3D Modelling of the Transport Phenomena in a Parallel-Plate Electrodeionization Reactor through CFD

Abstract

CFD has been used as a useful tool for the description of the phenomena occurring in electrochemical reactors. The present research studies the electrodeionization process from a 3D perspective, coupling the convection, diffusion and migration phenomena involved in the electrodeionization process using COMSOL Multiphysics and a validation of the simulation process is obtained using Digital Image Analysis and Electrodeionization experiments. The used reactor is a parallel plate reactor, previously used for an electrodialysis process with good results, the total volume of each of the 4 compartments ( one for diluted-treated solution, one for the concentrated-waste solution and two electrodic rinses to close the electrical circuit) is of about 19.2 mL. The diluted compartment is filled with IRA-67 ion exchange resin ( 0.5-0.75 mm of diameter) previously conditioned and hydrated. The treated solution is a 20 ppm fluoride solution from NaF and was pumped into de diluted and concentrated compartments at a velocity that allowed a one minute Time of Residence. The simulation was carried out with a 3D model of the reactor using its real measures, only the diluted and concentrated compartments were modelled. The flow of the solution in the concentrated compartment was considered as laminar and in the diluted compartment ( filled with ion exchange resin) a Brinkman-Darcy condition was applied. Nerst-Planck equations were used to describe the transport of the ionic species in the compartments and the flow through a ion exchange membrane. The results show a good flow distribution,as well as a good ion transport. The simulations, confirmed the experimental results. The analized data is very similar in flow distribution and mass transport in the compartments. The results were analized in a quantitative and qualitative form. The validation of this simulated results will allow the improvement of some problematic zones in the reactor and the methodology developed can be useful to other electrochemical reactors.