Patent Application
20100213066
1. Field of Invention
This invention relates to systems and methods of water treatment having a low potential for scale formation and, in particular, to reducing the potential for scale formation in systems that utilize electrically-motivated separation apparatus.
2. Discussion of Related Art
Electrically-motivated separation apparatus including, but not limited to, electrodialysis as well as electrodeionization devices, have been used to treat water. For example, Liang et al., in U.S. Pat. No. 6,649,037, disclose an electrodeionization apparatus and method for purifying a fluid by removing the ionizable species.
One or more aspects of the invention can relate to an electrodeionization apparatus having an anode compartment and a cathode compartment. The electrodeionization apparatus can comprise a first depleting compartment disposed between the anode compartment and the cathode compartment, a concentrating compartment in ionic communication with the depleting compartment, a second depleting compartment in ionic communication with the concentrating compartment, and a first barrier cell in ionic communication with and disposed between the first depleting compartment and at least one of the anode compartment and the cathode compartment.
Other aspects of the invention can relate to an electrodeionization apparatus comprising a depleting compartment and a first concentrating compartment in ionic communication with the depleting compartment, and defined at least partially by an anion selective membrane and a cation selective membrane. The first concentrating compartment typically contains, at least partially, a first zone comprising substantially of cation exchange media that is substantially separated from the anion selective membrane by a second zone comprising substantially of anion exchange media.
Other aspects of the invention can relate to an electrodeionization apparatus comprising a depleting compartment, a first concentrating compartment in ionic communication with the depleting compartment, and a second concentrating compartment in ionic communication with the depleting compartment. The first concentrating compartment typically comprises media with a first effective current resistance and the second concentrating compartment having a portion thereof comprising media with a second effective current resistance greater than the first effective current resistance.
Other aspects of the invention can relate to an electrodeionization apparatus comprising a depleting compartment, and a concentrating compartment in ionic communication with the depleting compartment. The concentrating compartment typically comprises a mixture of anion exchange resin and cation exchange resin and amounts of the anion exchange resin and cation exchange resin in the mixture varies relative to a flow path length of the concentrating compartment.
Other aspects of the invention can relate to an electrodeionization apparatus having at least one compartment with at least one outlet port defined by a distributor having a plurality of apertures. The electrodeionization apparatus can comprise a first layer of particles in the compartment bounded by ion selective membranes. The particles can comprise media having a first effective diameter less than the smallest dimension of the apertures. The electrodeionization apparatus further comprises a second layer of particles in the compartment downstream of the first layer. The second layer of particles typically has a second effective diameter greater than the first effective diameter and greater than the smallest dimension of the apertures.
Other aspects of the invention can relate to electrodeionization system comprising a source of water to be treated, a treating module comprising a depleting compartment and a concentrating compartment, the treating module fluidly connected to the source of water to be treated; an electrolytic module comprising an acid-generating compartment, and a source of a brine solution fluidly connected to an inlet of the acid-generating compartment of the electrolytic module. The electrolytic module can be fluidly connected upstream of the concentrating compartment.
Other aspects of the invention can relate to an electrodeionization apparatus comprising a compartment containing a mixture of anion exchange resins and cation exchange resins. The anion exchange resins having an average diameter at least 1.3 times greater than an average diameter of the cation exchange resins.
Other aspects of the invention can relate to an electrodeionization apparatus comprising a compartment containing a mixture of anion exchange resins and cation exchange resins. The cation exchange resins having an average diameter at least 1.3 times greater than an average diameter of the anion exchange resins.
Other aspects of the invention can relate to a water treatment system comprising a source of water to be treated, an electrodeionization device comprising a plurality of concentrating and depleting compartments and fluidly connected to the source of water to be treated, a chiller in thermal communication with the water to be introduced into at least one concentrating compartment of the electrodeionization device, a sensor disposed to provide a representation of a temperature of at least one of water to be introduced into the concentrating compartment and water exiting the concentrating compartment, and a controller configured to receive the temperature representation and generate a signal that promotes cooling the water to be introduced into the concentrating compartment.
Other aspects of the invention can relate to electrodeionization apparatus comprising a depleting compartment at least partially defined by a cation selective membrane and an anion selective membrane, and a concentrating compartment at least partially defined by the anion selective membrane and containing a first layer of anion exchange media and a second layer of media disposed downstream of the first layer, the second layer can comprise anion exchange media and cation exchange media.
Other aspects of the invention can relate to a method of treating water in an electrodeionization device having a depleting compartment and a concentrating compartment. The method typically comprises any one or more of measuring one of a temperature of a stream in the concentrating compartment, a temperature of a stream to be introduced into the concentrating compartment, and a temperature of a stream exiting from the concentrating compartment; reducing the temperature of the water to be introduced into the concentrating compartment to a predetermined temperature; introducing water to be treated into the depleting compartment; and removing at least a portion of at least one undesirable species from the water to be treated in the electrodeionization device.
Other aspects of the invention can relate to a method of treating water in an electrodeionization device typically comprises any one or more of introducing water having anionic and cationic species into a depleting compartment of the electrodeionization device, promoting transport of at least a portion of the cationic species into a first barrier cell disposed between the depleting compartment and a cathode compartment of the electrodeionization device, and promoting transport of at least a portion of the anionic species into a second barrier cell disposed between the depleting compartment and an anode compartment of the electrodeionization device.
Other aspects of the invention can relate to a method of treating water in an electrodeionization device having a depleting compartment and a concentrating compartment. The method typically comprises any one or more of introducing water to be treated into the depleting compartment of the electrodeionization device, promoting transport of an undesirable species from the depleting compartment into the concentrating compartment of the electrodeionization device. The concentrating compartment can contain a first layer of anion exchange media and a second layer of media disposed downstream of the first layer and the second layer can comprise a mixture of anion exchange media and cation exchange media.
Other aspects of the invention can relate to a method of treating water typically comprises any one or more of introducing water to be treated into a depleting compartment of an electrodeionization device, the depleting compartment typically having at least one layer of ion exchange media; and promoting transport of at least a portion of anionic species from the water introduced into the depleting compartment from a first layer of ion exchange media into a first concentrating compartment to produce water having a first intermediate quality. The first concentrating compartment can be defined, at least partially, by an anion selective membrane and a cation selective membrane. The first concentrating compartment can contain, at least partially, a first zone comprising cation exchange media that is substantially separated from the anion selective membrane by a second zone comprising, for example, anion exchange media.
Other aspects of the invention can relate to a method of treating water in an electrodeionization device. The method comprises introducing water to be treated comprising undesirable species into a depleting compartment of the electrodeionization device, promoting transport of the undesirable species from the depleting compartment to a concentrating compartment of the electrodeionization device to produce the treated water; electrolytically generating an acid solution in the ancillary module; and introducing at least a portion of the acid solution into the concentrating compartment.
Other aspects of the invention can relate to a water treatment system comprising a source of a water to be treated, and an electrodeionization device comprising a first depleting compartment and a second depleting compartment, each of the first and second depleting compartment fluidly connected to the source of water to be treated in a parallel flow configuration; and a first concentrating compartment in ionic communication with the first depleting compartment and a second concentrating compartment fluidly connected downstream of the first concentrating compartment.
Other aspects of the invention can relate electrodeionization apparatus comprising a plurality of depleting compartments configured to have liquid flowing therein along parallel flow paths, and a plurality of concentrating compartments in ionic communication with at least one depleting compartment, wherein at least portion of the concentrating compartments are arranged serially.
Further aspects of the invention can relate to a method of assembling an electrodeionization apparatus comprising introducing electroactive media in a concentrating compartment of the electrodeionization apparatus; and introducing electroactive media in a depleting compartment of the electrodeionization apparatus. The electroactive media in at least one of the concentrating compartment and the depleting compartment comprises inert media in an amount that adjusts the effective current resistance of at least a portion of the at least one of the concentrating compartment and the depleting compartment.
The accompanying drawings are not intended to be drawn to scale. In the drawings, each identical or nearly identical component that is illustrated in various figures is represented by a like numeral. For purposes of clarity, not every component may be labeled in every drawing.
In the drawings:
The invention, in some aspects or embodiments, provides electrically-driven separation apparatuses such as but not limited to filled compartment electrodeionization (CEDI) devices such as those disclosed in U.S. Pat. Nos. 4,632,745, 6,649,037, 6,824,662, and 7,083,733, each of which is incorporated herein by reference in their entirety for all purposes. In particular, the embodiments implementing one or more aspects of the invention provide can be, in some cases, characterized as having a lower potential or a lower likelihood of forming scale during operation thereof. Although the various aspects of the invention are presented through embodiments involving electrodeionization devices, any of the various aspects of the invention may be practiced, separately or in combination, in other electrically-driven or motivated separation apparatus that can facilitate treatment of a fluid having at least one undesirable species. Particularly pertinent aspects of the invention can involve electrodeionization apparatus utilized to treat or remove at least one dissolved species from a water stream or a body of water. Thus, the various aspects of the invention can advantageously provide electrodeionization apparatuses that are configured or operated to treat water having high scale potential.
An aspect of the invention can be implemented in the exemplary embodiment presented in
Other embodiments of the invention can involve one or more barrier cells that separate neutral or weakly ionized, or at least ionizable, species, such as, but not limited to silica, SiO2. Silica can precipitate from the bulk liquid if the concentration is high enough or where a pH change occurs, such as change from a high pH to a neutral pH. In electrodeionization apparatus, silica is typically removed while in its ionized state, at high pH. One or more barrier cells 132, preferably selective for particular kinds of species, can be disposed to ionically isolate an anode compartment 122 of electrodeionization apparatus 100, wherein hydrogen ions are typically generated and consequently can have low or neutral pH liquid flowing therein. If silica migrates from depleting compartment 114 into concentrating compartment 112 through anion selective membrane 140A, it can be trapped or inhibited from further migration by barrier cell 132 containing high pH liquid flowing therein and inhibited from further migration into the low or neutral pH compartment with neutral or near neutral pH, and thereby reduce the likelihood of polymerizing into silica scale. Cell 132, like cell 130, can be defined, at least partially, by cation selective membrane 140C and anion selective membrane 140A. Indeed, because any of the barrier cells of the invention can preferably also trap hydroxyl species, the resultant high pH level of the fluid therein can advantageously maintain silica in its ionized state. Barrier cell 132 can thus serve to trap pH-precipitatable species and prevent or at least inhibit precipitation of such species. Barrier cell 132 can also contain, at least partially, anion exchange media and cation exchange media or a mixture of both. Further, one or more of the barrier cells can further comprise inert media or other filler material that can facilitate assembly of the electrodeionization apparatus or provide a desirable characteristic such as resistance or flow distribution during, for example, operation of the apparatus. Likewise, one or more of the concentrating compartments, the depleting compartments, and the electrode compartments can contain, at least partially, a mixture of anion and cation exchange media. Indeed, a mixture of anion and cation exchange media in the concentrating compartments and electrode compartments can further reduce scaling potential by facilitating transport of precipitatable species away from the selective membranes which avoids accumulation of an ionic species that may occur in compartments or regions of compartments with a single type of active exchange media.
In some embodiments of the invention, the anode compartment can contain, at least partially, media that is substantially comprised of oxidation resistant substrate. Thus, for example, durable, highly cross linked ion exchange resin, such as commercially available cation resins, can be used in the anode compartment in which an oxidizing environment may be present. Further, cation exchange resin when utilized in the anode compartment can prevent or inhibit transport of chloride ions to the anode surface where such species may be converted to oxidizing chlorine.
The apparatus of the invention can treat water having hardness of greater than 1 mg/L as CaCO3 or silica content of greater than 1 mg/L, or both. Thus, the apparatus and techniques of the invention are not confined to conventional operating limits and, when used in a treatment system, can obviate at least one unit operation intended to soften the water to be treated or remove silica. This advantageously can reduce capital and operating costs while improving the treatment system's reliability and availability as well as capacity. For example, the treatment systems of the invention, comprising one or more electrodeionization devices described herein, can treat water without a two-pass reverse osmosis (RO) subsystem, while providing water having the same or comparable quality as a system that utilizes a two-pass RO device to remove or reduce the concentration of hardness causing components and silica before an electrodeionization device.
Further aspects of the invention can involve electrodeionization apparatus comprising at least one depleting compartment and/or at least one concentrating compartment having layered media contained therein. For example, one or more depleting compartments 112 of electrodeionization device 100 can comprise a first layer of particles 112A, at least a portion thereof comprising active media that facilitates transport or migration of a first target, typically ionized, species. Depleting compartment 112 can further comprise a second layer 112B comprising, at least partially, active media that facilitates transport of the first target species and a second target species, or both. First layer 112A can comprise particles having a first effective diameter and second layer 112B can have particles with a second effective diameter. Further embodiments can involve a third layer 112C in depleting compartment 112. Third layer 112C can have active or inert media, or a mixture of both, with a third effective diameter. The effective diameter can be a smallest dimension of a particle. Alternatively, the effective diameter can be an average diameter of the collective particles and is, for example, a calculated diameter of an analogous sphere of comparable volume and surface area. For example, the effective diameter of particles in a layer can be a function of the ratio of the volume of a particle to the surface area of a particle or an average of the smallest dimension of the particles. In a preferred configuration, the particles in a downstream layer have an effective diameter that is less than the effective diameter of particles in an upstream layer. For example, particles comprising layer 112C can be spherical particles with a larger effective diameter than the effective diameter of particles comprising layer 112B. Optionally, the effective diameter of the particles comprising layer 112A can be greater than the effective diameter of particles in layer 112B or 112C. One or more of the concentrating compartments may be similarly layered.
In a preferred embodiment, the particles in an upstream layer have an effective diameter that is at least the dimension of interstices between the particles of a downstream layer. In further embodiments, the upstream particles have an effective diameter or a smallest dimension that is less than the smallest dimension of the apertures of distributor 160 that defines an outlet port of depleting compartment 112. Distributor 160 can be a screen that serves to retain the media within the compartments. Thus, each of the depleting compartments and concentrating compartments containing media can have at least one distributor that permits fluid flow therethrough while retaining the media and a layer of media that are sized to retain particles in an upstream layer.
The apertures or openings of distributors are typically designed to retain resins having a diameter of about 500 μm to about 700 μm. In some of the configurations of the invention, anion and cation exchange resins may be utilized having smaller dimensions than the aperture dimensions which improves mass transfer kinetics throughout the apparatus. Further, smaller ion exchange resins can improve packing within the compartment and reduces the likelihood of channeling or flow bypass along the compartment walls. Close packed spheres or nearly spherical particles have interstitial spaces of about 0.414 times the radius of the spheres. Thus, the effective diameter of the upstream resin is preferably not less than such dimension. For example, the fine mesh resin beads having an effective diameter of about 62 μm to about 83 μm may be utilized in an upstream layer with a layer of resin beads having a diameter of about 300 μm to about 400 μm. Any of the layers may comprise any suitable fraction of the compartment. The depth of the upstream layer may be dependent on providing a desired performance. Further, advantageous configurations contemplate the use of cation resin beads having a smaller effective diameter or dimension with larger anion resin beads to facilitate cation migration activity. Notable arrangements are not limited to the use of active resin as the lower, downstream media and the invention may be implemented utilizing inert media in one or more of the downstream layers.
The interfaces between the layers may constitute a gradient of small and large resin beads. Thus, the boundary between layers need not be particularly delineated. Other configurations, moreover, can involve a mixture of the fine mesh resin beads mixed with larger resins.
Another aspect of the invention can involve electrodeionization apparatus comprising at least one concentrating compartment having layered media contained therein. As illustrated in
For example, in a typical electrodeionization apparatus, bicarbonate ions transfer through the anion exchange membrane near the inlet of the compartment but may be inhibited from migrating further from the membrane. When water splitting occurs, the hydroxyl species transported through the anion exchange membrane can react with the bicarbonate species to form carbonate which then reacts with calcium to form calcium carbonate scale.
By utilizing layers in one or more of the concentrating compartments, target species can be directed to locations where they are less likely to form scale. As shown in
The depleting compartments 212 and the other one or more layers 216 of the concentrating compartments 214 may contain mixed anion exchange and cation exchange media.
To further reduce or inhibit scale formation, layers of media can be disposed along a flow path length of the concentrating compartment. As shown in
In some cases, the first zone or second zone can be a mixture of differing amounts of types of ion exchange media. For example, zone 315C can comprise, consists essentially of, or consist of cation exchange media adjacent cation selective membrane 340C and zone 315D can comprise, consist essentially of, or consist of anion exchange media, wherein the amount of anion exchange media, relative to the amount of cation exchange media increases, or decreases, along the flow path length or lengthwise dimension, such that a boundary between zones which is defined by gradient boundary 351. In another embodiment, a third zone (not shown) of media can be disposed between the first and second zones. The third zone can comprise, consist essentially of, or consist of inert media, cation exchange media, anion exchange media, mixed media, or mixtures thereof. Further, one or more screens can be used between zones or within the zones to facilitate filling the compartments of the apparatus, which, during operation can also improve flow distribution and further inhibit scale formation. Assembly and filling can also be facilitated by utilizing a binder to secure the media of each zone. For example, media of the first zone can be mixed with a water soluble binder, such as starch. The mixture can then be placed into the compartment. A second mixture of media of the second zone can be similarly prepared and disposed in the compartment.
Zone 314B facilitates transport of anionic species, such as bicarbonate ions, away from anion selective membrane 340A and zone 315C facilitates transport of cationic species, such as calcium ions, away from anion selective membrane 340C. Such segregating zones thus reduce the likelihood of scale formation around membrane surfaces.
As illustrated in
Further aspects of the invention involve systems and techniques that modify the pH of a stream flowing in at least one concentrating compartment of an electrodeionization apparatus. The pH of the stream can be reduced to reduce the likelihood of scale formation by generating and adding an acidic solution to one or more of the concentrate and electrode compartments. The acidic solution can be generated or prepared by utilizing an electrolytic module. Further scale inhibition or tolerance can be effected by degasification of the concentrate liquid. Any acid generating module may be utilized such as those commercially available from Dionex Corporation, Sunnyvale, Calif.
Typically, an electrodeionization device can treat liquids having low hardness. This limitation limits the incoming feed water into electrodeionization devices to a hardness level of 1 ppm or less, as calcium carbonate. To treat water having a hardness value greater than 1 ppm, pretreatment processes such as two-pass RO or a softener RO, is typically used. The additional pretreatment unit operations increase system complexity and cost as well as waste. The electrodeionization devices of the present invention, however, can reliably treat water having higher hardness levels thereby eliminating or reducing the dependence on such pretreatment operations.
Addition of an acidic solution into the concentrating compartment of electrodialysis devices to reduce calcium precipitation is known; however adding acidic solutions to electrodeionization devices is not practiced because of low flow velocity of the streams in the concentrate compartments, especially in thick cell compartment. Further, a high quantity of acid is typically required. As illustrated in
In some cases, the acidic solution can be introduced into one or more of the depleting and concentrating compartments 412 and 414, as well as the electrode compartments of electrodeionization device 445. Preferably, acidic solution is added in an amount to provide a pH of the exiting stream solution leaving the compartment of between about 2.5 to 4.3 units. Further embodiments may involve neutralizing one or more streams from electrodeionization device 445. For example a basic solution produced from compartment 472 of electrolytic module 435 may be combined to neutralize an outlet stream, typically having a low pH, from concentrating compartment 414 before being discharged to drain 463 or the environment.
Degasification of the concentrate stream to remove carbon dioxide may further reduce or eliminate the precipitation potential in the concentrating compartment. Degasification can be accomplished by the addition of a degasification device or by membrane processes or other methods. Degasification may be relevant when utilizing an acidic solution in the concentrating compartment because of the potential formation of carbon dioxide gas, which can diffuse back through the membrane and reduce product quality. Further, the flow of the stream within the compartment may be countercurrent to facilitate gas removal.
Recirculation of the concentrate compartment using a pump and, optionally, a tank can further enhance the scale inhibition by the acidification and degasification techniques described herein.
The components, arrangements, and techniques of the invention also provide improved current distribution in an electrodeionization device. As schematically illustrated in
The effective current resistance of a compartment or portion thereof may be modified by mixing inert resin beads, or low or non-conducting materials, with in the concentrating compartment. Selectively increasing the effective current resistance effects a more uniform current distribution through the other compartments. The reduced variations in current throughout the depleting compartments, for example, improve overall performance.
In an electrodeionization device, the electrical resistance may depend on the types of media in the device as well as the active chemical form of those media, i.e., what ions are moving through the media. In layered bed compartments, the resistance typically varies between the layers because of the different types of resin and the form of the resins. Typically, the strongly charged species or ions are motivated and the water splitting phenomena and weakly ion promotion follow. Thus, media resins near the inlet of the compartment would exchange with the target species in the feed water while media near the outlet would be mostly in the hydrogen and hydroxide forms. Typically, most of the strongly charged ions must be removed, which may not be effected if the feed concentration and/or flow are high enough or if the current is low enough.
If the resistance in the compartments can vary between layers thereof or along the length of the bed, then the current density can also vary accordingly. However, the resistance through the entire module may not just be a function of the resistances of the depleting compartments. The depleting compartments are electrically in series with the membranes and the concentrating compartments and electrode compartments, which may or may not also vary in resistance along their length. If the resistances of the depleting compartments are a small portion of the total resistance through the module, then even if such resistances vary significantly, the overall resistance will be dominated by other factors and current distribution will be more uniform. However, if the depleting compartment resistances are high relative to the other resistances, the current distribution will be affected by resistance differences within the depleting compartments.
Typical electrodeionization devices incorporate screen filled concentrating and/or electrode compartments. In these configurations, the resistance of the water in these compartments is much greater than the resistance of the resin in the depleting compartments in most cases, and therefore, current distribution is not generally controlled by the resistances of the depleting compartments. Filling the concentrating and electrode compartments with resin as well as using lower resistance ion exchange membranes reduces the overall module resistance significantly. However, in certain circumstances this can lead to uneven current distribution as the module resistances become dominated by the resistances of the depleting compartments.
In some embodiments of the invention, therefore, screen filled concentrating and electrode compartments may minimize uneven current distribution. However, in most post RO applications, the water has very low conductivity leading to high module resistance. This high resistance further creates limitations if there are electrical potential constraints. The invention, in contrast, provides comparable performance without using brine injection into the stream flowing into the concentrating compartment thereby reducing operating cost and process complexity.
As noted, mixing inert resin in one or more concentrating and/or electrode compartment as fillers can increase the resistance in those compartments which improves current distribution through the module. As shown in
Other materials with low conductivity, such as polymeric screens or fiber material can be used to increase the resistance along with the above-noted inert resin beads.
Electrodeionization apparatus may be limited to a maximum recovery of 90-95% to prevent scale formation of limited solubility species in the feed water such as hardness and silica. If the feed water contains very low amounts of these species the device should be able to operate at higher recovery rates. Some aspects of the invention involve electrodeionization apparatus having multiple passes through concentrating compartments thereof thereby providing recovery rates. The multiple pass configurations facilitate maintaining a predetermined velocity without a recirculation pump and loop. However, this invention is may be preferably utilized in applications with recirculating loops wherein the feed water ion concentration is low and a very high recovery is desired to avoid wasting or discharging high purity water and/or increasing operating time of the makeup system. In some embodiments of the electrodeionization apparatus of the invention, the fluid flow rate is sufficient to reduce the likelihood of creating dead volumes, channeling and localized overheating within the compartments. For example, the desired fluid flow rate in a compartment can be at least about 2 gallons per minute per square foot in a concentrating compartment. Other fluid flow rates may be dictated by other factors including, but not limited to, the concentration of a component of the precipitating compound, the temperature of the fluid, and the pH of the fluid. Lower velocities may induce channeling.
Water to be treated is introduced into depleting compartments 614 and directed to point of use without following or tracking the flow of water through compartments 612, 612A, and 612B. The invention, however, is not limited to the number of associated concentrating compartment volumes relative to the number of depleting compartment volumes and any ratio of concentrating compartments to depleting compartments can be used to provide a desired high fluid flow rate through the compartments.
Different size cation and anion exchange resin beads in the mixed layers or compartment may be utilized to further reduce the transport rate of the larger bead counter-ions and facilitate transport of the smaller bead counter-ions.
Ion transport typically occurs through the ion exchange resins. Successful transport may thus depend on a complete path of like material between the beads and the membranes. A cationic species typically diffuses onto a cation resin bead and will tend to move toward the cathode following a path of cationic media until it reaches the cation selective membrane and passes through into the concentrating compartment. If the path is broken, the cationic species will have to diffuse out of the last bead and into the bulk solution, therefore reducing the chance it will be picked up later in the bed and increasing the chance it will end up in the product water. The path can be broken by poor packing such that the beads don't have good contact or it can be broken by a bead of the opposite charge.
Using a relatively thin cell or tightly packing the resins can increase the probability of maintaining the desired pathway. Utilizing cation and anion exchange resin of a similar and relatively uniform size will also increase the likelihood of maintaining the desired pathway. Using cation and anion exchange resin of different sizes, however, can block transfer.
In some cases, it may be advantageous to inhibit transport of either cations or anions. By selectively reducing the size of one type of resin in a mixed bed, the transfer of the smaller bead counter-ions will be enhanced due to more complete paths whereas the transfer of the larger bead counter-ions will be retarded due to fewer complete paths because as the size of the smaller beads approaches some fraction of the size of the larger beads, smaller resin beads tend to pack around the larger beads, which isolates and breaks the path from one large bead to the next. This phenomenon may also depend on the relative ratio of the large and small ion exchange resin beads. For example a mix of 50% small beads by volume would affect the transport of ions much differently than a mix of 25% or 75% small beads by volume.
Once the size and mix ratios of the media are appropriately selected to slow transport of a target or selected type of ion and increase transport of different type, hydrogen or hydroxyl ions must be transferred to maintain electro neutrality. For example, if a bed consisting essentially of cation resin is used in a depleting compartment as shown in
For example, an electrodeionization apparatus of the invention can comprise a compartment containing a mixture of anion exchange resins and cation exchange resins, the cation exchange resins having an average diameter at least 1.3 times greater than an average diameter of the anion exchange resins. Alternatively or in addition, the electrodeionization apparatus can comprise a compartment containing a mixture of anion exchange resins and cation exchange resins, the cation exchange resins having an average diameter at least 1.3 times greater than an average diameter of the anion exchange resins.
Further aspects of the invention can relate to a method of treating water in an electrodeionization device. The method, in some embodiment thereof, can comprise introducing water having anionic and cationic species into a depleting compartment of the electrodeionization device, promoting transport of at least a portion of the cationic species into a first barrier cell disposed between the depleting compartment and a cathode compartment of the electrodeionization device, and promoting transport of at least a portion of the anionic species into a second barrier cell disposed between the depleting compartment and an anode compartment of the electrodeionization device. The method can also comprise adjusting effective resistances of one or more compartments or portions of at least one compartment of the device.
Further aspects of the invention can relate to a method of treating water in an electrodeionization device having a depleting compartment and a concentrating compartment. The method can comprise introducing water to be treated into the depleting compartment of the electrodeionization device; and promoting transport of an undesirable species from the depleting compartment into the concentrating compartment of the electrodeionization device, the concentrating compartment containing a first layer of anion exchange media and a second layer of media disposed downstream of the first layer, the second layer comprising a mixture of anion exchange media and cation exchange media, wherein the first layer has an effective resistance that is about the same as the second layer.
Further aspects of the invention can relate to a method of treating water in an electrodeionization device. The method can comprise introducing water to be treated comprising undesirable species into a depleting compartment of the electrodeionization device; promoting transport of the undesirable species from the depleting compartment to a concentrating compartment of the electrodeionization device to produce the treated water; electrolytically generating an acid solution in the ancillary module; and introducing at least a portion of the acid solution into the concentrating compartment. The effective resistance of the concentrating and/or depleting compartment is, preferably, substantially uniform along its fluid flow path length. Electrolytically generating the acid solution can comprise introducing a halide salt solution into the ancillary module. The method can further comprise generating a basic solution in the ancillary module while generating the acid solution. The method can further comprise neutralizing an outlet stream from the concentrating compartment with the basic solution. The method can further comprise mixing a portion of the treated water with the brine solution and introducing the mixture into the ancillary module. The method can further comprise degasifying at least a portion of the liquid in the concentrating compartment. Introducing the acid solution into the concentrating compartment can comprise introducing an acidic solution having a pH of less than 4.3 into the concentrating compartment.
Further aspects of the invention can relate to electrodeionization apparatus comprising a plurality of depleting compartments configured to have liquid flowing therein along parallel flow paths; and a plurality of concentrating compartments in ionic communication with at least one depleting compartment, wherein at least portion of the concentrating compartments are arranged serially, and, preferably, the concentrating compartments have substantially the same effective current resistance therethrough. The plurality of concentrating compartments can define a single flow path through the electrodeionization apparatus.
Further aspects of the invention can relate to an electrodeionization apparatus comprising a depleting compartment; and a first concentrating compartment in ionic communication with the depleting compartment, and defined at least partially by an anion selective membrane and a cation selective membrane, the first concentrating compartment containing at least partially a first zone comprising substantially of cation exchange media that is substantially separated from the anion selective membrane by a second zone comprising substantially of anion exchange media, wherein the first concentrating compartment comprises electrochemically inert media in an amount that adjusts the effective current resistance of the first concentrating compartment to a desired effective resistance. The effective resistance of the first concentrating compartment, in some cases, is about the same as the effective current resistance of the second concentrating compartment.
The function and advantages of these and other embodiments of the invention can be further understood from the examples below, which illustrate the benefits and/or advantages of the one or more systems and techniques of the invention but do not exemplify the full scope of the invention.
This example describes the effect of temperature on the Langelier Saturation Index (LSI).
Calculating an LSI value is known in the art for a measure of the potential for scale formation. LSI is a function of pH, total dissolved solids (TDS), temperature, total hardness (TH), and alkalinity. Using the following estimates for these parameters for a concentrating compartment stream of an electrodeionization apparatus, the temperature of the stream relative to the LSI value can be defined and a representative relationship is shown in
When the LSI value of a stream, is positive scaling is likely to occur. To inhibit scaling, the LSI value of the stream is reduced to, preferably a negative quantity.
Cooling can be effected by thermally coupling a heat exchanger, or chiller, upstream of the electrodeionization apparatus. Other components and subsystems that facilitate removing thermal energy from the one or more streams into the apparatus may be utilized. For example, one or more sensors and controllers may be utilized to define a temperature control loop and facilitate maintaining the temperature of the stream to a target temperature or even to reduce the effective LSI value to a desired or target amount.
The target temperature can be determined empirically, by defining a temperature of the stream to be introduced into a concentrating compartment of the electrodeionization device, or be calculated based at least partially on the calculated LSI value. For example, an empirically established target temperature can be a temperature at which no scaling is historically observed with or without an additional margin to ensure that the scaling is further inhibited. An LSI-based target temperature may be defined based on a derived LSI-temperature relationship then calculating the target temperature associated with a set reduction in LSI value.
In this example, the effect of resin bead size on the performance of an electrodeionization apparatus in accordance with one or more aspects of the invention was studied.
In one test, an electrodeionization module was constructed using an equal mixture of anion resin with an average bead diameter of 575 μm and a cation resin with an average bead diameter of 350 μm in the depleting compartments. Both of these resins were uniform particle size according to industry standards.
The module was fed a water that was previously treated by reverse osmosis and contained about 0.5 ppm Mg and 1.5 ppm Ca (both as CaCO3) with a pH of about 6.1. The module was operated at almost 100% current efficiency and product quality was about 1-2 MΩ-cm without almost zero silica removal.
The product water hardness level was below detection as measured by a Hach spectrophotometer (<10 ppb) and the pH was reduced to about 5.7. This indicates that the module was preferentially removing cations over anions.
In this example, the effect on the performance of an electrodeionization apparatus with several layers of different bead sizes in compartments thereof in accordance with one or more aspects of the invention, was studied.
A module was constructed with three layers of ion exchange resin in the depleting compartments. The first and last layers consisted of an even mix of cation and anion resin of uniform particle diameters approximately 600 μm. The middle layer consisted of an even mix of cation exchange and anion exchange resins with particle diameters of 150-300 μm. The module spacer had slots in the flow distributor, which are used to hold resins in place, with a width of 254 μm. The module was operated for several months with no change in pressure drop, which indicates that the resins in the middle layer, of which some were smaller than the spacer apertures, did not pass through the bottom layer of resin and exit the module.
In addition, the addition of the middle layer of smaller resins improved the performance of a comparable electrodeionization device, control module. The module was operated in parallel with another electrodeionization module having compartments containing an even mix of cation exchange and anion exchange resins with particle diameters of about 600 μm. With a feed water previously treated by reverse osmosis having a conductivity of about 30 μS/cm and containing 3.75 ppm of CO2, the module comprising a layer of smaller ion exchange resins produced water having a resistivity of 16.4 MΩ-cm whereas the other typical module, without a layer of smaller ion exchange resins, produced water having a resistivity of 13.5 MΩ-cm. Further, the module comprising the layer of smaller exchange resins showed a silica removal of 96.6% versus 93.2% for the control module.
In this example, the effect on the performance of an electrodeionization apparatus with several or multiple passes through concentrating compartments thereof was studied.
An electrodeionization module was assembled with four depleting compartments, three concentrating compartments, and two electrode compartments. All of the depleting compartments were fed a water to be treated in to parallel to each other. The concentrating compartment and electrode compartments were fed in series so that the stream introduced into the concentrating compartments entered the cathode compartment first, then flowed sequentially through the concentrating compartments and finally through the anode compartment. This contrasts with the conventional configuration in which a water stream is typically fed into the electrode compartments in parallel with a water stream into the concentrating compartments. The module thus had five effective concentrating compartment passes.
Data for this module (labeled as “Series Concentrate”) along with performance data for a standard module operating with parallel flows (labeled as “Parallel Concentrate”) is listed in Table 1 below.
The data show that by serially arranging the stream to flow through the concentrating and electrode compartments, a fluid flow velocity similar to that when operating in parallel at a much lower reject flow rate. Therefore very high recoveries can be obtained while maintaining a minimum velocity in the concentrate.
In this example, the effect on the performance of an electrodeionization apparatus with horizontal and vertical layers in the concentrating compartment was studied.
Two modules were assembled with different layering configurations as shown in
After this period they were opened and no scale was observed. In contrast, a non-layered module containing mixed bed resin in the depleting and concentrating compartments showed scale on the anion membranes in the concentrate after two weeks of operation on the same feed water.
In this example, the effect on the performance of an electrodeionization apparatus with vertical layers in compartments thereof along with addition of an acidic solution, was studied.
Three modules were assembled with horizontal layering in the depleting compartment and vertically oriented zones or layers, along the flow path length, in the concentrating compartments. Barrier cells were also disposed adjacent both electrode compartments. The modules were operated for ninety days with post-RO feed water containing about 2 ppm of total hardness. An acidic solution was injected into the concentrating compartments at rate that provide a pH of the water stream exiting the concentrating compartments of about 2.5-3.5.
The controller of the system of the invention may be implemented using one or more computer systems. The computer system may be, for example, a general-purpose computer such as those based on an Intel PENTIUM®-type processor, a Motorola PowerPC® processor, a Sun UltraSPARC® processor, a Hewlett-Packard PA-RISC® processor, or any other type of processor or combinations thereof. Alternatively, the computer system may include specially-programmed, special-purpose hardware, for example, an application-specific integrated circuit (ASIC) or controllers intended for analytical systems.
The computer system can include one or more processors typically connected to one or more memory devices, which can comprise, for example, any one or more of a disk drive memory, a flash memory device, a RAM memory device, or other device for storing data. The memory is typically used for storing programs and data during operation of the treatment system and/or computer system. Software, including programming code that implements embodiments of the invention, can be stored on a computer readable and/or writeable nonvolatile recording medium, and then typically copied into memory wherein it can then be executed by the processor. Components of the computer system may be coupled by an interconnection mechanism, which may include one or more busses (e.g., between components that are integrated within a same device) and/or a network (e.g., between components that reside on separate discrete devices). The interconnection mechanism typically enables communications (e.g., data, instructions) to be exchanged between components of the computer system. The computer system can also include one or more input devices, for example, a keyboard, mouse, trackball, microphone, touch screen, and one or more output devices, for example, a printing device, display screen, or speaker. In addition, the computer system may contain one or more interfaces that can connect the computer system to a communication network (in addition or as an alternative to the network that may be formed by one or more of the components of the computer system).
According to one or more embodiments of the invention, the one or more input devices may include sensors for measuring parameters. Alternatively, the sensors, the metering valves and/or pumps, or all of these components may be connected to a communication network that is operatively coupled to the computer system. The controller can include one or more computer storage media such as readable and/or writeable nonvolatile recording medium in which signals can be stored that define a program to be executed by one or more processors. Storage medium may, for example, be a disk or flash memory. Although the computer system may be one type of computer system upon which various aspects of the invention may be practiced, it should be appreciated that the invention is not limited to being implemented in software, or on the computer system as exemplarily shown. Indeed, rather than implemented on, for example, a general purpose computer system, the controller, or components or subsections thereof, may alternatively be implemented as a dedicated system or as a dedicated programmable logic controller (PLC) or in a distributed control system. Further, it should be appreciated that one or more features or aspects of the invention may be implemented in software, hardware or firmware, or any combination thereof. For example, one or more segments of an algorithm executable by the controller can be performed in separate computers, which in turn, can be communication through one or more networks.
Those skilled in the art should appreciate that the parameters and configurations described herein are exemplary and that actual parameters and/or configurations will depend on the specific application in which the systems and techniques of the invention are used. Those skilled in the art should also recognize or be able to ascertain, using no more than routine experimentation, equivalents to the specific embodiments of the invention. It is therefore to be understood that the embodiments described herein are presented by way of example only and that, within the scope of the appended claims and equivalents thereto; the invention may be practiced otherwise than as specifically described.
As used herein, the term “plurality” refers to two or more items or components. The terms “comprising,” “including,” “carrying,” “having,” “containing,” and “involving,” whether in the written description or the claims and the like, are open-ended terms, i.e., to mean “including but not limited to.” Thus, the use of such terms is meant to encompass the items listed thereafter, and equivalents thereof, as well as additional items. Only the transitional phrases “consisting of” and “consisting essentially of,” are closed or semi-closed transitional phrases, respectively, with respect to the claims. Use of ordinal terms such as “first,” “second,” “third,” and the like in the claims to modify a claim element does not by itself connote any priority, precedence, or order of one claim element over another or the temporal order in which acts of a method are performed, but are used merely as labels to distinguish one claim element having a certain name from another element having a same name (but for use of the ordinal term) to distinguish the claim elements.
U.S. Provisional Patent Application Ser. No. 60/805,505, filed on Jun. 22, 2006, titled ENHANCED HARDNESS TOLERANCE OF CEDI MODULES; U.S. Provisional Patent Application Ser. No. 60/805,510, filed on Jun. 22, 2006, titled METHODS TO REDUCE SCALING IN EDI DEVICES; U.S. Provisional Patent Application Ser. No. 60/912,548, filed Apr. 18, 2007, titled USE OF INERT RESIN IN THE CONCENTRATE COMPARTMENT TO IMPROVE CURRENT DISTRIBUTION FOR EDI MODULES; and U.S. patent application Ser. No. 11/767,438, filed on Jun. 22, 2007, titled LOW SCALE POTENTIAL WATER TREATMENT, and published as U.S. Publication No. 2008/0067069 A1, are incorporated herein by reference in their entirety for all purposes.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/US08/60605 | 4/17/2008 | WO | 00 | 5/7/2010 |
| Number | Date | Country | |
|---|---|---|---|
| 60912548 | Apr 2007 | US | |
| 60805505 | Jun 2006 | US | |
| 60805510 | Jun 2006 | US | |
| 60912548 | Apr 2007 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 11767438 | Jun 2007 | US |
| Child | 12596279 | US |
