A method for in-situ combustion of extremely thin coal seam with hot flue gas modification and power generation with steam

Abstract

The present disclosure relates to the field of development and utilization of coal seam resources, and particularly relates to a method for in-situ combustion of extremely thin coal seam in cooperation with steam power generation by modifying hot flue gas. The method uses hot flue gas to modify the extremely thin coal seam, increases the permeability of the coal seam, and simultaneously uses the gas components of the flue gas to displace the coal seam gas, so as to improve the gas migration environment of the coal seam, ensure the flowability of the gas flow in the coal seam, and provide gas conditions for subsequent in-situ combustion of the coal seam. A water injection and heat recovery subsystem capable of cooperating with in-situ combustion of the extremely thin coal seam is formed by embedding a refractory water pipe in a bedding borehole, air is injected into the extremely thin coal seam to induce in-situ spontaneous combustion of the coal seam, so as to generate a large amount of heat energy and heat water to generate steam, thereby realizing extraction of the heat energy of the in-situ combustion of the coal seam. The present disclosure is aimed at the extremely thin coal seam, and the coal resources are developed and utilized by the method for in-situ combustion of the coal seam in cooperation with steam power generation, which has important significance for efficient utilization of coal resources in China and energy multistage.

Description

Technical Field

[0001] This disclosure relates to the field of coal seam resource development and utilization, and in particular to a method for in-situ combustion of hot flue gas-modified ultrathin coal seams in conjunction with steam power generation. Background Technology

[0002] Compared to main coal seams, thin coal seams have lower gas content, are more difficult to mine, have higher costs, and lower efficiency, and have long been considered marginal resources in coalbed methane development. Extremely thin coal seams, due to their small thickness and difficult mining, are often not developed or utilized. However, in recent years, chemical gasification methods for extremely thin coal seams involve gasifying the coal seam to produce combustible gases for extraction. However, the low efficiency of chemical reactions and the openness of the environment, such as coal seam faults, have a significant impact on chemical gasification methods. Summary of the Invention

[0003] Technical issues:

[0004] This invention provides a method and system for in-situ combustion combined with steam power generation in extremely thin, unminable coal seams, which simultaneously realizes the extraction of coalbed methane and the efficient extraction of thermal energy from in-situ combustion in extremely thin coal seams.

[0005] Technical solution:

[0006] On the one hand, a method for in-situ combustion of modified ultra-thin coal seams combined with steam power generation is provided, which includes the following steps:

[0007] (1) Divide the extremely thin coal seam into a combustion zone and a non-combustion zone located around the combustion zone; construct a extraction well and at least one gas injection well from the ground to the combustion zone; wherein the area between the extraction well and the gas injection well can cover the combustion zone;

[0008] (2) Hot flue gas modification of ultra-thin coal seams: Hot flue gas is injected into the combustion zone through the injection well via the gas injection equipment to expand and increase the number of coal seam fractures in the combustion zone of the ultra-thin coal seam, thereby increasing the permeability of the coal seam in the combustion zone. At the same time, the coalbed methane produced by the displacement effect of the hot flue gas is extracted from the extraction well using the extraction equipment. The extracted gas is then transported to the coalbed methane purification device for purification and utilization. The gas injection and extraction operations are stopped when the concentration of carbon dioxide in the extracted gas reaches 50%.

[0009] (3) Shaft 1 and Shaft 2 are constructed from the ground to the non-combustion zones on opposite sides of the combustion zone; two drilling faces are constructed adjacent to Shaft 1 and Shaft 2 along the direction of the extremely thin coal seam; multiple in-seam boreholes are constructed from the drilling faces along the direction of the extremely thin coal seam, wherein the in-seam boreholes penetrate the combustion zone; refractory water pipes are nested inside the in-seam boreholes; a main water inlet pipe and a main gas outlet pipe are set on the two drilling faces respectively, the first end of the refractory water pipe is connected to the main water inlet pipe, and the second end of the refractory water pipe is connected to the main gas outlet pipe; the main water inlet pipe extends from Shaft 1 to the ground and is connected to a water source, and a water pump and a water valve are installed on the main water inlet pipe; the main gas outlet pipe extends from Shaft 2 to the ground and is connected to a steam generator, and a steam pressure gauge and a gas outlet valve are installed on the main gas outlet pipe;

[0010] (4) Constructing fire-resistant walls: Constructing fire-resistant walls at the junction of the combustion zone and the non-combustion zone. The fire-resistant walls can separate the two drilling faces from the combustion zone, so as to protect the two drilling faces, shaft one and shaft two in the event of spontaneous combustion in the combustion zone of the subsequent extremely thin coal seam.

[0011] (5) Open the inlet valve and the outlet valve, and start the inlet pump to inject water from the inlet main pipe into the refractory water pipe until the water content in all pipes reaches 80%. Then, stop the water injection and close the inlet valve and the outlet valve. Then, inject air into the combustion zone through the air injection equipment from the air injection well to induce in-situ spontaneous combustion of the extremely thin coal seam. At the same time, use the extraction equipment to extract the tail gas produced by the in-situ spontaneous combustion of the extremely thin coal seam from the extraction well. The extracted gas is transported to the tail gas treatment device for purification and then discharged. Meanwhile, the high temperature generated by the in-situ spontaneous combustion of the extremely thin coal seam can heat the water in the refractory water pipe and produce water vapor. The water vapor pressure gauge can monitor the water vapor pressure in the outlet main pipe in real time. When the water vapor pressure in the outlet main pipe reaches the working pressure of the steam generator, open the outlet valve to allow the water vapor to enter the steam generator for power generation. The electrical energy generated by the steam generator is transmitted to the power user through the transmission line. The steam generated by the steam generator is transported to the heat user to recover the residual heat energy in the water vapor.

[0012] On the other hand, a hot flue gas modified ultra-thin coal seam in-situ combustion and steam power generation system is provided, comprising: an ultra-thin coal seam, a gas injection and extraction subsystem, a water injection and regenerative subsystem, a steam power generation system, and a refractory wall; the ultra-thin coal seam is divided into a combustion zone and a non-combustion zone located around the combustion zone; the refractory wall is located at the boundary between the combustion zone and the non-combustion zone; the gas injection and extraction subsystem includes an extraction well, extraction equipment, a coalbed methane purification device, a tail gas treatment device, at least one gas injection well, and at least one gas injection device; both the extraction well and the gas injection well extend from the ground to the combustion zone. Furthermore, the area between the extraction well and the injection well can cover the combustion zone; the injection equipment is configured to inject hot flue gas or air into the injection well; the extraction equipment is configured to extract coalbed methane produced by the displacement effect of the hot flue gas or tail gas produced by the spontaneous combustion of the combustion zone under the action of air from the extraction well; the coalbed methane purification device is connected to the extraction equipment to transport the coalbed methane to the coalbed methane purification device for processing; the tail gas treatment device is connected to the extraction equipment to transport the tail gas to the tail gas treatment device for processing; the water injection return The thermal subsystem includes shaft one, shaft two, two drilling faces, multiple in-seam boreholes along the direction of the extremely thin coal seam, a water source, a water pump, a water valve, a main water inlet pipe, a refractory water pipe, a main exhaust pipe, a steam pressure gauge, and an exhaust valve. Shaft one and shaft two extend from the ground to the non-combustion zones located on opposite sides of the combustion zone. The two drilling faces are respectively located adjacent to shaft one or shaft two and are configured to drill the in-seam boreholes. The in-seam boreholes penetrate the combustion zone. The refractory water pipes are nested inside the in-seam boreholes. The main water inlet pipe passes through the shafts. The first part of the refractory water pipe is connected to the first end of the refractory water pipe; the main water inlet pipe is connected to the water source; the water inlet pump and the water inlet valve are installed on the main water inlet pipe; the main vent pipe passes through the second vertical shaft and is connected to the second end of the refractory water pipe; the steam pressure gauge and the vent valve are installed on the main vent pipe; the steam power generation system includes a steam generator, a power transmission line, an electricity user, and a heat user; the steam generator and the electricity user are connected through the power transmission line; the steam generator is connected to the heat user to utilize the residual steam heat energy of the steam generator.

[0013] In some embodiments, there are two injection wells and two injection devices; the two injection wells are respectively located adjacent to two drilling faces; and the extraction well is located in the middle of the two injection wells.

[0014] Beneficial effects:

[0015] 1. The method of this invention utilizes high-temperature hot flue gas to thermally modify extremely thin coal seams. Specifically, the thermal effect of the hot flue gas promotes the gradual development and interconnection of coal seam fractures, forming an integral fracture network, increasing coal seam permeability, and providing a favorable gaseous environment for subsequent in-situ spontaneous combustion of extremely thin coal seams. Simultaneously, the flue gas components displace coalbed methane, thereby improving the coal seam gas migration environment and ensuring gas flow within the coal seam, providing the necessary gas conditions for subsequent in-situ combustion of extremely thin coal seams. A water injection regenerative subsystem, compatible with in-situ combustion of extremely thin coal seams, is constructed by nesting refractory water pipes within in-seam boreholes. Air required for in-situ combustion of extremely thin coal seams is then supplied to the combustion zone from the injection well to induce spontaneous combustion. Simultaneously, the extraction well extracts the exhaust gas produced during combustion, significantly reducing the content of suppressing gases during in-situ combustion of extremely thin coal seams and improving the combustion effect. The heat energy released by the spontaneous combustion of extremely thin coal seams is used to convert water into high-temperature water vapor, thereby realizing the extraction of heat energy from the in-situ combustion of extremely thin coal seams.

[0016] 2. In the method of this invention, the extracted gas obtained from the modification of extremely thin coal seams with hot flue gas is mainly coalbed methane. Therefore, the extracted gas is sent to a coalbed methane purification device for purification and utilization. When the carbon dioxide content in the extracted gas reaches more than 50%, it indicates that the pore connectivity and coalbed methane displacement degree of the extremely thin coal seam under the action of hot flue gas have reached a high level. At this time, the injection of hot flue gas is stopped, but the extraction operation is still maintained, and the extracted gas should be sent to a tail gas treatment device for purification and discharge.

[0017] 3. The heat-water-gas system formed by the in-situ combustion of ultra-thin coal seams in this invention is more stable than that of chemical gasification. The steam power generation technology used in this invention is mature and easy to promote and use. Furthermore, the residual heat energy in the steam can be recovered after power generation to supply heat users. Therefore, the method of this invention can achieve multi-polar utilization of energy.

[0018] 4. The method of the present invention simultaneously realizes the development and utilization of coal resources in extremely thin coal seams that are not minable underground. The energy development process is stable and controllable, and the coal resource extraction is multi-stage, efficient, and does not generate secondary pollution.

[0019] 5. This invention provides a method and system for in-situ combustion combined with steam power generation applicable to extremely thin, unminable coal seams, simultaneously realizing the extraction of coalbed methane and the efficient extraction of thermal energy from in-situ combustion in extremely thin coal seams. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in this disclosure, the accompanying drawings used in some embodiments of this disclosure will be briefly introduced below. However, the drawings described below are merely drawings of some embodiments of this disclosure, and those skilled in the art can obtain other drawings based on these drawings. Furthermore, the drawings described below can be regarded as schematic diagrams and are not intended to limit the actual size of the product, the actual flow of the method, the actual timing of the signals, etc., involved in the embodiments of this disclosure.

[0021] Figure 1 This is a structural diagram of a hot flue gas modified ultrathin coal seam in-situ combustion combined with steam power generation system according to some embodiments. Detailed Implementation

[0022] The technical solutions in some embodiments of this disclosure will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this disclosure, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments provided in this disclosure are within the scope of protection of this disclosure.

[0023] Unless the context otherwise requires, throughout the specification and claims, the term "comprising" is interpreted as open-ended and encompassing, meaning "including, but not limited to." In the description of the specification, terms such as "one embodiment," "some embodiments," "exemplary embodiment," "example," "specific example," or "some examples," etc., are intended to indicate that a particular feature, structure, material, or characteristic associated with that embodiment or example is included in at least one embodiment or example of this disclosure. The illustrative representations of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific feature, structure, material, or characteristic may be included in any suitable manner in any one or more embodiments or examples.

[0024] Hereinafter, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of embodiments of this disclosure, unless otherwise stated, "a plurality of" means two or more.

[0025] In describing some embodiments, the terms "coupled" and "connected," and their derivative expressions, may be used. The term "connected" should be interpreted broadly; for example, a "connection" can be a fixed connection, a detachable connection, or an integral part; it can be a direct connection or an indirect connection through an intermediate medium. The term "coupled" indicates that two or more components have direct physical or electrical contact. The term "coupled" or "communication coupling" may also refer to two or more components that do not have direct contact with each other but still cooperate or interact with each other. The embodiments disclosed herein are not necessarily limited to the content of this document.

[0026] "At least one of A, B and C" has the same meaning as "at least one of A, B or C", both including the following combinations of A, B and C: only A, only B, only C, combinations of A and B, combinations of A and C, combinations of B and C, and combinations of A, B and C.

[0027] "A and / or B" includes the following three combinations: A only, B only, and a combination of A and B.

[0028] As used herein, depending on the context, the term “if” may optionally be interpreted as meaning “when”, “in the event of”, “in response to determination”, or “in response to detection”. Similarly, depending on the context, the phrase “if it is determined that…” or “if [the stated condition or event] is detected” may optionally be interpreted as meaning “in the event of determination that…”, “in response to determination that…”, “when [the stated condition or event] is detected”, or “in response to the detection of [the stated condition or event]”.

[0029] The use of “applies to” or “configured to” in this article implies an open and inclusive language that does not preclude applicability to or configuration to devices that perform additional tasks or steps.

[0030] In addition, the use of “based on” implies openness and inclusivity, because processes, steps, calculations or other actions “based on” one or more of the stated conditions or values ​​may in practice be based on additional conditions or values ​​beyond those stated.

[0031] As used herein, “about,” “approximately,” or “approximately” includes the stated value and the average value within an acceptable range of deviation from the given value, wherein the acceptable range of deviation is determined by a person skilled in the art taking into account the measurement under discussion and the error associated with the measurement of the given quantity (i.e., the limitations of the measurement system).

[0032] As used herein, “parallel,” “perpendicular,” and “equal” include the described situation and situations that are similar to the described situation, within an acceptable range of deviation, which is determined by those skilled in the art taking into account the measurement under discussion and the error associated with the measurement of a particular quantity (i.e., the limitations of the measurement system). For example, “parallel” includes absolute parallelism and approximate parallelism, where an acceptable range of deviation for approximate parallelism may be, for example, within 5°; “perpendicular” includes absolute perpendicularity and approximate perpendicularity, where an acceptable range of deviation for approximate perpendicularity may also be, for example, within 5°; “equal” includes absolute equality and approximate equality, where an acceptable range of deviation for approximate equality may be, for example, a difference between the two equals being less than or equal to 5% of either one.

[0033] This document describes exemplary embodiments with reference to cross-sectional views and / or plan views, which are idealized exemplary drawings. In the drawings, the thickness of layers and regions is enlarged for clarity. Therefore, variations in shape relative to the drawings are contemplated due to, for example, manufacturing techniques and / or tolerances. Thus, exemplary embodiments should not be construed as limited to the shapes of the regions shown herein, but rather include shape deviations due to, for example, manufacturing processes. For example, etched regions shown as rectangular would typically have curved features. Therefore, the regions shown in the drawings are schematic in nature, and their shapes are not intended to show the actual shapes of the regions of the device, nor are they intended to limit the scope of the exemplary embodiments.

[0034] In some embodiments, a hot flue gas modified ultra-thin coal seam in-situ combustion combined with steam power generation system is provided, such as Figure 1 As shown, it includes: an ultra-thin coal seam 29, a gas injection and extraction subsystem, a water injection and regeneration subsystem, a steam generator system, a first refractory wall 23, and a second refractory wall 24; the ultra-thin coal seam 29 is divided into a combustion zone and a non-combustion zone located around the combustion zone to ensure that the combustion range of the ultra-thin coal seam 29 is controllable; the refractory walls (e.g. Figure 1 Firewall 1 (23) and firewall 2 (24) are located at the boundary between the combustion zone and the non-combustion zone; the gas injection and extraction subsystem includes extraction well 26, extraction equipment 25, coalbed methane purification device 27, tail gas treatment device 28, and at least one gas injection well (e.g., Figure 1 Injection well 17 and injection well 28) and at least one injection device (e.g. Figure 1 Gas injection equipment 15 and gas injection equipment 16); extraction well 26 and gas injection well (e.g. Figure 1 Both injection well 17 and injection well 28 extend from the ground to the combustion zone, and extraction well 26 and injection well (e.g. Figure 1 The area between injection well 17 and injection well 28 can cover the combustion zone; the injection equipment (e.g. Figure 1Gas injection devices 15 and 16 are configured to inject gas into injection wells (e.g., Figure 1 Hot flue gas (i.e., high-temperature flue gas) or air is injected into injection wells 17 and 28. Extraction equipment 25 is configured to extract coalbed methane produced by the displacement effect of hot flue gas or tail gas produced by spontaneous combustion in the combustion zone under the action of air from extraction well 26. Coalbed methane purification device 27 is connected to extraction equipment 25 to transport coalbed methane to extraction equipment 27 for processing. Tail gas treatment device 28 is connected to extraction equipment 25 to treat tail gas. The gas is transported to the tail gas treatment unit 28 for processing; the water injection regeneration subsystem includes shaft 19, shaft 20, two drilling faces (i.e., drilling face 1 21 and drilling face 2 22), multiple in-seam boreholes along the direction of the extremely thin coal seam 29, water source 1, water pump 2, water valve 3, main water inlet pipe 4, refractory water pipe 7, main gas outlet pipe 8, steam pressure gauge 9, and gas outlet valve 10; shaft 19 and shaft 20 extend from the ground to the location In the non-combustion zones on opposite sides of the combustion zone, drilling face 21 is located adjacent to shaft 19, and drilling face 22 is located adjacent to shaft 20, and is configured as a bedding-line drilling. The bedding-line drilling penetrates the combustion zone. Refractory water pipe 7 is nested inside the bedding-line drilling. The main water inlet pipe 4 passes through shaft 19 and is connected to the first end of the refractory water pipe 7. The main water inlet pipe 4 is connected to the water source 1. The water inlet pump 2 and the water inlet valve 3 are installed on the main water inlet pipe 4. The main exhaust pipe 8 passes through shaft 20 and is connected to the second end of the refractory water pipe 7. The steam pressure gauge 9 and the exhaust valve 10 are installed on the main exhaust pipe 8. The steam power generation system includes a steam generator 11, a transmission line 13, an electricity user 14, and a heat user 12. The steam generator 11 and the electricity user 14 are connected through the transmission line 13. The steam generator 11 is connected to the heat user 12 to utilize the residual steam heat energy of the steam generator 11.

[0035] In some embodiments, a method for in-situ combustion of modified ultra-thin coal seams combined with steam power generation is provided, comprising the following steps:

[0036] (1) Select a suitable area for in-situ combustion of the ultra-thin coal seam 29 as the combustion zone, and divide the ultra-thin coal seam 29 into the combustion zone and a non-combustion zone located around the combustion zone; construct extraction wells 26 and at least one gas injection well (e.g., from the surface to the combustion zone) for extraction wells 26 and at least one gas injection well (e.g., from the surface to the combustion zone). Figure 1 Injection well 17 and injection well 28); among them, extraction well 26 and injection well (e.g. Figure 1 The area between injection well 17 and injection well 28 can cover the combustion zone;

[0037] (2) Modification of extremely thin coal seams by hot flue gas: through gas injection equipment (e.g., Figure 1 Gas injection equipment 15 and gas injection equipment 16 are supplied by a gas injection well (e.g., Figure 1Hot flue gas is injected into the combustion zone through injection wells 17 and 18. The heat energy contained in the hot flue gas can significantly expand the coal seam fractures 30 in the combustion zone of the ultra-thin coal seam 29, while promoting the generation of more coal seam fractures 30, increasing the permeability of the coal seam in the combustion zone, and thus improving the environment for gas occurrence and migration in the combustion zone. At the same time, the methane gas in the ultra-thin coal seam 29 is desorbed from the coal seam under the displacement effect of the hot flue gas, and migrates along the direction of the coal seam fractures 30 under the pressure of the hot flue gas. Meanwhile, the coal seam gas produced by the displacement effect of the hot flue gas is extracted from the extraction well 26 by the extraction equipment 25, and the extracted gas is transported to the coal seam gas purification device 27 for purification and utilization. When the concentration of carbon dioxide in the extracted gas reaches 50%, it indicates that the coal seam fractures 30 are interconnected under the action of hot flue gas, and the permeability of the ultra-thin coal seam 29 has reached a high level, and the gas injection and extraction operations are stopped.

[0038] (3) Construct shaft 19 and shaft 20 from the ground to the non-combustion zones on opposite sides of the combustion zone; construct two drilling faces (i.e., drilling face 11 and drilling face 22) adjacent to shaft 19 and shaft 20 along the direction of the extremely thin coal seam 29; construct multiple in-seam boreholes along the direction of the extremely thin coal seam 29 from the drilling faces, wherein the in-seam boreholes penetrate the combustion zone; refractory water pipes 7 are nested inside the in-seam boreholes; at the two drilling faces (drilling faces) Face 1 (21) and Drilling Face 2 (22) are respectively equipped with a water inlet main pipe 4 and an air outlet main pipe 8. The first end of the refractory water pipe 7 is connected to the water inlet main pipe 4, and the second end of the refractory water pipe 7 is connected to the air outlet main pipe 8. The water inlet main pipe 4 extends from Shaft 1 (19) to the ground and is connected to the water source 1. A water inlet pump 2 and a water inlet valve 3 are installed on the water inlet main pipe 4. The air outlet main pipe 8 extends from Shaft 2 (20) to the ground and is connected to the steam generator 11. A steam pressure gauge 9 and an air outlet valve 10 are installed on the air outlet main pipe 8.

[0039] (4) Constructing fire-resistant walls: Constructing fire-resistant walls at the boundary between the combustion zone and the non-combustion zone. The fire-resistant walls (such as fire-resistant wall 1 23 and fire-resistant wall 24) can separate the two drilling faces (i.e., drilling face 1 21 and drilling face 2 22) from the combustion zone, so as to protect the two drilling faces (i.e., drilling face 1 21 and drilling face 2 22), shaft 1 19 and shaft 2 20 when the combustion zone of the subsequent ultra-thin coal seam 29 spontaneously combusts.

[0040] (5) Open the water inlet valve 3 and the air outlet valve 10, and turn on the water inlet pump 2 to inject water source 1 from the water inlet main pipe 4 into the refractory water pipe 7 until the water content in all pipelines reaches 80%. Then, stop the water injection and close the water inlet valve 3 and the air outlet valve 10. Then, inject air into the combustion zone through the air injection device from the air injection well to induce the in-situ spontaneous combustion of the ultra-thin coal seam 29. At the same time, use the extraction device 25 to extract the tail gas produced by the in-situ spontaneous combustion of the ultra-thin coal seam 29 from the extraction well 26. Due to the modification of the ultra-thin coal seam by the hot flue gas in step (2), the pore connectivity of the ultra-thin coal seam 29 is greatly enhanced. After the negative pressure extraction of the extraction well 26, the injected air can continuously move in the combustion zone to ensure that the ultra-thin coal seam has enough oxygen to react during spontaneous combustion. The extracted gas is transported to the tail gas treatment device 28 for purification and then discharged, reducing the emissions. The content of suppressing gases in the underground space during in-situ combustion of ultra-thin coal seams; at the same time, the high temperature generated by the in-situ spontaneous combustion of ultra-thin coal seam 29 can heat the water 5 in refractory water pipe 7 and produce high-temperature water vapor 6; the water vapor pressure gauge 9 can monitor the water vapor pressure in the gas outlet main pipe 8 in real time. When the water vapor pressure in the gas outlet main pipe 8 reaches the working pressure of steam generator 11, the gas outlet valve 10 is opened to allow water vapor to enter the steam generator 11 for power generation; the electrical energy generated by the steam generator 11 is transmitted to the power user 14 through the transmission line 13, and the steam generated by the steam generator 11 is transmitted to the heat user 12 to recover the residual heat energy in the water vapor; in the later stage of in-situ combustion of ultra-thin coal seams, when the water vapor pressure is insufficient for the steam generator 11 to continue generating electricity, the residual heat energy in the water vapor is mainly recovered.

[0041] In step (2) of this invention, the hot flue gas modifies the extremely thin coal seam, and the hot flue gas mainly expands the coal seam fractures through thermal action, increasing the coal seam permeability and promoting the gradual development and interconnection of the coal seam fractures to form an integral fracture network. The carbon dioxide in the hot flue gas can displace the coalbed methane present in the extremely thin coal seam. The displaced coalbed methane is affected by the pressure of the hot flue gas and moves along the extension direction of the coal seam fractures, so it can be separated from the extremely thin coal seam by extraction. In step (2) of the hot flue gas modifies the extremely thin coal seam, the obtained extracted gas is mainly coalbed methane, so the obtained extracted gas is sent to the coalbed methane purification device for purification and utilization. When the carbon dioxide content in the obtained extracted gas reaches more than 50%, it indicates that the pore connectivity and coalbed methane displacement degree of the extremely thin coal seam have reached a high level under the action of hot flue gas. At this time, the injection of hot flue gas is stopped, but the extraction operation is still maintained, and the extracted gas should be sent to the tail gas treatment device for purification and discharge.

[0042] This invention primarily utilizes high-temperature hot flue gas to thermally modify extremely thin coal seams. Specifically, the thermal effect of the flue gas increases the permeability of the coal seam, while the gas components of the flue gas displace the coalbed methane, thereby improving the gas migration environment and ensuring the fluidity of the gas flow within the coal seam. This provides the necessary gas conditions for subsequent in-situ combustion in the extremely thin coal seam. A water injection and regenerative subsystem, capable of supporting in-situ combustion in extremely thin coal seams, is constructed by embedding refractory water pipes within boreholes along the seam. Air is then injected into the extremely thin coal seam to induce in-situ spontaneous combustion, generating a large amount of heat energy. This heat energy is then used to convert water into high-temperature steam, thus extracting the heat energy from the in-situ combustion of the extremely thin coal seam.

[0043] In this invention, high-temperature hot flue gas is used to thermally modify extremely thin coal seams, displacing gas while expanding coal seam fissures. Its main purpose is to increase coal seam permeability so that gas can move more smoothly in the coal seam during subsequent combustion.

[0044] The present invention provides a method for in-situ combustion of ultra-thin coal seams with hot flue gas modification and combined with steam power generation. This method involves injecting high-temperature hot flue gas into ultra-thin coal seams to thermally modify them, significantly increasing the permeability and providing a favorable gas environment for subsequent in-situ spontaneous combustion. Air required for in-situ combustion of the ultra-thin coal seam is then supplied to the combustion zone from the injection well to induce spontaneous combustion. Simultaneously, the exhaust gas produced by combustion is extracted from the extraction well, thereby greatly reducing the content of flame-suppressing gases during in-situ combustion of ultra-thin coal seams and improving the combustion effect.

[0045] The heat-water-gas system formed by in-situ combustion of ultra-thin coal seams in this invention is more stable than that of chemical gasification. The steam power generation technology used in this invention is mature and easy to promote and use; furthermore, the residual heat energy in the steam can be recovered after power generation to supply heat users. Therefore, the method of this invention can achieve multi-polar utilization of energy.

[0046] The method of this invention simultaneously realizes the development and utilization of coal resources in extremely thin, unminable underground coal seams. The energy development process is stable and controllable, and the coal resource extraction is multi-stage, efficient, and does not generate secondary pollution.

[0047] In this invention, the gas injection wells and extraction wells are arranged alternately. When the extremely thin coal seam spontaneously combusts in situ, the gas injection wells inject air, and the extraction wells extract the tail gas, forming an airflow to reduce the content of the gas that suppresses combustion.

[0048] This invention utilizes in-situ combustion of extremely thin coal seams and extracts the combustion heat energy through water-gas conversion, thereby enabling the development and utilization of unminable coal seam resources. This is of great significance for the efficient utilization of coal resources and the diversified development of energy.

[0049] This invention addresses the development and utilization of coal resources in extremely thin, unminable coal seams by modifying hot flue gas to create in-situ combustion conditions, and further by using steam power generation to extract the heat energy from the in-situ combustion of the coal seam.

[0050] In some embodiments, the fire-resistant water pipe 7 is a high-strength fire-resistant water pipe.

[0051] In some embodiments, after the extraction well and the gas injection well are completed, in order to expand the extraction and gas injection effects, several boreholes can be drilled into the coal seam through directional drilling, but the effective extraction radius and the effective gas injection radius shall not overlap.

[0052] In some embodiments, such as Figure 1 As shown, injection well 17, extraction well 26 and injection well 28 are set up in sequence, with a spacing of 50m between adjacent wells.

[0053] In some embodiments, such as Figure 1 As shown, Shaft 19 is located 5-10m outside of Injection Well 17. Shaft 20 is located 5-10m outside of Injection Well 28.

[0054] In some embodiments, such as Figure 1 As shown, the drilling face is perpendicular to the direction of the extremely thin coal seam.

[0055] In some embodiments, there are two gas injection wells and two gas injection devices; the two gas injection wells are respectively located adjacent to two drilling faces; the extraction well 26 is located in the middle of the two gas injection wells.

[0056] In the description of the above embodiments, specific features, structures, materials, or characteristics may be combined in any suitable manner in one or more embodiments or examples.

[0057] The above description is merely a specific embodiment of this disclosure, but the scope of protection of this disclosure is not limited thereto. Any variations or substitutions conceived by those skilled in the art within the scope of the technology disclosed in this disclosure should be included within the scope of protection of this disclosure. Therefore, the scope of protection of this disclosure should be determined by the scope of the claims.

Claims

1. A method for in-situ combustion of modified ultra-thin coal seams with hot flue gas, combined with steam power generation, characterized in that, Includes the following steps: (1) Divide the extremely thin coal seam into a combustion zone and a non-combustion zone located around the combustion zone; construct a extraction well and at least one gas injection well from the ground to the combustion zone; wherein the area between the extraction well and the gas injection well can cover the combustion zone; (2) Hot flue gas modification of ultra-thin coal seams: Hot flue gas is injected into the combustion zone through the injection well via the gas injection equipment to expand and increase the number of coal seam fractures in the combustion zone of the ultra-thin coal seam, thereby increasing the permeability of the coal seam in the combustion zone. At the same time, the coalbed methane produced by the displacement effect of the hot flue gas is extracted from the extraction well using the extraction equipment. The extracted gas is then transported to the coalbed methane purification device for purification and utilization. The gas injection and extraction operations are stopped when the concentration of carbon dioxide in the extracted gas reaches 50%. (3) Shaft 1 and Shaft 2 are constructed from the ground to the non-combustion zones on opposite sides of the combustion zone; two drilling faces are constructed adjacent to Shaft 1 and Shaft 2 along the direction of the extremely thin coal seam; multiple in-seam boreholes are constructed from the drilling faces along the direction of the extremely thin coal seam, wherein the in-seam boreholes penetrate the combustion zone; refractory water pipes are nested inside the in-seam boreholes; a main water inlet pipe and a main gas outlet pipe are set on the two drilling faces respectively, the first end of the refractory water pipe is connected to the main water inlet pipe, and the second end of the refractory water pipe is connected to the main gas outlet pipe; the main water inlet pipe extends from Shaft 1 to the ground and is connected to a water source, and a water pump and a water valve are installed on the main water inlet pipe; the main gas outlet pipe extends from Shaft 2 to the ground and is connected to a steam generator, and a steam pressure gauge and a gas outlet valve are installed on the main gas outlet pipe; (4) Constructing a fire-resistant wall: Constructing a fire-resistant wall at the junction of the combustion zone and the non-combustion zone, wherein the fire-resistant wall can separate the two drilling working faces from the combustion zone; (5) Open the inlet valve and the outlet valve, and start the inlet pump to inject water from the inlet main pipe into the refractory water pipe until the water content in all pipes reaches 80%. Then, stop the water injection and close the inlet valve and the outlet valve. Then, inject air into the combustion zone through the air injection equipment from the air injection well to induce in-situ spontaneous combustion of the extremely thin coal seam. At the same time, use the extraction equipment to extract the tail gas produced by the in-situ spontaneous combustion of the extremely thin coal seam from the extraction well. The extracted gas is transported to the tail gas treatment device for purification and then discharged. Meanwhile, the high temperature generated by the in-situ spontaneous combustion of the extremely thin coal seam can heat the water in the refractory water pipe and produce water vapor. The water vapor pressure gauge can monitor the water vapor pressure in the outlet main pipe in real time. When the water vapor pressure in the outlet main pipe reaches the working pressure of the steam generator, open the outlet valve to allow the water vapor to enter the steam generator for power generation. The electrical energy generated by the steam generator is transmitted to the power user through the transmission line. The steam generated by the steam generator is transported to the heat user to recover the residual heat energy in the water vapor.

2. The method for in-situ combustion of ultra-thin coal seams modified with hot flue gas and combined with steam power generation according to claim 1, characterized in that, There are two gas injection wells and two gas injection devices; the two gas injection wells are set up adjacent to the two drilling faces respectively; the extraction well is located in the middle of the two gas injection wells.

3. A system for in-situ combustion of ultra-thin coal seams modified with hot flue gas, combined with steam power generation, characterized in that: include: Extremely thin coal seam, gas injection and extraction subsystem, water injection and regeneration subsystem, steam generator system and refractory wall; The extremely thin coal seam is divided into a combustion zone and a non-combustion zone surrounding the combustion zone; the fire-resistant wall is located at the boundary between the combustion zone and the non-combustion zone; The gas injection and extraction subsystem includes an extraction well, extraction equipment, a coalbed methane purification device, a tail gas treatment device, at least one injection well, and at least one injection device; both the extraction well and the injection well extend from the ground to the combustion zone, and the area between the extraction well and the injection well can cover the combustion zone; the injection device is configured to inject hot flue gas or air into the injection well; the extraction device is configured to extract coalbed methane produced by the displacement effect of the hot flue gas or tail gas produced by the spontaneous combustion of the combustion zone under the action of air from the extraction well; the coalbed methane purification device is connected to the extraction equipment; the tail gas treatment device is connected to the extraction equipment. The water injection and regeneration subsystem includes shaft one, shaft two, two drilling faces, multiple in-seam boreholes along the direction of the extremely thin coal seam, a water source, a water pump, a water valve, a main water inlet pipe, a refractory water pipe, a main exhaust pipe, a steam pressure gauge, and an exhaust valve. Shaft one and shaft two extend from the ground to the non-combustion zones located on opposite sides of the combustion zone. The two drilling faces are respectively located adjacent to shaft one or shaft two and are configured to drill the in-seam boreholes. The in-seam boreholes penetrate the combustion zone. The refractory water pipes are nested inside the in-seam boreholes. The main water inlet pipe passes through shaft one and is connected to the first end of the refractory water pipe. The main water inlet pipe is connected to the water source. The water pump and the water valve are installed on the main water inlet pipe. The main exhaust pipe passes through shaft two and is connected to the second end of the refractory water pipe. The steam pressure gauge and the exhaust valve are installed on the main exhaust pipe. The steam power generation system includes a steam generator, a transmission line, an electricity user, and a heat user; the steam generator and the electricity user are connected through the transmission line; the steam generator is connected to the heat user.

4. The hot flue gas modified ultra-thin coal seam in-situ combustion combined with steam power generation system according to claim 3, characterized in that, The gas injection and extraction subsystem includes two gas injection wells and two gas injection devices; the two gas injection wells are respectively located adjacent to the two borehole working faces; the extraction well is located in the middle of the two gas injection wells.

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