**Francisco M. Baena-Moreno \*, Mónica Rodríguez-Galán, Benito Navarrete and Luis F. Vilches**

Chemical and Environmental Engineering Department, Technical School of Engineering, University of Seville, C/Camino de los Descubrimientos s/n, 41092 Sevilla, Spain; mrgmonica@us.es (M.R.-G.);

bnavarrete@us.es (B.N.); luisvilches@us.es (L.F.V.) **\*** Correspondence: fbaena2@us.es

Received: 6 November 2020; Accepted: 25 November 2020; Published: 2 December 2020

**Abstract:** Herein, a novel method for energy recovery from molten synthetic slags is analyzed. In this work, the potential energy that could be recovered from the production of synthetic slag is estimated by means of an integrated experimental–theoretical study. The energy to be recovered comes from the cooling–solidification stage of the synthetic slag manufacturing. Traditionally, the solidification stage has been carried out through quick cooling with water, which does not allow the energy recovery. In this paper, a novel cooling method based on metal spheres is presented, which allows the energy recovery from the molten slags. Two points present novelty in this work: (1) the method for measuring the metal spheres temperature (2) and the estimation of the energy that could be recovered from these systems in slag manufacturing. The results forecasted that the temperature achieved by the metal spheres was in the range of 295–410 ◦C in the center and 302–482 ◦C on the surface. Furthermore, we estimated that 325–550 kJ/kg of molten material could be recovered, of which 15% of the energy consumption is in the synthetic slag manufacturing process. Overall, the results obtained confirmed the potential of our proposal for energy recovery from the cooling–solidification stage of synthetic slag manufacturing.

**Keywords:** sustainable synthetic slag production; energy recovery; metal spheres; fixed bed regenerator; waste and energy nexus
