Trace ozone synergistic low-temperature catalysis method

Abstract

The invention relates to the technical field of waste gas treatment, and particularly discloses a trace ozone synergistic low-temperature catalysis method which comprises the following steps: uniformly mixing SO2-containing tail gas with trace ozone (5-50 ppmv); enabling the mixed gas to sequentially pass through a composite bed layer consisting of a transition metal oxide low-temperature oxidation layer, a mist blocking coagulation layer and an activated carbon layer; sO2 is efficiently oxidized into SO3 at low temperature by using active oxygen generated by decomposition of ozone on the surface of the catalyst, synergistic removal of sulfuric acid mist and SO3 is realized through coagulation, adsorption and chemical fixation, and meanwhile, the residual ozone is ensured to be thoroughly decomposed; the concentration of SO2 at an outlet and the axial temperature difference delta Tr of a bed layer are monitored on line, the ozone adding amount is dynamically adjusted based on a closed-loop control strategy with the temperature difference delta Tr as a main control variable, and it is achieved that the concentration of SO2 at the outlet is smaller than or equal to 10 mg / Nm and tail gas is discharged by O3lt; and the stable ultralow emission of 0.1 ppmv is realized. The method realizes high-efficiency deep purification of SO2 under a low-temperature condition, and has the advantages of low energy consumption, no ozone escape, strong impact load resistance and stable and safe operation.

Description

Technical Field

[0001] This application relates to the technical field of waste gas treatment, and in particular to a trace ozone synergistic low-temperature catalytic method. Background Technology

[0002] In industries such as sulfuric acid, smelting, coal / gas combustion, and chemicals, trace amounts of SO2 (typically 5-300 mg / Nm³, but can reach 500-1000 mg / Nm³ under impact) and sulfuric acid mist formed from SO3 conversion still remain in the exhaust gas after primary treatment processes (such as dual-alkali process, wet absorption, and conversion-absorption). To meet increasingly stringent ultra-low emission standards, highly efficient end-of-pipe deep purification technologies are needed. Existing technologies have several shortcomings: high-temperature catalytic oxidation requires operation above 350°C, resulting in high energy consumption, slow system start-up and shutdown, poor adaptability to fluctuating exhaust gas temperatures, and the need for a complex absorption system after SO3 generation; wet deep absorption, while capable of operation under mild conditions, suffers from secondary pollution of wastewater / sludge, equipment corrosion, limited efficiency in acid mist removal, and a delayed response to instantaneous SO2 concentration shocks; activated carbon (AC) adsorption can adsorb SO2 and acid mist at low temperatures, but its adsorption capacity is limited, regeneration is difficult after saturation, and simple physical adsorption has weak low-temperature oxidation capacity for SO2, with bed pressure drop easily increasing due to dust and acid mist accumulation. Direct ozone oxidation can oxidize SO2 into more treatable SO3, but ozone alone can easily lead to side reactions, ozone escape causing secondary pollution, and material aging, and lacks precise control over the reaction process, resulting in low ozone utilization. Therefore, there is an urgent need to develop a deep SO2 removal technology that can operate efficiently and stably at low temperatures, has strong resistance to shock loads, low energy consumption, and no risk of secondary pollution. Summary of the Invention

[0003] To address the problem of residual sulfuric acid mist formed by the conversion of SO2 and SO3 after existing exhaust gas treatment, this application provides a trace ozone-coordinated low-temperature catalytic method.

[0004] This application provides a trace ozone-coordinated low-temperature catalytic method, which employs the following technical solution: A trace ozone-coordinated low-temperature catalysis method includes the following steps: S1: Mix SO2-containing exhaust gas with ozone evenly, with the ozone dosage being 5-50 ppmv of the dry basis volume of the exhaust gas; S2: The mixed gas in S1 is passed sequentially through a composite bed consisting of a low-temperature oxidation layer of transition metal oxides, a fog-blocking and condensation layer, and an activated carbon layer within a low-temperature catalytic polishing device; wherein: The transition metal oxide layer is used to oxidize SO2 to SO3, and the transition metal oxide layer and activated carbon layer are used to decompose the O3 surface to generate surface active oxygen to regenerate active sites on the catalyst. The fog-blocking and condensation layer is used to capture and condense sulfuric acid droplets and fine particles in the gas. The activated carbon layer is used to physically adsorb and chemically fix the generated SO3 and sulfuric acid mist, and to decompose and intercept residual ozone. S3: Monitor the SO2 concentration at the outlet and the axial temperature difference ΔTr of the composite bed online. Based on the closed-loop control method with the SO2 concentration at the outlet and ΔTr as the main control variables, dynamically adjust the ozone dosage to ensure that the SO2 at the outlet reaches the emission limit of ≤10 mg / Nm³ and the O3 in the tail emission is less than 0.1 ppmv.

[0005] By adopting the above technical solution, this invention constructs a multi-stage synergistic purification path of ozone-co-catalytic oxidation-droplet coagulation-adsorption fixation / ozone destruction, and introduces intelligent closed-loop control based on key parameters at the end. This method combines trace ozone as a controllable active oxygen source with a low-temperature catalyst, achieving efficient and directional oxidation of trace SO2 at low temperatures, overcoming the shortcomings of traditional high-temperature catalysis, such as high energy consumption, limited adsorption capacity of activated carbon, and lack of oxidation ability. At the same time, the end-stage activated carbon layer ensures zero ozone escape, solving the problem of secondary pollution caused by simple ozone oxidation technology. The introduction of closed-loop control enables the entire process to have adaptive capabilities, maintaining optimal ozone utilization efficiency and purification effect under different loads, achieving the goal of efficient, stable, safe, and energy-saving deep purification.

[0006] In some implementations, the ozone dosage is 10-25 ppmv during steady-state operation; when an SO2 load shock is detected, the ozone dosage is increased to 50-60 ppmv, and the high dosage duration is less than 10 minutes.

[0007] In some implementations, the closed-loop control method in S3 includes the following steps: S31: Collect outlet SO2 concentration, bed multi-point temperature T(z), pressure drop ΔP and inlet dew point, where outlet SO2 and ΔTr are closed-loop main variables, and acid mist number concentration, ΔP and dew point margin are limiting or interlocking variables. S32: SO2 error SO is obtained after filtering and boundary checking. 2err Extract the bed temperature difference ΔTr, the location of the thermal peak, and the recovery time T. rec And calculate d(SO) 2out ) / dt; S33: Based on O3 setting = PI〔w1·SO 2err + w2·ΔT rerr + w3·d(SO2) / dt〕and superimpose the dew point margin and the adaptive limit of the ΔP growth rate to generate the O3 setpoint; S34: When O 3outWhen the ozone concentration is ≥0.2 ppmv for ≥60 s, or the dew point margin is <5 °C or the ΔP growth rate exceeds the threshold, a safety interlock is executed: O3 is forced to 0, and the ozone destruction unit is fully opened while maintaining thermal purging and alarm. S35: During start-up and shutdown, the bed temperature must be ≥100 °C before O3 addition can be unlocked; when shutting down, cut off O3 and keep the destruction unit online for 10–15 minutes before stopping.

[0008] In some embodiments, the transition metal oxide low-temperature oxide layer is filled with a multi-metal composite oxide, the active component having a mass fraction of 5-20 wt%, and its morphology being honeycomb, strip, or spherical.

[0009] In some embodiments, the activated carbon layer is columnar or granular activated carbon with a specific surface area of ​​800–1200 m² / g, and is modified with alkali metals or alkaline earth metals or amination.

[0010] In some implementations, the fog-blocking condensation layer is a fiber pad or a metal wire mesh to reduce acid mist penetration and dust entrainment.

[0011] In some embodiments, in S1, the low-temperature catalytic polishing apparatus includes: Exhaust gas inlet and mixing and rectifier section; The ozone dosing branch includes an ozone generator, a mass flow controller, an online ozone analyzer and valve assembly, as well as an ozone safety destruction unit connected in parallel with the main branch; The composite reaction bed module contains, in sequence, a low-temperature oxidation layer of transition metal oxides, a mist-blocking and condensing layer, and an activated carbon layer. The online monitoring unit is used to detect the outlet SO2 concentration, outlet ozone concentration, acid mist concentration, bed pressure drop ΔP, and bed temperature at multiple points in real time. The control unit is connected to the mass flow controller, ozone destruction unit, and online monitoring unit, and is used to output control commands according to the closed-loop control method.

[0012] In some embodiments, the outer shell and inner lining of the low-temperature catalytic polishing device are made of acid-resistant materials or coatings, and the minimum temperature of the inner wall of the shell is guaranteed to be no lower than the dew point of the incoming gas +10°C during operation.

[0013] In some embodiments, the composite bed is a cylindrical or drawer-type replaceable structure, and the composite bed contains independently replaceable transition metal oxide low-temperature oxidation module, mist blocking and condensation module and activated carbon module, and each module has a positioning, anti-cross-contamination and sealing structure.

[0014] In some embodiments, the pore volume of the transition metal oxide low-temperature oxide layer is larger than that of the activated carbon layer to resist fogging and clogging; the particle size of the transition metal oxide low-temperature oxide layer is larger than that of the activated carbon layer to improve the residence and fixation efficiency of the mixed gas.

[0015] Compared with the prior art, this application includes at least one of the following beneficial technical effects: 1. This application utilizes active oxygen species generated by the decomposition of trace amounts of ozone on the surface of a specific transition metal oxide catalyst to efficiently oxidize SO2 at low temperatures. It does not require maintaining the high temperature of over 350°C required by traditional high-temperature catalytic oxidation processes, nor does it require a complex regeneration heat source for simple activated carbon adsorption. This significantly reduces the heating energy consumption and operating costs of the system, and achieves deep purification under low-temperature conditions. 2. Through a multi-stage synergistic and functionally integrated design of catalytic oxidation-coagulation-adsorption / chemical fixation-ozone end-of-pipe decomposition, not only is the efficient removal of SO2 and sulfuric acid mist ensured, but more importantly, through the dual action of physical adsorption and catalytic decomposition of the activated carbon layer, zero escape of residual ozone in the exhaust gas (O3 in the tail gas < 0.1 ppmv) is ensured, solving the inherent secondary pollution problem of ozone oxidation technology. At the same time, the entire dry process generates no wastewater or waste residue. 3. The intelligent closed-loop control system, which integrates multiple parameters such as outlet SO2 concentration and reaction bed temperature difference (ΔTr), can sense changes in operating conditions (such as SO2 concentration shocks) in real time and dynamically and accurately adjust the ozone dosage, enabling the system to have rapid response and self-regulation capabilities, effectively buffering inlet fluctuations, and ensuring that the outlet concentration can stably reach the ultra-low emission limit (≤10 mg / Nm³) under various operating conditions, thus improving the system's adaptability. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the overall process flow in the embodiments of this application.

[0017] Figure 2 This is a closed-loop control block diagram for O3 dosing in an embodiment of this application.

[0018] Figure 3 This is a flowchart illustrating the start / stop sequence logic in an embodiment of this application.

[0019] Figure 4 This is a diagram showing the functional zoning and mechanism of action of the bed layer in the embodiments of this application.

[0020] Figure 5 This is a schematic diagram of fault and interlocking handling in the embodiments of this application. Detailed Implementation

[0021] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0022] In the description of this application, it should be noted that, unless otherwise expressly specified and limited, the term "and / or" in this document is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. Furthermore, the character " / " in this document, unless otherwise specified, generally indicates that the preceding and following related objects have an "or" relationship.

[0023] Reference Figures 1 to 5 This application provides a trace ozone-coordinated low-temperature catalysis method, comprising the following steps: S1: Mix SO2 (exhaust gas temperature approximately 120-180°C, SO2 concentration approximately 50 mg / Nm³, containing a small amount of sulfuric acid mist) with ozone evenly. The amount of ozone added is 5-50 ppmv of the dry volume of the exhaust gas, where the dry volume of the exhaust gas refers to the volume occupied by the dry gas components after deducting the volume of water vapor (H2O). S2: The mixed gas in S1 is sequentially passed through a composite bed consisting of a low-temperature oxidation layer of transition metal oxides, a mist-blocking and condensation layer, and an activated carbon layer within a low-temperature catalytic polishing device; wherein... In the transition metal oxide layer, SO2 is oxidized to SO3 by surface active oxygen generated by ozone decomposition. At the same time, ozone decomposes on the surface of the transition metal oxide layer and the activated carbon layer to generate surface active oxygen to regenerate active sites on the catalyst. The fog-blocking condensation layer captures and condenses sulfuric acid droplets and fine particles in the gas; The activated carbon layer physically adsorbs and chemically fixes the generated SO3 and sulfuric acid mist, and decomposes and intercepts residual ozone. S3. At the device outlet, the online monitoring unit monitors the outlet SO2 concentration and the axial temperature difference ΔTr of the composite bed in real time. The control unit receives these signals and executes a closed-loop control method with the outlet SO2 concentration and ΔTr as the main control variables to dynamically adjust the ozone dosage. For example, when an upward trend in the outlet SO2 concentration is detected but has not yet exceeded the standard, the control system will slightly increase the ozone dosage according to the algorithm to enhance the oxidation capacity; conversely, it will reduce the dosage. ΔTr reflects the exothermic intensity of the reaction within the bed and is an indirect characterization of the internal SO2 oxidation process, used to assist in judgment and early adjustment. Through this dynamic adjustment, the outlet SO2 concentration is ultimately stably controlled at ≤10 mg / Nm³, while the outlet ozone concentration is below 0.1 ppmv.

[0024] By employing the above technical solution, trace ozone is combined with a controllable active oxygen source and a low-temperature catalyst to achieve efficient and targeted oxidation of trace SO2 at low temperatures. This overcomes the shortcomings of traditional high-temperature catalysis, such as high energy consumption, limited adsorption capacity of activated carbon, and lack of oxidation capability. Simultaneously, the terminal activated carbon layer ensures zero ozone escape, solving the problem of secondary pollution easily caused by simple ozone oxidation technology. The introduction of closed-loop control enables the entire process to be adaptive, maintaining optimal ozone utilization efficiency and purification effect under different loads, achieving the goal of efficient, stable, safe, and energy-saving deep purification.

[0025] Furthermore, in this embodiment, during steady-state system operation, for example, when the inlet SO2 concentration is stable at 30-80 mg / Nm³, the control system maintains the ozone dosage at a low range of 10-25 ppmv (e.g., 18 ppmv), which is sufficient to maintain normal deep purification requirements and maximize energy savings and reduce side reactions. When the online monitoring unit (e.g., the SO2 concentration meter at the front end) suddenly detects a sharp increase in the inlet SO2 concentration, indicating an SO2 load shock (e.g., a fluctuation in the front-end process causing the instantaneous SO2 concentration to rise above 300 mg / Nm³), the control system responds immediately. According to a preset program, the ozone dosage is rapidly increased to a higher range of 50-60 ppmv (e.g., 55 ppmv) to provide sufficient active oxygen to cope with the sudden increase in SO2. To prevent catalyst overheating or ineffective side reactions that may be caused by excessive ozone dosage, this high dosage mode has a duration limit, typically less than 10 minutes. Once the shock weakens and the system detects that the outlet SO2 concentration and ΔTr have returned to stability, it automatically adjusts the ozone dosage back to the steady-state operating range. This phased, variable ozone dosing strategy achieves a balance between operational economy and shock resistance robustness. Low-dose dosing under steady-state conditions reduces operating costs and long-term thermal stress on the catalyst. Under shock conditions, high-dose dosing over a short period rapidly enhances oxidation capacity, preventing excessive emissions and demonstrating the unit's strong buffering and emergency response capabilities. Time constraints prevent catalyst sintering or material damage that may result from prolonged high ozone concentrations, ensuring the system's long-term operational lifespan. This makes the method particularly suitable for industrial scenarios with frequent fluctuations in operating conditions.

[0026] Furthermore, the closed-loop control method in step S3 includes the following steps: S31: Data Acquisition: Real-time acquisition of outlet SO2 concentration (CSO) 2out The readings T(z) of multiple temperature sensors arranged axially along the bed (used to calculate the temperature difference ΔTr and locate the thermal peak), the total pressure drop ΔP of the bed, and the inlet gas dew point temperature (T) are also included. dp ).

[0027] S32: Data Processing and Feature Extraction: Filter and perform boundary validity checks on the collected raw data. Calculate the error (SO2 concentration error) between the outlet SO2 concentration and the set value (e.g., 8 mg / Nm³). 2err The temperature difference ΔTr in key bed layers (such as the temperature difference between the middle of the low-temperature oxide layer of transition metal oxides and the outlet of the activated carbon layer) is calculated based on temperature data, and the error between it and the set temperature difference (ΔTr) is extracted. err ). Calculate the rate of change of outlet SO2 concentration over time, d(SO). 2out The ratio ) / dt is used to predict trends. Simultaneously, the acid mist number concentration, ΔP, and calculated dew point margin (i.e., the minimum temperature of the inner wall of the shell and the incoming dew point T) are monitored.dp difference).

[0028] S33: Control Calculation and Output: The core control algorithm uses proportional-integral (PI) regulation, and its input consists of multiple weighted error signals. Specifically, the ozone setpoint (O... 3set =PI[w1·SO] 2err + w2·ΔT rerr + w3·d(SO2) / dt〕. Where w1, w2, and w3 are adjustable weighting coefficients, focusing on emission compliance, reaction intensity balance, and trend prediction, respectively. Based on this, the algorithm superimposes adaptive limits using dew point margin and ΔP growth rate as constraints. For example, when the dew point margin decreases, the algorithm limits the upper limit of ozone dosage to prevent excessive SO3 formation due to peroxidation from combining with water and exacerbating the risk of condensation; when ΔP increases too rapidly, it may indicate bed blockage, similarly limiting ozone dosage to mitigate reaction intensity.

[0029] S34: Safety Interlock: Multiple layers of safety protection are set up: When the outlet ozone concentration (O2) is monitored... 3out If the ozone concentration is ≥0.2 ppmv and persists for more than 60 seconds, it indicates that the end-of-pipe interception may have failed; or if the dew point margin is <5 °C, it indicates a serious risk of condensation corrosion; or if the ΔP growth rate exceeds the preset threshold, it indicates that the bed may be clogged. Once any of these conditions are triggered, the system immediately executes a safety interlock: forcibly setting the ozone dosage to 0, fully opening the ozone safety destruction unit (such as a thermocatalytic destruction device), simultaneously starting hot air to purge the bed, and triggering an audible and visual alarm to notify the operator.

[0030] S35: Start-up and Shutdown Procedures: When starting the unit, the composite bed must first be preheated to ≥100°C using hot air or the heat from the exhaust gas itself. Ozone can only be introduced after this temperature condition is met to prevent insufficient reaction at low temperatures, which could lead to ozone penetration or product condensation. When shutting down, the ozone supply must be cut off first, but exhaust gas circulation and the ozone destruction unit must be kept running online for 10-15 minutes to thoroughly decompose and purge any residual ozone in the system before complete shutdown.

[0031] This closed-loop control method elevates process control to a new level of intelligence and safety. It doesn't rely solely on single outlet SO2 concentration feedback, but integrates ΔTr reflecting the internal reaction state, differential terms predicting trends, and multiple safety constraint variables (dew point, pressure drop), forming a multi-variable, feedforward-feedback combined advanced control strategy. This significantly improves control accuracy, timeliness, and stability, enabling the system to respond more smoothly and energy-efficiently to various disturbances. Built-in multiple safety interlocks and strict start-up and shutdown procedures fundamentally eliminate safety risks such as ozone escape, equipment corrosion, and bed blockage, ensuring operational safety and reliability throughout the entire lifecycle of the unit and meeting the stringent requirements of automation and safety in industrial settings.

[0032] Furthermore, in this embodiment, the low-temperature oxide layer of transition metal oxides can be selected from, but is not limited to, at least one of the following catalysts: MnOx-CeOx / TiO2 (manganese-cerium-titanium system), FeOx-CuOx / TiO2 (iron-copper-titanium system), or multi-metal composite oxides formed by doping other metals (such as Co, Zr) based on them. The total mass fraction of the active component (such as MnOx+CeOx) is controlled between 5-20 wt% to ensure sufficient active site density and structural stability. The macroscopic morphology of the catalyst is preferably honeycomb-shaped to reduce system pressure drop; it can also be designed as strip-shaped or spherical according to the device structure for easy filling and replacement. The activated carbon layer uses columnar or granular activated carbon with a specific surface area between 800-1200 m² / g to ensure sufficient physical adsorption capacity. To enhance its chemical fixation capacity for SO3 and sulfuric acid, the activated carbon undergoes modification treatment. Modification methods can include: 1) Alkali metal or alkaline earth metal modification, such as impregnation with loaded potassium (K) or calcium (Ca) at a loading of 0.5-3 wt%, making the surface alkaline and readily reacting with acidic substances to form stable salts; 2) Amination modification, introducing nitrogen-containing basic functional groups onto the activated carbon surface, which also enhances chemical adsorption capacity. The fog-blocking and condensation layer specifically uses fiber mats made of glass fiber, polypropylene fiber, or polytetrafluoroethylene (PTFE) fiber, or metal mesh woven from corrosion-resistant metals such as stainless steel or titanium alloy. These materials efficiently capture submicron-sized acid mist droplets and fine particulate matter through mechanisms such as inertial impaction, direct interception, and Brownian diffusion, causing them to condense into larger droplets that are more easily captured by the subsequent activated carbon layer.

[0033] In some embodiments, the low-temperature catalytic polishing device in step S1 includes: an exhaust gas inlet and a mixing and rectification section: used to introduce the exhaust gas to be treated and to initially mix it with ozone, so that the flow field is uniformly distributed.

[0034] Ozone dosing branch: connected to the main branch, including an ozone generator, a mass flow controller (MFC, 32), an online ozone analyzer for monitoring the concentration of added ozone, and a valve group consisting of necessary shut-off valves and regulating valves arranged in sequence.

[0035] Ozone safety destruction unit: It is set in parallel with the ozone dosing branch and is usually a thermocatalytic decomposer. It is used to decompose any ozone that may remain in the branch when the device is started or stopped or when the safety interlock is triggered.

[0036] Composite reaction bed module: This is the core of the device. Inside its shell, along the airflow direction, a low-temperature oxidation layer of transition metal oxides, a mist-blocking and condensing layer, and an activated carbon layer are sequentially fixed.

[0037] Online monitoring unit: includes an online analyzer installed at the device outlet to detect SO2 concentration, O3 concentration and acid mist concentration at the outlet, a differential pressure sensor installed on the bed shell to measure the bed pressure drop ΔP, and multiple temperature sensors inserted at different depths inside the bed to measure the temperature at multiple points in the bed.

[0038] Control unit: Typically a DCS (Distributed Control System) or PLC (Programmable Logic Controller). Its signal input terminals are connected to the online monitoring unit and online ozone analyzer, while its signal output terminals are connected to the mass flow controller, ozone safety destruction unit, and related valves. The control unit has a built-in closed-loop control program as shown in step S3, which calculates and outputs control commands in real time based on the collected data to dynamically adjust the ozone dosage.

[0039] The outer shell and inner lining of the low-temperature catalytic polishing unit are made of acid-resistant stainless steel (such as 316L), fiberglass (FRP), or carbon steel lined with acid-resistant ceramic tiles, enamel, or fluoroplastic coatings (such as PTFE), etc., to ensure corrosion resistance. During operation, through insulation layer design and / or, when necessary, the introduction of low-pressure steam or electric heating into the shell jacket, strictly ensures that the minimum temperature at any point on the inner wall of the shell is not lower than the incoming gas dew point temperature +10 °C. The dew point temperature is monitored by an online dew point meter or calculated based on the exhaust gas composition. The selection of acid-resistant materials fundamentally resists the corrosion of the equipment body by highly corrosive media such as SO3 and sulfuric acid mist, extending the service life of the unit. The mandatory "dew point margin +10 °C" control strategy effectively prevents SO3 or sulfuric acid vapor generated during the process from condensing into liquid acid on the cold inner wall of the equipment, thereby completely avoiding serious safety accidents such as equipment perforation and leakage caused by condensed acid corrosion, and also avoiding the impact of acid accumulation on the performance of the bed material, ensuring the stability of long-term continuous operation.

[0040] The composite reaction bed module is designed as a replaceable, integral cylindrical or drawer-type structure. Taking the drawer-type as an example, the shell has parallel guide rails inside, and the transition metal oxide low-temperature oxidation catalytic module, the mist-blocking and condensation module, and the activated carbon module are installed in three independent frames (drawers). Each module frame has positioning pins / grooves to ensure accurate positioning after installation; high-temperature and acid-resistant elastic sealing strips are provided between the modules to form an anti-cross-contamination and sealing structure to prevent airflow short circuits. When a certain layer (such as the activated carbon layer) becomes saturated and needs to be replaced, or when the transition metal oxide low-temperature oxidation layer catalyst is deactivated, only the corresponding module can be extracted and replaced without disturbing other layers or emptying the entire reactor.

[0041] Taking a deep purification project of tail gas from a sulfuric acid plant as an example, the method and apparatus of this invention are adopted. Tail gas conditions: flow rate 50,000 Nm³ / h, temperature 140°C, SO₂ concentration 80 mg / Nm³, containing a small amount of acid mist. The catalyst is a honeycomb MnOx-CeOx / TiO₂, and the activated carbon layer is K-modified columnar activated carbon (a highly efficient special adsorbent material prepared by loading potassium compounds, such as KOH, K₂CO₃, and KI, onto columnar activated carbon through an impregnation-drying-heat treatment process).

[0042] After system startup, the bed was preheated to 120°C according to the closed-loop control method in S3 before ozone was introduced. During steady-state operation, the ozone dosage was automatically maintained at approximately 20 ppmv. The outlet SO2 concentration stabilized at 5-8 mg / Nm³, and outlet ozone was undetectable (<0.05 ppmv). During this period, a simulated front-end failure caused the SO2 concentration to momentarily rise to 400 mg / Nm³. The control system increased the ozone dosage to 55 ppmv within 2 seconds, and after 5 minutes, the impact weakened, and the system automatically reverted. Throughout the entire process, the outlet SO2 concentration only fluctuated slightly (reaching a maximum of 12 mg / Nm³) and recovered to 10 mg / Nm³ within 3 minutes. 3 No emissions exceeded standards, and the bed pressure drop remained stable. After one year of operation, only the activated carbon module needed to be replaced as planned, and the transition metal oxide low-temperature oxidation layer catalyst maintained good activity.

[0043] The above are all preferred embodiments of this application, and are not intended to limit the scope of protection of this application. Therefore, all equivalent changes made in accordance with the structure, shape and principle of this application should be covered within the scope of protection of this application.

Claims

1. A low-temperature catalytic method synergistic with trace amounts of ozone, characterized in that, Includes the following steps: S1: Mix SO2-containing exhaust gas with ozone evenly, wherein the amount of ozone added is 5-50 ppmv of the dry basis volume of the exhaust gas; S2: The mixed gas in S1 is passed sequentially through a composite bed consisting of a low-temperature oxidation layer of transition metal oxides, a fog-blocking and condensation layer, and an activated carbon layer within a low-temperature catalytic polishing device; wherein: The transition metal oxide layer is used to oxidize SO2 to SO3, and the transition metal oxide layer and activated carbon layer are used to decompose the O3 surface to generate surface active oxygen to regenerate active sites on the catalyst. The fog-blocking and condensation layer is used to capture and condense sulfuric acid droplets and fine particles in the gas. The activated carbon layer is used to physically adsorb and chemically fix the generated SO3 and sulfuric acid mist, and to decompose and intercept residual ozone. S3: Monitor the SO2 concentration at the outlet and the axial temperature difference ΔTr of the composite bed online. Based on the closed-loop control method with the SO2 concentration at the outlet and ΔTr as the main control variables, dynamically adjust the ozone dosage to ensure that the SO2 at the outlet reaches the emission limit of ≤10 mg / Nm³ and the O3 in the tail emission is less than 0.1 ppmv.

2. The trace ozone synergistic low-temperature catalysis method according to claim 1, characterized in that: The ozone dosage is 10-25 ppmv during steady-state operation; when an SO2 load shock is detected, the ozone dosage is increased to 50-60 ppmv, and the high dosage duration is less than 10 minutes.

3. The trace ozone synergistic low-temperature catalysis method according to claim 1, characterized in that: The closed-loop control method described in S3 includes the following steps: S31: Collect outlet SO2 concentration, bed multi-point temperature T(z), pressure drop ΔP and inlet dew point, where outlet SO2 and ΔTr are closed-loop main variables, and acid mist number concentration, ΔP and dew point margin are limiting or interlocking variables. S32: SO2 error SO is obtained after filtering and boundary checking. 2err Extract the bed temperature difference ΔTr, the location of the thermal peak, and the recovery time T. rec And calculate d(SO) 2out ) / dt; S33: Based on O3 setting = PI〔w1·SO 2err + w2·ΔT rerr + w3·d(SO2) / dt〕and superimpose the dew point margin and the adaptive limit of the ΔP growth rate to generate the O3 setpoint; S34: When O 3out When the ozone concentration is ≥0.2 ppmv for ≥60 s, or the dew point margin is <5 °C or the ΔP growth rate exceeds the threshold, a safety interlock is executed: O3 is forced to 0, and the ozone destruction unit is fully opened while maintaining thermal purging and alarm. S35: During start-up and shutdown, the bed temperature must be ≥100 °C before O3 addition can be unlocked; when shutting down, cut off O3 and keep the destruction unit online for 10–15 minutes before stopping.

4. The trace ozone synergistic low-temperature catalysis method according to claim 1, characterized in that: The transition metal oxide low-temperature oxide layer is filled with a multi-metal composite oxide, with an active component mass fraction of 5-20 wt%, and its morphology is honeycomb, strip, or spherical.

5. The trace ozone synergistic low-temperature catalysis method according to claim 1, characterized in that: The activated carbon layer is columnar or granular activated carbon with a specific surface area of ​​800–1200 m² / g, and is modified with alkali metals or alkaline earth metals or amination.

6. The method for synergistic low-temperature catalysis with trace amounts of ozone according to claim 1, characterized in that: The fog-blocking and condensation layer is a fiber pad or a metal wire mesh.

7. The method for synergistic low-temperature catalysis with trace amounts of ozone according to claim 1, characterized in that: In S1, the low-temperature catalytic polishing apparatus includes: Exhaust gas inlet and mixing and rectifying section; The ozone dosing branch includes an ozone generator, a mass flow controller, an online ozone analyzer and valve assembly, as well as an ozone safety destruction unit connected in parallel with the main branch; The composite reaction bed module contains, in sequence, the aforementioned low-temperature oxidation layer of transition metal oxide, the mist-blocking and condensing layer, and the activated carbon layer; The online monitoring unit is used to detect the outlet SO2 concentration, outlet ozone concentration, acid mist concentration, bed pressure drop ΔP, and bed temperature at multiple points in real time. The control unit is connected to the mass flow controller, ozone destruction unit, and online monitoring unit, and is used to output control commands according to the closed-loop control method.

8. The trace ozone synergistic low-temperature catalysis method according to claim 7, characterized in that: The outer shell and inner lining of the low-temperature catalytic polishing device are made of acid-resistant materials or coatings, and the minimum temperature of the inner wall of the shell is guaranteed to be no lower than the dew point of the incoming gas +10°C during operation.

9. The trace ozone-co-catalyzed low-temperature catalysis method according to claim 7, characterized in that: The composite bed is a replaceable cylindrical or drawer-type structure. The composite bed contains independently replaceable transition metal oxide low-temperature oxidation module, mist blocking and condensation module, and activated carbon module. Each module has a positioning, anti-cross-contamination and sealing structure.

10. The trace ozone-co-catalyzed low-temperature catalysis method according to claim 7, characterized in that: The pore volume of the transition metal oxide low-temperature oxide layer is larger than that of the activated carbon layer to resist fogging and clogging; the particle size of the transition metal oxide low-temperature oxide layer is larger than that of the activated carbon layer to improve the residence and fixation efficiency of the mixed gas.

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