Energy efficiency of batch and semi-batch (CCRO) reverse osmosis desalination

Abstract

ABSTRACT:As reverse osmosis (RO) desalination capacity increases worldwide, the need to reduce its specific energy consumption becomes more urgent. In addition to the incremental changes attainable with improved components such as membranes and pumps, more significant reduction of energy consumption can be achieved through time-varying RO processes including semi-batch processes such as closed-circuit reverse osmosis (CCRO) and fully-batch processes that have not yet been commercialized or modeled in detail. In this study, numerical models of the energy consumption of batch RO (BRO), CCRO, and the standard continuous RO process are detailed. Two new energy-efficient configurations of batch RO are analyzed. Batch systems use significantly less energy than continuous RO over a wide range of recovery ratios and source water salinities.Relative to continuous RO, models predict that CCRO and batch RO demonstrate up to 37 % and 64 % energy savings, respectively, for brackish water desalination at high water recovery. For batch RO and CCRO, the primary reductions in energy use stem from atmospheric pressure brine discharge and reduced streamwise variation in driving pressure. Fully-batch systems further reduce energy consumption by not mixing streams of different concentrations, which CCRO does. These results demonstrate that time-varying processes can significantly raise RO energy efficiency.

Effect of temperature on ion transport in nanofiltration membranes: Diffusion, convection and electromigration

“…Summary and implications for seawater transport at higher temperature 1. Rejection ratio of all divalent ions is ~100% at both temperatures studied, although it reduces slightly at the higher temperature.…”

“…In a world where water-scarcity is a burgeoning issue, methods of water-treatment and reuse that are economic and minimize energy consumption are of vital importance for the safekeeping of the environment [1]. Nanofiltration (NF) is a pressure driven membrane-based desalination technique.…”

A perspective on reverse osmosis water desalination: Quest for sustainability

“…In each cycle, salt buildup in the RO system during the period of complete concentrate recirculation is purged during subsequent period of concentrate discharge. In addition to enhanced operational flexibility, recent theoretical analysis under idealized plug‐flow conditions suggests that for a single stage RO, the approach can potentially be utilized as an alternative to using an energy recovery device . Nevertheless, existing analysis have yet to consider the impact of non‐ideal flow conditions in real RO systems, especially during the concentrate withdrawal period.…”

Comprehensive condensation flow regimes in air gap membrane distillation: Visualization and energy efficiency

“…Note that this quantification judges membrane performance, not system efficiency, and is not comparable to efficiency metrics used for other technologies, such as the second law efficiency for RO [62][63][64][65]. Another relevant parameter is the overall energy efficiency or GOR (gained output ratio), which compares the enthalpy of simply evaporating water to the heat input ̇… actually used:…”