Reverse Osmosis System Analysis Research Articles

Opportunities of Reducing the Energy Consumption of Seawater Reverse Osmosis Desalination by Exploiting Salinity Gradients.

This work presents a performance assessment of three seawater reverse osmosis-pressure-retarded osmosis (SWRO-PRO) hybrid schemes for energy consumption reduction in seawater desalination applications by using an external low salinity water source. For comparison purposes, another arrangement based on the conventional SWRO process combined with brackish water RO (BWRO) and desalination was analyzed. Reverse osmosis system analysis software environments were used to select the best SWRO configuration and operating conditions. A purposely developed model was used to evaluate the PRO system. Two different cases were assessed depending on the origin of the external low-salinity resource for the PRO process: industrial wastewater and urban treated wastewater. In the case of the industrial wastewater, due to regulations on wastewater reclamation, the best arrangement would be the first SWRO-PRO scheme which was analyzed with a specific energy consumption of 1.54 kWh/m3. If urban treated wastewater is available as an external resource, the results obtained show that this scheme, leading to the minimum specific energy consumption of 1.46 kWh/m3, is the conventional SWRO combined with BWRO. Therefore, hybrid SWRO-PRO systems are recommended to reduce the specific energy consumption of seawater desalination if an industrial wastewater source with low osmotic pressure is available.

Simulation and optimisation of a SWRO system in Cape Town, South Africa

Seawater reverse osmosis (SWRO) system is popular in most islands and coastal areas around the world with limited fresh water resources. A SWRO system was designed to fulfil 50% of the population water demand in Cape Town, South Africa, which can lead up to 383,353 m3/day in the next 15 years. The total dissolved solid (TDS) within the product (i.e. drinking water) was lowered to 600 ppm by referring to standard guideline stated by the World Health Organization (WHO). Design flowrate was set at 766,704 m3/day and the parameters such as feed, permeate, concentrate flowrate, number of vessels, number of membrane elements, number of stages, seawater chemical composition, temperature, pressure, and system configuration were considered in this study. Reverse Osmosis System Analysis (ROSA) 2017 software was integrated the design with simulation to further understand how different parameters affect one another in SWRO system. The TDS standard value of 600 ppm in the products were 73.76 ppm and 181.13 ppm after further optimisation. The efficiency of the SWRO system recovery rate was 75.87% and specific energy consumption (SEC) was 6.18 kwh/m3, greater than the previous value of 50% and 9.7 kwh/m3 in terms of recovery percentage and SEC respectively. The findings indicate that a lower amount of feed and energy is needed to achieve the desired production value. Hence, it is also resulting in major savings in terms of operating cost for SWRO system.

Correlations for Concentration Polarization and Pressure Drop in Spacer-Filled RO Membrane Modules Based on CFD Simulations.

Empirical correlations for mass transfer coefficient and friction factor are often used in process models for reverse osmosis (RO) membrane systems. These usually involve four dimensionless groups, namely Reynolds number (Re), Sherwood number (Sh), friction factor (f), and Schmidt number (Sc), with the associated coefficients and exponents being obtained by fitting to experimental data. However, the range of geometric and operating conditions covered by the experiments is often limited. In this study, new dimensionless correlations for concentration polarization (CP) modulus and friction factor are presented, which are obtained by dimensional analysis and using simulation data from computational fluid dynamics (CFD). Two-dimensional CFD simulations are performed on three configurations of spacer-filled channels with 76 combinations of operating and geometric conditions for each configuration, covering a broad range of conditions encountered in RO membrane systems. Results obtained with the new correlations are compared with those from existing correlations in the literature. There is good consistency in the predicted CP with mean discrepancies less than 6%, but larger discrepancies for pressure gradient are found among the various friction factor correlations. Furthermore, the new correlations are implemented in a process model with six spiral wound modules in series and the predicted recovery, pressure drop, and specific energy consumption are compared with a reference case obtained by ROSA (Reverse Osmosis System Analysis, The Dow Chemical Company). Differences in predicted recovery and pressure drop are up to 5% and 83%, respectively, highlighting the need for careful selection of correlations when using predictive models in process design. Compared to existing mass transfer correlations, a distinct advantage of our correlations for CP modulus is that they can be directly used to estimate the impact of permeate flux on CP at a membrane surface without having to resort to the film theory.

Study and Proposal for a Hyperfluorinated Brackish Water Treatment System in the Fatick Region, Case of Diouroup (Senegal)

Groundwater is the main resource for human consumption in many countries, especially in developing countries. This groundwater is often brackish and hyperfluorinated, which leads to diseases such as dental and bone fluorosis, etc. The water from the Diouroup water drainage facilities, like those from many other water drainage facilities in the regions of Fatick, Kaolack, Diourbel and the area of Touba, is facing this problem. To solve these problems, several physicochemical and membrane methods have been implemented. In this work we have briefly outlined some of these methods and we have chosen one of them, low pressure reverse osmosis. In addition, this technique is very simple to operate and maintain. Reverse osmosis provides good quality water in a single step, without the need for additional sterilization or remineralization treatments. We then carried out simulations with the Reverse Osmosis System Analysis (ROSA) software. For reasonable operating parameters, we have noticed a low feed pressure of 11.58 bars, a good average flow of raw water of 27.79 L/m2/h and a recovery rate of the first pass of 75.01%. The results obtained also showed a good quality of the permeate which respects the recommendations of the World Health Organization (WHO) on drinking water. The fluorides of 0.59 mg/L have a recovery rate of 90.8% while the chlorides of 59.09 mg/L have a recovery rate of 92.12% as for the Total Dissolved Solids of 184.90 mg/L for an abatement of 92%. Finally, the low energy consumption of the process makes it possible to consider it in coupling with an electric supply by photovoltaic solar collectors for isolated sites.

Design of reverse osmosis membrane for softening of groundwater at site of agriculture College –University of Tikrit –Iraq by using ROSA-72 software

Abstract This research paper is accomplished for designing reverse osmosis membrane for desalination and softening of groundwater at Tikrit University Site. The raw groundwater has TDS ranged between 1570 and 2910 mg/L, temperature, (23–25)C pH(6.27–8.6), Electrical conductivity (3070–3620) µs/cm, Ca(492–640) mg/L, Mg(41–437) mg/L, Total hardness (1400–3400) mg/L, SO4 (700–1296) mg/L, NO3(18.5–40) mg/L. Dissolved oxygen (1.5–4.5) mg/L and Turbidity (1.3–5)NTU. ROSA72, Reverse Osmosis System Analysis is applied to design the reverse osmosis system for softening the groundwater. The result showed reliable design criteria and high quality water which are feed water 0.3 m3/h, feed press 7.91 bar, concentration flow 0.26 m3/h ,membrane area 2.6 m2 permeate flow 0.05 m3/h. water recovery 15%, permeate TDS 39.41 mg/L. ROSA-72 software can be used efficiently in design of reverse osmosis systems.

Removal of Ca2+, Mg2+, Ba2+ and Sr2+ from shale gas flowback water from the Sichuan Basin in China by chemical softening under the guidance of OLI Stream Analyzer: precipitation behaviors and optimization study

The disposal of flowback water is recognized as a key issue for the sustainable shale gas development and discharge after reasonable treatment is considered as a feasible pathway. One of the challenges during treatment is the severe mineral scaling potential in reverse osmosis desalination, especially with high amounts of Ca2+, Mg2+, Ba2+ and Sr2+ in flowback water. In this study, precipitation behaviors of Ca2+, Mg2+, Ba2+ and Sr2+ during traditional chemical softening was evaluated so as to achieve optimal chemical dosage. Both jar tests and OLI Stream Analyzer simulation revealed that the main precipitates were CaCO3, SrCO3 and BaSO4 during Na2CO3 addition, and Ba2+ could not be removed efficiently by Na2CO3 unless a high dosage was applied since Ba2+ would react after the precipitation of Ca2+ and Sr2+. Reverse Osmosis System Analysis simulation indicated that Ba2+ was a concern because Ba2+ would form tenacious BaSO4 scale on the reverse osmosis membranes. Finally, the Na2SO4-NaOH-Na2CO3 process was proposed for chemical softening as it has a high removal efficiency and low chemical cost. Overall, this study presents an effective chemical softening method and OLI Stream Analyzer could serve as a reliable tool for the calculation, which would finally improve the design and operation of shale gas flowback water treatment.

Energy projection of the seawater battery desalination system using the reverse osmosis system analysis model

Water-stressed countries have been shifting their sources of clean water from inland freshwater to seawater. This led to a comprehensive exploration of seawater desalination processes to address water scarcity; however, membrane processes have expensive operational costs and high energy consumption. In this regard, this study presented a novel energy self-sufficient desalination system design that incorporates rechargeable seawater batteries as an additional energy storage system. Experimental data were projected using the reverse osmosis system analysis model to determine the configuration that achieved the lowest energy consumption and highest charging rate. The results show that the seawater battery achieved a satisfactory desalination performance with >90% and 74%−82% removal of sodium and chloride ions from actual water samples, respectively. Among the configurations, using ultrafiltration as pretreatment and applying 1.8 mA as initial current yielded the lowest energy consumption (1.35 kWh/m3) and the highest energy charging rate (1.01). Compared to the conventional reverse osmosis desalination plants (2.83 kWh/m3), the seawater battery-desalination system has a huge potential in addressing the major disadvantages of current desalination technologies.

Modeling solar desalination with reverse osmosis (RO) powered by concentrating solar power (CSP) plan

This article deals with the desalination of seawater and brackish water, which can deal with the problem of water scarcity that threatens certain countries in the world; it is now possible to meet the demand for drinking water. Currently, among the various desalination processes, the reverse osmosis technique is the most used. Electrical energy consumption is the most attractive factor in the cost of operating seawater by reverse osmosis in desalination plants. Desalination of water by solar energy can be considered as a very important drinking water alternative. For determining the electrical energy consumption of a single reverse osmosis module, we used the System Advisor Model (SAM) to determine the technical characteristics and costs of a parabolic cylindrical installation and Reverse Osmosis System Analysis (ROSA) to obtain the electrical power of a single reverse osmosis module. The electrical power of a single module is 4101 KW; this is consistent with the manufacturer's data that this power must be between 3900 kW and 4300 KW. Thus, the energy consumption of the system is 4.92 KWh/m3.Thermal power produced by the solar cylindro-parabolic field during the month of May has the maximum that is 208MWth, and the minimum value during the month of April, which equals 6 MWth. Electrical power produced by the plant varied between 47MWe, and 23.8MWe. The maximum energy was generated during the month of July (1900 MWh) with the maximum energy stored (118 MWh).

Experimental versus theoretical study of reverse osmosis pilot scaling: The case of Algerian brackish water desalination

Abstract In recent years, the increasing threat to ground water quality due to human activities has become a matter of great concern. The ground water quality problems present today are caused by contamination and by over exploitation or by combination of both. Reverse osmosis (RO) desalination is one of the main technologies for producing fresh water from sea water and brackish ground water. Algeria is one of the countries which suffer from the water shortage since many years, so desalination technology becomes inevitable solution to this matter. In this study, a comparison is provided of results of reverse osmosis desalination for three different qualities of brackish water from the central-east region of Algeria (Bouira and Setif Prefectures), wherein they cannot use it as human drinking or in irrigation systems. The main objective of our study is to establish a comparison of the reverse osmosis membrane TW30-2540 performances in the term of (permeate flow, recovery rate, permeate total dissolved solids – TDS and salts rejection) under different operation pressures (each one takes a time of 720 second for pilot scaling). In order to make an overview comparison between the experimental and the simulated results we used ROSA (Reverse Osmosis System Analysis) software. At the end of this study we noted that, the simulated results are lower than the pilot scaling values and the most removed salts are the sodium chlorides with 99.05% of rejection rate.

Urban wastewater reuse using a coupling between nanofiltration and ozonation: Techno-economic assessment

Combination of nanofiltration and ozonation was investigated for the treatment of urban wastewater. First objective was to demonstrate that nanofiltration can be used instead of reverse osmosis as it enables good rejection rates with reduced cost because of lower operating and maintenance costs. In this way, this paper presents an economic and technical evaluation of the proposed coupling where ozonation is used to treat retentates from nanofiltration. Reverse Osmosis System Analysis (ROSA) software was applied to simulate the filtration design. The effect of membrane choice on specific energy consumption, capital, operation and maintenance costs and scaling potential was investigated. It was demonstrated that using nanofiltration instead of reverse osmosis enable cost saving of 35 k$/year for 125 m3/h. Second objective was to evaluate the impact of the treatment of retentates by ozonation on the global cost. It was highlighted that the coupling would be an acceptable solution from an economic point of view for wastewater reuse. The possible reuse of both permeate and concentrate enable an operating cost saving of 15.4 k$/year for 125 m3/h. An optimum recovery rate of 80% was found for which cost of membrane process is balanced by a decrease in the cost of ozonation.

Demineralization of brackish surface water by reverse osmosis: The first experience in Morocco

Desalination technique is among the focused theme of the Moroccan kingdom’s universities. The implementation of reverse osmosis (RO) technology at the industrial level has proved that this RO technology delivers an affordable production of good water quality and quantity. The conception of mid-size to large RO (FILMTEC™ product) desalination plants are performed by means of reverse osmosis system analysis (ROSA) software. This study shed the light on how realistic the predictions are done by means of ROSA software to the real daily performance of the RO (FILMTEC™XLE440) membranes. The results obtained are then compared against the real industrial data collected from Khenifra desalination plant. This RO plant is designed to produce 36.290 m3/d of drinking water at the horizon of the year 2030. The performances collected are the pressure, temperature, permeate flow and permeate conductivity. The brackish water RO desalination plant has operated successfully and showed a steady behavior from the second half of 2013. The data collected within around 400 days showed that the ROSA modeling prediction matches in a conservative way to the real performance data collected from the plant at about 97%.

Numerical Modeling and Dynamic Analysis of a Wave-Powered Reverse-Osmosis System

A wave energy converter (WEC) system has the potential to convert the wave energy resource directly into the high-pressure flow that is needed by the desalination system to pump saltwater to the reverse-osmosis membrane and provide the required pressure level to generate freshwater. In this study, a wave-to-water numerical model was developed to investigate the potential use of a wave-powered desalination system (WPDS) for water production. The model was developed by coupling a time-domain radiation-and-diffraction method-based numerical tool (WEC-Sim) for predicting the hydrodynamic performance of WECs with a solution-diffusion model that was used to simulate the reverse-osmosis (RO) process. The objective of this research is to evaluate the WPDS dynamics and the overall efficiency of the system. To evaluate the feasibility of the WPDS, the wave-to-water numerical model was applied to simulate a desalination system that used an oscillating surge WEC device to pump seawater through the system. The hydrodynamics WEC-Sim simulation results for the oscillating surge WEC device were validated against existing experimental data. The RO simulation was verified by comparing the results to those from the Dow Chemical Company’s reverse osmosis system analysis (ROSA) model, which has been widely used to design and simulate RO systems. The wave-to-water model was then used to analyze the WPDS under a range of wave conditions and for a two-WECs-coupled RO system to evaluate the influence of pressure and flow rate fluctuation on the WPDS performance. The results show that the instantaneous energy fluctuation from waves has a significant influence on the responding hydraulic pressure and flow rate, as well as the recovery ratio and, ultimately, the water-production quality. Nevertheless, it is possible to reduce the hydraulic fluctuation for different sea states while maintaining a certain level of freshwater production, and a WEC array that produces water can be a viable, near-term solution to the nation’s water supply. A discussion on the dynamic impact of hydraulic fluctuation on the WPDS performance and potential options to reduce the fluctuation and their trade-offs is also presented.

Performance Evaluation of Reverse Osmosis Desalination Pilot Plants using ROSA Simulation Software

Desalination allows the use of non-conventional water sources such as seawater for the production of potable water. The performance of three pilot plants in Mallard Slough, namely RO1, RO2 and NF3 were investigated. Reverse Osmosis System Analysis (ROSA), a simulation software was adopted for verifying the performance of the existing pilot plants in treating seawater. By inserting the specific system configuration and selecting the membrane specification of the pilot plants, ROSA would help to generate the operating parameters such as feed pressure, flux, recovery ratio, permeate quality of the plants. These results were subsequently being used to compare with the experimental data of the pilot plants to determine their absolute deviations. It was found that all ROSA simulated feed pressures for RO1, RO2 and NF3 fell in the range of operational feed pressures of the existing pilot plants. Besides, the deviation of total dissolved solutes removal between the results simulated by the ROSA software and the results obtained from the experiments were noticeably insignificant. In terms of flux and recovery ratio, the simulated results and the experimental data showed a marginal discrepancy with deviations < 2% and < 8% for RO1 and NF3, respectively. In conclusion, the findings of this study confirmed the feasibility of adopting this ROSA software to verify the performance of a pilot plant with all operational parameters being ideally optimized.

Integrated treatment of acid mine drainage using BOF slag, lime/soda ash and reverse osmosis (RO): Implication for the production of drinking water

Acid mine drainage has been an issue of prime concern to international scientific communities. This is due to the magnitude, nature and extent of its environmental impacts. Acid mine drainage (AMD) contains hazardous and toxic chemical species that require removal prior discharging mine water to different environmental compartments. A number of mine water treatment technologies have been developed but they were reported to contain certain benefits and drawbacks. However, there is a need to come-up with environmental friendly and zero-liquid-discharge technologies. The purpose of this novel study was to produce drinking water and recover valuable minerals from acid mine drainage using an integration of Basic Oxygen Furnace (BOF) slag, lime, soda ash and Reverse Osmosis (RO) system. The process can produce very pure water and recover valuable minerals such as hematite, goethite, gypsum, and limestone. Furthermore, brine will be taken to free desalinator for further recovery of salts. To achieve the goals of this study, semi-pilot experiments were done in the laboratory using the aforementioned integrated approach. Interaction of BOF and AMD increased the pH of mine water to ≥8. >99% metals and 75% sulphate were also removal using BOF slag. Residual sulphates and hardness were reduced using lime and soda ash respectively. Gypsum and brucite were recovered as valuable minerals in the lime reactor. Ca as hydrated lime and limestone were recovered in the soda ash reactor. The recovered minerals could be sold as valuable minerals to metallurgical houses and off-set the process/running cost. Reverse Osmosis (RO) was used to further clean the water to meet drinking water quality. A single pass RO system was simulated in Reverse Osmosis System Analysis (ROSA). The produced water meets the requirements of the South African National Standard (SANS) 241 Drinking Water Specifications. As such, it can be concluded that this integrated technology has shown that drinking water and valuable minerals can be recovered from AMD.

An investigation of desalination by nanofiltration, reverse osmosis and integrated (hybrid NF/RO) membranes employed in brackish water treatment

BackgroundAs an appropriate tool, membrane process is used for desalination of brackish water, in the production of drinking water. The present study aims to investigate desalination processes of brackish water of Qom Province in Iran.MethodsThis study was carried out at the central laboratory of Water and Wastewater Company of the studied area. To this aim, membrane processes, including nanofiltration (NF) and reverse osmosis (RO), separately and also their hybrid process were applied. Moreover, water physical and chemical parameters, including salinity, total dissolved solids (TDS), electric conductivity (EC), Na+1 and Cl−1 were also measured. Afterward, the rejection percent of each parameter was investigated and compared using nanofiltration and reverse osmosis separately and also by their hybrid process. The treatment process was performed by Luna domestic desalination device, which its membrane was replaced by two NF90 and TW30 membranes for nanofiltration and reverse osmosis processes, respectively. All collected brackish water samples were fed through membranes NF90-2540, TW30-1821-100(RO) and Hybrid (NF/RO) which were installed on desalination household scale pilot (Luna water 100GPD). Then, to study the effects of pressure on permeable quality of membranes, the simulation software model ROSA was applied.ResultsResults showed that percent of the salinity rejection was recorded as 50.21%; 72.82 and 78.56% in NF, RO and hybrid processes, respectively. During the study, in order to simulate the performance of nanofiltartion, reverse osmosis and hybrid by pressure drive, reverse osmosis system analysis (ROSA) model was applied. The experiments were conducted at performance three methods of desalination to remove physic-chemical parameters as percentage of rejections in the pilot plant are: in the NF system the salinity 50.21, TDS 43.41, EC 43.62, Cl 21.1, Na 36.15, and in the RO membrane the salinity 72.02, TDS 60.26, EC 60.33, Cl 43.08, Na 54.41. Also in case of the rejection in hybrid system of those parameters and ions included salinity 78.65, TDS 76.52, EC 76.42, Cl 63.95, and Na 70.91.ConclusionsComparing rejection percent in three above-mentioned methods, it could be concluded that, in reverse osmosis process, ions and non-ion parameters rejection ability were rather better than nanofiltration process, and also better in hybrid compared to reverse osmosis process.The results reported in this paper indicate that the integration of membrane nanofiltration with reverse osmosis (hybrid NF/RO) can be completed by each other probably to remove salinity, TDS, EC, Cl, and Na.

Integration of hybrid power (wind-photovoltaic-diesel-battery) and seawater reverse osmosis systems for small-scale desalination applications

Desalination is a method used to produce water for human consumption and/or industrial use. Seawater treatment systems powered by renewable sources are regarded as sustainable methods for providing drinking water for coastal zones and islands where there is no electrical grid. This study evaluated the operations of seven different (off-grid) power systems (wind-photovoltaic-diesel-battery) used to satisfy the electrical energy demand of a small-scale reverse osmosis system with a capacity of 1m3/h used on Bozcaada Island, Turkey. The hybrid optimisation model for electric renewable (HOMER) software was selected to perform techno-economic analyses of the systems. On the other hand, the reverse osmosis system analysis model (ROSA) was used to determine the energy requirement of the reverse osmosis system examined in this study. The results of this study showed that the electricity cost was $0.308/kWh for the optimal system consisting of wind turbines with a rated power of 10kW, a 20kW PV panel, and a diesel generator with a rated power of 8.90kW, while the water cost was $2.20/m3. Additionally, the results showed that combining the hybrid power system and reverse osmosis system could be a cost-effective method for remote areas with good wind and solar power potential.

Recovery of drinking water and valuable minerals from acid mine drainage using an integration of magnesite, lime, soda ash, CO2 and reverse osmosis treatment processes

In this study, the possibility of recovering valuable minerals and drinking water from acid mine drainage was explored. Neutralisation of Acid Mine Drainage (AMD) and recovery of metals were done at 60 mins of equilibration. DOW water & Process solutions, Reverse Osmosis System Analysis (ROSA), version 9.1 was used to further purify the resultant water to meet the drinking quality standards as required by the South African National Standard (SANS) report (SANS 241). The obtained results revealed that drinking water, metals, gypsum, hydrated lime/limestone were recovered from the treatment process as valuable resources. This was confirmed by X-ray diffraction (XRD) and X-ray Fluorescence (XRF). Morphological properties of initial and recovered minerals were examined using High Resolution Scanning Electron Microscopy (HR-SEM). Carbon Dioxide (CO2) was bubbled through soda treated water to recover limestone and to stabilise the pH of the product water (pH≈7.5). Post treatment, the resultant water was further purified by simulated Reverse Osmosis (RO) system to produce water that meet the drinking water quality as stipulated by SANS 241 standards. The pH of recovered drinking water was≈6.5. The metals removal efficiency of the RO system was≈100%. In general, this study demonstrated that the integration of magnesite, lime, soda ash, CO2 and reverse osmosis treatment processes can convert environmental pollutants and waste resources into commercially valuable products that have industrial applications.

Reverse osmosis powered by concentrating solar power (CSP): A case study for Trapani, Sicily

The objective of this paper is to analyse the physical performance of two technologies in a water and electricity co-generation scheme: Concentrated Solar Power (CSP) plant coupled to a Reverse Osmosis (RO) unit for a location in the city of Trapani, in southern Italy. The modelled system is compared with the results of another study [2], in which a Multi-Effect Desalination (MED) is powered by a CSP plant for the same location in Italy, using as reference an existing stand-alone gas powered MED plant located at Trapani [3] (which has operated until very recently). The overall aim is to assess and compare these two cogeneration schemes, using as reference the existing MED plant. This work was conducted using as the main simulation tool: the System Advisor Model (SAM) developed by the US National Renewable Energy Laboratory (NREL); a recent upgrade to SAM made available to this work through Laboratorio Nacional de Energia e Geologia I.P. (LNEG); and the Reverse Osmosis System Analysis (ROSA) developed by the Dow Chemical Company. A technical visit to a real commercial RO plant in the south of Portugal (Alvor) was conducted, and the data gathered was used in the validation of the ROSA model. The results for the Trapani case study show that the CSP-RO arrangement has the capability to produce ~50% of the total production of the full scale plant at Trapani, if operated at nominal capacity, year round. Also, the CSP-RO system provides ~20% more electricity and water than the CSP-MED system throughout the studied period of one year. The two co-generation schemes provide promising potential to fight the issues related to fresh water shortages and dependency on fossil fuelled desalination. Thus, they can aid in decreasing the effects associated with CO2 emissions and climate change.

A conceptual NF/RO arrangement design in the pressure vessel for seawater desalination

The main objective of this study is to understand the operation mechanisms of reverse osmosis (RO) membrane and optimization of the operating mechanisms of the RO system in order to reduce the membrane fouling and/or energy requirements. Typically, the high-pressure RO membrane vessel is loaded with membrane elements having the same flux and salt rejection rate. It has been conceived that when different types of RO elements are loaded into the pressure vessel in a special arrangement according to their permeability and salt rejection rate, this arrangement has the potential for reducing the energy consumption of the RO plant. Here, a conceptual design is introduced to describe this new idea. The effects of feed salinity and temperature were investigated in this paper using the reverse osmosis system analysis filmtec membrane design software. A two pass membrane treatment process was designed for desalting seawater at different salinities varied from 35,000 ppm to 43,000 ppm. The results showed a net energy saving from 2.5 to 3% (depends on the feed salinity) could be achieved. The effect of the feed temperature was also investigated, and the new design was found to be more energy efficient. Membrane scaling was also investigated in this study, and it was found that the new membrane arrangement design was less efficient than old design at feed salinity 35,000 ppm and vice versa at feed salinity 45,000 ppm. This was attributed to the use of high membranes permeabilities in the new design.

Exergy analysis of dual-stage nanofiltration seawater desalination

Exergy analysis is a powerful tool for determining the efficiency of processes that influence system performance. Thus, the exergy of dual-stage NF (nanofiltration) seawater desalination was analyzed. Three different processes were simulated by Dow's Reverse Osmosis System Analysis, and the exergies were compared. The results indicated that the main exergy destruction in the conventional process occurred in the membrane and concentration stream valves. To reduce the exergy and energy consumption, concentration blending and an energy recovery device were applied in the improved process, which reduced the specific energy consumption and enhanced the exergetic efficiency and recovery ratio. The calculated specific energy consumption was reduced to 2.09 kWh/m3, and the system recovery ratio was increased to reach 42.78% under the condition specified in this paper. Thus, the development of a novel energy-saving membrane module and an energy recovery device is important in reducing energy consumption in dual-stage NF seawater desalination.