Several common organic waste gases (VOCs) and treatment technologies

1. Classification of common organic chemical waste gases

VOCs (Volatile organic compounds) are volatile organic compounds, which are a relatively common type of air pollutants that are caused by paint manufacturing, textile industry, metal spraying, chemical coatings, shoe tanneries, and wood-based panel manufacturing. , tire production and manufacturing, and other fields. Hazardous volatile organic compounds mainly include toluene, xylene, formic acid, dimethylaniline, indoor formaldehyde, n-hexane, butyl acetate, ethyl acetate, etc.

Volatile organic waste gases (VOCs) in enterprises are classified according to their origin. They mainly fall into the following categories:

1. Spraying exhaust gas: The main components are toluene, butanol, xylene, toluene, butyl acetate, butyl acetate and other volatile organic compounds. They are mainly formed in surface treatment companies such as paint spraying. Common disposal methods include oil curtain absorption, Cooling water curtain absorption, combined with second- and third-level activated carbon adsorption, etc.

2. Plastics and plastic waste gas: The main components are polymers released during the production process of plastics and plastic particles. Because the composition of plastics and plastics is relatively complex, the waste gas mainly contains butadiene, PE, and butadiene. Alkane plastic polymers such as olefin, acrylonitrile and butadiene are single, but the concentration is generally low and the exhaust volume is large. The companies involved mainly include recycled plastic pellet companies, chemical fiber manufacturing companies, injection molding processing companies, plastic manufacturing companies, etc. The specific solutions include activated carbon absorption, plasma purification, etc.

3. Shaped exhaust gas: The main components are aldehydes, ketones, hydrocarbons, oleic acid, alcohols, esters, lactones, heterocyclic compounds, and aromatic hydrocarbons. The companies involved are mainly printing and dyeing companies and chemical fiber manufacturing companies, which usually use water spraying process and electrostatic induction adsorption process.

4. Chemical waste gas from chemical plants: mainly caused by chemical plant emissions. The composition of waste gas is closely related to the type of chemical raw materials designed and manufactured by chemical plants. Purification collection solutions such as cold recycling and catalytic combustion technology are generally used.

5. Packaging and printing waste gas: The main components are xylene, non-methane gas total hydrocarbons, butyl acetate, ethyl acetate, etc. released from printing ink. The companies involved are mainly companies with printing ink processes, mainly companies such as packaging supplies, clothing printing, etc., which generally use activated carbon adsorption.

2. Summary of common VOC organic chemical waste gas purification treatment solutions

Prioritize low-cost, low-energy-consuming, non-secondary pollution-free exhaust gas purification solutions, make full use of the waste heat recovery of exhaust gas, and realize the cyclic utilization of natural resources. Generally speaking, due to the uniqueness of their manufacturing activities and the high concentration of exhaust pipes, petrochemical companies often use cooling, absorption, ignition and other methods to purify exhaust gases. In fields such as packaging and printing, the concentration of exhaust pipes is low, and adsorption, catalytic combustion and other methods are often used for exhaust gas purification treatment. The following is a brief description of these methods:

1. Cold doubt recovery method

The cooling method is to directly introduce the waste gas from industrial production into the cooler, and through the functions and reactions of adsorption, absorption, analysis, separation and other stages, valuable organic compounds are recycled, the waste heat of the waste gas is recycled, and the waste gas is purified , so that the exhaust gas meets environmental protection standards. When the concentration of chemical waste gas is high, the temperature is low, and the exhaust volume is low, the cold-wet method can be used for cleaning treatment, which is generally used in pharmaceutical and petrochemical industries. Usually, one or more levels of other organic chemical waste gas purification treatment equipment will be modified behind the cold recycling equipment to ensure that environmental protection standards are met.

2.Absorption method

In industrial production, the physical absorption method is often used, which is to introduce the waste gas into the absorption liquid for absorption and purification. After the absorption liquid is saturated, heating, analysis, cooling and other processing are carried out, and the waste heat is recovered. The absorption method can be used when the concentration is low, the temperature is low, and the exhaust volume is large, but heating analysis and recycling equipment must be equipped, which requires a large investment. When it comes to paint spraying companies, oil curtains and cooling water curtains are commonly used to absorb oil mist, which is the commonly used organic chemical exhaust gas absorption method.

3. Immediate ignition method

The direct ignition method uses auxiliary materials such as natural gas to ignite the exhaust gas to promote the conversion of carcinogens into harmless substances under high-temperature ignition. This method requires a small investment, is easy to use, and is suitable for high concentrations and small exhaust volumes. Exhaust gas, but its safety production technical requirements are higher.

4. Catalytic combustion method

The catalytic reaction then heats the exhaust gas and converts it into harmless carbon dioxide and water after catalytic combustion. This method is used to purify organic chemical waste gases with high temperature and concentration. It has the advantages of low ignition temperature, environmental protection and energy saving, high purification rate, and small floor area, but the investment is relatively large.

5. Adsorption method

Adsorption methods can be divided into three types:

1. Direct adsorption method uses activated carbon to adsorb and purify organic waste gas. The purification rate can reach more than 95%. This method has simple equipment and low investment, but requires frequent replacement of activated carbon and frequent loading and unloading. Procedures such as replacement and replacement increase operating costs.

2. Adsorption-recycling method. Chemical fiber activated carbon is used to adsorb organic chemical waste gas, causing it to be saturated with superheated steam to blow back to complete adsorption and regeneration.

3. New adsorption-catalytic combustion method. This method combines the advantages of adsorption method and catalytic combustion method, and has the advantages of stable operation, low investment, low operating cost, and easy maintenance. It uses new adsorption materials to adsorb chemical waste gas, allowing it to adsorb, analyze, and adsorb under the action of hot air close to saturation, and then introduces the waste gas into the catalytic combustion bed for flameless ignition treatment to complete the complete purification of the waste gas. Process and resolve. This method is suitable for exhaust gas purification solutions with low concentration and high wind speed. It is currently the used exhaust gas purification solution in China.

4. Ultra-low temperature plasma purification method

Plasma is the fourth state of chemical substances after solid, liquid, and vapor. When the additional voltage reaches the charging and discharging voltage, it is penetrated to form electronic devices, various ions, molecules, and oxygen. The combination of free radicals in it.

During the charging and discharging process, although the temperature of the electronic device is very high, the temperature of the heavy particles is very low, and the entire system is in a low temperature state, so it is called plasma technology. Low-temperature plasma dissolves pollutants by using active particles such as high-energy electronic devices and oxygen free radicals to dissolve the molecular structure of pollutants in a very short time and produce various subsequent reactions to dissolve pollutants. Purpose.

Traditional treatment methods for volatile organic pollutants (VOCs), such as absorption, adsorption, cooling and ignition, are difficult to achieve for lower concentrations of VOCs, and catalytic oxidation of VOCs has metal catalysts that are easily inactive. Problem, using plasma technology to solve VOCs can not be limited by the above standards, and has the advantage of uncertainty.

But because plasma is an interdisciplinary science including charge and discharge physics, charge and discharge organic chemistry, chemical change hydraulics and vacuum equipment and other basic sciences. Therefore, there are currently very few companies that can fully master this process, and of the promotions that use low-temperature plasma technology to solve waste gases do not have low-temperature plasma waste gas treatment technology in the true sense.

Summary

Different chemical waste gases and concentrations require different chemical waste gas treatment methods. Currently, based on factors such as technical originality, rationality, and equipment maintenance, general or activated carbon adsorption methods are used. . However, the activated carbon adsorption method has shortcomings such as the high cost of flushing out and recycling the spent activated carbon after the expiration date, and the migration of environmental pollution. Therefore, the new adsorption-catalytic combustion method has been widely used in technical transformation or new projects.

The low-temperature plasma purification method is being favored by many companies due to its low mid- and post-maintenance costs, but it also has the problem of high equipment operating costs. It is believed that with the development of new technologies and manufacturing, low-temperature plasma purification technology will become more complete, equipment investment will also be reduced, and it may be widely used by then.