A system and method for in-situ coal pyrolysis and direct air carbon dioxide capture

Abstract

The present invention belongs to the technical field of underground coal pyrolysis, and particularly relates to a system and method for in-situ coal pyrolysis and direct air capture of carbon dioxide, including: an in-situ coal pyrolysis module for fracturing an underground coal seam, pyrolyzing the underground coal seam by injecting a high-temperature and high-pressure heat carrier and mild oxidation heating, and sending the pyrolysis products into a product separation and processing module; a product separation and processing module for separating, processing and utilizing the pyrolysis products, and using part of the pyrolysis gas in the pyrolysis products for power generation; a waste heat recovery module for recovering the heat remaining in the underground coal seam after pyrolysis; and a direct air capture of carbon dioxide module for capturing carbon dioxide from the air, desorbing carbon dioxide by the high-temperature steam produced by the in-situ coal pyrolysis module and the waste heat recovery module, and realizing the recycling of substances and energy. The present invention uses coal resources greenly and efficiently through underground in-situ coal pyrolysis, directly captures carbon dioxide from the air through the direct air capture of carbon dioxide module, and supplies the energy consumption required for the adsorption and desorption links through pyrolysis gas power generation and waste heat recovery, so as to continuously capture carbon dioxide in the atmospheric environment and reduce the capture cost.

Description

Technical Field

[0001] The present invention belongs to the technical field of underground coal pyrolysis, and particularly relates to a system and method for in-situ coal pyrolysis and direct air capture of carbon dioxide. Background Art

[0002] China's energy structure presents a distribution pattern of "lacking oil, short of gas, and relatively rich in coal", and the situation that new energy sources such as wind energy, solar energy, nuclear energy, and biomass energy are difficult to replace traditional energy sources in the short term. This determines that the dominant energy position of coal will still be difficult to change in a quite long period in the future. In 2019, China's carbon emissions reached 9.8 billion tons, exceeding one-fourth of the total global carbon dioxide emissions, and has become the country with the largest carbon emissions in the world. In the past decade, the compound growth rate of China's carbon emissions has also been faster than the global average level, and the main source of China's carbon emissions is the use of traditional energy. Among them, the carbon emissions generated by using coal in 2020 accounted for 71.1%.

[0003] At present, all traditional coal pyrolysis technologies are surface pyrolysis, that is, coal is mined and transported underground, and after washing and processing, it enters surface pyrolysis equipment and is pyrolyzed into tar, gas, and semi-coke products through pyrolysis. However, surface pyrolysis has problems such as large floor area, difficult conversion and utilization of pyrolyzed semi-coke, damage to the ground during mining, atmospheric dust pollution, and groundwater pollution. The goals of "carbon peak" and "carbon neutrality" not only put forward higher requirements for the high-quality development of coal, but also pose new challenges to the clean and efficient utilization of coal. Underground coal pyrolysis is a process in which coal is directly pyrolyzed in-situ underground through heat transfer by a heat carrier. On the one hand, coal can be directly pyrolyzed underground into oil and gas resources, alleviating the situation of high external dependence on scarce oil and gas resources. On the other hand, there is still a large amount of waste heat in the underground coal seam after pyrolysis, which can be recycled.

[0004] The current technical routes for carbon dioxide capture mainly include oxy-fuel combustion capture, pre-combustion capture, and post-combustion capture. The carbon dioxide absorption methods include absorption separation methods such as physical absorption and chemical absorption, as well as adsorption separation methods such as temperature swing adsorption and pressure swing adsorption. However, these methods are mainly used for carbon dioxide capture from fixed sources, such as power plants and chemical plants, and have problems such as large floor area of the capture device and high capture cost. Therefore, a system and method for in-situ coal pyrolysis and direct air capture of carbon dioxide are of great significance for energy development. Summary of the Invention

[0005] The purpose of the present invention is to provide a system and method for in-situ coal pyrolysis and direct air capture of carbon dioxide to solve the technical problems of high cost and complicated steps in existing carbon dioxide capture technologies.

[0006] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0007] In a first aspect, a system for in-situ coal pyrolysis and direct air capture of carbon dioxide includes an in-situ coal pyrolysis module, a product separation and processing module, a direct air capture of carbon dioxide module, and a waste heat recovery module;

[0008] The in-situ coal pyrolysis module is used to fracture the underground coal seam, in-situ pyrolyze the underground coal seam through injecting high-temperature and high-pressure heat carriers and mild oxidation heating, and send the pyrolysis products to the product separation and processing module, and send the high-temperature steam to the direct air capture of carbon dioxide module;

[0009] The product separation and processing module is used to separate, process and utilize the pyrolysis products, and use the pyrolysis gas in the pyrolysis products to generate electricity and supply it to the in-situ coal pyrolysis system and the direct air capture of carbon dioxide module;

[0010] The direct air capture of carbon dioxide module is used to capture carbon dioxide from the air, and use the high-temperature steam produced by the in-situ coal pyrolysis module or the high-temperature steam recovered from the waste heat of the underground coal seam to circulate and desorb carbon dioxide and collect it;

[0011] The waste heat recovery module is used to utilize the heat remaining in the underground coal seam after pyrolysis to supply the direct air capture of carbon dioxide module.

[0012] A further improvement of the present invention lies in that: the in-situ coal pyrolysis module includes a first injection well, a horizontal well, a second injection well, a production well, a mild oxidation heat supply zone, an internal component vortex heat exchange device, a pressurizing device, a heating device, an ignition device, and a heat exchanger;

[0013] The output port of the pressurizing device is connected to the input port of the heating device, the output port of the heating device is respectively connected to the input ports of the first injection well and the second injection well, a horizontal well is provided between the outlets of the first injection well and the second injection well, a production well is provided at the center of the horizontal well, the output port of the production well is connected to the input port c of the heat exchanger, the input port d of the heat exchanger is connected to the second output port of the second separation device, the output port a of the heat exchanger is connected to the second input port of the direct air capture of carbon dioxide module, the output port b of the heat exchanger is connected to the product separation and processing module, the input port c of the heat exchanger is connected to the output port b, the input port d of the heat exchanger is connected to the output port a, the ignition device is respectively connected to the input ports of the first injection well and the second injection well, the first injection well, the second injection well, the production well and the horizontal well are arranged in the coal seam between the coal seam roof and the coal seam floor, there are several coal seam fissures and a mild oxidation heat supply zone in the coal seam, and internal component vortex heat exchange devices are provided at the bottoms of the first injection well and the second injection well and inside the horizontal well.

[0014] A further improvement of the present invention lies in that: the product separation and processing module includes a condenser, a gas-liquid separator, a second separation device, a third separation device, a heavy tar storage tank and a light tar storage tank;

[0015] The input port of the condenser is connected to the output port b of the heat exchanger. The output port of the condenser is connected to the input port of the gas-liquid separator. The first output port of the gas-liquid separator is connected to the input port of the second separation device. The second output port of the gas-liquid separator is connected to the gas turbine 21. The output port of the gas turbine 21 is connected to the air direct carbon dioxide capture module. The first output port of the second separation device is connected to the input port of the third separation device. The second output port of the second separation device is respectively connected to the input port d of the heat exchanger and the input port of the heating device. The first output port of the third separation device is connected to the heavy tar storage tank. The second output port of the third separation device is connected to the light tar storage tank.

[0016] A further improvement of the present invention lies in that: the air direct carbon dioxide capture module includes a carbon dioxide storage tank, a draft fan, an adsorption chamber, an adsorbent, a heat exchange tube, a desorption chamber, a control valve and a vacuum pump;

[0017] The outlet of the draft fan is connected to the adsorption chamber. A number of heat exchange tubes are provided in the adsorption chamber. The adsorbent is provided on each heat exchange tube. The desorption chamber is connected to the outer wall of the adsorption chamber. The outlets of the number of desorption chambers are connected to the vacuum pump through a number of control valves and a ventilation pipe. The output port of the vacuum pump is connected to the carbon dioxide storage tank.

[0018] A further improvement of the present invention lies in that: the waste heat recovery module includes a third injection well, a production well, a second heat exchanger, and a circulating water pump;

[0019] The outlet of the third injection well is connected to the inlet a of the second heat exchanger. The outlet d of the second heat exchanger is connected to the circulating water pump. The outlet c of the second heat exchanger is connected to the inlet of the heat exchange tube of the air direct carbon dioxide capture device. The outlet of the heat exchange tube of the air direct carbon dioxide capture device is connected to the inlet of the circulating water pump. The outlet of the circulating water pump is connected to the inlet of the third injection well.

[0020] A further improvement of the present invention lies in that: a carbon dioxide concentration detection device is provided at the air outlet of the air direct carbon dioxide capture module.

[0021] A further improvement of the present invention lies in that: the adsorbent is solid amine and is in the shape of a round cake.

[0022] In a second aspect, a method for in-situ coal pyrolysis and air direct carbon dioxide capture includes the following steps:

[0023] S1. Fracture the coal seam through the first injection well and the second injection well to generate coal seam fissures and a mild oxidation heat supply zone in the coal seam;

[0024] S2. Inject proppant into the coal seam fractures through the first injection well and the second injection well. Connect the first injection well, the second injection well and the production well through a horizontal well, and arrange an internal component vortex heat exchange device at the bottom of the first injection well, the second injection well and inside the horizontal well;

[0025] S3. Control the mild oxidation heat supply zone to burn through the ignition device to heat up the coal seam to be pyrolyzed. Produce high-temperature and high-pressure heat carrier through the pressurizing device and the heating device and inject it into the coal seam. Under the enhanced heat exchange effect of the internal component vortex heat exchange device and the proppant in the horizontal well, the coal is pyrolyzed in situ underground;

[0026] S4. Extract the pyrolysis products through the production well, send the pyrolysis products into the product separation and processing module through the heat exchanger, and at the same time use the heat generated in the heat exchanger to produce a high-temperature heat carrier and transport it to the air direct carbon dioxide capture module;

[0027] S5. Part of the pyrolysis gas after processing and separation is used for gas turbine power generation, and the remaining pyrolysis gas is injected into the coal seam again as a heat carrier for circulating heating;

[0028] S6. Part of the power generated by the gas turbine is transported to the air direct carbon dioxide capture module, and the air direct carbon dioxide capture module captures carbon dioxide in the air and sends it into the carbon dioxide storage tank;

[0029] S7. Pass the heat carrier into the coal seam after pyrolysis through the circulating water pump, and use the waste heat to generate a high-temperature heat carrier through the second heat exchanger and transport it to the air direct carbon dioxide capture module.

[0030] A further improvement of the present invention lies in that: the specific steps of capturing carbon dioxide in the air by the air direct carbon dioxide capture module in S6 and sending it into the carbon dioxide storage tank include the following steps:

[0031] S61. The induced draft fan sends air into the desorption chamber, and carbon dioxide in the air is adsorbed by a number of adsorbents (26) in the desorption chamber. After the adsorbed air is detected to meet the standard by the carbon dioxide concentration detector, it is discharged from the tail;

[0032] S62. After several hours, when the adsorbents in the adsorption chamber are saturated with adsorption, turn off the induced draft fan and close the air inlet of the adsorption chamber;

[0033] S63. The heat exchange tube heats the adsorbent containing saturated carbon dioxide through high-temperature steam, so that the carbon dioxide adsorbed on the adsorbent is desorbed by heating;

[0034] S64. Open all control valves and the vacuum pump, and send the desorbed carbon dioxide in the desorption chamber into the carbon dioxide storage tank.

[0035] A further improvement of the present invention lies in that: the steam temperature introduced into the heat exchange tube is 40 - 120 °C.

[0036] Compared with the prior art, the present invention has at least the following beneficial effects:

[0037] 1. Through in-situ coal pyrolysis, the present invention can utilize underground coal resources without mining, effectively solving problems such as large environmental pollution, high safety risks, and underground subsidence in traditional coal utilization methods.

[0038] 2. The present invention directly captures carbon dioxide from the air through the air direct carbon dioxide capture module, the pyrolysis gas generated by the product separation and processing module is used to generate electricity to supply the device and system with electrical energy, and high-temperature steam produced by using the heat of the in-situ coal pyrolysis products and the waste heat recovery module is used to desorb carbon dioxide, enabling continuous carbon dioxide capture in the air environment, which is safe and environmentally friendly.

[0039] 3. By directly converting coal into oil and gas resources underground through pyrolysis, the present invention alleviates the problem of high dependence on foreign countries due to the shortage of oil and gas resources.

[0040] 4. The present invention produces high-temperature steam from the underground waste heat after pyrolysis and supplies it to the device for direct air capture of carbon dioxide to desorb the carbon dioxide gas captured in the device, achieving the recycling of energy. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] The accompanying drawings forming a part of the present invention are used to provide a further understanding of the present invention. The schematic embodiments and descriptions thereof of the present invention are used to explain the present invention and do not constitute an improper limitation to the present invention. In the drawings:

[0042] Figure 1 is the system flow chart of a system for in-situ coal pyrolysis and direct air capture of carbon dioxide according to the present invention;

[0043] Figure 2 is the structural schematic diagram of a system for in-situ coal pyrolysis and direct air capture of carbon dioxide according to the present invention;

[0044] Figure 3 is the structural schematic diagram of the air direct carbon dioxide capture module in a system for in-situ coal pyrolysis and direct air capture of carbon dioxide according to the present invention;

[0045] Figure 4 is the structural schematic diagram of the positions of the adsorbent and the heat exchange tube in a system for in-situ coal pyrolysis and direct air capture of carbon dioxide according to the present invention;

[0046] Figure 5 is the structural schematic diagram of the combination of the air direct carbon dioxide capture device and waste heat utilization in a system for in-situ coal pyrolysis and direct air capture of carbon dioxide according to the present invention;

[0047] Figure 6This is a multi-loop schematic diagram in a system for in-situ coal pyrolysis and direct air capture of carbon dioxide according to the present invention.

[0048] In the figure: 1, coal seam roof; 2, coal seam; 3, coal seam floor; 4, first injection well; 5, horizontal well; 6, second injection well; 7, production well; 8, mild oxidation heat supply zone; 9, coal seam fracture; 10, internal component vortex heat exchange device; 11, pressurizing device; 12, heating device; 13, ignition device; 14, heat exchanger; 15, condenser; 16, gas-liquid separator; 17, second separation device; 18, third separation device; 19, heavy tar storage tank; 20, light tar storage tank; 21, gas turbine; 22, direct air capture of carbon dioxide module; 23, carbon dioxide storage tank; 24, induced draft fan; 25, adsorption chamber; 26, adsorbent; 27, heat exchange tube; 28, desorption chamber; 29, control valve; 30, vacuum pump; 31, third injection well; 32, production well; 33, second heat exchanger; 34, circulating water pump. Detailed implementation manners

[0049] The present invention will be described in detail below with reference to the accompanying drawings and in combination with embodiments. It should be noted that, without conflict, the embodiments in the present invention and the features in the embodiments can be combined with each other.

[0050] The following detailed descriptions are all exemplary descriptions, aiming to provide further detailed descriptions of the present invention. Unless otherwise specified, all technical terms adopted in the present invention have the same meaning as commonly understood by those of ordinary skill in the art to which the present invention pertains. The terms used in the present invention are only for describing specific implementation manners and are not intended to limit the exemplary embodiments according to the present invention.

[0051] Embodiment 1

[0052] As Figure 1 shown, a system for in-situ coal pyrolysis and direct air capture of carbon dioxide includes an in-situ coal pyrolysis module, a product separation and processing module, a waste heat recovery module, and a direct air capture of carbon dioxide module;

[0053] As Figure 2 shown, the in-situ coal pyrolysis module includes a coal seam roof 1, a coal seam 2, a coal seam floor 3, a first injection well 4, a horizontal well 5, a second injection well 6, a production well 7, a mild oxidation heat supply zone 8, a coal seam fracture 9, an internal component vortex heat exchange device 10, a pressurizing device 11, a heating device 12, an ignition device 13, and a heat exchanger 14;

[0054] The outlet of the pressurizing device 11 is connected to the first input port of the heating device 12. The outlet of the heating device 12 is respectively connected to the input ports of the first injection well 4 and the second injection well 6. A horizontal well 5 is provided between the outlets of the first injection well 4 and the second injection well 6. A production well 7 is provided at the center of the horizontal well 5. The outlet of the production well 7 is connected to the input port c of the heat exchanger 14. The input port d of the heat exchanger 14 is connected to the second output port of the second separation device 17. The outlet a of the heat exchanger is connected to the second input port of the air direct capture carbon dioxide module 22. The outlet b of the heat exchanger 14 is connected to the input port of the condenser 15. The input port c of the heat exchanger is connected to the outlet b, and the input port d of the heat exchanger is connected to the outlet a. The ignition device 13 is respectively connected to the input ports of the first injection well 4 and the second injection well 6. The first injection well 4, the second injection well 6, the production well 7 and the horizontal well 5 are arranged in the coal seam between the coal seam roof 1 and the coal seam floor 3. There are several coal seam fissures 9 and a mild oxidation heat supply zone 8 in the coal seam 2. Inner member vortex heat exchange devices 10 are provided at the bottoms of the first injection well 4 and the second injection well 6 and inside the horizontal well 5. The production well is provided with a heat preservation casing.

[0055] The underground coal pyrolysis module fractures the coal seam 2 to be mined through the first injection well 4 and the second injection well 6 to form coal seam fissures 9 and a mild oxidation heat supply zone 8; injects proppants into the coal seam fissures 9 through the first injection well 4 and the second injection well 6; connects the first injection well 4, the second injection well 6 and the production well 7 through the horizontal well 5, and arranges inner member vortex heat exchange devices 10 at the bottoms of the first injection well and the second injection well and inside the horizontal well; injects high-temperature and high-pressure heat carriers into the coal seam 2 and the coal seam fissures 9 through the first injection well 4 and the second injection well 6, and makes the coal reservoir undergo in-situ pyrolysis under the action of proppants and inner member vortex enhanced heat transfer; after pyrolysis, uses the ignition device 13 to carry out controllable mild oxidation combustion on the mild oxidation heat supply zone 8 through the first injection well 4 and the second injection well 6; extracts the pyrolysis products from the production well 7 to the ground for subsequent processing and separation;

[0056] The high-temperature and high-pressure heat carrier is one of nitrogen, water vapor, hydrocarbon-containing gas, etc. The hydrocarbon-containing gas comes from part of the pyrolysis gas in the product.

[0057] The energy consumption required by the heating device 12 comes from clean energy such as solar energy and wind energy.

[0058] Method for making proppants: Mix and grind the carrier material and red mud, and then carry out homogenization and refinement treatment to obtain a mixed powder. The particle size range of the mixed powder is 0.4 - 2.0 mm; mix the mixed powder with a binder evenly and send it into a granulator for granulation to obtain pellets; dry the pellets and calcine them at 1000 - 1200 °C to obtain proppants for underground in-situ coal pyrolysis.

[0059] In the mixed material, the carrier material accounts for 35% - 60 wt.% of the mass of the mixed powder; the red mud accounts for 40% - 65 wt.% of the mass of the mixed powder. The carrier material is one or more of ceramsite, metal aluminum balls, and resin-coated sand, and the binder is one or more of phenolic resin, polyurethane, and sodium silicate.

[0060] The product separation and processing module includes a condenser 15, a gas-liquid separator 16, a second separation device 17, a third separation device 18, a heavy tar storage tank 19, and a light tar storage tank 20;

[0061] The input port of the condenser 15 is connected to the output port b of the heat exchanger 14, the output port of the condenser 15 is connected to the input port of the gas-liquid separator 16, the first output port of the gas-liquid separator 16 is connected to the input port of the second separation device 17, the second output port of the gas-liquid separator 16 is connected to the gas turbine 21, the output port of the gas turbine 21 is connected to the air direct capture of carbon dioxide module 22, the first output port of the second separation device 17 is connected to the input port of the third separation device 18, the second output port of the second separation device 17 is connected to the carbon dioxide storage tank 23, the first output port of the third separation device 18 is connected to the heavy tar storage tank 19, and the second output port of the third separation device 18 is connected to the light tar storage tank 20;

[0062] The product separation and processing module is used to separate, process, and utilize the oil and gas products. The oil and gas products of the in-situ coal pyrolysis module underground are condensed and separated, the tar products are purified and processed, and after the gas products are separated, they are introduced into the power generation device for power generation;

[0063] The power generation device is a gas turbine.

[0064] As Figures 3 - 5 shown, the air direct capture of carbon dioxide module 22 includes a carbon dioxide storage tank 23, an induced draft fan 24, an adsorbent 26, a heat exchange tube 27, a desorption chamber 28, a control valve 29, and a vacuum pump 30;

[0065] The air outlet of the induced draft fan 24 is connected to the adsorption chamber 25. A number of heat exchange tubes 27 are provided in the adsorption chamber 25, and an adsorbent 26 is provided on each heat exchange tube 27. The desorption chamber 28 is connected to the outer wall of the adsorption chamber 25. The outlets of a number of desorption chambers 28 are connected to the vacuum pump 30 through a number of control valves 29 and a ventilation pipe, and the output port of the vacuum pump 30 is connected to the carbon dioxide storage tank 23.

[0066] The adsorbent 26 is a solid amine.

[0067] The induced draft fan 24 sends air into the desorption chamber 28. Carbon dioxide in the air is adsorbed by a number of adsorbents 26 in the desorption chamber 28, and then the adsorbed air is discharged from the tail. After several hours, the adsorbent 26 is saturated with adsorption. The induced draft fan 24 is turned off, and the desorption chamber 28 closes the air inlet. The heat exchange tube 27 heats the adsorbent 26 with steam, so that the carbon dioxide adsorbed on the adsorbent 26 is desorbed by heat. All control valves 29 and the vacuum pump are opened, and the gaseous carbon dioxide in the desorption chamber 28 is sent into the carbon dioxide storage tank 23.

[0068] The induced draft fan 24 is a centrifugal induced draft fan.

[0069] The adsorbent 26 is in the shape of a round cake.

[0070] The inlet of the heat exchange tube 27 is connected to the steam pipeline, and steam at 40 - 120 °C is introduced, so that the carbon dioxide adsorbed by the adsorbent 26 is desorbed by absorbing heat;

[0071] The absorption principle of the amine absorbent for carbon dioxide is:

[0072]

[0073] Adopt a mild oxidation heat supply zone, controllably burn part of the coal seam, and strengthen the pyrolysis of the underground coal seam through the internal component vortex heat exchange device to improve the pyrolysis efficiency.

[0074] The waste heat recovery module is used to supply the air direct carbon dioxide capture module 22 with the heat remaining in the underground coal seam after pyrolysis.

[0075] The waste heat recovery module includes a third injection well 31, a production well 32, a second heat exchanger 33, and a circulating water pump 34;

[0076] The outlet of the third injection well 31 is connected to the inlet a of the second heat exchanger 33, the outlet d of the second heat exchanger 33 is connected to the circulating water pump 34, the outlet c of the second heat exchanger 33 is connected to the inlet of the heat exchange tube 27 of the air direct carbon dioxide capture device, the outlet of the heat exchange tube 27 of the air direct carbon dioxide capture device is connected to the inlet of the circulating water pump 34, and the outlet of the circulating water pump 34 is connected to the inlet of the third injection well 31.

[0077] Embodiment 2

[0078] A method for in-situ coal pyrolysis and air direct carbon dioxide capture includes the following steps:

[0079] S1. Fracture the coal seam 2 through the first injection well 4 and the second injection well 6, so that coal seam fissures 9 and a mild oxidation heat supply zone 8 are generated in the coal seam 2;

[0080] S2. Inject proppant into the coal seam fractures 9 through the first injection well 4 and the second injection well 6, connect the first injection well 4, the second injection well 6 and the production well 7 through the horizontal well 5, and arrange the internal component vortex heat exchange device 10 at the bottoms of the first injection well and the second injection well and inside the horizontal well;

[0081] S3. Control the combustion of the mild oxidation heat supply zone through the ignition device 13 to heat up the coal seam to be pyrolyzed. Produce high-temperature and high-pressure heat carrier through the pressurizing device 11 and the heating device 12 and inject it into the coal seam 2, and complete in-situ pyrolysis of coal underground under the enhanced heat exchange effect of the internal component vortex heat exchange device 10 in the horizontal well 5;

[0082] S4. Extract the pyrolysis products through the production well 7, send the pyrolysis products into the product separation and processing module through the heat exchanger, and at the same time use the heat generated in the heat exchanger to produce high-temperature steam and transport it to the air direct carbon dioxide capture module 22;

[0083] S5. Part of the processed and separated pyrolysis products are used for power generation by the gas turbine 21, and the remaining pyrolysis gas is injected into the coal seam 2 again as a heat carrier for cyclic heating.

[0084] S6. Part of the power generated by the gas turbine 21 is transmitted to the air direct carbon dioxide capture module 22, and the air direct carbon dioxide capture module 22 captures carbon dioxide in the air and sends it into the carbon dioxide storage tank 23;

[0085] S7. Pass water into the coal seam 2 after pyrolysis through the circulating water pump 34, and use the waste heat to generate high-temperature steam through the second heat exchanger 33 and transport it to the air direct carbon dioxide capture module 22.

[0086] In S6, capturing carbon dioxide in the air by the air direct carbon dioxide capture module 22 and sending it into the carbon dioxide storage tank 23 specifically includes the following steps:

[0087] S61. The induced draft fan 24 sends air into the desorption chamber 28, carbon dioxide in the air is adsorbed by several adsorbents 26 in the desorption chamber 28, and the air after adsorption is discharged from the tail after passing the carbon dioxide concentration detector;

[0088] S62. After several hours, when the adsorbents 26 in the adsorption chamber are saturated with adsorption, turn off the induced draft fan 24 and close the air inlet of the adsorption chamber 25;

[0089] S63. The heat exchange tube 27 heats the adsorbent 26 with steam to desorb the carbon dioxide adsorbed on the adsorbent 26;

[0090] S64. Open all control valves 29 and the vacuum pump 30, and send the desorbed carbon dioxide in the desorption chamber 28 into the carbon dioxide storage tank 23.

[0091] The carbon dioxide in the carbon dioxide storage tank 23 is used for industrial purposes or geological storage.

[0092] Embodiment 3

[0093] As Figure 5 shown, a schematic structural diagram of the combination of the carbon dioxide direct air capture device and waste heat utilization in a coal in-situ pyrolysis and carbon dioxide direct air capture system. It includes 23, a carbon dioxide storage tank; 24, a draft fan; 25, an adsorption chamber; 26, an adsorbent; 27, a heat exchange tube; 28, a desorption chamber; 29, a control valve; 30, a vacuum pump; 31, a third injection well; 32, a production well; 33, a second heat exchanger; 34, a circulating water pump.

[0094] After pyrolysis is completed, water is injected into the third injection well 31 through the circulating water pump 34 to produce steam using the waste heat of the coal seam after pyrolysis, and superheated steam is extracted from the production well 32. Secondary steam is generated through heat exchange in the second heat exchanger 33 and enters the heat exchange tube 27 in the carbon dioxide direct air capture device. The adsorbent 26 captures carbon dioxide and undergoes a temperature-rising desorption process in the desorption chamber 28. After desorption is completed, the control valve 29 is opened, and the obtained gaseous carbon dioxide is extracted by the vacuum pump 30 and enters the carbon dioxide storage tank. The heat-exchanged water passes through the outlet pipeline and is injected into the underground coal seam again through the circulating water pump 34 and the third injection well 31.

[0095] Embodiment 4

[0096] Figure 6 shown, a multi-loop schematic diagram in a coal in-situ pyrolysis and carbon dioxide direct air capture system. It contains three layers of adsorption chambers. Air leaves after being adsorbed in the first layer and enters the second layer of the adsorption chamber, and then enters the third layer of the adsorption chamber. Finally, after the carbon dioxide concentration in the air is detected to be qualified at the end of the third layer of the adsorption chamber, it is discharged.

[0097] By circulating and adsorbing air in the adsorption chamber, the carbon dioxide capture efficiency of the device is improved, and the floor area of the device is reduced.

[0098] As is known by common technical knowledge, the present invention can be implemented by other embodiments that do not depart from its spirit or essential features. Therefore, the above-disclosed embodiments are illustrative in all aspects and are not exclusive. All changes within the scope of the present invention or equivalent to the present invention are encompassed by the present invention.

[0099] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them. Although the present invention has been described in detail with reference to the above embodiments, those of ordinary skill in the art should understand that: modifications or equivalent replacements can still be made to the specific embodiments of the present invention, and any modification or equivalent replacement that does not depart from the spirit and scope of the present invention should be covered by the protection scope of the claims of the present invention.

Claims

1. A system for in-situ coal pyrolysis and direct air capture of carbon dioxide, characterized in that, it includes an in-situ coal pyrolysis module, a product separation and processing module, a direct air capture of carbon dioxide module (22), and a waste heat recovery module; The in-situ coal pyrolysis module is used to fracture the underground coal seam, in-situ pyrolyze the underground coal seam through injecting high-temperature and high-pressure heat carriers and mild oxidation heating, and send the pyrolysis products to the product separation and processing module, and send the high-temperature steam to the direct air capture of carbon dioxide module (22); The product separation and processing module is used to separate, process and utilize the pyrolysis products, and use the pyrolysis gas in the pyrolysis products for power generation to supply the in-situ coal pyrolysis system and the direct air capture of carbon dioxide module (22); The direct air capture of carbon dioxide module (22) is used to capture carbon dioxide from the air, and use the high-temperature steam produced by the in-situ coal pyrolysis module or the high-temperature steam recovered from the waste heat of the underground coal seam to circulate and desorb carbon dioxide and collect it; The waste heat recovery module is used to recover the heat remaining in the underground coal seam after pyrolysis to supply the direct air capture of carbon dioxide module (22); The in-situ coal pyrolysis module includes a first injection well (4), a horizontal well (5), a second injection well (6), a production well (7), a mild oxidation heat supply zone (8), an internal component vortex heat exchange device (10), a pressurization device (11), a heating device (12), an ignition device (13), and a heat exchanger (14); The output port of the pressurization device (11) is connected to the input port of the heating device (12), the output port of the heating device (12) is respectively connected to the input ports of the first injection well (4) and the second injection well (6), a horizontal well (5) is provided between the outlets of the first injection well (4) and the second injection well (6), a production well (7) is provided at the center of the horizontal well (5), the output port of the production well (7) is connected to the input port c of the heat exchanger (14), the input port d of the heat exchanger (14) is connected to the second output port of the second separation device (17), the output port a of the heat exchanger is connected to the second input port of the direct air capture of carbon dioxide module (22), the output port b of the heat exchanger (14) is connected to the product separation and processing module, the input port c of the heat exchanger is connected to the output port b, the input port d of the heat exchanger is connected to the output port a, the ignition device (13) is respectively connected to the input ports of the first injection well (4) and the second injection well (6), the first injection well (4), the second injection well (6), the production well (7) and the horizontal well (5) are arranged in the coal seam (2) between the coal seam roof (1) and the coal seam floor (3), there are several coal seam fissures (9) and a mild oxidation heat supply zone (8) in the coal seam (2), and internal component vortex heat exchange devices (10) are provided at the bottoms of the first injection well (4) and the second injection well (6) and inside the horizontal well (5); The direct air capture of carbon dioxide module (22) includes a carbon dioxide storage tank (23), a draft fan (24), an adsorption chamber (25), an adsorbent (26), a heat exchange tube (27), a desorption chamber (28), a control valve (29), and a vacuum pump (30); The air outlet of the induced draft fan (24) is connected to the adsorption chamber (25). A number of heat exchange tubes (27) are provided in the adsorption chamber (25). An adsorbent (26) is provided on each heat exchange tube (27). The desorption chamber (28) is connected to the outer wall of the adsorption chamber (25). The outlets of the several desorption chambers (28) are connected to a vacuum pump (30) through several control valves (29) and a ventilation pipe. The output port of the vacuum pump (30) is connected to a carbon dioxide storage tank (23).

2. The system for in-situ coal pyrolysis and direct air capture of carbon dioxide according to claim 1, characterized in that, the product separation and processing module includes a condenser (15), a gas-liquid separator (16), a second separation device (17), a third separation device (18), a heavy tar storage tank (19) and a light tar storage tank (20); The input port of the condenser (15) is connected to the output port b of the heat exchanger (14). The output port of the condenser (15) is connected to the input port of the gas-liquid separator (16). The first output port of the gas-liquid separator (16) is connected to the input port of the second separation device (17). The second output port of the gas-liquid separator (16) is connected to the gas turbine 21. The output port of the gas turbine 21 is connected to the direct air capture of carbon dioxide module (22). The first output port of the second separation device (17) is connected to the input port of the third separation device (18). The second output port of the second separation device (17) is respectively connected to the input port d of the heat exchanger (14) and the input port of the heating device (12). The first output port of the third separation device (18) is connected to the heavy tar storage tank (19). The second output port of the third separation device (18) is connected to the light tar storage tank (20).

3. The system for in-situ coal pyrolysis and direct air capture of carbon dioxide according to claim 1, characterized in that, the waste heat recovery module includes a third injection well (31), a production well (32), a second heat exchanger (33), and a circulating water pump (34); The outlet of the third injection well (31) is connected to the inlet a of the second heat exchanger (33). The outlet d of the second heat exchanger (33) is connected to the circulating water pump (34). The outlet c of the second heat exchanger (33) is connected to the inlet of the heat exchange tube (27) of the direct air capture of carbon dioxide device. The outlet of the heat exchange tube (27) of the direct air capture of carbon dioxide device is connected to the inlet of the circulating water pump (34). The outlet of the circulating water pump (34) is connected to the inlet of the third injection well (31).

4. The system for in-situ coal pyrolysis and direct air capture of carbon dioxide according to claim 1, characterized in that, a carbon dioxide concentration detection device is provided at the air outlet of the direct air capture of carbon dioxide module (22).

5. The system for in-situ coal pyrolysis and direct air capture of carbon dioxide according to claim 1, characterized in that, the adsorbent (26) is a solid amine and is in the shape of a round cake.

6. A method for in-situ coal pyrolysis and direct air capture of carbon dioxide, characterized in that, it includes the following steps: S1. Fracture the coal seam (2) through the first injection well (4) and the second injection well (6) to generate coal seam fissures (9) and a mild oxidation heat supply zone (8) in the coal seam (2); S2. Inject proppants into the coal seam fissures (9) through the first injection well (4) and the second injection well (6). Connect the first injection well (4), the second injection well (6) and the production well (7) through the horizontal well (5), and arrange an internal component vortex heat exchange device (10) at the bottoms of the first injection well (4) and the second injection well (6) and inside the horizontal well (5); S3. Control the combustion of the mild oxidation heat supply zone through the ignition device (13) to heat up the coal seam to be pyrolyzed. Produce high-temperature and high-pressure heat carriers through the pressurizing device (11) and the heating device (12) and inject them into the coal seam (2). Under the enhanced heat exchange effect of the internal component vortex heat exchange device (10) and the proppants in the horizontal well (5), the coal is pyrolyzed in situ underground; S4. Extract the pyrolysis products through the production well (7), and send the pyrolysis products into the product separation and processing module through the heat exchanger (14). At the same time, use the heat generated in the heat exchanger (14) to produce high-temperature heat carriers and transport them to the air direct carbon dioxide capture module (22); S5. Part of the pyrolysis gas after processing and separation is used for power generation by the gas turbine (21), and the remaining pyrolysis gas is injected into the coal seam (2) again as a heat carrier for cyclic heating; S6. Part of the power generated by the gas turbine (21) is transmitted to the air direct carbon dioxide capture module (22), and the air direct carbon dioxide capture module (22) captures carbon dioxide in the air and sends it into the carbon dioxide storage tank (23); S7. Pass the heat carrier into the coal seam (2) after pyrolysis through the circulating water pump (34), and use the waste heat to generate high-temperature heat carriers through the second heat exchanger (33) and transport them to the air direct carbon dioxide capture module (22).

7. A method for in-situ coal pyrolysis and air direct carbon dioxide capture according to claim 6, characterized in that, the specific steps of capturing carbon dioxide in the air by the air direct carbon dioxide capture module (22) and sending it into the carbon dioxide storage tank (23) in S6 are as follows: S61. The induced draft fan (24) sends air into the desorption chamber (28), and carbon dioxide in the air is adsorbed by a number of adsorbents (26) in the desorption chamber (28). After the adsorbed air is detected to meet the standards by the carbon dioxide concentration detector, it is discharged from the tail; S62. After several hours, when the adsorbents (26) in the adsorption chamber are saturated with adsorption, the induced draft fan (24) is turned off, and the adsorption chamber (25) closes the air inlet; S63. The heat exchange tube (27) heats the adsorbent (26) containing saturated carbon dioxide with high-temperature steam to desorb the carbon dioxide adsorbed on the adsorbent (26); S64. Open all control valves (29) and the vacuum pump (30), and send the desorbed carbon dioxide in the desorption chamber (28) into the carbon dioxide storage tank (23).

8. A method for in-situ coal pyrolysis and air direct carbon dioxide capture according to claim 7, characterized in that, the steam temperature introduced into the heat exchange tube (27) is 40 - 120 °C.

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