An active fire prevention method using gas-liquid two-phase combined injection coupled inerting before mining in thick coal seams

Abstract

The present invention belongs to the field of coal mine safety and relates to a method for active fire prevention by combined gas-liquid two-phase injection coupled inerting before mining of thick coal seams. The method comprises the following steps: injecting an inhibitor solution, nitrogen and carbon dioxide composite inert gas into the coal body in sequence before mining at the working face, thereby effectively isolating the coal body from oxygen, forming a dual protection of gas-liquid two-phase coupled inerting, and effectively inhibiting or delaying the oxidation and spontaneous combustion of loose coal bodies in goafs and coal pillar areas, thereby achieving the purpose of proactively and actively preventing spontaneous combustion of coal in goafs, and providing an important technical means and approach for effectively solving the problem of comprehensive fire prevention and extinguishing during the initial mining and caving of fully-mechanized caving working faces in extra-thick coal seams.

Description

Technical Field

[0001] The invention belongs to the field of coal mine safety and relates to a gas-liquid two-phase combined injection coupled inerting active fire prevention method before mining of thick coal seams. Background Art

[0002] Coal fires are a constant threat during coal mining. Spontaneous combustion in goaf areas produces large quantities of toxic gases. In highly gassy mines, this can also detonate goaf gas during the fire. Coal-producing countries worldwide are deeply concerned about preventing and controlling coal fires, as they not only waste vast quantities of coal resources but also cause significant casualties and economic losses. Currently, over 80% of underground coal mine fires are caused by spontaneous combustion of coal seams. With the advancement of coal mining technology in my country, the widespread use of mechanical equipment, and the large-scale use of mining equipment in underground coal mines, while increasing production, spontaneous combustion in coal mines is also causing greater waste and damage to coal resources and equipment. Comprehensively mechanized top coal caving is a key technology for achieving high-yield, efficient, and intensive mining operations. The widespread adoption of fully mechanized top coal caving has significantly improved my country's coal mining efficiency.

[0003] However, the fully mechanized top-coal caving process also dictates that no coal is caved at the top of the working face's intake and return air tunnels. This makes caving difficult during initial mining due to untimely coal and rock collapse. Initial caving in fully mechanized top-coal caving faces in thick coal seams typically occurs 8-10 meters after the face has advanced through trial mining. During this initial mining phase, top coal caving is typically not performed or is performed incompletely, resulting in the goaf being filled with loose coal. Furthermore, stress concentration in the coal behind the face's starting line, as well as in the coal and coal pillars above the intake and return air tunnels, creates numerous fractures. Consequently, during initial mining phases in fully mechanized top-coal caving faces in thick coal seams, significant coal loss occurs, significant coal remains in the goaf, and coal fragmentation occurs in the pillars. This leads to a high probability of spontaneous combustion of the loose coal in these areas. Furthermore, the slow advance of the working face during initial mining poses significant challenges in predicting and preventing spontaneous combustion. The traditional fire prevention and extinguishing methods of nitrogen injection in the air intake tunnel and grouting in the return air tunnel are adopted. Since the goaf area has a small impact range during the initial mining period, the grouting fire prevention and extinguishing method may cause a large amount of slurry to flow out, and nitrogen injection is also likely to cause hypoxia in the working face. At the same time, the above methods have a small range of action and cannot effectively wrap the fractured areas around the initial working face and the collapsed coal body in the goaf area, resulting in poor initial fire prevention and extinguishing effects. It is generally difficult to prevent coal spontaneous combustion in advance during the initial mining of the fully mechanized caving working face.

[0004] Therefore, there is an urgent need to seek an efficient prevention and control technical means and method to proactively prevent the problem of spontaneous combustion of coal during the initial mining of thick coal seam fully mechanized caving working faces. Summary of the Invention

[0005] In view of this, the purpose of the present invention is to provide a method for active fire prevention by combined gas-liquid two-phase injection coupled inerting before mining of thick coal seams. By successively injecting inhibitor solution, nitrogen and carbon dioxide composite inert gas into the coal body before mining at the working face, the coal body is effectively isolated from oxygen, forming a dual protection of gas-liquid two-phase coupled inerting, effectively inhibiting or delaying the oxidation and spontaneous combustion of loose coal bodies in the goaf and coal pillar areas, thereby achieving the purpose of proactively and actively preventing spontaneous combustion of coal in the goaf.

[0006] To achieve the above-mentioned object, the present invention provides the following technical solution: a method for active fire prevention by gas-liquid two-phase combined injection coupled inerting before mining in thick coal seams, comprising the following steps:

[0007] S1, formulate and implement process design plan;

[0008] Complete the design of the gas-liquid two-phase combined injection process plan based on the working face mining design parameters and coal rock occurrence basic data;

[0009] S2, conduct fire prevention and extinguishing drilling construction;

[0010] After the mining roadway is formed at the working face, the first, second, and third groups of fire-fighting drill holes are drilled through the working face toward the coal body in front of, above, and behind the working face. A fourth group of fire-fighting drill holes is also drilled along the coal pillar in the return air lane of the working face. All drill holes are terminated through the entire thickness of the extra-thick coal seam to 0.5 m above the coal seam roof, and are sealed with mine-grade hole sealers.

[0011] S3, implementation of the inhibitor solution injection process;

[0012] After the drilling is completed, the inhibitor injection system is connected and the inhibitor solution is injected into the borehole, so that cracks are generated in the coal body under the action of fracturing. The inhibitor solution seeps into the coal body cracks, achieving the first level of protection against spontaneous combustion of the coal body.

[0013] S4, implementation of nitrogen and carbon dioxide composite inert gas pressure injection process;

[0014] After the borehole injection process of the inhibitor solution is completed, the borehole is connected to the nitrogen and carbon dioxide composite inert gas injection system, and the nitrogen and carbon dioxide composite inert gas is injected into the borehole, so that the gas is fully adsorbed and filled in the cracks and voids of the coal body, forming a layer of inert gas isolation zone, realizing the second level of protection against coal spontaneous combustion;

[0015] S5. During the mining process of the fully mechanized caving working face, the inhibitor injection system and the nitrogen and carbon dioxide composite inert gas injection system continue to be the main technical means to prevent and control spontaneous combustion of coal in the goaf area of ​​the working face and the coal pillar area of ​​the roadway.

[0016] Optionally, the distance l1 between the end point of the first group of anti-fire extinguishing drilling holes and the plane projection of the outline of the working face cutting eye is 10 to 15 meters, the opening point of the second group of anti-fire extinguishing drilling holes is located at the top of the tunnel, and the end point overlaps with the plane projection of the center line of the working face cutting eye, and the distance l3 between the end point of the third group of anti-fire extinguishing drilling holes and the plane projection of the outline of the working face cutting eye is 10 to 15 meters; the interval m1 of the anti-fire extinguishing drilling holes along the inclination direction of the working face is 15 to 20 meters.

[0017] Optionally, the diameter of the fire-proof drilling hole is 93mm or 113mm, and the sealer is a mining sealer, which consists of a water injection component, a rubber sealer, a connecting steel pipe, a connecting head, a sealing water supply pipe, and a water injection water supply pipe component, meeting the requirement that the water injection / gas injection pressure is not less than 25MPa.

[0018] Optionally, the components of the inhibitor solution include one or more combinations of sodium chloride, magnesium chloride, calcium hydroxide, etc., and flame retardants and cooling agents are added; the mass fraction of the inhibitor solution is 15% to 20%, the injection pressure is 15 to 25 MPa, the injection flow rate is 120 to 200 L / min, the injection time is 2 to 4 hours, or it is determined based on the coal body occurrence conditions.

[0019] Optionally, the concentration ratio of nitrogen and carbon dioxide composite inert gas is set to 3:7 or 4:6, or determined through experimental tests and simulation studies; the gas injection pressure is 0.5-0.7 MPa, the gas injection flow rate is 60-120 L / min, and the gas injection time is 2-4 hours, or determined based on factors such as the spontaneous combustion level of the coal seam, the thickness of the coal seam, the permeability of the coal seam, and the length of the gas pipeline.

[0020] The beneficial effects of the present invention are:

[0021] 1) The technical means and methods of the present invention overcome the drawbacks of using single fire prevention and extinguishing technical means such as grouting and nitrogen injection to prevent coal spontaneous combustion through the coupled inerting method of gas-liquid two-phase combined injection before mining, achieving advanced prevention, active prevention, and multiple protection, greatly improving the efficiency of coal mine fire prevention and extinguishing;

[0022] 2) Compared with the traditional method of spraying inhibitors for fire prevention and extinguishing, this invention adopts the method of pre-pressurizing the inhibitor solution to fracture and inject the coal body, which increases the external moisture of the coal body, reduces the coal body temperature, forms a liquid film around the coal blocks, and absorbs moisture from the air, keeping the coal surface moist for a longer period of time, isolating it from contact with oxygen, and effectively reducing the oxidation rate of the coal body;

[0023] 3) The present invention injects nitrogen and carbon dioxide as a composite inert gas for fire prevention and extinguishing. Nitrogen has a good inerting effect, while carbon dioxide has a high density and a good cooling effect. The combination of the two can give full play to their respective advantages, resulting in higher fire prevention efficiency and lower material costs.

[0024] 4) The method of the present invention provides a new and effective means for solving the problem of spontaneous combustion of coal seams. It can also be used as an active fire prevention and extinguishing technical means and method during the working face withdrawal stage and under conditions where there are close-range coal seams overlying the working face, and has broad application prospects.

[0025] Other advantages, objects, and features of the present invention will be described in part in the following description and, in part, will be apparent to those skilled in the art upon examination of the following description or may be learned from practice of the present invention. The objects and other advantages of the present invention may be realized and obtained through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention will be described in detail below with reference to the accompanying drawings, in which:

[0027] Figure 1 This is a flow chart of the present invention's pre-mining gas-liquid two-phase combined injection coupled inerting active fire prevention method for thick coal seams.

[0028] Figure 2 This is a plan view of the fire prevention and extinguishing drilling layout of the fully mechanized caving working face in a thick coal seam according to the present invention.

[0029] Figure 3 This is the cross-sectional layout diagram of the fire prevention and extinguishing drilling section II of the thick coal seam fully mechanized caving working face of the present invention. DETAILED DESCRIPTION

[0030] The following describes the embodiments of the present invention by means of specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the illustrations provided in the following embodiments are only schematic illustrations of the basic concept of the present invention, and the following embodiments and features in the embodiments can be combined with each other without conflict.

[0031] Among them, the accompanying drawings are only for illustrative purposes and represent only schematic diagrams rather than actual pictures, and should not be understood as limiting the present invention. In order to better illustrate the embodiments of the present invention, some parts of the accompanying drawings may be omitted, enlarged or reduced, and do not represent the dimensions of actual products. For those skilled in the art, it is understandable that some well-known structures and their descriptions may be omitted in the accompanying drawings.

[0032] The same or similar numbers in the drawings of the embodiments of the present invention correspond to the same or similar parts; in the description of the present invention, it should be understood that if there are terms such as "upper", "lower", "left", "right", "front", "back", etc. indicating directions or positional relationships, they are based on the directions or positional relationships shown in the drawings. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific direction, be constructed and operate in a specific direction. Therefore, the terms describing the positional relationship in the drawings are only used for illustrative purposes and cannot be understood as limiting the present invention. For ordinary technicians in this field, the specific meanings of the above terms can be understood according to specific circumstances.

[0033] See also Figures 1 to 3 , is a method for active fire prevention by gas-liquid two-phase combined injection coupled inerting before mining in thick coal seams, comprising the following steps:

[0034] 1. Formulate and implement the process design plan: According to the basic data such as working face mining design parameters and coal rock occurrence, complete the design of the gas-liquid two-phase combined injection implementation process plan.

[0035] 2. Carry out fire prevention and extinguishing drilling construction: After the mining tunnel of the working face is formed, cut through the working face, construct the first group of fire prevention and extinguishing drilling holes towards the coal body in front of the working face, construct the second group of fire prevention and extinguishing drilling holes towards the coal body above the working face, and construct the third group of fire prevention and extinguishing drilling holes towards the coal body behind the working face; after the drilling construction is completed, use a mining hole sealer to seal the hole.

[0036] The final hole positions of the fire-fighting drilling holes all pass through the full thickness of the extra-thick coal seam to 0.5m above the coal seam roof; the distance l1 between the final hole points of the first group of fire-fighting drilling holes and the plane projection of the outline line of the working face opening is 10 to 15m, the opening points of the second group of fire-fighting drilling holes are located at the top of the tunnel, and the final hole points overlap with the plane projection of the center line of the working face opening; the distance l3 between the final hole points of the third group of fire-fighting drilling holes and the plane projection of the outline line of the working face opening is 10 to 15m; the interval m1 of the fire-fighting drilling holes along the inclined direction of the working face is 15 to 20m.

[0037] In addition, in the return air lane of the working face, a fourth group of fire prevention and extinguishing drill holes are constructed along the direction of the coal pillar. The plane projection distance l4 between the drill holes and the outer side of the lane outline is 10 to 15 meters, and the interval m2 between the drill holes along the direction of the working face is 5 to 10 meters.

[0038] The diameter of the fire-fighting drilling hole is 93mm or 113mm; the specific opening position of the drilling hole can be determined based on the actual conditions on site.

[0039] The rubber tube expansion sealing process uses a mining sealer, which consists of a water injection component, a rubber sealer, a connecting steel pipe, a connecting head, a sealing water supply pipe, a water injection water supply pipe and other components to meet the requirement that the water / gas injection pressure is not less than 25MPa.

[0040] Common methods for sealing holes in coal mines include Marisan, cement mortar, and rubber tube expansion. Project applications show that Marisan sealing generally has a pressure resistance of approximately 3 MPa, and the sealing depth for coal borehole sealing is generally greater than 6 meters. This is not suitable for the medium- and high-pressure water injection requirements commonly used in coal seam water injection. Cement mortar sealing generally requires a sealing depth greater than 10 meters, but the shrinkage of the cement mortar after setting often leads to water leakage in the borehole, resulting in poor coal wetting effectiveness. Rubber tube expansion sealing offers advantages such as a high pressure resistance of approximately 30 MPa, adjustable sealing depth, and reusability. The sealer prevents interference between the sealing and water injection processes, ensuring it will not pop out if the water injection pressure is suddenly relieved. It also allows for easy adjustment of the sealing depth and is reusable.

[0041] 3. Implementation of the inhibitor solution injection process: After the drilling construction is completed, the inhibitor injection system is connected and the inhibitor solution is injected into the borehole, so that cracks are generated in the coal body under the action of fracturing. The inhibitor solution penetrates into the gaps in the coal body, filling the cavities and cracks in the coal body, thereby inhibiting and delaying the oxidation of the coal body, and realizing the first level of protection against spontaneous combustion of the coal body.

[0042] During the injection of the inhibitor solution, the coal is fractured by the fracturing action, and the inhibitor solution seeps into the coal cracks, filling the coal voids and cracks. During the mining process, if the coal collapses, the inhibitor solution continues to wrap the loose coal, effectively isolating it from air and reducing the coal's oxygen absorption capacity, thereby preventing the coal's oxidation process and preventing spontaneous combustion.

[0043] The inhibitor injection system can be set up as a permanent ground type, a semi-permanent type in the mining area, or a mobile type at the coal mining face, including an injection pool (injection box), an injection pump (boosting pump), a water supply pipeline, an injection pipeline, and other ancillary devices such as pressure gauges and valves.

[0044] The components of the inhibitor solution include one or more combinations of sodium chloride, magnesium chloride, calcium hydroxide, etc., and flame retardants, cooling agents, etc. are added; the mass fraction of the inhibitor solution is 15% to 20%, the injection pressure is 15 to 25 MPa, the injection flow rate is 120 to 200 L / min, the injection time is 2 to 4 hours, or it can be determined based on the coal body occurrence conditions.

[0045] 4. Implementation of nitrogen and carbon dioxide composite inert gas pressure injection process: After the borehole pressure injection process of the inhibitor solution is completed, the borehole is connected to the nitrogen and carbon dioxide composite inert gas pressure injection system, and nitrogen and carbon dioxide composite inert gas is continuously injected into the borehole to allow the gas to be fully adsorbed and filled in the cracks and voids of the coal body, increasing the external moisture content of the coal body while forming a layer of inert gas isolation zone, thus achieving a second level of protection against spontaneous combustion of the coal body.

[0046] During the mining process at the working face, the coal body collapses, and the nitrogen and carbon dioxide compound inert gas enters the loose coal body pores, cracks and working face goaf, and is adsorbed on the surface of the coal body cracks to form an isolation layer, which reduces the amount of oxygen adsorbed on the coal body surface and the oxygen concentration in the goaf, avoids direct contact between the coal body and oxygen to cause oxidation heat release, prevents further oxidation and spontaneous combustion of the coal, and thus avoids fire accidents such as coal body spontaneous combustion.

[0047] The nitrogen and carbon dioxide composite inert gas pressure injection system includes a gas injection device system, a gas transmission pipeline system and an automatic control system.

[0048] The concentration ratio of nitrogen and carbon dioxide composite inert gas is set to 3:7 or 4:6, or determined through experimental tests and simulation studies; the gas injection pressure is 0.5-0.7 MPa, the gas injection flow rate is 60-120 L / min, and the gas injection time is 2-4 hours, or determined based on factors such as the spontaneous combustion level of the coal seam, the thickness of the coal seam, the permeability of the coal seam, and the length of the gas pipeline.

[0049] 5. During the mining process of the fully-mechanized caving working face, the inhibitor injection system and the nitrogen and carbon dioxide composite inert gas injection system can continue to be the main technical means to prevent and control spontaneous combustion of coal in the goaf area of ​​the working face and the coal pillar area of ​​the roadway.

[0050] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not limiting. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention can be modified or replaced by equivalents without departing from the purpose and scope of the technical solutions, which should all be included in the scope of the claims of the present invention.

Claims

1. A method for active fire prevention by gas-liquid two-phase combined injection coupled inerting before mining in thick coal seams, characterized in that: The following steps are involved: S1, formulate and implement process design plan; Complete the design of the gas-liquid two-phase combined injection process plan based on the working face mining design parameters and coal rock occurrence basic data; S2, conduct fire prevention and extinguishing drilling construction; After the mining roadway is formed at the working face, the first, second, and third groups of fire-fighting drill holes are drilled through the working face toward the coal body in front of, above, and behind the working face. A fourth group of fire-fighting drill holes is also drilled along the coal pillar in the return air lane of the working face. All drill holes are terminated by penetrating the full thickness of the thick coal seam to 0.5 m above the coal seam roof and sealed with a mine-grade hole sealer. S3, implementation of the inhibitor solution injection process; After the drilling is completed, the inhibitor injection system is connected and the inhibitor solution is injected into the borehole, so that cracks are generated in the coal body under the action of fracturing. The inhibitor solution seeps into the coal body cracks, achieving the first level of protection against spontaneous combustion of the coal body. S4, implementation of nitrogen and carbon dioxide composite inert gas pressure injection process; After the borehole injection process of the inhibitor solution is completed, the borehole is connected to the nitrogen and carbon dioxide composite inert gas injection system, and the nitrogen and carbon dioxide composite inert gas is injected into the borehole, so that the gas is fully adsorbed and filled in the cracks and voids of the coal body, forming a layer of inert gas isolation zone, realizing the second level of protection against coal spontaneous combustion; S5. During the mining process of the fully mechanized caving working face, the inhibitor injection system and the nitrogen and carbon dioxide composite inert gas injection system continue to be the main technical means to prevent and control spontaneous combustion of coal in the goaf area of ​​the working face and the coal pillar area of ​​the roadway.

2. The method for active fire prevention by gas-liquid two-phase combined injection coupled inerting before mining thick coal seams according to claim 1 is characterized by: The distance l1 between the end point of the first group of fire-fighting drilling holes and the plane projection of the outline of the working face cutting eye is 10 to 15 meters. The opening point of the second group of fire-fighting drilling holes is located at the top of the tunnel, and the end point overlaps with the plane projection of the center line of the working face cutting eye. The distance l3 between the end point of the third group of fire-fighting drilling holes and the plane projection of the outline of the working face cutting eye is 10 to 15 meters. The interval m1 of the fire-fighting drilling holes along the inclination direction of the working face is 15 to 20 meters.

3. The method for active fire prevention by gas-liquid two-phase combined injection coupled inerting before mining thick coal seams according to claim 1 is characterized in that: The diameter of the fire-proof drilling hole is 93mm or 113mm, and the sealer is a mining sealer, which consists of a water injection component, a rubber sealer, a connecting steel pipe, a connecting head, a sealing water supply pipe, and a water injection water supply pipe component, meeting the requirement that the water / gas injection pressure is not less than 25MPa.

4. The method for active fire prevention by gas-liquid two-phase combined injection coupled inerting before mining thick coal seams according to claim 1 is characterized in that: The components of the inhibitor solution include one or more combinations of sodium chloride, magnesium chloride, and calcium hydroxide, and flame retardants and cooling agents are added; the mass fraction of the inhibitor solution is 15% to 20%, the injection pressure is 15 to 25 MPa, the injection flow rate is 120 to 200 L / min, and the injection time is 2 to 4 hours.

5. The method for active fire prevention by gas-liquid two-phase combined injection coupled inerting before mining thick coal seams according to claim 1 is characterized in that: The concentration ratio of nitrogen and carbon dioxide composite inert gas is set to 3:7 or 4:6, or determined through experimental tests and simulation studies; the gas injection pressure is 0.5-0.7 MPa, the gas injection flow rate is 60-120 L / min, and the gas injection time is 2-4 h.

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