What are the good technical processes for VOC control?

VOC waste gas treatment is mainly volatile organic compounds, the main components of VOC are: hydrocarbons, halogenated hydrocarbons, oxygen hydrocarbons and nitrogen hydrocarbons, it includes: benzene series, organic chlorides, Freon series, organic ketones, amines, alcohols, ethers, esters, acids and petroleum hydrocarbon compounds.

VOC is the English abbreviation of volatile organic compounds, and the chemicals (except heavy metals) that are harmful to the human body in wall paint are commonly referred to as VOCs. These volatile organic compounds include formaldehyde, ammonia, ethylene glycol, esters, and other substances. Treatment process:

Active adsorption method, induced air high-altitude emission method, combustion treatment method, absorption and degassing method, condensate collection method, etcBiological treatment method - microbial treatment biological method and micro DM microbial organic waste gas treatment integrated system, using alternative HAP solvent methods, etc.

The commonly used methods of VOC treatment include thermal destruction method, adsorption method, biological treatment method, pressure swing adsorption separation and purification technology, oxidation method, liquid absorption method, and condensation method, among which VOC adsorption device is a relatively scientific and environmentally friendly method at present.

Absorption method, condensation method, adsorption method, biological method, plasma method, etc.

1. Legislative control.

Following sulfur oxides, nitrogen oxides and freon, the pollution of volatile organic compounds has become the focus of attention of countries around the world, and developed countries and regions have continuously revised their laws to repeatedly reduce the emission concentration of VOCs.

In 1990, the United States amended the Air Pollution Law to stipulate 189 VOCs emission standards, in 2002 Japan's Odor Prevention and Control Law stipulated 149 VOCs emission standards, and the European Economic Community also established a unified emission standard for VOCs within the community in 1994, and required countries that have not yet enacted legislation to legislate within a time limit.

Due to the above reasons, the development of VOCs treatment technology and devices abroad is very fast. China's "Comprehensive Emission Standard for Air Pollutants" (GB16297--2004) and "Odor Pollutant Emission Standard" (GB14554--1993) limit the emission standards of more than ten kinds of VOCs.

2. Technical control.

There are many types of organic waste gases, often with complex compositions and irregular changes in concentration, which brings difficulties to the treatment. In recent years, there have been more and more complaints about industrial waste gas pollution from residents in residential areas. Therefore, it is urgent to find an effective treatment technology for this kind of waste gas.

After entering the 21st century, due to the further aggravation of regional atmospheric pollution in China and the deterioration of environmental quality, the state and local governments have increased investment in environmental legislation and technology research and development, and the treatment of organic waste gas from stationary sources in China has entered a stage of rapid development. Since the "Eleventh Five-Year Plan", the national and local departments have significantly increased the research and development of organic waste gas treatment technology, and promoted the research and development and application of new technologies and new materials.

VOCs (volatile organic compounds) waste gas treatment processes are mainly as follows:

Adsorption technology: Activated carbon, molecular sieves and other adsorbents are used to adsorb VOCs on the solid surface to achieve the purpose of removing VOCs in exhaust gas.

Combustion technology: VOCs are mixed with air, ignited for combustion, and VOCs are converted into harmless substances such as CO2 and water.

Biotechnology: Biodegradation methods are used to convert VOCs into harmless substances such as CO2, water, and inorganic salts using microbial starvation.

Condensing technology: The purpose of removing VOCs is achieved by reducing the temperature of the exhaust gas to change the VOCs from gaseous to liquid state.

Membrane separation and branch closure technology: use the microporous or selective permeability of the membrane to separate VOCs and achieve the purpose of removing VOCs.

Plasma technology: Uses a chemical reaction generated by the isolimb laughing child to convert VOCs into harmless substances.

Other technologies: such as oxidation technology, catalytic technology, etc.

VOC waste gas treatment process methods include: spray + plasma, spray + UV photolysis, spray + photolysis plasma, microbial method, RCO combustion method, concentration method. In the practical engineering application, the microbial method can be considered for the place with small gas volume and low concentration.

For waste gas with flammable properties, it is generally recommended to use spray pretreatment and then other treatment processes.

Advantages and disadvantages of various processes for VOC waste gas treatment:

1. Spray + plasma.

The core principle adopted is plasma field decomposition, which has the following advantages: the equipment occupies a small area and is mainly aimed at low concentrations; Disadvantages: There are certain safety hazards, and the purification effect is unstable.

2. Spray + UV photolysis.

The core principle adopted is ozone decomposition, which has the advantages: high purification effect, stable treatment effect, mainly for medium and low concentrations; Disadvantages: Oxidation residence time needs to be controlled.

3. Spray + photolysis plasma.

The core principle adopted is composite ozone and plasma, which has the following advantages: high purification efficiency, mainly for medium concentrations; Disadvantages: There are certain safety risks.

4. Microbial method.

The core principle adopted is biodegradation, which has the advantages: no secondary pollution, and low energy consumption of the equipment; Disadvantages: high operation requirements, large volume of equipment, need to replenish microorganisms regularly, high maintenance costs.

5. RCO combustion method.

The core principle adopted is high-temperature combustion, which has the advantages: mainly for high-concentration organic waste gas, and the pollutant components are completely decomposed; Disadvantages: high energy consumption, high operation requirements, large equipment volume, and certain safety hazards.

6. Concentration method.

The core principle adopted is extraction and concentration, and the advantages: mainly for the single composition of the exhaust gas, the composition with the value of Qiyou, and the economic benefits; Disadvantages: High operability requirements.

In practical engineering application, microbial method can be considered for places with small gas volume and low concentration. For waste gas with flammable properties, it is generally recommended to use spray pretreatment and then other treatment processes.

"VOCs emission reduction technologies include: adsorption method, absorption method, condensation method, membrane separation method, catalytic combustion method, thermal combustion method, biological method, plasma method, and photocatalytic method.

In general, abatement technologies include adsorption capture, dissociation and conversion, or adsorption and conversion mixture. The adsorption trap method is mainly based on adsorbent materials, using high surface area and pore volume to capture low concentrations of VOCs in the gas stream. Activated carbon, zeolite, and silica are rugged, well-established adsorbents that have been shown to be particularly effective at adsorbing a wide range of VOCs.

Activated carbon is a treated carbon with small volume pores and a high surface area, making it suitable for the adsorption of VOCs. Zeolites are microporous aluminosilicate minerals with a defined pore structure and tunable acidity, making them highly attractive adsorbents or catalysts for molecules of certain sizes and shapes. Newer materials include metal-organic frameworks (MOFs), which have become viable materials for VOC capture.

They are composed of metal ions that coordinate with organic ligands and form one-, two- or three-dimensional structures. Their high adsorption capacity and excellent surface area make them particularly suitable for VOCs capture.

Conversion methods (e.g., thermocatalytic oxidation, photocatalytic oxidation, low-temperature plasma technology) can be severely affected by catalytic performance. Catalysts are essential to ensure that these methods of destruction operate effectively. They reduce the activation energy required for thermocatalytic oxidation and photocatalytic oxidation, providing cost-effective and safer reaction conditions.

Commonly used catalysts include *** and mixed metal oxides and perovskites. It has been widely reported that ***-based catalysts have the highest VOC removal activity at low temperatures. Mixed metal oxide catalysts (MMOs) are less expensive to manufacture and prevent degradation of active materials.

The MMOs work in synergy, with one metal oxide acting as the active material and the other metal acting as a carrier. The use of MMOs (e.g., NiO2 SiO2, Mno2 SiO2, TiO2 SiO2 and Zro2 SiO2) showed better catalyst performance compared to single metal oxides (e.g., SiO2 and TiO2) for the oxidation of VOCs. Perovskites are perovskite minerals composed mainly of calcium titanate (catio3).

Many different cations can be embedded in perovskites, increasing their thermal stability and activity.

According to the industry, exhaust gases can be roughly divided into the following categories:

1. Spray paint VOCs treatment: the main components are acetone, xylene, butanol, toluene, ethyl acetate and butyl acetate and other volatile organic compounds.

2. Plastic and plastic VOCs control: The main reason for the production of plastic waste gas is the polymer monomer volatilized by plastic and other particles after being heated.

3. Chemical waste gas VOCs treatment: some chemical enterprises will produce some industrial waste gas due to the needs of production.

4. Pharmaceutical VOCs treatment: the waste gas of the pharmaceutical industry is more complex, the process of different products is quite different, and there are different conditions between the same products.

5. Packaging and printing waste gas: the use of a large number of solvent-based raw and auxiliary materials will be involved in the printing and pre-press and post-press processes.

Prospective Industry Research Institute pointed out that in addition to the above-mentioned types of waste gas, there are also stereotyped waste gases produced in the chemical fiber industry, rubber tire industry, etc., each type of waste gas because of different reasons and different components, so the VOCs treatment methods that need to be taken are not the same, and in order to achieve the best treatment effect, it is very important to choose the appropriate treatment method.

Different industries will produce VOCs, the main industries include: catering industry (Beijing's catering industry has restrictions on oil fume, particulate matter, and non-methane total hydrocarbon emission standards, which is the most detailed and strictest city in the country; Furniture manufacturing industry (Guangdong is the first city to formulate volatile organic compounds emission standards for the industry, followed by Tianjin and Beijing), packaging and printing industry (not only benzene, toluene, xylene, non-methane total hydrocarbons 4 basic pollutant indicators of emission concentration and emission rate have been limited, Beijing, Tianjin, Hebei, Guangdong and other 4 places will set the total concentration of toluene + xylene as a limiting index, instead of a single toluene and xylene emission concentration limit, operability and practicability are stronger), Footwear industry (according to the needs of local environmental management, only Zhejiang, Guangdong, Fujian three regions have separately formulated the provincial and municipal volatile organic compounds emission standards for the footwear industry, and more stringent than the national standards, the limited types of volatile organic pollutants are more, more detailed, more comprehensive), the electronics industry (only Beijing, Tianjin, Shaanxi, Sichuan and other four regions have separately formulated the emission standards of the electronics industry in their provinces and cities according to the needs of local environmental management, and compared with the The comprehensive emission standard for air pollutants (GB16297-1996) is more stringent), etc.