Closed circuit desalination series no-4: high recovery low energy desalination of brackish water by a new single stage method without any loss of brine energy

Desalination and Water Treatment

Wayman

Alatta

et al. 2016

The objective of this project is to design a new desalination system with energy efficiency approaching the theoretical thermodynamic limit-even at high recovery ratio. The system uses reverse osmosis (RO) and a batch principle of operation to overcome the problem of concentration factor which prevents continuous-flow RO systems from ever reaching this limit and thus achieving the minimum possible specific energy consumption, SEC. Batch operation comprises a cycle in 3 phases: pressurisation, purge and refill. Energy recovery is inherent to the design. Unlike in closedcircuit desalination, no feedwater is added to the pressure circuit during the pressurisation phase. The batch configuration is compared to standard configurations such as continuous single-stage RO (with energy recovery) and closed-circuit desalination (CCD). Theoretical analysis has shown that the new system is able to use 33% less energy than closed-circuit desalination at recovery ratio of 80%. A prototype has been constructed using readily available parts and tested with feedwater salinities and recovery ratios ranging from 2000-5000 ppm and 17.2-70.6% respectively. Results compare very well against the standard configurations. For example, with feedwater containing 5000 ppm NaCl and recovery ratio of 69%, a hydraulic SEC of 0.31 kWh/m 3 was obtained-better than the minimum theoretically possible with a single-stage continuous flow system with energy recovery device.

Section: Ecr = Sec Secmentioning

confidence: 99%

A desalination system with efficiency approaching the theoretical limits

Desalination and Water Treatment

Wayman

Alatta

et al. 2016

“…In contrast to the plethora of CP research on conventional (continuous steady mode) RO process, no studies pertaining to CP in batch-RO have been carried out, because not many commercially available batch-RO systems exist and research on batch-RO is at a relatively early stage [23][24][25]. Therefore, research about CP in batch-RO is necessary to obtain insight into the characteristics of mass transfer in transient hydrodynamic conditions as well as to contribute to the improvement of batch-RO.…”

Section: Symbolmentioning

confidence: 99%

Concentration polarization model of spiral-wound membrane modules with application to batch-mode RO desalination of brackish water

Qiu

2015

Desalination

Batch-mode RO (batch-RO) operation is considered a promising desalination method due to its low energy requirement compared to other RO system arrangements. To improve and predict batch-RO performance, studies on concentration polarization (CP) are carried out. The Kimura-Sourirajan mass-transfer model is applied and validated by experimentation with two different spiral-wound RO elements. Explicit analytical Sherwood correlations are derived based on experimental results. For batch-RO operation, a new genetic algorithm method is developed to estimate the Sherwood correlation parameters, taking into account the effects of variation in operating parameters. Analytical procedures are presented, then the mass transfer coefficient models are developed for different operation processes, i.e. batch RO and continuous RO. The CP related energy loss in batch-RO operation is quantified based on the resulting relationship between feed flow rates and mass transfer coefficients. It is found that CP increases energy consumption in batch RO by about 25% compared to the ideal case in which CP is absent. For continuous RO process, the derived Sherwood correlation predicted CP accurately. In addition, we determined the optimum feed flow rate of our batch-RO system.

“…Another BWRO desalination system that uses time-varying conditions called Closed Circuit Desalination (CCD) has been proposed and developed by Efraty [28,29]. The concept of CCD is illustrated schematically in Figure 10.…”

Section: Closed Circuit Mode Ro Operationmentioning

confidence: 99%

“…The operation parameters of the batch-RO system do not exceed the membrane specification provided by the manufacturer. Moreover, the loading with recycled brine and the unloading with fresh feed water can reduce the development of membrane fouling and scaling so it may even be advantageous [29].…”

Section: Comparison Of Different Configurationsmentioning

confidence: 99%

Comparison of Configurations for High-Recovery Inland Desalination Systems

Qiu

2012

Water

Desalination of brackish groundwater (BW) is an effective approach to augment water supply, especially for inland regions that are far from seawater resources. Brackish water reverse osmosis (BWRO) desalination is still subject to intensive energy consumption compared to the theoretical minimum energy demand. Here, we review some of the BWRO plants with various system arrangements. We look at how to minimize energy demands, as these contribute considerably to the cost of desalinated water. Different configurations of BWRO system have been compared from the view point of normalized specific energy consumption (SEC). Analysis is made at theoretical limits. The SEC reduction of BWRO can be achieved by (i) increasing number of stages, (ii) using an energy recovery device (ERD), or (iii) operating the BWRO in batch mode or closed circuit mode. Application of more stages not only reduces SEC but also improves water recovery. However, this improvement is less pronounced when the number of stages exceeds four. Alternatively and more favourably, the BWRO system can be operated in Closed Circuit Desalination (CCD) mode and gives a comparative SEC to that of the 3-stage system with a recovery ratio of 80%. A further reduction of about 30% in SEC can be achieved through batch-RO operation. Moreover, the costly ERDs and booster pumps are avoided with both CCD and batch-RO, thus furthering the effectiveness of lowering the costs of these innovative approaches.