Reactivity of iron oxide as an oxygen carrier for chemical-looping hydrogen production

Abstract

The three-reactor chemical-looping (TRCL) process is a three-step water-splitting cycle for production of hydrogen with intrinsic CO2 separation. Iron oxide (Fe2O3), a metal oxide acting as an oxygen carrier, is a strong reducing agent for steam circulating through reactors in the TRCL process. In the present study, the reactivity of iron oxide (20 wt% Fe2O3/ZrO2) was determined in a batch reactor by exposing it to reducing and oxidizing conditions to simulate the TRCL process in a moving bed operation. The minimum steam fraction in the CH4/H2O mixture and the reduction rate were determined under a reducing atmosphere. The water conversion and the oxidation rate were obtained under oxidizing conditions. Based on the reactivity data, key parameters such as bed inventory and the solid circulation rate of the system according to the extent of the solid conversion were calculated. It is found that 170–220 kg/MWth and 300–1410 kg/MWth of oxygen carriers are needed in the fuel and steam reactor, respectively. The solid circulation rate through the reactors was calculated as 2–4 kg/s-MWth. The bed inventory showed a minimum value when the iron oxide was reduced to FeO0.5 by methane and then oxidized to FeO by steam.