(735af) Advancing Separation Systems of High Brine Concentrations through Refined Thermodynamics and Process Intensification

Modeling separation processes for solutions with high brine concentrations requires accurate models of separation, which inherently incorporate heat and mass transport phenomena. These models are widely utilized in the water industry. Additionally, modeling of the involved unit operations necessitates accurate thermodynamic models to compute various electrolyte thermodynamic properties, such as the mean ionic activity coefficients in concentrated aqueous multi-electrolyte solutions. However, many current models incorporate the conventional electrolyte-nonrandom two-liquid (eNRTL) [1] model that lacks accuracy at high temperatures and concentrations.

In this study, the refined-eNRTL [2] model is used to refine the implementation of thermodynamic property models in the modeling of highly concentrated brine separation systems. In prior work, Stuber et al. [3] developed models of the unit operations of concentrator systems, representing an advanced separation process based on solar-powered multi-effect distillation (MED) with an absorption heat pump (AHP). The MED system was designed with the water-energy nexus in mind, which offers improved thermal efficiency from the AHP, and reduces the dependence on water-intensive power sources by utilizing solar thermal power as its primary energy source. This system’s set of unit operations served as the foundational model for this work, extending it with the inclusion of the refined-eNRTL model. The new model was developed in Pyomo with modular libraries of IDAES [1] and WaterTAP [4] to combine electrolyte thermodynamics, process modeling, simulation, and optimization for the process intensification of high brine concentration and separation systems. When accounting for non-ideality in the system, the inclusion of the refined e-NRTL model resulted in differences in mean ionic activities and a reduction in energy consumption compared to less accurate thermodynamic property methods. The system model was then used to study designs and operating conditions that intensify and optimize the process under varying amounts of water recovery in the separation process. In conclusion, this study shows how the accurate prediction of brine properties can support process intensification within the water-energy nexus, allowing for greater utilization and reuse of non-traditional water sources.

Acknowledgments

This study was supported by the National Alliance for Water Innovation (NAWI), funded by the U.S. Department of Energy, Energy Efficiency and Renewable Energy Office, Advanced Manufacturing Office.

References

[1] Lee, Andrew, Jaffer H. Ghouse, John C. Eslick, Carl D. Laird, John D. Siirola, Miguel A. Zamarripa, Dan Gunter et al. "The IDAES process modeling framework and model library—Flexibility for process simulation and optimization." Journal of Advanced Manufacturing and Processing 3, no. 3 (2021): e10095.

[2] Bollas GM et al. Refined Electrolyte-NRTL Model: Activity Coefficient Expressions for Application to Multi-Electrolyte Systems. AIChE J. 2008;54(6):1608-1624

[3] Stuber MD et al. Pilot demonstration of concentrated solar-powered desalination of subsurface agricultural drainage water and other brackish groundwater sources. Desalination. 2015;355:186-196.

[4] WaterTAP contributors. WaterTAP: An open-source water treatment model library. Version 0.6. Sponsored by California Energy Commission, National Alliance for Water Innovation, and USDOE. Available at https://github.com/watertap-org/watertap