Investigation of Suitable Oxygen Carriers for Chemical Looping Reforming
Chemical looping reforming (CLR) is an attractive process for hydrogen (H2) production from fossil fuels. The choice of oxygen carrier (OC) in CLR process is critical. A suitable OC should possess high mechanical strength and thermal stability as it reacts with fuel, steam and air in different reactors under severe conditions. Therefore, the OC should be selected after careful consideration of its physical and chemical properties. In this study, several candidate materials were analyzed based on their physical and chemical properties. The set of candidate materials which passed initial screening were assessed by using equilibrium calculations in order to determine their potential for methane (CH4) conversion and the amount of hydrogen (H2) produced per mole of fuel. Additionally, the solid circulation rate in the fuel reactor at different metal oxide content and solid conversion were also calculated. Oxides of iron (Fe), vanadium (V) and tungsten (W) were selected as the suitable oxygen carriers for CLR process. It was found that complete CH4 conversion is obtained at low temperatures for Fe oxide while the same is obtained at high temperatures for V oxide. H2 production per mole of CH4 is the highest for W oxide and it decreases steeply with increasing temperatures. Fe and W oxides have low oxygen partial pressures which indicates that the equilibrium reaction shifts towards the oxide formation. Solid circulation rate is the lowest for Fe oxide. Based on the results obtained in this study, it can be said the Fe oxide is the best option for H2 production in a three reactor CLR process.