Tube mill versus standard ball mill: select the combination of characteristics that correctly differentiates a tube mill (long mill) from a conventional ball mill used in fine grinding service.

Introduction / Context:
Both tube mills and ball mills are tumbling mills, but tube mills are optimized for very fine finish grinding (e.g., in cement) using smaller media and long residence times. Knowing their distinguishing traits ensures correct equipment selection in plant design or troubleshooting.

Given Data / Assumptions:

• Tube mills are long cylinders with L/D typically greater than 2.
• Fine grinding requires smaller balls and longer residence time.
• Finer product generally demands higher specific energy, raising power consumption for the same throughput.

Concept / Approach:
Geometry (L/D), media size, and energy demand co-vary. Increasing L/D allows staged grinding and extended classification effects. Smaller balls enhance surface contact for fine breakage. Finer targets typically increase kWh per ton.

Step-by-Step Solution:
Check L/D: tube mills > 2; standard ball mills near or modestly above 1.Check media: tube mills use smaller balls than coarse grinding ball mills.Check energy: finer product → higher specific energy → more power at similar capacity.

Verification / Alternative check:
Process handbooks and OEM literature describe tube mills as the long variant designed for finish grinding with smaller media and higher energy demand per tonne.

Why Other Options Are Wrong:
Each single statement (a), (b), or (c) is correct but incomplete. The only answer that captures the full, correct set of distinctions is “All (a), (b) and (c)”.

Common Pitfalls:
Assuming lower power for finer milling. In reality, as P80 decreases, specific energy requirements rise, so tube mills often draw more power for a given throughput than coarser-duty ball mills.

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