In this study, the distinguishing criterion of defluidization and unstable defluidization is to observe whether complete defluidization happens, which can be identified by a sudden pressure drop (about 100–200 Pa) in few seconds or by the visual observation. The distinguishing criterion of unstable defluidization and stable defluidization is to observewhether partial defluidization occurs at the beginning of fluidization, which can be identified by the occurrence of a ‘V’ type change of the pressure drop in the initial 10min or by the visual observation. It should be noted that such distinguishing criterion will bring some error (about 0.15 wt.%) on the critical carbon content value of distinguishing different fluidization behavior, which is acceptable.