Bubble-cap internals: for distillation columns with diameter roughly 1.5 to 4.5 metres, a typical bubble-cap diameter used in practice is approximately what value?

Introduction / Context:
Bubble caps are classic tray internals that distribute vapor through slots into the liquid on each tray. While many sizes exist, industry practice gravitates toward a few standard diameters that balance fabrication, capacity, and hydraulic performance for mid-size columns.

Given Data / Assumptions:

• Column diameter in the 1.5–4.5 m range.
• Round bubble caps used in conventional services.
• Typical operating pressures and vapor rates for refinery/petrochemical duties.

Concept / Approach:
Cap diameter influences riser area, slot area, jet velocity, and pressure drop. Too small a cap leads to excessive numbers of caps and layout congestion; too large reduces flexibility and can compromise distribution. Around 100 mm (about 4 inches) is a widely used standard cap diameter for such column sizes, offering a practical compromise across many services.

Step-by-Step Solution:

Verification / Alternative check:
Design handbooks list cap diameters in the 75–125 mm range for many services; 100 mm sits near the center of this practical spectrum.

Why Other Options Are Wrong:

• 10 mm or 50 mm: too small for practical throughput; would require excessive cap count.
• 150 mm: feasible in some cases, but 100 mm is more typical for the stated column size range.

Common Pitfalls:
Ignoring foaming tendencies and slot velocities; crowding caps and starving downcomer area; neglecting maintenance/cleaning access between caps.

Final Answer:
100 mm