Overview of Clean Production in the Automotive Painting Industry
Introduction
At present, regional combined-type air pollution characterized by ozone, fine particulate matter (PM2.5) and acid rain in China is becoming increasingly prominent, and the frequency of widespread and simultaneous occurrence of severe air pollution is increasing. Facing the severe environmental pollution situation, in order to protect the ecological environment and control fixed pollution sources and pollutant emissions in various regions, the national and local environmental protection departments have successively introduced corresponding policies, regulations and control standards, and have intensified the mandatory clean production audits for large enterprises from the source to control the generation of pollutants.
1. Introduction to Clean Production in Coating Industry
Clean Production (Cleaner Production) refers to continuously taking measures such as improving design, using clean energy and raw materials, adopting advanced process technologies and equipment, improving management, and comprehensively utilizing resources to reduce pollution at the source, improve resource utilization efficiency, and reduce or avoid the generation and emission of pollutants during production, services and product use, in order to mitigate or eliminate the hazards to human health and the environment.
The current standards implemented in the coating industry mainly include HJT293-2006 "Clean Production Standards for Automotive Manufacturing Coating". The standard mainly classifies technical indicators into three levels: international advanced level, domestic advanced level, and domestic basic level, and mainly requires the requirements for production processes and equipment, raw material indicators, resource and energy utilization indicators, pollutant generation indicators, and environmental management indicators. However, currently, few enterprises in China strictly implement the standards, and due to the existence of many unclear definitions of terms, parameters, and large discrepancies between the indicator values and the actual values in the standard, the implementation of clean production work is poorly implemented. Example 1: In the calculation method of indicators, the total coating production area in the standard refers to the actual area covered by all coating processes and coatings. This actual area is sometimes understood as the electrophoretic area and sometimes as the area designed by the computer-aided design system for sheet metal and steel plates. Example 2: In the calculation of power consumption, for the air conditioning in closed workshops, it is required not to be included, but the air conditioning in the automotive coating workshop usually does not use circulating air and uses fresh air instead. The proportion of this air conditioning power consumption is still relatively large, seriously affecting the calculation results.
Based on the calculation and analysis of data from multiple automotive factories, the clean production indicator data obtained by referring to the old standard HJT293-2006 shows that the power consumption, fresh water consumption, and wastewater generation in the coating workshops of most enterprises are several tens of times higher than the international clean production level. This reflects the unreasonable setting of the indicator values in this standard. (See Table 1). Therefore, it is necessary to improve and update the evaluation indicators of clean production in the coating industry, and must keep up with the development needs of the industry. In 2015, the National Development and Reform Commission, the Ministry of Environmental Protection, and the process informationization department jointly promoted the update of the "Evaluation Index System for Clean Production in the Coating Industry", and solicited suggestions for standard updates from all coating enterprises across the country. The new standard indicator system mainly targets the orderly coating production in industries such as automobiles and their components, electromechanical products, furniture (iron), and construction machinery, and divides clean production indicators into five categories, namely production process and equipment requirements, resource and energy consumption indicators, resource and energy comprehensive utilization indicators, pollutant generation indicators, and clean production management indicators. On the basis of the original standard, the new standard distinguishes several sections such as vehicle body coating, chemical pre-treatment, physical pre-treatment, spray painting (coating), powder coating, and general indicators, and each section has detailed regulations. Many ambiguous names have been defined, and qualitative and quantitative indicators are more in line with the current actual situation of the industry and can effectively guide the implementation of clean production improvement by enterprises.
In response to the new requirements, many enterprises that have already met the standards stipulated in HJT293-2006 "Clean Production Standards for the Automotive Manufacturing Industry - Painting" may still fail to meet the requirements. In such cases, enterprises need to continuously update and improve their clean production levels.
Currently, many domestic automotive companies have fully integrated their car body painting processes and quality with international standards. Their painting equipment is world-class, but they lag far behind international levels in terms of environmental protection, energy conservation, and clean production. Most car body painting lines have serious pollution problems and low resource utilization rates; the VOC emissions, painting energy consumption, CO2 emissions, water consumption, and wastewater discharge of each vehicle are 2 to 3 times or even more of the international advanced values. In equipment bidding, there are often no target values for energy consumption, environmental protection, and clean production, and the requirements for some indicators are also very backward. The new "Evaluation Index System for Clean Production in the Painting Industry" will provide a reference for enterprises' future environmental protection renovations.
2. Improvements for Clean Production in Painting
To meet the requirements of all the indicators in the painting clean production, various improvement measures must be taken from multiple aspects such as painting coatings, painting processes, and painting equipment, to improve the level of clean production indicators.
2.1 VOCs
At present, the requirements for VOCs emissions from the state and various provinces are becoming increasingly strict. Relevant national industry standards have also been successively issued to limit VOCs emissions. These values are much lower than the current situation of the painting industry. This requires all enterprises to undergo renovations to reduce the indicator data and ensure production in the workshop.
Therefore, many enterprises are now conducting research in terms of process, coating, and equipment, and introducing new technologies, new processes, and new equipment to significantly reduce VOCs emissions.
2.2 Water Waste Generation
The new clean production standard does not specify the amount of wastewater generated, but it limits the CODcr and total phosphorus content. These two data indicators are closely related to the amount of wastewater generated. Only by reducing the wastewater generation and concentration in the painting workshop can the CODcr value and total phosphorus content of the wastewater be reduced.
The wastewater generated by the painting workshop mainly concentrates in the pretreatment and electrophoretic areas. Currently, the relatively mature measures include:
1) Canceling passivation and vigorously promoting non-phosphating processes;
2) Separately discharging and treating degreasing, phosphating, and electrophoretic solutions, and conducting research on the frequency of wastewater discharge, and reducing the number of discharges while meeting the process requirements;
3) Improving the cleanliness of the incoming white body, increasing the filtration accuracy of degreasing and deplating equipment;
4) Introducing new equipment and technologies to extend the usage time of degreasing and cleaning solutions, clarifying the discharge concentration standards based on detection data, and discharging;
5) Application of water reuse technology, etc.
2.3 Waste渣 Generation
The main solid hazardous waste in the painting workshop is phosphating slag and waste paint slag； the adoption of non-phosphating processes in the pretreatment and electrophoretic areas can reduce the generation of phosphating slag； the use of optimized coatings and processes can reduce the amount of paint used； using electrostatic spraying robots， applying electrostatic spray guns for manual internal surface spraying， and improving the paint adhesion rate， etc.， can achieve the purpose of reducing the generation of waste渣.
2.4 Comprehensive Energy Consumption
Comprehensive energy consumption is an indicator required in the new painting clean production standard. High energy consumption and high CO2 emissions are also high； in the construction and application of the workshop， comprehensive energy consumption is also a point of concern for all units， as it determines the operating cost of the equipment. Currently， common measures for energy saving include： using variable frequency control for high-power equipment， circulating air conditioning， waste heat recovery， and using clean energy， etc. (Note: The new standard takes into account the inconsistent environmental conditions across different regions. It specifically notes that the energy consumption of air conditioners used for temperature regulation is not included. Here, the energy consumption accounts for one-fourth of the total energy consumption of the entire workshop. The definition of the energy consumption range is still under discussion at present.)
3 Conclusion
For production-oriented enterprises, clean production can be simply understood as: improving the efficiency of resource and energy utilization during the production process and reducing the amount of waste generated. According to local domestic standards and the requirements of the country for pollutant emissions, it is imperative for enterprises to implement clean production. Industry-related standards will also be revised more rapidly, effectively providing guidance and control. Corresponding enterprises will also carry out improvement and transformation in accordance with the national standards requirements. Those that fail to complete the transformation within the specified period may face the risk of being shut down, and it may also affect the application of new products. Therefore, before the standard is issued, appropriate countermeasures should be prepared in advance.
