Design, simulation and economic analysis of a stand-alone reverse osmosis desalination unit powered by wind turbines and photovoltaics

The fresh water shortage is a significant problem in many areas of the world such as deserts, rural areas, Mediterranean countries and islands. However, renewable energy potential in these areas is usually high using solar and wind energy. A desalination unit powered by renewable energy sources is a promising solution for this problem. This paper presents the design of a stand-alone hybrid wind-PV system to power a seawater reverse osmosis desalination unit, with energy recovery using a simplified spreadsheet model. A daily and monthly simulation and economic analysis were also performed. The calculated fresh water production cost was 5.2 ?/m³, and the realized energy saving was up to 48% when a pressure-exchanger-type energy recovery unit is considered.     

Assessment of institutional and policy conditions in Turkey: implications for the implementation of autonomous desalination systems

This paper provides an overview of the existing situation in Turkey and studies how this could become more attractive for the implementation of autonomous desalination systems (ADS). The analysis covers relevant policy and programmes, legislation and administrative procedures, water prices and subsidies, institutional framework of the water sector, capacity building and general awareness. In general, the framework conditions in Turkey are relatively good. The policy direction towards decentralisation will favour ADS. Many programmes offer support for water supply and renewable energy and there are simplified administrative procedures. On the other hand, water policy favours traditionally centralised conventional solutions. The awareness about ADS is very low and the research in the field still restricted. In this paper, concrete recommendations have been developed that suggest simple steps for the establishment of ADS in Turkey.     

Optimization of RO desalination systems powered by renewable energies. Part I: Wind energy

Operation of an experimental RO plant connected directly to a wind system without energy storage was studied. The data obtained confirm the wide spectrum of operation of the plant with respect to the power available and the operation of the system.     

Design and optimization of seawater reverse osmosis desalination plants using special simulation software

This paper introduces the Integrated process simulation environment (IPSEpro™) software, and its application to reverse osmosis desalination.The paper introduces the reader to the basic modeling concepts, and how individual process units can be simply simulated with a graphical, flowsheet style interface.The paper then goes on to describe an example simulation for off design of an integrated pump, membrane rack and isobaric energy recovery device, investigating the effects of changing water quality, membrane condition and also, the influence of isobaric energy recovery device overflush.     

Experimental studies on dynamic process of energy recovery device for RO desalination plants

A two-chamber hydraulic energy recovery unit with a programmable controller and a data acquisition system was set up. Tap water was used as the working fluid instead of the actual seawater and concentrate in SWRO desalination plants. Experimental results were obtained on the fluctuations of the pressure and flow rate to and from the energy recovery unit. Characteristics of the pressure at the chamber ends were discussed at the conditions of the chambers set horizontally or vertically, with and without pistons.     

Experiments of a prototype wind-driven reverse osmosis desalination system with feedback control

A prototype wind-powered reverse osmosis desalination system was constructed and tested on Coconut Island off the northern coast of Oahu, Hawaii, for brackish water desalination. The system has four major subsystems: a multi-vaned windmill/pump, a flow/pressure stabilizer, a reverse osmosis module, and a control mechanism. The feedback control mechanism, developed by this study, allowed this prototype system to be operated satisfactorily under mild ambient wind of 5 m/s or less. No auxiliary power source was needed. The system operational data showed that at an average wind speed of 5 m/s, brackish feedwater at a total dissolved solids concentration of 3000 mg/1 and at a flow rate of 13 1/min could be processed by this system. The average rejection rate of this prototype system was 97% and the average recovery ratio was 20%. The energy efficiency of the system was measured at 3 5%, which is comparable to the typical energy efficiency of well-operated multi-vaned windmills. Generally, the system's energy efficiency decreases as wind speed increases.     

Preliminary experimental study of a small reverse osmosiswind-powered desalination plant

The paper describes the work carried out in the development of a small wind-powered desalination plant. Analternative control system was studied to serve as a direct interphase between a reverse osmosis desalination plant and a small wind energy conversion system. The main purpose was to reduce or eliminate the need for an energy storage system (usually, a battery bank). In order to achieve this objective, an experimental prototype of a desalination plant and a wind generator simulator were developed. The systems were evaluated under laboratory-controlled conditions and subjected to field trials. The experimental plant desalinates highly saline seawater (35,000 mg/L) at a rate of approximately 0.4 m³/d. This amount of potable water is sufficient to supply the basic water demands in a small community in an isolated location. The paper also describes the identification of technical problems associated with operating a desalination plant with an intermittent source of energy (wind).     

Influence of temperature and permeate recovery on energy consumption of a reverse osmosis system

A model permits analysis of the influence of temperature on permeate recovery and energy consumption. The proposed model is based on the following assumptions: (1) membrane morphology is temperature-independent; (2) membrane rejection and other transport characteristics of membranes are position-independent; (3) specific water permeability of membranes was based on exponential dependence of viscosity vs. temperature; (4) temperature-dependence depembrane rejection is assumed to be linear. This allows for analyzing the influence of channel geometry, feed concentration, flow rate and temperature on permeate recovery and energy consumption. Calculated data are included. The solutionpresented can be segmented andbuilt into systems for comprehensive techno-economic evaluation of the RO-based process where temperature-dependence of process characteristics has to be considered.     

Humidification-dehumidification desalination system driven by geothermal energy

The work presented in this paper focuses on desalinating sea water system using a humidification-dehumidification process as it is supplied with water heated by geothermal energy as clean and renewable natural resources of energy. Computer simulation of the behavior under various working conditions of the desalination system was carried out to predict the variations of key output. Such variables include the ratio of sea water mass flow rate related to air mass flow rate, cooling water temperature difference across the condenser, geothermal source inlet temperatures to the heat exchanger and the amount of produced distilled water. To validate the computer program, a comparison between the experimental and theoretical results was conducted, and a good agreement had been obtained. The result showed that, the optimum value of the ratio between sea water mass flow rate to air mass flow rate was found to be in the range of 1.5 to 2.5. Improvement in the fresh water productivity at the optimum ratio of sea water mass flow rate to the air flow rate was observed by increasing both the geothermal source inlet temperature and the cooling water temperature difference across the condenser.     

Optimization of solar-powered reverse osmosis desalination pilot plant using response surface methodology

A solar thermal and photovoltaic-powered reverse osmosis (RO) desalination plant has been constructed and optimized for brackish water desalination. The central composite experimental design of orthogonal type and response surface methodology (RSM) have been used to develop predictive models for simulation and optimization of different responses such as the salt rejection coefficient, the specific permeate flux and the RO specific performance index that takes into consideration the salt rejection coefficient, the permeate flux, the energy consumption and the conversion factor. The considered input variables were the feed temperature, the feed flow-rate and the feed pressure. Analysis of variance (ANOVA) has been employed to test the significance of the RSM polynomial models. The optimum operating conditions have been determined using the step adjusting gradient method. An optimum RO specific performance index has been achieved experimentally under the obtained optimal conditions. The RO optimized plant guarantees a potable water production of 0.2 m³/day with energy consumption lower than 1.3 kWh/m³.     

Hybrid Reverse Osmosis‐Capacitive Deionization versus Two‐Stage Reverse Osmosis: A Comparative Analysis

Reverse osmosis (RO) is a high‐pressure single‐phase desalination process used to obtain freshwater from seawater/brackish water. The RO system shows high energy consumption for a given unit volume of pure water produced. The reported hybrid system of RO and capacitive deionization (CDI) aims at improving the RO water recovery and minimizing energy consumption. The RO‐CDI system is simulated and compared with two‐stage RO, to determine the effectiveness of the new hybrid system. The energy recovery from RO brine was also studied. The specific energy consumption by two‐stage RO for two different arrangements of the energy recovery device is higher than for RO‐CDI. The hybrid RO‐CDI system is energy efficient for the production of freshwater from brackish water.     

Marine reverse osmosis desalination plant — a case study

In the present work, one type of reverse osmosis desalination plant with 2.5 t/d product was introduced. An experimental study was carried out, the result of experiment was analyzed. The calculation data using ROSA software developed by Dow Chemical company was given. By regression analysis of the experimental data, the model correlations were given. The conclusion is that with the increment of operation pressure, the power consumption increased linearly, the flow rate of product and percent recovery increased accordingly, the concentration of product decreased reversibly.     

Exergy analysis of a reverse osmosis desalination plant in California

The exergy analysis of a 7250 m³/d reverse osmosis (RO) desalination plant in California was conducted by using actual plant operation data, and an alternative design was investigated to improve its performance. The RO plant is described in detail, and the exergies across the major components of the plant are calculated and illustrated using exergy flow diagrams in an attempt to assess the exergy destruction distribution. The primary locations of exergy destruction were the membrane modules in which the saline water is separated into the brine and the permeate, and the throttling valves where the pressure of liquid is reduced, pressure drops through various process components, and the mixing chamber where the permeate and blend are mixed. The largest exergy destruction occurred in the membrane modules, and this amounted to 74.07% of the total exergy input. The smallest exergy destruction occurred in the mixing chamber. The mixing accounted for 0.67% of the total exergy input and presents a relatively small fraction. The second law of efficiency of the plant was calculated to be 4.3%, which seems to be low. The analysis of the alternative design was based on the exergy analysis. It is shown that the second law of efficiency can be increased to 4.9% by introducing a pressure exchanger with two throttling valves on the brine stream, and this saved 19.8 kW electricity by reducing the pumping power of the incoming saline water.     

Fresh water by reverse osmosis based desalination: simulation and optimisation

The reverse osmosis (RO) desalination process to make fresh water from seawater has been studied here. First, a model for the process is developed. Sensitivity of different operating parameters (feed flow rate, feed pressure) and design parameters (internal diameter, total number of tubes) on the recovery ratio are studied via repetitive simulation. Finally, an optimisation framework for the process is developed so as to maximize the recovery ratio or a profit function using different energy recovery devices, subjectto general constraints. The optimal operating parameters (feed flow rate, feed pressure) and design parameters (internal diameter, total number of tubes) are determined by solving the optimisation problem using an efficient successive quadratic programming (SQP) based method. The optimal values for the decision variables depend on the constraints introduced, and are also sensitive to variations in water and energy prices, as well as feed concentration. The use ofthe emerging energy recovery devices is widely justified, reporting much higher reductions in operating costs than the traditional technology used for this purpose. Using a pressure exchanger device, it is possible to reduce energy consumption by up to 50%.     

Bench-scale evaluation of seawater desalination by reverse osmosis

In bench-scale tests of seawater reverse osmosis desalination it is important to carefully consider osmotic pressure effects and determine the extent of concentration polarization so that sources of flux variation—whether from fouling, compaction, or osmotic pressure changes—can be properly assessed. Rigorous modeling of concentration polarization is difficult because of the complex geometries and flow regimes in RO modules; typically, concentration polarization must be measured. However, concentration polarization measurement usually requires knowledge of membrane permeability, which can vary from coupon to coupon. In this study a method is presented to determine both the membrane permeability and the concentration polarization regime in a single test. The key to the test is to allow the salt concentration to vary over time in a predictable way and extract parameters from a model fitted to the flux data. The usefulness of this technique is highlighted by evaluating results from several seawater experiments. It was found that specific flux decline in the experiments was caused by changes in osmotic pressure and membrane compaction. RO fouling by seawater organic-matter was not significant for the several seawater samples tested.     

Renewable energy powered desalination in Baja California Sur, Mexico

Baja California Sur (BCS) is an arid sparsely populated coastal state in northwest Mexico. Population growth, agriculture and booming tourism have lead to severe overexploitation of underground aquifers and saline intrusion. This paper reviews the current water and energy situation in BCS. The state enjoys very high levels of solar radiation, typically above 5 kWh/m²/day, and the suitability of renewable energy powered desalination for BCS is discussed, including past efforts in BCS and present challenges for this technology.     

Cost analysis of seawater desalination with reverse osmosis in Turkey

Economically usable water resources per capita are decreasing due to excessive population increase each year in Turkey. For this reason, new water resources should be found in the near future. The potential water resources are seawater or well water both of which need removal of salinity. The most promising treatment method for salinity is reverse osmosis. While reverse osmosis becomes widespread, the cost of the process will decrease. There is no detailed information about cost of seawater desalination in Turkey. In this study, a cost analysis of seawater desalination in Turkey was performed for reverse osmosis systems. The basic parameters of cost analysis such as capacity, recovery, membrane life, energy, chemical costs and flux were evaluated based on the effects on capital, operating and total production costs.     

The SDAWES project: an ambitious R&D prototype for wind-powered desalination

This paper describes the design and operational strategies of an ambitious prototype for a desalination system powered exclusively by wind energy. The system, installed on the island of Gran Canaria, was designed with several objectives in mind: (a) to determine experimentally the feasibility of the stand-alone operation of wind farms isolated from the conventional power grids and supplying energy for a number of desalination techniques (reverse osmosis, electrodialysis reversal and vacuum vaporcompression; (b) to verify the operational feasibility of the various desalination techniques when the energy source driving the system is an intermittent one; and (c) to analyze the influence that a variety of operational strategies have on the volume and quality of the desalinated water produced and on the useful working life of the main components of the desalination plants. The first of these three questions has been resolved with the feasibility of such stand-alone systems now clearly demonstrated. As for the second question, initial tests would seem so far to indicate that the reverse osmosis technique is the most suitable for use in stand-alone wind-powered desalination systems. The results that are still to come from the remaining studies will be of vital importance for regions like the Canary Islands, which suffer from a scarcity of potable water, lack conventional energy sources, but do have at their disposal wind energy resources.     

Investigation of different operational strategies for the variable operation of a simple reverse osmosis unit

Recent studies and projects showed that a combination of a reverse osmosis desalination plant with a wind power supply is technologically feasible if the reverse osmosis plant is operated with fluctuating and intermittent loads and thus follow the energy supply characteristic of the wind turbine. On this background the goal of this paper is to simulate the system behaviour of a simple reverse osmosis plant under changing process parameters (e.g. feed pressure, recovery or feed flow). These variations are systematized within so-called operational strategies. Therefore, four different operational strategies are analysed in detail with regard to given restrictions e.g. by the membrane system. For each of these strategies the specific energy consumption over the total usable load range is computed with the simulated hydraulic characteristics of each operational strategy. The analysis of the gathered data shows that a membrane system should be operated with constant permeate recovery under fluctuating wind power. This operational strategy provides low specific energy consumption over a broad load range.     

A computer simulation of batch ion exchange membrane electrodialysis for desalination of saline water

A computer simulation program is developed for predicting desalinating performance of a batch electrodialysis process. The program includes the principle of ① mass transport, ② current density distribution, ③ cell voltage, ④ mass balance/energy consumption and ⑤ limiting current density. In this simulation the following parameters are inputted; ① membrane characteristics such as overall transport number, overall solute permeability, overall electro-osmotic permeability, overall hydraulic permeability, direct current electric resistance etc., ② electrodialyzer specifications such as flow-pass thickness, flow-pass width and flow-pass length in a desalting cell etc. and ③ electrodialytic conditions such as voltage, electrolyte concentration in a feeding solution, linear velocity in desalting cells, standard deviation of normal distribution of solution velocity ratio etc.The following phenomena were computed and discussed; ① Changes of electrolyte concentration and current density with operation time. ② Influence of cell voltage on operation time (batch duration), water recovery and energy consumption. ③ Influence of volume of an electrolyte solution prepared at first on operation time. ④ Influence of cell voltage, electrolyte concentration and standard deviation of solution velocity ratio in desalting cells on limiting current density. ⑤ Energy consumption in a reverse osmosis process. ⑥ Excepting limiting current density, the performance of an electrodialyzer is never influenced by the standard deviation of normal distribution of solution velocity ratio in desalting cells. ⑦ Energy consumption in electrodialysis is less than that in reverse osmosis at feeding saline water concentration less than about 2000 mg/l.