Reduction of magnetite for carbon capture in chemical-looping combustion

Abstract

Chemical looping combustion (CLC) is considered an energy-efficient technology compared to conventional combustion systems. Magnetite is a prevalent type of iron ore that can serve as an oxygen carrier, especially in the relatively higher reduction temperature range. To further enhance the sustainability and efficiency of the CLC, this study investigates the reduction of magnetite with graphite as a reducing agent. Limited studies have explored the reduction of magnetite. Thermogravimetric analysis (TGA) and derivative thermogravimetry (DTG) were employed to characterize the reduction behavior of magnetite and graphite mixtures at 1:1 and 2:1 ratios. The results indicated significant reduction rates at 1093 °C and 1110 °C, respectively. Comparative analysis of theoretical and experimental TGA curves quantified the extent of reduction, which then translates to an increased reduction at a relatively higher temperature range. Fourier-transform infrared spectroscopy (FTIR) results revealed the evolution of carbon monoxide CO and CO₂ gases. This indicates a combination of direct and indirect reduction mechanisms with char gasification. The earlier onset of reduction in the 1:1 ratio suggested a higher availability of reducing agents. The study validates that the reduction of magnetite with graphite produces a reduced iron product compatible as an oxygen carrier in CLC systems. By utilizing magnetite as an oxygen carrier, the process offers a pathway to capture CO₂, thus contributing to the sustainable production of energy. The results of this study are significant for further research into reducing magnetite for sustainable iron production and its potential integration into advanced combustion technologies.