Resource utilization system and method for large-scale synergistic solidification of low-purity CO2 by red mud

Abstract

The invention relates to the technical field of industrial solid waste resource utilization and carbon emission reduction technology crossing, in particular to a resource utilization system and method for red mud large-scale synergistic curing of low-purity CO2, and the system comprises a red mud pretreatment unit, a gas-liquid reaction unit, a product separation and modification unit, a resource recovery unit and an intelligent regulation and control unit. Through integrated unit design, full-process efficient cooperation of red mud treatment and CO2 curing is achieved, the red mud pretreatment unit adopts closed conveying and accurate online monitoring, the uniformity and stability of raw material slurry are guaranteed, the system can directly treat CO2 mixed gas (with the purity being 25%-35%) from an industrial kiln and other sources, expensive purification pretreatment is not needed, and the system is suitable for large-scale industrial production. Wherein trace SO2, NOX and other components can promote dissolution of alkaline substances in the red mud on the contrary, a synergistic enhancement effect of treating waste with waste is formed, and the comprehensive cost of carbon capture and solidification is reduced.

Description

Technical Field

[0001] This invention relates to the field of interdisciplinary technology of industrial solid waste resource utilization and carbon emission reduction, and in particular to a resource utilization system and method for large-scale synergistic solidification of low-purity CO2 from red mud. Background Technology

[0002] Industrial emission reduction and carbon reduction are of paramount importance. The alumina industry generates a large amount of red mud every year, with global annual emissions exceeding 150 million tons and my country's cumulative stockpile exceeding 600 million tons. Red mud is highly alkaline and has a high water content. Long-term stockpiling can easily lead to soil alkalization and groundwater pollution, becoming a prominent problem for the sustainable development of the aluminum industry. Boilers, cement, and lime kilns are also major carbon emitters, emitting approximately 1.2 billion tons of CO2 annually. The purity of CO2 in their flue gas is usually only 25%-35%. Currently, alumina plants are often located adjacent to boilers and lime kilns, but the co-processing of red mud and low-purity CO2 has not yet been achieved, resulting in the superposition of resource waste and environmental pressure.

[0003] Existing red mud carbon sequestration technologies are mostly in the experimental stage, often relying on high-purity CO2, and facing problems such as harsh reaction conditions, low carbon sequestration efficiency, and difficulty in scale-up. The resource utilization of red mud in building materials, soil improvement, and other fields is also constrained by its high alkalinity, heavy metal risks, and low product added value. Current processes lack a systematic integration of direct large-scale utilization of low-purity CO2, high-value product utilization, and intelligent control throughout the entire process, and have not yet formed an economically feasible industrial model. Summary of the Invention

[0004] The purpose of this invention is to address the problems that existing red mud carbon fixation technologies are mostly in the experimental stage, often rely on high-purity CO2, and face harsh reaction conditions, low carbon fixation efficiency, and difficulty in scale-up. Therefore, this invention proposes a resource utilization system and method for large-scale synergistic solidification of low-purity CO2 using red mud.

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

[0006] A resource utilization system for the large-scale synergistic solidification of low-purity CO2 from red mud includes:

[0007] The red mud pretreatment unit is used to mix red mud with water to prepare a pumpable homogeneous slurry;

[0008] The gas-liquid reaction unit is connected to the red mud pretreatment unit and is used to carry out a countercurrent carbonation reaction between the red mud slurry and a carbon dioxide-containing gas.

[0009] The product separation and modification unit is connected to the gas-liquid reaction unit and is used to dehydrate and separate the solid-liquid mixture after the reaction, and to crush and modify the solid product.

[0010] The resource recovery unit is connected to the liquid outlet and solid outlet of the product separation and modification unit, respectively, and is used to recover sodium carbonate products from the liquid and process the modified solid products into building materials or soil conditioners.

[0011] The intelligent control unit is connected to the signals of the above-mentioned units and is used to centrally monitor and control the operating parameters of the entire system.

[0012] Preferably, the gas-liquid reaction unit includes multiple sets of high-efficiency gas-liquid reaction towers arranged in parallel. The reaction towers are equipped with a pulse gas distribution device at the bottom and a countercurrent contact spray system at the top. The diameter of the gas holes of the pulse gas distribution device is 0.5-1mm, and the gas distribution uniformity error is ≤5%. The spray coverage area of ​​the countercurrent contact spray system is ≥95% of the cross-sectional area inside the tower.

[0013] Preferably, the system further includes a CO2 booster device for pressurizing carbon dioxide-containing gas with a purity of 25%-35% to 0.3-0.5 MPa and then delivering it to the pulse gas distribution device.

[0014] Preferably, the product separation and modification unit includes multiple filter presses arranged in parallel and a modifier addition system; the modifier addition system is used to add a modifier accounting for 5%-15% of the mass of the solid product to the dehydrated solid product, and the modifier is a compound system of fly ash and gypsum with a compounding ratio of 3:1.

[0015] Preferably, the resource recycling unit includes a wastewater recycling system, which uses a precipitation-filtration-sodium carbonate recovery process to treat the wastewater generated during dehydration, and sends the treated recycled water back to the red mud pretreatment unit for pulping.

[0016] Preferably, the intelligent control unit adopts a distributed control system and integrates an online environmental monitoring module for real-time monitoring and control of dust, SO2, and NO. X The emission concentration.

[0017] A method for using a resource utilization system that utilizes red mud for large-scale synergistic solidification of low-purity CO2, as described above, is provided, comprising the following steps:

[0018] Step 1, Slurry preparation: Mix red mud with water and stir to prepare a uniform slurry;

[0019] Step 2, Carbonation reaction: The slurry is introduced into the gas-liquid reaction unit, and at the same time, carbon dioxide gas is introduced from the bottom of the reaction unit, so that the slurry and gas come into countercurrent contact to carry out the carbonation reaction;

[0020] Step 3, Dehydration and Separation: The solid-liquid mixture after the reaction is dehydrated and separated to obtain a solid filter cake and wastewater;

[0021] Step 4, Resource Utilization: The solid filter cake is crushed and modified to be processed into building materials or soil conditioners;

[0022] Step 5, Sodium carbonate recovery: The wastewater is concentrated and crystallized to recover sodium carbonate, which is then recycled for use in Step 1.

[0023] Preferably, in step 1, the red mud is Bayer process red mud with a pH value of 10.29-11.83, which is mixed with water at a mass ratio of 1:1.2-1:1.5 to obtain a slurry with a water content of 60%-70%.

[0024] Preferably, in step 2, the carbon dioxide-containing gas is a low-purity gas from boiler, cement, or lime kiln industries, with a carbon dioxide volume concentration of 25%-35%, a gas pressure of 0.3-0.5 MPa, and a gas flow rate of 0.8-1.2 m / s; the spraying intensity of the slurry is 2-3 m³ / (h·m²), the reaction temperature is 15-40℃, and the reaction time is 30-60 minutes.

[0025] Preferably, in step 4, when modifying the solid filter cake, the added modifier is a mixture of fly ash and gypsum in a 3:1 ratio, and the amount added is 5%-15% of the mass of the solid filter cake; and the modification treatment includes a microwave-assisted process with a microwave power of 300-500W and a processing time of 5-10 minutes.

[0026] Compared with the prior art, the present invention has the following advantages:

[0027] 1. This invention achieves efficient synergy of red mud treatment and CO2 solidification throughout the entire process through integrated unit design. The red mud pretreatment unit adopts closed conveying and precise online monitoring to ensure the uniformity and stability of the raw material slurry, providing an ideal medium for subsequent reactions. The seamless connection of multiple units and centralized DCS control greatly improve the continuous operation capability and overall work efficiency of the system.

[0028] 2. In this invention, the gas-liquid reaction unit adopts a multi-tower parallel and countercurrent contact design, which significantly enhances the mass and heat transfer process. The pulse gas distribution device ensures that the low-purity CO2 gas is distributed very evenly in the slurry, while the countercurrent spray system maximizes the gas-liquid contact time and reaction area, thereby achieving efficient capture and solidification of CO2 under mild conditions, and fundamentally improving the reaction efficiency and rate.

[0029] 3. The system in this invention can directly process CO2 mixtures (purity 25%-35%) from sources such as cement kilns, without the need for expensive purification pretreatment, and also handles trace amounts of SO2 and NO. XThese components can actually promote the dissolution of alkaline substances in red mud, creating a synergistic enhancement effect of treating waste with waste, which helps reduce the overall cost of carbon capture and solidification.

[0030] 4. This invention can extract high-purity sodium carbonate chemical products through a resource recycling unit; the remaining solid phase can be compounded and modified to be directionally prepared into high-strength building aggregates or safe soil conditioners. The products have stable performance and market competitiveness, truly realizing zero discharge of solid waste and resource closed loop.

[0031] 5. This invention uses an intelligent control unit to monitor and dynamically adjust key parameters such as slurry concentration, reaction pressure, temperature, and modifier addition in real time. The system can adapt to fluctuations in raw materials, ensuring the stability of final carbon fixation efficiency and product quality, while controlling energy and material consumption at the optimal level, which helps to improve the overall intelligence of the system. Attached Figure Description

[0032] Figure 1 This is a flowchart of a red mud carbon fixation process for a red mud-based resource utilization system for large-scale synergistic solidification of low-purity CO2, as proposed in this invention. Detailed Implementation

[0033] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0034] Reference Figure 1 A resource utilization system for the large-scale synergistic solidification of low-purity CO2 from red mud includes a red mud pretreatment unit, a gas-liquid reaction unit, a product separation and modification unit, a resource recovery unit, and an intelligent control unit that coordinates the operation of each unit, connected in sequence.

[0035] The red mud pretreatment unit includes a closed conveyor belt, a red mud slurry tank, a slurry storage tank, and an online moisture content monitoring module; the effective volume of the red mud slurry tank is ≥50m³, the stirring speed is 600r / min, and it is equipped with a variable frequency speed control system; the total volume of the slurry storage tank is ≥400m³, and it has heat preservation and anti-sedimentation functions. The red mud pretreatment unit is used to mix red mud with water to prepare a pumpable homogeneous slurry. The red mud is taken from Bayer process red mud in a stockpile of an alumina plant. Its main chemical components are as follows: CaO 28.5%, Al2O3 22.3%, SiO2 18.7%, Fe2O3 11.2%, Na2O 8.6%, total alkaline component content 70.6%, particle size 1-100μm, specific surface area 15.8m² / g, pH value 10.29-11.83, water content 35%-45%, and dry basis density 2.7-2.9g / cm³. During the system start-up phase, tap water is used as the initial medium. After the system is running stably, it is switched entirely to internal circulating water to achieve closed-loop operation.

[0036] The gas-liquid reaction unit includes multiple high-efficiency gas-liquid reaction towers connected in parallel, a CO2 booster device, gas delivery pipelines, and a reaction parameter monitoring module. There are 10 high-efficiency gas-liquid reaction towers, each with a diameter of 3.2m and a height of 12m. Each reaction tower is equipped with a pulse gas distribution device at the bottom and a counter-current contact spray system at the top. The pulse gas distribution device has an orifice diameter of 0.5-1mm and a gas distribution uniformity error of ≤5%. The counter-current contact spray system uses a spiral structure for its spray heads, with a spray coverage area ≥95% of the tower's cross-sectional area. The CO2 booster device outputs pressures ranging from 0.3-0. The pressure is 0.5 MPa, equipped with a pressure stabilization and control module. The CO2 booster device is used to pressurize carbon dioxide-containing gas with a purity of 25%-35% to 0.3-0.5 MPa and then deliver it to the pulse gas distribution device. The gas-liquid reaction unit is connected to the red mud pretreatment unit. The gas-liquid reaction unit is used to carry out a countercurrent carbonation reaction between the red mud slurry and the carbon dioxide-containing gas. The carbon dioxide-containing gas is directly drawn from the tail gas pipeline of a cement plant kiln without any purification treatment. Its typical composition is: CO2 purity 30%±2%, containing 65%-68% N2, 2%-3% O2, 50-80 mg / m³ SO2, and NO. X 30-50 mg / m³ and dust 10-20 mg / m³;

[0037] The product separation and modification unit includes a filter press dewatering system, a crushing and screening device, a modifier addition system, and a performance testing module. The filter press dewatering system consists of 20 chamber filter presses connected in parallel, with a single press having a filtration area of ​​≥500m². The modifier addition system allows for precise control of the addition amount, ranging from 5% to 15%. The product separation and modification unit is connected to the gas-liquid reaction unit and is used to dewater and separate the solid-liquid mixture after the reaction, as well as to crush and modify the solid product. The modifier is a compound system of fly ash and gypsum in a 3:1 ratio. The modifier addition system is equipped with an automatic stirring and mixing module, achieving a mixing uniformity of ≥90%.

[0038] The resource recovery unit includes a high-efficiency centrifuge, crystallization device, drying and packaging equipment, and a wastewater recycling system. The high-efficiency centrifuge has a separation accuracy of ≥98%, and the wastewater recycling system adopts a "precipitation-filtration-recovery of sodium carbonate" process with a recycling rate of ≥98%. The resource recovery unit is connected to the liquid outlet and solid outlet of the product separation and modification unit, respectively. The resource recovery unit is used to recover sodium carbonate products from the liquid and process the modified solid products into building materials or soil conditioners. The wastewater recycling system uses a precipitation-filtration-neutralization process to treat the wastewater generated during dewatering and sends the treated circulating water back to the red mud pretreatment unit for pulping.

[0039] The intelligent control unit adopts a DCS centralized control system, covering the monitoring and control of key parameters of each unit, with a monitoring accuracy of ±0.1% and an overall equipment efficiency of ≥92%. The intelligent control unit is connected to the signals of the above-mentioned units for centralized monitoring and control of the operating parameters of the entire system. The intelligent control unit adopts a distributed control system and integrates an environmental protection online monitoring module for real-time monitoring and control of dust, SO2, and NO. X The emission concentrations are as follows: dust emission concentration ≤ 8 mg / m³, SO2 emission concentration ≤ 50 mg / m³, NO... X Emission concentration ≤30mg / m³.

[0040] When using this system, please follow these steps:

[0041] Step 1, Slurry Preparation: Bayer red mud with a moisture content of approximately 30% is continuously transported to a red mud slurry tank with an effective volume of 60 m³ via a closed conveyor belt. Simultaneously, circulating water treated by the resource recovery unit is pumped in at a mass ratio of 1:1.3 (dry red mud:water). The stirring device is started, with the speed set to 600 r / min, and stirred for 30 minutes to form a homogeneous slurry. The online moisture content monitoring module shows that the slurry moisture content is 65%, meeting the process requirements. The slurry is then pumped into an insulated slurry storage tank for later use.

[0042] Step 2, Carbonation Reaction: The red mud slurry in the storage tank is pumped into five high-efficiency gas-liquid reaction towers (five other sets are for standby or maintenance rotation). Simultaneously, kiln tail gas from a nearby cement plant, transported via pipeline, is directly introduced into the CO2 booster device without additional purification. After being pressurized to a stable 0.4 MPa, it is sent to the bottom of each reaction tower via a gas distribution pipeline. The gas is evenly dispersed into fine bubbles by a pulse gas distribution device and rises. The slurry is sprayed downwards through spiral spray heads at the top of the tower at an intensity of 2.5 m³ / (h·m²), forming a countercurrent flow to ensure sufficient contact with the rising CO2 gas. The gas velocity in the empty tower is controlled at 1.0 m / s, and the reaction temperature is maintained at 28℃ through circulating water heat exchange. The average residence time of the slurry in the tower is 45 minutes. The reaction parameter monitoring module shows good gas-liquid contact and stable pressure drop within the tower.

[0043] Step 3, Dehydration and Separation: The slurry from the completed carbonation reaction is discharged from the bottom of the reaction tower, collected through pipelines, and distributed to 10 parallel-operating chamber filter presses (the other 10 are used in rotation for unloading, flushing, and maintenance) for dehydration. The dehydration cycle is approximately 25 minutes. The resulting filter cake is blocky, with a moisture content reduced to 28%. The filtrate from the filter press is collected and sent to the resource recovery unit. The small amount of high-turbidity wastewater generated from rinsing the filter press is sent to the wastewater recycling system. After three steps of treatment—sedimentation, filtration, and neutralization—the specific process is as follows: first, suspended solids and colloids are removed through flocculation and sedimentation; then, deep purification is carried out using a multi-media filter; finally, a small amount of post-reaction slurry is added to neutralize the pH of the effluent, ensuring the water quality meets the standards for pulping and reuse. The effluent is then returned to the red mud slurry tank from step one for recycling. The system's recycling rate reaches over 98.5%. The entire system is centrally monitored by a DCS system, which collects real-time data on slurry density, reaction tower pressure and temperature, pH values ​​at key locations, and dust and SO2 / NO at the exhaust outlet. X More than 200 data points, including concentration;

[0044] Step 4, Resource Recovery: The filtrate from Step 3 is first sent to a high-efficiency centrifuge to separate the suspended fine particles (separation accuracy >98%). The clear liquid then enters a crystallization device, where sodium carbonate with a purity ≥98.5% is obtained through evaporation and crystallization. After drying and packaging, it is sold as a chemical raw material.

[0045] Solid-phase product modification: The dehydrated filter cake is crushed and sieved into 0-5mm particles. 1000kg of this particle material is fed into a modifier addition system equipped with an automatic mixing module. 80kg of a modifier, a mixture of fly ash and gypsum in a 3:1 ratio, is precisely added at an 8% addition ratio. The mixer is started and stirred for 10 minutes until the mixing uniformity reaches 92%. Subsequently, the mixture is fed into a microwave-assisted modification device and treated at 400W power for 8 minutes.

[0046] Product grading: The modified material is divided according to the particle size and performance test results: the coarse particles (>1mm) are tested after curing and their compressive strength reaches 32MPa, and are used as high-grade building aggregate; the fine particles (≤1mm) are tested and their pH value is 8.0, and they contain certain calcium, silicon and trace elements, and are packaged as special soil conditioner.

[0047] Step 5, Intelligent Control: The entire production process is coordinated by the DCS intelligent control unit. During stable system operation, it operates in Level 1 control mode. For example, if the inlet pressure of a reaction tower drops to 0.38 MPa, the system automatically adjusts the output of the booster device within 8 seconds to restore the pressure to the set value of 0.4 MPa. Level 2 control involves technicians conducting inspections every 2 hours to verify the operating status of key equipment and product quality data. During one inspection, technicians discovered that the pH value of the incoming red mud was too high, reaching 11.8. They immediately activated the Level 3 emergency control mechanism through the DCS system, retrieving a "high-alkali red mud" solution from the preset formula library. The system automatically adjusted the pulping water ratio to 1:1.5 and slightly increased the reaction gas flow rate to 1.1 m / s, successfully stabilizing the carbon fixation efficiency at 4.1%, ensuring the stability of the final product's performance. The environmental online monitoring module operates throughout the process. Data shows that there are no additional waste gas emissions during the process, with dust emission concentrations at the plant boundary of 5 mg / m³, SO2 of 35 mg / m³, and NO... X The concentration was 22 mg / m³, which is better than the design emission standard.

[0048] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A resource utilization system for the large-scale synergistic solidification of low-purity CO2 from red mud, characterized in that, include: The red mud pretreatment unit is used to mix red mud with water to prepare a pumpable homogeneous slurry; The gas-liquid reaction unit is connected to the red mud pretreatment unit and is used to carry out a countercurrent carbonation reaction between the red mud slurry and a carbon dioxide-containing gas. The product separation and modification unit is connected to the gas-liquid reaction unit and is used to dehydrate and separate the solid-liquid mixture after the reaction, and to crush and modify the solid product. The resource recovery unit is connected to the liquid outlet and solid outlet of the product separation and modification unit, respectively, and is used to recover sodium carbonate products from the liquid and process the modified solid products into building materials or soil conditioners. The intelligent control unit is connected to the signals of the above-mentioned units and is used to centrally monitor and control the operating parameters of the entire system.

2. The resource utilization system for large-scale synergistic solidification of low-purity CO2 from red mud according to claim 1, characterized in that, The gas-liquid reaction unit includes multiple sets of high-efficiency gas-liquid reaction towers arranged in parallel. The reaction tower is equipped with a pulse gas distribution device at the bottom and a countercurrent contact spray system at the top. The diameter of the gas holes of the pulse gas distribution device is 0.5-1mm, and the gas distribution uniformity error is ≤5%. The spray coverage area of ​​the countercurrent contact spray system is ≥95% of the cross-sectional area inside the tower.

3. The resource utilization system for large-scale synergistic solidification of low-purity CO2 from red mud according to claim 2, characterized in that, The system also includes a CO2 booster device, which pressurizes carbon dioxide-containing gas with a purity of 25%-35% to 0.3-0.5 MPa and then delivers it to the pulse gas distribution device.

4. The resource utilization system for large-scale synergistic solidification of low-purity CO2 from red mud according to claim 1, characterized in that, The product separation and modification unit includes multiple filter presses arranged in parallel, and a modifier addition system. The modifier addition system is used to add a modifier accounting for 5%-15% of the mass of the solid product to the dehydrated solid product. The modifier is a compound system of fly ash and gypsum with a compounding ratio of 3:

1.

5. The resource utilization system for large-scale synergistic solidification of low-purity CO2 from red mud according to claim 1, characterized in that, The resource recovery unit includes a wastewater recycling system, which uses a sedimentation-filtration-sodium carbonate recovery process to treat the wastewater generated during dehydration and sends the treated recycled water back to the red mud pretreatment unit for pulping.

6. The resource utilization system for large-scale synergistic solidification of low-purity CO2 from red mud according to claim 1, characterized in that, The intelligent control unit adopts a distributed control system and integrates an online environmental monitoring module for real-time monitoring and control of dust, SO2, and NO. X The emission concentration.

7. A method for the resource utilization of red mud based on the system described in any one of claims 1-6, characterized in that, Includes the following steps: Step 1, Slurry preparation: Mix red mud with water and stir to prepare a uniform slurry; Step 2, Carbonation reaction: The slurry is introduced into the gas-liquid reaction unit, and at the same time, carbon dioxide gas is introduced from the bottom of the reaction unit, so that the slurry and gas come into countercurrent contact to carry out the carbonation reaction; Step 3, Dehydration and Separation: The solid-liquid mixture after the reaction is dehydrated and separated to obtain a solid filter cake and wastewater; Step 4, Resource Utilization: The solid filter cake is crushed and modified to be processed into building materials or soil conditioners; Step 5, Sodium carbonate recovery: The wastewater is concentrated and crystallized to recover sodium carbonate, which is then recycled for use in Step 1.

8. The method for resource utilization of red mud according to claim 7, characterized in that, In step 1, the red mud is Bayer process red mud with a pH value of 10.29-11.83, which is mixed with water at a mass ratio of 1:1.2-1:1.5 to obtain a slurry with a water content of 60%-70%.

9. The method for resource utilization of red mud according to claim 7, characterized in that, In step 2, the carbon dioxide-containing gas is a low-purity gas from boiler, cement, and lime kiln industries, with a carbon dioxide volume concentration of 25%-35%, a gas pressure of 0.3-0.5 MPa, and a gas flow rate of 0.8-1.2 m / s; the spraying intensity of the slurry is 2-3 m³ / (h·m²), the reaction temperature is 15-40℃, and the reaction time is 30-60 minutes.

10. The method for resource utilization of red mud according to claim 7, characterized in that, In step 4, when modifying the solid filter cake, the added modifier is a mixture of fly ash and gypsum in a 3:1 ratio, and the amount added is 5%-15% of the mass of the solid filter cake; and the modification treatment includes a microwave-assisted process with a microwave power of 300-500W and a processing time of 5-10 minutes.

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