Which of the following statements is INCORRECT?
- AElectrostatic precipitators are widely used in thermal power plants.
- BBag filters work on the principle of interception and electrostatic attraction.
- CElectrostatic precipitators can collect dry or wet particulates.
- DCollection efficiency of the cyclone collector is high for smaller particles.Correct
Solution
Concept
Cyclone efficiency falls sharply for small particles. Cyclones are good mainly for coarse particles (about 10 μm and larger).
Step-by-step solution
1. Check A: ESPs are widely used in thermal power plants to remove fly ash. This is correct. 2. Check B: Bag filters capture particles by interception, impaction, diffusion and electrostatic attraction. This is acceptable as correct. 3. Check C: ESPs can collect both dry particles and wet particles (wet ESP). This is correct. 4. Check D: A cyclone uses centrifugal force, which is small on fine particles. So its efficiency is LOW for smaller particles. This statement is wrong. 5. The INCORRECT statement is (D).
Explanation
A cyclone separates dust by centrifugal force, and this force depends on particle mass. Small particles have little mass, so they escape with the gas. That is why cyclone efficiency is high for big particles and low for small ones.
Why the other options are wrong
A, B and C are all true statements about ESPs and bag filters, so none of them is the INCORRECT one.
Shortcut
Cyclone = coarse particles. ESP and bag filter = fine particles.
Common mistake
Thinking all air pollution control devices remove small particles efficiently.
Correct answer: D) Collection efficiency of the cyclone collector is high for smaller particles.