High-efficiency catalytic conversion device and method for steel plant lime kiln tail gas co2

Abstract

This invention discloses a high-efficiency catalytic conversion device and method for CO2 in lime kiln tail gas of steel plants. The high-efficiency catalytic conversion device for CO2 in lime kiln tail gas of steel plants includes a tail gas collection unit, an impurity adaptive pretreatment unit, a waste heat classification and utilization unit, a CO2 catalytic conversion unit, a product separation unit, and a circulation regulation unit arranged sequentially along the tail gas flow direction. The impurity adaptive pretreatment unit has a composite filter bag dust removal module that can remove dust and SO2 from the tail gas and a priority oxidation reforming module that can oxidize part of the CO in the tail gas to CO2. The waste heat classification and utilization unit divides the tail gas waste heat into three levels through a heat exchanger and a heat distribution controller. The low-temperature waste heat is used for preheating before the CO2 catalytic conversion of the raw material gas, the medium-temperature waste heat is used for reaction heating in the methanation reactor, and the high-temperature waste heat is used for electrolysis power supply in the solid oxide electrolysis cell. This can realize the on-site high-efficiency capture and high-value conversion of CO2 in lime kiln tail gas, which is very suitable for the existing energy conditions of steel plants.

Description

Technical Field

[0001] This invention relates to the technical field of CO2 high-value utilization, and in particular to the technical field of efficient catalytic conversion of CO2 in lime kiln tail gas of steel plants. Background Technology

[0002] The steel industry is one of the world's major sources of CO2 emissions. Lime kilns, as key auxiliary equipment in steel production, produce exhaust gases with high CO2 concentrations (typically 25%~35%), along with small amounts of dust, CO, SO2, and other impurities. These gases are a high-quality source of raw materials for the high-value utilization of CO2. Currently, CO2 treatment in the steel industry mainly relies on capture and storage, which suffers from high energy consumption, high costs, and no added value. However, CO2 high-value conversion technology can transform CO2 into high-value-added chemicals or fuels, turning waste into treasure, and is an important development direction for carbon emission reduction in the steel industry.

[0003] Existing CO2 catalytic conversion technologies face the following compatibility challenges, making them difficult to directly apply to the tail gas scenario of lime kilns in steel plants: Firstly, the composition of lime kiln tail gas is complex (containing a high concentration of oxygen (10%~15%) as well as impurities such as sulfur dioxide and dust). Most existing CO2 catalytic conversion processes are designed based on high-purity CO2 feed gas, which has poor tolerance to impurities in lime kiln tail gas. It is easy for dust and SO2 to cause catalyst poisoning and failure, as well as corrosion of pipelines and equipment, making it difficult to ensure long-term stable operation of the system. Secondly, regarding waste heat utilization, the temperature range of lime kiln exhaust gas is 300~1000℃ (containing a large amount of medium and high temperature waste heat), but the existing catalytic methanation process has poor matching with the kiln waste heat temperature, the waste heat cascade utilization design is lacking, and the comprehensive utilization rate of waste heat is generally less than 40%. Third, existing CO2 catalytic conversion technologies generally suffer from poor catalyst stability. The C=O bond energy in the CO2 molecule is extremely high (breaking this chemical bond requires a high energy input), while conventional copper-based catalysts are prone to deactivation phenomena such as sintering, oxidation, and carbon deposition under high-temperature hydrogenation conditions, resulting in a rapid decrease in conversion efficiency over time. Moreover, the reaction process often needs to be carried out under high temperature and high pressure conditions (resulting in high overall energy consumption). At the same time, existing catalytic conversion systems are also difficult to adapt to fluctuations in tail gas flow and CO2 concentration caused by load fluctuations in steel plants (when the load fluctuation is greater than 20%, the system efficiency decreases significantly). Fourth, existing CO2 catalytic conversion catalysts mostly rely on precious metals, which are costly, and it is difficult to balance catalytic efficiency and selectivity. Fifth, the existing conversion routes are too simplistic and have not been optimized in conjunction with the actual energy conditions (industrial water, electricity, steam, compressed air) of the steel plant, making it difficult to achieve engineering demonstration and stable operation.

[0004] In summary, developing a CO2 catalytic conversion device and method that is suitable for the tail gas of lime kilns in steel plants, has strong impurity tolerance, high waste heat utilization rate, good stability, and is engineerable has become one of the urgent technical problems to be solved. Summary of the Invention

[0005] This invention addresses the problems of poor impurity tolerance, unreasonable waste heat utilization, insufficient system stability, and poor engineering adaptability in the application of existing CO2 catalytic conversion technologies in lime kiln tail gas of steel plants. It provides a high-efficiency catalytic conversion device and method for CO2 in lime kiln tail gas of steel plants, which can realize the on-site efficient capture and high-value conversion of CO2 in lime kiln tail gas. It is well-suited to the existing energy conditions of steel plants, can reduce carbon emission reduction costs, and at the same time increase the added value of CO2 conversion, thus contributing to the carbon recycling of the steel industry.

[0006] To achieve the above objectives, this invention proposes a high-efficiency catalytic conversion device for CO2 in the tail gas of a lime kiln in a steel plant. The device includes a tail gas collection unit, an impurity adaptive pretreatment unit, a waste heat classification and utilization unit, a CO2 catalytic conversion unit, a product separation unit, and a circulation regulation unit, arranged sequentially along the tail gas flow direction. The tail gas collection unit is connected to the tail gas emission port of the lime kiln in the steel plant via a collection pipe simultaneously equipped with a flow meter and a pressure sensor. The impurity adaptive pretreatment unit has a composite filter bag dust removal module capable of removing dust and SO2 from the tail gas, and a preferential oxidation reforming module capable of partially oxidizing CO in the tail gas to CO2. The CO2 catalytic conversion unit utilizes a solid oxide electrolysis cell and a methanation... The reactor first electrolyzes the feed gas, which is a mixture of tail gas and water vapor, to generate syngas, which is then catalytically converted into methane. The waste heat utilization unit divides the tail gas waste heat into three levels through a heat exchanger and a heat distribution controller: low-temperature waste heat is used for preheating the feed gas before CO2 catalytic conversion, medium-temperature waste heat is used for heating the reaction in the methanation reactor, and high-temperature waste heat is used for electrolysis in the solid oxide electrolysis cell. The product separation unit sequentially cools, separates, and purifies the reaction products through a cooler, a separator, and a purification module. The circulation regulation unit returns the unconverted CO2 and syngas after product separation to the CO2 catalytic conversion unit for re-reaction through circulation pipelines, a flow controller, and a pressure regulation module.

[0007] Preferably, the composite filter bag dust removal module uses a filter bag with a composite felt layer structure of expanded polytetrafluoroethylene membrane and catalyst polytetrafluoroethylene with a pore size of 0.01~0.05μm, and the preferential oxidation reforming module is filled with Fe2O3-MoO3 catalyst with a reaction temperature of 280~350℃.

[0008] Preferably, the methanation reactor adopts an isothermal multi-stage structure with an inlet temperature controlled at 200±50℃ and a space velocity of 5000~10000h. -1The methanation reactor is filled with a CuO-MnO2-CeO2 composite catalyst and the catalyst bed temperature is controlled at 450±50℃. The mass ratio of CuO, MnO2 and CeO2 in the CuO-MnO2-CeO2 composite catalyst is 3~5:2~4:1~3.

[0009] Preferably, the system also includes an energy supply unit that provides the required energy to each unit via industrial water pipes, a power supply module, a steam pipe, and a compressed air pipe.

[0010] A method for efficient catalytic conversion of CO2 from tail gas of lime kiln in steel plant, based on the aforementioned efficient catalytic conversion device for CO2 from tail gas of lime kiln in steel plant, includes the following steps: S1. Exhaust gas collection: The exhaust gas collection unit collects exhaust gas from the lime kiln of the steel plant and sends it to the impurity adaptive pretreatment unit. S2. Impurity pretreatment: The exhaust gas first passes through the composite filter bag dust removal module to remove dust and SO2, then passes through the priority oxidation reforming module to oxidize some CO into CO2, and then is sent to the waste heat classification and utilization unit. S3. Waste heat classification and utilization: The heat exchanger and heat distribution controller divide the exhaust waste heat into high temperature waste heat, medium temperature waste heat and low temperature waste heat, which are respectively used for electrolysis energy supply, reaction heating and feed gas preheating of CO2 catalytic conversion unit. S4, CO2 catalytic conversion: The feed gas, which is a mixture of tail gas and water vapor, is preheated and first enters a solid oxide electrolysis cell to generate synthesis gas, which is then catalytically converted into methane in a methanation reactor; S5. Product separation and purification: The reaction products are sequentially passed through a cooler, a separator and a purification module for cooling, water separation and methane purification to obtain methane products. S6. Circulation Regulation: The unconverted CO2 after product separation is sent back to the CO2 catalytic conversion unit for re-reaction via circulation pipeline, flow controller and pressure regulation module.

[0011] Preferably, in step S1, the exhaust gas flow rate adjustment range is 500~2000 Nm. 3 / h, exhaust gas pressure is controlled at 0.1~0.3MPa.

[0012] Preferably, in step S2, the preferential oxidation reforming module adjusts the CO / CO2 molar ratio to 0.8~1.2.

[0013] Preferably, in step S3, the temperature of the high-temperature waste heat is 700~1000℃, the temperature of the medium-temperature waste heat is 400~600℃, the temperature of the low-temperature waste heat is 200~400℃, and the raw material gas is preheated to 200±50℃.

[0014] Preferably, in step S4, the solid oxide electrolytic cell has a coated anode and a double-layer cathode, and operates at a temperature of 750~950℃ and a current density of 0.6~1.2A / cm². 2 The molar ratio of CO2 to water vapor in the raw material gas is 1:1.2~1.8, and the molar ratio of H2 to CO in the synthesis gas is 3:0.5~1.5.

[0015] Preferably, in step S6, the system pressure is stabilized at 0.1~0.3MPa, and the recycling ratio of unconverted CO2 to syngas is 10~15%.

[0016] The beneficial effects of this invention are: 1) Integrated pretreatment design with strong impurity adaptability and prevention of catalyst poisoning: This invention innovatively adopts a composite filter bag dust removal module combined with a priority oxidation and reforming module to form an integrated impurity adaptive pretreatment structure, abandoning the traditional multi-stage complex pretreatment process and eliminating the need for additional large-scale supporting purification equipment; Among them, the expanded polytetrafluoroethylene composite filter bag can accurately intercept tail gas dust and simultaneously remove SO2 corrosive impurities in the tail gas, while the supporting Fe2O3-MoO3 catalytic reforming system can directionally oxidize part of CO, stabilizing the tail gas CO / CO2 molar ratio in the range of 0.8~1.2. This completely eliminates the problems of catalyst poisoning and equipment inner wall corrosion caused by dust and sulfides, ensuring long-term continuous operation of the device. On the other hand, it supplements the CO2 feed gas volume through CO directional conversion, fully adapting to the original gas source characteristics of large fluctuations in the composition of lime kiln tail gas and many types of impurities. While simplifying the process flow, it reduces the investment in equipment infrastructure and pipeline operation resistance, ensuring the stability of subsequent CO2 catalytic conversion processes from the gas source. 2) Three-stage distribution of waste heat from tail gas significantly improves waste heat utilization and reduces production energy consumption: This invention relies on the heat exchanger and heat distribution controller of the waste heat grading utilization unit to precisely divide the waste heat from the kiln tail gas at 300~1000℃ into three temperature zones: 700~1000℃ high-temperature waste heat, 400~600℃ medium-temperature waste heat, and 200~400℃ low-temperature waste heat, achieving targeted energy supply. Among them, the high-temperature waste heat is dedicated to the electrolysis of the solid oxide electrolysis cell, reducing the consumption of external high-power electricity; the medium-temperature waste heat is matched with the heat source required for the methanation reactor reaction, eliminating the energy consumption of the external heating furnace of the reactor; and the low-temperature waste heat is used to preheat the raw gas to the heat energy required for the process, fully recovering low-grade waste heat. This invention, through the coupling utilization of waste heat with the entire process reaction, can increase the overall waste heat utilization rate to over 65%, greatly reducing the energy consumption of external public works for the entire catalytic conversion system and effectively compressing the production cost of CO2 resource-based methane production. 3) Full-process load adaptive control, resistant to large fluctuations in tail gas conditions, and excellent engineering adaptability: This invention is equipped with a circulation adjustment unit at the product end. It relies on the linkage of circulation pipelines, flow controllers and pressure adjustment modules to form a closed-loop adaptive control system. It can follow the changes in steel plant production load in real time, automatically match the fluctuations in lime kiln tail gas flow and CO2 concentration, and stably adapt to the large range of fluctuations in gas source of ±30%. Unconverted CO2 and syngas are recycled back to the catalytic conversion unit for reaction again at a fixed circulation ratio of 10%~15%, which can effectively improve the overall utilization rate of CO2 raw materials. 4) Low-cost, non-precious metal composite catalyst with high catalytic activity and long service life: The methanation reactor uses a CuO-MnO2-CeO2 ternary composite non-precious metal catalyst with a ratio controlled within the range of 3~5:2~4:1~3, completely eliminating high-cost precious metal catalyst raw materials and significantly reducing catalyst procurement and replacement costs; combined with an isothermal multi-stage reactor structure, the reactor inlet temperature, space velocity, and bed temperature are precisely controlled, effectively suppressing catalyst defects such as high-temperature sintering, carbon deposition, and oxidation deactivation, and the actual service life of the catalyst can reach more than 8000 hours; relying on the synergistic optimization of the catalyst system and reactor structure, the entire process achieves a CO2 conversion rate of ≥85% and a methane product selectivity of ≥90%, balancing catalytic efficiency and product selectivity, and solving the industry problems of easy failure of existing copper-based catalysts and high cost of precious metal catalysts; 5) Relying on the existing public energy media of the steel plant, the amount of modification is small and it is easy to implement and promote the project: The present invention can rely on the existing public medium pipeline network of the steel plant to build a supply system for the device. The entire catalytic conversion device can be built directly on the idle land of the lime kiln nearby, without the need to build a new dedicated water supply, power supply and steam supply station, and without the need for large-scale technical transformation of the main steel production equipment. This greatly reduces the investment in civil engineering and supporting pipeline network transformation, lowers the early construction threshold of CO2 resource utilization projects, and facilitates rapid replication and engineering demonstration in lime kiln scenarios of major steel enterprises in China. 6) Turning waste into treasure through exhaust gas resource utilization, achieving dual benefits of carbon recycling and economic benefits: This device transforms the CO2 exhaust gas from lime kilns, which was originally directly vented and could only be stored and disposed of, into high-quality methane products with a purity of ≥99% through electrolysis-methanation, separation and purification. The produced methane can be recycled back to the steel plant as kiln fuel for self-use, reducing the cost of purchasing natural gas from the steel plant, or it can be sold as a chemical raw material to generate product revenue. Compared with the traditional CCUS carbon capture and storage technology, which only involves input and no output, this solution achieves high-value utilization of CO2 resources, creating economic benefits while fulfilling the carbon emission reduction targets of the steel industry, and helping steel companies complete carbon neutrality transformation at low cost.

[0017] The features and advantages of the present invention will be described in detail through embodiments and in conjunction with the accompanying drawings. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the structure of a high-efficiency catalytic conversion device for CO2 in the tail gas of a lime kiln in a steel plant. Figure 2 This is a schematic diagram of the structure of the impurity adaptive pretreatment unit; Figure 3 This is a schematic diagram of a high-efficiency catalytic conversion method for CO2 in the tail gas of a lime kiln in a steel plant.

[0019] In the diagram: 1-Exhaust gas collection unit, 11-Flow meter, 12-Pressure sensor, 2-Impurity adaptive pretreatment unit, 21-Composite filter bag dust removal module, 22-Preferred oxidation reforming module, 3-Waste heat classification and utilization unit, 31-Heat exchanger, 32-Heat distribution controller, 4-CO2 catalytic conversion unit, 41-Solid oxide electrolysis cell, 42-Methanation reactor, 5-Product separation unit, 51-Cooler, 52-Separator, 53-Purification module, 6-Circulation regulation unit, 7-Energy supply unit, 71-Industrial water pipeline, 72-Power supply module, 73-Steam pipeline, 74-Compressed air pipeline. Detailed Implementation

[0020] See Figure 1 and Figure 2 The CO2 high-efficiency catalytic conversion device for tail gas from lime kilns in steel plants includes a tail gas collection unit 1, an impurity adaptive pretreatment unit 2, a waste heat classification and utilization unit 3, a CO2 catalytic conversion unit 4, a product separation unit 5, and a circulation regulation unit 6 arranged sequentially along the tail gas flow direction.

[0021] The exhaust gas collection unit 1 includes a collection pipe, a flow meter 11, and a pressure sensor 12. The collection pipe is equipped with both the flow meter 11 and the pressure sensor 12, with one end connected to the exhaust gas outlet of the lime kiln in the steel plant and the other end connected to the impurity adaptive pretreatment unit 2. The exhaust gas collection unit 1 is used to collect the exhaust gas from the lime kiln and monitor the exhaust gas flow and pressure parameters in real time.

[0022] The impurity adaptive pretreatment unit 2 includes a composite filter bag dust removal module 21 for removing dust and SO2 from exhaust gas, and a preferential oxidation reforming module 22 for oxidizing CO in exhaust gas to CO2. The composite filter bag dust removal module 21 uses a filter bag with a composite felt layer structure of expanded polytetrafluoroethylene membrane and catalyst polytetrafluoroethylene, and the pore size is 0.03μm (dust removal accuracy ≤5mg / Nm). 3 The preferential oxidation reforming module 22 is filled with Fe2O3-MoO3 catalyst and the reaction temperature is 280~350℃.

[0023] The CO2 catalytic conversion unit 4 uses a solid oxide electrolyzer (SOEC) 41 and a methanation reactor 42 to first electrolyze the feed gas, which is a mixture of tail gas and water vapor, to generate syngas (H2+CO), and then catalytically convert it into methane. The methanation reactor 42 adopts an isothermal multi-stage structure with an inlet temperature controlled at 200±50℃ and a space velocity of 5000~10000h. -1 The methanation reactor 42 is filled with a CuO-MnO2-CeO2 composite catalyst and the catalyst bed temperature is controlled at 450±50℃. The mass ratio of CuO, MnO2 and CeO2 in the CuO-MnO2-CeO2 composite catalyst is 4:3:2 (catalyst lifetime ≥8000h).

[0024] The waste heat grading and utilization unit 3 divides the tail gas waste heat into three levels through heat exchanger 31 and heat distribution controller 32. The low-temperature waste heat is used for preheating before the catalytic conversion of raw material gas CO2, the medium-temperature waste heat is used for reaction heating in methanation reactor 42, and the high-temperature waste heat is used for electrolysis energy supply in solid oxide electrolysis cell 41. The heat exchanger 31 is connected to the tail gas waste heat pipeline of lime kiln in steel plant. The overall waste heat utilization rate is ≥65%.

[0025] The product separation unit 5 sequentially performs cooling, water separation, and methane purification on the reaction products through a cooler 51, a separator 52, and a purification module 53. Specifically, the cooler 51 cools the reaction products to room temperature, the separator 52 separates liquid water, and the purification module 53 uses pressure swing adsorption technology to ensure that the purified methane has a purity of ≥99% (which can be recycled as fuel for steel plants or as a chemical raw material).

[0026] The circulation regulation unit 6 sends the unconverted CO2 after product separation and syngas back to the CO2 catalytic conversion unit 4 for re-reaction through circulation pipelines, flow controllers, and pressure regulation modules. The flow controller can adjust the circulation flow rate in real time, while the pressure regulation module can stabilize the system pressure within the required range to ensure adaptive adjustment of the system load.

[0027] It also includes an energy supply unit 7, which provides the required energy medium to each unit through an industrial water pipeline 71, a power supply module 72, a steam pipeline 73 and a compressed air pipeline 74 (providing industrial water, electricity, steam and compressed air required for catalytic conversion, adapting to the existing energy medium parameters of the steel plant, without the need for additional energy supply equipment).

[0028] See Figure 3 A method for efficient catalytic conversion of CO2 from tail gas of lime kiln in steel plant, based on the aforementioned efficient catalytic conversion device for CO2 from tail gas of lime kiln in steel plant, includes the following steps: S1. Exhaust Gas Collection: Exhaust gas collection unit 1 collects exhaust gas from the lime kiln of the steel plant and sends it to impurity adaptive pretreatment unit 2; the exhaust gas flow rate adjustment range is 500~2000 Nm³. 3 / h, exhaust gas pressure is controlled at 0.1~0.3MPa; S2. Impurity pretreatment: The exhaust gas first passes through the composite filter bag dust removal module 21 to remove dust and SO2, and then passes through the priority oxidation reforming module 22 to oxidize part of the CO to CO2 (adjusting the CO / CO2 molar ratio to 0.8~1.2), and then is sent to the waste heat classification and utilization unit 3. S3. Waste heat utilization in stages: The heat exchanger 31 and the heat distribution controller 32 divide the waste heat of the tail gas into high-temperature waste heat (temperature 700~1000℃), medium-temperature waste heat (temperature 400~600℃) and low-temperature waste heat (temperature 200~400℃), which are respectively used to provide energy for electrolysis of CO2 catalytic conversion unit 4, reaction heating and feed gas preheating (preheating to 200±50℃). S4, CO2 catalytic conversion: The feed gas, which is a mixture of tail gas and water vapor (the molar ratio of CO2 to water vapor is 1:1.2~1.8), is preheated and first enters the solid oxide electrolysis cell 41, where it is electrolyzed at a temperature of 750~950℃ and a current density of 0.6~1.2A / cm² to generate syngas (H2+CO, and the molar ratio of H2 to CO is 3:1). Then it enters the methanation reactor 42 and is catalytically converted into methane (CO2 conversion rate ≥85%, methane selectivity ≥90%). S5. Product separation and purification: The reaction product is sequentially cooled, separated by water, and purified by cooling module 51, separator 52 and purification module 53 to obtain methane product. S6. Circulation Regulation: After product separation, the unconverted CO2 and syngas are sent back to CO2 catalytic conversion unit 4 for re-reaction via circulation pipeline, flow controller and pressure regulation module (system pressure is stabilized at 0.1~0.3MPa, and the circulation ratio of unconverted CO2 and syngas is 10~15%). At the same time, the flow controller and pressure regulation module are used to match the fluctuation of lime kiln tail gas flow and CO2 concentration in real time to ensure stable system operation (adaptable to fluctuations of tail gas flow and CO2 concentration of ±30%).

[0029] In addition, the energy supply unit continuously provides industrial water, electricity, steam, and compressed air to each unit to ensure the smooth operation of the entire process and realize the engineering demonstration operation.

[0030] The above-described apparatus and method are suitable for the existing energy conditions of steel plants, requiring no large-scale modification of existing facilities. A demonstration unit can be built using the site surrounding a lime kiln to achieve the entire process of CO2 catalytic conversion and its stable operation. Specific embodiments are as follows: Example 1

[0031] This embodiment provides a high-efficiency catalytic conversion device and method for CO2 in the tail gas of a lime kiln in a steel plant, which is applied to the treatment of tail gas from a lime kiln in a steel plant (tail gas CO2 concentration is 30% and contains 8mg / Nm³ of dust). 3 CO 2%, SO2 500mg / Nm 3 The steel plant is equipped with industrial water, electricity, steam, compressed air and other energy sources, and the parameters and reserves meet the requirements. Part of the lime kiln site of the steel plant was selected as a demonstration site to build a demonstration device.

[0032] The specific structure of the device is as follows: The diameter of the collection pipe of the exhaust gas collection unit 1 is 500mm, and the flow meter 11 has a range of 0~2500Nm. 3 / h, the pressure sensor 12 has a range of 0~0.5MPa; the filter bag of the impurity adaptive pretreatment unit 2 has a pore size of 0.03μm, and the preferential oxidation reforming module 22 is filled with Fe2O3-MoO3 catalyst (reaction temperature controlled at 300℃); the heat exchanger 31 of the waste heat classification utilization unit 3 has a heat exchange area of ​​50m². 2 The heat distribution controller 32 can realize the graded distribution of waste heat; the solid oxide electrolysis cell 41 of the CO2 catalytic conversion unit 4 operates at a temperature of 850℃ and a current density of 0.9A / cm³. 2 The space velocity of methanation reactor 42 is 7500 h⁻¹. -1 The catalyst bed temperature is controlled at 450℃ and filled with a CuO-MnO2-CeO2 composite catalyst (CuO:MnO2:CeO2=4:3:2); the product separation unit 5's cooler 51 has a cooling temperature of 25℃; the purification module 53 uses pressure swing adsorption technology with an adsorption pressure of 0.8MPa; the circulation regulating unit 6 has a circulation pipe diameter of 300mm and a flow controller range of 0~1000Nm. 3 / h; the industrial water flow rate of energy supply unit 7 is 5m³ / h. 3 / h, power supply capacity is 500kW, steam pressure is 0.6MPa, compressed air flow rate is 10Nm 3 / min.

[0033] The specific steps of the catalytic conversion method are as follows: Exhaust gas collection: Exhaust gas from the lime kiln is collected through a collection pipeline, and the flow rate is adjusted to 1200 Nm³. 3 / h, pressure up to 0.2MPa, is monitored in real time by flow meter 11 and pressure sensor 12, and sent to impurity adaptive pretreatment unit 2; Impurity adaptive pretreatment: The exhaust gas passes through the composite filter bag dust removal module 21 to remove dust and SO2 (dust content after treatment ≤3mg / Nm³). 3(SO2 content ≤ 50 mg / Nm³), and then enters the preferential oxidation reforming module 22 and under the action of Fe2O3-MoO3 catalyst, CO is partially oxidized to CO2 at 300℃ until the CO / CO2 molar ratio is adjusted to 1.0; Waste heat utilization in stages: The waste heat of lime kiln tail gas (850℃ high temperature waste heat + 500℃ medium temperature waste heat + 300℃ low temperature waste heat) is distributed in stages by heat distribution controller 32. The high temperature waste heat supplies energy to the solid oxide electrolysis cell 41, the medium temperature waste heat heats the methanation reactor 42, and the low temperature waste heat preheats the pretreated raw material gas to 200℃. CO2 catalytic conversion: Preheated feed gas (molar ratio CO2:H2O=1:1.5) enters solid oxide electrolysis cell 41 and is electrolyzed at 850℃ and 0.9A / cm² current density to generate syngas (H2:CO=3:1). The syngas then enters methanation reactor 42 and is electrolyzed at 450℃ for 7500 h⁻¹ under the action of CuO-MnO2-CeO2 composite catalyst. -1 At space velocity, it is catalytically converted into methane; Product separation and purification: The reaction product is cooled to 25°C by cooler 51, and liquid water is separated by separator 52. The remaining gas enters purification module 53 and is purified by pressure swing adsorption technology to finally obtain methane product with a purity of ≥99.5%. Circulation regulation and stable operation: Unconverted CO2 and syngas (accounting for about 12% of the total gas volume) are sent back to CO2 catalytic conversion unit 4 for re-reaction through circulation pipeline. The flow controller and pressure regulation module match the tail gas flow and CO2 concentration fluctuations in real time to ensure stable system operation (without significant efficiency reduction). In addition, the energy supply unit 7 continuously provides industrial water, electricity, steam, and compressed air to each unit to ensure the smooth operation of the entire process.

[0034] Implementation Results: In this embodiment, the CO2 conversion rate was 88%, the methane selectivity was 92%, the catalyst activity did not decrease significantly after 6000 hours of operation, the waste heat utilization rate reached 68%, the system can stably adapt to fluctuations of tail gas flow and CO2 concentration within ±30%, no additional pretreatment equipment is required, it is compatible with the existing energy conditions of the steel plant, and the engineering demonstration has been successfully implemented.

[0035] Example 2: The difference between this embodiment and Embodiment 1 is that the CO2 concentration in the lime kiln tail gas is 25% and it contains 10 mg / Nm³ of dust. 3 CO 3%, SO2 600mg / Nm 3 The solid oxide electrolytic cell 41 operates at a temperature of 750℃ and a current density of 0.6 A / cm³. 2 The space velocity of methanation reactor 42 is 5000 h⁻¹.-1 The catalyst bed temperature is controlled at 400℃, the reaction temperature of the preferential oxidation reforming module 22 is 280℃, and the CO / CO2 molar ratio is adjusted to 0.8.

[0036] Implementation results: CO2 conversion rate was 85%, methane selectivity was 90%, catalyst activity did not decrease significantly after 7000 hours of operation, waste heat utilization rate reached 65%, system operated stably, impurity removal effect met the standard, adapted to the tail gas characteristics of the lime kiln of the steel plant, and can realize engineering demonstration operation.

[0037] Example 3: The difference between this embodiment and Embodiment 1 is that the CO2 concentration in the lime kiln tail gas is 35% and the dust content is 6 mg / Nm³. 3 CO 1%, SO2 400mg / Nm 3 The solid oxide electrolytic cell 41 operates at a temperature of 950℃ and a current density of 1.2 A / cm³. 2 The space velocity of methanation reactor 42 is 10000 h⁻¹. -1 The catalyst bed temperature is controlled at 500℃, the reaction temperature of the preferential oxidation reforming module 22 is 350℃, and the CO / CO2 molar ratio is adjusted to 1.2.

[0038] Implementation results: CO2 conversion rate is 90%, methane selectivity is 93%, catalyst activity shows no significant decrease after 8000 hours of operation, waste heat utilization rate reaches 70%, system operates stably, can realize high-value CO2 conversion and engineering demonstration, and meet the carbon emission reduction needs of the steel industry.

[0039] The above embodiments are illustrative of the present invention and are not intended to limit the present invention. Any simple modifications to the present invention are within the scope of protection of the present invention.

Claims

1. A high-efficiency catalytic conversion device for CO2 in tail gas from a lime kiln in a steel plant, characterized in that: The system includes a tail gas collection unit (1), an impurity adaptive pretreatment unit (2), a waste heat classification and utilization unit (3), a CO2 catalytic conversion unit (4), a product separation unit (5), and a circulation regulation unit (6) arranged sequentially along the tail gas flow direction. The tail gas collection unit (1) is connected to the tail gas emission port of the lime kiln in the steel plant through a collection pipe equipped with a flow meter (11) and a pressure sensor (12). The impurity adaptive pretreatment unit (2) has a composite filter bag dust removal module (21) that can remove dust and SO2 from the tail gas and a priority oxidation reforming module (22) that can oxidize part of the CO in the tail gas to CO2. The CO2 catalytic conversion unit (4) uses a solid oxide electrolysis cell (41) and a methanation reactor (42) to process the mixture of tail gas and water vapor. The synthesized raw material gas is first electrolyzed to generate syngas and then catalytically converted into methane. The waste heat utilization unit (3) divides the tail gas waste heat into three levels through heat exchanger (31) and heat distribution controller (32). The low-temperature waste heat is used for preheating of the raw material gas CO2 before catalytic conversion, the medium-temperature waste heat is used for reaction heating of the methanation reactor (42), and the high-temperature waste heat is used for electrolysis energy supply of the solid oxide electrolysis cell (41). The product separation unit (5) sequentially performs cooling treatment, water separation treatment and methane purification treatment on the reaction products through cooler (51), separator (52) and purification module (53). The circulation regulation unit (6) sends the unconverted CO2 and syngas after product separation back to the CO2 catalytic conversion unit (4) for re-reaction through circulation pipeline, flow controller and pressure regulation module.

2. The high-efficiency catalytic conversion device for CO2 in lime kiln tail gas of a steel plant as described in claim 1, characterized in that: The composite filter bag dust removal module (21) adopts a filter bag with a composite felt layer structure of expanded polytetrafluoroethylene membrane and catalyst polytetrafluoroethylene and the pore size is 0.01~0.05μm. The preferential oxidation reforming module (22) is filled with Fe2O3-MoO3 catalyst and the reaction temperature is 280~350℃.

3. The high-efficiency catalytic conversion device for CO2 in lime kiln tail gas of a steel plant as described in claim 1, characterized in that: The methanation reactor (42) adopts an isothermal multi-stage structure with an inlet temperature controlled at 200±50℃ and a space velocity of 5000~10000h. -1 The methanation reactor (42) is filled with CuO-MnO2-CeO2 composite catalyst and the catalyst bed temperature is controlled at 450±50℃. The mass ratio of CuO, MnO2 and CeO2 in the CuO-MnO2-CeO2 composite catalyst is 3~5:2~4:1~3.

4. The high-efficiency catalytic conversion device for CO2 in lime kiln tail gas of a steel plant as described in claim 1, characterized in that: It also includes an energy supply unit (7), which provides the required energy to each unit through an industrial water pipe (71), a power supply module (72), a steam pipe (73) and a compressed air pipe (74).

5. A method for efficient catalytic conversion of CO2 in tail gas from lime kilns in steel plants, characterized in that, The high-efficiency catalytic conversion device for CO2 in tail gas from lime kilns of steel plants, based on any one of claims 1 to 5, comprises the following steps: S1. Exhaust gas collection: The exhaust gas collection unit (1) collects exhaust gas from the lime kiln of the steel plant and sends it to the impurity adaptive pretreatment unit (2). S2. Impurity pretreatment: The exhaust gas first passes through the composite filter bag dust removal module (21) to remove dust and SO2, and then passes through the priority oxidation reforming module (22) to oxidize part of the CO into CO2, and then is sent to the waste heat classification and utilization unit (3). S3, waste heat classification utilization: heat exchanger (31) and heat distribution controller (32) divide the tail gas waste heat into high temperature waste heat, medium temperature waste heat and low temperature waste heat, which are respectively used for CO2 catalytic conversion unit (4) for electrolysis energy supply, reaction heating and raw material gas preheating; S4, CO2 catalytic conversion: The raw gas, which is a mixture of tail gas and water vapor, is preheated and first enters the solid oxide electrolysis cell (41) to generate synthesis gas, and then enters the methanation reactor (42) to catalytically convert it into methane; S5. Product separation and purification: The reaction product is sequentially cooled, water separated and methane purified by passing through a cooler (51), a separator (52) and a purification module (53) to obtain methane product. S6. Circulation regulation: The unconverted CO2 and syngas after product separation are sent back to the CO2 catalytic conversion unit (4) for re-reaction via circulation pipeline, flow controller and pressure regulation module.

6. The method for efficient catalytic conversion of CO2 in tail gas from lime kilns in steel plants as described in claim 5, characterized in that: In step S1, the exhaust gas flow rate is adjusted within the range of 500~2000 Nm. 3 / h, exhaust gas pressure is controlled at 0.1~0.3MPa.

7. The method for efficient catalytic conversion of CO2 in tail gas from lime kilns in steel plants as described in claim 5, characterized in that: In step S2, the preferential oxidation reforming module (22) adjusts the CO / CO2 molar ratio to 0.8~1.

2.

8. The method for efficient catalytic conversion of CO2 in tail gas from a lime kiln in a steel plant as described in claim 5, characterized in that: In step S3, the temperature of the high-temperature waste heat is 700~1000℃, the temperature of the medium-temperature waste heat is 400~600℃, the temperature of the low-temperature waste heat is 200~400℃, and the raw material gas is preheated to 200±50℃.

9. The method for efficient catalytic conversion of CO2 in tail gas from a lime kiln in a steel plant as described in claim 5, characterized in that: In step S4, the solid oxide electrolytic cell (41) has a coated anode and a double-layer cathode, and operates at a temperature of 750~950℃ and a current density of 0.6~1.2A / cm². 2 The molar ratio of CO2 to water vapor in the raw material gas is 1:1.2~1.8, and the molar ratio of H2 to CO in the synthesis gas is 3:0.5~1.

5.

10. The method for efficient catalytic conversion of CO2 in tail gas from a lime kiln in a steel plant as described in claim 5, characterized in that: In step S6, the system pressure is stabilized at 0.1~0.3MPa, and the recycling ratio of unconverted CO2 to syngas is 10~15%.

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