Experimental Study on the Two-Phase Flow Structure in a Supercritical Water-Fluidized Bed

A supercritical water-fluidized bed (SCWFB) is a very promising reactor for the clean utilization of biomass. In the present article, the flow structure in SCWFB is analyzed from a microscopic point of view via a special measurement system based on a capacitance probe. Five groups of particles are fluidized under a supercritical condition in a wide range of operating parameters: 20-27 MPa and 410-570 degrees C. Fluctuations and distributions of local voidage are analyzed in detail to shed some light on the special flow structure. The results show that bubbles tend to move toward the axial line of SCWFB and slugging fluidization is formed at a higher superficial velocity. In particular, a Core-Annulus Flow in SCWFB is found, which is enhanced by the increase of superficial velocity or decrease of the particle diameter. The results may be useful for the development of the SCWFB technique.