Condensation is a treatment method for recovering valuable organic compounds from VOCs and reusing them as resources. Using the difference of saturated vapor pressure of organic matter at different temperatures and pressures, some substances are supersaturated, condensed and recovered by cooling and pressurizing. Condensation method has the advantages of large storage capacity of recycled materials, simple equipment and operating conditions, but the operating cost is too high because of the need for higher pressure or lower temperature. Condensation method is suitable for the treatment of high concentration organic waste gas.
2 absorption method
Absorption method is to treat organic waste gas by using the similar compatibility principle of absorption liquid and organic waste gas. It is suitable for the treatment of medium and high concentration waste gas, but it is difficult to choose cheap and low volatile absorption solution, and there are problems in waste liquid treatment, so the purification effect is not ideal.
3 thermal storage oxidation method
Regenerative oxidation method uses high-efficiency ceramic regenerator to store the heat generated by decomposition of organic waste gas, and uses the heat energy stored by ceramic regenerator to heat untreated organic waste gas, thus achieving high thermal efficiency. Through the program switching of exhaust gas flow, the heat storage and heat release of heat storage materials are realized. The heat recovery efficiency is generally above 95%, the oxidation temperature is generally between 800℃ and 980℃, and the purification rate is above 98%. Suitable for the treatment of medium and high concentration and complex VOCs. For the treatment of organic waste gas with low concentration and large air volume, there are some shortcomings such as large equipment investment and high operating cost.
4 catalytic oxidation method
The waste gas is heated to 200℃ ~ 300℃ and oxidized and decomposed into carbon dioxide and water under the action of catalyst to achieve the purpose of purification. It has the advantages of low light-off temperature, high purification rate, no secondary pollution, simple process, convenient maintenance and good safety. This technology is suitable for the treatment of medium and high concentration organic waste gas, and the process is mature. For the treatment of organic waste gas with low concentration and large air volume, there are some shortcomings such as large equipment investment and high operating cost.
5 adsorption method
Using adsorbents with high porosity and high specific surface area, vOCs gas molecules can be separated from waste gas by physical adsorption (reversible reaction) or chemical adsorption (irreversible reaction). The purification rate can reach 95%, with simple equipment and less investment. However, there are also some problems, such as the adsorbent can not be regenerated after saturation, the cost of adsorbent replacement is high, and there is secondary pollution.
6. Adsorption and recovery methods
Organic waste gas is adsorbed by adsorbents such as activated carbon fiber or granular carbon, and then desorbed and regenerated by water vapor or inert gas. The regenerated high-concentration gas is condensed and separated to recover liquid. This technology is suitable for the treatment of medium and high concentration organic waste gas with recycling value.
7 adsorption. Catalytic combustion method
A new type of activated carbon was used to adsorb and concentrate low concentration organic waste gas. After the adsorption is close to saturation, hot air is introduced to regenerate activated carbon. The desorbed high-concentration organic waste gas enters the catalytic combustion bed for flameless oxidation and decomposition, and the hot gas is recycled in the system or a secondary heat exchanger is added for heat energy recovery. Generally, there are more than two adsorption beds, one for desorption or standby, and the other for adsorption to ensure the continuous and stable operation of the system. This technology reduces the amount of waste gas to be oxidized, reduces the scale of subsequent catalytic combustion equipment, and reduces equipment investment. Although the concentration of treated organic matter is low, the concentration of concentrated exhaust gas can reach above the state of spontaneous combustion. Therefore, in the combustion stage, the additional heat source power required by the catalytic combustion device is small or unnecessary, and the activated carbon regeneration heat source comes from the burned exhaust gas, so the operating cost is low. This technology combines the advantages of adsorption method and catalytic oxidation method, overcomes the shortcomings of their separate use, and solves the problem of treating low concentration and large volume organic waste gas. It is a mature and practical technology for treating high concentration organic waste gas at present.
8 biological method
This method is developed on the basis of mature sewage biological treatment technology, which has the characteristics of low energy consumption and low operating cost, and has a certain application scale abroad. Its disadvantage is that pollutants need to have enough residence time in the process of mass transfer and digestion, thus increasing the occupation of equipment. At the same time, because microorganisms have certain impact load limit, the control of the whole treatment system during shutdown and start-up is increased. At present, the application of this method in waste gas treatment of sewage stations in China is small, and it is less used in industrial waste gas treatment.
9 low temperature plasma technology
At room temperature, high-voltage pulse corona produces a large number of high-energy electrons or active particles such as O, OH and N excited by high-energy electrons. At the same time, ozone can also be produced. Various active particles and ozone react with VOCs, destroying chemical bonds such as C-C, C-H or C=C in VOCs. Due to the strong oxidizing ability of O, OH groups and ozone, it decomposes to produce CO: and H2O. This technology does not use adsorbent, does not need regeneration treatment, does not need special person to be responsible, has no secondary pollution, and is convenient to replace and maintain. However, plasma is an interdisciplinary subject including basic disciplines such as discharge physics, discharge chemistry, chemical reaction engineering and vacuum technology. At present, few units can master this technology maturely. Although there are engineering application cases, the purification rate is quite different.