First-Principles Non-Equilibrium Dynamic Modelling of Agitated Thin-Film Evaporators

Agitated Thin-Film Evaporators (ATFE) are frequently employed in the industrial practice for instance they found important applications in pharmaceuticals, pulp & paper, bio-based chemicals production and food industry. They are characterized by the possibility to process high viscosity liquids or liquids with suspended solid particles exploiting the mixing turbulence realized by the impeller. These features allow, for instance, to recover light heat sensitive compounds from high-boiling viscous liquids or to strip volatiles from a product up to residual traces. Their performance and optimal design is significantly influenced by blades number, impeller speed, heating policy and changes in the inlet mixture composition. The latter is a quite common issue, especially in the food and biotech industry. This paper deals with the development of a first-principles non-equilibrium evaporator dynamic model that is able to predict the influence of the key operating conditions and boundary conditions on the evaporator performance. The adopted modelling strategy implies the use of the finite volumes method, by discretising the evaporator into several slices that are modelled as two-phase pseudo-CSTRs. Moreover, heat and mass transfer are considered with the use of suitable correlations. Finally, a case study, based on the ATFE for sugar aqueous solution concentration, is used to test the model.