Discussion on Treatment Methods of VOCs Waste Gas in 4S Shop

Abstract: This paper investigates the management of VOCs emissions from automobile 4S stores, the emission parameters of VOCs and the concentration of VOCs in automobile 4S shop. Combining with the related technologies of VOCs on the market, this paper analyzes the technical stability, investment and construction costs, operation costs and operation Difficult degree of comparative analysis, than the selection of technical stability, construction and operation of low cost, simple operation of the technology to promote, so that the car 4s shop VOCs emission control standards and norms.

1VOCs definition and harm

Volatile organic compounds (VOCs) are organic chemicals that have a vapor pressure of 0.1 mmHg (13.3 Pa) or more and a boiling point of 260 ° C (500 ° F) or less under normal conditions (20 ° C, 101.3 kPa). Such substances because of its small molecular weight, low boiling point, volatile, generally exist in gaseous form, including aliphatic, aromatic hydrocarbons, halogenated hydrocarbons, aldehydes, ketones, alcohols and so on. At the same time, these substances are also a key prerequisite for atmospheric ozone and secondary organic aerosol pollution.

The main hazards of VOCs are: acute poisoning is easily caused when the concentration of volatile organic compounds in the indoor air is too high, and the headache, dizziness, cough, nausea, vomiting, Quickly unconscious, some may also have life-threatening.

24S shop spray paint the mainstream form of the room

4S shop spray paint room is divided into: cross-flow paint room, side under the red paint room, all under the red paint room.

Cross-flow paint room: air flow from one end of the room to the other end. This model low cost, easy to install. The disadvantage is that the mist moves along the side of the body, and the mist can not be removed from the periphery of the operator's face, and the working environment is not satisfactory. Indoor paint temperature is not balanced. Affect the quality.

Side under the red paint room: air through the ceiling filter device into the paint room, the room by the side wall of the root discharge. This is the mid-range price of the paint room. As the fog away from the body, and can remove the mist from the operator's surroundings, so the spray paint and the working environment are better.

All-rounder paint room reflects today's most advanced technology. Air enters from the ceiling and is discharged outside through the pit or basement.

At present, 4S shops mainly take the side of the next-style paint room and all-under-red paint room in two forms.

3 shop spray paint room air volume and VOCs concentration estimates

According to statistics, the car 4S shop spray paint room's internal space 70m3 ~ 75m3, the number of ventilation in 220 times / h ~ 320 times / h, the spray paint room exhaust gas volume between 15000m3 ~ 25000m3, the calculation according to 20000m3 calculation. 4S shop paint / color the amount of paint is generally 2 ~ 5kg / d.

There is a big fluctuation in the amount of paint, especially in the paint spray paint when the amount of paint larger, which also directly causes the concentration of pollutants in paint spray volatility greater value. In the actual painting process, due to spray painter operation reasons, the amount of paint may be greater, when more vehicles need painting, paint + paint time may be compressed.

According to the amount of paint, paint composition and painting properties, the average content of VOCs is 20%, the amount of paint is generally 0.2 ~ 3.2L / time, the xylene yield of drying section is 20.0 ~ 436.8mg / m3, TVOC production is 39.9 ~ 873.6mg / m3.

This shows that the concentration of pollutants fluctuate in a wide range and belong to intermittent emissions.

4 Existing governance techniques

According to the survey statistics, the current car 4S shop spray paint exhaust are basically used activated carbon adsorption method. Activated carbon adsorption capacity is limited, need to be run in strict accordance with the requirements or frequency of replacement, desorption, in order to ensure that activated carbon on the exhaust treatment, but due to the actual management and regulatory difficulties, the use of activated carbon adsorption exhaust treatment shop mostly Activated carbon in strict accordance with the requirements of the replacement or desorption, so the late treatment results are not satisfactory.

5 other processing techniques

End-of-pipe technology in two big chunks: Recycling Technologies, Destruction Technologies, and a combination of these two technologies. Recycling technologies include: condensation, absorption (washing), adsorption, membrane separation; destruction techniques include: combustion, catalytic combustion, biodegradation, photocatalytic degradation, plasma technology. One of the membrane separation technology, photocatalytic degradation and plasma technology for the rise of new technologies in recent years.

Photocatalytic degradation: photocatalytic degradation of VOCs in two forms: one is the direct irradiation of light of a certain wavelength to decompose VOCs; the other is the presence of a catalyst, the decomposition of light VOCs. TANAKA Kazuyuki and Mitsuhiro TOKYO et al. Studied the use of UV light to decompose VOCs. Under the irradiation of 185 nm UV light, both organic and chlorofluorocarbons can decompose within a very short period of time. The decomposition rate of halogenated products Is greater than that of HCFCs; trichlorethylene can be decomposed into oxygen, chlorine, fluorine gas, etc. within a few seconds. Photolysis can produce intermediate products, sodium hydroxide solution can be treated or extended residence time and other means of final removal. The basic principle of the photocatalyst is that under a certain wavelength of irradiation, the photocatalyst makes H2O to generate (-H), then -OH oxidizes (VO) into carbon dioxide and water. Due to its high molecular diffusion and mass transfer rate and easier chain reaction, photocatalysts have much higher activity on gas-phase chemical pollutants than aqueous solutions.

Low Temperature Plasma Catalysis Technology: When using plasma technology to decompose VOCs pollutants, the high-energy electrons in the plasma play a decisive role. Tens of thousands of degrees of high-energy electrons and gas molecules (atoms) inelastic collision occurs, the energy is converted to the ground state molecules (atoms) of the internal energy, excitation, dissociation, ionization and a series of processes so that the gas is activated. When the electron energy is low (<10eV), active radicals are generated, and the activated contaminant molecules are removed by the plasma-oriented chain chemical reaction. When the average electron energy exceeds the chemical bond energy of contaminant molecules, the molecular bonds break and the pollutants decompose.

Treatment of volatile organic compounds with plasma combined catalyst, the degradation rate is relatively high, generally can reach more than 90%.

6 different management techniques related parameters

6.1 Catalytic oxidation method, the exhaust gas volume is from 1000m3 / h to 100000m3 / h, the concentration range is from 2000mg / m3 to 8000mg / m3, and the suitable temperature range is above or equal to 0 ℃.

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