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

• Defluidization time increased with increasing the addition amount of MgO and CaO.
• Adding MgO reduced particle adhesion and agglomeration tendency more effectively.
• The coating layer of MgO·FeO and CaO·FeO generated on the surface.
• The coating layer avoided the connection of precipitated iron on the surface.

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.

Defluidization was prolonged with increasing the addition amount of MgO and CaO. The adding of Mg reduced particle cohesiveness and bed agglomeration tendency more effectively. The SEM/EDS analysis showed that the coating layer of magnesio-wustite (MgO⋅FeO) and calcio-wustite (CaO⋅FeO) generated on the surface during reduction process. This coating layer suppressed the connection of precipitated iron, and thus avoided the surfaces of bed particles to adhere.Figure optionsDownload as PowerPoint slide