1.Adsorption method
Adsorption method is the organic waste gas through the filled bed filled with adsorbent, adsorption of organic matter to reduce air pollution purposes. The key lies in the performance of the selected adsorbent, high-performance adsorbent should have a large adsorption capacity, uniform adsorption pore size, easy to regenerate and other characteristics. Common industrial adsorbents are mainly activated carbon, activated carbon fiber, coke powder particles, molecular sieve zeolite and so on. Activated carbon has a dense microporous structure, great internal surface area, good adsorption performance, stable chemical properties, so it can be applied to the adsorption and purification of VOCs in the paint exhaust gas; but the humidity is greater than 60% of the exhaust gas, the adsorption effect will be significantly reduced; if there is no regeneration device, the replacement of the activated carbon to increase the operating costs; if hot air regeneration is prone to cause a fire. Molecular sieve than activated carbon with high temperature resistance, non-flammable, strong hydrophobicity and other characteristics, can be regenerated by hot air, for humidity is not higher than 90% of the exhaust gas also shows good adsorption effect.

2.Absorption method
Absorption method is to use the VOCs in the paint exhaust gas in some solvents in the high solubility, with a high boiling point, low vapor pressure of oil-soluble solvents to absorb the VOCs of a purification method. Absorption method is divided into physical absorption and chemical absorption, and physical absorption is generally used in real industrial treatment process, and whether the absorbent is cheap, easy to obtain and harmless is the key issue to be considered. He Luhong et al. used the nonionic surfactant Tween-20 as the main surfactant, added the co-surfactant sodium dodecylbenzene sulfonate (SDBS) and the auxiliary sodium chloride to form a complex aqueous absorbent to treat toluene-based VOCs exhaust gas, and the optimal toluene removal rate could reach 77%. Xiao Xiao et al. compared the absorption effect of absorbents such as diethylhydroxylamine, polyethylene glycol 400, silicone oil, edible oil, used engine oil, 0# diesel oil, etc. on toluene exhaust gas through experiments, and found that diethylhydroxylamine absorbed toluene the most under the same experimental conditions. Li A-liang et al. [experimental study found that 4% of 1,4 butanediol (BDO) on the toluene exhaust gas has a good absorption effect, the highest absorption concentration of up to 43.87 mg / L. In addition to physical absorption, industrial production will also be used as an absorbent sodium hypochlorite and other lyes or acids as an absorbent for chemical absorption of exhaust gas.

3.Combustion method
Combustion method is to spray paint waste gas in the organic combustion and oxidation, converted to CO2 and H2O harmless substances to achieve the purpose of waste gas purification. Combustion method can be divided into direct combustion method, thermal combustion method, catalytic combustion method, thermal combustion method and other types.
(1)direct combustion method of high concentration of combustible organic waste gas should be used direct combustion method. Direct combustion method requires a high enough temperature, and to ensure that the combustion space has enough oxygen. If the amount of oxygen is insufficient, the combustion is incomplete; if the amount of oxygen is too much, the concentration of combustibles will not be in the ignition limit range leading to incomplete combustion. In order to prevent gas explosions, generally in the boiler or open burner combustion of exhaust gases, combustion temperature of 1100 ℃; but when the combustion is incomplete, it will lead to a number of pollutants and soot emissions into the atmosphere, while the combustion of the heat can not be recovered, resulting in fuel energy loss.
(2) Thermal combustion method low concentration of combustible organic waste gas can be treated by thermal combustion method. Concentration of low combustible substances in the combustion process is not enough to release the energy required to support the entire combustion process, which requires the addition of auxiliary fuels as combustion gases, through the combustion of combustion gases to increase the heat, so that the exhaust gas to reach the reaction temperature and full combustion. Thermal combustion method temperature is generally in the range of 500 ~ 900 ℃, lower than the temperature of direct combustion method.

4.Condensation method
Condensation recovery method is the organic waste gas into the condenser, the use of VOCs at different temperatures under different partial pressures of vapor, so that the VOCs gradually condensed into liquid recovery. Condensation method is suitable for dealing with high concentration, small flow of organic waste gas, mainly used in pharmaceutical, chemical and other industries; spraying, printing and dyeing and other industries if the condensation method, usually first of all, the lower concentration of spray paint waste gas compression before processing. The process is the organic waste gas to the pre-cooling level unit pretreatment, the general temperature control at 5 ℃, to remove the water vapor contained in the cooling level evaporator to avoid frost and affect the heat transfer; pre-cooled organic waste gas cooling through the cooling level evaporator cooling, the temperature is controlled at -30 ℃ or so, the VOCs condensed into a liquid state. Condensation recovery is simple to operate, the effect is stable, its closure by the external temperature and pressure changes have little impact, its operating temperature is lower than the condensed liquid flash, safer, but too low a condensing temperature leads to high energy consumption, condensing equipment performance requirements and equipment investment and operating costs are also higher. Among them, refrigerant selection has different impacts on refrigeration efficiency as well as recovery effect.