A comprehensive overview of common exhaust gas treatment methods!

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A comprehensive overview of common exhaust gas treatment methods! Air pollution is one of the most prominent environmental problems worldwide today. The main source of pollutants is industrial waste gas; depending on the production processes, different types of pollutants are generated, and different treatment methods should be employed for each type of pollutant. 1. Organic waste gases 1) Main sources: Various organic waste gases are generated during industrial production, including various hydrocarbons, alcohols, aldehydes, acids, ketones, and amines. The sources of these exhaust gases are very diverse; they include emissions from petrochemical and organic synthesis equipment in the chemical industry, organic solvents used in inks in the printing industry, emissions from mechanical painting processes in the machinery industry, odors generated by metal products, emissions from vehicle painting processes and casting production equipment in the automotive industry, as well as emissions from spraying equipment used in hardware and furniture manufacturing plants. 2) Hazards of organic waste gases: In production, the emission of organic waste gases has always been a significant problem, and the vast majority of such gases are harmful to human health. When organic waste gases enter the human body through the respiratory tract and skin, they can cause temporary or permanent damage to systems and organs such as the respiratory system, blood, and liver. In particular, polycyclic aromatic hydrocarbons like benzo[a]pyrene can directly cause cancer in humans, posing a threat to human health. Organic waste gases can also cause severe air pollution. Some organic substances, once they enter the atmosphere, can form photochemical smog under certain conditions, resulting in secondary pollution ； Some organic substances, once they reach the stratosphere, undergo photochemical reactions with ozone under ultraviolet radiation, resulting in ozone layer holes ； Some organic substances possess the dual nature of causing foul odors and emitting harmful gases ； There are also some organic substances that cause the greenhouse effect. 3) Waste gas treatment methods: a. Water film dust removal + activated carbon adsorption method ； b. Dry filtration for dust removal + activated carbon adsorption method c. Activated carbon adsorption + catalytic combustion method ； 2. Acid mist waste gas 1) Main sources: Acidic and alkaline waste gases emitted during the operations in industries such as chemicals, electronics, metallurgy, electroplating, textiles (fiber optics), food processing, and machinery manufacturing, including those from flavoring foods, acid production, pickling, electroplating, electrolysis, and battery manufacturing. 2) Hazards of acid mist exhaust gases: The air pollution caused by acid mist gases poses significant harm to human health; in particular, it causes direct damage to workers on site as well as to crops and soil in the vicinity of factories, and the indirect effects are often impossible to quantify in monetary terms. 3) Waste gas treatment methods: water film packed tower + absorption with alkaline (acidic) solution. 3. Furnace waste gas and smoke from power generation: 1) Main sources: Metal dust particles generated by furnace equipment in the metal melting process in the hardware industry, die-casting industry, and casting industry; harmful gases such as SO2 and NOX produced during the combustion of diesel (heavy oil); as well as waste gas generated during the operation of generators due to the combustion of diesel (heavy oil). 2) Hazards of furnace exhaust gases and generator smoke: Furnace exhaust gases and generator smoke are the main causes of acid rain, leading to significant air pollution; they cause direct damage as well as indirect effects on the workers on site, the crops near the factory, and the soil. 3) Treatment methods: Cyclone water washing and spraying method + alkali solution absorption. For the exhaust gases from furnaces and the black smoke emitted by generator sets, the conventional approach currently used is the cyclone plate water washing and spraying method, which involves employing a cyclone plate-type spray tower. Within this tower, the gas moves upward at high speed, coming into contact with the washing liquid that is sprayed from above. The presence of multiple layers of cyclone plates in the tower increases the surface area and contact time between the gas and the liquid, allowing the exhaust gases to come into full contact with water both within the tower and on the plates. The pollutant in exhaust gases, carbon black, is fully adsorbed by the spray water upon contact, thereby being purified ； Gaseous pollutants such as NOx and SO2 in exhaust gases are neutralized by making the spray water alkaline by adding a certain proportion of NaOH to it. During the spraying process, when the water comes into contact with the exhaust gases, chemical reactions occur, which enables the neutralization of these gaseous pollutants and achieves good treatment results. 4. Kitchen fumes and smoke 1) Main sources: Kitchen fumes are gas molecules generated during cooking in the kitchens of various types of factories. Soot is a harmful gas emitted when a stove burns completely or incompletely; it consists mainly of free carbon in the form of black dust that is flocculent in structure and tends to stick to solid substances. The remaining components are COX, SO2, and NOX, representing high-concentration gaseous pollutants. 2) Hazards of kitchen fumes and smoke: Kitchen fumes contain many substances that are highly harmful to the human body, and they increase the risk of lung cancer. Kitchen smoke is also one of the major sources of air pollution; the gases are acidic and can form acids when they come into contact with water, thereby contaminating water sources and soil as well as corroding buildings. 3) Treatment methods: A. Fume treatment a. Filtration and adsorption-based fume purification: Equipment for purifying fumes using filtration and adsorption can employ organic polymer composite fabrics or felts with high oil-absorbing capabilities, as well as inorganic filtering materials (such as hydrophobic perlite, ceramsite, coke, etc., used alone or in combination). The filtering materials can be arranged either perpendicular or parallel to the direction of smoke flow, with a purification efficiency of over 80% required. b. Electrostatic oil fume purification: The electrostatic deposition method involves introducing oil fumes and smoke into a high-voltage electric field, causing the particles present in these fumes and smoke to become charged. Under the influence of the electric field force, these particles move toward the dust collection electrode and settle there. The purification efficiency can typically reach over 85%, with a low pressure drop. c. Low-temperature plasma method: Its principle involves using high-voltage electrostatic methods; simultaneously, a plasma field is created at the front end of the electrostatic field. The large number of free radicals generated by this high-energy plasma are used to degrade the oil fume particles, thereby reducing their viscosity ； During plasma generation, the high energy generated by high-frequency discharge can break the chemical bonds of certain harmful gases, causing them to decompose into elemental atoms or harmless molecules. This technology is the most advanced available on the market for dealing with kitchen fumes and smoke; it features a high removal efficiency (over 90%), the treated gas has no unpleasant odor, and it is easy to maintain, although the equipment investment is high. B. Smoke: For high-concentration kitchen smoke gases, a swirl plate wet scrubbing method is used, with swirl plate scrubber towers employed. Within these towers, the gas moves upward at high speed, coming into contact with the washing liquid that is sprayed from above. The presence of multiple layers of swirl plates in the tower increases the area and duration of gas-liquid contact, ensuring thorough interaction between the exhaust gases and water both within the tower and on the plates. The pollutant in exhaust gases, carbon black, is fully adsorbed by the spray water upon contact, thereby being purified ； Gaseous pollutants such as NOx and SO2 in exhaust gases are neutralized by making the spray water alkaline by adding a certain proportion of NaOH to it. During the spraying process, when the water comes into contact with the exhaust gases, chemical reactions occur, which enables the neutralization of these gaseous pollutants and achieves good treatment results.