Introduction to Five Commonly Used VOCs Treatment Technologies

To promote the reduction of VOCs, there have been many efficient and energy-saving methods for the treatment of organic waste gas in recent years.The methods used for volatile organic waste gas include thermal oxidation, adsorption, biological treatment, absorption, condensation, etc.

1. VOCs waste gas treatment technology — Thermal oxidation method 

Thermal oxidation is a method that directly and auxiliary burns organic gases, that isVOCs, or uses suitable catalysts to accelerate theVOCschemical reaction, ultimately achieving the reduction of organic concentration to a level that is no longer harmful.

Thermal oxidation method has a good effect on the treatment of organic waste gas with high concentration, so it is widely used in the treatment of high concentration waste gas. This method is mainly divided into two types, namely direct flame combustion and catalytic combustion. Direct flame combustion has a relatively high thermal treatment efficiency for organic waste gas, which can generally reach 99%. Catalytic combustion refers to the acceleration of the chemical reaction rate of organic waste gas under the action of a catalyst. This method takes less time than direct combustion and is the preferred technology for the purification of high concentration and low flow rate organic waste gas.

2. VOCs Waste Gas Treatment Technology — Adsorption Method

The adsorption method is mainly applicable to low-concentration and high-volume organic waste gas in the treatment of organic waste gas. At this stage, this method of treating organic waste gas is already quite mature, with relatively small energy consumption, but the treatment efficiency is very high, and it can completely purify harmful organic waste gas. Practice has proved that this method of treatment is worth promoting and applying.

However, this method also has some defects, it requires equipment with a large volume, and the process flow is relatively complex; if there are a large number of impurities in the waste gas, it is easy to block the adsorbent. Therefore, the key to using this method to treat waste gas is the adsorbent. At present, the adsorption method is often used to treat organic waste gas, and activated carbon is often used, mainly because activated carbon has a good mesoporous structure and strong adsorption.

Three, VOCs waste gas treatment technology —— Biological treatment method

Biological treatment method for purifying VOCs waste gas is a new air pollution control technology developed in recent years. It has less investment, low operation cost, simple operation and wide range of application, and is the most promising new technology to replace the combustion method and adsorption purification method. In terms of the basic principle of treatment, the organic waste gas is treated by using the physiological process of microorganisms to convert harmful substances in organic waste gas into simple inorganic substances, such as CO2, H2O and other simple inorganic substances. This is a harmless way to treat organic waste gas.

Biological purification method actually uses the life activities of microorganisms to transform harmful substances in waste gas into simple inorganic substances (such as carbon dioxide and water) and cell substances, etc., and the main processes are biological washing method, biological filtration method and biological trickling method.

Gaseous pollutants with different components, concentrations and gas volumes have their own effective biological purification systems. Biological washing tower is suitable for treating waste gas with small gas volume, large concentration, high solubility and low metabolic rate; for waste gas with large gas volume and low concentration, biological filter bed can be used; and for those with high load and pollutants degradation will generate acidic substances, it is better to use biological trickling filter bed.

Biological treatment of organic waste gas is a new technology, and due to the involvement of gas, liquid, and solid phase mass transfer in the reactor, as well as the biochemical degradation process, there are many factors that affect it, and the relevant theoretical research and practical application are not deep and extensive enough, and many issues need to be further explored and studied.

Under normal circumstances, a complete biological treatment process for organic waste gas includes 3 basic steps: a) organic pollutants in the organic waste gas first come into contact with water, which can rapidly dissolve in water; b) the dissolved organic matter in the liquid membrane can be gradually diffused into the biofilm in the case of low concentration in the liquid state, and then absorbed by the microorganisms attached to the biofilm; c) the organic waste gas absorbed by the microorganisms will be degraded in its own physiological metabolism and finally converted into substances that do not damage the environment.

IV. VOCs Waste Gas Treatment Technology —— Pressure Swing Adsorption Separation and Purification Technology

The adsorption separation and purification technology is based on the property that gas components can be adsorbed on solid materials. In the organic waste gas and separation purification device, the pressure of the gas will change to a certain extent, and the organic waste gas is treated through this pressure change.

PSA technology mainly applies physical method to purify organic waste gas. The main material used is zeolite molecular sieve. Zeolite molecular sieve has certain advantages in both adsorption selectivity and adsorption amount. Under certain temperature and pressure, this kind of zeolite molecular sieve can adsorb the organic components in organic waste gas, and then transport the remaining gas to the next link. After adsorbing organic waste gas, it is converted through certain processes to maintain and improve the regeneration ability of adsorbent, so that adsorbent can be used again, and then the above steps are repeated,cycled repeatedly, until the organic waste gas is purified.

In recent years, this technology has begun to be applied in industrial production, and has a good effect on gas separation. The main advantages of this technology are: low energy consumption, low cost, automated process operation, high purity of the separated mixture, and small environmental pollution. The use of this technology has a good effect on the recovery and treatment of gases of certain value, and the market development prospects are broad, becoming the development direction of future organic waste gas treatment technology.

5. VOCs waste gas treatment technology —— Condensation recovery method

At different temperatures, the saturation of organic matter is different, and the condensation recovery method takes advantage of this characteristic of organic matter to play a role. By reducing or increasing the system pressure, the organic matter in the steam environment can be extracted by condensation. After the condensation extraction, the organic waste gas can be purified to a higher degree. The disadvantage is that the operation is more difficult, and it is not easy to complete with cooling water at room temperature, so it is necessary to cool the condensate, thus requiring more energy.

This treatment method is mainly applicable to the treatment of organic waste gas with high concentration and low temperature. It is usually suitable for the recovery and treatment of organic waste gas with high VOCs content (several percent) and small gas volume, because most VOCs are flammable and explosive gases, and are limited by the explosion limit, the content of VOCs in the gas will not be too high, so in order to achieve a higher recovery rate, it is necessary to use a very low temperature condensing medium or high pressure measures, which will inevitably increase the equipment investment and treatment cost, so this technology is generally used as a primary treatment technology and combined with other technologies.