Thermodynamic analysis on the theoretical energy consumption of seawater desalination

• A novel model is proposed for calculating the TEC of seawater desalination.
• Activity coefficient and osmotic coefficient are considered in the model.
• Seawater is assumed to be NaCl–MgCl2–MgSO4 rather than aqueous NaCl solution.

It's well known that there are various methods being used in seawater desalination, which lead to different energy consumptions. However, the theory of thermodynamics reveals that the theoretical energy consumption (TEC, equivalent to the minimum work Wmin) of seawater desalination is only related to the initial and final state. Thermodynamic analysis of the TEC can contribute to the energy-saving of seawater desalination. In this paper, a novel mathematical model is proposed to calculate the TEC of seawater desalination concerning the recovery ratio, by assuming seawater to be aqueous NaCl–MgCl2–MgSO4 solution rather than aqueous NaCl solution. The activity coefficients of salts and the osmotic coefficients of water are calculated by the Pitzer model. The effect of ionic strength, recovery ratio, the activity coefficients of salts and the osmotic coefficients of water, seawater substitution on the TEC are also discussed. It is shown that ionic strength, recovery ratio, activity coefficients of salts and osmotic coefficients of water, seawater substitution have their different effects.