Search

Reverse electrodialysis in nanochannels has become an innovative method to obtain clean energy. To enhance the power generation efficacy of the nanochannel, the finite element method was employed to model the impact of the temperature gradient on the power generation efficiency of the conical channel. The investigation primarily focused on the nanochannel structure, as well as the direction and magnitude of the solution temperature gradient. The results show that the overall power generation performance is superior for ions diffusing from the large pore end to the small pore end in the presence of a negatively charged wall surface. The nanochannel system with a negative temperature gradient shows better power generation performance than that with a positive temperature gradient under the same nanochannel parameters and solution conditions. [ABSTRACT FROM AUTHOR]

The removal of phenol from simulated wastewater by a reverse electrodialysis reactor (REDR) wastewater treatment system is experimentally investigated in independent or synergetic degradation circulation mode under specific conditions. Results demonstrated that the total degradation efficiencies (ηde,tot) and the total chemical oxygen demand (COD) removal efficiencies (ηCOD,tot) in an independent degradative circulation mode were better than those in a synergetic degradative circulation mode. After 2 h of treatment, the ηde,tot of phenol reached 100% and 99.7%, and ηCOD,- tot reached 59.6% and 51.3%, under two circulation modes, respectively. However, the synergistic degradation cycle mode achieved a balance between hydrogen ion production and consumption during the wastewater treatment process. When the synergetic circulation mode was applied, the pH of the wastewater was always maintained at around 3 without the addition of acid, which reduced the wastewater treatment costs. Moreover, the general current efficiency and the energy consumption of REDR in the synergetic degradative circulation mode were 51.1% and 168.8 kWh/kgCOD, respectively, after 2 h. Therefore, the implementation of REDR with a suitable circulation mode and operating conditions offered a viable alternative to achieve a win-win situation for both energy and the environment. [ABSTRACT FROM AUTHOR]

In this study, the possibility of preparing fresh water through environmental friendly process of hybrid electrodialysis (ED)-reverse electrodialysis (RED) has been investigated. Therefore, the process performance has been evaluated with regard to both desalination and energy generation. Besides, the process has been modeled with real and synthetic concentrated brine with high salinity of up to 200,000 ppm from Persian Gulf seawater and synthetic and real brackish water with the salinity of up to 7,240 ppm from rivers in Bushehr province, Iran. Results demonstrated that the RED system was capable of generating the energy needed to desalinate brackish water with the salinity of less than 1,000 ppm, while for higher salinities, an extra amount of electrical energy is required. It was also revealed that the best desalination performance (salt removal percentage) for brackish water with initial concentration of 1,000; 2,000 and 4,000 ppm was 42%, 53% and 52%, respectively. Moreover, due to high level of salinity along with the presence of a variety of minerals in river waters, the rate of electricity production and desalination was less than that of the synthetic water samples on a pilot scale; for example, for the Mond River with an initial salinity of 2,690 ppm, the salinity reduction was around 27.17%. [ABSTRACT FROM AUTHOR]

Perchlorate (ClO4) is a toxic anion that inhibits iodine uptake by the thyroid gland and subsequently disrupts thyroid hormone production. In this study, the feasibility of using reverse electrodialysis (RED) was examined for the treatment of perchlorate in salt (5% NaCl; w/v) water. RED uses direct electricity, produced by salinity gradients in a membrane stack, to drive the electrochemical treatment of wastewater. Operational conditions such as salinity gradient (S.G.), number of membrane pairs, and stack solution flowrates were varied and their effects on electricity generation and perchlorate reduction were investigated. Experimental batch results showed that a higher number of membrane pairs and salinity gradient gave higher values of power density, which also resulted in higher abatement of perchlorate. In contrast, the reduction of perchlorate was lowered upon increasing the stack solution flowrate. The maximum abatement of perchlorate (38.76%) was achieved using 15 pairs of cation and anion exchange membranes and 5 M/0.005 M salinity ratio (S.G. 1,000) of high and low concentrated NaCl solutions at 1.5 mL/min stack solution flowrate. This study successfully demonstrated that RED can be a sustainable alternative method for the abatement of perchlorate in salt waters. [ABSTRACT FROM AUTHOR]–) is a toxic anion that inhibits iodine uptake by the thyroid gland and subsequently disrupts thyroid hormone production. In this study, the feasibility of using reverse electrodialysis (RED) was examined for the treatment of perchlorate in salt (5% NaCl; w/v) water. RED uses direct electricity, produced by salinity gradients in a membrane stack, to drive the electrochemical treatment of wastewater. Operational conditions such as salinity gradient (S.G.), number of membrane pairs, and stack solution flowrates were varied and their effects on electricity generation and perchlorate reduction were investigated. Experimental batch results showed that a higher number of membrane pairs and salinity gradient gave higher values of power density, which also resulted in higher abatement of perchlorate. In contrast, the reduction of perchlorate was lowered upon increasing the stack solution flowrate. The maximum abatement of perchlorate (38.76%) was achieved using 15 pairs of cation and anion exchange membranes and 5 M/0.005 M salinity ratio (S.G. 1,000) of high and low concentrated NaCl solutions at 1.5 mL/min stack solution flowrate. This study successfully demonstrated that RED can be a sustainable alternative method for the abatement of perchlorate in salt waters. [ABSTRACT FROM AUTHOR]

The energy consumption due to pumping power is a crucial issue in membrane processes. Spacers provide mechanical stability and promote mixing, yet increasing pressure drop. Woven spacers and their behaviour at low Reynolds numbers are less studied in the literature. Nevertheless, they are typical of some membrane technologies, as reverse electrodialysis (RED). RED is a promising technology for electric power generation by the chemical potential difference of two salt solutions within a stack equipped by selective ion-exchange membranes. The mechanical energy required for pumping the feed solutions, can dramatically reduce the net power output. In this work computational fluid dynamics (CFD) simulations of spacer-filled channels at low Reynolds numbers were carried out in parallel with an experimental campaign focused on the collection of data for model validation. Woven spacers 280–480 μm thick were investigated at the flow rates typical of RED channels. The construction of the computational domain was based on measurements made by optical microscopy and micrometer. Fully developed flow conditions were assumed, thus, periodic boundary conditions were adopted (unit cell approach). The experiments were carried out in a flow cell with one channel. Pressure drops were measured with and without the spacer, in order to quantify the effect of inlet–outlet channel and identify the distributed pressure drops due to the woven nets. Experimental results showed that the distributed pressure drop along the spacer-filled channel for the cases investigated is around 40% of the overall pressure loss. The significant contribution of the manifolds is due to the relatively high velocity of the fluid entering and leaving the channel in radial direction in the inlet and outlet holes, as in the RED stacks commonly used. However, an improved geometry of the distribution and collection system can easily result in a significant reduction of hydraulic loss in this part of the stack. Therefore, the optimization of the spacer geometry is crucial. In this regard, a good agreement between CFD results and experimental data on hydraulic loss along the channel was found, thus confirming that a simple CFD model (as the one presented in this work) can be a powerful and cheap tool, able to efficiently evaluate the pressure drops within spacer-filled channels of any customised geometry. [ABSTRACT FROM AUTHOR]

Reverse electrodialysis (RED) is a technology to obtain energy from mixing waters with different salinity. Small intermembrane distances and high flow velocities are preferred to obtain high power generating capacity accompanying high power consumption, however. To increase power generation without redundant power consumption, we designed a new water feeding pattern system. The new water feeding pattern was designed to configure additional water inlet and outlet, instead of single inlet and outlet. The experimental results showed that the new design was beneficial to promote the flow distribution, thus reduced the solution resistance compared to the traditional water feeding pattern system. The net power density in the new water feeding pattern system increased by 36.4% than that in the previous system. Results of fouling-resistant experiments also demonstrated that the RED stack with the new water feeding pattern showed significantly less sensitivity to fouling under natural conditions and a 20-d operation than the traditional one. These results suggest that the new spacer design is very effective to obtain higher power density and simultaneously reduce the membrane fouling tendency. [ABSTRACT FROM PUBLISHER]

The use of closed-loop salinity gradient power (SGP) technologies has been recently presented as a viable option to generate power using low-grade heat, by coupling a SGP unit with a thermally-driven regeneration process in a closed loop where artificial solutions can be adopted for the conversion of heat into power. Among these, the closed-loop reverse electrodialysis (RED) process presents a number of advantages such as the direct production of electricity, the extreme flexibility in operating conditions and the recently demonstrated large potentials for industrial scale-up. Ammonium hydrogen carbonate (NH4HCO3) is a salt suitable for such closed-loop RED process thanks to its particular properties. At temperatures above 40–45°C, it decomposes into a gaseous phase containing NH3, CO2and water. Thus, the use of NH4HCO3solutions for feeding a RED unit would allow their easy regeneration (after the power generation step) just using low-temperature waste heat in a purposely designed regeneration unit. This work aims at presenting an experimental investigation performed on a RED system fed with NH4HCO3solutions. Laboratory tests were carried out to find the best conditions for maximizing the power density and process performances of a RED unit by investigating a number of operating parameters such as fluid velocity and feed solutions concentration. [ABSTRACT FROM PUBLISHER]

Reverse electrodialysis (RED) is a very promising technology allowing the electrochemical potential difference of a salinity gradient to be directly converted into electric energy. The fluid dynamics optimization of the thin channels used in RED is still an open problem. The present preliminary work focuses on the computational fluid dynamics simulation of the flow and concentration fields in these channels. In particular, three different configurations were investigated: a channel unprovided with a spacer (empty channel) and two channels filled with spacers, one made of overlapped filaments and the other of woven filaments. The transport of two passive scalars, representative of the ions present in the solution, was simulated in order to evaluate concentration polarization phenomena. Computational domain effects were also addressed. Results show that: (i) the adoption of a computational domain limited to a single unit cell along with periodic boundary conditions provides results very close to those obtained in a larger domain; (ii) the woven spacer-filled channel is the best compromise between pressure drop and concentration polarization. Future work will address the inclusion of electrical effects along with the migrative transport of the ions in the channel. [ABSTRACT FROM PUBLISHER]

Reverse electrodialysis (RE) is a promising technology for electric power generation from controlled mixing of two differently concentrated salt solutions, where ion-exchange membranes are adopted for the generation of ionic currents within the system. Channel geometry strongly influences fluid flow and thus crucial phenomena such as pressure drop and concentration polarization. Profiled membranes are an alternative to the more commonly adopted net spacers and offer a number of advantages: avoiding the use of non-conductive and relatively expensive materials, reducing hydraulic losses and increasing the active membrane area. In this work, Computational Fluid Dynamic simulations were performed to predict the fluid flow and mass transfer behaviour in channels with profiled membranes for RE applications. In particular, channels equipped with pillars were simulated. The influence of channel geometry on fluid flow and concentration polarization was assessed by means of a parametric analysis for different profile geometries. The unit cell approach along with periodic boundary conditions was adopted to simulate fully developed boundary conditions. Transport equations, valid also for concentrated solutions, were obtained from the rigorous Stefan–Maxwell equation along with the assumptions of binary electrolyte and local electroneutrality. Simulation results show that, in the geometries investigated here, the pumping power consumption is much lower than in a conventional net spacer and very close to that of the empty channel, while calm zones are generated by the profiles, which may accentuate polarization phenomena. [ABSTRACT FROM PUBLISHER]

Reverse electrodialysis (RED) is a very promising technology allowing the electrochemical potential difference of a salinity gradient to be directly converted into electric energy. The fluid dynamics optimization of the thin channels used in RED is still an open problem. The present preliminary work focuses on the computational fluid dynamics simulation of the flow and concentration fields in these channels. In particular, three different configurations were investigated: a channel unprovided with a spacer (empty channel) and two channels filled with spacers, one made of overlapped filaments and the other of woven filaments. The transport of two passive scalars, representative of the ions present in the solution, was simulated in order to evaluate concentration polarization phenomena. Computational domain effects were also addressed. Results show that: (i) the adoption of a computational domain limited to a single unit cell along with periodic boundary conditions provides results very close to those obtained in a larger domain; (ii) the woven spacer-filled channel is the best compromise between pressure drop and concentration polarization. Future work will address the inclusion of electrical effects along with the migrative transport of the ions in the channel. [ABSTRACT FROM AUTHOR]

Reverse electrodialysis (RE) is a promising technology for electric power generation from controlled mixing of two differently concentrated salt solutions, where ion-exchange membranes are adopted for the generation of ionic currents within the system. Channel geometry strongly influences fluid flow and thus crucial phenomena such as pressure drop and concentration polarization. Profiled membranes are an alternative to the more commonly adopted net spacers and offer a number of advantages: avoiding the use of non-conductive and relatively expensive materials, reducing hydraulic losses and increasing the active membrane area. In this work, Computational Fluid Dynamic simulations were performed to predict the fluid flow and mass transfer behaviour in channels with profiled membranes for RE applications. In particular, channels equipped with pillars were simulated. The influence of channel geometry on fluid flow and concentration polarization was assessed by means of a parametric analysis for different profile geometries. The unit cell approach along with periodic boundary conditions was adopted to simulate fully developed boundary conditions. Transport equations, valid also for concentrated solutions, were obtained from the rigorous Stefan–Maxwell equation along with the assumptions of binary electrolyte and local electroneutrality. Simulation results show that, in the geometries investigated here, the pumping power consumption is much lower than in a conventional net spacer and very close to that of the empty channel, while calm zones are generated by the profiles, which may accentuate polarization phenomena. [ABSTRACT FROM AUTHOR]

Technologies for the exploitation of renewable energies have been dramatically increasing in number, complexity and type of source adopted. Among the others, the use of saline gradient power is one of the latest emerging possibilities, related to the use of the osmotic/chemical potential energy of concentrated saline solutions. Nowadays, the fate of this renewable energy source is intrinsically linked to the development of the pressure retarded osmosis and reverse electrodialysis technologies. In the latter, the different concentrations of two saline solutions is used as a driving force for the direct production of electricity within a stack very similar to the conventional electrodialysis ones. In the present work, carried out in the EU-FP7 funded REAPower project, a multi-scale mathematical model for the Salinity Gradient Power Reverse Electrodialysis (SGP-RE) process with seawater and concentrated brines has been developed. The model is based on mass balance and constitutive equations collected from relevant scientific literature for the simulation of the process under extreme conditions of solutions concentration. A multi-scale structure allows the simulation of the single cell pair and the entire SGP-RE stack. The first can be seen as the elementary repeating unit constituted by cationic and anionic membrane and the relevant two channels where dilute and concentrate streams flow. The reverse electro-dialysis stack is constituted by a number of cell pairs, the electrode compartments and the feed streams distribution system. The model has been implemented using gPROMS®, a powerful dynamic modelling process simulator. Experimental information, collected from the FUJIFILM laboratories in Tilburg (the Netherlands), has been used to perform the tuning of model formulation and eventually to validate model predictions under different operating conditions. Finally, the model has been used to simulate different possible scenarios and perform a preliminary analysis of the influence of some process operating conditions on the final stack performance. [ABSTRACT FROM AUTHOR]

Flows within very thin channels, typically filled with spacers, can be often encountered in many processes such as electrodialysis (ED) and reverse electrodialysis (RED). Although the ED and the RED processes have been studied for a long time, the optimization of the fluid dynamics within the channels is still an open problem. In the present work, realized within the EU-FP7 funded REAPower project, computational fluid dynamics simulations were carried out in order to predict the fluid flow field inside a single ED/RED channel. Some different configurations were tested which includes: an empty channel, a channel provided with a spacer, and a channel filled with a purposely manufactured fiber porous medium. Two types of spacers were investigated: (1) a commercial type made of woven perpendicular filaments and (2) an overlapped perpendicular filament spacer. A sensitivity analysis concerning computational grid size and topology was performed. For the cases investigated, adopting the hybrid grids mainly composed of hexahedral volumes was found to be more reliable and less computational demanding than tetrahedral grids. As concerns the dependence of the pressure drops on the flow rate, the empty channel was found to guarantee the lowest pressure drops at a given fluid flow rate, as expected. Conversely, the woven spacer filled channel was found to provide larger pumping costs. The pressure drops along the channel filled with a porous medium even at low flow rate were very high thus suggesting that this specific configuration may be unsuitable and that further investigations should be devoted to this topic. [ABSTRACT FROM AUTHOR]

Reverse electrodialysis is a conversion technique to obtain electricity from salinity gradients. Over the past few years, the performance of reverse electrodialysis on laboratory scale has improved considerably. In this paper, we discuss the challenges we are still facing concerning the economic and technological feasibility and the developing path of reverse electrodialysis. We focus on the following issues: (i) the development of low-cost membranes, (ii) pre-treatment in relation to stack design and operation, and (iii) the economics of reverse electrodialysis. For membranes, the challenge is to increase availability (>km²/year) at reduced cost (<2 €/m²). The membranes should be manufactured at high speed to meet this challenge. For pre-treatment, a capital-extensive micro-screen filter with 50 µm pores was selected and tested. Such a straightforward pre-treatment is only sufficient given the fact that the reverse electrodialysis stack was redesigned towards a more robust spacer-free system. For the economic feasibility, a 200 kW repetitive unit was designed. The cost price is estimated to be less than 0.08 €/kWh (excluding any subsidy or compensation), comparable with that of wind energy. The feasibility of the technology should be proved with a scaled-up system under practical conditions. The intended pilot facility at the Afsluitdijk (The Netherlands) will be an essential step towards implementation of reverse electrodialysis for power generation. [ABSTRACT FROM AUTHOR]

Fresh water and oil/gas based energy will become scarce since their actual (increase in) consumption rate is definitely unsustainable, when considering their restricted world reserves. Moreover, the large scale burning of such fuels for the production of electrical energy or in industry/transport results in a significant rising of the carbon dioxide concentration in the atmosphere and therefore a rising of global temperatures. Research and development regarding alternative energy sources such as e.g. nuclear fusion is proceeding but mankind also becomes more aware of the sun as being a giant fusion reactor, already at their free disposition and able to act as a lasting and sustainable energy source. The sun in fact delivers continuously about 89,000 TW of usable insolation (photons) power to our planet while the actual global power consumption is about 15 TW. From this point of view, the sun is thus able to provide about 6000 times the world's energy demand, thus highlighting the enormous potential of solar energy from such numbers in a very obvious way. A major disadvantage of insolation energy of course is its discontinuous and fluctuating availability during daytime. To circumvent such, a solution could eventually be found in the storage of solar power as osmotic energy in highly concentrated salt solutions. The development of salinity gradient power (SGP) based on reverse electrodialysis (SGP-RED) could therefore possibly become an important alternative approach. When combined with classic or solar power based seawater desalination technologies, the resulting hybrid system could well be a candidate for the simultaneous production of potable water and electrical energy. The concentration of the brine from the seawater desalination unit (SWDU) could be substantially increased by using solar energy while also producing additional sweet water (condensate). Electricity could then be produced from the mixing energy of the highly concentrated brine and seawater, by using the principle of reverse electrodialysis (RED). In this way the disadvantageous brine waste situation in seawater desalination could eventually be converted into an opportunity regarding the production of a large amount of additional fresh water, a significant amount of electrical energy and an answer to the brine disposal environmental problem. The theoretical simulation results from SGP-RED stack modeling using highly concentrated brine and seawater (brackish water) point to the absolute need of the development of a battery oriented SGP-RED stack configuration, requiring thin ion conductive membranes and thin spacers as to minimize the internal battery resistance and maximize the electrical power output. [ABSTRACT FROM AUTHOR]

Reverse electrodialysis electrical power generation is based on the transport of salt ions through ion conductive membranes. The ion flux, equivalent to an electric current, results from a salinity gradient, induced by two salt solutions at significantly different concentrations. Such equivalent electric current in combination with the corresponding electrochemical potential difference across the membrane, equivalent to an electric potential, results in a battery equivalency. While having a co-current fluid flow of both solutions in the reverse electrodialysis cell pair compartments, a mathematical model needs to be based on both diffusion and convective mass transport equations in the compartments and on the, electromigration-based, ion transport through the membranes. The steady state salt ion flux through the membranes and the corresponding ion concentration distribution within the salt solution compartments of a reverse electrodialysis cell pair (in the absence of electrodes) was theoretically analysed by using two-dimensional finite element (FEM) modelling. Fundamental information on the effect of membrane thickness and fluid flow velocity was obtained. FEM simulations support the theoretical insight into reverse electrodialysis phenomena and thus assist in the planning/design of experimental work. The FEM approximation is superior with respect to a modelling of the combined effect of all complex and simultaneous ion transport mechanisms in the reverse electrodialysis cell pair compartments and ion conductive membranes. In fact, this first time reporting of a FEM modelling of a half cell pair obviously also includes the complex and dynamic drop in salinity gradient, between influent side and effluent side, over the height of the half cell pair compartments. [ABSTRACT FROM AUTHOR]