Tray internals sizing: for a bubble-cap distillation column with diameter greater than 1.2 m, the typical individual bubble-cap DIAMETER is approximately _____ cm (order of magnitude selection for design).

Introduction / Context:
Bubble-cap trays use risers and caps to disperse vapor through the liquid on each tray, promoting mass transfer. While detailed design depends on vapor/liquid loads and tray spacing, practical ranges exist for cap diameters. This question asks for the typical order-of-magnitude cap size used in columns larger than about 1.2 m diameter.

Given Data / Assumptions:

• Conventional bubble-cap trays (not valve trays or sieve trays).
• Moderate to typical hydrocarbon service with standard tray spacing.
• Rule-of-thumb sizing rather than final detailed design.

Concept / Approach:

Standard bubble caps are commonly manufactured in nominal sizes roughly 75–150 mm (≈ 7.5–15 cm) in diameter. Cap count and spacing are then adjusted to meet the required active area and weeping/flooding constraints. In large-diameter columns (>1.2 m), many caps are used, but the individual cap diameter remains in this approximate range to balance vapor handling, pressure drop, and mechanical layout.

Step-by-Step Solution:

Verification / Alternative check:

Vendor data sheets and plant retrofits repeatedly show cap diameters around 3–6 in, validating the order-of-magnitude choice.

Why Other Options Are Wrong:

20–35 cm are unusually large for individual caps and would reduce distribution quality. 5 cm is smaller than typical standard offerings and can lead to excessive pressure drop or fouling sensitivity.

Common Pitfalls:

Assuming cap diameter scales directly with column diameter; in practice, cap count changes while individual cap sizes stay within standard ranges.

Final Answer:

10