Packed towers using Pall rings: redistributors are typically installed every 6 m or 5–10 times the column diameter (whichever is less). What is the recommended maximum packing size relative to column diameter?

Introduction / Context:
Random packing size selection balances pressure drop, capacity, and mass-transfer efficiency. Oversized packing relative to the column diameter causes wall effects and poor liquid distribution, while undersized packing increases pressure drop and risk of flooding.

Given Data / Assumptions:

• Pall ring random packing in gas–liquid service.
• Reasonable distributor quality; redistributors installed per guidance (6 m or 5–10 D).
• Standard industrial turndown and fouling considerations.

Concept / Approach:
To maintain an adequate number of pieces across the cross-section and avoid channeling, the maximum packing size is limited to a small fraction of the column diameter. A widely applied rule is to keep packing size below roughly one-tenth to one-fifteenth of the column diameter, ensuring many packing elements span the cross-section for good distribution and efficiency.

Step-by-Step Solution:
Relate packing size to column diameter to minimize wall/channeling effects.Select maximum size ≈ D/10 to D/15 to ensure sufficient count across the area.Use redistributors to correct inevitable maldistribution over height.

Verification / Alternative check:
Packed tower design charts and vendor catalogs recommend limiting element size to about 0.07–0.10 D for most services, aligning with the 1/10–1/15 guideline.

Why Other Options Are Wrong:
(b) Too large—risk of severe maldistribution; (c) may be overly small for economy; (d) unrealistic; (e) false—diameter matters for packing size selection.

Common Pitfalls:
Ignoring distributor quality; assuming vacuum service allows arbitrarily large packing; neglecting fouling tendencies when selecting size.

Final Answer:
About 1/10 to 1/15 of the column diameter