Question

Cyclones are used for -
(A) The removal of particles of 10 micron or more in diameter from air stream
(B) Separating particles from liquids
(C) Separating liquid droplets from gases
(D) Reducing the size of particles of 10 micron or more in diameter
Choose the correct answer from the options given below:

• A. (A) and (B) only.
• B. (A), (C) and (D) only.
• C. (A), (B) and (C) only.
• D. (A), (B), (C) and (D).

Hint:

Remember that a cyclone is a separator, not a size-reduction machine. Any option stating that cyclones reduce particle size can be immediately ruled out.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
Cyclone separators are gas-solid or liquid-solid separation devices that use centrifugal force to separate dispersed particles or droplets from a carrier fluid stream (gas or liquid).

Step 2: Detailed Explanation:
Let us analyze each statement to determine the functions of cyclones:

Statement (A): The removal of particles of 10 micron or more in diameter from an air stream: This is the primary industrial application of a standard air cyclone.
The dirty air stream enters tangentially at the top of a conical chamber, creating a high-speed vortex.
Centrifugal force throws the denser solid particles outward against the wall, where they slide down and collect in the hopper, while the cleaned air exits upward through the center.
This process is highly effective for particles larger than 10 microns. Thus, (A) istrue.

Statement (B): Separating particles from liquids: A specialized class of cyclones calledhydrocyclones is used to separate solid particles from a liquid carrier fluid.
They operate on the same centrifugal principles to separate sand, silt, or starch granules from water. Thus, (B) istrue.

Statement (C): Separating liquid droplets from gases: Cyclones are also designed as demisters or droplet separators to remove liquid mist or droplets from gas streams, protecting downstream equipment like compressors. Thus, (C) istrue.

Statement (D): Reducing the size of particles of 10 micron or more in diameter: Cyclones are strictly separation and collection devices; they do not perform size reduction. Particle size reduction requires mechanical energy input from mills, grinders, or crushers. Thus, (D) isfalse.
Combining these, the valid applications are (A), (B), and (C).

Step 3: Final Answer:
The correct option is (C), representing (A), (B), and (C) only.