MATHEMATICAL MODELLING AND APPARATUS ARRANGEMENTS OF DEEP DRYING PROCESS OF GRANULAR POLYMERS

A computer - aided analysis is made of the factors influencing the kinetics of the continuous deep drying of granular polymers on the basis of a two-level mathematical model. In terms of the lower (microkinetic) level, which deals with the drying of separate granules, consideration is given to the accuracy of determining the moisture diffusion coefficients in polymers as functions of temperature and concentration D=f(U,t). The expedience of employing the solution of linear and non-linear differential diffusion equations in microkinetic calculations is also considered. In terms of the macrokinetic level, which takes account of the influence of the hydrodynamic and heat-and-mass transfer drying conditions in the dryer, a numerical study is undertaken of how the kinetics is influenced by the granules' dimension nonuniformity and by the difference in the granules' residence time in the dryer. The results are graphically presented in generalised variables. The travel of 12 granular polymers in the shaft (column) dryers is experimentally studied depending on definite determining parameters. Accordingly, some recommendations aimed at ensuring the uniform drying are given. Presented are also the experimental results on the longitudinal mixing for different polymers for a continuous shaft dryer with a ring material layer and with the drying agent performing the radial motion. The findings make it possible to determine the mixing rate and to outline some practical recommendations. The investigations carried out allow one to find the rational construction of the dryer for the deep drying of granular polymers and to refine the kinetic calculations.