A method of heating for in situ coal pyrolysis underground

Abstract

The present application belongs to the technical field of coal in-situ pyrolysis, and particularly relates to a heating method for coal in-situ pyrolysis underground. An injection well and a production well are opened, and a coal seam is fractured to form fissures; a movable underground mixed heat carrier generator is installed at the bottom of the injection well. Natural gas, pyrolysis gas and air are supplied to the generator, the excess air coefficient is controlled to be 1.1-1.3, high-temperature mixed heat carriers are generated by ignition, and the excess high-temperature oxygen enters the coal seam to cause partial oxidation exothermic reaction with the coal. The gasification products and the high-temperature mixed heat carriers are used to gas-drive oil and gas resources. After a period of operation, the air equivalence ratio is controlled to be 1.0, and the generator is moved upward to heat the upper coal seam. The production is separated to obtain tar and pyrolysis gas, and the pyrolysis gas is reused as fuel. The method can generate heat carriers in the coal seam, reduce the energy consumption of heat carrier transportation and heat preservation, and improve the heating efficiency of the coal seam.

Description

[0001] This application is a divisional application of the invention patent application with application number 202311867036.5, application date December 29, 2023, entitled "A heating device and method for underground in-situ pyrolysis of coal". Technical Field

[0002] This invention belongs to the field of coal in-situ pyrolysis technology, specifically relating to a heating method for underground in-situ pyrolysis of coal. Background Technology

[0003] Coal, a crucial component of global energy consumption, accounted for 27.2% of total primary energy consumption in 2020. Its dominance as a primary energy source is unlikely to change for a considerable period. Therefore, developing coal-to-oil and coal-to-natural-gas projects is of great significance. On the other hand, coal is also a major source of greenhouse gas emissions; thus, green mining and clean, efficient utilization of coal are particularly important.

[0004] In recent years, scholars have proposed underground in-situ coal mining technology based on in-situ heating mining technology for oil shale. This involves pyrolyzing coal underground without mining, using a heat carrier to transfer heat. The resulting oil and gas products are then extracted to the surface through wells for separation and further processing. Compared to conventional surface pyrolysis technology, underground in-situ pyrolysis has advantages such as smaller footprint, prevention of ground subsidence, lower carbon footprint, and lower mining costs. The underground semi-coke environment after pyrolysis can also be used for carbon dioxide sequestration. Therefore, underground in-situ coal pyrolysis technology has broad prospects and can achieve efficient utilization of coal.

[0005] The defects and shortcomings of the existing technology are as follows.

[0006] Coal mining requires a large amount of heat energy input. Current technologies primarily utilize high-pressure gases such as high-temperature steam, carbon dioxide, and nitrogen as heat carriers, injecting them into coal seam fractures through injection wells to heat and decompose the coal. Coal needs to reach temperatures above 400℃ to pyrolyze and produce the desired oil and gas products, thus requiring heat carrier insulation. Existing heat carrier heating technologies involve heating the heat carrier on the surface and then transporting it underground via pipelines. This entire process requires heat carrier insulation, resulting in high costs, long transmission distances, and high energy consumption. Therefore, efficient heating technologies for underground coal seams urgently need to be developed. Summary of the Invention

[0007] The purpose of this invention is to provide a heating method for underground in-situ pyrolysis of coal, so as to solve the technical problems of low heating efficiency and high heating cost caused by the difficulty of heat carrier insulation and transportation in the existing underground in-situ pyrolysis process.

[0008] To achieve the above objectives, the present invention adopts the following technical solution.

[0009] A heating method for underground in-situ pyrolysis of coal, comprising: Injection wells and production wells are constructed to fracture the coal seam and create coal seam fissures. A single underground mixed heat carrier generator that can move up and down along the injection well is installed at the bottom of the injection well. Its initial position is at the bottom of the injection well, and its outlet extends into the coal seam.

[0010] Natural gas and pyrolysis gas are supplied to the underground mixed heat carrier generator via fuel pipelines, and air is supplied to the underground mixed heat carrier generator via combustion aid pipelines. Oxygen is introduced, and the excess air coefficient is controlled at 1.1 to 1.3. Ignition and combustion are carried out, allowing the high-temperature mixed heat carrier to enter the coal seam fissures. The excess high-temperature oxygen enters the coal seam and undergoes a partial oxidation exothermic reaction with the coal, thus gasifying the coal seam.

[0011] Oil and gas resources generated by coal-fired gasification using gasification products and high-temperature mixed heat carrier gas are extracted through production wells.

[0012] After running for a period of time, the oxygen content is reduced and the air equivalent ratio is controlled at 1.0 to ensure that no excess oxygen enters the coal seam. At the same time, the underground mixed heat carrier generator is moved upward along the injection well to heat the upper coal seam. The extracted oil and gas products are separated to obtain tar and pyrolysis gas. The pyrolysis gas is sent back to the underground mixed heat carrier generator as fuel through the fuel pipeline.

[0013] Furthermore, the high-temperature mixed heat transfer fluid includes carbon dioxide, water vapor, and nitrogen, and the temperature of the high-temperature mixed heat transfer fluid is greater than or equal to 600°C.

[0014] Furthermore, an insulating sleeve installed on the outer wall of the production well is used to insulate the oil and gas products extracted from the production well.

[0015] Furthermore, the oil and gas products are fed into a condenser separator, and the temperature of the condenser separator is controlled between room temperature and 80°C using water cooling or air cooling to separate tar from the oil and gas products; the gaseous products after tar separation are fed into a gas separator to separate tail gas and pyrolysis gas.

[0016] Furthermore, the pyrolysis gas includes small molecule alkanes, hydrogen, and carbon monoxide; the pyrolysis gas outlet of the gas separator is connected to the inlet of the fuel pipeline via a pressurized pump.

[0017] Furthermore, the ignition device is located at the top of the combustion zone of the underground mixing heat carrier generator, and is used to ignite the mixed components in the combustion zone.

[0018] Furthermore, the underground mixed heat carrier generator has an internal cavity and a through hole on its side wall, through which the high-temperature mixed heat carrier generated by combustion enters the coal seam fissure.

[0019] Furthermore, both the outlet of the fuel pipeline and the outlet of the combustion-supporting agent pipeline are equipped with on / off valves.

[0020] Compared with the prior art, the present invention has at least the following beneficial effects: This invention produces a heat carrier in the coal seam by setting up an underground mixed heat carrier generator in the coal seam. The heat carrier does not need to be transported or stored and can be directly applied to the coal seam, thereby improving heating efficiency and reducing heating costs.

[0021] This invention recycles pyrolysis gas through a separation module, eliminating the need for additional separation steps, making it simple to use and inexpensive.

[0022] This invention uses an electric heater for heat preservation, eliminating the need for continuous fuel supply and thus saving energy.

[0023] The carbon dioxide in the high-temperature mixed heat carrier can not only participate in the pyrolysis reaction of coal, but also has the characteristic of reducing the viscosity of tar, which can improve the tar extraction efficiency; excess high-temperature oxygen enters the coal seam and undergoes a partial oxidation exothermic reaction with the coal, and the underground mixed heat carrier generator moves upward along the injection well to heat the upper coal seam. Attached Figure Description

[0024] The accompanying drawings, which form part of this specification, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings: Figure 1 A schematic diagram of the apparatus used to implement the underground in-situ pyrolysis heating method for coal of the present invention; Figure 2 This is a schematic diagram illustrating the use of electric heating for heat preservation in the later stages of this invention; Figure 3 A schematic diagram showing the arrangement of the mixing heat carrier generator when a circular structure is used at the bottom of the injection well; Figure 4 A schematic diagram showing the arrangement of the mixing heat carrier generator when a square structure is used at the bottom of the injection well; Figure 5 A schematic diagram of an underground mixed heat carrier generator coupled with a coal partial oxidation process; Figure 6 This is a schematic diagram of the mounting holes.

[0025] In the diagram: 1. Upper boundary of coal seam; 2. Coal seam; 3. Lower boundary of coal seam; 4. Injection well; 5. Fuel pipeline; 6. Combustion accelerant pipeline; 7. Coal seam fracture; 8. Temperature monitor; 9. Mixed heat carrier generator; 10. Production well; 11. Mounting hole; 12. Insulation sleeve; 13. Electric heater; 14. Cable; 15. Pressurization pump; 16. Separation module; 161. Condensation separator; 162. Gas separator. Detailed Implementation

[0026] The present invention will now be described in detail with reference to the accompanying drawings and embodiments. It should be noted that, unless otherwise specified, the embodiments and features described herein can be combined with each other.

[0027] The following detailed description is exemplary and intended to provide further detailed explanation of the invention. Unless otherwise specified, all technical terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art. The terminology used in this invention is for describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention.

[0028] Example 1 A heating device for underground in-situ pyrolysis of coal, such as Figures 1-2 As shown, the structure includes a vertically arranged injection well 4 and a production well 10, located above the lower boundary 3 of the coal seam. The injection well 4 and production well 10 pass through the upper boundary 1 and the coal seam 2. An installation hole 11 is provided on the side wall of the injection well 4, located in the coal seam 2. A mixing heat carrier generator 9 is installed inside the installation hole 11. A temperature monitor 8 is installed on the outer wall of the mixing heat carrier generator 9. A fuel pipeline 5 and an oxidizer pipeline 6 are provided inside the injection well 4. The outlets of the fuel pipeline 5 and the oxidizer pipeline 6 are connected to the inlet of the mixing heat carrier generator 9. Fuel and oxidizer... The fuel is transported to the mixing heat carrier generator 9 through the fuel pipeline 5 and the combustion-supporting agent pipeline 6, where it is fully mixed. The mixing heat carrier generator 9 is equipped with an ignition device and an electric heater 13 on its outer wall. The injection well 4 is also equipped with a cable 14, which is electrically connected to the ignition device, the electric heater 13 and the temperature monitor 8. The gas outlet of the production well 10 is connected to the gas inlet of the separation module 16 through a pipeline. The gas outlet of the separation module 16 is connected to the gas inlet of the fuel pipeline 5 through a pressurization pump 15.

[0029] Specifically, the outer wall of the extraction well 10 is fitted with an insulation sleeve 12 to keep the extracted pyrolysis gas warm.

[0030] Specifically, the bottom of well 10 is sealed to prevent the product from seeping into the coal seam.

[0031] Specifically, the separation module 16 includes a condenser separator 161 and a gas separator 162. The pyrolysis products are first fed into the condenser separator 161 to separate tar. The outlet of the condenser separator 161 is connected to the inlet of the gas separator 162. The gas separator 162 is used to separate pyrolysis gas and tail gas. The pyrolysis gas outlet of the gas separator 162 is connected to the inlet of the fuel pipeline 5 through a pressurization pump 15. The tail gas outlet of the gas separator 162 is used to discharge and store the tail gas.

[0032] Specifically, both the outlet of the fuel pipeline 5 and the outlet of the combustion-supporting agent pipeline are equipped with switching valves.

[0033] Specifically, the temperature of the condenser separator 161 is room temperature to 80°C, and it is water-cooled or air-cooled to achieve the condensation of pyrolysis tar. The gas separation device 162 forcefully separates the pyrolysis gas, which mainly consists of small molecule alkanes, H2, and CO. The separated pyrolysis gas enters the mixed heat carrier generator 9 through the fuel pipeline 5 to achieve the reuse of the pyrolysis gas.

[0034] Specifically, the fuel is a gaseous fuel, a liquid fuel, or pyrolysis gas produced by in-situ underground pyrolysis, and the combustion accelerant is oxygen or air. Gaseous fuels include natural gas and coal gas, while liquid fuels include coal-water slurry or oil products.

[0035] Specifically, the ignition device is located at the top of the combustion zone to achieve combustion of the mixed components within the combustion zone.

[0036] Specifically, the mixed heat carrier generator 9 undergoes a combustion reaction that releases a large amount of heat and generates a high-temperature mixed heat carrier, mainly consisting of high-temperature CO2, H2O, N2, etc., with a temperature greater than or equal to 600℃.

[0037] Specifically, the current inlet of cable 14 is connected to the current outlet of the renewable energy power generation device, which supplies power to various devices in the well.

[0038] Specifically, such as Figures 3-6 As shown, several mixing heat carrier generators 9 can be arranged side by side in the mounting hole 11. A portion of the mixing heat carrier generators 9 is arranged in the coal seam 2, and the side wall of the mixing heat carrier generators 9 is provided with through holes.

[0039] Example 2 A heating method for underground in-situ coal pyrolysis, based on a heating device for underground in-situ coal pyrolysis in Example 1, includes the following steps: The injection well 4 and the production well 10 are used to fracture the coal seam 2. During the initial slow heating stage, a single underground mixed heat carrier generator 9 is installed at the bottom of the injection well 4, with the generator outlet extending into the coal seam 2. Fuel and oxidizer pipelines 6 are connected. The fuel is gaseous natural gas and pyrolysis gas, and the oxidizer is air, with the air equivalence ratio controlled at 1.0. The ignition device is activated, and a combustion reaction occurs inside the generator. The generated high-temperature mixed heat carrier enters the coal seam fracture 7 through the outlet, heating the coal seam 2. The high-temperature mixed heat carrier drives the oil and gas resources generated from the coal, which are then extracted through the production well 10. The production well 10 includes an insulated casing 12 to keep the oil and gas products warm. The products are separated to obtain tar and pyrolysis gas. The pyrolysis gas is reused as fuel and enters the mixed heat carrier generator 9 through the fuel pipeline 5. In the later stage of using renewable energy for electric heating and insulation, an electric heater 13 is installed underground. The exhaust gas and pyrolysis gas enter the electric heater 13 directly without separation and are heated before entering the coal seam 2 to provide heat to the underground coal seam 2 and purge the pyrolysis products, so that the coal seam 2 can continue to pyrolyze.

[0040] Example 3 A heating method for underground in-situ pyrolysis of coal, referenced Figure 1 and Figure 3 It mainly includes the following steps: The mining operation includes an injection well 4 and a production well 10. The bottom of the injection well 4 is square, and the coal seam 2 is fractured to form fissures. Multiple mixed heat carrier generators 9 are compactly installed at the bottom of the injection well 4, with the generator outlets extending into the coal seam 2. Fuel and combustion aid pipelines 6 are connected. The fuel is liquid coal-water slurry and pyrolysis gas, and the combustion aid is oxygen, with the air equivalence ratio controlled at 1.0. The ignition device is activated, and a combustion reaction occurs within the mixed heat carrier generators 9. The generated high-temperature mixed heat carrier enters the coal seam fissures 7 through the outlet, heating the coal seam 2. The high-temperature mixed heat carrier performs gas drive on the oil and gas resources generated from the coal, which are then extracted through the production well 10. The production well 10 includes an insulated casing 12 to keep the oil and gas products warm. The products are separated by a separation device to obtain tar and pyrolysis gas. The pyrolysis gas is reused as fuel and enters the mixed heat carrier generator 9 through the fuel pipeline 5.

[0041] Example 4 A heating method for underground in-situ pyrolysis of coal, referenced Figure 1 , Figure 4 and Figure 6 It mainly includes the following steps: The injection well 4 and the production well 10 are used to fracture the coal seam 2. A single underground mixed heat carrier generator 9 is installed at the bottom of the injection well 4. The generator can move up and down along the injection well 4, with its initial position at the bottom of the injection well 4 and its outlet extending into the coal seam 2. Fuel and oxidizer pipelines 6 are connected. The fuel is gaseous natural gas and pyrolysis gas, and the oxidizer is air. Oxygen is introduced, and the excess air coefficient is controlled at 1.1-1.3. The ignition device is activated, and a combustion reaction occurs inside the generator. The generated high-temperature mixed heat carrier enters the coal seam fracture 7 through the outlet, heating the coal seam 2. Excess high-temperature oxygen enters the coal seam. 2 undergoes a partial oxidation and exothermic reaction with coal to gasify coal seam 2; the gasification products are mixed with a high-temperature heat carrier to drive the oil and gas resources generated from the coal, and are extracted through production well 10; production well 10 includes an insulated casing 12 to keep the oil and gas products warm; after running for a period of time, the amount of oxygen is reduced to control the air equivalent ratio to 1.0 so that no excess oxygen enters coal seam 2, and at the same time the mixed heat carrier generator 9 is moved upward along injection well 4 to heat the upper coal seam 2; the products are separated to obtain tar and pyrolysis gas; the pyrolysis gas is recycled as fuel and enters the mixed heat carrier generator 9 through fuel pipeline 5.

[0042] Example 5 A heating method for underground in-situ pyrolysis of coal, referenced Figure 1 , Figure 5 and Figure 6 It mainly includes the following steps: The injection well 4 and the production well 10 are used to fracture the coal seam 2. Two underground mixed heat carrier generators 9 are installed at the bottom of the injection well 4, with their outlets extending into the coal seam 2. Fuel and oxidizer pipelines 6 are connected; the fuel is gaseous natural gas and pyrolysis gas, and the oxidizer is air. Oxygen is introduced into the upper mixed heat carrier generator 9 at an air equivalence ratio of 1.0, while excess oxygen is introduced into the lower mixed heat carrier generator 9. The ignition device is activated, and combustion occurs in the upper generator. The resulting high-temperature mixed heat carrier enters the coal seam fracture 7 through its outlet, heating... Combustion reaction occurs in the lower layer generator of coal seam 2; the generated high-temperature mixed heat carrier enters the coal seam fracture 7 through the outlet, where excess high-temperature oxygen enters coal seam 2 and undergoes a partial oxidation exothermic reaction with the coal, gasifying coal seam 2; the gasification products and the high-temperature mixed heat carrier drive the oil and gas resources generated from the coal, and are extracted through the production well 10; the production well 10 includes an insulated casing 12 to keep the oil and gas products warm; the products are separated by a separation device to obtain tar and pyrolysis gas; the pyrolysis gas is recycled as fuel and enters the mixed heat carrier generator 9 through the fuel pipeline 5.

[0043] As is known from common technical knowledge, this invention can be implemented through other embodiments that do not depart from its spirit or essential characteristics. Therefore, the disclosed embodiments described above are merely illustrative in all respects and are not the only ones. All modifications within the scope of this invention or equivalent to the scope of this invention are included in this invention.

[0044] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A heating method for in-situ underground pyrolysis of coal, characterized in that, include: An injection well (4) and a production well (10) are opened to fracture the coal seam (2) and form a coal seam fracture (7); a single underground mixed heat carrier generator (9) that can move up and down along the injection well (4) is installed at the bottom of the injection well (4), with its initial position at the bottom of the injection well (4) and its outlet extending into the coal seam (2). Natural gas and pyrolysis gas are supplied to the underground mixed heat carrier generator (9) via fuel pipeline (5), and air is supplied to the underground mixed heat carrier generator (9) via combustion aid pipeline (6); oxygen is introduced, the excess air coefficient is controlled to 1.1 to 1.3, and combustion is carried out, so that the high-temperature mixed heat carrier enters the coal seam fissure (7), where the excess high-temperature oxygen enters the coal seam (2) and undergoes a partial oxidation exothermic reaction with the coal, thus gasifying the coal seam (2); Oil and gas resources generated by coal driving using gasification products and the high-temperature mixed heat carrier gas are extracted through the extraction well (10). After running for a period of time, the amount of oxygen is reduced and the air equivalent ratio is controlled to 1.0 so that no excess oxygen enters the coal seam (2). At the same time, the underground mixed heat carrier generator (9) is moved upward along the injection well (4) to heat the upper coal seam (2). The extracted oil and gas products are separated to obtain tar and pyrolysis gas. The pyrolysis gas is sent back to the underground mixed heat carrier generator (9) as fuel through the fuel pipeline (5).

2. The heating method for underground in-situ pyrolysis of coal according to claim 1, characterized in that, The high-temperature mixed heat transfer fluid includes carbon dioxide, water vapor, and nitrogen, and the temperature of the high-temperature mixed heat transfer fluid is greater than or equal to 600°C.

3. The heating method for underground in-situ pyrolysis of coal according to claim 1, characterized in that, The oil and gas products extracted through the well (10) are insulated by using an insulating sleeve (12) fitted on the outer wall of the well (10).

4. The heating method for underground in-situ pyrolysis of coal according to claim 1, characterized in that, The extracted oil and gas products include: The oil and gas products are fed into a condenser (161), and the temperature of the condenser (161) is controlled between room temperature and 80°C by water cooling or air cooling in order to separate tar from the oil and gas products. The gaseous products after tar separation are passed into a gas separator (162) to separate the tail gas and pyrolysis gas.

5. The heating method for underground in-situ pyrolysis of coal according to claim 4, characterized in that, The pyrolysis gas includes small molecule alkanes, hydrogen and carbon monoxide; the pyrolysis gas outlet of the gas separator (162) is connected to the inlet of the fuel pipeline (5) via a pressurization pump (15).

6. The heating method for underground in-situ pyrolysis of coal according to claim 1, characterized in that, The ignition device is located at the top of the combustion zone of the underground mixed heat carrier generator (9) and is used to ignite the mixed components in the combustion zone.

7. The heating method for underground in-situ pyrolysis of coal according to claim 1, characterized in that, The underground mixed heat carrier generator (9) has an internal cavity and a through hole on its side wall. The high-temperature mixed heat carrier generated by combustion enters the coal seam fissure (7) through the through hole.

8. The heating method for underground in-situ pyrolysis of coal according to claim 1, characterized in that, Both the outlet of the fuel pipeline (5) and the outlet of the combustion-supporting agent pipeline (6) are equipped with switching valves.

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