Mechanically agitated spouted beds have proven to be an alternative to conventional equipment, especially in the drying of sticky materials. Starting from this premise, the objective of this study was to compare three different types of mechanical agitators (straight-blades, inclined-blades and screw) in the drying of calcium carbonate and skimmed milk in a spouted bed. The results showed that there was a significant decrease from around 0.025 to around 0.015 m3 s–1 in the air flow rate, pressure drop and other fluid dynamic parameters of the spouted bed with the mechanical stirring systems. This causes the exhaust air to come out more saturated, improving drying. The drying kinetics, moisture content and particle size distribution of the product, in addition to the usual operating variables, were also a function of the rotation velocity of the mechanical agitators. The effect of mechanical agitation on spouted bed paste drying was most noticeable during transient. In general, mechanical agitators can extend the operating ranges of the spouted bed because they improve stability and product circulation even at low air flow rates. A mathematical model was developed to predict the minimum air flow rate as a function of dimensionless parameters, showing excellent agreement with experimental data (R2 > 0.98) for all three agitator configurations.
Barros et al. (2026) studied this question.