Bubble-cap trays: for a fixed cap geometry, which factors set the required number of caps per tray in an industrial column?

Introduction / Context:
In bubble-cap trays, vapor rises through risers and discharges via cap slots into the liquid layer. The count of caps per tray governs total vapor-handling area, slot velocities, and contacting uniformity. Determining this count requires a holistic view of hydraulics and geometry rather than a single parameter.

Given Data / Assumptions:

• Cap size and slot geometry are fixed (catalog item).
• Normal distillation/absorption service with crossflow trays.
• Goal: meet capacity, efficiency, and pressure drop constraints.

Concept / Approach:
Allowable slot velocity limits entrainment and pressure drop; plate spacing affects froth height and disengagement, constraining workable vapor rates; column diameter sets available plan area and hence the feasible layout (cap pitch, active area versus downcomer area). Therefore, the cap count emerges from all three factors acting together through tray rating procedures.

Step-by-Step Solution:

Verification / Alternative check:
Vendor rating software iterates these constraints; sensitivity shows each factor materially impacts cap counts and spacing.

Why Other Options Are Wrong:

• Choosing only one parameter ignores the coupled hydraulic and geometric constraints that define workable cap layouts.

Common Pitfalls:
Overcrowding caps and starving downcomers; ignoring fouling allowances; setting slot velocities too high for foamy systems.

Final Answer:
All (a), (b) and (c)