今天是2024年03月29日

Luan Zhiqiang: emission reduction approach, treatment technology and main problems of VOCs

 

    Abstract: VOCs emission reduction is an important task of air pollution prevention and control, which is more difficult than other air pollutants control, which is mainly determined by VOCs emission characteristics: VOCs are of various types, chemical and physical properties are different; there are many discharge industries, complex emission conditions, different treatment technologies are needed; there are many emission sources, and many industries are difficult to collect unorganized emissions; VOCs is flammable and explosive. Safety should be considered first when dealing with them. The way to reduce VOCs emission of industrial sources is mainly considered from three aspects: source substitution, process control and end treatment.

    VOCs emission reduction is an important task of air pollution prevention and control, which is more difficult than other air pollutants prevention and control. This is mainly determined by the emission characteristics of VOCs: VOCs are of various types, and the chemical and physical properties are different; there are many emission industries, relatively complex emission conditions, and different treatment technologies are needed; there are many emission sources, and many industries collect unorganized emissions Difficult; VOCs are inflammable and explosive, and safety issues should be considered first when dealing with them.

 ▶ The way of reducing VOCs emission from industrial sources

    The emission reduction approaches of VOCs from industrial sources are mainly considered from three aspects: source substitution, process control and end treatment.

    First, in the long run, the potential to reduce VOCs use and emissions from the source is very large, which is the fundamental way to reduce VOCs emission. The most important part of industrial source emission is the adaptation of solvents, including four aspects: coating, packaging printing, adhesive use and cleaning. The potential of source substitution is very large. Nowadays, many industries can use water-based coatings to replace them. For example, the replacement work of automobile industry has been carried out in an all-round way. Several major automotive industries in Beijing have completed the replacement work of water-based coatings, and other places are also in progress.

    Secondly, in the process control, strengthening the control of production process is the main way to reduce VOCs leakage and unorganized emission. For example, in petrochemical and chemical industries, to achieve VOCs emission reduction, a set of leakage detection management system is needed first. Now, there are some refineries and large petrochemical enterprises all over the country, which have done a lot of work in this regard. The first thing that all regions pay attention to in emission reduction of VOCs is leakage detection and repair LDAR technology. In the solvent adaptation industry, such as coating production, ink production and other production processes, VOCs emissions are inevitable due to the special properties of the production process. In these links, we should collect VOCs effectively first, and we can't manage them if they can't be collected. This is the premise of governance. Article 45 of the new law on prevention and control of air pollution clearly stipulates that the production and service activities of the waste gas producing volatile organic compounds shall be carried out in the confined space, the exhaust gas shall be collected and treated after collection. If it is impossible to collect it, some measures shall be taken to reduce the emission during the leakage process.

    Third, the end governance issues. The main task of VOCs Pollution Prevention and control in key industries is to achieve the standard emission through end treatment. End governance is only a phased measure, but now because of the large stock, enterprises can not produce without end governance. In many production processes involving VOCs as raw materials, VOCs emission is inevitable, but after the discharge, it must be treated, such as oil and gas recovery, gas station, terminal of oil depot, etc.

 ▶ VOCs governance technology system

    VOCs governance technology system is very complex, and the operation requirements and governance costs of governance facilities are relatively high, which is also the reason why it is difficult to promote at present. At present, the mature and mainstream treatment technologies mainly include four types: adsorption technology (including adsorption recovery technology and adsorption concentration technology), thermal incineration technology, catalytic combustion technology and biological purification technology. The first three types are widely used in VOCs governance at home and abroad. Biotechnology has developed rapidly in recent years, and the industry used is also expanding. Compared with foreign countries, biotechnology of domestic related enterprises is basically following up. There are also some auxiliary treatment technologies, such as absorption technology, condensation technology, membrane technology, etc. Auxiliary governance technology does not mean that technology is not important in itself, but it is only narrow in scope of application, but in some cases it is essential.

    From the current situation of VOCs treatment in China, the most difficult is the low concentration of odor treatment. The low concentration odor emission range is wide, the treatment requirements and costs are very high, but its treatment technology is not mature compared with the current mainstream technology. Especially in recent years, there are many low-temperature ionomer technologies, low-temperature catalysis technologies, catalytic technologies, photooxidation technologies, and some of them are in a mess. Because of the lack of basic research and insufficient understanding of technology, the technology selection is lack of pertinence. In fact, VOCs governance often uses a variety of technology combinations. In most cases, it requires two or more technical combinations to achieve the standard ranking

    Requirements for release. For example, low concentration waste gas is used for concentration at first, and then activated carbon is used for adsorption and recovery after the adsorption concentration is finished. This is a way of low concentration waste gas adsorption and recovery, which is also used more at home and abroad.

▶ The main problems in VOCs governance

One is the problem of technical choice.

    The technical choice needs to be considered from two aspects, namely, the technical feasibility and the economic rationality. The technical feasibility mainly considers whether the emission can be achieved; the economic rationality is that on the basis of achieving the standard emission, the cost of governance is the lowest, including the one-time investment and operation cost. When selecting technology, the concentration of pollutants is considered first. For high concentration, those that can be recovered shall be recovered, and those that cannot be recovered can be incinerated; similarly, if there is recovery value for medium concentration gas, adsorption recovery shall be carried out, and incineration treatment can be carried out for those with no recycling value, and heat energy can be recovered at the same time. The treatment of VOCs with low concentration is more complicated, and can be absorbed and concentrated and incinerated. At present, the treatment of low concentration VOCs is relatively fast, but the enterprises have not enough knowledge of some technologies. Therefore, in the process of governance, we should first know the level of technology development, and then make choices.

    In addition, the detailed analysis of pollutants is an easy to ignore problem in the current treatment. Many enterprises may have been on a treatment equipment, such as activated carbon adsorption equipment, and found problems after installation. Finally, it was found that the composition of pollutants was not clear, and some organic matter with high boiling point could not be absorbed into the activated carbon, and the activated carbon would fail. Therefore, in the process of technical selection, the components of pollutants should be clear first, and field experiments should be carried out when necessary. Otherwise, the project failure caused by blind installation will cause great loss to the enterprise.

Secondly, the overall design of purification process should be emphasized.

First, the design of exhaust system is the premise of VOCs governance. The exhaust system is a bridge connecting production equipment and end treatment equipment. The design of exhaust system is unreasonable, and the exhaust air volume design is too large, the cost of subsequent treatment equipment will be increased. Secondly, the pretreatment process design of waste gas, including temperature regulation, humidity control, particle removal, etc., should be designed reasonably.

Thirdly, the safety design of purification system.

    At present, there is no specification to be used for reference in this respect, which leads to a problem - different manufacturers do not have the specification as reference when designing the same governance equipment, and the performance of the equipment is very different. At present, the safety design of purification system has not been paid enough attention. The probability of safety accidents in recent years is high for incineration equipment, catalytic combustion equipment, and even many adsorption equipment. In fact, in the design of chemical equipment, there are very strict and relatively perfect safety design specifications. As long as the design is in accordance with the specifications, it is necessary to understand the meaning of the specification. When designing the equipment, it is necessary to design strictly according to the safety design rules.