Industrial fluidised bed direct reduction kinetics of hematite ore fines in H2 rich gases at elevated pressure

Reduction kinetics of iron ore fines were investigated under fluidised bed conditions with hydrogen-rich gas mixtures in the temperature range from 400 to 700 °C at a pressure of 10 bar. Kinetic parameters were determined for the reactions hematite to magnetite, magnetite to wuestite and wuestite to iron from experimental data. To be able to investigate the influence of both temperature and reducing gas composition on the reaction rate, a laboratory scale pressurised fluidised bed reactor was used which is able to apply process conditions close to those in industrial plants. Appropriate to heterogeneous reactions, a rate expression considering the specific surface area was derived. The time dependent function for the transient evolution of specific surface area was generated from measured mercury porosimetry data. Kinetic parameters such as frequency factor, energy of activation and reaction orders were determined for the consecutive reactions from hematite to magnetite, magnetite to wuestite and wuestite to iron by numerical integration and parameter estimation from measured rate data. A comparison to the evaluation of kinetic parameters without considering specific surface area confirm the results of this work.