A Thermodynamical Approach for Evaluating Energy Consumption of the Nanofiltration-Crystallization Process on Selective Separation of Chloride and Sulfate

• Main Authors: Ming-yuan Du, Lan-mu Zeng, Xiao-lin Wang
• Format: Article
• Language: English
• Published: MDPI AG 2018-03-01
• Series: Water
• Subjects: nanofiltration; process simulation; energy consumption; separation; chloride and sulfate; saline wastewater
• Online Access: http://www.mdpi.com/2073-4441/10/3/331

Nanofiltration (NF) coupling processes have been applied to treat high salinity wastewater in many studies. The main reason that affects the industrialization of the wastewater treatment is the high cost, which is mainly caused by the energy consumption of the entire system. Therefore, how to evaluate the energy consumption of different process configurations is an important issue. In this work, a thermodynamical approach was explained in detail, which could be used for evaluating energy consumption for pressure-driven membrane processes (e.g., NF and reverse osmosis) and osmotically driven membrane processes (e.g., forward osmosis). The coupling process configurations of NF, reverse osmosis (RO) and crystallization (Cryst) were selected to evaluate the energy consumption for high NaCl and Na2SO4 concentration wastewater in this paper. Four different process configurations (NF-Cryst, RO-Cryst, RO-NF-Cryst, NF-RO-Cryst) were simulated using Aspen Plus. The processes were discussed using a thermodynamical approach with a customized NF model. The electrolyte Non-Random Two-Liquid (electrolyte-NRTL) model was employed to calculate the thermodynamic properties of the solutions. The simulation results showed that the energy consumption per cubic meter of treated water (Ewater) in NF-Cryst and NF-RO-Cryst processes were lower than that of RO-Cryst and RO-NF-Cryst. When c f , N a 2 S O 4 was low (e.g., 15 g·L−1), there was not much difference in energy consumption between NF-Cryst and NF-RO-Cryst processes. Moreover, the high efficiency of NF was revealed in the separation of salt and decrease in the energy consumption of the whole process.