Comparison of novel ladle slag treatment and handling systems based on resource-efficiency metrics

Ladle slag is a by-product common to electric and basic oxygen steelmaking furnaces which is gaining increasing attention as a secondary material. Its main recycling path is internal to steelmaking process, since it can replace the lime used to remove impurities. However, storing and handling slag for internal recycling is problematic because cooled ladle slag soon becomes extremely dusty, determining harsh environmental conditions at the plant. Recently, a novel solution based on granulation of ladle slag was presented on the market, which could be integrated in the steelmaking process using diverse handling and storage systems. The implementation of such systems requires resources, specifically energy, but may produce benefits such as lower pollution from particulate emissions and easier storage, leading to lower material losses, reduced landfill disposal and savings of primary mineral resources. In this paper, three alternative treatment and handling systems are analyzed and ranked using ad hoc defined first level resource efficiency metrics. Results show that the best alternative in terms of carbon emission intensity is the more advanced configuration, which includes granulation within a casing and automatic transport with apron conveyors; however, open granulation with current handling systems apparently minimizes primary energy intensity. A possible cause for this discrepancy is that emission factors and primary energy consumption factors obtained from official sources refer to different years, and hence to a different electric energy generation mix. A clear ranking between the basic and the most advanced configuration cannot be obtained, but the resource efficiency evaluation leads to exclude the intermediate configuration (granulation within a casing and traditional materials handling) which is apparently dominated by the remaining alternatives.