Question

Mechanical agitation is required only in ____________

(a) Packed bed

(b) Airlift reactor

(c) Stirred tank

(d) Bubble column

I have been asked this question by my college professor while I was bunking the class.

My doubt stems from Bioreactor Configurations in division Reactor Engineering of Bioprocess Engineering

Answer 1

The correct answer is:

(c) Stirred tank

Explanation:

• (a) Packed bed: Mechanical agitation is generally not required in packed bed reactors. These reactors rely on the flow of liquids or gases through a packed column to achieve the desired chemical or biological reactions. The agitation is typically provided by the flow itself, not by mechanical means.

• (b) Airlift reactor: In airlift reactors, the agitation is provided by the movement of gases (usually air) that create circulation within the reactor. Mechanical agitation is not typically used in these reactors because the gas flow itself induces the necessary mixing.

• (c) Stirred tank: Correct. Stirred tank reactors (STRs) rely on mechanical agitation to mix the contents of the tank. This mixing is crucial for ensuring uniform distribution of nutrients, oxygen, and other components in bioprocesses. The agitation also helps in preventing the settling of cells or other solid particles and ensures efficient heat transfer.

• (d) Bubble column: Like airlift reactors, bubble column reactors use bubbles (usually from injected gases like air or oxygen) to achieve mixing and do not require mechanical agitation.

Therefore, stirred tank reactors are the ones that typically require mechanical agitation, making option (c) the correct choice.