Multi-path split cell spacer and electrodialysis stack design

Abstract

An electrodialysis method and apparatus include a source of concentrate fluid, a source of dilute fluid, a collector of treated concentrate fluid, a collector of dilute fluid, an anode and a cathode. A plurality of generally planar spacers are interleaved with a plurality of membranes to define a plurality of cells providing electrically conductive fluid connection between the anode and the cathode. Each of the spacers comprises a gasket that defines a first aperture and a second aperture. Each of said first and second apertures define an independent cell between interleaved membranes. The symmetrical, multiple split cell spacer configuration channels fluid flow through two or more narrow and elongated paths. The split cell arrangement allows for operation of the stack in parallel or in series. The invention improves the ion removal efficiency of a given membrane area, requires significantly less energy than other electrodialysis systems and substantially reduces stack assembly, materials and fabrication costs.

Description

[0001] Not Applicable[0002] Not Applicable[0003] 1. Field of Invention[0004] This invention pertains to a method and apparatus for the purification and reuse or disposal of polluted liquids.[0005] More particularly, this invention pertains to an electrodialysis stack for the removal and concentration of ions from aqueous solutions and certain aqueous / organic solutions.[0006] 2. Description of the Related Art[0007] There are presently a number of systems for treating and recycling aqueous and aqueous / organic waste streams on the market. Present state of the art systems, including de-ionization methods that are available to industrial waste stream generators, are deficient in their ability to consistently and economically produce a cleansed fluid of sufficient quality that can be continuously recycled and reused, especially in the case of small to medium volume liquid waste generation. The initial high cost of purchasing many of these systems is beyond the economic resources of many b...

AI Technical Summary

Benefits of technology

[0015] The novel multiple split cell design can be operated in parallel as a roughing de-mineralizer (or operated in a batch recirculation mode) or operated in series allowing for single-pass continuous flow. When operated in the series mode, the split cell design permits separate voltage and flow control when a higher purity fluid is desired. The split cell design permits separate cell control of concentrate stream salinity content. The roughing cell may be operated with a higher concentrate stream TDS, with the salinity of the polish cell concentrate stream correspondingly reduced to the salinity content of the de-mineralized stream. This prevents back diffusion and allows for efficient removal of ions in feed water of low TDS. In short, the split cell design incorporates the benefits of hydraulic and electrical staging without the inherent complexity and expense of commercial electrodialysis systems.

[0017] It is an object of the present invention to provide a simpler stack assembly of low production cost. Stack assembly cost is reduced as a result of the novel split cell / gasket geometry. A reduced number of expensive machined components are required. Simpler and lighter components lower material costs for a given membrane area. Inexpensive center bolts provide an alternative to typical hydraulic force application arrangements, which also improves the uniformity of the clamping force distribution on the gasket area. Threaded bolts also reduce assembly labor time, i.e., it is easier to hold the configuration in place and also facilitate change-out of membranes when they are spent, as the cell geometry reduces stress on the end points as is found inherent with some conventional stack assemblies.

[0019] The cell gasket geometry can be more easily and inexpensively fabricated from a larger range of materials in comparison to conventional designs, allowing the process to be used in more harsh environments through the use of a wide range of chemically resistant materials. It is still another object of the present invention to provide an apparatus and method that combines a unique arrangement of small to intermediate scale unit operations for the economical recovery / reclamation of a wide range of fluids and that can also be scaled to a large system size, further improving the economics of large scale electrodialysis systems by reducing both capital and operating costs.

Problems solved by technology

Present state of the art systems, including de-ionization methods that are available to industrial waste stream generators, are deficient in their ability to consistently and economically produce a cleansed fluid of sufficient quality that can be continuously recycled and reused, especially in the case of small to medium volume liquid waste generation.

The initial high cost of purchasing many of these systems is beyond the economic resources of many businesses, thus prohibiting cost-effective recycling for environmental compliance or beneficial reuse.

The most serious design problem for both flow arrangements for multi-membrane and multi-cell stacks is that of assuring uniform fluid flow to the various compartments and effective transport of the ions to the membrane surfaces.

These difficulties are the major obstacles to simple, single stage demineralization of brackish liquids.

In particular, reducing concentration polarization is one of the most important design issues for electrodialysis.

This water splitting is extremely detrimental to electrodialysis efficiency.

Polarization is objectionable not only from the standpoint of the inefficient increase in energy consumption, but also the change of pH of the concentrate stream as a result of water splitting, which tends to cause scale deposition.

The number of cells in a stack is limited mainly by the practical considerations of assembly and maintenance requirements.

Since the failure of a single membrane can seriously impair stack performance, the necessity to be able to disassemble and reassemble a stack to replace a membrane, and the necessity to be able to perform this quickly and easily, effectively limits the number of membranes that can be practically utilized in a stack.

However, use of single electrodes for larger assemblies typically causes end-cell heating that results in rapid membrane deterioration.

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