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2017

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05

Spraying VOCs waste gas and treatment methods, responding to the key points of the inspector (III)

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The third part of the surface coating (automobile manufacturing industry) and 4S shop paint exhaust gas treatment method selection of organic waste gas treatment method, in general should be based on the following factors: the type of organic pollutants, organic pollutants concentration level, exhaust temperature of organic waste gas, organic waste gas emission flow, the level of particulate emission, the need to achieve the level of pollutant control. 3-1 regular treatment methods for spray paint waste gas treatment of the inapplicability of organic waste gas treatment methods are various, with different characteristics, commonly used water spray method, condensation method, absorption method, combustion method, catalytic method, adsorption method and so on. 1) water spray method: generally used for paint

Part 3 Surface Painting (Automobile Manufacturing Industry) and Selection of Treatment Methods for Paint Exhaust from 4S Shop

The choice of organic waste gas treatment method should be based on the following factors: the type of organic pollutants, the concentration level of organic pollutants, the exhaust temperature of organic waste gas, the emission flow of organic waste gas, the level of particulate emission, and the level of pollutant control that needs to be achieved.

3-1 regular treatment method is not applicable to the treatment of paint waste gas

There are many kinds of organic waste gas treatment methods with different characteristics, such as water spray method, condensation method, absorption method, combustion method, catalytic method, adsorption method and so on.

1) water spray method: generally used for the filtration of paint mist, for three benzene and other VOCs gas invalid. China's paint mist filtration 80 ~ 90% of the use of wet filtration, such as water curtain, water spin, oil curtain and other ways. Foreign countries are 80 to 90% of the use of dry filtration, developed countries do not allow the use of wet filtration (because of oil pollution of water today there is no ideal solution in the world. According to the State Environmental Protection Administration revealed: 2015 to ban the use of wet paint mist filtration equipment, in order to reduce, block off oil pollution of water). Water curtain spray cabinet equipment investment, low filtration effect, high operating costs. Take a 2m × 3m water curtain painting cabinet as an example, the pumps, pipes, water tanks (or oil tanks), baffles and other equipment used for water and oil are about 1~20000 yuan. There are also electricity, water (or oil), paint coagulant and other expenses in operation. Water will cause corrosion to the equipment; Frequent water exchange and cleaning will also cause shutdown and delay work; the water (or oil) curtain is discontinuous due to the deposited oil stain, which reduces the filtration efficiency. The loud noise and splashing water (or oil) make the work station environment humid and affect the quality of the paint surface. And it is not conducive to the health of operators. The discharge of waste water causes secondary pollution; The small paint capacity, low efficiency and frequent replacement of paint fog cotton all cause the increase of production cost.

2) Condensation recovery method: the exhaust gas is condensed directly or after adsorption and concentration, and the condensate is separated and recovered with valuable organic matter. The method is used for the treatment of waste gas with high concentration, low temperature and small air volume. However, this method has large investment, high energy consumption and high operating cost. The concentration of "triphenyl" and other exhaust gases in the paint exhaust gas is generally lower than 300mg/m3, the concentration is low, and the air volume is large (the air volume in the paint workshop of the automobile manufacturing industry is usually above 100000). Moreover, due to the complex composition of organic solvents in the paint exhaust gas, the recovered solvents are difficult to handle and use, and easy to produce secondary pollution, therefore, this method is generally not used in the treatment of coating waste gas.

3) absorption method: can be divided into chemical absorption and physical absorption, but "three benzene" exhaust gas chemical activity is low, generally do not use chemical absorption. Physical absorption is a liquid absorbent with a small volatility, which has a high affinity with the absorbed component, and is reused after heating and cooling after saturation. The method is used for atmospheric volume, low temperature, low concentration of waste gas, complex device, large investment, the selection of absorption liquid is difficult, liquid absorption purification rate is only 60% ~ 80%, this method in practical application of absorption efficiency is not high, oil mist entrainment phenomenon, generally difficult to meet the national emission standards, and there is a secondary pollution problem;

4) Direct combustion method: the heat released by the combustion of auxiliary fuels such as gas or fuel oil is used to heat the mixed gas to a certain temperature (700~800 ℃) and reside for a certain period of time to burn the combustible and harmful gases. The process is simple, less equipment investment, but high energy consumption and high operating cost. For the automobile manufacturing industry, the emission of paint exhaust gas often reaches hundreds of thousands of millions of air volume. Due to the low concentration, it is not economical to choose the direct combustion method, and it is a waste of energy.

5) catalytic combustion method: the exhaust gas is heated to 200~300 ℃ through the catalytic bed combustion, to achieve the purpose of purification. The method has low energy consumption, high purification rate of 95%, no secondary pollution, simple process and convenient operation. It is suitable for the treatment of high temperature and high concentration of organic waste gas with small air volume and high exhaust gas temperature, and is not suitable for the treatment of organic waste gas with low concentration and large air volume. The concentration of "three benzene" and other exhaust gases in the spray paint exhaust gas is generally less than 300mg/m3, so the catalytic combustion method is not suitable.
6) Adsorption method:

Direct adsorption method: organic gas directly through the activated carbon, can reach 95% of the purification rate, simple equipment, small investment, convenient operation, but the need to replace the activated carbon, if there is no regeneration device, the operating cost is too high; therefore, it can be used for low concentration, pollutants do not need to recover the occasion.

② adsorption recovery method: organic gas by activated carbon adsorption, activated carbon saturated with hot air desorption regeneration.

Through the above-mentioned regular methods in the spray paint exhaust gas treatment on the status quo, in the paint fog treatment industry there are backward products, complex operation management, late investment and high characteristics. Therefore, it is an urgent need for the development of the industry to find a treatment technology with high efficiency, high price ratio, stable performance, convenient operation, low operating cost and in line with environmental protection standards.

In view of the emission characteristics of automobile painting and painting exhaust gas, through the comparative study of various treatment methods, Beijing Dahua Mingke Environmental Protection Technology Co., Ltd. has developed ECB technology and applied it to the spraying industry. Through three years of practical application, a large number of practical success cases have been achieved.
3-2 Advantages of ECB Technology in Paint Waste Gas Treatment

1)ECB process flow

 

 

The total process consists of filtration, plasma discharge section, multi-band optical excitation section, deexcitation and catalytic layer, spray and absorption section. Among them, the plasma discharge section, the multi-band light excitation section, the deexcitation and the catalytic layer constitute the main process (ECB) of the process, and the gas enters through the filter section and is discharged through the spray absorption section.

The plasma discharge section is structurally isolated and does not directly contact with waste gas during design. The air purification and cold drying station are supporting facilities. Fresh cold and dry gas, which accounts for about 1% of the intake air volume, is injected into the reaction chamber with a large amount of excited substances (such as ozone, active oxygen ions, etc.) through the plasma discharge section.

How ECB works:

ECB refers to excitation-catalysis-deexcitation (exitation-catalysis-back). The so-called excitation means that after atoms or molecules absorb energy, some electrons in the outer layer are in a higher energy state, and their chemical reaction activity is completely activated. Although it is not yet in an ionized state, as long as it collides with other atoms or molecules, a chemical reaction will occur. For example, inert substances such as helium, neon, argon, xenon, etc., do not react with other substances under normal conditions, but react as long as they are in an excited state. It can be seen that the chemical activity of excited substances is high.

The high-energy ion generation section produces a large number of intermediate molecules, such as ozone, active oxygen atoms, etc., through the "three-intersection" discharge. Because the diffusion coefficient of ozone is very large, it immediately mixes with the exhaust gas and enters the multi-band light excitation section; this section consists of a variety of ultraviolet rays to meet the resonance absorption requirements of different exhaust gas components. Various exhaust gas components, oxidation components in this section of the chemical reaction and in a dynamic process. The core of the deexcitation and catalytic layer is an adsorbent, which adsorbs and catalyzes the reaction of various excited active substances, and then automatically desorbs and desorbs after becoming low-energy molecules.

The spray absorption section is a secondary quiet mechanism to ensure that various components in the exhaust gas meet the emission standards. The absorption liquid adopts a special deodorizing spray liquid, which can not only wet the particulate matter, but also absorb the odor molecules instantaneously.

2) Stereogram of host structure

 

3) Technical advantages

Filter part

① Coarse filtration: G3 grade glass fiber filter layer is used to remove large particles, paint mist, etc.

② Fine filtration: F7 grade glass fiber filter layer is used to remove small particles.

Long running time, low cost; do not need frequent replacement.

The paint mist particles, powder recovery processing is simple, will not cause secondary pollution.

⑤ The storage volume is 5.6% of the use volume, which is convenient for transportation and storage.

The flat type (suction type) or vertical type (side suction type) can be used.

⑦ Wind speed: 0.3~1.0 m/s, dust holding capacity: 6~28 ㎏/㎡, filtration efficiency: 95~99.5.

⑧ In the front of the induced draft fan with air volume regulating valve to adjust the wind speed, can improve the filtering effect and save paint.

⑨ Operation and maintenance: The filter components need to be replaced regularly. The replacement cycle depends on various factors such as net dust load, use time, paint mist concentration, etc. Therefore, the replacement cycle needs to be determined according to the site conditions. Usually 4 to 8 months. The replacement parts generally do not require in-depth treatment, and can be used continuously after directly beating and removing dust, and the damaged parts can be discarded directly.

 

Host ECB Technology

①High cost performance: low one-time investment, large air volume, small footprint and long service life;

The purification effect is good: the odor removal efficiency can reach more than 99%, and the removal rate of "triphenyl" and non-methane total hydrocarbons can meet the requirements of the GB16927-1996 "Comprehensive Emission Standard of Air Pollutants;

Simple structure: no special pretreatment, such as heating, humidification, etc., the working environment temperature of the equipment is normal temperature;

4 wide range of application: can remove all kinds of common odor, can be applied to different concentration range, atmospheric, different odor gas deodorization purification treatment;

⑤ Low operating cost: low energy consumption of the equipment, extremely low wind resistance of the equipment <80pa, no need for special management and daily maintenance;

⑥ Safety and environmental protection: the toxic and harmful substances in the paint exhaust gas are completely decomposed to achieve harmless emission without secondary pollution;

Catalytic section

① strong ability to withstand impact, can adapt to the working characteristics of the spray booth.

Special catalyst, strong adsorption performance.

The replacement cycle is increased by more than 10 times to reduce operating costs.

Spray absorption section

① Filler spray, high speed, small size, low requirements for water mist equipment.

Add a transient reaction deodorant, immediately deodorant.

4) 3D drawing of spray paint waste gas treatment system