my country is a big manufacturing country. In the process of industrial production, the coating process involves many industries, including all industries involved in the coating process, such as motor vehicle manufacturing and maintenance, furniture, household appliances, metal product processing, color steel plates, and containers. , Shipbuilding, electrical equipment, pipe industry, etc.

The coating industry belongs to the field of new materials. Environmentally friendly coatings include: water-based coatings, powder coatings, radiation curing coatings and high-solid coatings. As environmental coatings are still in the early stages of research and development, some key technical issues are far from being resolved. Therefore, the use of solvent coatings accounts for 50-60 of the total coatings. The output of industrial coatings in my country in 2009 was 9.114 million tons, of which solvent-based coatings accounted for 60. The output of coatings in 2010 (China Coatings Industry Yearbook, 2011) was 9.7 million tons. Among them, solvent-based coatings accounted for 52.1. About 3.5 million tons of VOCs (including the thinner used in coating) volatilize into the atmosphere during the use of coatings (only xylene has hundreds of thousands of tons), and pollution is very wasteful. severe. Due to the very rapid development in recent years, the average growth rate is 15 million. In 2012, the output reached more than 12 million tons (import and export volume can be ignored), of which industrial coatings accounted for about 70, that is, about 8.4 million tons. VOCs emissions are about 6 million tons or more. It has become the largest source of China’s industrial VOCs emissions and has the greatest impact on my country’s industrial VOCs emissions.

The production and application process will cause environmental hazards: such as VOC emissions, formaldehyde and heavy metal residues, and free TDI volatilization. my country has formulated a series of compulsory coatings national standards. In 2009 alone, five compulsory coating standards represented by "GB24408-2009 Limits of Hazardous Substances in Building Exterior Wall Coatings" were revised. At the same time, stricter foreign environmental protection regulations (such as HAPs, VOCs, REACH, RoHS, etc.) have set higher thresholds for the export of domestic paint products, raw materials, and downstream end products such as home appliances, toys, and furniture (green Barriers and technical barriers). For this reason, under the situation of increasingly strict supervision, it is the general trend of development to strengthen the innovation of coating technology and develop and upgrade environmentally friendly coatings. At the same time, users who use conventional solvent coatings need to strengthen the innovation of VOCs treatment technology

1. Current status of coating technology and equipment

my country's coating technology and equipment are developing rapidly. There is a big gap in environmental protection, energy conservation, emission reduction, and resource utilization. The VOC emissions of many coating lines do not meet the standard, and the energy consumption, water consumption and coating material consumption per unit coating area are all high, and there is no corresponding mandatory policy. For example, although my country is a big country in automobile production, it is not a powerful country, and automobile painting is no exception.

1) Conventional car craft (complete craft)

Body-in-white enters the pre-treatment electrophoresis electrophoresis drying (lysate emission) electrophoresis polishing (dust particle emission) weld sealing (VOCs emission) PVC undercarriage spraying (VOCs emission) intermediate coating spraying (VOCs emission) intermediate coating leveling (VOCs emission) Intermediate coating drying (VOCs emission) Intermediate coating reporting finishing paint spraying (including varnish) (VOCs emission) finishing paint (VOCs emission) finishing paint drying (VOCs emission) checkpoint repair (VOCs emission) finishing Warranty cavity wax spraying (VOCs emission) assembly workshop

2) Conventional auto parts process (complete process)

Pre-treatment (electrophoresis electrophoresis drying) or (dehydration drying) middle coat spraying middle coat leveling middle coat drying top coat spraying top coat flow flat paint drying

3) Conventional container craft (complete craft)

Sandblasting, zinc blasting, middle coating, spraying, middle coating, leveling, middle coating, drying, top coat, spraying, top coat, flow, flat paint drying

4) Conventional home appliance process (complete process)

Pre-treatment (electrophoresis electrophoresis drying) or (dehydration drying) middle coat spraying middle coat leveling middle coat drying top coat spray top coat flow flat paint drying   pre-treatment dehydration drying powder spraying powder drying (no VOCs emission)

5) Conventional spray booth equipment

The spray booths larger than 95 are forced to supply and exhaust with fresh air, and VOCs are directly discharged at high altitude with low concentration and large air volume. If VOCs are processed, a VOCs concentration device must be added. The spray booth adopts a circular form of forced air supply and exhaust, and the VOCs concentration is relatively high, which can be discharged after treatment. This form is only suitable for automatic spray booths, not for manual spray booths.

6) Conventional leveling room equipment

The concentration of VOCs is relatively high and can be discharged after treatment. However, only 5-10 equipment in China are equipped with VOCs treatment devices, and the usage of the treatment devices during normal production is unknown.

7) Conventional paint drying room equipment

The concentration of VOCs is relatively high and can be discharged after treatment. However, only 5-10 equipment in China are equipped with VOCs treatment devices, and the usage of the treatment devices during normal production is unknown.

8) Conventional VOCs treatment device

Commonly used domestic VOCs treatment devices are activated carbon adsorption, catalytic combustion, high temperature incineration (RTO, TNV), medium temperature incineration (expansion of the drying chamber heating device, such as quaternary unit), and radiant VOCs treatment (CIR). Activated carbon adsorption and catalytic combustion have low investment, high cost of use, and poor treatment effect. They are generally used in small production lines and have low equipment utilization. High-temperature incineration (RTO, TNV) has a high initial investment, low use cost, and high treatment effect. It is generally used in medium and large production lines, and the equipment utilization rate is relatively high, especially the waste heat of TNV is used in the drying room, and the equipment utilization rate is Very high.

2. Existing problems

1) Unbalanced technological development, environmental protection coatings, new processes, and new equipment need to be improved

Although my country has become the largest paint producer and consumer country, it is not yet a strong country in paint technology and painting engineering. The technical level of the paint varieties produced by domestic companies is uneven, and the technological level of domestic painting engineering is uneven, and there are still comparisons. Big gap. In particular, environmental protection coatings, new technologies for energy saving and emission reduction, and new equipment in various fields need to be improved urgently.  Because China does not have compulsory energy-saving and emission-reduction policies for coating projects, companies have no enthusiasm for reforming existing coating production lines, and the application of new energy-saving and environmentally-friendly coatings, new processes, and new equipment cannot be promoted.

2) Many enterprises, small scale, weak environmental protection technology, and poor environmental awareness

According to statistics, there are currently about 8,000 paint manufacturing companies in my country, most of which are small and medium-sized enterprises. Low-level redundant construction is very serious, production capacity is surplus, human resources are used inefficiently, and there is a lot of waste. For high-level, high-tech environmental protection coatings, environmental protection equipment investment is very small, some companies are equipped with environmental protection equipment but rarely use. Therefore, strengthening enterprise specialization, characteristic guidance, expanding the scale of the enterprise, concentrating resources to develop environmentally friendly coatings, and cost-effective environmental protection equipment are important topics for achieving sustainable development.

3) The situation dominated by non-environmental paints needs to be improved

In my country's paint output, 50-60 are solvent-based paints. It can cause nearly 3.5 million tons of volatile organic compounds (VOCs) to be discharged into the atmosphere every year, and pollution and waste are very serious. In companies using solvent-based coatings, about 95 VOCs in the spray booth are directly discharged at high altitude with low concentration and large air volume, 90 VOCs in the drying room and leveling room are directly discharged at high altitude with high concentration and small air volume, and the rest are equipped with VOCs treatment devices. However, the technology of VOCs treatment equipment is uneven, and because there is no long-term supervision system, the utilization rate of VOCs treatment equipment is not high during normal production.

4) A system that promotes the healthy development of the coating industry and environmental protection equipment based on standards and regulations has not yet been formed

At present, my country's environmental protection coating standard system, VOCs emission system and related important basic standards have only been initially established and need to be improved. The backwardness of standards has slowed the process of my country's coating industry and environmental protection equipment in line with international standards, and has affected my country's coating industry and environmental protection equipment. The improvement of international competitiveness.

2. Characteristics of coating (spraying) process exhaust gas:

(1) Usually accompanied by a large amount of oversprayed paint mist particles;

(2) There are many types of coatings, different solvents used, and complex organic components (organic solvents in coatings include: benzene, ethers, lipids, ketones, alcohols, alcohol ethers, hydrocarbons, etc.) Some low-molecular additives may be restored to the atmosphere, and some benzene, alcohol and lipids belong to the double-high-yield and tertiary substances);

(3) During the spraying process, forced air delivery and exhaust operations are compulsory, with large exhaust air volume and low organic matter concentration. Therefore, the treatment of coating waste gas is difficult, the treatment cost is high, and the treatment effect is poor, which is a difficult problem in the treatment of industrial VOCs emissions in my country. In some of the key industries involved in painting technology in my country, such as motor vehicle manufacturing and maintenance, furniture, home appliances, machinery and equipment manufacturing, pipe industry, shipbuilding, containers, etc., the treatment of spraying exhaust gas has just started in recent years. A small part of the exhaust gas has been treated, and the existing treatment equipment has low operating efficiency, poor operating conditions and poor emission reduction effects. As our country is a big manufacturing country, in the heavy pollution industries with high VOCs emissions, such as furniture manufacturing, containers, shipbuilding, automobiles, home appliances, etc., all occupy a high share in the world. Therefore, in the future of my country's industrial fixed source VOCs emission reduction, the treatment of coating waste gas is the top priority.

development plan

With structural adjustment and development mode transformation as the main line, implement the strategy of adjustment, transformation, innovation and upgrading, under the guidance of relevant national policies, focus on adjusting the industrial technology structure and corporate organizational structure, strengthen independent innovation and form independent technologies, standards and brands, and increase Cultivate and develop new varieties of environmentally friendly coatings, promote the application of new technologies and new equipment, and accelerate the transformation of existing coating production lines that are poor in terms of energy conservation and environmental protection.

1) Speed up the development of environmentally friendly coating products

Solvent coating: In the coating process of automotive products, the coating cost is less than 20% of the entire coating cost, and the remaining 80 is the cost consumed in the coating process. Therefore, reducing the volatile organic compound (VOC) content in the coating, shortening the coating process, optimizing the layout of the coating line, rationally arranging production, and improving the first pass rate of the product, which can reduce the cost of the entire vehicle and save energy and environmental protection.  Environmental protection coatings: promote the application of new technologies such as water-based, solvent-free (powder coatings, radiation-cured coatings) and high-solid differentiation.

2) Promote the application of new technology and new equipment

For example, for the whole vehicle painting, the intermediate coating-free process of the entire vehicle painting is promoted, at the same time, the intermediate coating grinding process is eliminated, the painting production line is simplified, the environmental pollution is reduced, and the waste discharge is reduced. Promote the use of automatic spraying devices to reduce paint overspray (reduce paint consumption), adopt circulating air supply and exhaust devices and configure VOCs processing devices. Promote high-efficiency and energy-saving VOCs processing devices to reduce operating costs.

3) Accelerate the transformation of existing coating production lines 

 Most of the existing coating production lines in China are relatively poor in technology, equipment and technology, and have no VOCs treatment devices, resulting in a lot of environmental pollution. The relevant national policies are directed to this. The transformation and upgrading of production lines is the top priority for reducing VOCs emissions.

4) Speed up the formulation of relevant national policies, have clear regulations on the treatment and emission of VOCs, and establish a long-term monitoring system for the use of VOCs treatment devices.

Link to this article： Analysis of the status quo of coating process equipment and future development plans

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