1. Flue Gas Characteristics and Treatment Challenges of Aluminum Alloy Quenching Process

1.1 Characteristics of Aluminum Alloy Quenching Process

• Solution Heat Treatment: The aluminum alloy is heated to 450-550℃ and kept warm for more than 2 hours to fully dissolve alloy elements such as Cu and Mg.

• Rapid Cooling: Water quenching (60-100℃ water) or oil quenching is adopted to form supersaturated solid solution and improve the strength and hardness of aluminum alloy products.

1.2 Flue Gas Characteristics

• High Temperature and High Humidity: The flue gas temperature ranges from 80℃ to 120℃, containing a large amount of water vapor generated by quenching water evaporation.

• Complex Components:

• Oil Mist: Evaporated quenching oil with a particle size of 0.1-10μm and strong viscosity.

• Metal Oxides: Ultra-fine particles such as Al₂O₃ (0.01-200μm).

• Fluorides: Fluoride-containing water vapor, especially generated during water quenching.

• VOCs: Organic compounds volatilized from quenching oil.

• Flammable and Explosive Risk: Aluminum dust mixed with air can form explosive mixtures.

1.3 Traditional Treatment Difficulties

• Dry dust removal equipment is easy to be blocked and requires frequent maintenance.

• Common filters have low purification efficiency for strongly viscous oil mist.

• Ultra-fine particles such as PM2.5 are difficult to remove.

• There is potential explosion risk during operation.

2. Core Working Principle: Synergistic Mechanism of High-voltage Static Electricity and Water Film Ash Cleaning

2.1 High-voltage Ionization and Particle Charging Stage

• Electric Field Establishment: A high-voltage DC power supply (60-100kV) supplies power to cathode wires (thorn wires / star wires), while the anode is grounded to form a strong electric field (≥30kV/cm).

• Gas Ionization: Gas molecules are ionized in the strong electric field to generate a large number of electrons and positive ions.

• Particle Charging: Electrons collide with oil mist and particulate matter in flue gas to charge pollutants negatively.

2.2 Electrostatic Adsorption and Collection Stage

• Directional Migration: Negatively charged particles move toward the anode (collecting electrode) under the action of electric field force (Coulomb force).

• High-efficiency Capture: Even ultra-fine particles of 0.01μm can be adsorbed with a collection efficiency ≥99%.

• Synergistic Removal: Oil mist, particulate matter and partial VOCs are captured simultaneously.

2.3 Water Film Ash Cleaning and Discharge Stage

• Continuous Water Film: The top spray system (0.3-0.5MPa) forms a uniform water film on the anode surface.

• Automatic Ash Cleaning: Pollutants are flushed into the liquid collection tank at the bottom to avoid secondary dust re-entrainment.

• Purified Discharge: The treated flue gas (particulate matter ≤5mg/m³) is discharged up to standard.

• Wastewater Treatment: Oily wastewater is treated and recycled with a reuse rate ≥90%.

3. Complete Technological Process: Systematic Scheme of Pre-treatment + WESP + Post-treatment

3.1 Pre-treatment System (Key Front-end Device)

3.1.1 Cooling and Humidity Conditioning

• Heat Exchanger: Cool the flue gas from 80-120℃ to 40-60℃, the optimal operating temperature for WESP.

• Spray Tower: Realize humidification and cooling to ensure saturated flue gas humidity and improve dust removal efficiency.

3.1.2 Oil and Large Particle Removal

• Cyclone Separator: Remove large particles above 10μm with a removal efficiency of 60-80%.

• Venturi Scrubber: The liquid-gas ratio is 1.5L/m³. High-speed airflow mixes with water mist to capture oil mist and coarse particles.

3.1.3 Special Treatment for Aluminum Alloy Characteristics

• Alkali Spray: Adopt 8-12% NaOH solution to remove acidic gas such as HF, reducing HF concentration to 10-20mg/m³.

• Conditioner Addition: Adjust flue gas conductivity to improve particle charging efficiency.

3.2 Main Process of Wet Electrostatic Precipitator

3.2.1 Electric Field Configuration

• Multi-stage Series Connection: 2-3 electric fields with independent power supplies for each stage, achieving a total purification efficiency ≥99.9%.

• Anode Structure: Honeycomb tubular structure (anti-blocking, suitable for high oil mist working conditions); plate structure (easy maintenance). Anode materials include 316L stainless steel, FRP and titanium alloy.

• Cathode Design: Titanium alloy thorn wire with high discharge intensity and excellent corrosion resistance.

3.2.2 Spray and Ash Cleaning System

• Continuous Spraying: Maintain 0.3-0.5MPa to form stable water film and prevent plate scaling.

• Regular High-pressure Flushing: 0.8-1.2MPa high-pressure water is used to remove stubborn attachments.

• Spiral Nozzles: Achieve full coverage without dead zones to ensure thorough ash cleaning effect.

3.2.3 Airflow Optimization

• Flow Distribution Plate: Ensure uniform flue gas velocity (≤2.8m/s) with residence time ≥2s.

• Deflector Blades: Reduce airflow turbulence and improve particle capture efficiency.

3.3 Post-treatment and Circulation System

• Secondary Demisting: Mechanical demisting device reduces water vapor entrainment in discharged flue gas.

• Wastewater Treatment: Adopt oil separation tank and air flotation to realize oil-water separation; the purity of recovered quenching oil can reach 90%. Automatic pH adjustment and flocculation sedimentation are applied, and the circulating water reuse rate is ≥90%.

• Sludge Treatment: Dewatered dry sludge is safely disposed, and metal elements are recycled.

4. Special Process Parameters for Aluminum Alloy Quenching

5. Adaptation Advantages for Aluminum Alloy Quenching Process

• High-efficiency Oil Mist Removal: The quenching oil mist removal rate exceeds 95%, which is far better than traditional filtration equipment.

• Anti-adhesion Design: Continuous water film cleaning solves the problem of oil mist adhesion on plates and avoids equipment failure.

• Safety and Explosion-proof Performance: Wet operation eliminates electric spark risks, which is suitable for flammable and explosive flue gas containing aluminum dust. Water mist reduces dust concentration and inhibits explosion hazards.

• Resource Recycling: About 12 tons of quenching oil can be recycled every year with an economic value of approximately 150,000 RMB. The water circulation utilization rate exceeds 90% to save water resources.

• Strong Synergistic Treatment Capacity: It simultaneously removes PM2.5, oil mist, fluorides and partial VOCs, eliminates blue smoke plume caused by oil mist condensation and improves the factory operating environment.

6. Application Case: Flue Gas Treatment for Automobile Hub Quenching

6.1 Project Overview

• Treatment Object: 7075 aluminum alloy hub quenching flue gas (oil quenching).

• Treatment Air Volume: 30,000m³/h.

• Original Pollutant Concentration: Oil mist and dust ≈120mg/m³, containing a small amount of fluorides.

• Process Route: Gas collection hood → Pipeline → Cyclone separation → Venturi scrubber → WESP → Demister → Induced draft fan → Chimney.

6.2 Core Operating Parameters

• WESP Configuration: 2 electric fields with single-stage voltage of 70kV, honeycomb titanium alloy anode.

• Spray Mode: Continuous spraying at 0.4MPa + regular flushing at 1.0MPa every 8 hours.

6.3 Treatment Effect and Benefit

• Outlet Concentration: Particulate matter ≤3mg/m³, no detectable oil mist.

• Economic Benefit: Approximately 18 tons of quenching oil are recycled every year with an economic value of about 220,000 RMB. The circulating water consumption is reduced by 70%, saving about 80,000 RMB in water fees annually.

7. Summary