The core technology of wet electrostatic precipitator (WESP) for boiler flue gas after desulfurization and denitrification combines high-voltage electrostatic adsorption with water film ash cleaning. Targeting the saturated wet flue gas characteristics including high humidity, PM2.5, acid mist and heavy metals after boiler desulfurization and denitrification, the equipment performs terminal advanced purification to ensure emission compliance and eliminate white smoke plume. The specific working principle and process are described as follows:
I. Core Working Principle
1. Flue Gas Pre-treatment and Uniform Distribution
After denitrification (SCR/SNCR) and wet flue gas desulfurization (FGD), the boiler flue gas firstly passes through a high-efficiency demister to remove large-size slurry droplets (concentration ≤50mg/m³). Then the flue gas evenly enters the electric field through a flow distribution plate. Meanwhile, the flue gas temperature is controlled at 40-60℃ to adapt to WESP operating conditions, preventing electric field breakdown at excessive high temperature and condensation corrosion at low temperature.
2. High-voltage Ionization and Particle Charging
A high-voltage power supply (60-100kV DC high voltage) supplies power to high-discharge-intensity thorn cathode wires, while anode plates or tubes (honeycomb/plate type) are grounded to form a strong electric field. Gas molecules in the electric field are ionized into electrons and positive ions. Electrons collide with fine pollutants such as PM2.5, SO₃ acid mist and heavy metals (Hg, As) in the flue gas to charge the pollutants negatively.
3. Electrostatic Adsorption and Collection
Under the action of electric field force (Coulomb force), negatively charged pollutant particles move towards the anode and firmly adhere to the anode surface to form a pollutant film, preventing pollutant escape with flue gas.
4. Water Film Ash Cleaning and Gas Discharge
The top spray system continuously sprays clean water (or reused desulfurization wastewater) to form a uniform water film on the anode surface, which flushes adhered pollutants into the water tank at the bottom. The purified flue gas (particulate matter ≤5mg/m³) is discharged through the chimney up to standard. The polluted wastewater is delivered to the desulfurization wastewater treatment system for centralized disposal (reuse or discharge after neutralization, flocculation and sedimentation).
II. Typical Technological Process
1. Process Positioning
As a terminal advanced treatment equipment for boiler flue gas, the WESP is installed after the denitrification reactor and desulfurization tower to remove fine pollutants that cannot be eliminated by previous processes. It serves as the key equipment to realize ultra-low emission (particulate matter ≤5mg/m³).
2. Complete Process Flow
Boiler flue gas → Economizer (waste heat recovery and cooling) → Denitrification reactor (SCR/SNCR, NOx removal) → Electrostatic fabric dust collector (pre-dedusting for coarse particle removal) → Desulfurization tower (wet FGD, SO₂ removal) → High-efficiency demister (large droplet/slurry removal) → Wet electrostatic precipitator (advanced purification for PM2.5/acid mist/heavy metals) → Induced draft fan → Chimney discharge
3. Exclusive Process Design for Boiler Working Conditions
Enhanced Pre-treatment: Due to the large fluctuation of dust concentration in boiler flue gas, a front-mounted electrostatic fabric dust collector is applied to control the inlet dust concentration below ≤30mg/m³ and avoid electrode scaling and blockage. A high-efficiency demister is installed at the desulfurization tower outlet to reduce slurry droplets entering the WESP.
Optimized Electric Field Configuration: 2-4 electric fields are connected in series with a single electric field voltage of 60-80kV, achieving a total purification efficiency ≥99.9%. It adapts to complex pollutant components in boiler flue gas to ensure stable ultra-low emission compliance.
Customized Spray System: Wear-resistant and anti-blocking fan-shaped nozzles are adopted with spray pressure of 0.3-0.5MPa. Continuous spraying mode is applied according to boiler flue gas characteristics to achieve full coverage of anode plates and avoid local scaling.
Upgraded Corrosion-resistant Materials: Anode plates/tubes are made of 316L stainless steel or FRP (fiberglass reinforced plastic). The shell adopts Q345R steel plate with anti-corrosion coating to adapt to acidic wet flue gas after desulfurization, with equipment service life ≥15 years.
III. Adaptation Advantages for Boiler Working Conditions
High Purification Accuracy: It efficiently removes PM2.5 (removal efficiency ≥99%), SO₃ acid mist (removal efficiency ≥95%) and heavy metals, completely eliminating white smoke plume and meeting ultra-low emission requirements specified in GB 13223-2011 Emission Standard of Air Pollutants for Thermal Power Plants.
Stable and Reliable Operation: Water film ash cleaning replaces dry rapping without secondary dust re-entrainment. The equipment can withstand boiler load fluctuation ranging from 50% to 110%, maintaining stable purification efficiency under fluctuating flue gas parameters.
Strong Synergistic Treatment Capacity: It treats multiple pollutants simultaneously without additional acid removal and heavy metal removal equipment, simplifying the flue gas treatment process and reducing overall investment cost.
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