A device and method for testing oxidation of coal body around a borehole under pressure control

Abstract

The application discloses a kind of pressure control condition under the oxidation testing device of coal body around borehole, including test tank body, gas supply device is arranged at the bottom of test tank body, gas detection device is arranged at the top of test tank body, the porous supporting plate is fixedly connected at the bottom of test tank body, the porous top plate is fixedly connected at the top of test tank body, heat shrink tube is arranged between porous top plate and porous supporting plate, coal sample is arranged in heat shrink tube, pressure cavity is formed between the outer wall of heat shrink tube and the inner wall of test tank body, the sliding groove is arranged in porous top plate, the sliding block is slidably connected in sliding groove, the drill rod is rotatably connected to sliding block, the drill sleeve is fixedly connected to the lower end of drill rod, the pre-charged inflatable rubber membrane elastic pipe column is arranged outside drill rod, and the lancet is fixedly connected to sliding block. On the one hand, the pipe column is broken and shrinks, the internal pore of coal sample collapses, the effect of borehole surrounding coal body breaking under the action of simulated test pressure is simulated, and the test working condition is consistent with the actual situation. On the other hand, the application can simulate the actual coal oxidation process under different gas environments.

Description

Technical Field

[0001] This invention relates to the field of coal oxidation characteristic testing technology, and in particular to a device and method for testing coal oxidation around a borehole under pressure control conditions. Background Technology

[0002] Spontaneous combustion of coal is the main cause of mine fires, accounting for more than 90% of all mine fires. Deep mining is situated in complex geological environments where coal and rock masses are subjected to high ground stress, high ground temperature, high pore pressure, and intense disturbance, leading to the coupling of multiple disasters such as spontaneous combustion of coal, gas explosions, and rock bursts, resulting in increasingly complex disaster characteristics.

[0003] As coal mining depths increase in my country, ground stress gradually rises, temperatures continue to rise, and coal permeability decreases. These factors lead to increased demand for coal seam pressure relief and increased difficulty in gas extraction. Mines often adopt measures such as increasing borehole density to relieve pressure and improve permeability, increasing negative pressure during gas extraction, and extending extraction time to manage mine pressure and prevent gas disasters. However, using these measures may exacerbate air leakage near boreholes, inducing spontaneous combustion of the coal. At the same time, under the influence of mine pressure, the fragmentation and plasticity of the coal and rock mass increase, altering the mechanical properties of the coal and rock. Pores in the coal body will develop, expand, deform, and connect, enhancing gas seepage and diffusion. The oxygen absorption characteristics of coal, the accumulation and release patterns of heat, and the heat storage environment will change significantly. As a result, the spontaneous combustion characteristics of coal in deep mining processes are significantly different from those in shallow mining, and the spontaneous combustion process, oxidation characteristics, and prevention technologies become more complex.

[0004] The prior art discloses a testing device, patented as "Deep Mining Deformed Coal Oxidation Characteristics Testing Device", patent application number: CN201410625651.X. This device applies pressure or depressurizes the coal sample to obtain information on coal body deformation under pressure depressurization, crack generation, penetration, and fracture. A data acquisition system obtains the deformation changes in CO, O2, CH4, CO2, C2H4, temperature, stress, and strain of the experimental coal sample before and after deformation. Based on the collected gas composition and concentration, internal coal temperature and deformation, and exhaust gas temperature, the device studies the deformation and oxidation characteristics of mined coal bodies under deep mining conditions, thus providing a theoretical basis for prevention and control technologies and early spontaneous combustion identification methods for deep mining coal seams.

[0005] Because the coal sample is confined by the heat shrink tubing on the outside, the fracturing effect of the coal sample is not obvious after the pressure is released on the outside. The inside of the coal sample does not have sufficient contact with oxygen, which is quite different from the actual excavation method used for coal seams. Therefore, the working conditions tested are insufficient to cope with the complex scenarios of coal mining. Summary of the Invention

[0006] The purpose of this invention is to address the shortcomings of existing technologies by proposing a device and method for testing the oxidation of coal around a borehole under pressure control conditions.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] A test device for testing coal oxidation around a borehole under pressure control includes a test tank, a gas supply device at the bottom of the test tank, a gas detection device at the top of the test tank, a perforated support plate fixedly connected to the bottom of the test tank, a perforated top plate fixedly connected to the top of the test tank, a heat shrink tubing between the perforated top plate and the perforated support plate, a coal sample placed inside the heat shrink tubing, a pressure chamber formed between the outer wall of the heat shrink tubing and the inner wall of the test tank, the pressure chamber being filled with hydraulic oil, a sliding groove provided on the perforated top plate, a slider slidably connected within the sliding groove, a drill rod rotatably connected to the slider, a drill sleeve fixedly connected to the lower end of the drill rod, the drill sleeve having a diameter larger than the drill rod diameter, a pre-inflated rubber membrane elastic tube sleeved around the drill rod, and a piercing needle fixedly connected to the slider for piercing the tube sleeve.

[0009] Preferably, the outer wall of the pressurization chamber is fixedly connected to the pressure relief cylinder, the piston is slidably connected inside the pressure relief cylinder, a compression chamber is formed between the piston and the outer closed end of the pressure relief cylinder, the compression chamber is fixedly connected to the air supply hose between the tubing and the column, and a telescopic rod is fixedly connected to the outer closed end of the pressure relief cylinder, and the telescopic end of the telescopic rod is fixedly connected to the piston.

[0010] Preferably, the porous top plate is rotatably connected to a turntable, and the slider is located on the turntable.

[0011] Preferably, a sealing cover is fixedly connected to the upper side of the turntable.

[0012] Preferably, a vertical plate is fixedly connected to the upper side of the slider, and a sliding block is slidably connected to the vertical plate. The sliding block is driven to rise and fall by a driving device.

[0013] A support plate is fixedly connected to one side of the sliding block. The support plate is rotatably connected to the drill rod, which is a hollow structure. The drill rod is driven to rotate by a power device. A bracket is fixedly connected to the upper side of the support plate. The bracket is fixedly connected to the spiral feeder, which extends into the drill rod. The slider is provided with a rotating hole. A protective sleeve is rotatably connected inside the rotating hole. The tubing is expanded and supported between the protective sleeve and the outer wall of the drill rod.

[0014] Preferably, the support plate is fixedly connected to a box body on one side, and the box body is configured to correspond to the discharge pipe of the spiral feeder.

[0015] The present invention also discloses a method for testing the oxidation of coal around a borehole under pressure control conditions, using the above-mentioned testing device to perform coal oxidation testing.

[0016] The advantages of this invention are as follows: The device and method for testing coal oxidation around boreholes under pressure control provided by this invention drills ducts at different locations within the coal sample by lowering the drill rod. These ducts are filled and supported by an inflatable tubing string. After depressurization outside the coal sample, the tubing string is punctured, causing it to shrink and lose support for the ducts. This results in deformation and crack formation in the coal sample within the ducts. Combined with oxygen input from the bottom, this method can simulate the disruption of the internal stress balance of the coal body caused by actual drilling. Furthermore, by setting up multiple testing devices of this invention, different devices can change the position of the slider in the chute and rotate the turntable to change the angle. This allows for comparison of the differences in coal structure and composition at different locations during drilling, as well as the differences in oxidation test results. This provides a more comprehensive understanding of the internal deformation and crack evolution characteristics of the coal body and its oxygen adsorption and seepage patterns, thus providing theoretical guidance for the prevention and control of spontaneous combustion of surrounding coal bodies in deep mining coal seam depressurization boreholes and gas pre-drainage boreholes.

[0017] This invention uses a telescopic rod to push the piston outward, causing pressure relief within the compression chamber. Simultaneously, the cavity at the right end of the piston is compressed, and additional gas is delivered to the tubing via a gas supply hose. This causes the weak point on the outside of the tubing to expand and contact the needle, resulting in the tubing rupturing and shrinking. The coal sample is then subjected to the residual pressure of the hydraulic oil in the pressurized chamber. Even when outward deformation and crack formation are not obvious, this causes the internal channels of the coal sample to collapse, leading to coal sample fragmentation. Compared to existing testing devices, this invention demonstrates a more significant fracturing effect, allowing for sufficient oxidation upon contact with oxygen. Furthermore, the simulated working conditions more closely resemble actual drilling operations, mimicking the stress disturbance and structural damage to the coal seam, and facilitating theoretical research beforehand. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the basic structure of the present invention;

[0019] Figure 2 This is a schematic diagram of the internal structure of the present invention;

[0020] Figure 3 This is a schematic diagram of the connection structure between the slider and the column in this invention;

[0021] Figure 4 yes Figure 3 A schematic diagram of the structure after removing the tubing and spiral feeder. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0023] like Figure 1-4As shown, the present invention provides a coal oxidation testing device under pressure control conditions, including a test tank 1. A gas supply device is installed at the bottom of the test tank 1, and a gas detection device 11 is installed at the top of the test tank 1. The gas supply device and the gas detection device 11 adopt existing technical structures. The test tank 1 is also equipped with a heating device, sensors, etc., as disclosed in the existing structure with patent publication number CN104316668A. A porous support plate 2 is fixedly connected to the bottom of the test tank 1, and a porous top plate 3 is fixedly connected to the top of the test tank 1. The porous top plate 3 and the porous support plate 2 are connected to the coal oxidation testing device 1. A heat shrink tubing 4 is installed between the trays 2, and a coal sample 5 is placed inside the heat shrink tubing 4. A pressure chamber 6 is formed between the outer wall of the heat shrink tubing 4 and the inner wall of the test tank 1. The pressure chamber 6 is filled with hydraulic oil. A groove 31 is provided on the perforated top plate 3. A slider 32 is slidably connected in the groove 31. The slider 32 is rotatably connected to the drill rod 33. The lower end of the drill rod 33 is fixedly connected to the drill sleeve 34. The diameter of the drill sleeve 34 is larger than the diameter of the drill rod 33. A pre-inflated rubber membrane elastic tube 35 is sleeved outside the drill rod 33. A piercing needle 36 is fixedly connected to the slider 32. The piercing needle 36 is used to pierce the tube 35.

[0024] The perforated top plate 3 is rotatably connected to the turntable 311, the slider 32 is located on the turntable 311, the upper side of the turntable 311 is fixedly connected to the sealing cover 312, the sealing cover 312 seals the top of the turntable 311, and the gas detection device 11 is installed inside the sealing cover 312.

[0025] During testing, the coal sample 5 is sealed tightly with heat-shrink tubing. Strain gauges are attached to the outside of the sample as needed. Hydraulic oil is injected into the pressurization chamber 6 to the set pressure. The lower end of the drill rod 33 is initially positioned at the top of the coal sample 5. The position of the slider 32 within the groove 31 is adjusted (either by an electric push rod or manual adjustment). The drill rod 33 descends to drill holes at different locations within the coal sample 5, which are filled and supported by an inflated tubing 35. After depressurization outside the coal sample 5, the tubing 35 is punctured, causing it to shrink and lose support for the holes. The coal sample 5 deforms and cracks form within the holes, coinciding with the introduction of oxygen from the bottom. On the one hand, it can simulate the damage to the internal stress balance of coal body caused by actual construction drilling. On the other hand, by setting up multiple testing devices of the present invention, different testing devices can change the position of slider 32 in chute 31 and rotate turntable 311 to change the angle, so as to compare the differences in coal body structure and composition at different locations of coal body excavation and the differences in oxidation test. This can more comprehensively benefit the internal deformation and fracture evolution characteristics of coal body and its oxygen adsorption and seepage law, thus providing theoretical guidance for the prevention and control of spontaneous combustion of surrounding coal bodies such as deep mining coal seam depressurization drilling and gas pre-drainage drilling.

[0026] In one embodiment of the present invention, a pressure relief cylinder 61 is fixedly connected to the outer wall of the pressure chamber 6, and a piston 62 is slidably connected inside the pressure relief cylinder 61. A compression chamber is formed between the piston 62 and the outer closed end of the pressure relief cylinder 61. An air supply hose is fixedly connected between the compression chamber and the tubing 35. A telescopic rod 63 is fixedly connected to the outer closed end of the pressure relief cylinder 61. The telescopic rod 63 is electric or hydraulic, and the telescopic end of the telescopic rod 63 is fixedly connected to the piston 62.

[0027] In this embodiment, the telescopic rod 63 pushes the piston 62 outward to slide, causing pressure relief in the compression chamber 6. At the same time, the cavity at the right end of the piston 62 is compressed and additional gas is delivered to the tubing 35 through the gas supply hose. This causes the weak point set on the outside of the tubing 35 to expand and contact the needle 36. The tubing 35 ruptures and shrinks. The coal sample 5 is subjected to the residual pressure of the hydraulic oil in the pressurization chamber 6. When the outward deformation and crack formation are not obvious, the internal channels of the coal sample 5 collapse and the coal sample 5 breaks. Compared with the existing testing device, the rupture effect is obvious and the oxidation can be fully achieved by contacting oxygen. On the other hand, the simulated working conditions are closer to the stress disturbance and structural damage of the coal seam during actual drilling, and it is easier to conduct theoretical research in advance.

[0028] In one embodiment of the present invention, the upper side of the slider 32 is fixedly connected to the vertical plate 7, the vertical plate 7 is slidably connected to the sliding block, and the sliding block is driven to rise and fall by a driving device. The driving device is a conventional structure, such as a lead screw slider mechanism.

[0029] A support plate 72 is fixedly connected to one side of the sliding block. The support plate 72 is rotatably connected to the drill rod 33. The drill rod 33 is a hollow structure and is driven to rotate by a power device. The power device is a conventional structure, such as a pulley structure or a motor gear structure. A bracket 73 is fixedly connected to the upper side of the support plate 72. The bracket 73 is fixedly connected to the spiral conveyor 74, which extends into the drill rod 33. The spiral conveyor 74 is existing technology and uses a spiral shaft for material conveying. A box 741 is fixedly connected to one side of the support plate 72, and the box 741 corresponds to the spiral conveyor. The discharge pipe of the feeder 74 is designed to vertically transport and clean the slag generated from cutting the lower end of the drill rod 33 to the box 741. The slider 32 is provided with a rotating hole, and the sheath 75 is rotatably connected inside the rotating hole. The tube column 35 is expanded and supported between the sheath 75 and the outer wall of the drill rod 33. The inflated tube column 35 expands and seals with the sheath 75. When the drill rod 33 goes deeper, the expanded tube column 35 can be relatively easily axially displaced with the sheath 75 (if it passes directly through the slider 32, it needs to rotate relative to the sheath, and the tube column 35 may easily lose its sealing effect if it twists).

[0030] In this embodiment, the holes in the porous top plate 3 are sealed with rubber columns, and a cover plate that completely covers the slide groove 31 is provided on the side of the slider 32. After the pipe column 35 is punctured and breaks, losing support for the inner channel of the coal sample 5, the seal between the pipe column 35 and the sheath 75 is lost, and the inner wall of the excavated channel deforms and breaks. Tests are conducted on the excavated channel and compared with coal sample 5 without excavated channels, so as to flexibly test coal oxidation under different conditions, and provide a multi-condition theoretical basis for the prevention and control technology of spontaneous combustion in deep coal seams and the early spontaneous combustion identification method.

[0031] The present invention also discloses a method for testing the oxidation of coal around a borehole under pressure control conditions, using the above-mentioned testing device to perform coal oxidation testing.

[0032] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A device for testing oxidation of coal around a borehole under pressure control, comprising a test tank (1), a gas supply device arranged at the bottom of the test tank (1), a gas detection device (11) arranged at the top of the test tank (1), a perforated support plate (2) fixedly connected to the bottom of the test tank (1), a perforated top plate (3) fixedly connected to the top of the test tank (1), a heat shrink tube (4) arranged between the perforated top plate (3) and the perforated support plate (2), a coal sample (5) arranged in the heat shrink tube (4), a pressurized cavity (6) formed between the outer wall of the heat shrink tube (4) and the inner wall of the test tank (1), and hydraulic oil filled in the pressurized cavity (6). characterized in that The perforated top plate (3) is provided with a sliding groove (31), a sliding block (32) is slidingly connected in the sliding groove (31), a drill rod (33) is rotatably connected to the sliding block (32), a drill sleeve (34) is fixedly connected to the lower end of the drill rod (33), the diameter of the drill sleeve (34) is larger than the diameter of the drill rod (33), a pre-charged and expanded rubber membrane elastic pipe column (35) is arranged on the drill rod (33), a lancet (36) is fixedly connected to the sliding block (32), and the lancet (36) is used to pierce the pipe column (35). An outer wall of the pressurized cavity (6) is fixedly connected with a pressure relief cylinder (61), a piston (62) is slidingly connected in the pressure relief cylinder (61), a compression cavity is formed between the piston (62) and the outer closed end of the pressure relief cylinder (61), a gas supply hose is fixedly connected between the compression cavity and the pipe column (35), an outer closed end of the pressure relief cylinder (61) is fixedly connected with a telescopic rod (63), and the telescopic end of the telescopic rod (63) is fixedly connected with the piston (62). The perforated top plate (3) is rotatably connected with a turntable (311), and the sliding block (32) is located on the turntable (311). A vertical plate (7) is fixedly connected to the upper side of the sliding block (32), a sliding block is slidingly connected to the vertical plate (7), and the sliding block is driven to ascend and descend by a driving device. A support plate (72) is fixedly connected to one side of the sliding block, the drill rod (33) is rotatably connected to the support plate (72), the drill rod (33) is a hollow structure, the drill rod (33) is driven to rotate by a power device, a bracket (73) is fixedly connected to the upper side of the support plate (72), a spiral discharger (74) is fixedly connected to the bracket (73), the spiral discharger (74) extends into the drill rod (33), the sliding block (32) is provided with a rotating hole, a sheath (75) is rotatably connected in the rotating hole, and the pipe column (35) is expanded and supported between the sheath (75) and the outer wall of the drill rod (33).

2. The device for testing the oxidation of coal body around a borehole under pressure control conditions according to claim 1, characterized in that: A sealing cover (312) is fixedly connected to the upper side of the turntable (311).

3. The device for testing the oxidation of coal body around a borehole under pressure control conditions according to claim 1, characterized in that: A box body (741) is fixedly connected to one side of the support plate (72), and the box body (741) is provided with a discharge pipe corresponding to the spiral discharger (74).

4. A method for testing oxidation of coal surrounding a borehole under pressure control conditions, characterised by: The coal oxidation test is performed by using the test device according to any one of claims 1 to 3.

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