Ceramic vs. metallic recuperators: For the same heat-recovery duty, how do ceramic recuperators compare with metallic recuperators in furnace service?

Introduction / Context:
Recuperators transfer heat continuously from hot flue gas to combustion air. Material choice affects allowable temperature, footprint, cost, and pressure drop. Ceramics enable very high preheats but influence layout and hydraulics.

Given Data / Assumptions:

• Same duty (same heat transfer required).
• Ceramic units use refractory/ceramic elements; metallic units use high-temperature alloys.
• Designs target comparable approach temperatures and cleanliness.

Concept / Approach:
Ceramics tolerate higher temperatures but have lower thermal conductivity than metals and require thicker sections and larger surface area to achieve the same duty at comparable allowable stresses. This generally results in bulkier equipment and larger installation footprints.

Step-by-Step Solution:
Compare material properties: metals have higher thermal conductivity and thinner walls; ceramics need larger exchange area.For the same duty, expect greater volume/space for ceramic designs.Therefore, select the option stating they occupy more space.

Verification / Alternative check:
Vendor catalogues show ceramic honeycomb modules assembled into larger housings than comparable metallic tubular recuperators for the same duty, confirming greater space requirements.

Why Other Options Are Wrong:

• Lighter in weight: not reliably true; total installed weight depends on casing and refractories; footprint, not mass, is the consistent differentiator.
• Less costly: ceramics are typically costlier per duty due to materials and fabrication.
• Always higher pressure differential: pressure drop depends on geometry; while small hydraulic diameters can increase drop, it is not an absolute rule.

Common Pitfalls:
Equating higher temperature capability with better performance across all metrics; ignoring layout and maintenance space impacts.

Final Answer:
They occupy more space for equivalent duty.