Optimization of crystalline powders vacuum contact drying with intermittent stirring

摘要

Modified literature models were successfully applied to simulate the evolution of the average solvent content(ethanol)of potassium chloride bed during vacuum contact drying with intermittent stirring.Our new modeling approach introduced the following modifications:taking account of jacketed vessel wall heat transfer coefficient;taking account of an accumulation term in the heat balance for the heated wall;application of alternate static bed and stirred bed conditions;modeling of all the three drying phases,namely the constant rate phase,the transition phase and the falling rate phase.Several identification and validation experiments were carried out with a reliable laboratory vacuum contact dryer at different operating conditions.A good agreement between the simulated and experimental drying curves was observed and the experimental drying times were also very well predicted by the improved model with six fitting parameters in the most complicate case.The duration of periods with stirring and without stirring were optimized with the aim to obtain high mean drying rates with a low total stirring time in order to reduce the attrition and agglomeration phenomena.