Annealing Furnace Exhaust Heat Recovery Heat Exchanger

Annealing Furnace Exhaust Heat Recovery Heat Exchanger

Annealing Furnace: An industrial furnace used in metallurgy, machinery manufacturing, and other industries to perform heat treatment (heating, holding, and slow cooling) on metal workpieces to eliminate internal stresses and improve material properties.

Exhaust Gas: Emissions generated during the heating process of an annealing furnace, typically resulting from fuel combustion or the use of protective gases. These gases usually have temperatures ranging from 300°C to 600°C or even higher. Direct discharge of these gases results in significant energy waste.

Waste Heat Recovery: Recovers thermal energy from these exhaust gases for applications such as preheating combustion air, heating process water, or generating steam.

Finned Tubes: The core component of this heat exchanger type, addressing the fundamental issue of low heat transfer efficiency in gas-to-gas systems.

Why Choose Finned Tube Heat Exchangers? (Core Advantages)

The heat transfer coefficient of gases (such as exhaust gases) is significantly lower than that of liquids or metals. Using bare tubes (plain steel tubes without fins) would require an extremely large heat exchange area, resulting in bulky and costly equipment.

Finned tubes solve this problem through the following mechanisms:

Significantly increased heat transfer area: Within a limited volume, fins dramatically expand the surface area exposed to exhaust gases, achieving 5 to 20 times the area of bare tubes.

Enhanced gas-side heat transfer: Fins disrupt the laminar boundary layer of exhaust gases, inducing turbulence that improves heat transfer efficiency.

Compact structure and cost-effectiveness: For equivalent heat transfer capacity, finned tube heat exchangers are smaller, lighter, and use less material than smooth tube heat exchangers, resulting in lower manufacturing costs and reduced footprint.

High-temperature exhaust gas (e.g., 450°C) from the annealing furnace flows over the outer surface of the finned tubes. The cold medium to be heated (e.g., combustion air or water) flows inside the tubes.

Heat Transfer: Heat from the high-temperature exhaust gas is transferred via conduction through the base tube walls and fins, then via convection to the cold medium flowing inside the tubes.

Temperature Changes:

The exhaust gas is cooled (e.g., from 450°C to 200°C) and then discharged.

The cold medium is heated (e.g., combustion air preheated from 20°C to 300°C; or water heated to hot water/steam).

Energy Cycle:

The preheated combustion air is directly returned to the annealing furnace burner, significantly increasing the theoretical combustion temperature of the fuel and saving fuel (typically 10%–30%). The hot water or steam can be used for other production processes or heating.

Primary Application Forms

Air Preheater: Preheats combustion air. This is the most common and economically advantageous application. Directly reduces fuel consumption and increases furnace temperature.

Hot Water/Steam Generator: Produces hot water for cleaning, heating, or domestic use, or generates low-pressure steam for industrial processes.

Material Preheating: Preheats workpieces or materials entering the annealing furnace, reducing furnace load.