Gas injection end structure of gas injection pipe for underground coal gasification

Abstract

The application belongs to the technical field of energy equipment, and discloses an injection end structure of a gas injection pipe for underground coal gasification, which comprises a gasification agent injection main pipe and at least two gasification agent injection branch pipes which are movably connected with the gasification agent injection main pipe and have variable end-to-end distances, wherein the multiple injection branch pipes are elastically connected through elastic components, and the ends of all the injection branch pipes are constrained together by releasable constraint members. The injection end with the continuous pipe can enter the underground coal seam gasification area through a narrow borehole and a gasification passage, the constraint members are released under external action, the ends of the multiple injection branch pipes are unfolded, and the gasification agent is dispersed to the gasification area. The end structure of the injection pipe is improved, so that the injected gasification agent can be more dispersed, quickly contacts the gasified coal surface, covers a larger coal seam gasification surface, and further improves the coal gasification amount of a single borehole.

Description

TECHNICAL FIELD

[0001] The application belongs to but is not limited to the technical field of energy equipment, and particularly relates to an injection end structure of a gas injection pipe for underground coal gasification. BACKGROUND

[0002] Underground coal gasification, especially well-less underground coal gasification, is to inject a gasification agent into an underground coal seam through a borehole to make the two occur a combustion gasification reaction, and the generated coal gas is transported to the ground through the borehole for collection and utilization. The diameter of the thinnest section of the borehole determines the maximum diameter of the equipment entering the coal seam, especially the maximum diameter of the injection pipe in the continuous pipe retreating injection gasification (CRIP), which will affect the injection amount of the gasification agent, the coal gasification amount of a single borehole, and the coal gas production. Usually, the diameter of the thinnest section of the borehole is not greater than 200 mm.

[0003] In the continuous pipe retreating injection gasification technology, the diameter of the injection pipe is smaller than that of the thinnest section of the borehole, and usually the front end of the injection pipe has only one gasification agent outlet, or the front end of the injection pipe is designed as a flower pipe structure for dispersing the gasification agent. Compared with the gas injection pipe with only one gasification agent outlet, the injection pipe with the flower pipe structure at the front end can improve the dispersion degree of the gasification agent, and thus improve the coal gasification amount of a single borehole, but the improvement ratio is relatively low. Because with the gasification of the coal seam near the gasification passage where the front end of the gas injection pipe is located, the combustion empty area generated by the gasification gradually expands, the front end of the gas injection pipe is farther and farther away from the coal seam, and the dispersed gasification agent flows to the gas outlet passage in the axial direction while diffusing in the lateral direction. Once the front end of the gas injection pipe is moved, an olive ball-shaped or pear-shaped gasification zone (also called a combustion empty area) is formed, and a series of gasification zones are formed by moving the front end of the gas injection pipe at intervals. The width of the radial expansion of the gasification zone depends on many factors such as gasification pressure, temperature, gasification agent composition, etc., and the most critical factor is whether the gasification agent can quickly reach the radial coal surface of the gasification passage and react with it. SUMMARY

[0004] In view of the problems in the prior art, the application provides an injection end structure of a gas injection pipe for underground coal gasification.

[0005] The application is implemented in the following manner. An injection end structure of a gas injection pipe for underground coal gasification, which comprises:

[0006] The gasification agent injection main pipe and at least two gasification agent injection sub-pipes with variable end-to-end distance are movably connected. The end of the injection sub-pipe connected with the injection main pipe is a movable end, and the other end is a terminal end. The movable ends of the two injection sub-pipes are connected by elastic components. The connection position of the elastic components is the side of the injection sub-pipe close to the wall of the injection main pipe. The side of the movable end of each injection sub-pipe corresponding to the connection position of the elastic components is connected with the injection main pipe by a hinge. The terminal ends of each injection sub-pipe are constrained together by releasable constraints. The injection end can enter the underground coal gasification area through a narrow borehole and a gasification channel with the continuous pipe. Under external action, the constraints are released, the terminal ends of the injection sub-pipes are away from each other (i.e. unfolded), the gasification agent is dispersed to the gasification area, the gasification agent contacts the gasification coal surface as soon as possible, covers a larger coal seam section, and further gasifies more coal.

[0007] Further, one end of the injection main pipe is provided with two ear-shaped structures parallel to each other and parallel to the wall of the injection main pipe. The movable end of each injection sub-pipe is provided with two ear-shaped structures. One of the ear-shaped structures is used for hinge connection with the injection main pipe, which is called a hinge ear, and the ear surface of the hinge ear is perpendicular to the central axis of the injection sub-pipe. The other ear-shaped structure is used for elastic connection, which is called an elastic ear, and the ear surface of the elastic ear is an extension cut of the wall of the injection sub-pipe. Each injection sub-pipe is connected with the ear-shaped structure of the injection main pipe through a hinge structure. The elastic ears of the two injection sub-pipes are connected by elastic components to adjust the distance between the terminal ends of the injection sub-pipes. Preferably, when the number of injection sub-pipes is even, the elastic ears of the two symmetrically distributed injection sub-pipes are connected by elastic components. When the number of injection sub-pipes is odd, one of the injection sub-pipes is selected, and the remaining injection sub-pipes are symmetrically and elastically connected. Then, the selected injection sub-pipe is elastically connected with the injection sub-pipe close to it (for example, the A injection sub-pipe), and the elastic ear of the A injection sub-pipe is connected with the elastic ears of the other two injection sub-pipes to achieve the maximum distance between the terminal ends of the different injection sub-pipes.

[0008] Further, the terminal end of the injection sub-pipe is provided with constraints to constrain the terminal ends of each injection sub-pipe together, reduce the occupied space volume, and be sent into the underground gasification area through a narrow borehole. At this time, the elastic components connecting the injection sub-pipes are in a tension or stretching state. After reaching the gasification area, the constraints can be released under external action (such as gasification agent pressure, temperature, mechanical force, etc.), the elastic components contract, the injection sub-pipes rotate around the hinge structure as the axis, and the unfolded state of the terminal ends of the different injection sub-pipes is achieved.

[0009] Further, the constraints can be a rope that can be melted at a certain temperature, a plurality of connected plugs that can be ejected from the injection sub-pipe under a certain gas pressure, or a plug with a hole that is gasified as the temperature rises, or a sleeve that can be decomposed as the underground coal seam is gasified, such as a PVC sleeve.

[0010] Further, the injection sub-pipes can be multiple, and the cross section of each injection sub-pipe is approximately a sector with an angle of 360 / n degrees (n is the number of injection sub-pipes), so that the space utilization can be improved to a greater extent. Preferably, the injection sub-pipes are two, and the cross section of the injection sub-pipes is approximately a semicircle, which is relatively simple in structure and easy to fix. More importantly, when the gasification agent is dispersed to the coal seam in the lower area of the edge of the combustion cavity in the underground coal gasification, the gas distribution is optimal, so that more coal can be gasified.

[0011] Further, after the end of the injection sub-pipe is expanded, the injection main pipe and the central axis of the injection sub-pipe form an angle a (0°<a≤60°), preferably 30°~ 45°.

[0012] Further, the equivalent diameter (outer diameter) of the multiple injection sub-pipes is less than or equal to the equivalent outer diameter of the injection main pipe, and the length of the injection sub-pipe is greater than or equal to 3 times, preferably 5~10 times, the equivalent outer diameter of the injection main pipe. This can make the gasification agent uniformly dispersed, the continuity of the combustion cavity is good, and the connection strength and elasticity of the main pipe and the sub-pipe are considered.

[0013] Further, a plurality of gas distribution holes are arranged on the injection sub-pipe along the length direction, so that the gasification agent dispersed by the injection sub-pipe is more dispersed and contacts the coal seam as soon as possible to react.

[0014] Further, a sealing member can be arranged at the connection part of the injection main pipe and the injection sub-pipe, so as to reduce the leakage of the gasification agent from the gap between the two, and more gasification agent flows along the injection sub-pipe and is distributed to the coal seam at the edge of the combustion cavity. The sealing member is preferably made of flexible rubber material with pressure resistance and high temperature resistance, for example, when there are two injection sub-pipes, the sealing member is a Y-shaped rubber pipe, the main pipe (i.e. the lower part of Y) of the rubber pipe is fixed inside the injection main pipe, and the branch pipes (i.e. the upper branches of Y) of the rubber pipe are fixed in the two injection sub-pipes, respectively.

[0015] In combination with the above technical solutions and the technical problems solved, the technical solutions protected by the present application have the following advantages and positive effects:

[0016] First, in order to promote the gasification agent to quickly reach the radial coal surface of the gasification channel and react with it, the end structure of the injection pipe is improved in the present application, so that the gasification agent injected can be more dispersed, contact the gasification coal surface as soon as possible, cover a larger coal seam gasification surface, and thus improve the amount of coal gasified by a single well.

[0017] The equivalent diameter (outer diameter) of the plurality of injection sub-pipes is less than or equal to the equivalent outer diameter of the injection main pipe, and the length of the injection sub-pipe is greater than or equal to 3 times, preferably 5-10 times, the equivalent outer diameter of the injection main pipe. In theory, the longer the length of the injection sub-pipe, the farther the gasification agent can be dispersed from the gasification channel after the end of each injection sub-pipe is spread out, which is conducive to the expansion of the width of the gasification zone (or the combustion air zone). However, the distribution of the gasification agent along the direction of the injection sub-pipe needs to be considered. Too long injection sub-pipes will cause the gasification agent to be concentrated around the end of the injection sub-pipe, while there is less gasification agent at the connection between the injection sub-pipe and the injection main pipe, thereby forming multiple gasification zones or combustion air zones with less overlap, resulting in coal mining loss and resource waste. Alternatively, the injection sub-pipe has a gas distribution hole in the length direction. Too long injection sub-pipes will cause the gasification agent to be dispersed from the gas distribution hole before it reaches the end of the injection sub-pipe, so the part of the injection sub-pipe near the end will not play a role in gas distribution. In addition, the length of the injection sub-pipe is designed to be greater than or equal to 3 times, preferably 5-10 times, the equivalent outer diameter of the injection main pipe, considering the connection strength of the injection sub-pipe and the injection main pipe, and the driving ability of the elastic member between different injection sub-pipes.

[0018] Second, according to the pilot test data, under the condition that all other conditions are the same, the cross-sectional area of the combustion air zone of the injection end with the injection sub-pipe is 2 times larger than that of the injection end without the injection sub-pipe. In real underground gasification of coal seams, when all other process parameters are the same, using the injection end with the injection sub-pipe for gasification and using the injection end without the injection sub-pipe for gasification, the cross-sectional area of the combustion air zone obtained by the former is conservatively estimated to be 1.5 times that of the latter, and the amount of gasified coal is estimated to be 1.5 times that of the latter. Only the construction cost of the gasification channel in the coal seam (the cost of drilling a hole in the coal seam in a non-well underground gasification project is 4000-6000 yuan / m, and the coal seam drilling is usually 100-200 m) can save more than 33%, and the labor cost and time cost can also be saved but are not easy to estimate.

[0019] The technical solution of the present application only needs to match appropriate injection sub-pipes to expand the expected width of the gasification combustion air zone in the lateral direction through the narrow gasification channel of the coal seam. Before this solution, the width of the lateral expansion of the combustion air zone was uncontrollable and could only be appropriately affected by increasing the pressure and flow rate of the injected gasification agent, making it difficult to achieve the desired result. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 is a schematic diagram of the injection end structure provided by the embodiment of the present application;

[0021] Figure 2 is a schematic diagram of the end of the injection main pipe provided by the embodiment of the present application;

[0022] Figure 3 is a schematic diagram of the end of the injection sub-pipe provided by the embodiment of the present application;

[0023] Figure 4 is a connection diagram of injection sub-pipes provided by the embodiment of the present application;

[0024] Figure 5 is a cross-sectional diagram of a combustion and emptying area of the prior art provided by the embodiment of the present application;

[0025] Figure 6 is a cross-sectional diagram of a combustion and emptying area provided by the embodiment of the present application;

[0026] Figure 7 is a diagram of a conventional underground gasification combustion and emptying area provided by the embodiment of the present application;

[0027] Figure 8 is a diagram of an underground gasification combustion and emptying area of the present application provided by the embodiment of the present application;

[0028] Figure 9 is a cross-sectional diagram of a conventional underground gasification combustion and emptying area provided by the embodiment of the present application;

[0029] Figure 10 is a cross-sectional diagram of an underground gasification combustion and emptying area of the present application provided by the embodiment of the present application;

[0030] Figure 11 is a cross-sectional diagram of a conventional underground gasification combustion and emptying area of 19cm*21cm provided by the embodiment of the present application;

[0031] Figure 12 is a cross-sectional diagram of an underground gasification combustion and emptying area of 40cm*22cm of the present application provided by the embodiment of the present application;

[0032] Figure 13 is a diagram of connection of injection main pipes, injection sub-pipes and sealing members provided by the embodiment of the present application;

[0033] Figure 14 is a diagram of a connection part of an injection main pipe and a sealing member main pipe provided by the embodiment of the present application;

[0034] In the diagram: 1, injection main pipe; 2, injection sub-pipe; 3, hinge; 4, ear-shaped structure; 5, elastic part; 6, sealing member main pipe; 7, sealing member branch pipe; 8, sleeve; 9, tension ring. DETAILED DESCRIPTION

[0035] In order to make the purpose, technical scheme and advantages of the present application more clear, the present application is further described in detail below with embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application, and are not used to limit the present application.

[0036] In the coal underground gasification project, the existing gas injection pipe structure generally faces the problems of limited space, uneven gas distribution and insufficient coal seam coverage. These problems directly lead to the inability of gasification agent to quickly contact the coal surface, low gasification reaction efficiency and insufficient coal conversion rate. Especially when the pipe is sent into the underground combustion area through a narrow borehole or gasification channel, the end of the traditional rigid pipe lacks a variable structure, often only forming local gas distribution, and cannot meet the demand of covering a large range of coal seam section. Therefore, how to expand the gas injection end in a limited space and evenly distribute the gasification agent is a key problem that the industry has been trying to solve for a long time.

[0037] The "gas injection end structure" proposed in this application provides a systematic solution to this technical dilemma. By setting a hinge 3 and elastic component 5 combination structure between the injection main pipe 1 and multiple injection sub-pipes 2, the end of the injection sub-pipe 2 can automatically expand around the hinge after the constraint is removed, showing a scissors-like expansion effect. The presence of the elastic component 5 allows the end of each injection sub-pipe 2 to quickly open when the force is released, forming a larger gas distribution range. This structure avoids the fixed form of rigid pipes and realizes the dual functions of transportation and expansion under limited borehole conditions.

[0038] In terms of working mechanism, the constraint component undertakes the task of volume folding during transportation and can be in the form of a fuse rope, a connected plug, etc. When the gas injection end reaches the target gasification area, the external temperature, pressure or the action of the gasification agent itself can trigger the constraint to be removed, and the elastic component to contract, causing the ends of the injection sub-pipes to move away from each other, achieving the expansion effect. This process does not require additional complex mechanical operations and can be realized relying on the coal seam environmental conditions, demonstrating the advantages of structure self-adaptation and coal seam coupling.

[0039] After the end expands, each injection sub-pipe 2 is at an angle (the angle is greater than 0 degrees and less than or equal to 60 degrees, preferably 30 to 45 degrees) with the main pipe according to the designed angle, which can effectively disperse the gasification agent to the edge and lower part of the combustion area. Compared with straight-through gas distribution, the present application is beneficial to improve the overall coal gasification rate. This guided gas distribution mode not only improves the utilization rate of the combustion area, but also reduces the residual coal and improves the gas production.

[0040] In addition, the injection sub-pipe 2 is provided with gas distribution holes along the length direction, and a pressure-resistant and high-temperature-resistant rubber sealing element (such as a Y-shaped rubber pipe) is used to seal the joint between the injection main pipe and the injection sub-pipe, further ensuring efficient transfer and dispersion of the gasification agent. The sealing structure significantly reduces the gap leakage, so that more gasification agent can enter the injection sub-pipe and ultimately act on the coal seam, improving energy efficiency and coal utilization rate.

[0041] The significance of the gas injection end structure in industrial application is that it can solve the engineering feasibility of entering narrow passages and achieve efficient and wide coverage of gas distribution in the coal seam combustion area. The working principle embodies the four-step cycle mechanism of "constraint-release-expansion-uniform distribution", relying on the mechanical cooperation of elastic components and hinges, and showing high reliability and easy operation under extreme underground conditions. This innovative design significantly improves the efficiency and potential for large-scale application of the underground coal gasification process.

[0042] The application provides a gas injection end structure of a gas injection pipe for underground coal gasification, which comprises a gasification agent injection main pipe 1 and at least two gasification agent injection branch pipes 2 with variable end-to-end distance, which are movably connected with the gasification agent injection main pipe. One end of the injection branch pipe 2 connected with the injection main pipe 1 is a movable end, and the other end is a terminal end. The movable ends of the two injection branch pipes 2 are connected through elastic components 5. The connection part of the elastic components 5 is the side of the injection branch pipe 2 close to the pipe wall of the injection main pipe 1. The side of each injection branch pipe 2 corresponding to the connection part of the elastic components 5 is connected with the injection main pipe 1 through a hinge 3. The terminal ends of the plurality of injection branch pipes 2 are constrained together by releasable constraint members. The gas injection end with the continuous pipe can enter the underground coal seam gasification area through a narrow borehole and gasification passage. Under external action, the constraint members are released, the terminal ends of the plurality of injection branch pipes 2 move away from each other, disperse the gasification agent to the gasification area, and quickly contact the gasification coal surface, so as to cover a larger coal seam section with the gasification agent, and further gasify a larger amount of coal.

[0043] As shown in Figure 2 , one end of the injection main pipe 1 is provided with two ear-shaped structures 4 parallel to each other and parallel to the pipe wall of the injection main pipe 1. The movable end of the injection branch pipe 2 is provided with two ear-shaped structures 4. One of the ear-shaped structures 4 can be used as a hinge, referred to as a hinge ear, and the ear surface of the hinge ear is perpendicular to the central axis of the injection branch pipe 2. The other ear-shaped structure is used for elastic connection, referred to as an elastic connection ear, and the ear surface of the elastic connection ear is an extension cut of the pipe wall of the injection branch pipe 2. Each injection branch pipe 2 is hingedly connected with the ear-shaped structure of the injection main pipe through a hinge structure. The elastic connection ears of the injection branch pipe 2 are connected through elastic components 5. The distance between the terminal ends of the injection branch pipe 2 is adjusted through the expansion and contraction of the elastic components 5.

[0044] As shown in Figure 3 , the injection branch pipe 2 can be multiple, and the cross section of each injection branch pipe 2 is approximately fan-shaped, and the fan angle is 360 / n degrees (n is the number of injection branch pipes 2). In this way, the space utilization can be improved to the greatest extent. Preferably, the injection branch pipe 2 is two, and the cross section of the injection branch pipe 2 is approximately semicircular. The structure is relatively simple, easy to fix, and more importantly, when dispersing the gasification agent to the combustion area in the underground coal gasification, the gas distribution to the lower area of the edge of the combustion area is the best, so that more coal can be gasified.

[0045] The end of each injection sub-pipe 2 is expanded after the connection, and the central axis of the injection main pipe 1 and the injection sub-pipe 2 forms an angle a (0° < a ≤ 60°), preferably 30°-45°. In this angle range, the coal gasification effect is best.

[0046] The injection sub-pipe 2 is provided with a gas distribution hole along the length direction thereof, so as to increase the gasification agent dispersion efficiency.

[0047] The connection part of the injection main pipe 1 and the injection sub-pipe 2 can be provided with a sealing member, so as to reduce the leakage of the gasification agent from the gap between the two, and more gasification agent flows along the injection sub-pipe and is distributed to the coal seam at the edge of the combustion and gasification area; the sealing member is preferably made of flexible rubber material with pressure resistance and high temperature resistance, such as Y-shaped rubber pipe, the main pipe of the rubber pipe is fixed in the injection main pipe 1, and the branch pipes of the rubber pipe are respectively fixed in the injection sub-pipe 2.

[0048] The end of the injection sub-pipe 2 is provided with a restraint member, the ends of the plurality of injection sub-pipes 2 are restrained together, the space volume is reduced, and the injection sub-pipes 2 can be sent into the underground gasification area through a narrow borehole, at this time, the elastic member connecting the injection sub-pipes is in a tension or stretching state. After reaching the gasification area, the restraint member can be released under external action such as gasification agent pressure, temperature, mechanical force and the like, the elastic member is contracted, the injection sub-pipe 2 rotates around the hinge structure as the axis, and the ends of the different injection sub-pipes 2 are expanded.

[0049] The restraint member can be a rope that can be melted at a certain temperature, or a plurality of connected plugs that can be sprayed out of the injection sub-pipe 2 under a certain gas pressure, or a plug with holes that is gasified and removed as the temperature rises.

[0050] The use method (steps) of the present application:

[0051] 1. The injection main pipe 1 and the injection sub-pipe 2 of the gas injection end are connected, the different injection sub-pipes 2 are connected together through the elastic member, and each injection sub-pipe 2 is connected to the injection main pipe through the hinge structure.

[0052] 2. One end of the injection main pipe 1 is connected to the continuous pipe for conveying the gasification agent.

[0053] 3. The ends of all the injection sub-pipes 2 are restrained together through the restraint member, at this time, the elastic member is in a tension (stretching) state.

[0054] 4. The gas injection end follows the continuous pipe and is sent into the predetermined position of the underground coal seam to be gasified through the narrow borehole and the coal seam gasification channel.

[0055] 5. After ignition, the gasification agent and the coal have a combustion-gasification reaction, the restraint member is released in the high temperature and high pressure environment, the elastic member 5 is contracted, drives each injection sub-pipe 2 to rotate around the hinge structure as the axis, and the ends of each injection sub-pipe 2 are slightly expanded.

[0056] 6. As coal seam gasification proceeds, the gasification channel where the gas injection end is located gradually widens, and the end of injection branch pipe 2 is fully expanded, dispersing the gasifying agent towards the edge of the gasification zone to achieve the best effect.

[0057] 7. After gasification for a period of time, the continuous pipe is withdrawn. Due to the narrowing of the gasification channel, the channel walls force the ends of each injection branch pipe 2 to move closer to each other (i.e., injection branch pipe 2 is retracted), and the elastic component is once again in a tensioned (stretched) state. In this way, one deployment and retraction of injection branch pipe 2 is completed. After reaching the new position, injection branch pipe 2 continues to inject gasifying agent to gasify the coal seam.

[0058] 8. As coal seam gasification proceeds, the gasification channel where the gas injection end is located gradually widens, and multiple injection pipes 2 can gradually expand to disperse the gasifying agent to the edge of the gasification zone.

[0059] Repeat steps 6-8 above until the expected underground coal seam is completely gasified.

[0060] Example 1

[0061] like Figures 1-4 As shown, a gas injection end structure for an underground coal gasification gasification pipe includes a main injection pipe 1, with two ear-shaped structures 4 extending along the pipe wall at its end. Two branch injection pipes 2 each have two ear-shaped structures 4 at their movable ends. One ear-shaped structure is connected to the ear-shaped structure of the main injection pipe via a hinge 3, and the other ear-shaped structure is connected to the adjacent branch injection pipe via an elastic component 5. During transportation, the ends of the two branch injection pipes 2 are fixed together by restraints to maintain a folded state.

[0062] like Figure 4 As shown in the attached figure, during use, the injection end enters the coal seam gasification zone along with the continuous pipe. Under high temperature or pressure, the restraints are released, and the elastic components contract, causing each injection branch pipe 2 to unfold around the hinge 3. After the ends of each injection branch pipe 2 unfold, the gasifying agent is injected into the combustion air zone through each injection branch pipe 2, thereby expanding the gas distribution range and achieving rapid coverage of the coal seam cross-section. The combustion air zone morphology obtained by underground coal seam gasification using the injection end structure designed in this application is shown in the attached figure. Figure 6 , Figure 8 , Figure 10 ) and conventional gas injection end structure ( Figure 5 , Figure 7 , Figure 9 Compared to the previous method, the width of the combustion zone and the degree of gasification of the underlying coal seam are significantly increased.

[0063] Example 2

[0064] The injection end of the injection pipe for underground coal gasification is provided with two injection branch pipes 2 with approximately semicircular cross sections below the injection main pipe 1. The two injection branch pipes are kept in parallel and folded state under the action of the constraint member, and can enter the coal seam combustion area through the narrow borehole. After reaching the target position, the constraint member is released under the action of external force, and the end of the injection branch pipe 2 is unfolded under the action of the elastic member to form a fan-shaped distribution.

[0065] After the injection branch pipe 2 is unfolded, the injection direction corresponds to the lower edge area of the combustion area, and the gasification agent can directly flow to the lower edge of the coal seam, and preferentially gasify the bottom coal, as shown in Figure 8 In the underground coal gasification using the conventional injection structure, the coal in the lower area is difficult to contact the gasification agent, which is easy to cause coal loss and waste of resources. The design improves the overall coal gasification efficiency and increases the utilization rate of the coal seam.

[0066] Embodiment 3

[0067] In another embodiment, an angle is formed between the injection branch pipe 2 and the axis of the injection main pipe 1 after the injection branch pipe 2 is unfolded. The range of the angle is controlled to be 30 to 45 degrees, which ensures that the injection branch pipe 2 can disperse the gasification agent after unfolding, and does not interfere with each other. The range of the angle can be controlled by selecting different specifications of the elastic member. For example, the elastic member is a spring, and the angle after the injection branch pipe is unfolded can be controlled by selecting springs of different lengths. The longer the spring is stretched, the larger the angle after the injection branch pipe 2 is unfolded (i.e. after the spring is contracted), and vice versa.

[0068] In actual operation, the two injection branch pipes 2 respectively inject the gasification agent in different directions after unfolding, covering a larger range of coal seam section in the combustion area. Compared with the traditional linear gas distribution, this angle gas distribution method can reduce the dead angle area, improve the coal mining rate and gas production.

[0069] Embodiment 4

[0070] A plurality of gas distribution holes are uniformly arranged along the length direction of the injection branch pipe 2, and the diameter of the gas distribution hole is controlled within a reasonable range, so that the gasification agent can be uniformly discharged during the transportation of the injection branch pipe 2. The distribution of the gas distribution holes gradually increases from the end close to the injection main pipe 1 to the end of the injection branch pipe 2, forming a gradient arrangement.

[0071] During the gasification process, the gasification agent is not only injected from the end of the injection branch pipe 2, but also released step by step along the gas distribution hole, so that the gasification agent forms a multi-point gas distribution mode in the combustion area of the coal seam. This mode increases the contact area between the gasification agent and the coal surface, improves the coal reaction rate, and reduces the risk of local temperature unevenness.

[0072] Embodiment 5

[0073] As shown in Figure 13 ,Figure 14 As shown, at the connection between the injection main pipe 1 and the injection branch pipe 2, a high-temperature and high-pressure resistant flexible rubber seal is installed. The flexible rubber seal includes a seal main pipe 6 and a plurality of seal branch pipes 7 at one end of the seal main pipe 6 and in communication with the seal main pipe 6. A plurality of holes or inwardly extending sleeves are provided on the seal main pipe 6 near the connection with the seal branch pipes 7, through which the elastic members 5 of the injection branch pipe 2 can pass into the interior of the seal main pipe 6. When connected, the seal main pipe 6 is placed in the injection main pipe 1, and the seal branch pipes 7 are respectively placed in the plurality of injection branch pipes 2.

[0074] The elastic members 5 of the injection branch pipe 2 pass through the small holes or sleeves 8 on the seal main pipe 6 into the interior of the seal main pipe 6, and are then connected by the elastic members 5. The small holes or sleeves 8 on the seal main pipe 6 and the elastic members 5 of the injection branch pipe 2 can be tightly fitted or tightly fitted by fasteners. For example, a tension ring 9 is provided in the seal branch pipe 7 and the seal main pipe 6, so that the wall of the seal pipe and the wall of the injection pipe are tightly fitted together.

[0075] The seal can withstand the high-temperature and high-pressure environment of the coal seam and maintain good sealing performance. The seal can be made of any suitable material, and the shape can be adjusted according to the number of injection branch pipes 2.

[0076] During operation, when the gasifying agent flows from the injection main pipe 1 to the injection branch pipe 2, the seal effectively blocks the leakage at the joint, allowing more gasifying agent to enter the injection branch pipe 2 and flow to the coal seam combustion area. By reducing the amount of leakage, the utilization efficiency of the gasifying agent is improved, and the overall uniformity of the coal seam gasification is improved.

[0077] Example 6

[0078] In a specific application, high-temperature fusible ropes are used as restraining members at the ends of the injection branch pipes 2 to tightly bind the ends of the two injection branch pipes 2. After the gas injection end enters the coal seam gasification area, the high-temperature environment of the coal seam causes the ropes to automatically melt and break, and the injection branch pipes 2 rapidly expand under the action of the elastic members, forming a gas distribution structure.

[0079] In another way, the restraining member is a connected plug that is inserted into the mouth of the injection branch pipe 2. Under the action of the gasifying agent pressure, the connected plug is pushed out and discharged with the gas flow, or the perforated plug is gradually decomposed by the high-temperature environment of the coal seam. This structure does not require manual intervention and can automatically release the restraint under certain conditions to achieve automatic expansion of the gas injection end structure.

[0080] In another way, the constraint member adopts a dissolvable sleeve, such as a PVB sleeve, which can be a single sleeve or multiple sleeves connected together. If it is a single sleeve, all the injection sub-pipes 2 can be sleeved at the end. If it is multiple sleeves connected together, the sleeves can be designed according to the number of injection sub-pipes, so that each sleeve can sleeve the end of one injection sub-pipe 2. In later use, the sleeve gradually gasifies and decomposes in the high-temperature environment of the coal seam, thereby releasing the constraint on the end of the injection sub-pipe 2.

[0081] Example 7

[0082] In the underground coal gasification pilot furnace, the coal blocks of 80 cm*80 cm*80 cm are spliced into a coal seam of 80 cm*80 cm*640 cm, the lower part of each coal block is punched with a 2 cm diameter hole, which is connected to simulate the gasification channel in the coal seam, the surrounding and upper part of the coal seam is rammed with loess, and the conventional gasification agent injection pipe (inner diameter of 15 mm) is lowered into the gasification channel for gasification. When the total content of the effective components of the coal gas is monitored to decrease by 10%, the gasification agent injection pipe is withdrawn by a distance (20 cm) again, the total content of the effective components of the coal gas gradually increases, and after a period of stabilization, it begins to decrease again. When it decreases by 10%, the gasification agent injection pipe is withdrawn by a distance (20 cm) again. After such repeated withdrawal for at least 5 times, nitrogen is injected to extinguish the fire, reduce the temperature and pressure, the experimental furnace is opened, the loess layer is peeled off, and the width of the cross section of the conventional underground gasification combustion void is measured to be 19 cm, and the height is 21 cm (as shown in Figure 11

[0083] In the comparative experiment, the gasification agent injection pipe is replaced with an injection pipe with injection sub-pipes 2 (the total pipe inner diameter is 15 mm, and the length of the two injection sub-pipes is 5 cm), and all the devices, operating parameters, and operation steps are the same as those in the above experiment. The width of the cross section of the underground gasification combustion void of the present application is 40 cm, and the height is 22 cm (as shown in Figure 12

[0084] Figure 11 Figure 12 The comparison shows the difference in the actual underground gasification combustion void cross-sectional area between the conventional injection pipe and the gas injection end structure of the present application. The cross section of the combustion void formed by the conventional injection pipe is about 19 cm*21 cm, while the cross section of the combustion void under the action of the gas injection end structure of the present application can reach 40 cm*22 cm, which is about 2.2 times the cross-sectional area of the conventional injection pipe underground gasification combustion void, obviously expanding the cross-sectional area of the combustion void. This result shows that the present application can realize the more distant dispersion supply of the gasification agent in the coal seam, thereby effectively expanding the combustion void, improving the utilization rate of coal resources, and avoiding the leakage of mining and resource waste.

[0085] ​​​The above merely provides the specific implementation of the present application, but the protection scope of the present application is not limited to this. Any modification, equivalent replacement and improvement made by any person skilled in the art within the technical scope disclosed by the present application, and within the spirit and principle of the present application, should be covered within the protection scope of the present application.

Claims

1. A structure of a gas injection end of a gas injection pipe for underground coal gasification, characterized by, The injection manifold comprises a gasification agent injection main pipe and at least two injection sub-pipes connected to the end of the injection main pipe; The end of the injection sub-pipe connected to the injection main pipe is a movable end, and the other end is a terminal end. The movable ends of the two injection sub-pipes are connected by an elastic component. The connection part of the elastic component is located on the side of the injection sub-pipe close to the wall of the injection main pipe. The side of the movable end of each injection sub-pipe corresponding to the connection part of the elastic component is connected to the injection main pipe by a hinge. The terminal ends of the injection sub-pipes are fixed together by a restraint. Under external action, the restraint is removed, and the terminal ends of the injection sub-pipes can be separated from each other. The end of the injection main pipe is provided with two ear-shaped structures extending along the wall of the pipe. The movable end of each injection sub-pipe is also provided with two ear-shaped structures. One of the ear-shaped structures is used for hinge connection with the injection main pipe, and the other ear-shaped structure is used for connection with the elastic component. At the connection between the injection main pipe and the injection sub-pipes, a high-temperature and high-pressure resistant flexible rubber sealing element is installed. The flexible rubber sealing element comprises a sealing element main pipe and a plurality of sealing element branch pipes connected to one end of the main pipe and in communication with the main pipe. A plurality of holes or inwardly extending sleeves are provided on the sealing element main pipe and close to the connection of the sealing element branch pipes, which can be used for the elastic component of the injection sub-pipe to pass through and enter the inside of the sealing element main pipe. When connected, the sealing element main pipe is placed in the injection main pipe, and the sealing element branch pipes are placed in the plurality of injection sub-pipes, respectively. The restraint is a component that can be removed under certain temperature or gas pressure conditions. The restraint is a fuse rope, a connected plug that can be sprayed under gas pressure, or a sleeve that can be decomposed during the coal gasification process.

2. The gas injection end structure of claim 1, wherein The cross section of the injection sub-pipe is a sector, and the sector angle is equal to 360 degrees divided by the number of sub-pipes. When the number of sub-pipes is 2, the cross section of the injection sub-pipe is a semicircle.

3. The gas injection end structure of claim 2, wherein When the terminal ends of the injection sub-pipes are separated from each other, the injection sub-pipes form an included angle with the central axis of the injection main pipe. The included angle is greater than 0 degrees and less than or equal to 60 degrees.

4. The gas injection end structure of claim 3, wherein The included angle is 30 to 45 degrees.

5. The gas injection end structure of claim 1, wherein The length of the injection sub-pipe is greater than or equal to 3 times the equivalent outside diameter of the injection main pipe.

6. The gas injection end structure of claim 1, wherein The injection sub-pipe is provided with a plurality of gas distribution holes along its length direction, which are used to expand the contact area of the coal seam during the dispersion of the gasification agent.

7. The gas injection end structure of claim 1, wherein The connection part of the injection main pipe and the injection sub-pipe is provided with a sealing element, which is used to reduce the leakage of the gasification agent at the connection gap and make more gasification agent flow along the injection sub-pipe.

8. The gas injection end structure of claim 7, wherein The sealing element is a pressure-resistant and high-temperature-resistant flexible rubber pipe structure. The main pipe end of the rubber pipe is fixed inside the injection main pipe, and the branch pipe end is fixed in each injection sub-pipe.

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