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

This work presents the experimental results obtained during auto-thermal chemical-looping reforming (CLRa) in a semicontinuous pressurized fluidized bed reactor working with two Ni-based oxygen carriers and using methane as fuel. During operation the effect of the total pressure, reduction reaction temperature, and oxygen carrier-to-fuel molar ratio on CH4 conversion, gas outlet concentrations, and carbon formation was analyzed. In the range of pressures analyzed (up to 10 bars), it was found that an increase in the total operating pressure did not produce a negative effect on the gas product distribution obtained in the process. At all operating pressures the CH4 conversion was very high (>98%) and no carbon formation was detected. The most important variable affecting the gas product distribution was the solid circulation rate, that is, the oxygen carrier-to-fuel molar ratio (NiO/CH4).The oxygen carriers were physically and chemically characterized by several techniques before and after using in the pressurized fluidized bed reactor. Important changes in the surface texture and the solid structure of the oxygen carrier particles were not detected. These results suggest that these oxygen carriers could have a high durability, being suitable for use in a pressurized CLRa system.