Crystallisation in concentrated systems: A modelling approach

Water crystallisation in concentrated systems has been studied using a combination of mathematical modelling and experimental work. Two different freezing models have been employed to describe primary and secondary mechanisms (i.e. non-seeded and seed-induced processes, respectively) in sucrose solutions up to 60% (w/w). Differential Scanning Calorimetry (DSC) has been employed to characterise the phase change of the binary water-sucrose system in primary processes, and the kinetic and thermodynamic parameters obtained were coupled to the heat transfer equation to obtain the product temperature distribution. A recently developed method has been also employed to measure crystal growth rates in seed-induced crystallisation systems. Simulated results for the secondary crystallisation mechanism were able to reproduce experimentally observed trends for growth rates. An evaluation of the energy consumption during freezing/crystallisation processes has been carried out to assess each mechanism performance (crystallisation will occur at temperatures approximately 20 °C higher in seeded processes) considering different process conditions and product formulations (i.e. solids and air fractions).