Lime manufacture—kiln selection for calcination of limestone Calcination of limestone (CaCO3 → CaO + CO2) to produce lime is commonly carried out in which type(s) of kiln?

Introduction / Context:
Lime production requires decomposing calcium carbonate at elevated temperature. The choice of kiln affects fuel efficiency, product reactivity, and capacity. Two popular industrial choices dominate due to their heat transfer characteristics and throughput flexibility.

Given Data / Assumptions:

• Objective: industrial-scale quicklime (CaO) production.
• Feed: sized limestone, controlled residence time.
• Technology: widely practiced, not niche laboratory methods.

Concept / Approach:
Rotary kilns (long cylindrical, slightly inclined, rotating) provide good solids mixing and temperature control, suitable for various stone sizes and fuels. Vertical shaft kilns are energy-efficient for uniformly sized limestone with counter-current flow. Tunnel kilns are primarily used in ceramics for firing bricks/tiles rather than lime calcination.

Step-by-Step Solution:

Verification / Alternative check:
Industry surveys show global lime output from rotary and vertical shaft kilns, with selection driven by stone size, fuel, and capacity.

Why Other Options Are Wrong:

• Tunnel kiln: uncommon for limestone calcination.
• Single selections (b) or (c) alone omit the other widely used kiln type.

Common Pitfalls:
Assuming a single 'best' kiln—economics and raw material sizing often dictate the choice.

Final Answer:
Both (b) and (c)