Reverse Osmosis Desalination System Research Articles

Novel design and modeling of a photovoltaic hydro electromagnetic reverse osmosis (PV-HEMRO) desalination system

Novel design and modeling of a photovoltaic hydro electromagnetic reverse osmosis (PV-HEMRO) desalination system

Saving energy with an optimized two-stage reverse osmosis system

We optimize the design and operation of two-stage reverse osmosis desalination systems and identify the operating conditions that will maximize energy savings.

Thermoeconomic analysis and optimization of a reverse osmosis desalination system driven by ocean thermal energy and solar energy

Thermoeconomic analysis and optimization of a reverse osmosis desalination system driven by ocean thermal energy and solar energy

Optimization of Seawater Reverse Osmosis Desalination Networks with Permeate Split Design Considering Boron Removal

Increasingly strict constraints on the boron concentration for safe drinking and irrigation water present a tremendous challenge for the design of seawater reverse osmosis (RO) desalination systems. This work presents an optimization study of a seawater reverse osmosis RO network with permeate split (PS) design under boron concentration restrictions. Front part permeates with better quality and higher flux are sent directly to the product, and back part permeates are reprocessed in pass 2 with high pH value. The irreversible thermodynamic model is employed to describe the membrane transport behavior of boron. Constraints for the system flow and operation conditions are added to guarantee safe operating of the RO system. Both single-product and two-product RO systems are optimized for different types of feed seawater. Results show that the PS design is mainly dominated by the boron constraints, while the system recovery is mainly controlled by the feed salt concentration. Due to the upper bound of pH for p...

Design of a cost-effective wind/photovoltaic/hydrogen energy system for supplying a desalination unit by a heuristic approach

The techno-economic assessment, optimization, and sizing of grid independent renewable energy systems affects not only the likelihood of deployment but also their reliability to supply potable water and electricity where needed. Despite many investigations on hybrid renewable energy systems (photovoltaic/wind), the reverse-osmosis desalination unit powered by solar and wind electricity production systems with hydrogen energy storage, and effects of integrating water desalination alongside meeting load demand, is rarely found. In this paper, a hybrid photovoltaic/wind/hydrogen/reverse osmosis desalination system is modeled and designed for increasing the fresh water availability and to meet the load demand to a stand-alone region in Iran. The configuration of the proposed hybrid system is optimally determined with respect to two optimization criteria, the life cycle cost of the economic evaluation and the loss of power supply probability concept for the reliability. For this aim, an efficient metaheuristic technique based on artificial bee swarm optimization is used. From the results it is seen that at a maximum loss of power supply probability set to 0–10% the photovoltaic/hydrogen/reverse osmosis desalination is the most cost-effective energy system and photovoltaic/wind/hydrogen/reverse osmosis desalination and wind/hydrogen/reverse osmosis desalination systems are in the other ranks.

Energy and exergy analysis of solar PV powered reverse osmosis desalination

In the current paper presented short review of the state of the art of solar powered reverse osmosis (RO) desalination systems, basic parameters, energy demand of RO process and also exergy analysis. In order to identify the main energy losses in desalination processes, to improve their performances from a thermodynamic point of view, there is a need for exergy analysis. The exergy analysis or second law analysis involves a comparison of exergy input and exergy destruction along various desalination processes. Using the exergy analysis methodology, presented in the current paper, the specific exergy and exergy flow rates at various points of a RO system can be evaluated. Once exergy flow rates are available, exergy destroyed within any component can be determined from exergy balance.

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.

An operational and economic study of a reverse osmosis desalination system for potable water and land irrigation

Desalination is a method for producing water for human consumption, irrigation or industrial utilisation. In this study, a reverse osmosis (RO) system for brackish water desalination was theoretically investigated to produce both potable drinking and agricultural water with a lower overall and specific energy consumption. As a case study, the Main Outfall Drain in Iraq is used as the brackish water source. A numerical model based on solution-diffusion theory was developed in Matlab Simulink and used to analyse the design and performance of an RO system. The effect of feed water temperature, pressure, salinity and recovery ratio on the efficiency of the whole RO system was investigated for a wide range of design considerations. The design of an RO system for this application was optimised and economic assessment carried out. Results show that with boosting recovery ratio from 30% to 60%, the specific energy of desalinated water production below 400ppm was reduced from 2.8kWh/m3 to a more economically favourable value of 0.8kWh/m3, when utilizing a pressure exchanger as a recovery device. Salt rejection was reduced from 97% to 88% to obtain large quantities of water for irrigation with an acceptable salinity (<1600ppm), for agricultural use. The reduction in salt rejection is influenced by the feed water temperature and pressure; also the average pore diameter of the RO membrane and in turn determines the reduction in system energy consumption. It was found that the total cost to produce 24,000m3/d of water from a feed salinity of 15,000ppm and a water quality of <400ppm would be 0.11£/m3 with a corresponding investment cost of £14.4million for the drinking water, and for irrigation) obtained product <1600ppm) are £0.9/m3 and £11.3million.

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.

Effect of Membrane Module and Feed Flow Configuration on Performance in Pressure Retarded Osmosis

Recently, reverse osmosis (RO) is the most common process for seawater desalination. A common problem in both RO and thermal processes is the high energy requirements for seawater desalination. The one energy saving method when utilizing the osmotic power is utilizing pressure retarded osmosis (PRO) process. The PRO process can be used to operate hydro turbines for electrical power production or can be used directly to supplement the energy required for RO desalination system. This study was carried out to evaluate the performance of both single-stage PRO process and two-stage PRO process using RO concentrate for a draw solution and RO permeate for a feed solution. The major results, were found that increase of the draw and feed solution flowrate lead to increase of the production of power density and water permeate. Also, comparison between CDCF and CDDF configuration showed that the CDDF was better than CDCF for stable operation of PRO process. In addition, power density of two-stage PRO was lower than the one of single-stage. However, net power of two-stage PRO was higher than the one of single-stage PRO.

Control performance evaluation of reverse osmosis desalination system based on model predictive control and PID controllers

AbstractIn this study, to design an efficient control system for a Reverse osmosis (RO) desalination plant, a model predictive control (MPC) was established and compared to the obtained control system based on proportional–integral–derivative (PID) controllers. In order to control two controlled variables, namely permeate flow rate and conductivity, two PID controllers’ parameters were tuned based on the internal model control (IMC) rule and an MPC controller was established using the dynamic matrix control algorithm. The control performance assessment of both PID and MPC controllers were carried out using prediction error approach and their control performances were compared to that of the PID controllers which tuned by Ziegler–Nichols rule from the literature. The results showed that among the designed controllers, the PID controllers tuned by IMC method are more capable than other controllers to control the considered RO desalination plant.

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%.

An optimization algorithm-based pinch analysis and GA for an off-grid batteryless photovoltaic-powered reverse osmosis desalination system

Freshwater pinch analysis (FWaPA) as an extended pinch analysis technique has been proposed for retrofitting the off-grid batteryless photovoltaic-powered reverse osmosis system (PVS-RO) with a water storage tank to minimize the required outsourced freshwater. The freshwater composite curve (FWaCC) as the graphical tool, and freshwater storage cascade table (FWaSCT) as the numerical tool of the FWaPA are introduced to determine the optimal delivered electricity to the RO system, water storage tank capacity, and wasted electricity in each time-interval with minimized outsourced freshwater. A multi-objective optimization algorithm by combining FWaPA numerical tool and genetic algorithm (FWaPA-GA) minimizes three objective functions including required outsourced freshwater during first operation year, outsourced freshwater during normal operation year, and total annual cost of the system to obtain the optimal number of PV panels, membranes, and capacity of water storage tank. The FWaPA-GA was implemented to find optimal design of an off-grid PVS-RO-WT system for a case study in Kish island, Iran. The results clearly represented that the FWaPA-GA can be used to grassroots design of the desalination systems with renewable energy sources, where the designed PVS-RO-WT system for the case study needs 178.5 m3 freshwater to provide 10 m3/d freshwater-on-demand with the total annual cost of 13,652 $/year.

Novel design and operational control of integrated ultrafiltration — Reverse osmosis system with RO concentrate backwash

A novel design for a reverse osmosis (RO) desalination system directly integrated with an ultrafiltration (UF) pre-treatment unit was developed. The integration involves direct RO feed from the UF filtrate and UF backwash using the RO concentrate. This alignment reduces overall plant footprint, while the use of RO concentrate for UF backwash allows 100% UF recovery and implementation of flexible backwash strategies. The present system design utilizes a control scheme, whereby RO productivity can be prescribed independently of the UF system which self-adjusts to provide the RO system with its required feed flow rate at the specified RO pump inlet pressure. UF backwash, achieved via direct RO concentrate flow from the RO system provided a continuous flow for sequential UF backwash which was additionally integrated with pulse backwash using a hydraulic accumulator. Seawater desalination field studies with a UF–RO pilot system of 12,000gal/day permeate production capacity successfully demonstrated the advantage of RO concentrate UF backwash that was triggered based on a membrane resistance threshold. The above self-adaptive UF backwash strategy significantly extended the projected UF operation period (by a factor of nine) to the threshold of required chemical cleaning.

Exergy analysis of two-pass reverse osmosis (RO) desalination with and without energy recovery turbine (ERT)

The paper presents the exergy analysis of an actual two-pass RO desalination system considering the seawater solution as a real mixture and not an ideal mixture. The actual 127 ton/h two-pass RO desalination was modelled using IPSEpro software and validated against operating data. The results showed that using the energy recovery turbine (ERT) reduced the seawater RO (SWRO) desalination total power consumption by 30% and specific power consumption for SWRO per m³ water from 7.2 kW/m³ to 5.0 kW/m³. In addition, the exergy efficiency of the RO desalination improved by 49% and exergy destruction was reduced by 40%. The results also showed that the rejected seawater, when the ERT was not in use, accounted for 42% of the total exergy destruction.

Improvement of PV/T Based Reverse Osmosis Desalination Plant Performances Using Fuzzy Logic Controller

Photovoltaic based reverse osmosis desalination systems (PV/RO) present an effective method of water desalination especially in remote areas. The increase of the feed water temperature leads to an amelioration of the plant performances. Photovoltaic Thermal Collector (PV/T) represents an ideal power source as it provides both electric and thermal energies for the reverse osmosis process. Nevertheless, PV/T based RO plants should be controlled in order to solve operation problems related to electrical efficiency, reverse osmosis membrane, produced water and the rejected salts. This paper suggests a fuzzy logic controller for the flow rate of the circulating fluid into the PV/T collectors so as to ameliorate the system performances. The designed controller has improved the PV/T field electrical efficiency and preserved the reverse osmosis membrane which upgrades the system productivity. LABVIEW software is used to simulate the controlled system and validate the effectiveness of the controller.

Performance analysis of an organic Rankine cycle for a reverse osmosis desalination system using zeotropic mixtures

The use of low-grade thermal energy to power desalination processes by coupling an organic Rankine cycle (ORC) with seawater reverse osmosis (RO) is a promising technology to reduce the cost and environmental impact associated with the use of fossil fuel sources. A low-enthalpy geothermal ORC for a RO desalination system with zeotropic mixtures is proposed. Zeotropic mixtures can improve the thermodynamic performance of ORC systems owing to their excellent temperature glide characteristics during evaporation and condensing processes. A case study with butane/pentane (R600/R601) and butane/isopentane (R600/R601a) is investigated, aiming to analyze the effect of seawater temperature increase on the cycle performance. In the temperature range investigated, the power profit first increases rapidly then decreases. For the mixture R600/R601 at a mole fraction of 0.9/0.1, the maximum power profit value of 29.3kW occurred with the temperature rise of 26K, and for the mixture R600/R601a at a mole fraction of 0.9/0.1, the maximum power profit value of 30.9kW occurred with the temperature rise of 27K. The results show that, it is necessary to consider the effects of seawater temperature increase in both the ORC and RO simultaneously to design the ORC-RO system.

Effects of nearshore evaporation rates on the design of seabed gallery intake systems for SWRO facilities located along the Red Sea shoreline of Saudi Arabia

Feed water to seawater reverse osmosis desalination systems should have a constant salinity with minimal variation. Intake systems that extract water from shallow nearshore areas in arid regions can exhibit significant fluctuations in salinity caused by high rates of evaporation and lack of circulation. Such fluctuations in salinity could inhibit the design, construction, and operation of seabed gallery intake systems located in shallow nearshore areas, such as the Red Sea inner shelf. Water depths range from 0 to 2 m between the beach and the edge of the fringing reef in the optimal locations for the development of seabed gallery intakes along the coast of the Red Sea of Saudi Arabia. The evaporation rate in this area is between 2 and 3 m per year. The bottom consists of mostly a marine hardground containing a thin veneer of unlithified sediment and no significant cover of corals or seagrass. The rather barren nature of the bottom suggests that periodic hypersalinity may contribute to the formation of hardgrounds on the bottom by causing supersaturation of the seawater with calcium carbonate and may limit the growth of corals and grasses. To assess the changes in salinity, a conceptual model was developed which assumes that a shallow circulation cell develops between the shoreline and deeper water offshore. Lower salinity seawater should migrate landward to replace water loss caused by evaporation with seaward moving of high-salinity water occurring along the bottom to balance the flow with ultimate mixing before the reef tract. To test this circulation pattern, a series of sensors were deployed to continuously monitor the water temperature, conductivity, and salinity at the surface and at the bottom during several periods of high air temperature. Surprisingly, the results show very little variation in salinity, despite the very high evaporation loss. The water salinity ranged between 39,000 and 40,000 mg/L with no diurnal variations of significance. Based on the monitoring and weather station data collected nearby, it appears that the predominant strong onshore wind, particularly during the afternoon and early evening, causes near-continuous mixing of the water between the reef tract and the shoreline. Therefore, the development of seabed gallery intake systems within the shallow water between 1 and 2 m of depth is feasible based on the measured salinity which is similar to that occurring further offshore in water depths between 2 and 20 m.

Robust water quality controller for a reverse osmosis desalination system

This paper presents two-degree-of-freedom (2-DOF) robust loop-shaping control methodology to stabilize a reverse osmosis (RO) desalination system operating under significant uncertainties, external disturbances and measurement noises, and to reduce product water cost. This method has the advantages that no information about the plant uncertainty is required and it can deal with external disturbance and noise simultaneously. The controlled RO plant is a multi-input multi-output (MIMO) system. The two controlled variables are product water flow and product water salinity, which are fundamental in water desalination. The result shows that the achieved controller has very good performance which can deal with up to 52% uncertainty, and eliminate 60% of disturbance and 70% of noise, while common existing controllers in RO desalination can't cover the uncertainty and disturbance or can only deal with small values of these factors. Now that the software and hardware in the RO plant are sufficiently robust, it is possible to use this powerful method for better water quality control of RO systems.

Employing groove-textured surface to improve operational performance of rotary energy recovery device in membrane desalination system

A rotary energy recovery device (RERD) is widely used in a reverse osmosis desalination system. In order to maintain the device running in an available torque and obtaining a long service life, a portion of high pressure seawater is usually sacrificed to work as lubrication to reduce the friction torque of the device. However, when using such method, a certain amount of energy recovery efficiency will be lost due to the lubrication or leakage. This paper focuses on improving operating performance of a rotary energy recovery device by making textured grooves on the surfaces of two end covers of the RERD. The experimental results show that compared to the un-textured RERD, the textured RERD reduces the device's torque by half, and successfully improved the efficiency by 40% under the mating clearance of 0.035mm, operating pressure of 6.0MPa and rotary speed of 500rpm. In addition, thanks to the groove textured surface which dramatically reduces the RERD's torque and permits the mating clearance to be minimized. Under the small clearance of 0.025mm, the energy recovery efficiency of the textured RERD can be increased up to 96.3% at an operating pressure of 6.0MPa which can well satisfy the requirement of the industry application.