Powerful science popularization! The "Golden Three" of VOCs Unorganized Waste Gas Collection System
Volatile Organic Compounds (VOCs) refer to organic compounds that participate in atmospheric photochemical reactions, including non-methane hydrocarbons (alkanes, alkenes, alkynes, aromatic hydrocarbons, etc.), oxygen-containing organic compounds (aldehydes, ketones, alcohols, ethers, etc.), chlorine-containing organic compounds, nitrogen-containing organic compounds, and sulfur-containing organic compounds. It doesn't matter!
Strongly explain to you in detail and thoroughly
From a literal perspective, these substances are organic chemical substances with "vaporization properties". In short, VOCs are a category of organic compounds with physical volatility and chemical reactivity.
Physical volatility - Whether it evaporates or not depends on "saturated vapor pressure" or "boiling point";
Chemical reactivity - As an active substance, it has reactivity and can participate in atmospheric photochemical reactions.
VOCs have not only complex and diverse definitions, but also a large family! It includes non-methane hydrocarbons (alkanes, alkenes, alkynes, aromatic hydrocarbons, etc.), oxygen-containing organic compounds (aldehydes, ketones, alcohols, ethers, etc.), chlorine-containing organic compounds, nitrogen-containing organic compounds, sulfur-containing organic compounds, etc.
VOCs: The Invisible "Killer" Behind Fog and Ozone
VOCs not only have strong toxicity and are a primary pollution source in the air, but also are important precursors for the formation of PM2.5 and O3, causing secondary pollution such as photochemical smog, and can be regarded as the "killer" lurking behind them.
VOCs vs. PM2.5
Mist is the result of an increase in PM2.5 values, and VOCs are an important precursor for PM2.5. VOCs undergo a series of photochemical reactions, and some lower vapor pressure secondary organic substances can form secondary organic aerosols (SOA) through nucleation, condensation, and gas-particle partitioning processes, becoming part of the particulate matter. Therefore, VOCs are the hidden hand behind PM2.5.
VOCs vs. O3
When exposed to sunlight, VOCs react with chemical substances such as nitrogen oxides in the air, mainly generating ozone, peroxy nitrophenyl (PAN), aldehydes, etc., forming photochemical smog. The oxidation process of VOCs breaks the balance among NO2-, NO, and O3, leading to the generation and accumulation of O3. Tips
The ventilation equipment, operation stations, workshop buildings, etc. should, under the premise of complying with relevant safety production and occupational health regulations, adopt reasonable ventilation volume in accordance with the requirements of industry operation procedures and standards, industrial building and cleanroom ventilation design specifications, etc.
② The setting of exhaust hoods (collecting hoods) of the waste gas collection system should comply with the provisions of GB/T 16758.
Tips
For those using external exhaust hoods, the control wind speed should be measured in accordance with the methods stipulated in GB/T 16758 and AQ/T 4274-2016. The measurement points should be selected at the farthest position from the opening of the exhaust hood for VOCs unorganized emissions. The control wind speed should not be lower than 0.3 m/s (if there are specific regulations in relevant industry norms, they should be followed).
The setting of the collection hoods is as follows:
Closed hoods (local, overall)
External hoods (upward suction, downward suction, side suction, etc.), priority should be given to closed collection and classified collection.
③ The conveying pipelines of the waste gas collection system should be sealed. Tips
The exhaust gas collection system should operate under negative pressure. If it is in a positive pressure state, leakage detection should be conducted at the sealing points of the conveying pipeline components. The leakage detection value should not exceed 500 μmol/mol, and there should be no perceptible leakage. The requirements for leakage detection frequency, repair and record should be carried out in accordance with the provisions of Chapter 8 of the GB37822 standard.
