In blast furnace hot-blast stoves, the outer combustion chamber is typically lined with which type of refractory brick to provide insulation and structural protection at service temperatures?

Introduction / Context:
Hot-blast stoves used with blast furnaces have a combustion chamber and checkerwork that must withstand sustained thermal cycling. Different zones see different temperatures and chemical environments, so refractories are selected accordingly. This question checks understanding of where fireclay (alumino-silicate) bricks are commonly applied within the stove lining scheme.

Given Data / Assumptions:

• Component: outer combustion chamber of a blast-furnace stove.
• Operating environment: hot gases, but lower peak skin temperatures than the inner hot face or checker dome.
• Goal: adequate refractoriness, insulation, economy, and compatibility with brickwork load-bearing.

Concept / Approach:

Stove linings are graded. The hottest, highly silica-tolerant zones (e.g., dome and checker areas) often use silica bricks for creep resistance at very high temperatures. The outer combustion chamber and backup courses typically use fireclay bricks due to adequate temperature rating, thermal shock tolerance, availability, and cost effectiveness. Ultra-high-end refractories (e.g., zirconia, chrome–magnesite) are reserved for extreme conditions (basic slags, severe corrosion), not usually required for the outer chamber lining of stoves.

Step-by-Step Solution:

Verification / Alternative check:

Typical stove-lining schedules in ironmaking practice show silica bricks at the high-temperature crown/dome and checker zones, with fireclay courses used outward for insulation and structural backing where temperatures are lower.

Why Other Options Are Wrong:

Silica bricks: Common at the hottest crowns/domes, not usually for the outer chamber courses. Chrome–magnesite: Basic refractories for corrosive basic slags, not needed here. Zirconia: Very high temperature specialty; over-specified and uneconomical for this zone.

Common Pitfalls:

Assuming the same brick is used everywhere; ignoring lining gradation and cost-performance optimization.

Final Answer:

Fireclay bricks