Underground coal gasification method and gas injection equipment

Abstract

The invention belongs to but not limited to the technical field of underground coal gasification, and discloses an underground coal gasification method and gas injection equipment. Constructing a directional drill hole and a gasification channel penetrating through the underground coal seam; a gas injection pipe with a plasma torch is put into the gasification channel, a gasification agent is injected, and in-situ gasification of the underground coal seam is implemented; and the generated gas is conveyed to the ground for collection through the drill hole. According to the underground coal gasification method and the gas injection equipment provided by the invention, the gasification agent is activated by the plurality of plasma torches arranged in the directional channel at the tail end of the gas injection pipe and then is directionally jetted to the coal seam, so that the gasification agent is in contact with the coal seam in a short time and is gasified, the directional conveying of the plasma gasification agent is realized, and the effective utilization rate of the plasma gasification agent is improved; meanwhile, a combustion space area of the coal seam after gasification can be expanded in a fan shape in the longitudinal direction with the gasification agent outlets of the plasma torches as the center, the expansion equivalent radius of the combustion space area is relatively large, and a large amount of coal can be gasified through one gasification channel.

Description

Technical Field

[0001] The present invention belongs to, but is not limited to, the technical field of underground coal gasification, and particularly relates to a method for underground coal gasification and an air injection device. Background Art

[0002] In the process of underground coal plasma gasification, a gasifying agent (such as one or more of air, water vapor, oxygen, etc.) is first plasmaized by a plasma torch and then contacts the coal seam to undergo a gasification reaction, which can be converted into gas with a higher content of effective components (such as carbon monoxide, hydrogen, methane, etc.). In the existing underground coal plasma gasification technology, usually a plasma torch is arranged at the end of the gasifying agent injection pipe, and the injected gasifying agent is converted into an activated gasifying agent (plasmaized free radicals) by the action of the plasma torch, shoots out of the injection pipe and enters the high-temperature gasification area to act on the coal seam for gasification. As Figure 1 shown, the problem is that the ejection direction of the gasifying agent is uncontrollable. If the activated gasifying agent cannot contact the coal seam in time to react in the gasification area, it will be converted into a non-activated gasifying agent (no longer plasmaized free radicals), losing the significance of plasmaization, and the effective utilization rate of the plasma gasifying agent will be greatly affected, resulting in a low content of effective components in the gas; at the same time, the burned-out area after gasification of the coal seam usually expands in a fan shape longitudinally ( Figure 1 along the A-A section in

[0003] centered on the gas injection channel), and the expansion radius of the burned-out area is relatively small, and the amount of gasified coal is relatively small. In the scenario of in-situ underground coal gasification, gasifying agents such as oxygen / steam need to be directly injected into the coal seam through a narrow wellbore, making it difficult to achieve the axial shunting or multi-directional jet of the gasifying agent in the slender injection pipe, and it is also impossible to form a "fan-shaped coverage" type plasma gas flow in the narrow gasification area. The plasma (activated) gasifying agent becomes inactivated because it fails to contact and act on the coal seam in a short time, resulting in a low utilization rate of the activated gasifying agent. Summary of the Invention

[0004] Aiming at the problems existing in the prior art, the present invention provides a method for underground coal gasification and an air injection device, which use multiple plasma torches to inject the gasifying agent and make the gasifying agent shoot towards the coal seam directionally, shortening the time for the gasifying agent to reach the coal seam and expanding the gasification surface.

[0005] The present invention is implemented as follows. A method for underground coal gasification includes the following steps:

[0006] S1, constructing a directional borehole and a gasification channel penetrating the underground coal seam;

[0007] S2, lowering an injection pipe carrying a plasma torch into the gasification channel and injecting a gasifying agent to implement in-situ gasification of the underground coal seam; the gasifying agent is shunted to multiple plasma torches through a diversion channel at the end of the injection pipe and is directionally shot towards the coal seam after being activated by the plasma torch;

[0008] S3. The generated coal gas is transported to the ground for collection through the boreholes.

[0009] Furthermore, after the injection pipe carrying the plasma torches reaches the predetermined position of the gasification channel, the ground control system is used to move the ends of the plasma torches away from each other, so as to make the range of the gasifying agent spread wider.

[0010] Furthermore, the method for moving the ends of the plasma torches away from each other includes, but is not limited to: moving each plasma torch relative to the end of the injection pipe through the diverging channels to move away from each other, or gasifying the coal seam for a period of time to increase the temperature of the environment where the plasma torches are located, releasing the rigging that restricts the plasma torches, and the plasma torches restore their original set orientations under the resilience of the connecting pipes, so as to achieve the mutual separation of the ends of the plasma torches.

[0011] Furthermore, the injected gasifying agent is a mixture of one or more of water vapor, carbon dioxide, air and oxygen; preferably a combination of carbon dioxide and oxygen.

[0012] Furthermore, the volume fraction of oxygen is between 30% and 70%; preferably between 40% and 55%.

[0013] Another object of the present invention is to provide an underground coal gasification gas injection device, which includes a gasifying agent injection pipe, a gas injection pipe driving system, and multiple plasma torches arranged at the end section of the gasifying agent injection pipe, and the directions of the gasifying agent ejected by each plasma torch are different.

[0014] The interior of the end section of the injection pipe is a multi-diverging channel, and each diverging channel can accommodate a plasma torch, so that the plasma gasifying agents ejected by different plasma torches face different directions; the multiple plasma torches in the injection pipe can be arranged side by side or front and back.

[0015] Furthermore, at one end of the gasification agent flow channels of each plasma torch away from the plasma gasification agent outlet, they are aggregated. A tensioning part is arranged on the outer periphery of the aggregated pipe section of the plasma torch flow channels. The tensioning part expands outwards under the action of gas or external force, so as to cut off the gap between the outer edge of the aggregated pipe section and the inner wall of the injection pipe.

[0016] Furthermore, when arranged side by side, each diverging channel is internally provided with a plasma torch, and each plasma torch can move relative to the diverging channel.

[0017] Furthermore, when arranged front and back, a directional guiding part is arranged on each plasma torch to make each plasma torch move towards each diverging channel; the directional guiding part can be an arrow fixed to the end of the plasma torch and passing through the diverging channel, or a protrusion (or groove) cooperating with a groove (or protrusion) arranged on the inner wall of the diverging channel.

[0018] Furthermore, the injection device may be provided with a restraining portion, which is preferably a rigging that can be melted at 200-400°C.

[0019] In combination with the above technical solutions and the technical problems solved, the advantages and positive effects of the technical solutions to be protected by the present invention are as follows:

[0020] The present invention proposes an underground coal gasification method and gas injection equipment, in which the gasifying agent is activated by multiple plasma torches built into the branch channel at the end of the gas injection pipe and then directed toward the coal seam. The gasifying agent contacts the coal seam and is gasified in a relatively short period of time, thereby realizing the directional transportation of the plasma gasifying agent and improving the effective utilization rate of the plasma gasifying agent, thereby increasing the effective component content of the coal gas. At the same time, the combustion zone of the gasified coal seam will expand in a fan shape in the longitudinal direction with the gasifying agent outlet of each plasma torch as the center. The expansion equivalent radius of the combustion zone is relatively large, and one gasification channel can gasify a large amount of coal.

[0021] The integrated multi-torch configuration with directional channels breaks away from the traditional linear heat source model of single-nozzle gas injection. Multiple plasma torches are arranged in a fan-shaped pattern along the end of the gas injection pipe, with their jet directions staggered. This allows for the simultaneous establishment of multiple gasification zones within thick coal seams, creating an annular oxidation zone and a uniform reaction front. This spatial distribution significantly reduces residual carbon content, shortens combustion channel formation time, and stabilizes the pressure distribution in the gasification zone, directly increasing single-well gas production and carbon conversion.

[0022] The combination of the converging pipe section and the tensioning section ensures that the gasifying agent first merges and then diverges within the gas injection pipe. The tensioning section expands under pressure to form a circumferential contact seal. This prevents "bypass" leakage of the gasifying agent along the pipe wall, ensuring that all the gasifying agent flows through the plasma torch and is activated. It also stabilizes the relative position of the gas injection pipe and each plasma torch, reducing the adverse effects of airflow vibration on the plasma torch.

[0023] The guide and relative movement mechanism allow for adjustable release positions of the plasma torch underground. Under varying installation conditions, the torch can smoothly move along the directional channel and lock at preset limits, ensuring the jet angle matches the coal seam inclination. This structure improves the device's adaptability to varying wellbore diameters, coal seam thicknesses, and orientations, eliminating repeated drilling operations and alleviating the stringent requirements for precise wellbore deviation on-site.

[0024] The constraint uses a heat-melt trigger material to hold the multiple plasma torches together during the run-down phase. The overall outer diameter is nearly identical to the inner diameter of the gas injection pipe, allowing for easy passage through narrow or tortuous well sections. Upon reaching the target location, spontaneous heating or coal seam temperature rise causes the constraint to fuse securely, allowing the plasma torches to elastically expand via the connecting pipe. This allows for a transition from "compact transport" to "deployed operations," streamlining the run-down process and reducing the risk of wellbore damage from mechanical intervention. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 is a schematic diagram of underground coal seam plasma gasification provided by the prior art;

[0026] Figure 2 is a schematic diagram of the longitudinal section morphology of the combustion air zone provided by an embodiment of the present invention;

[0027] Figure 3 is a schematic diagram of the cross-section at the end of the gas injection pipe provided by an embodiment of the present invention;

[0028] Figure 4 is a schematic diagram of multiple plasma torches juxtaposed provided by an embodiment of the present invention;

[0029] Figure 5 is a schematic diagram of each plasma torch after the restraint is released provided by an embodiment of the present invention;

[0030] Figure 6 is a schematic diagram of the cross-section of the gas injection pipe with a guiding part provided by an embodiment of the present invention;

[0031] Figure 7 is a schematic diagram of the movable connection cross-section of the plasma torch and the gas injection pipe provided by an embodiment of the present invention;

[0032] Figure 8 is a schematic diagram of the front and back settings of each plasma torch provided by an embodiment of the present invention;

[0033] Figure 9 is a schematic diagram of the end of the plasma torch and the fixed arrow provided by an embodiment of the present invention;

[0034] Figure 10 is a flowchart of the underground coal gasification method provided by an embodiment of the present invention;

[0035] In the figure: 1. Gas injection pipe; 2. Plasma torch; 3. Diversion channel; 4. Tension part; 5. Guiding part; 6. Gas injection pipe wall; 7. Plasma torch outer wall; 8. Arrow; 9. Plasma torch flow channel collecting pipe section; 10. Gasification channel; 11. Injection pipe with plasma torch. Detailed implementation manners

[0036] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0037] An embodiment of the present invention provides an underground coal gasification gas injection device, including a gasification agent injection pipe 1, a gasification injection pipe drive system, and multiple plasma torches 2 arranged at the end section of the gasification agent injection pipe. The directions in which each plasma torch 2 injects the gasification agent are different; it can enable the plasma gasification agent to come into contact with the coal seam in a timely manner to undergo a gasification reaction, cover a larger coal seam gasification surface, and improve the effective utilization rate of the plasma gasification agent.

[0038] The gasifying agent flow channels of each plasma torch 2 converge at one end far from the plasma gasifying agent outlet, so as to realize the diversion of the gasifying agent conveyed by the injection pipe 1 into each plasma torch. In order to make the gasifying agent flow through the plasma torch 2 as much as possible, a tensioning part 4 is arranged on the outer periphery of the plasma torch flow channel converging pipe section 9. The tensioning part 4 expands outwards under the action of gas or external force, so as to cut off the gap between the outer edge of the converging pipe section and the inner wall of the injection pipe 1, prevent the gasifying agent from flowing through the gap into the gasification area instead of entering the gasification area after being activated by the plasma torch, and improve the plasma ionization rate of the gasifying agent.

[0039] Each plasma torch 2 is built into the injection pipe 1, and under the action of the ground driving system, each plasma torch descends into the underground gasification channel 10 together with the injection pipe. That is, an injection pipe 11 with a plasma torch is laid in the gasification channel 10.

[0040] As Figure 3 shown, the inner part of the end section of the injection pipe 1 is a multi-directional channel 3, and each multi-directional channel 3 can accommodate a plasma torch 2, so that the plasma gasifying agents ejected by different plasma torches 2 face different directions. The multiple plasma torches 2 in the injection pipe 1 can be arranged in parallel or in front and back.

[0041] As Figure 4 shown, when arranged in parallel, each multi-directional channel houses a plasma torch 2, and each plasma torch can move relative to the multi-directional channel 3 of the injection pipe.

[0042] As Figure 8 shown, when arranged in front and back, a directional guiding part 5 ( Figure 6 ) is arranged on each plasma torch 2 to realize the purpose of each plasma torch 2 moving towards each multi-directional channel 3. The directional guiding part 5 can be an arrow 8 fixed at the end of the plasma torch and passing through the multi-directional channel ( Figure 9 ), or a protrusion (or groove) that cooperates with a groove (or protrusion) arranged on the inner wall of the multi-directional channel ( Figure 7 ). This solution can realize the deviation of the orientation of each plasma torch when the outer diameter of the end of the injection pipe is not much different (≤30%) from the outer diameter of the main body of the injection pipe.

[0043] When multiple plasma torches 2 are axially installed in sequence on the injection pipe 1, the plasma torches 2 can be relatively moved along the direction of the injection pipe 1 through an external driving mechanism, so as to increase the distance between the ends of each plasma torch.

[0044] To ensure uniform supply of the gasifying agent, each plasma torch 2 is provided with an independent gasifying agent flow channel. All the gasifying agent flow channels converge into the injection pipe 1 at one end farthest from the gasifying agent outlet (i.e., at the last plasma torch 2 located upstream); subsequently, the gasifying agent flow in the injection pipe 1 is distributed back to the flow channels of each plasma torch 2 in a branched form to achieve stable and balanced supply of the gasifying agent.

[0045] The injection device can also be designed with a restraining part to restrain the plasma torches together. The restraining part can release the restraint under certain conditions, preferably a cable that can melt at 200 - 400°C. This design is particularly suitable for use when all or part of each plasma torch 2 penetrates through the corresponding diversion channel. The plasma torches restrained together at the end segment can follow the injection pipe 1 through a narrow borehole to reach the target position, without the need to move each plasma torch 2 relative to the diversion channel 3 through a ground control system. Just gasify the coal seam for a period of time first to raise the temperature of the environment where the plasma torches are located and melt the cable that restrains each plasma torch 2. After the restraint is released, the ends of each plasma torch 2 move away from each other under the resilience of the connecting pipe, and the ejected plasma gasifying agent can contact the gasified coal seam in a relatively short time and cover a larger area of the gasified coal seam region, as Figure 5 shown.

[0046] As Figure 10 shown, an embodiment of the present invention provides a method for underground coal gasification, including the following steps:

[0047] S1, constructing a directional borehole and a gasification channel that penetrate the underground coal seam;

[0048] S2, lowering an injection pipe carrying plasma torches into the gasification channel and injecting a gasifying agent to implement in-situ gasification of the underground coal seam; the gasifying agent is shunted to multiple plasma torches through the diversion channels at the end segment of the injection pipe and is directed towards the coal seam after being activated by the plasma torches;

[0049] S3, transporting the generated coal gas to the ground for collection through the borehole.

[0050] After the injection pipe carrying the plasma torches reaches the predetermined position in the gasification channel in the embodiment of the present invention, the ground control system is used to move the ends of each plasma torch away from each other to make the range of the gasifying agent spread larger.

[0051] After directional drilling is completed, this solution disperses the gasifier into multiple plasma torches through a gas injection pipe equipped with multiple directional channels. Once inside the torch chamber, the gasifier is excited by the arc, instantaneously heated into a high-enthalpy plasma (activated free radicals). This then enters the coal fissures as a directional, high-speed jet. This significantly shortens the distance and time it takes for the gasifier to reach the target, reducing the deactivation rate of the already plasma-formed gasifier (activated free radicals) while ensuring the jet momentum is sufficient to penetrate the pulverized zone, allowing the activated free radicals to directly act on the fresh coal surface. This achieves efficient utilization of the plasma gasifier and, in turn, increases the effective component content of the coal gas. Furthermore, the gasified coal seam's combustion zone expands vertically in a fan-shaped pattern centered on the gasifier outlets of each plasma torch. This expansion has a relatively large equivalent radius, allowing a single gasification channel to gasify a large volume of coal.

[0052] Methods for moving the plasma torch tips away from each other include but are not limited to:

[0053] The plasma torches are moved relative to the end of the gas injection pipe through the directional channel, moving away from each other. This solution requires the use of a ground drive system. First, each plasma torch is built into the gas injection pipe. Under the action of the ground drive system, each plasma torch is lowered into the underground gasification channel along with the gas injection pipe. Then, after reaching the predetermined position, the drive system is adjusted to drive only the plasma torches while keeping the gas injection pipe stationary. The plasma torches are separated from each other through the directional channel at the end of the gas injection pipe, achieving different directions of gasification agent injection and being closer to the coal seam to be gasified than the end of the gas injection pipe (the position of the plasma torches in existing underground coal seam plasma gasification technology).

[0054] Alternatively, after a period of coal seam gasification, as the ambient temperature of the plasma torch increases, the restraining parts (preferably rigging that can melt at 200°C~400°C) that restrain each plasma torch are released, and each plasma torch restores its original set direction under the toughness of the connecting tube, so that the ends of each plasma torch are moved away from each other.

[0055] The gasifying agent injected in the embodiment of the present invention is a mixture of one or more of water vapor, carbon dioxide, and air with oxygen; preferably a combination of carbon dioxide and oxygen. The volume fraction of oxygen is between 30% and 70%, preferably between 40% and 55%.

[0056] Because the plasma torches passing through the diversion channels face different directions, the direction of the plasma gasifying agent ejected by each plasma torch is also different. Compared with the plasma gasifying agent ejected by a single, single-direction plasma torch, it can cover a larger cross-section of the coal seam in a shorter travel distance, and contact and act with the coal seam in a shorter time, and can produce gas with a higher content of effective components. Taking CO2 (volume content 35%), O2 (volume content 45%) and water vapor (volume content 20%) as the gasifying agent, under other unchanged conditions, comparing the components of the gas produced by the existing (plasma gasification technology) single, single-direction plasma torch gasifying the underground coal seam with the components of the gas produced by the underground coal gasification method of the present invention, the increase in the content of the effective components of the gas is usually between 10% and 30%. The comparison is shown in Table 1 below.

[0057] Table 1 Gas components produced by different methods

[0058]

[0059] The above is only the specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, any modification, equivalent replacement and improvement made within the spirit and principle of the present invention shall be covered within the protection scope of the present invention.

Claims

1. A method for underground coal gasification, comprising the following steps: S1, constructing directional drilling holes and gasification channels through underground coal seams; S2, a gas injection pipe equipped with a plasma torch is lowered into the gasification channel and a gasifying agent is injected to implement in-situ gasification of the underground coal seam; S3, the generated gas is transported to the ground through a borehole for collection; It is characterized in that the gasifying agent is diverted to multiple plasma torches through the diversion channel at the end of the gas injection pipe, and is directionally injected into the coal seam after being activated by the plasma torch.

2. The underground coal gasification method according to claim 1, characterized in that, After the gas injection pipe carries the plasma torch to a predetermined position in the gasification channel, the ends of the plasma torches are moved away from each other through ground manipulation.

3. The underground coal gasification method according to claim 2, characterized in that, The method of moving the ends of the plasma torches away from each other includes but is not limited to: moving each plasma torch relative to the end of the gas injection pipe through the directional channel, away from each other; or first gasifying the coal seam for a period of time to increase the temperature of the environment in which the plasma torches are located, and then melting the rigging that constrains each plasma torch at high temperature, so that each plasma torch restores its original set direction under the toughness of the connecting pipe, thereby achieving the goal of moving the ends of each plasma torch away from each other.

4. The underground coal gasification method according to claim 1, characterized in that, The injected gasifying agent is a mixture of one or more of water vapor, carbon dioxide, and air with oxygen; the volume fraction of oxygen is between 30% and 70%, preferably between 40% and 55%.

5. An underground coal gasification gas injection device for implementing the method according to any one of claims 1 to 4, characterized in that, The invention comprises a gasifying agent injection pipe, a gasifying agent injection pipe driving system, and a plurality of plasma torches arranged at the end of the gasifying agent injection pipe, wherein each plasma torch ejects the gasifying agent in a different direction.

6. The coal underground gasification gas injection equipment according to claim 5, characterized in that, The interior of the end section of the gas injection pipe is a multi-directional channel, each of which can accommodate a plasma torch, so that the plasma gasification agent ejected by different plasma torches has different directions; the multiple plasma torches in the gas injection pipe are arranged in parallel or in front and behind.

7. The coal underground gasification gas injection device according to claim 5, characterized in that, The gasifying agent flow channels of each plasma torch converge at one end away from the plasma gasifying agent outlet. A tensioning portion is provided on the outer periphery of the plasma torch flow channel converging pipe section. The tensioning portion expands outward under the action of gas or external force, thereby separating the gap between the outer wall of the converging pipe section and the inner wall of the gas injection pipe.

8. The coal underground gasification gas injection device according to claim 6, characterized in that, When arranged in parallel, each directional channel has a built-in plasma torch, and each plasma torch can move relative to each directional channel.

9. The coal underground gasification gas injection device according to claim 6, wherein When arranged in front and back, each plasma torch is provided with a directional guide part to enable each plasma torch to move toward each directional channel; the directional guide part is an arrow fixed to the end of the plasma torch and passed through the directional channel, or a protrusion that cooperates with the groove provided on the inner wall of the directional channel, or a groove that cooperates with the protrusion provided on the inner wall of the directional channel.

10. The coal underground gasification gas injection device according to claim 5, wherein, The injection device is provided with a restraining part, which can restrain multiple plasma torches together and release the restraint on the plasma torches under certain conditions; the restraining part is preferably a rigging that can be melted at 200-400°C.

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