Hydrothermal bio-char as a foaming agent for electric arc furnace steelmaking: Performance and mechanism

Electric arc furnace (EAF) foaming agent protects the furnace lining, reduces electricity consumption, and shortens smelting time in steelmaking process. Carbon-neutral EAF foaming agents with satisfactory foaming performance are of great significance for energy-saving and emission reduction in EAF steelmaking. In this study, effects of hydrothermal variables on the foaming performance of EAF slag with bio-char and the associated mechanism were investigated. Meanwhile, the existing method for evaluating EAF slag foaming performance was upgraded, by developing a real-time, dynamic and accurate monitoring method. It was demonstrated that effects of hydrothermal variables on EAF slag foaming with the resultant bio-char followed the order of hydrothermal temperature > solid/liquid ratio > agitation speed > residence time. A combination of hydrothermal temperature at 280 degrees C, residence time for 4 h, agitation speed at 1050 r/min, solid/liquid ratio of 1:30 resulted in biochar as the foaming agent with the effective foaming time up to 353 s, much higher than that of fossil derived foaming agent (219 s). When applied with EAF slag for foaming, the porous structure of bio-char contributed to a more constant slag viscosity at 0.30-0.32 Pa.s, and a decelerated reduction of surface tension, which effectively extended the foaming time and stabilized the foaming performance. The application of bio-char also led to a more complete reaction in EAF in a shorter time. Bio-char obtained via hydrothermal carbonization of pine sawdust performed satisfactorily as an EAF foaming agent and it is advantageous over the fossil derived foaming agent.