CFD Modelling of a Counter-Current Spray Drying Tower

A steady state, 3D, multiphase CFD modelling of a pilot-plant counter-current spray drying tower is carried out to study the drying of slurry to generate detergent powder. The commercial software package Fluent is employed to solve the heat, mass and momentum transfer between the hot gas and the droplets/particles. The coupling of the two phases is achieved by the Eulerian-Lagrangian approach. The continuous phase is modelled using the Reynolds-stress model (RSM) for turbulence. A semi empirical droplet/particle drying model is incorporated using user-defined functions. The particle-wall interaction is considered by specifying the coefficient of restitution as a function of moisture content. The results demonstrate that the particle-wall interaction is one of the factors that cause significant changes in the velocity and hence temperature and moisture profiles of the gas as well as the particles. The CFD model predictions are compared with the data collected from a large scale pilot-plant spray tower. A reasonable agreement is obtained for the powder temperature, moisture content and exhaust gas temperature, considering the complexity of the spray drying process, simplifying assumptions made in modelling and the errors associated with the measurements.