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FLUID ELECTRICAL CONNECTED FLOW-THROUGH ELECTROCHEMICAL CELLS, SYSTEM AND METHOD
REFERENCE TO PRIOR APPLICATION
 This application is based on and claims priority from U.S. Provisional Patent Application Serial No. 60/210, 035, filed Jun. 7, 2000, hereby incorporated by reference in its entirety.
 This invention was funded under contract with the United States Defense, Advanced Research Projects Agency (DARPA), under Contract No. DAAD 19-99-C-0033. The United States government may have certain rights in the invention.
BACKGROUND OF THE INVENTION
 Flow-through electrochemical cells (FTC or FTCs) generally include flow-through capacitors, flow-through batteries, and flow-through fuel cells. FTCs are useful for energy storage, energy generation, and water purification. FTCs differ from ordinary electrochemical cells in that the tonically conductive solution between the electrodes, or the electrolyte, is introduced into the cell via one port, flows through or between the electrodes, and exits via another port or ports. The cell may be configured with a cartridge holder or container. FTCs are described in U.S. Pat. Nos. 5,192, 432, issued Mar. 9, 1993; 5,196,115, issued Mar. 23, 1993; 5,200,068, issued Apr. 6, 1993; 5,360,540, issued Nov. 1, 1994; 5,415,768, issued May 16, 1995; 5,425,858, issued Jun. 20, 1995; 5,538,611, issued Jul. 23, 1996; 5,547,581, issued Aug. 20, 1996; 5,620,597, issued Apr. 15, 1997; 5,748,437, issued May 5, 1998; 5,779,891, issued Jul. 14, 1998; and 5,954,937, issued Sep. 21, 1999, each hereby incorporated by reference.
 An FTC suffers the limitation that each FTC cell requires a high operating current or amperage. The amperage required to operate the cell increases with cell size, flow rate, and concentration of ions in solution. High amperage power is cumbersome and expensive to supply, requiring heavy duty relays and wires. Operating an FTC at too low a voltage leads to poor performance, so that, for example, when used for water purification, the water is not purified sufficiently. Operating an FTC at too high a voltage may lead to cell burnout, hazardous gas generation, or oxidation and deterioration of electrodes. For example, under some conditions, it is desirable to limit the maximum voltage of an individual cell in a carbon electrode FTC to 1 volt or less. This creates a need to monitor and control each cell in a series stack individually. Therefore, a need exists for a means of monitoring and controlling voltage in individual cells, so as to be able to operate the flow-through capacitor with ordinary, higher voltage power, while being able to control the voltage of each individual cell.
SUMMARY OF THE INVENTION
 The invention comprises an FTC system and method, which include a plurality of FTCs in electrical and fluid connection.
 A controlled FTC system and method which include a plurality of FTCs connected in an electrical series
arrangement with fluid flow-through, and having an electrical control circuit to monitor and control the voltage on each individual FTC in the series.
 The invention comprises a flow-through electrochemical system which includes a plurality of flow-through electrochemical cells, the system configured to place each of the cells in electrical connection and in fluid connection with each of the other cells. The invention also includes a fluid stream, a means for connecting the system of the invention to a power supply, a means for monitoring the voltage of each of a plurality of cells and a means for controlling the voltage of each of the plurality of cells.
 A means for controlling the system of the invention can include a valve, for example, a bypass valve, the bypass valve can be actuated in a feedback loop to control the voltage of each of the cells of the invention. The valve of the invention can be an incremental valve, a differential valve, or a linearly-actuated valve. The controlling means of the invention can also include a transistor or a zener diode.
 In one embodiment, the flow-through electrochemical system of the invention includes a flow-through capacitor and a plurality of cells that form a series stack. The charge of the series stack can be proportional to the sum of the capacitance of each of the cells multiplied by the voltage of each of the cells.
 The means for monitoring the voltage of the cells of the invention emits a signal, the signal is compared to a reference signal so as to activate the controlling means when the comparison is outside a preset range, whereby the controlling means decreases the extent of fluid connection between one or more of the cells and the remaining cells of said plurality of cells in the system.
 The monitoring means of the invention can include a differential amplifier, which amplifier's signal is inverted. The monitoring means of the invention can further include an error amplifier which emits a signal.
 The electrical connection between cells may be a series connection or a parallel connection. The fluid connection between cells may be a series connection or a parallel connection. Preferably, the electrical connection of the invention is a series connection, and the fluid connection of the invention is a parallel connection.
 In one embodiment, the system of the invention can be an electrical generator. The system of the invention further can also be an electrical storage system or a water purification system. Fluids useful in the invention can be water, water-soluble ionic solutions, or fuels, for example, gasoline, methane, or hydrocarbons. Additional fluids useful as fuels are known to those skilled in the art.
 The method of the invention can include a method of removing a chemical species from water, the method including the steps of providing the flow-through electrochemical system of the invention, the fluid stream being a water stream. The chemical species may be absorbed by one or more of the cells so as to remove the chemical species from the water stream.
 Another method of the invention can include a method of generating electricity by the system of the invention, in which case and the fluid stream of the system is a
fuel stream. The method of the invention includes operating the system of the invention, the fluid stream of the invention being a fuel stream.
BRIEF DESCRIPTION OF THE DRAWINGS
 FIG. 1 shows an FTC system with a plurality of FTCs in series and with an error control circuit;
 FIG. 2 shows, in greater detail, a section of the circuit of FIG. 1;
 FIGS. 3A and 3B show further separate, optional embodiments of the error control circuits;
 FIG. 4 shows further separate, optional embodiments of the error control circuits;
 FIG. 5 shows further separate, optional embodiments of the error control circuits; and
 FIG. 6 shows an FTC with separate electrically isolated monitory leads.
 To achieve a system of FTCs, the flow-through capacitor with ordinary, higher voltage power, while being able to control the voltage of each individual cell, multiple FTCs are connected in series. The voltage of the series stack will be additive, proportional to the multiple of the individual cell voltages, and the amperage will be proportionately reduced, thereby obtaining a system which utilizes the same amount of power, but with higher volts and less amps. In one embodiment combined in electrical connection in series, the cells are interconnected by manifold valve means, so that fluid flow goes through each cell.
 A preferable option is series electrical connection and parallel fluid connection. The parallel fluid flow may be achieved by a manifold valve or a series of linearly-actuated valves with feedback control from flow or pressure controllers in order to maintain equal flow through each cell. For example, flow-through capacitors are connected electrically in series, and fluid flow is connected in parallel, by a manifold valve, or with interspersed bypass valves, such as in FIG. 5. Fluid flow in parallel to an electrical series connected flow-though electrochemical cell stack is particularly advantageous as a means to maintain steady voltage among individual cells. This is especially important where flow-through capacitors are employed, since these cells change voltage per unit time. Parallel fluid flow-through electrically connected in series flow-through capacitors helps to maintain similar voltages among each of the cells. This flow may be equally distributed by control valves or adjusted individually for each cell as a means to maintain voltage or product water quality according to this invention. Alternatively, electrical connection in series, combined with fluid flow in series, would be useful in certain instances where adding flow-through capacitor cells in fluid series was of interest, to increase percentage purification or to add additional purification stages. Downstream capacitors, in this case, could be sized to be larger than the upstream ones, as an aid to achieve similar capacitance of each cell in the electrical series stack. For simplicity and for the purposes of this invention, it is understood that a series cell is any combination of parallel FTCs that are connected in series, either electrically or in a fluid sense. For example, one or
more individual FTCs may be electrically connected in parallel. These combined parallel FTCs may in turn be connected in series. Therefore, any combination of electrical and fluid series and parallel connection is possible. The amperage draw is directly proportional to the size of the electrical series connected cells. This size may be varied, dynamically if desired, in order to adjust to changing power availability. For example, if high amperage but lower voltage power is available, it may be desirable to parallel connect individual FTC's in order to provide larger series connectable units. For example, two or more FTC cells at a time may be hooked electrically in parallel, and these combined units of two cells or more may in turn by hooked electrically in series. An interesting option would have flow initially parallel through the individual cells, but switch during the charge cycle to series flow through the entire stack, or through the bundled parallel connected cells that form the series units within the series stack, in order to maintain product purity for a longer amount of time in a given charge cycle.
 When connecting FTCs electrically in series, a problem arises in that the cells do not necessarily self adjust to the desired voltage. Parallel flow is useful to maintain similar voltages between individual cells of the series stack. In addition to parallel flow, individual FTC monitoring and control are a preferred embodiment of this invention. Individual cells may deviate from each other, in spite of parallel fluid flow, due to a number of factors, including the difficult to manufacture uniform cells that maintain the same capacitance or charge characteristics during the life of the cell. It is desirable to control both the individual cell voltages in order to prevent overcharging individual cells. Should a cell fail entirely, it is desirable to cut off the flow so as to maintain product water quality. Should a cell fall within a desired range, it is desirable to regulate the individual cell voltage. This may be done by either electronically or by utilizing fluid flow as a means to regulate voltage. If done electronically, it is necessary to combine this with a means to shut off the flow cell from fluid flow so as to protect the product water quality. It is further desirable to control these voltages in such as way as to be able to set a limit on the maximum voltage an individual cell may reach.
 There is a large amount of literature on how to control electronically series electrochemical cells of the non-flow type. All of these means can be applied to control electronically FTCs, when combined with the flow control means of this patent, including without limitation: U.S. Pat. Nos. 4,238,721; 4,719,401; 5,764,027; 5,773,957; 5,821, 733; 5,886,503; 5,969,505; 5,982,143, each hereby incorporated by reference. These methods utilize electronic means such as diodes and resistors, to regulate the-voltage to each individual electrochemical cell in the series stack. FTCs connected electrically in series provide the additional option of being able to utilize valves to regulate the individual cell flow and/or voltages, or as a shut-off to stop the flow of electrolyte from a failed flow-through capacitor cell, in order to protect the product water quality, or to prevent additional fuel or fluid from entering a failed fuel cell or failed vanadium redox battery in an electrical series stack of such cells. Generally, voltages, amperages, and rates of change of volts and amps may be measured for individual cells and input into a logic means, such as an alogorithm, that is used to regulate the individual cell voltages according to the present invention. This logic means may be a com