20

2017

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05

Spraying VOCs waste gas and treatment methods, responding to the key points of the inspector (I)

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According to the Ministry of Environmental Protection, on May 16 and 2, there were 34 VOCs treatment problems. From May 1 to 15, 179 VOCs treatment was not in place. The phenomenon of VOCs treatment facilities not installed in painting process and other industries or abnormal operation of pollution treatment facilities was more prominent, and the phenomenon of "leakage" was serious. Surface Coating of Automobile Manufacturing Industry and Solution of Paint Exhaust Gas in 4S Store Part 1 Composition and Hazard of Paint Exhaust Gas 1-1 Formation of Jet Exhaust Gas and Main Composition Paint Technology is widely used in machinery, automobile, electrical equipment, household appliances, ships, furniture and other industries. Spray paint raw materials-paint coatings by non-volatile

According to the Ministry of Environmental Protection, on May 16 and 2, there were 34 VOCs treatment problems. From May 1 to 15, 179 VOCs treatment was not in place. The phenomenon of VOCs treatment facilities not installed in painting process and other industries or abnormal operation of pollution treatment facilities was more prominent, and the phenomenon of "leakage" was serious.

Automotive Manufacturing Surface Painting and 4S Shop Paint Exhaust Solution

Part 1 Composition and Hazards of Paint Exhaust Gas

1-1 Formation and main components of jet exhaust gas

Painting process is widely used in machinery, automobiles, electrical equipment, home appliances, ships, furniture and other industries.

Paint raw materials-paint coatings are composed of non-volatile and volatile components. The non-volatile components include film-forming substances and auxiliary film-forming substances. Volatile thinner is used to dilute the paint and achieve the purpose of smooth and beautiful paint surface.

Paint mist and organic waste gas pollution are mainly produced in the paint spraying process. The paint is atomized into particles under high pressure. During spraying, part of the paint does not reach the surface of the painted object and disperses with the air flow to form paint mist. Organic waste gas comes from the volatilization of thinner, and organic solvent will not adhere to the surface of the painted object with the paint. During the painting and curing process, all organic waste gas will be released to form (there are hundreds of volatile organic waste gas, they belong to alkanes, cycloalkanes, alkenes, aromatic compounds, alcohols, aldehydes, ketones, esters, ethers and other compounds).

1-2 Sources and Characteristics of Automobile Coating Exhaust Gas

The automobile painting workshop shall carry out pre-paint treatment, electrophoresis and painting on the workpiece. The painting process includes painting, leveling and drying, in which organic waste gas (VOCs) and over-painting mist are produced.

 

1) Exhaust gas from paint spraying room
In order to maintain the working environment of spraying, according to the provisions of the Labor Safety and Health Law, the air shall be continuously changed in the spray booth during spraying, and the air change speed shall be controlled within the range of (0.25~1)m/s. The main components of the air exhaust gas in the spray booth are organic solvents that are volatile from the spray paint. The main components are aromatic hydrocarbons (three benzene and non-methane total hydrocarbons), alcohol ethers, and ester organic solvents. The exhaust volume of the spray booth is large, so the total concentration of organic waste gas discharged is very low, usually around 100mg/m3. In addition, the exhaust of the spray booth often contains a small amount of untreated complete paint mist, especially the dry paint mist trapping spray booth, the exhaust paint mist is more, may become an obstacle to waste gas treatment, waste gas treatment must be pretreated.
2) Exhaust gas from air-drying room
The topcoat shall be levelled and dried before it is dried after spraying. The wet paint film volatilizes the organic solvent during the drying process. In order to prevent the organic solvent from gathering and exploding in the drying room, the drying room shall be continuously changed with the air change speed generally controlled at about 0.2 m/s. The composition of the exhaust gas is similar to that of the exhaust gas in the spray room, but does not contain paint mist, the total concentration of organic waste gas is larger than that of the spray booth. According to the different exhaust air volume, it is generally about 2 times of the exhaust gas concentration in the spray booth, which can reach 300mg/m3. It is usually mixed with the exhaust of the spray booth for centralized treatment. In addition, the paint room and the topcoat sewage circulating pool also discharge similar organic waste gas.
3) Drying exhaust gas
The composition of the drying exhaust gas is more complex, in addition to containing organic solvents, some plasticizers or resin monomers and other volatile components, but also contains thermal decomposition products, reaction products. Electrophoretic primer and solvent-based topcoat drying have exhaust emissions, but their composition and concentration are quite different. The analysis shows that the waste gas from the paint spraying room, drying room, paint blending room and topcoat sewage treatment room is low concentration and large flow room temperature waste gas, and the main components of pollutants are aromatic hydrocarbons, alcohol ethers and ester organic solvents. Compared with the "Comprehensive Emission Standard 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 standard, most automobile factories adopt the method of high-altitude emission. Although this method can meet the current emission standards, the exhaust gas is essentially untreated and diluted. The total amount of gas pollutants emitted by a large car body coating line may be as high as hundreds of tons per year, which causes serious harm to the atmosphere.
1-3 Hazards of paint exhaust gas





Organic solvents in paint mist-benzene, toluene, xylene, etc. are strong toxic solvents, which are distributed to the air in the workshop during operation. Workers can cause acute and chronic poisoning after inhaling through respiratory tract, mainly causing damage to the central nervous system and hematopoietic system. Short-term inhalation of benzene vapor with high concentration (above 1500mg/m3) can cause aplastic anemia, often inhaled low concentrations of benzene vapor can also cause nausea, vomiting, confusion and other neurological symptoms, a few can also cause neurasthenia syndrome, toluene on the central nervous system than benzene, the role of the hematopoietic system is lower than benzene. It is reported that when the mass concentration of benzene is 188~375mg/m3, long-term exposure can have obvious symptoms. The chronic harm of toluene is less than benzene, and the concentration is 430~1300mg/m3, which can cause poisoning symptoms. The mixture of three benzene can also cause irritation to the eyes and nasal mucosa, and the neurological symptoms are more serious.

The harm of paint mist to workers can not be ignored. Enterprises can take practical measures to reduce the emission of pollutants and reduce the health damage of toxic and harmful substances to workers.