Severe haze and other heavy pollution weather, how to reduce volatile organic compounds (VOCs) has become a widespread concern in society. Automotive coating, printing and packaging, petrochemical and other industries listed as VOCs by the state focus on reducing the industry. Currently, many provinces and municipalities such as Beijing and Shanghai have already levied sewage charges on these VOCs key emission-sector enterprises.
Today, the issue facing VOCs emitters is how to control their emissions of VOCs. In this regard, this column invited a number of industry experts to VOCs emissions control technology at home and abroad made a systematic review, and domestic and foreign technology and equipment for comparative analysis.
Key industries VOCs control technology
Automotive coating industry
VOCs emissions from the automotive coating industry come mainly from paint sprays and organic solvents used in the painting and drying processes. Paint fog from the air spray operation in the solvent-based paint flying. The organic solvent comes from the solvent and diluent in the coating process. Most of the organic solvents are volatile emissions. The main pollutants are xylene, benzene and toluene.
Spray process, mainly through the use of water-based paint, powder coating, high-solids coatings and other environmentally friendly paint to reduce VOCs emissions. At present, all new European and American countries have adopted the primer coating primer coating or powder coating, the use of water-based paint or powder coating, topcoat with water-based background plus solid varnish. Japan is also actively developing and promoting water-based coatings, high solids and ultra-high solid sub-varnish.
The technology of automotive exhaust gas drying is mainly regenerative direct combustion (RTO). In addition, the recuperative thermal combustion (TAR) and regenerative catalytic combustion (RCO) systems are used by some enterprises. A small amount of catalytic combustion technology Business use. Recycling in the foreign thermal combustion system (TAR) more applications.
Packaging and printing industry
VOCs emissions from the packaging and printing industry mainly come from the use of ink solvents, volatilization of ink and solvent during printing, printing and drying, as well as the use of thinners, fountain solutions and cleaning agents. Volatile organic compounds (VOCs) produced in this industry are highly concentrated and vary widely in concentration and require higher recovery and destruction technologies.
Source control aims to promote the use of low-VOCs or VOCs-free raw materials such as eco-friendly inks, adhesives and cleaners, reducing VOCs in raw and auxiliary materials from the beginning of the process. Promote the drying device optimization control system in the process is to control the VOCs emissions in the industry an effective technology.
The current control technologies used in the end control mainly include two types: one is to adopt the adsorption method to recover the high-concentration part of exhaust gas generated by the dryer. Adsorbent activated carbon fiber and granular activated carbon two. The second is the use of adsorption and concentration catalytic incineration of the workshop to purify the low concentration of exhaust emissions. Adsorbent honeycomb activated carbon and granular activated carbon, purification efficiency is generally above 90%. Some enterprises have adopted a foreign zeolite wheel adsorption enrichment device, the effect is good. At present, there is not a good solution to the modification of the adsorbent zeolite in China.
Petrochemical industry
The production facilities in the petrochemical industry are complex and, as a result, there are many pollutants emitted, the composition is complex and the concentration varies greatly. Pollutant emissions from the petrochemical industry are divided into unorganized emissions and organized emissions.
The organized emissions of VOCs from the petrochemical industry are mainly man-made emissions from the production process. Organic waste gas generated during the process can not be completely recycled. Although some of the organic waste gas is still discharged into the atmosphere despite incineration, adsorption and condensation treatment, Mainly include catalytic cracking catalyst regeneration flue gas, acid gas recovery device exhaust, organic exhaust gas collection and treatment device exhaust and other three categories.
Unorganized emissions are an important means of VOCs emissions from the petrochemical industry. There are three main sources: â‘ There are different degrees of leakage and man-made discharge problems in production, storage and transportation. â‘¡ In the open space of the wastewater collection and transportation system, the VOCs temporarily dissolved in the wastewater will be re-dispersed and volatilized into the atmosphere to have a secondary impact on the environment. â‘¢ Light oil and volatile chemicals and solvents during storage will also produce emissions of VOCs.
According to the typical characteristics of the petrochemical industry, the control of VOCs should first focus on the collection of unorganized emissions. General use of multi-level technology in series, integrated condensation, membrane and adsorption recovery process can achieve milligram-level technical standards.
At present, in the air pollution sources, the organized discharge can be basically disposed of in the terminal treatment. However, the unorganized discharge is difficult to control and the terminal treatment has insurmountable drawbacks. For example, the change of the wind direction can also affect the control of the VOCs. So VOCs control focus or start from the source, starting from the production process.
Comparison of VOCs control technology at home and abroad
In terms of control technology of VOCs, the mainstream technologies in our country include adsorption and recovery, catalytic oxidation, regenerative combustion and other methods. These technologies are also the mainstream VOCs treatment technologies in the world.
However, due to the late start of the research on VOCs in our country, especially the results based on long-term observation are not enough. Although the technologies of treatment have been in line with international standards, the control of VOCs is not enough, the development of domestic equipment can not keep up with the demand of technology, Excessive pursuit of low cost materials and equipment, the general efficiency is low; while abroad is to choose efficient and reasonable advanced materials and equipment. Compared with foreign VOCs governance, the gap in our country is mainly reflected in the following aspects:
First, most of the instruments and equipment used to monitor VOCs use foreign products, which are expensive and the core monitoring equipment has not yet reached the localization level. Although some domestic research institutes and enterprises do some research on Fourier spectroscopy, on-line chromatography and on-line mass spectrometry, some applications have also been made. However, on the whole, there is no systematic on-line VOCs monitoring technology and no set Of the application demonstration, VOCs online monitoring technology and stable operation of accurate testing also need more validation. In addition, there are few applications of VOCs monitoring process control.
Second, there are many kinds of VOCs, involving many pollution industries and processes. The emission of polluting gases is very different. The above properties determine that a single treatment technology can not meet all the emission control requirements. In foreign countries, multi-stage tandem combined depth technologies are commonly used, such as adsorption concentration-catalysis (thermal storage catalysis), oxidation integration technology, adsorption condensation-condensation recovery integration technology, adsorption concentration- absorption integration technology and the like. In contrast, the domestic governance technology is not so rich, a separate application of activated carbon adsorption ratio.
Third, the single from a technology point of view, such as adsorption technology, due to the lower cost of activated carbon, widely used in China, and foreign countries have long been using molecular sieve runner enrichment wheel adsorption
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