Packed or plate column performance metric: in commercial operations, the practical representative values of HETP (height equivalent to a theoretical plate) commonly fall within which approximate range in metres?

Introduction / Context:
HETP (height equivalent to a theoretical plate) is a convenient way to relate mass transfer efficiency to tower height for both packings and trays (by analogy). Knowing typical ranges helps in quick screening and sanity checks before detailed vendor rating.

Given Data / Assumptions:

• Industrial columns operating away from extremes (no very low liquid rates or very viscous systems).
• Reasonably designed distributors for packed towers; standard tray hydraulics.
• Normal surface tensions and moderate relative volatilities.

Concept / Approach:
For many systems, practical HETP values lie in the sub-metre range. Good random packing or modern trays often deliver HETP roughly 0.4–0.9 m, depending on loading, physical properties, and fouling tendencies. Substantially lower values typically require high-performance structured packings under ideal conditions, while higher values indicate poor contacting, maldistribution, or off-design operation.

Step-by-Step Solution:
Relate separation duty (number of theoretical stages) to tower height via HETP.Apply typical commercial experience: H ≈ N * HETP with HETP ≈ 0.4–0.9 m.Choose the range that reflects mainstream practice.

Verification / Alternative check:
Vendor datasheets for common random packings (e.g., 1–2 inch sizes) often report HETP in this neighborhood for hydrocarbon service with good distribution.

Why Other Options Are Wrong:
0.1–0.2: Too optimistic for general services; requires exceptional conditions/packings.0.2–0.5: Lower end may occur, but the full practical span is better captured by 0.4–0.9.1.2–1.5: Typically indicates underperforming contact or very difficult systems.

Common Pitfalls:
Using a single HETP for all loads; ignoring distributor quality which dominates packed-tower efficiency.

Final Answer:
0.4–0.9