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

摘要

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 γ-Al_2O_3 and α-Al_2O_3 were used during more than 50 h of operation with each oxygen carrier. During operation the effect of different operating variables, like fuel reactor temperature, H_2O/CH_4 molar ratio and solid circulation rate, on CH_4 conversion and gas product distribution was analyzed. It was found that in all operating conditions CH_4 conversion was very high (>98%) and the most important variable affecting to the gas product distribution was the solid circulation rate, that is, NiO/CH_4 molar ratio. Similar gas product distribution was obtained working with both oxygen carriers although at different NiO/CH_4 molar ratios. The oxygen carrier of NiO on α-Al_2O_3 needed lower NiO/CH_4 molar ratio to reach the same gas product composition than the oxygen carrier of NiO on γ-Al_2O_3. Working at optimal operating conditions, 2.5 moles of H_2 per mol of CH_4 could be obtained in this process.rnDuring 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.