Hot-blast main (carrying preheated air at about 1000 °C) in blast-furnace practice: which refractory brick is commonly used for lining the main?

Introduction / Context:
The hot-blast main transports preheated air from stoves to the blast furnace, typically around 900–1100 °C. Lining selection must balance thermal shock resistance, cost, and adequacy of refractoriness for continuous service in oxidizing conditions.

Given Data / Assumptions:

• Operating temperature circa 1000 °C.
• Oxidizing gas stream (air), thermal cycling during startup/shutdown.
• Need a practical, economical brick choice widely used in industry.

Concept / Approach:
Fireclay bricks are commonly used for hot-blast mains because they provide adequate refractoriness at ~1000 °C, decent thermal shock resistance, and good economy. Silica bricks, while excellent at very high steady temperatures, have poor thermal shock tolerance and are therefore less suited to cyclic conditions in mains. Basic bricks (magnesite, chrome-magnesite) are unnecessary for an oxidizing air stream and are costlier. Zirconia is premium and reserved for extreme duty zones; it is over-specified here.

Step-by-Step Solution:
Match temperature (~1000 °C) to fireclay capability.Consider thermal cycling: fireclay handles it better than silica in this duty.Exclude basic and ultra-premium bricks as uneconomical for air mains.Select “Fireclay bricks.”

Verification / Alternative check:
Practice notes and lining schedules for blast furnace auxiliaries frequently specify fireclay linings for hot-blast mains and uptakes.

Why Other Options Are Wrong:
Silica: poor shock resistance under cyclic temperatures of mains.Magnesite/Chrome-magnesite: unnecessary chemistry and higher cost.Zirconia: excessive cost/capability for this duty.

Common Pitfalls:
Assuming the same brick as stoves’ checkerwork (often silica) should be used in mains; service conditions differ.

Final Answer:
Fireclay bricks