Air & Noise Pollution

Particulate Control Devices

Cyclones, electrostatic precipitators, fabric filters and the Deutsch–Anderson efficiency model.

PART 1

Topic Breakdown & Traps

The Engineering Principle

Particulates are removed by gravity settling, cyclonic (centrifugal) separation, fabric filtration (bag-houses), wet scrubbing and electrostatic precipitation (ESP). ESPs charge particles and collect them on plates; their efficiency follows the Deutsch–Anderson equation. Cyclones are cheap but poor for fine particles; ESPs and bag-houses achieve > 99 % on fine dust.

The Core Formula Matrix

Deutsch–Anderson (ESP):

η = 1 - e^{- w A / Q}

(

w

= drift velocity,

A

= collection area,

Q

= gas flow)

Cyclone cut size

d_{50}

: the particle diameter collected at 50 % efficiency.

Selection by size: cyclones for coarse (> 10 µm); ESP/bag-house for fine (< 1 µm).

Settling velocity (Stokes):

v_{s} = \frac{g d ^{2} ( ρ _{p} - ρ )}{18 μ}

The ‘IIT Traps’

⚠
ESP efficiency depends on A/Q (specific collection area) — larger area or lower flow raises η.
⚠
Cyclones are inefficient for fine particles; don't use them for PM₂.₅.
⚠
Drift velocity w, not gas velocity, drives the Deutsch–Anderson equation.

📚 Standard references

Air Pollution Control Engineering — Noel de Nevers · Particulate Control
Environmental Pollution Control Engineering — C.S. Rao

PART 2

Progressive 3-Tier Question Suite

Q1MEDIUM2 Marks · NAT

An ESP has collection area A = 200 m², drift velocity w = 0.1 m/s and gas flow Q = 50 m³/s. By Deutsch–Anderson, its efficiency is _____ %.

Q2BASIC1 Mark · MCQ

Which control device is least effective for fine (sub-micron) particulate matter?

Q3HARD2 Marks · MCQ

In the Deutsch–Anderson equation, ESP efficiency increases when: