Abstract
When performing electrodialysis (ED) to desalinate a stream, both the energy for desalination and the energy for pumping contribute to the total energy consumption, although under typical working conditions (e.g., brackish water desalination) the latter is usually negligible. However, the energy penalty might increase when desalinating viscous mixtures (i.e., viscosity of 2–20 cP). In this work, we experimentally investigate the desalination performance of an ED-unit operating with highly viscous water-polymer mixtures. The contribution of desalination and pumping energy to the total energy consumption was measured while varying diverse parameters, i.e., salinity and viscosity of the feed, and geometry and thickness of the spacer. It was found that the type of spacer did not significantly influence the energy required for desalination. The pumping energy was higher than predicted, though in most cases minimal compared to the energy for desalination. Only when using thin spacers (300 μm) and/or highly viscous feeds (12 cP), the pumping energy accounted for 50% of the total energy for low salinity feeds. Therefore, the main contributor to the energy consumption of viscous solutions is the desalination energy, provided that large spacer thicknesses (at least 450 μm) and adequate operating conditions are utilized to limit pumping energy losses.
Highlights
When performing electrodialysis (ED) to desalinate a stream, both the energy for desalination and the energy for pumping contribute to the total energy consumption, under typical working conditions the latter is usually negligible
The viscosity of the feed solution may influence the mass transfer between the solution and the membranes and the energy required for desalination [9,10], and the energy required to pump the feed through the electrodialyzer
Electrodialysis uses an applied electrical potential difference as driving force to desalinate one of the streams circulating through an electrodialyzer, which consists of a series of anion and cation exchange membranes (AEMs and CEMs, respectively) placed alternately between two electrodes and separated by spacers
Summary
When performing electrodialysis (ED) to desalinate a stream, both the energy for desalination and the energy for pumping contribute to the total energy consumption, under typical working conditions (e.g., brackish water desalination) the latter is usually negligible. New applications for ED are rapidly emerging, such as removal of lactic acid from acid whey [5], desalination of glycerol [6], of fish sauce [7], and of viscous produced water from the oil and gas industry [8] These applications have in common the high viscosity of the feed solutions, typically in the range of 2–20 cP, i.e., several times higher than sea or brackish water. Spacers play an important role for both energy contributions They are placed between the ion-exchange membranes to create a constant intermembrane distance and to improve the mixing of the solutions inside the compartments. The selection of spacer thickness is crucial to enhance the process performance under given process and feed
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