Prevention of agglomeration/defluidization in fluidized bed reduction of Fe2O3 by CO: The role of magnesium and calcium oxide

Influence of magnesium and calcium oxide on control of agglomeration and defluidization during Fe2O3 reduction was investigated in a visual fluidized bed reactor. Added MgO and CaO extended the defluidization time and thus inhibited agglomeration significantly. According to the controlled defluidization tests, the particle cohesiveness and agglomeration tendency of bed materials were reduced by adding MgO and CaO. And the inhibition of MgO was more effective. However, the inhibition effect was reduced with increasing the operating temperature. The coating layers of bed particles were examined by the scanning electron microscope/energy-dispersive spectroscopy (SEM/EDS), coupled with X-ray diffraction (XRD). Results showed that a coating layer on the surface was composed of magnesio-wustite (MgO·FeO) and calcio-wustite (CaO·FeO) generated by the reactions between Mg/Ca oxides and Fe2O3/FeO. During reduction process this coating layer was difficult to reduce and thus suppressed the connection of precipitated iron. Consequently, the bed particles became less sticky and avoided the surfaces of bed particles to adhere.