Applications of shaft furnaces: Shaft-type furnaces (vertical reactors with descending burden and rising gases) are typically used for which thermal processes?

Introduction / Context:
Shaft furnaces are vertical, countercurrent thermal reactors in which solids descend by gravity while hot gases flow upward. Their design supports a wide range of high-temperature processes in minerals and metals industries.

Given Data / Assumptions:

• Generic shaft furnace geometry and operation.
• Appropriate refractory and gas-handling systems.
• Feedstocks include ores, fluxes, and limestone.

Concept / Approach:
Because solids and gases move countercurrently in a compact vertical path, shaft furnaces enable efficient heat and mass transfer, making them suitable for: (a) smelting (e.g., iron blast furnace), (b) calcining (e.g., lime kilns), and (c) roasting (sulfide ores), depending on gas composition and temperature profile.

Step-by-Step Solution:

Verification / Alternative check:
Industrial examples include blast furnaces (smelting), shaft lime kilns (calcining CaCO3 to CaO), and roasting furnaces for sulfides to oxides with SO2 evolution.

Why Other Options Are Wrong:

Common Pitfalls:
Assuming “shaft furnace” implies only ironmaking; the geometry suits many chemistries when gas composition and temperature are tuned.

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