Seawater Reverse Osmosis Desalination Systems Research Articles

A system-level CFD simulation model for investigating the energy dissipation mechanism of seawater pump and rotary energy recovery device in SWRO desalination system

Seawater reverse osmosis (SWRO) technology has been universally adopted because of its high efficiency, economic benefits, easy maintenance, and high-pressure seawater pump (HPSP) and energy recovery device (ERD) are essential components, which determine the specific energy consumption of SWRO system. However, it is still unclear about energy dissipation mechanism and mixing characteristics from the perspective of system. For that, this thesis proposes a novel system-level Computational Fluid Dynamics (CFD) model considering all interfaces in HPSP and integrated energy recovery and pressure boost device (IERPBD). To profoundly investigate the system performance under various operating conditions, the pressure and composition distribution, power loss of each interface and mixing rate are numerically calculated and analyzed. Additionally, experiment of the effect of temperature on SWRO system performance is conducted to practically verify the proposed model, which indicates that the presented model could precisely reflect the energy dissipation and mixing characteristics. Besides, it is advised that the rotating speed of HPSP and IERPBD should not be set too high which could increase the mixing rate and energy consumption, and higher temperature might lower the quality of produced freshwater. This study offers a feasible way to reveal the energy dissipation mechanism of SWRO desalination system.

Multi-objective optimization and energy efficiency improvement for rotor duct in integrated energy recovery-pressure boost device

To reduce the volumetric mixing rate of the integrated energy recovery-pressure boost device, a novel symmetrical duct structure with diversion surface was proposed. The surrogate model-based multi-objective optimization framework was established, and obtained the optimal ducts V1 and V2 combined with computational fluid dynamics simulation. Numerical results indicate that optimized duct structure could promote the formation of plug flow and effectively improve the collision efficiency between high-pressure brine and low-pressure seawater, and the volumetric mixing rate corresponding to the ducts V1 and V2 was reduced by 31.52% and 22.18%, and the duct volume efficiency was increased by 16.04% and 19.56%, respectively. Finally, the performance of optimized device was verified through seawater reverse osmosis desalination system under actual working conditions. Experimental results showed that the mixing rate of optimized ducts had a significant decrease of 30.86% and 20.53% in the applicable range, and the energy recovery efficiency improved at most 5.41% and 7.55%, respectively. The optimized ducts could significantly reduce the specific energy consumption of the desalination system by 26.01% and 18.22%, respectively, and the specific energy consumption reached the lowest level of 3.02 kWh/m3, demonstrating the superiority of the structure and the accuracy and effectiveness of the optimization strategy.

Numerical study on the energy consumption characteristics of a novel integrated pump-motor unit for SWRO desalination system

Energy recovery device (ERD) is a critical component in seawater reverse osmosis (SWRO) desalination systems, which recovers hydraulic energy from the high-pressure brine and effectively reduces system energy consumption. In this thesis, a novel integrated seawater desalination pump-motor energy recovery device (ISPM-ERD) without the slipper/swashplate interface is proposed to further reduce energy consumption and improve system integration, which is able of concomitantly achieving seawater pressurization and energy recovery. A co-simulation multibody dynamic model with rigid-flexible coupling is applied to precisely examine the internal power loss of ISPM-ERD, especially volumetric loss and mechanical loss of the key lubricating interface. Besides, the influence of shaft rotational speed and working pressure on the power loss and overall efficiency of ISPM-ERD are comparatively investigated. In addition, a performance study of the presented ISPM-ERD is carried out based on the co-simulation model, which reveals the energy recovery efficiency and specific energy consumption (SEC) of ISPM-ERD under various operating conditions. The results indicate that the proposed ISPM-ERD is sufficient to meet the needs of the small-scale SWRO systems, whose energy recovery efficiency is more than 90.1 % in the 3.0–7.0 MPa operating pressure range and the SEC of freshwater production is 2.94 kW·h/m3 under rated working conditions.

Research on the pressure and flow characteristics of seawater axial piston pump considering cavitation for reverse osmosis desalination system

Seawater axial piston pump (SWAPP) has been widely used as the power component in the seawater reverse osmosis (SWRO) desalination systems, whose flow quality could result in significant influences on the performance of RO membranes and SWRO system. This thesis proposed an efficient fully parameterized mathematical approach for the flow and pressure characteristics of SWAPP that is modeled by lumped parameter techniques considering gaseous and vaporous cavitation simultaneously. To address the complex structure of the port plate in SWAPP, especially silencing groove, an innovative model based on the Monte Carlo method was originally proposed, and In-depth comparison with piecewise functions validated the accuracy, efficient and convenient of Monte Carlo approach for calculating the flow area of SWAPP. Particularly, the influence of shaft rotational speed and inlet pressure on the instantaneous discharge flow and pressure of SWAPP was comparatively studied. In addition, a SWRO desalination system was constructed to evaluate the effect of discharge pressure of SWAPP on the RO concentrated brine pressure. The results indicate that the presented model can precisely capture the instantaneous discharge pressure and flow of SWAPP. Besides, increasing the shaft rotational speed and inlet pressure are reliable solutions to enhance the flow performance of SWRO system.

Performance fluctuations and evaluation of a piston type integrated high pressure pump-energy recovery device

The development of energy recovery device (ERD) is a decisive factor for the recent prevalence of reverse osmosis (RO) technology in the seawater desalination field. Unlike broadly studied large scale ERDs, the investigations of small scale ERDs are scarcely reported, especially on the performance fluctuations under variable operating conditions. Based on an authors’ exploratory research on a piston type integrated high pressure pump-energy recovery device (HPP-ERD), further performance exploitation of the HPP-ERD is conducted. With a constructed experiment platform, the influences of inlet seawater temperature, inlet seawater salinity, as well as the operating frequency on the performance of the HPP-ERD coupled with seawater reverse osmosis (SWRO) desalination system are investigated. The temperature and salinity of the inlet seawater are numerically correlated with the specific energy consumption (SEC) of the HPP-ERD. With the correlated equation, the marine hydrological data of two observatories acquired from a national authoritative database, and the annualized life cycle cost approach incorporated, annual performance assessment is proposed for an SWRO desalination system equipped with the HPP-ERD in the light of energy and economic indices. The study results indicate that the proposed HPP-ERD is competent under various operating conditions for SWRO desalination systems.

Development of a computational tool for the design of seawater reverse osmosis desalination systems powered by photovoltaics for crop irrigation

Access to fresh water is a major human right as mankind existence depends on it. The balance between fresh water supply and actual water demand for agricultural purposes (irrigation) relies on the availability of fresh water in the underground aquifers or surface water resources. Water resources are under great pressure due to the high demand for irrigation to sustain crop productivity and cover domestic use as a result of demographic growth. Desalination of sea or brackish water is one of the solutions to provide water for irrigation in remote areas of limited freshwater reserves. In such areas, if desalination is powered by renewable energy sources, then it can become a lot more sustainable. This paper presents the development of an innovative computational tool for the optimal (economically and technically) design of seawater reverse osmosis desalination systems for sustainable water production for crop irrigation. In order to further reduce the cost of water produced, an energy management and control system was also designed and included in the computational tool to ensure the optimal operation of the desalination plant. This system allows the seawater reverse osmosis unit to operate at variable load and determines its optimal operation point using computational intelligence techniques based on fuzzy cognitive maps. According to the results, the implementation of the computational tool for the design of PV-SWRO system presents the lowest cost as compared to the system designed with the conventional methodology.

Numerical and experimental research on the integrated energy recovery and pressure boost device for seawater reverse osmosis desalination system

Rotary energy recovery devices (RERDs) play a significant role in reducing the consumption of energy used in the desalination of seawater by reverse osmosis (SWRO). An integrated energy recovery and pressure boost device (IERPBD) applied to the recovery of hydraulic energy from the concentrated brine and pressurizes synchronously the seawater is introduced. To address the complex motion of the multiple lubricating gaps in IERPBD, especially piston ball/slipper and slipper/swashplate interfaces, an innovative computational fluid dynamics (CFD) model based on User Defined Function (UDF) is originally proposed. The characteristics of pressure, flow and mixing are analyzed to reveal the influence of multiple lubricating gaps leakage and mixing on energy recovery process. In addition, a SWRO system is built to investigate the effect of operating parameters and seawater salinities on the energy recovery and mixing properties of the IERPBD, and its structural parameters are optimized by parametric study, which further reveals the comprehensive characteristics of the IERPBD. The results indicate that the proposed CFD methodology can precisely analyze the energy loss and mixing properties of RERDs, and the utilization of IERPBD can diminish 25.7% of the energy consumption of SWRO system with 24.2% freshwater recovery ratio and 10 m3/d freshwater production.

Numerical methodology and CFD simulations of a rotary vane energy recovery device for seawater reverse osmosis desalination systems

• Novel analytical grid generation methodology for rotary vane machines. • Removal of backflows and torque peaks through flow port optimisation. • Sensitivity analysis to reduce cavitation and improve volumetric efficiency. • Volumetric efficiency with optimal speed and blade design equal to 91.6%. Energy recovery devices in Seawater Reverse Osmosis Systems (SWRO) reduce energy consumption and may facilitate the large-scale deployment of desalination systems. In this paper, a Rotary Vane Energy Recovery Device (RVERD) is analysed and optimised by aiming at weakening cavitation and improving the volumetric performance of the machine. An innovative analytical methodology based on user defined nodal displacement is proposed to address the need to discretise the rotating and deforming computational domain of double-acting vane machines. The generated grids are interfaced with the ANSYS FLUENT solver for multi-phase computational fluid dynamics simulations. The flow topology is analysed to reveal the flow and cavitation features especially in the blade tip regions. A port optimisation is then carried out followed by a sensitivity analysis on the design parameters to improve RVERD performance. The results show that delaying the discharge angle at the high-pressure outlet port by 3° and an optimal port to stator length ratio of 70% helped to prevent backflows and eliminate torque peaks. The sensitivity analysis has identified the rotational speed and the blade tip clearance as the two most influential factors affecting cavitation and, in turn, the volumetric efficiency of the machine. With respect to the baseline design configuration, at the optimal rotational speed of 1000 RPM and with a tip clearance gap of 50 μm, the volume-averaged vapour volume fraction in the core decreased from 20.6 × 10 −3 to 0.6 × 10 −3 while the volumetric efficiency increased from 85.7% to 91.6%. The axial clearance gap of 70 μm contributed to 2.9% of the volumetric losses.

Development and operational stability evaluation of new three-cylinder energy recovery device for SWRO desalination system

The energy recovery device (ERD) plays an important role in reducing energy consumption of seawater reverse osmosis (SWRO) system. However, for reciprocating-switcher energy recovery device (RS-ERD), stroke switching will cause flowrate and pressure pulsations of high and low pressure fluids, which will affect the operation stability of SWRO system. In this paper, we develop a three-cylinder energy recovery device (TC-ERD) and a matching control strategy with instantaneous overlap function to simultaneously reduce the flowrate and pressure pulsations of high and low pressure fluids. Under design capacity (30 m3/h) and 5.0 MPa operating pressure, the pressure pulsation amplitude of HP brine is only 0.0675 MPa, which is 86.5% lower than that of RS-ERD. The flowrate pulsation amplitude (0.954 m3/h) of LP seawater decreases by 68.2% compared with RS-ERD, while that (1.336 m3/h) of HP brine is approximately doubled. The doubling of HP brine flowrate pulsation arises from the fact that the actual operating point of the boost pump is much lower than its rated operating point, which can be improved by optimizing pump selection in future work. The energy recovery efficiency of the TC-ERD is as high as 97.1% at design capacity and 5.0 MPa operating pressure.

Energy analysis of a seawater reverse osmosis desalination system for small marine vessels

Energy analysis of a seawater reverse osmosis desalination system for small marine vessels

Sustainable Seawater Reverse Osmosis Desalination as Green Desalination in the 21st Century

Seawater reverse osmosis desalination (SWRO) requires less energy compared with the distillation method and thus is an important technology except Middle Eastern countries whereenergy costs are higher. Recently, even Middle Eastern countries where the distillation method is still a major technology, have begun adopting the RO method in new desalinationplants in line with government policy and the trend is for the development of larger (in excess of half mega-ton per day or mega-ton per day size) so-called “Mega-SWRO” plants.With these trends in the global market, the requirements of sustainable SWRO desalination as green desalination for the 21st century are summarized under three subjects: 1) Energyresources:Renewable energy, 2) Seawater RO system: Advanced membrane and membrane system, 3) Reduction of marine pollution: Green desalination. The “Mega-ton Water System” projecthas been conducted to solve issues related to subjects 2) and 3) as Japanese national project.a. By combining a low pressure SWRO membrane and a low pressure two-stage high recovery SWRO system, 20% energy reduction was possible. And 30% energy saving in totalwas also possible as the SWRO-PRO hybrid system.b. For low environmental impact as green desalination, less chemical and less chemical cleaning for reliable operation have been established.c. Low-cost renewable energy, particularly solar energy, is now available to solve issues related to subject 1. By combining these sophisticated technologies, the cost of seawaterdesalination will be $ 0.50/ m3/day or less.

Economic, Energy, Exergo-Economic, and Environmental Analyses and Multiobjective Optimization of Seawater Reverse Osmosis Desalination Systems with Boron Removal

We presented economic, energy, exergo-economic, and environmental analyses and multiobjective optimization (MOO) of seawater reverse osmosis (RO) desalination systems with boron restrictions. Exergo-economic unit cost for flows and exergy destruction for components were included. Life cycle assessment (LCA) principles with the contributions of construction and operating were introduced. An improved augmented e-constraint method was adopted for solving the MOO problems. Unnecessary iterations were avoided by bypass parameter. Results showed that the Pareto-solution with a weighting of 0.4 could provide good performances for all objective functions. The CO2 emissions reduction of 9.0% could be achieved, while the water cost is increased by 3.3%. Fixed cost dominates EUC. The environmental impact of construction is neglectable, while electricity consumption accounts for the largest share of CO2 emissions from 93.4% to 97.8%. The details of energy utilization for components, the irreversibility, and equipment...

A novel autonomous PV powered desalination system based on a DC microgrid concept incorporating short-term energy storage

Seawater reverse osmosis (SWRO) desalination units coupled with renewable energy technologies such as photovoltaics are a very appealing suggestion, especially in remote areas, such as islands and coastal regions, which often face lack or low quality fresh water coupled with electrical energy shortages. This paper regards an experimental investigation of a PV powered small-scale SWRO desalination system which employs hydraulic energy recovery, based on a DC microgrid concept and incorporates a short term electric energy storage in the form of hybrid capacitors and a short term hydraulic energy storage in the form of pressure vessels. Α multi-agent decentralized energy management system which relies on intelligent agents and employs Fuzzy Cognitive Maps for its implementation, allowing for efficient operation of the desalination system under variable conditions (variable feed pressure), was developed and implemented. The experimental results show that it is feasible to operate efficiently such PV powered SWRO system. Furthermore, the desalination unit produces potable water during daytime even at periods when the produced energy from the PV array is not sufficient to operate the desalination unit. Moreover, the SWRO system shows a continuous and smooth operation, meaning small feed water pressure variations at sharp rapid solar irradiation intensity variations due to the incorporated short-term storage. In addition, the intelligently managed PV powered SWRO system with short term storage produces considerably more fresh water, especially at days with variable solar irradiation, as compared to the same SWRO system directly PV driven without storage and any control.

Theoretical performance prediction of a reverse osmosis desalination membrane element under variable operating conditions

Sea Water Reverse Osmosis (SWRO) desalination systems powered by Renewable Energy (RE) can reduce drastically costs, specific energy consumption and CO2 emissions. A direct connection of a SWRO desalination system with RE technologies such as photovoltaics, can result in lowering the specific energy consumption due to the part-load operation of the desalination unit. However, due to the variable nature of solar energy, the membranes could operate outside of their nominal operating ranges. Therefore, research is needed to investigate the effect of the variable operation (non-stable pressure and flow rate) on the membranes. This paper presents the development of a dynamic mathematical model of a spiral wound reverse osmosis membrane module aiming to investigate the mass transfer in the membrane under non-constant operating conditions. The main pursue of the model is to investigate the physical compaction, as well as the raise of the concentration polarization in order to predict the performance of the membrane under variable operating conditions. The results show a water flux drop of 0.2×10−3kg/m2·s due to the sudden increase in the applied pressure, when the impact of physical membrane compaction was taken into consideration under non-constant operating conditions.

A review of the current status of small-scale seawater reverse osmosis desalination

ABSTRACTThe current status of small-scale desalination (produced water capacity 100 m3/day or less) is reviewed to provide an overview of the market segment. The use of energy-recovery devices in this market segment is also reviewed. We find that the Middle East accounts for the largest market share worldwide at present, and reverse osmosis is overwhelmingly dominant among the desalination technologies adopted. Implementation of energy-recovery devices at small scale is rare, which leads to relatively high energy consumption for small-scale seawater reverse osmosis desalination systems.

Capacity flexibility evaluation of a reciprocating-switcher energy recovery device for SWRO desalination system

The adoption of energy recovery device (ERD) in seawater reverse osmosis (SWRO) system has become a practical way for reducing the power consumption and permeating cost of the desalting system. The performance requirement of the ERD basically depends upon the configurations and operating parameters of the SWRO system. The temperature and salinity of the seawater feed are two typical parameters that should be considered, whose fluctuations may induce significant changes in the membrane separation performance and thus the flow balance of the SWRO system, which requires the ERD having a good adaptability to meet the practical demands. In this paper, a SWRO desalination platform is built to evaluate the capacity flexibility of a reciprocating-switcher energy recovery device (RS-ERD). The experimental results show that the RS-ERD can run in 66.7%–150.0% of the design capacity (30m3/h) and maintain a relative constant efficiency above 96.50% and leakage ratio about 2.62%–3.95%, which proves the wide-range adaptability of the RS-ERD to the varying conditions of the SWRO desalination system.

The Economics of Reverse Osmosis Desalination Projects

Desalination applications based on reverse osmosis (RO) technology today comprise over 50% of the capacity of all desalination systems worldwide and represent 75-85% of new desalination projects being implemented. The major reason for the shift in desalination projects to RO technology is the high energy efficiency of the RO process. There are three major application categories of large capacity, RO-based desalination projects: brackish RO; advanced municipal wastewater reclamation; and seawater RO. In the two first categories (brackish RO and wastewater reclamation), the systems’ configuration and equipment components are well defined. Therefore, project costs and operating expenses are fairly predictable. In seawater RO desalination systems, the RO process configuration is also very similar; however, some variability exists regarding the configuration of seawater water delivery and feed water pretreatment. The rest of the system’s components and system operation methods are very uniform. However, an evaluation of published cost data of medium- to large-scale water RO desalination projects illustrates significant variability in costs of desalination systems. This paper will analyze current economic conditions of seawater desalination, and highlight the limitations and possibilities of additional improvements of the economics of the SWRO desalination process.

Development and experimental studies on a fully-rotary valve energy recovery device for SWRO desalination system

Isobaric energy recovery devices (ERDs) are developing rapidly and playing a significant role in reducing specific energy consumption (SEC) of seawater reverse osmosis (SWRO) desalination systems. However, leakage, abrasion and large pressure loss are still big challenges and remain big problems unsolved among the present ERDs. In this paper, a novel isobaric ERD based on so-called fully-rotary valves (FRVs) is developed to resolve these problems. The key fully-rotary valve energy recovery device (FRV-ERD) consists of only two FRVs and pipelines. The performance of the FRV-ERD is tested by means of an ERD performance test system. The hydraulic performance of the device is tested under laboratory conditions with the test pressure about 3.0MPa. Experiments show that the operation of the FRV-ERD is stable and the pressure fluctuations of high pressure streams are small. The leakage is not detected and therefore excellent seal performance is proved through tests as well. The measured pressure loss is low and the energy recovery efficiency is as high as 98.47% which is among the best of the reported values.

Thermophysical properties of seawater: A review and new correlations that include pressure dependence

In a previous paper, the authors have given correlations for seawater thermophysical properties as functions of temperature and salinity, but only for near atmospheric pressures. Seawater reverse osmosis (SWRO) systems operate routinely at pressures of 6MPa or more; however, experimental data for seawater properties at elevated pressures (P=0.1–12MPa) are limited to a salinity of 56g/kg. To accurately model and design SWRO and thermal desalination systems, a reliable method of estimating the effect of pressure on seawater properties is required. In this work, we present this method and new correlations for seawater thermophysical properties that are valid within the range: t=0–120°C, S=0–120g/kg, and P=0–12MPa. Seawater isothermal compressibility data, available until a salinity of 56g/kg, were used to develop a correlation for compressibility that is extrapolated to 160g/kg. Thermodynamic identities were then used to develop accurate pressure dependent correlations for seawater: density, isobaric expansivity, specific heat capacity, enthalpy, entropy and Gibbs energy. New correlations were proposed for seawater: vapor pressure, thermal conductivity and activity of water. Recent work on seawater surface tension and osmotic coefficient were reviewed. Uncertainty bounds were calculated for each correlation.

Functionality test of an innovative single-cylinder energy recovery device for SWRO desalination system

Energy recovery devices (ERDs) are widely used in seawater reverse osmosis (SWRO) desalination systems, and have become a vital facility of the system due to their great contribution for significant reductions of the power consumption. The innovative single-cylinder ERD (SC-ERD) technology is an improved pressure exchanger concept which follows the principle of positive displacement, and provides more advantages than the current devices, including the simple installation, flexible operation and stable performance. This paper focuses on verifying the functionality of the SC-ERD and evaluating its operating performance based on the industrial conditions. Experiments are carried out by using two sets of SC-ERD working in parallel and the performance of the devices are evaluated by employing an inhouse emulational SWRO system with the flow rate of 30m3/h and the operating pressure of 6.5MPa. The experimental results show that two SC-ERDs in parallel have reached the basic function of the double-cylinders ERD (DC-ERD). The pressure fluctuation of the SC-ERD has been reduced about 80% compared with the DC-ERD under the same operating conditions and the energy recovery efficiency could still be remained as high as 98%.