Packed columns near limiting operation: At (or toward) the flooding region for a given packing and fluids, how does pressure drop per metre of packed height respond to increases in fluid rates or operating pressure?

Introduction / Context:
In packed towers (absorption, stripping, distillation), hydraulic behavior dictates capacity limits. As gas and/or liquid rates rise, pressure drop increases. Approaching flooding, liquid holdup grows rapidly, channels fill, and pressure drop escalates sharply, signaling the operational limit.

Given Data / Assumptions:

• Fixed packing and fluid pair.
• Operation pushed toward the flooding point (capacity limit).
• Steady-state behavior without foaming or fouling complications.

Concept / Approach:
Frictional drop in packed beds stems from gas flow through wetted voids and liquid holdup. Increasing gas rate boosts shear and entrainment; increasing liquid rate thickens films and holdup. Near flooding, the void fraction available to gas collapses and ∆P/m rises dramatically. Higher operating pressure (at fixed mass rates) can reduce gas volumetric flow, but “toward flooding,” the governing trend with rising load is a steep ∆P rise.

Step-by-Step Solution:

Verification / Alternative check:
Design charts (e.g., generalized pressure drop correlations) show steepening pressure drop curves as approach to flooding is made, confirming the trend.

Why Other Options Are Wrong:

• Decrease or no change contradicts observed hydraulics near flooding.
• Dependence on gas solubility is secondary; hydraulic limit is dominated by two-phase flow, not dissolution.

Common Pitfalls:
Confusing “loading” with “flooding.” Loading is the onset of liquid accumulation; flooding is the capacity limit with runaway ∆P. Operators should maintain adequate margin below flooding.

Final Answer:
Increases