Painting exhaust gas treatment introduction and process selection
Coating refers to covering the metal or non-metallic surface with a protective layer or decorative layer, and is the basic technical means used for product surface protection and decoration. The painting process can be simply summarized as: pretreatment → spraying → drying or curing. Pre-treatment generally includes degreasing, derusting, and passivation (phosphating) processes. According to different coating and anti-corrosion requirements, degreasing, derusting, phosphating and other treatment methods should be selected according to the condition of the workpiece raw materials. In the pre-treatment derusting process, sand blasting, shot blasting or sanding processes are also used as required by different departments in different industries. With the rapid development of coating technology, coating waste gas treatment equipment has made obvious progress in automatic coating production. Electrostatic spraying, electrophoretic coating, and powder spraying technology have been applied and popularized. However, the coatings currently used are all organic solvent-based coatings. According to the coating production process, the coating waste gas mainly comes from the pretreatment, spraying, and drying processes. The pollutants discharged are mainly: the dust or acid mist generated during the pretreatment process, the paint mist and organic solvent generated during painting, drying Organic solvent generated when volatilized. The paint mist mainly comes from the part of the solvent-based paint flying in the air spraying operation, and its composition is consistent with the paint used. Organic solvents mainly come from solvents and thinners in the process of coating, and most of them are volatile emissions. The main pollutants are xylene, benzene and toluene. The harmful exhaust gas discharged during painting is mainly concentrated on the painting production line, among which the painting room, drying room and drying room are the main sources of exhaust gas.
The treatment of coating waste gas can be divided into two ways: prevention and treatment. Prevention is mainly to reduce the emission of exhaust gas, and treatment is mainly to purify the inevitable exhaust gas.
1. Reduce exhaust emissions, source control, reduce the use of organic solvents
In order to reduce the exhaust emissions during the coating process, you can start from the source, do not use or less use of organic solvent-containing coatings, such as powder coatings, water-based coatings, high solids coatings, etc. Powder coatings do not use organic solvents. Except for generating paint dust during the coating process, they basically do not emit harmful exhaust gas. Therefore, in recent years, they have developed rapidly and the scope of application has increased significantly. Water-soluble coatings and high-solids coatings can also effectively reduce harmful exhaust emissions during the coating process, which is the development trend of the coating industry. In the coating process, choose high-solids coatings or coatings that do not use organic solvents. Although the coating price is more expensive, it reduces the emission of organic solvents, reduces the difficulty of waste gas treatment and the scale of the treatment facility, which is in line with cleaner production and energy saving. Emissions reduction requirements.
2. Improve paint utilization rate and reduce usage
In painting production, spraying is a common method. However, there are many paint mists generated by spraying, and the paint will evaporate into the air in the form of paint mist.
The coating efficiency is affected by many factors. When coating large-area workpieces, the coating efficiency of these coating methods is very high. However, only high-volume low-pressure air spray guns (HVLP) and electrostatic spraying can meet the coating efficiency of 60%. In addition, the use of robotic spraying and rotary atomization can improve the utilization rate of paint.
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