Browsing by Subject "Desalination"

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Bioinspired membrane design, synthesis, and characterization to control microstructure and enable efficient molecular separations
(2021-05) Song, Woochul; Freeman, B. D. (Benny D.); Kumar, Manish, Ph. D.; Lynd, Nathaniel; Hwang, Gyeong S
Natural resources are limited, and the failure to capture, store, and re-supply such resources can cause global economic, political, and humanitarian crises such as water scarcity. To mitigate these global risks, membrane separations have been an attractive technology due to their energy efficient and environment-friendly nature compared to other separation technologies such as distillation or chromatography. However, the development of new membranes with good separation properties and processability have been an ongoing challenge. One example is biomimetic membranes. Due to the unexpectedly fast transport and selective separation performances observed in nature, biological membrane components have been attempted for integration into scalable membranes. But maintaining the coherence of their nanoscale transport property at practice-relevant scales have been critically challenging. Bioinspired synthetic membranes have emerged as a good alternative to help resolve these roadblocks faced by biomimetic membranes. Molecular designs of synthetic membranes components enable precise control of microstructures and improve the nanoscale homogeneity of the membranes, both of which are critical for improving membrane separation properties, while increasing reproducibility, cost-efficiency, and processability of the membranes. This dissertation research aims to provide scientific details needed for the developments of bioinspired membranes, spanning the broad considerations from nano- to macroscopic perspectives. First, a new type of artificial water channels (AWCs) is presented as a transport element of bioinspired membranes. A new water permeation mechanism, water-wire networks formed by these AWCs, was shown to achieve fast and selective water transport that exceeds current polymer membranes’ permeability-selectivity limit. Next, a strategy of integrating such bioinspired membrane components, AWCs and amphiphilic block copolymers as transport and barrier elements respectively, into scalable membranes are studied. A series of analyses on transport experiments and computer simulations indicated a strong coherence between nanoscale and membrane scale transport properties, demonstrating successful channel integration for molecular separations. Lastly, further insights on transforming the AWC structures to viable membranes for large-scale applications are presented, specifically targeting gas separations. Leveraging these studies, this dissertation intends to provide guidance to researchers on development of new bioinspired membranes.
Bipolar electrochemistry for enrichment, separations, and membraneless electrochemically mediated desalination
(2015-08) Knust, Kyle Nicholas; Crooks, Richard M. (Richard McConnell); Shear, Jason B; Mullins, Charles B; Webb, Lauren J; Stevenson, Keith J
Developments in bipolar electrochemistry for the simultaneous separation and enrichment of charged species and membraneless electrochemically mediated desalination (EMD) are presented. Each of these techniques requires an electrochemically generated local electric field within a microchannel and control over bulk fluid flow. In addition to bipolar electrochemical studies, investigations of ion depletion zone formation and EMD in a two-electrode microelectrochemical cell are presented. The dual-channel bipolar electrode (BPE) configuration is employed for the simultaneous enrichment and separation of anions and cations within a single microchannel at an ion depletion zone generated by buffer neutralization. Moreover, this experimental design is also used to generate an ion depletion zone and associated electric field gradient by Cl⁻ oxidation, where we demonstrate partial seawater desalination without the need for a physical membrane. Expanding upon the fundamentals of BPE focusing, we demonstrate proof-of-concept biomolecule separation and enrichment. Moreover, without the need for a direct external electrical connection, one hundred BPEs are operated simultaneously in parallel to enrich multiple analyte bands. Metal deposition at a BPE is used to mediate BPE focusing. Ion depletion zones arising from Cl⁻ oxidation are investigated by making axial electric field measurements while varying key experimental parameters affecting ion depletion zone formation, location, and strength. We investigate the capabilities of EMD by modifying the electrode design to increase the local electric field strength in an effort to increase the percentage of salt rejection. We also examine the possibility to lower, or even eliminate the electrical energy requirements of EMD by driving Cl⁻ oxidation photoelectrochemically. Lastly, on-line capacitively coupled contactless conductivity measurements are presented to rapidly and reliably quantify ion separation for EMD.
Electrode separation effects in capacitive deionization desalination systems
(2012-08) Pierce, Kena Marie; Crawford, Richard H.; Hidrovo, Carlos
A more energy efficient and sustainable method of desalinating water is needed due to increasing water shortages and contamination of current freshwater sources. Capacitive deionization (CDI), a new emerging technology, is a type of electric desalination that uses an applied voltage to pull the salt ions out of the salty solution and store the ions in porous carbon electrodes. CDI uses less applied energy than more commonly used methods of desalination like reverse osmosis and multi-flash distillation and has the added advantage of energy recovery. This report details experiments conducted to analyze the effect of different separation distances between the electrodes on salt ion adsorption for a high concentration solution under various flow rates and a 1 V voltage potential difference. The testing was performed in the Multiscale Thermal-Fluids Laboratory at The University of Texas at Austin using a uniquely fabricated CDI cell. Voltage, elapsed time, and electrical conductivity measurements were taken during the testing. Electrical conductivity was used to signify salinity of the solution. Two different separation distances were created by placing either one 2mm mesh between the electrodes or by using two 2 mm meshes between the electrodes. The results did not agree with the expectation that the one-mesh tests would adsorb twice the amount of salt ions as the two-mesh tests because of the differences in the electric field between the two types of tests. This is believed to be due to the high concentration tested. Future testing should include repeating these tests to verify the results and performing the tests for lower concentrations to see if they followed the expectation.
The energy water nexus : increasing water supply by desalination integrated with renewable power and reducing water demand by corporate water footprinting
(2013-08) Clayton, Mary Elizabeth; Webber, Michael E., 1971-
Growing populations and periodic drought conditions have exacerbated water stress in many areas worldwide. Consequently, it would be valuable to manage both supply and demand of water to fully address water sustainability. Additionally, the inextricable link of water and energy -- energy is required to pump, treat, and distribute water and water is often used in the production of energy -- creates the need to study the use of these resources together. In response to water stress, some municipalities have considered desalination of saline water as a freshwater supply. Unfortunately, desalination requires a sizeable energy investment and causes significant carbon emissions with conventional approaches. However, renewable energy technologies can be paired with desalination to mitigate concern over the environmental impacts of increased energy use. At the same time, desalination can be operated in an intermittent way to match the variable availability of renewable resources. Both wind and brackish groundwater resources are plentiful in the Panhandle region of West Texas, making an integrated wind-powered desalination facility an option for meeting increasing water demands. Integrating wind power and brackish groundwater desalination generates a high-value product (drinking water) from two low-value resources (saline water and wind power without storage). This thesis presents a thermoeconomic, geographic, and operational analysis of an integrated wind-powered reverse osmosis facility treating brackish groundwater in West Texas. The results demonstrate the favorability of the integrated facility under certain economic, geographic, and operating conditions. Also in response to water stress, corporations are becoming increasingly interested in identifying water vulnerabilities in their operational portfolios to minimize physical, reputational, regulatory, and financial risks associated with potential water shortages. The water footprint is one tool available to assess water use, identify vulnerabilities, and guide mitigation strategies. This thesis provides an accounting methodology for water reporting that includes direct water uses and indirect (embedded in energy, services, and products) water uses in the operations. Further, a case study is considered to illustrate the methodology by assessing the water impact of a mixed-use facility in Palo Alto, California. The results demonstrate the importance of considering the indirect water uses, which requires a more exhaustive analysis.
The energy-water nexus : an analysis and comparison of various configurations integrating desalination with renewable power
(2015-05) Gold, Gary M.; Webber, Michael E., 1971-
Water stress is a worldwide reality. Planners and managers of water resources around the world are tasked with finding new, creative, and innovative solutions to challenges posed by growing populations and declining water supplies. Securing safe drinking water, however, has impacts beyond the water sector. In particular, the connection between energy and water must be carefully considered to avoid unwelcome increases in energy consumption as a result of new water management strategies. One strategy that is gaining increasing attention is desalination of brackish groundwater. However, desalination is an energy-intensive process and could have negative impacts in the energy sector if conventional approaches are used. Relying on fossil fuels for desalination could drive up carbon dioxide emissions associated with water treatment and increase the cost required to produce drinking water. Integrating desalination with renewable power sources such as wind and so- lar energy can mitigate concerns regarding the energy intensity of desalination. By coupling water treatment with non-carbon emitting sources of power, it is possible to meet growing water demands in a sustainable manner. At the same time, water pro- duction offers an opportunity to address problems associated with the intermittent nature of wind and solar power production. Desalination is a time-flexible process that pairs well with wind and solar power, two sources of energy that are limited in application by their daily and seasonal variability. Integrating desalination with wind and solar power offers a solution to energetic challenges of water production while using wind and solar power for desalination offers a solution to challenges associated with the intermittent nature of renewable power. Additionally, utilizing photovoltaic-thermal (PVT) solar modules in an inte- grated facility could be advantageous to both the water and solar power production processes. Brackish groundwater, which is at a relatively cool temperature, can be used to cool solar panels, which suffer from losses in efficiency associated with tem- perature increases. At the same time, solar panels can be used to preheat feed water, a process that reduces the energetic requirement for reverse osmosis desalination. Us- ing the temperature difference between brackish groundwater and solar panels to an engineering advantage can be beneficial for the production of both solar power and drinking water. This thesis offers an investigation of desalination powered by wind and solar energy, including a study of a configuration using PVT solar panels. First, a water treatment was developed to estimate the power requirement for brackish groundwa- ter reverse-osmosis (BWRO) desalination. Next, an energy model was designed to (1) size a wind farm based on this power requirement and (2) size a solar farm to preheat water before reverse osmosis treatment. Finally, an integrated model was developed that combines results from the water treatment and energy models. The integrated model uses optimization to simulate the performance of the proposed facil- ity by maximizing daily operational profits. Results indicate that integrated facility can reduce grid-purchased electricity costs by 88% during summer months and 89% during winter when compared to a stand-alone desalination plant. Additionally, the model suggests that the integrated configuration can generate $574 during summer and $252 from sales of wind- and solar-generated electricity to supplement revenue from water production. These results indicate that an integrated facility combin- ing desalination, wind power, and solar power can potentially reduce reliance on grid-purchased electricity and advance the use of renewable power. In addition, this analysis fills a knowledge gap in understanding the advantages and tradeoffs between using wind power, solar power, and a combination of wind and solar power for desali- nation. By providing insight into the potential operations of an integrated facility, the investigation discussed in this report aids to the understanding of the water-energy nexus associated with new sources of drinking water. Results from this thesis indicate that integrating desalination with renewable power provides an opportunity for collaboration that can be mutually beneficial to both the water and energy sectors. In particular combining desalination, wind power, and solar power can overcome challenges associated with each of these technologies and may be preferable to stand-alone water or power producing facilities.
Erosion of a sharp density interface by homogeneous isotropic turbulence
(2019-05) Lagade, Joel Albano; Johnson, Blair Anne
Desalination, commonly used for potable water production, generates brines that are ultimately released back into the environment. Desalination brines discharged into coastal regions with weak currents and mild bathymetry, such as the Gulf of Mexico, do not necessarily mix with surrounding natural waters and remain stably stratified (Hodges et al., 2011). Because dense immobile saline layers from these discharges can cause hypoxia and threaten local ecosystems, we are conducting an experimental study to investigate the effect of turbulence on a sharp density interface to identify mechanisms of turbulence that promote and/or inhibit interfacial erosion. There remains a gap in the literature regarding the interaction of mean shear free homogeneous isotropic turbulence with a sharp density interface, a critical component in understanding dynamics across a stably stratified system. To address this fundamental question, we use randomly actuated synthetic jet arrays (RASJA - Variano & Cowen (2008)) to generate homogeneous isotropic turbulence, absent mean shear, above a dense fluid layer. The Richardson number is varied to ascertain the thresholds at which the density interface erodes and mixing between the stratified layers occurs. As in Johnson & Cowen (2018), who characterized the mean shear free turbulent boundary layer at solid and sediment beds, particle image velocimetry is used to complete a statistical analysis of the turbulent flow field at and above density interface. Simultaneous laser induced fluorescence measurements are obtained to capture erosion, sharpening, and mixing. Statistical metrics of the turbulence are coupled with the evolution of concentration profiles and mixing, which is determined by measuring temporally resolved isopycnal displacements. In the current work, we provide the first experimental data to test quantifying entrainment across stratified fluids as described and applied in direct numerical simulation studies by Zhou et al. (2017). By examining the interplay between mean shear free homogeneous isotropic turbulence and a sharp density gradient, we aim to deduce under what environmental conditions it is sustainable to discharge brine into relatively quiescent flows, considering key factors such as ambient turbulence and relative salinity variance between the brine and surrounding waters.
Feasibility of brackish water desalination as an alternative water supply in the Barton Springs/ Edwards Aquifer conservation district
(2015-05) Barraza, Alan; King, Carey Wayne, 1974-; Kreitler, Charles W.
Growing demands for water across the State of Texas has prompted many entities to take into consideration alternative means of obtaining water. The Edwards Aquifer within the Barton Springs/Edwards Aquifer Conservation District (BSEACD) has long been an invaluable and reliable resource in providing high quality water at a low cost. The continued population growth within the BSEACD along with continued drought conditions have strained the resource to the point of having restrictions being placed on production. These restrictions are in response to the potential impact of over-pumping water wells, water quality, springflow, and endangered species. At current permitted pumping, even with all curtailments allowed by statutory authority and current rules, the BSEACD cannot meet Desired Future Conditions during an ongoing drought of record. Within the boundaries of the BSEACD, there exist opportunities for groundwater production in the brackish portion of the Edwards and Trinity aquifers. This paper presents the economic feasibility of undertaking a brackish groundwater desalination project in the saline portion of the Edwards aquifer and also considers technical and regulatory obstacles. It is based upon a model that incorporates prevailing market and hydrogeologic conditions within Central Texas and the BSEACD, such as total dissolved solids content, brackish well depth, concentrate well depth, capital and operational costs of desalination facilities, electricity demands and costs, and water costs into its calculation. Results from this study indicate a reverse osmosis desalination project between the modeled range of 1.25 MGD to 12.5 MGD would be economically feasible. At 2.76 MGD the water would cost $748 per acre foot ($2.30 per 1,000 gal) to produce and gradually decreases in cost as the size of the facility increases due to economics of scale. At approximately 10 MGD of desired daily product generation the optimal price of $648 per acre-foot ($1.99 per 1,000 gal) is reached. While a desalination project within the BSEACD may be economically feasible, there are technical and regulatory obstacles that must be overcome before such project can take commence.
Fundamental water and ion transport characterization of sulfonated polysulfone desalination materials
(2014-08) Cook, Joseph Reuben; Freeman, B. D. (Benny D.)
Sulfonated polysulfones BisAS and BPS were fabricated into dense polymer films, and their water and ion transport properties were systematically characterized. Fundamental NaCl and water transport properties were correlated with polymer chemistry, and water and NaCl permeability were found to increase with degree of sulfonation due to the increasing polymer water content. The BisAS backbone structure was found to result in greater water uptake, increasing water and salt permeability, though the polysulfones show evidence of sensitivity to the thermal casting process as well. Additionally, water and ion permeability and sorption values were determined for select polymers when exposed to a feed consisting of mixtures of monovalent and divalent cation salts. The divalent cations were found to sorb into the polymer much more favorably than the monovalent sodium, similarly to charged materials found in the literature. The sodium permeability of sulfonated polysulfones was found to increase in the presence of divalent cations by ratios of 2 to 5 times more than when exposed to an equivalent increase in feed charge concentration of monovalent cations. It has been hypothesized the more strongly charged divalent cations are neutralizing the sulfonate charges and suppressing Donnan exclusionary effects that reduce salt transport in charged polymers.
Improving recovery in reverse osmosis desalination of inland brackish groundwaters via electrodialysis
(2010-08) Walker, William Shane, 1981-; Lawler, Desmond F.; Freeman, Benny D.; Katz, Lynn E.; Kinney, Kerry A.; Liljestrand, Howard M.
As freshwater resources are limited and stressed, and as the cost of conventional drinking water treatment continues to increase, interest in the development of non-traditional water resources such as desalination and water reuse increases. Reverse osmosis (RO) is the predominant technology employed in inland brackish groundwater desalination in the United States, but the potential for membrane fouling and scaling generally limits the system recovery. The general hypothesis of this research is that electrodialysis (ED) technology can be employed to minimize the volume of concentrate waste from RO treatment of brackish water (BW) and thereby improve the environmental and economic feasibility of inland brackish water desalination. The objective of this research was to investigate the performance sensitivity and limitations of ED for treating BWRO concentrate waste through careful experimental and mathematical analysis of selected electrical, hydraulic, and chemical ED variables. Experimental evaluation was performed using a laboratory-scale batch-recycle ED system in which the effects of electrical, hydraulic, and chemical variations were observed. The ED stack voltage showed the greatest control over the rate of ionic separation, and the specific energy invested in the separation was approximately proportional to the applied voltage and equivalent concentration separated. An increase in the superficial velocity showed marginal improvements in the rate of separation by decreasing the thickness of the membrane diffusion boundary layers. A small decrease in the nominal recovery was observed because of water transport by osmosis and electroosmosis. Successive concentration of the concentrate by multiple ED stages demonstrated that the recovery of BWRO concentrate could significantly improve the overall recovery of inland BWRO systems. A mathematical model for the steady-state performance of an ED stack was developed to simulate the treatment of BWRO concentrates by accounting for variation of supersaturated multicomponent solution properties. A time-dependent model was developed that incorporated the steady-state ED model to simulate the batch-recycle experimentation. Comparison of the electrical losses revealed that the electrical resistance of the ion exchange membranes becomes more significant with increasing solution salinity. Also, a simple economic model demonstrated that ED could feasibly be employed, especially for zero-liquid discharge.
Influence of water content on ion sorption and transport in cross-linked polymer membranes
(2020-02-03) Jang, Eui Soung; Freeman, B. D. (Benny D.); Paul, Donald R.
Polymer membrane-based technologies have been successfully utilized for a variety of desalination applications, including reverse osmosis (RO), forward osmosis (FO), electrodialysis (ED), and others. In these applications, separation of water and ions is possible because of differences in their transport rates through the membrane. Generally, high water permeability through a membrane can be achieved by using more hydrophilic (i.e., highly water swollen) polymers. However, increasing water permeability often leads to a decrease in water/ion selectivity in hydrophilic polymers, rendering controlling water content of a polymer a key factor to achieve desirable ion separation properties. Thus, a fundamental understanding of ion transport in polymers with various water contents is essential for designing and optimizing polymer membranes. The relationship between ion size and sorption/diffusion properties in water swollen uncharged polymers was investigated as a model system for understanding ion sorption and transport in more complex systems (i.e., charged polymer networks). Alkali metal chloride (e.g., LiCl, NaCl, and KCl) sorption and diffusion coefficients in a series of cross-linked poly(ethylene glycol) diacrylate (XLPEGDA) polymer membranes were measured as a function of external salt concentrations ranging from 0.01-1.0 M. Generally, ion sorption and diffusion coefficients increase as polymer water content increases. Salt activity coefficients in the polymers were quantified to better understand the thermodynamic non-ideality of ions in polymer networks. The Flory-Rehner theory was used to predict water volume fraction in the polymers equilibrated with salt solution, based on salt sorption measurements. A series of cross-linked cation exchange membranes (CEMs) were synthesized with different water uptake values and similar fixed charge group concentrations to study the effect of water content on ion sorption. Equilibrium co-ion sorption data were interpreted using a thermodynamic model based on Donnan’s theory and Manning’s counter-ion condensation theory. The inhomogeneous morphology of the membranes was characterized by small angle X-ray scattering (SAXS). The Manning parameter was used as an adjustable constant to account for morphological heterogeneity. Finally, the classic Merten and Lonsdale transport model for reverse osmosis membranes was reformulated to explicitly demonstrate the effects of concentration polarization and solution phase thermodynamic non-idealities on salt transport. A framework presented here accounts for the concentration dependence of ion activity coefficients in salt solutions, which was not explicitly included in the classic model.
Ionic separation in electrodialysis : analyses of boundary layer, cationic partitioning, and overlimiting current
(2010-08) Kim, Younggy; Lawler, Desmond F.; Liljestrand, Howard M.; Katz, Lynn E.; Meyers, Jeremy P.; Sepehrnoori, Kamy
Electrodialysis performance strongly depends on the boundary layer near ion exchange membranes. The thickness of the boundary layer has not been clearly evaluated due to its substantial fluctuation around the spacer geometry. In this study, the boundary layer thickness was defined with three statistical parameters: the mean, standard deviation, and correlation coefficient between the two boundary layers facing across the spacer. The relationship between the current and potential under conditions of the competitive transport between mono- and di-valent cations was used to estimate the statistical parameters. An uncertainty model was developed for the steady-state ionic transport in a two-dimensional cell pair. Faster ionic separations were achieved with smaller means, greater standard deviations, and more positive correlation coefficients. With the increasing flow velocity from 1.06 to 4.24 cm/s in the bench-scale electrodialyzer, the best fit values for the mean thickness reduced from 40 to less than 10 μm, and the standard deviation was in the same order of magnitude as the mean. For the partitioning of mono- and di-valent cations, a CMV membrane was examined in various KCl and CaCl₂ mixtures. The equivalent fraction correlation and separation factor responded sensitively to the composition of the mixture; however, the selectivity coefficient was consistent over the range of aqueous-phase ionic contents between 5 and 100 mN and the range of equivalent fractions of each cation between 0.2 and 0.8. It was shown that small analytic errors in measuring the concentration of the mono-valent cation are amplified when estimating the selectivity coefficient. To minimize the effects of such error propagation, a novel method employing the least square fitting was proposed to determine the selectivity coefficient. Each of thermodynamic factors, such as the aqueous- and membrane-phase activity coefficients, water activity, and standard state, was found to affect the magnitude of the selectivity coefficient. The overlimiting current, occurring beyond the electroneutral limit, has not been clearly explained because of the difficulty in solving the singularly perturbed Nernst-Planck-Poisson equations. The steady-state Nernst-Planck-Poisson equations were converted into the Painlevé equation of the second kind (P[subscript II] equation). The converted model domain is explicitly divided into the space charge and electroneutral regions. Given this property, two mathematical formulae were proposed for the limiting current and the width of the space charge region. The Airy solution of the P[subscript II] equation described the ionic transport in the space charge region. By using a hybrid numerical scheme including the fixed point iteration and Newton Raphson methods, the P[subscript II] equation was successfully solved for the ionic transport in the space charge and electroneutral regions as well as their transition zone. Above the limiting current, the sum of the ionic charge in the aqueous-phase electric double layer and in the space charge region remains stationary. Thus, growth of the space charge region involves shrinkage of the aqueous-phase electric double layer. Based on this observation, a repetitive mechanism of expansion and shrinkage of the aqueous-phase electric double layer was suggested to explain additional current above the limiting current.
Methods for evaluating the potential to power industrial processes with geospatially and temporally varying renewable energy resources
(2018-12) Aminfard, Sam; Webber, Michael E., 1971-; Hall, Matthew; Leibowicz, Benjamin D; Zhang, Changyong
One pathway to decarbonizing global energy systems is to replace fossil fuels with renewable forms of energy such as solar and wind. However, the geo-spatially and temporally variant nature of these energy sources makes their integration into conventional electric grids a technically and economically onerous effort. By identifying processes compatible with intermittent renewable energy sources, energy-intensive industries can displace the need for fossil fuels globally while circumventing many of the barriers to integrating these energy sources into electricity grids. This dissertation assessed the techno-economic feasibility of utilizing wind and solar resources to meet the energy demands of desalination facilities, as well as electrified pneumatic control systems at oil and gas production sites. The first study in this dissertation developed a method for assessing the technical and economic viability of using these renewable forms of energy to power brackish groundwater desalination facilities. The method relies on a multi-layered, spatial model that incorporated multiple variables such as depth of water resource, salinity levels, magnitude of local renewable energy resources, distance to water infrastructure, and, for comparative purposes, the local price of water. To illustrate this method, it was applied to 1,445 site locations on state of Texas lands owned by the General Land Office that overlay brackish aquifer resources. Using this approach, 193 potentially economically viable sites were identified that have estimated renewable desalination water production costs lower than local municipal water prices. The results of this analysis showed that using wind to power a desalination facility is economically preferable to solar power at 145 of the 193 sites; solar was preferable at the remaining 48 sites. Solar and wind resources are both abundant in Texas; however, the particularly high capacity factors for wind across much of the state helps wind deliver electricity costs that are often lower than those provided by solar. The second study sought to assess the technical and economic viability of using variable renewable energy to power electrified well site pneumatic control systems. Conventional pneumatic control systems vent methane-containing well gas during their operation. Electrifying these systems can avoid the venting of methane, which is a potent greenhouse gas. Under this study, two different strategies were considered for replacing pneumatic systems powered by well gas. One option is to exchange all components controllers, actuators and pumps to equipment that is directly powered by electricity. This scheme is referred to as the electric configuration. The second option, referred to as the electro-pneumatic configuration, is to retain the pneumatic system, but power its components with instrument air, which is ambient air that has been compressed by an electrically-driven compressor. This option thus replaces the emission of methane with ambient air. First, an energy simulator was developed to serve as a screening tool to determine the temporally-varying power demands incurred by switching a standard pneumatic system to an electrified one. The tool uses a comprehensive set of user inputs to simulate site-specific single-day power loads for the electric and electro-pneumatic configurations of well site control systems based on specifications from controllers, valve actuators, and chemical pumps commonly used at well sites. To assess the viability of meeting well site power loads with intermittent renewable energy, electric and electro-pneumatic systems were modeled with solar photovoltaic (PV) power generation and electric battery storage during one year of typical conditions at sites located near Midland, Texas (Permian Basin), Nacogdoches, Texas (Haynesville Shale), and Edmonton, Canada (Kaybob-Duvernay Formation) using a time-resolved energy flow model. The electro-pneumatic model included a thermodynamic analysis to simulate storage of energy as compressed air in addition to electric battery storage. Of the two configurations, the all-electric option was found to be cheaper than the electro-pneumatic option while potentially supplying power to the system more reliably. An electric battery with a capacity of 1-2 kWh can deliver 100% reliability under typical meteorological conditions for the all-electric configuration utilizing a 200-250 W solar panel for sites located in Texas, resulting in a methane abatement cost of $190-$200 per ton of avoided methane emissions. The solar-powered electric system could potentially be employed at a well site in Alberta, Canada. However, because its solar resource is less abundant than in Texas, ensuring a high level of reliability would be 14% more costly. Other forms of on-site power generation such as geothermal energy might be more viable, or could possibly be used in conjunction with solar PV to ensure reliable operation during the winter when insolation levels are considerably lower. The higher power demands required by the electric air compressor in the electro-pneumatic design require larger PV generation capacity to achieve high levels of reliability. However, if the electro-pneumatic design is implemented, well-gas could potentially be used as a back-up to the air compressor to achieve equivalent reliability of the systems currently used in the field without the PV/battery system providing meet 100% of energy demands. While it is technically and economically feasible for electro-pneumatic systems to utilize compressed air tanks as the primary energy storage medium, electric batteries are the more viable option due to their energy density, stability and relative affordability. For new well sites, the all-electric option will be more cost-effective. However, if electrification is performed as a retrofit, the electro-pneumatic configuration might be more cost effective if installing the electric system requires more than a week of downtime. Together, these studies illustrate methods that can be used to assess the techno-economic viability of integrating variable forms of renewable energy into carbon and energy-intensive industries.
Polyamide desalination membrane characterization and surface modification to enhance fouling resistance
(2010-05) Van Wagner, Elizabeth Marie; Freeman, B. D. (Benny D.); Sharma, Mukul M.; Paul, Donald R.; Bonnecaze, Roger T.; Lawler, Desmond F.; Mickols, William E.
The market for polyamide desalination membranes is expected to continue to grow during the coming decades. Purification of alternative water sources will also be necessary to meet growing water demands. Purification of produced water, a byproduct of oil and gas production, is of interest due to its dual potential to provide water for beneficial use as well as to reduce wastewater disposal costs. However, current polyamide membranes are prone to fouling, which decreases water flux and shortens membrane lifetime. This research explored surface modification using poly(ethylene glycol) diglycidyl ether (PEGDE) to improve the fouling resistance of commercial polyamide membranes. Characterization of commercial polyamide membrane performance was a necessary first step before undertaking surface modification studies. Membrane performance was found to be sensitive to crossflow testing conditions. Concentration polarization and feed pH strongly influenced NaCl rejection, and the use of continuous feed filtration led to higher water flux and lower NaCl rejection than was observed for similar tests performed using unfiltered feed. Two commercial polyamide membranes, including one reverse osmosis and one nanofiltration membrane, were modified by grafting PEGDE to their surfaces. Two different PEG molecular weights (200 and 1000) and treatment concentrations (1% (w/w) and 15% (w/w)) were studied. Water flux decreased and NaCl rejection increased with PEGDE graft density ([microgram]/cm2), although the largest changes were observed for low PEGDE graft densities. Surface properties including hydrophilicity, roughness and charge were minimally affected by surface modification. The fouling resistance of modified and unmodified membranes was compared in crossflow filtration studies using model foulant solutions consisting of either a charged surfactant or an oil in water emulsion containing n-decane and a charged surfactant. Several PEGDE-modified membranes demonstrated improved fouling resistance compared to unmodified membranes of similar initial water flux, possibly due to steric hindrance imparted by the PEG chains. Fouling resistance was higher for membranes modified with higher molecular weight PEG. Fouling was more extensive for feeds containing the cationic surfactant, potentially due to electrostatic attraction with the negatively charged membranes. However, fouling was also observed in the presence of the anionic surfactant, indicating hydrodynamic forces are also responsible for fouling.
The potential of desalination as an alternative water supply in the United States
(2009-05) Naini, Anjali Nina; Butler, Kent S.
Many parts of the United States are facing water shortages. Planners have to ensure that there will be an adequate water supply to meet the needs of the growing population. Though many places encourage water conservation, and some even enforce water restrictions, this is not always enough to make up for the shortages. Thus, alternative water sources need to be considered in some cases. The states of Texas and Florida both face uncertainties with their future water supply. To meet the needs of their current and future populations, both states have recently been using desalination at a large scale to supplement their water supplies. This report examines the desalination facilities in El Paso, Texas and Tampa Bay, Florida to determine if desalination is a feasible water supply and to explore the consequences of pursuing the development of this water resource.
Preparation and characterization of disulfonated polysulfone films and polyamide thin film composite membranes for desalination
(2011-12) Xie, Wei, 1982-; Freeman, B. D. (Benny D.); Paul, Donald R.; Sanchez, Isaac C.; Bielawski, Christopher W.; McGrath, James E.
The current reverse osmosis desalination membrane market is dominated by aromatic polyamide thin film composite (TFC) membranes. However, these polyamide membranes suffer from poor resistance to continual exposure to oxidizing agents such as chlorine in desalination applications. To overcome these problems, we have synthesized and characterized a new generation of materials, disulfonated poly(arylene ether sulfone) (BPS) random copolymer, for desalination membranes. A key technical feature of these new materials is their high tolerance to chlorine in feed water and their excellent reproducibility in synthesis. In this study, water and sodium chloride solubility, diffusivity and permeability in BPS copolymers were measured for both acid and salt form samples at sulfonation levels from 20 to 40 mol percent. The hydrophilicity of these materials, based on water uptake, increased significantly as sulfonation level increased. The water and salt diffusivity and permeability were correlated with water uptake, consistent with expectations from free volume theory. In addition, a tradeoff was observed between water/salt solubility, diffusivity, and permeability selectivity and water solubility, diffusivity and permeability, respectively. The influence of cation form and degree of sulfonation on free volume, as probed via positron annihilation lifetime spectroscopy (PALS), was determined in BPS random copolymers in both the dry and hydrated states. PALS-based free volume data for hydrated polymers were correlated with water and salt transport properties. The influence of processing history on transport properties of BPS films was also studied. Potassium form BPS films having a 32 mol% sulfonation level were acidified using solid state and solution routes. Additionally, several films were subjected to various thermal treatments in the solid state. The influence of acidification, thermal treatment, and counter-ion form on transport properties was investigated. Finally, the influence of synthesis methods of polyamide TFC membranes from m-phenylenediamine (MPD) and trimesoyl chloride (TMC) via interfacial polymerization on transport properties is reported. Then, a disulfonated diamine monomer (S-BAPS) was used instead of MPD to prepare TFC membranes. The resulting membranes exhibited reduced chlorine tolerance than those prepared from MPD. However, introduction of S-BAPS to the MPD/TMC polymerization system increased the fouling resistance of the resulting polyamide TFC membranes.
Sulfonated polysulfone desalination membranes by melt extrusion
(2015-05) Oh, Hee Jeung; Freeman, B. D. (Benny D.); Paul, Donald R.; Ellison, Christopher J; Sanchez, Isaac C; Li, Wei
This dissertation discusses preparation and transport property characterization of sulfonated polysulfone desalination membranes by melt processing. One route to melt processing of high glass transition temperature polyelectrolytes, such as disulfonated poly(arylene ether sulfone) (BPS), involves mixing a plasticizer with the polymer. In this study, poly(ethylene glycol) (PEG) was used as a plasticizer for BPS. Currently, most ion containing membranes used for desalination, electrodialysis, etc. are prepared using solvent-based processing, which is costly and environmentally unfriendly. The goal of this study has been to conduct a fundamental exploration of processing conditions useful for preparing desalination membranes without the use of solvents. Long term, this research may has the foundation for melt processing to prepare desalination membranes having equivalent or better separation properties as those of conventional solution processed membranes.
Techno-economic analysis of integrated power generation and desalination systems
(2018-05-02) Reimers, Andrew Samuel; Webber, Michael E., 1971-; Baldick, Ross; Buckingham, Fred; Hebner, Robert; Hall, Matthew; Haas, Derek
Demand for energy and water are increasing worldwide, contributing to concerns about climate change and water scarcity. These concerns have motivated a wide range of research on the “energy-water nexus," i.e., the ways by which energy and water systems interact with each other. One strategy for dealing with water scarcity is to desalinate seawater or brackish groundwater. Because desalination is more energy intensive than conventional water treatment, it puts additional stress on energy systems and efforts to reduce carbon emissions. Thus, managing water scarcity requires a holistic approach to evaluating water and energy systems. This manuscript presents two studies on energy-water systems that focus on electric power generation and desalination. The first study is a grid-level analysis of power generation and desalination systems in Kuwait with the goal of identifying strategies for reducing the cost and emissions. The second of study is a systems level analysis of a reverse osmosis (RO) desalination plant integrated with a combined cycle natural gas plant using the Texas electricity and gas market as a case study. The first study uses a unit-commitment model to simulate the operation of power generation and desalination plants in Kuwait. The model is used to evaluate the optimal allocation of fuel among Kuwait's power and desalination plants, the effect of building solar PV and new RO capacity in Kuwait, and the effect of implementing a tax on CO₂ emissions in Kuwait. These analyses find that any of these strategies could be effective at reducing emissions of CO₂, SO₂, and NO [sunscript x] in Kuwait while also reducing costs or incurring a modest increase in cost. The second study uses a mixed integer program to model the operation of an RO plant integrated with a small-scale combined cycle natural gas plant (CCGT) where the power plant can either power the RO plant or sell electricity to the grid. This facility is compared against a standalone RO plant to determine if the economic and environmental benefits of an on-site power plant outweigh its higher capital costs. These analyses indicate that a small-scale CCGT plant could share intake infrastructure with the RO plant, would have lower emissions than electricity from the grid, and that the levelized cost of water for an integrated CCGT-RO plant would be lower than a standalone RO plant. This manuscript presents two studies on energy-water systems that focus on electric power generation and desalination. The first study is a grid-level analysis of power generation and desalination systems in Kuwait with the goal of identifying strategies for reducing the cost and emissions. The second of study is a systems level analysis of a reverse osmosis (RO) desalination plant integrated with a combined cycle natural gas plant using the Texas electricity and gas market as a case study. The first study uses a unit-commitment model to simulate the operation of power generation and desalination plants in Kuwait. The model is used to evaluate the optimal allocation of fuel among Kuwait's power and desalination plants, the effect of building solar PV and new RO capacity in Kuwait, and the effect of implementing a tax on CO2 emissions in Kuwait. These analyses find that any of these strategies could be effective at reducing emissions of CO2, SO2, and NOx in Kuwait while also reducing costs or incurring a modest increase in cost. The second study uses a mixed integer program to model the operation of an RO plant integrated with a small-scale combined cycle natural gas plant (CCGT) where the power plant can either power the RO plant or sell electricity to the grid. This facility is compared against a standalone RO plant to determine if the economic and environmental benefits of an on-site power plant outweigh its higher capital costs. These analyses indicate that a small-scale CCGT plant could share intake infrastructure with the RO plant, would have lower emissions than electricity from the grid, and that the levelized cost of water for an integrated CCGT-RO plant would be lower than a standalone RO plant.
Water and salt transport structure/property relationships in polymer membranes for desalination and power generation applications
(2012-12) Geise, Geoffrey Matthew; Paul, Donald R.; Freeman, B. D. (Benny D.)
Providing sustainable supplies of water and energy is a critical global challenge. Polymer membranes dominate desalination and could be crucial to power generation applications, which include reverse osmosis (RO), nanofiltration (NF), forward osmosis (FO), pressure-retarded osmosis (PRO), electrodialysis (ED), membrane capacitive deionization (CDI), and reverse electrodialysis (RED). Improved membranes with tailored water and salt transport properties are required to extend and optimize these technologies. Water and salt transport structure/property relationships provide the fundamental framework for optimizing polymer materials for membrane applications. The water and salt transport and free volume properties of a series of sulfonated styrenic pentablock copolymers were characterized. The polymers' water uptake and water permeability increase with degree of sulfonation, and the block molecular weights could be used to tune water uptake, permeability, and selectivity properties. The presence of fixed charge groups, i.e., sulfonate groups, on the polymer backbone influence the material's salt transport properties. Specifically, the salt permeability increases strongly with increasing salt concentration, and this increase is a result of increases in both salt sorption and diffusivity with salt concentration. The data for the sulfonated polymers, including a sulfonated polysulfone random copolymer, are compared to those for an uncharged polymer to determine the influence of polymer charge on salt transport properties. The sulfonated styrenic pentablock copolymer permeability data are compared to literature data using the water permeability and water/salt selectivity tradeoff relationship. Fundamental transport property comparisons can be made using this relationship. The effect of osmotic de-swelling on the polymers and the transport properties of composite membranes made from sulfonated styrenic pentablock copolymers are also discussed. The sulfonated styrenic pentablock copolymers were exposed to multi-valent ions to determine their effect on the polymer's salt transport properties. Magnesium chloride permeability depends less on upstream salt concentration than sodium chloride permeability, presumably due to stronger association between the sulfonate groups and magnesium compared to sodium ions. Triethylaluminum was used to neutralize the polymer's sulfonic acid functionality and presumably cross-link the polymer. The mechanical, transport, and free volume properties of these aluminum neutralized polymers were studied.