WO2001089671A1

WO2001089671A1 - Capacitive deionization cell structure with voltage distribution control

Info

Publication number: WO2001089671A1
Application number: PCT/US2001/016384
Authority: WO
Inventors: Colin E. J. Bowler; Mohamed Y. Haj-Maharski; Aaron M. Jungreis; John Tarnawaski
Original assignee: Abb Power T & D Company Inc.
Priority date: 2000-05-22
Filing date: 2001-05-22
Publication date: 2001-11-29
Also published as: AU2001264756A1

Abstract

The present invention relates to fluid purification systems incorporating capacitive deionization cells (110) having a stack of serially connected deionization capacitors (300). The capacitor stack is electrically connected in parallel to a voltage-balancing device that is capable of sharing charge with the deionization capacitors, such that the overall voltage is substantially uniform from the top of the cell stack to the bottom of the cell stack.

Description

CAPACITINE DEIONIZATION CELL STRUCTURE WITH VOLTAGE

DISTRIBUTION CONTROL

Cross Reference to Other Applications: This application is related to co-pending applications, "Capacitive

Deionization Cell Structure for Control of Electrolysis" Attorney Docket No. ABTT- 0218/B000121; "Capacitive Deionization Cell Power Supply" Attorney Docket ABTT- 0220/B000161; and "Integrated Electrode for Electrolytic Capacitor Applications" Attorney Docket ABTT-0221/B000171, filed herewith and incorporated by reference in their entireties.

Field of the Invention

The present invention relates generally to capacitive deionization cells that are used for deionizing electrolytic fluids. Specifically, the present invention relates generally to apparatuses and systems incorporating a plurality of capacitive deionization cells that allow for voltage sharing.

Background of the Invention

It is generally known to use capacitive deionization technology ("CDT") electro-static cell devices to purify water of ionic species for applications such as water desalination, purification of water for human consumption, and other related industrial and commercial applications. Water may contain impurities such as, for example, ionic salts that include calcium, calcium carbonate, sodium, sodium chloride, and magnesium; or other impurities such as copper, iron, zinc, silica, nitrates, arsenic, chrome, potassium, carbonates, cadmium, cesium, and biological organisms such as bacteria and/or microbes that need to removed. CDT cells may be effective in removing such impurities from water or any other aqueous-based system.

CDT cells are essentially capacitors or electrical charge storage devices. These devices store electric energy in the form of an electric field generated in the space between two separated, oppositely charged electrodes. Capacitance itself is a property of space whereby two conductors that are separated by a dielectric layer store charge. Capacitance is measured in units called Farads, calculated according to -equation (1) fof a parallel plate capacitor, where C equals capacitance, k is the dielectric constant, A is the area of the parallel charged plates, and d is the distance between the plates.

C = kA/d (l) According to equation (1), capacitance "C" increases with the surface area "A" of the conductive plates, and is inversely proportional to the distance "d" between the plates. When an electric potential is applied across the conductive plates, the capacitors store charge according to equation (2), where Q equals charge, and N equals voltage.

Q = C N (2) Briefly, a typical CDT cell may be comprised of an electric charge capacitor that contains electrodes, such as activated carbon electrodes, and a water dielectric. The application of an electrical potential to the electrodes can cause the hydrated ions of one or more salts within the water dielectric to be electrostatically attracted to the electrodes based upon the electric potential of the salt ions. For example, a salt such as sodium chloride ("ΝaCl") is hydrated when mixed with water to produce dissociation of the sodium cation from the chloride anion. The positively charged sodium cation is electro-statically attracted to the negatively charged plate whereas the negatively charged chloride anion is attracted to the positive plate potential. This ion attraction can proceed with the water flowing until all of the storage locations on the electrode surface are covered with ions. During this time, the output water ion content may be reduced or purified by the ions that remain within the CDT cell. After the ion storage locations are exhausted, the cell potential can be reduced to zero and the output water can be switched to a waste stream. When this occurs, the salt ions are re-hydrated within the water and swept out of the cell. This cycle, of alternatively purifying and discharging a waste, can be repeated indefinitely. CDT cells, sometimes referred to as flow through capacitors, are essentially capacitors of the electric double layer type designed to provide a flow path for water. There are many examples of CDT cells that are used in the art for water purification or similar purposes. In this regard, U. S. Pat. Νos., 5192432, 5186115, 5200068, 5360540, 5415768, 5547581, 5620597, 5415768, 5,779,891 issued to Andehnan (referred to herein as the "Andehnan patents" and incorporated herein by reference in their entireties) and U. S. Pat. No. 5538611 to Toshiro Otowa (referred to herein as the "Otowa patent" and incorporated herein by reference in its entirety) disclose traditional cylindrical structure capacitors. Other examples of geometries in the prior art include electric double layer capacitors with facing electrodes that may include spiral wound, stacked disk, flat plate, or bundles of polygonal electrodes. These capacitors may differ in terms of the pathway of fluid through the device. Generally, however, the ionic contaminants are pulled perpendicular to the flow path of the fluid or drawn into the electrode such as the activated carbon surface.

FIG. 1 (prior art) provides an illustration of a typical CDT cell. The CDT cell 10 consists of layers 11 that are held together by a mechanical clamp arrangement 12. FIG. 2 (prior art) provides a detailed illustration of a typical layer structure for a CDT cell. Water, or another electrolytic fluid, is retained within cell 10 through a manifold 13.

Referring to FIG. 2, each layer 11 consists of a conductive substrate 14, conductive silver- loaded resin glue 15, a carbon aerogel 16, and a water sealing gasket 17. Silver-loaded resin glue 15 bonds carbon aerogel 16 to one or more surfaces of conductive substrate 14. As FIG. 1 and FIG. 2 illustrate, water, or another electrolytic fluid, passes into fluid inlet 8 of manifold 13 through each layer of the cell in the direction shown by arrow 18 through open slots 19 before exiting the cell at fluid outlet 9 of manifold 13. Each conductive substrate 14 in the layer is connected either to an electrical input terminal 20 or an electrical output terminal 21. The electrical input terminal 20 and electrical output terminal 21 are of opposite polarity with respect to each other as shown in FIG. 1. Terminals 20 and 21 are typically connected across a DC power source (not shown in FIG.

1).

Upon applying a DC voltage across terminals 20 and 21, ionic contaminants electrostatically absorb to the carbon aerogel 16, with an equivalent amount of electronic charge. The CDT cell holds the charge and stores energy when disconnected from the power source, in the same manner as an ordinary capacitor. Typical voltages for a CDT cell for purifying water range from about 1.0 to about 2.0 N. The amount of voltage that an individual CDT cell can withstand is limited by the Νernst potential of the water or electrolytic fluid that flows through the cell. For example, the Νernst potential for the breakdown of water is 1.24N. As long as the charging voltage does not exceed the Νernst potential for electrochemistry to occur, the ions contained within the water absorb electrostatically to the charged surface. When the voltage of the cell exceeds the Νernst potential for the fluid that is processed through the cell, the fluid may generate hydrogen bubbles or draw excess current due to electrolysis at this voltage. Further, the electrodes within the cell may become corroded and will not perform as effectively in removing ions or other impurities from the fluid.

As described above, capacitive deionization of water, or another electrolytic fluid, involves inducing an electrical field across capacitor plates which surround a section of water, or other electrolytic fluid to be de-ionized, such that ions are electrostatically pulled out of the fluid and onto the capacitor plates. For systems in which water is the electrolytic fluid, the low breakdown voltage of water limits the allowable capacitor voltage to its Nernst potential, or 1.24 V, if no electrolysis of water is allowed to take place. To minimize the electrical losses and cost of a power conversion system, it would be beneficial to electrically connect a plurality of CDT cells in series. However, in such an arrangement, there are voltage balancing problems between the cells. The resistance of a CDT cell varies with the salinity of the water of the electrolytic fluid that passes through the cell. Due to the deionization process, the water or fluid at the input of the structure will have more ions, and therefore less resistance, than the water at the output of the structure. This resistance gradient normally makes it difficult to share voltage across a series stack of cells. There is a need in the art to provide methods and systems to allow even voltage sharing in an electrical series of cells. There is a further need in the art to maintain the resistance or balance the resistance of the fluid as it progresses through the cell.

Current systems incorporating CDT cells are low voltage, high current systems. In this regard, these systems require a large power supply to operate. There is a need in the art to provide systems incorporating CDT cells that allow smaller power supplies, or commercial power supplies, to operate economically and reliably. Moreover, there is a need in the art to provide systems incorporating CDT cells that allow for the purification of electrolytic fluids, such as water, at higher volumes.

These and other aspects of the invention will become more apparent from the following detailed description.

Summary of the Invention

The present invention relates to fluid purification systems incorporating capacitive deionization cells that are electrically connected to voltage balancing devices. In accordance with the present invention there has now been provided a system for the deionization of an electrolytic fluid comprising a plurality of capacitive deionization cells disposed between and in fluid communication with a fluid inlet manifold and a fluid outlet manifold. Each of the cells within the series is electrically connected in parallel to a voltage balancing device that is capable of sharing charge with the cells, such that the voltage is equalized among the plurality of cells.

In accordance with one embodiment of the present invention, there is provided a system for the deionization of an electrolytic fluid, the system comprising: a fluid inlet manifold and a fluid outlet manifold; a plurality of capacitive deionization cells disposed between and in fluid communication with the fluid inlet and outlet manifolds wherein each of the cells is electrically and hydraulically connected in series, and a plurality of pairs of anti-parallel diodes that are electrically connected in parallel to each of the cells for balancing voltage. In certain embodiments of the present invention, the pair of anti-parallel diodes comprise zener diodes. In accordance with a further embodiment of the present invention, there is provided a system for the deionization of an electrolytic fluid, the system comprising a fluid inlet manifold and a fluid outlet manifold; a plurality of capacitive deionization cells disposed and in fluid communication with the fluid inlet and outlet manifolds wherein each of the cells is electrically and hydraulically connected in series, and a plurality of capacitive deionization capacitors that are electrically connected in parallel to each of the cells for balancing voltage. In certain embodiments of the present invention, the capacitive deionization capacitors are comprised of the same layers as the layers that comprise the capacitive deionization cells.

Brief Description of the Drawings

The foregoing summary, as well as the following detailed description of the preferred embodiments, is better understood when read in conjunction with the appended drawings.

FIG. 1 (prior art) shows a typical CDT cell of the prior art. FIG. 2 (prior art) provides a detailed view of a layer structure for a typical

CDT cell of the prior art. FIG. 3 provides a side view of one embodiment of a CDT cell of the present invention.

FIG. 3a provides an electrical schematic of the CDT cell of FIG. 3.

FIG. 3b provides a view of the CDT cell taken along line A-A of FIG. 3. FIG. 4a provides a top view of a further embodiment of a CDT cell of the present invention.

FIG. 4b provides a side view of a further embodiment of a CDT cell of the present invention.

FIG. 5 provides an illustration of a deionization system that may incorporate one or more CDT cells of the present invention.

FIG. 6 provides an electrical schematic of an embodiment of the present invention.

FIG. 7 provides an electrical schematic of a further embodiment of the present invention. FIG. 8 shows a view of one embodiment of the present invention that incorporates a CDT cell similar to the embodiment of FIG. 3.

FIG. 9 shows a front view of an embodiment of the present invention, comprising a series of capacitive deionization cells comiected in parallel to a series of charge distribution capacitors. FIG. 10 shows an electrical schematic of an embodiment similar to that shown in FIG. 9.

It is to be understood that both the foregoing general description and the following detailed description are exemplary and are intended to provide further explanation of the invention as claimed. The accompanying drawings are included to provide a further understanding of the invention. In the drawings, like reference characters denote similar elements throughout several views. It is to be understood that various elements of the drawings are not intended to be drawn to scale.

A more complete understanding of the present invention, as well as further features of the invention, such as its application to other electrical or mechanical devices, will be apparent from the following Detailed Description and the accompanying drawings. Detailed Description of Preferred Embodiments

This present invention satisfies those needs in the art by providing systems, methods, and apparatuses that balance the voltage gradients within capacitive deionization ("CDT") cells, or arrays or systems comprising such cells, that are preferably electrically and hydraulically connected in series. In the systems, methods, and apparatuses of the present invention, there is provided voltage balancing devices that are electrically connected in parallel to the series of CDT cells. As electrolytic fluid progresses through the series of CDT cells, the cells closest to the fluid inlet remove a higher number of ions than the cells that are closest to the fluid outlet. The electrical resistance of the cells nearest the fluid inlet is therefore lower than the electrical resistance of the cells nearest the fluid outlet. The voltage-balancing device of the present invention shares charge with the CDT cells that it is electrically connected in parallel with such that voltage is equalized among the CDT cells within the series.

The systems and apparatuses of the present invention comprise a plurality of CDT cells that are electrically and hydraulically connected in series. FIG. 3 provides an example of one embodiment of a CDT cell 100 that may be used in the systems and apparatuses of the present invention. FIG. 3 a provides an electrical schematic of CDT cell 100 that may be used in the systems and apparatuses of the present invention.

Referring to FIG. 3 a, the power supply of the CDT cell 100 is shown as a DC power source 101 and an external resistance Rs 102. CDT cell 100 is depicted as two double layer capacitors 103 and 104, each of which represents the electrodes that comprise the cell with opposite polarity. Resistance R 105 is shown in parallel within capacitors 103 and 104, respectively, to represent that the cell electrical performance has a steady state DC current after the capacitors are fully charged. Resistance 105 within CDT cell 100 is undesirable because it implies that electrolysis may be occurring within cell 100 that can damage the cell components after continuous cycles. For example, in CDT cells where the electrolytic fluid may be salt water, chloride oxidation may occur at the anode and sodium reduction may occur at the cathode which creates gaseous by-products as well as other chemical species. Water gap resistance, Rw 106, is shown as a variable representing the variability of the ions within the electrolyte and the physical dimensions of gap length, or distance between the electrodes within the cell 100 and surface area of the electrode. Referring now to FIG. 3, in one embodiment, individual cell 100 is comprised of a plurality of layers of conductive substrates 107. FIG. 3 provides a side view of cell 100 with gasket material 99 removed to reveal the cell structure. Conductive substrates 107 are supported by rod 108. Rod 108 may comprise any retaining structure, such as a threaded screw or bolt, that acts to align more than one CDT cells within a series. Rod 108 is encased on one or both sides by a gasket material 99. Preferably, there are at least four rods 108, or at least one rod per side, to effectively retain and align the CDT cells within the series of cells. Gasket material 99 may be comprised of, but not limited to, silicone, rubber, or any other water impermeable material to retain the electrolytic fluid within the stack or array of CDT cells. Depending upon the modulus of the gasket material, gasket material 99 may further comprise an underlying structural support (not shown) to comprise the sidewalls of CDT cell 100.

Rods 108 hold and align conductive substrates 107 in place within the overall structure through one or more alignment holes, 109 within the substrate 107. FIG. 3b provides a top view of conductive substrate 107 taken along line A-A in FIG. 3 (with front gasket material 99 removed). Although conductive substrate 107 is shown has having a rectangular shape, it is understood that other geometries for conductive substrate 107 may be used without departing from the spirit of the present invention. Conductive substrate 107 also includes one of more apertures, 110, for the passage of an electrolyte or fluid through the cell. In a series of CDT cells, for example, it is preferable that the alignment holes 109 for support rods 108 and apertures 110 for electrolyte flow for each CDT cell be of uniform dimensions to allow for maximum alignment of the cells contained within the manifold or other housing. Conductive substrates 107 are generally flat, thin corrosion resistant, metallic sheets. In some embodiments, conductive substrates 107 may be comprised of titanium metal. While conductive substrate 107 may be a solid conductive material such as a metal, a fiberglass composite sheet with copper plated material may be preferred to reduce manufacturing cost and to ease solderability or bonding of substrate 107 to the high surface area material 111.

Conductive substrates 107 are preferably electrically connected to a DC power source (not shown in FIG. 3 and FIG. 3b). Alternatively, conductive substrates 107 may be connected to an AC power source with a controlled rectifier. Preferably, conductive substrates 107 further comprise terminals (not shown in FIG. 3 and FIG. 3b) that may be either an electrical input terminal or an electrical output terminal which are, in turn, electrically connected to a power source. The electrical input terminal and electrical output terminals are of opposite polarity with respect to each other so that the alternating conductive substrates may also be of opposite polarity (refer to FIG. 3). The amount of voltage that is applied to cell 100 is limited by the Nernst potential of the electrolyte that is passed through the cell as well as other factors such as, for example, the voltage drop in cell 100 components. The CRC Handbook of Chemistry and Physics (79th ed. 1998), pp. 8.21-8.31, provides Nernst potential values for a variety of reactions measured at 25°C and at a pressure of 1 atm. Using a DC constant power source, a voltage of about 0.5 to about 5 V may be applied to cell 100, depending upon the Nernst potential of the electrolytic fluid and other variables such as the voltage drop in cell 100 components. For cells in which the electrolytic fluid is water, the amount of voltage that may be applied to the terminals attached to the conductive substrate may range from about 1 V to about 2 V. Referring to FIG. 3, a high surface area material 111 is bonded to one or both surfaces of conductive substrate 107 to comprise the electrode and serve as either the cathode or anode depending upon its electrical polarity. High surface area material 111 may be a thin sheet that preferably covers a substantial portion of the surface of conductive substrate 107. Preferably, material 111 comprises a porous, conductive, monolithic material, such as a carbon aerogel or carbon aerogel composite. Carbon aerogels or carbon aerogel composites are preferable because the porosity, surface area, pore size, and/or particle size may be tailored over a broad range. The BET specific surface area of high surface area material 111 may range from about 400 to about 2,600 m²/g, preferably from about 600 to about 2,000 m²/g, more preferably from about 800 to about 1,600 m²/g. The pore size of the high surface area material may preferably be about 100 run or less, more preferably about 75 nm or less, or more preferably about 50 nm or less. In certain embodiments, high surface material 111 may be comprised of a solid matrix having interconnected colloidal-like particles or continuous intersecting fibrous chains having a fiber diameter of about 10 nm or less. Examples of high surface area materials that may be suitable for the CDT cells that are incorporated into the present invention may include, for example, the materials found in U. S. Pat. Nos. 5,190,610, 5,260,855, 5,385,802,

5,980,977, 5,993,996, and the article entitled "Carbon Aerogel Composite Electrodes, by Joseph Wang et al., in Anal. Chem. 1993, vol. 65, pp. 2300-03, the disclosures of which are incorporated herein by reference in their entireties. Further materials that may be suitable as high surface area material 111 include carbon nanotubes, or carbon tubes that are a few nanometers across and have a high surface area relative to its volume.

In a preferred embodiment of the present invention depicted in FIG. 3, there is provided an electrode that comprises a high surface area material 111 such as a carbon aerogel and an insulating spacer 112 both of which are conductively bonded to conductive substrate 107 with solder or other means of attachment known in the art. Even though FIG. 3 shows insulating spacer 112 and carbon aerogel layer 111 as distinctive layers, it is understood, however, that insulating spacer 112 and carbon aerogel 111 may be integrated into or be incorporated within carbon aerogel 111 to form one layer. Insulating spacer

112, which is preferably a thin layer that allows the flow of current to aerogel 111, may be comprised of any electrically insulating material, including but not limited to, alumina, polypropylene, polyester, polyimide, polycarbonate, PNC, polyamide, PBTP, KENLAR® (a poly-paraphenylene terephthalamide manufactured by DuPont Corporation of Wilmington, Delaware), ΝOMEX® (a poly-metaphenylene diamin manufactured by DuPont Corporation of Wilmington, Delaware), and DELRTΝ® (an acetal resin manufactured by DuPont Corporation of Wilmington, Delaware). In some embodiments, insulating spacer 112 is comprised of a polyester cloth weave lay-up. Preferably, insulating spacer 112 is porous to increase the bonding surface area between spacer 112 and carbon aerogel 111 as well as allow current to flow freely to carbon aerogel 111.

Insulating spacer 112 may preferably be comprised of a reticulated foam insulation spacer.

The bond between the carbon aerogel 111, and insulating spacer 112, depending upon the embodiment, with conductive substrate 107 to form the electrode may be formed via any bonding method known in the art. These methods may include, for example, the sputtering, plasma-spraying, vapor deposition, chemical vapor deposition, electroplating, or electroless plating of a thin layer of a high melting point temperature metal (not shown in FIG. 3) that is preferably applied to the side of each carbon aerogel element 111 that faces conductive substrate 107. The term, "high melting point temperature metal", as used herein relates to metals whose melting point is at least about 260°C or greater. This thin layer of a high melting point temperature material facilitates the low temperature solder bonding of aerogel 111 to conductive substrate 107 and may also avoid a wicking effect of the solder into the pores of the material 111. The term "low temperature solder bonding", as used herein, relates to solder bonding that occurs at temperatures of at least about 156°C or lower. Insulating spacer 112 also aids in avoiding the wicking effect of the solder into the pores of the material as well as enhances the electrical connection between conductive substrate 107 and aerogel 111. In certain embodiments of the present invention, the high temperature melting point surface that is applied to conductive substrate 107 may be additionally plated with a further high temperature melting point alloy, such as, but not limited to a tin lead alloy, to facilitate the low temperature solder bond to conductive substrate 107.

In other embodiments of the present invention, CDT cell 100 may comprise an integral conductive substrate 107 and high surface area material 111. In this embodiment, conductive substrate 107 may comprise a porous micro-mesh metal fabric, such as copper or other electrically conductive metal, that is surrounded by two layers of an electrically insulating material, such as a fiber-glass veil, prior to the application of the aerogel resin preparation. The micro-mesh metal fabric preferably has a conductivity value that is an order of magnitude higher than the high surface area material 111. The micro-mesh metal fabric may be made from a metal wire drawn from about 5 to about 20 micron diameter, preferably about 7 to about 15 micron diameter, and more preferably about 10 to about 13 micron diameter. The metal wire is then chopped to lengths of about 20 mm or below, preferably about 15 mm or below, and more preferably about 10 mm or below to provide metal fibers. The metal fibers are then calendered, to provide a cloth of uniform thickness, and sintered to provide a porous, stable cloth material. The micro mesh metal fabric and surrounding electrically insulating material may be infused with an electrically conductive resin material, such as a carbon aerogel, cured and pyrolized in a reducing furnace to form the carbon aerogel with an integral conductive substrate. FIGs. 4a and 4b provide the top and side view, respectively, of another embodiment of a CDT cell 200 that may be used in the present invention. As FIG. 4a and 4b illustrate, CDT cell 200 is comprised of a plurality of T-shirt shaped conductive substrates 201 having alignment holes 202 and fluid flow aperture 203; high surface area materials 204 having a central aperture for fluid flow; and a porous separator 205 having a central aperture for fluid flow. When assembled as shown in FIG. 4b, the apertures within the substrates 201, high surface area materials 204, and porous separator 205 are in alignment. T-shirt shaped conductive substrates 201 are preferably comprised of a thin, non-corrosive metal such as, for example, the materials used for conductive substrate 107 in CDT cell 100 of FIG. 3. Substrates 201 are electrically connected to a power source such as a DC power source via terminals on conductive substrates 201 (not shown in FIG. 4a and FIG. 4b) and during operation are of opposite electrical polarity with respect to each other. High surface area materials 204 are comprised of an electrically conductive, porous material such as a carbon aerogel, or any of the materials previously discussed in connection with the high surface area material 111 in CDT cell 100 of FIG. 3. High surface area materials 204 are held in mechanical compression with substrates 201. Porous separator 205 is inserted between high surface area materials 205 as shown in FIG. 4b. Porous separator 205 is comprised of an electrically insulating material, or any of the materials previously discussed in connection with insulating spacer 112 in CDT cell 100 of FIG. 3. Examples of suitable electrically insulating material may include, but are not limited to, any of the electrically insulating materials previously discussed. Unlike CDT cell 100 wherein the electrolytic fluid flows through the cell in a serpentine fashion, the electrolytic fluid in CDT cell 200 flows through aperture 203 in the center of the cell where it is directed through porous separator 205 from aperture 203 to the outside edges of the cell and adjacent to and in intimate contact with the high surface area materials 204 or electrodes.

CDT cells that are used in the present invention may operate in a variety of different ways to remove ions from an electrolytic fluid. Preferably, the CDT cells that are used in the present invention operate in two bipolar cycles that are composed of three phases: clean, static rinse, and dynamic rinse phases. The cycles are bipolar in that the three phases, the clean, static rinse, and dynamic rinse phases, are each conducted in two opposite electric polarities. FIG. 5 provides an illustration of a deionization system that may incorporate one or more CDT cells of the present invention. It is understood, however, that the present invention is not limited to the system of FIG. 5. As FIG. 5 illustrates, one or more CDT cells 100 is preferably in a system that comprises an electrical circuit 113 and a fluid circuit 114 wherein fluid circuit 114 regulates the flow of the fluid stream through one or more CDT cells 100 under the control of electrical circuit 113. Electrical circuit 113 comprises, inter alia, a power supply 115 to power one or more CDT cells 100 and an amplifier 116, which is electrically connected across positive terminal 117a and negative terminal 117b and in electrical communication with processor 128 and switch 118 to control the flow of power and fluid to the cell(s) depending upon whether the cell(s) is charging (i.e., during the cleaning or deionization phase) or discharging (i.e., during the static rinse phase). Fluid circuit 114 comprises, inter alia, a pump 119 to direct the flow of feed fluid in the direction of the arrows through the CDT cell(s), a valve 120 that is interposed between pump 119 and a electrolytic fluid feed reservoir 121, a pressure flow meter 122 to measure the pressure of the input fluid into the CDT cell(s), a fluid input conductivity meter 123 to measure the amount of ions present in the fluid at the input end of the cell(s), a fluid output conductivity meter 124 to measure the amount of ions present in the fluid at the output end of the cell(s), a plurality of output valves 125 to direct the outgoing flow of fluid from the cell(s) to either a clean fluid output 126, a waste fluid output 127, or into the electrolytic fluid reservoir 121. The system further comprises a processor 128 that is in electrical communication (see dashed lines on FIG. 5) with the conductivity meters 123 and 124, pressure flow meter 124, and the input 120 and output valves 125 to control the different phases of the process cycle. Additional components that may be added to fluid circuit 114 may include, for example, thermocouples to monitor the temperature at the fluid inlet and/or outlet end and pH sensors to measure the pH level at the inlet and/or outlet end which are in electrical communication with processor 128 for process control and monitoring. Processor 128 is also operatively connected to amplifier 116 which is connected across terminals 117a and 117b to switch 118 to control the charging or discharging of CDT cell(s) 100 based upon the readings from conductivity meters 123 and 124 and other criteria.

Based upon the measurements from conductivity meters 123 and 124, and/or other criteria, processor 128 will control amplifier 116 to either open switch 118 to charge cell(s) 100 for the clean, or deionization phase, of operation or close switch 118 or disconnect power from power supply 115 for discharge of cell(s) 100 i.e., the rinse phase. During the clean phase, a continuous supply of power is applied to the electrodes of CDT cell(s) 100. The clean phase can be viewed as the "charging" stage in which the electrodes of the CDT cell(s) are being charged during the process of removing the ions from the electrolytic fluid. Using the CDT cell 100 depicted in FIG. 3, an electrolytic fluid such as water travels through cell 100 in a serpentine fashion in the direction shown by the arrows. This allows the fluid to be in intimate contact with the high surface area materials 111 of opposite polarity that act as electrodes. The ions or other impurities within the electrolytic fluid become ionized and are electrostatically attracted to the electrodes, or the high surface area material 111, as the fluid progresses through cell 100. Referring to FIG. 5, the "clean" fluid, or fluid in which the ions are removed, progresses through and out of the cell(s) to clean fluid output 126. After a sufficient amount of ions are extracted from the fluid and become stored upon high surface area material 111, and the amount of ions in the output fluid begins to rise as the ion removal rate is reduced below the ion arrival rate in the input fluid, the "clean phase" is ended. A conductivity meter such as 124, or similar means to determine the amount of ions within the output water, may be used in conjunction with cell(s) 100 to detect the end of the clean phase. Thus, the time duration of the clean phase varies based a variety of factors that include the initial level of ions within the electrolyte, measured by conductivity meter 123 in comparison to the level of ions within the clean output, if any, and the ion storage locations of high surface area material 111.

During the next phase of operation of the CDT cell(s), or the static rinse phase, the flow of the electrolytic fluid is stopped by, for example, closing inlet valve 120, and the power supply is turned off by, for example, closing switch 118. This leads to a residual decaying voltage resulting from the capacitance energy discharge of the previous phase, or clean phase. The static rinse phase can be viewed as the "discharging" stage in which power is turned off to the electrodes of the CDT cell(s) and the stored energy of the cell(s) is being discharged. Energy is returned from the cell(s), a portion of which is being consumed by the internal and external resistive losses of the cell(s) and power supply. The other portion of energy allows for the rehydration of the ions stored on the high surface area material 111 in the static water that remain within the cell(s). This cycle may continue for a fixed period of time.

The last phase, or the dynamic rinse phase, begins after the static rinse phase is completed. During this phase, the electrolytic fluid flow is turned on to allow fluid to flow through the cell(s). However, the output of the cell(s) is directed to the waste fluid output 127. Power is supplied to the cell but the electrical polarity and value is chosen to reverse the residual cell voltage experienced during the static rinse phase. For example, a static rinse that begins at 0.5 N will be followed by a dynamic rinse at -0.5 N. The ionic concentration of the "waste" fluid output reaches its highest concentration, or peak release, due to the static rinse phase in which the ions were accumulating within the water trapped in the cell(s). The dynamic rinse phase continues for a fixed period of time during which the ions from the previous clean cycle are removed from the high surface area material, or electrodes.

The systems and apparatuses of the present invention preferably comprise a plurality of CDT cells that are electrically and hydraulically connected in series. As discussed previously, the resistance of the fluid within the CDT cells varies with the amount of ions present within the fluid. For a series of CDT cells, the electrical resistance of the cells near the inlet of the series will be less than the resistance of the cells near the output of the series. To remedy this, a voltage balancing device ("NBD") may be employed, that is electrically connected in parallel to each CDT cell within the series, to obviate this resistance gradient. This voltage balancing device may include, for example, additional capacitors or diodes. It is anticipated that there may be other devices that may be connected in parallel with the CDT cells within the series that may balance the voltage across the series without departing from the spirit of the present invention.

FIGs. 6 and 7 provide electrical schematics of two embodiments of the present invention incorporating a plurality of CDT cells such as the CDT cell presented in FIG. 3. The capacitive deionization cells 100, which are electrically and hydraulically connected in series, are electrically connected in parallel to a voltage-balancing device. In the embodiment provided in FIG. 6, the voltage-balancing device comprises a pair of zener diodes 207. In the embodiment provided in FIG. 7, the voltage-balancing device comprises a pair of anti-parallel diodes 208. In embodiments such as FIG. 6 where zener diodes are used, the break over (or forward drop of ordinary diodes) value of zener diodes will be set appropriately for the electrolytic fluid being de-ionized to prevent electrolysis of the fluid. For example, where the fluid being de-ionized is water, diodes 207 would be set to break over at approximately 1.2 volts. The diode current that flows at diode voltage break-over will allow the deionization of the higher conductivity series cell forcing a balancing of voltages in the series string of capacitors. This electronic arrangement may facilitate the transportation of charge to capacitors elsewhere in the series or cells that are not yet voltage restricted. In one embodiment of the present invention, the diodes are surface mounted onto the conductive substrate as shown in FIG. 8. In this configuration, the diodes 210 may be conveniently maintained within the same housing of the cell 100. In certain embodiments, the diode may be surface mounted onto an isolated conductive pad 211 for CDT cells in which a copper clad fiberglass composite is used as the material for conductive substrate 107. The isolated pad 211 is used to bus one end of the diode to the next capacitor layer both above and below in a series string. In other embodiments, the diodes may be external to the cell.

FIG. 9 provides another embodiment of the present invention, wherein the voltage-balancing device is a series of charge distribution capacitors 300 that are connected in parallel to a stack of capacitive deionization cells 110. In preferred embodiments, stack 110 of capacitive deionization cells 100 are connected electrically and hydraulically in series. During operation, an electrolytic fluid such as water travels through the stack 110 in a serpentine fashion in the direction shown by the arrows 150. Electrolytic fluid that passes through the stack 110 is not exposed to the stack of charge distribution capacitors 300. Capacitors 300 may be regarded as "no flow" capacitors and may contain a highly ionic fluid as its dielectric. In some embodiments of the present invention, capacitors 300 may be charged, for example, through stack 110 of capacitive deionization cells. While FIG. 9 shows the capacitive deionization capacitors and the charge distribution capacitors as sharing conductive substrates (either a single substrate or two axially aligned and coupled together), other configurations of connecting the elements in parallel may be employed, including having the elements housed in separate apparatuses. FIG. 10 illustrates an example circuit model of an embodiment similar to that shown in FIG. 9. The electrical arrangement of the systems and apparatuses of the present invention, in which the voltage is balanced as the fluid with variable ionic content progresses through the system, allows the system or apparatus to be powered by high voltage, low current power supplies rather than low voltage, high current power supplies, although, of course one can use the latter if desired. The amount of power to be supplied to the system or apparatus may vary depending upon the number of stacks within the apparatus and the number of cells that comprise each stack. The figures, and corresponding written description above, show examples of single cell configurations for using the systems of the present invention, particularly for illustrating the voltage balancing means in conjunction with capacitive deionization capacitors. The systems of the present invention preferably comprise a plurality of cells for removing ions from high volumes of fluid, i.e., processing about one million or more gallons per day. The plurality of cells can be similarly configured or configured and arranged in different manners in order to customize the systems for varying utilities, including combining the cells as illustrated with the present invention with those known in the art. While the present invention has been particularly shown and described with reference to the presently preferred embodiments thereof, it will be understood by those skilled in the art that the invention is not limited to the embodiments specifically disclosed herein. Those skilled in the art will appreciate that various changes and adaptations of the present invention may be made in the form and details of these embodiments without departing from the true spirit and scope of the invention as defined by the following claims.

Claims

We claim:

1. A system for the deionization of an electrolytic fluid, the system comprising: a fluid inlet manifold and a fluid outlet manifold; and a plurality of capacitive deionization cells electrically connected in series and disposed between and in fluid communication with the fluid inlet and outlet manifolds; wherein each cell is electrically connected in parallel to a voltage-balancing device capable of sharing charge with the cell such that voltage is equalized among the plurality of cells.

2. The system of claim 1, wherein the capacitive deionization cells comprise a plurality of layers defining a passage for electrolytic fluid therethrough.

3. The system of claim 2, wherein the layers comprise high surface area material.

4. The system of claim 3, wherein the high surface area material comprises a carbon aerogel.

5. The system of claim 1, wherein the voltage-balancing device is a charge distribution capacitor.

6. The system of claim 1 , wherein the voltage-balancing device is a pair of anti- parallel diodes.

7. The system of claim 6, wherein the diodes are zener type.

8. The system of claim 7, wherein the zener diodes are set to break over at 1.2 volts.

9. The system of claim 6, wherein the diodes are surface mounted onto the capacitive deionization cells.

10. The system of claim 1 , wherein maximum voltage of each of the cells is from about

1.0 to about 2.0 volts.

11. A system for the deionization of an electrolytic fluid, the system comprising: a fluid inlet manifold and a fluid outlet manifold; a plurality of capacitive deionization cells disposed between and in fluid communication with the fluid inlet and outlet manifolds wherein each of the cells is electrically and hydraulically connected in series, and a plurality of pairs of anti-parallel diodes that are electrically connected in parallel to each of the cells for balancing voltage.

12. The system of claim 11 , wherein the diodes are zener type.

13. The system of claim 12, wherein the zener diodes are set to break over at 1.2 volts.

14. The system of claim 11, wherein the diodes are surface mounted onto the capacitive deionization cells.

15. A system for the deionization of an electrolytic fluid, the system comprising: a fluid inlet manifold and a fluid outlet manifold; a plurality of capacitive deionization cells disposed and in fluid communication with the fluid inlet and outlet manifolds wherein each of the cells is electrically and hydraulically connected in series, and a plurality of capacitive deionization capacitors that are electrically connected in parallel to each of the cells for balancing voltage.

16. The system of claim 15, wherein the capacitive deionization cells comprise a plurality of layers defining a passage for electrolytic fluid therethrough.

17. The system of claim 16, wherein the capacitive deionization capacitors comprise the same layers as the cells.