Bed-to-Wall Contact Dynamics in a Gas–Solid Fluidized Bed with Downward Solid Movement

The bed-to-wall contact dynamics present a significant effect on heat transfer performance according to the packet renewal model proposed by Mickley and Fairbanks [Mechanism of heat transfer to fluidized beds. AIChE J. 1955 1 (1), 374–384]. However, the systematical investigations on contact dynamics are scarce, especially in a pilot-scale fluidized bed with downward solid movement. Therefore, a pilot-scale experimental setup was constructed to study the hydrodynamics behavior and contact dynamics in a gas–solid fluidized bed with downward solid movement, a configuration typical in catalyst coolers in the FCC process. Results indicate that the coupling of downward solid movement can break up large bubbles in turbulent fluidization, leading to a small bubble size and a high bubble frequency near the immersed surface. Moreover, the downward solid movement increases the contact distance between the packet and the immersed surface in the bubbling fluidization. The packet renewal model is modified by introducing local and global packet contact time. An empirical correlation was provided to predict the contact distance by considering the impact of solid radial mixing, solid particle size, and solid mass flux.