Energy Recovery and Process Design in Continuous Flow–Electrode Capacitive Deionization Processes

Flow-electrode capacitive deionization (FCDI) is an electrically driven water desalination process based on the adsorption of ions in pumpable carbon flow-electrodes, also called slurry electrodes, which act as an electrical double-layer capacitor. The pumpability of the electrodes enables a fully continuous operation of FCDI and a whole range of new process designs in contrast to capacitive deionization processes based on static electrodes. In this work, we demonstrate continuous energy recovery of up to 36% of the energy applied during the desalination step during the regeneration of the carbon flow-electrodes. The process performance and energy demand for desalination and pumping of the flow-electrodes are investigated for different FCDI process layouts. The potential of FCDI systems is compared to state-of-the-art desalination methods regarding the energy demand. The energy demand and influence of specific process parameters, such as the applied voltage and the feedwater salinity, are discussed on the basis of theoretical calculations. The findings indicate further directions for the development of FCDI processes which may make it competitive.