Effect of bed particle size and temperature variation on the minimum fluidisation velocity: A comparison with minimum fluidisation velocity correlations for bubbling fluidised bed designs

Abstract

This work presents hydrodynamic studies on the effect of temperature and bed particle variation on minimum fluidisation velocity. A lab-scale bubbling fluidised bed made of stainless steel, with column height of 1 m and internal diameter of 0.15 m was used. Five Geldart-B-type alumina bed materials of mean particle sizes 75, 177, 250, 320 and 500 µm were used and the bed temperature was varied between 50 ℃ and 600 ℃. The hydrodynamic results showed that minimum fluidisation velocity varied directly with mean particle size and inversely with temperature. The pressure drop was found to increase with bed temperature for all the sizes of bed particles. The minimum fluidisation velocity is a key parameter in the design of fluidised bed systems and as such its prediction lies with good choice of correlation. The experimental values were compared with predicted minimum fluidisation velocity from six correlations, with the overall objective of verifying the most suitable correlation. Of the correlations used, the Hartman et al. correlation showed very good fitting with experimental data for beds of 75 and 177 µm particles, and the Mohanta et al. correlation showed good fitting with 250–500 µm bed particles. The models exhibited very good coefficient of multiple determination (R²), very low fitting errors and low geometric standard deviations across the range of particle sizes and temperature variation. However, the lack of understanding of the parameters such as voidage, particle sphericity, density and viscosity would need more attention, particularly in view of the sensitivity of the minimum fluidisation velocity predictions to these parameters. Further studies are therefore recommended for the verification of the correlations in this regard.