Hydrodynamics of Liquid-Solid and Three-Phase Inverse Circulating Fluidized Beds
Abstract
The hydrodynamics of inverse liquid-solid circulating fluidized bed (ILSCFB) is experimentally studied in a 5.4 m tall and 0.076 m ID column. 5 types of low density particles are investigated with different particle terminal velocities.
Solids holdup distribution is found to be uniform in a wide range of superficial liquid velocities and over 10 solid circulation rates. Average solids hold is not sensitive to particle properties. Clustering phenomenon is found to be significant affecting the slip velocity in the ILSCFB. And the cluster phenomenon is directly related to particle Reynolds number (Ret). Particles with little Ret tends to have higher slip velocity which is believed as an indicator of clustering phenomenon. A modified Richardson-Zaki equation is proposed for the prediction of solids holdup in ILSCFB
Comparative study between upward and inverse liquid-solid CFBs is conducted. General hydrodynamics is found to be similar. Axial solids holdup is uniform in both systems. Radial flow structure is also uniform although some decreasing trend from center to the wall is observed in inverse liquid-solid circulating fluidized bed due to the effect of lifting force. Residence time per unit height is used as a tool to compare different reactor performance, and also compare particle properties. Particles with little Retwill lead to less homogeneous behavior in the circulating fluidized bed for both heavy and low density particles.
A new type of circulating fluidized bed, conventional circulating fluidized bed, operating below particle terminal velocity, is proposed and experimentally investigated. Solids holdup is found to be significantly increased compared with both conventional fluidization and regular circulating fluidization. And better solids holdup control is achieved with the help of solids circulation.
Preliminary study on the counter-current flow of liquid and solids is carried out with both heavy and density particles. Inverse gas-liquid-solid circulating fluidized bed is proposed, and its hydrodynamics is experimentally investigated.
A detail flow regimes map is presented and discussed based on flow directions of liquid and solids. The studied configurations of liquid-solid fluidization systems in this research are highlighted in the flow regimes map, which greatly enriches the operating modes of liquid-solid fluidization.