Hydrogen production by chemical-looping reforming in a circulating fluidized bed reactor using Ni-based oxygen carriers

This work presents the experimental results obtained during auto-thermal chemical-looping reforming (CLR) in a 900 W-th circulating fluidized bed reactor under continuous operation using methane as fuel. Two oxygen carriers based on NiO and supported on gamma-Al2O3 and alpha-Al2O3 were used during more than 50h of operation with each oxygen carrier. During operation the effect of different operating variables, like fuel reactor temperature, H2O/CH4 molar ratio and solid circulation rate, on CH4 conversion and gas product distribution was analyzed. It was found that in all operating conditions CH4 conversion was very high (>98%) and the most important variable affecting to the gas product distribution was the solid circulation rate, that is, NiO/CH4 molar ratio. Similar gas product distribution was obtained working with both oxygen carriers although at different NiO/CH4 molar ratios. The oxygen carrier of NiO on alpha-Al2O3 needed lower NiO/CH4 molar ratio to reach the same gas product composition than the oxygen carrier of NiO on gamma-Al2O3. Working at optimal operating conditions, 2.5 moles of H-2 per mol of CH4 could be obtained in this process. During operation the oxygen carrier particles maintained their physical and chemical properties. These results suggest that these oxygen carriers could have a high durability, being suitable oxygen carriers for a CLR system. (C) 2008 Elsevier B.V. All rights reserved.