Distillation tray hydraulics: when the liquid gradient (height difference across a tray) becomes excessive, which malfunctions are most likely to occur?

Introduction / Context:
Successful tray operation requires a controlled interaction between rising vapor and flowing liquid. Excess liquid gradient—large height differences from inlet to outlet—creates uneven hydraulic conditions that compromise vapor distribution and contacting, damaging capacity and efficiency.

Given Data / Assumptions:

• Conventional sieve or cap trays with standard weirs and downcomers.
• Vapor and liquid loads within normal design ranges but with an excessive hydraulic gradient across the tray.
• No unusual internals beyond standard calming zones.

Concept / Approach:
A large gradient raises local liquid head near the outlet and lowers it near the inlet, skewing vapor-liquid contact. The inlet may weep while the outlet area froths excessively. Vapor seeks the path of least resistance, causing maldistribution and potential gas bypass beneath caps or through perforations in undesired zones, and liquid can back-trap in eddies near downcomers.

Step-by-Step Solution:
Recognize that gradient = higher static head at the outlet than the inlet.Higher outlet head increases local pressure drop demand on vapor, diverting vapor to lower-head regions → maldistribution.Unequal heads also promote recirculation pockets and back-trapping of liquid.Local vapor jets can blow beneath skirts/perforations where seal conditions degrade, creating erratic froth and entrainment.

Verification / Alternative check:
Tray rating tools and field troubleshooting guides correlate high gradients with patterns of weeping near inlets, jet flooding near outlets, and erratic pressure-drop profiles—consistent with all effects listed.

Why Other Options Are Wrong:
Each of (a), (b), and (c) can occur together; choosing any subset understates the risk. Therefore (d) is most accurate.

Common Pitfalls:
Ignoring inlet calming sections; over-tight weir/flow path causing excessive path length; neglecting tray leveling which can mimic high gradient effects.

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