DRYING KINETICS AND PARTICLE RESIDENCE TIME IN SPRAY DRYING

ABSTRACT

A unique experimental equipment for extensive trials on the spray drying kinetics and particles residence time involving “in situ” analysis of the properties of continuous and dispersed phases was designed, built, and tested. Advanced experimental techniques (including laser techniques) to determine current parameters of spray drying process (temperature, humidity, moisture content) and current structure of spray (particle size distribution, particle velocities, etc.) were employed. Full scale spray drying tests of baker's yeast and maltodextrin enabled identification of the effect of process parameters on drying kinetics and spray residence time in the tower. Quantitative relationship describing spray drying kinetics as a function of atomization ratio and drying agent temperature were determined. The experimental results proved that spray residence time was controlled by atomization ratio and airflow rate. Drying kinetics in spray drying process is presented for the first time in the literature.

Keywords:

• Drying curves
• Laser techniques
• Spray behavior

ACKNOWLEDGMENTS

This study was carried out as part of the research project entitled “Drying and degradation kinetics of heat sensitive products in spray drying,” sponsored by the International Fine Particle Institute in 2000 (Project No. ARR35) and the Statutory Work K-105/2000.

Notes

*This is equal to 276.4, 460.6, 690.9 Nm³/h for 175°C. This is equal to 251.3, 418.8, 628.2 Nm³/h for 220°C.

**Initial moisture content of yeast in the form of a solid brick delivered by a manufacturer is equal to 73% of water. To make raw material pumpable, a certain amount of water had to be added which resulted in high initial content of water in the feed. However, the aim of the experiments was not to find optimal conditions for drying of yeast but to analyze drying and degradation process.