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Introduction to the Technical System of VOCs Pollution Prevention and Control


Time:

2022-08-03

The technical system of VOCs pollution prevention and control mainly includes four parts: source substitution, process control, end treatment, and fine control.

The technical system of VOCs pollution prevention and control mainly includes four parts: source substitution, process control, end treatment, and fine control.

 

◉ Source Substitute Materials for VOCs Raw and Auxiliary Materials

(1) Petrochemical/Chemical Industry

Use raw and auxiliary materials with low (no) VOCs content and low reactivity to accelerate the green replacement of aromatic hydrocarbons and halogen-containing organic compounds.

(2) Packaging and Printing Industry

Water-based, radiation-curable, plant-based inks with low VOCs content can be selected.

Adhesives with low VOCs content such as water-based, hot-melt, solvent-free, radiation curing, modification, and biodegradation can be selected.

Cleaners with low VOCs content and low reactivity can be selected.

(3) Industrial Coating Industry

Water-based, powder, high-solids, solvent-free, radiation-cured and other low-VOCs coatings are available.

 

◉ Technical Standard for Low Volatile VOCs Material Products

The currently published product technical requirements for low volatility raw and auxiliary materials include:

Ministry of Ecology and Environment: "Technical Requirements for Environmental Labeling Products Waterborne Coatings" (HJ 2537-2014), "Technical Requirements for Environmental Labeling Products Gravure Inks and Flexo Printing Inks" (HJ 371-2018), "Technical Requirements for Environmental Labeling Products Offset Printing Inks" (HJ/T 370—2007), “Technical Requirements for Environmental Labeling Products Adhesives” (HJ 2541—2016), “Household Detergents for Environmental Labeling Products Technical Requirements” (HJ 458—2009).

Ministry of Industry and Information Technology: "Water-based Liquid Diatom Coatings for Interior Walls" (HG/T 5172—2017), "Water-based Primers for Rusty Coatings" (HG/T 5173—2017), "Decorative Uses for Glass and Ceramic Products" Waterborne Coatings (HG/T 5175—2017), Waterborne Coatings for Automotive Plastic Parts (HG/T 5180—2017), Waterborne Ultraviolet (UV) Curing Wood Coatings (HG/T 5183—2017).

 

◉ Explanation of Proper Nouns

Radiation Curing
Radiation curing is a process in which chemically formulated substances (coatings, inks and adhesives) are converted from liquid to solid by means of energy irradiation.

The practical application of radiation curing technology can be traced back to the 1960s, when Germany introduced the first generation of UV coatings (UV coatings refer to coatings that are cured by UV radiation. UV-curable coatings can be applied to ink printing and exposed to UV radiation. Its The solid content can be as high as 100%, so there are no volatile components and no pollution to the environment. The high solid content also enables the application of very thin films. UV-curable coatings can also be used to coat glass and plastic, wood, and aluminum beverage bottles etc.), has been initially applied in the wood coating industry. Later, radiation curing technology gradually expanded from a single substrate of wood to the coating application of paper, various plastics, metals, stone, and even cement products, fabrics, leather and other substrates. The appearance of processed products has also developed from the initial high-gloss type to matt type, pearl type, bronzing type, texture type and so on.

The energy source for radiation curing can be infrared (IR), ultraviolet (UV), electron beam (EB), and the like.

 

High Solids Coatings

High solids coatings refer to solvent-based coatings that have a much lower solvent content than conventional coatings. Generally refers to solvent-based coatings with a solid content of 60% to 80% by mass. In practice, different regions, different industries, and different departments have different definitions of high solids content.

According to the "Comprehensive Catalogue of Environmental Protection (2017)", for automotive coatings, high solids are defined as "more than 65% solids for mid-coat construction, more than 60% for monochrome paint construction, and more than 60% for flash paint construction. 45%, varnish construction solids must be higher than 55%”.

According to a document issued by the Wire and Cable Branch of China Electrical Equipment Industry Association in 2015, "At present, the internationally recognized maximum solid content of enameled wire products is about 50%, and at the same time, there is no mature alternative product."

According to "Limits of Hazardous Substances in Architectural Exterior Wall Coatings" (GB24408-2009), the national standard requirement for high solid content is > 30%.

 

 

◉ ntroduction of Advanced Technology for VOCs Emission Reduction

At present, it is mainly through the use of fully enclosed, continuous, automated and other production technologies, as well as high-efficiency process equipment, to effectively reduce fugitive emissions in the process.

Volatile organic liquid loading is preferably bottom loading.

The petrochemical and chemical industries focus on promoting the use of low (no) leakage pumps, compressors, filters, centrifuges, drying equipment, etc., and popularize the use of online oil blending technology and closed circulating water cooling systems.

The industrial coating industry focuses on promoting the use of compact coating processes, promoting the use of roller coating, electrostatic spraying, high-pressure airless spraying, air-assisted airless spraying, thermal spraying and other coating technologies, and encouraging enterprises to use automated and intelligent spraying equipment to replace manual labor Spray, reduce the use of air spray technology.

The packaging and printing industry vigorously promotes the use of solvent-free lamination, extrusion lamination, and co-extrusion lamination technology, and encourages the use of water-based gravure printing, alcohol-water gravure printing, radiation curing gravure printing, flexographic printing, and water-free offset printing.

 

 

◉ Improve VOCs Waste Gas Collection Rate

Following the principle of "collecting as much as possible and collecting by quality", the waste gas collection system is scientifically designed to convert unorganized emissions into organized emissions for control.

If a fully closed gas collecting hood or closed space is used, unless the industry has special requirements, a slightly negative pressure state should be maintained, and the ventilation volume should be reasonably set according to relevant specifications.

If a partial gas collecting hood is adopted, the unorganized emission position of VOCs farthest from the opening surface of the gas collecting hood shall control the wind speed of not less than 0.3 m/s, and the relevant regulations shall be implemented if there are industry requirements.

 

◉ VOCs Terminal Treatment Technology

For low-concentration and high-air volume exhaust gas, concentration technologies such as activated carbon adsorption, zeolite rotor adsorption, and air reduction and concentration should be used to increase the concentration of VOCs and then purify them;

For high-concentration waste gas, priority should be given to solvent recovery. If it is difficult to recover, high-temperature incineration, catalytic combustion and other technologies should be used;

Oil and gas (solvent) recovery should adopt technologies such as condensation + adsorption, adsorption + absorption, membrane separation + adsorption;

Photocatalysis and photooxidation technology are mainly suitable for the treatment of odor and odor;

Low-temperature plasma and biological methods are mainly suitable for low-concentration VOCs waste gas treatment and odor treatment;

Water-insoluble VOCs waste gas is prohibited from being sprayed and absorbed by water or aqueous solution;

If the one-time activated carbon adsorption technology is adopted, the activated carbon should be replaced regularly, and the waste activated carbon should be regenerated or disposed of;

Conditioned industrial parks and industrial clusters, etc., promote centralized spraying, centralized solvent recovery, and centralized regeneration of activated carbon, etc., to strengthen resource sharing and improve the efficiency of VOCs treatment.

 

◉ Corresponding Technical Specifications for End Treatment Devices

As of June 2020, the Ministry of Ecology and Environment has formulated engineering technical specifications for 3 commonly used terminal treatment devices. They are:
"Technical Specification for Industrial Organic Waste Gas Treatment Engineering by Adsorption Method" (HJ 2026—2013)

"Technical Specification for Industrial Organic Waste Gas Treatment Engineering by Catalytic Combustion Method" (HJ 2027—2013)

"Technical Specification for Industrial Organic Waste Gas Treatment Engineering by Regenerative Combustion Method" (HJ 1093-2020)

 

Safety Precautions for the Operation and Maintenance of Adsorption Equipment

1. In addition to the adsorption and recovery of organic waste gas from the solvent and oil and gas storage, transportation and sales devices, the concentration of organic matter in the organic waste gas entering the adsorption device should be lower than 25% of the lower limit of the explosion limit. When the concentration of organic matter in the exhaust gas is higher than 25% of the lower limit of the explosion limit, it should be reduced to 25% of the lower limit of the explosion limit before adsorption purification can be carried out.

2. The content of particulate matter entering the adsorption device should be less than 1mg/m3.

3. The temperature of the exhaust gas entering the adsorption device should be lower than 40℃.

4. During the adsorption operation period, the temperature in the adsorption bed after adsorbing the organic gas should be lower than 83 ℃. When the temperature in the adsorption device exceeds 83°C, it should be able to automatically alarm and start the cooling device immediately.

 

Safety Precautions for Operation and Maintenance of Catalytic Combustion Units

1. Concentration dilution facilities should be set up before the exhaust fan. When the reactor outlet temperature reaches 600 ℃, the control system should be able to alarm, and automatically open the dilution facility to dilute the waste gas.

2. Catalytic combustion or high temperature combustion device should have overheat protection function.

3. The catalytic combustion or high temperature combustion device should be insulated as a whole, and the outer surface temperature should be lower than 60℃.

4. The concentration of organic matter in the exhaust gas entering the catalytic combustion device should be lower than 25% of the lower limit of its explosion limit. When the concentration of organic matter in the exhaust gas is higher than 25% of the lower limit of the explosion limit, it should be reduced to 25% of the lower limit of the explosion limit through pretreatment processes such as supplemental gas dilution before catalytic combustion treatment can be carried out.

 

Safety Precautions for Operation and Maintenance of Regenerative Combustion Device

1. When the concentration of exhaust gas fluctuates greatly, real-time monitoring of exhaust gas should be carried out, and measures such as dilution and buffering should be taken to ensure that the concentration of exhaust gas entering the regenerative combustion device is lower than 25% of the lower limit of the explosion limit.

2. A flame arrester or fire damper should be installed in the piping system between the treatment project and the main production process equipment. The flame arrester should comply with the relevant regulations of GB/T13347-2010, and the fire damper should comply with the relevant regulations of GB15930-2007.

3. When the air inlet and exhaust pipes of the treatment project are made of metal, measures such as flange jumper connection and system grounding should be taken to prevent the generation and accumulation of static electricity.

4. When the gas temperature of the pipeline exceeds 60℃ or the temperature of the accessible parts on the surface of the regenerative combustion device is higher than 60℃, thermal insulation protection or relevant warning signs shall be provided, and the thermal insulation design shall comply with the relevant regulations of SGBZ-0805.

5. The fuel supply system should be equipped with high and low pressure protection and leakage alarm devices.

6. The compressed air system should be equipped with high and low pressure protection and leakage alarm devices.

 

 

 

Attachment: Case Study on Investment and Operating Costs of Common VOCs Technologies (for reference only)

According to the survey, the current mainstream organic waste gas treatment technologies include adsorption (fixed bed adsorption, fluidized bed adsorption), absorption, condensation, combustion (thermal combustion, catalytic combustion), etc. The investment costs of typical exhaust gas treatment technology application cases that can achieve standard emissions are given below.

(1) Regenerative Combustion Technology

A color printing enterprise uses the technology of "reduced air and increased concentration + RTO (regenerative combustion)" technology to treat exhaust gas from 3 printing machines and 2 dry compound machines. The total investment cost of construction investment is 3.469 million yuan. The NMHC concentration at the exhaust gas inlet is 781.94~1226.02 mg/m3, the RTO purification efficiency is 98.4~99.5%, and the exhaust gas emission NMHC concentration is 7.65~21.12 mg/m3. The operating cost of the terminal treatment facilities is 188,000 yuan/year, and the energy-saving benefit is 1.772 million yuan/year.

(2) Photocatalytic Oxidation (UV) + Adsorption Technology

A plastic products company used 2 sets of "photocatalytic oxidation (UV) + adsorption technology" to control the organic waste gas generated by the injection molding process of 24 injection molding machines. The designed air volume is 6000 m³/h. Among them, the photocatalytic oxidation devices are designed with 30 sets of lamps, and the exhaust gas residence time is 2s; the activated carbon adsorption facilities are designed with exhaust gas residence time of 4.7s, filtration speed of 0.4m/s, and total activated carbon capacity of 4.5 m3. After testing, the removal efficiency of non-methane total hydrocarbons is over 90%, the NMHC concentration in the exhaust gas is less than 1.5 mg/m3, the total investment and installation cost of the equipment is about 400,000 yuan, and the operating cost is 1,800 yuan/day.

(3) Spray Washing + Electrostatic Adsorption Technology

A textile printing and dyeing enterprise uses "spray washing + electrostatic adsorption technology" to treat the waste gas generated during the high temperature setting machine treatment process. The design air volume of the shaping machine is 1500 m3/h. After monitoring, the concentration of NMHC in the exhaust gas at the outlet of the exhaust gas treatment facility is 0.044~0.121 mg/m3, and the annual operation and maintenance cost of each facility (mainly electricity) is about 55,000 yuan.

(4) Adsorption + Condensation Recovery Technology

A packaging and printing enterprise uses 2 sets of "activated carbon adsorption + condensation recovery" treatment facilities for waste gas treatment. The total designed treatment air volume of the treatment facilities is 64,000 m3/h. The comprehensive design treatment efficiency of the treatment facility is above 93%. After treatment, the emission concentration of "total VOCs" is 22.1~46.5mg/m3. The total equipment investment and installation cost is about 3.4 million yuan, and the operating cost is mainly electricity, which is about 150,000 yuan / year.

(5) Regenerative Catalytic Combustion Technology

A synthetic leather manufacturing enterprise adopts rotary regenerative catalytic technology (RCO) to purify and dry organic waste gas. The concentration of VOCs at the outlet of the system can meet the requirements of emission standards, and the purification efficiency of VOCs can reach more than 98%. The total investment cost of the equipment is about 1.7 million yuan, and the annual operating cost is about 171,000 yuan.

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