Among common industrial units, which furnace typically operates on natural draft rather than relying on forced or induced draft fans?

Introduction / Context:
Draft is the driving force that supplies combustion air and removes flue gases. Furnaces may use natural draft (buoyancy-driven) or mechanical draft (forced or induced via fans). Knowing which units commonly rely on natural draft is important for understanding control simplicity and operating limits.

Given Data / Assumptions:

• Natural draft arises from the density difference between hot flue gases and cooler ambient air.
• Mechanical draft systems use fans for control and higher firing rates.
• We compare typical industry practice for each unit listed.

Concept / Approach:
Coke ovens (especially traditional or by-product types) often employ natural draft through their flues and regenerators, relying on chimney height and gas temperature. In contrast, utility/industrial boilers and rotary kilns widely use forced and/or induced draft fans for better control. The LD converter (basic oxygen furnace) is not a natural-draft-fired furnace; it is an oxygen-blown metallurgical reactor with specialized off-gas handling.

Step-by-Step Solution:
Identify which listed unit commonly uses natural-draft passages: coke oven batteries.Exclude boilers and kilns that typically require FD/ID for stable control.Exclude LD converter as it is not a combustion-based draft system.

Verification / Alternative check:
Operating descriptions of coke oven batteries highlight chimney-regenerator arrangements relying primarily on buoyancy-driven flow, with dampers for distribution.

Why Other Options Are Wrong:
Boiler/Rotary kilns: Usually use FD/ID fans to control excess air and pressure.L.D. converter: Not a furnace that depends on flue-gas draft in the same sense.

Common Pitfalls:

• Assuming all large heat-consuming units must use fans; traditional coke ovens are a notable exception.
• Equating “stack present” with mechanical draft—stacks can be purely natural draft.

Final Answer:
Coke oven