Waste-heat recovery classification: Which of the following is not a continuous flue-gas waste-heat recovery device used on furnaces?

Introduction / Context:
Flue-gas heat recovery improves thermal efficiency. Devices can be continuous (simultaneous hot- and cold-side flow) or cyclic (periodically reversing flow to store and release heat). Identifying this distinction helps in selecting equipment for different furnace duties and temperatures.

Given Data / Assumptions:

• Economisers, waste-heat boilers, and tubular/ceramic recuperators operate with continuous counter/cocurrent flow.
• Regenerators store heat in a checkerwork and require periodic flow reversal; thus they are cyclic, not continuous.

Concept / Approach:
Continuous devices achieve steady-state heat exchange. Regenerators alternately heat and cool a thermal mass, providing high-temperature air but in a time-switched manner. Therefore, among the options, the regenerator is the non-continuous device.

Step-by-Step Solution:
List options and classify their mode.Identify the cyclic device: regenerator.Select “Regenerator”.

Verification / Alternative check:
Open-hearth/ glass furnaces classically use regenerators with periodic valve reversal, confirming the cyclic nature.

Why Other Options Are Wrong:
Economiser / waste-heat boiler / ceramic recuperator / air preheater: all function continuously.

Common Pitfalls:
Confusing “regenerator” with “recuperator”; they differ precisely by cyclic versus continuous operation.

Final Answer:
Regenerator