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Wet electrostatic precipitator for flue gas of coal-fired power plant

As the key equipment for advanced flue gas purification in coal-fired power plants, the Wet Electrostatic Precipitator (WESP) can effectively remove PM2.5 particulate matter, SO₃ acid mist and other pollutants to achieve clean flue gas emission. The detailed introduction is as follows:1. Working Pr...

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Product Introduction

Focus on the production of environmental protection equipment

1. Working Principle

1.1 Charging

Tens of thousands of volts of DC high voltage is applied between the anode tube and cathode wire inside the WESP to ionize gas and generate positive and negative ions. When flue gas containing dust and acid mist enters the equipment, dust and mist particles collide with ions and become charged.

1.2 Collection

Under the Coulomb force of the high-voltage electrostatic field, charged particles move directionally towards the anode and cathode according to their charge polarity. The particles release charges and adhere to the electrode surfaces to complete pollutant capture.

1.3 Ash Cleaning

WESP adopts periodic flushing ash cleaning. Water flow scours dust on electrode plates to avoid secondary dust emission.

2. Structural Composition

2.1 Shell

Mostly made of corrosion-resistant steel. The shell of coastal power plants is additionally coated with anti-corrosion layers. It is used to contain and protect internal components and guide flue gas flow.

2.2 Anode Device

Serving as the dust collection electrode, it is manufactured from corrosion-resistant conductive materials. Honeycomb conductive stainless steel tube bundles are widely applied due to excellent dust collection performance and stable structure.

2.3 Cathode Device

Composed of cathode wires, mostly high-efficiency thorn wires made of 304 stainless steel. It generates corona discharge to ionize gas and provide charging conditions for dust particles.

2.4 Insulation Device

It isolates electrodes and supporting structures to prevent short circuits and ensure stable electric field operation, requiring regular maintenance and inspection.

2.5 Flushing System

Consists of nozzles, water pipes and water pumps. It sprays water to clean electrode plates, and water quality and pressure shall be adjusted according to actual working conditions.

2.6 High-voltage Power Supply

It provides tens of thousands of volts of DC high voltage. Its stability and precise output voltage control directly affect dust removal efficiency. Advanced WESP is equipped with an intelligent high-voltage power supply to automatically adjust parameters according to flue gas conditions.

3. Technical Advantages

3.1 High Dust Removal Efficiency

As one of the advanced PM2.5 control technologies, it realizes PM2.5 emission concentration lower than 1.5mg/m³ and total particulate emission concentration lower than 10mg/m³.

3.2 Flexible Structural Layout

Adopting new corrosion-resistant composite materials, it can be independently arranged at the clean flue duct outlet of the desulfurization tower, installed on the top of the desulfurization tower, or separately placed in the open area of power plants.

3.3 Low Operation Energy Consumption

Continuous alkaline water injection is not required during operation. Mist droplets in flue gas are collected in the electric field to form overflow water inside the tube bundles for self-flow ash cleaning, featuring low power consumption and flow resistance less than 350Pa.

4. Application Status

4.1 Application Background

With increasingly stringent national atmospheric pollutant emission standards, traditional dust removal equipment cannot meet ultra-low emission requirements. WESP has become an ideal choice for coal-fired power plants due to its excellent performance.

4.2 Layout Modes

The main layout forms include vertical independent arrangement, vertical integrated arrangement with wet desulfurization equipment, and horizontal independent arrangement. The horizontal independent arrangement is the mainstream technology for coal-fired power plants.

5. Classification

Wet electrostatic precipitators have two basic structural types: tubular type and plate type. The plate type can be further divided into independent vertical arrangement and independent horizontal arrangement.

Design Code for Flue Gas Wet Electrostatic Precipitator of Coal-fired Power Plants

I. Core Standards and Application Scope

1. Main Technical Standards

DL/T 1589-2016 Technical Specification for Wet Electrostatic Precipitator: An electric power industry standard specifying requirements for design, construction, commissioning, acceptance and maintenance, applicable to flue gas treatment after wet desulfurization in thermal power plants.
DL/T 5592-2021 Design Code for Flue Gas Dust Removal of Coal-fired Power Plants: It stipulates the selection and system design requirements of wet electrostatic precipitators, applicable to boilers with evaporation capacity of 400t/h and above.

2. Applicable Working Conditions

Fine treatment of wet flue gas after desulfurization (temperature: 40-60℃, humidity＞90%).
Ultra-low emission renovation (particulate matter ≤5mg/m³).
Collaborative removal of PM2.5, SO₃ acid mist, heavy metals and other pollutants.

II. Basic Design Parameter Specifications

1. Flue Gas Condition Requirements

Parameter	Limit Value	Description
Inlet Dust Concentration	≤30mg/m³ (standard state); ≤100mg/m³ for special working conditions	-
Inlet Flue Gas Temperature	<60℃	Ensure saturated flue gas state
Electric Field Flue Gas Velocity	Plate type ≤3.5m/s; Tubular type ≤3.0m/s	Excessive velocity reduces dust removal efficiency
Flow Uniformity	Root mean square deviation ≤0.15	Flow equalization device is mandatory

2. Performance Indicators

Dust removal efficiency: ≥99.9% (meet ultra-low emission standard).
Pressure loss: ≤300Pa (reduce fan energy consumption).
Air leakage rate: ≤2% (avoid adverse impact on subsequent equipment).
Outlet droplet concentration: ≤50mg/m³.
Service life: ≥30 years (matched with unit service life).

III. Core System Design Requirements

1. Overall Structural Design

Basic Composition: Flue gas system, collection system, sewage discharge system and electric control system.

Layout Modes:

Vertical Type (bottom-in and top-out): Small floor area, suitable for projects with limited space.
Horizontal Type: Convenient for maintenance, applicable to large-scale units.

Key Design Requirements:

No bypass flue duct shall be set to ensure the operation rate of environmental protection equipment.
Manhole door size: ≥450mm×600mm (rectangular) for convenient maintenance.
Platform load capacity: ≥4kN/m² to meet maintenance requirements.

2. Electrode System Design

Component	Design Key Points
Anode (Dust Collection Electrode)	• Plate type / honeycomb structure• Electrode spacing: 250-400mm• Material: 316L/2205 stainless steel (corrosion resistance)
Cathode (Discharge Electrode)	• Thorn wire / star wire structure• Uniform discharge performance• Material: Nichrome alloy (good conductivity and high strength)
Electrode Spacing	Homopolar spacing deviation ≤±5mm to ensure uniform electric field

3. Spraying and Flushing System

Design Principles:

Spraying Mode: Continuous liquid film for high-viscosity dust; intermittent flushing (cycle: 1-4h) for conventional dust.
Nozzle Layout: Multi-layer staggered arrangement for full coverage of electrode plates; fan-shaped / atomizing nozzles with working pressure of 0.3-0.5MPa.
Water Volume Control: Form continuous thin water film without excessive droplets to avoid electric field performance degradation.

4. Electrical System Design

High-voltage Power Supply:

Output voltage: 60-100kV (adjusted according to electrode spacing).
Output current: Determined by flue gas treatment capacity and dust concentration.
High-frequency power supply is preferred (energy saving rate: 30-50%).

Safety Protection:

Interlock protection: Manhole door interlocked with high-voltage power supply; power cut is mandatory before personnel entry.
Grounding system: Grounding resistance ≤4Ω to ensure personal safety.
Over-current and over-voltage protection to prevent equipment damage.

IV. Material Selection Standards

1. Main Structure

Shell: Q345R steel plate + anti-corrosion coating (resist wet flue gas corrosion).
Internal components: 316L/2205 stainless steel (acid corrosion resistance).

2. Key Components

Spraying pipeline: PPR/FRP (acid and alkali resistance).
Demister: Glass fiber reinforced plastic / polytetrafluoroethylene (corrosion and temperature resistance).

V. Auxiliary System Design Points

1. Drainage System

Drainage slope ≥3‰ for smooth water discharge.
Water seal structure is equipped to prevent flue gas leakage.
Waste water shall be reused or discharged after reaching the standard (pH value: 6-9).

2. Control System

Monitoring Parameters: Electric field voltage/current, inlet and outlet dust concentration, pressure loss, water pressure/flow rate, flue gas temperature.

Control Functions:

Automatic spraying flow adjustment according to dust concentration.
Spark tracking and protection function.
Fault alarm and interlock protection.

VI. Construction and Acceptance Specifications

1. Installation Accuracy Control

Item	Allowable Deviation
Equipment Center Line	≤10mm
Horizontal Degree	≤1‰
Electrode Plate Flatness	≤5mm/m
Cathode Wire Straightness	≤3mm/m

2. Commissioning and Acceptance Process

Commissioning Stage:

Single equipment commissioning (fan, water pump, high-voltage power supply).
Sub-system commissioning (water system, circuit, gas circuit).
Overall commissioning (simulate working conditions and optimize electric field parameters).

Performance Acceptance Indicators:

Dust removal efficiency ≥ design value (≥99.9%).
Pressure loss ≤300Pa.
Air leakage rate ≤2%.
Outlet dust concentration ≤5mg/m³.
Continuous stable operation duration ≥72h.

VII. Safety Design Key Points

1. Electric Shock Prevention

Obvious warning signs shall be set in high-voltage areas.
All electrical equipment shall be reliably grounded.
Discharge and electricity inspection are mandatory before operation.

2. Anti-corrosion and Explosion-proof

All components contacting wet flue gas shall be treated with anti-corrosion measures.
Explosion-proof doors shall be installed under special working conditions.

3. Maintenance Safety

Cut off power supply, discharge electricity and ventilate before maintenance.
Internal maintenance requires no less than two operators with breathing apparatus equipped.

VIII. Operation and Maintenance Requirements

1. Daily Maintenance

Daily inspection: Electric field parameters, water flow rate and temperature.
Weekly inspection: Clean filters and check electrode cleanliness.
Monthly inspection: Fully inspect equipment corrosion and fasten connecting parts.

2. Common Fault Handling

Electrode scaling: High-pressure water flushing during shutdown (descaling agent is added if necessary).
Waterway blockage: Clean filters and inspect nozzles.
Declined electric field efficiency: Check electrode spacing and adjust high-voltage parameters.

IX. Design Optimization Suggestions

1. Treatment for High Specific Resistance Dust

Install SO₃ injection device at the desulfurization tower outlet to reduce dust specific resistance.
Adopt pulse power supply to enhance particle charging effect.

2. Energy-saving Design

Adopt zonal power supply and intermittent power supply mode.
Optimize spraying control according to actual unit load.

X. Summary

The design of wet electrostatic precipitators for coal-fired power plants must strictly comply with DL/T 1589-2016 and DL/T 5592-2021 standards. The core design points are summarized as follows:

Parameter Matching: Control inlet dust concentration ≤30mg/m³ and flue gas temperature <60℃ to meet basic flue gas requirements.
Structural Optimization: Select reasonable electrode type, spacing and flue gas velocity to ensure electric field efficiency.
System Coordination: Realize organic cooperation of spraying, electrical and drainage systems.
Material Selection: Adopt corrosion-resistant materials for key components to guarantee 30-year service life.

Note: This code is applicable to the design of newly-built, expanded and renovated wet electrostatic dust removal systems for coal-fired power plants. Actual projects shall be optimized combining specific working conditions and the latest industry standards.

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