Dynamic modeling of a packed-bed glycerol-water distillation column

The study of the dynamics of a packed-bed glycerol-water distillation Colum n is valuable for precise control to improve product quality and to conserv e material. A differential dynamic model has been established for the conti nuous distillation of the glycerol-water system at 10 mmHg absolute. In thi s model, hydraulic and mass transfer models of structured packing were used to estimate the vapor and liquid holdups and the mass transfer coefficient s. The model equations were solved numerically using the finite difference method. It was found that numerical solution of the proposed dynamic model with liquid, vapor, and reflux drum holdups took less computation time than the other models even when either liquid or vapor holdup was neglected. Th is method of solution reduced the size of system of differential equations from 2n + 1 to n + 1, thus improving the numerical accuracy and saving comp utation time. The effect of liquid, vapor, and reflux drum holdup on the dy namic behavior of the column was studied. It was, found that the liquid and vapor holdups have almost no effect on the dynamics of the packed column. The response of the composition along the height of the column showed nonli near behavior in response to changes in the reflux drum temperature. The re sults of this work shed some light on the dynamic behavior of packed-bed di stillation columns with highly nonlinear equilibrium relationship due to st ep changes in the reflux drum temperature.