A two-step strong and weak filling method of continuous mining and continuous filling with biomass ash combined with carbon sequestration

Abstract

The present invention discloses a two-step, strong and weak filling method for continuous mining and filling with biomass ash and carbon sequestration. In the first filling step, biomass ash is used to replace cement or fly ash to increase the strength of the filling body and form a strong filling. In the second filling step, carbon dioxide is simultaneously injected to create a carbon sequestration cavity, forming a weak filling. Both filling steps adopt a full filling method, requiring the filling slurry to connect with the roof. The present invention adopts an alternating arrangement of strong and weak filling, effectively sealing and sealing carbon dioxide while strictly ensuring the safety and stability of the overburden above the mining site. It also recycles biomass ash solid waste, reduces material preparation and carbon sequestration costs, and improves economic and social benefits.

Description

Technical Field

[0001] The invention relates to a two-step strong and weak filling method for continuous mining and filling with biomass ash and carbon sequestration, belonging to the technical field of coal mine cementation filling. Background Art

[0002] In recent years, with the introduction of the "dual carbon" goals, carbon sequestration technology has regained attention and has developed rapidly. Carbon sequestration technology involves the safe storage of carbon dioxide in a certain enclosed space to prevent its release into the atmosphere and the greenhouse effect. The underground goaf created by coal mining methods is a suitable storage space, but traditional caving mining inevitably causes rock cracking, making it difficult to store gas. Therefore, it is necessary to combine cemented filling mining technology to maintain the safety and stability of the goaf. In addition, the filling pipes used in cemented filling can also provide a convenient injection path for underground carbon dioxide storage.

[0003] Cemented filling is a filling mining method that is currently widely used in the coal mining field. It is a method of forming a filling slurry by mixing the solid waste by-products (i.e., coal gangue and fly ash) generated during the mining and combustion of coal resources with cement and water. The slurry is pumped into the underground goaf along a pre-installed filling pipeline, where it solidifies into a cemented filling body to support the movement and deformation of the overburden in the mining area. It has significant economic and social benefits for protecting the surface and other ecological environments. At present, there are two technologies: longwall fully mechanized mining frame followed by cemented filling (Zhang Jixiong, Yan Hao, Zhou Nan, et al. A longwall fully mechanized mining cemented filling device and method for near-horizontal coal seams [P]. CN108468565B, 2020-07-17.) and full negative pressure continuous mining and continuous filling cemented filling (Li Yongliang, Lu Bin, Yang Renshu, et al. Coal mine continuous mining and continuous filling cemented filling mining technology and typical engineering cases [J]. Journal of China Coal Society, 2022, 47(03):1055-1071.). The former requires a large capital investment and may cause the "frame pressure" phenomenon, which has certain limitations. Therefore, the continuous mining and continuous filling cemented filling mining process is usually adopted, and the mining is carried out in two steps (i.e., mining one every other step).

[0004] Combined with the previous research results of the inventors ([1] Qi T, Wang H, Feng G, et al. Effects ofCorn Stalk Fly Ash (CSFA) on the Mechanical and Deformation Properties ofCemented Coal Gangue Backfill[J]. Advances in Materials Science andEngineering, 2020, 2020: 7421769. [2] Wang H, Qi T, Feng G, et al. Effect ofpartial substitution of corn straw fly ash for fly ash as supplementarycementitious material on the mechanical properties of cemented coal ganguebackfill[J]. Construction and Building Materials, 2021, 280: 122553.), it can be seen that recycling the solid waste by-product after combustion and power generation in biomass power plants - biomass ash, to replace part of the cement or fly ash in the raw materials used in the preparation of coal mine cementitious backfill materials can effectively improve their compressive strength and reduce the preparation cost of the materials. It is the only choice for creating a "strong filling" environment. Therefore, in the present invention, a novel two-step strong and weak filling method of continuous mining and filling is proposed by adopting the idea of combining biomass ash with carbon sequestration. Summary of the Invention

[0005] The present invention aims to provide a two-step strong and weak filling method for continuous mining and filling with biomass ash and carbon sequestration. In the continuous mining and filling process, strong and weak filling are arranged alternately. While effectively sealing and sealing carbon dioxide, the safety and stability of the overburden above the mining site are strictly guaranteed, and biomass ash solid waste is recycled and utilized, thereby reducing the cost of material preparation and carbon sequestration, and improving economic and social benefits.

[0006] The concept of the present invention is as follows: During the continuous mining and continuous filling two-step cemented filling process, if carbon dioxide is injected, it will inevitably lead to an increase in the internal porosity of the filling body and a decrease in strength, which will be detrimental to the support of the overburden above the mining site and make it difficult to maintain the stability of the goaf and the ground surface. Therefore, the carbon sequestration filling can only be set in the second filling step, but at the same time, the compressive strength of the first filling step must also be increased to comprehensively guarantee the bearing effect of the filling body, and no additional capital investment can be added. The present invention adopts the idea of combining biomass ash with carbon sequestration to propose a new type of continuous mining and continuous filling two-step strong and weak filling method. In the first filling step, biomass ash is used to replace cement or fly ash to increase the strength of the filling body and form a strong filling. In the second filling step, carbon dioxide is injected simultaneously to create a carbon sequestration cavity and form a weak filling. Both steps of filling adopt a full filling method, which requires the filling slurry to be connected to the roof. The first step is to monitor the surface deformation after filling to ensure that it is less than the Level I mining damage index in the "Specifications for Coal Pillar Retention and Compression Coal Mining in Buildings, Water Bodies, Railways and Main Shafts and Tunnels".

[0007] The present invention provides a two-step strong and weak filling method for continuous mining and filling of biomass ash combined with carbon sequestration, the specific steps of which are as follows:

[0008] 1) Arrange the working face tunnels: According to the tunnel layout of longwall fully mechanized mining, excavate the return air level tunnel, transport level tunnel, and cut holes in advance to form full negative pressure ventilation at the working face. The working face length is designed to be 50-200 m.

[0009] 2) Collect filling raw materials: Collect coal gangue, fly ash, biomass ash, and cement. Crush the coal gangue and sieve it into fine gangue with a particle size of 0-5 mm, medium gangue with a particle size of 5-10 mm, and coarse gangue with a particle size of 10-15 mm. Pass the fly ash and biomass ash through a 1 mm sieve to remove impurities.

[0010] 3) Divide and mine branch lanes at intervals: Divide the coal seam to be mined in the working face into several branch lanes at intervals of 4 to 6 meters parallel to the direction of the cut. Deploy continuous miners, bolting trolleys, and loaders to mine the branch lanes at intervals.

[0011] 4) The first step is preparation before filling: Place blocking templates or hoist filling bags at both ends of the mined branch tunnels, lay filling pipes in the return air level tunnels and branch tunnels, and check the installation to ensure correct connections;

[0012] 5) Prepare biomass ash filling slurry and perform the first filling: biomass ash accounts for 7% to 10% by weight, cement accounts for 7% to 8% by weight, fly ash accounts for 12% to 15% by weight, fine gangue accounts for 12% to 18% by weight, medium gangue accounts for 14% to 21% by weight, coarse gangue accounts for 14% to 21% by weight, and water accounts for 16% to 24% by weight. After mixing and stirring evenly, pump the mixture through pipelines to fill the mined branch tunnels, completing the first filling step;

[0013] 6) Maintain the backfill and monitor ground deformation: Maintain the backfill for 7 to 28 days, and monitor the ground deformation in the mining area in real time. When the backfill strength is no less than 4 MPa and the ground deformation is stable within the Class I mining damage index specified in the "Specifications for Coal Pillar Retention and Compressed Coal Mining in Buildings, Water Bodies, Railways, and Main Wells and Lanes," the first step of backfill is considered to have achieved strong backfill.

[0014] 7) Mining out the coal from the unmined branch tunnels: deploying continuous miners, anchor trolleys, and loaders. Under the strong filling support of the first filling step, the interval coal pillars that were not mined in step (3) are mined out to form filling space for the second filling step.

[0015] 8) Carbon dioxide capture: Collect carbon dioxide from the exhaust of thermal power plants or biomass power plants and store it in cylinders through pipes;

[0016] 9) Step 2: Preparation before filling: Place blocking templates or hoist filling bags at both ends of the mined branch tunnels, strictly seal the gaps between the top and bottom templates and the roof and floor plates, place CO2 alarms and CO2 absorbers on the blocking templates or filling bags to ensure strict CO2 sealing, and check that the filling pipes in the return air tunnel and branch tunnels are connected correctly.

[0017] 10) Prepare filling slurry for the second filling step and simultaneously inject carbon dioxide: cement accounts for 5% to 10% by weight, fly ash accounts for 20% to 30% by weight, fine gangue accounts for 12% to 18% by weight, medium gangue accounts for 14% to 21% by weight, coarse gangue accounts for 14% to 21% by weight, and water accounts for 15% to 20% by weight. After mixing and stirring evenly, pump it through the pipeline to fill the mining branch lane. Carbon dioxide is simultaneously released from the cylinder and injected into the filling pipeline through the catheter. The injection pressure is 0.1 to 0.5 MPa. Injection is stopped after the carbon dioxide alarm is activated;

[0018] The working face is fully mined and filled. The biomass ash filling body filled in the first step and the carbon sequestration filling body filled in the second step are arranged alternately. The biomass ash filling body filled in the first step builds a strong filling support environment, and cooperates with the carbon sequestration filling body with relatively weak mechanical properties filled in the second step to ensure the safety and stability of the overburden above the mining area.

[0019] Weak backfill, due to its inherently large carbon dioxide content and numerous internal pores, has relatively weak mechanical properties. Weak backfill primarily serves to sequester carbon and can also complement biomass ash backfill to achieve a synergistic load-bearing effect. The injection of carbon dioxide has no impact on the backfill pipeline or goaf.

[0020] The concepts of strong and weak filling are relative. Their primary purpose is to achieve the cost-effectiveness and multifunctionality of cemented filling in coal mines, thereby facilitating the promotion and advancement of coal mine filling mining technology. As long as the first step of filling meets the requirements for strong filling, that is, the filling body's condensation strength is not less than 4 MPa and the surface deformation is stable within the Class I mining damage index specified in the "Specifications for the Installation of Coal Pillars and Compressed Coal Mining for Buildings, Water Bodies, Railways, and Major Wells and Tunnelings," the second step of filling can be implemented as weak filling with other functions, not just carbon sequestration, such as storing oil and gas resources, storing nuclear waste, and constructing underground space.

[0021] In the above method, the biomass ash can be one or more of rice husk ash, bagasse ash, poplar leaf ash, willow leaf ash, and corn straw ash, and can be obtained by collecting after natural incineration or directly collecting from a biomass power plant.

[0022] In the above method, the water can be domestic water or mine water, the cement can be ordinary silicate 425# cement, and the fly ash can be Class F II fly ash.

[0023] Beneficial effects of the present invention:

[0024] (1) Storing carbon dioxide can slow global warming, and injecting it into the pipeline can reduce the cost of carbon storage and improve economic and social benefits;

[0025] (2) Recycling and utilizing biomass ash solid waste can solve problems such as land occupation and environmental pollution, and provide a "strong filling" supporting environment for carbon sequestration;

[0026] (3) Biomass ash combined with carbon sequestration forms a pattern of alternating strong and weak filling, which can effectively ensure the safety and stability of the overburden above the stope, realize the multifunctionality of coal mine cement filling, and facilitate its promotion and application in actual mining projects. This invention has important strategic significance for the realization of the "dual carbon" goals and the advancement of the multifunctionality of coal mine cement filling mining technology. It can also provide certain guidance and reference for the efficient utilization of underground space. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 The working face tunnel and mining sequence layout diagram of the method of the present invention;

[0028] In the figure: 1. Return air tunnel; 2. Transport tunnel; 3. Cutting eye; 4. Mining branch tunnel; 5. Mining branch tunnel. DETAILED DESCRIPTION

[0029] The present invention is further illustrated below by way of examples, but is not limited to the following examples.

[0030] Example 1:

[0031] (1) Arrangement of working face tunnels: According to the tunnel arrangement of longwall fully mechanized mining, the return air level tunnel 1, the transport level tunnel 2, and the cutting hole 3 are excavated in advance, and the working face is fully negatively ventilated. The working face length is designed to be 100 m.

[0032] (2) Calculation of filling system capacity: The filling system capacity required is mainly determined by the length of the filling working face, mining height, filling step distance, mining-filling ratio and the time required to complete the filling operation. The calculation formula is as follows:

[0033] (1)

[0034] Where, Q f ——Filling capacity, m 3 / h;

[0035] L ——coal wall length of working face, m;

[0036] M ——mining height, m;

[0037] d ——Filling step distance, m;

[0038] k f ——production-to-fill ratio;

[0039] S 1——cross-sectional area of the transport road on the working face, m 2 ;

[0040] S 2——cross-sectional area of material channel on the working face, m 2 ;

[0041] T f ——Effective filling time, h;

[0042] k p ——Filling pump efficiency coefficient.

[0043] (3) Collect filling raw materials: Collect coal gangue, fly ash, biomass ash, and cement. Crush the coal gangue and sieve it into fine gangue with a particle size of 0-5 mm, medium gangue with a particle size of 5-10 mm, and coarse gangue with a particle size of 10-15 mm. Fly ash and biomass ash are sieved through a 1 mm sieve to remove impurities.

[0044] (4) Divide and mine branch tunnel 4 at intervals: Divide the coal seam to be mined in the working face into several branch tunnels at intervals of 5 m along the direction parallel to the cutting hole 3, and deploy continuous miners, anchor trolleys, and loaders to mine branch tunnel 4 at intervals;

[0045] (5) The first step is preparation before filling: Place blocking templates or hoist filling bags at both ends of the mined branch tunnel, lay filling pipelines in the return air tunnel 1 and the mining branch tunnel 4, and check the installation to ensure that the connection is correct;

[0046] (6) Prepare biomass ash filling slurry and perform the first filling: biomass ash accounts for 10% by weight, cement accounts for 8% by weight, fly ash accounts for 12% by weight, fine gangue accounts for 15% by weight, medium gangue accounts for 17% by weight, coarse gangue accounts for 18% by weight, and water accounts for 20% by weight. After mixing and stirring evenly, pump it through a pipeline to fill the mined branch tunnel 4, completing the first filling step;

[0047] (7) Maintain the filling body and monitor the surface deformation: Maintain the filling body for 14 days and monitor the surface deformation of the mining area in real time. When the filling body has a coagulation strength of not less than 4 MPa and the surface deformation is stable within the range of the Class I mining damage index specified in the "Specifications for the Retention of Coal Pillars and Compressed Coal Mining in Buildings, Water Bodies, Railways and Main Wells and Tunnelings", the first step of filling is considered to have achieved strong filling.

[0048] (8) Probability integral method for estimating surface deformation: The probability integral method uses the normal distribution function as the influencing function and uses an integral formula to represent surface subsidence. It is also the only prediction method written into the "Specifications for the Installation of Coal Pillars and Compressed Coal Mining in Buildings, Water Bodies, Railways and Major Wells and Tunnelings". It has the characteristics of clear physical meaning of the prediction parameters, high prediction accuracy when the parameters are selected appropriately, and easy use of computers to realize automatic calculations. The prediction mathematical model is as follows:

[0049] (2)

[0050] Where, W cm —the maximum subsidence value after full mining of the surface;

[0051] r —Main impact radius;

[0052] D - mining area;

[0053] x,y ——Relative coordinates of the calculation point.

[0054] Maximum sinking value W cm Use the following formula to calculate:

[0055] (3)

[0056] Where, M c ——equivalent mining thickness, mm;

[0057] q —the subsidence coefficient when fully mined;

[0058] ——Inclination of coal seam.

[0059] Equivalent mining thickness M c Calculate according to the following formula:

[0060] (4)

[0061] Where, B —Shrinkage rate of filling material;

[0062] h f ——Amount of insufficient filling, mm, and , A The degree of unfilling;

[0063] M ——coal seam mining thickness, mm;

[0064] h m ——Amount of top and bottom plates moved closer before filling, mm.

[0065] (9) Mining out the coal from the unmined branch tunnels: deploy continuous miners, anchor trolleys, and loaders. Under the strong filling support of the first filling step, the interval coal pillars that were not mined in step (3) are mined out to form filling space for the second filling step.

[0066] (10) Carbon dioxide capture: Collect carbon dioxide from the exhaust of thermal power plants or biomass power plants and store it in cylinders through pipes;

[0067] (11) The second step is preparation before filling: Place plugging templates or hoist filling bags at both ends of the mining branch tunnel 5, strictly seal the gaps between the upper and lower templates and the top and bottom plates, place carbon dioxide alarms and carbon dioxide absorbers on the plugging templates or filling bags to achieve strict sealing of carbon dioxide, and check that the filling pipelines in the return air tunnel 1 and the mining branch tunnel 5 are connected correctly;

[0068] (12) Prepare filling slurry for the second filling step and inject carbon dioxide simultaneously: cement accounts for 10% by weight, fly ash accounts for 20% by weight, fine gangue accounts for 15% by weight, medium gangue accounts for 17% by weight, coarse gangue accounts for 18% by weight, and water accounts for 20% by weight. After mixing and stirring evenly, pump it through the pipeline to fill the mining branch tunnel 5. Carbon dioxide is simultaneously released from the cylinder and injected into the filling pipeline through the catheter. The injection pressure is 0.1~0.5 MPa. The injection is stopped after the carbon dioxide alarm is awakened.

[0069] Biomass ash, combined with carbon sequestration, creates an alternating pattern of strong and weak filling, effectively ensuring the safety and stability of the overburden above the stope. This multifunctionalization of coal mine cementing and filling is beneficial for its application in actual mining projects. This invention has important strategic significance for achieving the "dual carbon" goals and advancing the multifunctionalization of coal mine cementing and filling mining technology. It can also provide guidance and reference for the efficient utilization of underground space.

Claims

1. A two-step strong and weak filling method for continuous mining and filling of biomass ash combined with carbon sequestration, characterized by: In the first filling step, biomass ash is used to replace cement or fly ash to improve the filling strength and form a strong filling. In the second filling step, carbon dioxide is injected simultaneously to create a carbon sequestration cavity and form a weak filling. Both filling steps adopt the full filling method, requiring the filling slurry to be connected to the roof. The two-step strong and weak filling method of continuous mining and filling of biomass ash combined with carbon sequestration has the following specific steps: (1) Arrangement of working face tunnels: According to the tunnel arrangement method of longwall fully mechanized mining, the return air level tunnel, transport level tunnel, and cutting hole are excavated in advance, and full negative pressure ventilation is formed on the working face. The working face length is designed to be 50~200 m; (2) Collect filling raw materials: Collect coal gangue, fly ash, biomass ash, and cement; crush the coal gangue and sieve it into fine gangue with a particle size of 0-5 mm, medium gangue with a particle size of 5-10 mm, and coarse gangue with a particle size of 10-15 mm; and pass fly ash and biomass ash through a 1 mm sieve to remove impurities; (3) Divide and mine branch tunnels at intervals: Divide the coal seam to be mined in the working face into several branch tunnels at intervals of 4 to 6 m along the direction parallel to the cutting eye, and deploy continuous miners, anchor trolleys, and loaders to mine branch tunnels at intervals; (4) The first step is preparation before filling: lay out blocking templates or hoist filling bags at both ends of the mined branch tunnel, lay out filling pipelines in the return air level tunnel and branch tunnel, and check the installation to ensure that the connection is correct; (5) Prepare biomass ash filling slurry and perform the first filling: biomass ash accounts for 7%~10% by weight, cement accounts for 7%~8% by weight, fly ash accounts for 12%~15% by weight, fine gangue accounts for 12%~18% by weight, medium gangue accounts for 14%~21% by weight, coarse gangue accounts for 14%~21% by weight, and water accounts for 16%~24% by weight. After mixing and stirring evenly, pump it through a pipeline to fill the mined branch tunnel, completing the first filling step; (6) Maintain the filling and monitor the surface deformation: Maintain the filling for 7 to 28 days, monitor the surface deformation of the mining area in real time, and wait until the setting strength of the filling is not less than 4 MPa; (7) Mining out the coal from the unmined branch tunnels: deploy continuous miners, anchor trolleys, and loaders. Under the strong filling support of the first filling step, the interval coal pillars that were not mined in step (3) are mined out to form filling space for the second filling step. (8) Carbon dioxide capture: Collect carbon dioxide from the exhaust port of thermal power plants or biomass power plants and store it in cylinders through pipes; (9) The second step is preparation before filling: Place plugging templates or hoist filling bags at both ends of the mined branch tunnel, strictly seal the gaps between the upper and lower templates and the top and bottom plates, place carbon dioxide alarms and carbon dioxide absorbers on the plugging templates or filling bags to achieve strict sealing of carbon dioxide, and check that the filling pipes in the return air tunnel and branch tunnel are connected correctly; (10) Prepare filling slurry for the second filling step and inject carbon dioxide simultaneously: cement mass accounts for 5%~10%, fly ash mass accounts for 20%~30%, fine gangue mass accounts for 12%~18%, medium gangue mass accounts for 14%~21%, coarse gangue mass accounts for 14%~21%, water mass accounts for 15%~20%, mix and stir evenly, and then pump it through the pipeline to fill the mining branch tunnel. Carbon dioxide is simultaneously released from the cylinder and injected into the filling pipeline through the catheter. The injection pressure is 0.1~0.5 MPa. The injection is stopped after the carbon dioxide alarm wakes up.

2. The two-step strong and weak filling method for continuous mining and filling of biomass ash and carbon sequestration according to claim 1 is characterized by: The working face is fully mined and filled. The biomass ash filling body filled in the first step and the carbon sequestration filling body filled in the second step are arranged alternately. The biomass ash filling body filled in the first step builds a strong filling support environment, and cooperates with the carbon sequestration filling body with relatively weak mechanical properties filled in the second step to ensure the safety and stability of the overburden above the mining area.

3. The two-step strong and weak filling method for continuous mining and filling of biomass ash and carbon sequestration according to claim 1 is characterized by: During step (6) of maintaining the filling body and monitoring the surface deformation, when the surface deformation is stable within the range of the Class I mining damage index specified in the "Specifications for the Retention and Compressed Coal Mining of Coal Pillars in Buildings, Water Bodies, Railways and Main Wells and Tunnelings", it is considered that the first step of filling has achieved strong filling.

4. The two-step strong and weak filling method for continuous mining and filling of biomass ash and carbon sequestration according to claim 1 is characterized by: Biomass ash is one or more of rice husk ash, sugarcane bagasse ash, poplar leaf ash, willow leaf ash, and corn straw ash, and is obtained by collecting it after natural incineration or directly collecting it from a biomass power plant.

5. The two-step strong and weak filling method for continuous mining and filling of biomass ash and carbon sequestration according to claim 1 is characterized by: The water is domestic water or mine water, the cement is ordinary silicate 425# cement, and the fly ash is Class F II fly ash.

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