Researchers Outline Pathways for Decarbonizing of Steel Using Slag

The Decarbonization of the iron and steel industry, contributing approximately 8% of current global anthropogenic CO2 emissions, is challenged by the persistently growing global steel demand and limitations of techno-economically feasible options for low-carbon steelmaking. A diversified team of researchers Yongqi Sun, Sicong Tian, Philippe Ciais, Zhenzhong Zeng, Jing Meng & Zuotai Zhang from School of Environmental Science & Engineering, Southern University of Science and Technology Shenzhen China, School of Chemical Engineering at University of Queensland Brisbane Australia, Laboratoire des Sciences du Climat et de l’Environnement in France, The Bartlett School of Sustainable Construction at University College London & The Key Laboratory of Municipal Solid Waste Recycling Technology & Management of Shenzhen City in China have explored the inherent potential of recovering energy and re using materials from waste streams, high temperature slag, and re investing the revenues for carbon capture and storage. In a pathway based on energy recovery and resource recycling of glassy blast furnace slag and crystalline steel slag, we show that a reduction of 28.5 ± 5.7% CO2 emissions to the sectoral 2 degree Celsius target requirements in the iron and steel industry could be realized in 2050 under strong Decarbonization policy consistent with low warming targets. The technological schemes applied to engineer this high-potential pathway could generate revenue of USD 35-40 billion globally in 2035 and 2050, respectively. If this revenue is used for carbon capture and storage implementation, equivalent CO2 emission to the 2 degree Celsius sectoral target requirements is expected to be reduced before 2050, without any external investments.To achieve the 2 degree Celsius climate goals, the iron and steel sector will need to reduce the emission intensity from 1.58 tonnes of CO2 per tonne of crude steel in 2020 to a target of 0.52 tonnes of CO2 per tonne in 2050. The emission scenario in the iron and steel sector for the 2 degree Celsius target is set from the International Energy Agency and the outputs of crude steel and pig iron in 2020-2050 are estimated based on the production scenario given by the United Nations Industrial Development Organization. Based on the annual CO2 emission levels required in 2020-2050 toward the 2 degree Celsius climate goal, they have estimated the CO2 emission reduction potentials of current pathways and schemes based on the heat recovery and resource recycling of waste streams in the iron and steel sector The BF slag forms two final states depending on the cooling rate: glassy and crystalline states. If slag is in the glassy state, it can be used as a cement feedstock and substituted to limestone calcination CO2 emissions, which has a mean emission intensity of ~0.9 tonnes of CO2 per tonne of cement. If slag is in the crystalline state, the economic value is significantly reduced. The critical cooling rate is the key parameter determining the glass-forming ability of liquid slag, the lowest cooling rate required to fully transform BF slag into the glassy state. Currently, three main approaches have been proposed to cool hot BFS with heat recovery and resource recycling, namely natural cooling, water quenching, and dry granulation, with quite different practical cooling rates and states of the cooled slag. Accordingly, three strategies are proposed for BF slag treatmentBFS-Glassy/WaterBFS-Glassy/DryBFS-Crystalline/DryThe crystallization ability of steel slag is quite strong due to the high basicity and FeO concentration, different from BF slag. It is difficult to fully avoid the crystallization behavior of SS because of the high liquidus temperature. In this case, it will be challenging to obtain a 100% glassy state using a dry granulation method, as a crystalline state of steel slag is generally obtained. Nevertheless, if the steel slag is water quenched and held for a long time, a glassy state with a small crystalline content can still be formed. Then, there are two possible approaches for using the remaining unavoidable crystalline steel slag, low economic-value recycling for construction, road and landfilling and high economic-value reuse of CaO to replace limestone calcination in the cement or steel sector like for slag making after necessary iron and phosphorus separations. Three strategies are proposed for steel slag treatmentSS-Crystalline/DrySS-Crystalline/Dry-RSS-Glassy/WaterStarting from the fundamental properties and treatment strategies for BF slag and steel slag, researchers have developed nine pathways for the iron and steel sector, consistent with the 2 degree Celsius global Decarbonization scenarios and targets