Electronic Thesis and Dissertation Repository

Thesis Format

Monograph

Degree

Master of Engineering Science

Program

Chemical and Biochemical Engineering

Supervisor

Zhu, Jingxu

2nd Supervisor

Zheng, Ying

Co-Supervisor

Abstract

A novel type of circulating fluidized bed operating below the particle terminal velocity known as conventional circulating fluidized bed (CCFB) was proposed and tested for the first time in this study. The experiments were carried out in a liquid-solid circulating fluidized bed system, where both liquid and solid flew upwards in the riser and solids exiting the top of the riser were separated from liquid and then returned to the bottom of the riser via an accompanying downer. The system was essentially operated in the conventional fluidization regime but with continuously feeding of particles into riser bottom and particles moving up the riser to achieve solids circulation or circulating fluidization. The hydrodynamic of the CCFB was investigated at various operating conditions with two types of particles. The solids holdup of the conventional circulating fluidization was clearly higher when compared to conventional fluidization. Particles with a higher terminal velocity have higher solids holdup.

Summary for Lay Audience

In chemical, biochemical and environmental processes, fluidized bed reactors are an excellent candidate for multi-phase reactions due to its good liquid-solid contact efficiency and intensified solids movement.

A new type of Liquid-Solid Circulating Fluidized Beds, called Conventional Circulating Fluidized Bed (CCFB), is conceived and tested for the first time which can be operated below the particle terminal velocity while a regular circulating fluidized bed would operate beyond the particle terminal velocity. Taking advantages of both circulating fluidized beds and conventional fluidized beds, significant dense particle population can be achieved in the CCFB. The particles represent reactant or catalyst in the fluidized bed reactor. Higher particle concentration is anticipated to result in higher reaction efficiency.

The study carried out in this thesis project focuses on the hydrodynamics of the conventional circulating fluidized bed operating at ambient temperature and pressure with particles heavier than liquid. In the CCFB, solids holdup is found to be uniform, following that of the conventional liquid-solid fluidized beds. Solids holdup is increasing with solids circulation rate and decreasing with superficial liquid velocity. It is believed that particle-particle interaction is intensified in the CCFB.

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