Recuperative furnace example Identify which of the following furnaces commonly employs a recuperator (continuous heat exchanger) for air preheating rather than classic regenerators.

Introduction / Context:
Heat recovery in high-temperature furnaces is achieved either by regenerators (cyclic heat storage in checkers) or by recuperators (continuous gas-to-air heat exchangers). Knowing which furnaces typically use which device helps in understanding layouts and efficiency expectations.

Given Data / Assumptions:

• Open-hearth and coke ovens are historical examples well known for regenerative checkerwork.
• Soaking pits for billets/ingots are frequently equipped with recuperators to preheat combustion air using flue gases.
• Electric arc furnaces do not rely on combustion-air preheat for the main energy input.

Concept / Approach:
Regenerators alternate flow through hot checker bricks, while recuperators continuously transfer heat across a wall. Open-hearth and coke ovens are classic regenerative designs; soaking pits often adopt compact metallic or ceramic recuperators for simplicity and continuous preheat.

Step-by-Step Solution:

Verification / Alternative check:
Plant schematics and vendor literature for soaking pits show inline recuperators feeding preheated air to burners.

Why Other Options Are Wrong:

• Open-hearth / Coke ovens: Use regenerators with flow reversal through checkerwork.
• None of these: Incorrect because soaking pits are known recuperative applications.
• Electric arc furnace: Electrical heating; burner air preheat is not the defining energy path.

Common Pitfalls:
Assuming all large furnaces are regenerative; many medium-duty units prefer recuperators for lower complexity.

Final Answer:
Soaking pit