Multicriteria assessment of pre-treatment and material handling systems for improved recycling of ladle slag in electric steelmaking

• Cost-benefit assessment of a novel technology to prevent ladle slag dust pollution • Model-based estimates of dust emission reductions range between 70% and 95% • Material handling system design has a significant impact on economic, environmental and safety performance • Reduced carbon equivalent emissions from lower quicklime supply offset emissions from additional fuel and electricity consumption • A fuzzy multi-criteria AHP model supports the selection of the most complex materials handling configuration Ladle Slag (LS) is a by-product of electric steelmaking that can be recycled internally in the electric arc furnace (EAF) to partially replace quicklime as a flux. However, LS cooled at ambient conditions becomes dusty and unstable, which limits the industrial uptake of this practice. A novel fast cooling approach was recently proposed to improve LS properties, but the literature does not provide information on its viability on an industrial scale. This paper fills this gap by investigating the integration of such LS pre-treatment system into a real EAF plant recycling LS. The costs and benefits of three alternative pre-treatment and handling solutions are assessed against the baseline system without pre-treatment, using a fuzzy AHP MCDA model. The introduction of pre-treatment systems is estimated to increase annual equivalent costs by a factor of 2 to 5 and primary energy demand by a factor of approximately 4 to 7. The estimated reduction in dust emissions is in the order of 600 to 900 t/year. Considering the avoided Scope 3 emissions for quicklime production due to improved recycling, the additional carbon equivalent emissions from increased fuel and electricity consumption are offset in most configurations and savings in the order of 80-120 tCO2eq/year are estimated. The selection of material handling systems has a remarkable impact on performance. The MCDA approach identifies the most complex configuration, including a casing and automatic conveyors, as the best compromise considering environmental and economic performance as well as qualitative criteria such as occupational safety and workplace conditions.