Universita' degli studi di padova ___________________________________________________________________

Abstract

In order to give a concrete response to the need of predictive contact drying simulation tools in pharmaceutical industry, simulation programs for contact drying of pharmaceutical powders were developed in this thesis work. These are two programs for simulate the two main contact drying operation conditions used in the pharmaceutical industry: vacuum and atmospheric contact drying of agitated beds. The programs give a predictive estimation of drying rate curve and bulk bed temperature during contact drying. Only initial conditions, operating conditions, geometrical data, type of substances, solid phase properties and two parameter for the evaluation of an empirical mixing coefficient, are required as input data. Each program consist in a main program for contact drying simulation, based on Penetration theory. Several programs are used for evaluating: heat and mass transfer coefficients, effective particulate bed properties, physical and thermodynamic properties of gas and liquid phases. All these values are calculated several times along the process simulation, as function of the actual value of bed temperature and bed moisture content. The models used in these programs are choosen from literature as the most suitable for the simulation purpose and adapted to the scope of the work. A first validation of the developed programs was made on experimental data from literature, regarding two common pharmaceutical excipient powders, wetted with water and dried in a disc contact dryer. The simulation results show a good agreement with the experimental data. Few deviation was identified, and a delimitation of the prediction limit of the used models is proposed. Then, the programs give a predictive and accurate insight of the drying behaviour of the analyzed powders. With further validation on other substances and on industrial scale, the developed programs would be an useful tool for design, analysis, optimization and control of industrial contact dryers.