A comparative study of a spray dryer with rotary disc atomizer and pressure nozzle using computational fluid dynamic simulations

Spray drying operations with rotary disc atomizers as well as pressure nozzles as atomizing devices are widely used in diverse industries. The design of spray dryers is typically optimized for the design conditions. However, users sometimes need to use the same spray dryer chamber with some modifications due to the requirements of different products and or production rates. In this paper, we present results of a computational fluid dynamic study carried out to investigate the possibility of multi-functional applications of a specific spray dryer chamber. The predicted airflow pattern is validated by favorable comparison with published data. The airflow pattern and temperature distributions predicted by the model at different levels in the drying charnber are presented and discussed. The effects of different atomizer designs are also investigated. Note that the two types of atomizers yield very different droplet size distributions as well as spray patterns. The volumetric evaporation rate values, heat transfer intensity and thermal energy consumption per unit evaporation are computed and compared for drying of a 42.5% solids maltodextrin suspension in a spray chamber 2.2 m in diameter with a cylindrical top section 2.0 m high and a bottom cone 1.7 m high. Wall regions most susceptible to formation of undesirable deposits are also identified. Computed droplet trajectories for the two spray patterns are shown to display very different flow, temperature and drying characteristics. (c) 2005 Elsevier B.V. All rights reserved.