Plastic is a commonly used material in human life. All household and production items can be made of this material. Depending on the product, people use recycled plastic or virgin plastic to make suitable items.
However, plastic production causes health and environmental problems when ingredients in plastic such as polymers, additives, colorants, etc. can harm the body in the form of inorganic or in gas form, causing lung and respiratory diseases, eye irritation, skin irritation, etc.
In Vietnam, the plastic resin production industry is one of the fastest growing industries with an average growth rate in the past 10 years of 20 – 25% strong>. Besides the development that brings high profit growth, the plastic resin production process also creates many negative impacts on the environment, one of which is particle emissions. plastic.
To ensure that emissions from plastic resin production activities meet the requirements, it is necessary to build and install plastic resin production exhaust gas treatment systems at factories and facilities with Direct production of plastic beads.
What is the process of generating emissions from plastic resin production?
The plastic pellet production process goes through 6 basic stages: Scrap plastic is ground, including PP and PE plastic, classified based on color and washed, then mixed. Put them all into a coarse filter mill with a temperature of 300oC.
The softened plastic is fed to the wire drawing machine through a mesh maintained at atemperature of 150oC. The soft plastic wire is passed through a cooling water tank to harden the plastic wire and transferred to a cutting machine to create plastic beads with a particle size of about 0.3cm in diameter and 0.5cm in length.
At the end of this process, the plastic pellets are bagged, stored and sold as finished plastic pellets.
Plastic granule production process
The plastic pellet production process mainly causes dust, plastic vapors and odors to be released into the surrounding air, specifically:
Dust generated during the stages of: loading, unloading, packaging of raw materials and from the rough rolling of raw materials,… for production.
Toxic emissions: the wire heating and drawing process generates gases VOC, CO2, SO2; vinyl chloride. These are 3 types of extremely toxic substances, especially if exposed for a long time, they will cause cancer. Evaporation of circulating cooling water system: organic solvents, grease,… in the water will evaporate.
Odor pollution: the smell of volatile organic solvents (plastic smell) in the stages of melting plastic granules, grinding waste products, creating plastic granules,…
Technology diagram of plastic granule production exhaust gas treatment system
Technology diagram for treating waste gas from plastic granule production
To maximally treat plastic pellet production emissions, it is necessaryto treat two components in plastic production emissions, including dust and toxic emissions from plastic pellet production.
Treating dust in plastic pellet production exhaust
After following the inlet into the device, the airflow containing dust enters the body of the cyclone in a tangential direction to the body of the cyclone at the top and then gradually spirals down along the height of the device to meet the funnel-shaped body.
The exhaust fan helps dust move in a spiral direction. Dust, under the effect of centrifugal force, is thrown into the pipe wall, gradually losing velocity and falling downwards. The vortex containing clean gas gradually reduces the vortex diameter and direction
Treatment of toxic gases in plastic pellet production emissions
The exhaust gas stream, after dust removal, goes to the absorption tower to treat the remaining toxic gases.
The application principle of toxic exhaust gas treatment technology in plastic resin factories is to collect and treat exhaust gases through oxidation, alkalinization, and neutralization of gases with lime water to break toxic gas circuits. and absorb toxic gases before being released into the environment.
Adsorption technology and oxidation of plastic particle emissions
After being collected by an exhaust hood, the exhaust gas is passed through a pressurized tank (to cool and neutralize the gas), then sent to an oxidation tank (with a mixture of oxidants in the form of a mist spray) to break the circuit. durability of odor.
The exhaust gas then continues to be passed through the tower using activated carbon to absorb the harmful gases one last time.
Activated carbon can be reconstituted and used many times. Activated carbon has a very large outer surface area, if calculated in mass units, it isfrom 500 to 2,500 m2/g, so it is a Ideal for filtering and absorbing a variety of chemicals.
Thus, using suction hoods and activated carbon to adsorb plastic vapors generated at the plastic wire drawing stage will ensure no environmental pollution.
Accordingly, install an air intake funnel in the plastic granule grinding and cooking area, and build 3 consecutive cement tanks in the factory. Chemicals used: KMnO4 0.3% solution poured into oxidation tank; 1% NaOH alkaline solution poured into the alkalization tank. Tank 3 is filled with large pellets of activated carbon to ensure ventilation.
To operate the system in the best way, it is necessary to periodically check the entire system, ensuring that all parts operate according to technical procedures; add chemicals, change new solution and activated carbon.