Thermodynamic modeling of a combined photo-electrodialysis-chloralkali system for sustainable desalination

Abstract

In this paper, a thermodynamic model of a combined photo-electrodialysis-chloralkali system for desalination is developed. The waste stream from an electrodialysis unit is sent to a chloralkali reactor, which produces several useful commodities namely; H2, Cl2, and NaOH. Photoactive materials BiVO4 and Cu2O are utilized as photo-electrode coatings for the electrodialysis and chloralkali units, respectively. Photovoltaic panels are also used to provide the required electricity for the electrochemical processes. A sensitivity analysis is performed to find the effects of changing the salinity, temperature, flow rate, and recovery rate on the system performances. The feed salinity is ranged from 10 to 35 g/kg and the freshwater capacity is ranged from 35 to 350 m3/day in the system. The specific energy requirements for the electrodialysis and chloralkali units are found to be 1.225 kWh/m3 of freshwater produced and 2.5 kWh/kg Cl2 produced respectively for a salt rejection rate of 0.96 and a recovery rate of 0.77. Furthermore, the energy efficiencies for the photo-assisted electrodialysis (PED) and photo-assisted chloralkali (PCA) units are found to be 42.56% and 48.04%, respectively. Finally, the overall combined system energy and exergy efficiencies are found to be 23.93% and 33.14%, respectively.