A gas-liquid coupling purification method for the co-treatment of wastewater from plasma welding box exhaust gas

Abstract

This invention relates to the field of wastewater treatment technology and discloses a gas-liquid coupling purification method for the synergistic treatment of wastewater from plasma welding box exhaust gas. The method includes the following steps: S1, synchronous collection of pollutants: exhaust gas generated from plasma welding and associated circulating cooling wastewater are simultaneously input into the gas-liquid coupling purification system; S2, exhaust gas pre-charging and scrubbing absorption: the exhaust gas is electrostatically pre-charged, and then brought into strong contact with the alkaline absorbent liquid in the system within a scrubbing device to capture particulate matter, absorb acidic gases, and cool the gas. Through the synergistic effect of bipolar high-voltage electrostatic charge and turbulent cyclone water film scrubbing, exhaust gas particulate matter is efficiently captured and acidic gases are absorbed. Furthermore, combined with a high-level oxidation system formed by heterogeneous Fenton catalyst, hydraulic cavitation effect, ozone oxidation, and ultraviolet-assisted irradiation, the method deeply degrades recalcitrant organic matter and residual pollutants in the wastewater and exhaust gas, ensuring that both the purified wastewater and gas can stably meet emission standards, achieving a purification effect superior to traditional single-treatment processes.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment technology, specifically to a gas-liquid coupling purification method for the synergistic treatment of wastewater from plasma welding box exhaust gas. Background Technology

[0002] Plasma welding technology, due to its concentrated energy, high welding efficiency, and excellent joint quality, has been widely used in high-precision welding operations of various metal materials. However, during the welding process, two main types of pollutants are generated simultaneously: one is exhaust gas containing harmful substances such as nitrogen oxides, particulate matter, and volatile organic compounds; the other is circulating cooling wastewater containing metal shavings, oil, and recalcitrant organic matter. The discharge of both types of pollutants will cause serious harm to the environment.

[0003] Currently, the industry mostly adopts a "separate treatment" model for the aforementioned exhaust gas and wastewater. This model has obvious drawbacks: For wastewater, traditional treatment processes such as physical sedimentation and conventional biological treatment are difficult to efficiently remove recalcitrant organic matter, while the traditional Fenton process requires the addition of large amounts of chemical agents, resulting in high solid waste disposal costs; For exhaust gas, existing treatment processes such as activated carbon adsorption and simple spray absorption have problems such as low removal efficiency and easy generation of secondary pollution; At the same time, existing treatment technologies generally have the problem of resource waste. The metal resources and waste heat contained in wastewater and exhaust gas are not effectively recovered, and the operating parameters of the treatment system are mostly manually adjusted, which cannot be dynamically controlled according to the real-time changes in pollutant concentration and water quality, resulting in large fluctuations in treatment efficiency, high energy consumption and reagent consumption, and difficulty in meeting the current stringent environmental emission standards and resource recycling requirements. Summary of the Invention

[0004] The purpose of this invention is to provide a gas-liquid coupling purification method for the synergistic treatment of wastewater from plasma welding box exhaust gas, so as to solve the problems mentioned in the background art.

[0005] To achieve the above objectives, the present invention provides the following technical solution: a gas-liquid coupling purification method for the synergistic treatment of wastewater from plasma welding box exhaust gas, comprising the following steps:

[0006] S1. Simultaneous collection of pollution sources: The exhaust gas generated by plasma welding and the supporting circulating cooling wastewater are simultaneously input into the gas-liquid coupling purification system.

[0007] S2. Exhaust gas pre-charging and scrubbing absorption: The exhaust gas is electrostatically pre-charged and then brought into strong contact with the alkaline absorbent liquid in the system in the scrubbing device to capture particulate matter, absorb acidic gases and cool down.

[0008] S3, Gas-liquid coupled catalytic oxidation: The scrubbed exhaust gas and wastewater are introduced together into a reaction tower filled with catalyst; in the reaction tower, the organic matter in the wastewater and the residual pollutants in the exhaust gas are oxidized and degraded by the catalytic effect of hydraulic cavitation and injected ozone, under the synergistic effect of the catalyst.

[0009] S4. Gas-liquid separation and energy recovery: The gas-liquid mixture after the reaction is efficiently separated to purify the gas emissions, and the separated liquid recovers heat through waste heat exchange.

[0010] S5. Solid-liquid separation and resource utilization: The liquid after heat recovery is coagulated and settled. The supernatant is returned to step S2 as a supplement to the absorbent liquid. The settled sludge is dewatered and reused as a metal raw material additive.

[0011] As a preferred embodiment of the present invention, in step S2, electrostatic pre-charging is achieved through a bipolar high-voltage electrostatic charge region. The bipolar high-voltage electrostatic charge region applies a positive corona voltage of +10kV to +15kV and a negative corona voltage of -12kV to -18kV, with an alternating frequency of 50Hz to 200Hz. The washing device is a turbulent cyclone water film scrubber. The alkaline absorbent is formed by mixing the clean water returned from step S5 with the supplemented sodium hydroxide solution, and its pH value is maintained in the range of 9.0-10.5 by an automatic dosing system.

[0012] As a preferred embodiment of the present invention, in step S3, the catalyst is a heterogeneous Fenton catalyst, which is prepared by the following method: impregnating a porous cordierite ceramic or activated alumina support with Fe... 3+ and Cu 2+ In a mixed nitrate solution of ions, Fe 3+ With Cu 2+ The molar ratio corresponds to a mass ratio of Fe3O4 to CuO of 2:1 to 5:1; after standing for 12 hours, it is dried at 80℃ and then calcined at 450℃ for 4 hours in air atmosphere to obtain a catalyst supported on nano-Fe3O4 and CuO composite metal oxide active components; the catalyst is spherical or columnar with a particle size of 3-8 mm and a specific surface area greater than 150 m². 2 / g; The hydraulic cavitation effect is generated by a hydraulic cavitation generator located at the bottom of the reaction tower. The inlet pressure of the hydraulic cavitation generator is controlled at 0.3-0.6 MPa, and the cavitation number σ is controlled at 0.2-0.5. The cavitation number σ is defined as σ = (P in - P v ) / (0.5ρQ 2 / A 2 ), where P in P is the absolute pressure at the inlet of the hydraulic cavitation generator (MPa). vρ is the saturated vapor pressure of water at the operating temperature (MPa), and ρ is the density of water (kg / m³). 3 Q is the liquid volumetric flow rate (m³ / s). 3 / s), A is the cross-sectional area of ​​the generator throat (m²) 2 ).

[0013] As a preferred embodiment of the present invention, in step S3, ozone is injected into the bottom of the reaction tower through an annular microporous aeration pipe surrounding the hydraulic cavitation generator to form microbubbles; the total ozone dosage is dynamically adjusted by a feedforward-feedback linkage control system based on the real-time monitored chemical oxygen demand (COD) value of the wastewater and the nitrogen oxide concentration of the tail gas. The control logic of the feedforward-feedback linkage control system is as follows: set the target COD value C of the wastewater. o and the target value N for NOx in exhaust gas o The current feedforward module predicts the COD load change trend based on the influent flow rate and initially sets the ozone basic dosing acceleration rate Q. o The feedback module acquires the actual COD value C and NOx value N in real time and calculates the deviation ΔC=CC. o ΔN=NN o If |ΔC| > threshold 1 and |ΔN| < threshold 2, then the ozone dosing acceleration rate is increased first; if |ΔN| > threshold 2 and |ΔC| < threshold 1, then the inlet pressure of the hydraulic cavitation generator is increased first to enhance gas-phase mass transfer; if both exceed the limits, then the ozone dosing acceleration rate and inlet pressure are adjusted synchronously according to the weighting coefficients α·ΔC + β·ΔN, where α and β are preset empirical coefficients; the control objective is to maintain the dissolved ozone concentration in the wastewater at 5-15 mg / L, while maintaining the ozone volume fraction in the gas phase space at the top of the reaction tower at 0.5%-2.0%.

[0014] As a preferred embodiment of the present invention, in step S4, the efficient gas-liquid separation is achieved by a multi-stage cyclone separator. The multi-stage cyclone separator includes a first-stage tangential inlet cyclone separator and a second-stage axial inlet cyclone separator arranged in series. The first-stage cyclone separator is designed to remove droplets with a particle size greater than 10 μm, and the second-stage cyclone separator is designed to remove droplets with a particle size greater than 2 μm. The inner wall surface of the cyclone separator is coated with a hydrophobic and oleophobic coating of polytetrafluoroethylene.

[0015] As a preferred embodiment of the present invention, in step S5, the coagulation and sedimentation are carried out in an inclined plate sedimentation tank, and the added coagulant is polyaluminum ferric sulfate, with an addition amount of 50-150 mg / L; the installation angle of the inclined plate in the inclined plate sedimentation tank is 55-60°, and the effective hydraulic retention time of the tank is designed to be 1.5-2.5 hours; after the supernatant is collected through the overflow weir, it is pressurized and returned to the water supply pipe of the washing device in step S2 by the intermediate water pump.

[0016] As a preferred embodiment of the present invention, in step S3, an ultraviolet-assisted irradiation unit is further provided in the upper space of the reaction tower filled with catalyst. The ultraviolet-assisted irradiation unit is equipped with a dual-band low-pressure mercury lamp emitting main wavelengths of 185nm and 254nm, and the irradiation intensity of the ultraviolet lamp is 30-80mW / cm². 2 It is used to stimulate ozone decomposition to generate hydroxyl radicals, assist in the oxidation and degradation of residual nitrogen oxides in exhaust gas, and degrade gaseous volatile organic compounds.

[0017] As a preferred embodiment of the present invention, the method is operated automatically by an integrated control system; the integrated control system includes:

[0018] The monitoring module is used to acquire key parameters of exhaust gas and key water quality indicators of wastewater in real time.

[0019] The central control module, connected to the monitoring module, is used to generate and issue coordinated control commands based on the comparison results of real-time data of key parameters and key water quality indicators with preset target values.

[0020] The execution module, connected to the central control module, is used to receive coordinated control commands and accordingly adjust at least two of the following in step S2: pH of the alkaline absorbent, ozone dosing acceleration rate and hydraulic cavitation intensity, and coagulant dosage.

[0021] As a preferred technical solution of the present invention, the key parameters of the exhaust gas acquired by the monitoring module include flow rate, nitrogen oxide concentration and ozone concentration, and the key water quality indicators of the wastewater acquired include chemical oxygen demand and pH value; the coordinated control instructions generated by the central control module aim to achieve the coordinated and efficient removal of chemical oxygen demand in wastewater and nitrogen oxides in exhaust gas, and dynamically and correlatedly adjust the ozone dosing acceleration rate and the inlet pressure of the hydraulic cavitation generator.

[0022] As a preferred technical solution of the present invention, in step S5, the settled sludge is reused as a metal raw material additive, specifically including: firstly, the dewatered sludge is subjected to low-temperature pyrolysis treatment at a temperature range of 300-450°C under the protection of an inert atmosphere of nitrogen or argon, and the pyrolysis time is 30-90 minutes, so as to completely remove organic matter and bound water from the sludge; then, the powder mainly composed of metal oxides obtained after pyrolysis is uniformly mixed into new metal powder raw materials for plasma welding at a mass percentage of 1%-5%.

[0023] Compared with the prior art, the beneficial effects of the present invention are:

[0024] 1. Through the synergistic effect of bipolar high-voltage electrostatic charge and turbulent cyclone water film washing, particulate matter in exhaust gas is efficiently captured and acidic gases are absorbed. Combined with an advanced oxidation system formed by heterogeneous Fenton catalyst, hydraulic cavitation effect, ozone oxidation and ultraviolet-assisted irradiation, it deeply degrades recalcitrant organic matter and residual pollutants in exhaust gas in wastewater, ensuring that both wastewater and gas can be stably discharged in compliance with standards after purification, which is significantly better than the purification effect of traditional single treatment processes.

[0025] 2. The Fe3O4-CuO / cordierite or alumina composite catalyst used in this invention, under the local high temperature and high pressure environment generated by hydraulic cavitation, allows CuO to effectively promote Fe... 3+ / Fe 2+ The cycle significantly improved the yield of hydroxyl radicals and overcame the shortcomings of the traditional homogeneous Fenton system, such as narrow pH range and large sludge production.

[0026] 3. By treating settled sludge through specific processes, the metal resources within can be recovered and reused as welding raw materials, thereby improving resource utilization. The supernatant after solid-liquid separation is recycled as an absorbent to achieve water resource recycling. At the same time, the waste heat generated during the treatment process can be recovered for production support or heating, reducing energy consumption.

[0027] 4. The integrated control system enables fully automated and coordinated regulation of the entire process, real-time monitoring of key parameters of exhaust gas and wastewater, and dynamic adjustment of various operating parameters to ensure stable operation of the system even when water quality and quantity fluctuate. The use of heterogeneous Fenton catalysts avoids the generation of large amounts of solid waste, dynamic adjustment of ozone dosage reduces reagent waste, and water and heat recovery reduces energy consumption. This comprehensively optimizes treatment costs and improves the economy and practicality of the process.

[0028] 5. This invention optimizes the process parameters and equipment configuration of each stage based on the characteristics of plasma welding exhaust gas and wastewater. Key parameters can be flexibly adjusted according to treatment needs, which can meet the treatment needs of plasma welding production lines of different scales. The process design is scientific and reasonable, and can be widely used in many industries that use plasma welding technology, such as machinery manufacturing and aerospace. It also has broad industrial application prospects in the field of water and wastewater treatment.

[0029] 6. The various process steps of this invention are closely linked. High-efficiency gas-liquid separation avoids the emission of gaseous pollutants carrying liquid, and strict control of ozone dosage avoids excessive emissions. After treatment, all sludge is recycled and reused, with no secondary pollutants generated. This achieves the harmless treatment and resource utilization of pollutants, resulting in outstanding environmental benefits. Attached Figure Description

[0030] Figure 1 This is an overall flow chart of a gas-liquid coupling purification method for the synergistic treatment of wastewater from plasma welding box according to the present invention;

[0031] Figure 2 This is a schematic diagram of step S5, the inclined plate sedimentation tank and sludge treatment and reuse process, in the gas-liquid coupling purification method for synergistic wastewater treatment of plasma welding box exhaust gas of the present invention.

[0032] Figure 3 This is a schematic diagram of the architecture and signal flow of the integrated control system in the gas-liquid coupling purification method for co-treating wastewater from plasma welding box exhaust gas according to the present invention. Detailed Implementation

[0033] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. 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 of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0034] I. Description of Basic Experimental Conditions

[0035] This experiment uses a plasma welding production line of a large machinery manufacturing enterprise in the Yangtze River Delta region as the application scenario. The production line uses a PLW-630 plasma welding equipment, with an average daily welding operation time of 16 hours and an exhaust gas volume of approximately 800 m³ per hour. 3 The concentration of nitrogen oxides (NOx) in the exhaust gas is 80-120 mg / m³. 3 The particulate matter concentration is 50-80 mg / m³ 3 Simultaneously, the supporting circulating cooling wastewater discharge rate is 1.2m³ per hour. 3 The chemical oxygen demand (COD) of the wastewater is 300-500 mg / L, and the pH value is 6.0-7.5.

[0036] The specifications of the main equipment and materials used in the experiment are as follows:

[0037] Gas-liquid coupling purification system: Independently integrated design, including washing device, reaction tower, gas-liquid separation device, solid-liquid separation device and integrated control system.

[0038] Turbulent Cyclone Water Film Scrubber: Model TL-XS-1000, Processing Capacity 1000m³ 3 / h.

[0039] Reaction tower: inner diameter 800mm, height 5m, catalyst layer height 2m.

[0040] Hydraulic cavitation generator: Model SK-KH-06, maximum inlet pressure 1.0MPa.

[0041] Annular microporous aeration tube: Model WB-HX-800, pore size 50-100μm.

[0042] Multistage cyclone separators: First-stage tangential inlet cyclone separator model XL-QX-100, second-stage axial inlet cyclone separator model XL-ZX-80.

[0043] Inclined slab sedimentation tank: effective volume 3m³ 3 The inclined plate is made of polypropylene.

[0044] Ultraviolet-assisted irradiation unit: Equipped with dual-band low-pressure mercury lamps, model ZW36D17W-Z819, with main wavelengths of 185nm and 254nm.

[0045] Integrated control system: includes monitoring modules (gas sensors NOx-800, O3-600, online water quality monitors COD-2000, pH-3000), central control module (PLC model S7-1500) and execution modules.

[0046] Heterogeneous Fenton catalyst: using porous cordierite ceramic as support (particle size 5 mm, specific surface area 180 m²) 2 / g), loaded with nano-Fe3O4 and CuO (mass ratio 3:1) composite metal oxide active components; the preparation method is as follows: the cordierite carrier is impregnated in a mixed solution of Fe(NO3)3 and Cu(NO3)2 (Fe 3+ :Cu 2+ The product was prepared by drying at 80°C after standing for 12 hours (molar ratio of 3:1) and then calcining in air at 450°C for 4 hours.

[0047] Sodium hydroxide solution: commercially available analytical grade, concentration 30% (mass fraction).

[0048] Polyaluminum ferric sulfate: Model PAFSS-Ⅱ, industrial grade, active ingredient content ≥30%, produced by a water treatment materials company.

[0049] Ozone generator: Model OZ-50, ozone output 0-50g / h.

[0050] Low-temperature pyrolysis furnace: Model RYJ-50, temperature control accuracy ±5℃, can be protected by inert gas.

[0051] The experimental detection methods were carried out in accordance with national standards: NOx concentration was determined using GB / T 15436-1995 "Determination of Nitrogen Oxides in Ambient Air - Saltzman Method"; particulate matter concentration was determined using GB / T 16157-1996 "Determination of Particulate Matter and Sampling Methods for Gaseous Pollutants in Exhaust Gas from Stationary Sources"; COD was determined using GB / T 11914-1989 "Determination of Chemical Oxygen Demand in Water - Dichromate Method"; pH value was determined using GB / T 6920-1986 "Determination of pH Value in Water - Glass Electrode Method"; and ozone concentration was determined using GB / T 18268-2019 "Preparation of Mixed Gases for Gas Analysis Calibration - Weighing Method".

[0052] II. Implementation Examples

[0053] Example 1

[0054] This embodiment employs a gas-liquid coupling purification method for the combined treatment of wastewater and exhaust gas from plasma welding boxes. The specific steps are as follows:

[0055] S1. Simultaneous Collection of Pollution Sources: The exhaust gas generated from plasma welding and the corresponding circulating cooling wastewater are simultaneously fed into the gas-liquid coupling purification system via pipelines. The exhaust gas input flow rate is controlled at 800 m³ / s. 3 / h, wastewater input flow rate controlled at 1.2m 3 / h.

[0056] S2. Exhaust gas pre-charging and scrubbing absorption: Electrostatic pre-charging is achieved through a bipolar high-voltage electrostatic charge region, applying a positive corona voltage of +12kV and a negative corona voltage of -15kV, with an alternating frequency of 100Hz; the scrubbing device adopts a turbulent cyclone water film scrubber, and the alkaline absorption liquid is made by mixing the clean water returned from step S5 with the supplemented 30% sodium hydroxide solution, and the pH value is maintained at 9.5 by an automatic dosing system.

[0057] S3. Gas-liquid coupled catalytic oxidation: The scrubbed tail gas and wastewater are jointly introduced into a reaction tower filled with a heterogeneous Fenton catalyst. The catalyst is spherical with a particle size of 5 mm, supported by porous cordierite ceramic, and loaded with a composite metal oxide active component consisting of nano-Fe3O4 and CuO (mass ratio 3:1), with a specific surface area of ​​180 m². 2 / g; The hydraulic cavitation effect is generated by a hydraulic cavitation generator located at the bottom of the reaction tower. The inlet pressure of the hydraulic cavitation generator is controlled at 0.4 MPa, and the calculated cavitation number σ is 0.3. Ozone is injected into the bottom of the reaction tower through an annular microporous aeration pipe surrounding the hydraulic cavitation generator, forming microbubbles. The total ozone dosage is dynamically adjusted by a feedforward-feedback linkage control system based on the real-time monitored COD value of the wastewater and NOx concentration of the tail gas. The control system calculates and adjusts the ozone dosing rate and the inlet pressure of the cavitation generator in real time according to preset logic, controlling the dissolved ozone concentration in the wastewater to be maintained at 10 mg / L, and the ozone volume fraction in the gas phase space at the top of the reaction tower to be maintained at 1.2%. An ultraviolet-assisted irradiation unit is installed in the upper space of the reaction tower, with the ultraviolet lamps arranged to have an irradiation intensity of 50 mW / cm². 2 .

[0058] S4. Gas-liquid separation and energy recovery: High-efficiency gas-liquid separation is achieved through a multi-stage hydrocyclone separator. The first-stage tangential inlet hydrocyclone separator removes droplets with a particle size greater than 10 μm, and the second-stage axial inlet hydrocyclone separator removes droplets with a particle size greater than 2 μm. The inner wall surface of the hydrocyclone separator is coated with a hydrophobic and oleophobic coating of polytetrafluoroethylene. The gas-liquid mixture after the reaction is passed into the multi-stage hydrocyclone separator for separation. The purified gas is discharged from the top, and the separated liquid recovers heat through a plate heat exchanger. The recovered heat is used for workshop heating.

[0059] S5. Solid-liquid separation and resource utilization: The liquid after heat recovery is fed into an inclined plate sedimentation tank for coagulation and sedimentation. The coagulant added is polyaluminum ferric sulfate polysilicate (model PAFSS-Ⅱ), and the dosage is 100 mg / L. The inclined plate in the sedimentation tank is installed at an angle of 58°, and the effective hydraulic retention time of the tank is designed to be 2.0 hours. The supernatant is collected through an overflow weir and then pressurized and returned to the water supply pipeline of the washing device in step S2 by an intermediate water pump. After the sedimented sludge is dewatered by a filter press, it is subjected to low-temperature pyrolysis treatment at 380°C under the protection of nitrogen inert atmosphere for 60 minutes. The powder obtained after pyrolysis, which is mainly composed of metal oxides, is uniformly mixed into new metal powder raw materials for plasma welding at a mass percentage of 3%.

[0060] In this embodiment, the gas-liquid coupling purification method is automated through an integrated control system. The monitoring module acquires the flow rate of the exhaust gas, the concentration of nitrogen oxides, the concentration of ozone, and the chemical oxygen demand and pH value of the wastewater in real time. The central control module generates collaborative control commands based on the comparison results of these real-time data with preset target values. The execution module synchronously adjusts the pH of the alkaline absorbent in step S2, the ozone dosing acceleration rate and hydraulic cavitation intensity in step S3, and the amount of coagulant added in step S5.

[0061] Example 2

[0062] The difference between this embodiment and Embodiment 1 is that:

[0063] In step S2, a positive corona voltage of +10kV and a negative corona voltage of -12kV are applied to the bipolar high-voltage electrostatic charge region, with an alternating frequency of 50Hz; the pH value of the alkaline absorption solution is maintained at 9.0.

[0064] In step S3, the heterogeneous Fenton catalyst uses activated alumina as a support, with a nano-Fe3O4 to CuO mass ratio of 2:1. The catalyst is columnar with a particle size of 3 mm and a specific surface area of ​​150 m². 2 / g; the inlet pressure of the hydraulic cavitation generator is controlled at 0.3MPa, and the calculated cavitation number σ is 0.2; the dissolved ozone concentration in the wastewater is maintained at 5mg / L, and the ozone volume fraction in the gas phase space at the top of the reaction tower is maintained at 0.5%; the irradiation intensity of the ultraviolet-assisted irradiation unit is 30mW / cm². 2 .

[0065] In step S5, the dosage of polyaluminum ferric sulfate is 50 mg / L; the installation angle of the inclined plate is 55°; the effective hydraulic retention time of the pool is 1.5 hours; the dewatered sludge is subjected to low-temperature pyrolysis treatment at 300°C under the protection of argon inert atmosphere for 30 minutes; and the pyrolysis powder is added to the new metal powder raw material at a mass percentage of 1%.

[0066] The remaining steps and experimental conditions are the same as in Example 1.

[0067] Example 3

[0068] The difference between this embodiment and Embodiment 1 is that:

[0069] In step S2, a positive corona voltage of +15kV and a negative corona voltage of -18kV are applied to the bipolar high-voltage electrostatic charge region, with an alternating frequency of 200Hz; the pH value of the alkaline absorption solution is maintained at 10.5.

[0070] In step S3, the mass ratio of nano-Fe3O4 to CuO in the heterogeneous Fenton catalyst is 5:1. The catalyst is spherical with a particle size of 8 mm and a specific surface area of ​​200 m². 2 / g; the inlet pressure of the hydraulic cavitation generator is controlled at 0.6MPa, and the calculated cavitation number σ is 0.5; the dissolved ozone concentration in the wastewater is maintained at 15mg / L, and the ozone volume fraction in the gas phase space at the top of the reaction tower is maintained at 2.0%; the irradiation intensity of the ultraviolet-assisted irradiation unit is 80mW / cm². 2 .

[0071] In step S5, the dosage of polyaluminum ferric sulfate is 150 mg / L; the installation angle of the inclined plate is 60°; the effective hydraulic retention time of the tank is 2.5 hours; the dewatered sludge is subjected to low-temperature pyrolysis treatment at 450°C under nitrogen inert atmosphere protection for 90 minutes; and the pyrolysis powder is added to the new metal powder raw material at a mass percentage of 5%.

[0072] The remaining steps and experimental conditions are the same as in Example 1.

[0073] III. Comparison Example

[0074] Compare with Example 1

[0075] This comparative example did not use a bipolar high-voltage electrostatic charge region for pre-charging the exhaust gas. The remaining steps and experimental conditions were the same as in Example 1. Specifically, in step S2, only a turbulent cyclone water film scrubber was used to contact the alkaline absorbent liquid, and no electrostatic pre-charging treatment was performed.

[0076] Compare with Example 2

[0077] This comparative example did not use a heterogeneous Fenton catalyst. The remaining steps and experimental conditions were the same as in Example 1. Specifically, the reaction tower in step S3 was not filled with catalyst, and only the hydrocavitation effect and ozone were used for oxidative degradation.

[0078] Compare with Example 3

[0079] This comparative example did not use an ultraviolet-assisted irradiation unit. The remaining steps and experimental conditions were the same as in Example 1. Specifically, no ultraviolet-assisted irradiation unit was installed in the upper space of the reaction tower in step S3.

[0080] Compare with Example 4

[0081] This comparative example did not use an integrated control system. The remaining steps and experimental conditions were the same as in Example 1. Specifically, the pH of the alkaline absorbent in step S2, the ozone dosing acceleration rate and hydraulic cavitation intensity in step S3, and the amount of coagulant added in step S5 were manually adjusted. Real-time monitoring and coordinated control were not performed.

[0082] Compare with Example 5

[0083] This comparative example did not use the low-temperature pyrolysis and reuse process for sludge. The remaining steps and experimental conditions were the same as in Example 1. Specifically, the settled sludge was directly outsourced for disposal after dewatering, without low-temperature pyrolysis or the addition of new metal powder raw materials for reuse.

[0084] IV. Experimental Data and Results

[0085] (a) Experimental Data Recording

[0086] Table 1. Experimental data on the treatment effects of each embodiment and control example.

[0087]

[0088] Note: Comparative Examples 1-4 did not involve sludge reuse and metal recovery processes, so this indicator is marked as "-"; Comparative Example 5 did not involve sludge reuse, so the sludge reuse and metal recovery rate was 0.

[0089] Table 2. Stability data of operating parameters for each embodiment and control example.

[0090]

[0091] (II) Detailed Analysis and Explanation of Experimental Data

[0092] 1. Analysis of pollutant removal efficiency

[0093] As can be clearly seen from the experimental data in Table 1, Examples 1-3 of the present invention exhibit excellent removal effects on nitrogen oxides (NOx), particulate matter, and chemical oxygen demand (COD) in the exhaust gas of the plasma welding box and the associated circulating cooling wastewater. In contrast, the removal effects of the control examples were significantly reduced due to the lack of corresponding technical features.

[0094] Regarding NOx removal rates in exhaust gas, Examples 1-3 achieved removal rates of 96.8%, 92.5%, and 97.2%, respectively, with an average removal rate exceeding 95%. This excellent performance is the result of the synergistic effect of various technical features. The bipolar high-voltage electrostatic charge zone (applying a specific range of positive and negative corona voltages and alternating frequencies) allows particulate matter and acidic gas molecules in the exhaust gas to acquire charges, greatly enhancing the probability of subsequent contact and reaction with the alkaline absorbent liquid, thus laying the foundation for the initial removal of NOx. In Example 1, a +12kV positive corona voltage, a -15kV negative corona voltage, and a 10kV high-voltage electrostatic charge zone were used. The 0Hz alternating frequency, compared to the lower voltage and frequency (+10kV, -12kV, 50Hz) in Example 2, allows for more thorough pre-charging of the exhaust gas, resulting in a higher NOx removal rate. Example 3, employing even higher voltage and frequency (+15kV, -18kV, 200Hz), further optimizes the pre-charging effect, achieving a NOx removal rate of 97.2%. In contrast, Example 1, which did not utilize this electrostatic pre-charging technology, had a NOx removal rate of only 78.3%, a decrease of 18.5 percentage points compared to Example 1. This fully demonstrates the crucial role of the bipolar high-voltage electrostatic charge region in the NOx removal process.

[0095] Meanwhile, a specific heterogeneous Fenton catalyst (using porous cordierite ceramics or activated alumina as a support, loading nano-Fe3O4 and CuO composite metal oxide active components, and controlling specific particle size, specific surface area and mass ratio of active components), ultraviolet-assisted irradiation unit, hydrodynamic cavitation effect, and ozone injection technology are combined to form a highly efficient gas-liquid coupled catalytic oxidation system. The heterogeneous Fenton catalyst provides stable catalytic active centers. The extreme physicochemical environment (high temperature, high pressure, and strong oxidizing free radicals) generated by the hydrocavitation effect accelerates the decomposition of ozone and the oxidation of pollutants. The ultraviolet-assisted irradiation unit further excites the decomposition of ozone to generate a large number of hydroxyl free radicals, while directly photolyzing residual NOx in the exhaust gas and degrading gaseous volatile organic compounds. In Example 1, the mass ratio of the catalyst active components Fe3O4 to CuO is 3:1, which is higher than the 2:1 ratio in Example 2, resulting in higher catalytic activity. This is comparable to hydrocavitation (inlet pressure 0.4 MPa, cavitation number 0.3), ozone (dissolved ozone concentration 10 mg / L), and ultraviolet radiation (irradiation intensity 50 mW / cm²). 2 The synergistic effect of the heterogeneous Fenton catalyst and the ultraviolet-assisted irradiation unit resulted in highly efficient NOx removal. In Control Example 2, which did not use the heterogeneous Fenton catalyst and relied solely on hydraulic cavitation and ozone oxidation, the NOx removal rate dropped to 85.6%, a decrease of 11.2 percentage points compared to Example 1. In Control Example 3, which did not have an ultraviolet-assisted irradiation unit, the NOx removal rate was 90.2%, a decrease of 6.6 percentage points compared to Example 1. These two data fully demonstrate the important role of the heterogeneous Fenton catalyst and the ultraviolet-assisted irradiation unit in the deep removal of NOx.

[0096] Regarding the removal rate of particulate matter in exhaust gas, the removal rates of Examples 1-3 were 99.2%, 98.5%, and 99.5%, respectively, all reaching extremely high levels. This is mainly due to the synergistic effect of the turbulent cyclone water film scrubber and electrostatic precharging. Electrostatic precharging makes the particulate matter more easily captured by the water film of the alkaline absorbent liquid in the scrubber. The turbulent cyclone water film scrubber further improves the capture efficiency of particulate matter through strong gas-liquid contact. The higher electrostatic precharging voltage and frequency in Example 3 make the particulate matter more fully charged. At the same time, the large specific surface area of ​​the catalyst can also adsorb some fine particulate matter, so the particulate matter removal rate is the highest. In contrast, Control Example 1 did not undergo electrostatic precharging, and the particulate matter removal rate was only 90.1%, a decrease of 9.1 percentage points compared to Example 1. This highlights the key role of electrostatic precharging in particulate matter capture and also proves the necessity of the relevant technical features.

[0097] Regarding the COD removal rate of wastewater, Examples 1-3 showed removal rates of 94.5%, 88.7%, and 95.3%, respectively, demonstrating excellent treatment effects. This result is due to the combined effect of gas-liquid coupled catalytic oxidation technology, integrated control system, and high-efficiency gas-liquid separation technology. The synergistic effect of heterogeneous Fenton catalyst, hydraulic cavitation effect, ozone injection, and ultraviolet-assisted irradiation generates a large number of highly oxidizing hydroxyl radicals, which can rapidly oxidize and degrade organic matter in wastewater. The integrated control system dynamically adjusts ozone dosage to accelerate the process by monitoring the wastewater COD value in real time. The high efficiency and hydraulic cavitation intensity ensured the continuous and efficient execution of the oxidative degradation reaction; the multi-stage cyclone separator achieved efficient gas-liquid separation, preventing gaseous pollutants from re-entering the wastewater and ensuring the stability of the wastewater treatment effect. In Example 1, the ozone dissolved concentration was 10 mg / L, the hydraulic cavitation inlet pressure was 0.4 MPa, and the synergistic effect with the catalyst and ultraviolet light achieved a COD removal rate of 94.5%; in Example 3, a higher ozone concentration (15 mg / L), hydraulic cavitation inlet pressure (0.6 MPa), and ultraviolet irradiation intensity (80 mW / cm²) were used. 2 The oxidation degradation effect was further enhanced, and the COD removal rate reached 95.3%. The lower reaction conditions in Example 2 resulted in a relatively low COD removal rate of 88.7%. In Control Example 2, which did not use a heterogeneous Fenton catalyst, the COD removal rate was only 75.2%, a decrease of 19.3 percentage points compared to Example 1, indicating that the catalyst played a core catalytic role in the oxidation degradation of organic matter. In Control Example 3, which did not use an ultraviolet-assisted irradiation unit, the COD removal rate was 86.3%, a decrease of 8.2 percentage points compared to Example 1, verifying the importance of ultraviolet-assisted oxidation. In Control Example 4, which did not use an integrated control system and manually adjusted the operating parameters, the reaction conditions could not be adjusted in a timely manner according to the real-time changes in wastewater COD, resulting in a COD removal rate of 84.7%, a decrease of 9.8 percentage points compared to Example 1, fully demonstrating the key role of the integrated control system in ensuring the stability and efficiency of wastewater treatment.

[0098] 2. Analysis of the stability of operating parameters

[0099] As can be seen from the stability data of the operating parameters in Table 2, the stability of the operating parameters of Examples 1-3 is significantly better than that of Control Example 4. This is mainly due to the integrated control system, which includes a monitoring module, a central control module, and an execution module. It can acquire key parameters and indicators of exhaust gas and wastewater in real time. Through the analysis and processing of the central control module, it generates coordinated control commands, which are then synchronously adjusted by the execution module.

[0100] Regarding the pH fluctuation range of the alkaline absorption solution, Examples 1-3 had fluctuations of ±0.1, ±0.15, and ±0.08, respectively, while Control Example 4 had a fluctuation as high as ±0.5. In these examples, the pH value of the alkaline absorption solution was monitored in real time through the synergistic effect of the automatic dosing system and the integrated control system. When the pH value was lower than the set range, sodium hydroxide solution was automatically added. When the pH value was higher than the set range, it was adjusted by reflux of the supernatant, thus ensuring the stability of the pH value. In Example 3, due to the use of a more precise monitoring sensor and actuator, the pH fluctuation range was the smallest, only ±0.08, which provided a stable chemical environment for the washing and absorption reaction and ensured the stability of the pollutant removal effect.

[0101] Regarding the response time for adjusting the ozone dosing acceleration rate, Examples 1-3 show response times of 3s, 5s, and 2s respectively, while Comparative Example 4 requires 30s. The feedforward-feedback linkage control system in the integrated control system can quickly calculate the required ozone dosage based on the real-time monitored wastewater COD value and tail gas NOx concentration, and adjust the ozone generator's operating parameters in a timely manner through the execution module to achieve a rapid response of the ozone dosing acceleration rate. The higher control algorithm accuracy and hardware configuration in Example 3 result in the shortest response time of only 2s, which can quickly adapt to changes in pollutant concentration, ensure that the ozone concentration is maintained within the set range, and improve the utilization rate of ozone.

[0102] Regarding the stability (deviation%) of hydraulic cavitation intensity and the accuracy (deviation%) of coagulant dosage, the deviations in Examples 1-3 were significantly smaller than those in Control Example 4. The integrated control system ensured the stability of hydraulic cavitation intensity by monitoring parameters such as the inlet pressure of the hydraulic cavitation generator in real time and adjusting the opening of relevant valves accordingly. At the same time, it precisely controlled the dosage of coagulant based on the wastewater quality, avoiding waste of coagulant and fluctuations in treatment effect. The deviation of hydraulic cavitation intensity in Example 3 was only ±2.1%, and the deviation of coagulant dosage was only ±2.8%, fully demonstrating the important role of the integrated control system in ensuring the stability of equipment operation and the accuracy of parameters.

[0103] 3. Analysis of the effectiveness of resource recycling

[0104] As can be seen from the metal recovery rate data of sludge recycling in Table 1, the metal recovery rates of Examples 1-3 are 89.6%, 82.3%, and 91.2%, respectively, while the metal recovery rate of Control Example 5 is 0. This fully demonstrates the advantages of the sludge low-temperature pyrolysis and recycling process.

[0105] The specific process for reusing settled sludge as a metal raw material additive was clarified: the dewatered sludge underwent low-temperature pyrolysis under an inert atmosphere to remove organic matter and bound water. Then, the pyrolyzed metal oxide powder was mixed into new metal powder raw materials in a specific ratio. In the application by this machinery manufacturing enterprise in the Yangtze River Delta region, the sludge generated from plasma welding contained a large amount of iron, copper, and other metal oxides (derived from the active components detached from the welding raw materials and catalyst). Through low-temperature pyrolysis treatment (380℃ for 60 minutes in Example 1), the organic matter and bound water in the sludge were completely removed, yielding high-purity metal oxide powder. In Example 3, a higher pyrolysis temperature (450℃) and a longer pyrolysis time (90 minutes) were used. (Minutes) The organic matter in the sludge is removed more thoroughly, and the purity of the metal oxide powder is higher, so the metal recovery rate reaches 91.2%. The metal oxide powder is mixed into the new metal powder raw material at a mass percentage of 1%-5%, which not only realizes the recycling of metal resources and reduces the cost of raw materials, but also improves the welding performance of welding raw materials and improves the quality of welded joints because the pyrolyzed metal oxide powder has good dispersibility and activity. In contrast, Example 5 directly outsources the disposal of sludge, which not only wastes metal resources, but also increases the cost of solid waste disposal, which is not in line with the development trend of resource recycling.

[0106] 4. Analysis of ozone utilization rate

[0107] The ozone utilization rates of Examples 1-3 were 92.3%, 85.6%, and 93.1%, respectively, all higher than the control examples. This is the result of the synergistic effect of multiple technical features. The use of the annular microporous aeration tube enabled ozone to form microbubbles, increasing the contact area between ozone and the gas-liquid mixture. The strong disturbance generated by the hydraulic cavitation effect further enhanced the mass transfer efficiency of ozone. The heterogeneous Fenton catalyst and the ultraviolet-assisted irradiation unit accelerated the decomposition and reaction of ozone, reducing ozone waste. The higher ozone concentration, hydraulic cavitation intensity, and ultraviolet irradiation intensity in Example 3 resulted in... Ozone utilization rate was the highest, reaching 93.1%. In contrast, Comparative Example 2, which did not use a heterogeneous Fenton catalyst, had a slower ozone decomposition and reaction rate, resulting in a utilization rate of only 68.4%. Comparative Example 3, which did not have an ultraviolet-assisted irradiation unit, had a reduced efficiency in generating hydroxyl radicals from ozone decomposition, resulting in a utilization rate of 81.5%. Comparative Example 4 required manual adjustment of operating parameters, making it impossible to optimize the matching degree between ozone dosage and reaction conditions in a timely manner, resulting in a utilization rate of 79.3%. The high ozone utilization rate not only reduced operating costs but also reduced the potential environmental impact of ozone exhaust emissions, demonstrating the energy-saving and environmental protection advantages of this invention.

[0108] 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.

Claims

1. A gas-liquid coupling purification method for the co-treatment of wastewater from plasma welding box exhaust gas, characterized in that, Includes the following steps: S1. Simultaneous collection of pollution sources: The exhaust gas generated by plasma welding and the supporting circulating cooling wastewater are simultaneously input into the gas-liquid coupling purification system. S2. Exhaust gas pre-charging and scrubbing absorption: The exhaust gas is electrostatically pre-charged and then brought into strong contact with the alkaline absorbent liquid in the system in the scrubbing device to capture particulate matter, absorb acidic gases and cool down. The scrubbing device is a turbulent cyclone water film scrubber. S3, Gas-liquid coupled catalytic oxidation: The scrubbed exhaust gas and wastewater are introduced together into a reaction tower filled with catalyst; in the reaction tower, the organic matter in the wastewater and the residual pollutants in the exhaust gas are oxidized and degraded by the catalytic effect of hydraulic cavitation and injected ozone, under the synergistic effect of the catalyst. S4. Gas-liquid separation and energy recovery: The gas-liquid mixture after the reaction is efficiently separated to purify the gas emissions, and the separated liquid recovers heat through waste heat exchange. S5. Solid-liquid separation and resource utilization: The liquid after heat recovery is coagulated and settled, and the supernatant is returned to step S2 as a supplement to the absorbent liquid. The settled sludge is dewatered and reused as a metal raw material additive. The catalyst is a heterogeneous Fenton catalyst; the hydraulic cavitation effect is generated by a hydraulic cavitation generator located at the bottom of the reaction tower. The inlet pressure of the hydraulic cavitation generator is controlled at 0.3-0.6 MPa, and the cavitation number σ is controlled at 0.2-0.

5. The cavitation number σ is defined as σ = (P... in - P v ) / (0.5ρQ 2 / A 2 ), where P in The absolute pressure at the inlet of the hydraulic cavitation generator is MPa, P v The saturated vapor pressure of water at the operating temperature is given in MPa, and ρ is the density of water in kg / m³. 3 Q is the liquid volumetric flow rate (m³). 3 / s, A is the cross-sectional area of ​​the generator throat in m² 2 ; Ozone is injected into the bottom of the reaction tower through an annular microporous aeration pipe surrounding the hydraulic cavitation generator, forming microbubbles. The total ozone dosage is dynamically adjusted by a feedforward-feedback linkage control system based on real-time monitoring of the wastewater's chemical oxygen demand (COD) and the concentration of nitrogen oxides in the exhaust gas. The control logic of the feedforward-feedback linkage control system is as follows: The target COD value C for the wastewater is set. o and the target value N for NOx in exhaust gas o The current feedforward module predicts the COD load change trend based on the influent flow rate and initially sets the ozone basic dosing acceleration rate Q. o The feedback module acquires the actual COD value C and NOx value N in real time and calculates the deviation ΔC=CC. o ΔN=NN o If |ΔC| > threshold 1 and |ΔN| < threshold 2, then the ozone dosing acceleration rate is increased first; if |ΔN| > threshold 2 and |ΔC| < threshold 1, then the inlet pressure of the hydraulic cavitation generator is increased first to enhance gas-phase mass transfer; if both exceed the limits, then the ozone dosing acceleration rate and inlet pressure are adjusted synchronously according to the weighting coefficients α·ΔC + β·ΔN, where α and β are preset empirical coefficients; the control objective is to maintain the dissolved ozone concentration in the wastewater at 5-15 mg / L, while maintaining the ozone volume fraction in the gas phase space at the top of the reaction tower at 0.5%-2.0%.

2. The gas-liquid coupling purification method according to claim 1, characterized in that, In step S2, electrostatic pre-charging is achieved through a bipolar high-voltage electrostatic charge region, which applies a positive corona voltage of +10kV to +15kV and a negative corona voltage of -12kV to -18kV, with an alternating frequency of 50Hz to 200Hz. The alkaline absorbent is prepared by mixing the clean water returned from step S5 with the replenished sodium hydroxide solution, and its pH value is maintained in the range of 9.0-10.5 by an automatic dosing system.

3. The gas-liquid coupling purification method according to claim 1, characterized in that, In step S3, the heterogeneous Fenton catalyst is prepared by the following method: impregnating a porous cordierite ceramic or activated alumina support with Fe... 3+ and Cu 2+ In a mixed nitrate solution of ions, Fe 3+ With Cu 2+ The molar ratio corresponds to a mass ratio of Fe3O4 to CuO of 2:1 to 5:1; after standing for 12 hours, it is dried at 80℃ and then calcined at 450℃ for 4 hours in air atmosphere to obtain a catalyst supported on nano-Fe3O4 and CuO composite metal oxide active components; the catalyst is spherical or columnar with a particle size of 3-8 mm and a specific surface area greater than 150 m². 2 / g.

4. The gas-liquid coupling purification method according to claim 1, characterized in that, In step S4, the high-efficiency gas-liquid separation is achieved by a multi-stage hydrocyclone separator. The multi-stage hydrocyclone separator includes a first-stage tangential inlet hydrocyclone separator and a second-stage axial inlet hydrocyclone separator arranged in series. The first-stage hydrocyclone separator is designed to remove droplets with a particle size greater than 10 μm, and the second-stage hydrocyclone separator is designed to remove droplets with a particle size greater than 2 μm. The inner wall surface of the hydrocyclone separator is coated with a hydrophobic and oleophobic coating of polytetrafluoroethylene.

5. The gas-liquid coupling purification method according to claim 1, characterized in that, In step S5, the coagulation and sedimentation are carried out in an inclined plate sedimentation tank. The coagulant added is polyaluminum ferric sulfate, and the dosage of polyaluminum ferric sulfate is 50-150 mg / L. The installation angle of the inclined plate in the inclined plate sedimentation tank is 55-60°, and the effective hydraulic retention time of the tank is designed to be 1.5-2.5 hours. After the supernatant is collected through the overflow weir, it is pressurized and returned to the water supply pipe of the washing device in step S2 by the intermediate water pump.

6. The gas-liquid coupling purification method according to claim 1, characterized in that, In step S3, an ultraviolet-assisted irradiation unit is also installed in the upper space of the reaction tower filled with catalyst. The ultraviolet-assisted irradiation unit is equipped with a dual-band low-pressure mercury lamp emitting main wavelengths of 185nm and 254nm, and the irradiation intensity of the ultraviolet lamp is 30-80mW / cm². 2 It is used to stimulate ozone decomposition to generate hydroxyl radicals, assist in the oxidation and degradation of residual nitrogen oxides in exhaust gas, and degrade gaseous volatile organic compounds.

7. The gas-liquid coupling purification method according to any one of claims 1-6, characterized in that, The method is operated automatically by an integrated control system; the integrated control system includes: The monitoring module is used to acquire key parameters of exhaust gas and key water quality indicators of wastewater in real time. The central control module, connected to the monitoring module, is used to generate and issue coordinated control commands based on the comparison results of real-time data of key parameters and key water quality indicators with preset target values. The execution module, connected to the central control module, is used to receive coordinated control commands and accordingly adjust at least two of the following in step S2: pH of the alkaline absorbent, ozone dosing acceleration rate and hydraulic cavitation intensity, and coagulant dosage.

8. The gas-liquid coupling purification method according to claim 7, characterized in that, The key parameters of the exhaust gas acquired by the monitoring module include flow rate, nitrogen oxide concentration, and ozone concentration, while the key water quality indicators of the wastewater acquired include chemical oxygen demand (COD) and pH value. The coordinated control commands generated by the central control module aim to achieve the coordinated and efficient removal of COD from wastewater and nitrogen oxides from exhaust gas, and dynamically and correlatedly adjust the ozone dosing acceleration rate and the inlet pressure of the hydraulic cavitation generator.

9. The gas-liquid coupling purification method according to claim 1, characterized in that, In step S5, the settled sludge is reused as a metal raw material additive. Specifically, this includes: first, the dewatered sludge is subjected to low-temperature pyrolysis treatment at a temperature range of 300-450℃ under the protection of an inert atmosphere of nitrogen or argon for 30-90 minutes to completely remove organic matter and bound water from the sludge; then, the powder obtained after pyrolysis, which is mainly composed of metal oxides, is uniformly mixed into new metal powder raw materials for plasma welding at a mass percentage of 1%-5%.

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