Electrodialysis Desalination Plants Research Articles

Explicit prediction models for brackish water electrodialysis desalination plants: Energy consumption and membrane area

With the demand for desalination systems to mitigate freshwater scarcity worldwide, there is a need for a reliable and straightforward model for the design and evaluation of desalination systems. Two critical metrics for membrane-based desalination systems are specific energy consumption and the required membrane size. The current study presents a strategy to develop simple explicit models for electrodialysis desalination systems. The procedure starts with determining important independent parameters using global sensitivity analysis on a dataset generated using a detailed analytical model of the electrodialysis system. Multi regression models are then developed using the model inputs standardized using their means and standard deviations. The set procedure was applied to an electrodialysis system configuration taken from the literature. After developing regression models for specific energy consumption and the total required membrane area, statistical and residual analyses were carried out to analyze the performance of the developed models. The developed models work for feedwater with salinity ranging from 1000 to 15000 ppm, while the permeate salinity is fixed at 200 ppm. The results showed that the developed regression models predict the specific energy consumption and the required membrane area with mean absolute percentage errors of 2.6% and 3.6%, respectively.

Normalized sensitivity analysis of electrodialysis desalination plants for mitigating hypersalinity

Brackish water desalination can be performed efficiently using electrodialysis (ED). The technology can also be used to mitigate hypersalinity (>50,000 parts per million (ppm)). In this study, a simple and modified lumped ED model combined with cost calculations is used to perform a normalized sensitivity analysis up to 160,000 ppm. The model takes care of the effect of Donnan potential as well as boundary layers (films) and water transport through charged membranes. The analysis reveals that the (linear) velocity and feed concentration are generally the most significant factors affecting ED performance. Considering both control and cost issues, for the specific energy consumption per unit of salt removed, an optimal flow velocity should be chosen. For the rate of salt removal, a combination of lower flow velocity and optimal feed concentration is recommended. In the ED design case, the analysis shows that the feed concentration is generally the most significant factor. Considering both control and cost issues, for the total membrane area and rate of salt removal, a lower feed concentration is recommended irrespective of cost considerations.

The impact of thermodynamic potentials on the design of electrodialysis desalination plants

Electrodialysis desalination (ED) is an efficient method to desalinate brackish water and to mitigate the salinity of high saline resources (>50 parts per thousand (ppt)). Many models were proposed to investigate ED systems; however, these models require detailed simulations. One of the simplest methods is a lumped model, which shows a reasonable and limited accuracy that can only be used for low salinities, i.e., brackish water (<8 ppt). In this paper, an improved lumped model is presented to tackle the salt separation by ED for a wide range of salinities (~200 ppt). Electrochemical equilibrium is implemented in a membrane interface to determine Donnan's potential and concentrations on the membrane surface based on membrane characteristics and bulk solution. The boundary film effect is then calculated based on the pre-calculated concentrations at the membrane and bulk solution. The spacer effect is also included which is important for the separation process in terms of area shading factor and channel porosity more than its contribution in cell pair resistance. Water transport through charged membranes is also considered. The modified model results show a substantial improvement in ED performance values. It could help researchers, engineers, and designers for the design and analysis of desalination plants.

Improvement in design of electrodialysis desalination plants by considering the Donnan potential

Electrodialysis desalination (ED) is an efficient process to desalinate brackish water and to minimize brine salinities to the level of seawater salinity. From the many models reported in the literature, some are simple but have a limited accuracy while others are complicated with a good accuracy. In this context, we explore the improvement of a fundamentally ‘lumped’ model by considering the voltage drop at the interfaces between membranes and solutions (which is the so-called Donnan potential) while conserving the model simplicity. The present model is developed by accounting for an electrical resistance of the Donnan potential in the total cell pair resistance. The results are presented in terms of total membrane area, flow path length, number of stacks and specific energy consumption. The results show that the improvement resulting from involving the Donnan potential was substantial for a high difference between the feed and product salinities as well as for low salinities (<500 ppm) of the product water and low flow velocities (<0.05 m/s). In general, the inclusion of Donnan potential improved the results from 4.4% up to 39.2% based on the studied cases.

Design of electrodialysis desalination plants by considering dimensionless groups and variable equivalent conductivity

Electrodialysis desalination plants, for brackish water, are designed based on different parameters such as feed concentration, current density, and stack construction. Among the various model assumptions, the constancy of the equivalent conductivity of the diluate and concentrate streams is considered a prominent one. In this paper, this assumption is relaxed at different levels and closed-form solutions are obtained to ascertain its effects. It is shown that previously published results can be replicated. Also, a comparison between the lumped and staged model shows that using the inlet flow rate in the lumped model instead of the product flow rate provides more accurate results. Further analysis reveals a non-dimensional number, termed the electrodialytic Biot number, which is the ratio of the total to exit concentration based average cell pair volume resistance. It was found to be physically equivalent to the number of stacks. This provided a clear criterion as to when the lumped model should be used. Specifically, as long as the electrodialytic Biot number is (less than or) equal to 1, the lumped model should be used, otherwise the staged model is a more appropriate choice. It also provides direction for future research. A design chart is also developed to facilitate the calculation procedure.

The development, testing and implementation of electrodialysis desalination plant on ships

The article deals with automatic control at the arc of plasma welding and associated processes and technologies. The article engages mathematical techniques common in the description of automatic control systems. The article presents the results of the analytical study of dynamic processes occurring in the circuit of an electric arc with a capacity. The results of mathematical modeling that allow predicting the instability of the system with an integrated linear or non-linear load are rendered. Accounting for the reference to the object of automatic regulation (arc or plasma), the suggested materials can be of particular interest for a wide range of specialists in the field of welding production, as well as those engaged in the research of automatic control systems in converters.

Electrodialysis desalination designed for off-grid wind energy

An electrodialysis desalination plant has been set up and tested to treat brackish water while driven from an off grid wind energy system. The tests were carried out in the framework of a wider scope project, located on Gran Canaria Island (Spain). The main goal of this project was to test and identify the most suitable desalination systems for connection to the above-mentioned medium-scale off grid wind farm. After having previously analysed the behaviour of the system on-grid, the following stage was to develop an operational envelope for the electrodialysis reversal (EDR) unit while operating off grid, i.e., only coupled to the wind farm. The unit included power converters for the membrane stacks (DC-drivers) and variable frequency drivers (VFD) for the feed pumps. The tests were carried out to establish the power intervals for the EDR unit depending on the product flow rate specified as well as water quality. Product flow rate between 3 and 8.5 m 3/h, power requirements between 4 and 19 kW, while product water conductivity ranged between 200 and 500 μS/cm were recorded. The desalination unit showed good flexibility, adapting smoothly to variations in wind power, even when sudden drops or rises occurred. The control system, slightly modified from a standard design, can cope with such sudden variations. Good agreement between performance predicted with software and the actual operating performance was observed. The presence of harmonics in the electric system due to DC drivers and VFD became harmful for the control and electric system, and care must be taken through appropriate mitigating measures.

Designing of an electrodialysis desalination plant

The design and operation of an electrodialysis desalination process are based on a set of fixed and variable parameters such as stack construction, feed and product concentration, membrane properties, flow velocities, current density, recovery rates, etc. These parameters are interrelated and may be rather different for different applications. For an efficient operation of an electrodialysis desalination plant, the process has to be optimized in terms of overall costs considering component properties and operating parameters. In this study the design and optimization of an electrodialysis plant to be used for brackish water desalination has been treated. The required equations were derived or, as in the case of the limiting current density, were experimentally determined. As an example, an electrodialysis plant with a sheet-flow stack construction and given feed solution composition was designed and optimized in terms of overall costs and the sensitivities of the different parameters are analyzed.

Electrodialysis desalination designed for wind energy (on-grid tests)

An electrodialysis desalination plant has been set up and tested while driven from an off-grid wind-energy system. Prior to analysing the behaviour of the system off-grid, a thorough knowledge of the operational modes and constraints is required. That information is obtained through a number of tests done on-grid. This paper presents some results obtained while operating on-grid in a work carried out within the framework of a wider scope project, located in Gran Canaria Island (Spain). The main goal of this project is to test and identify the most suitable desalination systems for connection to the above-mentioned medium-scale off-grid wind farm. After preliminary modelling using proprietary software, a number of on-grid tests at different flow rates and fixed feed conductivity were carried out. The results include curves for the relationship between voltage applied and product conductivity (between 100 and 280 μS/cm), as well as unit energy consumption (from 1.48 to 2.32 kWh/m 3). The data gathered showed that EDR can easily adapt to a variable power supply such as wind energy, and they were used later in off-grid tests.

Performance of the first sea water electrodialysis desalination plant in India

The problem of potable Water shortage in some of the islands and coastal areas of India has led to consider sea water desalination for potable purposes. One of the membrane processes, namely, the electrodialysis(ED) has been designed and fabricated to meet the demand of a section of the population of Kavaratti island (Lakshad weep, Union Territory). The plant having a capacity of 5.5 m 3/day is based on two stage reduction of salt wherein the first stage reduction upto 85% is achieved by recirculation of sea water. The plant commissioned in February, 1989 is running satisfactorily to its rated capacity. Useful information obtained during the period of first one year is reported here. A novel method of preventing scale formation and other salient features are brought about. An awareness is being created to go in for such plants in near future based on the performance of the above first experimental unit.

Performance analysis of photovoltaic electrodialysis desalination plant at Tanote in Thar desert

The 450 peak watts photovoltaic panel coupled electrodialysis( PV-ED) plant of size 30 × 60 cms with 42 cell pairs operating at about 80 volts gives about 1000 litres per day of product water with salinity less than 1000 ppm from feed water having total dissolved solids(tds) of about 5000 ppm. The flow is fixed at 120 litres per hour for 8 hours operation per day between 8.30 a.m. to 4.30 pm.

Performance analysis of photovoltaic electrodialysis desalination plant at tanote in thar desert

Performance analysis of photovoltaic electrodialysis desalination plant at tanote in thar desert

Performance of an electrodialysis desalination plant in rural area

The provision of potable water in problem villages of Gujarat, Rajasthan, Tamil Nadu and Andhra Pradesh has been given high priority by the Government of India. To meet the demands of these villages having population of about one thousand, desalination by membrane techniques, eloectrodialysis plant of 1.25 m 3/h capacity built and commissioned by the institute in Adalsar village of Gujara tSate to desalt a brackish well water of ⋍ 4000 ppm tds and hardness of ⋍ 1200 ppm CaCO 3 is described. The cost of treatment and economics of desalination in a rural set up are presented

The water problem in egypt

Egypt faces the prospect of rapid growth of populatlon which is a vital problem since agricultural land is not available at the same rate. More land should be reclaimed through development of water resources. The Nile river constitutes an immense water supply but one third of its water is lost through pumping low salinity drainage water to the Mediterranean Sea utilizing costly electric power. Therefore, feasibility studies on recycling this water must be carried out. Along the banks of the Nile, drinking water could be obtained supplied through either small water purification plants or electrodialysis desalination plants, and the economics of the two methods should be compared before deciding on either method. Another source is underground water with a salinity varying between 2000 and 11,000 ppm. For such brackish water, either the electrodialysis or reverse osmosis process can be used. Then there is the Egyptian sea shore which extends over 3000 km. and where the salinity of the sea varies between 33,000 and 45,000 ppm. Here flash distillation processes are suitable. The present paper briefly describes available water resources in Egypt and discusses possible solutions to supplying the fresh water required in different areas. The present investigation concentrates on the feasibility and economics of utilizing the electric supply from the grid at periods other than the peak loads for operating electrodialysis plants. It is estimated that a series of electrodialysis plantsrunning for lOh/day would provide 2.6 million m 3/day at an operating cost of 10¢/m 3 in addition to capital costs.

Determination of transport properties and limiting current densities of ion exchange membrane stacks

For the economy of electrodialysis desalination plants it is important to know the permselectivities and permeabilities of the ion exchange membranes used. In particular, when dealing with high salt contents the permeabilities should be small. The relationship between ion flux density and current density was measured with a membrane stack. The experimental data are reasonably accurate, however only as obtained for a combination of an anion exchange membrane with a cation exchange membrane. The permselectivities are compared with data of the apparent permselectivities as obtained from measurements of the membrane potential. In addition, permeabilities were calculated from data of tracer experiments as well as from electrochemical membrane data. Economic assessments also require a knowledge of the limiting current density of the combination of a cation- and an anion exchange membrane, for at higher current densities there will be a loss of both energy and product water. The limiting current density was determined for various membrane combinations as a function of liquid flow.

Hydraulic principles for the design of electrodialysis desalination plants

The cost of membrane replacement is a considerable part of expenses at brackish water desalination by electrodialysis. That's why to lessen the membrane surface it is desirable to carry out the process of electrodialysis desalination with high current density. But if one uses high current density a danger arises for membrane hard polarization. To prevent the membrane polarization one should increase the velocity of saline water flow in the compartments of electrodialysis unit which require some additional electric energy. To decrease the critical velocity of the polarization the authors studied the hydraulic peculiarities of the water passage through the compartments of the electrodialysis unit. The zig-zag type compartments and the compartments with spacers were studied. Corrugated and perforated PVC sheets, expanded PVC sheets and several types of the nylon network were used as spacer materials. Dependence of hydraulic resistance coefficient of zig-zag type compartments and compartments with various types of turbulising spacer on Reynolds number was established as well as dependence of critical current density on saline water velocity and its salt content. Taking these dependences into account optimal conditions of brackish water desalination in various types of electrodialysis unit construction were found.