Simulation method for spontaneous combustion law of residual coal in goaf in low-temperature nitrogen environment

Abstract

The invention discloses a simulation method for a spontaneous combustion rule of residual coal in a goaf in a low-temperature nitrogen environment, and relates to the technical field of coal spontaneous combustion rule research. An adopted simulation system comprises a control box, a heat preservation box, a sample bin and a nitrogen cylinder, the sample bin has good leakproofness and heat conductivity, the heat preservation box is connected with a nitrogen injection pipeline, and the nitrogen injection pipeline is connected with the nitrogen cylinder and used for providing normal-temperature nitrogen into the heat preservation box; the sample bin is provided with a gas inlet, a gas outlet and a monitoring mechanism for monitoring temperature and pressure; the control box is used for controlling parameter setting of the monitoring mechanism and opening or closing of the nitrogen cylinder; according to the system, coal samples of different treatment times in a low-temperature nitrogen environment are obtained according to experimental requirements, and analysis is carried out in combination with professional knowledge. According to the invention, the spontaneous combustion rule of residual coal under the condition that low-temperature nitrogen is injected into a goaf can be simulated more truly, and theoretical support is provided for mine fire prevention and extinguishing work.

Description

Technical Field

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

[0002] Spontaneous combustion of coal is one of the major hazards to the world's energy security and environment. The goaf of the working face is the key area where spontaneous combustion of coal occurs. To address this problem, nitrogen injection in the goaf has been widely used for fire prevention and extinguishing. However, when conventional room temperature nitrogen cannot achieve the effect of rapid fire prevention and extinguishing, low temperature nitrogen injection in the goaf is often used to reduce the risk of spontaneous combustion of the coal.

[0003] Low-temperature nitrogen has the dual functions of inerting the goaf and reducing the temperature of the goaf. On the one hand, the low-temperature characteristics of low-temperature nitrogen are used to absorb the heat of the coal body inside the goaf to reduce the coal temperature; on the other hand, the nitrogen environment formed by low-temperature nitrogen prevents the coal body from further oxidation and combustion, isolates and seals the goaf, and the internal coal body is in an oxygen-free state for a period of time.

[0004] The macroscopic effect of cryogenic nitrogen on the goaf is manifested in its destruction of the temperature field and flow field in the goaf. At the same time, cryogenic nitrogen also has a certain impact on the coal in the goaf, causing changes in its oxidation and spontaneous combustion characteristics and performance, which has a promoting or inhibiting effect on the macroscopic inhibitory effect of cryogenic 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 index gas, and coal spontaneous combustion characteristic stage analysis, which provides 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 cryogenic nitrogen at 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 treat coal samples with liquid nitrogen, 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 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 low-temperature nitrogen injection into the goaf, 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 residue in a goaf in a low-temperature nitrogen environment. The simulation system used includes a control box, an insulation box, a sample bin and a nitrogen bottle. The sample bin has good airtightness and thermal conductivity. The insulation box is connected to a nitrogen injection pipeline, which is connected to a nitrogen bottle and is used to provide room-temperature nitrogen to the insulation box. The sample bin 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.

[0009] The simulation method comprises the following steps:

[0010] Step 1: Prepare coal samples: select fresh coal samples and pre-treat the outer oxide layer of the coal samples, grind and crush them after drying to obtain coal powder with a particle size of 60 to 80 mesh as the coal sample;

[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 bin, place the coal sample prepared in step 1 in the sample bin, and introduce nitrogen into the sample bin to fill the sample bin with nitrogen, so as to ensure that the sample is tested under oxygen-free conditions;

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

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

[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 goaf in a low-temperature nitrogen environment, the control box includes a box body, a control instrument and a control button, the actual situation of the sample bin and the insulation box is observed through the readings of the control instrument, and the opening or closing of the nitrogen bottle is started or paused through 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 residue in a goaf in a low-temperature nitrogen environment, the thermal 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 thermal insulation box.

[0019] In the above-mentioned method for simulating the spontaneous combustion law of coal residue in goaf in a low-temperature nitrogen environment, the sample bin is made of 304 stainless steel and is sealed by silica gel, and the pressure resistance range of the sample bin 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, the air inlet of the sample bin is equipped with an air inlet angle valve, the exhaust port of the sample bin is equipped with an exhaust angle valve, and the sample bin 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 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, which 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 simulation method for 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 bin. The sample bin always maintains a slightly positive pressure state to prevent carbon dioxide from entering the sample bin 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 performance, easy coal sample preparation conditions and low production cost. The simulation method of the present invention can more realistically simulate the spontaneous combustion law of coal left under the condition of low-temperature nitrogen injection in the goaf, providing theoretical support for mine fire prevention and extinguishing work. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0027] Figure 1 It is a structural schematic diagram of the simulation system adopted by the present invention;

[0028] Figure 2 It is a schematic diagram of the structure of the sample bin of the present invention;

[0029] In the figure:

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

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

[0032] It is understandable that the connection relationship described in this application refers to direct or indirect connection. 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 through one or more other electrical components. For example, A and C can be directly connected, and C and B can be directly connected, so that A and B are connected through C. It is also understandable that the "A connects B" described in this application can be a direct connection between A and B, or an indirect connection between A and B through one or more other electrical components.

[0033] In the description of this application, words such as "first" and "second" are only used to distinguish different objects, and do not limit the quantity and execution order, and words such as "first" and "second" do not necessarily limit differences. 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 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 bottle 10.

[0035] The control box 1 includes a box body, a control instrument 4 and a control button. The actual conditions of the sample bin and the incubator are observed through the readings of the control instrument 4, and the opening or closing of the nitrogen cylinder is started or paused through the control button. The control instrument is located on the panel of the control box. The control instrument is an intelligent four-way controller. The control mode is two-position control and PID control. It is equipped with a temperature alarm device and a pressure alarm device. The control buttons include a main power button 5, a pressure display button 6, a temperature display button 7 and a setting button 8. The simulation system can be controlled by switching several different buttons. 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 incubator is connected to a nitrogen injection pipeline 9, which is connected to a nitrogen bottle 10 for providing room temperature nitrogen to the incubator. Dry ice is initially laid in the incubator, and after the sample bin is placed in the incubator, the dry ice covers the sample bin. The incubator 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 arranged in the incubator. The material of the insulation layer in the incubator is six-sided PU, and the PU thickness is ≥5mm. The inner size of the box is 37cmx25cmx33cm.

[0037] like Figure 2 As shown, the sample bin is equipped with an air inlet, an air outlet and a monitoring mechanism for monitoring temperature and pressure. The sample bin 3 has good airtightness and thermal conductivity. The main body is made of 304 stainless steel, with a quick-open structure and silicone seal, and has good airtightness and thermal conductivity. The pressure range of the sample bin is -0.09 to 1.6Mpa. An air inlet angle valve 11 is provided at the air inlet, an exhaust angle valve 12 is provided at the exhaust port, and there are three sensor interfaces, including a temperature sensor interface, a pressure sensor interface, and a spare sensor interface. The temperature sensor interface is connected to the temperature sensor 2 13, the pressure sensor interface is connected to the pressure sensor 15, and the spare sensor interface is connected to the spare sensor 14.

[0038] The temperature sensor 1 in the incubator and the temperature sensor 2 on the sample chamber are of the same model, both of which are Pt100, with a temperature range of -50°C to 200°C, a graduation of 0.1°C, 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 meshes 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 in goaf in a low-temperature nitrogen environment comprises the following steps:

[0042] Step 1: Prepare coal samples: select fresh coal samples and pre-treat the outer oxide layer of the coal samples, grind and crush them after drying to obtain coal powder with a particle size of 60 to 80 mesh as the coal sample;

[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 bin, place the coal sample prepared in step 1 in the sample bin, and introduce nitrogen into the sample bin to fill the sample bin with nitrogen, so as to ensure that the sample is tested under oxygen-free conditions;

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

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

[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 in conjunction with specific embodiments.

[0049] Embodiment 1:

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

[0051] Step 1. Take fresh coal samples from the coal wall just exposed at 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 as the control group, and the rest are treated with low-temperature nitrogen.

[0052] Step 2: Check whether the simulation system is intact, check whether all parts of the simulation system are complete and intact, check whether there is enough gas in the nitrogen bottle, and check whether the incubator and sample compartment are clean and pollution-free. Turn on the power and check whether all buttons and switches are normal; check whether the control instrument display is 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 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 for the pressure to rise to 0.1Mpa, close the intake angle valve, let it stand for 5 seconds, and exhaust the gas to the sample chamber with a slight 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, and start timing when the temperature in the sample chamber drops to the required temperature (Note: during the cooling process, the pressure reading will drop, and the sample chamber can be maintained at a positive pressure without excessive pressure).

[0058] Step 8. When it is time to take coal samples, you must wear protective gloves to prevent frostbite. When taking coal samples, first open the exhaust angle valve to discharge the pressure, then open the quick-opening compartment cover and take out the coal samples. According to the experimental requirements, you can obtain coal samples with different treatment times in a low-temperature nitrogen environment and analyze them in combination 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 low-temperature nitrogen injection 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 only used to illustrate the present application and are not intended to be limiting of the present application. As long as they are within the spirit of the present application, appropriate changes and modifications to the above embodiments should fall within the scope of protection of the claims of the present application.

Claims

1. A method for simulating the spontaneous combustion law of coal in goaf in a low-temperature nitrogen environment, characterized in that: The simulation system used includes a control box, an insulated box, a sample chamber and a nitrogen bottle. The sample chamber has good airtightness and thermal conductivity. The insulated box is connected to a nitrogen injection pipeline, which is connected to the nitrogen bottle and is used to provide room-temperature nitrogen to the insulated 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 simulation method comprises the following steps: Step 1: Prepare coal samples: select fresh coal samples and pre-treat the outer oxide layer of the coal samples, grind and crush them after drying to obtain coal powder with a particle size of 60 to 80 mesh as the coal sample; 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 bin, place the coal sample prepared in step 1 in the sample bin, and introduce nitrogen into the sample bin to fill the sample bin with nitrogen, so as to ensure that the sample is tested under oxygen-free conditions; Step 4: open the insulated box, place the sample bin containing the coal sample in the insulated box, and continue to add dry ice into the insulated box until the sample bin is completely covered; Step 5: Observe the pressure and temperature readings of the sample bin through the monitoring mechanism. When the temperature of the sample bin drops to the temperature required for the experiment, start timing. Take out the coal sample after the specified time of the experiment. 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 law of coal in goaf in a low-temperature nitrogen environment according to claim 1, characterized in that: The control box comprises a box body, a control instrument and a control button. The actual conditions of the sample bin and the incubator are observed through the readings of the control instrument, and the opening or closing of the nitrogen bottle is started or paused through the control button.

3. The method for simulating the spontaneous combustion law of coal in 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 law of coal in goaf in a low-temperature nitrogen environment according to claim 1, characterized in that: The thermal insulation box comprises 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 arranged inside the thermal insulation box.

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

6. The method for simulating the spontaneous combustion law of coal in goaf in a low-temperature nitrogen environment according to claim 4 is characterized in that: The air inlet of the sample chamber is equipped with an air inlet angle valve, the air outlet of the sample chamber is equipped with an air 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 law of coal in 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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