Thermal efficiency among furnace types — which is highest? Considering typical industrial practice, which furnace type is generally the most thermally efficient?

Introduction / Context:
Thermal efficiency measures how effectively a furnace converts fuel energy into useful process heat. Differences in heat-transfer mode, exhaust losses, and heat-recovery features lead to wide efficiency variation across furnace types.

Given Data / Assumptions:

• Typical industrial designs with common levels of heat recovery.
• Boiler furnaces are optimized to transfer heat to water/steam with extensive convective surfaces.
• Reverberatory furnaces, rotary kilns, and reheating furnaces often have larger radiative and exhaust losses.

Concept / Approach:
Boiler furnaces use well-developed heat-transfer surfaces (waterwalls, superheaters, economizers, air preheaters) and controlled draft, achieving high fuel-to-steam efficiency. Process furnaces like reverberatory and rotary kilns have higher shell radiation and flue losses due to geometry and duty (e.g., long residence, high exit gas temperature). Reheating furnaces are intermediate but typically below well-designed boiler systems in thermal efficiency.

Step-by-Step Solution:
Compare heat-recovery equipment: boilers have economizers and air preheaters as standard.Assess exhaust temperatures and surface losses: often lower in boilers due to extensive convection banks.Select the furnace with the highest typical efficiency: boiler furnace.

Verification / Alternative check:
Typical figures: modern boiler efficiencies (fuel-to-steam) commonly exceed those of rotary kilns or reverberatory furnaces under comparable technology levels.

Why Other Options Are Wrong:

• Reverberatory/Rotary kilns: higher radiative and exhaust losses, less surface area per unit duty for recovery.
• Reheating furnace: efficient with recuperation/regeneration but usually below boilers designed for maximum heat recovery.

Common Pitfalls:

• Comparing specialized, heavily recovered process furnaces with baseline boilers; even then, boilers typically retain an advantage in thermal efficiency due to duty symmetry and surface design.

Final Answer:
Boiler furnace