Effect of Slag Composition on Reaction Kinetics of Carbon Composite Agglomerate in the Temperature Range of 1273 K to 1573 K (1000 °C to 1300 °C)

Abstract

To effectively use high Al₂O₃ iron ore in carbon composite agglomerate (CCA) reduction process, the effect of slag composition on the isothermal reaction kinetics of CCA was investigated between 1273 K and 1573 K (1000 °C and 1300 °C). Reduction of the particular oxide by CO and gasification reactions of the carbon by CO₂ were separately measured by quadruple mass spectrometry gas analysis. To better understand the reaction kinetics, the conventional unimolecular reaction model was modified to get two rate equations for reduction and gasification controls with the reaction thermodynamic driving force incorporated. Based on the gas composition data and modified kinetic model, the rate-controlling steps of CCA at various temperatures and reaction stages were determined. In case, the gasification reaction controls the overall reaction, CaO-Al₂O₃ Slag increased the reaction rate by accelerating the gasification reaction while CaO-SiO₂ Slag decreased the rate by retarding the gasification. As the reduction reaction became dominant in controlling the overall reaction, the addition of slag component had adverse effect on the rate although such effect diminished at higher temperature. Finally, the activation energy values calculated by conventional unimolecular reaction model were compared with those evaluated by modified model. It was found that the gas composition data during the course of reaction and the modified model are of great value in interpreting the reaction kinetics when the controlling reaction is changed over with temperature and reaction time. This study is helpful to understand the theoretical aspects on the usage of high Al₂O₃-based iron ores for DRI production.