electrostatic-precipitator

name	electrostatic-precipitator
description	Electrostatic precipitator (ESP) — Deutsch-Anderson equation, collection efficiency, specific collecting area, corona discharge, resistivity effects, rapping, gas flow, NFPA 496, EPA AP-42, industrial stack emission control.
metadata	{"priority":7,"promptSignals":{"phrases":["electrostatic precipitator","ESP","Deutsch Anderson","particle collection efficiency","corona discharge","dust collection ESP"],"minScore":3}}

Electrostatic Precipitator (ESP) — Complete Skill

ESP Operating Principle

Process:

1. Inlet gas with particles enters ESP
2. Discharge electrode (corona wire) creates corona discharge → ionizes gas → negative ions
3. Ions migrate to collecting plate (positive) → charge particles in transit
4. Charged particles migrate toward collecting electrode (Coulomb force) → deposit
5. Electrodes rapped periodically → dislodge collected dust → hopper

Particle charging: Field charging (d > 0.5 μm): particle in electric field accumulates ions on surface Diffusion charging (d < 0.5 μm): thermal diffusion of ions to particle surface Combined: most particles charged by both mechanisms

Saturation charge (field charging): q_sat = 3ε/(ε+2) × π ε₀ d_p² × E [C; ε = dielectric constant; ε₀ = 8.85×10⁻¹² F/m; d_p = particle diameter; E = field strength]

Deutsch-Anderson Equation

Collection efficiency: η = 1 - exp(-w × A / Q) [dimensionless] w = migration velocity [m/s]; A = collecting electrode area [m²]; Q = volumetric flow rate [m³/s]

Effective migration velocity: w = q × E_p / (3π μ d_p) [Stokes law; q = particle charge; E_p = precipitating field; μ = gas viscosity] Typical w: 0.05–0.15 m/s for fly ash; 0.05–0.10 for cement; 0.15–0.30 for paper

Modified Deutsch (White, accounts for gas distribution): η = 1 - exp(-(w/A_correction × SCA)) SCA = A/Q = specific collecting area [m²/(m³/s) = s/m]

SCA for high efficiency:

Efficiency target	Required SCA [s/m]
90%	15–25
99%	30–50
99.5%	40–70
99.9%	80–120

Corona Discharge

Corona wire field: E_corona = V / (r_w × ln(R_plate / r_w)) [V/m; r_w = wire radius; R_plate = wire-to-plate half-spacing] Onset voltage: V_onset = 3.1×10⁶ × r_w × ln(R_plate / r_w) [V; Peek's law approximation]

Operating voltage: 30–70 kV DC (negative corona preferred for most applications; more stable, higher efficiency) Spark rate: optimal: 50–150 sparks/min (controlled by voltage regulation); sparks → momentary field collapse

Wire-plate ESP geometry: Wire spacing: 300 mm typical; Plate spacing: 250–400 mm; Collection plate height: 5–15 m

Precipitating field: E_p = V / S_half [S_half = half plate spacing; average field between discharge and collecting electrode]

Resistivity Effects

Particle resistivity critical parameter: Low resistivity (< 10⁷ Ω·cm): particles discharge quickly → re-entrainment; negative corona back-ionization Optimal resistivity: 10⁸–10¹⁰ Ω·cm High resistivity (> 10¹⁰ Ω·cm): back corona → positive ions from surface → reduce charge → efficiency drops

Back corona: flashover/sparking on collecting electrode surface from high resistivity particles Detection: rapid rise in secondary current at low voltage; erratic voltage waveform

Resistivity control: Flue gas conditioning: SO₃ injection (reduces resistivity of fly ash) — 10–30 ppm SO₃ lowers resistivity from 10¹² to 10⁹ Ω·cm Moisture injection: increases conductivity of surface film Temperature: resistivity minimum at 150–200°C for many materials; design operation at minimum resistivity temperature

Rapping System

Purpose: dislodge accumulated dust without re-entraining it Rap frequency: 0.1–10 raps/hour per electrode Rap force: impact generates acceleration > 100 g on electrode Re-entrainment: main loss mechanism; minimize by:

• Rap with gas flow off (intermittent flow rapping)
• Use "sonic rapping" (vibration at resonance)
• Collect rapped dust in hopper quickly (steep hopper angle > 55°)

Sneakage: gas bypassing active field (under/over electrodes) Mitigation: gas distribution plate at inlet; anti-sneakage baffles around hoppers

Gas Flow Distribution

Inlet duct: gas must be distributed uniformly across ESP cross-section Non-uniformity → hot spots in velocity → local re-entrainment + low efficiency at high-velocity zones Coefficient of variation: CV = σ_v / v̄ < 15% (target); < 25% (acceptable) Perforated plate: pressure drop ΔP/q_dyn = 0.5–2.0 (achieve uniform distribution)

Gas volume and velocity: Inlet velocity: 1–2 m/s (typical); > 2.5 m/s → excessive re-entrainment Treatment time: t = L_ESP / v_gas ≈ 5–15 s (collection time)

Sizing Example

Given: Q = 100 m³/s (gas flow), target η = 99.5%, w = 0.10 m/s Required A = -Q × ln(1-η) / w = -100 × ln(0.005) / 0.10 = 100 × 5.30 / 0.10 = 5300 m² SCA = A/Q = 53 s/m

Physical dimensions: Collection plate height H = 10 m, plate length L = 10 m; plate area = 100 m²/plate pair Number of plate pairs = A / (H × L) = 5300 / 100 = 53 plates → 26.5 plate pairs Total ESP width = 27 × 0.3 m (plate spacing) = 8.1 m

Emission Calculation

Outlet particle concentration: C_out = C_in × (1 - η) [mg/m³] Emission rate: ṁ_emission = Q × C_out [g/s or kg/hr]

US EPA emission limits: PM2.5 from coal: 0.020 lb/MMBtu (ESP needed to achieve) EU ELV (for coal plants): PM < 10–30 mg/m³ at standard conditions

Standards

Standard	Scope
NFPA 496	Purged/pressurized equipment (electrical in dusty environments)
EPA AP-42	Emission factors for EPS performance estimation
IEEE 548	ESP performance
ASME PTC-21	Particulate matter collection equipment performance testing
ASHRAE 52.2	MERV rating for filters (alternative to ESP)

Output

Provide: gas flow Q [m³/s], inlet particle concentration C_in [mg/m³], target η [%] and resulting C_out [mg/m³], migration velocity w [m/s], required SCA [s/m], total collecting area A [m²], operating voltage [kV] and polarity, corona wire spacing [mm], plate spacing [mm], number of plate pairs, gas velocity [m/s] and treatment time [s], particle resistivity [Ω·cm] and back corona risk, gas conditioning method (if high resistivity), rap frequency [raps/hr], emission rate [kg/hr] and compliance with EPA/EU limit, and applicable standard (ASME PTC-21, EPA AP-42).