Development of a spiral finned crystallizer for progressive freeze concentration process

Abstract

Progressive freeze concentration (PFC) has emerged as a viable technology for concentration of liquid solution. For this present research, a new spiral finned crystallizer was designed and fabricated as the main component in the PFC system. The spiral finned crystallizer was designed with the aim of increasing productivity and quality of product. Further analysis on its performance, a process optimization and modelling study were carried out after the completion of the design. For the performance analysis, glucose solution was used as a liquid food model solution. The performance of the crystallizer was analysed through the system efficiency assessed in parallel with the effect of operating conditions. It was found that the effective partition constant (K) was satisfactorily low at intermediate coolant temperature, high circulation flowrate, intermediate circulation time and intermediate shaking speed. A low K value and a high solute recovery (Y) value represent the best performance of the PFC system. In terms of Y, the highest achieved was approximately 0.98 g of glucose obtained per 1 g of initial glucose. A mass validation was successfully obtained from the experimental results. The evaluation of the crystallizer in terms of ice production, fluid mechanic and heat transfer characteristics was also carried out. 0.64 g/m2s1 of maximal ice production was attained, reflecting a good function of the spiral fin. A process optimization employing Response Surface Methodology (RSM) in Statistica software was applied to study the relationships of coolant temperature, circulation flowrate, circulation time and shaking speed on K and Y. The optimum conditions to produce the best K and Y were found to be 10.30 °C of coolant temperature, 3097.50 mL/min of circulation flowrate, 64 minutes of circulation time and 29.53 ohm of shaking speed. The best K predicted was 0.25 and 0.99 for Y. A heat transfer model was also successfully developed in order to study ice crystal mass formation.