Circulating fluidized bed system and method for generating power by utilizing complementary energy of low-carbon coal gangue and low-concentration gas

Abstract

The invention relates to the technical field of novel circulating fluidized bed boilers and solid waste resource utilization, and discloses a circulating fluidized bed system and method for generating power by utilizing complementary energy of low-carbon coal gangue and low-concentration gas, and the circulating fluidized bed system comprises a feeding assembly, a material returning assembly, a combustion assembly, a flue gas waste heat recovery assembly, a gas grading and blending assembly and a tail gas treatment assembly; according to the system, gas mined from a coal seam is diluted to the safe concentration of 3-5%, a gas-air-gas three-stage air distribution mode is formed through a three-stage air pipe, and raw materials fed by the feeding assembly are mixed and combusted with high-temperature bed materials in a fluidized state in the combustion assembly in a matched mode. Safe and efficient cooperative utilization of two low-grade energy sources of low-concentration gas and coal gangue is achieved, it is ensured that the gas concentration is stabilized within a safe range through the flue gas recirculation technology, the combustion efficiency is enhanced through a three-level air distribution mode, and the energy utilization efficiency and the environmental protection benefits are improved.

Description

Technical Field

[0001] This invention relates to the field of novel circulating fluidized bed boilers and solid waste resource utilization technology, specifically to a circulating fluidized bed system and method for generating electricity using low-carbon coal gangue and low-concentration gas waste energy. Background Technology

[0002] Low-concentration methane, a waste product generated during coal mining, is mostly at its explosive limit and unusable as fuel due to its low concentration. The amount of methane released into the atmosphere annually through exhaust ventilation in my country is roughly equivalent to the annual gas volume transported by the West-East Gas Pipeline, generating a greenhouse gas effect equivalent to 200 million tons of carbon dioxide. This not only exacerbates global warming but also results in a massive waste of resources. Methane with a concentration >30% is mainly used as chemical raw material and domestic fuel; methane with a concentration between 8% and 30% is mainly used for power generation in methane-fired generators; and methane with a concentration below 3% is used in small quantities for oxidation. However, methane with a concentration between 3% and 8% accounts for 37% of coal mine methane resources, and currently, large quantities are released into the atmosphere without effective means of resource recovery.

[0003] Chinese patent document CN120537591A discloses a system and method for synergistic enrichment and fluidized bed regenerative combustion of coal mine exhaust gas. The system includes a ventilation shaft diffusion tower and an exhaust gas collection device. The method includes the following steps: exhaust gas collection and compression, adsorption tower cooling and pressurization, pressure equalization in the adsorption tower, desorption by heating and depressurization in the adsorption tower, pressure equalization in the adsorption tower, cyclic operation of the adsorption tower, preheating of the regenerative furnace bed, fluidized bed regenerative oxidation of coal gangue and gas, and waste heat recovery. Although this patent utilizes both coal gangue and gas for power generation, the power generation process mainly utilizes exhaust gas with a concentration of 0.1-0.5%, and requires a gas enrichment process to increase the gas concentration to 1-2%, increasing costs and energy consumption. Furthermore, it does not propose a solution for gas concentrations of 3-8%. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a circulating fluidized bed system and method for generating electricity using waste energy from low-carbon coal gangue and low-concentration methane, achieving efficient, clean, and comprehensive utilization of coal gangue and methane, and solving the problem that methane with a concentration of 3-8% cannot be effectively utilized as a resource.

[0005] To achieve the above objectives, the present invention provides a circulating fluidized bed system for generating electricity using low-carbon coal gangue and low-concentration gas waste heat, comprising: a feeding assembly, a return assembly, a combustion assembly, a flue gas waste heat recovery assembly, a gas grading and distribution assembly, and a tail gas treatment assembly. The combustion assembly includes: a combustion chamber, a tertiary air duct located at the top of the combustion chamber and distributing air in parallel, a secondary air duct located in the middle of the combustion chamber and distributing air vertically, a primary air duct located at the bottom of the combustion chamber and distributing air vertically, a slag cooler located at the slag discharge port of the combustion chamber, and a water-cooled wall located inside the combustion chamber. The gas grading and distribution component includes: a gas grading and distribution system, a reflux control valve connected to external low-concentration gas, a methane concentration sensor installed between the gas grading and distribution system and the reflux control valve, a No. 2 fan whose inlet end is connected to the gas blower distribution system and whose outlet end is connected to the tertiary air duct, a No. 3 fan whose inlet end is connected to external air and whose outlet end is connected to the secondary air duct, a No. 1 fan whose inlet end is connected to the gas blower distribution system and whose outlet end is connected to the primary air duct, and a No. 4 fan whose inlet end is connected to the dust collector and whose outlet end is connected to the gas grading and distribution system; the gas grading and distribution system dilutes the gas using the flue gas after dust removal by the No. 4 fan, based on the data from the methane concentration sensor.

[0006] As a further improvement of the present invention, the feeding assembly includes: a coal gangue feeding device, a limestone feeding device, and a mixing crusher connected to the ends of the coal gangue feeding device and the limestone feeding device.

[0007] As a further improvement of the present invention, the return material assembly includes: an air inlet connected to a cyclone separator in the combustion chamber, a tail flue of the cyclone separator connected to a flue gas waste heat recovery assembly, and a return material port of the cyclone separator connected to the combustion assembly.

[0008] As a further improvement of the present invention, the flue gas waste heat recovery assembly includes: a heat exchanger connected to a cyclone separator, a superheater and an economizer connected in sequence to the heat exchanger, and a steam drum connected to the economizer; the economizer is connected to external boiler water, and the steam drum is connected to the heat exchanger and the superheater.

[0009] As a further improvement of the present invention, the exhaust gas treatment assembly includes a dust collector, a chimney connected to the outside atmosphere, and a No. 5 fan connecting the dust collector and the chimney; one outlet of the dust collector is connected to the gas grading and distribution assembly through a No. 4 fan.

[0010] This invention also proposes a circulating fluidized bed method for generating electricity using low-carbon coal gangue and low-concentration methane waste energy, applicable to the aforementioned circulating fluidized bed system for generating electricity using low-carbon coal gangue and low-concentration methane waste energy, comprising the following steps: S1. Coal gangue is fed into the coal gangue feeding device and limestone is fed into the limestone feeding device for mixing. After being crushed by the mixing crusher, it is sent into the combustion chamber. S2. After the gas is extracted from the coal seam, it is preheated by the reflux control valve and the methane concentration sensor and then enters the gas grading and distribution system to mix and dilute with the low-temperature flue gas entering through the No. 4 blower. After passing through the gas distribution and regulation system, part of the gas supply enters the bottom of the combustion chamber through the No. 1 blower and the primary air duct, and the other part of the gas supply enters the upper part of the combustion chamber through the No. 2 blower and the tertiary air duct. At the same time, the outside air enters the middle of the combustion chamber through the No. 3 blower and the secondary air duct, thus forming a gas-air-gas three-level air distribution mode. S3. The raw materials fed by the feeding assembly, along with the three-stage air distribution, are mixed and combusted with the high-temperature bed material in the combustion assembly under fluidized conditions to generate a large amount of flue gas and heat. The heat generated by combustion is exchanged through the water-cooled wall. During the combustion process, primary air is sent from the bottom of the furnace through the primary air duct, secondary air is sent from the middle of the furnace through the secondary air duct, and tertiary air is supplied parallel from the top of the furnace through the tertiary air duct. The ash and slag after the coal gangue combustion enter the slag cooler through the slag discharge port and are then discharged for use in cement building materials. S4. The high-temperature flue gas carrying materials in the combustion assembly enters the return assembly. The high-temperature flue gas is separated from the unburned material by the action of the cyclone separator. Most of the solid unburned material is separated out and returns to the combustion assembly through the return port to burn again and release heat. The high-temperature flue gas enters the flue gas waste heat recovery assembly through the tail flue. S5. High-temperature flue gas enters the flue gas waste heat recovery component from the tail flue, and undergoes heat exchange through the heat exchanger, superheater and economizer respectively, and is transformed into low-temperature flue gas and discharged from the flue gas waste heat recovery component and enters the tail gas treatment component. S6. Boiler water is preheated by the economizer and enters the steam drum. The hot water in the steam drum is converted into saturated steam through the heat exchanger and returned to the steam drum. The saturated steam enters the superheater from the steam drum and is converted into superheated steam to drive the steam turbine generator set. S7. After the low-temperature flue gas enters the dust collector for dust removal, part of it is drawn into the gas classification and distribution component by fan No. 4, and the other part is drawn into the chimney by fan No. 5 and then discharged into the atmosphere.

[0011] As a further improvement of the present invention, in S1, coal gangue and limestone are mixed at a mass ratio of 8:1 and crushed to a particle size of less than 8mm by a mixing crusher (3).

[0012] As a further improvement of the present invention, in S2, the gas concentration after dilution by the gas grading and distribution system (20) is maintained at 3-5%.

[0013] Compared with the prior art, the present invention provides a circulating fluidized bed system and method for generating electricity using low-carbon coal gangue and low-concentration methane waste energy, which has the following beneficial effects: 1. This invention couples coal gangue and gas combustion for power generation in a novel circulating fluidized bed, and combines it with a graded and layered air and gas supply system to form a three-stage gas-air-gas distribution mode. This enhances the turbulent mixing and combustion stability of coal gangue in the fluidized state, improves the co-combustion efficiency of coal gangue and gas, and increases the combustion efficiency by 20% compared with ordinary combustion. At the same time, it efficiently utilizes low-concentration gas with a concentration of 3-8% and low-carbon coal gangue, solving the pollution problems of the two types of waste and generating clean energy.

[0014] 2. This invention uses a gas grading and distribution system to dilute methane based on data from a methane concentration sensor, ensuring that the gas concentration in the air supply is maintained at 3-5%, thereby improving combustion safety and preventing explosions caused by methane concentrations exceeding 5%, which could lead to safety hazards. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the overall structure of a circulating fluidized bed system for generating electricity using low-carbon coal gangue and low-concentration methane waste energy, according to the present invention.

[0016] Explanation of reference numerals in the attached figures: 1. Coal gangue feeding device; 2. Limestone feeding device; 3. Mixing crusher; 4. Cyclone separator; 5. Heat exchanger; 6. Water-cooled wall; 7. Combustion chamber; 8. Tertiary air duct; 9. Secondary air duct; 10. Primary air duct; 11. No. 1 blower; 12. Slag cooler; 13. No. 2 blower; 14. Superheated steam; 15. Superheater; 16. Steam drum; 17. Boiler feedwater; 18. Economizer; 19. No. 3 blower; 20. Gas grading and distribution system; 21. No. 4 blower; 22. Methane concentration sensor; 23. Reflux control valve; 24. Dust collector; 25. No. 5 blower; 26. Chimney. Detailed Implementation

[0017] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0018] Example 1 In this embodiment, see Figure 1 A circulating fluidized bed system for generating electricity using low-carbon coal gangue and low-concentration gas waste heat includes: a feeding assembly, a return assembly, a combustion assembly, a flue gas waste heat recovery assembly, a gas grading and distribution assembly, and a tail gas treatment assembly. The combustion assembly includes: a combustion chamber 7, a tertiary air duct 8 located at the top of the combustion chamber 7 and distributing air in parallel, a secondary air duct 9 located in the middle of the combustion chamber 7 and distributing air vertically, a primary air duct 10 located at the bottom of the combustion chamber 7 and distributing air vertically, a slag cooler 12 located at the slag discharge port of the combustion chamber 7, and a water-cooled wall 6 located inside the combustion chamber 7. The gas grading and distribution component includes: a gas grading and distribution system 20, a reflux control valve 23 connected to external low-concentration gas, a methane concentration sensor 22 installed between the gas grading and distribution system 20 and the reflux control valve 23, a No. 2 fan 13 whose inlet end is connected to the gas blower distribution system and whose outlet end is connected to the tertiary air duct 8, a No. 3 fan 19 whose inlet end is connected to external air and whose outlet end is connected to the secondary air duct 9, a No. 1 fan 11 whose inlet end is connected to the gas blower distribution system and whose outlet end is connected to the primary air duct 10, and a No. 4 fan 21 whose inlet end is connected to the dust collector 24 and whose outlet end is connected to the gas grading and distribution system 20; the gas grading and distribution system 20, based on the data from the methane concentration sensor 22, uses the flue gas after dust removal by the No. 4 fan 21 to dilute the gas, ensuring that the gas concentration in the supplied air is maintained at 3-5%.

[0019] In the above setup, after the 3-8% low-concentration methane is extracted from the coal seam, it is preheated by the reflux control valve 23 and the methane concentration sensor 22 before entering the methane grading and distribution system 20. It mixes and dilutes with the flue gas entering through the No. 4 blower 21 to ensure that the methane concentration is maintained at 3-5%. After passing through the methane distribution and regulation system, part of the supply methane enters the bottom of the combustion chamber 7 through the No. 1 blower 11 and the primary air duct 10, and the other part of the supply methane enters the upper part of the combustion chamber 7 through the No. 2 blower 13 and the tertiary air duct 8. At the same time, external air enters the middle of the combustion chamber 7 through the No. 3 blower 19 and the secondary air duct 9, thus forming a three-stage methane-air-methane distribution mode. The raw materials fed by the feeding assembly are mixed and burned with the high-temperature bed material in the combustion assembly in a fluidized state. The heat generated by combustion is exchanged through the water-cooled wall 6. The ash and slag after the coal gangue combustion enter the slag cooler 12 through the slag discharge port for cooling and discharge, and are used for cement building materials.

[0020] Furthermore, the feeding assembly includes: a coal gangue feeding device 1, a limestone feeding device 2, and a mixing crusher 3 connected to the ends of the coal gangue feeding device 1 and the limestone feeding device 2.

[0021] Preferably, coal gangue is mixed with limestone via coal gangue feeding device 1 and limestone via limestone feeding device 2 at a mass ratio of 8:1, and then crushed to a particle size of less than 8 mm by mixing crusher 3 before being fed into combustion chamber 7.

[0022] Furthermore, the return assembly includes: an air inlet connected to a cyclone separator 4 in the combustion chamber 7, a tail flue of the cyclone separator 4 connected to a flue gas waste heat recovery assembly, and a return port of the cyclone separator 4 connected to the combustion assembly.

[0023] In the above setup, the high-temperature flue gas carrying materials in the combustion assembly enters the return assembly. After being separated by the cyclone separator 4, most of the solid materials are separated and returned to the combustion assembly through the return port. The high-temperature flue gas enters the flue gas waste heat recovery assembly through the tail flue.

[0024] Furthermore, the flue gas waste heat recovery assembly includes: a heat exchanger 5 connected to the cyclone separator 4, a superheater 15 and an economizer 18 connected in sequence to the heat exchanger 5, and a steam drum 16 connected to the economizer 18; the economizer 18 is connected to the external boiler feed water 17, and the steam drum 16 is connected to the heat exchanger 5 and the superheater 15.

[0025] In the above configuration, high-temperature flue gas enters the flue gas waste heat recovery component from the tail flue, and undergoes heat exchange through heat exchanger 5, superheater 15 and economizer 18 respectively, becoming low-temperature flue gas that is discharged from the flue gas waste heat recovery component and enters the tail gas treatment component; boiler water 17 is preheated by economizer 18 and enters steam drum 16, the hot water in steam drum 16 is converted into saturated steam through heat exchanger 5 and returned to steam drum 16, the saturated steam enters superheater 15 from steam drum 16 and is converted into superheated steam 14 for power generation.

[0026] Preferably, in combustion chamber 7, coal gangue and low-concentration methane are fully combusted, and the heat released preheats the boiler feedwater 17 via economizer 18 before it enters steam drum 16. The water in steam drum 16 is converted into saturated steam via heat exchanger 5, and then enters superheater 15 to be heated into superheated steam 14 (temperature approximately 350-500℃, pressure 2.8-4 MPa), which is used to drive the steam turbine generator set.

[0027] Furthermore, the exhaust gas treatment assembly includes a dust collector 24, a chimney 26 connected to the outside atmosphere, and a No. 5 fan 25 connecting the dust collector 24 and the chimney 26; one outlet of the dust collector 24 is connected to the gas grading and distribution assembly via a No. 4 fan 21.

[0028] In the above setup, after the low-temperature flue gas enters the dust collector 24 for dust removal, part of it is drawn into the gas grading and distribution component by the No. 4 fan 21 and diluted to 3-5% low-concentration gas. The other part is drawn into the chimney 26 by the No. 5 fan 25 and then discharged into the atmosphere.

[0029] Example 2 This embodiment provides a circulating fluidized bed method for generating electricity using low-carbon coal gangue and low-concentration methane waste energy. It is applicable to the aforementioned circulating fluidized bed system for generating electricity using low-carbon coal gangue and low-concentration methane waste energy, and includes the following steps: S1. Coal gangue is fed into coal gangue feeding device 1. Limestone is fed into limestone feeding device 2 and then mixed at a mass ratio of 8:1. After being crushed by mixing crusher 3 to a particle size of less than 8mm, it is sent into combustion chamber 7.

[0030] S2, 3-8% low-concentration methane is extracted from the coal seam and preheated by the reflux control valve 23 and methane concentration sensor 22 before entering the methane grading and distribution system 20. It is mixed and diluted with the low-temperature flue gas entering through the No. 4 blower 21 to ensure that the methane concentration is maintained at 3-5%. After passing through the methane distribution and regulation system, part of the supply methane enters the bottom of the combustion chamber 7 through the No. 1 blower 11 and the primary air duct 10, and the other part of the supply methane enters the upper part of the combustion chamber 7 through the No. 2 blower 13 and the tertiary air duct 8. At the same time, external air enters the middle of the combustion chamber 7 through the No. 3 blower 19 and the secondary air duct 9, thus forming a three-level methane-air-methane distribution mode.

[0031] S3. The raw materials fed by the feeding assembly, combined with the three-stage air distribution, are mixed and combusted with the high-temperature bed material in the combustion assembly under fluidized conditions, generating a large amount of flue gas and heat. The heat generated by combustion is exchanged through the water-cooled wall 6. Under the heat transfer effect of the water-cooled wall 6, the furnace temperature is maintained at about 800-950℃, and the coal gangue quickly ignites and enters the stable combustion stage. During the combustion process, primary air is sent from the bottom of the furnace through primary air duct 10 at a temperature of about 280℃; secondary air is sent from the middle of the furnace through secondary air duct 9 at a temperature of about 300℃; and tertiary air is supplied parallel from the top of the furnace through tertiary air duct 8. The ash and slag after the coal gangue combustion enter the slag cooler 12 through the slag discharge port for cooling and discharge, and are used for cement building materials.

[0032] S4. The high-temperature flue gas carrying materials in the combustion assembly enters the return assembly. The high-temperature flue gas is separated from the unburned material by the action of the cyclone separator 4. Most of the solid unburned material is separated out and returns to the combustion assembly through the return port to burn again and release heat. The high-temperature flue gas enters the flue gas waste heat recovery assembly through the tail flue.

[0033] S5. High-temperature flue gas enters the flue gas waste heat recovery component from the tail flue, and undergoes heat exchange through heat exchanger 5, superheater 15 and economizer 18 respectively, and is transformed into low-temperature flue gas and discharged from the flue gas waste heat recovery component and enters the tail gas treatment component. S6. Boiler water 17 is preheated by economizer 18 and enters steam drum 16. The hot water in steam drum 16 is converted into saturated steam by heat exchanger 5 and returns to steam drum 16. The saturated steam enters superheater 15 from steam drum 16 and is converted into superheated steam 14 (temperature about 350-500℃, pressure 2.8-4 MPa), which is used to drive steam turbine generator set.

[0034] S7. After the low-temperature flue gas enters the dust collector 24 for dust removal, part of it is drawn into the gas classification and distribution component by the No. 4 fan 21, and the other part is drawn into the chimney 26 by the No. 5 fan 25 and then discharged into the atmosphere.

[0035] Example 3 In this embodiment, the coal gangue feed rate is 12 t / h, which is conveyed to the combustion chamber 7 via the coal gangue feeding device 1; the limestone feed rate is 1.8 t / h, and desulfurizing agent is supplemented through the limestone feeding device 2. The low-concentration methane concentration is 3.8%, which is detected by the methane concentration sensor 22 and diluted by the reflux control valve 23 to maintain at approximately 3.2–3.5%, and the temperature of the combustion chamber 7 is stabilized at 900℃. Under these conditions, the boiler feedwater 17 is preheated by the economizer 18 and then enters the steam drum 16, where it is converted into saturated steam via the heat exchanger 5, and then converted into superheated steam 14 via the superheater 15, reaching a temperature of 450℃ and a pressure of approximately 3.8 MPa. The resulting steam drives the steam turbine to generate electricity, increasing the power generation efficiency to 34%.

[0036] The exhaust gas, after being treated by cyclone separator 4 and dust collector 24, is emitted through chimney 26. The measured NOx emission concentration is approximately 45 mg / Nm³. 3 SO2 emission concentration is approximately 18 mg / Nm³. 3 After the ash is discharged through the ash cooler 12, the bricks are tested and their compressive strength is 15.16 MPa, which meets the MU15 clay brick standard in GB / T 5101-2017.

[0037] Example 4 In this embodiment, the coal gangue feed rate is 6 t / h, and the limestone feed rate is 1.2 t / h. The low-concentration methane gas with a methane concentration of approximately 5.0% is diluted to 4.0% by blower No. 4 21 and then fed into combustion chamber 7 in stages through gas grading and distribution system 20 and blowers No. 1 11, No. 2 13, and No. 3 19. The temperature inside combustion chamber 7 is approximately 870°C.

[0038] Under these operating conditions, the boiler outputs superheated steam at a temperature of approximately 410℃ and a pressure of 3.0 MPa. The system operates stably under medium to low loads. After treatment, the NOx concentration in the exhaust gas is below 50 mg / Nm³. 3 SO2 concentration is approximately 22 mg / Nm 3 After the ash is discharged through the ash cooler 12, the bricks are tested and their compressive strength is 12.25 MPa, which meets the MU10 clay brick standard in GB / T 5101-2017.

[0039] Example 5 Under high-load conditions, the coal gangue feed rate is 15 t / h, which is fed into the furnace through coal gangue feeding device 1; the limestone feed rate is 2.5 t / h, which is fed into the desulfurization system through limestone feeding device 2. The low-concentration methane concentration is 4.2%, which is maintained at 3.6–3.8% after dilution by the gas grading and distribution system 20. The temperature of combustion chamber 7 reaches 930℃.

[0040] The system outputs superheated steam 14 at a temperature of approximately 470℃ and a pressure of 4.0 MPa, increasing power generation efficiency to 35%. The exhaust gas, after being treated by dust collector 24, is emitted through chimney 26, with a NOx concentration of approximately 42 mg / Nm³. 3 SO2 concentration is approximately 16 mg / Nm 3 Dust concentration less than 8 mg / Nm 3 The ash produced after combustion is discharged through the ash cooler 12 and then used to make bricks for testing. Its compressive strength is 14.15 MPa, which meets the MU10 clay brick standard in GB / T5101-2017.

[0041] Example 6 Under low-load operating conditions, the coal gangue feed rate is about 5 t / h, the limestone feed rate is about 0.8 t / h, the gas concentration is about 3.2%, and after dilution by the reflux control valve 23, it is controlled at about 3.0%, and the temperature of the combustion chamber 7 is maintained at 820℃.

[0042] At this time, the boiler outputs superheated steam 14 at a temperature of approximately 380℃ and a pressure of 2.8 MPa, with a power generation efficiency of approximately 28%. The exhaust gas, after being purified by cyclone separator 4 and dust collector 24, is emitted through chimney 26, with a NOx concentration of less than 55 mg / Nm³. 3 SO2 concentration less than 22 mg / Nm 3 After the combustion ash is discharged through the ash cooler 12, it is used to make bricks and tested. The compressive strength is 11.37 MPa, which meets the MU10 clay brick standard in GB / T 5101-2017.

[0043] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A circulating fluidized bed system for power generation using low-carbon coal gangue and low-concentration methane waste heat, comprising a feeding assembly, a return assembly, a combustion assembly, a flue gas waste heat recovery assembly, a methane grading and distribution assembly, and a tail gas treatment assembly, characterized in that: The combustion assembly includes: a combustion chamber (7), a tertiary air duct (8) disposed on the upper part of the combustion chamber (7) and parallel to the air distribution, a secondary air duct (9) disposed in the middle part of the combustion chamber (7) and vertically to the air distribution, a primary air duct (10) disposed at the bottom of the combustion chamber (7) and vertically to the air distribution, a slag cooler (12) disposed at the slag discharge port of the combustion chamber (7), and a water-cooled wall (6) disposed inside the combustion chamber (7); The gas grading and distribution assembly includes: a gas grading and distribution system (20), a reflux control valve (23) connected to external low-concentration gas, a methane concentration sensor (22) installed between the gas grading and distribution system (20) and the reflux control valve (23), a No. 2 fan (13) whose inlet end is connected to the gas blower distribution system and whose outlet end is connected to the tertiary air duct (8), a No. 3 fan (19) whose inlet end is connected to the external air and whose outlet end is connected to the secondary air duct (9), a No. 1 fan (11) whose inlet end is connected to the gas blower distribution system and whose outlet end is connected to the primary air duct (10), and a No. 4 fan (21) whose inlet end is connected to the dust collector (24) and whose outlet end is connected to the gas grading and distribution system (20).

2. A circulating fluidized bed system for power generation using low-carbon coal gangue and low-concentration methane waste energy as described in claim 1, characterized in that: The gas grading and distribution system (20) dilutes the gas based on the data from the methane concentration sensor (22) and the flue gas after dust removal by the No. 4 fan (21).

3. A circulating fluidized bed system for power generation using low-carbon coal gangue and low-concentration methane waste energy as described in claim 2, characterized in that: The feeding assembly includes: a coal gangue feeding device (1), a limestone feeding device (2), and a mixing crusher (3) connected to the ends of the coal gangue feeding device (1) and the limestone feeding device (2).

4. A circulating fluidized bed system for power generation using low-carbon coal gangue and low-concentration methane waste energy as described in claim 3, characterized in that: The return assembly includes: an air inlet connected to a cyclone separator (4) in the combustion chamber (7), a tail flue of the cyclone separator (4) connected to a flue gas waste heat recovery assembly, and a return port of the cyclone separator (4) connected to the combustion assembly.

5. A circulating fluidized bed system for power generation using low-carbon coal gangue and low-concentration methane waste energy as described in claim 4, characterized in that: The flue gas waste heat recovery assembly includes: a heat exchanger (5) connected to the cyclone separator (4), a superheater (15) and an economizer (18) connected in sequence to the heat exchanger (5), and a steam drum (16) connected to the economizer (18); the economizer (18) is connected to the external boiler water (17), and the steam drum (16) is connected to the heat exchanger (5) and the superheater (15).

6. A circulating fluidized bed system for power generation using low-carbon coal gangue and low-concentration methane waste energy according to claim 5, characterized in that: The exhaust gas treatment assembly includes: a dust collector (24), a chimney (26) connected to the outside atmosphere, and a No. 5 fan (25) connecting the dust collector (24) and the chimney (26); one outlet of the dust collector (24) is connected to the gas grading and distribution assembly through a No. 4 fan (21).

7. A circulating fluidized bed method for generating electricity using low-carbon coal gangue and low-concentration methane waste energy, applicable to any of the circulating fluidized bed systems for generating electricity using low-carbon coal gangue and low-concentration methane waste energy as described in claims 1-6, characterized in that, Includes the following steps: S1. Coal gangue is fed into the coal gangue feeding device (1), limestone is fed into the limestone feeding device (2) and then mixed. After being crushed by the mixing crusher (3), it is sent into the combustion chamber (7). S2. After the gas is mined from the coal seam, it is preheated by the return control valve (23) and the methane concentration sensor (22) and then enters the gas grading and distribution system (20) to mix and dilute with the low-temperature flue gas entering through the No. 4 blower (21). After passing through the gas distribution and regulation system, part of the supply gas enters the bottom of the combustion chamber (7) through the No. 1 blower (11) and the primary air duct (10), and the other part of the supply gas enters the upper part of the combustion chamber (7) through the No. 2 blower (13) and the tertiary air duct (8). At the same time, the outside air enters the middle of the combustion chamber (7) through the No. 3 blower (19) and the secondary air duct (9), thus forming a gas-air-gas three-level air distribution mode. S3. The raw materials fed by the feeding assembly, along with the three-stage air distribution, are mixed and burned with the high-temperature bed material in the combustion assembly under fluidized conditions to generate a large amount of flue gas and heat. The heat generated by combustion is exchanged through the water-cooled wall (6). During the combustion process, primary air is sent from the bottom of the furnace through the primary air duct (10); secondary air is sent from the middle of the furnace through the secondary air duct (9); tertiary air is supplied parallel from the top of the furnace through the tertiary air duct (8); the ash and slag after the coal gangue combustion enter the slag cooler (12) through the slag discharge port, are cooled and discharged, and used for cement building materials. S4. The high-temperature flue gas carrying the material in the combustion component enters the return component. The high-temperature flue gas is separated from the unburned material by the action of the cyclone separator (4). Most of the solid unburned material is separated out and returns to the combustion component through the return port to burn again and release heat. The high-temperature flue gas enters the flue gas waste heat recovery component through the tail flue. S5. High-temperature flue gas enters the flue gas waste heat recovery component from the tail flue, and undergoes heat exchange through heat exchanger (5), superheater (15) and economizer (18) respectively, and is transformed into low-temperature flue gas and discharged from the flue gas waste heat recovery component and enters the tail gas treatment component. S6. Boiler water (17) is preheated by economizer (18) and enters steam drum (16). The hot water in steam drum (16) is converted into saturated steam by heat exchanger (5) and returned to steam drum (16). The saturated steam enters superheater (15) from steam drum (16) and is converted into superheated steam (14) to drive steam turbine generator set. S7. After the low-temperature flue gas enters the dust collector (24) for dust removal, part of it is drawn into the gas classification and distribution component by the No. 4 fan (21), and the other part is drawn into the chimney (26) by the No. 5 fan (25) and then discharged into the atmosphere.

8. A circulating fluidized bed method for generating electricity using low-carbon coal gangue and low-concentration methane waste energy according to claim 7, characterized in that: In S1, coal gangue and limestone are mixed at a mass ratio of 8:1 and then crushed to a particle size of less than 8 mm by a mixing crusher (3).

9. A circulating fluidized bed method for generating electricity using low-carbon coal gangue and low-concentration methane waste energy according to claim 7, characterized in that: In S2, the gas concentration after dilution by the gas grading and distribution system (20) is maintained at 3-5%.

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