Drying kinetics of droplets containing solids using reaction engineering approach

Spray drying is an essential unit operation for production of powders from liquid slurry. Important events occurring inside the spray dryer are droplet formation, droplet drying and interactions between droplets and fine particles. The final goal of our project is to predict the dried solid particle size and mass flux distributions under conditions of collision, coalescence and agglomeration of droplets and particles. A coarse-grained simulation tool is developed which will enable the design more efficient spray dryers that can produce higher throughputs. One of the key ingredients of this simulation tool is the modelling of the drying characteristics of droplets containing solids. In this paper, a model is presented for drying of a droplet containing solids using a reaction engineering approach. The model is validated with experimental literature data for the drying of a single droplet of whole milk and skim milk, initially containing 20% solids. We compare the simulated droplet temperature, mass, drying rate and droplet diameter for different temperatures and solid content with experimental results. We compare correlations of Lin and Chen (2002) and Ranz and Marshall (1952) for the determination of the heat and mass transfer coefficients. Moreover, simulations of a single drying drop of whole milk, containing 30% solid, are compared with photographic results from the literature. We present preliminary simulation results of drying of many droplets in a section of a large scale spray dryer