Particle-liquid mass transfer in solid–liquid fluidized beds

• Solid–liquid circulating multistage fluidized bed (SLCMFB) has been investigated.
• Values of mass transfer coefficient (kSL) have been measured for SLFB and SLMFB.
• Effect of the distributor and bed height on kSL has been measured experimentally.
• Correlations have been developed for the estimation of kSL.

Solid–liquid mass transfer coefficient (kSL) was measured in both conventional solid–liquid fluidized bed (SLFB) and solid–liquid multistage fluidized bed (SLMFB) by using the system of dissolution of benzoic acid in water. The particle size was varied in the range of 165–890 μm and the voidage in the range of 0.4–0.9. The dependence of solid–liquid mass transfer coefficient on important variables associated with the distributor design has been studied for SLFB. It was observed that the orifice density (number of orifices per unit area), per cent free area and the pressure drop across the distributor play important role on the values of kSL. The effect of the inerts (glass beads) on the mass transfer coefficient was investigated. For the voidages below 0.6, intensification in kSL was observed due to the presence of inerts in the system. As the voidage increases, the presence of inerts was found to have increasing effect on the mass transfer coefficient. For SLMFB, an increment of up to 15% in mass transfer rate was observed in comparison to that in conventional SLFB under a wide range of operating conditions like superficial liquid velocity and particle diameter. All the past correlations have been critically analyzed and suitable recommendations have been made. A new generalized correlation has been proposed for the estimation of mass transfer coefficient for both SLFB and SLMFB based on the experimental data. These correlations have been shown to be valid for all the available data in the published literature.