A device and method for measuring coal pore structure changes based on nuclear magnetic resonance technology

Abstract

The present invention relates to the field of coal pore structure, and specifically to a device and method for measuring coal pore structure changes based on nuclear magnetic resonance technology, including a coal sample holder, a heating device, a liquid nitrogen cooling device, a temperature controller, a constant pressure pump, a gas chromatograph and a control valve. The coal sample holder is connected to five pipelines, and the five pipelines include two pipelines connecting a nitrogen cylinder and an air compressor pump, a pipeline connecting a gas chromatograph, a pipeline connecting a gas storage tank and a pipeline connecting a constant pressure pump. The invention provides high and low temperature environments for coal samples respectively through heating rods and liquid nitrogen cooling, and uses a constant pressure pump to provide underground stress loads to the device; the invention is also provided with a gas detection device, which can monitor gas changes in the adsorption and analysis process in real time. Therefore, the present invention measures the pore structure of coal more accurately.

Description

Technical Field

[0001] The invention relates to the field of coal body pore structure, and in particular to a device and method for measuring coal pore structure changes based on nuclear magnetic resonance technology. Background Art

[0002] Coal spontaneous combustion disaster is one of the safety issues that the coal industry still needs to solve. Among the accidents caused by coal spontaneous combustion in mines, accidents caused by direct or indirect ignition of coal bodies by gas combustion account for a very large proportion, and the pore structure of coal bodies is a key factor affecting the storage and migration of gas. Studies have shown that the adsorption of coal surface is due to the presence of unsaturated energy on the surface of coal pores, which interacts with non-polar gas molecules to produce van der Waals forces, thereby adsorbing gas molecules. The cause of coal spontaneous combustion is the physical and chemical adsorption between coal and oxygen, which then undergoes a chemical reaction, releases the generated adsorption heat and chemical reaction heat, and the process of combustion is triggered by the gradual accumulation of heat, which causes the coal body temperature to rise. The pore size distribution is an important parameter for comprehensive and quantitative analysis of the adsorption capacity of different gases, micro-deformation caused by adsorption, and flow-gas coupling. Therefore, studying the effects of different temperatures and gas adsorption on the pore structure of coal bodies is of great significance for in-depth research on coal spontaneous combustion prevention and control technology, coalbed methane extraction, and coal mine safety production.

[0003] At present, the determination of coal porosity using nuclear magnetic resonance technology is mainly carried out at room temperature, and the influence of gas adsorption and desorption on the porosity structure of the coal body is not considered, resulting in inaccurate and unreliable measurement data. Summary of the invention

[0004] The purpose of the present invention is to overcome the defect that the existing test method does not consider the relationship between the change of coal pore structure and different temperatures and gas adsorption, and does not monitor the changes of adsorbed gas consumption and generation in real time, thus causing inaccurate experimental data. In order to ensure the accuracy of the measured coal pore structure data, the relationship between the change of coal pore structure and different temperatures and gas adsorption and analysis is considered, and the gas changes in the adsorption and analysis process are monitored in real time. The present invention provides a coal pore structure change measurement device and method based on nuclear magnetic resonance technology, which is used to measure the structure of coal pores.

[0005] The technical solution adopted by the present invention to solve its technical problems is: a device and method for measuring coal pore structure changes based on nuclear magnetic resonance technology, including a coal sample holder, a heating device, a liquid nitrogen cooling device, a temperature controller, a constant pressure pump, a gas chromatograph and a control valve. The coal sample holder is connected to five pipelines, and the five pipelines include two pipelines connecting the liquid nitrogen cylinder and the air compression pump, a pipeline connecting the gas chromatograph, a pipeline connecting the gas storage tank and a pipeline connecting the constant pressure pump.

[0006] The heating device comprises five heating rods, wherein one heating rod is located in the center and the other four heating rods are arranged around the center heating rod, and the heating rods penetrate the coal pillar.

[0007] The liquid nitrogen cooling device comprises: a liquid nitrogen cylinder, an air compression pump, and a liquid nitrogen nozzle. A low-temperature electromagnetic valve is arranged on the top of the liquid nitrogen cylinder. The liquid nitrogen cylinder is connected to the air compression pump and the liquid nitrogen nozzle arranged between the double-layer high-temperature resistant quartz glass.

[0008] The control valve includes two cooling valves, a gas flow rate control valve, a constant pressure valve and an air intake valve. The cooling valve is connected between the air compression pump and the coal sample holder, the gas flow rate control valve is connected between the gas chromatograph and the coal sample holder, the air intake valve is connected between the gas storage tank and the coal sample holder, and the constant pressure valve is connected between the constant pressure pump and the coal sample holder.

[0009] The material of the coal sample cavity is a double-layer high-temperature resistant quartz glass, and the outermost layer of the coal sample cavity is an aluminum silicate fiber layer.

[0010] The temperature sensor is arranged inside the double-layer high-temperature resistant quartz glass, one is arranged at the upper and lower ends of the left and right sides of the coal pillar, and the temperature sensor is connected to the temperature controller through a wire.

[0011] A device and method for measuring coal pore structure changes based on nuclear magnetic resonance technology, characterized in that it includes the following steps:

[0012] Step 1: Test sample preparation

[0013] A test coal column of suitable size is produced, the double-layer high-temperature resistant quartz glass and the coal sample holder are opened, the test coal column is placed in the coal sample chamber, and then the double-layer high-temperature resistant quartz glass and the coal sample holder are closed;

[0014] Step 2: Provide a stressful environment

[0015] Open the constant pressure valve, start the constant pressure pump, pressurize to the formation pressure, and keep the pressure constant;

[0016] Step 3: Change the atmosphere of the device

[0017] Open the air inlet valve, and the gas in the gas tank flows into the inner layer of the double-layer high-temperature resistant quartz glass through the ventilation pipe;

[0018] Step 4: Heating process or cooling process

[0019] Heating process: Turn on the temperature controller and set the target temperature. If heating is required, the temperature controller starts 5 heating rods to heat the coal pillar. The temperature sensor detects the temperature of the coal pillar in real time. When the average temperature of the four temperature sensors is equal to the temperature of the underground coal seam, the change of the coal pore structure in the heating process is measured.

[0020] Cooling process: Turn on the temperature controller and set the target temperature. If cooling is required, turn on the air compression pump and the low-temperature solenoid valve. The nitrogen in the liquid nitrogen cylinder is introduced into the liquid nitrogen nozzles on the left and right sides of the coal sample holder through the air compression pump and enters between the double-layer high-temperature resistant quartz glass. When the temperature sensor displays the set temperature, the liquid nitrogen nozzle will make the liquid nitrogen flow uniform or stop spraying.

[0021] Step 5: Gas Detection

[0022] Open the gas flow rate control valve and the gas enters the gas chromatograph through the pipeline.

[0023] The beneficial effects of the present invention are:

[0024] Heating rods and liquid nitrogen cooling are used to provide different high and low temperature environments for the coal sample in the coal sample chamber respectively, and a constant pressure pump is used to provide underground stress load to the device. Compared with other measurement methods, the relationship between pore structure changes and different temperature environments is taken into account to improve the accuracy and authenticity of the measured pore structure.

[0025] The present invention is provided with a gas detection device, which can monitor the gas changes in the adsorption and desorption processes in real time, and take into account the relationship between the pore structure changes and the adsorbed and desorbed gases, so as to measure the pore structure of the coal body more accurately. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a schematic diagram of the structure of a device for measuring coal pore structure changes based on nuclear magnetic resonance technology according to the present invention;

[0027] In the figure, 1-air compression pump, 2-low temperature solenoid valve, 3-coal sample chamber, 4-liquid nitrogen cylinder, 5-constant pressure pump, 6-constant pressure valve, 7-temperature sensor, 8-spiral connector, 9-gas storage tank, 10-gas chromatograph, 11-gas flow rate control valve, 12-cooling valve, 13-insulation layer, 14-heating rod, 15-cooling cavity, 16-coal column, 17-double-layer high temperature resistant quartz glass, 18-coal sample holder, 19-intake valve, 20-temperature controller, 21-wire, 22-liquid nitrogen nozzle. DETAILED DESCRIPTION

[0028] In order to further explain the technical means and effects adopted by the present invention to achieve the predetermined invention purpose, the specific implementation method, structure, characteristics and effects of the present invention application are described in detail below in combination with the accompanying drawings and preferred embodiments.

[0029] A device and method for measuring changes in coal pore structure based on nuclear magnetic resonance technology, comprising a coal sample holder (18), a heating device, a liquid nitrogen cooling device, a temperature controller (20), a constant pressure pump (5), a gas chromatograph (10) and a control valve, wherein the coal sample holder (18) is connected to five pipelines, the five pipelines comprising two pipelines connecting a liquid nitrogen cylinder (4) and an air compression pump (1), a pipeline connecting the gas chromatograph (10), a pipeline connecting a gas storage tank (9) and a pipeline connecting the constant pressure pump (5).

[0030] The heating device comprises five heating rods (14), wherein one heating rod is located in the center and the other four heating rods are located around the center heating rod. The heating rods (14) penetrate the coal pillar (16).

[0031] The liquid nitrogen cooling device comprises: a liquid nitrogen cylinder (4), an air compression pump (1), and a liquid nitrogen nozzle (22); a low-temperature electromagnetic valve (2) is provided on the top of the liquid nitrogen cylinder (4); the liquid nitrogen cylinder (4) is connected to the air compression pump (1) and the liquid nitrogen nozzle (22) provided between the double-layer high-temperature resistant quartz glass (17).

[0032] The control valve comprises two cooling valves (12), a gas flow rate control valve (11), a constant pressure valve (6) and an air intake valve (19); the cooling valve (12) is connected between the air compression pump (1) and the coal sample holder (18); the gas flow rate control valve (11) is connected between the gas chromatograph (10) and the coal sample holder (18); the air intake valve (19) is connected between the gas storage tank (9) and the coal sample holder (18); and the constant pressure valve (6) is connected between the constant pressure pump (5) and the coal sample holder (18).

[0033] The material of the coal sample chamber (3) is a double-layer high-temperature resistant quartz glass (17), the double-layer high-temperature resistant quartz glass (17) is connected via a spiral connection port (8), and the outermost layer of the coal sample chamber (3) is provided with a heat-insulating layer (13).

[0034] The temperature sensor (7) is arranged at the upper and lower ends of the left and right sides of the coal pillar (16), respectively. The temperature sensor (7) is connected to the temperature controller (20) via a wire (21).

[0035] A device and method for measuring coal pore structure changes based on nuclear magnetic resonance technology, characterized in that it includes the following steps:

[0036] Step 1: Test sample preparation

[0037] Produce a test coal column of appropriate and correct size, open the double-layer high-temperature resistant quartz glass (17) and the coal sample holder (18), place the test coal column in the coal sample chamber (3), and then close the double-layer high-temperature resistant quartz glass (17) and the coal sample holder (18);

[0038] Step 2: Provide a stressful environment

[0039] Open the constant pressure valve (6), start the constant pressure pump (5), increase the pressure to the formation pressure, and keep the pressure constant;

[0040] Step 3: Change the atmosphere of the device

[0041] The air inlet valve (19) is opened, and the gas in the gas storage tank (9) enters the inner layer of the double-layer high-temperature resistant quartz glass (17) along the ventilation pipe (9). After the air flow is stable and has been passed for a period of time, relevant tests and measurements are performed.

[0042] Step 4: Heating process or cooling process

[0043] Heating process: Turn on the temperature controller (20) and set the target temperature. If heating is required, the temperature controller starts the five heating rods (14) to heat the coal pillar. The temperature sensor (7) detects the temperature of the coal pillar in real time. When the average temperature obtained by the four temperature sensors (7) is equal to the temperature of the underground coal seam, the change in the coal pore structure during the heating process is measured. If the heating rate needs to be adjusted, it can be adjusted in the temperature control device.

[0044] Cooling process: Turn on the temperature controller (20) and set the target temperature. If cooling is required, turn on the air compression pump (1) and the cryogenic solenoid valve (2). The nitrogen in the liquid nitrogen cylinder (4) is introduced into the liquid nitrogen nozzles (22) on the left and right sides of the coal sample holder (18) through the air compression pump (1), and enters the cooling cavity (15) between the double-layer high-temperature resistant quartz glass (17). When the temperature sensor (7) displays the set temperature, the liquid nitrogen nozzle (22) will make the liquid nitrogen flow rate uniform or stop spraying.

[0045] Step 5: Gas Detection

[0046] The gas flow rate control valve (11) is opened, and the gas enters the gas chromatograph (10) through the pipeline. If the change of adsorbed gas at a certain temperature is to be measured, it is only necessary to open the gas flow rate control valve (11) after measuring the pore structure at a certain temperature, and then perform the test on the gas chromatograph (10).

[0047] Specifically, when measuring the changes in the pore structure of the coal body during the heating process, according to the principle of similarity, a constant pressure pump and a heating rod are used to provide similar underground stress loads and high temperature environments for the experimental coal samples in the coal sample chamber, and to ensure constant temperature, aluminum silicate fiber insulation materials must be attached to the outer wall. The equipment uses a heating device, turns on the temperature control device and temperature sensor, and heats five heating rods at the same time. The temperature sensor detects the dynamic temperature changes of the coal column in real time and transmits it to the temperature control device; when the temperature control device shows that the required temperature range has been reached and the temperature is in a stable state, nuclear magnetic resonance is used to measure the changes in the pore structure of the coal column during the entire process.

[0048] When measuring the changes in the pore structure of the coal body during cooling or low temperature, the constant pressure pump and liquid nitrogen cooling are still used according to the similarity principle to provide similar underground stress loads and low temperature environments for the experimental coal samples in the coal sample cavity. The equipment uses a liquid nitrogen cooling device. When liquid nitrogen is drilled, the air switch and the low temperature solenoid valve are turned on, and the nitrogen in the liquid nitrogen cylinder is passed into the hoses on the left and right sides of the coal sample holder through the air compressor, and flows through the hose to the middle of the double-layer high temperature resistant quartz glass.

[0049] To measure the changes in the pore structure of the coal body during the heating or cooling process under different atmospheres, it is only necessary to open the pressure reducing valve of the gas storage tank, control the gas flow entering the device by adjusting the gas flow rate, and then introduce the gas into the device through the pipeline. After the gas flow is stable and the gas has been introduced for a period of time, turn on the heating device or liquid nitrogen cooling device to measure the pore structure.

[0050] To measure the gas changes during gas adsorption and analysis, you only need to open the gas flow rate control valve connected to the tail of the coal sample holder, let the gas enter the gas chromatograph through the pipeline, and then measure it. If you want to measure the gas changes at a certain temperature, you only need to measure the porosity at that temperature, and repeat the above process to complete the measurement.

Claims

1. A device for measuring coal pore structure changes based on nuclear magnetic resonance technology, characterized in that: The invention comprises a coal sample holder (18), a heating device, a liquid nitrogen cooling device, a temperature controller (20), a constant pressure pump (5), a gas chromatograph (10) and a control valve, wherein the coal sample holder (18) is connected to five pipelines, the five pipelines comprising two pipelines connecting a liquid nitrogen cylinder (4) and an air compression pump (1), a pipeline connecting the gas chromatograph (10), a pipeline connecting a gas storage tank (9) and a pipeline connecting the constant pressure pump (5), and the coal sample holder (18) is provided with a coal sample cavity (3) for placing a coal column (16); The heating device comprises five heating rods (14), wherein the five heating rods (14) have one heating rod in the center and the other four heating rods are arranged around the central heating rod, and the heating rods (14) penetrate the coal pillar (16); The liquid nitrogen cooling device comprises: a liquid nitrogen cylinder (4), an air compression pump (1), and a liquid nitrogen nozzle (22); a low-temperature electromagnetic valve (2) is provided on the top of the liquid nitrogen cylinder (4); the liquid nitrogen cylinder (4) is connected to the air compression pump (1) and the liquid nitrogen nozzle (22) provided between the double-layer high-temperature resistant quartz glass (17); The control valve comprises two cooling valves (12), a gas flow rate control valve (11), a constant pressure valve (6) and an air intake valve (19); the cooling valve (12) is connected between the air compression pump (1) and the coal sample holder (18); the gas flow rate control valve (11) is connected between the gas chromatograph (10) and the coal sample holder (18); the air intake valve (19) is connected between the gas storage tank (9) and the coal sample holder (18); and the constant pressure valve (6) is connected between the constant pressure pump (5) and the coal sample holder (18); The temperature controller (20) is connected to the temperature sensor (7) via a wire (21), and the temperature sensor (7) is arranged at the upper and lower ends of the left and right sides of the coal pillar (16), respectively.

2. The device for measuring coal pore structure changes based on nuclear magnetic resonance technology according to claim 1, characterized in that: The material of the coal sample chamber (3) is a double-layer high-temperature resistant quartz glass (17), and the outermost layer of the coal sample chamber (3) is provided with a heat-insulating layer (13).

3. A method for using the coal pore structure change determination device based on nuclear magnetic resonance technology as described in any one of claims 1-2, characterized in that: The steps include: Step 1: Test sample preparation A test coal column of suitable size is produced, the double-layer high-temperature resistant quartz glass (17) and the coal sample holder (18) are opened, the test coal column is placed in the coal sample chamber (3), and then the double-layer high-temperature resistant quartz glass (17) and the coal sample holder (18) are closed; Step 2: Provide a stressful environment Open the constant pressure valve (6), start the constant pressure pump (5), increase the pressure to the formation pressure, and keep the pressure constant; Step 3: Change the atmosphere of the device Open the air inlet valve (19), and the gas in the gas storage tank (9) enters the inner layer of the double-layer high-temperature resistant quartz glass (17) along the ventilation pipe; Step 4: Heating process or cooling process Heating process: Turn on the temperature controller (20) and set the target temperature. If heating is required, the temperature controller starts the five heating rods (14) to heat the coal pillar. The temperature sensor (7) detects the temperature of the coal pillar in real time. When the average temperature obtained by the four temperature sensors (7) is equal to the temperature of the underground coal seam, the change in the coal pore structure during the heating process is measured. Cooling process: Turn on the temperature controller (20) and set the target temperature. If cooling is required, turn on the air compression pump (1) and the cryogenic solenoid valve (2). The nitrogen in the liquid nitrogen cylinder (4) is introduced into the liquid nitrogen nozzles (22) on the left and right sides of the coal sample holder (18) through the air compression pump (1) and enters between the double-layer high-temperature resistant quartz glass (17). When the temperature sensor (7) displays the set temperature, the liquid nitrogen nozzle (22) will make the liquid nitrogen flow rate uniform or stop spraying; Step 5: Gas Detection The gas flow rate control valve (11) is opened, and the gas enters the gas chromatograph (10) through the pipeline.

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