New Operational Modes to Increase Energy Efficiency in Capacitive Deionization Systems

Abstract

In order for capacitive deionization (CDI) as a water treatment technology to achieve commercial success, substantial improvements in the operational aspects of the system should be improved in order to efficiently recover the energy stored during the deionization step. In the present work, to increase the energy efficiency of the adsorption-desorption processes, we propose a new operational procedure that utilizes a concentrated brine stream as a washing solution during regeneration. Using this approach, we demonstrate that by replacing the electrolyte during regeneration for a solution with higher conductivity, it is possible to substantially increase round-trip energy efficiency. This procedure was experimentally verified in a flow cell reactor using a pair of carbon electrodes (10(2) cm geometric area) and NaCl solutions having concentrations between 50 and 350 mmol·L(-1). According to experimental data, this new operational mode allows for a better utilization of the three-dimensional structure of the porous material. This increases the energetic efficiency of the global CDI process to above 80% when deionization/regeneration currents ratio are optimized for brackish water treatment.

Reducing impedance to ionic flux in capacitive deionization with Bi-tortuous activated carbon electrodes coated with asymmetrically charged polyelectrolytes

“…Round trip efficiencies for the bi-tortuous electrodes compare favorably with previous studies on MCDI systems despite the fact that there will be depletion within the electrode structure as compared to no depletion in MCDI when covered with IEMs. Previous studies on CDI systems have reported round-trip efficiencies up to 65% (García-Quismondo et al., 2013; 2016). For fb-MCDI, Zhao et al.…”

Energy breakdown in capacitive deionization

“…The promise of CDI for energy efficient processing of lower concentration inlet feeds has led to a number of studies concerning energy loss (Alvarez-Gonzalez et al, 2016;Choi, 2015;Demirer et al, 2013;García-quismondo et al, 2015;García-Quismondo et al, 2013;Kang et al, 2014;. These have generally focused on the total energy loss of the process, which is useful for comparison with different technologies or among different CDI designs, but provides little insight for optimizing CDI operation or refining current CDI designs.…”

Interconnected metal oxide CNT fibre hybrid networks for current collector-free asymmetric capacitive deionization

“…7 This comes out as 34%, with large room for improvement using new operational modes. 9 The resulting net energy consumption, at 0.26 W h g À1 , is exceptionally low (Table 2), nearly an order of magnitude lower than optimised systems based on AC tested under similar salt concentrations.…”

“…4 The energy stored can be subsequently retrieved in the electrode discharge step using the same working principle as in a capacitor (see the ESI †). [5][6][7][8][9][10] Amongst its envisaged advantages over other desalination methods are: lower energy consumption to treat medium salt concentration streams (2-10 g L À1 ), 6,8,[11][12][13][14] low fouling and scaling risk [15][16][17] and higher water recovery rates, thus achieving substantial reductions in the volume of brine. 12,18,19 The design and choice of materials for CDI and capacitive dye removal follows similar principles to standard EDLC, hence most cells consist of two porous carbon electrodes supported on a current collector; 20 in the case of CDI a corrosion-resistant metal, typically Ti, or a non-metallic substrate such as expanded graphite is used.…”