Underground coal gasification method and gas injection equipment

Abstract

The present invention belongs to, but is not limited to, the technical field of underground coal gasification, and discloses an underground coal gasification method and gas injection equipment; constructs a directional borehole and a gasification channel that penetrates an underground coal seam; lowers a gas injection pipe carrying a plasma torch into the gasification channel and injects a gasifying agent to implement in-situ gasification of the underground coal seam; and the generated coal gas is transported to the surface through the borehole for collection. The underground coal gasification method and gas injection equipment proposed by the present invention activate the gasifying agent through multiple plasma torches built into the directional channel at the end of the gas injection pipe and then directionally injects it into the coal seam. The gasifying agent contacts and gasifies the coal seam in a relatively short period of time, thereby achieving 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 coal seam after gasification will expand in a fan-shaped manner longitudinally with the gasifying agent outlet of each plasma torch as the center. The expansion equivalent radius of the combustion zone is relatively large, and a single gasification channel can gasify a large amount of coal.

Description

Technical Field

[0001] The present invention belongs to but is not limited to the technical field of underground coal gasification, and in particular relates to an underground coal gasification method and gas injection equipment. Background Art

[0002] In the underground coal plasma gasification process, the gasifying agent (such as one or more of air, water vapor, oxygen, etc.) is first plasmatized by a plasma torch, and then contacts the coal seam to undergo a gasification reaction, which can be converted into coal gas with a higher content of effective components (carbon monoxide, hydrogen, methane, etc.). In existing underground coal plasma gasification technology, a plasma torch is usually installed at the end of the gasifying agent injection pipe. The injected gasifying agent is converted into an activated gasifying agent (plasmaized free radicals) by the plasma torch. It is ejected from the injection pipe into the high-temperature gasification zone and reacts with the coal seam to gasify. Figure 1 As shown in the figure, the problem is that the direction of the gasification agent injection is uncontrollable. If the activated gasification agent cannot contact and react with the coal seam in time in the gasification zone, it will be converted into an inactivated gasification agent (no longer a plasma-formed free radical), losing the meaning of plasma formation. The effective utilization rate of the plasma gasification agent will be greatly affected, resulting in a low content of effective components in the coal gas. At the same time, the combustion zone of the coal seam after gasification is usually centered on the gas injection channel in the vertical direction ( Figure 1 The expansion radius of the combustion zone is relatively small, and the amount of gasified coal is relatively small.

[0003] In the underground in-situ coal gasification scenario, gasifying agents such as oxygen and steam need to be injected directly into the coal seam through a narrow wellbore. This makes it difficult to achieve axial diversion or multi-directional jetting of the gasifying agent in the slender gas injection pipe, and it is also impossible to form a "fan-shaped covering" plasma airflow in the narrow gasification zone. The plasma (activated) gasifying agent is deactivated due to its failure to contact and react with the coal seam in a short period of time, resulting in low utilization of the activated gasifying agent. Summary of the Invention

[0004] In response to the problems existing in the prior art, the present invention provides an underground coal gasification method and gas injection equipment, which uses multiple plasma torches to inject gasifying agents and direct the gasifying agents toward the coal seam, shortening the time it takes for the gasifying agents to reach the coal seam and expanding the gasification surface.

[0005] The present invention is implemented as follows: an underground coal gasification method comprises the following steps:

[0006] S1, constructing directional drilling holes and gasification channels through underground coal seams;

[0007] 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; the gasifying agent is diverted to multiple plasma torches through a diversion channel at the end of the gas injection pipe, and then activated by the plasma torches and directed toward the coal seam;

[0008] S3, the generated gas is transported to the ground through drilling and collected.

[0009] Furthermore, 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 the ground control system, so that the gasification agent is spread over a wider range.

[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 gas injection pipe through the directional channel, away from each other, or increasing the temperature of the environment in which the plasma torch is located by coal seam gasification for a period of time, releasing the rigging that constrains each plasma torch, and each plasma torch restoring its original set direction under the toughness of the connecting pipe, thereby achieving the distance between the ends of each plasma torch.

[0011] Furthermore, the injected gasifying agent is a mixture of one or more of water vapor, carbon dioxide, and air with 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, comprising a gasifying agent injection pipe, a gasifying agent injection pipe drive system, and multiple plasma torches arranged at the end of the gasifying agent injection pipe, each plasma torch ejecting gasifying agent in a different direction.

[0014] 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 can be arranged in parallel or in front and behind.

[0015] Furthermore, the gasifier flow channels of each plasma torch converge at one end away from the plasma gasifier outlet, and 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 isolating the gap between the outer edge of the converging pipe section and the inner wall of the gas injection pipe.

[0016] Furthermore, when arranged in parallel, each directional channel has a built-in plasma torch, and each plasma torch can move relative to the directional channel.

[0017] Furthermore, when arranged in front and back, each plasma torch is provided with a directional guide portion to enable each plasma torch to move toward each directional channel; the directional guide portion can be an arrow fixed to the end of the plasma torch and passed through the directional channel, or it can be a protrusion (or groove) that cooperates with the groove (or protrusion) provided on the inner wall of the directional 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 It is a schematic diagram of underground coal seam plasma gasification provided by the prior art;

[0026] Figure 2 Schematic diagram of the longitudinal section of the combustion-air zone provided by an embodiment of the present invention;

[0027] Figure 3 1 is a schematic cross-sectional view of the end of the gas injection pipe provided by an embodiment of the present invention;

[0028] Figure 4 This is a schematic diagram of multiple plasma torches arranged side by side according to an embodiment of the present invention;

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

[0030] Figure 6 is a schematic cross-sectional view of a gas injection pipe with a guide portion provided by an embodiment of the present invention;

[0031] Figure 7 2 is a cross-sectional schematic diagram of the movable connection between the plasma torch and the gas injection pipe provided by an embodiment of the present invention;

[0032] Figure 8 Schematic diagram of the front and back arrangement of each plasma torch provided by an embodiment of the present invention;

[0033] Figure 9 Schematic diagram of the plasma torch tip and fixed arrow provided in an embodiment of the present invention;

[0034] Figure 10 This is a flow chart 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. Directional channel; 4. Tensioning part; 5. Guide part; 6. Gas injection pipe wall; 7. Outer wall of plasma torch; 8. Arrow; 9. Plasma torch flow channel collection pipe section; 10. Gasification channel; 11. Injection pipe with plasma torch. DETAILED DESCRIPTION

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

[0037] An embodiment of the present invention provides underground coal gasification gas injection equipment, including a gasifying agent injection pipe 1, a gasifying agent injection pipe drive system, and multiple plasma torches 2 arranged at the end of the gasifying agent injection pipe, each plasma torch 2 ejecting the gasifying agent in a different direction; the plasma gasifying agent can be brought into contact with the coal seam in a timely manner to produce a gasification reaction, covering a larger coal seam gasification surface, and improving the effective utilization rate of the plasma gasifying agent.

[0038] The gasifier flow channels of each plasma torch 2 are converged at one end away from the plasma gasifier outlet to realize the diversion of the gasifier transported by the gas injection pipe 1 to each plasma torch. In order to make the gasifier flow through the plasma torch 2 as much as possible, a tensioning portion 4 is provided on the outer periphery of the plasma torch flow channel converging pipe section 9. The tensioning portion 4 expands outward under the action of gas or external force to cut off the gap between the outer edge of the converging pipe section and the inner wall of the gas injection pipe 1, preventing the gasifier from flowing through the gap into the gasification zone instead of entering the gasification zone after being activated by the plasma torch, thereby improving the plasmatization rate of the gasifier.

[0039] Each plasma torch 2 is built into the gas injection pipe 1. Under the action of the surface drive system, each plasma torch is lowered into the underground gasification channel 10 along with the gas injection pipe. That is, an injection pipe 11 with a plasma torch is laid in the gasification channel 10.

[0040] like Figure 3 As shown, the end section of the gas injection pipe 1 is internally provided with multiple directional channels 3, each of which can accommodate a plasma torch 2, so that the plasma gasification agent emitted by different plasma torches 2 is directed in different directions. The multiple plasma torches 2 in the gas injection pipe 1 can be arranged side by side or in front and behind.

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

[0042] like Figure 8 As shown, when the front and back are arranged, each plasma torch 2 is provided with a directional guide 5 ( Figure 6 ), so as to realize the purpose of moving each plasma torch 2 to each branch channel 3. The directional guide 5 can be an arrow 8 ( Figure 9 ), or it may be a protrusion (or groove) that matches the groove (or protrusion) provided on the inner wall of the diverter channel ( Figure 7 This solution can achieve the offset of the direction of each plasma torch when the outer diameter of the gas injection pipe end is not much different from the outer diameter of the gas injection pipe body (≤30%).

[0043] When multiple plasma torches 2 are installed on the gas injection pipe 1 in an axial manner in sequence, the plasma torches 2 can be relatively moved along the gas injection pipe 1 by an external driving mechanism, thereby increasing the distance between the ends of the plasma torches.

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

[0045] The injection device can also be designed with a constraint part to constrain the plasma torches together. The constraint part can release the constraint under certain conditions, and preferably the rigging can be melted at 200~400℃. This design is particularly suitable for use when each plasma torch 2 is fully or partially provided with a corresponding directional channel. The plasma torches constrained together at the end can follow the gas injection pipe 1 through the narrow borehole to reach the target position. There is no need to move the plasma torches 2 relative to the directional channel 3 through the ground control system. It is only necessary to gasify the coal seam for a period of time, increase the temperature of the environment in which the plasma torch is located, and melt the rigging that constrains the plasma torches 2. After the constraint is released, the ends of the plasma torches 2 move away from each other due to the toughness of the connecting pipe, and the ejected plasma gasification agent can contact the gasified coal seam in a shorter time, and the covered gasified coal seam area is larger, such as Figure 5 shown.

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

[0047] S1, constructing directional drilling holes and gasification channels through underground coal seams;

[0048] 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; the gasifying agent is diverted to multiple plasma torches through a diversion channel at the end of the gas injection pipe, and then activated by the plasma torches and directed toward the coal seam;

[0049] S3, the generated gas is transported to the ground through drilling and collected.

[0050] In the embodiment of the present invention, 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 a ground control system, so that the gasifying agent spreads over a wider range.

[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 directional channels face different directions, the plasma-generated gasifying agent ejected from each torch also faces different directions. Compared to plasma-generated gasifying agent ejected from a single, single-directional plasma torch, this method can cover a larger coal seam cross-section within a shorter stroke and interact with the coal seam in a shorter period of time, producing coal gas with a higher content of effective components. Using CO2 (35% by volume), O2 (45% by volume), and water vapor (20% by volume) as gasifying agents, and with other conditions remaining unchanged, a comparison of the composition of coal gas produced by conventional (plasma gasification technology) single, single-directional plasma torch gasification of underground coal seams with the underground coal gasification method of the present invention shows a typical increase in effective component content of between 10% and 30%. This comparison is shown in Table 1.

[0057] Table 1 Gas components produced by different methods

[0058]

[0059] The above description is only a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any modifications, equivalent substitutions and improvements made by any technician familiar with this technical field within the technical scope disclosed by the present invention and within the spirit and principles of the present invention should be covered by the scope of protection of the present invention.

Claims

1. A method for underground coal gasification, characterized in that: The following steps are involved: 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; The invention is characterized in that the gasifying agent is diverted to multiple plasma torches through the diverting channel at the end of the gas injection pipe, and is activated by the plasma torches and then directed toward the coal seam; After the gas injection pipe carries the plasma torch to the predetermined position of the gasification channel, the ends of the plasma torches are moved away from each other through ground control; The method for moving the ends of the plasma torches away from each other includes: moving the plasma torches relative to the ends of the gas injection pipes through the directional channels, 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 melting the rigging that constrains the plasma torches at high temperature, so that the plasma torches restore their originally set directions under the toughness of the connecting pipes, thereby achieving the goal of moving the ends of the plasma torches away from each other.

2. 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%.

3. An underground coal gasification gas injection device for implementing the method according to any one of claims 1 to 2, 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.

4. The underground coal gasification gas injection equipment according to claim 3, 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.

5. The underground coal gasification gas injection equipment according to claim 3, characterized in that: The multiple plasma torches in the gas injection pipe are arranged front and back.

6. The underground coal gasification gas injection equipment according to claim 3, 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.

7. The underground coal gasification gas injection equipment according to claim 4, 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.

8. The underground coal gasification gas injection equipment according to claim 5, characterized in that: 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.

9. The underground coal gasification gas injection equipment according to claim 3, characterized in that: The injection equipment 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 a rigging that can be melted at 200-400°C.

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