## Doctoral Dissertations

Winter 1993

Dissertation

Engineering

#### Degree Name

Doctor of Philosophy

Ihab Farag

#### Abstract

The investigation of the hydrodynamics of gas-particle suspension in a circulating fluidized bed (CFB) focused on the radial (lateral) particle flux measurement, the mechanism of the radial particle concentration distribution, the mechanism and the model of particle convection heat transfer, and the pressure balance in the CFB loop, all of which affect the hydrodynamics, thermal efficiency and stability of a CFB.

The radial particle fluxes in a cold-flow CFB riser (14.0 cm i.d., 6.4 m high) were directly measured by specially designed probes. Two types of particles were used; glass beads of 200 $\mu$m diameter, and FCC catalyst of 70 $\mu$m diameter. Particle concentration was measured by a capacitance probe.

Results show that the radial particle flux was much greater near the CFB wall than that at the center. Under certain operating conditions, the radial particle flux was even higher than the net axial particle flux. The measured radial profile of particle flux is similar to that of the particle concentration. The radial particle flux is mainly dependent on the particle concentration.

The radial particle concentration distribution in the riser, which was dilute at the center region and dense near the wall, was analyzed based on momentum balance. Consideration of the momentum transfer due to the lateral particle motion predicted the existence of a dense-core and dilute-annulus particle concentration distribution during gas-solid, cocurrent, fast downflow in the downcommer.

The nature of the heat transfer between the gas-particle suspension in the bulk and the CFB wall was investigated. The radial particle flux data were used to develop a preliminary model to estimate the heat transfer coefficient. Comparison of the calculated heat transfer coefficient with published data shows good agreement.

A switch wafer setup was used to measure the pressure profiles in the CFB. The pressure balance in the CFB loop was analyzed. A computer model was developed to predict pressure changes in the CFB system. The model took into account the different flow regions in the CFB loop. Agreement of model and data was good.

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