Perforated (sieve) plate towers — Which of the following statements are typically true for design and operation of perforated plate (sieve) columns?

Introduction:
Sieve trays are widely used due to simple construction and low pressure drop. Correct ranges for hole size and fractional open area help achieve adequate vapour–liquid contact while minimising weeping and entrainment.

Given Data / Assumptions:

• Conventional hydrocarbon/aqueous services.
• Standard hole and pitch practices.
• Comparison to bubble-cap trays.

Concept / Approach:
Small holes (≈1/8–3/16 in, about 3–5 mm) and an open area ≈6–15% typically give good performance across a range of loads. Compared with bubble-cap trays, sieve trays have fewer elements obstructing flow, leading to lower pressure drop at comparable capacities, though with a somewhat narrower operating range.

Step-by-Step Solution:
Recognise standard hole sizes: 1/8–3/16 in common, larger sizes used for fouling services.Open area target: 6–15% balances weeping risk and pressure drop.Compare pressure drops: sieve trays < bubble-cap due to simpler flow path.

Verification / Alternative check:
Tray vendor datasheets corroborate these ranges and the relative pressure drop advantage of sieve trays.

Why Other Options Are Wrong:

• Each of (a), (b), and (c) is accurate; hence the combined choice (d) is correct.

Common Pitfalls:
Overlooking fouling tendency which may require larger holes; ignoring that valve trays can extend turndown compared to plain sieve trays.

Final Answer:
all (a), (b) and (c).