A system and method for carbon dioxide removal in soda ash production using calcium carbide slag slurry.

Abstract

This invention relates to the field of environmental protection technology and discloses a system and method for removing carbon dioxide using carbide slag slurry in soda ash production. The system includes the following steps: S1, slurry preparation; S2, flue gas pretreatment; S3, integrated CO2 absorption and reaction control; S4, slurry post-treatment and lime slurry recovery; and S5, process control. Addressing the problems of unstable absorption processes and limited efficiency caused by insufficient slurry performance control in existing technologies, this invention achieves resource utilization of carbide slag and efficient carbon dioxide capture through refined preparation and online control of the absorption slurry, combined with flue gas pretreatment, countercurrent absorption reaction, and product separation and recovery. Simultaneously, it can recover high-quality lime slurry products for reuse in the soda ash production process, reducing raw material costs while decreasing carbon emissions. This achieves an organic combination of environmental protection and resource recycling, improving the overall economic and environmental benefits of the process.

Description

Technical Field

[0001] This invention relates to the field of environmental protection technology, and in particular to a system and method for removing carbon dioxide using calcium carbide slag slurry in soda ash production. Background Technology

[0002] As a crucial basic chemical industry, the soda ash industry emits large amounts of boiler flue gas during its production process. This flue gas contains high concentrations of pollutants such as carbon dioxide (CO2), sulfur dioxide (SO2), nitrogen oxides (NOx), and particulate matter. CO2, in particular, is a major greenhouse gas, and its emissions are subject to strict regulations. Traditional CO2 capture technologies, such as amine absorption, while mature, suffer from high energy consumption, strong corrosiveness, and absorbent degradation, resulting in high operating costs and difficulty in effectively utilizing the captured products. Meanwhile, in chemical production using acetylene as a raw material, the hydrolysis of calcium carbide to remove acetylene gas generates a large amount of industrial solid waste, namely calcium carbide slag. The main chemical component of calcium carbide slag is calcium hydroxide (Ca(OH)2). It is produced in large quantities, has a high water content, and is difficult to treat and dispose of. Improper storage can easily lead to land occupation, dust pollution, and alkalization of water and soil. Therefore, how to efficiently and economically treat calcium carbide slag and realize its high-value utilization is an urgent problem to be solved.

[0003] The aforementioned and existing related technologies often suffer from the following drawbacks: In the process of CO2 capture from flue gas using calcium carbide slag slurry, key performance parameters such as the slurry's solid content, particle size distribution, viscosity, and pH value have a decisive impact on gas-liquid mass transfer efficiency, reaction rate, and stable system operation. However, existing technologies typically employ relatively simple and imprecise methods for controlling the circulating slurry, leading to fluctuations in slurry performance during preparation and use. This, in turn, affects the sufficiency and stability of the CO2 absorption reaction, limiting further improvements in overall process efficiency. Summary of the Invention

[0004] The technical problem to be solved by this invention is that the preparation and control of circulating slurry in the existing technology are often not precise enough, which leads to unstable absorption process and incomplete reaction. To this end, we propose a system and method for removing carbon dioxide using calcium carbide slag slurry in soda ash production.

[0005] To achieve the above objectives, this application adopts the following technical solution: a method for removing carbon dioxide using calcium carbide slag slurry in soda ash production, comprising the following steps:

[0006] S1. Slurry preparation: Mix carbide slag and process water in a slurry mixing tank at a mass ratio of 1:1.5 to 1:2.5 and stir to prepare a carbide slag absorption slurry with a solid content of 15% to 25% and d90≤45um.

[0007] S2. Flue gas pretreatment: The boiler flue gas generated from soda ash production is passed into the flue gas pretreatment unit for desulfurization, denitrification and dust removal, thereby obtaining purified flue gas.

[0008] S3 and CO2 integrated absorption and reaction control: Purified flue gas is introduced from the bottom of the absorption tower, while the calcium carbide slag absorption slurry prepared in S1 is sprayed down from the top of the tower. The operating temperature inside the tower is controlled at 40℃ to 65℃, and the liquid-to-gas ratio is 5L / m³ to 15L / m³, so that the flue gas and slurry are in full countercurrent contact inside the tower. The CO2 in the flue gas reacts with the calcium hydroxide in the slurry to generate a slurry rich in calcium carbonate. Through regulation, the unreacted calcium hydroxide inside the tower is retained in the liquid phase.

[0009] S4. Post-treatment of slurry and recovery of lime milk: Some of the calcium carbonate-rich slurry discharged from the bottom of the absorption tower enters the solid-liquid separation device for solid-liquid separation. The separated calcium carbonate solid residue is discharged or utilized as a resource. The separated liquid phase is sent to the lime milk storage tank and, after being conditioned and qualified, is transported to the ammonia stripping unit of the soda ash production system for use.

[0010] S5. Process control: By monitoring the pH value of the circulating slurry in the absorption tower online, the pH value is controlled within the range of 9.5 to 11.5, and the replenishment flow rate of fresh carbide slag absorption slurry and the ratio of circulating slurry are dynamically adjusted accordingly.

[0011] Preferably, the specific implementation steps for slurry preparation in S1 are as follows:

[0012] S11. Pretreatment and particle size optimization of calcium carbide slag raw materials: The calcium carbide slag raw materials are screened to remove impurities, and then mechanically activated by a vertical roller mill. The grinding disc speed, grinding pressure and system air volume are controlled to ensure that the particle size meets d90≤45μm, while the material temperature is maintained at 50-65℃.

[0013] S12. Selection and pretreatment of process water: The condensate of the soda ash production system is preheated to 25-35℃ as process water, and a composite additive consisting of 0.05% sodium hexametaphosphate and 0.02% polycarboxylate dispersant relative to the mass fraction of process water is added to it.

[0014] S13. Gradient mixing and online rheological control: Gradient mixing is adopted. First, 70% of the process water and all the carbide slag powder are mixed at a speed of 800-1200 rpm. Then, the remaining 30% of water is added and the mixture is stirred at a speed of 300-500 rpm. The apparent viscosity of the slurry is controlled at 150-400 mPa·s by an online viscometer.

[0015] S14. Homogenization and maturation of slurry and verification of key performance: The mixed slurry is transferred to a maturation tank and slowly stirred at 30-60 rpm at 30-40℃ for at least 30 minutes. Then, its solid content, pH value and particle size distribution are tested. After passing the test, it is transported to the slurry circulation tank at the top of the absorption tower for later use.

[0016] Preferably, after the qualified slurry in S14 is transported to the slurry circulation tank, it is stirred at a low speed of 20-30 rpm. An inclined guide plate is installed at the bottom of the circulation tank to prevent sedimentation. The particle size and apparent viscosity are checked every 2 hours to ensure the stability of the slurry performance.

[0017] Preferably, the specific implementation steps of flue gas pretreatment in S2 are as follows:

[0018] S21. Desulfurization and simultaneous resource utilization pretreatment: Flue gas is introduced into a calcium-based wet desulfurization tower, the slurry pH is controlled at 5.2-5.8, SO2 is removed to below 35mg / Nm³, and a crystal-directing agent is added to the oxidation tank to convert the by-product into calcium sulfate dihydrate whiskers.

[0019] S22. Low-temperature catalytic oxidation denitrification and ammonia slip control: The desulfurized flue gas is cooled to 180-220℃ and enters a reactor filled with vanadium-titanium catalyst. Ammonia gas evaporated from dilute ammonia water is injected for denitrification. The NOx concentration is controlled below 50mg / Nm³ by controlling the ammonia-nitrogen molar ratio at 0.85-0.95.

[0020] S23. Deep dust removal and SO3 aerosol synergistic removal: The flue gas is passed sequentially through a low-temperature electrostatic precipitator and a tubular wet electrostatic precipitator operating at 90-100℃, reducing the outlet dust concentration to below 10mg / Nm³ and synergistically removing SO3 aerosol.

[0021] S24. Flue gas conditioning and cooling: The flue gas enters the direct contact cooling tower and is cooled to 55±2℃ and close to saturated humidity. Finally, the online analyzer and control system are linked to adjust the induced draft fan to output purified flue gas with stable parameters for use in CO2 absorption in step S3.

[0022] Preferably, in S21, the crystal-directing agent is a 2:1 mixture of magnesium sulfate and citric acid, and the addition amount is 0.03%-0.05% of the mass of the desulfurization slurry; in S22, an ammonia slip monitor is installed at the outlet flue of the denitrification reactor filled with vanadium-titanium catalyst to monitor the ammonia slip concentration in the flue gas after denitrification in real time, and automatically reduces the ammonia injection rate when the concentration exceeds 3mg / Nm³.

[0023] Preferably, the specific implementation steps for the integrated CO2 absorption and reaction regulation in S3 are as follows:

[0024] S31. Enhanced gas-liquid distribution and mass transfer interface: The purified flue gas rises uniformly from the bottom of the absorption tower at an empty tower velocity of 1.2-1.8 m / s, while the carbide slag slurry is atomized into 80-150 micrometer droplets from the top of the tower and sprayed downwards. The two are in countercurrent contact for mass transfer within the structured packing layer.

[0025] S32. Non-isothermal absorption reaction process and temperature gradient control: By adjusting the jacket cooling water and the heat exchanger in the tower, an increasing temperature gradient is formed in the absorption tower from 40-45℃ at the top to 60-65℃ at the bottom.

[0026] S33. Online diagnosis of reaction process and regulation of slurry property evolution: By monitoring the density, pH and conductivity of circulating slurry online, the replenishment of fresh slurry and the discharge of circulating slurry are dynamically adjusted according to the established correlation model to stabilize the pH of circulating slurry in the slurry circulation tank at 9.5-11.5.

[0027] S34. Dynamic equilibrium control of absorption reaction: The amount of CO2 absorbed and the amount of Ca(OH)2 consumed are calculated in real time. When the mass fraction of calcium carbonate in the circulating slurry reaches 12%-18% and the Zeta potential is stable at -25 to -15mV, part of the post-reaction slurry is led out to the slurry post-treatment unit in step S4.

[0028] Preferably, the specific implementation steps for post-treatment of slurry and recovery of lime slurry in S4 are as follows:

[0029] S41. Flocculation and Thickening Pretreatment: Add anionic polyacrylamide and modified starch mixed in a mass ratio of 1:2 to 1:3 to the calcium carbonate-rich slurry as a flocculant. Flocculate and thicken the slurry in a buffer thickening tank to increase the solid content of the underflow slurry to 30%-40%.

[0030] S42. Two-stage solid-liquid separation: The thick slurry is pumped into a two-stage separation system consisting of a horizontal screw sedimentation centrifuge and a chamber filter press connected in series. The centrifuge separates the coarse residue at 3000-3500G. The mother liquor is then filtered at 0.8-1.2MPa to obtain a filtered clear liquid containing calcium hydroxide.

[0031] S43. Resource utilization of calcium carbonate solid residue: Wash, dry and classify the centrifuged coarse residue to obtain calcium carbonate powder; the filter cake of the filter press is washed with dilute acid, dried and activated to convert it into precipitated calcium carbonate.

[0032] S44. Conditioning of lime slurry products: Add a certain amount of sodium hydroxide solution to the filtrate to adjust the pH of the filtrate to 11.5-12.5, and inject nitrogen to remove oxygen before storing it in a nitrogen-sealed insulated lime slurry storage tank. Stir gently at 30-40℃.

[0033] Preferably, the pH of the circulating slurry in the slurry circulation tank is dynamically adjusted based on a correlation model to maintain its stability, and the calculation formula is as follows:

[0034] ;

[0035] In the formula: u represents the real-time adjustment coefficient, used to dynamically control the ratio of fresh slurry replenishment flow rate to circulating slurry return flow rate; i represents the summation index variable, taking values ​​of 1 and 2, indicating the superposition of two tanh terms with the same structure; a i b represents the weighting coefficient of the hyperbolic tangent term; i denoted by ρ, representing the slope coefficient of the hyperbolic tangent term; P represents the real-time pH value of the mixed slurry at the outlet of the slurry circulation tank; P0 represents the target set value of the slurry pH; ρ represents the real-time density of the slurry; ρ0 represents the target set value of the slurry density; c represents the rate of change damping coefficient; dP / dt represents the rate of change of pH over time; κ represents the real-time conductivity of the slurry; κ0 represents the baseline value of the slurry conductivity.

[0036] Preferably, the S44 insulated lime slurry storage tank maintains a temperature of 30-40°C through a jacket, monitors the oxygen content in real time, and adds nitrogen when the oxygen content in the storage tank exceeds 0.5%; the pressure filtrate is filtered before conditioning to remove solid impurities with a particle size greater than 10μm.

[0037] Preferably, the present invention provides another technical solution: a system for removing carbon dioxide using calcium carbide slag slurry in soda ash production, the system comprising:

[0038] The flue gas pretreatment unit is equipped with a flue gas inlet and a purified flue gas outlet, and is used to desulfurize, denitrify and remove dust from boiler flue gas.

[0039] The calcium carbide slag slurry preparation unit includes a calcium carbide slag storage silo, a quantitative feeding device, a slurry mixing tank and a stirring device. The calcium carbide slag storage silo is connected to the slurry mixing tank through the quantitative feeding device. The slurry mixing tank is equipped with a process water inlet and a slurry outlet, which are used to mix and stir calcium carbide slag and water at a set mass ratio to prepare calcium carbide slag absorbent slurry with a predetermined solid content and particle size distribution.

[0040] The integrated CO2 absorption and lime slurry preparation unit includes an absorption tower and a slurry circulation tank. The absorption tower is equipped with a purified flue gas inlet, a purified flue gas outlet, a slurry inlet, a CO2-enriched slurry outlet, and a gas distributor.

[0041] The purified flue gas inlet is connected to the purified flue gas outlet of the flue gas pretreatment unit via the first pipeline;

[0042] The slurry inlet is connected to the slurry outlet of the carbide slag slurry preparation unit via a second pipeline, and is also connected to the circulating slurry outlet of the slurry circulation tank via a third pipeline.

[0043] The gas distributor is located in the lower part of the absorption tower. It is used to make the flue gas and the slurry flowing down from the top of the tower come into full contact in a countercurrent. The CO2 in the flue gas is absorbed by the calcium hydroxide in the slurry to generate calcium carbonate. At the same time, part of the slurry is converted into lime milk with calcium hydroxide as the main component during the absorption process.

[0044] The inlet of the slurry circulation tank is connected to the circulating slurry outlet in the lower part of the absorption tower via the fourth pipeline;

[0045] The slurry post-treatment unit includes a solid-liquid separation device and a clear liquid storage tank. The inlet of the solid-liquid separation device is connected to the CO2 enriched slurry outlet of the absorption tower via the fifth pipeline. The solid phase outlet of the solid-liquid separation device is used to discharge calcium carbonate solid slag, and its liquid phase outlet is connected to the inlet of the clear liquid storage tank via the sixth pipeline. The outlet of the clear liquid storage tank is connected to the lime slurry inlet of the ammonia stripping unit of the soda ash production system via the seventh pipeline.

[0046] The technical effects and advantages of this invention are as follows:

[0047] This invention constructs a complete system and method encompassing refined formulation of carbide slag slurry, deep purification of flue gas, integrated CO2 absorption and reaction control, slurry post-treatment, and lime slurry recovery. This system enables online monitoring and dynamic optimization control of key parameters such as slurry solid content, particle size, viscosity, and pH value. First, the carbide slag is mechanically activated and gradient-mixed to prepare a stable absorption slurry. Then, the purified flue gas and slurry are brought into countercurrent contact within the absorption tower. By precisely controlling the temperature gradient and liquid-to-gas ratio, and adjusting slurry replenishment and circulation in real-time based on an established dynamic model, the CO2 absorption reaction proceeds stably under optimal conditions. Finally, the post-reaction slurry is separated to obtain a resource-recyclable calcium carbonate product and high-quality lime slurry that can be directly reused in the soda ash ammonia stripping process. This achieves efficient CO2 capture while simultaneously realizing the resource-recycling of waste residue and captured products. Attached Figure Description

[0048] The disclosure of this invention is illustrated with reference to the accompanying drawings. It should be understood that the drawings are for illustrative purposes only and are not intended to limit the scope of protection of this invention. In the drawings, the same reference numerals are used to refer to the same parts:

[0049] Figure 1 This is an overall flow chart of a system and method for removing carbon dioxide using calcium carbide slag slurry in the production of soda ash according to the present invention.

[0050] Figure 2 This is a flowchart of step S1 in a system and method for removing carbon dioxide using calcium carbide slag slurry in the production of soda ash according to the present invention.

[0051] Figure 3This is a flowchart of step S2 in a system and method for removing carbon dioxide using calcium carbide slag slurry in the production of soda ash according to the present invention.

[0052] Figure 4 This is a flowchart of step S3 in a system and method for removing carbon dioxide using calcium carbide slag slurry in the production of soda ash according to the present invention.

[0053] Figure 5 This is a flowchart of step S4 in a system and method for removing carbon dioxide using calcium carbide slag slurry in the production of soda ash according to the present invention.

[0054] Figure 6 This is a system architecture diagram of a system and method for removing carbon dioxide using calcium carbide slag slurry in soda ash production according to the present invention. Detailed Implementation

[0055] It is readily understood that, based on the technical solution of this invention, those skilled in the art can propose various interchangeable structural methods and implementations without altering the essential spirit of the invention. Therefore, the following detailed embodiments and accompanying drawings are merely illustrative examples of the technical solution of this invention and should not be considered as the entirety of the invention or as limitations or restrictions on the technical solution of this invention.

[0056] Reference Figures 1-5 As shown, this invention provides a technical solution: a method for removing carbon dioxide from soda ash production using calcium carbide slag slurry. This method, through refined preparation of the calcium carbide slag slurry, efficient flue gas pretreatment, integrated CO2 absorption and reaction control, and slurry post-treatment and lime slurry recovery, aims to achieve efficient capture and resource utilization of CO2 in soda ash boiler flue gas. Simultaneously, the recovered lime slurry can be directly used in the ammonia stripping unit of soda ash production, significantly increasing the utilization value of calcium carbide slag, reducing soda ash production costs, and significantly reducing carbon emissions. The specific implementation steps are as follows:

[0057] Step 1: Slurry Preparation: Calcium carbide slag and process water are mixed in a slurry mixing tank at a mass ratio of 1:1.5 to 1:2.5, and stirred to prepare a calcium carbide slag absorption slurry with a solid content of 15% to 25% and a d90 ≤ 45 μm. This step aims to prepare a calcium carbide slag absorption slurry with high activity, good dispersibility, and suitable particle size to ensure the efficiency and stability of the subsequent CO2 absorption reaction. The specific implementation steps are as follows:

[0058] S11. Pretreatment and particle size optimization of carbide slag raw materials:

[0059] First, the calcium carbide slag raw material taken from the storage silo is screened to remove any large particles or impurities to prevent clogging of subsequent equipment. Then, the screened calcium carbide slag is mechanically activated using a vertical roller mill. The vertical roller mill pulverizes the calcium carbide slag and controls its particle size by adjusting the grinding disc speed, grinding pressure, and system airflow, ensuring that its d90 (i.e., 90% of the particle diameter is less than or equal to this value) is ≤45μm, preferably ≤30μm. This particle size range significantly increases the specific surface area of ​​the calcium carbide slag (mainly composed of Ca(OH)2), improving its reactivity with CO2, while avoiding separation difficulties caused by excessively fine particles. During the grinding process, the material temperature is controlled at 50-65℃, preferably 55-60℃, to further promote the activation of calcium hydroxide crystals in the calcium carbide slag, making them easier to hydrate and disperse. This temperature also utilizes the waste heat from the soda ash production process, reducing energy consumption.

[0060] S12. Selection and pretreatment of process water:

[0061] The condensate discharged from the soda ash production system is selected as the process water and preheated to 25-35℃, preferably 30℃. Preheating the condensate increases the initial hydration rate of the carbide slag and facilitates the dissolution and dispersion of subsequent additives. A composite additive is added to the preheated process water. This additive consists of 0.05% sodium hexametaphosphate and 0.02% polycarboxylate-based dispersant relative to the mass fraction of the process water. Sodium hexametaphosphate, as a chelating dispersant, effectively inhibits calcium ion scaling and maintains slurry stability; the polycarboxylate-based dispersant improves slurry fluidity, reduces apparent viscosity, prevents solid-phase sedimentation and agglomeration, and makes the slurry easier to pump and spray.

[0062] S13, Gradient Mixing and Online Rheological Control:

[0063] The slurry was prepared in a slurry mixing tank using a gradient mixing method. First, 70% of the pretreated process water was vigorously mixed with all the carbide slag powder at a high speed of 800-1200 rpm (preferably 1000 rpm) to ensure sufficient wetting and initial dispersion of the carbide slag particles. High-speed mixing quickly breaks down the agglomeration forces between particles, forming a uniform initial slurry. Then, the remaining 30% of process water was added, and the stirring speed was adjusted to 300-500 rpm (preferably 400 rpm) for continued stirring. This low-speed stirring at this stage aims to promote slurry maturation and homogenization while reducing air entrainment. During the mixing process, the apparent viscosity of the slurry was monitored in real time using an online viscometer, and the stirring speed, water-cement ratio, or additive dosage was dynamically adjusted based on the monitoring results to control the apparent viscosity of the slurry within 150-400 mPa·s, preferably 200-300 mPa·s. This viscosity range ensures the fluidity of the slurry while preventing particle sedimentation.

[0064] S14. Slurry homogenization maturation and key performance verification:

[0065] The mixed slurry is transferred to a maturation tank, which is a container equipped with a stirring device. In the maturation tank, the slurry is slowly stirred at a low speed of 30-60 rpm (preferably 45 rpm) for at least 30 minutes at 30-40°C, preferably 35°C. The maturation process helps to further hydrate, transform, and stabilize the calcium hydroxide particles in the slurry, eliminating localized inhomogeneities that may occur during the initial mixing process, and stabilizing the slurry properties. After maturation, the slurry is tested for solid content, pH value, and particle size distribution. The solid content should be controlled between 15% and 25%, preferably 20%; the pH value should be within the range of 12.0-12.8; and the particle size distribution should meet the requirement of d90≤45μm. Only slurry that passes the tests can be transported through pipelines to the slurry circulation tank at the top of the absorption tower for later use.

[0066] After the qualified slurry in S14 is transported to the slurry circulation tank, it is stirred at a low speed of 20-30 rpm to ensure the stability of the slurry's performance during long-term storage and use. This is to prevent the sedimentation and agglomeration of solid particles in the slurry and maintain its uniform dispersion. An inclined guide plate is also installed at the bottom of the slurry circulation tank to facilitate uniform circulation of the slurry and prevent sedimentation in dead zones. To monitor the slurry performance in real time, the particle size and apparent viscosity of the slurry in the circulation tank are rechecked every 2 hours. If an increase in particle size or abnormal apparent viscosity is detected, the stirring parameters are adjusted promptly or a small amount of activating additive is added to ensure the stability of the slurry performance and meet the CO2 absorption requirements.

[0067] Step Two: Flue Gas Pretreatment: The boiler flue gas generated during soda ash production is passed into the flue gas pretreatment unit for desulfurization, denitrification, and dust removal, thereby obtaining purified flue gas. This step aims to remove pollutants such as SO2, NOx, and dust from the soda ash production boiler flue gas, preventing them from interfering with subsequent CO2 absorption and protecting the equipment. The specific implementation steps are as follows:

[0068] S21. Desulfurization and simultaneous resource recovery pretreatment:

[0069] Flue gas from the soda ash production boiler (entering through the flue gas inlet) is directed to a calcium-based wet desulfurization tower. In the tower, a slurry containing calcium carbonate or calcium hydroxide (or lime slurry recovered from this system) is sprayed onto the flue gas, causing SO2 in the flue gas to react with alkaline substances in the slurry, generating calcium sulfite, which is further oxidized to calcium sulfate. The pH of the desulfurization slurry is controlled at 5.2-5.8, preferably 5.5. The SO2 concentration is reduced to below 35 mg / Nm³, preferably 20 mg / Nm³. To achieve simultaneous resource utilization, a crystal-directing agent, preferably a mixture of magnesium sulfate and citric acid in a 2:1 mass ratio, is added to the oxidation tank during desulfurization, at a dosage of 0.03%-0.05% of the desulfurization slurry mass. This crystal-directing agent promotes the conversion of by-products into high-quality calcium sulfate dihydrate whiskers, increasing the added value of gypsum and realizing the resource utilization of desulfurization by-products.

[0070] S22, Low-Temperature Catalytic Oxidation Denitrification and Ammonia Slip Control:

[0071] The desulfurized flue gas (temperature approximately 150-180℃) is cooled to 180-220℃, preferably 200℃. The flue gas then enters a denitrification reactor packed with a vanadium-titanium catalyst. In the reactor, ammonia gas obtained from the evaporation of dilute ammonia water is injected to carry out a selective catalytic reduction (SCR) denitrification reaction, reducing nitrogen oxides (NOx) to harmless nitrogen and water. By precisely controlling the ammonia-nitrogen molar ratio at 0.85-0.95, preferably 0.90, the NOx concentration is controlled below 50 mg / Nm³, preferably 30 mg / Nm³. To prevent ammonia escape, an ammonia escape monitor is installed at the outlet flue of the denitrification reactor to monitor the ammonia escape concentration in the denitrification flue gas in real time. When the ammonia escape concentration exceeds 3 mg / Nm³ (preferably 1.5 mg / Nm³), the control system automatically reduces the ammonia injection rate to ensure that ammonia escape meets environmental protection requirements and reduces the impact on downstream equipment and the environment.

[0072] S23. Synergistic removal of deep dust and SO3 aerosol:

[0073] The denitrified flue gas passes sequentially through a low-temperature electrostatic precipitator operating at 90-100℃ and a tubular wet electrostatic precipitator. The low-temperature electrostatic precipitator utilizes the low temperature to condense some SO3 in the flue gas into droplets, which are then captured by electrostatic principles. The wet electrostatic precipitator further utilizes a water film and electric field to efficiently capture fine dust and SO3 aerosols. Through this two-stage dust removal process, the dust concentration at the flue gas outlet is reduced to below 10 mg / Nm³, preferably below 5 mg / Nm³, and SO3 aerosols are also removed, preventing them from corroding or polluting the subsequent CO2 absorption process.

[0074] S24. Flue gas conditioning and cooling:

[0075] After deep dust removal, the flue gas enters the direct contact cooling tower. The cooling tower cools the flue gas to 55±2℃ and brings it close to saturation humidity through spraying cooling water. This temperature range is one of the optimal ranges for CO2 absorption reaction in calcium carbide slag slurry. Simultaneously, through online analyzer and control system linkage, the operating parameters of the induced draft fan are adjusted to ensure that the purified flue gas output from the flue gas pretreatment unit has stable flow rate, temperature, and CO2 concentration, for use in CO2 absorption in step three.

[0076] Step 3: Integrated CO2 Absorption and Reaction Control: Purified flue gas is introduced from the bottom of the absorption tower, while the carbide slag absorption slurry prepared in S1 is sprayed down from the top of the tower. The operating temperature inside the tower is controlled at 40℃ to 65℃, and the liquid-to-gas ratio is 5L / m³ to 15L / m³, ensuring sufficient countercurrent contact between the flue gas and the slurry within the tower. The CO2 in the flue gas reacts with the calcium hydroxide in the slurry to generate a slurry rich in calcium carbonate. Unreacted calcium hydroxide is retained in the liquid phase through control. This step is the core of the invention; through countercurrent contact between the flue gas and the slurry within the absorption tower, efficient CO2 capture is achieved, generating a calcium carbonate-rich slurry and recovering lime milk. Specific implementation steps are as follows:

[0077] S31. Enhancement of gas-liquid distribution and mass transfer interface:

[0078] The purified flue gas obtained in step two is uniformly raised from the bottom of the absorption tower through the purified flue gas inlet. A gas distributor is installed above the purified flue gas inlet to ensure uniform dispersion of the flue gas. Simultaneously, the carbide slag slurry prepared in step one is sprayed down from the top of the absorption tower through the slurry inlet, and atomized into droplets of 80-150 micrometers (preferably 100-120 micrometers) through nozzles. This droplet size provides a large gas-liquid contact area, greatly enhancing the mass transfer efficiency. The absorption tower is filled with a structured packing layer, and the flue gas and slurry undergo countercurrent contact and full mass transfer within the packing layer. The structured packing has the advantages of low pressure drop and high mass transfer efficiency, which can effectively improve the CO2 absorption rate. The flue gas rises at an empty tower velocity of 1.2-1.8 m / s (preferably 1.5 m / s) to ensure optimal gas phase kinetic conditions. The liquid-to-gas ratio is controlled at 5-15 L / m³, preferably 8-12 L / m³, to ensure sufficient liquid volume for CO2 absorption.

[0079] S32. Non-isothermal absorption reaction process and temperature gradient control:

[0080] The reaction between CO2 and Ca(OH)2 is exothermic. To optimize absorption efficiency and product crystal form, the absorption tower is designed for non-isothermal operation. By adjusting the jacket cooling water and the heat exchangers (located in different sections of the tower), an increasing temperature gradient is created axially within the absorption tower, ranging from 40-45°C at the top to 60-65°C at the bottom (preferably 42°C at the top and 62°C at the bottom). The lower temperature at the top of the tower is conducive to the dissolution and absorption of CO2, while the higher temperature at the bottom is conducive to the growth and purification of calcium carbonate crystals, while ensuring that unreacted calcium hydroxide remains active.

[0081] S33. Online diagnosis of reaction process and regulation of slurry property evolution:

[0082] By monitoring key parameters such as density, pH, and conductivity of the circulating slurry online and dynamically adjusting the replenishment flow rate of fresh carbide slag absorption slurry and the discharge rate of circulating slurry based on a pre-established correlation model, the pH value of the circulating slurry in the slurry circulation tank is stabilized within the range of 9.5-11.5, preferably 10.0-10.5. This pH range is the optimal range for CO2 absorption and calcium carbonate formation, ensuring absorption efficiency while preventing a decrease in Ca(OH)2 utilization due to excessively low pH.

[0083] The pH of the circulating slurry in the slurry circulation tank is dynamically adjusted based on a correlation model to maintain stability. ;

[0084] In the formula: u represents the real-time adjustment coefficient, used to dynamically control the ratio of fresh slurry replenishment flow rate to circulating slurry return flow rate; i represents the summation index variable, taking values ​​of 1 and 2, indicating the superposition of two tanh terms with the same structure. This double tanh term structure can more flexibly simulate the nonlinear adjustment response of the system under different pH deviations; a i The weighting coefficients for the hyperbolic tangent term are used to adjust the adjustment intensity across different pH deviation ranges; b i The slope coefficient of the hyperbolic tangent term is used to control the speed of the adjustment response; P represents the real-time pH value of the mixed slurry at the outlet of the slurry circulation tank; P0 represents the target setpoint for the slurry pH, typically 10.0-10.5; ρ represents the real-time density of the slurry; ρ0 represents the target setpoint for the slurry density; c represents the rate-of-change damping coefficient, used to smooth the adjustment process and avoid excessive oscillation; dP / dt represents the rate of change of pH over time. Introducing this term allows for proactive control, adjusting in advance based on the pH change trend; κ represents the real-time conductivity of the slurry; κ0 represents the baseline value of the slurry conductivity, usually related to the ion concentration in the slurry, especially Ca. 2+ and CO3 2- Concentration-dependent, its changes can serve as an auxiliary indicator of the degree of reaction.

[0085] By integrating multiple key parameters such as real-time pH (P), target pH value (P0), real-time density (ρ), target density value (ρ0), pH change rate (dP / dt), and real-time conductivity (κ) of the mixed slurry at the outlet of the slurry circulation tank, a multivariate coupled real-time adjustment coefficient (u) calculation relationship was constructed. The hyperbolic tangent function (tanh) term was used to sensitively capture the positive and negative deviations of the pH value relative to the set value and to impart a nonlinear adjustment response, ensuring that the adjustment tends to be gradual when approaching the target range. By introducing a logarithmic term for the density deviation, changes in the slurry solid content or degree of reaction were incorporated into the adjustment considerations. A damping term (e^(c|dP / dt|)) with the pH change rate as an exponent was used to smoothly suppress rapid pH fluctuations, avoiding excessively frequent adjustment actions due to instantaneous fluctuations. Simultaneously, the ratio of real-time conductivity to the baseline value (κ / κ0) was used as part of the denominator to reflect the correlation between ionic strength and reaction progress in the slurry, allowing the adjustment process to synchronously adapt to the evolution of the slurry's chemical state. Based on the real-time adjustment coefficient (u) calculated using this formula, the process control system can dynamically and precisely adjust the ratio between the replenishment flow rate of fresh carbide slag absorption slurry and the return flow rate of circulating slurry. This allows the pH of the circulating slurry to be stabilized within the optimal range (9.5-11.5) even as the absorption reaction continues and the slurry properties constantly change. This not only achieves steady-state control of the CO2 absorption reaction environment within the absorption tower, improving CO2 capture efficiency and calcium hydroxide utilization, but also ensures the stability of the calcium carbonate product quality. It is the core algorithm supporting the efficient and automated operation of the entire integrated absorption and reaction control process.

[0086] S34. Dynamic equilibrium control of absorption reaction:

[0087] The CO2 absorption and Ca(OH)2 consumption are calculated in real time. When the mass fraction of calcium carbonate in the circulating slurry reaches 12%-18% (preferably 15%), and the slurry's Zeta potential is stable within the range of -25 to -15 mV (preferably -20 mV), the zeta potential is a crucial parameter for evaluating particle dispersion stability. A stable negative potential indicates that the calcium carbonate particles carry a net negative charge on their surface, repelling each other and preventing agglomeration, which is beneficial for subsequent solid-liquid separation. At this point, a portion of the reacted calcium carbonate-rich slurry is drawn out through the CO2-enriched slurry outlet and transported via pipeline to the slurry post-treatment unit in step four. The remaining slurry is returned to the slurry circulation tank via pipeline for reuse.

[0088] Step 4: Slurry Post-treatment and Lime Slurry Recovery: A portion of the calcium carbonate-rich slurry discharged from the bottom of the absorption tower enters a solid-liquid separation unit for solid-liquid separation. The separated calcium carbonate solid slag is discharged externally or utilized as a resource. The separated liquid phase is sent to a lime slurry storage tank, and after conditioning and meeting quality standards, it is transported as lime slurry to the ammonia stripping unit of the soda ash production system. This step aims to separate the calcium carbonate-rich slurry, recover the calcium carbonate solid slag, and prepare lime slurry that can be used in soda ash production. The specific implementation steps are as follows:

[0089] S41. Flocculation and Thickening Pretreatment:

[0090] The calcium carbonate-rich slurry discharged from the absorption tower first enters the buffer thickening tank in the flocculation and thickening unit. In the buffer thickening tank, a flocculant, a mixture of anionic polyacrylamide (PAM) and modified starch at a mass ratio of 1:2 to 1:3 (preferably 1:2.5), is precisely added to the slurry. The flocculant promotes the aggregation of fine calcium carbonate particles into larger flocs, accelerating sedimentation. Flocculation and thickening are carried out under low-speed stirring, increasing the solid content of the underflow slurry from approximately 12-18% to 30%-40% (preferably 35%), achieving preliminary solid-liquid separation and concentration.

[0091] S42, Two-stage solid-liquid separation:

[0092] The thickened slurry is pumped into a two-stage solid-liquid separation system consisting of a horizontal spiral sedimentation centrifuge and a chamber filter press connected in series.

[0093] First, the thick slurry enters a horizontal screw centrifuge. Under a high centrifugal force of 3000-3500G (gravitational acceleration), the centrifuge performs coarse separation of the slurry. Through centrifugation, larger calcium carbonate particles are separated into coarse residue, while a mother liquor containing some fine particles and dissolved Ca(OH)₂ is obtained. The coarse residue flows out of the solid phase outlet of the horizontal screw centrifuge.

[0094] Subsequently, the centrifuged mother liquor enters a chamber filter press for a second stage of fine separation. The chamber filter press operates at a pressure of 0.8-1.2 MPa (preferably 1.0 MPa), which can efficiently capture fine calcium carbonate particles in the centrifuged mother liquor and ensure that the separated liquid phase (i.e., the filter press clear liquid) has an extremely low solid content, thereby obtaining a high-quality filter press clear liquid containing calcium hydroxide.

[0095] In step S44, the filtered liquid is filtered before conditioning to remove solid impurities with a particle size greater than 10 μm. This filtration step is crucial for ensuring the quality of the lime slurry product, guaranteeing its purity, and preventing impurities from causing wear or contamination to the soda ash ammonia stripping unit.

[0096] S43. Resource utilization of calcium carbonate solid slag:

[0097] The coarse residue separated from the horizontal spiral sedimentation centrifuge is washed, dried and classified by the calcium carbonate washing, drying and classification unit to finally obtain high-purity calcium carbonate powder, which can be discharged as a filler, raw material for paper or plastics industry or utilized as a resource.

[0098] The filter cake separated from the chamber filter press is mainly composed of fine calcium carbonate with higher purity. This filter cake is washed with dilute acid (such as dilute hydrochloric acid or dilute acetic acid) to remove surface impurities, and then undergoes drying and activation treatment. The activation treatment, by adjusting the drying temperature and grinding method, prepares precipitated calcium carbonate (PCC) with a large specific surface area and high activity. This PCC can then be discharged externally or utilized for high-value resource recovery, such as in the rubber, plastics, and coating industries.

[0099] S44. Conditioning and recycling of lime slurry products:

[0100] The filtrate obtained from the chamber filter press mainly consists of calcium hydroxide dissolved in water. This filtrate enters the lime slurry storage tank through the lime slurry product conditioning unit. In the lime slurry product conditioning unit, a measured amount of sodium hydroxide (NaOH) solution is added to the filtrate to precisely adjust its pH value to 11.5-12.5, preferably 12.0. This pH range is the pH requirement for lime slurry in the soda ash production ammonia stripping unit. Simultaneously, to prevent calcium hydroxide from carbonizing with CO2 in the air during storage and to avoid the impact of oxidation on the quality of the lime slurry, nitrogen gas is injected into the filtrate to remove oxygen and reduce the oxygen content. Then, the conditioned lime slurry is injected into a nitrogen-sealed insulated lime slurry storage tank. The insulated lime slurry storage tank maintains a constant temperature of 30-40°C (preferably 35°C) through a jacket to prevent calcium hydroxide precipitation and improve its stability. The oxygen content in the storage tank is monitored in real time. When the oxygen content exceeds 0.5% (preferably 0.2%), nitrogen is automatically added for nitrogen sealing protection. The lime slurry is kept under slow, gentle stirring to ensure uniformity and prevent stratification. The conditioned lime slurry is directly transported via pipeline to the ammonia stripping unit of the soda ash production system, replacing traditional quicklime in lime slurry preparation and achieving closed-loop resource recycling.

[0101] Step 5, Process Control: The pH value of the circulating slurry in the absorption tower is monitored online and controlled within the range of 9.5 to 11.5. Based on this, the replenishment flow rate of fresh carbide slag absorption slurry and its ratio to the circulating slurry are dynamically adjusted. This step is crucial throughout the entire method, ensuring the stable and efficient operation of the system. The specific implementation steps are as follows:

[0102] The pH value of the circulating slurry within the absorption tower is monitored online, preferably using the online diagnostic system described in S33. The pH value is strictly controlled within the range of 9.5 to 11.5 (preferably 10.0-10.5). This pH window represents the optimal balance between CO2 absorption efficiency, Ca(OH)2 utilization, and calcium carbonate formation. Based on the real-time monitored pH value, the ratio of the replenishment flow rate of fresh carbide slag absorption slurry to the circulating slurry is dynamically adjusted through the process control system. When the pH value is too low, the replenishment flow rate of fresh slurry is increased; when the pH value is too high, the replenishment of fresh slurry is reduced, while the discharge of circulating slurry is increased to maintain the dynamic balance of the system. This refined process control ensures the stability of absorption efficiency and the consistency of product quality.

[0103] Reference Figure 6 As shown in this embodiment: The present invention also provides a system for removing carbon dioxide using calcium carbide slag slurry in soda ash production. This system applies the above-mentioned method for removing carbon dioxide using calcium carbide slag slurry in soda ash production, and the system includes:

[0104] Flue gas pretreatment unit:

[0105] It is equipped with a flue gas inlet and a purified flue gas outlet, used for desulfurization, denitrification, and dust removal of flue gas from soda ash production boilers. Specifically, it includes a calcium-based wet desulfurization tower, a denitrification reactor, a low-temperature electrostatic precipitator, a tubular wet electrostatic precipitator, a direct contact cooling tower, and an induced draft fan. The desulfurization tower removes SO2 from the flue gas and recovers gypsum whiskers; the denitrification reactor removes NOx; the two-stage dust collector deeply removes dust and SO3 aerosols; and the cooling tower conditions and cools the flue gas. The flue gas parameters output from the purified flue gas outlet are stable.

[0106] Calcium carbide slag slurry preparation unit:

[0107] The system includes a calcium carbide slag storage silo, a quantitative feeding device, a slurry mixing tank, and a stirring device. The calcium carbide slag storage silo is connected to the slurry mixing tank via the quantitative feeding device to precisely control the amount of calcium carbide slag added. The slurry mixing tank is equipped with a process water inlet and a slurry outlet, used to mix and stir calcium carbide slag and water at a set mass ratio to prepare a calcium carbide slag absorbent slurry with a predetermined solid content and particle size distribution. The calcium carbide slag slurry preparation unit preferably also includes a vertical roller mill for activating and grinding the calcium carbide slag, and a maturation tank for homogenizing and maturing the slurry. An online viscometer is used for real-time monitoring and control of the slurry rheological properties.

[0108] Integrated CO2 absorption and lime slurry preparation unit:

[0109] It includes an absorption tower and a slurry circulation tank. The absorption tower is equipped with a purified flue gas inlet, a purified flue gas outlet, a slurry inlet, a CO2-enriched slurry outlet, and a gas distributor.

[0110] The purified flue gas inlet is connected to the purified flue gas outlet of the flue gas pretreatment unit through the first pipeline, and the purified flue gas is sent into the absorption tower.

[0111] The slurry inlet is connected to the slurry outlet of the carbide slag slurry preparation unit via a second pipeline, and is also connected to the circulating slurry outlet of the slurry circulation tank via a third pipeline, ensuring the replenishment of fresh slurry and the return of circulating slurry.

[0112] The gas distributor is located in the lower part of the absorption tower to ensure uniform distribution of flue gas within the tower. The flue gas and the downward-flowing slurry come into full countercurrent contact within the tower. CO2 in the flue gas reacts with calcium hydroxide in the slurry to form calcium carbonate. Some unreacted calcium hydroxide remains in the liquid phase, forming a lime slurry primarily composed of calcium hydroxide.

[0113] The inlet of the slurry circulation tank is connected to the circulating slurry outlet in the lower part of the absorption tower via a fourth pipeline, used to receive a portion of the circulating slurry drawn from the absorption tower. The absorption tower is also equipped with a jacketed cooling water system and an internal heat exchanger to enable non-isothermal absorption processes and temperature gradient control.

[0114] Post-treatment unit for slurry:

[0115] It includes a solid-liquid separation unit and a lime slurry storage tank. The inlet of the solid-liquid separation unit is connected to the CO2 enriched slurry outlet of the absorption tower via a fifth pipeline.

[0116] The solid phase outlet of the solid-liquid separation unit is used to discharge calcium carbonate solid slag, and its liquid phase outlet is connected to the inlet of the lime slurry storage tank through the sixth pipeline.

[0117] The outlet of the lime slurry storage tank is connected to the lime slurry inlet of the ammonia stripping unit of the soda ash production system via the seventh pipeline, which transports the conditioned lime slurry to the soda ash production system.

[0118] The slurry post-treatment unit preferably includes a flocculation and thickening unit (including a buffer thickening tank), a horizontal spiral sedimentation centrifuge, and a chamber filter press to achieve two-stage solid-liquid separation. It also includes a calcium carbonate washing, drying, and grading unit and an activated precipitated calcium carbonate preparation unit for the resource utilization of calcium carbonate solid slag. The lime slurry storage tank is actually an insulated lime slurry storage tank, equipped with a stirring device and a nitrogen sealing device. The lime slurry undergoes pH adjustment and oxygen removal treatment through a lime slurry product conditioning unit.

[0119] Process control system:

[0120] The process control system integrates online sensors (such as pH meters, viscometers, dissolved oxygen meters, and ammonia slip monitors), data acquisition modules, industrial controllers (PLC / DCS), and a human-machine interface. By real-time monitoring of key parameters such as pH, density, and conductivity of the circulating slurry within the absorption tower, and combining this with predictive control models (such as calculation formulas), the system dynamically adjusts the ratio of fresh carbide slag absorber slurry replenishment flow to circulating slurry, ammonia injection volume, and cooling water flow rate, ensuring stable operation and optimized control of the entire process.

[0121] Working principle: The boiler flue gas generated during the soda ash production process first enters the flue gas pretreatment unit, where it undergoes calcium-based wet desulfurization, medium-low temperature catalytic oxidation denitrification, and deep purification through low-low temperature electrostatic precipitator and wet electrostatic precipitator, resulting in purified flue gas with stable temperature, humidity, and pollutant content. At the same time, the carbide slag raw material is screened and mechanically activated by a vertical roller mill, and then mixed in a gradient with preheated process water containing composite additives in a slurry mixing tank to prepare a carbide slag absorption slurry that meets the requirements in terms of solid content, particle size, and rheological properties. After maturation and performance verification, the slurry is transported to the slurry circulation tank at the top of the absorption tower. The purified flue gas rises uniformly from the bottom of the absorption tower and comes into countercurrent contact with the atomized calcium carbide slag slurry sprayed from the top of the tower within the structured packing layer. Under the conditions of a top-to-bottom increasing temperature gradient and optimized liquid-to-gas ratio created by system regulation, the CO2 in the flue gas undergoes a highly efficient absorption reaction with the calcium hydroxide in the slurry, generating a slurry rich in calcium carbonate. By monitoring parameters such as pH, density, and conductivity of the circulating slurry online and based on an established dynamic adjustment model, the replenishment of fresh slurry and the discharge of circulating slurry are controlled in real time to keep the absorption process stable within the optimal reaction range. After the reaction, part of the slurry is drawn into the slurry post-treatment unit. After flocculation and thickening, and two-stage solid-liquid separation, the solid calcium carbonate slag is washed, dried, and activated for resource utilization. The separated calcium hydroxide-containing filter liquid is conditioned and deoxygenated before being stored in an insulated lime milk storage tank and reused as qualified lime milk product in the ammonia stripping process of soda ash production. The entire system realizes the resource utilization of carbide slag waste, the efficient capture and conversion of flue gas CO2, and the closed-loop recovery of lime slurry. While significantly reducing the production cost of soda ash, it effectively reduces carbon emissions and improves the environmental friendliness and economy of the process.

[0122] The technical scope of this invention is not limited to the content described above. Those skilled in the art can make various modifications and variations to the above embodiments without departing from the technical concept of this invention, and all such modifications and variations should fall within the protection scope of this invention.

Claims

1. A method for removing carbon dioxide using calcium carbide slag slurry in soda ash production, characterized in that, Includes the following steps: S1. Slurry preparation: Mix carbide slag and process water in a slurry mixing tank at a mass ratio of 1:1.5 to 1:2.5 and stir to prepare a carbide slag absorption slurry with a solid content of 15% to 25% and d90≤45um. S2. Flue gas pretreatment: The boiler flue gas generated from soda ash production is passed into the flue gas pretreatment unit for desulfurization, denitrification and dust removal, thereby obtaining purified flue gas. S3, CO2 integrated absorption and reaction control: The purified flue gas is introduced from the bottom of the absorption tower, while the carbide slag absorption slurry prepared in S1 is sprayed down from the top of the tower. The operating temperature inside the tower is controlled at 40℃ to 65℃, and the liquid-to-gas ratio is 5L / m³ to 15L / m³, so that the flue gas and slurry are in full countercurrent contact inside the tower. The CO2 in the flue gas reacts with the calcium hydroxide in the slurry to generate a slurry rich in calcium carbonate. By control, the unreacted calcium hydroxide inside the tower is retained in the liquid phase. S4. Post-treatment of slurry and recovery of lime milk: Some of the calcium carbonate-rich slurry discharged from the bottom of the absorption tower enters the solid-liquid separation device for solid-liquid separation. The separated calcium carbonate solid residue is discharged or utilized as a resource. The separated liquid phase is sent to the lime milk storage tank and, after being conditioned and qualified, is transported to the ammonia stripping unit of the soda ash production system for use. S5. Process control: By monitoring the pH value of the circulating slurry in the absorption tower online, the pH value is controlled within the range of 9.5 to 11.5, and the replenishment flow rate of fresh carbide slag absorption slurry and the ratio of circulating slurry are dynamically adjusted accordingly. The specific implementation steps of the integrated CO2 absorption and reaction regulation in S3 are as follows: S31. Enhanced gas-liquid distribution and mass transfer interface: The purified flue gas rises uniformly from the bottom of the absorption tower at an empty tower velocity of 1.2-1.8 m / s, while the carbide slag slurry is atomized into 80-150 micrometer droplets from the top of the tower and sprayed downwards. The two are in countercurrent contact for mass transfer within the structured packing layer. S32. Non-isothermal absorption reaction process and temperature gradient control: By adjusting the jacket cooling water and the heat exchanger in the tower, an increasing temperature gradient is formed in the absorption tower from 40-45℃ at the top to 60-65℃ at the bottom. S33. Online diagnosis of reaction process and regulation of slurry property evolution: By monitoring the density, pH and conductivity of circulating slurry online, the replenishment of fresh slurry and the discharge of circulating slurry are dynamically adjusted according to the established correlation model to stabilize the pH of circulating slurry in the slurry circulation tank at 9.5-11.

5. S34. Dynamic equilibrium control of absorption reaction: Real-time calculation of CO2 absorption and Ca(OH)2 consumption. When the mass fraction of calcium carbonate in the circulating slurry reaches 12%-18% and the Zeta potential is stable at -25 to -15mV, part of the post-reaction slurry is led out to the slurry post-treatment unit in step S4. The pH of the circulating slurry in the slurry circulation tank is dynamically adjusted based on an association model to maintain stability. The calculation formula is as follows: ； In the formula: u represents the real-time adjustment coefficient, used to dynamically control the ratio of fresh slurry replenishment flow rate to circulating slurry return flow rate; i represents the summation index variable, taking values ​​of 1 and 2, indicating the superposition of two tanh terms with the same structure; a i b represents the weighting coefficient of the hyperbolic tangent term; i denoted by ρ, representing the slope coefficient of the hyperbolic tangent term; P represents the real-time pH value of the mixed slurry at the outlet of the slurry circulation tank; P0 represents the target set value of the slurry pH; ρ represents the real-time density of the slurry; ρ0 represents the target set value of the slurry density; c represents the rate of change damping coefficient; dP / dt represents the rate of change of pH over time; κ represents the real-time conductivity of the slurry; κ0 represents the baseline value of the slurry conductivity.

2. The method for removing carbon dioxide using calcium carbide slag slurry in soda ash production according to claim 1, characterized in that: The specific implementation steps for slurry preparation in S1 are as follows: S11. Pretreatment and particle size optimization of calcium carbide slag raw materials: The calcium carbide slag raw materials are screened to remove impurities, and then mechanically activated by a vertical roller mill. The grinding disc speed, grinding pressure and system air volume are controlled to ensure that the particle size meets d90≤45μm, while the material temperature is maintained at 50-65℃. S12. Selection and pretreatment of process water: The condensate of the soda ash production system is preheated to 25-35℃ as process water, and a composite additive consisting of sodium hexametaphosphate with a relative mass fraction of 0.05% and polycarboxylate dispersant of 0.02% is added to it. S13. Gradient mixing and online rheological control: Gradient mixing is adopted. First, 70% of the process water and all the carbide slag powder are mixed at a speed of 800-1200 rpm. Then, the remaining 30% of water is added and the mixture is stirred at a speed of 300-500 rpm. The apparent viscosity of the slurry is controlled at 150-400 mPa·s by an online viscometer. S14. Homogenization and maturation of slurry and verification of key performance: The mixed slurry is transferred to a maturation tank and slowly stirred at 30-60 rpm at 30-40℃ for at least 30 minutes. Then, its solid content, pH value and particle size distribution are tested. If qualified, it is sent to the slurry circulation tank at the top of the absorption tower for later use.

3. The method for removing carbon dioxide using calcium carbide slag slurry in soda ash production according to claim 2, characterized in that: After the qualified slurry in S14 is transported to the slurry circulation tank, it is stirred at a low speed of 20-30 rpm. An inclined guide plate is installed at the bottom of the circulation tank to prevent sedimentation. The particle size and apparent viscosity are checked every 2 hours to ensure the stability of the slurry performance.

4. The method for removing carbon dioxide using calcium carbide slag slurry in soda ash production according to claim 1, characterized in that: The specific implementation steps of flue gas pretreatment in S2 are as follows: S21. Desulfurization and simultaneous resource utilization pretreatment: Flue gas is introduced into a calcium-based wet desulfurization tower, the slurry pH is controlled at 5.2-5.8, SO2 is removed to below 35mg / Nm³, and a crystal-directing agent is added to the oxidation tank to convert the by-product into calcium sulfate dihydrate whiskers. S22. Low-temperature catalytic oxidation denitrification and ammonia slip control: The desulfurized flue gas is cooled to 180-220℃ and enters a reactor filled with vanadium-titanium catalyst. Ammonia gas evaporated from dilute ammonia water is injected for denitrification. The NOx concentration is controlled below 50mg / Nm³ by controlling the ammonia-nitrogen molar ratio at 0.85-0.

95. S23. Deep dust removal and SO3 aerosol synergistic removal: The flue gas is passed sequentially through a low-temperature electrostatic precipitator and a tubular wet electrostatic precipitator operating at 90-100℃, reducing the outlet dust concentration to below 10mg / Nm³ and synergistically removing SO3 aerosol. S24. Flue gas conditioning and cooling: The flue gas enters the direct contact cooling tower and is cooled to 55±2℃ and close to saturated humidity. Finally, the online analyzer and control system are linked to adjust the induced draft fan to output purified flue gas with stable parameters for use in CO2 absorption in step S3.

5. The method for removing carbon dioxide using calcium carbide slag slurry in soda ash production according to claim 4, characterized in that: In S21, the crystal-directing agent is a 2:1 mixture of magnesium sulfate and citric acid, and the addition amount is 0.03%-0.05% of the mass of the desulfurization slurry; in S22, an ammonia slip monitor is installed at the outlet flue of the denitrification reactor filled with vanadium-titanium catalyst to monitor the ammonia slip concentration in the flue gas after denitrification in real time. When the concentration exceeds 3mg / Nm³, the ammonia injection rate is automatically reduced.

6. The method for removing carbon dioxide using calcium carbide slag slurry in soda ash production according to claim 1, characterized in that: The specific implementation steps for slurry post-treatment and lime slurry recovery in S4 are as follows: S41. Flocculation and Thickening Pretreatment: Add anionic polyacrylamide and modified starch mixed in a mass ratio of 1:2 to 1:3 to the calcium carbonate-rich slurry as a flocculant. Flocculate and thicken the slurry in a buffer thickening tank to increase the solid content of the underflow slurry to 30%-40%. S42. Two-stage solid-liquid separation: The thick slurry is pumped into a two-stage separation system consisting of a horizontal screw sedimentation centrifuge and a chamber filter press connected in series. The centrifuge separates the coarse residue at 3000-3500G. The mother liquor is then filtered at 0.8-1.2MPa to obtain a filtered clear liquid containing calcium hydroxide. S43. Resource utilization of calcium carbonate solid residue: Wash, dry and classify the centrifuged coarse residue to obtain calcium carbonate powder; the filter cake of the filter press is washed with dilute acid, dried and activated to convert it into precipitated calcium carbonate. S44. Conditioning of lime slurry product: Add a certain amount of sodium hydroxide solution to the filtered liquid to adjust the pH of the filtered liquid to 11.5-12.5, and inject nitrogen to remove oxygen before storing it in a nitrogen-sealed insulated lime slurry storage tank and stirring slowly at 30-40℃.

7. A method for removing carbon dioxide using calcium carbide slag slurry in soda ash production according to claim 6, characterized in that: The insulated lime slurry storage tank in S44 maintains a temperature of 30-40°C through a jacket and monitors the oxygen content in real time. When the oxygen content in the storage tank exceeds 0.5%, nitrogen is added. Before conditioning, the pressure-filtered liquid is filtered to remove solid impurities with a particle size greater than 10μm.

8. A system for removing carbon dioxide from calcium carbide slag slurry in soda ash production, employing the method for removing carbon dioxide from calcium carbide slag slurry in soda ash production as described in claim 1, characterized in that: The system includes: The flue gas pretreatment unit is equipped with a flue gas inlet and a purified flue gas outlet, and is used to desulfurize, denitrify and remove dust from boiler flue gas. A calcium carbide slag slurry preparation unit includes a calcium carbide slag storage silo, a quantitative feeding device, a slurry mixing tank, and a stirring device. The calcium carbide slag storage silo is connected to the slurry mixing tank through the quantitative feeding device. The slurry mixing tank is provided with a process water inlet and a slurry outlet, and is used to mix and stir calcium carbide slag and water at a set mass ratio to prepare a calcium carbide slag absorbent slurry with a predetermined solid content and particle size distribution. The integrated CO2 absorption and lime slurry preparation unit includes an absorption tower and a slurry circulation tank. The absorption tower is equipped with a purified flue gas inlet, a purified flue gas outlet, a slurry inlet, a CO2-enriched slurry outlet, and a gas distributor. The purified flue gas inlet is connected to the purified flue gas outlet of the flue gas pretreatment unit via a first pipeline. The slurry inlet is connected to the slurry outlet of the carbide slag slurry preparation unit via a second pipeline, and is also connected to the circulating slurry outlet of the slurry circulation tank via a third pipeline. The gas distributor is located in the lower part of the absorption tower, which is used to make the flue gas and the slurry flowing down from the top fully contact each other in a countercurrent in the tower. The CO2 in the flue gas is absorbed by the calcium hydroxide in the slurry to generate calcium carbonate. At the same time, part of the slurry is converted into lime milk with calcium hydroxide as the main component during the absorption process. The inlet of the slurry circulation tank is connected to the circulating slurry outlet in the lower part of the absorption tower via a fourth pipeline. The slurry post-treatment unit includes a solid-liquid separation device and a clear liquid storage tank. The inlet of the solid-liquid separation device is connected to the CO2 enriched slurry outlet of the absorption tower via a fifth pipeline. The solid phase outlet of the solid-liquid separation device is used to discharge calcium carbonate solid slag, and its liquid phase outlet is connected to the inlet of the clear liquid storage tank via a sixth pipeline. The outlet of the clear liquid storage tank is connected to the lime slurry inlet of the ammonia stripping unit of the soda ash production system via a seventh pipeline.

Images