Mass coordinates for dynamic simulation of column operations involving dimensional changes of packing material

A modeling approach is presented for simulating column operations where the packing material undergoes dimensional changes and some dead volume is formed in the column. Modeling of such systems is complicated by a moving discontinuity at the dead volume-packed bed interface. The discontinuity was eliminated by employing two coordinate systems (a Lagrangian and an arbitrary) and spanning two calculation grids in the axial direction of the column. The mass of the packing material was used as the spatial variable in the packed bed. Coupled intraparticle diffusion and reaction was also described by using a Lagrangian coordinate system, in which the mass of a single particle was used as the spatial variable. The advantage of the proposed modeling approach is that it enables the use of simple numerical schemes on a relatively difficult modeling task. Model predictions were compared with experimental data for a column process where the height of an ion-exchange resin bed decreased by 15%.