Where should refractories have low thermal conductivity? Select the application that primarily demands insulating (low-k) refractories.

Introduction / Context:
Thermal conductivity (k) of refractories dictates heat flow. In some equipment, the refractory must actively transfer or store heat (favoring higher k), while in others the primary goal is energy conservation and shell-temperature control (favoring lower k). Recognizing which services prioritize insulation prevents excessive heat loss and inefficiency.

Given Data / Assumptions:

• Coke ovens and regenerators rely on heat storage/transfer across checkerwork.
• Muffle furnaces require an insulated enclosure to separate product from flame.
• “Insulation” in the options refers to backup and energy-saving linings whose role is minimizing heat loss.

Concept / Approach:
Insulating refractories are engineered for low thermal conductivity via porosity and microstructure. They serve as backup linings behind dense hot-face bricks or as energy-conservation layers, reducing heat loss and keeping the steel shell cool. Conversely, regenerators benefit from higher k to store/release heat efficiently; coke-oven hot faces and some muffles may balance insulation with durability but the explicit application that primarily demands low k is insulation itself.

Step-by-Step Solution:

Verification / Alternative check:
Design manuals specify multilayer linings with an insulating backup of low k, followed by denser hot-face bricks suited to chemical and mechanical attacks.

Why Other Options Are Wrong:

Common Pitfalls:
Specifying ultra-insulating hot-face materials where thermal shock or chemical attack dominates; ignoring multilayer design.

Final Answer:
Insulation (backup linings and energy conservation)