Water conservation method for coal mining in loess region

Abstract

The application discloses a water-preserved coal mining method in loess areas, and relates to the technical field of water-preserved coal mining. A plurality of continuous silt pools are arranged along the strike of a coal mining face in the vertical projection area of the ground of the coal mining face. The silt pools are communicated with the ground, but the adjacent silt pools are not communicated. Then, the coal mining face is mined along the strike of the coal mining face. In the advancing process of the coal mining face, a silt pool behind the current advancing position of the coal mining face is filled, and the filled silt pool is continuously mechanically stirred until the coal mining is completed. The water-preserved coal mining method can achieve the purpose of water preservation, and has the advantages of high coal resource recovery rate, low cost, short time period, stable effect, simplicity and easy implementation.

Description

Technical Field

[0001] This invention relates to the field of water-conserving coal mining technology, and in particular to a water-conserving coal mining method in loess areas. Background Technology

[0002] To prevent water loss, water-conserving mining methods are needed for coal mining in loess areas. Traditional water-conserving mining methods mainly include: backfilling mining, strip mining, loess self-healing, reducing mining height, layered mining, water resource coordination management based on ecological water levels, negative pressure reconstruction of aquitards, artificial grouting reinforcement, and freezing of aquifers. However, the above-mentioned traditional water-conserving mining methods have the following drawbacks:

[0003] (1) The water-conserving mining method of strip mining, reducing the mining height and layered mining results in low coal recovery rate and waste of coal resources.

[0004] (2) The water-conserving mining methods of filling mining, artificial grouting reinforcement and freezing of aquifers have a large amount of engineering costs and are expensive.

[0005] (3) The water-retaining coal mining method using loess self-healing and negative pressure to recreate the water-retaining layer requires too long a time cycle and the effect is unstable.

[0006] (4) The water-conserving coal mining method based on ecological water level requires large-scale water level monitoring and scheduling, which is not easy to implement.

[0007] Therefore, there is an urgent need for a new water-conserving coal mining method in the loess region to solve the above problems. Summary of the Invention

[0008] The purpose of this invention is to provide a water-conserving coal mining method in loess areas, which achieves the goal of water-conserving coal mining while taking into account the advantages of high coal resource recovery rate, low cost, short time cycle, stable effect, and simple implementation.

[0009] To achieve the above objectives, the present invention provides the following solution:

[0010] A water-conserving coal mining method in loess areas, the method comprising:

[0011] Within the vertical projection area of ​​the coal mining face on the ground, multiple continuous sludge pits are set along the direction of the coal mining face; the sludge pits are connected to the ground, but adjacent sludge pits are not connected; the vertical projection area on the ground is the area obtained by projecting the coal mining face onto the ground;

[0012] Coal mining is carried out along the direction of the coal mining face; during the advancement of the coal mining face, the sludge pit at the current advancement position of the coal mining face is filled, and the filled sludge pit is continuously mechanically stirred until the coal mining is completed.

[0013] According to specific embodiments provided by the present invention, the present invention discloses the following technical effects:

[0014] This invention provides a water-conserving coal mining method in loess areas. Multiple continuous sludge pits are set up along the vertical projection area of ​​the coal mining face, connected to the ground but not connected to adjacent pits. Coal is then mined along the direction of the coal mining face. During the advancement of the coal mining face, the next sludge pit at the current advancement position is filled, and the filled sludge pits are continuously mechanically stirred until coal mining is completed. This invention can completely retain all coal resources within the coal mining face. After mining is completed, the coal resource recovery rate is high. Taking advantage of the opening of fractures during the pressure during coal mining, gravity and the eddy currents formed by stirring are used to effectively seal the fractures by gravity, which can save engineering costs and is relatively low. Utilizing the good sealing properties of silt, coal mining and sealing can be carried out simultaneously, shortening the time cycle and achieving better results. There is no need for large-scale water level monitoring and scheduling, and it is simple and easy to implement. Therefore, this invention can achieve the purpose of water-conserving coal mining, and at the same time has the advantages of high coal resource recovery rate, low cost, short time cycle, stable effect and simple implementation. Attached Figure Description

[0015] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0016] Figure 1 This is a flowchart of the water-conserving coal mining method provided in Embodiment 1 of the present invention;

[0017] Figure 2 This is a detailed flowchart of the water-conserving coal mining method provided in Embodiment 1 of the present invention. Detailed Implementation

[0018] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0019] The purpose of this invention is to provide a water-conserving coal mining method in loess areas, which achieves the goal of water-conserving coal mining while taking into account the advantages of high coal resource recovery rate, low cost, short time cycle, stable effect, and simple implementation.

[0020] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0021] Example 1:

[0022] like Figure 1 and Figure 2 As shown in the figure, this embodiment provides a water-conserving coal mining method in loess areas, the water-conserving coal mining method includes:

[0023] S1: In the vertical projection area of ​​the coal mining face on the ground, multiple continuous sludge pits are set along the direction of the coal mining face; the sludge pits are connected to the ground, but adjacent sludge pits are not connected; the vertical projection area on the ground is the area obtained by projecting the coal mining face onto the ground.

[0024] In this embodiment, the coal mining face refers to the working location where coal is mined, i.e., the three-dimensional working area where coal mining is to be carried out. By projecting the coal mining face onto the ground, the vertical projection area of ​​the coal mining face on the ground can be determined. Then, multiple continuous sludge pits are set within the vertical projection area of ​​the coal mining face on the ground. The multiple sludge pits are distributed along the direction of the coal mining face, and each sludge pit is connected to the ground. There are no gaps between adjacent sludge pits, but they are not connected to each other.

[0025] In this embodiment, each sludge pit has the same structure, with a cover to prevent evaporation and a closed perimeter. Each sludge pit has a width of 1.5 to 2.5 times D, a distance from the pressure point to the working face that is 1.1 to 1.3 times the length of the inclined plane of the coal mining face, and a height of 2 to 4 times M × (1-w). That is, in this embodiment, the width of the sludge pit is 1.5D to 2.5D, the length is 1.1C to 1.3C, and the height is 2M(1-w) to 4M(1-w), where D is the pressure step distance of the coal mining face, C is the inclined plane of the coal mining face (i.e., the width of the coal mining face), M is the coal mining thickness of the coal mining face, and w is the subsidence coefficient of the coal mining face.

[0026] To determine the size of the sludge pond, two parameters of the coal face need to be determined before coal mining: the subsidence coefficient *w* and the pressure step distance *D*. Specifically, a physical similarity model can be established based on the borehole columnar section, and the subsidence coefficient *w* and pressure step distance *D* can be determined through physical simulation. The methods for determining the pressure step distance and subsidence coefficient include: establishing a physical similarity model of the coal face based on the borehole columnar section. The borehole columnar section is one of the most important data outputs in drilling geological logging. It is a raw map compiled based on observation, identification, sampling and analysis of borehole cores (or rock cuttings, rock powder), and various tests conducted within the borehole. It visually represents the rock strata, ore bodies, and their interrelationships traversed by the borehole, and is a primary basis for compiling comprehensive maps and calculating mineral reserves. According to the data, the main contents of the map include drilling footage per cycle, core recovery rate, stratigraphic position and thickness of strata or ore bodies, core characteristics (including material composition, structure, contact relationship and dip angle of rock or ore), as well as sampling and testing, simple hydrogeological observations in the borehole, and geophysical logging results. After obtaining the drilling columnar section of the coal mining face, a physical simulation model of the coal mining face can be established using existing methods. This physical simulation model can be considered as a scaled-down version of the coal mining face. Then, physical simulation is performed on the physical similarity model of the coal mining face to determine the pressure step distance and subsidence coefficient of the coal mining face. The physical simulation method is a mature existing method and will not be elaborated here.

[0027] This embodiment combines the theory of mine pressure and rock strata movement, and calculates the volume of the fracture based on the subsidence coefficient and pressure step distance, so as to design the size of the sludge pond and quantitatively control the required sludge.

[0028] S2: Coal mining is carried out along the direction of the coal mining face; during the advancement of the coal mining face, the sludge pit at the current advancement position of the coal mining face is filled, and the filled sludge pit is continuously mechanically stirred until the coal mining is completed.

[0029] In this embodiment, the process of mining coal at the coal face is the process of advancing the coal face. This embodiment requires sequential filling before the coal face advances to the sludge pits. Specifically, during the advancement of the coal face, multiple sludge pits are filled sequentially. The filling timing for each sludge pit is as follows: one sludge pit ahead of the current advancing position is filled; that is, during the advancement of the coal face, the sludge pit following the current advancing position is filled. This process continues sequentially as the coal face advances. It should be noted that in this embodiment, "before" and "after" are defined according to the direction of the coal face's movement; the direction of the coal face's advancement can be considered as "after".

[0030] In this embodiment, the materials filled into the sludge pool may include sludge, clean mine water, coal gangue, and live Bacillus megaterium and its metabolic products. The sludge is sludge dredged from the water body and passed through a 100-200 mesh sieve. The clean mine water is mine water that is discharged directly from the borehole without being mixed with coal, lubricating oil, etc. The coal gangue contains more than 0.1% P2O3, more than 60% clay minerals, and has been crushed through a 100-200 mesh sieve. Filling the sludge pit at the current advancing position of the coal mining face can include: filling the sludge pit at the current advancing position of the coal mining face with sludge, clean mine water, coal gangue, and live Bacillus megaterium and its metabolites. The clean mine water is mine water discharged directly from the borehole. The mass ratio of sludge, clean mine water, coal gangue, and live Bacillus megaterium and its metabolites is 1-2:1-2:0.3-0.5:0.0001-0.0002.

[0031] In this embodiment, coal gangue and Bacillus megaterium are added to the sludge pond, which is beneficial for the decomposition of phosphate fertilizer in the coal gangue by Bacillus megaterium, and is conducive to subsequent vegetation restoration.

[0032] After the sludge pond is filled, it is continuously mechanically stirred until the coal mining is completed. During the continuous mechanical stirring of the filled sludge pond, the stirring speed can be greater than 30 r / min.

[0033] This embodiment also includes setting up an underground mud pumping system for the coal mining face before coal mining. Specifically, before mining coal along the direction of the coal mining face, the water-conserving coal mining method in this embodiment further includes setting up a one-hour pumping capacity for the underground mud pumping system at the coal mining face. The one-hour pumping capacity of the underground mud pumping system is greater than 1.2B, where B is the sum of the one-hour water inflow of the aquifer mine and the one-hour water inflow of the maximum volume of the sludge pit. The one-hour water inflow of the aquifer mine can be calculated using the industry-established large-well method or analogy method. The one-hour water inflow of the maximum volume of the sludge pit can be obtained based on existing fissures on the ground, using experiments under the same water head height and filling material. The water head height refers to the difference between the bottom height of the sludge pit and the top height of the coal mining face.

[0034] Since this embodiment operates based on pressure, when mining coal at the coal face, if the advancing distance reaches 1.1 times the pressure step distance D but no pressure is applied, manual forced roof caving is performed until coal mining is completed. Specifically, during the advancing process of the coal face, the water-conserving coal mining method of this embodiment further includes: determining whether the advancing distance of the coal face is greater than 1.1D, where the advancing distance is 0 after pressure is applied to the coal face, and D is the pressure step distance; if so, manual forced roof caving is performed, and the advancing distance is set to 0.

[0035] To further protect the ecological environment of the Loess Plateau, the surface silt pits and filling materials are removed 3 to 12 months after coal mining ends, and vegetation is replanted on the ground. Specifically, after coal mining ends, the water-conserving coal mining method in this embodiment also includes: determining whether the time interval from the end of coal mining is greater than a preset period, which can be 3 to 12 months; if so, the silt pits and filling materials in the silt pits are removed, and vegetation is planted on the ground.

[0036] The water-conserving coal mining method for loess areas provided in this embodiment not only achieves the goal of water-conserving coal mining, but also has the following advantages compared with existing technologies:

[0037] (1) High coal resource recovery rate

[0038] Because water-conserving mining methods such as strip mining, lowering the mining height, and stratified mining can result in situations where coal resources in certain areas of the mining face cannot be mined, the water-conserving mining method used in this embodiment in the loess region can enable normal mining of coal resources within the mining face, allowing all coal resources to be mined. Therefore, compared to water-conserving mining methods such as strip mining, lowering the mining height, and stratified mining, this embodiment can improve the coal resource recovery rate and avoid wasting coal resources.

[0039] (2) The cost is relatively low

[0040] Since backfilling mining, artificial grouting reinforcement, and water-retaining coal mining methods that freeze aquifers are all underground backfilling methods, they require underground backfilling processes and drilling. Furthermore, these methods aim to prevent the formation of fissures, placing high demands on the performance of the binding materials, resulting in significant engineering costs and high prices. Compared to traditional grouting, this embodiment considers the presence of loess, which prevents sudden water inrush and sand collapse. Additionally, the development of fissures after loess mining is relatively limited, allowing for sealing with silt. Therefore, this embodiment's water-retaining coal mining method utilizes the favorable opportunity of fissure opening during coal mining pressure, effectively sealing the fissures through gravity and the eddy currents generated by stirring. Since a silt pit is set up on the surface, it is a surface backfilling method, eliminating the need for drilling. Moreover, since the goal is to create and then seal the fissures, the performance requirements for the binding materials are not high. Therefore, compared to backfilling mining, artificial grouting reinforcement, and water-retaining coal mining methods that freeze aquifers, this embodiment's water-retaining coal mining method saves engineering costs and is relatively cheaper.

[0041] (3) Shorter cycle and better results

[0042] The traditional method of water-retaining coal mining using loess self-healing and negative pressure regeneration of the impermeable layer separates coal mining and sealing, with sealing occurring only after mining is completed. This process is time-consuming and the results are inconsistent. In contrast, the water-retaining coal mining method of this embodiment utilizes the excellent sealing properties of silt. Compared to traditional soil layers, silt has a permeability coefficient that is more than one order of magnitude lower. While this process is relatively slow, silt can be used to seal cracks during both mining and stabilization, without requiring additional time. Therefore, this water-retaining coal mining method can simultaneously perform coal mining and sealing, shortening the time cycle and achieving better results compared to the traditional method of loess self-healing and negative pressure regeneration of the impermeable layer.

[0043] (4) Simple and easy to implement

[0044] Since the water-conserving coal mining method based on ecological water level requires large-scale water level monitoring and scheduling, it is not easy to implement. However, the water-conserving coal mining method in this embodiment does not require large-scale water level monitoring and scheduling. Therefore, compared with the water-conserving coal mining method based on ecological water level, the water-conserving coal mining method in this embodiment is simple and easy to implement.

[0045] The water-conserving coal mining method of this embodiment involves the intersection of mine hydrogeology and mining engineering. In view of the defects of traditional water-conserving coal mining methods, a new water-conserving coal mining method for loess areas is provided, which can solve the problems of traditional water-conserving coal mining methods. Compared with the prior art, the beneficial effects of this embodiment are: (1) simple and easy to implement; (2) relatively low cost; (3) high coal resource recovery rate; (4) short cycle and better effect.

[0046] Here, this embodiment provides an application example:

[0047] In a mining area with ecologically fragile loess soil, groundwater loss occurred during the previous mining of the No. 2-2 coal face, leading to significant ecological degradation. To achieve water-conserving mining, the following work was carried out during the mining of the 2204 working face:

[0048] Step 1: Determine two parameters of the coal mining face, including the subsidence coefficient w and the pressure step distance D. Specifically, establish a physical similarity model based on the borehole columnar section, and determine the subsidence coefficient w = 0.65 and the pressure step distance D = 24 meters through physical simulation.

[0049] Step Two: Construct sludge pits in the vertical projection area of ​​the coal face. The sludge pits are distributed along the direction of the coal face. Each pit is 1.5 to 2.5 times the width of the face (D), therefore the width is 36 to 60 meters. The distance from the pressure point is 1.1 to 1.3 times the length of the face's slope, therefore the length is 132 to 156 meters. The height is 2 to 4 times M × (1-w), where M × (1-w) = 3.5 × 0.35 = 1.225, therefore the height is 2.45 to 4.9 meters. The sludge pits are connected to the ground and covered with lids to prevent evaporation. They are sealed on all sides and not interconnected.

[0050] Step 3: Before the coal face advances to the sludge pit, it is filled sequentially. The filling materials include sludge, clean mine water, coal gangue, and live Bacillus megaterium and its metabolites. The ratio of sludge:clean mine water:coal gangue:live Bacillus megaterium and its metabolites is 1.5:1.5:0.4:0.00015. The sludge is sludge dredged from the water body and passed through a 200-mesh sieve. The clean mine water is mine water discharged directly from the borehole without mixing with coal, lubricating oil, etc. The coal gangue refers to coal gangue containing more than 0.1% P2O3, with a clay mineral content of 72%, and crushed and passed through a 200-mesh sieve. Filling is carried out one sludge pit ahead of the coal face advance position. After filling the sludge pit, mechanical stirring is carried out until the end of coal mining, and stirring is stopped at a speed of 60 r / min.

[0051] Step Four: Before coal mining, install an underground mud pumping system at the coal face. The underground mud pumping system has a pumping capacity of 600 cubic meters per hour. 3 / h is 1.3 times the hourly water inflow of an aquifer mine plus the hourly water inflow of the maximum volume of the sludge pond.

[0052] Step 5: Coal mining commences at the coal face. On two occasions, when the coal face reached 26.4 meters without any pressure applied, manual forced roof caving was performed until all coal was mined.

[0053] Step Six: Ten months after the end of coal mining, remove the silt pits and filling materials from the ground and replant vegetation on the ground.

[0054] After coal mining, the silt filled the impermeable soil layer in this working face. One year later, the water level recovered, and the vegetation on the ground was more lush than before coal mining. At the same time, the coal resources were mined efficiently and with a high recovery rate, achieving the goal of water-conserving coal mining.

[0055] This document uses specific examples to illustrate the principles and implementation methods of the present invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of the present invention. Furthermore, those skilled in the art will recognize that, based on the ideas of the present invention, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A method for water-conserving coal mining in loess areas, characterized in that, The water-conserving coal mining method includes: Within the vertical projection area of ​​the coal mining face on the ground, multiple continuous sludge pits are set along the direction of the coal mining face; the sludge pits are connected to the ground, but adjacent sludge pits are not connected; the vertical projection area on the ground is the area obtained by projecting the coal mining face onto the ground; the width of the sludge pit is 1.5D~2.5D, the length is 1.1C~1.3C, and the height is 2M(1-w)~4M(1-w); where D is the pressure step distance of the coal mining face; C is the inclined length of the coal mining face; M is the coal mining thickness of the coal mining face; and w is the subsidence coefficient of the coal mining face. Coal mining is carried out along the direction of the coal mining face; during the advancement of the coal mining face, the sludge pit at the current advancement position of the coal mining face is filled, and the filled sludge pit is continuously mechanically stirred until the coal mining is completed.

2. The water-conserving coal mining method according to claim 1, characterized in that, The method for determining the pressure step distance and subsidence coefficient includes: establishing a physical similarity model of the coal mining face based on the borehole columnar section of the coal mining face; performing physical simulation on the physical similarity model to determine the pressure step distance and subsidence coefficient of the coal mining face.

3. The water-conserving coal mining method according to claim 1, characterized in that, The filling of the sludge pit at the current advancing position of the coal mining face specifically includes: The sludge, clean mine water, coal gangue, and live Bacillus megaterium and its metabolites are filled into the sludge pit at the current advance position of the coal mining face; the mass ratio of the sludge, the clean mine water, the coal gangue, and the live Bacillus megaterium and its metabolites is 1~2:1~2:0.3~0.5:0.0001~0.0002; the clean mine water is mine water discharged directly from the borehole.

4. The water-conserving coal mining method according to claim 1, characterized in that, When mechanically stirring the filled sludge tank continuously, the stirring speed should be greater than 30 r / min.

5. The water-conserving coal mining method according to claim 1, characterized in that, Before mining coal along the direction of the coal mining face, the water-conserving coal mining method further includes: setting the one-hour pumping capacity of the underground mud pumping system of the coal mining face; the one-hour pumping capacity is greater than 1.2B; wherein, B is the sum of the one-hour water inflow of the aquifer mine and the one-hour water inflow of the maximum volume of the sludge pond.

6. The water-conserving coal mining method according to claim 1, characterized in that, During the advancement of the coal mining face, the water-conserving coal mining method further includes: Determine whether the advancing distance of the coal mining face is greater than 1.1D; the advancing distance is 0 after the coal mining face is pressed, and D is the pressing step distance; If so, then manually force the top to drop and set the advance distance to 0.

7. The water-conserving coal mining method according to claim 1, characterized in that, After the coal mining is completed, the water-conserving coal mining method further includes: Determine whether the time interval from the end of coal mining is greater than the preset duration; If so, remove the sludge pond and the filling material inside the sludge pond, and plant vegetation on the ground.

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