Understanding the structural changes on Fe 2 O 3 /Al 2 O 3 oxygen carriers under chemical looping gasification conditions

Chemical Looping Gasification (CLG) has emerged recently as a promising technology for producing non N 2 -diluted syngas without the need for an external power supply or the expensive use of pure O 2. Many studies have focused on development of oxygen carriers since they are considered a crucial factor in CLG processes. Fe 2 O 3 /Al 2 O 3 (FeAl) oxygen carriers have been proposed due to previous experience in Chemical Looping Combustion (CLC). However, the aggressive conditions of gasification cause a decrease in the mechanical stability of the particles, which can be a challenge for their use in CLG. In this work, the operating conditions and Fe-content required to maintain the particle integrity of oxygen carrier particles during redox cycles in both CLC and CLG operations were determined. Long-term tests, consisting of 300 redox cycles, were conducted in a TGA to simulate the operation in a continuous unit and the results were compared with attrition data obtained from a 1.5 kW th CLG unit. Three oxygen carriers with varying Fe 2 O 3 -content (10, 20 and 25 wt%) were used, and three different solid conversions (0–25 %, 75–100 % and 0–100 %) were performed to emulate CLC or CLG atmospheres at three temperatures (850 °C, 900 °C and 950 °C). The evolution of the microstructure of particles was analyzed using a scanning electron microscope (SEM) and it was found that the lower the Fe 2 O 3 content in the particles, the greater their stability in redox cycles, an increase in the reaction temperature led to a more rapid degradation of the oxygen carrier particles, and the solid conversion variation and degree of reduction/oxidation during redox cycles strongly influenced the evolution of the mechanical stability of the oxygen carrier particles.