Quality of fluidization in gas–solid unary and packed fluidized beds: An experimental study using gamma ray transmission technique

Pairing Experimental and Mathematical Modeling Studies on Fluidized Beds for Enhancement of Models Predictive Quality: A Current Status Overview

Modeling of gas-solid fluidized systems has been a prevailing challenge over the last few decades. With different approaches and implementing different sub-models to capture the essential multiphase and multiscale phenomena in these systems, major advances have been achieved, even though most models are only subject to a practical validation of macroscopic parameters. The current description of fluidized beds through mathematical models relies on the inclusion of vast sub-models, leading to an unquantifiable degree of uncertainty on the models’ applicability for extrapolation studies. Furthermore, each closure and fitting parameter in the model represents a possible source of deviation, and their optimization, hence, becomes another major challenge. The recent advances in measurement techniques can enable us to troubleshoot and optimize the implemented models and sub-models based on local scale measurements. Local multiphase hydrodynamic information obtained by advanced measurement techniques can enable the validation of local predictions and optimization of the coupled sub-models, leading to the development of simplified and highly predictive models. Thus, pairing advanced experimental studies on these systems with insightful modeling approaches is required to advance the shortcoming and enhance the predictive quality of the models. In this work, an overview of the status of modeling and experimental measurement techniques for gas-solid fluidized beds is presented; then, an overview on pairing both experimental and modeling studies to improve the models’ local predictions for fluidized beds is presented.

Minimum Fluidization Velocity of Intermediate Sized Particles in Conventional and Packed Fluidized Bed

Typical Geldart B class particles are often used in a gas-solid fluidized bed for various industrial applications. The quality of fluidization of Geldart B particles depends upon the geometry of the bed containing vessel, properties of fluidization medium and the gas flow rate. The presence of large bubbles/slugs that can happen in beds with intermediate class particles is undesirable. The bubbling and slugging, which decrease the quality of fluidization can be prevented with the phenomenon called packed fluidization. Experiments were carried out on the conventional fluidized bed and packed fluidized bed to investigate some of the hydrodynamic characteristics as a function of bed temperature, small particle size, fluidization medium and fraction of voids of packing filled with small particles. The superficial gas velocity required for packed fluidization reduces significantly than conventional fluidization. The minimum fluidization velocity of particles increases with an increase in density of the fluidization gas and decreases with increase in temperature of the bed. A correlation established from experimental data fairly predicts the minimum fluidization velocity for the packed fluidized bed.

Effect of Fines Content on Fluidity of FCC Catalysts for Stable Operation of Fluid Catalytic Cracking Unit

Effect of fines content (weight % of particles with diameter less than 45 μm) on bed fluidity was determined to get a base for good fluidization quality in the fluid catalytic cracking (FCC) unit. The fines content in equilibrium FCC catalysts (Ecat) from commercial units were controlled by adding or removing the fines to simulate commercial situation. To get the fluidity values (Umb/Umf) of seven different FCC catalysts (2 Ecats and 5 fresh catalysts) and their mixture, minimum fluidization velocity (Umf) and minimum bubbling velocity (Umb) were measured in a fluidized bed reactor (0.05 m ID). The fluidity decreased with loss of fines content and increased with increments of makeup of fresh catalysts or additive with the controlled fines content. The fluidities of catalysts increase with increases of normalized particle diameter variation by the fines addition. The obtained fluidities have been correlated with the fines contents and the catalyst and gas properties. The proposed correlation could guide to keep good catalyst fluidity in the FCC unit.