Atmospheric environmental problems are becoming more and more serious, and the treatment of exhaust gas emissions is getting more and more attention from governments and all walks of life. Organic waste gas, as the main component of industrial waste gas, has a large impact on the atmospheric environment and the human body. At the same time, due to its complex sources and components, the difficulty of treatment and the treatment methods adopted are also different. This paper briefly analyzes the types and components of common organic waste gas, and the treatment technology of common organic waste gas.
I. Common Organic Waste Gas Classification
VOCs (Volatile organic compounds) are volatile organic compounds, which are a common type of air pollutants. They are produced in paint production, chemical fiber industry, metal coating, chemical coating, shoe leather, plywood manufacturing, tire manufacturing and other industries. The harmful volatile organic compounds mainly include acetone, toluene, phenol, dimethylaniline, formaldehyde, n-hexane, ethyl acetate, ethanol and the like.
The volatile organic waste gases (VOCs) in industrial enterprises are classified according to the source of generation, and there are mainly the following:
1. Spray paint exhaust gas: The main components are volatile organic compounds such as acetone, butanol, xylene, toluene, ethyl acetate, and butyl acetate. They are mainly produced by surface treatment companies such as paint spraying. Common treatment methods include oil curtain absorption, Water curtain absorption, combined with secondary carbon adsorption, etc.
2. Plastic and plastic waste gas: The main components are polymer monomers volatilized during the thermal processing of particles such as plastic and plastic. Due to the complex composition of plastic and plastic, the waste gas mainly contains ethylene, propylene, styrene, acrylic acid, and acrylic acid. Butadiene and other olefinic plastic polymer monomers, but the concentration is generally low and the air volume is large. The enterprises involved are mainly plastic granulation enterprises, chemical fiber production enterprises, injection molding enterprises, rubber production enterprises, etc. The treatment methods mainly include activated carbon absorption and plasma purification.
3. Shaped exhaust gas: The main components are aldehydes, ketones, hydrocarbons, fatty acids, alcohols, esters, lactones, heterocyclic compounds, and aromatic compounds. The enterprises involved are mainly dyeing and finishing enterprises and chemical fiber production enterprises, and usually adopt water spray treatment and electrostatic adsorption treatment.
4. Chemical organic waste gas: It is mainly produced by chemical companies. The composition of the exhaust gas has a greater relationship with the types of chemical products designed and produced by chemical companies. Generally, purification and treatment methods such as condensation recovery and catalytic combustion technology are used.
5. Printing waste gas: The main components are toluene, non-methane total hydrocarbons, ethyl acetate, ethanol, etc., which are volatilized from the ink. The companies involved are mainly companies that include ink printing processes, such as packaging, printing and other companies that generally use activated carbon adsorption.
Summary of common VOC organic waste gas purification treatment methods
It is preferred to choose an exhaust gas purification treatment method with low cost, low energy consumption and no secondary pollution, make full use of the waste heat of the exhaust gas, and realize the recycling of resources. In general, due to the special nature of its production activities and the high concentration of exhaust gas, petrochemical companies often adopt methods such as condensation, absorption, and combustion for purification of exhaust gas. The exhaust concentration of printing and other industries is low, and adsorption, catalytic combustion and other methods are often used for purification of exhaust gas. The following briefly summarizes these methods:
Condensation recovery method
The condensing method is to directly introduce industrially produced exhaust gas into the condenser, and through the action and reaction of adsorption, absorption, analysis, and separation, recover valuable organic matter, recover the waste heat of the exhaust gas, and purify the exhaust gas so that the exhaust gas reaches the emission standard. When the concentration of organic waste gas is high, the temperature is low, and the air volume is small, the condensation method can be used for purification treatment, and it is generally used in pharmaceutical and petrochemical enterprises. Usually, one or more other organic exhaust gas purification devices are installed behind the condensation recovery device to achieve the standard discharge.
2. Absorption method
In industrial production, the physical absorption method is mostly used, that is, the exhaust gas is introduced into the absorption liquid for absorption purification, and the absorption liquid is saturated and then subjected to heating, analysis, condensation and other treatments to recover the waste heat. In the case of low concentration, low temperature, and large air volume, the stepping absorption method can be used, but it needs to be equipped with a heating analysis and recovery device, and the investment is large. It involves the method of oil mist and water curtain absorbing paint mist commonly used by paint coating operation enterprises, that is, the common organic exhaust gas absorption method.
3.Direct combustion method
The direct combustion method is to ignite the exhaust gas by using auxiliary materials such as gas to promote the conversion of harmful substances into harmless substances under high temperature combustion. This method has small investment and simple operation. It is suitable for high concentration and low air volume exhaust gas, but its safety Technical requirements are high.
4. Catalytic Combustion
Catalysis then heats the exhaust gas and converts it into harmless carbon dioxide and water after catalytic combustion. This method is suitable for high temperature and high concentration organic waste gas purification treatment. It has the advantages of low combustion temperature, energy saving, high purification rate, and small floor area, but it has a large investment.
5. Adsorption method
The adsorption method can be divided into three types:
1. Direct adsorption method, which 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. Frequent loading and unloading and replacement procedures increase operating costs.
2. Adsorption-recovery method. The fiber activated carbon is used to adsorb organic waste gas, so that the superheated steam is blown back in a saturated state, so as to realize desorption regeneration.
3. New adsorption-catalytic combustion method. The method combines the advantages of the adsorption method and the catalytic combustion method, and has the advantages of stable operation, low investment, low operating cost, simple maintenance and the like. It uses a new type of adsorption material to perform adsorption treatment on organic exhaust gas, so that it is adsorbed, resolved, and desorbed under the action of hot air in a near-saturated state, and then the exhaust gas is introduced into a catalytic combustion bed for flameless combustion treatment, thereby achieving a thorough exhaust gas treatment. Purification treatment. This method is suitable for exhaust gas purification treatment with low concentration and high wind power, and is currently the most widely used exhaust gas purification treatment method in China.
6. Low temperature plasma purification method
Low temperature plasma is the fourth state of matter after solid, liquid, and gaseous states. When the applied voltage reaches the discharge voltage of the gas, the gas is broken down to produce a mixture including electrons, various ions, atoms and free radicals.
Although the electron temperature is high during the discharge, the temperature of the heavy particles is very low, and the whole system is in a low temperature state, so it is called low temperature plasma. Degradation of pollutants by low-temperature plasma is to use these high-energy electrons, free radicals and other active particles to cause the pollutant molecules to decompose in a very short time, and various subsequent reactions occur to achieve the purpose of degrading the pollutants.
Traditional treatment methods of volatile organic pollutants (VOCs), such as absorption, adsorption, condensation, and combustion, are difficult to achieve at low concentrations of VOCs, while photocatalytic degradation of VOCs has the problem of easy deactivation of the catalyst. Low temperature plasma treatment is used. VOCs can be free from the above conditions and have potential advantages.
But plasma is an interdisciplinary discipline that includes basic disciplines such as discharge physics, discharge chemistry, chemical reaction engineering, and vacuum technology. Therefore, there are very few units capable of mastering the technology at present, and most of the publicity for the use of low-temperature plasma technology to treat exhaust gas is not a true low-temperature plasma waste gas treatment technology.
to sum up
Different organic waste gas components and concentrations are suitable for different organic waste gas treatment methods. At present, the comprehensive technology is mature, economical, and equipment maintenance. The most widely used is activated carbon adsorption method. However, the activated carbon adsorption method has the disadvantages of high cost of elution and recovery of waste activated carbon after the expiration date, and pollution transfer. Therefore, the new adsorption-catalytic combustion method has been widely used in technical reform or new projects.
The low-temperature plasma purification method is favored by more and more enterprises because of its low maintenance cost and other advantages, but there are also problems such as high equipment investment costs. It is believed that with the development of technology and industry, the low-temperature plasma purification technology will become more and more mature, and the investment in equipment will also decline, and it will be widely used by then.