Blast furnace troughs and runners: Hot metal runners are commonly lined with which class of refractory bricks for serviceability and economy?

Introduction / Context:
In blast furnaces, hot metal (liquid iron) and slag are guided through troughs and runners. The lining selection must balance thermal shock resistance, corrosion/erosion resistance, cost, and ease of maintenance. Different materials are favored for hot metal versus slag handling.

Given Data / Assumptions:

• Question targets the typical, widely used lining class for hot metal runners.
• Service involves high temperature, molten iron contact, and intermittent thermal cycling.
• Economy and availability also affect choice.

Concept / Approach:
Fireclay and high-alumina refractories have long been used in hot metal runners owing to acceptable resistance to iron erosion and thermal cycling at reasonable cost. Silicon carbide is used in some severe-wear zones, but broadly and economically, fireclay-based shapes and ramming mixes have been prevalent, especially historically and in general practice. Silica refractories are more suited to coke ovens and hot blast stoves; magnesite is a basic refractory better matched to basic slags in furnaces, not the standard choice for hot metal runners.

Step-by-Step Solution:

Verification / Alternative check:
Operations manuals and refractory vendor literature list fireclay/high-alumina castables and bricks as the standard baseline for runners, with SiC used selectively.

Why Other Options Are Wrong:

• Silica: Excellent at high temperatures in stoves but not the go-to for molten iron runners.
• Carborundum (SiC): Used in high-wear areas; not the most common general lining historically.
• Magnesite: Basic slag service; not standard for hot metal runners.

Common Pitfalls:
Assuming the most wear-resistant material (SiC) is always chosen; cost and repairability matter in large-scale ironmaking logistics.

Final Answer:
fireclay