Water Desalination Using Capacitive Demixing: A Theoretical Analysis Of Temperature Effects

Abstract

At any place where a river flows into the sea, fresh and saline water are mixed. This salinity-gradient energy or ``blue energy" can be harvested, e.g. using capacitive mixing. The reverse process is also possible: water desalination using capacitive demixing in a three-step cycle. In this thesis, the aim is to find the optimal desalination cycle, such that the required work per liter desalinated water is minimal. In order to find the optimal cycle, the parameter space of two variables is explored: the temperature, and the ratio between the engine volume and the water volume that is made fresh during one cycle. Numerical solutions to the lattice-gas Poisson-Boltzmann equation for parallel-plate capacitors show that desalination processes are the most efficient at low temperatures. Calculations regarding the volume ratio indicate that desalination processes are the most efficient for the case when the volume of secured fresh water per cycle is large compared to the engine volume.