Effect of density and size of inert particles in an alternative rotary dryer applied to paste-like material

Abstract

The drying of pastes to produce powdered materials has become increasingly important in the chemical, pharmaceutical, and food industries. An attractive alternative to the conventional spray-drying technique is the use of inert particles for paste drying. In this work, a rotary dryer with an inert bed, a device developed at Federal University of Uberlândia, was used to dry a fruit pulp into a powdered material. However, the efficient use of this device still presents significant challenges to be overcome. Besides appropriate operating conditions, the correct choice of inert material is crucial. This study investigated the effect of inert particles of different densities and sizes on the performance of this alternative system. Simulations using the Discrete Element Method (DEM) were conducted to investigate the behavior of inert flow inside the drum, and experimental tests were performed to quantify the effect of operating variables on process yield, aiming for an optimization study. Spheres of stainless steel (ρ_s = 8000 kg/m³), ceramic (ρ_s = 2300 kg/m³), and polypropylene (ρ_s = 900 kg/m³) were used as inert materials, with west indian cherry pulp as the paste material. The DEM simulation results showed that when inert stainless steel particles were used, the collision forces were 424.77 % higher than those obtained with inert ceramic particles and 1209.27 % higher than those from polypropylene particles. The optimization study revealed that the highest process yield was achieved using a maltodextrin concentration of 21.7 %, a fraction of smaller inert particles of 75 %, and a temperature of 95.7°C. The nonconventional rotary dryer successfully produced powdered fruit, highlighting its potential as an efficient alternative to traditional drying techniques for paste-like substances. This research underscores the dryer’s innovative design offering promising applications in food processing and other industries requiring efficient solutions.