Filling mining method for reducing gas concentration of fully mechanized caving face based on coal-based activated carbon

Abstract

The invention provides a filling mining method for reducing gas concentration of a fully mechanized caving face based on coal-based activated carbon, which comprises the following steps of: firstly, testing and analyzing physical and mechanical parameters and lithologic characteristics of a coal rock layer in a mining area, and determining roadway width and coal pillar width for implementing strip mining at the top of an extra-thick coal seam; and further determining the mechanical mining height of top coal caving through a simulation method. In the strip mining implementation period, the mined coal is prepared into activated carbon with good mechanical strength and high gas adsorption performance, the activated carbon is filled into a strip roadway, in the fully mechanized caving mining process at the bottom of the ultra-thick coal seam, gas generated when top coal is broken and dropped can be adsorbed by the activated carbon on the upper portion, and the gas can be absorbed by the activated carbon on the lower portion. Meanwhile, the activated carbon and the coal flow can be discharged and recycled together, and by detecting the adsorption saturation of the activated carbon and implementing gas analysis, trapping of mine gas and cyclic utilization of the activated carbon are achieved. The method can effectively solve the problems of top coal crushing of the fully mechanized caving face and instantaneous gushing of a large amount of gas in the caving link.

Description

Technical Field

[0001] The present invention relates to the field of coal mining, and particularly to a filling mining method for reducing the gas concentration in the fully mechanized caving face based on coal-based activated carbon, which is particularly applicable to the fully mechanized caving face of extra-thick coal seams in high-gas and outburst mines with coal types having high fixed carbon content and low ash content. Background Art

[0002] In China, the reserves of extra-thick coal seams are rich. For the mining of extra-thick coal seams, the most commonly used method at present is the fully mechanized top coal caving mining method. However, due to the large one-time mining space and the large amount of caved coal, gas control has always been one of the main problems faced in the mining of fully mechanized caving faces. Especially for high-gas and outburst coal seams, due to the intermittency of top coal caving, the gas emission is extremely uneven, and a large amount of gas often gushes out instantaneously at the working face, resulting in frequent gas overrun and even mine disaster accidents.

[0003] At present, for the gas control of fully mechanized caving faces in extra-thick coal seams, mainly drilling drainage, roadway drainage and pipe drainage methods are adopted. According to statistics, only some mines with good drainage conditions and perfect technical equipment in China have a relatively high drainage rate of about 70%, while the gas drainage rate of most mines is about 30% - 50%. Therefore, even after gas drainage, there is still a large amount of gas in the coal body. For fully mechanized caving mining, the coal seam gas will be concentrated and released during the instant crushing and caving process of the top coal. In addition, for some coal seams with complex geological structures such as a large number of faults, folds, and fracture zones, during the construction of gas drainage boreholes, not only the borehole orientation needs to be repeatedly changed, resulting in increased borehole construction difficulty, but also the soft and broken fault planes, joint fissures, etc. are extremely likely to cause problems such as borehole deformation, collapse, and blockage, greatly affecting the drainage efficiency.

[0004] More importantly, for all current methods of gas control for fully mechanized caving faces in extra-thick coal seams, whether it is drainage control (drilling drainage, roadway drainage, pipe drainage), ventilation control, or auxiliary control measures such as pressure relief and permeability enhancement, they cannot effectively solve the problem of a large amount of gas gushing out during the top coal crushing and caving links. Summary of the Invention

[0005] The purpose of the present invention is to provide a filling mining method for reducing the gas concentration in the fully mechanized caving face based on coal-based activated carbon, which can effectively control the large amount of gas gushing out in the fully mechanized caving face of extra-thick coal seams, strongly improve the gas control level of high-gas and outburst coal seams, has great innovation and engineering significance, and broad application prospects.

[0006] In order to achieve the above-mentioned invention purpose, the technical solution adopted by the present invention is specifically as follows: The present invention provides a filling mining method for reducing the gas concentration in the fully mechanized caving face based on coal-based activated carbon, including the following steps:

[0007] Step 1: Drill and sample in the mining area, test and obtain the physical and mechanical parameters and lithological characteristics of the coal seam and the roof and floor rock strata. The physical and mechanical parameters include compressive strength, tensile strength, density, cohesion, internal friction angle, bulk modulus, and shear modulus. The lithological characteristics include the mineral components and contents of each rock stratum.

[0008] Step 2: Arrange strip mining areas at the top of the extra-thick coal seam, design the driving height of the strip roadways in the mining area, and determine the driving width of the strip roadways and the width of the coal pillars left.

[0009] Step 3: Through a combination of physical similarity simulation and numerical simulation, simulate the caving process of the top coal during fully mechanized top coal caving mining at the bottom of the extra-thick coal seam after strip mining is implemented at the top of the extra-thick coal seam, and determine the reasonable cutting height for fully mechanized top coal caving mining at the bottom of the extra-thick coal seam.

[0010] Step 4: Drive the strip roadways and prepare the mined raw coal into coal-based activated carbon with high gas adsorption performance. The preparation of the coal-based activated carbon includes washing and desliming, mixing and forming, staged carbonization, KOH-steam co-activation, pickling and purification, and surface ammoniation.

[0011] Step 5: After the strip roadways are driven, build a filling retaining wall at one end of the strip roadways, fill the prepared activated carbon into the strip roadways, compact the activated carbon to contact the roof. When the whole strip roadway is full, build a filling retaining wall for sealing.

[0012] Step 6: Arrange a fully mechanized top coal caving working face at the bottom of the extra-thick coal seam, adopt the coal caving technology of double-wheel sequential coal caving and coal caving every two cuts for mining, and control the coordinated discharge of activated carbon and coal body through the established coal-char-gangue identification system.

[0013] Step 7: Use the vacuum low-temperature desorption method to desorb the gas from the adsorption-saturated activated carbon, recover, remove impurities and purify the desorbed gas, and then use the gas for power generation or heating. The desorbed activated carbon is then continued to be used for filling and gas adsorption.

[0014] Preferably, in Step 2, the driving width a of the strip roadways and the width b of the coal pillars left are determined by the following formula:

[0015]

[0016] In the formula: a is the driving width of the strip roadways, m; b is the width of the strip coal pillars left, m; K is the safety factor; σ t is the tensile strength of the immediate roof, Pa; h is the roadway height, m; γ is the average unit weight of the overlying rock, N / m 3 ; H is the roadway mining depth, m; n is the load distribution coefficient of adjacent coal pillars in the coal pillar group; σ cis the uniaxial compressive strength of the direct roof, in Pa.

[0017] Preferably, in step four, the preparation method of the coal-based activated carbon includes:

[0018] a. Washing and deashing: Wash and remove impurities from the raw coal, then crush it into 1 - 3 mm coal powder, and reduce the ash content to 3 - 5% after acid washing and deashing;

[0019] b. Mixing and forming: Mix the coal powder with KOH and binder, and then form it into a cylindrical green body under high pressure with a density of 0.85 - 0.90 g / cm 3 , and then dry it to make the volatile matter < 5%;

[0020] c. Stepwise carbonization: Carry out stepwise temperature-rising carbonization on the cylindrical green body under nitrogen protection to form carbonized material;

[0021] d. KOH-steam co-activation: Immerse the carbonized material in KOH solution, and then activate it under the co-action of nitrogen and steam. After activation, cool it to room temperature to obtain activated carbon;

[0022] e. Acid washing purification and surface ammoniation: Carry out acid washing purification and surface ammoniation treatment on the activated carbon after activation.

[0023] Preferably, when mixing and forming, mix the coal powder, KOH and binder at 80 °C for 40 minutes, where the binder is coal tar, and the mass ratio of KOH to the carbonized material is 2:1 - 4:1.

[0024] Preferably, during stepwise carbonization, the carbonization is divided into three stages: a low-temperature stage of 350 °C, a medium-temperature stage of 600 °C and a high-temperature stage of 800 °C. The heating rate in each stage ≤ 5 °C / min and keep it at a constant temperature for 1 - 2 hours. After stopping heating, continue to introduce nitrogen until the temperature drops below 200 °C, and then cool it to room temperature naturally.

[0025] Preferably, during KOH-steam co-activation, place the carbonized material in KOH solution, stir and immerse it at room temperature for 12 - 24 h, then dry it at 80 °C and place it in a tube furnace, introduce nitrogen, heat it to 800 °C at a rate of 10 °C / min, keep it at a constant temperature for 1.5 h, and introduce steam for co-activation after the temperature reaches 450 °C. The steam flow rate is 1.2 L / min·kg.

[0026] Preferably, during pickling purification and surface ammoniation, the activated carbon is placed in a hydrochloric acid solution with a concentration of 3 mol / L, stirred at room temperature for 3 h, and then the activated carbon is repeatedly rinsed with a large amount of deionized water until the pH value of the filtrate is close to 7. Finally, the washed activated carbon is dried in an oven at 105-110 °C to a constant weight; the pickling-purified activated carbon is placed in a three-necked beaker, and 25% ammonia water by mass fraction is added to the beaker to make the liquid-solid ratio 3-8:1. Then, the stirring is started and heated to 70 °C. After reacting for 2-4 h, it is cooled to room temperature, rinsed with deionized water and dried to obtain surface-ammoniated activated carbon.

[0027] Preferably, in step six, the coal-char-gangue identification system includes: a UWB through-earth radar fixed at the front of the caving hydraulic support roof beam in fully mechanized caving mining for identifying the thickness of top coal and activated carbon, a vibration acceleration sensor installed on the coal-discharging chute for collecting the vibration signal of the discharged material, and a magnetostrictive displacement sensor installed on the tail beam and chute cylinder of the caving hydraulic support in fully mechanized caving mining for accurately controlling the action of the coal-discharging chute.

[0028] Preferably, in step five, when filling the activated carbon, the roof of the rib roadway is supported by threaded steel bolts, and the mine-use polyester fiber mesh is fixed on the roof of the roadway through the bolts. And when the width of the rib roadway is greater than 7 m, single hydraulic props are set along the center line of the rib roadway, and the filling operation is carried out synchronously on both sides of the props, and the single hydraulic props are withdrawn as the filling progresses.

[0029] Preferably, in step six, a rapid specific surface area and pore analyzer is used to detect the specific surface area and pore volume of the activated carbon. If the specific surface area value and pore volume value are significantly smaller than those of the activated carbon in the fully saturated state, it can continue to be used as a filling and gas adsorption material; if the specific surface area value and pore volume value are close to or equal to those of the activated carbon in the fully saturated state, it indicates that the activity has been adsorbed saturated, and the gas adsorbed by the activated carbon needs to be desorbed.

[0030] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0031] 1. The present invention first fills the activated carbon with high gas adsorption performance prepared in the top coal caving area of the fully mechanized caving face. Affected by mining, the gas released from the broken top coal flows upward along the fissures to the upper activated carbon filling area and is then adsorbed by the activated carbon. During the process of top coal caving, the activated carbon is in full contact with the broken coal body to further adsorb the gas in the coal body, which can effectively solve the problem of instantaneous large amount of gas gushing during the top coal breaking and caving process in the fully mechanized caving face. Moreover, the activated carbon adsorbed with gas is discharged and recovered together with the top coal. The gas can be collected and utilized through desorption, and the desorbed activated carbon can be filled into the coal seam again for gas adsorption.

[0032] 2. The method of filling activated carbon by excavating roadways can, on the one hand, play a role in pressure relief and permeability enhancement of the coal seam during roadway excavation, and on the other hand, filling activated carbon in the roadway can absorb the gas released from the coal seam in advance. At the same time, since the roadway is arranged at the coal-rock interface at the top of the coal seam, and the activated carbon filled in the roadway is a loose material, combined with the wire mesh and support on the roadway roof, it plays a role in coal-rock segmentation before mining, which is beneficial to the separation of coal and gangue and accurate coal caving during the coal caving process, and improves the extraction rate.

[0033] 3. Integrate and optimize the preparation process parameters of high-pressure forming, staged carbonization, and KOH-steam co-activation, and match the modification scheme of pickling purification and surface ammoniation to prepare block coal-based activated carbon with good mechanical strength and high gas adsorption capacity, which provides an important guarantee for improving the gas adsorption effect during the top coal caving process.

[0034] Therefore, whether this method is used alone or in combination with methods such as pre-drainage of coal seam gas, it can effectively control the large amount of gas gushing in the fully-mechanized caving face of extra-thick coal seams, strongly improve the gas control level of high-gas and outburst coal seams, and has great innovation and engineering significance and broad application prospects. Description of the Drawings

[0035] The drawings are used to provide a further understanding of the present invention and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the present invention and do not constitute a limitation to the present invention.

[0036] Figure 1 It is a plan view of mining strip coal pillars and filling activated carbon in the strip mining area provided by the present invention;

[0037] Figure 2 It is a sectional view of arranging a fully-mechanized caving face at the bottom of an extra-thick coal seam provided by the present invention;

[0038] Figure 3 It is a sectional view during the fully-mechanized caving mining process provided by the present invention;

[0039] Figure 4 It is a process flow diagram of the adsorption efficiency test of activated carbon provided by the present invention;

[0040] In the figures, 1 - haulage roadway, 2 - return airway, 3 - strip coal pillar, 4 - strip roadway, 5 - activated carbon, 6 - coal seam roof, 7 - coal seam floor, 8 - fully-mechanized caving hydraulic support, 9 - gangue, 10 - pressure reducing valve, 11 - steam bottle, 12 - buffer bottle, 13 - constant temperature water bath, 14 - tail gas purification pipe, 15 - adsorption column, 16 - gas chromatograph, 17 - gas storage tank. Detailed Embodiments

[0041] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Of course, the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0042] See Figures 1 - 3 , this embodiment provides a filling mining method for reducing the gas concentration in the fully-mechanized caving face based on coal-based activated carbon, including the following steps:

[0043] Step 1: Drill and sample the rock strata of the coal seam roof 6 and the coal seam floor 7 in the mining area, make the sampled coal and rock into standard specimens for physical and mechanical tests, and obtain the physical and mechanical parameters such as the compressive strength, tensile strength, density, cohesion, internal friction angle, bulk modulus and shear modulus of each rock stratum of the coal seam and the roof and floor.

[0044] Step 2: Arrange strip mining areas at the top of the extra-thick coal seam. The driving height of the strip roadway 4 in the mining area is designed to be 5 m. According to the mining geological conditions and the physical and mechanical test results, the tensile strength σ of the immediate roof t = 2×10 6 Pa; the roadway height h = 5 m; the average unit weight γ of the overlying rock = 25×10 3 N / m 3 ; the mining depth H = 300 m; the load distribution coefficient n of adjacent coal pillars in the coal pillar group = 1; the uniaxial compressive strength σ of the immediate roof c = 40×10 6 Pa. Taking the safety factor K = 2, the driving width a of the strip roadway 4 is calculated according to the following formula to be a ≤ 11.7 m, taking 10 m, and the width b of the strip coal pillar 3 is b ≥ 4.25 m, taking 5 m.

[0045]

[0046] Step 3: According to the determined mining height h = 5 m, mining width a = 10 m, and width b = 5 m of the strip coal pillar 3 of the strip roadway 4, combined with the physical and mechanical parameters and lithological characteristics such as mineral components and contents of each coal and rock stratum obtained by testing, the physical similarity simulation and numerical simulation methods are respectively used to simulate the top coal caving process of fully-mechanized top coal caving mining at the bottom of the extra-thick coal seam after the implementation of strip mining at the top of the extra-thick coal seam, and determine the reasonable mechanical mining height that can ensure that all the top coal including the strip coal pillar 3 is smoothly caved.

[0047] Step 4: Drive the transportation roadway 1, return airway 2, mining area cutting roadway and each strip roadway 4 in the strip mining area by using a continuous miner to cut coal, a shuttle car to transport coal, and a crusher to break coal, and transport the mined raw coal to the ground through a belt conveyor to prepare activated carbon 5 with high gas adsorption performance. The preparation method of the activated carbon 5 is as follows:

[0048] a. Washing and deashing: The raw coal is washed and purified and then crushed into 1 - 3 mm coal powder. The coal powder is soaked in 5% hydrofluoric acid for 24 hours, and then rinsed with deionized water until neutral, reducing the ash content to 3 - 5%.

[0049] b. Mixing and forming: The coal powder, KOH, and coal tar binder are mixed in a twin - shaft mixer at 80°C for 40 minutes, with the moisture content controlled at 12 - 15%. Then it is sealed and left for 24 hours to evenly distribute the moisture. A 50 MPa high - pressure molding machine is used to press the mixture into cylindrical blanks (hereinafter referred to as blanks) with a diameter of 100 mm and lengths ranging from 50 to 150 mm. The pressure - holding time is 3 minutes to ensure a density of 0.85 - 0.90 g / cm3, and then it is dried at 105°C for 12 hours to make the volatile matter < 5%.

[0050] c. Staged carbonization: The blanks are placed in a tubular furnace. The air in the furnace is replaced with nitrogen to ensure that the oxygen content is less than 1%. Then it is heated at a rate of 3°C / min to 350°C and held for 1 hour for low - temperature carbonization; then heated at a rate of 5°C / min to 600°C and held for 2 hours for medium - temperature carbonization; finally heated at a rate of 2°C / min to 800°C and held for 1 hour to achieve high - temperature carbonization. After stopping heating, nitrogen is continuously introduced until the temperature drops below 200°C, and then it is naturally cooled to room temperature.

[0051] d. KOH - steam co - activation: The carbonized material is placed in a KOH solution so that the mass ratio of the carbonized material to KOH is 1:2 - 1:4, and it is stirred and impregnated at room temperature for 12 - 24 h. Then it is dried at 80°C and placed in a tubular furnace. Nitrogen is introduced, and it is heated at a rate of 10°C / min to 800°C and held at a constant temperature for 1.5 h. During the heating process, when the temperature reaches 450°C, the steam generator is started, and steam is introduced into the tubular furnace at a flow rate of 1.2 L / min·kg to co - activate with the carbonized material containing KOH. After the activation is completed, it is cooled to room temperature to obtain activated carbon.

[0052] e. Acid washing purification and surface ammoniation: The activated carbon is placed in a hydrochloric acid solution with a concentration of 3 mol / L and stirred at room temperature for 3 h. Then the activated carbon is repeatedly rinsed with a large amount of deionized water until the pH value of the filtrate is close to 7. Finally, the washed activated carbon is placed in a drying oven at 105 - 110°C and dried to a constant weight; the acid - washed and purified activated carbon is placed in a three - necked flask, and 25% ammonia water with a mass fraction is added to the flask so that the liquid - solid ratio is 3 - 8:1. Then the stirring is started and heated to 70°C. After reacting for 2 - 4 h, it is cooled to room temperature, rinsed with deionized water and dried to obtain surface - ammoniated activated carbon 5.

[0053] Step 5: During the driving of the strip roadway 4, rib steel bolts are used to support the roof 6 of the roadway, and the mine-use polyester fiber mesh is fixed to the roof 6 of the roadway through the bolts. At the same time, a single hydraulic prop is driven every 2 m along the center line of the strip roadway to support the roof. After the driving of the strip roadway 4 is completed, a filling retaining wall is built at one end of the strip roadway 4, and a set of transportation and throwing filling system is arranged on both sides of the single hydraulic prop. The prepared activated carbon 5 is filled into the strip roadway 4 through a waste rock throwing machine, and then the activated carbon is compacted against the roof through a waste rock pushing mechanism. During the filling operation, the single hydraulic prop is withdrawn and recycled in time as the throwing machine moves backward. Finally, when the whole strip roadway 4 is full, a filling retaining wall is built for sealing.

[0054] Step 6: Repeat Step 5 to realize the driving and filling of all strip roadways 4 in the strip mining area.

[0055] Step 7: Drive a strip roadway at the bottom of the extra-thick coal seam, and arrange a longwall fully-mechanized top coal caving face. Make the working face advancing direction perpendicular to the driving direction of the strip roadway. The working face uses a fully-mechanized top coal caving hydraulic support 8, with an inserted plate type coal discharging. The cutting depth of the shearer is 0.865 m, and a coal discharging technology of double-wheel sequential coal discharging and discharging coal every two cuts is adopted.

[0056] Step 8: Establish a coal-char-gangue identification system for intelligent and accurate coal and char discharging. That is: use a bolt kit to fix the UWB through-earth radar on the front part of the top beam of the double-conveyor fully-mechanized top coal caving hydraulic support 8 for identifying the thickness of the top coal and activated carbon; install a vibration acceleration sensor on the coal discharging inserted plate, and provide a benchmark for terminating coal and char discharging by collecting the vibration signals of the discharged coal, activated carbon, and gangue 9; install a magnetostrictive displacement sensor on the tail beam and the inserted plate oil cylinder of the support 8 to achieve precise control of the movement of the coal discharging inserted plate.

[0057] Step 9: During the coal discharging process, the top coal and activated carbon 5 are discharged through the coal-char-gangue identification system, and the activated carbon 5 is transported back to the ground through a belt transportation system. Use a rapid specific surface area and pore volume analyzer to sample and detect the specific surface area and pore volume of the activated carbon 5. If the specific surface area value and pore volume value are significantly smaller than those of the activated carbon in the fully saturated state, the filling and gas adsorption utilization can continue; if the specific surface area value and pore volume value are close to or equal to those of the activated carbon in the fully saturated state, the gas desorption of the activated carbon 5 is carried out.

[0058] Step 10: Use the vacuum low-temperature desorption method to carry out gas desorption of the adsorption-saturated activated carbon 5, and recover, purify and refine the desorbed gas, and then use the gas for power generation or heating. The desorbed activated carbon 5 can continue to be used as a filling and gas adsorption material.

[0059] Performance detection:

[0060] The compressive strength test was carried out on the prepared activated carbon 5: Select the prepared block-shaped activated carbon, process it into standard specimens with a diameter of 50 mm and a height of 100 mm, and use an electro-hydraulic servo universal testing machine to conduct a uniaxial compressive strength test on it. A total of 5 groups of specimens were tested, and the test results were 27.7 MPa, 24.9 MPa, 29.6 MPa, 31.3 MPa, and 25.4 MPa respectively. The average compressive strength was 27.8 MPa, indicating that the prepared activated carbon has good mechanical strength.

[0061] The adsorption performance test was carried out on the prepared activated carbon, including specific surface area, pore structure, and methane adsorption efficiency tests. Among them, the specific surface area and pore structure were measured using a SA3100 rapid specific surface area and pore size analyzer produced by Beckman Coulter, Inc., USA. Specifically, at a constant temperature, the adsorption amount of activated carbon for methane gas at different relative pressures was measured, the adsorption isotherm curve was plotted, and based on this, the specific surface area was calculated using the standard BET method, the mesopore 2 - 50 nm distribution characteristics were obtained using the BJH method, and the micropore <2 nm distribution characteristics were obtained using the HK method.

[0062] The test results were as follows: The total specific surface area was 2779.2 m² / g, the specific surface area of micropores was 2106.6 m² / g, accounting for 75.8%; the specific surface area of mesopores was 664.2 m² / g, accounting for 23.9%. It can be seen that the prepared activated carbon has an ultra-high specific surface area and forms a micropore-mesopore hierarchical structure.

[0063] The test for methane adsorption efficiency was carried out using an isothermal adsorption experiment, as Figure 4 shown:

[0064] The equipment required for the isothermal adsorption experiment includes a pressure reducing valve 10, a steam bottle 11, a buffer bottle 12, a constant temperature water bath 13, an exhaust gas purification pipe 14, an adsorption column 15, a gas chromatograph 16, and a gas storage tank 17; the buffer bottle 12 and the adsorption column 15 are arranged in the constant temperature water bath 13. The pipelines at the outlets of the gas storage tank 17 and the steam bottle 11 are merged into the main pipeline and then connected to the buffer bottle 12. Pressure reducing valves 10 are provided on the pipelines at the outlets of the gas storage tank 17 and the steam bottle 11; the bottom of the adsorption column 15 is connected to the opening of the buffer bottle 12. A thermal conductivity detector of the gas chromatograph 16 is connected to the inlet and outlet of the adsorption column 15. At the same time, the outlet of the adsorption column 15 is connected to the exhaust gas purification pipe 14;

[0065] The prepared activated carbon was placed in the adsorption column 15. The gas storage tank 17 was filled with methane with a mass concentration of 3000 mg / m 3The methane gas, the flow rate of the methane gas is controlled to be 0.2 m / s by the pressure reducing valve 10 of the gas storage tank 17, the humidity of the methane gas is controlled to be 50% by the steam bottle 11 and the pressure reducing valve 10, the temperature of the room temperature and the constant temperature water bath 13 is 20 °C, and a thermal conductivity detector of a gas chromatograph 16 is connected to the inlet and outlet of the adsorption column 15 to detect the change law of the gas mass concentration at the inlet and outlet of the adsorption column 15, so as to calculate the adsorption efficiency as follows:

[0066]

[0067] In the formula, η is the adsorption efficiency, %; ρ0 and ρ are the mass concentrations of methane gas before and after adsorption by activated carbon, mg / m 3 . During the test process, the methane gas enters the activated carbon adsorption column through the buffer bottle 12 in the environment of the constant temperature water bath, and the gas after adsorption enters the tail gas purification pipe 14 for treatment.

[0068] A total of 5 groups of adsorption tests were carried out this time. The measured adsorption efficiencies of the activated carbon were: 92.3%, 94.7%, 93.0%, 95.3%, 94.8%, and the average adsorption efficiency was 94.0%. It can be seen that under the test conditions similar to the coal mine underground mining conditions, the prepared activated carbon has excellent adsorption capacity for methane.

[0069] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A filling mining method for reducing the gas concentration in the fully-mechanized caving face based on coal-based activated carbon, characterized in that, It includes the following steps: Step 1: Drill and sample in the mining area, test and obtain the physical and mechanical parameters and lithological characteristics of the coal seam and the roof and floor rock strata. The physical and mechanical parameters include compressive strength, tensile strength, density, cohesion, internal friction angle, bulk modulus, and shear modulus. The lithological characteristics include the mineral components and contents of each rock stratum; Step 2: Arrange a strip mining area at the top of the extra-thick coal seam, design the driving height of the strip roadway in the mining area, and determine the driving width of the strip roadway and the width of the coal pillar left; Step 3: Through the combination of physical similarity simulation and numerical simulation, simulate the top coal caving process of fully mechanized top coal caving mining at the bottom of the extra-thick coal seam after strip mining is implemented at the top of the extra-thick coal seam, and determine the reasonable mechanized mining height of fully mechanized top coal caving mining at the bottom of the extra-thick coal seam; Step 4: Drive the strip roadway and prepare the extracted raw coal into coal-based activated carbon with high gas adsorption performance. The preparation of the coal-based activated carbon includes washing and deashing, mixing and forming, staged carbonization, KOH-steam co-activation, pickling purification, and surface ammoniation; Step 5: After the strip roadway driving is completed, build a filling retaining wall at one end of the strip roadway, fill the prepared activated carbon into the strip roadway, compact the activated carbon to contact the roof. When the whole strip roadway is full, build a filling retaining wall for sealing; Step 6: Arrange a fully mechanized top coal caving working face at the bottom of the extra-thick coal seam, adopt the coal caving technology of double-wheel sequential coal caving and coal caving every two cuts for mining, and control the coordinated discharge of activated carbon and coal body through the established coal-char-gangue identification system; Step 7: Use the vacuum low-temperature desorption method to carry out gas desorption on the adsorption-saturated activated carbon, recover, remove impurities, and purify the desorbed gas, and then use the gas for power generation or heat supply. The desorbed activated carbon is then continued to be used for filling and gas adsorption.

2. The method according to claim 1, characterized in that In Step 2, the driving width a of the strip roadway and the width b of the coal pillar left are determined by the following formula: Where: a is the driving width of the strip roadway, m; b is the width of the strip coal pillar left, m; K is the safety factor; σ t is the tensile strength of the immediate roof, Pa; h is the roadway height, m; γ is the average unit weight of the overlying strata, N / m 3 ; H is the mining depth of the roadway, m; n is the load distribution coefficient of adjacent coal pillars in the coal pillar group; σ c is the uniaxial compressive strength of the immediate roof, Pa.

3. The method according to claim 1, wherein In Step 4, the preparation method of the coal-based activated carbon includes: a. Washing and deashing: Wash and remove impurities from the raw coal and then crush it into 1-3 mm coal powder. After pickling and deashing, the ash content is reduced to 3-5%; b. Mixing and forming: Mix pulverized coal with KOH and a binder, and then form it into a cylindrical green body under high pressure with a density of 0.85 - 0.90 g / cm 3 , and then dry it to make the volatile matter < 5%; c. Staged carbonization: Carry out stepwise temperature rise carbonization on the cylindrical blank under nitrogen protection to form carbonized material; d. KOH-steam co-activation: Immerse the carbonized material in KOH solution and activate it under the co-action of nitrogen and steam. After the activation is completed, cool it to room temperature to obtain activated carbon; e. Pickling purification and surface ammoniation: Carry out pickling purification and surface ammoniation treatment on the activated carbon after activation.

4. The method according to claim 3, wherein When mixing and forming, mix the coal powder, KOH, and binder at 80 °C for 40 minutes. The binder is coal tar, and the mass ratio of KOH to the carbonized material is 2:1-4:

1.

5. The method according to claim 3, characterized in that When carrying out staged carbonization, the carbonization is divided into three stages: a low-temperature stage of 300-400 °C, a medium-temperature stage of 500-700 °C, and a high-temperature stage of 750-850 °C. The heating rate in each stage ≤ 5 °C / min and keep it constant for 1-2 hours. After stopping heating, continue to introduce nitrogen until the temperature drops below 200 °C, and then naturally cool to room temperature.

6. The method according to claim 3, wherein During the KOH-steam co-activation process, the carbonized material is placed in a KOH solution and stirred and impregnated at room temperature for 12 to 24 hours. Then it is dried at 80°C and placed in a tubular furnace. Nitrogen is introduced, and the temperature is raised to 800°C at a rate of 10°C / min and kept constant for 1.5 hours. After the temperature reaches 450°C, steam is introduced for co-activation, and the steam flow rate is 1.2 L / min·kg.

7. The method according to claim 3, characterized in that, During pickling purification and surface ammoniation, the activated carbon is placed in a hydrochloric acid solution with a concentration of 3 mol / L and stirred at room temperature for 3 hours. Then the activated carbon is repeatedly rinsed with a large amount of deionized water until the pH value of the filtrate is close to 7. Finally, the washed activated carbon is dried in an oven at 105 - 110°C until a constant weight is achieved. The pickling-purified activated carbon is placed in a three-necked flask, and 25% ammonia water by mass is added to the flask to make the liquid-solid ratio 3 - 8:

1. Then the stirring is started and heated to 70°C. After reacting for 2 - 4 hours, it is cooled to room temperature, rinsed with deionized water and dried to obtain surface-ammoniated activated carbon.

8. The method according to claim 1, wherein In step six, the coal-carbon-gangue identification system includes: a UWB through-the-earth radar fixed at the front of the top beam of the fully-mechanized caving hydraulic support for identifying the thickness of the top coal and activated carbon, a vibration acceleration sensor installed on the coal-discharging chute for collecting the vibration signals of the discharged materials, and a magnetostrictive displacement sensor installed on the tail beam and the chute cylinder of the fully-mechanized caving hydraulic support for precisely controlling the movement of the coal-discharging chute.

9. The method according to claim 1, wherein In step five, when filling the activated carbon, threaded steel bolts are used to support the roof of the strip roadway, and the mine-used polyester fiber mesh is fixed to the roadway roof through the bolts. When the width of the strip roadway is greater than 7 m, single hydraulic props are set along the center line of the strip roadway, and the filling operation is carried out synchronously on both sides. The single hydraulic props are withdrawn as the filling progresses.

10. The filling mining method according to claim 1, characterized in that, In step six, a rapid specific surface area and pore analyzer is used to detect the specific surface area and pore volume of the activated carbon. If the specific surface area value and pore volume value are significantly smaller than those of the activated carbon in the fully saturated state, it can continue to be used as a filling and gas adsorption material; if the specific surface area value and pore volume value are similar to or equal to those of the activated carbon in the fully saturated state, it indicates that the activity has been adsorbed saturated, and the gas adsorbed by the activated carbon needs to be desorbed.

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