Energy recovery from high temperature slags

Molten slags represent one of the largest untapped energy sources in metal manufacturing operations. The waste heat of slags amounting to ∼220 TWh/year at temperatures in the range of 1200–1600 °C, presents an opportunity to lower the energy intensity of metal production. Currently, three types of technologies are under development for utilizing the thermal energy of slags; recovery as hot air or steam, conversion to chemical energy as fuel, and thermoelectric power generation. The former route is most developed with its large scale trials demonstrating recovery efficiencies up to 65%. The latter two are emerging as the next generation methods of waste heat recovery. An evaluation of these methods shows that for both thermal and chemical energy recovery routes, a two-step process would yield a high efficiency with minimal technical risk. For thermoelectric power generation, the use of phase change materials appears to solve some of the current challenges including the mismatch between the slag temperature and operating range of thermoelectric materials.

► A comprehensive review of waste energy of slag and its recovery methods are presented.
► The waste heat of slags amounts to ∼220 TWh/year.
► Recovery of three energy forms from slag heat is under development: thermal, chemical, thermoelectric.