(725g) Performance of Multi-Stage Vacuum Membrane Distillation Integrated with Mechanical Vapor Compression

Treatment of hypersaline (>100g/L) wastewater is challenging, and only distillation-based technologies can treat such streams. Among distillation-based technologies, membrane distillation (MD) has shown great potential for treating highly concentrated brine. Different MD configurations have been utilized for desalination of hypersaline brine; among those, vacuum membrane distillation (VMD) is an ideal candidate where the driving force is increased by reducing the permeate pressure, thereby high fluxes are usually achieved. Recovering the heat of condensation from the permeate vapor product is crucial for improving the energy efficiency of the system. Recent studies showed that a multi-stage vacuum membrane distillation (MSVMD) enables the consecutive heat recovery between the feed and the permeate vapor via a series of heat exchangers.¹ Results on analysis gained output ratio (GOR) - a representative of the energy efficiency in MD - indicate that the multi-stage configuration enhances energy efficiency. More enhancement in energy efficiency and water recovery could be achieved when VMD is integrated with other processes such as mechanical vapor compression (MVC).

In this presentation, we will discuss the strategies to integrate MSVMD with MVC to enhance the heat/water recovery. In this effort, our goal was to optimize MSVMD-MVD to achieve higher energy efficiency. The VMD model was established based on the mass and heat balances involved in the VMD process in Aspen Custom Modeler (ACM) V10 ². The pre-validated thermodynamic model (eNRTL-RK) for thermo-physical properties of produced water was incorporated in Aspen Properties for the first time. The VMD unit was first validated against the lab-scale experimental results in terms of water vapor flux at different feed temperatures, feed flow rates, and permeate pressures.³ Process simulation on MSVMD- MVC was implemented in Aspen Plus V10 by importing the validated VMD model from ACM into the MVC-VMD flowsheet. The effects of operating conditions were investigated with respect to production and gain output ration (GOR).

References

(1) Chung, H. W.; Swaminathan, J.; Warsinger, D. M.; Lienhard V, J. H. Multistage Vacuum Membrane Distillation (MSVMD) Systems for High Salinity Applications. J. Memb. Sci. 2016, 497, 128–141. https://doi.org/10.1016/j.memsci.2015.09.009.

(2) Mengual, J. I.; Khayet, M.; Godino, M. P. Heat and Mass Transfer in Vacuum Membrane Distillation. Int. J. Heat Mass Transf. 2004, 47 (4), 865–875. https://doi.org/10.1016/j.ijheatmasstransfer.2002.09.001.

(3) Malmali, M.; Fyfe, P.; Lincicome, D.; Sardari, K.; Wickramasinghe, S. R. Selecting Membranes for Treating Hydraulic Fracturing Produced Waters by Membrane Distillation. Sep. Sci. Technol. 2017, 52 (2), 266–275. https://doi.org/10.1080/01496395.2016.1244550.