Packed versus plate (tray) towers: Identify the incorrect statement when comparing performance and selection criteria for packed and plate columns.

Introduction / Context:
Choosing between packed and plate (tray) towers requires considering hydraulics, mass transfer, fouling tendency, thermal effects, and equipment weight. Many rules of thumb exist, but some statements can be misleading without context, especially regarding relative weights and ancillary features such as interstage cooling.

Given Data / Assumptions:

• Similar duty and separation difficulty.
• Comparable shell sizes and materials.
• Random/structured packing versus typical sieve/valve/bubble-cap trays.

Concept / Approach:
Trayed columns allow straightforward interstage cooling/heating, side draws, and liquid sampling; they also tolerate solids better than packed beds that plug. For large temperature swings, trays avoid the risk of packing damage, especially with ceramic or brittle packings. Regarding dry equipment weight, packed columns frequently carry substantial packing mass; therefore, it is not generally correct to assert that a trayed column is “usually much heavier.”

Step-by-Step Reasoning:

Verification / Alternative check:
Vendor data for comparable diameter/height show significant packing mass (especially ceramic/metal random or structured packing), sometimes exceeding tray weights per equivalent height.

Why Other Options Are Wrong (or Not Best):

• (a), (b), and (d) reflect accepted design practice.
• (e) is also questionable; however, option (c) is the single most clearly incorrect statement among the given choices.

Common Pitfalls:
Assuming “one-size-fits-all” rules; ignoring solids handling and thermal shock; overlooking maintenance access and revamp needs when choosing internals.

Final Answer:
The total dry weight of a plate tower is usually much greater than that of a dry packed tower designed for the same duty.