Split-feed counterflow reverse osmosis for brine concentration

Abstract

Brine concentration allows for increased recovery ratios in water treatment systems, reduction of waste volumes, and the production of minerals from saline brines. Existing methods of brine concentration, while robust, are often very energy intensive. Better efficiency may be possible using Counterflow Reverse Osmosis (CFRO), a membranebased, pressure-driven brine concentration technology. The present work develops a model for CFRO. Using this model, a single CFRO module is simulated and its performance characterized. Exergy destruction within a single-stage system is analyzed, which provides insights for configuring and optimizing multistaged systems. Additionally, a parametric analysis of membrane parameters provides direction for the development of CFRO-specific membranes. Two existing configurations of CFRO are discussed, and compared with a new third configuration, split-feed CFRO, which is presented here for the first time. Split-feed CFRO systems are simulated and optimized to provide guidance for system design. A variety of multistage systems operating at a range of recovery ratios are simulated, and the results compared are with existing desalination and brine concentration technologies, showing the potential for improved recovery ratios and reduced energy consumption.Keywords: brine concentration, desalination, energy efficiency, counterflow reverse osmosis, zero liquid discharge

The relative insignificance of advanced materials in enhancing the energy efficiency of desalination technologies

“…6,121,122 Novel high-salinity RO-based process designs, such as osmotically assisted RO [123][124][125] and low salt rejection RO, 126 have the potential to reduce the hydraulic pressure required to achieve high brine salinities, expanding the applicability of RO to minimal-and zero-liquid discharge processes. [127][128][129] Further work is required to overcome key challenges, including internal concentration polarization and optimal membrane spacer design, that have thus far limited the practical realization of processes in which both sides of the membrane are in contact with saline streams.…”

Membrane processes

“…Higher efficiency may be feasible using counterflow reverse osmosis (CFRO), a membrane‐based, pressure‐driven brine concentration technology. Bouma (2018) simulated a split‐feed CFRO and optimized it as a guiding design for this new system. A variety of multistage systems operations showed the potential for improved recovery ratios and reduced energy consumption.…”

Energy Savings in Desalination Technologies: Reducing Entropy Generation by Transport Processes

“…(3) Closed-cycle RO is a semi-batch process that has been commercialized for brackish water desalination [40,41]. (4) Counterflow RO, in which feed and permeate are counterflowing, so that osmotic pressure differences are kept low [42,43]. The reduced osmotic pressure difference reduces the hydraulic pressure and pump work required.…”

“…This technology appears most promising for feeds at salinities greater than seawater. Multi-stage, split-feed CFRO has been estimated to require only 3.9 kWh/m 3 to concentrate a feed from 35,000 ppm to 200,000 ppm, equivalent to a 49% second-law efficiency [43]. Commercial deployment is in progress.…”