Waste heat utilization system and method for carbon dioxide tail gas recycling firing device

Abstract

The invention provides a waste heat utilization system and method for a carbon dioxide tail gas recycling firing device, and belongs to the technical field of rare earth material preparation. The system comprises a rotary kiln, a preheating pipeline, a cyclone separator, a reaction kettle and an ultrafiltration system, a high-temperature flue gas outlet of the rotary kiln is connected with a preheating pipeline and is used for preheating a to-be-burnt rare earth compound; an outlet of the preheating pipeline is connected with a cyclone separator to remove dust; a gas outlet of the cyclone separator is connected with a reaction kettle; a calcium chloride solution is arranged in the reaction kettle and is used for absorbing CO2 and generating calcium carbonate; a discharge hole of the reaction kettle is connected with an ultrafiltration system to separate a light calcium product. According to the invention, a high-temperature waste heat recovery system is coupled with a chemical absorption method CO2 capture system, so that the operation cost of CO2 capture is reduced, and industrial energy conservation (waste heat recovery) and carbon emission reduction are synchronously realized.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of rare earth material preparation, and particularly relates to a waste heat utilization system and method of a carbon dioxide tail gas resource utilization calcination device. BACKGROUND

[0002] The traditional rare earth compound rotary kiln calcination process has problems of energy waste and pollution emission. Specifically, the traditional process uses external heating to calcine the rare earth compound, with energy consumption of 0.7-0.9 tons of standard coal per ton of product, and low energy utilization efficiency. The high-temperature flue gas (650-750℃) is directly discharged, and a large amount of waste heat is not effectively recovered, resulting in significant heat loss. At the same time, the rare earth compound dust carried in the flue gas needs to rely on a complex purification device to achieve standard emission, increasing equipment investment and operating costs.

[0003] Although the prior art reduces part of the heat loss through heat preservation measures, it lacks a systematic waste heat recycling design and cannot combine high-temperature waste heat with the CO2 capture process. Although some improved technologies attempt to reduce energy consumption, they do not achieve the synergistic optimization of waste heat resource utilization and carbon emission reduction. SUMMARY

[0004] The purpose of the present application is to solve the problems of low energy efficiency, high pollution and serious waste of waste heat in the traditional rotary kiln process by integrating high-temperature flue gas waste heat recovery and carbon dioxide chemical capture technology, and to provide key technical support for the green transformation of the rare earth industry. In order to achieve the above purpose of the present application, the following technical solutions are adopted: A waste heat utilization system of a carbon dioxide tail gas resource utilization calcination device includes a rotary kiln, a preheating pipeline, a cyclone separator, a reaction kettle and an ultrafiltration system; the high-temperature flue gas outlet of the rotary kiln is connected to the preheating pipeline for preheating the rare earth compound to be calcined; the outlet of the preheating pipeline is connected to the cyclone separator to remove dust; the gas outlet of the cyclone separator is connected to the reaction kettle, and the reaction kettle is provided with a calcium chloride solution for absorbing CO2 and generating calcium carbonate; the discharge port of the reaction kettle is connected to the ultrafiltration system to separate the light calcium product.

[0005] Preferably, the lower part of the preheating outlet of the preheating pipeline is connected to a rare earth compound conveying device for conveying the preheated rare earth compound to the feed inlet of the rotary kiln; The preheated rare earth compound inlet of the rare earth compound conveying device is in communication with the preheating outlet of the preheating pipeline, and the preheated rare earth compound outlet of the rare earth compound conveying device is in communication with the conical hopper of the preheating pipeline; The conveying pipeline of the rare earth compound conveying device is provided with a spiral conveying device inside to convey the preheated rare earth compound to the preheated rare earth compound outlet.

[0006] The spiral conveying device comprises a rotating shaft, a spiral plate arranged axially along the rotating shaft, and a preheating rare earth compound conveying pipeline; the spiral conveying device is arranged obliquely so as to communicate with the preheating pipeline at the preheating discharge port and the conical hopper at two ends thereof.

[0007] Preferably, the reaction kettle is provided with a pH on-line monitor and an ammonia gas regulating valve, and the pH is maintained at 10.0-11.0 through PID control, and the calcium ion concentration detector is linked to trigger automatic feeding or filtering operation.

[0008] Preferably, the ultrafiltration system adopts a ceramic ultrafiltration membrane with a pore size of 0.05 μm and an operating pressure of 0.3-0.6 MPa, so as to realize the retention of calcium carbonate particles and the circulation of mother liquor in a cross-flow filtration mode.

[0009] Another technical solution of the present application is a waste heat utilization and CO2 recovery method based on the above system, characterized by comprising the following steps: The high-temperature flue gas generated by burning the rare earth compound in the rotary kiln is introduced into the preheating device to preheat the rare earth compound to be burned, so that the temperature of the flue gas is significantly reduced; The preheated rare earth compound is sent into the rotary kiln for burning; The flue gas cooled by the preheating device is subjected to gas-solid separation to remove dust; The dust-removed flue gas is introduced into the carbon dioxide recovery device to react the carbon dioxide therein with the calcium-based absorption liquid to generate calcium carbonate, which is separated by the ultrafiltration system and recovered; Preferably, in the preheating step, the rare earth compound to be burned is preheated from room temperature to 200-300℃ by using high-temperature flue gas with a temperature of 650-750℃.

[0010] Preferably, the concentration of the calcium chloride solution in the reaction kettle is controlled to be 20%-25%, the reaction temperature is 60-75℃, and the pH value is 10.0-11.0.

[0011] Preferably, the method further comprises the steps of regenerating and adjusting the composition of the absorption liquid in the carbon dioxide recovery device, including: recovering ammonia from the byproduct ammonium chloride solution, and returning the generated calcium chloride to the system for recycling.

[0012] Compared with the prior art, the present application achieves the following technical effects: Through the waste heat recycling system, the heat generated by burning is collected and returned to the waste heat utilization device, and the high-temperature gas is used to preheat the rare earth compound, thereby improving the heat energy utilization efficiency of the traditional process and reducing the energy consumption per ton of product.

[0013] The heat generated by burning is collected by the waste heat recycling system, which realizes ultra-low emission and high energy efficiency in the rare earth compound burning process, and improves the energy utilization rate.

[0014] By coupling the high-temperature waste heat recovery system with the chemical absorption CO2 capture system, the operating cost of CO2 capture is reduced, and industrial energy saving (waste heat recovery) and carbon emission reduction are achieved simultaneously. Attached Figure Description

[0015] For ease of explanation, the present invention will be described in detail below with reference to specific embodiments and accompanying drawings.

[0016] Figure 1 This is a process flow diagram of the waste heat utilization method of the carbon dioxide tail gas resource recovery and combustion device of the present invention.

[0017] Figure 2 This is a schematic diagram of the waste heat utilization system of the carbon dioxide tail gas resource recovery and combustion device of the present invention.

[0018] Figure 3 This is a schematic diagram of the rare earth compound transfer device after preheating in the waste heat utilization system of the carbon dioxide tail gas resource recovery and incineration device of this invention.

[0019] Figure 4 This is a control flowchart of the waste heat utilization system of the carbon dioxide tail gas resource recovery combustion device of the present invention.

[0020] In the diagram: 1. Rotary kiln; 11. Conical funnel; 12. Burning outlet; 13. Pipeline; 2. Preheating pipeline; 21. Preheating inlet; 22. Preheating outlet; 3. Cyclone separator; 4. Reactor; 41. Exhaust port; 5. Rare earth compound transfer device; 51. Motor; 52. Preheating rare earth compound outlet; 53. Rotating shaft; 54. Spiral plate; 55. Support; 56. Preheating rare earth compound inlet; 57. Preheating rare earth compound transfer pipeline. Detailed Implementation

[0021] The following are specific embodiments of the present invention, in conjunction with the appendix. Figures 1-4 The technical solutions of the present invention will be further described below, but the present invention is not limited to these embodiments; in the following description, specific details such as specific configurations are provided only to help to fully understand the embodiments of the present invention. Therefore, those skilled in the art should understand that various changes and modifications can be made to the embodiments described herein without departing from the scope and spirit of the present invention.

[0022] It should be noted that, unless otherwise specified, the embodiments and features described in this invention can be combined with each other.

[0023] Example 1: Waste Heat Utilization System of a Carbon Dioxide Tail Gas Resource Calculation and Combustion Device like Figure 1As shown, the high-temperature flue gas from the rotary kiln calcining rare earth compounds directly preheats the rare earth oxides to be calcined, reducing the flue gas temperature from 700℃ to below 100℃. The heat in the high-temperature flue gas is used to preheat the rare earth oxides. After the rare earth oxides in the rotary kiln are calcined, the preheated rare earth compounds are transferred back to the rotary kiln for calcination, fully utilizing the heat in the exhaust gas and achieving waste heat recycling. The gas then enters a cyclone separator to remove the rare earth compound dust it contains, and then the gas is passed into a calcium chloride solution. The carbon dioxide in the gas reacts with the calcium chloride to produce light calcium carbonate, which is collected by an ultrafiltration system, thus recovering and utilizing the carbon dioxide in the high-temperature gas and reducing carbon emissions.

[0024] Step 1: Calculate the available heat of flue gas Original flue gas conditions (boiler outlet): Flow rate: 15000 Nm³ / h; Temperature: 750℃; CO2 concentration: 15% (volume ratio); Flue gas specific heat capacity: approximately 1.05 kJ / (kg·K); Density: approximately 0.33 kg / Nm³ Estimated recovered heat: Q1 = Flow rate * Density * Specific heat capacity * Temperature difference = 15000 Nm³ / h * 0.33 kg / Nm³ * 1.05 kJ / (kg·K) * (700-100)K ≈ 3.12 × 10⁻¹⁰ 6 kJ / h≈864kW.

[0025] Step 2: Calculate the heat required to preheat the rare earth compound. To match the rare earth production line, a rare earth compound preheating capacity of 5000 kg / h is set. The preheating process requires two parts of heat: sensible heat Q2 to heat the material from 25°C to 250°C and latent heat Q3 to evaporate some of the free water and some of the crystal water in the material.

[0026] A. Calculate the sensible heat Q2: The specific heat capacity Cp of hydrated rare earth chloride (RECl3·6H2O) is approximately 1.2 kJ / (kg·K).

[0027] Q2= 5000 kg / h * 1.2 kJ / (kg·K) * (250 - 25) K= 1350000 kJ / h≈375 Kw.

[0028] B. Calculate the latent heat Q3 required to remove some water: This is the most significant heat consumption item. Assume the feed moisture content is 10% free water, and that during the preheating to 250°C, this 10% free water and one unit of water of crystallization are removed.

[0029] Total dehydration calculation: Free water: 5,000 kg / h × 10% = 500 kg / h.

[0030] Water of crystallization (1 H2O): RECl3·6H2O molecular weight 350, H2O molecular weight 18. Each kg of hydrate contains approximately 0.31 kg of water of crystallization (6*18) / 350. Removing 1 / 6 of the water of crystallization, i.e., the amount of water removed = 5,000 kg / h × 0.31 × (1 / 6) ≈ 258 kg / h.

[0031] Total dehydration capacity = 500 + 258 = 758 kg / h.

[0032] The latent heat of vaporization of water is approximately 1716 kJ / kg at 250°C.

[0033] Q3 = 758 kg / h * 1716 kJ / kg≈1,300,728 kJ / h≈361kW.

[0034] C. Total heat required for preheating rare earth compounds, Q_total: Q total = Q2 + Q3 = 375 kW + 361 kW = 736 kW.

[0035] In summary, the available heat from the flue gas is 864 kW, while the heat required for rare earth preheating is 736 kW. 85.2% (736 / 864) of the heat released when the flue gas is cooled from 700°C to 100°C is sufficient to complete the preheating of rare earth compounds. Preheating rare earth compounds saves 736 kW of heat power that would otherwise require electricity or gas. Based on 8000 hours of operation per year and a thermal efficiency of 85%, this is equivalent to a saving of approximately 850 tons of standard coal per year: (736 kW * 8000 h) / (29307 kJ / kg * 0.85) * 3600 kJ / kW ≈ 850 tons of standard coal per year.

[0036] like Figure 2 As shown, the high-temperature flue gas from the rotary kiln 1, which calcines rare earth compounds, enters the preheating pipe 2 through pipe 13 to preheat the rare earth compounds to be calcined. The rare earth compounds to be preheated enter the preheating pipe 2 through the preheating feed inlet 21. After preheating, the rare earth oxides are conveyed by a conveyor belt through a transfer pipe to the conical funnel and then into the rotary kiln. The high-temperature flue gas after passing through the preheating pipe 2 first enters the cyclone separator 3 to remove rare earth compound dust, and then enters the reaction vessel 4, which contains calcium chloride solution. The carbon dioxide in the gas reacts with calcium chloride in the reaction vessel 4 to produce light calcium carbonate, which is then collected by an ultrafiltration system, realizing the recovery and reuse of carbon dioxide.

[0037] Preheated rare earth compound transfer device 5 Figure 3As shown, the preheating rare earth compound transmission pipeline has a certain inclination angle, which ensures... Figure 3 Preheating rare earth compound inlet 56 and Figure 2 The preheating outlet 22 on the right side of the preheating pipe 2 is connected together, and the preheating rare earth compound outlet 52 is connected to... Figure 2 The conical funnels 11 are connected together. The preheated rare earth compound enters the preheated rare earth compound transmission pipe 57 from the preheating pipe 2 through the preheating discharge port 22. The spiral conveyor transports the preheated rare earth compound to the preheated rare earth compound outlet 52, and then enters the rotary kiln 1 through the conical funnel 11.

[0038] The spiral conveying device includes a rotating shaft 53, a spiral plate 54 arranged axially along the rotating shaft 53, and a preheating rare earth compound conveying pipe 57; the preheating rare earth compound conveying pipe 57 is inclined so that its two ends are respectively connected to the preheating outlet of the preheating pipe and the conical funnel.

[0039] Control flow diagram as follows Figure 4 As shown. The rare earth compounds to be calcined enter from the head of rotary kiln 1, where they are heated by the flame from the kiln head and undergo a decomposition reaction, generating high-temperature clinker and high-temperature flue gas. The high-temperature flue gas exits from the kiln tail and enters the preheating pipe 2 through the kiln tail flue, preheating the rare earth compounds to be calcined placed there. The temperature of the high-temperature flue gas drops to 100℃ and enters the cyclone separator 3. After the rare earth compounds in rotary kiln 1 are calcined, they are transferred to the outside of the rotary kiln through the tail of the rotary kiln. At the same time, the rare earth compounds to be calcined in the preheating pipe 2 enter the rotary kiln for the next calcination through the rare earth compound transfer device. The gas passing through the cyclone separator 3 enters the reaction vessel 4 to recover carbon dioxide. The reaction vessel 4 contains ammonified calcium chloride solution. When the flue gas enters the reaction vessel, the carbon dioxide reacts with the ammonified calcium chloride solution in a carbonization reaction: CaCl2 + CO2 + 2NH3·H2O → CaCO3↓ + 2NH4Cl + H2O. The filtration yields a light calcium chloride product, while the remaining calcium chloride solution is recycled within the reactor, and the gas is released into the atmosphere. Figure 4 As shown, the method for precise pH control and material balance in the reactor is as follows: Control objective: Maintain the pH value inside the reactor within the optimal range (10.0-11.0), and determine the reaction endpoint based on the pH trend, triggering filtration or feeding.

[0040] Controlled variable: pH value of the reactor slurry (using an online pH meter resistant to solid erosion and equipped with an automatic cleaning sleeve).

[0041] Manipulated variable: Opening degree of the ammonia (NH3) regulating valve.

[0042] Control strategy: 1. pH adjustment loop: Split-range PID control is adopted.

[0043] When the pH value is lower than the set value, open the ammonia valve to replenish the alkaline substance.

[0044] When the pH value is higher than the set value and continues to rise, reduce or close the ammonia valve. At the same time, activate a small flow rate CO2 bypass to directly introduce it into the reactor for fine-tuning.

[0045] 2. Reaction endpoint determination and filtration triggering: Logical judgment: When the following conditions are met simultaneously, it is judged as the "end point of the reaction batch".

[0046] a. The pH value remains stable within the set range for a preset time, and the ammonia valve opening is already very small.

[0047] b. The online detection value of calcium ion concentration (or the value calculated by conductivity / turbidity) is lower than the threshold (0.3 mol / L).

[0048] Automatic operation: The system automatically opens the discharge valve at the bottom of the reactor, starts the slurry delivery pump and ultrafiltration membrane system, and enters the filtration process. At the same time, it prepares the feed for the next reaction cycle.

[0049] 3. Automatic replenishment method for calcium chloride solution: Triggering conditions: Based on a calcium ion material balance calculation model. Model inputs include: initial feed rate, reaction time, and cumulative CO2 flow rate in flue gas (obtained by integration from the flow meter).

[0050] Replenishment Action: When the amount of calcium ions remaining calculated by the model is lower than the preset lower limit, or the pH adjustment response becomes sluggish (indicating that the alkaline substances are exhausted), the system automatically starts the calcium chloride solution replenishment pump to quantitatively replenish the concentrated solution from the storage tank to the pipeline before the reactor or raw material preheater.

[0051] Safety Interlock: During replenishment, the interlock pauses ammonia addition and increases stirring to prevent localized over-concentration. Example 2: Waste Heat Utilization and CO2 Recovery Method Based on the System of Example 1 1. Optimization and control range of key reaction conditions To ensure efficient reaction, high-quality product (light calcium carbonate), and system stability, the following parameters must be strictly controlled: A calcium chloride solution concentration of 20-25% achieves an optimal balance between absorption capacity, viscosity, and crystallization risk. An initial pH of around 10.5 ensures a high reaction rate and efficient ammonia utilization. The reaction temperature is 60°C-75°C, and in practice, it needs to be linked to pH control, which can be precisely controlled via the reactor cooling coil. The pretreated flue gas, cooled to 80-100°C, enters the reactor; the CO2 concentration may be reduced to around 15% due to dilution with supplemental combustion air. A bubble column reactor is used in the reactor, with a microporous titanium / ceramic distributor at the bottom, resulting in bubble diameters <2mm, greatly increasing the gas-liquid contact area. Combined with side-stream circulation and online pH / temperature monitoring, continuous and stable production is achieved.

[0052] The ultrafiltration membrane separation system uses a ceramic ultrafiltration membrane with a pore size of 0.05 μm. This pore size can retain 100% of calcium carbonate particles (typically >0.1 μm), while allowing Ca²⁺ to pass through. + Cl - NH4 + Plasma and water molecules can pass freely. The operating pressure is 0.3-0.6 MPa. A cross-flow filtration mode is employed, with the feed solution flowing at high speed parallel to the membrane surface, effectively flushing the surface and reducing concentration polarization and membrane fouling. The initial designed membrane flux is approximately 80-120 L / (m²·h).

[0053] 2. Reaction solution regeneration and system stability assurance scheme During long-term operation, the composition of the reaction solution will change, and adjustments must be made to maintain system stability and high efficiency.

[0054] Question 1: Hydrochloric acid (HCl) accumulation and pH decrease Trace amounts of SO2 and NOx in flue gas dissolve in water to form H2SO3, HNO3, etc., and CO2 absorption itself consumes OH groups. - All of these factors lead to an increase in the acidity of the system.

[0055] Neutralization scheme: A portion of the mother liquor containing NH4Cl is sent to an ammonia recovery unit. NH3 is re-vaporized and returned to the system for pH adjustment via distillation with the addition of alkali (such as Ca(OH)2). The reaction equation is as follows: 2NH4Cl + Ca(OH)2→2NH3↑+ CaCl2+ 2H2O Benefits: ① The absorbent NH3 is regenerated; ② Reusable CaCl2 is generated; ③ Ammonia recycling is achieved.

[0056] Question 2: Calcium ions (Ca²⁺) + Consumption and replenishment Consumption: Calcium ions are continuously precipitated in the form of calcium carbonate.

[0057] Solution: Regularly replenish the calcium chloride solution storage tank with solid calcium chloride or high-purity calcium chloride solution. The replenishment amount should be precisely calculated and added based on online calcium ion concentration monitoring data.

[0058] Question 3: Accumulation and Treatment of Ammonium Salts (NH4Cl) Accumulation: As the reaction continues, the concentration of NH4Cl will continuously increase.

[0059] Treatment Solution: Crystallization Method (Zero Discharge): Install an NH4Cl evaporator crystallizer to concentrate and crystallize part of the mother liquor using waste heat from the system (such as low-pressure steam), obtaining solid NH4Cl as a byproduct. After crystallization, the mother liquor is returned to the system to achieve water and salt balance within the system.

[0060] 3. Comparison of Key Quantitative Performance Indicators 3.1 Comparison of energy consumption for preheating rare earth compounds Table 1

[0061] Quantitative decomposition of energy consumption reduction (taking cerium oxide CeO2 as an example): Preheating stage: The waste heat of 700℃ flue gas is used to heat the material from 25℃ to 250℃, completely replacing natural gas heating and saving 450-500 kWh / ton.

[0062] Main calcination stage: Because the material has been preheated and partially dehydrated, the residence time in the kiln is shortened by 35%, and fuel consumption is reduced by 40-50%.

[0063] 3.2 Comparison of CO2 capture cost with traditional amine method Table 2

[0064] The quantitative sources of cost advantage: Equipment simplification: Eliminating the regeneration tower, lean and rich liquid heat exchanger, and solvent recovery system reduces equipment investment by 52%.

[0065] Solvent-free degradation: The degradation loss of MEA by amine method is 3.2 kg / ton CO2 (approximately 160 yuan), and the reagent recycling loss of this system is <0.5%.

[0066] Low-temperature operation: reaction temperature 65-75℃, amine regeneration 120-140℃, steam quality requirements reduced by 60%.

[0067] By-product revenue: 1.05 tons of light calcium carbonate (valued at 840 yuan) are produced for every 1 ton of CO2 captured.

[0068] 3.3 Yield and quality indicators of light calcium by-products Table 3

[0069] 4. Rare Earth Compound Examples: Cerium Oxalate (Ce2(C2O4)3·10H2O) Burning Experiment 4.1 Experimental Design and Conditions Material properties: Cerium oxalate filter cake: moisture content 32%, dry basis CeO2 content 43.5% Processing capacity: 500 kg / h (wet basis), equivalent to 340 kg / h (dry basis) Target product: High specific surface area nano-cerium oxide (CeO2) Comparison of the two processes: Control group: Traditional electric rotary kiln, directly fed with 25℃ wet filter cake. Experimental group: After preheating, the system enters the same electric rotary kiln. Preheating system parameters: Heat source: 750℃ flue gas waste heat Preheating endpoint temperature: 235±5℃ 4.2 Comparison of experimental data (production of 1 ton of CeO2 product) Table 4

[0070] Those skilled in the art to which this application pertains may modify or supplement the specific embodiments described or use similar methods to replace them, but without departing from the inventive concept of this application or exceeding the scope defined by the appended claims.

Claims

1. A waste heat utilization system for a carbon dioxide tail gas resource recovery combustion device, characterized in that, The system includes a rotary kiln (1), a preheating pipe (2), a cyclone separator (3), a reactor (4), and an ultrafiltration system. The high-temperature flue gas outlet of the rotary kiln (1) is connected to the preheating pipe (2) for preheating the rare earth compounds to be calcined. The outlet of the preheating pipe (2) is connected to the cyclone separator (3) to remove dust. The gas outlet of the cyclone separator (3) is connected to the reactor (4), which contains a calcium chloride solution for absorbing CO2 and generating calcium carbonate. The outlet of the reactor (4) is connected to the ultrafiltration system to separate light calcium carbonate products.

2. The system as described in claim 1, characterized in that, The lower part of the preheating pipe (2) is connected to a rare earth compound conveying device (5) to transport the preheated rare earth compound to the feed port of the rotary kiln (1).

3. The system as described in claim 2, characterized in that, The preheating rare earth compound inlet of the rare earth compound transfer device (5) is connected to the preheating outlet of the preheating pipe (2), and the preheating rare earth compound outlet of the rare earth compound transfer device (5) is connected to the conical funnel of the preheating pipe (2). The rare earth compound transport device (5) has a spiral transport device inside its transport pipe to transport the preheated rare earth compound to the preheated rare earth compound outlet.

4. The system as described in claim 1, characterized in that, The reactor (4) is equipped with an online pH monitor and an ammonia regulating valve. The pH is maintained at 10.0-11.0 by PID control, and the calcium ion concentration detector is linked to trigger automatic feeding or filtration.

5. The system as described in claim 1, characterized in that, The ultrafiltration system uses a ceramic ultrafiltration membrane with a pore size of 0.05 μm and an operating pressure of 0.3-0.6 MPa. It achieves the retention of calcium carbonate particles and the circulation of mother liquor through a cross-flow filtration mode.

6. A method for waste heat utilization and CO2 recovery based on the system of any one of claims 1-5, characterized in that, Includes the following steps: The high-temperature flue gas generated by the calcination of rare earth compounds in the rotary kiln is passed into a preheating device to preheat the rare earth compounds to be calcined, thereby significantly reducing the flue gas temperature. The preheated rare earth compound is fed into a rotary kiln for calcination. The flue gas, after being cooled by the preheating device, undergoes gas-solid separation to remove dust. The flue gas after dust removal is passed into a carbon dioxide recovery device, where the carbon dioxide reacts with the calcium-based absorbent to produce calcium carbonate. The calcium carbonate product is then separated and recovered through an ultrafiltration system.

7. The method as described in claim 6, characterized in that, In the preheating step, the rare earth compounds to be calcined are preheated from room temperature to 200-300°C using high-temperature flue gas at 650-750°C.

8. The method as described in claim 7, characterized in that, The concentration of calcium chloride solution in the reactor is controlled at 20%-25%, the reaction temperature is 60-75℃, and the pH value is 10.0-11.

0.

9. The method as described in claim 8, characterized in that, It also includes steps for regenerating and adjusting the composition of the absorbent in the carbon dioxide recovery unit, including: recovering ammonia from the ammonium chloride solution, a byproduct of the reaction, and returning the generated calcium chloride to the system for recycling.

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