Chemistry: electrical and wave energy – Processes and products – Electrophoresis or electro-osmosis processes and electrolyte...
Reexamination Certificate
2001-04-05
2002-11-19
Phasge, Arun S. (Department: 1741)
Chemistry: electrical and wave energy
Processes and products
Electrophoresis or electro-osmosis processes and electrolyte...
C204S533000, C204S536000, C204S632000, C204S634000
Reexamination Certificate
active
06482304
ABSTRACT:
The present invention relates to an apparatus for a method of recirculating electrodeionisation involving improved purification of purified water.
Apparatus and methods for electrodialysis to provide purified water are well known, see for example our GB-A-2311999 and U.S. Pat. No. 4687561. Generally, water to be purified is passed along a deionising path set between or along an anode and a cathode. The application of a potential difference between the anode and cathode causes anions and cations in the impure water to migrate towards their respective attracting electrodes through perm-selective membranes. A concentrating path is arranged therewith to collect and remove the unwanted anions and cations.
The purified outflow water from such apparatus is then available for use. However, the general rates of flow of water through such apparatus do not allow a significant volume of purified water to be available for use quickly. The alternative is to collect the purified outflow water in a holding tank, from which a larger volume of water could be drawn when desired. However, water held in a tank, especially that at high purities such as <0.1 &mgr;S/cm, absorbs impurities from the environment, such as carbon dioxide from the atmosphere thus increasing its conductivity.
It is an object of the present invention to provide an electrodeionisation method and apparatus which is capable of providing a volume of water of a high ionic purity ready for use when desired.
Thus, according to one aspect of the present invention, there is provided an electrodeionisation apparatus comprising a first deionising flow path for water to be purified through an anion exchange material and/or a cation exchange material, in either order where both materials are used, and an integral second deionising flow path through an anion exchange material and a cation exchange material, in either order, wherein the outflow from the first path is held in a holding tank prior to passage through the second flow path, and the outflow from the second path is available for use.
Optionally, part or all of the second path outflow could be returned to the holding tank, e.g. when not required for use.
The recirculation of the already purified water in the holding tank maintains the water in the holding tank at a higher standard than otherwise ‘standing’ purified water.
Outflow from the second path may be passed around a ringmain with one of more take-off points before any remaining water is returned to the tank.
In one embodiment of the present invention, purified water held in the holding tank could be separately made available for use. Thus, the present invention could provide for the provision of purified water from the holding tank directly, and/or of further purified water available directly from the outflow of the second deionising flow path. Water from the outflow of the second deionising flow path will usually be at a higher purity than water in the holding tank.
The holding tank may, and generally will, however hold a relatively substantially volume of purified water, all of which is immediately available for use, whilst the time for collection of direct further purified water from the outlet of the second deionising flow path is dependent on the flow rate therefrom.
Preferably, the anion exchange material is an anion exchange resin, and the cation exchange material is a cation exchange resin. Also preferably, the exchange materials are held in separated chambers.
Preferably, the first deionising flow path involves both an anion exchange material and a cation exchange material in either order.
If necessary or desired, the anode and/or cathode could be housed within chambers housing the anion and/or cation exchange materials. Preferably, the anode and/or cathode are housed in chambers separate from the first and second deionising flow paths.
In an alternative arrangement, the anode and/or cathode are not separate from either the first and/or second deionising flow paths.
In another embodiment of the present invention, the chamber for the anion exchange material of the first deionising flow path is adjacent the chamber for the anion exchange material for the second deionising flow path, and the chamber for the cation exchange material of the first deionising flow path is adjacent the chamber for the cation exchange material for the second deionising flow path.
Preferably, the water to be purified or further purified passes through an anion exchange material first, followed by passage through a cation exchange material.
The apparatus also preferably includes a concentrating chamber into which the anions and cations desired to be removed from the water are concentrated and removed from the electrodeionisation apparatus. The apparatus could include a concentrating chamber adjacent each anion and/or cation exchange material chamber. Preferably, the apparatus includes at least a centrally arranged concentrating chamber.
Also preferably, at least one of the or any anode chambers, cathode chambers, and concentrating chambers has a flushing stream passing therethrough to remove electrode gases and/or the unwanted ions. Purified and repurified water from the first and/or second flow paths could be used for the or each flushing stream. Such water could be passed successively through two or more of the anode chamber(s), cathode chamber(s) and/or concentrating chambers(s). Preferably the flushing stream runs countercurrent to the water flow through the, or at least one of, the adjacent purified water chambers.
According to a preferred embodiment of the present invention, the electrodeionisation apparatus is a stack comprising seven chambers, a first chamber housing an anode, a second chamber containing cation exchange material for the second deionisation flow path, a third chamber housing cation exchange material for the first deionising flow path, a fourth chamber being a central concentrating chamber, a fifth chamber housing anion exchange material for the first deionising flow path, a sixth chamber housing anion exchange material for the second deionising flow path, and a final seventh chamber housing a cathode.
The chambers housing the anode and/or cathode may contain also one or more conducting materials. These may be cation exchange material in the anode chamber and anion exchange material in the cathode chamber.
The chambers can be separated by relevant perm-selective membranes as known to those skilled in the art. Any piping required for the deionising flow paths between the various exchange materials and/or chambers is also well known in the art.
According to a second aspect of the present invention, there is provided a method of providing purified water wherein water to be purified is passed through a first deionising flow path followed by a passage through a second deionising flow path, wherein the outflow from the first path is held in a holding tank prior to passage through the second flow path, and wherein the outflow from the second path is available for use. Optionally, such outflow is partly or fully returned to the holding tank.
The method of the present invention could use deionisation apparatus as described above, and preferably includes the water in the holding tank being available for use also.
Thus, according to a third aspect of the present invention there is provided apparatus for providing a volume of purified water available immediately for use, comprising a first deionising flow path for water to be purified through an anion exchange material and/or a cation exchange material, in either order where both materials are used, and an integral second deionising flow path through an anion exchange material and a cation exchange material, in either order, wherein the outflow from the first path is held in a holding tank adapted to hold the volume of purified water, and wherein water in the holding tank is intermittently or continuously circulated through the second flow path and wholly or partly returned to the holding tank.
The further purity of the outflow from the second deionising flow path, which has hi
Emery Nigel
Whitehead Paul
Woodward Roger
OTV Societe Anonyme
Wolf, Greenfield&Sacks, P.C.
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