Power efficient flow through capacitor system

Abstract

The invention features a flow-through capacitor system that achieves enhanced power efficiency by sequential control and actuation of at least two or more flow-through capacitor cells within the flow-through capacitor system. Alternatively or in addition, power efficiency is enhanced by integrating the purification stages of the system, for example, by placing more than one cell within a single cell casing. Preferably, integrated stage flow-through capacitors are controlled sequentially.

Description

REFERENCE TO PRIOR APPLICATION [0001] This application is based on and claims priority from U.S. provisional patent application Ser. No. 60 / 492,938, filed Aug. 6, 2003, which is hereby incorporated by reference.FIELD OF THE INVENTION [0002] The field of the invention is systems for capacitive deionization of fluids by the use of flow through capacitors. BACKGROUND OF THE INVENTION [0003] It is generally recognized that, in order to purify concentrated water, flow-through capacitor purification systems need to be staged. It is an objective of the present invention to improve the staging and power efficiency of flow-through capacitors. Power efficiency is a measure of how well power is distributed in a multi-cell system, and is defined here as the averaged percent of power needed by a flow-through capacitor system divided by the system's peak power needs. Staging efficiency is a measure of how well a staged system is designed to limit the inter-stage mixing caused by inter-stage dead ...

AI Technical Summary

Benefits of technology

[0006] The integrated stage design embodiment of the present invention eliminates the need, cost, and complication of connecting separate cartridge holders per stage by containing multiple stages within the same cartridge holder. This integrated stage design reduces the band broadening that would otherwise be caused by mixing of the band of purified water with dead volume as it moves from stage to stage. Staging efficiencies of 50% or more are possible by using sequential charge cycles coupled with integrated stage design. Another advantage achieved by organizing a flow-through capacitor system so that some or all stages are physically integrated is to diminish the amount of dead volume that otherwise exists between the capacitor layers and the inside the walls of the cartridge holder or capacitor container.

[0007] The integrated stage design of the present invention incrementally sharpens purified and concentrated bands of feed solution as it flows from stage to stage. In individually staged capacitors of the prior art, a dead volume exists between each multilayer capacitor cell and the internal walls of the housing of the cartridge holder. In the integrated stage embodiment, each stage shares common capacitor material layers. Only the current collectors, or, where electrodes are conductive enough not to need a current collector, the electrodes, are independently actuated and electrically separated from each other. Therefore, multiple stages can share the same cartridge holder, thereby eliminating the need for separate current collectors. Eliminating excess dead volume through integrated staging allows operation of the capacitor at lower voltage while, at the same time, obtaining a deep purification peak. The result of this is that the capacitor may be operated at lower, more energy efficient voltages.

[0009] An additional advantage of the sequential charging system of the present invention is to provide power in steps between multiple cells in order to optimize peak power usage to allow use of lower wattage, less expensive power supplies, so as to avoid the requirement for peak power at the initial application of voltage and distribute power to banks, or stages, of flow-through capacitor cells which may be fluid or electrically staged in a combination of parallel or in series. By sequentially spreading out the application of peak power to individual cells in a multi-cell system, power efficiencies of up to 50% to 100% are possible. In other words, power usage may approach the averaged power needed over the sum of the individual cell cycles.

[0011] Load leveling may be achieved by such sequential control of flow-through capacitors cells according to the present invention whereby capacitor cells are charged or discharged in a timed sequence. In doing so, the present invention avoids the multiplication of peak power needs, thereby minimizing the size and cost of power supplies required to power a multiple flow-through capacitor system. The cells may be progressively powered or charged in parallel, or in series. If powered or charged in series, the voltage is stepped up as each cell is switched in an additive sequence onto the others in series. Parallel cells may be powered or charged by switching onto a common bus. Individual cells may have individual or common power supplies. Flow-through capacitor cells can be integrated within a single cartridge holder, or may be discrete cells in a combination of series or parallel electrical or fluid flow. Upstream cells within an integrated stage cartridge holder, or individual stages with one cell per cartridge holder, or groups of cells, may be charged first, then additional downstream stages or cells are charged with a time delay. Cells connected together, either singly or in groups, in parallel or series in an electrical or fluid flow sense, may be sequentially actuated or controlled according to the present invention. This time delay may be selected so that the peak capacitive charging peaks do not overlap, in order to obtain a lower average peak charging current.

Problems solved by technology

The mixing effect also leads to a need to operate with greater numbers of stages, and may reach a lower voltage limit, as voltage is lowered when used with concentrated water such as sea water.

Charging banks or stages of capacitors all at once multiplies this peak power, thereby increasing the wattage rating and cost of power supplies needed to provide this power.

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