One of the biggest losses in steel industry from environmental aspect is that steel slag has a notable unused energy potential, since temperature of the slag could be up to 1450-1550°C. Steel slag is typically processed to a by-product without recovering its heat energy and ton of slag contains 1-2 GJ of energy. Slag is typically cooled on contact with the atmosphere or by water during the solidification process. Currently in many cases in steel industry slag is poured on the ground to cool down or gathered in pots before being poured on the ground in the separate location to cool down. A traditional approach to control the cooling time of the hot slag is water quenching, which only consumes huge amount of water and fails to recover the heat of the slag. (Mendoza-Cuenca et al. 2015, Zhang et al. 2013)

Heat recovery

By recovering heat from the steel slag, industry can make some significant profits and create zero emission and green energy. The main problem of the heat recovery is that how to do it efficiently and with low cost. Instead of cooling the slag down on the ground it, the heat energy is possible to recover by using RecHeat® heat exchanger. Heat recovery with the heat exchanger technology is based on the metal structure with a large heat transfer area, on which the liquid hot slag is poured on. From the transport vessel the hot medium is poured on the heat exchanger structure. The hot slag heats up the air flow, which is sucked/blown through the metal structure of the heat exchanger. The metal structure works as a kind of tube heat exchanger, and without water consumption.

Hot air from the heat exchanger has multiple usage applications. The most efficient and cost-effective way of all is use air for drying. ModHeat® material dryer is capable of drying various materials from steel industry sludges to biomasses. In biomass energy is bound. By drying, the energy content of the product increases, and it also increases the value of the product. The dried biomass can be used for energy production and as higher value-added product e.g. biochar. Sludges are not utilized and recovered in a large scale and one big reason is moisture and fineness of the material. Drying of these materials is also possible and efficient with ModHeat®. ModHeat® is a scalable and modular unit and its capacity is up to 20 000 tons/year. After the drying, by-products get more value and with totally free and green energy. This recovery method with these patented units has been studied in collaboration with leading research centers in the field.

Benefits of recovering the heat energy from waste slag with RecHeat®

  • By using RecHeat®, part of the heat energy can be recovered. This energy is totally green and zero emission.
  • No water needed for cooling down the slag.
  • Utilization of waste heat can substitute the need of primary energy in various use cases.
  • Excess heat can be used to dry by-products and biomass with ModHeat®.
  • Waste heat temperature up to 200 to 300°C.
  • Over 10% heat recovery of overall heat capacity of slag.
  • Slag quality is enhanced because of the accelerated cooling instead of quenching.
  • Heat exchanger structure is easy to clean and maintain.



J.L. Mendoza-Cuenca, M. Mayorga, L. Romero-Salazar, H.T. Yee-Madeira, J. Jiménez-Gallegos, J.C. Arteaga-Arcos, 2015. Advances in the Use of the Steel Industry by-products when Manufacturing Traditional Ceramics for Sustainable Purposes

Available at: [Accessed: 22 January 2021]

Hui Zhang, Hong Wang, Xun Zhu, Yong-Jun Qiu, Kai Li, Rong Chen, Qiang Liao, 2013. A review of waste heat recovery technologies towards molten slag in steel industry.

Available at: [Accessed 25 January 2021]