The Spray Drying of Slurries of Fine Particles and the Strength of Spray-dried Particles

Abstract

Slurries composed of water, binders and roseki, which is a kind of clayey particles having a particle size less than 10μm, have been atomized and dried in a spray dryer with pneumatic atomizers to examine the influence of operating variables and the properties of slurries on the mass median diameter and size distribution of spray-dried particles. The strength of single spray-dried particles obtained under various experimental conditions has also been studied experimentally and theoretically.
The conclusions obtained are summarized as follows. The mass median diameter of spray-dried particles was found to be estimated by both Kim-Marshall's equation and a mass balance on the solids in a slurry droplet and a dry particle. However the apparent viscosity of slurries at the shear rate of 300s^-1 was used in calculating the Kim-Marshall's equation. The size distribution of the dry particles approximated to the logarithmic normal distribution and the geometric standard deviation, one of the parameters in the distribution, could be expressed by using the mass and number median diameters, respectively.
A theoretical equation was moreover derived on the crushing strength of single spray-dried particles and was found to show a good correlation with observed values. The crushing strength of the single dry particles was also observed to be nearly equal to the constant, 1/b, in Kawakita's equation, which was obtained from packing or compression experiments on dry particles.