In 2020, a world leading company producing metallic structures in Medina de Campo (Valladolid, Spain) started a heat recovery project . The company has a galvanizing line with a capacity to produce 50,000 tons/year. This project recovers the heat available in the exhaust fumes of the galvanizing furnace by means of a fume/water exchanger called an economizer together with all the necessary auxiliary equipment (fans, valves, filters, etc.) for efficient and safe operation.

The economizer heats a closed hot water circuit which supplies heat to the various consumers in the galvanizing plant:

• Flux circuit.
• Degreasing circuit.
• Dryer.
• Combustion air.

Since the heat available in the exhaust fumes of the galvanizing furnace is not sufficient to cover all the consumption of the galvanizing plant, a back-up boiler is available to partially compensate for the lack of heat. In the event that the galvanizing furnace is shut down or with very low production, the heat demands of the various consumers are reduced:

• Decrease the flux temperature from 40ºC to 35ºC.
• Decrease the degreasing temperature from 55ºC to 45ºC.
• Decrease the temperature of the dryer from 90ºC to 70ºC.
• Momentarily cancel the heating of the combustion air.
• Override the air heating of the dryer if low production is prolonged.

When the galvanizing furnace increases its production again, the different consumers are reset in reverse order and the setpoint temperatures are increased. The heat recovery system is automatically stabilized by its own thermal inertia and by the partial backup provided by the back-up boiler.