High-temperature heat recovery—materials for ceramic recuperators Ceramic recuperators used for furnace heat recovery are generally made of which refractory material?

Introduction / Context:
Recuperators reclaim heat from hot flue gases to preheat combustion air. Ceramic designs are employed at very high temperatures where metallic heat exchangers would oxidize or creep. Material selection must account for thermal shock, corrosion from combustion products, mechanical strength at temperature, and thermal conductivity.

Given Data / Assumptions:

• Service in hot flue gas streams and preheated air streams.
• Exposure to thermal cycling and potential corrosive species.
• Need for durability and heat transfer performance.

Concept / Approach:
Silicon carbide components offer a compelling combination: excellent thermal shock resistance, high thermal conductivity for efficient heat transfer, good strength retention at elevated temperatures, and oxidation resistance under many furnace atmospheres. These attributes make silicon carbide a common choice for ceramic recuperator elements such as tubes, honeycombs, or plates. Fireclay and high alumina refractories provide refractoriness but have lower thermal conductivity and often poorer thermal shock resistance for thin-section heat exchange elements. Calcium carbide is not used as a structural refractory for recuperators and decomposes under humid or oxidizing conditions.

Step-by-Step Solution:

Verification / Alternative check:
Industrial furnace catalogs and refractory datasheets consistently present silicon carbide as the preferred material for ceramic recuperator tubes and cores due to high conductivity and robustness.

Why Other Options Are Wrong:

• Calcium carbide: chemically unsuitable in hot, potentially moist, oxidizing environments.
• Fireclay bricks: lower conductivity and thermal shock resistance for thin sections.
• High alumina bricks: good refractoriness but less ideal conductivity and shock behavior for recuperator elements.

Common Pitfalls:
Equating refractoriness alone with suitability. Heat exchangers need both refractoriness and thermal conductivity, where silicon carbide excels.

Final Answer:
silicon carbide.