Heat energy utilization and carbon sequestration system based on underground coal gasification

Abstract

The heat energy utilization and carbon sequestration system comprises a water injection well, a drainage well and a water injection device, the water injection well and the drainage well are communicated at the well bottom through a horizontal section, and the horizontal section is located in an underlying rock layer of a coal seam; the well bottom of the operation well is located in the coal seam, the fracturing section is communicated with the operation well, the fracturing section is located in an overlying strata of the coal seam, and the end, away from the operation well, of the gasification channel is located in an underlying strata and faces the horizontal section; the device further comprises a primary combustion assembly, a secondary combustion assembly, a sealing assembly and an oxygen supply assembly. The invention is used for solving the problems of insufficient carbon solidification, low combustion efficiency and low heat utilization rate in the carbon sequestration technology in the prior art, and realizes the purposes of more sufficiently sequestering underground carbon elements, improving the combustion efficiency and better utilizing the combustion heat energy.

Description

Technical Field

[0001] The present invention relates to the field of underground coal gasification, and in particular to a thermal energy utilization and carbon sequestration system based on underground coal gasification. Background Art

[0002] As the importance of environmental protection and sustainable development becomes increasingly prominent, underground coal gasification technology has gradually attracted attention. Compared with traditional underground or open-pit mining, underground coal gasification technology is a clean, low-carbon, safe and efficient new energy acquisition method. It uses deep coal resources for redox reactions to convert coal into gas, which can reduce coal mining costs, reduce environmental pollution and carbon dioxide emissions. At present, there are generally two methods for treating waste gas mixed with coal gas extracted from underground. One is to discharge it directly into the atmosphere, which will undoubtedly aggravate the global greenhouse effect; the other is to discharge it into underground goafs and pores in rock formations. However, my country's coal seams generally have the characteristic of a low proportion of cracks, so the fixation of waste gases such as underground carbon dioxide is low. Therefore, scholars at home and abroad have proposed many methods to improve carbon fixation, such as injecting carbon dioxide into pores and cracks in rocks by pressurization. However, these technologies have some problems, such as small carbon fixation and carbon dioxide spillover.

[0003] In order to effectively solve the above problems, a type of in-situ carbon sequestration technology has emerged in the prior art, which can utilize the heat energy of the underground reactor and realize the in-situ solidification of carbon. However, the existing carbon sequestration technology generally performs in-situ storage in the coal seam, which has the problems of insufficient carbon solidification, low combustion efficiency and low heat utilization rate. Summary of the invention

[0004] The present invention provides a thermal energy utilization and carbon sequestration system based on underground coal gasification to solve the problems of insufficient carbon solidification, low combustion efficiency and low heat utilization rate in the carbon sequestration technology in the prior art, so as to achieve the purpose of more fully sealing underground carbon elements, improving combustion efficiency and better utilizing combustion heat energy.

[0005] The present invention is achieved through the following technical solutions:

[0006] A thermal energy utilization and carbon sequestration system based on underground coal gasification, comprising a water injection well, a drainage well, and a water injection device for supplying water to the water injection well, wherein the water injection well and the drainage well are connected at the bottom of the well through a horizontal section, and the horizontal section is located in the underlying rock layer of the coal seam;

[0007] It also includes an operating well with a bottom in the coal seam, a fracturing section and a gasification channel connected to the operating well, the fracturing section is located in the overlying stratum of the coal seam, and an end of the gasification channel away from the operating well is located in the underlying stratum and faces the horizontal section;

[0008] Also includes:

[0009] A primary combustion component, used for gasifying the coal seam and sending the coal gas obtained by gasification into the gasification channel;

[0010] A secondary combustion assembly is used for secondary gasification of the coal gas output from the gasification channel in the underlying rock formation;

[0011] A sealing assembly, used to deliver the secondary gasification product into the fracturing stage;

[0012] The oxygen supply component is used to supply oxygen to the primary combustion component and the secondary combustion component.

[0013] In view of the problems of insufficient carbon solidification, low combustion efficiency and low heat utilization rate in the carbon sequestration technology in the prior art, the inventors of this case found in the research process that the prior art generally directly ignites the coal seam, realizes circulation through connected water injection wells and drainage wells, and then takes out the heat of combustion in the coal seam for utilization. Most of the carbon-containing gasification products after the coal seam combustion are re-sealed in the coal seam in the form of adsorption, which leads to extremely low carbon sequestration level and heat utilization rate. In order to overcome the above problems, the present invention proposes a thermal energy utilization and carbon sequestration system based on underground coal gasification, in which water injection wells, drainage wells, water injection devices, etc. can adopt existing technologies, and the bottom of the water injection well and the bottom of the drainage well are connected through a horizontal section to realize the utilization of combustion heat energy.

[0014] Different from the prior art in which operations are performed in the coal seam, the horizontal section in this application is located in the underlying rock formation of the coal seam. Therefore, the water injection well and drainage well in this application need to be drilled through the coal seam, and the bottoms of both wells need to enter the underlying rock formation. In addition to the water injection well and drainage well, this application also drills an operating well, and performs a fracturing operation in the operating well to obtain a fracturing section located in the overlying rock formation. Among them, the drilling operation process of the operating well and the hydraulic fracturing process at the designated stratum can be achieved by using the existing mature technologies of petroleum and natural gas engineering or coalbed methane mining engineering, which will not be elaborated here.

[0015] The present application also drills a gasification channel in the working well, so that one end of the gasification channel is connected to the inside of the working well, and the other end enters the underlying rock formation and faces the horizontal section; wherein the formation of the gasification channel can be achieved by using the directional drilling technology in the prior art or other mature processes, which will not be elaborated here. The oxygen supply component in the present application can supply oxygen to the primary combustion component and the secondary combustion component respectively, and can control the required oxygen supply for each component respectively, thereby achieving the required combustion effect. Of course, when oxygen is introduced into the oxygen supply component, it can simultaneously provide the catalyst required for the primary combustion and the secondary combustion.

[0016] During the specific operation of this application, the coal seam is ignited by the primary combustion component, and incomplete combustion and gasification occur in the coal seam to obtain coal gas, which is then sent to the gasification channel. The coal gas enters the underlying rock formation through the gasification channel, and is ignited again by the secondary combustion component in the underlying rock formation to undergo secondary combustion and gasification to obtain secondary gasification products. The secondary gasification products are sent to the fracturing section by the sealing component, and enter the overlying rock formation through the fracturing section, where they are solidified and sealed in the overlying rock formation. In this process, water is injected from the ground into the injection well, returned to the ground through the horizontal section and the drainage well, and carries out the heat generated during the secondary gasification process.

[0017] Compared with the in-situ storage method in the coal seam in the prior art, this application:

[0018] (1) The coal seam is ignited twice through a primary combustion component and a secondary combustion component. The purpose of the first ignition is to gasify the coal seam. Therefore, the oxygen supply can be controlled to prevent incomplete combustion in the coal seam until sufficient oxygen is provided during the second ignition to fully burn the coal gas. This allows more substances in the coal seam that cannot be gasified or cannot be ignited a second time (such as water, etc.) to remain in the coal seam, thereby reducing the pressure deficit in the goaf. (2) The present application introduces the gasified coal gas into the underlying rock formation to achieve orderly and complete combustion of the coal gas in the underlying rock formation. Compared with the chaotic and disordered combustion in the coal seam, this can significantly improve the artificial control of the combustion process, thereby facilitating a more effective and controllable use of the combustion efficiency, making the heating process of the horizontal section uniform and stable, and significantly improving the utilization efficiency of the combustion heat energy. (3) The present application delivers the secondary gasification product into the overlying rock formation for storage. Compared with the prior art method of directly storing in situ in the coal seam, the present application utilizes the characteristics of the dense overlying rock formation and the difficulty of carbon dioxide escaping from it, thereby significantly improving the carbon storage effect. (4) The present application utilizes the fracturing section to achieve carbon sequestration in the overlying rock formation, and utilizes the proppant remaining in the well after fracturing flowback to provide long-term support capacity for long-term operation. At the same time, it can increase the contact area between water, carbon dioxide waste gas and the rock formation, thereby improving the carbon storage efficiency. In summary, the present application can enable underground carbon resources to be better developed and utilized, and has significant advantages in terms of environmental protection, safety, and economic benefits.

[0019] Furthermore, the primary combustion assembly includes a first ignition device located at the bottom of the working well, a first extraction device located in the working well, and a gas pipe connected to the output end of the first extraction device, wherein the gas pipe enters the gasification channel and is connected to the secondary combustion assembly.

[0020] Since the bottom of the working well is located in the coal seam, the first ignition device ignites the coal seam at the bottom of the working well, and cooperates with the oxygen supply component to provide the set oxygen to the primary combustion component, thereby ensuring incomplete combustion in the coal seam. The obtained gasified coal gas is extracted into the gas pipe by the first extraction device, passes through the gasification channel through the gas pipe, and reaches the secondary combustion component.

[0021] Furthermore, the secondary combustion assembly includes a second ignition device located at an end of the gasification passage away from the operating well.

[0022] In the present application, one end of the gasification channel away from the working well is located in the underlying rock formation and faces the horizontal section. Therefore, the second ignition device in this scheme also faces the horizontal section, so that the secondary combustion is fully carried out around the horizontal section, which is convenient for fully heating the water flow flowing through the horizontal section, which is beneficial to improving the efficiency of thermal energy utilization.

[0023] Furthermore, the secondary combustion assembly also includes a heating tube sleeved on the outside of the horizontal section, and both axial ends of the heating tube are closed; the second ignition device is located in the heating tube.

[0024] This solution allows the secondary combustion to take place in the heating tube, so that the secondary combustion process is completed in a limited space, which can effectively improve the combustion efficiency, reduce heat dissipation, and transfer heat to the horizontal section to the greatest extent, significantly improving the thermal energy utilization efficiency.

[0025] Furthermore, the sealing assembly includes an exhaust pipe and a second extraction device arranged on the exhaust pipe; one end of the exhaust pipe is located at an end of the gasification channel away from the operating well, and the other end is connected to the fracturing section.

[0026] After the coal gas is fully burned in the secondary combustion component, the gas produced is mainly carbon dioxide, which is extracted into the exhaust pipe through the second extraction device and transported to the fracturing section through the exhaust pipe. Since the fracturing section is located in the overlying rock formation, the fully burned gas products mainly composed of carbon dioxide enter the overlying rock formation, where a small part is adsorbed and sealed by the pores of the formation, and most of it reacts with formation water to form carbonic acid, which then reacts with the formation to form carbonate for stable sealing.

[0027] Furthermore, the sealing assembly also includes a water injection pipe lowered from the operating well, and the bottom end of the water injection pipe is located in the fracturing section.

[0028] In the case where the formation water content in the overburden is low or the salt content in the formation water is relatively saturated, this solution can inject water into the overburden through the water injection pipe at the wellhead, thereby ensuring stable carbon sequestration in the overburden.

[0029] Furthermore, the sealing assembly further comprises a booster device arranged on the exhaust pipe and a sensing device for monitoring the carbon dioxide concentration in the fracturing section; the booster device is located downstream of the second extraction device. When the carbon dioxide concentration monitored by the sensing device is lower than a set threshold, the booster device can be activated.

[0030] Furthermore, the oxygen supply assembly includes an oxygen supply device located on the ground and an oxygen injection pipe connected to the oxygen supply device. The oxygen injection pipe is located in the working well, and the bottom end of the oxygen injection pipe is connected to a first diversion pipe and a second diversion pipe. The first diversion pipe is connected to the coal seam, and the second diversion pipe extends to the secondary combustion assembly.

[0031] In this solution, oxygen is injected into the oxygen injection pipe through the oxygen supply device, and is divided into the first shunt pipe and the second shunt pipe at the bottom of the oxygen injection pipe. Of course, in this solution, the first shunt pipe and the second shunt pipe can be provided with corresponding valves or flow control valves, etc., to achieve more accurate control of the oxygen supply. In addition, an appropriate amount of catalyst can be simultaneously introduced into the oxygen injection pipe to ensure effective combustion in the formation environment.

[0032] Furthermore, an oxygen injection hole located in the coal seam is drilled in the working well, and the first diversion pipe is located in the oxygen injection hole; and the second diversion pipe passes through the gasification channel.

[0033] This solution injects oxygen into the coal seam through the oxygen injection hole, which is beneficial to increase the overall oxygen content in the coal seam, so that after the coal seam is ignited, the overall gasification effect of the coal seam is improved.

[0034] Furthermore, the overburden is basic rock. Those skilled in the art should understand that basic rock is a type of igneous rock with a low silicon dioxide content and a high iron, magnesium and calcium content. When the overburden is basic rock, the present application can achieve an excellent carbon sequestration effect, so the present application is particularly suitable for carbon sequestration in coal seams whose overburden is basic rock.

[0035] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0036] 1. The thermal energy utilization and carbon sequestration system based on underground coal gasification of the present invention performs two ignitions in the stratum, which can allow more substances in the coal seam that cannot be gasified or cannot be secondary ignited (such as moisture, etc.) to remain in the coal seam, thereby reducing the pressure deficit in the goaf.

[0037] 2. The thermal energy utilization and carbon sequestration system based on underground coal gasification of the present invention introduces the coal gas obtained by gasification into the underlying rock strata, thereby realizing orderly and sufficient combustion of the coal gas in the underlying rock strata. Compared with the chaotic and disordered combustion in the coal seam, it can significantly improve the artificial control over the combustion process, thereby facilitating more effective and controllable utilization of combustion efficiency, making the heating process of the horizontal section uniform and stable, and significantly improving the utilization efficiency of combustion heat energy.

[0038] 3. The thermal energy utilization and carbon sequestration system based on underground coal gasification of the present invention delivers the products of secondary gasification into the overlying rock strata for sequestration. Compared with the prior art method of directly sealing in situ in the coal seam, it utilizes the characteristics of the overlying rock strata being dense and carbon dioxide not easily escaping therefrom, thereby significantly improving the carbon sequestration effect.

[0039] 4. The present invention provides a thermal energy utilization and carbon sequestration system based on underground coal gasification, which utilizes a fracturing section to achieve carbon sequestration in the overlying rock formation, and utilizes the proppant remaining in the well after fracturing flowback to provide long-term support capacity to facilitate long-term operation. At the same time, it can increase the contact area between water, carbon dioxide waste gas and the rock formation, thereby improving the carbon sequestration efficiency.

[0040] 5. The thermal energy utilization and carbon sequestration system based on underground coal gasification of the present invention can inject water into the overlying rock formation through a water injection pipe at the wellhead, thereby ensuring stable carbon sequestration in the overlying rock formation. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] The drawings described herein are used to provide a further understanding of the embodiments of the present invention, constitute a part of this application, and do not constitute a limitation of the embodiments of the present invention. In the drawings:

[0042] Figure 1 is a schematic diagram of a specific embodiment of the present invention;

[0043] Figure 2 It is a partial schematic diagram of a specific embodiment of the present invention;

[0044] Figure 3 It is a schematic diagram of the distribution of the fracturing sections in a specific embodiment of the present invention.

[0045] Marks and corresponding parts names in the attached drawings:

[0046] 1-operating well, 2-water injection well, 3-drainage well, 4-pressure gauge, 5-fracturing section, 6-gasification channel, 7-heating pipe, 8-first ignition device, 9-oxygen injection hole, 10-crack, 11-water injection device, 12-first control valve, 13-second control valve, 14-third control valve, 15-oxygen supply device, 16-ground control center, 17-overburden, 18-coal seam, 19-underburden, 20-fourth control valve, 21-fifth control valve, 22-boosting device, 23-sensing device, 24-second extraction device, 25-first extraction device, 26-oxygen injection pipe, 27-water injection pipe, 28-exhaust pipe, 29-gas pipe, 30-tee joint, 31-horizontal section, 32-second ignition device, 33-first diversion pipe, 34-second diversion pipe. DETAILED DESCRIPTION

[0047] In order to make the objects, technical solutions and advantages of the present invention clearer, the present invention is further described in detail below in conjunction with the examples and the accompanying drawings. The schematic embodiments of the present invention and the description thereof are only used to explain the present invention and are not intended to limit the present invention. In the description of the present application, it should be understood that the orientation or positional relationship indicated by terms such as "front", "rear", "left", "right", "up", "down", "vertical", "horizontal", "high", "low", "inside", "outside", etc. is based on the orientation or positional relationship shown in the accompanying drawings, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the scope of protection of the present application.

[0048] Embodiment 1:

[0049] like Figure 1 and Figure 2 A thermal energy utilization and carbon sequestration system based on underground coal gasification is shown, and this system is particularly suitable for use in coal seams with overlying rock strata 17 being basic rocks; specifically, it comprises: a water injection well 2, a drainage well 3, and a water injection device 11 for supplying water to the water injection well 2, wherein the water injection well 2 and the drainage well 3 are connected at the bottom of the well through a horizontal section 31, and the horizontal section 31 is located in the underlying rock strata 19 of the coal seam 18;

[0050] It also includes an operating well 1 with a bottom located in a coal seam 18, a fracturing section 5 and a gasification channel 6 connected to the operating well 1, wherein the fracturing section 5 is located in an overlying stratum 17 of the coal seam 18, and an end of the gasification channel 6 away from the operating well 1 is located in the underlying stratum 19 and faces the horizontal section 31;

[0051] Also includes:

[0052] A primary combustion component, used for gasifying the coal seam 18 and sending the gasified coal gas into the gasification channel 6;

[0053] A secondary combustion assembly is used to perform secondary gasification on the coal gas output from the gasification channel 6 in the underlying rock formation 19;

[0054] A sealing assembly for delivering the secondary gasification product to the fracturing stage 5;

[0055] The oxygen supply component is used to supply oxygen to the primary combustion component and the secondary combustion component.

[0056] The primary combustion assembly includes a first ignition device 8 located at the bottom of the working well 1, a first extraction device 25 located in the working well 1, and a gas pipe 29 connected to the output end of the first extraction device 25. The gas pipe 29 enters the gasification channel 6 and is connected to the secondary combustion assembly.

[0057] The secondary combustion assembly includes a second ignition device 32 located at an end of the gasification channel 6 away from the working well 1. Preferably, one end of the gas pipe 29 entering the gasification channel 6 is connected to the second ignition device 32.

[0058] The secondary combustion assembly further includes a heating tube 7 sleeved on the outside of the horizontal section 31 , and both axial ends of the heating tube 7 are closed; the second ignition device 32 is located inside the heating tube 7 .

[0059] In this embodiment, the water injection well 2 and the drainage well 3 are both vertical wells, and their bottoms are both transitioned to the horizontal section 31 through the inclination section. The working well 1 is preferably a vertical well. When the working well 1 is drilled to a specified depth in the overburden stratum 17, perforation, fracturing, and flowback operations are performed in sequence to obtain a fracturing section 5, and a fissure 10 is generated in the overburden stratum 17. During the fracturing operation, the fracturing fluid used contains proppant, and after fracturing and flowback, the proppant remains in the fissure 10 to provide long-term support capacity.

[0060] The first ignition device 8 and the second ignition device 32 in this embodiment can both be implemented by existing ignition devices, and the ground control center 16 can start and control them.

[0061] In this embodiment, the gasification channel 6 is in an inverted L shape, so that the gas pipe 29 therein is also in an inverted L shape, which is beneficial for dehydrating and drying the gas during the gas transportation process, and further improving the combustion efficiency during the secondary combustion.

[0062] In a more preferred embodiment, the heating tube 7 is made of heat-insulating material to better prevent heat from dissipating.

[0063] In a more preferred embodiment, the distribution of the fracturing stage 5 is as follows: Figure 3As shown, multiple fracturing stages 5 are distributed in different directions on the operating well 1. This arrangement can be achieved by using multi-stage hydraulic fracturing technology, the purpose of which is to increase the reaction space, that is, to increase the contact area between carbon dioxide, water and the overlying rock formation, thereby improving the reaction efficiency.

[0064] In a more preferred embodiment, the carbon dioxide concentration can be monitored in real time in each fracturing stage 5 by a carbon dioxide sensor, and the carbon dioxide pressure value can be monitored by a pressure gauge. All monitoring data are transmitted to the ground control center 16.

[0065] In a more preferred embodiment, in each fracturing stage 5, a one-way sealing device is installed in the direction close to the operating well 1 to prevent the reverse leakage of carbon dioxide gas, such as by using a one-way valve.

[0066] In a more preferred embodiment, each fracturing section 5 should be far away from the coal seam. For example, in this embodiment, the fracturing section 5 is 100 m vertically away from the coal seam, and the fluidity of the rock pore medium can be ignored, preventing carbon dioxide from entering the coal seam and affecting coal gasification.

[0067] Example 2

[0068] A thermal energy utilization and carbon sequestration system based on underground coal gasification, based on Example 1, as Figure 1 and Figure 2 As shown, the sealing assembly includes an exhaust pipe 28 and a second extraction device 24 arranged on the exhaust pipe 28; one end of the exhaust pipe 28 is located at the end of the gasification channel 6 away from the operating well 1, and the other end is connected to the fracturing section 5.

[0069] The sealing assembly in this embodiment further includes a water injection pipe 27 lowered from the working well 1, and the bottom end of the water injection pipe 27 is located in the fracturing section 5. The sealing assembly further includes a booster device 22 disposed on the exhaust pipe 28, and a sensing device 23 for monitoring the carbon dioxide concentration in the fracturing section 5; the booster device 22 is located downstream of the second extraction device 24.

[0070] The oxygen supply assembly includes an oxygen supply device 15 located on the ground and an oxygen injection pipe 26 connected to the oxygen supply device 15. The oxygen injection pipe 26 is located in the working well 1, and the bottom end of the oxygen injection pipe 26 is connected to a first branch pipe 33 and a second branch pipe 34. The first branch pipe 33 is connected to the coal seam 18, and the second branch pipe 34 extends to the secondary combustion assembly.

[0071] The working well 1 is drilled with an oxygen injection hole 9 in the coal seam 18 , and the first shunt pipe 33 is located in the oxygen injection hole 9 ; the second shunt pipe 34 passes through the gasification channel 6 .

[0072] In this embodiment, the boosting device 22 is a boosting pump, and the sensing device 23 is a carbon dioxide concentration sensor. When more than a set number of sensing devices 23 detect that the real-time concentration of carbon dioxide is lower than 90%, the boosting device 22 is turned on; carbon dioxide is injected into the fracturing section at a specified pressure; when more than a set number of sensing devices 23 detect that the real-time concentration of carbon dioxide is higher than 90%, the boosting device 22 is turned off.

[0073] The bottom end of the oxygen injection pipe 26 is connected to the first shunt pipe 33 and the second shunt pipe 34 via a three-way joint 30 .

[0074] In addition, the height of the oxygen injection hole 9 is higher than the height of the connection position between the gasification channel 6 and the working well 1 .

[0075] In this embodiment, the output end of the water injection device 11 is connected to the water injection well 2 and the water injection pipe 27 respectively; a first control valve 12 is installed on the communication path between the water injection device 11 and the water injection well 2, and a second control valve 13 is installed on the communication path between the water injection device 11 and the water injection pipe 27.

[0076] In this embodiment, the output end of the oxygen supply device 15 is connected to the oxygen injection pipe 26, and the third control valve 14 is installed on the communication path.

[0077] In a more preferred embodiment, a fourth control valve 20 is further installed in the oxygen injection hole 9; and a fifth control valve 21 is installed on the gas pipe.

[0078] In a more preferred embodiment, a conversion joint is installed at the connection between the operating well 1 and each fracturing stage 5 so that carbon dioxide gas can be discharged from one exhaust pipe 28 to multiple fracturing stages 5. In addition, the conversion joint can also be used to allow water injected from the ground to enter multiple fracturing stages 5 from one water injection pipe 27.

[0079] Example 3

[0080] A method for heat energy utilization and carbon sequestration based on underground coal gasification is implemented using the system in Example 1 or 2, and specifically includes the following steps:

[0081] S1, oxygen and catalyst are introduced into the oxygen injection pipe 26 through the oxygen supply device 15; cold water is injected into the water injection well 2 through the water injection device 11;

[0082] S2, the first ignition device 8 ignites, ignites the coal seam, and incomplete combustion and gasification occur in the coal seam to obtain coal gas; the coal gas is extracted through the first extraction device 25 and enters the coal gas pipe 29, and enters the heating pipe 7 through the second ignition device 32;

[0083] S3, the second ignition device 32 ignites and burns in the heating tube 7; the cold water flowing through the horizontal section 31 is heated, so that the heated water returns to the ground from the drainage well 3;

[0084] S4, start the second extraction device 24, extract the fully burned gas in the heating tube 7 into the exhaust pipe 28, and transport it to the fracturing section 5 through the exhaust pipe 28; at the same time, inject water into the fracturing section 5 through the water injection pipe 27 through the water injection device 11.

[0085] It can be seen that in this embodiment, the gas combustion process is completed in a limited space in the heating tube 7 through two ignitions, which can effectively improve the combustion efficiency. At the same time, the thermal insulation of the heating tube can further prevent heat from escaping. The generated heat energy heats the cold water and obtains hot water to be transported to the ground.

[0086] The specific implementation methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation method of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

[0087] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In addition, the term "connected" used in this article can be directly connected or indirectly connected via other components without special explanation.

Claims

1. A thermal energy utilization and carbon sequestration system based on underground coal gasification, comprising a water injection well (2), a drainage well (3), and a water injection device (11) for supplying water to the water injection well (2), wherein the water injection well (2) and the drainage well (3) are connected at the bottom of the well through a horizontal section (31), characterized in that: The horizontal section (31) is located in the underlying rock layer (19) of the coal seam (18); It also comprises an operating well (1) with a bottom located in a coal seam (18), a fracturing section (5) and a gasification channel (6) connected to the operating well (1), wherein the fracturing section (5) is located in an overlying rock formation (17) of the coal seam (18), and an end of the gasification channel (6) away from the operating well (1) is located in the underlying rock formation (19) and faces the horizontal section (31); Also includes: A primary combustion component, used for gasifying the coal seam (18) and sending the coal gas obtained by gasification into the gasification channel (6); A secondary combustion assembly, used for performing secondary gasification on the coal gas output from the gasification channel (6) in the underlying rock formation (19); A sealing assembly, used for delivering the secondary gasification product to the fracturing section (5); The oxygen supply component is used to supply oxygen to the primary combustion component and the secondary combustion component.

2. The thermal energy utilization and carbon sequestration system based on underground coal gasification according to claim 1 is characterized in that: The primary combustion assembly comprises a first ignition device (8) located at the bottom of the working well (1), a first extraction device (25) located in the working well (1), and a gas pipe (29) connected to the output end of the first extraction device (25); the gas pipe (29) enters the gasification channel (6) and is connected to the secondary combustion assembly.

3. The thermal energy utilization and carbon sequestration system based on underground coal gasification according to claim 1 is characterized in that: The secondary combustion assembly comprises a second ignition device (32) located at an end of the gasification passage (6) away from the operating well (1).

4. The thermal energy utilization and carbon sequestration system based on underground coal gasification according to claim 3 is characterized in that: The secondary combustion assembly further comprises a heating tube (7) sleeved on the outside of the horizontal section (31), and both axial ends of the heating tube (7) are closed; the second ignition device (32) is located inside the heating tube (7).

5. The thermal energy utilization and carbon sequestration system based on underground coal gasification according to claim 1 is characterized in that: The sealing assembly comprises an exhaust pipe (28) and a second extraction device (24) arranged on the exhaust pipe (28); one end of the exhaust pipe (28) is located at an end of the gasification channel (6) away from the operating well (1), and the other end is connected to the fracturing section (5).

6. The thermal energy utilization and carbon sequestration system based on underground coal gasification according to claim 5 is characterized in that: The sealing assembly further comprises a water injection pipe (27) lowered from the operating well (1), and the bottom end of the water injection pipe (27) is located in the fracturing section (5).

7. The thermal energy utilization and carbon sequestration system based on underground coal gasification according to claim 5, characterized in that: The sealing assembly further comprises a pressure-boosting device (22) arranged on the exhaust pipe (28) and a sensing device (23) for monitoring the concentration of carbon dioxide in the fracturing section (5); the pressure-boosting device (22) is located in the downstream direction of the second extraction device (24).

8. The thermal energy utilization and carbon sequestration system based on underground coal gasification according to claim 1 is characterized in that: The oxygen supply assembly comprises an oxygen supply device (15) located on the ground, and an oxygen injection pipe (26) connected to the oxygen supply device (15); the oxygen injection pipe (26) is located in the working well (1), and the bottom end of the oxygen injection pipe (26) is connected to a first shunt pipe (33) and a second shunt pipe (34); the first shunt pipe (33) is connected to the coal seam (18), and the second shunt pipe (34) extends to the secondary combustion assembly.

9. The thermal energy utilization and carbon sequestration system based on underground coal gasification according to claim 8, characterized in that: An oxygen injection hole (9) located in the coal seam (18) is drilled in the working well (1), and the first shunt pipe (33) is located in the oxygen injection hole (9); the second shunt pipe (34) passes through the gasification channel (6).

10. A thermal energy utilization and carbon sequestration system based on underground coal gasification according to any one of claims 1 to 9, characterized in that: The overlying rock layer (17) is basic rock.

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