Reduction-oxidation-cycling in a fixed bed reactor with periodic flow reversal

Simulations have been carried out for a modified steam-iron-process as a test reaction for processes where reduction-oxidation cycles will occur in two separated steps in a fixed bed reactor. The particularity of the used reaction system is the combination of a relatively fast exothermic gas-solid reaction in one half-cycle with a slow endothermic one in the other half cycle. A simple pseudohomogeneous, one-dimensional dispersion model yields a complex dynamic behaviour due to the interaction of gas concentration, temperature and oxygen content inside the bed. The simulations show that a periodic change of the flow direction is necessary for utilizing the heat released by the exothermic reaction for the endothermic step and for maintaining a higher conversion rate in the case of a separated equilibrium reaction. Wether the flow reversal should be after a half cycle or a full cycle depends on the reaction system. For the evaluation of these operation alternatives the conversion rate: the time for reaching the periodic steady state and the maximum temperature during the whole process were used.