Ion-exchange membrane electrodialysis program and its application to multi-stage continuous saline water desalination

A computer simulation program of ion-exchange membrane electrodialysis is developed for saline water desalination. Inputting the specifications of an electrodialyzer and operating conditions into the program, the following performance of the electrodialyzer is computed. Ion flux and solution flux across a membrane pair; Energy consumption; Salt concentration at the outlets of desalting and concentrating cells; Desalting ratio; Water recovery; Current efficiency; Limiting current density; Current density distribution; Electric resistance of desalting and concentrating solutions and a membrane pair; Electric current leakage; Pressure drop. Constant voltage mode single-pass electrodialysis program is written in the Excel spread sheet and it is integrated in the website. The program in the website can be operated easily with trial-and-error calculation.

Simulation of an ion exchange membrane electrodialysis process for continuous saline water desalination

Irreversible thermodynamics is the fundamental principle in ion exchange membrane electrodialysis. The mechanism of saline water desalination is explained based on irreversible thermodynamics. The overall mass transport equation is developed on the basis of the electrodialysis experiments. The phenomenological equation appearing in irreversible thermodynamics is substantially identical to the overall mass transport equation. The overall membrane pair characteristics appearing in the overall mass transport equation are expressed by functions of the overall hydraulic permeability of the membrane pair. In an electrodialyzer, solution velocities in desalting cells vary between the cells. Salt concentrations are decreased along the flow-passes in desalting cells. These events give rise to electric resistance distribution and current density distribution in the electrodialyzer and exert an influence on the limiting current density of the electrodialyzer. The electrodialysis process is classified into a continuous (one-pass flow), a batch, and a feed-and-bleed process. The performance of each process is discussed using computer simulation (electrodialysis program) and by applying the principles of mass transport, current density distribution, cell voltage, energy consumption, and limiting current density. An electrodialysis program is operated for desalinating saline water, and the performance of a practical-scale electrodialyzer is discussed with figures created using computer simulation. The program aims to work as a pilot plant operation.

Comparison of salt adsorption capacity and energy consumption between constant current and constant voltage operation in capacitive deionization

A computer simulation of batch ion exchange membrane electrodialysis for desalination of saline water

Membrane capacitive deionization (MCDI) is a water desalination technology based on applying a cell voltage between two oppositely placed porous electrodes sandwiching a spacer channel that transports the water to be desalinated. In the salt removal step, ions are adsorbed at the carbon–water interface within the micropores inside the porous electrodes. After the electrodes reach a certain adsorption capacity, the cell voltage is reduced or even reversed, which leads to ion release from the electrodes and a concentrated salt solution in the spacer channel, which is flushed out, after which the cycle can start over again. Ion-exchange membranes are positioned in front of each porous electrode, which has the advantage of preventing the co-ions from leaving the electrode region during ion adsorption, while also allowing for ion desorption at reversed voltage. Both effects significantly increase the salt removal capacity of the system per cycle. The classical operational mode of MCDI at a constant cell voltage results in an effluent stream of desalinated water of which the salt concentration varies with time. In this paper, we propose a different operational mode for MCDI, whereby desalination is driven by a constant electrical current, which leads to a constant salt concentration in the desalinated stream over long periods of time. Furthermore, we show how the salt concentration of the desalinated stream can be accurately adjusted to a certain setpoint, by either varying the electrical current level and/or the water flow rate. Finally, we present an extensive dataset for the energy requirements of MCDI, both for operation at constant voltage and at constant current, and in both cases also for the related technology in which membranes are not included (CDI). We find consistently that in MCDI the energy consumption per mole of salt removed is lower than that in CDI. Within the range 10–200 mM ionic strength of the water to be treated, we find for MCDI a constant energy consumption of ∼22 kT per ion removed. Results in this work are an essential tool to evaluate the economic viability of MCDI for the treatment of saltwater.

Comparison of energy consumption in desalination by capacitive deionization and reverse osmosis

Entropy generation analysis of heat and water recovery from flue gas by transport membrane condenser

High water recovery and improved thermodynamic efficiency for capacitive deionization using variable flowrate operation

Statistical uncertainty quantification to augment CDI electrode design and operation optimization

The computer simulation program of a practical scale reverse electrodialysis process has been developed based on the program for saline water electrodialysis. The program is applied to compute the performance of an industrial-scale reverse electrodialysis stack (effective membrane area S = 1 m × 1 m = 1 m2, cell pair number N = 300 pairs). The stack operatingconditions are optimized. Seawater and brackish water are supplied to compute the overall membrane pair characteristics, ion and solution flux across a membrane pair, ion transport efficiency, generation efficiency, electric current leakage, stack electric resistance, stack voltage, external current, electric power, power density, pressure drop, limiting current density, and etc. When seawater (35000 ppm) and brackish water (1000 ppm) are used, the maximum power density is 0.85 W/m2 (15 °C), 1.10 W/m2 (25 °C) and 1.35 W/m2 (35 °C). Membrane electric resistance is less than brackish water electric resistance. Electric current leakage increases the electric power generation of the RED unit. Limiting current density is very large, so the unit is operated stably. By arranging 12 stacks, a small-scale reverse electrdialysis plant (N= 12×300 = 3600 pairs) is assembled. The plant is operated to compute the performance changing external electric resistance.

A computer simulation of feed and bleed ion exchange membrane electrodialysis for desalination of saline water

Performance of a wick return AMTEC cell with a micromachined condenser

A novel implementation of water recovery from whey: “forward–reverse osmosis” integrated membrane system

Development of a computer simulation program of batch ion-exchange membrane electrodialysis for saline water desalination