Tray columns in petroleum refining (column diameter > 3 ft): what is the minimum recommended tray (plate) spacing typically used?

Introduction / Context:
Tray spacing is the vertical distance between adjacent trays in a distillation column. It influences pressure drop, entrainment, capacity, and maintenance accessibility. Refinery columns of moderate to large diameter commonly follow standardized spacing to balance performance and practicality.

Given Data / Assumptions:

• Columns larger than about 3 ft diameter.
• Conventional trays (sieve/valve/bubble-cap) with typical downcomers.

Concept / Approach:
Too small a spacing increases entrainment and hinders access; too large a spacing adds unnecessary height and cost. Industry practice has converged on about 18 inches as a minimum spacing that allows adequate disengagement and manual access for tray removal during shutdowns.

Step-by-Step Solution:

Verification / Alternative check:
Refinery design handbooks and vendor catalogs list common spacings of 18–24 inches; 18 inches is a frequent minimum for large towers.

Why Other Options Are Wrong:

• 6 or 12 inches: Too tight for personnel access and adequate disengagement.
• 34 inches: Possible but not a minimum; increases column height and cost.

Common Pitfalls:
Ignoring fouling/foam tendencies that may require larger spacing; not coordinating with internal lifting/clearance requirements for tray panels.

Final Answer:
18 inches