Simulation method of spontaneous combustion law of coal left in goaf in low temperature nitrogen environment

Abstract

The present invention discloses a method for simulating the spontaneous combustion law of coal residue in goaf in a low-temperature nitrogen environment, and relates to the technical field of research on the spontaneous combustion law of coal. The simulation system adopted includes a control box, an insulation box, a sample chamber and a nitrogen bottle. The sample chamber has good airtightness and thermal conductivity. The insulation box is connected to a nitrogen injection pipeline, which is connected to the nitrogen bottle and is used to provide room-temperature nitrogen into the insulation box; the sample chamber is equipped with an air inlet, an air outlet and a monitoring mechanism for monitoring temperature and pressure. The control box is used to control the parameter setting of the monitoring mechanism and the opening or closing of the nitrogen bottle; the system of the present invention is used to obtain coal samples with different processing times in a low-temperature nitrogen environment according to experimental requirements, and conduct analysis in combination with professional knowledge. The present invention can more realistically simulate the spontaneous combustion law of coal residue under the condition of low-temperature nitrogen injection in the goaf, and provide theoretical support for mine fire prevention and extinguishing work.

Description

Technical Field

[0001] The present invention relates to the technical field of research on coal spontaneous combustion laws, and in particular to a method for simulating the spontaneous combustion laws of coal left in goafs in a low-temperature nitrogen environment. Background Art

[0002] Spontaneous combustion of coal is a major threat to global energy security and the environment. Goafs within working faces are a key area of ​​coal spontaneous combustion. To address this issue, nitrogen injection into goafs has become widely used for fire prevention and extinguishing. However, when conventional room-temperature nitrogen is insufficient for rapid fire prevention and extinguishing, low-temperature nitrogen injection into goafs is often used to reduce the risk of spontaneous combustion of residual coal.

[0003] Low-temperature nitrogen has the dual purpose of inerting the goaf and reducing its temperature. Firstly, its low-temperature properties absorb heat from the coal within the goaf, lowering the coal temperature. Secondly, the nitrogen environment created by the low-temperature nitrogen prevents further oxidation and combustion of the coal, isolating and sealing the goaf, keeping the coal within oxygen-free for a period of time.

[0004] The macroscopic effect of low-temperature nitrogen on the goaf is manifested in its destruction of the temperature field and flow field in the goaf. At the same time, low-temperature nitrogen also has a certain impact on the coal in the goaf itself, causing changes in its oxidation and spontaneous combustion characteristics and performance, thereby promoting or inhibiting the macroscopic inhibitory effect of low-temperature nitrogen on spontaneous combustion in the goaf. Domestic and foreign scholars have done a lot of research on the evolution of coal spontaneous combustion structure, coal spontaneous combustion indicator gases, and coal spontaneous combustion characteristic stage analysis, providing an important scientific theoretical basis for the study of coal sample oxidation and spontaneous combustion. However, the pore and fracture structure of coal samples treated with low-temperature nitrogen for different times and temperatures, and its influence on the oxidation and spontaneous combustion characteristics and performance of coal samples need to be further improved. At present, most experimental methods use liquid nitrogen to treat coal samples, which cannot truly restore the actual state of low-temperature nitrogen injection in the goaf.

[0005] This shows that the prior art needs to be further improved. Summary of the Invention

[0006] The purpose of the present invention is to provide a method for simulating the spontaneous combustion law of coal left in goaf in a low-temperature nitrogen environment, which can more realistically simulate the spontaneous combustion law of coal left in goaf under the condition of injecting low-temperature nitrogen, and provide theoretical support for mine fire prevention and extinguishing work.

[0007] In order to achieve the above object, the present invention adopts the following technical solutions:

[0008] A method for simulating the spontaneous combustion law of coal left in a goaf in a low-temperature nitrogen environment. The simulation system adopted by the method includes a control box, an insulation box, a sample chamber and a nitrogen cylinder. The sample chamber has good airtightness and thermal conductivity. The insulation box is connected to a nitrogen injection pipeline, which is connected to the nitrogen cylinder and is used to provide room-temperature nitrogen into the insulation box. The sample chamber is equipped with an air inlet, an air outlet and a monitoring mechanism for monitoring temperature and pressure. The control box is used to control the parameter setting of the monitoring mechanism and the opening or closing of the nitrogen cylinder.

[0009] The simulation method comprises the following steps:

[0010] Step 1: Prepare coal samples by selecting fresh coal samples and pre-treating the outer oxide layer of the coal samples. After drying, the coal samples are ground and crushed to obtain coal powder with a particle size of 60 to 80 mesh as the coal samples.

[0011] Step 2: Lay dry ice on the bottom of the insulated box. After the laying is completed, keep the insulated box in a sealed state and pre-cool the insulated box with dry ice;

[0012] Step 3: Open the sample chamber, place the coal sample prepared in step 1 in the sample chamber, and introduce nitrogen into the sample chamber to fill it with nitrogen, ensuring that the sample is tested under oxygen-free conditions;

[0013] Step 4: Open the insulated box, place the sample chamber containing the coal sample in the insulated box, and continue to add dry ice into the insulated box until the sample chamber is completely covered;

[0014] Step 5: Observe the pressure and temperature readings of the sample bin through the monitoring mechanism. Start timing when the temperature of the sample bin drops to the temperature required for the experiment. Take out the coal sample after the specified time is reached.

[0015] Step 6. Obtain coal samples that have been treated for different times in a low-temperature nitrogen environment according to experimental requirements, and conduct analysis based on professional knowledge.

[0016] The above-mentioned method for simulating the spontaneous combustion law of coal residue in a goaf in a low-temperature nitrogen environment, the control box includes a box body, a control instrument and a control button. The actual conditions of the sample bin and the insulation box are observed by reading the control instrument, and the opening or closing of the nitrogen bottle is started or paused by the control button.

[0017] The above-mentioned method for simulating the spontaneous combustion law of coal residue in a goaf in a low-temperature nitrogen environment, the control instrument is located on the panel of the control box, the control instrument is an intelligent four-way controller, which is equipped with a temperature alarm device and a pressure alarm device; the control buttons include a main power button, a pressure display button, a temperature display button and a setting button.

[0018] The above-mentioned method for simulating the spontaneous combustion law of coal left in the goaf in a low-temperature nitrogen environment, the insulation box includes a box body and a box cover, the inner material of the box body is food-grade PP, the outer material of the box body is PE material, and a temperature sensor is configured in the insulation box.

[0019] In the above-mentioned method for simulating the spontaneous combustion law of coal left in goaf in a low-temperature nitrogen environment, the sample chamber is made of 304 stainless steel and is sealed by silica gel. The pressure range of the sample chamber is -0.09 to 1.6 MPa.

[0020] The above-mentioned method for simulating the spontaneous combustion law of coal residue in a goaf in a low-temperature nitrogen environment is as follows: the air inlet of the sample chamber is equipped with an air inlet angle valve, the exhaust port of the sample chamber is equipped with an exhaust angle valve, and the sample chamber is also equipped with three sensor interfaces, which are respectively connected to a pressure sensor, a second temperature sensor and a spare sensor.

[0021] The above-mentioned method for simulating the spontaneous combustion law of coal left in a goaf in a low-temperature nitrogen environment produces a coal sample with a mass of 5 to 10 g, a storage temperature of -50°C to -30°C, and a storage time of 0 to 10 hours.

[0022] Compared with the prior art, the present invention brings the following beneficial technical effects:

[0023] The present invention proposes a method for simulating the spontaneous combustion law of coal left in goaf in a low-temperature nitrogen environment. The method can realize low-temperature nitrogen treatment of coal samples through the cooperation of a control box, an insulation box, a sample bin and a nitrogen bottle.

[0024] The present invention proposes a method for simulating the spontaneous combustion law of coal left in goaf in a low-temperature nitrogen environment. First, room-temperature nitrogen is cooled to low-temperature nitrogen through an insulated box, and then the low-temperature nitrogen is injected into a sample chamber. The sample chamber always maintains a slightly positive pressure state to prevent carbon dioxide from entering the sample chamber and affecting the coal sample. The coal sample is in a low-temperature nitrogen environment, thereby achieving the purpose of low-temperature nitrogen treatment of the coal sample. The formed low-temperature nitrogen-treated coal sample can also be used for other experiments, and can also be combined with theoretical knowledge for analysis and research to study the influence of low-temperature nitrogen on the characteristic parameters of the coal sample.

[0025] The simulation system used in the present invention has good sealing properties, is easy to prepare coal samples, and has low production costs. The simulation method of the present invention can more realistically simulate the spontaneous combustion of coal in goafs under the conditions of low-temperature nitrogen injection, providing theoretical support for mine fire prevention and extinguishing work. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The present invention will be further described below with reference to the accompanying drawings:

[0027] Figure 1 A schematic structural diagram of the simulation system used in the present invention;

[0028] Figure 2 Schematic diagram of the structure of the sample bin of the present invention;

[0029] In the picture:

[0030] 1-Control box; 2-Insulation box; 3-Sample chamber; 4-Control instrument; 5-Main power button; 6-Pressure display button; 7-Temperature display button; 8-Set button; 9-Nitrogen injection pipeline; 10-Nitrogen cylinder; 11-Inlet angle valve; 12-Exhaust angle valve; 13-Temperature sensor 2; 14-Spare sensor; 15-Pressure sensor. DETAILED DESCRIPTION

[0031] The technical solutions in the embodiments of the present application will be described clearly and completely below in conjunction with the drawings in the embodiments of the present application.

[0032] It is understood that the connection relationships described in this application refer to direct or indirect connections. For example, the connection between A and B can be either a direct connection between A and B or an indirect connection between A and B via one or more other electrical components. For example, A and C can be directly connected, and C can be directly connected to B, so that A and B are connected through C. It is also understood that the description of "A connecting to B" in this application can be a direct connection between A and B or an indirect connection between A and B via one or more other electrical components.

[0033] In the description of this application, words such as "first" and "second" are used only to distinguish different objects and do not limit the quantity or execution order. In addition, words such as "first" and "second" do not necessarily mean different. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions.

[0034] The present invention proposes a method for simulating the spontaneous combustion law of coal left in goaf in a low-temperature nitrogen environment. The simulation system used is as follows: Figure 1 As shown, it includes a control box 1, an insulation box 2, a sample chamber 3 and a nitrogen cylinder 10.

[0035] The control box 1 includes a housing, a control instrument 4, and control buttons. The readings from the control instrument 4 allow the actual conditions of the sample chamber and insulated box to be observed, and the control buttons are used to start or pause the opening or closing of the nitrogen cylinder. The control instrument, located on the control box's panel, is an intelligent four-way controller that uses two-position and PID control. It is equipped with temperature and pressure alarms. The control buttons include a main power button 5, a pressure display button 6, a temperature display button 7, and a setting button 8. By switching between these buttons, the simulation system can be controlled. The pressure display button 6 and the temperature display button 7 are used to display the temperature and pressure parameters of the simulation system.

[0036] The insulated box is connected to a nitrogen injection pipe 9, which is connected to a nitrogen cylinder 10 for providing room temperature nitrogen to the insulated box. Dry ice is initially laid in the insulated box. After the sample compartment is placed in the insulated box, the dry ice covers the sample compartment. The insulated box includes a box body and a box cover. The inner material of the box is food-grade PP, and the outer material of the box is PE. A temperature sensor is provided in the insulated box. The insulation layer in the insulated box is made of six-sided PU with a thickness of 5mm or more. The inner dimensions of the box are 37cmx25cmx33cm.

[0037] like Figure 2 As shown, the sample chamber is equipped with an air inlet, an air outlet, and monitoring mechanisms for temperature and pressure. Sample chamber 3 has excellent airtightness and thermal conductivity. The main body is made of 304 stainless steel, has a quick-opening structure, and is sealed with silicone rubber, offering excellent airtightness and thermal conductivity. The sample chamber has a pressure resistance range of -0.09 to 1.6 MPa. The air inlet is equipped with an air inlet angle valve 11, the exhaust port is equipped with an exhaust angle valve 12, and three sensor interfaces, including one each for temperature, pressure, and backup sensors. The temperature sensor interface is connected to temperature sensor 2 13, the pressure sensor interface is connected to pressure sensor 15, and the backup sensor interface is connected to backup sensor 14.

[0038] The temperature sensor 1 located in the insulation box and the temperature sensor 2 on the sample chamber are of the same model, both are Pt100, with a temperature range of -50℃ to 200℃, a graduation of 0.1℃, a lead wire material of three-core silver-plated shielded wire, and a temperature sensor protection tube made of seamless 316 stainless steel.

[0039] The measuring range (gauge pressure) of the pressure sensor is 0~1MPa, the overload pressure is ≤ 2 times the upper limit of the measuring range, the nonlinearity is 0.25%, the repeatability is 0.1%, the hysteresis is 0.2%, the operating temperature range is -40℃~+85℃, the compensation temperature range is 0℃~50℃, and the shell protection level is IP54.

[0040] The coal sample selected in the present invention is a small volume coal sample with a particle size of 60 to 80 mesh or a small volume coal block and a mass of 5 to 10 g. The quantity that can be produced at one time is 5 to 10 portions, the storage temperature is -50°C to -30°C, and the storage time is 0 to 10 hours.

[0041] A method for simulating the spontaneous combustion law of coal left in a goaf in a low-temperature nitrogen environment comprises the following steps:

[0042] Step 1: Prepare coal samples by selecting fresh coal samples and pre-treating the outer oxide layer of the coal samples. After drying, the coal samples are ground and crushed to obtain coal powder with a particle size of 60 to 80 mesh as the coal samples.

[0043] Step 2: Lay dry ice on the bottom of the insulated box. After the laying is completed, keep the insulated box in a sealed state and pre-cool the insulated box with dry ice;

[0044] Step 3: Open the sample chamber, place the coal sample prepared in step 1 in the sample chamber, and introduce nitrogen into the sample chamber to fill it with nitrogen, ensuring that the sample is tested under oxygen-free conditions;

[0045] Step 4: Open the insulated box, place the sample chamber containing the coal sample in the insulated box, and continue to add dry ice into the insulated box until the sample chamber is completely covered;

[0046] Step 5: Observe the pressure and temperature readings of the sample bin through the monitoring mechanism. Start timing when the temperature of the sample bin drops to the temperature required for the experiment. Take out the coal sample after the specified time is reached.

[0047] Step 6. Obtain coal samples that have been treated for different times in a low-temperature nitrogen environment according to experimental requirements, and conduct analysis based on professional knowledge.

[0048] The present invention will be further described below with reference to specific embodiments.

[0049] Example 1:

[0050] A method for simulating the spontaneous combustion law of coal left in a goaf in a low-temperature nitrogen environment specifically comprises the following steps:

[0051] Step 1: Take fresh coal samples from the newly exposed coal wall of the working face, seal them on site and bring them to the laboratory. After grinding off the outer oxide layer of the coal samples and drying them, grind one part into several coal samples of 10mm×10mm×10mm; crush and sieve the other part, and select coal powder with a particle size of 60-80 mesh, all of which are used as experimental coal samples; divide the sieved coal samples into 5 parts, one part as the control group, and the rest are treated with low-temperature nitrogen.

[0052] Step 2: Check the simulation system to see if it is in good condition. Check all components of the simulation system to see if they are complete and intact. Check if the nitrogen cylinder has sufficient gas. Check if the insulated box and sample compartment are clean and free of contamination. Turn on the power and check if all buttons and switches are functioning properly. Check if the control instrument displays are normal.

[0053] Step 3: Place dry ice at the bottom of the insulated box and cover the box for pre-cooling.

[0054] Step 4: Open the sample bin, place the coal sample, close the sample bin cover, and seal it by tightening the quick-open screws (coal samples should be placed in the order of sampling, with those obtained later placed closer to the inside and those obtained earlier placed closer to the outside).

[0055] Step 5. Oxygen isolation operation of the sample chamber: (1) Connect the nitrogen pipeline, close the exhaust angle valve, close the intake angle valve, open the nitrogen bottle valve, and adjust the nitrogen pressure reducer to 0.1-0.2Mpa. (2) Open the intake angle valve, introduce nitrogen, wait until the pressure rises to 0.1Mpa, close the intake angle valve, let it stand for 5 seconds, and exhaust the gas to the sample chamber micro-pressure. (3) After repeating (2) operation 5 times, introduce nitrogen into the sample chamber, and close the intake angle valve to maintain the pressure when the pressure reaches 0.15-0.2Mpa.

[0056] Step 6. Place the sample chamber into the insulated box and continue to add dry ice until the sample chamber is completely covered.

[0057] Step 7. Observe the pressure and temperature readings in the sample chamber. Start timing when the temperature in the sample chamber drops to the required temperature (Note: During the cooling process, the pressure reading will drop. The sample chamber only needs to be maintained at a positive pressure without excessive pressure).

[0058] Step 8: When you need to collect coal samples at the designated time, wear protective gloves to prevent frostbite. To collect the coal sample, first open the exhaust angle valve to release the pressure, then open the quick-opening chamber cover and remove the coal sample. Depending on the experimental requirements, you can obtain samples of coal treated in a low-temperature nitrogen environment for different times and analyze them in conjunction with professional knowledge.

[0059] The coal samples were treated in a low-temperature nitrogen environment at different times, and the results are shown in Table 1.

[0060] Table 1

[0061]

[0062] In summary, the present invention provides a method for simulating the spontaneous combustion law of coal residue in goaf in a low-temperature nitrogen environment, which can more realistically simulate the spontaneous combustion law of coal residue under the condition of injecting low-temperature nitrogen into the goaf, and provide theoretical support for mine fire prevention and extinguishing work.

[0063] Parts not described in the present invention can be implemented by referring to the existing technology.

[0064] Those skilled in the art should recognize that the above embodiments are merely intended to illustrate the present application and are not intended to limit the present application. Any appropriate changes and modifications to the above embodiments should fall within the scope of protection of the claims of the present application as long as they are within the spirit of the present application.

Claims

1. A method for simulating the spontaneous combustion law of coal left in goaf in a low-temperature nitrogen environment, characterized in that: The simulation system used includes a control box, an insulation box, a sample chamber and a nitrogen cylinder. The sample chamber has good airtightness and thermal conductivity. The insulation box is connected to a nitrogen injection pipeline, which is connected to the nitrogen cylinder and is used to provide room-temperature nitrogen into the insulation box. The sample chamber is equipped with an air inlet, an air outlet and a monitoring mechanism for monitoring temperature and pressure. The control box is used to control the parameter settings of the monitoring mechanism and the opening or closing of the nitrogen cylinder. The simulation method comprises the following steps: Step 1: Prepare coal samples by selecting fresh coal samples and pre-treating the outer oxide layer of the coal samples. After drying, the coal samples are ground and crushed to obtain coal powder with a particle size of 60 to 80 mesh as the coal samples. Step 2: Lay dry ice on the bottom of the insulated box. After the laying is completed, keep the insulated box in a sealed state and pre-cool the insulated box with dry ice; Step 3: Open the sample chamber, place the coal sample prepared in step 1 in the sample chamber, and introduce nitrogen into the sample chamber to fill it with nitrogen, ensuring that the sample is tested under oxygen-free conditions; Step 4: Open the insulated box, place the sample chamber containing the coal sample in the insulated box, and continue to add dry ice into the insulated box until the sample chamber is completely covered; Step 5: Observe the pressure and temperature readings of the sample bin through the monitoring mechanism. Start timing when the temperature of the sample bin drops to the temperature required for the experiment. Take out the coal sample after the specified time is reached. Step 6. Obtain coal samples that have been treated for different times in a low-temperature nitrogen environment according to experimental requirements, and conduct analysis based on professional knowledge.

2. The method for simulating the spontaneous combustion of coal in a goaf in a low-temperature nitrogen environment according to claim 1, characterized in that: The control box includes a box body, a control instrument and a control button. The actual conditions of the sample chamber and the insulation box are observed through the readings of the control instrument, and the opening or closing of the nitrogen cylinder is started or paused through the control button.

3. The method for simulating the spontaneous combustion law of coal left in a goaf in a low-temperature nitrogen environment according to claim 2, characterized in that: The control instrument is located on the panel of the control box. The control instrument is an intelligent four-way controller, which is equipped with a temperature alarm device and a pressure alarm device; the control buttons include a main power button, a pressure display button, a temperature display button and a setting button.

4. The method for simulating the spontaneous combustion of coal in a goaf in a low-temperature nitrogen environment according to claim 1, characterized in that: The thermal insulation box includes a box body and a box cover. The inner material of the box body is food-grade PP, and the outer material of the box body is PE. A temperature sensor is configured in the thermal insulation box.

5. The method for simulating the spontaneous combustion law of coal left in a goaf in a low-temperature nitrogen environment according to claim 1, characterized in that: The sample chamber is made of 304 stainless steel and is sealed with silica gel. The pressure range of the sample chamber is -0.09 to 1.6 MPa.

6. The method for simulating the spontaneous combustion of coal in a goaf in a low-temperature nitrogen environment according to claim 4, characterized in that: The air inlet of the sample chamber is equipped with an air inlet angle valve, the exhaust port of the sample chamber is equipped with an exhaust angle valve, and the sample chamber is also equipped with three sensor interfaces, which are respectively connected to a pressure sensor, a second temperature sensor and a spare sensor.

7. The method for simulating the spontaneous combustion of coal in a goaf in a low-temperature nitrogen environment according to claim 1, characterized in that: The mass of the prepared coal sample is 5 to 10 g, the storage temperature is -50°C to -30°C, and the storage time is 0 to 10 hours.

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