High temperature fluidized bed reactor kinetics with sintering inhibitors for iron oxidation

High purity hydrogen is produced through a thermochemical water splitting process that utilizes iron reduction-oxidation (redox) reactions. An iron powder bed is fluidized to improve heat and mass transfer thus improving the reaction kinetics. Inert additives which act as sintering inhibitors, such as silica (SiO₂) and zirconia (ZrO₂), are added to the iron powder, and their effectiveness in inhibiting sintering in the oxidation step is evaluated. The influence of particle size, composition, mass fraction and bed temperature on reaction kinetics is investigated. Incorporation of zirconia in the powder bed is done by mixing it with iron powder or by coating the iron particles with a mixture of 1-3 μm and 44 μm zirconia particles. Two different batches of silica are used for blending with iron powder. The silica powder batches include particle diameters ranging from 0-45 μm and 200-300 μm. The mixing ratios of silica to iron are 0.33, 0.5, 0.67 and 0.75 by apparent volume. Experimental studies are conducted in a bench scale experimental fluidized bed reactor at bed temperatures of 450, 550, 650, 750 and 850°C. It is verified that increasing the bed temperature and the steam residence time increases the hydrogen yield. Increasing the iron particle size reduces the specific surface area and reduces the hydrogen yield. It has been found that sintering can be completely inhibited by mixing iron with 0-45 μm silica powder and maintaining the reaction temperature below 650°C.