Finned-Tube Radiator for Waste Heat Recovery from Foundry Heat Treatment Furnaces for Workshop Heating

Finned-Tube Radiator for Waste Heat Recovery from Foundry Heat Treatment Furnaces for Workshop Heating

In foundry workshops, heat treatment furnaces (such as annealing, normalizing, and quenching furnaces) continuously emit medium-to-high temperature exhaust gases ranging from 300°C to 600°C during operation. These exhaust gases carry substantial thermal energy, which was traditionally vented directly into the atmosphere. The core of this solution involves installing a finned tube heat exchanger on the exhaust duct of the heat treatment furnace. This recovers residual heat from the exhaust gases to heat air or water, ultimately providing winter heating for the large foundry workshop.

System Operating Principle

Heat Recovery Process:

High-temperature exhaust gases from the heat treatment furnace are introduced into the shell side of the finned tube heat exchanger (flowing outside the fins).

Ambient air (or circulating water) from the workshop is delivered by a fan (or pump) into the tube side of the heat exchanger (flowing through the tubes).

Heat Transfer:

The heat from the exhaust gas is efficiently transferred through the finned tube walls to the clean air or water.

The exhaust gas temperature is reduced from high levels to 150°C ~ 250°C before being discharged through the chimney.

Heating Applications:

Option A (Hot Air Heating): Heated air (70°C to 120°C) is delivered directly to workshop work areas via insulated ductwork.

Option B (Hot Water Heating): Heated water (typically 85°C / 60°C) serves as the heat transfer medium, supplied to the workshop's existing radiator or fan coil system for space heating.

Key Design Considerations and Challenges (for Foundry Workshops)

Dust Accumulation and Blockage:

Challenge Source: Exhaust gases from foundry heat treatment furnaces may contain impurities like iron oxide scale, graphite powder, and oil residues, which readily accumulate between fins.

Solutions:

Use widely spaced fins (recommended minimum spacing of 6mm) or anti-clogging fin types such as spiral-grooved tubes.

Automatic cleaning devices, such as compressed air pulse-jet systems, must be installed for periodic automated dust removal.

Design removable end caps or access doors to facilitate manual maintenance and cleaning.

Corrosion Issues:

Challenge Source: Sulfur in fuels and chlorides from processes may condense on low-temperature surfaces, causing acid dew point corrosion.

Solutions:

Material Selection: Choose corrosion-resistant materials like ND steel or stainless steel (e.g., 304) based on exhaust gas composition.

Temperature Control: Design to ensure the metal wall temperature on the exhaust gas outlet side of the heat exchanger remains above the acid dew point temperature (typically achieved by adjusting medium flow rate and temperature).

Abrasion Issues:

Challenge Source: Hard particulates in exhaust gases cause erosion wear on heat exchange tubes (especially on the windward side).

Solutions: Optimize exhaust gas velocity design; install wear-resistant sleeves on vulnerable sections.

System Integration and Control:

Heating Demand Alignment with Furnace Conditions: Heat treatment furnaces operate cyclically through heating, holding, and cooling phases. An intelligent control system is required to automatically adjust medium flow based on exhaust gas temperature and workshop conditions, ensuring stable operation and switching to backup heat sources during furnace shutdowns.

Benefit Analysis

Direct Economic Benefits:

Zero-Fuel-Cost Heating: Utilizing otherwise wasted thermal energy for heating yields substantial savings on gas or steam costs throughout the heating season.

Short Payback Period: Typically, the investment payback period for such projects ranges from 1 to 3 years.

Indirect and Environmental Benefits:

Improved Workshop Environment: Elevates winter workshop temperatures, safeguards worker health, and boosts production efficiency.

Energy Conservation and Carbon Reduction: Substantially lowers overall workshop energy consumption while reducing greenhouse gas (CO₂) and pollutant (SOx, NOx) emissions.

Lower Flue Gas Temperature: Helps alleviate the load on downstream dust removal equipment (e.g., baghouse filters), extending their operational lifespan.