Coke sizing for ironmaking: Blast-furnace grade metallurgical coke is usually sized within which of the following ranges (in millimetres)?

Introduction:
Proper coke size is vital for permeability, burden support, and stable gas flow in a blast furnace. Oversized or undersized coke degrades bed hydraulics and can cause pressure drop or excessive fines generation.

Given Data / Assumptions:

• Standard blast-furnace operations handling sinter/pellet burden.
• Need for strong, relatively uniform coke lumps.

Concept / Approach:
Typical metallurgical coke is screened to a mid-size fraction that balances surface area for reaction (e.g., with CO2) and structural strength. Industry practice commonly uses about 25–80 mm as the accepted size range for BF coke charged at the top.

Step-by-Step Solution:
Recall standard screen cuts: fines removed; extreme sizes avoided.Identify accepted plant specification ≈ 25–80 mm.Select the matching option.

Verification / Alternative check:
Ironmaking texts and plant specs specify coke of roughly 25–80 mm for large furnaces to ensure good permeability and CSR/CRI performance.

Why Other Options Are Wrong:

• 0–15, 5–10, 15–25 mm: Too small; cause gas channelling and pressure drop.
• >100 mm: Too large; poor packing and reactivity.

Common Pitfalls:
Assuming that smaller always reacts faster; mechanical strength and bed permeability constrain the size upward.

Final Answer:
25–80