Optimization of a Chemical-Looping Auto-Thermal Reforming System Working with a Ni-based Oxygen-Carrier

In chemical-looping auto-thermal reforming (CLRa), hydrogen is produced without the need of an exterior heat supply. Thus, an important aspect to be considered in the design of a CLRa system is the heat balance. In this work, mass and heat balances have been done to determine the auto-thermal operating conditions that maximize H-2 production in a CLRa system working with a Ni-based oxygen carrier with a 20 wt % of active metal oxide (NiO). It was found that the oxygen-to-methane molar ratio should be higher than 1.25 to reach auto-thermal conditions, which means that the H-2 yield is 2.7 mol H-2/mol CH4. The control of the oxygen-to-methane ratio by the air flow to the air-reactor was preferred against controlling the oxygen transferred by the solids circulation rate because a lower excess of air was needed in the first case to reach auto-thermal conditions. (C) 2011 Published by Elsevier Ltd.