Question

Flooding in a distillation column is detected by a sharp

• A. Increase in Murphree plate efficiency
• B. Increase in pressure drop
• C. Decrease in pressure drop
• D. Decrease in liquid holdup in the column

Hint:

Flooding in a distillation column is indicated by a sharp rise in pressure drop, signaling excessive liquid holdup and disrupted vapor-liquid flow.

Answer 1

The Correct Option is B

Step 1: Understand flooding in a distillation column.
Flooding occurs in a distillation column when the vapor and liquid flows are too high, preventing proper countercurrent flow. In a tray column, this happens when the upward vapor flow impedes the downward liquid flow, causing liquid to accumulate on the trays. In a packed column, it occurs when liquid holdup becomes excessive, blocking vapor flow. Step 2: Analyze the effects of flooding.
When flooding occurs:
Pressure drop: The accumulation of liquid on trays or in packing increases resistance to vapor flow, leading to a sharp increase in pressure drop across the column. This is a primary indicator of flooding, as the vapor struggles to push through the liquid-filled spaces.
Murphree plate efficiency: Flooding reduces the efficiency of mass transfer because the trays become overwhelmed with liquid, leading to poor vapor-liquid contact. Efficiency typically decreases, not increases.
Liquid holdup: Liquid holdup increases during flooding, as liquid cannot flow down the column effectively due to the high vapor flow.
Other effects: Flooding can also cause entrainment (liquid carried upward by vapor) and reduced separation efficiency.
Step 3: Evaluate the options.
(1) Increase in Murphree plate efficiency: Incorrect, as flooding reduces tray efficiency due to poor vapor-liquid contact, not increases it. Incorrect.
(2) Increase in pressure drop: Correct, as flooding causes a sharp increase in pressure drop due to liquid accumulation obstructing vapor flow. Correct.
(3) Decrease in pressure drop: Incorrect, as pressure drop increases, not decreases, during flooding. Incorrect.
(4) Decrease in liquid holdup in the column: Incorrect, as liquid holdup increases during flooding due to liquid accumulation on trays or in packing. Incorrect. Step 4: Select the correct answer.
Flooding in a distillation column is detected by a sharp increase in pressure drop, matching option (2).