The galvanizing process (especially electro-galvanizing, hot-dip galvanizing, etc.) will produce waste gas containing acidic gases (HCl, H₂SO₄ mist), alkaline dust (NaOH, ZnO), cyanide (cyanide galvanizing process) and heavy metal particles (zinc mist), which must be effectively treated to meet emission standards.
Author: Marisa
The galvanizing process (especially electro-galvanizing, hot-dip galvanizing, etc.) will produce waste gas containing acidic gases (HCl, H₂SO₄ mist), alkaline dust (NaOH, ZnO), cyanide (cyanide galvanizing process) and heavy metal particles (zinc mist), which must be effectively treated to meet emission standards.
Galvanizing waste gas treatment technology
1. Acid mist/alkaline mist treatment
(1) Wet treatment (spray tower)
Principle: The waste gas passes through the packed tower and contacts with the spray liquid (NaOH solution neutralizes the acid mist, H₂SO₄ solution neutralizes the alkaline mist) in countercurrent, and a chemical reaction occurs to remove pollutants.
Equipment:
Acid mist spray tower: Made of PP/FRP material, filled with ball rings or hollow balls.
Circulating liquid: pH automatic control (acid mist tower pH 8~10, alkaline mist tower pH 2~4).
Efficiency: 90%~98%, which can meet the "Comprehensive Emission Standard of Air Pollutants" (GB 16297-1996).
(2) Electrostatic precipitator
Applicable scenarios: high-concentration acid mist (such as hot-dip galvanizing zinc pot flue gas).
Advantages: It can capture submicron particles and reduce the pressure drop.
2. Hydrogen cyanide (HCN) treatment
(1) Alkaline chlorination method
Principle: Spray sodium hypochlorite (NaClO) solution onto cyanide-containing waste gas to oxidize HCN into CO₂ and N₂.
2HCN + 5NaClO → 2CO₂↑ + N₂↑ + 5NaCl + H₂O
Key parameters: ORP (oxidation-reduction potential) ≥300mV, pH ≥10.
(2) Activated carbon adsorption + catalytic combustion
Applicable scenarios: low-concentration hydrogen cyanide waste gas.
3. Zinc dust/zinc mist treatment
(1) Bag filter
Applicable: zinc dust at room temperature (such as zinc spraying and polishing processes).
Filter material selection: anti-static polyester coated filter bag (temperature resistance ≤130℃).
(2) Wet electrostatic precipitator (WESP)
Applicable: high temperature zinc mist (hot dip galvanizing zinc pot flue gas, temperature 200~400℃).
Advantages: can remove zinc mist and acid mist at the same time, efficiency>99%.
4. Combined process (recommended)
Typical process:
Gas hood → cyclone dust removal (pretreatment) → spray tower (acid mist neutralization) → wet electrostatic precipitator (deep purification) → activated carbon adsorption (to ensure exhaust gas) → 15m high exhaust stack discharge
Emission standards:
Zinc and its compounds: ≤1.0 mg/m³ (GB 16297-1996)
HCl: ≤30 mg/m³
HCN: ≤1.9 mg/m³