A process for treating high-salt, high-dust flue gas

Abstract

This invention relates to the field of industrial flue gas purification technology, specifically disclosing a treatment process for high-salt, high-dust flue gas. The core of this process lies in constructing a multi-stage synergistic treatment system coupling efficient pretreatment and deep purification. High-temperature, high-dust, and high-salt flue gas generated during industrial processes first undergoes high-temperature dry pretreatment, significantly reducing dust load; subsequently, it enters a rapid cooling and conditioning stage to achieve rapid cooling and preliminary removal of some soluble salts and fine particulate matter; the washed flue gas undergoes secondary impurity removal through catalytic oxidation; finally, the flue gas enters a deep purification unit for final treatment. Through multi-stage synergistic control, the problems of blockage, corrosion, and low efficiency in collection pipes and subsequent treatment equipment easily caused by such high-salt, high-dust flue gas are effectively solved, resulting in stable overall system operation and high treatment efficiency.

Description

Technical Field

[0001] This invention relates to the field of industrial flue gas purification technology, specifically a treatment process for high-salt, high-dust flue gas. Background Technology

[0002] Many industrial production processes, such as waste incineration, hazardous waste treatment, biomass combustion, steel sintering, ceramic kilns, and converter steelmaking, generate large amounts of complex flue gas characterized by high temperatures, high dust levels, and high salinity. These flue gases share common characteristics: extremely high concentrations of dust, such as metal oxides and fly ash; and due to the complexity of raw materials, such as chlorine-containing waste, coal, and additives, they often contain high levels of salt (e.g., HCl, alkali metal chlorides, heavy metal chloride salts), and are frequently accompanied by various pollutants such as CO, SO2, NOx, and TOC.

[0003] The collection and treatment technologies for high-salt and high-dust flue gas generated from incineration mainly employ dry, semi-dry, or wet combination processes. However, existing technologies still have significant drawbacks: high-salt flue gas (especially HCl and chlorides) easily causes high-temperature corrosion, salt accumulation, and scaling blockage in the waste heat boiler, evaporative cooler, and flue in the gas collection system, seriously affecting the safe and stable operation of the system; if wet dust removal is used, all the high-salt content in the flue gas will be transferred to the washing water, generating a large amount of high-salt wastewater. The treatment cost of this wastewater is extremely high and it is prone to causing secondary pollution; although existing dry dust removal methods (such as high-voltage electrostatic precipitators) can efficiently remove dust, they have virtually no ability to remove gaseous acidic gases such as HCl and SO2.

[0004] With increasingly stringent environmental standards, such flue gas also faces the need for advanced treatment, including desulfurization, denitrification (NOx), and removal of total organic matter (TOC). However, high levels of dust, such as metal oxide dust and high-salt components, in the flue gas can cause severe wear, blockage, and poisoning of subsequent purification equipment, leading to its rapid failure. Existing technologies (whether wet or dry) are insufficient to effectively address the problems of equipment corrosion, blockage, wastewater pollution, and difficulties in the synergistic purification of multiple pollutants caused by the coexistence of high salinity and high dust in industrial flue gas.

[0005] These problems stem from a lack of integrated collection and purification innovations targeting the high salinity and high dust characteristics of industrial flue gas, resulting in a heavy environmental burden and poor economic efficiency. Therefore, a treatment process for high-salinity, high-dust flue gas is proposed. Summary of the Invention

[0006] The purpose of this invention is to provide a treatment process for high-salt, high-dust flue gas by constructing a multi-stage synergistic treatment system that couples efficient pretreatment and deep purification. High-temperature, high-dust, and high-salt flue gas generated in industrial processes first undergoes high-temperature dry pretreatment to significantly reduce dust load; then it enters a rapid cooling and conditioning stage to achieve rapid cooling and preliminary removal of some soluble salts and fine particulate matter; the washed flue gas undergoes secondary impurity removal through catalytic oxidation; finally, the flue gas enters a deep purification unit for final treatment. Through multi-stage synergistic control, the problems of blockage, corrosion, and low efficiency in collection pipes and subsequent treatment equipment easily caused by such high-salt, high-dust flue gas are effectively solved, resulting in stable overall system operation and high treatment efficiency.

[0007] To achieve the above objectives, the present invention provides the following technical solution: This invention provides a process for treating high-salt, high-dust flue gas, the process of which is as follows: High-salt, high-dust flue gas enters a selective non-catalytic reduction (SNR) denitrification system; it is treated using a high-temperature electrostatic precipitator; then it is fed into a quenching and conditioning tower where sodium bicarbonate-containing atomized water is injected and introduced into a nano-atomizer; a composite adsorbent is dry-sprayed into the downstream pipeline of the quenching and conditioning tower; after the reaction is complete, fine particles are collected by a polytetrafluoroethylene (PTFE) membrane bag filter, and then oxidized in a fixed-bed manganese-cerium catalytic reactor; a low-temperature selective catalytic reduction system injects ammonia for deep denitrification; a wet scrubbing tower uses sodium hydroxide solution to deeply remove residual pollutants; the flue gas discharged from the wet scrubbing tower is heated before being discharged; the wastewater generated by the wet scrubbing tower undergoes heat pump-assisted membrane distillation and forced circulation crystallization. The composite adsorbent was prepared by dry mixing calcium hydroxide, sodium bentonite, activated carbon, and sodium bicarbonate in a V-type mixer for 2 hours. The mass ratio of calcium hydroxide, sodium bentonite, activated carbon, and sodium bicarbonate was 30-50:25-45:10:15.

[0008] Preferably, high-salt, high-dust flue gas enters a selective non-catalytic reduction denitrification system, where a cerium dioxide additive is mixed with a urea solution and then sprayed. The urea solution concentration is 22%-32%, the spray volume is based on a NOx concentration of 1.0-1.5:1 molar ratio, the spray gun pressure is 0.3-0.5 MPa, and the CeO2 additive is mixed with the urea solution at a mass fraction of 0.5%-1.0% (relative to the mass of the urea solution) and sprayed together; the reaction is 4NO + 2(NH2)2CO + O2 → 4N2 + 4H2O + 2CO2; the specific mixing method is as follows: CeO2 additive powder with a particle size of 30-40 nm is added to the urea solution, and polyethylene glycol with a mass fraction of 0.1% CeO2 is added as a dispersant. The mixture is dispersed in a high-shear emulsifier at 5000 rpm for 30 minutes to form a stable suspension, which is then sprayed together.

[0009] Preferably, the high-temperature electrostatic precipitator operates at a temperature of 350-450℃, which is higher than the salt dew point. It mainly removes particles larger than PM10 and collects dry coarse fly ash.

[0010] Preferably, the injection rate of the composite adsorbent is determined by a calcium-to-sulfur molar ratio of 1.0-2.5:1. The outlet temperature of the quenching and conditioning tower is strictly controlled at 160-200℃. A dual-fluid atomizing spray gun is used to spray atomized water containing 1% sodium bicarbonate, with a nozzle pressure of 0.4-0.6 MPa and a liquid-to-gas ratio of 0.5-1.0 L / Nm³. The droplet size generated by the nano-atomizer (model Siansonic Widemist) is 10-50 nm; the tower height is 15 m, the diameter is 3 m, and the gas velocity is 3 m / s to avoid scaling. The calcium-to-sulfur molar ratio is the ratio of the total alkaline component of the adsorbent to the total acidic component of the flue gas.

[0011] Preferably, the processing of the PTFE-coated bag filter includes: selecting long fibers as the base fabric and PTFE short fibers as the surface layer, forming a felt material through needle punching, followed by singeing, heat setting, and calendering. Then, a 0.5-5 μm thick expanded PTFE film is hot-pressed onto the felt surface to form a composite filter material. The coating temperature is 240-260℃, the pressure is 0.2-0.7 MPa, and the area weight is 750-800 g / m². The bag filter is then sewn together to form the PTFE-coated bag filter. The dust collector operates at 155℃, the filter bag material is PTFE-coated filter material, the offline pulse cleaning pressure is 0.5-0.7 MPa, and the cycle time is 10-20 minutes.

[0012] Preferably, the manganese-cerium treatment in the fixed-bed manganese-cerium catalytic reactor includes: dissolving manganese nitrate tetrahydrate and cerium nitrate hexahydrate in deionized water, adding alumina for dispersion, adding citric acid and heating to form a gel, adjusting the pH to acidic, allowing it to stand for aging, then soaking, drying and calcining. The fixed-bed catalytic reactor carrier is a ceramic honeycomb, with a Ce-Mn catalytic layer coated on the surface with a thickness of 50-100 μm for preliminary oxidation of CO and TOC; the coating amount is 20-50 g per square meter of membrane surface.

[0013] Preferably, the low-temperature selective catalytic reduction system uses manganese oxide-cerium oxide composite oxides for secondary denitrification, operates at a temperature of 160-220℃, requires no additional heating, has an ammonia-nitrogen molar ratio of 0.9-1.05, and a space velocity of 3000-5000 h⁻¹. -1 .

[0014] Preferably, before heat pump-assisted membrane distillation, polyacrylamide flocculant is added for sedimentation; forced circulation crystallization is performed to form sodium chloride crystals; polyacrylamide (PAM) flocculant is added for sedimentation until the heat pump-assisted membrane distillation membrane is PTFE at a temperature of 60-80℃, a vacuum degree of 0.05-0.10MPa, and a permeation flux of 10-20L / m²h. The molecular weight of polyacrylamide is 1.2×10⁻⁶. 7.

[0015] Preferably, in high-salt, high-dust flue gas, the dust concentration is 80 g / Nm³. 3 SO2 20g / Nm 3 HCl 10g / Nm 3 NOx 300mg / Nm 3 Total organic carbon (TOC) 100 mg / Nm 3 CO2 00mg / Nm 3 .

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. By introducing nano-sized CeO2 additive and co-spraying urea solution into a high-temperature SNCR denitrification system, the NOx reduction selectivity and reaction window width are significantly improved. CeO2's high oxygen storage and release capacity promotes urea pyrolysis to generate more active NH2 free radicals, inhibiting the side reaction to produce N2O, while simultaneously enhancing the directional conversion of NO to N2. The additive's ultrafine particle size and high specific surface area ensure uniform dispersion and extend catalytic activity lifespan. The system achieves efficient denitrification over a wide temperature range without additional heating, reducing the risk of ammonia escape and synergizing with subsequent SCR for further deep purification. The overall nitrogen oxide removal pathway is stable and reliable, with emission concentrations far below standard limits. It also demonstrates the same high efficiency and stability in treating NOx from flue gas in industries such as waste incineration and hazardous waste treatment.

[0017] 2. A high-temperature electrostatic precipitator and a quenching and conditioning tower are connected in series to efficiently capture coarse particles and rapidly cross the dioxin re-synthesis temperature range. Under the action of the electrostatic field, dry fly ash is completely separated. The quenching tower generates ultrafine water mist through a dual-fluid system and a nano-atomizer, instantly lowering the flue gas temperature below the dew point and preventing the condensation and adhesion of acidic gases. Precise control of the quenching rate inhibits the low-temperature catalytic regeneration of dioxin precursors. Combined with subsequent activated carbon adsorption and catalytic oxidation, a multi-level barrier is established, achieving near-complete elimination of dioxin-like substances. The emission toxicity equivalent is far superior to the strictest standards, and the system has strong anti-scaling capabilities. This process is also applicable to the treatment of flue gas from other high-salt industrial kilns that are prone to dioxin generation.

[0018] 3. This invention integrates dry composite adsorbent injection with high-efficiency PTFE membrane bag filter technology to achieve synergistic removal of acidic gases, heavy metals, and sticky salts. Sodium-based bentonite physical coating prevents bag clogging, activated carbon targets and adsorbs gaseous mercury and organic matter, and Ca(OH)2 and NaHCO3 rapidly neutralize HCl and SO2. The micropores of the membrane filter precisely intercept submicron particles, and pulse cleaning maintains low resistance and long-term operation. The adsorption-filtration coupling mechanism converts multiple pollutants into solid-phase trapping, significantly reducing the subsequent wet scrubbing load. The system operates stably, has a long maintenance cycle, and high overall removal efficiency. This synergistic removal technology is widely applicable to flue gas containing complex acidic gases, heavy metals, and sticky salts, such as those from biomass combustion and sintering.

[0019] 4. A fixed-bed Ce-Mn catalytic reactor is installed after the bag filter dust collector, utilizing the waste heat of flue gas to achieve low-temperature catalytic oxidation of CO and TOC. The MnO2-CeO2 composite layer constructed by the sol-gel method possesses abundant oxygen vacancies and strong redox properties, efficiently activating O2 molecules to attack CO and volatile organic compound molecular chains, converting them into harmless CO2 and H2O. The high porosity of the ceramic honeycomb carrier ensures low pressure drop, and the optimized thickness and composition of the catalytic layer balance activity and durability. It can deeply purify exhaust gas without an external heat source, reducing energy consumption and the risk of secondary pollution, resulting in high emission cleanliness. Low-temperature catalytic oxidation technology can be widely applied to the purification of various industrial exhaust gases containing CO and TOC.

[0020] 5. This invention constructs a zero-discharge system for high-salinity wastewater, consisting of heat pump-assisted membrane distillation and forced circulation crystallization, achieving high-rate water recovery and salt purification. The PTFE hydrophobic membrane selectively permeates gas under low vacuum, while the heat pump efficiently recovers latent heat to maintain the transmembrane temperature difference. The concentrate enters the crystallization unit to precipitate high-purity NaCl. Pre-flocculation removes suspended solids and protects the membrane surface, resulting in strong anti-fouling capabilities and stable permeate flux. The process boasts low energy consumption, high water recovery rate, and industrial-grade salt purity, completely eliminating the discharge of saline wastewater and achieving closed-loop circulation and resource utilization. This zero-discharge system is a universal, economical, and efficient solution for addressing the problem of high-salinity wastewater generated by various industrial processes. Attached Figure Description

[0021] Figure 1 This is a process flow diagram for treating high-salt, high-dust flue gas according to the present invention; Figure 2 The results show the test results of TOC, particulate matter, CO, NOx, SO2 and HCl content after high-salt and high-dust flue gas treatment in Examples 1-4 and Comparative Examples 1-9 of this invention. Detailed Implementation

[0022] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0023] Please see Figures 1 to 2 This invention provides a process for treating high-salt, high-dust flue gas, the technical solution of which is as follows: Example 1 S1 flue gas is discharged from the flue gas system outlet; the total waste gas treatment capacity is 1000 Nm³, the flow rate is 500 Nm³ / h, and the dust concentration is 80 g / Nm³. 3 SO2 20g / Nm3 HCl 10g / Nm 3 NOx 300mg / Nm 3 Total organic carbon (TOC) 100 mg / Nm 3 CO2 00mg / Nm 3 The solution enters the high-temperature SNCR denitrification system; the high-temperature SNCR denitrification system is located at the boiler outlet, with an injection urea solution concentration of 22%, an injection rate based on a NOx concentration molar ratio of 1.1, a spray gun pressure of 0.3 MPa, and an atomized particle size of 50-100 μm. The residence time is 2 s. CeO2 additive is mixed with the urea solution at a mass fraction of 0.5% (relative to the mass of the urea solution) and injected together. The flue gas velocity is 5 m / s, and the temperature control accuracy is ±10℃; the CeO2 purity is >99%, the average particle size is <100 nm, and the specific surface area is >60 m² / g. The S2 high-temperature electrostatic precipitator operates at a temperature of 350℃, which is higher than the salt dew point, and the dust is in a dry state.

[0024] The S3 quench and conditioning tower has an inlet temperature of approximately 350℃ and an outlet temperature strictly controlled at 160℃. It uses a dual-fluid atomizing spray gun to spray atomized water containing 1% baking soda, with a nozzle pressure of 0.4MPa and a liquid-to-gas ratio of 0.5L / Nm³. A nano-atomizer is also incorporated.

[0025] S4 dry adsorption conditioning agent is sprayed onto the pipeline after the quench tower, and a composite powder is injected through a Venturi tube. The composition and addition ratio of the substances are as follows: 40% Ca(OH)2 for deacidification (HCl and SO2), 35% sodium-based bentonite (200-mesh sieved) for physical coating of sticky salts to prevent bag clogging, 10% activated carbon for adsorbing dioxins, TOC, and Hg, and 15% NaHCO3 for rapid reaction. The injection rate is adjusted according to the SO2-HCl concentration and the Ca / S molar ratio of 2.0. The reaction time is greater than 2 seconds, and the injection rate is 5 g / Nm³. 3 The pressure is 0.3 MPa, and the injection point is set on a straight pipe section at least 15 meters away from the dust collector inlet to ensure a reaction time of more than 2 seconds.

[0026] S5 first passes through a bag filter and then through a fixed-bed catalytic reactor located after the bag filter. The bag filter operates at a temperature of 155℃, using polytetrafluoroethylene (PTFE) membrane filter media. The filtration velocity is less than 0.8 m / min, the offline pulse cleaning pressure is 0.5 MPa, the cycle is 20 min, and the filtration area is 500 m². The PTFE membrane filter media is manufactured by using long PTFE fibers (3 dtex) as the base fabric and short PTFE fibers (average length 48 mm) as the surface layer. These are needle-punched into felt, which is then singed, heat-set, and calendered. A 0.5 μm thick expanded PTFE film (pore size 0.3 μm, air permeability 5 L / m²·s) is hot-pressed onto the felt surface at a temperature of 240℃ and a pressure of 0.2 MPa to form a composite filter media. These composite filter media are then sewn together to form filter bags. The amount of filter media used per square meter is calculated based on the filtration area, and the total amount used is the filtration area multiplied by the area weight.

[0027] The Ce-Mn catalyst layer was prepared using a sol-gel method. Manganese nitrate tetrahydrate (Mn(NO3)2·4H2O) and cerium nitrate hexahydrate (Ce(NO3)3·6H2O) were dissolved in deionized water at a molar ratio of 1:1. Commercial nano-Al2O3 powder (particle size 20nm, purity 99.9%, specific surface area 150m² / g) was added and ultrasonically dispersed. Citric acid was added as a complexing agent. The mixture was stirred and heated to 85℃ to form a sol. The pH was adjusted to 3, and after 24 hours of static aging, the sol was coated onto the surface of a ceramic honeycomb. The sol was then immersed for 60 minutes, dried at 120℃ for 2 hours, and calcined at 500℃ for 4 hours. The catalyst layer composition was 40% MnO2-CeO2 by weight, and 60% ceramic honeycomb by weight. The S6 low-temperature SCR denitrification unit uses Mn-based catalyst, operates at 160℃ without additional heating, has an ammonia-to-nitrogen molar ratio of 0.9, and a space velocity of 3000 h⁻¹. -1 The Mn-based catalyst is prepared using the same method as the Ce-Mn catalyst layer described in S5.

[0028] The S7 wet scrubbing tower absorbs NaOH solution with a pH controlled at 9.0 and an operating temperature of 60℃. It deeply removes residual SO2, HCl, TOC, and escaped ammonia SO3 aerosols, generating a small amount of high-concentration saline wastewater, primarily composed of Na2SO4 and NaCl. The flue gas is reheated (GGH, using steam to heat to above 185℃) before being discharged through the exhaust stack. Simultaneously, the wastewater is treated by a high-salinity wastewater zero-discharge system. The S8 high-salt wastewater zero-discharge system collects wastewater with TOC 5000 mg / L and Cl⁻ 20000 mg / L. After pretreatment, the pH is adjusted to 8, and 2.5 L of 5 mg / L polyacrylamide (PAM) flocculant is added. After settling for 60 min, the wastewater is distilled through a heat pump-assisted membrane (PTFE membrane, temperature 60℃, vacuum 0.05 MPa, permeation flux 10 L / m²h). The system then undergoes forced circulation crystallization at evaporation temperature 90℃ for 4 h, yielding NaCl with a purity greater than 98%. The heat pump recovery coefficient is 3. The exhaust gas temperature is greater than 185℃, the height is 50 m, and the flow rate is 10 m / s.

[0029] Example 2 In S1, the urea solution concentration is 28%, the injection volume is based on a NOx concentration of 1.3 molar ratio, the spray gun pressure is 0.5 MPa, and the CeO2 additive is mixed with the urea solution in the form of a mass fraction of 0.8% (relative to the mass of the urea solution) and then sprayed together. The S2 high-temperature electrostatic precipitator operates at a temperature of 400℃. The S3 outlet temperature is strictly controlled at 180℃, the nozzle pressure is 0.6MPa, and the liquid-to-gas ratio is 0.8L / Nm³. S4 contains 30% Ca(OH)2 (deacidified), HCl and SO2, and 45% sodium-based bentonite (sieved through a 200-mesh sieve) with physical coating of sticky salts to prevent bag clogging; the spraying amount is adjusted according to the SO2-HCl concentration and the Ca / S molar ratio of 1.5. The S5 dust collector operates at a temperature of 165℃, with an offline pulse cleaning pressure of 0.7MPa and a cycle of 15min. The 2.5μm thick layer is hot-pressed onto the felt surface at a coating temperature of 250℃ and a pressure of 0.4MPa. The catalyst layer composition is 50% MnO2-CeO2 by weight. The S6 operates at 180℃, requires no additional heating, has an ammonia-to-nitrogen molar ratio of 1.00, and a space velocity of 4000 h⁻¹. -1 ; S8 added PAM flocculant 8mg / L, sedimentation time 50min, to heat pump assisted membrane distillation membrane PTFE temperature 70℃ vacuum degree 0.08MPa permeation flux 15L / m²h, concentrate water recovery rate 96%. Other treatment processes are consistent with Example 1.

[0030] Example 3 In S1, the urea solution concentration is 30%, the injection volume is based on a NOx concentration of 1.5 molar ratio, the spray gun pressure is 0.4 MPa, and the CeO2 additive is mixed with the urea solution in the form of a mass fraction of 1.0% (relative to the mass of the urea solution) and then sprayed together. The S2 high-temperature electrostatic precipitator operates at a temperature of 430℃. The S3 outlet temperature is strictly controlled at 170℃, the nozzle pressure is 0.5MPa, and the liquid-to-gas ratio is 1.0L / Nm³. S4 contains 50% Ca(OH)2 by weight, deacidified with HCl and SO2, and 25% sodium-based bentonite sieved through a 200-mesh sieve. It also contains physically coated sticky salts to prevent bag clogging. The spraying amount is adjusted according to the SO2-HCl concentration and the Ca / S molar ratio of 1.0. The S5 dust collector operates at a temperature of 165℃, with an offline pulse cleaning pressure of 0.7MPa and a cycle of 10min. A 2.5μm thick layer is hot-pressed onto the felt surface at a coating temperature of 250℃ and a pressure of 0.4MPa. The catalyst layer composition is 50% MnO2-CeO2 by weight. The S6 operates at 200℃ without additional heating, with an ammonia-to-nitrogen molar ratio of 1.05 and a space velocity of 5000 h⁻¹. -1 ; S8 adds 10 mg / L of PAM flocculant, settles for 30 min, then proceeds to heat pump assisted membrane distillation (PTFE membrane, temperature 80°C, vacuum 0.10 MPa, permeation flux 20 L / m²h, concentrate recovery rate 97%). Other treatment processes remain consistent with Example 1.

[0031] Example 4 In S1, the urea solution concentration is 32%, the injection volume is based on a NOx concentration of 1.0 molar ratio, the spray gun pressure is 0.5 MPa, and the CeO2 additive is mixed with the urea solution in the form of a mass fraction of 1.0% (relative to the mass of the urea solution) and then sprayed together. The S2 high-temperature electrostatic precipitator operates at a temperature of 450℃. The S3 outlet temperature is strictly controlled at 180℃, the nozzle pressure is 0.6MPa, and the liquid-to-gas ratio is 0.8L / Nm³. S4 contains 30% Ca(OH)2 by weight, deacidified with HCl and SO2, and 45% sodium-based bentonite sieved through a 200-mesh sieve. It also contains physically coated sticky salts to prevent bag clogging. The spraying amount is adjusted according to the SO2-HCl concentration and the Ca / S molar ratio of 2.5. The S5 dust collector operates at a temperature of 165℃, with an offline pulse cleaning pressure of 0.6MPa and a cycle of 20min. A 5μm thick layer is hot-pressed onto the felt surface at a coating temperature of 260℃ and a pressure of 0.5MPa. The catalyst layer composition is 60% MnO2-CeO2 by weight. The S6 operates at a temperature of 220℃, requires no additional heating, has an ammonia-to-nitrogen molar ratio of 0.95, and a space velocity of 4000 h⁻¹. -1 ; S8 added PAM flocculant 8mg / L, sedimentation time 45min, to heat pump assisted membrane distillation membrane PTFE temperature 70℃ vacuum degree 0.08MPa permeation flux 15L / m²h, concentrate water recovery rate 96%. Other treatment processes are consistent with Example 1.

[0032] Comparative Examples 1-10 Unlike Example 1, the following processing parameters were adjusted, as shown in Table 1. ; Test Example 1 The water obtained from the high-salt, high-dust flue gas treatment in Examples 1-4 and Comparative Examples 1-9 was tested for TOC content, particulate matter, CO, NOx, SO2, and HCl content. The specific testing methods are as follows: TOC content was determined using HJ 1006-2018 "Determination of Total Organic Carbon in Exhaust Gas from Stationary Sources - Non-dispersive Infrared Adsorption Method", with a sampling volume of 1-5 L and a detection limit of 0.5 mg / Nm³. Particulate matter was determined according to GB / T16157-1996 "Determination of Particulate Matter and Sampling Method of Gaseous Pollutants in Exhaust Gas from Stationary Sources", using isokinetic sampling and gravimetric method, with a sampling time of 30-60 min and a detection limit of 0.1 mg / Nm³. CO was determined according to HJ 1035-2019 "Determination of Carbon Monoxide in Exhaust Gas from Stationary Sources - Non-dispersive Infrared Method", using a non-dispersive infrared (NDIR) analyzer for continuous monitoring. The calibrated gas concentration range was 0-500 mg / Nm³, with an accuracy of ±2%. NOx: Determination of nitrogen oxides in exhaust gas from stationary sources by constant potential electrolysis method according to HJ 693-2014, using a chemiluminescence analyzer, sampling flow rate 0.5-1 L / min, detection limit 1 mg / Nm³; SO2: Determination of sulfur dioxide in exhaust gas from stationary sources using constant potential electrolysis method according to HJ57-2017, with continuous monitoring using an ultraviolet fluorescence analyzer, calibration range 0-100 mg / Nm³, accuracy ±5%; HCl: Determination of hydrogen chloride in exhaust gas from stationary sources by ion chromatography according to HJ548-2016 "Ion Chromatography Method". Ion chromatography analysis was performed after sampling with absorption liquid. The sampling volume was 10-20 L and the detection limit was 0.1 mg / Nm³. The test results are recorded in Table 2 and Figure 2 middle.

[0033] Table 2 Test results of Examples 1-4 and Comparative Examples 1-9 ; The test results above show that Examples 1-4 demonstrate that under optimized process parameters, the treatment effect of high-salt and high-dust flue gas is good. The content of all pollutants is far below the national ultra-low emission standards, namely particulate matter less than 5 mg / Nm³, CO less than 50 mg / Nm³, NOx less than 50 mg / Nm³, SO2 less than 35 mg / Nm³, HCl less than 5 mg / Nm³, and TOC less than 50 mg / Nm³. The average removal rate is greater than 95%, which reflects the advantages of multi-stage synergy such as SNCR and SCR denitrification, dry adsorption and wet fine treatment deacidification, and catalytic oxidation of TOC / CO. The system is stable and resource recovery is highly efficient.

[0034] Comparative Examples 1-9 showed a 10-50% decrease in the removal efficiency of specific pollutants due to adjustments in key parameters. For example, adjusting S1 in Comparative Examples 1-2 increased NOx and CO; in Comparative Example 3, low temperature in S2 resulted in excessive particulate matter; adjustments to S3 and S5 in Comparative Examples 4 and 7 significantly increased TOC and CO; adjustments to S4 in Comparative Example 5 significantly increased TOC, SO2, and HCl; adjustments to S4 and S7 in Comparative Examples 6 and 9 resulted in high SO2 and HCl residues; and in Comparative Example 8 (low temperature in S6), NOx removal was incomplete. Overall, the pollutant content in the comparative examples was significantly higher than that in the examples, failing to meet the standards. This highlights the importance of parameters such as CeO2 additive, temperature control, adsorbent ratio, and pH, demonstrating the necessity of adjusting treatment process parameters.

[0035] Test Example 2 The concentrations (ngTEQ / Nm³, toxic equivalent) of dioxins and furans (PCDD / Fs) in Examples 1-4, Comparative Examples 3, 4, 5, and Comparative Example 7 were tested using HJ77.2-2008, "Determination of Dioxins in Ambient Air and Exhaust Gases - Isotope Dilution High-Resolution Gas Chromatography-High-Resolution Mass Spectrometry". Flue gas samples (sampling volume 20-50 m³) were collected after labeling with an internal standard using the isotope dilution method. After Soxhlet extraction and silica gel column purification, the samples were analyzed using high-resolution gas chromatography-high-resolution mass spectrometry (GC-HRMS). The detection limit was 0.001 ngTEQ / Nm³, and the toxic equivalent was calculated based on WHO-TEF. The results are summarized in Table 3.

[0036] Table 3. Results of dioxin and furan tests in Examples 1-4, Comparative Examples 3-5, and Comparative Example 7. ; Test results show that the concentrations of dioxins and furans in Examples 1-4 are all between 0.034-0.02 ng TEQ / Nm³, which are far below the limit of 0.1 ng TEQ / Nm³ in GB18485-2014 "Standard for Pollution Control of Municipal Solid Waste Incineration", meeting the standard requirements. This demonstrates the multi-stage synergistic effect of rapid cooling in the quench tower, activated carbon adsorption, and catalytic oxidation in inhibiting resynthesis and capturing the substances, with a removal rate of >99%.

[0037] The concentrations of Comparative Examples 3-5 and 7 increased to 0.25-0.42 ngTEQ / Nm³, all exceeding the standard by 2.5-4.5 times and failing to meet the standard limits. Specifically, the low S2 temperature in Comparative Example 3 led to dust residue promoting catalytic formation; the high S3 temperature in Comparative Example 4 intensified resynthesis; the insufficient activated carbon in S4 in Comparative Example 5 weakened adsorption; and the removal of S5 from the catalytic reactor in Comparative Example 7 resulted in the unoxidized precursor, leading to a significant increase in concentration. This highlights the importance of temperature control, adsorbent ratio, and catalytic steps.

[0038] Test Example 3 The concentrations of mercury (Hg) and ammonia (NH3) (mg / Nm³, ammonia slip) were tested in Examples 1-4 and Comparative Examples 1, 2, 3, 5 and 7-8. Mercury concentration was determined using HJ543-2009 "Determination of Mercury in Waste Gas from Stationary Sources - Cold Atomic Absorption Spectrophotometry". The sample was taken from the absorption liquid and analyzed using a cold atomic absorption spectrophotometer. The sampling volume was 10-20 L, and the detection limit was 0.0025 mg / Nm³. Ammonia concentration was determined using HJ533-2009 "Determination of Ammonia in Ambient Air and Waste Gas - Nessler's Reagent Spectrophotometry". The sample was taken from the absorption liquid and analyzed using a spectrophotometer. The sampling volume was 10-20 L, and the detection limit was 0.1 mg / Nm³. The test results are summarized in Table 4.

[0039] Table 4. Results of mercury and ammonia concentration tests in Examples 1-4, Comparative Examples 1-3, Comparative Examples 5, and Comparative Examples 7-8 ; Overall results show that the mercury concentration in Examples 1-4 was 0.01-0.018 mg / Nm³ and the ammonia concentration was 1.2-1.8 mg / Nm³, which are far below the target limits. Among them, mercury <0.05 mg / Nm³ and ammonia <10 mg / Nm³, which meet the requirements of GB18485-2014 "Standard for Pollution Control of Municipal Solid Waste Incineration". This demonstrates the highly efficient synergy of activated carbon adsorption, catalytic oxidation and denitrification selectivity, with a removal rate >98%.

[0040] The concentrations of comparative samples 1-3, 5, and 7-8 increased, with mercury exceeding the standard by 1.6-2.4 times and ammonia exceeding the standard by 1.5-2 times, failing to meet the standard limits. The overall removal rate decreased by 20-40%, highlighting the importance of adsorbents, temperature control, and additives. Comparative Example 1: Removing the CeO2 additive reduced SNCR selectivity, leading to increased ammonia slip and an ammonia concentration of 15 mg / Nm³. Comparative Example 2: Reducing the urea solution concentration to 15% may result in poor atomization or uneven distribution in the high-temperature zone, leading to incomplete urea pyrolysis or low NOx contact efficiency. This resulted in decreased denitrification efficiency (NOx increased to 48.92 mg / Nm³) and excessive escape of unreacted ammonia (from urea decomposition) (ammonia concentration increased to 18.3 mg / Nm³). Comparative Example 3: Lowering the S2 temperature to 300℃ increased dust residue, hindering Hg capture and increasing mercury concentration. Comparative Example 5: Reducing the activated carbon weight ratio weakened Hg adsorption, increasing mercury concentration to 0.122 mg / Nm³. Comparative Example 7: Removing the S5 fixed-bed catalytic reactor resulted in incomplete Hg oxidation and increased mercury concentration. Comparative Example 8: Lowering the S6 temperature to 130℃ reduced SCR activity, leading to incomplete ammonia conversion and an ammonia concentration of 19.9 mg / Nm³.

[0041] Test Example 4 Wastewater recovery rate (%) was tested for Examples 1-4 and Comparative Example 10. The mass balance method was used for calculation. According to the requirements of HJ2029-2013, the recovered water volume / total wastewater volume × 100% was calculated by mass balance. The influent and effluent volumes were continuously monitored using a flow meter (accuracy ±1%). Water quality sampling and analysis were combined before and after distillation (TOC and Cl⁻ concentrations were used to verify purity). The test cycle was 24 hours to ensure system stability. The test results are shown in Table 5.

[0042] Table 5. Wastewater recovery rate test results ; Under the conditions described in the embodiments of the present invention, the wastewater recovery rate is high. In Example 1, parameters such as temperature 60℃, vacuum degree 0.05MPa, and flux 10L / m²h are optimized to ensure efficient membrane distillation concentration and crystallization separation, minimizing impurities and achieving a recovery rate of 95%. In Example 2, the temperature is increased to 70℃, vacuum degree 0.08MPa, and flux 15L / m²h to improve the water evaporation rate and heat pump recovery efficiency, reducing energy consumption loss, and achieving a recovery rate of 96%. In Example 3, the temperature is increased to 80℃, vacuum degree 0.10MPa, and flux 20L / m²h to further optimize the permeate flux and crystallization purity, resulting in more thorough impurity separation and a recovery rate of up to 97%. In Example 4, the temperature is increased to 70℃, vacuum degree 0.08MPa, and flux 15L / m²h, balancing energy consumption and efficiency with similar parameters to Example 2, and the recovery rate remains stable at 96%.

[0043] In Comparative Example 10, increasing the vacuum to 0.15 MPa resulted in excessively high membrane pressure, unstable flux, potential membrane fouling, and decreased evaporation efficiency, leading to increased concentrated water loss and a lower recovery rate compared to the Example. Overall, the wastewater recovery rate of the treatment process of this invention is high.

[0044] Test Example 5 Test Examples 1-4 and Comparative Examples 3, 5, 7, and 9 were used to test the opacity (Ringelmann blackness, grade) and total heavy metal concentration (Pb, Cd, Cr, As, Ni, mg / Nm³) of flue gas. Opacity was determined using the Ringelmann blackness diagram method (HJ / T 398-2007) for determination of the opacity of flue gas emitted from stationary sources. The Ringelmann blackness diagram was visually compared for 5 consecutive minutes, and the average blackness grade was recorded. The detection limit was 0.1 grade. Total heavy metal concentration was determined using inductively coupled plasma optical emission spectrometry (ICP-OES) (HJ777-2015) for determination of heavy metals in exhaust gas from stationary sources. ICP-OES analysis was performed after isokinetic sampling into the filter cartridge and absorbent, followed by acid digestion. The sampling volume was 50-100 Nm³, and the detection limit was 0.001 mg / Nm³. The test results are shown in Table 6.

[0045] Table 6. Results of Transparency and Heavy Metal Concentration Tests ; In Examples 1-4, the flue gas opacity was all <1, far below the GB18485-2014 limit of 1, and the total heavy metal concentration was <0.02mg / Nm³, achieving a compliance rate of 100%. This demonstrates the advantages of high-temperature electrostatic and bag filter synergistic capture, as well as the physical coating of adsorbent to inhibit heavy metal volatilization and particle escape.

[0046] In Comparative Example 3, the S2 temperature was reduced to 300℃, below the salt dew point control temperature of 350℃. This caused the dust to become sticky and scale to form on the electrodes, resulting in a sharp drop in the efficiency of the electrostatic precipitator. A large amount of heavy metal-rich particles penetrated the precipitator, leading to an excess of the total heavy metal concentration by 13 times, highlighting the necessity of temperature control in high-temperature dust removal. In Comparative Example 5, the activated carbon content was reduced to 3%, resulting in insufficient adsorption capacity and weakened gaseous heavy metal capture, with the total concentration rising to 0.089 mg / Nm³, demonstrating the critical role of activated carbon content in the synergistic removal of gaseous heavy metals. In Comparative Example 7, the catalytic oxidation in the fixed-bed catalytic reactor was lacking, and gaseous heavy metals were not converted into easily captured states, with a total concentration of 0.112 mg / Nm³, emphasizing the role of the catalytic layer in the transformation of heavy metal speciation. In Comparative Example 9, the pH was reduced to 7.0, indicating insufficient acidity in wet absorption, leading to increased solubility and release of heavy metals, with a total concentration of 0.045 mg / Nm³, demonstrating the importance of precise pH control.

[0047] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A process for treating high-salt, high-dust flue gas, characterized in that, The processing technology is as follows: The high-salt, high-dust flue gas enters a selective non-catalytic reduction (SCR) denitrification system; it is treated using a high-temperature electrostatic precipitator; then it is fed into a quenching and conditioning tower where sodium bicarbonate-containing atomized water is sprayed and introduced into a nano-atomizer, the droplets produced by the nano-atomizer having a particle size of 10-50 nm; a composite adsorbent is dry-sprayed into the downstream pipeline of the quenching and conditioning tower; after the reaction is completed, fine particles are collected by a polytetrafluoroethylene (PTFE) membrane bag filter, and then oxidized in a fixed-bed manganese-cerium catalytic reactor; ammonia is sprayed into the low-temperature selective catalytic reduction system for denitrification; and residual pollutants are removed using a sodium hydroxide solution in a wet finishing tower. The flue gas discharged from the wet purification tower is heated before being released; the wastewater generated from the wet purification tower is subjected to heat pump-assisted membrane distillation and forced circulation crystallization. The composite adsorbent is composed of calcium hydroxide, sodium bentonite, activated carbon, and sodium bicarbonate; the mass ratio of calcium hydroxide, sodium bentonite, activated carbon, and sodium bicarbonate is 30-50:25-45:10:

15. The high-salt, high-dust flue gas enters the selective non-catalytic reduction denitrification system, where cerium dioxide additive is mixed with urea solution and then injected. The injection rate of the composite adsorbent is determined by the calcium-sulfur molar ratio of 1.0-2.5:1; the high-temperature electrostatic precipitator has a processing temperature of 350-450℃. The process of the polytetrafluoroethylene (PTFE) membrane bag filter includes: selecting PTFE long fibers as the base fabric and PTFE short fibers as the surface layer, making a felt material by needle punching, and after singeing, heat setting and calendering, hot pressing an expanded PTFE film onto the surface of the felt material to form a composite filter material, and sewing it to make the PTFE membrane bag filter. The manganese-cerium treatment of the fixed-bed manganese-cerium catalytic reactor includes: dissolving manganese nitrate tetrahydrate and cerium nitrate hexahydrate in deionized water, adding alumina for dispersion, adding citric acid and heating to form a gel, adjusting the pH to acidic, allowing it to stand and age, coating it onto the surface of a ceramic honeycomb, and then soaking, drying and calcining it by impregnation. The fixed-bed catalytic reactor carrier is the ceramic honeycomb, with a Ce-Mn catalytic layer of 50-100 μm thickness coated on the surface for preliminary oxidation of CO and TOC. The coating amount is 20-50 g per square meter of membrane surface.

2. The treatment process for high-salt, high-dust flue gas according to claim 1, characterized in that, The low-temperature selective catalytic reduction system uses manganese oxide-cerium oxide composite oxide for secondary denitrification.

3. The treatment process for high-salt, high-dust flue gas according to claim 1, characterized in that, Before the heat pump-assisted membrane distillation treatment, polyacrylamide flocculant is added for sedimentation; the forced circulation crystallization is sodium chloride crystallization.

4. The treatment process for high-salt, high-dust flue gas according to claim 1, characterized in that, The high-salt, high-dust flue gas contained 80 g / Nm³ of dust. 3 SO2 20g / Nm 3 HCl 10g / Nm 3 NOx 300mg / Nm 3 Total organic carbon (TOC) 100 mg / Nm 3 CO2 00mg / Nm 3 .

Images