Automobile spray painting exhaust gas treatment

Automobile spray painting exhaust gas treatment:
The automotive painting workshop needs to perform pre-treatment, electrophoresis, and spray painting on the workpieces. The painting process includes spray painting, leveling, and drying, during which organic waste gases (VOCs) and overspray mist are generated.
1) Spray booth exhaust gas
In order to maintain the working environment for spraying, according to the regulations of the Labor Safety and Health Law, the spraying room should be continuously ventilated during spraying operations, and the ventilation speed should be controlled within the range of (0.25-1) m/s. The main component of the exhaust gas from the spray booth ventilation system is the volatile organic solvents used in spray painting, which are mainly composed of aromatic hydrocarbons (triphenyls and non methane total hydrocarbons), alcohol ethers, and ester organic solvents. Due to the large exhaust volume of the spray booth, the total concentration of organic waste gas emitted is very low, usually around 100mg/m3. In addition, the exhaust of the paint booth often contains a small amount of untreated paint mist, especially in dry paint mist capture paint booths. There is a lot of paint mist in the exhaust, which may become an obstacle to exhaust gas treatment. Pre treatment is necessary before exhaust gas treatment.
2) Exhaust gas from drying room
Before drying the topcoat after spraying, it should be leveled and dried. During the drying process, organic solvents evaporate from the wet paint film. To prevent explosion accidents caused by the accumulation of organic solvents in the drying room, the drying room should be continuously ventilated at a speed generally controlled at around 0.2m/s. The composition of the exhaust gas is similar to that of the exhaust gas from the paint spraying room, but does not contain paint mist. The total concentration of organic exhaust gas is higher than that of the exhaust gas from the paint spraying room. Depending on the size of the exhaust volume, it is generally about twice the concentration of the exhaust gas from the paint spraying room, which can reach 300mg/m3. It is usually mixed with the exhaust gas from the paint spraying room and treated centrally. In addition, the paint mixing room and the paint wastewater circulation pool should also discharge similar organic waste gases.

3) Drying exhaust gas

The composition of drying exhaust gas is relatively complex, including volatile components such as organic solvents, some plasticizers or resin monomers, as well as thermal decomposition products and reaction products. Both electrophoretic primer and solvent based topcoat have exhaust emissions during drying, but their composition and concentration differ significantly.
Analysis shows that the exhaust gases from paint spraying rooms, drying rooms, paint mixing rooms, and paint wastewater treatment rooms are low concentration, high flow ambient temperature exhaust gases, and the main components of pollutants are aromatic hydrocarbons, alcohol ethers, and ester organic solvents. According to the Comprehensive Emission Standards for Air Pollution, the concentration of these exhaust gases is generally within the emission limit. In order to meet the emission rate requirements in the standards, most automobile manufacturers adopt high-altitude emission methods. Although this method can meet current emission standards, the exhaust gas is essentially diluted and discharged without treatment. A large car body painting line may emit hundreds of tons of gas pollutants annually, causing serious harm to the atmosphere.