State dependence of magnetized fluidized bed reactor on operation mode.

• Bed states obtained under four typical operation modes were compared for the MFB. • MFB state depended also on operation mode within certain operating zones. • In these zones MFB could have different states at the same operating condition. • Internal friction inside the bed caused MFB to be polymorphic in these zones. • Many of these bed states were demonstrated to be amorphous and metastable. There exist four typical modes to operate the magnetized fluidized bed (MFB) reactor: magnetization-FIRST, de-fluidization, magnetization-LAST, and de-magnetization. This work aimed to compare the bed states obtained under these operation modes for both the MFB with purely magnetizable particles and the MFB with the binary admixture of magnetizable and nonmagnetizable particles. It was found that the covered operating range could be divided into four zones. Particularly in zones I to III, the bed state depended not only on the magnetic field intensity (H) and superficial gas velocity (U g) but also on the operation mode, i.e., the bed state was a path function. Such a path-dependence feature resulted from that the MFB therein could have different equilibrium states at the same H and U g. From our perspective, such a polymorphic characteristic was caused by the internal friction inside the bed. Furthermore, many of these bed states were demonstrated to be metastable. The metastable states in zones II and III behaved like the metastates of water. They evolved directly and quickly into the corresponding stable states after relatively large perturbations. The metastable states in zone I behaved like the amorphous/glass state. They resided at another metastable state during the evolution towards the stable state after relatively large perturbations. In zone I, the metastable states formed from the sharp increase of internal friction with decreasing U g. The particles lost the ability to move before reaching the stable positions and were entrapped at the intermediate and metastable positions. [ABSTRACT FROM AUTHOR]