Working principle of electrostatic precipitator

ESP (Electrostatic Precipitator) is a flue gas dust removal device that uses a high-voltage direct-current electric field to charge dust particles and then collects the dust onto collecting plates under the action of electric force. It is widely applied for the efficient removal of particulate matter (dust) from flue gas generated by coal combustion, metallurgy, cement production and other processes.

## I. Basic Working Principle (Four Steps)

1️⃣ Corona Discharge (Flue Gas Ionization)

- High-voltage direct current (typically −40kV ~ −70kV) is applied to the discharge electrode (cathode wire / barbed wire).

- The surrounding air or flue gas is ionized to generate negative ions and electrons (corona zone).

2️⃣ Dust Charging

- Dust particles passing through the flue gas collide with negative ions.

- Most dust particles acquire negative charges.

3️⃣ Migration of Charged Dust toward Collecting Electrodes

- Driven by Coulomb force, negatively charged dust moves toward the anode (collecting plate).

4️⃣ Dust Collection and Ash Cleaning

- Dust deposits on the collecting plate and forms an ash layer.

- Periodic rapping (mechanical or electromagnetic rapping) dislodges the ash layer, which falls into the ash hopper and then enters the ash conveying system.

- The discharge electrodes also require synchronous rapping to prevent ash accumulation.

Flue gas → Ionization at discharge electrode (–) → Dust charged (–) → Migration to collecting electrode (+) → Rapping for ash removal → Clean flue gas discharged

## II. Typical Structural Components

| Component | Description |

| ---- | ---- |

| Discharge Electrode (Cathode) | Barbed wire, spiral wire or fishbone wire, suspended inside the electric field |

| Collecting Electrode (Anode) | C-type, Z-type or flat plate collecting plates |

| High-Voltage Power Supply Unit | Silicon-controlled, high-frequency or pulse power supply for supplying negative high-voltage direct current |

| Rapping Device | Separately raps cathodes and anodes to control re-entrainment of dust |

| Ash Hopper & Ash Conveying System | Star-shaped ash discharge valves, bin pumps, scraper conveyors, etc. |

| Shell & Thermal Insulation | Prevents condensation and corrosion (often equipped with liners or flake coatings) |

## III. Common Types

- Horizontal Electrostatic Precipitator (most widely used): Flue gas flows horizontally, with 2 to 5 electric fields connected in series.

- Vertical Electrostatic Precipitator: Flue gas flows vertically upward or downward; small footprint, less frequently used.

- Wet Electrostatic Precipitator (WESP): Ash is removed by water washing. It can remove acid mist, aerosols and PM₂.₅, and is often used at the terminal for ultra-low emission requirements.

## IV. Key Factors Affecting Dust Removal Efficiency

| Factor | Influence |

| ---- | ---- |

| Specific Resistance (ρ) | The most critical factor. The ideal range is 10⁴～10¹⁰ Ω·cm; excessively high resistance causes back corona, while excessively low resistance leads to dust re-entrainment. |

| Electric Field Gas Velocity | Normally 0.8～1.2 m/s; higher velocity reduces efficiency. |

| Dust Concentration & Particle Size | Coarse particles are easy to capture, while ultra-fine particles are difficult. |

| Voltage / Current | Higher values facilitate dust charging (limited by flashover). |

| Rapping Schedule | Improper settings result in dust re-entrainment or bridging of accumulated ash. |

| Flue Gas Temperature / Humidity | Affects dust specific resistance (humidification can reduce high specific resistance). |

⚠️ Dust with high specific resistance (e.g., dust from certain dry flue gas) triggers back corona and causes a sharp drop in efficiency. Common countermeasures include flue gas conditioning (steam or SO₃ injection), or switching to electrostatic-bag composite precipitators or baghouse dust collectors.

## V. Performance Characteristics

Advantages:

- Dust removal efficiency exceeds 99% (up to 99.9% for suitable dust).

- Low pressure drop (≈200～300 Pa) and low energy consumption.

- Capable of handling large flue gas volumes with reliable continuous operation.

- Strong adaptability to high temperatures (≤400℃) and high dust concentrations.

Disadvantages:

- Poor performance for high-specific-resistance dust and ultra-fine dust.

- Large equipment size, high steel consumption and high initial investment.

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