Distillation tray detailing: What is the purpose and recommended placement/size of weep holes provided in tray decks, and which combined statement best captures industry practice?

Introduction / Context:
Weep holes are small openings in distillation tray decks that ensure reliable drainage at shutdown and help maintain tray cleanliness. Their sizing and placement affect start-up behavior, fouling tolerance, and unintended weeping during operation.

Given Data / Assumptions:

• Perforated trays with downcomers and an overflow weir are considered.
• Unit may process fouling or clean services.
• Weep holes exist in addition to active perforations/valves/caps.

Concept / Approach:
In shutdown or low-vapor scenarios, liquid needs an escape path to prevent pooling and corrosion. Placing weep holes near the weir aligns any residual drainage path with normal liquid flow, preventing stagnant zones. Hole diameter must balance fouling tolerance (too small plugs easily) with operational integrity (too large causes excessive leakage at turndown).

Step-by-Step Solution:

Verification / Alternative check:
Tray design manuals and vendor guidelines specify limited weep-hole areas and strategic placement to avoid bypassing active bubbling zones.

Why Other Options Are Wrong:

• Only drainage: incomplete; placement and size matter.
• Placement-only: omits the function and sizing criterion.
• Size-only: omits purpose and placement rationale.

Common Pitfalls:
Oversizing holes leading to weeping at low vapor rates; randomly placing holes and creating maldistribution or dead zones; neglecting fouling characteristics when selecting size.

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