Modeling Radial-Flow Ion-Exchange Bed Performance

Abstract

A theoretical model is developed that predicts the performance of an annular ion-exchange bed involving the exchange of two cations. In the model, the solution to be treated is assumed to flow radially through the fixed bed either away from the bed’s axis or toward it. Unlike an earlier model, this model does not assume that an instantaneous equilibrium exists between the two phases. The model incorporates mass-transfer terms including film diffusion and solution-phase phenomena. The exchange phase is assumed to consist of randomly packed synthetic and spherical resin beads of a narrow size range. The binary equilibrium relationship is characterized by a form of the Langmuir equation. The model permits the performance of an ion-exchange bed to be predicted. Breakthrough times and composition profiles within the bed may also be calculated. The model is validated by comparing its predictions with those made by a purposebuilt annular ion-exchange bed. The performance of the radial bed is studied for both the exhaustion and regeneration cycles for the Na + -H + and Ca 2+ -H + cation binary systems. Using the validated radial-flow model, the ion-exchange performances of a nonlinear (radial) bed under different operating conditions are also studied.