Abstract
Electrodialysis (ED) has been recently introduced in a variety of processes where the recovery of valuable resources is needed; thus, enabling sustainable production routes for a circular economy. However, new applications of ED require optimized operating modes ensuring low energy consumptions. The application of pulsed electric field (PEF) electrodialysis has been demonstrated to be an effective option to modulate concentration polarization and reduce energy consumption in ED systems, but the savings in energy are usually attained by extending the operating time. In the present work, we conduct a comprehensive simulation study about the effects of PEF signal parameters on the time and energy consumption associated with ED processes. Ion transport of NaCl solutions through homogeneous cation-exchange membranes is simulated using a 1-D model solved by a finite-difference method. Increasing the pulse frequency up to a threshold value is effective in reducing the specific energy consumption, with threshold frequencies increasing with the applied current density. Varying the duty cycle causes opposed effects in the time and energy usage needed for a given ED operation. More interestingly, a new mode of PEF functions with the application of low values of current during the relaxation phases has been investigated. This novel PEF strategy has been demonstrated to simultaneously improve the time and the specific energy consumption of ED processes.
Highlights
Electrodialysis (ED) is a mature separation process used to obtain concentrated and diluted streams from saline solutions [1]
When high current densities are applied, electrical instabilities emerge in the depleted solution layers and promote an additional supply of ions from the bulk solution toward the membrane surface [13,14]. Another choice is the operation of ED systems with pulsed electric fields (PEF), which alternate periods of current application with pauses, where the intensity of concentration polarization decreases
A finite difference method applied to a simplified ion transport model is used to evaluate the interplay between the duration and level of applied current during the pulse and pause periods, when PEFs are implemented in a system formed by a cation-exchange membrane and NaCl solutions
Summary
Electrodialysis (ED) is a mature separation process used to obtain concentrated and diluted streams from saline solutions [1]. When high current densities are applied, electrical instabilities emerge in the depleted solution layers and promote an additional supply of ions from the bulk solution toward the membrane surface [13,14] Another choice is the operation of ED systems with pulsed electric fields (PEF), which alternate periods of current application with pauses, where the intensity of concentration polarization decreases. A finite difference method applied to a simplified ion transport model is used to evaluate the interplay between the duration and level of applied current during the pulse and pause periods, when PEFs are implemented in a system formed by a cation-exchange membrane and NaCl solutions. The specific energy consumption (kJ/m2) for a given degree of desalination or number of charges transported can be calculated by integrating the product between the voltage drop through the membrane system and the input function of operating current density over time: tf. Urtenov et al in a previous work [32]
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