A flue gas dry desulfurization and deacidification agent composition and a method of applying the same

Abstract

The application discloses a flue gas dry desulfurization and deacidification agent composition and an application method thereof. The composition comprises the following raw materials: 65-75% of sodium bicarbonate, 15-30% of calcium hydroxide and 5-10% of modified activated carbon. The modified activated carbon is prepared by the following method: the activated carbon is soaked in a dilute nitric acid solution with a mass fraction of 3-5%, and then is washed with water until neutral, and is dried to obtain pretreated activated carbon; the pretreated activated carbon is immersed in a potassium permanganate solution, the liquid-solid ratio of the potassium permanganate solution to the pretreated activated carbon is 5:1-10:1 mL / g, a redox reaction is carried out by heating, the potassium permanganate is reduced to generate nanometer manganese dioxide on the surface and in the pore channel of the activated carbon, and the modified activated carbon is obtained after filtration, washing and drying. The composition can effectively solve the problem that the existing alkaline desulfurization and deacidification agent such as sodium bicarbonate and calcium hydroxide has low removal efficiency on acidic components such as HCl and SO2 in flue gas.

Description

Technical Field

[0001] This application relates to the field of environmental protection technology, and in particular to a flue gas dry desulfurization and deacidification agent composition and its application method. Background Technology

[0002] Dry flue gas desulfurization and deacidification processes are widely used in the treatment of acidic gases from small and medium-sized boilers, industrial furnaces, and incinerators due to their advantages such as short process flow, no wastewater discharge, and minimal equipment corrosion. The core of this process involves injecting powdered alkaline absorbent into the flue gas duct, causing a gas-solid reaction with acidic components such as HCl, SO2, and SO3 in the flue gas. The reaction products are then collected by a dust collector. The reactivity, utilization rate, and adaptability of the absorbent directly determine the deacidification efficiency and operating costs.

[0003] Currently, the commonly used absorbents for dry acid removal are sodium bicarbonate (sodium bicarbonate) and calcium hydroxide (calcium hydroxide). Sodium bicarbonate rapidly decomposes into porous sodium carbonate with a high specific surface area at flue gas temperatures, exhibiting high reaction rates and near-theoretical alkali utilization for both HCl and SO2. However, it is expensive, and the decomposition products tend to sinter and become dense under large fluctuations in flue gas temperature or instantaneous overheating, leading to a significant decrease in activity. Calcium hydroxide is widely available, inexpensive, and has good tolerance to high-temperature conditions, but its dry reaction activity is significantly lower, especially in SO2 removal. The molar volume of the calcium sulfate produced in the reaction expands, easily forming a dense product layer on the particle surface, hindering the diffusion of acidic gases into the particle interior, resulting in low calcium utilization. To balance economy and acid removal efficiency, the two are often used in combination in practice: the sodium-based absorbent ensures basic acid removal efficiency, while the calcium-based absorbent reduces costs and improves high-temperature adaptability.

[0004] However, the above-mentioned compound system still shows insufficient SO2 removal efficiency. Under dry conditions, SO2 itself has low gas-solid reactivity with solid alkaline absorbents, especially when SO2 concentrations are high or flue gas conditions fluctuate. The effective contact and reaction between SO2 and absorbent are insufficient, and simply increasing the absorbent injection rate does not significantly improve SO2 removal efficiency. Summary of the Invention

[0005] This application aims to address the problem of insufficient SO2 removal efficiency of existing desulfurization and deacidification agents composed of sodium bicarbonate and calcium hydroxide.

[0006] In a first aspect, this application provides a flue gas dry desulfurization and deacidification agent composition, comprising the following raw materials in weight percentages: 65-75% sodium bicarbonate, 15-30% calcium hydroxide, and 5-10% modified activated carbon; wherein the modified activated carbon is prepared by the following method: Activated carbon is placed in a dilute nitric acid solution with a mass fraction of 3% to 5%, soaked, washed with water until neutral, and dried to obtain pretreated activated carbon. The pretreated activated carbon is immersed in a potassium permanganate solution with a liquid-to-solid ratio of 5:1 to 10:1 mL / g. The mixture is heated to carry out an oxidation-reduction reaction, which reduces the potassium permanganate on the surface and in the pores of the activated carbon to generate nano-manganese dioxide. After filtration, washing, and drying, modified activated carbon is obtained.

[0007] In some embodiments, the concentration of the potassium permanganate solution is 0.1–0.3 mol / L.

[0008] In some embodiments, the redox reaction is carried out at a temperature of 60–90°C for 2–6 hours.

[0009] In some embodiments, the immersion treatment is performed at a temperature of 80–90°C for 1–2 hours.

[0010] Under dry conditions, the gas-solid reaction activity of SO2 with alkaline absorbents is inherently low. When HCl and SO2 coexist in the flue gas, SO2 is at a disadvantage in the gas-solid reaction with the alkaline absorbent, further limiting the removal efficiency. MnO2 can oxidize SO2 to SO3, and SO3 has a much higher reactivity with calcium hydroxide or sodium carbonate than SO2. However, if MnO2 is directly mixed with baking soda or calcium hydroxide in a conventional manner, it is difficult to effectively exert its catalytic oxidation effect. Conventional chemical-grade MnO2 (D50≥20μm) has a low specific surface area and limited active sites; although nano-MnO2 has high activity, it is extremely prone to agglomeration, especially during powder injection and pipeline transportation. Agglomerated particles not only clog the spray gun and pipeline but also are difficult to disperse uniformly in the flue gas, failing to fully contact SO2. Furthermore, during simple mixing, there is a lack of a stable contact interface between MnO2 and absorbent particles, making it difficult for the catalytically generated SO3 to be captured by the alkaline components.

[0011] This application effectively solves the aforementioned problems by in-situ loading nano-MnO2 onto the surface and within the pores of activated carbon. Activated carbon itself possesses a high specific surface area and a well-developed pore structure, allowing for the loading of some sodium bicarbonate and calcium hydroxide. Simultaneously, it provides numerous nucleation and anchoring sites for MnO2, enabling it to be highly dispersed at the nanoscale and significantly increasing the effective catalytic activity. Furthermore, the pores inhibit the growth and aggregation of MnO2 particles during preparation and spraying. Nitric acid pretreatment further increases the number of oxygen-containing functional groups, such as carboxyl groups, on the activated carbon surface. These functional groups can serve as anchoring sites for MnO2, enhancing loading stability, and also improve the activated carbon's adsorption and enrichment capacity for SO2, increasing the local concentration of SO2 near the catalytic site and promoting the oxidation reaction. The SO3 generated from SO2 catalyzed by MnO2 exhibits a much higher reactivity with calcium hydroxide or sodium carbonate than SO2, thereby improving the SO2 removal rate. Simultaneously, activated carbon itself also has adsorption properties for pollutants such as dioxins and heavy metals, enabling the composition to possess a certain multi-pollutant synergistic purification capability while deacidifying.

[0012] In some embodiments, the calcium hydroxide is ultrafine calcium hydroxide with a D50 of 3–8 μm and a D90 ≤ 20 μm.

[0013] In some embodiments, the method for preparing the ultrafine calcium hydroxide includes the following steps: Quicklime with a D50 of 20-30 μm is mixed with sodium hexametaphosphate at a mass ratio of 100:0.2-0.5 to obtain a premix. The premixed material is added to a mechanical impact mill for grinding. During the grinding process, an atomizing liquid of sodium dihydrogen phosphate aqueous solution with a mass concentration of 20% to 30% is added. The amount of liquid sprayed is 1.0% to 1.5% of the mass of hydrated lime. The mixture is then ground.

[0014] In some embodiments, the linear velocity of the grinding process is 45–65 m / s, and the grinding chamber temperature is 55–75 °C.

[0015] The ultrafine calcium hydroxide used in this application has a D50 controlled at 3–8 μm, which has significant advantages over commercially available conventional chemical-grade slaked lime. Conventional slaked lime has a coarser particle size and smaller specific surface area. When it reacts with SO2 or HCl, a dense layer of calcium sulfate or calcium chloride quickly forms on the particle surface, encapsulating the unreacted calcium hydroxide inside, resulting in low calcium utilization and difficulty in improving desulfurization efficiency. When it is ground to a D50 of 3–8 μm, the particle specific surface area increases significantly, the diffusion path of acidic gases is shortened, and the reactivity is significantly improved. Under dry conditions, it can more effectively remove SO2, SO3, and HCl.

[0016] However, directly grinding conventional slaked lime to this fineness can easily lead to over-grinding. The newly formed calcium hydroxide surface during the grinding process has high activity, and Ca... 2+ With OH- Fine particles readily recombine, exhibiting a self-healing phenomenon. This causes qualified particles to re-adhere and grow within the grinding chamber, preventing them from being promptly carried out of the grinding chamber by the discharge airflow. Simultaneously, the strong van der Waals forces between fine particles easily lead to agglomeration, forming loose flocs. This results in decreased classification efficiency, with qualified particles being repeatedly ground, ultimately producing a large number of excessively fine particles (the smaller the D10 value, the greater the number of excessively fine particles in the system). These excessively fine particles are prone to absorbing moisture and agglomerating during subsequent spraying and conveying, clogging pipes and reducing actual dispersibility, thus lowering the desulfurization and deacidification reaction efficiency.

[0017] This application employs sodium dihydrogen phosphate and sodium hexametaphosphate as synergistic grinding aids during mechanical impact milling. This effectively reduces the generation of excessively fine particles. Sodium dihydrogen phosphate molecules are relatively small and, under mechanical stress, can penetrate into the microcracks and cleavage planes of calcium hydroxide crystals. The phosphate ions released from sodium dihydrogen phosphate react with the newly exposed CaO on the surface. 2+ The reaction forms an extremely thin layer of insoluble calcium phosphate or hydroxyapatite. This thin layer is firmly anchored to the crack surface, preventing Ca from reacting. 2+ With OH - The rearrangement and combination of these molecules inhibits particle self-healing. Due to the extremely small amount of phosphate added, the resulting coating layer is very thin and discontinuous, and will not significantly consume effective calcium components or hinder subsequent deacidification reactions. Instead, it improves the overall reaction efficiency by inhibiting self-healing and refining particle size. Sodium hexametaphosphate has a large molecular weight and is a long-chain polyphosphate. During grinding, its long-chain structure adsorbs onto the outer surface of calcium hydroxide particles, forming a negatively charged coating layer. This produces a significant steric hindrance effect, preventing direct contact between adjacent particles. At the same time, electrostatic repulsion further prevents the agglomeration of fine particles. The synergistic cooperation of these two different molecular scales allows the grinding products to be promptly carried away from the grinding chamber by the airflow, reducing over-grinding and the generation of excessively fine particles, ensuring that the final ultrafine calcium hydroxide has a narrow particle size distribution and high desulfurization and deacidification activity.

[0018] In some embodiments, the baking soda has a D90 ≤ 20 μm and a D50 of 5–10 μm.

[0019] In some embodiments, the activated carbon is coconut shell-based or wood-based activated carbon, with a D50 of 5–15 μm and a D90 ≤ 30 μm.

[0020] Secondly, this application provides a method for applying a flue gas dry desulfurization and deacidification agent composition, specifically, the composition is used for flue gas dry desulfurization and deacidification, and the flue gas temperature is 160-300℃ during injection.

[0021] In summary, this application has the following beneficial effects: The flue gas dry desulfurization and deacidification agent composition provided in this application achieves highly efficient removal of acidic gases such as SO2 through the synergistic effect of sodium bicarbonate, ultrafine calcium hydroxide, and modified activated carbon. Sodium bicarbonate decomposes into porous sodium carbonate at flue gas temperatures, providing basic deacidification activity and reaction rate. Ultrafine calcium hydroxide, through a grinding-aided process, achieves a narrower particle size distribution, improving the utilization rate of the calcium-based component for SO2 and HCl reactions, reducing reagent costs, and improving high-temperature adaptability. Nano-MnO2, in situ supported on the modified activated carbon, catalyzes the oxidation of SO2 to the more reactive SO3, thereby increasing the SO2 removal rate in the competitive reaction with acidic gases. The synergistic effect of these three components enables the composition to maintain stable desulfurization and deacidification performance over a wide flue gas temperature range, reduces operating costs, and improves powder conveying performance. Detailed Implementation

[0022] Preparation Example 1-1 This preparation example provides a modified activated carbon, the preparation method of which is as follows: Take coconut shell-based activated carbon (BET specific surface area 1200 m²) 2 / g, total pore volume 0.75cm³ 3 100g of a pretreated activated carbon (D50=10μm, D90=25μm) was added to 750mL of a 4% (w / w) dilute nitric acid solution. The mixture was stirred and soaked at 85℃ for 1.5 hours, filtered, and washed with deionized water until the pH of the filtrate was neutral. The filter cake was then vacuum-dried at 120℃ for 4 hours to obtain pretreated activated carbon. 23.7g of potassium permanganate was dissolved in 750mL of deionized water and stirred until completely dissolved to obtain a 0.2mol / L potassium permanganate solution. 750mL of the potassium permanganate solution was added to 100g of the pretreated activated carbon, and the mixture was stirred and reacted in a 75℃ water bath for 4 hours. After the reaction, the mixture was filtered, and the filter cake was washed with deionized water until the filtrate was colorless and the pH was neutral. The mixture was then vacuum-dried at 120℃ for 4 hours to obtain modified activated carbon.

[0023] Preparation Examples 1-2 This preparation example provides a modified activated carbon, the preparation method of which is as follows: Take coconut shell-based activated carbon (BET specific surface area 1200 m²) 2 / g, total pore volume 0.75cm³ 3100g of a pretreated activated carbon (D50=10μm, D90=25μm) was added to 500mL of a 3% (w / w) dilute nitric acid solution. The mixture was stirred and soaked at 80℃ for 1 hour, filtered, and washed with deionized water until the pH of the filtrate was neutral. The filter cake was then vacuum-dried at 120℃ for 4 hours to obtain pretreated activated carbon. 7.9g of potassium permanganate was dissolved in 500mL of deionized water and stirred until completely dissolved to obtain a 0.1mol / L potassium permanganate solution. 500mL of the potassium permanganate solution was added to 100g of the pretreated activated carbon, and the mixture was stirred and reacted in a 60℃ water bath for 2 hours. After the reaction, the mixture was filtered, and the filter cake was washed with deionized water until the filtrate was colorless and the pH was neutral. The filtrate was then vacuum-dried at 120℃ for 4 hours to obtain modified activated carbon.

[0024] Preparation Examples 1-3 This preparation example provides a modified activated carbon, the preparation method of which is as follows: Take coconut shell-based activated carbon (BET specific surface area 1200 m²) 2 / g, total pore volume 0.75cm³ 3 100g of a pretreated activated carbon (D50=10μm, D90=25μm) was added to 1000mL of a 5% (w / w) dilute nitric acid solution and stirred at 90℃ for 2 hours. The mixture was then filtered, washed with deionized water until the pH of the filtrate was neutral, and the filter cake was vacuum-dried at 120℃ for 4 hours to obtain pretreated activated carbon. 47.4g of potassium permanganate was dissolved in 1000mL of deionized water and stirred until completely dissolved to obtain a 0.3mol / L potassium permanganate solution. 100g of the pretreated activated carbon was added to 1000mL of the potassium permanganate solution and stirred in a 90℃ water bath for 6 hours. After the reaction, the mixture was filtered, washed with deionized water until the filtrate was colorless and the pH was neutral, and then vacuum-dried at 120℃ for 4 hours to obtain modified activated carbon.

[0025] Preparation Example 2-1 This preparation example provides an ultrafine calcium hydroxide, which is prepared by the following method: 1000g of conventional chemical-grade slaked lime (D50=25μm, D90=48μm, moisture content 0.8%) and 3.5g of sodium hexametaphosphate were placed in a V-type mixer and mixed at 60rpm for 15 minutes to obtain a premix. The premix was continuously fed into a mechanical impact mill (ACM type) via a screw feeder. The classifying wheel and induced draft system were turned on, and the linear velocity of the impact rotor was set to 55m / s, the classifying wheel speed to 4200rpm, and the system airflow was maintained to stabilize the pressure difference between the mill inlet and outlet at 4kPa. After the mill was running stably, 11.5g of sodium dihydrogen phosphate was dissolved in 37.5g of deionized water to prepare a 25% sodium dihydrogen phosphate aqueous solution. A portion of this solution was sprayed into the mill chamber through a metering pump and a dual-fluid atomizing nozzle, with the total spray volume controlled at 13g. During the grinding process, the temperature of the mill chamber was controlled at around 65℃ by cooling water in the jacket of the mill casing. After grinding, the discharged material was collected to obtain ultrafine calcium hydroxide powder.

[0026] Preparation Example 2-2 This preparation example provides an ultrafine calcium hydroxide, which is prepared by the following method: 1000g of conventional chemical-grade slaked lime (D50=25μm, D90=48μm, moisture content 0.8%) and 2.2g of sodium hexametaphosphate were placed in a V-type mixer and mixed at 60rpm for 15 minutes to obtain a premix. The premix was fed into a mechanical impact mill (ACM type) via a screw feeder. The impact rotor linear velocity was set to 48m / s, the classifier wheel speed to 3800rpm, and the system airflow was adjusted to maintain a stable mill inlet and outlet pressure difference of 3.5kPa. 10g of sodium dihydrogen phosphate was dissolved in 40g of deionized water to prepare a 20% sodium dihydrogen phosphate aqueous solution, which was sprayed into the mill chamber through a dual-fluid atomizing nozzle, with a total spray volume of 12g. During the grinding process, the mill chamber temperature was stabilized at 60℃ through jacket cooling and inlet air temperature regulation. After grinding, the discharged material was collected to obtain ultrafine calcium hydroxide powder.

[0027] Preparation Examples 2-3 This preparation example provides an ultrafine calcium hydroxide, which is prepared by the following method: 1000g of conventional chemical-grade slaked lime (D50=28μm, D90=52μm, moisture content 1.0%) and 4.8g of sodium hexametaphosphate were placed in a V-type mixer and mixed at 60rpm for 15 minutes to obtain a premix. The premix was fed into a mechanical impact mill (ACM type), with the impact rotor linear velocity set to 62m / s, the classifier wheel speed set to 4600rpm, and the system airflow maintained at a stable mill inlet and outlet pressure difference of 4.5kPa. 15g of sodium dihydrogen phosphate was dissolved in 35g of deionized water to prepare a 30% sodium dihydrogen phosphate aqueous solution, which was sprayed into the grinding chamber through a dual-fluid atomizing nozzle, with a total spray volume of 15g. During the grinding process, the grinding chamber temperature was controlled at 70℃ using a cooling system. After grinding, the discharged material was collected to obtain ultrafine calcium hydroxide powder.

[0028] Preparation Examples 2-4 This preparation example provides an ultrafine calcium hydroxide, which differs from Preparation Example 2-1 in that an equal mass of sodium hexametaphosphate is used instead of sodium dihydrogen phosphate.

[0029] Preparation Examples 2-5 This preparation example provides an ultrafine calcium hydroxide, which differs from Preparation Example 2-1 in that an equal mass of sodium dihydrogen phosphate is used instead of sodium hexametaphosphate.

[0030] Preparation Examples 2-6 This preparation example provides an ultrafine calcium hydroxide, which differs from Preparation Example 2-1 in that sodium hexametaphosphate was not added during the grinding process. The specific grinding steps are as follows: 1000g of conventional chemical-grade slaked lime (D50=25μm, D90=48μm, moisture content 0.8%) was continuously fed into a mechanical impact mill (ACM type) via a screw feeder. The classifying wheel and induced draft system were turned on, and the linear velocity of the impact rotor was set to 55m / s, the classifying wheel speed to 4200rpm, and the system airflow was maintained at a stable inlet-outlet pressure difference of 4kPa. After the mill stabilized, 11.5g of sodium dihydrogen phosphate was dissolved in 37.5g of deionized water to prepare a 25% sodium dihydrogen phosphate aqueous solution. This solution was then sprayed into the grinding chamber through a metering pump and a dual-fluid atomizing nozzle, with the total spray volume controlled at 13g. During the grinding process, the temperature of the grinding chamber was controlled at approximately 65℃ using cooling water from the casing jacket. After grinding, the discharged material was collected to obtain ultrafine calcium hydroxide powder.

[0031] Preparation Examples 2-7 This preparation example provides an ultrafine calcium hydroxide, which differs from Preparation Example 2-1 in that sodium dihydrogen phosphate is not added during the grinding process. The specific grinding steps are as follows: 1000g of conventional chemical-grade hydrated lime (D50=25μm, D90=48μm, moisture content 0.8%) and 3.5g of sodium hexametaphosphate were placed in a V-type mixer and mixed at 60rpm for 15 minutes to obtain a premix. The premix was continuously fed into a mechanical impact mill (ACM type) via a screw feeder. The classifying wheel and induced draft system were turned on, and the linear velocity of the impact rotor was set to 55m / s, the speed of the classifying wheel to 4200rpm, and the system airflow was maintained to stabilize the pressure difference between the mill inlet and outlet at 4kPa. During the grinding process, the temperature of the grinding chamber was controlled at around 65℃ by cooling water in the jacket of the mill. After grinding, the discharged material was collected to obtain ultrafine calcium hydroxide powder.

[0032] Example 1

[0033] This embodiment provides a flue gas dry desulfurization and deacidification agent composition and its application method, wherein the preparation method of the flue gas dry desulfurization and deacidification agent composition is as follows: Take 700g of baking soda (after grinding, D90=16μm, D50=7μm), 220g of ultrafine calcium hydroxide obtained according to Preparation Example 2-1, and 80g of modified activated carbon obtained according to Preparation Example 1-1, add them together to a V-type mixer, mix at 50rpm for 20 minutes, and discharge to obtain a flue gas dry desulfurization and deacidification agent composition.

[0034] The application method is as follows: A dry desulfurization evaluation device is used, which consists of a simulated flue gas preparation section, a heating section, an injection section, a bag filter, and an induced draft fan connected in sequence. Compressed air is used as the carrier gas in the simulated flue gas, and standard gases of SO2, HCl, and SO3 are introduced separately. The flow rates of each gas are controlled by a mass flow meter to ensure that the initial SO2 concentration in the mixed flue gas is 800 mg / Nm³. 3 The initial concentration of HCl was 500 mg / Nm³. 3 The initial SO3 concentration was 25 mg / Nm³. 3 The simulated flue gas was heated by an electric heater to a temperature controlled at 200±5℃ before the injection point. A K-type thermocouple was used to measure the flue gas temperature 0.3m before the injection point. The above composition was fed through a screw feeder at a rate of 120mg / Nm³. 3 The flue gas is injected at a constant rate into the Venturi injector and then into the flue at the injection point. The injection pressure is 0.4 MPa, and the outlet gas velocity is 35 m / s. The residence time of the flue gas from the injection point to the inlet of the bag filter is 3 seconds. The bag filter uses PTFE membrane filter bags with a filtration velocity of 1.0 m / min. A sampling port is set at the outlet of the bag filter. The SO2 concentration is determined by non-dispersive infrared absorption spectrometry, the HCl concentration by ion chromatography, and the SO3 concentration by controlled condensation-ion chromatography. The emission concentrations of each component are recorded, and the removal rate is calculated.

[0035] Example 2

[0036] This embodiment provides a flue gas dry desulfurization and deacidification agent composition and its application method, wherein the preparation method of the flue gas dry desulfurization and deacidification agent composition is as follows: Take 660g of baking soda with D90=14μm and D50=6μm after grinding, 290g of ultrafine calcium hydroxide obtained according to Preparation Example 2-2, and 50g of modified activated carbon obtained according to Preparation Example 1-2, and add them together into a V-type mixer. Mix at 50rpm for 20 minutes, and discharge to obtain a flue gas dry desulfurization and deacidification agent composition.

[0037] The application method is as follows: A dry desulfurization evaluation device is used, which consists of a simulated flue gas preparation section, a heating section, an injection section, a bag filter, and an induced draft fan connected in sequence. Compressed air is used as the carrier gas in the simulated flue gas, and standard gases of SO2, HCl, and SO3 are introduced separately. The flow rates of each gas are controlled by a mass flow meter to ensure that the initial SO2 concentration in the mixed flue gas is 1200 mg / Nm³.3 The initial concentration of HCl was 300 mg / Nm³. 3 The initial SO3 concentration was 30 mg / Nm³. 3 The simulated flue gas was heated by an electric heater to a temperature controlled at 170±5℃ before the injection point. A K-type thermocouple was used to measure the flue gas temperature 0.3m before the injection point. The above composition was fed through a screw feeder at a rate of 150mg / Nm³. 3 The flue gas is injected at a constant rate into the Venturi injector and then into the flue at the injection point. The injection pressure is 0.35 MPa, and the outlet gas velocity is 30 m / s. The residence time of the flue gas from the injection point to the inlet of the bag filter is 3.5 seconds. The bag filter uses PTFE membrane filter bags with a filtration velocity of 1.0 m / min. A sampling port is set at the outlet of the bag filter. The SO2 concentration is determined by non-dispersive infrared absorption spectrometry, the HCl concentration by ion chromatography, and the SO3 concentration by controlled condensation-ion chromatography. The emission concentrations of each component are recorded, and the removal rate is calculated.

[0038] Example 3

[0039] This embodiment provides a flue gas dry desulfurization and deacidification agent composition and its application method, wherein the preparation method of the flue gas dry desulfurization and deacidification agent composition is as follows: 750g of baking soda with D90=18μm and D50=8μm after grinding, 150g of ultrafine calcium hydroxide obtained according to preparation examples 2-3, and 100g of modified activated carbon obtained according to preparation examples 1-3 were added together into a V-type mixer and mixed at 50rpm for 20 minutes. The mixture was then discharged to obtain a flue gas dry desulfurization and deacidification agent composition.

[0040] The application method is as follows: A dry desulfurization evaluation device is used, which consists of a simulated flue gas preparation section, a heating section, an injection section, a bag filter, and an induced draft fan connected in sequence. Compressed air is used as the carrier gas in the simulated flue gas, and standard gases of SO2, HCl, and SO3 are introduced separately. The flow rates of each gas are controlled by a mass flow meter to ensure that the initial SO2 concentration in the mixed flue gas is 600 mg / Nm³. 3 The initial concentration of HCl was 800 mg / Nm³. 3 The initial SO3 concentration was 20 mg / Nm³. 3 The simulated flue gas was heated by an electric heater to a temperature controlled at 280±5℃ before the injection point. A K-type thermocouple was used to measure the flue gas temperature 0.3m before the injection point. The above composition was fed through a screw feeder at a rate of 100mg / Nm³. 3The flue gas is injected at a constant rate into the Venturi injector and then into the flue at the injection point. The injection pressure is 0.4 MPa, and the outlet gas velocity is 35 m / s. The residence time of the flue gas from the injection point to the inlet of the bag filter is 3 seconds. The bag filter uses PTFE membrane filter bags with a filtration velocity of 1.0 m / min. A sampling port is set at the outlet of the bag filter. The SO2 concentration is determined by non-dispersive infrared absorption spectrometry, the HCl concentration by ion chromatography, and the SO3 concentration by controlled condensation-ion chromatography. The emission concentrations of each component are recorded, and the removal rate is calculated.

[0041] Example 4

[0042] This embodiment provides a flue gas dry desulfurization and deacidification agent composition and its application method. The difference from Example 1 is that the ultrafine calcium hydroxide obtained in Preparation Example 2-1 is replaced with the ultrafine calcium hydroxide obtained in Preparation Example 2-4 in equal mass.

[0043] Example 5

[0044] This embodiment provides a flue gas dry desulfurization and deacidification agent composition and its application method. The difference from Example 1 is that the ultrafine calcium hydroxide obtained in Preparation Example 2-1 is replaced with the ultrafine calcium hydroxide obtained in Preparation Example 2-5 in equal mass.

[0045] Example 6

[0046] This embodiment provides a flue gas dry desulfurization and deacidification agent composition and its application method. The difference from Example 1 is that the ultrafine calcium hydroxide obtained in Preparation Example 2-1 is replaced with the ultrafine calcium hydroxide obtained in Preparation Example 2-6 in equal mass.

[0047] Example 7

[0048] This embodiment provides a flue gas dry desulfurization and deacidification agent composition and its application method. The difference from Example 1 is that the ultrafine calcium hydroxide obtained in Preparation Example 2-1 is replaced with the ultrafine calcium hydroxide obtained in Preparation Example 2-7 in equal mass.

[0049] Example 8

[0050] This embodiment provides a flue gas dry desulfurization and deacidification agent composition and its application method. The difference from Example 1 is that the ultrafine calcium hydroxide obtained in Preparation Example 2-1 is replaced with an equal mass of conventional chemical grade slaked lime (D50=25μm, D90=48μm, moisture content 0.8%).

[0051] Comparative Example 1 This comparative example provides a flue gas dry desulfurization and deacidification agent composition and its application method. The difference from Example 1 is that an equal amount of coconut shell-based activated carbon (BET specific surface area 1200 m²) is used. 2 / g, total pore volume 0.75cm³ 3(g, D50=10μm, D90=25μm) to replace the modified activator carbon obtained in Example 1-1.

[0052] Comparative Example 2 This comparative example provides a flue gas dry desulfurization and deacidification agent composition and its application method. The difference between this example and Example 1 is that the formulation of the flue gas dry desulfurization and deacidification agent composition is different, as detailed below: 700g of baking soda (ground to D90=16μm, D50=7μm), 220g of ultrafine calcium hydroxide obtained according to Preparation Example 2-1, 70.8g of pretreated activated carbon (same as the activated carbon used in Preparation Example 1-1, pretreated with dilute nitric acid and dried, D50=10μm, D90=25μm), and 9.2g of nano-MnO2 (D50≤100nm) were added together into a V-type mixer and mixed at 50rpm for 20 minutes. The mixture was then discharged to obtain a dry flue gas desulfurization and deacidification agent composition. The amounts of activated carbon and nano-MnO2 used in the comparative example were calculated based on the amount of modified activated carbon used in Example 1.

[0053] Performance testing and analysis: 1. Test of particle size distribution of ultrafine calcium hydroxide Approximately 10 g of the ultrafine calcium hydroxide samples prepared in each preparation example were dried in a vacuum drying oven at 60℃ for 4 hours before use. The particle size was measured using a laser particle size analyzer equipped with a dry dispersion unit. The test conditions were: dry dispersion pressure 0.2–0.4 MPa, shading 1%–3%, particle refractive index 1.57, absorptivity 0.1, and particle density 2.24 g / cm³. 3 Each sample was measured three times consecutively, and the average value was recorded. The values ​​of D10, D50, and D90 were then calculated using the formula: Distance = (D90 - D10) / D50; Wherein, D50 is the particle size corresponding to 50% of the cumulative volume fraction, i.e., the median particle size, representing the average size of ultrafine calcium hydroxide particles; D10 is the particle size corresponding to 10% of the cumulative volume fraction, reflecting the distribution of excessively fine particles in the particle group; the smaller the D10 value, the more excessively fine particles there are in the system; D90 is the particle size corresponding to 90% of the cumulative volume fraction, reflecting the distribution of coarse particles in the particle group; the diameter distance is a dimensionless parameter for evaluating the width of the particle size distribution; the larger the diameter distance, the more severe the coarseness and fineness differentiation of the particle group, and the wider the distribution; the smaller the diameter distance, the more concentrated and uniform the particle size distribution. The test results are shown in Table 1.

[0054] Table 1. Test results of particle size distribution of ultrafine calcium hydroxide

[0055] Removal rate test The removal rate of each component is calculated using the following formula:

[0056] Where η is the removal rate (%), and C0 is the initial concentration (mg / Nm³). 3 C1 represents the emission concentration (mg / Nm³). 3 The test results are recorded in Table 2.

[0057] Table 2. Results of the removal rate test

[0058] Based on the test results in Tables 1 and 2, we can conclude that: Compared to Example 1, Example 4, which used the ultrafine calcium hydroxide obtained in Examples 2-4 (with sodium hexametaphosphate replacing sodium dihydrogen phosphate), showed a decrease in SO2 removal rate and a slight reduction in HCl removal rate. This indicates that using only sodium hexametaphosphate is insufficient to simultaneously suppress self-healing and agglomeration. The reason is that the lack of sodium dihydrogen phosphate resulted in the ineffective suppression of the self-healing phenomenon on the surface of the newly formed calcium hydroxide. Particles that had reached the required size re-agglomerated within the grinding chamber and failed to be carried out of the chamber by the airflow in time, producing a large number of excessively fine particles. These particles exhibited poor dispersibility during spraying and conveying, leading to reduced reaction efficiency.

[0059] Example 5 uses the ultrafine calcium hydroxide obtained in Examples 2-5 (sodium dihydrogen phosphate instead of sodium hexametaphosphate). The SO2 removal rate decreases and the HCl removal rate decreases slightly. The reason may be that although sodium dihydrogen phosphate inhibits self-healing, the agglomeration between particles cannot be effectively controlled. The grinding product contains a lot of agglomerated flocs, which prevents the qualified particles from being carried out of the grinding chamber by the airflow in time, resulting in over-grinding and some overly fine particles. These particles are difficult to disperse evenly during spraying and conveying, which affects the deacidification effect.

[0060] In Example 6, using the ultrafine calcium hydroxide obtained in Examples 2-6 (without sodium hexametaphosphate, only a sodium dihydrogen phosphate solution was sprayed in), the removal rates of SO2 and HCl decreased significantly. This may be because small-molecule sodium dihydrogen phosphate alone cannot adequately prevent the agglomeration of fine particles. The long-chain coating and electrostatic repulsion of sodium hexametaphosphate are crucial for maintaining the dispersibility of the powder during and after grinding. Without these properties, particle agglomeration is severe, leading to over-grinding and excessively fine particles, further exacerbating the agglomeration of the grinding products, resulting in a reduced effective reaction area and decreased deacidification effect.

[0061] Example 7 uses the ultrafine calcium hydroxide obtained in Examples 2-7 (without sodium dihydrogen phosphate, only sodium hexametaphosphate added). The SO2 removal rate and HCl removal rate both decreased. This may be because while sodium hexametaphosphate can prevent particle agglomeration, it cannot prevent the self-healing of microcracks within the particles. This leads to the re-densification of some of the refined calcium hydroxide, resulting in over-grinding and excessively fine particles that are difficult to disperse evenly during spraying and conveying, thus reducing reactivity.

[0062] In Example 8, replacing ultrafine calcium hydroxide with an equal amount of conventional chemical-grade slaked lime (D50=25μm) significantly reduced the removal rates of both SO2 and HCl. Conventional slaked lime has a coarse particle size and small specific surface area; when it reacts with acidic gases, the surface product layer rapidly densifies, preventing the internal calcium hydroxide from continuing to participate in the reaction, thus drastically reducing calcium utilization. This demonstrates that ultrafine processing plays a crucial role in improving deacidification efficiency.

[0063] In Comparative Example 1, replacing the modified activated carbon (without MnO2) with an equal amount of coconut shell-based activated carbon significantly reduced the SO2 removal rate, while the removal rates of HCl and SO3 showed little change. This may be because the process of catalytic oxidation of SO2 to SO3 by MnO2 was missing, and SO2 still reacted with the alkaline absorbent in a less reactive form, limiting the removal efficiency. This indicates that in-situ loading of MnO2 has a significant effect on improving the SO2 removal rate.

[0064] Comparative Example 2 replaced the modified activated carbon with a physical blend of pretreated activated carbon and nano-MnO2. The SO2 removal rate was improved compared to Comparative Example 1, but still lower than that of Example 1. This indicates that the physically mixed nano-MnO2, due to agglomeration and lack of a close contact interface with the alkaline absorbent, makes it difficult for the SO3 generated by catalytic oxidation to be captured by the adjacent absorbent in a timely manner, thus failing to fully utilize the advantages of catalytic oxidation. This demonstrates the importance of in-situ loading for improving catalytic desulfurization efficiency.

[0065] Although this application has been disclosed above with reference to preferred embodiments, it is not intended to limit this application. Any person skilled in the art can make possible changes and modifications to the technical solutions of this application by utilizing the methods and techniques disclosed above without departing from the spirit and scope of this application. Therefore, any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of this application without departing from the content of the technical solutions of this application shall fall within the protection scope of the technical solutions of this application.

Claims

1. A composition for dry flue gas desulfurization and deacidification, characterized in that, The raw materials include the following percentages by weight: 65-75% baking soda, 15-30% calcium hydroxide, and 5-10% modified activated carbon; the modified activated carbon is prepared by the following method: Activated carbon is placed in a dilute nitric acid solution with a mass fraction of 3% to 5%, soaked, washed with water until neutral, and dried to obtain pretreated activated carbon. The pretreated activated carbon is immersed in a potassium permanganate solution with a liquid-to-solid ratio of 5:1 to 10:1 mL / g. The mixture is heated to carry out an oxidation-reduction reaction, which reduces the potassium permanganate on the surface and in the pores of the activated carbon to generate nano-manganese dioxide. After filtration, washing, and drying, modified activated carbon is obtained.

2. The flue gas dry desulfurization and deacidification agent composition according to claim 1, characterized in that, The concentration of the potassium permanganate solution is 0.1–0.3 mol / L.

3. The flue gas dry desulfurization and deacidification agent composition according to claim 1, characterized in that, The redox reaction is carried out at a temperature of 60–90°C for 2–6 hours.

4. The flue gas dry desulfurization and deacidification agent composition according to claim 1, characterized in that, The soaking treatment is performed at a temperature of 80–90°C for 1–2 hours.

5. The flue gas dry desulfurization and deacidification agent composition according to claim 1, characterized in that, The calcium hydroxide is ultrafine calcium hydroxide with a D50 of 3–8 μm and a D90 ≤ 20 μm.

6. The flue gas dry desulfurization and deacidification agent composition according to claim 5, characterized in that, The preparation method of the ultrafine calcium hydroxide includes the following steps: Quicklime with a D50 of 20-30 μm is mixed with sodium hexametaphosphate at a mass ratio of 100:0.2-0.5 to obtain a premix. The premixed material is added to a mechanical impact mill for grinding. During the grinding process, an atomizing liquid of sodium dihydrogen phosphate aqueous solution with a mass concentration of 20% to 30% is added. The amount of liquid sprayed is 1.0% to 1.5% of the mass of hydrated lime. The mixture is then ground.

7. The flue gas dry desulfurization and deacidification agent composition according to claim 6, characterized in that, The grinding linear velocity is 45–65 m / s, and the grinding chamber temperature is 55–75 °C.

8. The flue gas dry desulfurization and deacidification agent composition according to claim 1, characterized in that, The baking soda has a D90 ≤ 20 μm and a D50 of 5–10 μm.

9. The flue gas dry desulfurization and deacidification agent composition according to claim 1, characterized in that, The activated carbon is coconut shell-based or wood-based activated carbon with a D50 of 5–15 μm.

10. The method of applying the flue gas dry desulfurization and deacidification agent composition according to any one of claims 1 to 9, characterized in that, The composition is used for dry desulfurization and deacidification of flue gas, with the flue gas temperature at 160–300°C during injection.

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