I. Commonly Used Particulate Matter Control Technologies in the Foundry Industry

1. Cyclone Dust Removal Technology

This technology removes heavy particulate matter or high-concentration particulate matter, but is less effective for light and fine particulate matter. It must be used in conjunction with bag or cartridge dust removal technologies. It is suitable for pre-treating particulate matter in exhaust gases from processes such as metal smelting (chemical processing), sand shakeout, cleaning, sand treatment, and sand regeneration.

2. Bag Dust Removal Technology

When used in foundry production, this technology typically achieves a filtration velocity between 0.7 m/min and 1.5 m/min, a system resistance typically below 1500 Pa, and a dust removal efficiency exceeding 99%. It is suitable for controlling particulate matter in exhaust gases from various processes in foundry enterprises. Use of this technology must comply with the relevant requirements of HJ 2020. Applications involving explosive dust must comply with relevant explosion-proof regulations.

3. Cartridge Dust Removal Technology

When used in foundry production, this technology typically operates at filtration speeds between 0.6 m/min and 1.2 m/min, with system resistance typically below 1000 Pa. Dust removal efficiencies typically exceed 99%. It is suitable for controlling particulate matter in exhaust gases from all casting processes. Applications involving explosive dust must comply with relevant explosion-proof regulations.

4. Wet Dust Removal Technology

This technology is suitable for capturing particles sized 1 μm to 10 μm and is suitable for cleaning aluminum and magnesium alloy castings, drying sand molds (cores), and pouring small, low-dust castings such as fasteners and brake discs. However, this technology is less effective at removing fine particles.

5. Paint Mist Treatment Technology

It is suitable for controlling paint mist from spray exhaust gases during surface coating processes and for pre-treatment of VOCs. This technology includes dry media (such as labyrinth-type paper boxes) paint mist treatment technology and hydrocyclone spray booths. Paint mist removal efficiencies typically exceed 85%.

II. Commonly Used Sulfur Dioxide Control Technologies in the Foundry Industry

1. Wet Desulfurization Technology

This technology uses alkaline solutions such as sodium hydroxide (NaOH), sodium carbonate (Na2CO3), and sodium bicarbonate (NaHCO3) to absorb SO2. Desulfurization efficiencies generally exceed 90%, making it suitable for desulfurization of cupola exhaust gases. This technology includes sodium-alkali desulfurization and dual-alkali desulfurization. This technology requires supporting facilities such as automatic desulfurizer addition equipment, automatic pH monitoring, and aeration. Inefficient and simple alkaline desulfurization technologies are prohibited.

2. Dry Desulfurization Technology

This technology uses calcium-based (Ca(OH)₂, CaO) or sodium-based (NaHCO₃) desulfurization absorbents. The absorbents react with acidic substances in the flue gas to form solid compounds. This technology generally achieves a desulfurization efficiency of over 85%. It is suitable for desulfurization of cupola exhaust gases and requires automatic desulfurization agent dosing equipment. The fineness of sodium-based absorbents used in the foundry industry is generally no less than 800 mesh, while the fineness of calcium-based absorbents is generally no less than 300 mesh.

III. Commonly Used VOC Control Technologies in the Foundry Industry

1. Adsorption Technology

Adsorption technologies are methods and technologies that use adsorbents (such as activated carbon and molecular sieves) to absorb and separate VOCs from exhaust gases. These technologies primarily include fixed-bed adsorption, moving-bed adsorption, fluidized-bed adsorption, and rotary adsorption. Fixed-bed and rotary adsorption are commonly used adsorption technologies in the foundry industry.

a) Fixed-bed adsorption technology generally uses activated carbon as the adsorption material. The adsorbent can be replaced or recycled after desorption. The inlet exhaust gas particulate matter concentration should be less than 1 mg/m³, the temperature should be less than 40°C, and the relative humidity (RH) should be less than 80%. This technology is suitable for VOCs waste gas treatment in foundry production and its use should comply with the relevant requirements of HJ 2026.

b) Rotary adsorption technology generally uses molecular sieves as the adsorption material, and the desorbed waste gas is treated using combustion technology. The inlet exhaust gas particulate matter concentration should be less than 1 mg/m³, the temperature should be less than 40°C, and the relative humidity (RH) should be less than 80%. It is suitable for VOCs waste gas treatment in the foundry industry's coating process using solvent-based coatings under relatively continuous and stable working conditions. Its use should comply with the relevant requirements of HJ 2026.

2. Combustion Technology

Combustion technology converts VOCs in exhaust gas into substances such as carbon dioxide and water through thermal combustion or catalytic combustion. These technologies primarily include catalytic combustion, regenerative combustion, and thermal combustion.

a) Catalytic combustion converts VOCs in exhaust gas into substances such as carbon dioxide and water under the action of a catalyst. It is suitable for treating exhaust gas with particulate matter concentrations below 10 mg/m³ and temperatures below 400°C. This technology generally achieves a VOC removal efficiency exceeding 95%, making it suitable for treating VOC exhaust gas generated by various processes in the foundry industry. It is typically used in conjunction with adsorption technology and must comply with the relevant requirements of HJ 2027.

b) Regenerative combustion uses combustion to convert VOCs in exhaust gas into substances such as carbon dioxide and water, and utilizes the heat generated by combustion in a regenerative medium. Its VOC removal efficiency generally exceeds 95%. It is suitable for treating VOC exhaust gas from surface coating processes in the foundry industry where solvent-based coatings are used and the operating conditions are relatively continuous and stable. It is typically used in conjunction with adsorption technology and must comply with the relevant requirements of HJ 1093.

c) Thermal combustion technology uses combustion to convert VOCs in exhaust gas into substances such as carbon dioxide and water. The combustion temperature for this technology should be controlled between 800°C and 1000°C. The exhaust gas should be introduced into a high-temperature flame zone, with a typical residence time of no less than 0.5 seconds. VOC removal efficiencies can generally exceed 95%. Thermal combustion facilities should operate continuously and maintain a stable high-temperature environment (e.g., a continuous annealing furnace).

3. Absorption Technology

This technology uses liquid absorbents to remove one or more gaseous components from the exhaust gas. It can generally be categorized as chemical absorption or physical absorption. Chemical absorption (acid-base neutralization) is commonly used to treat triethylamine generated during the cold-box core production process (triethylamine-catalyzed hardening), with removal efficiencies generally exceeding 60%. Physical absorption is commonly used during hot-box core production and some casting processes, with removal efficiencies generally exceeding 60%. This technology generates wastewater.

IV. Oil Mist Treatment Technologies for the Foundry Industry

1. Mechanical Filtration Technology

This technology uses centrifugal force or metal mesh filter elements, fiber filter elements, multi-layer filter felt, and other filter materials to separate oil mist from exhaust gas. Mechanical filtration devices typically have a filtration velocity below 0.5 m/s and a system resistance below 1200 Pa. Oil mist removal efficiencies typically exceed 90%. They are used to treat oil mist exhaust gas generated by release agent spraying during pressure casting (die casting) processes.

2. Electrostatic Purification Technology

This technology applies an electric field to oil mist exhaust gas, causing charged oil mist particles to deposit on a collection plate with opposite polarity. Gravity ultimately separates the oil mist from the air. Electrostatic purification devices typically operate with an electric field voltage of 10 kV to 15 kV, a gas flow rate below 1.2 m/s, and a system resistance below 400 Pa. Oil mist removal efficiencies typically exceed 90%, making them suitable for treating oil mist exhaust gas generated by release agent spraying during pressure casting (die casting) processes.