A Generalized Flow Regime Diagram for Fluid-Solid Vertical Transport

An ideal generalized flow regime diagram was proposed for fluid-solids vertical transport systems with no bottom and top restrictions. Such an ideal flow regime diagram was further extended to shed light onto the understanding of the flow regimes and instabilities encountered in bottom- restricted bubbling and circulating fluidized bed systems

EFFECT OF DISTRIBUTOR DESIGN ON SOLIDS CIRCULATION AND GAS BYPASS IN AN INTERNAL CIRCULATING FLUIDIZED BED REACTOR

The effect of the distributor design on the gas bypass and solids circulation was investigated for the flat, cylindrical and conical gas distributors in a cold model internal circulating fluidized bed to provide design and operating criteria for the future application of ICFB deNOx reactor. A high gas bypass ratio from the annulus to draft tube and low from the draft tube to annulus were identified for all tested distributors. The solids circulation rates increased with the increase of both annulus and draft tube gas velocities, where the conical distributor exhibited a more flexible and stable operation. The particle size and the reactor configuration exhibited significant effects on the operating characteristics of the hot model ICFB reactor

Experimental and Computational Studies of Gas Mixing in Conical Spouted Beds

The residence time distribution data in a conical spouted bed, obtained both from the bed bottom and the bed surface at different radial positions, were analyzed to obtain the mean residence time and the Peclet number. In parallel, local flow structures of a bed with the same dimensions and operating conditions as in the experiment were generated from the computational fluid dynamics (CFD) simulation using the FLUENT codes, and then were used for the simulation of gas dispersion. The results show that CFD simulations agree reasonably well with experiments. The radial distribution of the Peclet number is quite complex, with a maximum value at r=0.135 m under three operating conditions investigated

Monitoring Electrostatic Charges in Fluidized Beds

A novel analysis procedure for dynamic collision probes has been developed to monitor the charge density of particles in gas-solids fluidized beds based on the mean and normalized standard deviation of current signals. The contribution from hydrodynamic changes is decoupled from the changes in specific particle charge density based on the principles that the average current is related to charge transfer and/or triboelectrification due to the contact between the probe and particles, whereas the normalized standard deviation of current signals is mainly related to the hydrodynamic changes of the fluidized bed. The correlation between hydrodynamic changes and current signal fluctuations is confirmed from experimental data of both current fluctuations and pressure fluctuations measured from a 0.1 m diameter fluidized bed using polymer particles. Utilizing these findings, dynamic collision probes can potentially be applied in industrial fluidized bed reactors to monitor electrostatic charge build-up

EFFECTS OF PARTICLE SIZE AND FLUIDIZING VELOCITY ON THE CHARGE DENSITY OF ENTRAINED FINES

A previously-developed Faraday cup fluidized bed unit was modified to facilitate the in-situ monitoring of the transient entrainment rate and net charge of entrained fine powders. This enabled the determination of the transient charge density as a function of particle size and residence time of entrained fine particles. The results showed that the charge density increased significantly with increasing size of entrained fines, but was not very sensitive to the residence time and the fluidizing gas velocity for the finest entrained particles at gas velocities of 0.24 and 0.36 m/s. At Ug=0.48 m/s, the charge density of larger particles increased with increasing particle residence time