How to control the emissions of industrial coating VOCs?

How to control the emissions of industrial coating VOCs?

introduction

Industrial coatings use a large amount of organic solvents in coatings and thinners. Organic solvents are also consumed in steps such as cleaning and degreasing before painting, equipment cleaning after painting, and color-changing cleaning. Therefore, VOCs are emitted by the evaporation and escape of organic solvents. There are many industries involved in industrial coating, including automobiles, ships, containers, furniture, communication equipment and other electronic terminal products, general equipment, special equipment and electrical machinery and equipment manufacturing; etc .; VOCs emit a large amount of emissions, accounting for approximately the entire industrial source VOCs More than 20%, and emits rich in aromatic hydrocarbons and oxygen-containing organic substances, such as photochemically reactive and highly toxic substances, so China should focus on VOCs emissions from industrial coating processes.

VOCs emissions from industrial coatings

Industry composition

According to the "Statistical Yearbook of the Chinese Coatings Industry", in 2015, China's total coating output was 17.118 million tons, and in 2016 the total coating output reached 18.9978 million tons, a year-on-year increase of 7.2%, of which industrial coating output accounted for more than 2/3 of the total coating output About 13.05 million tons. Among industrial coatings, only about 150,000 tons of original automotive coatings, 70,000 tons of waterborne wood coatings and 1.38 million tons of powder coatings are coatings with low (no) VOCs content, and the others are solvent-based coatings, with dilution added. The VOCs content in the ready-to-use state after the dosage is 50% to 70%, and a large amount of VOCs is emitted during use.

VOCs types

Based on the testing of organic components of coatings and combined emission test results, the main types of VOCs emitted by industrial coating companies are summarized in Table 1. It can be seen that the industrial coating process using solvent-based coatings has a higher detection rate of VOCs emissions of benzene series, both MIR and FAC values ​​are large, and the photochemical reaction is strong, and the production of O3 and PM2.5 is relatively large. influences.

Countermeasures for VOCs Pollution Control in Industrial Coating Process

Industrial coating, as a production link of surface manufacturing process, involves many industries. Therefore, the governance of industrial coating processes should be based on comprehensive advancement, highlighting key industries, selecting high concentration of industries, high VOCs emission intensity, and mature governance technologies. 2. Governance of industries with little difficulty in reforming should be carried out first. The seven major industries of automobiles, ships, containers, furniture, construction machinery, coils, and steel structures are relatively concentrated, and the VOCs generated account for more than 40% of all industrial coating processes, and should be used as the industry's key control industry.

Implement the whole process of "source-process-end" pollution prevention

VOCs emissions from industrial coating processes are mainly from the use of coatings, thinners and other organic solvent products. To reduce VOCs emissions from industrial coating processes, source control must be considered first. At present, the most important way is to use powder coatings, water-based coatings, and high solids. Coatings with low (no) VOCs content such as coatings and UV curing. Among them, powder coatings do not contain VOCs. Except for the production of coating dust during the coating process, VOCs are basically not generated. Using powder coatings instead of solvent-based coatings can reduce VOCs emissions by more than 95%; water-based, high-solids, and UV-curable coatings Low VOCs content, compared with traditional solvent-based low-solids coatings, can reduce VOCs emissions by about 50%.

For the coating process, different types of industrial products use different coating processes and coating equipment, so theoretically there is no optimal coating process and equipment. However, at present, industrial coating companies in China generally use manual air spray guns with the lowest spray transfer efficiency for spraying operations. The spray transfer efficiency is usually only about 25% to 40%, which causes excessive spraying problems, which increases the coating consumption and the coating process. VOCs emissions. Therefore, industrial coating companies can improve the coating process and equipment, and choose high-efficiency coatings such as air-assisted airless spraying, airless spraying, electrostatic spraying, roller coating, and dip coating according to the material and shape of industrial products. Technology to reduce VOCs emissions in industrial coating processes.