Supercritical CO2 secondary reheating system based on steel mill waste gas and multi-energy combined supply method

Abstract

The invention discloses a supercritical CO2 secondary reheating system based on waste gas of a steel mill and a multi-energy combined supply method. A coke oven gas output pipeline, a blast furnace gas output pipeline and a converter gas output pipeline of the steel mill are connected with a gas classified collection unit; the fluidized bed reactor hearth is provided with a primary air inlet, a secondary air inlet, a coal feeding port, a hydrogen inlet and a carbon monoxide inlet; a carbon capture device is arranged on the downstream side of the tail flue and is connected with the coal gas classified collection unit; the coal gas classified collection unit is connected with a hydrocarbon separation module; the hydrocarbon separation module is provided with a carbon monoxide outlet, a carbon dioxide outlet and a hydrogen outlet; the carbon monoxide outlet is connected with the carbon monoxide inlet, the hydrogen outlet is connected with the hydrogen inlet, the carbon dioxide outlet is connected with the gas storage station, and the gas storage station is connected with the supercritical carbon dioxide secondary reheating system. According to the scheme, near-zero emission of hydrocarbon resources of a power plant of a steel mill is realized through graded purification and directional utilization.

Description

Technical Field

[0001] The present invention belongs to the field of combustion technology, and in particular relates to a supercritical CO2 secondary reheating system based on steel mill waste gas and a multi-energy co-supply method. Background Art

[0002] The steel industry's production process generates by-product gases such as coke oven gas, converter gas, and blast furnace gas, which need to be utilized more efficiently. Circulating fluidized bed boilers, on the other hand, contain a large amount of inert, hot bed material, preventing sudden flameouts during operation. Even if a boiler malfunctions and the main fuel is tripped, the furnace temperature does not drop suddenly. Therefore, circulating fluidized bed boilers have a low low-load stable combustion zone and can operate stably at 30% of rated load or less, thus offering promising application prospects. Existing technologies for both steel industry by-product gases and circulating fluidized bed boilers require improvement in energy efficiency. Furthermore, current requirements for carbon and hydrogen emissions from steel mills are increasing, and no effective solution is currently available. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to provide a supercritical CO2 secondary reheating system and a multi-energy cogeneration method based on steel plant waste gas, so as to solve the problems that the existing technology needs to improve in terms of energy utilization efficiency. The steel plant is combined with a circulating fluidized bed boiler, which not only realizes cogeneration of heat and power, but also effectively utilizes the steel plant process gas in the gas boiler, which helps the steel plant to achieve near-zero emissions of carbon and hydrogen resources and can provide a stable and reliable source of electricity for the steel plant.

[0004] According to the technical solution of the present invention, a supercritical CO2 secondary reheating system based on steel plant waste gas is provided, which includes a steel plant, a fluidized bed reactor, a gas classification collection unit and a supercritical carbon dioxide secondary reheating system; the coke oven gas output pipeline, the blast furnace gas output pipeline and the converter gas output pipeline of the steel plant are connected to the gas classification collection unit; the fluidized bed reactor includes a furnace, a cyclone separator and a tail flue connected in sequence; a primary air inlet, a secondary air inlet, a coal feeding port, a hydrogen inlet and a carbon monoxide inlet are provided on the furnace; the primary air inlet is located at the bottom of the furnace, the coal feeding port is located above the primary air inlet, the secondary air inlet and the hydrogen inlet are located above the coal feeding port, and the carbon monoxide inlet is located at the top of the furnace; a carbon capture device is provided on the downstream side of the tail flue, and the carbon capture device It is connected to the coal gas classification and collection unit; the coal gas classification and collection unit is connected to a hydrocarbon separation module, which has a carbon monoxide outlet, a carbon dioxide outlet and a hydrogen outlet; the carbon monoxide outlet is connected to the carbon monoxide inlet, the hydrogen outlet is connected to the hydrogen inlet, the carbon dioxide outlet is connected to the gas storage station, and the gas storage station is connected to the supercritical carbon dioxide secondary reheating system; the supercritical carbon dioxide secondary reheating system includes a high-temperature superheater, a high-pressure cylinder, a high-temperature reheater, a low-pressure cylinder and a low-pressure superheater connected in sequence, and the outlet of the low-pressure superheater is further connected to the low-pressure cylinder; the high-pressure cylinder and the low-pressure cylinder are coaxially connected to the generator; the high-temperature superheater is located in the furnace, the high-temperature reheater is located outside the fluidized bed reactor and is connected to the furnace through a material circulation pipeline, and the low-pressure superheater is located in the tail flue.

[0005] In some embodiments, a reducing agent spray gun is provided at the top inlet of the cyclone separator, and an SCR denitration catalyst layer is provided in the tail flue.

[0006] In some embodiments, a primary economizer and a secondary economizer are further provided in the tail flue, and a low-temperature superheater, a secondary economizer, an SCR denitrification catalyst layer, a primary economizer, and a carbon capture device are arranged in sequence along the flue gas transport direction.

[0007] In some embodiments, the hydrocarbon separation module further has a residual coke oven gas outlet, which is connected to the primary air inlet.

[0008] In some embodiments, the top of the furnace is connected to the top of the cyclone separator through an intermediate flue, and the bottom of the cyclone separator is connected to the furnace through a material return device.

[0009] In some embodiments, the furnace is further provided with an ash discharge port, and the height position of the ash discharge port is located between the primary air inlet and the coal feeding port.

[0010] According to the technical solution of the present invention, the present invention also provides a multi-energy cogeneration method, which adopts the supercritical CO2 secondary reheating system based on steel mill waste gas described in the present invention, and includes the following pretreatment steps: The coke oven gas generated by the steel plant is fed into the hydrocarbon separation module after desulfurization; The blast furnace gas generated by the steel plant is input into the hydrocarbon separation module after dust removal and residual pressure power generation; The converter gas generated by the steel plant is input into the hydrocarbon separation module after wet dust removal.

[0011] In some embodiments, after the pretreatment step, the hydrocarbon separation module further includes the following gas separation step: The pretreated coke oven gas is used to extract high-purity hydrogen through pressure swing adsorption or membrane separation. The purity of the high-purity hydrogen is greater than 99.9% and is transported to the hydrogen outlet. The remaining components of the pretreated coke oven gas are returned to the furnace of the fluidized bed reactor with the primary air for combustion. The pre-treated converter gas is subjected to low-temperature distillation to separate carbon monoxide, with a purity of >98%, and transported to the carbon monoxide outlet; The remaining components of the pretreated converter gas and the pretreated blast furnace gas are enriched with carbon dioxide using chemical absorption or low-temperature separation methods. After the carbon dioxide is purified to more than 95%, it is transported to the carbon dioxide outlet and then pressurized and liquefied and stored in a gas storage station.

[0012] In some embodiments, high-purity hydrogen is heated by waste heat treatment in a steel plant and then injected into the furnace, and the hydrogen blending ratio is 5% to 20%.

[0013] In some embodiments, the primary air and the secondary air are heated by the waste heat treatment of the steel plant and then injected into the furnace.

[0014] Compared with the prior art, the beneficial technical effects of the present invention are as follows: The supercritical CO2 secondary reheating system and multi-energy co-supply method based on steel mill waste gas of the present invention enriches carbon dioxide, hydrogen and carbon monoxide in three types of coal gases, namely coke oven gas, converter gas and blast furnace gas, of the steel mill through graded purification and targeted utilization, and applies them to the working medium circulation of the supercritical carbon dioxide secondary reheating system and the combustion system of the fluidized bed reactor, thereby achieving near-zero emissions of carbon and hydrogen resources of the steel plant power plant; moreover, the carbon dioxide working medium circulating in the supercritical carbon dioxide secondary reheating system is directly derived from the steel mill waste gas and the fluidized bed combustion tail gas, forming a "capture-utilization-recapture" closed loop, thereby reducing dependence on external carbon sources. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a schematic diagram of the system structure provided by the present invention.

[0016] Description of reference numerals in the accompanying drawings: 1. Coal gas classification and collection unit; 11. Hydrocarbon separation module; 2. Supercritical carbon dioxide secondary reheating system; 21. High-temperature superheater; 22. High-pressure cylinder; 23. High-temperature reheater; 24. Low-pressure cylinder; 25. Low-temperature superheater; 31. Furnace; 311. Primary air inlet; 312. Secondary air inlet; 313. Coal feed port; 314. Hydrogen inlet; 315. Carbon monoxide inlet; 316. Ash discharge port; 32. Cyclone separator; 321. Reductant spray gun; 322. Intermediate flue; 323. Return device; 33. Tail flue; 331. Primary economizer; 332. Secondary economizer; 333. SCR denitrification catalyst layer; 4. Carbon capture device; 5. Gas storage station. DETAILED DESCRIPTION

[0017] The present invention provides a supercritical CO2 secondary reheating system and a multi-energy co-supply method based on steel mill waste gas, which mainly involve hydrogen-doped fluidized bed combustion technology and supercritical CO2 secondary reheating technology. It aims to solve the problems that the existing technology needs to improve in terms of energy utilization efficiency. By combining the steel mill with a circulating fluidized bed boiler, not only cogeneration of heat and power is achieved, but also the steel mill process gas is effectively utilized in the gas boiler, which helps the steel mill to achieve near-zero emissions of carbon and hydrogen resources and can provide a stable and reliable source of electricity for the steel mill.

[0018] See also Figure 1 The present invention provides a supercritical CO2 secondary reheating system based on steel plant waste gas, which includes a steel plant, a fluidized bed reactor, a gas classification and collection unit 1 and a supercritical carbon dioxide secondary reheating system 2.

[0019] One of the key innovations of this solution is the integration of fluidized bed combustion technology with steel mills, for example by building a small power plant within or near the steel mill. The steel mill's coke oven gas, blast furnace gas, and converter gas output pipelines are connected to the gas classification and collection unit 1, allowing the gases from these byproducts to be efficiently utilized in the fluidized bed reactor combustion system.

[0020] The fluidized bed reactor includes a furnace 31, a cyclone separator 32, and a tail flue 33, which are connected in sequence. The furnace 31 is provided with a primary air inlet 311, a secondary air inlet 312, a coal feed port 313, a hydrogen inlet 314, and a carbon monoxide inlet 315. The primary air inlet 311 is located at the bottom of the furnace 31, the coal feed port 313 is located above the primary air inlet 311, the secondary air inlet 312 and the hydrogen inlet 314 are located above the coal feed port 313, and the carbon monoxide inlet 315 is located at the top of the furnace 31. More specifically, the secondary air inlet 312 and the hydrogen inlet 314 are located on the left and right walls of the cold wall of the furnace 31. The primary and secondary air are supplied in layers to optimize the air volume. High-purity hydrogen is injected into the furnace for mixed combustion, which helps to improve combustion stability. Carbon monoxide is injected into the reduction zone at the top of the furnace 31 through an independent pipe, reacting with NOx in the combustion flue gas to reduce nitrogen oxide emissions. A carbon capture device 4 is provided on the downstream side of the tail flue 33 , and the carbon capture device 4 is connected to the coal gas classification collection unit 1 , so that the carbon dioxide in the tail gas of the fluidized bed reactor is also recovered to the coal gas classification collection unit 1 .

[0021] The coal gas classification collection unit 1 is connected to a hydrocarbon separation module 11, which has a carbon monoxide outlet, a carbon dioxide outlet, and a hydrogen outlet. The carbon monoxide outlet is connected to the carbon monoxide inlet 315, the hydrogen outlet is connected to the hydrogen inlet 314, and the carbon dioxide outlet is connected to the gas storage station 5, which is connected to the supercritical carbon dioxide secondary reheat system 2.

[0022] The CO2 working fluid of the supercritical carbon dioxide secondary reheating system 2 comes from the hydrocarbon separation module and the fluidized bed combustion tail gas carbon capture. The structure adopts high-pressure and low-pressure dual cylinders, and the work capacity of the CO2 working fluid is improved through double reheating. Figure 1The dashed line represents the flow direction of the CO2 working fluid, including heat transfer and work production. Specifically, the supercritical CO2 secondary reheat system 2 comprises a high-temperature superheater 21, a high-pressure cylinder 22, a high-temperature reheater 23, a low-pressure cylinder 24, and a low-temperature superheater 25, which are connected in sequence. The outlet of the low-temperature superheater 25 is further connected to the low-pressure cylinder 24. The high-pressure cylinder 22 and the low-pressure cylinder 24 are coaxially connected to the generator. The high-temperature superheater 21 is located within the furnace 31, while the high-temperature reheater 23 is located outside the fluidized bed reactor (i.e., arranged in an external bed) and connected to the furnace 31 via a material circulation line for heat exchange. The low-temperature superheater 25 is located in the tail flue 33, and its temperature is controlled by adjusting the flue damper and the ash content in the external bed. The high-temperature reheater 23 is designed to be placed in the external bed, which provides more flexible control over temperature, combustion, and heat transfer than an internal bed. As a supplementary explanation, the low-pressure cylinder exhaust pipeline of the low-pressure cylinder 24 is ultimately connected to the gas box, and the gas box outlet is then connected to the inlet of the high-temperature superheater 21 to form a circulation of the carbon dioxide working medium; the gas storage station 5 is connected to the gas box so as to be able to adjust the total amount of carbon dioxide working medium circulation in the supercritical carbon dioxide secondary reheating system 2.

[0023] The composition, output and theoretical combustion temperature of various coal gases are shown in Table 1 below.

[0024] Table 1 Composition and characteristics of steelmaking by-product gas

[0025] It can be seen that coke oven gas contains more hydrogen, blast furnace gas contains more carbon dioxide, and converter gas contains more carbon monoxide and carbon dioxide, so they can be used in combustion systems and supercritical carbon dioxide secondary reheating systems.

[0026] Circulating fluidized bed boilers contain a large amount of inert, hot bed material, preventing sudden flameouts during operation. Even if a boiler malfunction causes a main fuel trip, the furnace temperature will not drop suddenly. Therefore, the low-load stable combustion zone of circulating fluidized bed boilers is relatively low, allowing stable operation at 30% of rated load or less. During low-load operation, hydrogen-blended combustion can further improve combustion stability. This allows the recovery and utilization of hydrogen contained in coke oven gas, leading to the development of efficient, energy-saving, and environmentally friendly co-firing technologies for circulating fluidized bed boilers.

[0027] Secondary reheat technology is currently a major development trend in thermal power generation. Under frequently fluctuating loads, secondary reheat units suffer from low economic performance and limited flexibility. Steel mill blast furnace gas and converter gas can provide CO2 as a working fluid for the turbine cycle system, maintaining high unit thermal efficiency under variable load conditions.

[0028] Furthermore, the fluidized bed reactor also includes an SCR denitrification device, which includes a reductant spray gun 321 located at the top inlet of the cyclone separator 32. An SCR denitrification catalyst layer 333 is installed within the tail flue 33. More specifically, the tail flue 33 also includes a primary economizer 331 and a secondary economizer 332. The low-temperature superheater 25, the secondary economizer 332, the SCR denitrification catalyst layer 333, the primary economizer 331, and the carbon capture device 4 are arranged in sequence along the flue gas conveyance direction. In this embodiment, a layer of SCR catalyst is added between the secondary economizer 332 and the primary economizer 331 to form the SCR denitrification catalyst layer 333.

[0029] It should be noted that during normal operation of a circulating fluidized bed boiler, the locations that can meet the required denitrification reduction reaction temperatures include the furnace outlet (840°C-870°C), the cyclone inlet (960°C-1000°C), and the superheating section from the cyclone outlet to the high-temperature superheater (higher than the inlet) (860°C-900°C). A comparative analysis shows that injecting the reducing agent at the furnace outlet has the longest reaction time but requires significant boiler water-cooled wall modifications. Injecting the reducing agent in the transition section from the cyclone outlet to the high-temperature superheater (higher than the inlet) results in a shorter reaction time, resulting in low denitrification efficiency and increased ammonia slip. The cyclone inlet is connected by a steel plate with an internal castable, making it suitable for opening and injecting the reducing agent. After the cyclone inlet is stirred, the reactants are evenly mixed, and the reaction time at the rear end is prolonged, allowing the reducing agent to fully react with NOx in the flue gas and minimizing ammonia slip. Therefore, in this solution, the reducing agent spray gun 321 is preferably installed at the cyclone inlet.

[0030] Preferably, the hydrocarbon separation module 11 further has a residual coke oven gas outlet, which is connected to the primary air inlet 311, and returns the coke oven gas after hydrogen extraction to the fluidized bed for combustion, so as to be fully utilized.

[0031] More specifically, the top of the furnace 31 is connected to the top of the cyclone separator 32 via an intermediate flue 322, while the bottom of the cyclone separator 32 is connected to the furnace 31 via a return device 323. The outlet of the return device 323 corresponds to the coal feed port 313, for example, at a similar height and located on the left and right side walls of the cold wall of the furnace 31. The furnace 31 is also equipped with an ash discharge port 316 for discharging ash. The ash discharge port 316 is located between the primary air inlet 311 and the coal feed port 313.

[0032] It is understandable that each pipeline component in the system is further provided with valves and a power system as required to control the delivery of each substance as needed.

[0033] The operating principle of the system of the exemplary embodiment of the present invention is as follows.

[0034] Hot primary air entering from beneath the bed of a circulating fluidized bed boiler fully fluidizes the bed material and coal particles (less than 8mm in size). Ignition ignites beneath the bed, causing intense collision and heat exchange between the coal particles and the bed material. Large particles burn within the bed, while fine particles flow with the flue gas to the dilute phase region above the furnace, where they continue to burn and exchange heat. Some of these fine particles aggregate into large clusters, unable to overcome gravity, and move downward near the furnace wall, while the relatively dilute gas-solid phase in the center of the furnace continues to move upward, forming a strong internal circulation of particles. This relatively dilute gas-solid phase, carrying a large number of unburned particles, leaves the furnace and enters a cyclone separator, which separates most of the material particles carried in the flue gas. These particles are then returned to the furnace bed via a return device for continued combustion and utilization, forming a large external circulation of materials. The boiler's combustion status is primarily determined by the bed temperature and bed pressure.

[0035] When the circulating fluidized bed boiler is operating at, for example, 30% of the rated load or lower, hydrogen recovered from the coke oven gas is added to improve combustion stability. The primary air temperature is, for example, 130°C to 150°C. The secondary air of the circulating fluidized bed boiler is used to control the total air volume and provide the oxygen required for combustion of the unburned fuel in the dilute phase zone at the upper part of the furnace. The ratio of secondary air to primary air is preferably 2.2 to 2.5. A CO inlet is provided at the top of the fluidized bed and injected into the reduction zone through an independent pipe to react with NOx in the combustion flue gas to reduce nitrogen oxide emissions. In addition, a reducing agent spray gun is added at the flue gas outlet of the cyclone separator, and a layer of SCR catalyst is added between the secondary economizer and the primary economizer of the circulating fluidized bed boiler. The staged air distribution and SCR denitrification technologies work together to effectively control the emission of nitrogen oxides.

[0036] The steel mill's blast furnace gas and converter gas provide the CO2 working fluid for the secondary reheat system. Supercritical CO2 first passes through a high-temperature superheater, then reaches the high-temperature reheater after performing work in the high-pressure cylinder. It then enters the low-pressure cylinder, performs work, enters the low-pressure superheater, and finally exits the low-pressure cylinder after performing work, completing a cycle. This system maintains high unit thermal efficiency under variable load conditions, providing the steel mill with a stable and reliable source of power.

[0037] Based on the above technical solution of the present invention, the present invention provides a multi-energy co-generation method, which includes the following pretreatment steps: The coke oven gas generated by the steel plant is input into the hydrocarbon separation module 11 after desulfurization; The blast furnace gas generated by the steel plant is input into the hydrocarbon separation module 11 after dust removal and residual pressure power generation; The converter gas generated in the steel plant is input into the hydrocarbon separation module 11 after wet dust removal.

[0038] In addition, the combustion tail gas of the fluidized bed reactor enters the carbon capture device 4 to obtain carbon dioxide which is input into the hydrocarbon separation module 11 .

[0039] Furthermore, after the pretreatment step, the hydrocarbon separation module 11 further includes the following gas separation steps: The pretreated coke oven gas is subjected to pressure swing adsorption or membrane separation to extract high-purity hydrogen with a purity of >99.9%, which is then transported to the hydrogen outlet. The remaining components of the pretreated coke oven gas are returned to the furnace 31 of the fluidized bed reactor with the primary air for combustion. The pretreated converter gas is subjected to low-temperature distillation to separate carbon monoxide. Specifically, a low-temperature distillation tower is used at a temperature of -180°C to -150°C. The purity of the carbon monoxide is greater than 98%, and the carbon monoxide is transported to a carbon monoxide outlet. The remaining components of the pretreated converter gas (mainly carbon dioxide) and the pretreated blast furnace gas are enriched with carbon dioxide using chemical absorption or low-temperature separation methods. After the carbon dioxide is purified to more than 95%, it is transported to the carbon dioxide outlet and then pressurized and liquefied and stored in the gas storage station 5.

[0040] The carbon dioxide from the carbon capture device 4 is also transported to the carbon dioxide outlet, and then pressurized and liquefied and stored in the gas storage station 5.

[0041] Preferably, high-purity hydrogen is injected into the furnace 31 through the hydrogen inlet 314 only when the fluidized bed reactor is operating at medium or low load (for example, 30% of the rated load or lower), and the high-purity hydrogen is heated by the steel plant waste heat treatment and then injected into the furnace 31 to fully utilize the steel plant waste heat; the hydrogen mixing ratio is 5% to 20% to avoid coking caused by excessive temperature in the fluidized bed.

[0042] Similarly, the primary and secondary air are preferably heated by the steel mill waste heat treatment before being injected into the furnace 31. Heating by the steel mill waste heat treatment can be achieved by, for example, using only the steel mill waste heat system for heating, without an air preheater in the fluidized bed reactor, or by combining the steel mill waste heat system with the air preheater of the fluidized bed reactor to achieve heating together.

[0043] In summary, the supercritical CO2 secondary reheating system and multi-energy co-supply method based on steel plant waste gas of the present invention enriches the carbon dioxide, hydrogen and carbon monoxide in the three types of coal gas, namely coke oven gas, converter gas and blast furnace gas of the steel plant through graded purification and targeted utilization, and applies them to the working fluid circulation of the supercritical carbon dioxide secondary reheating system and the combustion system of the fluidized bed reactor, thereby achieving near-zero emissions of carbon and hydrogen resources in the steel plant power plant; moreover, the carbon dioxide working fluid circulating in the supercritical carbon dioxide secondary reheating system is directly derived from the steel plant waste gas and the fluidized bed combustion tail gas, forming a "capture-utilization-recapture" closed loop, thereby reducing dependence on external carbon sources.

[0044] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; obviously, the embodiments described are part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention; for ease of description, only the parts related to the relevant inventions are shown in the accompanying drawings. In the absence of conflict, the embodiments of the present invention and the features in the embodiments can be combined with each other; modifying the technical solutions described in the aforementioned embodiments, or making equivalent replacements for some of the technical features therein, does not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A supercritical CO2 secondary reheating system based on steel mill waste gas, characterized in that: It includes a steel plant, a fluidized bed reactor, a gas classification collection unit (1) and a supercritical carbon dioxide secondary reheating system (2); The coke oven gas output pipeline, blast furnace gas output pipeline, and converter gas output pipeline of the steel plant are connected to the gas classification collection unit (1); The fluidized bed reactor comprises a furnace (31), a cyclone separator (32) and a tail flue (33) connected in sequence; the furnace (31) is provided with a primary air inlet (311), a secondary air inlet (312), a coal feeding port (313), a hydrogen inlet (314) and a carbon monoxide inlet (315); the primary air inlet (311) is located at the bottom of the furnace (31), the coal feeding port (313) is located above the primary air inlet (311), the secondary air inlet (312) and the hydrogen inlet (314) are located above the coal feeding port (313), and the carbon monoxide inlet (315) is located at the top of the furnace (31); a carbon capture device (4) is provided on the downstream side of the tail flue (33), and the carbon capture device (4) is connected to the coal gas classification collection unit (1); The coal gas classification collection unit (1) is connected to a hydrocarbon separation module (11), and the hydrocarbon separation module (11) has a carbon monoxide outlet, a carbon dioxide outlet, and a hydrogen outlet; the carbon monoxide outlet is connected to a carbon monoxide inlet (315), the hydrogen outlet is connected to a hydrogen inlet (314), the carbon dioxide outlet is connected to a gas storage station (5), and the gas storage station (5) is connected to a supercritical carbon dioxide secondary reheating system (2); The supercritical carbon dioxide secondary reheating system (2) includes a high-temperature superheater (21), a high-pressure cylinder (22), a high-temperature reheater (23), a low-pressure cylinder (24) and a low-temperature superheater (25) which are connected in sequence, and the outlet of the low-pressure superheater (25) is connected to the low-pressure cylinder (24); the high-pressure cylinder (22) and the low-pressure cylinder (24) are coaxially connected to the generator; the high-temperature superheater (21) is located in the furnace (31), the high-temperature reheater (23) is located outside the fluidized bed reactor and is connected to the furnace (31) through a material circulation pipeline, and the low-temperature superheater (25) is located in the tail flue (33).

2. The supercritical CO2 secondary reheating system based on steel mill waste gas according to claim 1 is characterized in that: A reducing agent spray gun (321) is provided at the top inlet of the cyclone separator (32), and an SCR denitration catalyst layer (333) is provided in the tail flue (33).

3. The supercritical CO2 secondary reheating system based on steel mill waste gas according to claim 2 is characterized in that: A first-stage economizer (331) and a second-stage economizer (332) are also provided in the tail flue (33), and a low-temperature superheater (25), a second-stage economizer (332), an SCR denitration catalyst layer (333), a first-stage economizer (331), and a carbon capture device (4) are sequentially arranged along the flue gas conveying direction.

4. The supercritical CO2 secondary reheating system based on steel mill waste gas according to claim 1 is characterized in that: The hydrocarbon separation module (11) also has a residual coke oven gas outlet, which is connected to the primary air inlet (311).

5. The supercritical CO2 secondary reheating system based on steel mill waste gas according to claim 1 is characterized in that: The top of the furnace (31) is connected to the top of the cyclone separator (32) through the intermediate flue (322), and the bottom of the cyclone separator (32) is connected to the furnace (31) through the return device (323).

6. The supercritical CO2 secondary reheating system based on steel mill waste gas according to claim 1 is characterized in that: The furnace (31) is further provided with an ash discharge port (316), and the height position of the ash discharge port (316) is located between the primary air inlet (311) and the coal feeding port (313).

7. A multi-energy co-generation method, characterized in that: It adopts the supercritical CO2 secondary reheating system based on steel mill waste gas according to any one of claims 1 to 6, which includes the following pretreatment steps: The coke oven gas produced by the steel plant is desulfurized and then fed into the hydrocarbon separation module (11); The blast furnace gas generated by the steel plant is input into the hydrocarbon separation module (11) after dust removal and residual pressure power generation; The converter gas generated in the steel plant is fed into the hydrocarbon separation module (11) after wet dust removal.

8. The multi-energy cogeneration method according to claim 7, characterized in that: After the pretreatment step, the hydrocarbon separation module (11) further includes the following gas separation steps: The pretreated coke oven gas is subjected to pressure swing adsorption or membrane separation to extract high-purity hydrogen, the purity of the high-purity hydrogen being greater than 99.9%, and is transported to a hydrogen outlet; the remaining components of the pretreated coke oven gas are returned to the furnace (31) of the fluidized bed reactor along with the primary air for combustion; The pre-treated converter gas is subjected to low-temperature distillation to separate carbon monoxide, with a purity of >98%, and transported to the carbon monoxide outlet; The remaining components of the pretreated converter gas and the pretreated blast furnace gas are enriched with carbon dioxide using chemical absorption or cryogenic separation methods. The carbon dioxide is purified to more than 95% and then transported to the carbon dioxide outlet, where it is pressurized, liquefied, and stored in a gas storage station (5).

9. The multi-energy cogeneration method according to claim 8, characterized in that: High-purity hydrogen is heated by waste heat treatment in a steel plant and then injected into the furnace (31), with the hydrogen mixing ratio being 5% to 20%.

10. The multi-energy cogeneration method according to claim 7, characterized in that: The primary air and secondary air are heated by the steel mill waste heat treatment and then injected into the furnace (31).

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