Ceramic recuperators for waste-heat recovery from high-temperature flue gases are typically fabricated from which refractory material?

Introduction / Context:
Ceramic recuperators recover heat from hot flue gases to preheat combustion air, improving furnace efficiency. The material must withstand high temperatures, thermal shock, oxidation/corrosion, and erosive gas streams while providing good thermal conductivity to transfer heat efficiently.

Given Data / Assumptions:

• Flue gas temperatures often exceed 1000 °C.
• Thermal cycling is common due to operation changes.
• High thermal conductivity is desirable for compact, efficient heat exchange.

Concept / Approach:
Silicon carbide (SiC) is a go-to material for recuperator elements because it combines high thermal conductivity, good strength at elevated temperatures, and solid oxidation resistance (forming a protective SiO2 layer). Compared to fireclay or siliceous fireclay, SiC offers far superior heat transfer and shock resistance. While corundum (alumina) has excellent refractoriness, its thermal conductivity is lower than SiC, and thermal shock resistance is generally inferior for thin-walled heat-exchange parts.

Step-by-Step Solution:
List requirements: high T strength, shock resistance, thermal conductivity.Match properties: SiC excels on all three counts for recuperator tubes/plates.Exclude lower-conductivity oxides for heat-exchange efficiency.Select “Silicon carbide (SiC).”

Verification / Alternative check:
Manufacturer datasheets for ceramic recuperator components frequently specify reaction-bonded or recrystallized SiC grades for long service life and efficient heat transfer.

Why Other Options Are Wrong:
Fireclay/Siliceous fireclay: economical but lower conductivity and shock resistance.Corundum: refractory but not the preferred heat-exchange material versus SiC.Mullite only: used in some parts, but SiC is the archetypal choice.

Common Pitfalls:
Confusing structural linings (often fireclay/high-alumina) with heat-exchange elements which demand high conductivity.

Final Answer:
Silicon carbide (SiC)