External combustion and external heating type pulverized coal pyrolysis system and pulverized coal pyrolysis method

Abstract

The present application relates to a kind of external combustion external heat type pulverized coal pyrolysis system and pulverized coal pyrolysis method, the external combustion external heat type pulverized coal pyrolysis system includes coal dry distillation device, flue gas heat exchange system and raw gas system;The flue gas heat exchange system includes external coal gas combustion furnace, high-temperature flue gas distribution system and flue gas mixing temperature control system;The raw gas system includes raw gas cooling gas collection system and raw flue gas purification system;The coal dry distillation device adopts the three-section structure of low-temperature pyrolysis drying section, medium-high temperature pyrolysis section and upgraded coal cooling section, and the waste gas produced by the combustion of coal gas in external coal gas combustion furnace is passed into medium-high temperature pyrolysis section and indirectly heat-transferred with fine coal, to realize the cascade pyrolysis of raw material fine coal;The import flue gas temperature of medium-high temperature pyrolysis section and low-temperature pyrolysis drying section is controllable, which is conducive to improving the service life of equipment and stabilizing product quality;The present application can stably and continuously realize fine coal pyrolysis, with good product quality and high investment return rate.

Description

Technical Field

[0001] This invention relates to the field of low-rank coal dry distillation technology, and in particular to an external combustion and external heating pulverized coal pyrolysis system and pulverized coal pyrolysis method. Background Technology

[0002] Low-rank coal is characterized by abundant reserves, shallow burial depth, and low economic cost of mining. According to statistics, the global geological reserves of low-rank coal are as high as 4 trillion tons, accounting for 40% of the world's total coal reserves. In my country, the development and utilization of high-quality coal types such as bituminous coal and anthracite have reached saturation, while the large-scale development and utilization of low-rank coal is just beginning.

[0003] Currently, the industrial sector commonly uses internally heated vertical furnaces to upgrade low-rank coal, involving the combustion and dry distillation of a mixture of coal gas and air injected into the furnace. However, this process produces a large volume of coal gas, but its quality is low, with ineffective components such as nitrogen accounting for over 50%. This low-quality coal gas is often only sent to power plants for combustion and power generation, and cannot be further processed into high-value-added chemicals. Furthermore, due to the characteristics of the internally heated vertical furnace process, it cannot process fine coal with a particle size of less than 13 mm. To date, the efficient graded utilization of fine coal remains a major obstacle to the industrial application of low-rank coal.

[0004] Chinese patent application CN105018120A discloses a "continuous dry distillation process and apparatus for low-rank pulverized coal." Low-rank pulverized coal enters an externally heated continuous dry distillation refractory furnace through a double-sealed feeding device and a material buffer bin. Raw coal gas is collected through a gas collecting device and a gas collecting chamber and then discharged through a gas collecting system. The furnace charge after dry distillation is discharged through a discharge device. This process achieves continuous dry distillation of low-rank pulverized coal in an externally heated continuous dry distillation furnace. The raw coal gas generated during dry distillation can be quickly discharged, improving light oil yield and coal gas calorific value. During coke discharge, the fine coke can be controlled for uniform and continuous discharge, and the quality of semi-coke is controllable and adjustable. However, because the furnace body is entirely constructed of refractory bricks, the heat transfer efficiency of the apparatus is low, resulting in a small unit capacity and a large overall investment.

[0005] Chinese patent application CN112708434A discloses a "Modular Combination Unit Continuous Low-Rank Coal Pyrolysis Furnace," which can be used for the processing of low-rank coal semi-coke, particularly showing good targeting and applicability for small-particle-size coal and pulverized coal. The overall structure of the pyrolysis furnace consists of multiple furnace body units arranged in a row, each unit being a fully functional furnace body. Each unit is constructed from multiple detachable functional modules. This modular structure allows the coke oven to be disassembled and replaced, reducing construction costs and facilitating maintenance. However, the use of refractory prefabricated modules results in difficult overall casting, complex structure, and low yield, making practical industrial application and promotion challenging.

[0006] Chinese patent application CN111518581A discloses a "Vertical Multi-Pipe Segmented Gas-Conducting External Heating Method and Apparatus for Pulverized Coal Drying," which utilizes a tubular dry distillation process and employs a tower-shaped segmented vertical tubular structure to process raw coal. From top to bottom, the process consists of a drying stage, two dry distillation stages, and a cooling stage. This apparatus can improve the quality of semi-coke, has high heat exchange efficiency, and increases resource utilization and production capacity. However, due to the characteristics of the heat-resistant materials in the dry distillation stage, the high-temperature section equipment experiences unstable production. Summary of the Invention

[0007] This invention provides an external combustion and external heating pulverized coal pyrolysis system and method. The coal dry distillation device adopts a three-stage structure: a low-temperature pyrolysis drying section, a medium-high temperature pyrolysis section, and an upgraded coal cooling section. The exhaust gas generated by the combustion of coal gas in an external coal gas combustion furnace is introduced into the medium-high temperature pyrolysis section to indirectly transfer heat with the pulverized coal, realizing the cascade pyrolysis of the raw material pulverized coal. The inlet flue gas temperature of the medium-high temperature pyrolysis section and the low-temperature pyrolysis drying section is controllable, which is beneficial to improving the service life of the equipment and stabilizing product quality. This invention can stably and continuously realize the pyrolysis of pulverized coal, with good product quality and high return on investment.

[0008] To achieve the above objectives, the present invention employs the following technical solution:

[0009] An externally combusted and externally heated pulverized coal pyrolysis system includes a coal dry distillation unit, a flue gas heat exchange system, and a raw coal gas system. The coal dry distillation unit is sequentially configured from top to bottom as a low-temperature pyrolysis drying section, a medium-high temperature pyrolysis section, and an upgraded coal cooling section. The flue gas heat exchange system includes an externally mounted coal gas burner, a high-temperature flue gas distribution system, and a flue gas mixing and temperature control system. The raw coal gas system includes a raw coal gas cooling and collection system and a raw flue gas purification system. The maximum heat resistance temperature of the low-temperature pyrolysis drying section is >900℃. The maximum heat resistance temperature of the medium-high temperature pyrolysis section is >1400℃. Multiple coal flow areas and flue gas flow areas are alternately arranged in the low-temperature pyrolysis drying section, the medium-high temperature pyrolysis section, and the upgraded coal cooling section, forming... The system includes vertically connected coal and flue gas flow channels. The flue gas inlet of the medium-high temperature pyrolysis section is connected to the high-temperature flue gas outlet of an external coal gas combustion furnace via a high-temperature flue gas distribution system. The flue gas outlet of the medium-high temperature pyrolysis section is connected to the high-temperature flue gas inlet of a flue gas blending and temperature control system. The mixed flue gas outlet of the flue gas blending and temperature control system is connected to the flue gas inlet of the low-temperature pyrolysis drying section. The flue gas outlet of the low-temperature pyrolysis drying section is connected to a flue gas purification system via an outlet flue gas pipeline, which is also connected to the low-temperature return flue gas inlet of the flue gas blending and temperature control system. Both the low-temperature pyrolysis drying section and the medium-high temperature pyrolysis section are equipped with multiple raw coal gas outlets, which are connected to the raw coal gas purification system via a raw coal gas cooling and collection system.

[0010] The coal dry distillation unit is equipped with a furnace top silo at the top feed inlet and a coke pusher and semi-coke conveying device at the bottom discharge outlet.

[0011] The low-temperature pyrolysis drying section is made of one or more materials selected from carbon steel, cast steel, heat-resistant stainless steel, and silicon carbide ceramics; the medium-high temperature pyrolysis section is made of one or more materials selected from refractory materials, cast steel, heat-resistant stainless steel, and silicon carbide ceramics; multiple baffles are respectively installed in the flue gas flow channels of the low-temperature pyrolysis drying section and the medium-high temperature pyrolysis section.

[0012] The high-temperature flue gas distribution system consists of a horizontally arranged high-temperature flue gas conveying pipe and a high-temperature flue gas distribution pipe. One end of the high-temperature flue gas conveying pipe is connected to the high-temperature flue gas outlet of an external gas combustion furnace through a high-temperature flue gas pipeline, and the other end of the high-temperature flue gas conveying pipe is connected to the high-temperature flue gas distribution pipe. Multiple high-temperature flue gas distribution holes are provided at the top of the high-temperature flue gas distribution pipe, corresponding to multiple flue gas areas in the medium-high temperature pyrolysis section. Along the high-temperature flue gas flow direction, the high-temperature flue gas distribution pipe has a gradually decreasing cross-sectional area.

[0013] The high-temperature flue gas conveying pipe is equipped with a high-temperature flue gas temperature detection device and a high-temperature flue gas pressure detection device.

[0014] The flue gas blending and temperature control system consists of a first-stage flue gas pipeline, a blending sleeve, a blending flue gas regulating valve, a second-stage flue gas pipeline, a first-stage flue gas temperature detection device, and a second-stage flue gas temperature detection device. One end of the first-stage flue gas pipeline is connected to the flue gas outlet of the medium-high temperature pyrolysis section, and the other end of the first-stage flue gas pipeline is connected to the second-stage flue gas pipeline through a high-temperature expansion joint. A blending sleeve is installed on the first-stage flue gas pipeline, and a low-temperature return flue gas inlet is installed on the blending sleeve. A blending gas regulating valve is installed at the low-temperature return flue gas inlet. The other end of the second-stage flue gas pipeline is connected to the flue gas inlet of the low-temperature pyrolysis drying section. A first-stage flue gas temperature detection device is installed on the first-stage flue gas pipeline, and a second-stage temperature detection device is installed on the second-stage flue gas pipeline.

[0015] The raw coal gas cooling and gas collection system has an ammonia water spray cooling and washing device inside the main raw coal gas pipe; the raw coal gas purification system is connected to the external coal gas pipeline through the purified coal gas pipeline, and a coal gas fan is installed on the purified coal gas pipeline; the purified coal gas pipeline is also connected to the coal gas inlet pipeline of the external coal gas combustion furnace, and the coal gas inlet pipeline is also connected to the lean coal gas pipeline; a combustion furnace gas regulating valve is installed on the coal gas inlet pipeline near the external coal gas combustion furnace.

[0016] A method for pyrolysis of pulverized coal includes the following processes:

[0017] 1) The raw material fine coal enters the low-temperature pyrolysis drying section of the coal dry distillation unit through the coal bunker at the top of the furnace. It flows down along the coal flow channel and indirectly exchanges heat with the flue gas in the flue gas flow channel in a countercurrent manner to achieve drying and low-temperature dry distillation. The fine coal after low-temperature dry distillation enters the medium-high temperature pyrolysis section for pyrolysis and upgrading. The upgraded coal generated enters the upgraded coal cooling section under the action of gravity and is cooled to room temperature. The cooled upgraded coal is controlled by the coke pusher to control the coke discharge rate and is transported out through the semi-coke conveying device.

[0018] 2) The raw coal powder produced by low-temperature dry distillation in the low-temperature pyrolysis drying section and pyrolysis in the medium-high temperature pyrolysis section, as well as the raw coal gas, tar and moisture, are collected in sections and uniformly combined into the raw coal gas cooling and collection system. After being purified by the raw coal gas purification system, high-calorific-value coal gas is obtained. After being pressurized by the coal gas blower, part of it is sent out as external coal gas and the other part is sent to the external coal gas combustion furnace as rich coal gas for re-combustion.

[0019] 3) The fuel gas for the external gasifier includes rich coal gas from reheating and / or lean coal gas from external sources. The external gasifier controls the combustion heat through a gas regulating valve, maintaining the temperature of the generated high-temperature flue gas at 1100–1400℃. The high-temperature flue gas is evenly distributed to each flue gas flow area of ​​the medium-high temperature pyrolysis section through a high-temperature flue gas distribution system, and indirectly exchanges heat with the fine coal in the coal flow area within the medium-high temperature pyrolysis section. The outlet flue gas temperature of the medium-high temperature pyrolysis section is controlled at 800–950℃. The flue gas exiting the medium-high temperature pyrolysis section is mixed with low-temperature recycled flue gas through a flue gas mixing and temperature control system to control the inlet flue gas temperature of the low-temperature pyrolysis drying section within the range of 600–900℃. The mixed coal gas entering the low-temperature pyrolysis drying section undergoes countercurrent indirect heat exchange with the raw material fine coal, and the outlet flue gas temperature of the low-temperature pyrolysis drying section is controlled within the range of 150–250℃. The flue gas exiting the low-temperature pyrolysis drying section is pressurized by a flue gas fan, with a portion entering the flue gas purification system and the other portion entering the flue gas mixing and temperature control system as low-temperature recycled flue gas.

[0020] The particle size of the raw material fine coal is <13mm.

[0021] The raw coal gas cooling and collection system has an ammonia water spraying cooling and washing device installed in the raw coal gas main pipe to cool the raw coal gas; the flue gas purification system includes a flue gas desulfurization and denitrification system.

[0022] Compared with the prior art, the beneficial effects of the present invention are:

[0023] 1) The coal dry distillation unit adopts a three-section structure: a low-temperature pyrolysis drying section, a medium-high temperature pyrolysis section, and an upgraded coal cooling section. The exhaust gas generated by the combustion of coal gas in the external coal gas combustion furnace is introduced into the medium-high temperature pyrolysis section to indirectly transfer heat with the fine coal, thereby realizing the step-by-step pyrolysis of the raw material fine coal.

[0024] 2) The maximum heat resistance temperature of the low-temperature pyrolysis drying section is >900℃, and the maximum heat resistance temperature of the medium-high temperature pyrolysis section is >1400℃. This invention utilizes a flue gas mixing and temperature control system to mix low-temperature recycled flue gas into the high-temperature flue gas output to the medium-high temperature pyrolysis section, controlling the inlet flue gas temperature of the low-temperature pyrolysis drying section within the range of 600-900℃. The high-temperature flue gas temperature generated by the external gas combustion furnace is controlled within the range of 1100-1400℃ through the combustion furnace gas regulating valve. This achieves controllable inlet flue gas temperatures for both the medium-high temperature pyrolysis section and the low-temperature pyrolysis drying section, which is beneficial for improving the service life of the coal dry distillation unit and stabilizing product quality.

[0025] 3) This invention can stably and continuously achieve pyrolysis of fine coal, resulting in high product quality and high return on investment. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the structure of an external combustion and external heating pulverized coal pyrolysis system according to the present invention.

[0027] Figure 2 This is a schematic diagram of the high-temperature flue gas distribution system described in this invention.

[0028] Figure 3 This is a schematic diagram of the flue gas mixing and temperature control system described in this invention.

[0029] In the diagram: 1. Furnace top silo 2. Low-temperature pyrolysis drying section 3. Medium-high temperature pyrolysis section 4. Upgrading coal cooling section 5. Coke pusher 6. Semi-coke conveying device 7. External gas combustion furnace 8. High-temperature flue gas distribution system 801. High-temperature flue gas conveying pipe 802. High-temperature flue gas distribution pipe 803. High-temperature flue gas distribution hole 804. High-temperature flue gas temperature detection device 805. High-temperature flue gas pressure detection device 806. Hot waste gas chamber 807. Coal pyrolysis chamber 9. Flue gas blending and temperature control system 901. Flue gas outlet of medium-high temperature pyrolysis section; 902. First-stage flue gas pipeline; 903. Blending sleeve; 904. Blending flue gas regulating valve; 905. High-temperature expansion joint; 906. Second-stage flue gas pipeline; 907. Flue gas inlet of low-temperature pyrolysis drying section; 908. First-stage flue gas temperature detection device; 909. Second-stage flue gas temperature detection device; 10. Flue gas fan; 11. Raw coal gas cooling and collecting system; 12. Raw coal gas purification system; 13. Gas fan; 14. Combustion furnace gas regulating valve.

[0030] A. Raw coal powder B. Upgraded coal C. Raw coal gas D. High-calorific-value coal gas E. External coal gas F. Rich coal gas from remelting G. Lean coal gas H. High-temperature flue gas J. Flue gas from the outlet of the medium-high temperature pyrolysis section K. Flue gas from the inlet of the low-temperature pyrolysis drying section L. Flue gas from the outlet of the low-temperature pyrolysis drying section M. Flue gas entering the flue gas purification system N. Low-temperature recycled flue gas Detailed Implementation

[0031] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings:

[0032] like Figures 1-3 As shown, the external combustion and external heating pulverized coal pyrolysis system of the present invention includes a coal dry distillation device, a flue gas heat exchange system, and a raw coal gas system.

[0033] The coal dry distillation unit adopts a vertical furnace structure, and from top to bottom are arranged the furnace top silo 1, low temperature pyrolysis drying section 2, medium and high temperature pyrolysis section 3, upgraded coal cooling section 4, coke pusher 5, and semi-coke conveying device 6.

[0034] The low-temperature pyrolysis drying section 2 consists of multiple coal flow areas and flue gas flow areas spaced apart, with multiple baffles installed in the flue gas flow areas. The maximum heat resistance temperature of the low-temperature pyrolysis drying section 2 is >900℃, and the materials used include, but are not limited to, carbon steel, cast steel, heat-resistant stainless steel, and silicon carbide ceramics.

[0035] The medium-high temperature pyrolysis section 3 consists of multiple coal flow areas (i.e., coal pyrolysis chambers 807) and flue gas flow areas (i.e., hot exhaust gas chambers 806) spaced apart, with multiple baffles installed in the flue gas flow areas. The maximum heat resistance temperature of the medium-high temperature pyrolysis section 3 is >1400℃, and the materials used include, but are not limited to, carbon steel, cast steel, heat-resistant stainless steel, and silicon carbide ceramics.

[0036] The flue gas heat exchange system includes a combustion furnace gas regulating valve 14, an external gas combustion furnace 7, a high-temperature flue gas distribution system 8, a flue gas mixing and temperature control system 9, and a flue gas fan 10. The combustion furnace gas regulating valve 14 is installed on the gas inlet pipe of the external gas combustion furnace 7. The external gas combustion furnace 7 is connected to the high-temperature flue gas distribution system 8 via a high-temperature flue gas pipe. The high-temperature flue gas distribution system 8 is connected to the exhaust gas inlets of multiple hot exhaust gas chambers 806 of the medium-high temperature pyrolysis section 3 via multiple high-temperature flue gas distribution holes 803. The flue gas outlet 901 of the medium-high temperature pyrolysis section is connected to the flue gas mixing and temperature control system 9. The mixed flue gas outlet of the flue gas mixing and temperature control system 9 is connected to the flue gas inlet 907 of the low-temperature pyrolysis drying section. A flue gas fan 10 is installed on the low-temperature flue gas pipe downstream of the low-temperature pyrolysis drying section flue gas outlet to provide power for the flue gas circulation of the flue gas heat exchange system.

[0037] The high-temperature flue gas distribution system 8 is equipped with a high-temperature flue gas conveying pipe 801, a high-temperature flue gas distribution pipe 802, and multiple high-temperature flue gas distribution holes 803 sequentially along the flow direction of the high-temperature flue gas. The high-temperature flue gas conveying pipe is equipped with a high-temperature flue gas temperature detection device and a high-temperature flue gas pressure detection device. Each high-temperature flue gas distribution hole 803 is connected to a hot waste gas chamber 806 of the medium-high temperature pyrolysis section. Between two adjacent hot waste gas chambers 806 is a coal pyrolysis chamber 807 of the high-temperature pyrolysis section. The high-temperature flue gas distribution pipe 802 has a gradually decreasing cross-section and area along the flow direction of the high-temperature flue gas.

[0038] In the flue gas blending and temperature control system 9, a first-stage flue gas duct 902 is connected to the flue gas outlet 901 of the medium-high temperature pyrolysis section. A blending sleeve 903 is installed on the first-stage flue gas duct 901. A blending gas regulating valve 904 is installed at the low-temperature return flue gas inlet of the blending sleeve 903. The first-stage flue gas duct 902 is connected to the second-stage flue gas duct 906 through a high-temperature expansion joint 905. The second-stage flue gas duct 906 is connected to the flue gas inlet 907 of the low-temperature pyrolysis drying section. A first-stage flue gas temperature detection device 908 and a second-stage flue gas temperature detection device 909 are respectively installed on the first-stage flue gas duct 902 and the second-stage flue gas duct 906.

[0039] The raw coal gas system includes a raw coal gas cooling and collection system 11, a raw coal gas purification system 12, and a coal gas blower 13. The raw coal gas cooling and collection system 11 is connected to multiple raw coal gas outlets in the low-temperature pyrolysis drying section 2 and the medium-high temperature pyrolysis section 3, and is equipped with an ammonia water spray cooling and washing device.

[0040] In this embodiment, the pyrolysis process of pulverized coal is as follows:

[0041] 1) Raw material fine coal A (particle size <13mm) enters the coal flow channel of the low-temperature pyrolysis drying section 2 of the coal dry distillation unit through the coal bunker 1 at the top of the furnace. It is dried and pyrolyzed at low temperature by countercurrent heat exchange with the flue gas. Then it enters the medium-high temperature pyrolysis section 3 for further medium-high temperature pyrolysis and upgrading. The resulting upgraded coal B flows into the upgraded coal cooling section 4 under gravity and is cooled to room temperature. At the bottom of the upgraded coal cooling section 4, the upgraded coal B is discharged at a rate controlled by the coke pusher 5 and finally sent out through the semi-coke conveying device 6.

[0042] 2) The raw coal gas C, tar and moisture produced by the raw coal fines A in the low temperature pyrolysis drying section 2 and the medium and high temperature pyrolysis section 3 are collected in sections and uniformly summarized to the raw coal gas cooling and collection system 11. After being purified by the raw coal gas purification system 12, high calorific value coal gas D is obtained. After being pressurized by the coal gas blower 13, it is used as external coal gas E or as rich coal gas F for re-combustion.

[0043] 3) The fuel gas for the external gasifier 7 includes recycled rich coal gas F and / or external lean coal gas G. The combustion heat of the external gasifier 7 is controlled by the combustion furnace gas regulating valve 14, and the temperature of the generated high-temperature flue gas H is controlled at 1100-1400℃. The high-temperature flue gas H is evenly distributed to the hot waste gas chamber 806 of the medium-high temperature pyrolysis section 3 through the high-temperature flue gas distribution system 8, and indirectly exchanges heat with the fine coal in the coal pyrolysis chamber 807 of the medium-high temperature pyrolysis section 3. The temperature of the flue gas J at the outlet of the medium-high temperature pyrolysis section is controlled at 800-950℃. The flue gas J at the outlet of the medium-high temperature pyrolysis section is mixed with low-temperature recycled flue gas N through the flue gas mixing and temperature control system 9, and the temperature of the flue gas K at the inlet of the low-temperature pyrolysis drying section is controlled between 600-900℃ to ensure the service life of the low-temperature pyrolysis drying section 2. After the inlet flue gas K of the low-temperature pyrolysis drying section enters the low-temperature pyrolysis drying section 2, it continues to exchange heat indirectly with the fine coal in a countercurrent flow. The temperature of the outlet flue gas L of the low-temperature pyrolysis drying section after cooling is controlled at 150-250℃. The outlet flue gas L of the low-temperature pyrolysis drying section is pressurized by the flue gas fan 10. Part of it is used as flue gas M entering the flue gas purification system, and the other part is used as low-temperature return flue gas N entering the flue gas mixing and temperature control system 9.

[0044] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for pulverized coal pyrolysis, based on an external combustion and external heating pulverized coal pyrolysis system; characterized in that, The external combustion and external heating pulverized coal pyrolysis system includes a coal dry distillation unit, a flue gas heat exchange system, and a raw coal gas system. The coal dry distillation unit, from top to bottom, comprises a low-temperature pyrolysis drying section, a medium-high temperature pyrolysis section, and an upgraded coal cooling section. The flue gas heat exchange system includes an external coal gas combustion furnace, a high-temperature flue gas distribution system, and a flue gas mixing and temperature control system. The raw coal gas system includes a raw coal gas cooling and collection system and a raw coal gas purification system. The maximum heat resistance temperature of the low-temperature pyrolysis drying section is >900℃; the maximum heat resistance temperature of the medium-high temperature pyrolysis section is >1400℃. Multiple coal flow areas and flue gas flow areas are spaced apart in the low-temperature pyrolysis drying section, the medium-high temperature pyrolysis section, and the upgraded coal cooling section, forming vertically connected coal flow channels and flue gas flow channels. The flue gas inlet of the medium-high temperature pyrolysis section is connected to the high-temperature flue gas outlet of the external coal gas combustion furnace through the high-temperature flue gas distribution system. The outlet of the flue gas system is connected to the high-temperature flue gas inlet of the flue gas blending and temperature control system, and the mixed flue gas outlet of the flue gas blending and temperature control system is connected to the flue gas inlet of the low-temperature pyrolysis drying section. The flue gas outlet of the low-temperature pyrolysis drying section is connected to the flue gas purification system through an outlet flue gas pipeline, which is also connected to the low-temperature return flue gas inlet of the flue gas blending and temperature control system. The low-temperature pyrolysis drying section and the medium-high temperature pyrolysis section are each equipped with multiple raw coal gas outlets, which are connected to the raw coal gas purification system through a raw coal gas cooling and collection system. The raw coal gas main pipe of the raw coal gas cooling and collection system is equipped with an ammonia water spray cooling and washing device. The raw coal gas purification system is connected to the external coal gas pipeline through a purified coal gas pipeline, and a coal gas fan is installed on the purified coal gas pipeline. The purified coal gas pipeline is also connected to the coal gas inlet pipeline of the external coal gas combustion furnace, and the coal gas inlet pipeline is also connected to the lean coal gas pipeline. A combustion furnace gas regulating valve is installed on the coal gas inlet pipeline near the external coal gas combustion furnace. The pulverized coal pyrolysis method includes the following processes: 1) Raw material fines with a particle size of <13mm enter the low-temperature pyrolysis drying section of the coal dry distillation unit through the coal bunker at the top of the furnace. They go down along the coal flow channel and exchange heat indirectly with the flue gas in the flue gas flow channel in a counter-current manner to achieve drying and low-temperature dry distillation. After low-temperature dry distillation, the fines enter the medium-high temperature pyrolysis section for pyrolysis and upgrading. The upgraded coal generated enters the upgraded coal cooling section under gravity and is cooled to room temperature. The cooled upgraded coal is controlled by the coke pusher to discharge coke at a rate that is controlled by the coke pusher and is transported out through the semi-coke conveying device. 2) The raw coal powder produced by low-temperature dry distillation in the low-temperature pyrolysis drying section and pyrolysis in the medium- and high-temperature pyrolysis section, including raw coal gas, tar, and moisture, are collected in stages and uniformly combined into the raw coal gas cooling and collection system. After purification by the raw coal gas purification system, high-calorific-value coal gas is obtained. After being pressurized by a coal gas blower, part of it is used as external coal gas, and the other part is sent to the external coal gas combustion furnace as rich coal gas for re-combustion. The raw coal gas cooling and collection system is equipped with an ammonia water spray cooling and washing device in the raw coal gas main pipe to cool the raw coal gas. 3) The fuel gas for the external gasifier includes rich coal gas from reheating and / or lean coal gas from external sources. The external gasifier controls the combustion heat through a gas regulating valve, maintaining the temperature of the generated high-temperature flue gas at 1100–1400℃. The high-temperature flue gas is evenly distributed to each flue gas flow area of ​​the medium-high temperature pyrolysis section through a high-temperature flue gas distribution system, and indirectly exchanges heat with the fine coal in the coal flow area within the medium-high temperature pyrolysis section. The outlet flue gas temperature of the medium-high temperature pyrolysis section is controlled at 800–950℃. The flue gas is mixed with low-temperature recycled flue gas through a flue gas blending and temperature control system to control the inlet flue gas temperature of the low-temperature pyrolysis drying section within the range of 600–900°C. The mixed coal gas entering the low-temperature pyrolysis drying section undergoes countercurrent indirect heat exchange with the raw material fine coal, and the outlet flue gas temperature of the low-temperature pyrolysis drying section is controlled within the range of 150–250°C. The outlet flue gas of the low-temperature pyrolysis drying section is pressurized by a flue gas fan, with a portion entering the flue gas purification system and the other portion entering the flue gas blending and temperature control system as low-temperature recycled flue gas. The flue gas purification system includes a flue gas desulfurization and denitrification system.

2. The method for pyrolysis of pulverized coal according to claim 1, characterized in that, The coal dry distillation unit is equipped with a furnace top silo at the top feed inlet and a coke pusher and semi-coke conveying device at the bottom discharge outlet.

3. The method for pyrolysis of pulverized coal according to claim 1, characterized in that, The low-temperature pyrolysis drying section is made of one or more materials selected from carbon steel, cast steel, heat-resistant stainless steel, and silicon carbide ceramics; the medium-high temperature pyrolysis section is made of one or more materials selected from refractory materials, cast steel, heat-resistant stainless steel, and silicon carbide ceramics; multiple baffles are respectively installed in the flue gas flow channels of the low-temperature pyrolysis drying section and the medium-high temperature pyrolysis section.

4. The method for pyrolysis of pulverized coal according to claim 1, characterized in that, The high-temperature flue gas distribution system consists of a horizontally arranged high-temperature flue gas conveying pipe and a high-temperature flue gas distribution pipe. One end of the high-temperature flue gas conveying pipe is connected to the high-temperature flue gas outlet of an external gas combustion furnace through a high-temperature flue gas pipeline, and the other end of the high-temperature flue gas conveying pipe is connected to the high-temperature flue gas distribution pipe. Multiple high-temperature flue gas distribution holes are provided at the top of the high-temperature flue gas distribution pipe, corresponding to multiple flue gas areas in the medium-high temperature pyrolysis section. Along the high-temperature flue gas flow direction, the high-temperature flue gas distribution pipe has a gradually decreasing cross-sectional area.

5. The method for pyrolysis of pulverized coal according to claim 4, characterized in that, The high-temperature flue gas conveying pipe is equipped with a high-temperature flue gas temperature detection device and a high-temperature flue gas pressure detection device.

6. The method for pyrolysis of pulverized coal according to claim 1, characterized in that, The flue gas blending and temperature control system consists of a first-stage flue gas pipeline, a blending sleeve, a blending flue gas regulating valve, a second-stage flue gas pipeline, a first-stage flue gas temperature detection device, and a second-stage flue gas temperature detection device. One end of the first-stage flue gas pipeline is connected to the flue gas outlet of the medium-high temperature pyrolysis section, and the other end of the first-stage flue gas pipeline is connected to the second-stage flue gas pipeline through a high-temperature expansion joint. A blending sleeve is installed on the first-stage flue gas pipeline, and a low-temperature return flue gas inlet is installed on the blending sleeve. A blending gas regulating valve is installed at the low-temperature return flue gas inlet. The other end of the second-stage flue gas pipeline is connected to the flue gas inlet of the low-temperature pyrolysis drying section. A first-stage flue gas temperature detection device is installed on the first-stage flue gas pipeline, and a second-stage temperature detection device is installed on the second-stage flue gas pipeline.

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