Study of defluidization of iron- and manganese-based oxygen carriers under highly reducing conditions in a lab-scale fluidized-bed batch reactor

摘要

Oxygen carriers play an important role in chemical looping processes to transport oxygen for fuel conversion. In this study, the defluidization phenomena of oxygen carriers were examined under highly reducing conditions in a fluidized-bed batch reactor. This is highly relevant to chemical-looping gasification, where oxygen carriers could be reduced to a significant extent compared to that in chemical-looping combustion. Only a few studies have reported the physical phenomena in a fluidized bed system under highly reducing conditions. Three iron- and two manganese-based oxygen carriers were investigated at 900 degrees C at several degrees of reduction in this study. Some oxygen carriers that have been exposed to several hours of operation in a 300 W chemical-looping reactor unit were also included in this study to provide a comparison to the fresh-calcined materials. Defluidization of particle beds occurred with the iron-based oxygen carriers, except for LD slag, which has a low content of iron. The defluidization was caused by the formation of elemental iron on the oxygen carriers' surface at high degree of reduction. All defluidizations occurred at a mass-based conversion (Delta omega) between 3.2-5.0%. The manganesebased materials were found to be less prone to defluidization.