| Abstract: | Abstract The article presents a full set of spray drying experiments for selected products performed in a co-current spray drying tower developed at Lodz Technical University. The experiments enabled identification of process and atomization parameters (feed properties, feed rate and feed temperature, drying agent temperature, air flow rate, atomization ratio, etc.) on drying and degradation kinetics, spray structure, particle residence time, and final product properties. Drying agent temperature measurements showed, in all cases, the initial increase of gas temperature in the spray envelope caused by the spray expansion and then a decrease induced by liquid evaporation and heat losses to the environment. PDA analysis confirmed that the initial velocity of particles was a function of a diameter and also the function of the distance from the axis. Practically an identical particle size distribution was observed in each cross-sectional area of the dryer. Negative values of particle velocity in the vicinity of the axis and at the edge of the spray envelope were found which proved that recirculation of particles appeared in the column. Analysis of final product properties showed that for agglomerate-like materials a decrease of bulk density with an increase of air temperature was related to morphological changes that occurred during drying and affected the shape of particles, surface structure, etc. The experiments proved that air/liquid ratio for two-fluid atomization and gas temperature were the most decisive factors controlling drying and degradation process rate and final product properties. |
