rated current 500A), and overload (1.5 times rated current), and establish a temperature compensation database; the controller automatically corrects the measurement deviation caused by the contact thermal resistance based on the real-time clamping force change of the metal sheet temperature control clamp 15, ensuring an accuracy of ±0.5℃ under all operating conditions.

[0066] In summary, this invention solves the long-standing problems of unreliable installation and limited functionality in distributed fiber optic temperature measurement in coal mines. It provides fire warnings 30% earlier and can increase the success rate of underground personnel evacuation from 85% to over 98%, thereby reducing casualties.

Claims

1. A coal mine natural fire monitoring device based on fiber Bragg grating sensors, comprising an optical cable (2) and a unit box (3) arranged on a coal mine roadway (1), wherein the unit box (3) comprises multiple fiber Bragg grating temperature sensors, which are connected in series on a single optical cable (2) using wavelength division multiplexing technology, and are laid along the coal mine roadway (1) or goaf area, characterized in that: An installation component (4) is installed on the coal mine roadway (1) using an anchor bolt machine. The installation component (4) includes a support anchor bolt (401). The support anchor bolt (401) penetrates the coal mine roadway (1) and extends into the soil layer. The support anchor bolt (401) is a hollow rod structure. One end of the support anchor bolt (401) is provided with a sharp end (403). The surface of the support anchor bolt (401) is also provided with grouting holes (402). There are multiple grouting holes (402). The multiple grouting holes (402) are distributed along the length direction of the support anchor bolt (401). The grouting holes (402) penetrate both the inner and outer surfaces of the support anchor bolt (401). The mounting component (4) also includes a mounting plate (405), which is a hexagonal plate structure. The mounting plate (405) has a grouting hole in the middle, which is connected to the interior of the support anchor rod (401). The mounting plate (405) is integrally set on the end of the support anchor rod (401) away from the sharp end (403). The surface of the mounting plate (405) is provided with reserved holes (404). There are multiple reserved holes (404), which are distributed in a circular array. The unit box (3) is installed in the corresponding reserved hole (404) using screws.

2. The coal mine natural fire monitoring device based on fiber optic grating sensor according to claim 1, characterized in that: An annular rubber pad (406) is provided between the reserved hole (404) and the inner wall of the coal mine roadway (1), and the annular rubber pad (406) is movably sleeved on the outer ring of the supporting anchor rod (401).

3. The coal mine natural fire monitoring device based on fiber optic grating sensor according to claim 2, characterized in that: A connecting pipe (407) is fixedly installed on the side of the reserved hole (404) near the supporting anchor rod (401). The connecting pipe (407) is a hollow tubular structure. The outer ring of the connecting pipe (407) has external threads, and the inner ring of the supporting anchor rod (401) has internal threads. The connecting pipe (407) is connected to the end of the supporting anchor rod (401) away from the sharp end (403) by threaded connection.

4. The coal mine natural fire monitoring device based on fiber optic grating sensor according to claim 3, characterized in that: The connecting pipe (407) is connected to the support anchor (401) by threaded connection, and then the annular rubber pad (406) is compressed between the reserved hole (404) and the inner wall of the coal mine roadway (1).

5. The coal mine natural fire monitoring device based on fiber optic grating sensor according to claim 1, characterized in that: The grouting hole on the mounting plate (405) is sealed by a plug (408).

6. The coal mine natural fire monitoring device based on fiber optic grating sensor according to claim 1, characterized in that: Micro-vibration sensor, gas sensor and stress sensor are installed on the corresponding reserved hole (404).

7. A method for arranging a coal mine natural fire monitoring device based on a fiber optic grating sensor, characterized in that: The coal mine natural fire monitoring device based on a fiber optic grating sensor, as described in any one of claims 1-6, further includes: S1: Drilling and anchor installation; Use an anchor bolting machine to drill holes in the sidewall or roof of the coal mine roadway (1), with a hole diameter of Φ32mm and a hole depth of 2.0-2.5m; align the sharp end (403) of the support anchor bolt (401) with the hole position, and use a pneumatic anchor bolting machine to screw the support anchor bolt (401) into the hole with an air pressure of 0.5MPa and a rotation speed of 600r / min until the installation plate (405) is tightly attached to the roadway wall; S2: Grouting reinforcement; A mining grouting pump is connected to the grouting hole. The grout is a cement and water glass dual-liquid grout, and the initial setting time is controlled at 30-60 seconds. The grout flows through the grouting hole, the inner cavity of the support anchor (401), and the grouting round hole (402) in sequence, and seeps into the surrounding rock fissures. S3: Unit box installation and sealing; M6 threaded holes are machined on the back of the unit box (3), and stainless steel hexagon socket screws are passed through the reserved holes (404) to fix the unit box (3) to the mounting plate (405). S4: Optical cable laying and splicing; The optical cable (2) is suspended along the top of the tunnel (1), and a unit box (3) is set every 50m. Inside the unit box (3), the temperature sensing fiber in the optical cable (2) is fused with the fiber optic fusion splicer in the unit box (3) with a fusion loss of <0.05dB and encapsulated with a protective sleeve. At the same time, a micro-vibration sensor or a gas sensor is installed on the reserved hole (404). S5: System debugging and calibration; Start the ground demodulator and calibrate the initial center wavelength of each fiber Bragg grating sensor; record the temperature-wavelength curves under three operating conditions: cable no-load, rated load, and overload, and establish a temperature compensation database. The controller automatically corrects the measurement deviation caused by the contact thermal resistance based on the real-time clamping force change of the metal sheet temperature control clamp (15), ensuring an accuracy of ±0.5℃ under all working conditions.

8. The arrangement method of the coal mine natural fire monitoring device based on fiber optic grating sensor according to claim 7, characterized in that: The grouting pump has a working flow rate of 5-10 L / min and a pressure of 1-2 MPa.

9. The arrangement method of the coal mine natural fire monitoring device based on fiber optic grating sensor according to claim 7, characterized in that: The volume ratio of the cement and water glass slurry is 1:0.

5.

10. The arrangement method of the coal mine natural fire monitoring device based on fiber optic grating sensor according to claim 7, characterized in that: During installation, the annular rubber pad (406) is placed over the connecting pipe (407), and the rubber pad is compressed by tightening the thread, with a compression of 2-3 mm.

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