Tray internals: typical bubble-cap tray layout—what is the usual pitch (center-to-center spacing) as a multiple of the cap outside diameter?

Introduction / Context:
Bubble-cap trays distribute vapor through risers and caps to contact the liquid on the tray deck. The geometric pitch of caps governs hydraulics, froth regime, tray pressure drop, and mass-transfer area per tray. Recognizing typical pitch ranges helps during preliminary layout and vendor discussions.

Given Data / Assumptions:

• Conventional bubble-cap trays handling hydrocarbon or aqueous systems at moderate pressure.
• Standard cap sizes and risers; no special high-capacity designs.
• Uniform staggering pattern across the active area.

Concept / Approach:
Caps must be close enough to ensure uniform vapor distribution and adequate interfacial area, yet far enough apart to limit hydraulic interference and excessive pressure drop. Industry practice typically places caps at roughly 1.6–2.0 times the cap outside diameter (OD), balancing area with froth stability.

Step-by-Step Solution:
Identify the common heuristic: pitch ≈ (1.6–2.0) * OD.Compare options: the offered range in option (b) matches standard design practice.Reject ranges that are too tight (≈1.3 * OD) or too loose (>3 * OD), which risk maldistribution or excessive pressure drop.

Verification / Alternative check:
Vendor catalogs and tray rating tools provide similar pitch guidance, adjusted for cap size, vapour rates, and desired capacity/efficiency trade-offs.

Why Other Options Are Wrong:
(a) is generally tight and may increase interference; (c) “exactly 2.5” is too rigid and typically high; (d) is overly broad; (e) is excessive for most services.

Common Pitfalls:
Assuming one pitch works for all cap sizes; neglecting downcomer layout and active area fraction; ignoring pressure drop constraints when crowding caps.

Final Answer:
1.6 to 2 times the cap OD