A well-known domestic automotive chassis parts manufacturer primarily handles the corrosion protection treatment of large structural components such as truck frames and subframes in its electrophoretic painting workshop. During production, volatile organic solvents from the electrophoretic tank mix with electrophoretic paint mist to form high-concentration exhaust gases. The main pollutants include xylene, ethyl acetate, alcohol ether solvents, and paint mist particles, with an exhaust gas flow rate of 80,000 m³/h and an initial concentration of non-methane total hydrocarbons (NMHC) of approximately 1,200 mg/m³, along with about 200 mg/m³ of paint mist. Due to the exhaust gases' high humidity (relative humidity exceeding 85%), sticky paint mist, and complex composition, traditional single-stage treatment processes struggle to achieve stable compliance, leading to issues such as equipment corrosion and frequent consumable replacements.
The project employs a combined process of "dry paint mist filtration + zeolite rotary wheel concentration + RTO regenerative thermal oxidation." During the pretreatment stage, a three-stage dry filtration system is installed: the first stage uses G4 pre-filtration cotton to intercept paint mist particles with a particle size >50μm; the second stage employs F7 medium-efficiency bag filters to remove sticky paint mist particles of 10-50μm; the third stage utilizes F9 high-efficiency filters to further purify fine particulate matter, ensuring that the dust content in the exhaust gas entering the rotary wheel is <1mg/m³. The zeolite rotary wheel features a hydrophobic molecular sieve with a honeycomb structure and a diameter of 4.2m, designed for a 20-fold concentration ratio, converting low-concentration, high-volume exhaust gas into high-concentration, low-volume exhaust gas (reducing airflow to 4000m³/h while increasing concentration to 24000mg/m³). The RTO furnace adopts a three-chamber regenerative structure, with ceramic honeycomb packing as the heat storage material, achieving a thermal recovery efficiency of ≥95%. The combustion temperature is maintained between 800-850°C, with a residence time >1.2s, ensuring a VOCs removal rate of ≥99%.
During the system debugging phase, it was found that oxygen-containing solvents such as ethylene glycol monobutyl ether, which volatilize from the electrophoresis tank, are prone to "breakthrough" during rotary adsorption. By optimizing the rotor rotation speed (from 3-8 h⁻¹ to 5 h⁻¹) and increasing the regeneration air temperature (from 180°C to 200°C), the adsorption efficiency was significantly improved. Operational data showed that the NMHC concentration in the treated exhaust gas remained stable below 30 mg/m³, far below the limit specified in the "Comprehensive Emission Standard for Atmospheric Pollutants." The paint mist removal rate reached 99.5%, effectively preventing subsequent equipment blockages. Annual VOC emissions were reduced by approximately 86 tons, with recovered waste heat used for winter heating in the workshop, saving 120,000 cubic meters of natural gas annually. The payback period for the investment was about 2.8 years. The key to this case lies in optimizing the pretreatment process for high-humidity, high-viscosity exhaust gas and addressing the adsorption challenges of special solvents through dynamic parameter adjustments.
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