1,721,253 research outputs found
Economic Analysis of an Innovative Scheme for the Treatment of Produced Waters
Full text linkDuring the crude oil extraction processes, for each barrel of oil turns out an equivalent of 3 barrels of
wastewaters on average. These wastes are known as Produced Waters (PWs) and their dramatic impact on
the environment has attracted the attention of researchers in order to find an economic and efficient method for
their treatment. Dealing with PWs is not easy: the long exposure with oil increases their hydrocarbon fraction,
while the contact with the underground wells increases their concentration in salts and minerals. The direct
discharge of PWs into the sea is obviously not allowed by law and PWs are usually re-injected into the well.
The present work deals with a novel and innovative treatment chain (including assisted reverse electrodialysis
(ARED) as dilution step) able to reduce both the salinity and organic content of PWs. The innovative scheme
includes an ultrafiltration unit as pre-treatment, upstream an ARED unit for the PW dilution. Once the salinity
level has been reduced down to a value affordable for a bioremediation step, PWs are sent to a bio-reactor,
where the organic compounds are digested. Finally, a reverse osmosis unit is used to recover water from the
treated PWs and to recycle it as diluted stream in the ARED unit. A techno-economic model was purposely
developed in the present work to assess the economic feasibility of the proposed scheme. Preliminary results
suggest that the treatment costs are lower than 5 € m-3
PW and fully competitive with current PWs treatment
technologies
Salinity Reduction of Real Produced Waters via Assisted Reverse Electrodialysis
Full text linkProduced waters (PWs) are waste streams generated during the crude oil extraction processes. The management of these wastewaters is complicated by the large volumes extracted during the oil recovery operations: these depends on the life of the oil-well: typically, 3 barrels of PWs on average are produced for each barrel of oil extracted. After oil separation, PWs are usually re-injected into the well, but this approach is not always possible without a preliminary and suitable treatment. Bioremediation techniques might be a good option, but they fail due to the PWs high salinity, which inhibit bacteria growth and metabolism. Thus, reducing their salinity upstream a bioremediation unit is a matter of crucial importance. To this aim, Assisted Reverse electrodialysis (ARED) along with the use of a dilute stream typically available on site is here proposed as a novel solution. In ARED an additional voltage is applied in the same direction of the salinity gradient through the membranes in order to enhance the passage of ions from the PW to the diluted solution, thus significantly reducing the required membrane area. An experimental campaign was carried out in order to assess the process feasibility. A fixed volume of real PWs was fed to a laboratory scale ARED unit. Each experimental test lasted for three days to reduce the salinity down to about 20 g l-1, a value compatible with the biomass metabolism for a downstream bioremediation step. Two different types of commercial membranes were tested and relevant energy consumptions were calculated. The long-runs performed did not show a significant loss of efficiency due to fouling, thus suggesting that ARED might a suitable technology for a pre-dilution of produced water
A comprehensive multi-scale model for bipolar membrane electrodialysis (BMED)
Full text linkBipolar membrane electrodialysis (BMED) is a technology combining solute and solvent dissociation to produce chemicals. In the recent decades, it has been typically studied for the production of valuable acid and base solutions from salt streams. Although many works have been devoted to the experimental investigation of BMED, only a few efforts have focused on its mathematical modelling. In the present work, a comprehensive process model based on a multi-scale approach with distributed parameters is presented for the first time. Five models related to four different dimensional scales were fully integrated to form a comprehensive tool. The integrated model was developed by using the process simulator gPROMS Model builder and was based on a semi-empirical approach combining high prediction accuracy and low computational demand. Once validated through a wide range of experimental data, the model capability was shown by carrying out a broad sensitivity analysis assessing the performance of the BMED technology for industrial-scale applications. Results showed how the performance of a BMED unit changes with both varying process conditions and the installed membrane area. Particularly, the non-ideal phenomena that reduce the produced NaOH concentration and increase the energy consumption were thoroughly investigated. Finally, this study demonstrated that a Levelized Cost Of Caustic Soda of about 280 € ton-1NaOH can be obtained, thus making this technology a possible candidate for the industrial production of caustic soda from brines in the future
Producing Hydrogen and Fresh Water from Brackish Water Desalination via Electrodialysis
Full text linkNowadays scientists and communities are particularly worried about climate change and the transition towards renewable energies is a matter of crucial importance. In this context, European Community is strongly promoting the production of green hydrogen, i.e. the electrolysis of water coupled with renewable electrical sources. In addition to the energy issue, United Nations have identified the lack of water as another big issue for modern society. Electrodialysis (ED) is an electro-membrane process able to desalinate a salty feed by the application of an external power supply. It takes advantage of the use of ionic exchange membranes which allow a controlled separation of ions from the salty feed to obtain freshwater and brine as outputs.
The present work tries to address the above issues by proposing the simultaneous production of fresh water and hydrogen with an integrated hydrogen-electrodialysis (HED) unit. The aim of the present work is that of assessing the economic feasibility of the process. To this purpose, a techno-economic model has been developed to predict the behaviour of the HED unit. The model is able to predict experimental data and should be regarded as a simple yet reliable tool to assess the process economic feasibility. Preliminary analyses suggest that the simultaneous production of hydrogen and fresh water may be profitable
Dynamic Simulations of the Electrodialysis Process as Energy Buffer for Polygeneration Systems
No full textElectro-membrane Processes for the Green Hydrogen Production
Full text linkSince the last century, humanity has been facing challenging scenarios, like global warming, environmental
pollution and the dramatic increase in energy demand. In this framework, green hydrogen has been identified
as the most promising energy vector to achieve carbon neutrality. With this respect, the idea of the present work
is to combine the Reverse Electrodialysis (RED) membrane process with hydrogen production. Experimental
RED tests were carried out by feeding the unit with different concentrated solutions to study the process
performance. Collected results suggest that this approach is a viable way to produce hydrogen with high faradic
efficiencies, up to a maximum of 99 %, highlighting also the technology advantage of producing hydrogen by
exploiting the salinity gradient energy, thus leading to a production with Specific Energy Consumption close to
zero
A comprehensive multi-scale process model of bipolar membrane electrodialysis (BMED) systems
Full text linkBipolar membrane electrodialysis (BMED) uses electrical energy to produce acidic and alkaline solutions by water dissociation. Its great versatility has increasingly gained the interest in chemical/biochemical industry and in environmental protection. Co-ion leakages through the membranes and shunt currents pose major issues leading to significant drops in current efficiency.
This work focuses on the development of a novel model based on a multi-scale approach. Four different dimensional scales were fully integrated within a comprehensive simulating tool with distributed parameters. The lowest scale, which is represented by the channel, includes two sub-models. The CFD simulations sub-level estimates polarization phenomena and pressure losses, while the other sub-level calculates the physical properties of the solutions. The middle-low level simulates the triplet, i.e. the repetitive unit of the stack, by computing mass balances, membrane fluxes, electrical resistance and electromotive force. The middle-high scale, represented by the stack model, is made up of two sub-levels: one is intended to compute the shunt currents through the manifolds, the other one aims at calculating pressure losses in the whole stack. Finally, the highest level simulates the external hydraulic circuit accounting for external pressure losses and dynamic mass balances in the tanks.
The model was experimentally validated with both an original campaign and literature data, showing a good agreement. A sensitivity analysis was performed in order to assess the behavior of BMED systems. The process performance was evaluated by comparing current efficiency and power consumption in different scenarios. The outcome of the analysis illustrates the influence of operating variables (e.g. current density and mean flow velocity) and of the system geometry. Results highlight the key role of the manifolds features on the process efficiency
Desalination of oilfield produced waters via reverse electrodialysis: A techno-economical assessment
Full text linkProduced waters (PWs) are oilfield waste streams rich in minerals and hydrocarbons whose production rate is largely increased in last decades following the corresponding increase of energy demand. The high salinity level of PWs inhibits the adoption of cheap biological treatments. Also, desalination techniques based on osmotic membranes would require severe pre-treatments. As an alternative, Reverse ElectroDialysis (RED) and Assisted Reverse ElectroDialysis (ARED) are here proposed for the first time to reduce the salinity level of PWs. RED may also guarantee an operation cost reduction thanks to its energy generation. An ad-hoc model for RED and ARED is here developed in order to deal suitably with PWs. This is done by a calibration and validation with experimental data purposely collected via RED and ARED units fed by real PWs. The model is integrated with economical equations and a techno-economic analysis is carried out in order to identify the best configuration for the desalination purposes. Results suggest that ARED operation mode is the best option guaranteeing a minimum in the controlled dilution cost corresponding to a 1.32 € per m3 of PWs treated, thus leaving room for an affordable future implementation of more sophisticated treatment chains based on bioremediation
Mathematical modelling of hollow-fiber haemodialysis modules
Full text linkThis chapter provides an overview of the principles and modelling of membrane-based modules for haemodialysis, the most common renal replacement therapy. Following an introduction on the structure, function and diseases of the kidney, the technological evolution of membranes for blood purification is outlined and the main transport mechanisms involved are described, making a distinction between pure
haemodialysis, haemodiafiltration and haemofiltration. The main performance figures of a hollow-fiber module are introduced and their dependence on the parameters that characterize the device is illustrated. A multi-scale modelling approach is then presented, in which preliminary single-fiber CFD simulations are used to derive the hydraulic permeability of a fiber bundle and the relevant mass transfer coefficients as functions of the local velocities. The predicted correlations are then fed to a module-scale model, in which blood and dialysate compartments are simulated as interpenetrated porous media while appropriate source terms account for the exchange of solutes andwater between the two fluids. The model predictions are three-dimensional flow and concentration distributions, from which, in particular, performance figures such as clearance and ultrafiltration flow rate can be extracted as functions of the module geometrical and physical characteristics. Validation tests are also presented and the results of a parametrical sensitivity assessment are discussed
Electrodialysis with bipolar membranes for the sustainable production of chemicals from seawater brines at pilot plant scale
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