A coal underground direct pyrolysis product separation system coupled with oxygen-enriched combustion

Abstract

This invention discloses a coal underground direct pyrolysis product separation system coupled with oxy-fuel combustion, comprising an air separation unit, pyrolysis product separation equipment, carbon capture equipment, an oxy-fuel combustion boiler, and heaters inside the boiler. The air separation unit provides nitrogen and oxygen for both underground direct pyrolysis and oxy-fuel combustion. The oxy-fuel combustion boiler heats the nitrogen, providing a heat source for the underground coal seam pyrolysis, and also heats the pyrolysis products, thereby removing solid particles through gas-solid separation rather than liquid-solid separation, reducing the difficulty of product separation. The separated pyrolysis gas can be used to reduce nitrogen oxides generated during oxy-fuel combustion. This invention utilizes the heat generated by oxy-fuel combustion to efficiently separate tar from the coal underground direct pyrolysis products, and by coupling the separation of underground direct pyrolysis products with oxy-fuel combustion, improves the system's economic efficiency and reduces nitrogen oxide emissions during oxy-fuel combustion.

Description

Technical Field

[0001] This invention belongs to the field of efficient coal utilization, product separation and carbon capture, and specifically relates to a coal underground direct pyrolysis product separation system coupled with oxygen-enriched combustion. Background Technology

[0002] Coal tar production technology, also known as underground in-situ coal tar production technology, is a novel coal-to-oil technology. This technology eliminates the need to mine coal to the surface; instead, heat is transferred underground to cause a pyrolysis reaction in the coal seam. The pyrolysis products are then transported to the surface for separation, ultimately yielding coal tar. Compared to traditional above-ground coal tar production technology, underground direct pyrolysis effectively avoids the waste of coal resources and ecological damage commonly encountered during coal mining, making it more environmentally friendly. In the underground direct pyrolysis process, using high-temperature nitrogen to heat the underground coal seam and carry the pyrolysis products to the surface is a promising heating method. However, the nitrogen production process in air separation equipment is energy-intensive, limiting its economic benefits when used solely in underground direct pyrolysis. In addition, the pyrolysis products extracted from the ground are complex mixtures including gas, liquid and solid phases. Coal tar is a viscous liquid at room temperature, and it is difficult to separate coal tar from solid particles. If the coal tar is heated to exist in a gaseous state, it is relatively easy to remove solid particles, but heating requires a lot of heat energy and additional heating equipment.

[0003] Oxygen-enriched combustion is one of the effective ways to achieve carbon capture. In the process of oxygen-enriched combustion, pure oxygen and recirculated flue gas are mixed and sent into the furnace as combustion-supporting gas, which can make the carbon dioxide in the flue gas at the tail end of the boiler reach a higher concentration, which is convenient for carbon dioxide capture and storage. However, the oxygen production of air separation equipment is energy-intensive and has limited economic benefits, which is an important reason hindering the promotion of oxygen-enriched combustion. Moreover, oxygen-enriched combustion also generates nitrogen oxides, causing environmental pollution. Summary of the Invention

[0004] The purpose of this invention is to provide a coal underground direct pyrolysis product separation system coupled with oxygen-enriched combustion. By coupling the separation of coal underground direct pyrolysis products with oxygen-enriched combustion, this system solves the problems of high separation difficulty, high energy consumption, low economic efficiency, and certain nitrogen oxide emissions in the process of separating coal underground direct pyrolysis products.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] A coal underground direct pyrolysis product separation system coupled with oxygen-enriched combustion includes a pyrolysis product heater, a high-temperature gas-solid separation device, an air separation device, a gas-liquid separation device, an oil-water separation device, a gas separation device, a nitrogen storage device, a nitrogen heater, a nitrogen pump, a blower, an air preheater, and an oxygen-enriched combustion boiler body.

[0007] The pyrolysis product heater, nitrogen heater and air preheater are installed inside the oxygen-enriched combustion boiler body. The furnace of the oxygen-enriched combustion boiler body is divided into a burnout zone, a reburning zone and a main combustion zone from top to bottom.

[0008] The gas-liquid-solid mixture obtained from the extraction well is heated by a pyrolysis product heater, causing the liquid tar to evaporate. At this point, the gas-liquid-solid mixture becomes a high-temperature gas-solid mixture. The high-temperature gas-solid mixture is then passed through a high-temperature gas-solid separation device to remove solid particles. The purified high-temperature gas is cooled by the separated low-temperature nitrogen and low-temperature oxygen in an air separation unit, causing the gaseous tar to condense into a liquid state. The liquid tar is carried by the gas and sent to a gas-liquid separation device for gas-liquid separation. The crude tar obtained is then passed through an oil-water separation device to remove moisture. The gas obtained from the gas-liquid separation device is sent to a gas separation device to separate the nitrogen and pyrolysis gas. The separated pyrolysis gas is sent to the recombustion zone of the oxygen-enriched combustion boiler. The separated nitrogen is mixed with nitrogen in a nitrogen storage device, heated by a nitrogen heater, and then injected underground by a nitrogen pump to provide a heat source for the pyrolysis of the underground coal seam.

[0009] The air separation unit separates nitrogen and oxygen from the air. The nitrogen is stored in a nitrogen storage device and serves as one of the sources of heating medium for underground coal seams. The oxygen is mixed with the flue gas obtained from the flue gas treatment equipment and sent to the air preheater for heating by a blower. After heating, it is sent to the main combustion zone and the burnout zone.

[0010] A further improvement of the present invention is that it also includes a tar storage device, which stores the dehydrated tar.

[0011] A further improvement of the present invention is that it also includes a flue gas treatment device and a carbon capture and storage device. The flue gas generated by oxygen-enriched combustion is treated by the flue gas treatment device. Part of the treated flue gas is mixed with oxygen and sent back to the boiler, while the other part is sent to the carbon capture and storage device.

[0012] A further improvement of the present invention is that, after the flue gas generated by oxygen-enriched combustion is treated by the flue gas treatment equipment, a portion of it is mixed with oxygen obtained from the air separation equipment to become combustion-supporting gas. The oxygen concentration is adjusted by changing the ratio of flue gas to oxygen to meet the needs of oxygen-enriched combustion under different conditions. The combustion-supporting gas is sent back to the boiler by the feed fan, and another portion of the flue gas is sent to the carbon capture and storage equipment for carbon dioxide capture and storage.

[0013] A further improvement of the present invention is that the pyrolysis gas refers to the gas generated during coal pyrolysis, which includes methane, hydrogen, carbon monoxide, and carbon dioxide.

[0014] A further improvement of the present invention is that the gas-liquid-solid mixture obtained from the extraction well is heated to 500-600°C by the high-temperature flue gas inside the oxygen-enriched coal-fired boiler body through the pyrolysis product heater, causing the liquid tar in it to evaporate. At this time, the gas-liquid-solid mixture becomes a high-temperature gas-solid mixture, and then the solid particles in it are removed by the high-temperature gas-solid separation equipment, thereby avoiding the difficult liquid-solid separation process.

[0015] A further improvement of the present invention is that the cold energy of the low-temperature nitrogen and low-temperature oxygen separated by the air separation equipment is used to cool the high-temperature gas obtained from the high-temperature gas-solid separation equipment, so that the gaseous tar in the high-temperature gas is condensed into liquid, while the nitrogen and oxygen are heated, thereby reducing the energy consumption of the system.

[0016] A further improvement of the present invention is that nitrogen is recovered from the gas by a gas separation device, and nitrogen is supplemented by a nitrogen storage device according to the needs of the underground direct pyrolysis process of coal. After the two are mixed, they are heated to 600-700°C by the high-temperature flue gas inside the oxygen-enriched coal-fired boiler body by a nitrogen heater, so as to provide a heat source for the pyrolysis of underground coal seams.

[0017] A further improvement of this invention is that the pyrolysis gas obtained from the gas separation device is sent to the re-combustion zone inside the oxygen-enriched coal-fired boiler body for combustion, thereby achieving the harmless and resource-based treatment of the pyrolysis gas. At the same time, the reducing gas in the pyrolysis gas is used to reduce nitrogen oxides, thereby reducing nitrogen oxide emissions.

[0018] The present invention has at least the following beneficial technical effects:

[0019] 1. This invention utilizes the heat provided by oxygen-enriched combustion to efficiently separate tar from the direct underground pyrolysis products of coal. The pyrolysis products obtained from the extraction well are complex mixtures including gas, liquid, and solid phases. This invention uses the high-temperature flue gas inside the oxygen-enriched combustion boiler to heat the tar in the pyrolysis products into a gaseous state, transforming the gas-liquid-solid three-phase mixture into a high-temperature gas-solid mixture. Then, a high-temperature gas-solid separation device removes the solid particles, thus avoiding the difficult liquid-solid separation process. This allows for efficient separation of tar from the direct underground pyrolysis products of coal without the need for additional heating equipment.

[0020] 2. The air separation unit in this invention provides nitrogen and oxygen for direct underground pyrolysis and oxygen-enriched combustion of coal, thereby improving the utilization efficiency of the air separation unit and mitigating the low economic benefits of the system due to the high energy consumption of the air separation unit. This invention also utilizes the cold energy of the low-temperature nitrogen and low-temperature oxygen separated in the air separation unit to condense the gaseous tar in the high-temperature gas into a liquid state, while the nitrogen and oxygen are heated, thereby reducing the energy consumption of the system.

[0021] 3. This invention can recover nitrogen used for heating underground coal seams, and this nitrogen can be recycled, thereby reducing nitrogen waste; the nitrogen storage equipment can replenish a certain amount of nitrogen, and the replenishment amount can be flexibly adjusted to meet different production needs; the nitrogen is heated by the high-temperature flue gas inside the oxygen-enriched combustion boiler, without the need for additional heating equipment.

[0022] 4. This invention can achieve the harmless and resource-based treatment of pyrolysis gas, and can also reduce nitrogen oxide emissions. The gas generated during coal pyrolysis is separated from nitrogen by a gas separation device and then sent to the re-combustion zone inside the oxygen-enriched coal-fired boiler for combustion, thus achieving the harmless and resource-based treatment of the pyrolysis gas; at the same time, the reducing gas in the pyrolysis gas can be used to reduce nitrogen oxides, thereby reducing nitrogen oxide emissions.

[0023] 5. This invention can achieve carbon dioxide capture and storage. A portion of the treated flue gas is mixed with oxygen and sent back to the boiler as a combustion-supporting gas. The oxygen concentration of the combustion-supporting gas can be flexibly adjusted by changing the ratio of flue gas to oxygen to meet the needs of oxygen-enriched combustion under different conditions. Another portion of the flue gas is sent to carbon capture and storage equipment for carbon dioxide capture and storage. The carbon dioxide concentration in the flue gas produced by oxygen-enriched combustion is relatively high, making carbon dioxide capture and storage less difficult and less costly. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of a coal underground direct pyrolysis product separation system coupled with oxygen-enriched combustion.

[0025] Explanation of reference numerals in the attached figures:

[0026] 1 is a pyrolysis product heater; 2 is a high-temperature gas-solid separation device; 3 is an air separation device; 4 is a gas-liquid separation device; 5 is an oil-water separation device; 6 is a tar storage device; 7 is a gas separation device; 8 is a nitrogen storage device; 9 is a nitrogen heater; 10 is a nitrogen pump; 11 is a blower; 12 is an air preheater; 13 is a flue gas treatment device; 14 is a carbon capture and storage device; and 15 is an oxygen-enriched combustion boiler body. Detailed Implementation

[0027] The present invention will now be described in further detail with reference to the accompanying drawings:

[0028] See Figure 1 The present invention proposes a coal underground direct pyrolysis product separation system coupled with oxygen-enriched combustion, comprising a pyrolysis product heater 1, a high-temperature gas-solid separation device 2, an air separation device 3, a gas-liquid separation device 4, an oil-water separation device 5, a tar storage device 6, a gas separation device 7, a nitrogen storage device 8, a nitrogen heater 9, a nitrogen pump 10, a blower 11, an air preheater 12, a flue gas treatment device 13, a carbon capture and storage device 14, and an oxygen-enriched combustion boiler body 15.

[0029] The gas-liquid-solid mixture obtained from the extraction well is heated to 500-600°C by the high-temperature flue gas inside the oxygen-enriched combustion boiler in the pyrolysis product heater 1, causing the liquid tar in it to evaporate. At this time, the gas-liquid-solid mixture becomes a high-temperature gas-solid mixture. Then, the solid particles in it are removed by the high-temperature gas-solid separation equipment 2, thereby avoiding the difficult liquid-solid separation process, improving the efficiency of product separation, and eliminating the need for additional heating equipment.

[0030] Air separation unit 3 is based on low-temperature air separation technology. First, the air is liquefied through cooling and other methods. Then, the two are separated by utilizing the difference in boiling points of nitrogen and oxygen. The purified high-temperature gas is sent to air separation unit 3 for cooling. The cold energy of the low-temperature nitrogen and oxygen separated in air separation unit 3 is used to condense the gaseous tar in the high-temperature gas into a liquid state. At the same time, the nitrogen and oxygen are heated, thereby reducing the energy consumption of the system. The liquid tar is carried by the gas to gas-liquid separation unit 4 for gas-liquid separation. The crude tar obtained by separation is then processed by oil-water separation unit 5 to remove water. The dehydrated tar is stored in tar storage unit 6.

[0031] The gas obtained from the gas-liquid separation device 4 is sent to the gas separation device 7 to separate the nitrogen and pyrolysis gas in the gas. The pyrolysis gas is sent to the recombustion zone inside the oxygen-enriched coal-fired boiler body 15 for combustion, realizing the harmless and resource-based treatment of the pyrolysis gas. At the same time, the reducing gas in the pyrolysis gas can be used to reduce nitrogen oxides, thereby reducing nitrogen oxide emissions. The pyrolysis gas refers to the gas generated during coal pyrolysis, which includes components such as methane, hydrogen, carbon monoxide, and carbon dioxide. The separated nitrogen can be recycled to reduce nitrogen waste. This recovered nitrogen is mixed with some nitrogen provided by the nitrogen storage device 8 and then heated to 600-700℃ by the high-temperature flue gas inside the oxygen-enriched combustion boiler by the nitrogen heater 9. Then, it is injected underground by the nitrogen pump 10 to provide a heat source for the pyrolysis of underground coal seams. The amount of nitrogen supplemented by the nitrogen storage device 8 can be flexibly adjusted to meet different production needs.

[0032] Air separation unit 3 provides nitrogen and oxygen for direct underground pyrolysis and oxygen-enriched combustion of coal, thereby improving the utilization efficiency of the air separation unit and mitigating the low economic benefits of the system due to the high energy consumption of the air separation unit. The nitrogen obtained from air separation unit 3 is sent to nitrogen storage unit 8 for storage, and a portion of it is used to heat the underground coal seam. The oxygen obtained from air separation unit 3 is mixed with the flue gas treated by flue gas treatment unit 13 to form a combustion-supporting gas with a certain oxygen concentration. This gas is sent to air preheater 12 for heating by blower 11, and then sent to the main combustion zone and burnout zone inside the oxygen-enriched coal-fired boiler body 15. The oxygen concentration of the combustion-supporting gas can be flexibly adjusted by changing the ratio of flue gas to oxygen to meet the needs of oxygen-enriched combustion under different conditions. After the flue gas produced by oxygen-enriched combustion is treated by flue gas treatment unit 13, a portion of the flue gas is mixed with oxygen and sent back to the boiler as a combustion-supporting gas, while the other portion is sent to carbon capture and storage unit 14 for carbon dioxide capture and storage. The carbon dioxide concentration in the flue gas produced by oxygen-enriched combustion is relatively high, making carbon dioxide capture and storage easier and less costly.

[0033] The specific working process of this invention is as follows: The gas-liquid-solid mixture obtained from the extraction well is heated to 500-600°C by the pyrolysis product heater 1, where the high-temperature flue gas inside the oxygen-enriched combustion boiler evaporates the liquid tar. At this point, the gas-liquid-solid mixture becomes a high-temperature gas-solid mixture, and then the solid particles are removed by the high-temperature gas-solid separation device 2. The purified high-temperature gas is sent to the air separation device 3 for cooling. The cold energy of the low-temperature nitrogen and low-temperature oxygen separated in the air separation device 3 is used to condense the gaseous tar in the high-temperature gas into a liquid state, while the nitrogen and oxygen are heated. The liquid tar is carried by the gas to the gas-liquid separation device 4 for gas-liquid separation. The crude tar obtained by separation is removed by the oil-water separation device 5, and the dehydrated tar is stored in the tar storage device 6. The gas obtained from the gas-liquid separation device 4 is sent to the gas separation device 7 to separate the nitrogen and pyrolysis gas in the gas. The pyrolysis gas is sent to the recombustion zone inside the oxygen-enriched coal-fired boiler body 15, and the recovered nitrogen is stored with nitrogen storage. Part of the nitrogen supplied by equipment 8 is mixed and heated to 600-700℃ by the high-temperature flue gas inside the oxygen-enriched combustion boiler via nitrogen heater 9. It is then injected underground by nitrogen pump 10 to provide a heat source for the pyrolysis of underground coal seams. The amount of nitrogen supplemented by nitrogen storage equipment 8 can be flexibly adjusted. Air separation equipment 3 provides nitrogen and oxygen for direct underground pyrolysis of coal and oxygen-enriched combustion, respectively. The nitrogen is sent to nitrogen storage equipment 8 for storage, and part of it is used to heat underground coal seams. The oxygen is mixed with the flue gas treated by flue gas treatment equipment 13 to form a combustion-supporting gas with a certain oxygen concentration. It is sent to air preheater 12 for heating by blower 11. After heating, it is sent to the main combustion zone and burnout zone inside the oxygen-enriched coal-fired boiler body 15. The oxygen concentration of the combustion-supporting gas can be flexibly adjusted by changing the ratio of flue gas and oxygen. After the flue gas generated by oxygen-enriched combustion is treated by flue gas treatment equipment 13, part of the flue gas is mixed with oxygen and sent back to the boiler as a combustion-supporting gas, and the other part is sent to carbon capture and storage equipment 14 for carbon dioxide capture and storage.

[0034] The above content is only a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any simple deductions or substitutions made by those skilled in the art to the technical solutions of the present invention, as long as they do not depart from the concept of the present invention, should be regarded as falling within the scope of patent protection of the present invention as determined by the submitted claims.

Claims

1. A coal underground direct pyrolysis product separation system coupled with oxygen-enriched combustion, characterized in that, It includes a pyrolysis product heater (1), a high-temperature gas-solid separation device (2), an air separation device (3), a gas-liquid separation device (4), an oil-water separation device (5), a gas separation device (7), a nitrogen storage device (8), a nitrogen heater (9), a nitrogen pump (10), a blower (11), an air preheater (12), and an oxygen-enriched combustion boiler body (15). The pyrolysis product heater (1), nitrogen heater (9) and air preheater (12) are installed inside the oxygen-enriched combustion boiler body (15). The furnace of the oxygen-enriched combustion boiler body (15) is divided into a burnout zone, a reburning zone and a main combustion zone from top to bottom. The gas-liquid-solid mixture obtained from the extraction well is heated by the pyrolysis product heater (1) to evaporate the liquid tar in it. At this time, the gas-liquid-solid mixture becomes a high-temperature gas-solid mixture. The high-temperature gas-solid mixture is passed through a high-temperature gas-solid separation device (2) to remove the solid particles. The purified high-temperature gas is cooled by the separated low-temperature nitrogen and low-temperature oxygen in the air separation device (3) to condense the gaseous tar into liquid. The liquid tar is carried by the gas to the gas-liquid separation device (4) for gas-liquid separation. The crude tar obtained by separation is passed through an oil-water separation device (5) to remove the water. The gas obtained from the gas-liquid separation device (4) is sent to the gas separation device (7) to separate the nitrogen and pyrolysis gas in the gas. The separated pyrolysis gas is sent to the reburning zone of the oxygen-enriched combustion boiler body (15). The separated nitrogen is mixed with the nitrogen in the nitrogen storage device (8), heated by the nitrogen heater (9), and then injected into the ground by the nitrogen pump (10) to provide a heat source for the pyrolysis of the underground coal seam. The air separation unit (3) separates nitrogen and oxygen from the air. The nitrogen is stored in the nitrogen storage unit (8) as one of the sources of heating medium for underground coal seams. The oxygen is mixed with the flue gas obtained from the flue gas treatment unit (13) and sent to the air preheater (12) for heating by the blower (11). After heating, it is sent to the main combustion zone and the burnout zone.

2. The coal underground direct pyrolysis product separation system coupled with oxygen-enriched combustion according to claim 1, characterized in that, It also includes a tar storage device (6), in which the dehydrated tar is stored.

3. The coal underground direct pyrolysis product separation system coupled with oxygen-enriched combustion according to claim 1, characterized in that, It also includes flue gas treatment equipment (13) and carbon capture and storage equipment (14). The flue gas generated by oxygen-enriched combustion is treated by the flue gas treatment equipment (13). Part of the treated flue gas is mixed with oxygen and sent back to the boiler, and the other part is sent to the carbon capture and storage equipment (14).

4. The coal underground direct pyrolysis product separation system coupled with oxygen-enriched combustion according to claim 3, characterized in that, The flue gas generated by oxygen-enriched combustion is treated by the flue gas treatment equipment (13). Part of it is mixed with oxygen obtained from the air separation equipment (3) to become combustion-supporting gas. The oxygen concentration is adjusted by changing the ratio of flue gas to oxygen to meet the needs of oxygen-enriched combustion under different conditions. The combustion-supporting gas is sent back to the boiler by the blower (11), and another part of the flue gas is sent to the carbon capture and storage equipment (14) for carbon dioxide capture and storage.

5. The coal underground direct pyrolysis product separation system coupled with oxygen-enriched combustion according to claim 1, characterized in that, The pyrolysis gas refers to the gas produced during coal pyrolysis, which includes methane, hydrogen, carbon monoxide, and carbon dioxide.

6. The coal underground direct pyrolysis product separation system coupled with oxygen-enriched combustion according to claim 1, characterized in that, The gas-liquid-solid mixture obtained from the extraction well is heated to 500-600°C by the high-temperature flue gas inside the oxygen-enriched coal-fired boiler body (15) through the pyrolysis product heater (1), causing the liquid tar in it to evaporate. At this time, the gas-liquid-solid mixture becomes a high-temperature gas-solid mixture, and then the solid particles in it are removed by the high-temperature gas-solid separation equipment (2), thereby avoiding the difficult liquid-solid separation process.

7. The coal underground direct pyrolysis product separation system coupled with oxygen-enriched combustion according to claim 1, characterized in that, The cold energy of the low-temperature nitrogen and low-temperature oxygen separated by the air separation unit (3) is used to cool the high-temperature gas obtained from the high-temperature gas-solid separation unit (2), so that the gaseous tar in the high-temperature gas is condensed into liquid, while the nitrogen and oxygen are heated, thereby reducing the energy consumption of the system.

8. The coal underground direct pyrolysis product separation system coupled with oxygen-enriched combustion according to claim 1, characterized in that, Nitrogen is recovered from the gas by the gas separation device (7), and nitrogen is supplemented by the nitrogen storage device (8) according to the needs of the direct underground pyrolysis process of coal. After the two are mixed, they are heated to 600-700℃ by the high-temperature flue gas inside the oxygen-enriched coal-fired boiler body (15) by the nitrogen heater (9), so as to provide a heat source for the pyrolysis of the underground coal seam.

9. A coal underground direct pyrolysis product separation system coupled with oxygen-enriched combustion according to claim 1, characterized in that, The pyrolysis gas obtained from the gas separation device (7) is sent to the re-combustion zone inside the oxygen-enriched coal-fired boiler body (15) for combustion, so as to achieve the harmless and resource-based treatment of the pyrolysis gas. At the same time, the reducing gas in the pyrolysis gas is used to reduce nitrogen oxides, thereby reducing the emission of nitrogen oxides.

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