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Summary of VOCs Pollution Prevention and Control Technology
Origin：Hefan Hit： Time：2019-09-14
VOCs (volatile organic compounds) is a general term for a class of chemical substances, with high vapor content at room temperature and pressure. VOCs in current Chinese standards refer to all organic compounds with vapor pressure greater than or equal to 0.01 kPa at 20 (?) C, or with volatility under specific applicable conditions, or with volatility under specific applicable conditions.
VOCs are composed of alkanes, olefins, aromatic hydrocarbons, halogenated hydrocarbons, oxygenated hydrocarbons, nitrogen hydrocarbons, sulfur hydrocarbons, low boiling point polycyclic aromatic hydrocarbons and so on. The common VOCs are toluene Toluene, Xylene, Para-dichlorobenzene, Ethyl benzene, Styrene, Formaldehyde and Acetaldehyde.
Sources of VOCs
The sources of VOCs emission can be divided into natural and man-made sources. On the global scale, VOCs emissions are mainly from natural sources, but for key regions and cities, anthropogenic emissions are much higher than natural sources, which is 6-18 times higher than natural sources.
In cities, the natural sources of VOCs are mainly green vegetation, which are basically uncontrollable sources, while the anthropogenic sources mainly include incomplete combustion behavior, solvent use, industrial processes, oil volatilization and biological effects. At present, VOCs emissions in China mainly come from fixed-source combustion, the use of road traffic solvents and industrial processes. Among many anthropogenic sources, industrial sources are the main sources of VOCs pollution, which have the characteristics of concentrated emission, high emission intensity, high concentration and complex components.
II. VOCs Prevention and Control Technology
According to the principle of VOCs generation in atmosphere and the physical and chemical properties of VOCs, the control technology can be divided into two categories: process control and end control. Process control is aimed at the production process of VOCs. It reduces the generation of VOCs from the principle of VOCs. It is generally realized through process upgrading, technological transformation and leakage control. End control is aimed at the chemical characteristics of VOCs, focusing on the treatment of VOCs exhaust gas, using combustion, decomposition and other methods to control VOCs emissions.
Path Classification of VOCs Control Technology
1. Common prevention and control techniques
VOCs pollution control technology generally includes: recovery technology and destruction technology. Recycling technology mainly includes adsorption technology, absorption technology, condensation technology, membrane separation technology, etc. Destruction technology mainly includes catalytic combustion, biodegradation, plasma, photocatalytic technology and so on. Following is a review of some pollution control technologies.
VOCs Recovery Technology
1: Adsorption Technology
Principle: Use adsorbents and pollutants (VOCs) for physical or chemical reactions and removal of contaminants.
Scope of application: Purification of VOCs with medium and low concentration.
Advantages: High removal efficiency, easy to automate control.
Disadvantage: It is not suitable for high concentration and high temperature organic waste gas, and the adsorbent material needs to be replaced regularly.
2: Absorption Technology
Principle: VOCs are removed from the exhaust gas by contact with the washing liquid, and then neutralized, oxidized or destroyed by chemical agents.
Scope of application: VOCs with high water solubility are not suitable for low concentration gases.
Advantages: mature technology, removal of gaseous and particulate matter, low investment cost, small space occupation, high mass transfer efficiency, and efficient removal of acid gas.
Disadvantages: follow-up wastewater treatment problems, high particulate matter concentration, tower blockage, high maintenance costs, may emit white smoke.
3: Condensation Technology
Principle: Condensation will cool the exhaust gas below the dew point of VOCs component, and make it condense into liquid state, then recycle it.
Scope of application: It is mostly used for the treatment of VOCs with high concentration and recovery value of single component. The treatment cost is high, so the VOCs concentration (> 5000ppm) is usually suitable for condensation treatment, and its efficiency is between 50% and 85%. When the VOCs concentration (> 1%, the recovery efficiency can reach more than 90%. Condensation is often combined with other control technologies, such as incineration, adsorption, washing, etc. as pretreatment steps.
Advantages: The exhaust gas can be purified to a high degree.
Disadvantages: high cooling temperature and pressure requirements; relatively high treatment costs.
4: Membrane Separation Technology
Principle: Separation of VOCs by synthetic membranes.
Scope of application: High concentration VOCs, recovery efficiency is higher than 97%.
Advantages: recoverable components; high efficiency; integration of other technologies.
Disadvantages: high cost; membrane fouling; poor stability of membrane; low flux.
VOCs Destruction Technology
1: Catalytic combustion technology
Principle: A series of decomposition, polymerization and free radical reactions occur, through oxidation and pyrolysis, thermal decomposition, the final product is water, carbon dioxide and other non-toxic and harmless substances.
Scope of application: It can be applied to the treatment of high and low concentration organic waste gases.
Advantages: wide application, simple equipment, less investment, easy operation and thorough purification.
Disadvantage: The equipment composition and operation cost are relatively high.
2: Biodegradation Technology
Principle: Using microorganisms to digest and metabolize pollutants in waste gas, the pollutants are transformed into harmless water, carbon dioxide and other inorganic salts.
Scope of application: Microbial decomposable substances are the main source of food for microorganisms. Pollutants that can be biotreated include various organic compounds composed of hydrocarbon and oxygen, simple organic sulfides, organic nitrides, hydrogen sulfide and ammonia, etc.
Advantages: low energy consumption, low cost; complete oxidation; low energy consumption.
Disadvantages: energy utilization; photocatalyst deactivation; visible light.
3: plasma technology
Principle: The plasma field enriches a large number of active species, such as ions, electrons, excited atoms, molecules and free radicals; the active species dissociates pollutant molecules from small molecules.
Scope of application: Low concentration VOCs, indoor air purification.
Advantages: low temperature removal of VOCs; suitable for VOCs with low concentration and high air volume; high treatment efficiency, low energy consumption; clean and fresh air.
Disadvantage: high one-time investment; there are potential safety hazards.
4: Photocatalytic Technology
Principle: Photocatalyst nanoparticles are stimulated to produce electron hole pairs under a certain wavelength of light irradiation. The water adsorbed on the surface of the catalyst is decomposed by the hole to produce hydroxyl radicals. Electrons reduce the oxygen around the catalyst to reactive ionic oxygen, thus possessing a strong redox ability and destroying various pollutants on the surface of the photocatalyst.
Scope of application: It is suitable for deodorizing or sterilizing micro harmful gases in semi-enclosed or enclosed space.
Advantages: mild conditions, normal temperature and pressure; simple equipment, easy maintenance; reduce or even no secondary pollution.
Disadvantages: large area; large climate impact; large impact of changes in working conditions.
