The overall solution of VOCs exhaust gas for small, medium and micro enterprises in the coating industry!

With the rapid development of the coating industry in my country, the group of small, medium and micro enterprises is growing.
Due to the small scale of the enterprise and the extensive production methods, the printing and spraying are generally based on open manual operations, the pollution control level is not high, and the fugitive emissions are serious.
Environmental problems caused by the resulting volatile organic compounds (VOCs) have also received increasing attention.
In order to implement the "Notice of the Ministry of Industry and Information Technology and the Ministry of Finance on Printing and Distributing the Action Plan for Reduction of Volatile Organic Compounds in Key Industries" (Gongxin Ministry Lianjie [2016] No.
217), to effectively reduce the total emissions of volatile organic compounds in printing, packaging, coating and other industries , Combined with the Jiangsu Province "Surface Coating (Furniture Manufacturing) Emission Standard of Volatile Organic Compounds" (DB32/3152-2016) that was implemented in February 2017, and in accordance with the requirements of the Environmental Protection Agency, it is determined that the printing, packaging, coating and other industries Comprehensive rectification of volatile organic compounds.
Aiming at the characteristics of small, medium and micro enterprises, this article implements the requirements of environmental protection governance, combined with actual engineering cases, and proposes an economical and applicable overall solution com" href="http://">coatingol.
com.
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Waste gas source The waste gas in the workshop mainly comes from the spraying and drying process, and the pollutants emitted are mainly: paint mist and organic solvents generated during spraying, and organic solvents generated during drying and volatilization.
The paint mist mainly comes from the scattered parts of the solvent-based paint in the air spraying operation, and its composition is consistent with the paint used.
Organic solvents mainly come from solvents and thinners in the coating process, and most of them are volatile emissions.
The main pollutants are xylene, benzene, toluene, etc.
These ingredients are harmful to human health and living environment, and have a foul smell.
If people inhale low-concentration organic waste gas for a long time, they will cause chronic respiratory diseases such as cough, chest tightness, asthma and even emphysema.
They are currently recognized as strong carcinogens.
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The status quo of the enterprise 2.
1 In terms of economy, due to the small scale of the enterprise, the unstable benefits and the average economic capacity, it cannot bear the high cost of environmental protection equipment.
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2 Process facilities Most companies have simple and backward printing and spraying processes, and mainly rely on open labor.
Most of the inks and coatings used are solvent-based products.
A small number of companies are equipped with dedicated operation areas and waste gas treatment facilities, but the operation areas are not standardized and not closed, the treatment facilities are simple and backward, and the functions are single, which cannot meet the current environmental protection governance requirements, and the site lacks management.
The scattered pollution is more serious and some are dangerous.
The products are not properly placed, and there are certain hidden safety hazards.
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3 Operating conditions Due to the particularity of the machinery industry, most companies cannot form assembly line operations, and most of them are spraying operations in stages.
Through communication with many companies, general operating conditions data are collected, as listed in Table 1.

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The overall solution The overall solution of VOCs waste gas mainly includes four aspects: waste gas emission reduction, waste gas collection, waste gas treatment and management monitoring.
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1 Waste gas emission reduction 3.
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1 Use of clean and environmentally friendly raw materials According to different processes, it is recommended to use environmentally friendly raw materials with low VOCs content to replace the original solvent-based raw materials.
For example, the printing and packaging industry uses water-based, hot-melt, solvent-free, UV-curable, high-solids and biodegradable adhesives, and the ink uses water-based inks, UV inks, gravure inks, radiation curing inks, etc.
; The coating industry chooses green coating products such as water-based coatings, powder coatings, high-solid coatings, solvent-free coatings, UV coatings and so on.
Due to the emergence of environmental protection issues in recent years, the country has vigorously promoted the application of environmentally friendly coatings.
At present, the environmental assessment of new production lines requires the use of environmentally friendly coatings.
Due to the strong applicability and reasonable price of water-based coatings, it has gradually become popular in various coating industries.
Its main component is water, and the solvent content is 10%-25%, which is far lower than solvent-based coatings.
The use of water-based coatings can reduce the emission of VOCs in the exhaust gas from the root cause.
The reference values ​​of VOCs content of various coatings ("Interim Measures for Calculation of Volatile Organic Compound Emissions in Key Industries in Jiangsu Province") are listed in Table 2.

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2 Process improvement and optimization to increase the utilization rate of raw materials.
Encourage enterprises to implement continuous and automatic technological transformation, promote the use of electrostatic spraying, curtain coating, roller coating, dip coating and other coating processes with higher coating efficiency, and promote the use of advanced processes Technology, optimization process and equipment.
In the painting process, paint is often used in the form of spraying, and more paint mist is generated during the spraying process.
Paint mist is the source of particulate matter in the spray exhaust gas.
Therefore, increasing the utilization rate of the coating can greatly reduce the particulate matter in the exhaust gas and reduce the difficulty of exhaust gas treatment.
The coating utilization rates of different spraying methods are listed in Table 3.

It can be seen from Table 3 that only a large-capacity low-pressure air spray gun or electrostatic spraying can meet at least 65% of the paint utilization rate.
In addition, the use of robot spraying can also increase the utilization rate of paint.
At present, the domestic coating industry is implementing internal spray robots, that is, the entire coating line is sprayed to achieve unmanned, all using robot spraying, which greatly improves the utilization of paint rate.
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2 Exhaust gas collection At present, most companies use open-air spraying operations without any waste gas collection facilities, and organic waste gas is directly emitted into the atmosphere.
A small number of companies use gas collecting hoods for waste gas collection.
The general gas collecting hood waste gas collection efficiency is only 30-50%.
The uncollected gas still exists in the atmosphere in an unorganized form, which is far from meeting the requirements for waste gas collection.
Only the collected waste gas can be treated.
Therefore, enterprises are encouraged to implement a closed production process, set up a closed and independent operation area, and be equipped with efficient organic gas collection devices to form a closed negative pressure collection state.
The organic waste gas volatilized in the workshop needs to be concentrated by the exhaust system Exhaust and run synchronously with the production process to prevent open air and open spraying operations.
The workshop should be equipped with good ventilation equipment, and there should be no obvious odor in the space outside the workshop.
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3 Waste gas treatment 3.
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1 Analysis of waste gas treatment technology At present, the recognized treatment technology in the waste gas treatment industry can be divided into recycling technology and destruction technology.
The specific breakdown of the overall VOCs pollution prevention technology is shown in Figure 1.

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1 The absorption method uses low-volatility or non-volatile organic solvents to absorb and treat VOCs.
Due to the addition of organic solvents in the waste gas treatment process, secondary pollution such as mixed solvent wastewater is generated, which does not conform to the concept of clean production and is conventional The machinery companies in China do not have wastewater treatment capabilities, so they are not suitable for the coating industry.
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2 The adsorption method uses solid adsorbents (activated carbon, molecular sieve, etc.
) to adsorb and purify pollutants.
Although the adsorption process is mature, has a certain treatment effect, and the equipment investment is moderate, the adsorbent is a consumable product.
Although the adsorbent regeneration function can be configured, the performance of the adsorbent after regeneration is greatly reduced, and the life is short.
The replaced adsorbent The agent is a hazardous waste and requires additional treatment costs.
Generally, the equipment is relatively large and occupies a lot of land.
Most machinery companies have tight internal land and cannot provide too much space for the waste gas treatment equipment, so they are not suitable for painting.
industry.
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3 Condensation method is to reduce the temperature to convert VOCs waste gas from gaseous to liquid.
Although it can be recovered, its recovery rate is not high, generally only 40-60%, and it is only suitable for high-concentration waste gas pretreatment.
Treatment, so it is not suitable for the coating industry.
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4 Membrane separation method is to use the membrane's ability to selectively penetrate different substances to control VOCs.
The equipment investment is relatively high, and the membrane's selective ability has certain limitations, so it is not suitable for the coating industry.
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5 Combustion method and activated carbon adsorption/zeolite rotor adsorption+RTO/RCO is currently recognized as the most thorough technology for VOCs treatment, but its equipment investment is high, usually ranging from 1 to 5 million, and the equipment occupies a relatively large area.
Large, far beyond the economic range of small, medium and micro enterprises, so it is not suitable for small, medium and micro enterprises.
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6 Biological method uses microbial metabolism to degrade VOCs.
The process of converting it into harmless small molecular substances.
Because biological strains have strong specificity in the digestion of organic matter, they are more sensitive to environmental conditions, and a large amount of excreta will be produced during the degradation process, causing solid waste pollution.
, The overall equipment occupies a large area, so it is not suitable for small, medium and micro enterprises.
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7 Low-temperature plasma technology uses plasma with extremely high temperature generated by dielectric discharge to repeatedly bombard gas molecules in the exhaust gas at a very fast speed, deactivate, ionize, and crack various components in the exhaust gas, through a series of complex oxidations, etc.
The chemical reaction of the complex macromolecular pollutants into some small molecules of safe substances (such as carbon dioxide and water), or the toxic and harmful substances into non-toxic, harmless or low-toxic and low-harm substances.
Although this technology has high VOCs removal efficiency, its plasma temperature is high, and there are great safety hazards when dealing with flammable and explosive volatile organic compounds.
Therefore, the Tianjin Municipal Work Safety Supervision Bureau issued the "On learning from accidents and carrying out special safety measures for environmental protection facilities" In the "Notice of Inspection", the official banned the low-temperature plasma technology for the first time.
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8 UV photolysis technology uses high-energy UV ultraviolet rays to crack organic gas molecules, break chemical bonds, and form free atoms or groups (C*, H*, O*, etc.
).
At the same time, the oxygen in the mixed gas is UV light cracks to form free oxygen atoms and combines to produce ozone [UVO2→OO*(active oxygen) O*O2→O3(ozone)]; water vapor in the mixed gas is cracked by ultraviolet light to produce hydroxyl groups [UVH2O→HOH-(hydroxyl group) )], and these generated ozone and hydroxyl have strong oxidizing properties, which can oxidize the atoms and groups generated by the cleavage of exhaust gas molecules into pollution-free low-molecular compounds such as H2O and CO2.
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2 Overall plan Develop the existing complete set of waste gas collection and treatment equipment.
The waste gas collection efficiency of the whole set of equipment is more than 90%, the waste gas treatment efficiency is more than 95%, and the waste gas emission meets the current emission standards.
Fully consider the actual situation of small, medium and micro enterprises, the equipment price is economical and reasonable, the safety is high, the area is small, the adaptability is low, the operating cost is low, and the daily maintenance is simple and convenient.
The whole set of equipment is composed of ALF-PF airtight spray booth, ALF-AH dust removal filter, ALF-UV photolysis, ALF-AC activated carbon adsorption, pipelines, and fans.
8UV photolysis technology uses high-energy UV ultraviolet rays to crack organic gas molecules and break chemical bonds to form free atoms or groups (C*, H*, O*, etc.
).
At the same time, the oxygen in the mixed gas is cracked by ultraviolet light.
Free oxygen atoms are formed and combined to generate ozone [UVO2→OO*(active oxygen) O*O2→O3(ozone)]; water vapor in the mixed gas is split by ultraviolet light to produce hydroxyl groups [UVH2O→HOH-(hydroxyl)], These generated ozone and hydroxyl have strong oxidizing properties, and can oxidize the atoms and groups produced by the cleavage of exhaust gas molecules into non-polluting low-molecular compounds such as H2O and CO2.
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2 Overall plan Develop the existing complete set of waste gas collection and treatment equipment.
The waste gas collection efficiency of the whole set of equipment is more than 90%, the waste gas treatment efficiency is more than 95%, and the waste gas emission meets the current emission standards.
Fully consider the actual situation of small, medium and micro enterprises, the equipment price is economical and reasonable, the safety is high, the area is small, the adaptability is low, the operating cost is low, and the daily maintenance is simple and convenient.
The whole set of equipment is composed of ALF-PF airtight spray booth, ALF-AH dust removal filter, ALF-UV photolysis, ALF-AC activated carbon adsorption, pipelines, and fans.
8UV photolysis technology uses high-energy UV ultraviolet rays to crack organic gas molecules, break chemical bonds, and form free atoms or groups (C*, H*, O*, etc.
).
At the same time, the oxygen in the mixed gas is cracked by ultraviolet light.
Free oxygen atoms are formed and combined to generate ozone [UVO2→OO*(active oxygen) O*O2→O3(ozone)]; water vapor in the mixed gas is split by ultraviolet light to produce hydroxyl groups [UVH2O→HOH-(hydroxyl)], These generated ozone and hydroxyl have strong oxidizing properties, which can oxidize the atoms and groups produced by the cleavage of exhaust gas molecules into non-polluting low-molecular compounds such as H2O and CO2.
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2 Overall plan Develop the existing complete set of waste gas collection and treatment equipment.
The waste gas collection efficiency of the whole set of equipment is more than 90%, the waste gas treatment efficiency is more than 95%, and the waste gas emission meets the current emission standards.
Fully consider the actual situation of small, medium and micro enterprises, the equipment price is economical and reasonable, the safety is high, the area is small, the adaptability is low, the operating cost is low, and the daily maintenance is simple and convenient.
The whole set of equipment is composed of ALF-PF airtight spray booth, ALF-AH dust removal filter, ALF-UV photolysis, ALF-AC activated carbon adsorption, pipelines, and fans.

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In response to this situation, it is recommended to use water-based paints that do not contain benzene components to control the amount of volatile organic compounds produced from the source.

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