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Thesis Format

Integrated Article

Degree

Doctor of Philosophy

Program

Chemical and Biochemical Engineering

Supervisor

Zhu, Jesse

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.

Summary for Lay Audience

In chemical and biochemical processes, multiphase contact is of great importance for mass transfer, heat transfer and reaction performance. And fluidized bed is an approved candidate due to its intensified solids movement within the fluid. This study focuses on the hydrodynamics of multiple liquid fluidization systems which covers both co-current and counter-current flow of liquid and solid with both light and heavy density particles in relative to liquid.

In Inverse Liquid-Solid Circulating Fluidized Bed, solids holdup distribution is found to be uniform both axially and radially. And solids holdup is increasing solid circulating rate and decreasing with superficial liquid velocity. The effects of particle properties is not significant in determining solids holdup, but quite notable in affecting the slip velocity between liquid and solid. A model is presented for the prediction of solids holdup.

A new type of Liquid-Solid Circulating Fluidized Bed is proposed that can operate below particle terminal is proposed that can increase solids holdup significantly.

Preliminary study on the counter-current flow of liquid and solids were studied with both heavy and density particles. Inverse gas-liquid-solid circulating fluidized bed is proposed and experimentally investigated the hydrodynamic.

Comparative study on the flow of heavy and light density particles were conducted and some clustering phenomenon were believed to exist in particles with low terminal velocity. And a discussion on liquid fluidization based on Four-Quadrant Fluidization Regime Map is conducted at the end that summarized the studied systems and may also lead to findings in new liquid fluidization regimes.

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