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Image of aluminum furnace
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The aluminum smelting process creates many exhaust environmental problems such as exhaust gas streams withhigh temperature,metal dust type, gases include CO2, SO2, CO, NOx, fluorine compound gas,…. If these issues are not handled thoroughly, they will seriously affect the environment and especially human health. To ensure that emission factors in the aluminum smelting process are controlled and meet requirements, the article below will introduce the technologyto treat aluminum smelting emissions.
What is aluminum smelting technology?
Below includes the main steps in the aluminum smelting process. From there it will be shown where the emission sources in the aluminum smelting industry come from. And what are the main components of the emission source? There are6 stages that take place in the aluminum production process.
Step 1: Adding additive compounds to liquid aluminum
Pure aluminum needs to be adjusted by adding some additive alloys. To achieve certain required properties (mechanical properties, physics, and machinability) in various applications. Becausealuminum is too softto be used in industrial and construction applications. The elements useddepend on the product‘s needs. They help improvehardness and mechanical properties of aluminum. The most common alloying elements are Silicon (Si), Magnesium (Mg), Manganese (Mn), Copper (Cu), Zinc (Zn), Iron (Fe) and Titanium (Ti). After adding the elements, additive alloys, and liquid aluminum, the composition will be tested again to ensure the composition ratio is appropriate or not.
Step 2: Stirring and scraping off slag
Before adding intermediate alloys, it is necessary to scrape off the slag layer on the liquid aluminum surface with a mechanical shovel gas. This slag layer is mainly aluminum oxides, andmust be scraped off. Otherwise it may react directly with additive elements (especially Mg and produce harmful impurities such as spinel (Al2MgO4)). After the additive alloys are placed into the furnace using a mechanical shovel, the liquid aluminum is stirred to properly dissolve the alloys. After stirring, the slag mixed in the aluminum will float and will be scraped off again.
Step 3: Trough
When the furnace is tilted, liquid aluminum will flow through the trough to the casting plate and will be purified by equipment such as degassing machines and CFF filters.
Step 4: Loading crystallization nucleation agent
Using crystallization nucleation agent in DC casting is necessary to form a balanced structure with better properties. In addition, nuclear points will reduce the risk of defects and the probability of porosity, and also help distribute the alloy in Liquid aluminum is more uniform. The nuclear point is created with an alloy such as (Al-Ti-B) – usually in the form of wire or rod. In billet casting, normally 1 ton of liquid aluminum will require about 1 kg of nucleating agent.
Step 5: Purification process
Purification of liquid aluminum is one of the essential concerns in the casting process. Impurities such as alkali metals (lithium, calcium and sodium), dissolved gases (especially hydrogen) and other non-metallic impurities (carbides, oxides) will affect the quality of the casting surface. Methods such as ceramic filter and air bubble filtration (SNIF) can significantly reduce the amount of impurities in liquid aluminum.
Step 6: Homogenization furnace
Billets will be kept in the homogenization furnace at 550oC temperature for a certain period of time. The goal of assimilation is to provide better workability for the billet, bringing the elements in the billet to the correct position, reducing segregation and creating a more microscopic structure. After that, the billets will be cooled, the edges at both ends cut, wrapped and transported to other stages such as pressing and shaping. Thus, the main exhaust components from aluminum smelting activities include aluminum dust and substances including CO, SO2, NOx, ….
Characteristics of the plume stream
The aluminum smelting industry produces a plume stream with a relatively high temperature,about 500 – 700o C. strong> Due to cooking at high temperatures, the smoke and dust are also mixed with a part of aluminum oxide dust (Al2O3). In addition, the dust also contains a small part of CO, NO2, SO2, and metals such as Mg, Pb, Si…, due to combustion reactions and input aluminum ingredients. It can be seen that people working in environments containing a lot of aluminum dust are at very high risk of poisoning. If you inhale aluminum dust concentration in the airthat exceeds 0.15 mg/m3, it will affect your health and thereby lead to diseases of the heart. intestinal tract and respiratory system,…
Concentration table of dust and smoke components arising from the aluminum cooking process
Through the data table above, it can be seen that the composition of substances in the exhaust gas from the aluminum smelting process exceeds the QCVN standards for column A and column B many times the allowable limit. Especially the parameters of total dust, CO, NOx, SO2,… Therefore, it is necessary to build a system aluminum smelting waste gas treatment and system management to ensure output parameters meet requirements according to QCVN 19:2009/BTNMT: Standard National technical specifications for industrial emissions of dust and inorganic substances.
Dust and smoke generated in the aluminum smelting furnace and related stages will be thoroughly recovered by dust collectors. Dust is guided through pipes to the dust treatment device Cyclon using a high-capacity exhaust fan. Here, most of the dust is retained under the settling chamber of the device and periodically removed. The gas leaving the top of the tower is brought into the buffer absorption tower by 01 exhaust fan. Here, the process of absorbing toxic substances in exhaust smoke occurs before being released into the environment. The released gas meets column B of QCVN 19:2009/BTNMT on industrial emissions for dust and inorganic substances, applicable to operating factories and facilities.
Some features to note when designing the system
Design valves that open and close at locations where exhaust gases are generated to optimize the smoke extraction process. Dust when pouring molten aluminum as well as when maintenance is needed.
The operating capacity of the system is adjusted up or down corresponding to the operating capacity of the system to minimize operating costs.
The capacity of the fan, the size of the exhaust hoods and the air collection piping system must be calculated so that get all the gas released
Treating dust from aluminum cooking exhaust
Image of suction and vacuum pipe – Aluminum exhaust
The exhaust gas stream is collected by the exhaust fan and sent to the Cyclon dust separator. Dust follows the duct into the door to the area near the top of the device. Then, the airflow containing dust enters the body of the Cyclon in a tangential direction to the body Cyclon at the top then spirals down to gradually meet the funnel-shaped tube. The exhaust fan helps dust move in a spiral direction. Dust, under the effect of centrifugal force, is thrown into the walls of the Cyclon and gradually loses speed and falls to the bottom of the Cyclon. The gas stream, after being dust-removed, follows the pipeline upward to a fabric bag dust filter and an absorption tower to treat the gas components in the gas stream after dust separation.
Treatment of gases in aluminum cooking exhaust gas
After removing dust, the exhaust gas stream continues to enter the buffer absorption tower. The absorption liquid used here is NaOH
Image of model of aluminum smelting exhaust gas treatment technology
Exhaust gas goes from the bottom to the top of the tower, Water containing absorbent NaOH is pumped and distributed evenly onto the surface of the buffer layer divided into two floors in the treatment tower, absorbing toxic substances in the exhaust gas. The process of treating aluminum smelting exhaust gas goes through 4 stages as follows:
Treatment by rain spray rig – exhaust gas is preliminarily treated by spray rig rain (first treatment stage). On the first floor, a specialized anti-clogging spray nozzle is arranged to evenly distribute the amount of water in the tower, wastewater is sprayed with high pressure. At the same time, due to the structure of the specialized nozzle, a mist layer is formed in the entire space below the tower, increasing the effectiveness of the dust mass in contact with the liquid. Most of the remaining dust after passing through Cyclon is retained here.
Treatment with the first buffer layer – exhaust gas passes through the first layer of buffer material with diameter and height of the buffer layer according to design calculations. Here the exhaust gas stream collides with the buffer layer at the surface of the buffer layer, coming into contact with the absorbent. Neutral absorption processes are expressed through the following reaction processes: NaOH + CO2 --> Na2CO3 + H2O 2NaOH + SO2 --> Na2SO3 + H2O
Processing is enhanced by arranging Add a layer of padding with the same structure as the first padding layer. The purpose of separating the two buffer layers is to ensure that the adsorbent concentration is maintained over the entire length of the buffer layer.
High-temperature exhaust gas containing water vapor and small water molecules from the exhaust fan comes into contact with the blind separation layer arranged in the top of the tower. Here steam and water are retained. Thus, to thoroughly treat aluminum smelting exhaust gas, it is necessary Apply multiple devices and measures at the same time to process each part that has the same characteristics. As managers and supervisors of aluminum smelting factories, they need to build a specific system suitable to the scale, expertise, etc. of the factory to meet the environmental requirements of agencies. have authority. Please contact us immediately at 0972221608 or website https://xulymoitruong360.com/. HASY ENVIRONMENT is ready to consult Advise and answer your questions about exhaust gas and aluminum dust treatment technology.
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