Tunnel kilns in refractory and ceramic processing are predominantly employed for which stage of manufacture or treatment?

Introduction / Context:
Tunnel kilns are long continuous kilns through which cars loaded with product move at controlled speed through preheat, firing, and cooling zones. They are widespread in the ceramic and refractory industries for consistent, high-throughput thermal treatment.

Given Data / Assumptions:

• Continuous kiln with controlled temperature profile.
• Products: refractories, bricks, tiles, and ceramics.
• Operations include drying/tempering or firing depending on plant configuration.

Concept / Approach:
In many refractory plants, tunnel kilns are used for long, uniform drying/tempering and firing cycles that ensure dimensional stability and adequate mechanical properties. The listed alternatives (pyrite roasting, slab reheating, glass melting) involve different equipment: multiple hearth/roasters, reheating furnaces, and glass tanks respectively.

Step-by-Step Solution:
1) Match equipment to industry: tunnel kilns ↔ ceramics/refractories.2) Identify typical operation: controlled drying/tempering and firing.3) Select the closest listed application: drying/tempering of refractories.

Verification / Alternative check:
Process layouts for brick/refractory plants show green products dried and then fired in tunnel kilns with zoned heating.

Why Other Options Are Wrong:
roasting of pyrites: Uses roasters, not tunnel kilns.reheating of slabs: Performed in dedicated reheating furnaces in rolling mills.melting of glass: Done in continuous tank furnaces.

Common Pitfalls:
Assuming all continuous high-temperature processes use tunnel kilns—equipment is application-specific.

Final Answer:
drying/tempering of refractories.