Paste Residence Time in a Spouted Bed Dryer. III: Effect of Paste Properties and Quality Interactions

Abstract

The aim of this study was to evaluate the effects of paste properties on residence time during drying in a spouted bed dryer with inert bodies. The effect of paste solids content, surface tension, and viscosity on the residence time distribution and the mean residence times were studied using factorial experimental designs. The inert bodies used were glass and polyethylene beads. The mean residence times varied from 13.6 to 16.3 and 12.2 to 17.7 min for drying on glass and polyethylene beads, respectively. The analysis of variance showed that mean residence times significantly depended on solids content and surface tension for glass beads and also on viscosity for polyethylene beads. The residence time distributions for all conditions studied fitted well to the perfect mixing cell when applying the continuous stirred vessels in series model analysis. The powder density, flowability, and particle size depended on paste properties and inert type.

Keywords:

• Factorial design
• Product quality
• Solids content
• Surface tension
• Viscosity

ACKNOWLEDGEMENTS

Financial support from FAPESP (03/09447-6) and grants to the authors (05/53934-4/FAPESP and PQ-2/CNPq) are gratefully acknowledged.

Notes

Replicates of expts. ∗2 and ∗∗7.

Replicates of: ∗2 and ∗∗7 (see Table 3).

Significant at: ^a 1%; ^b 5% and ^c 10%.

Significant at: ^a 1%; ^b 5%, and ^c 10%.

Symbols: ↑ increase, ↓ decrease, and x not significant.