Chemistry: electrical and wave energy – Processes and products – Electrophoresis or electro-osmosis processes and electrolyte...
Reexamination Certificate
2000-03-22
2001-08-14
Phasge, Arun S. (Department: 1741)
Chemistry: electrical and wave energy
Processes and products
Electrophoresis or electro-osmosis processes and electrolyte...
C204S525000, C204S533000, C204S536000, C204S632000
Reexamination Certificate
active
06274018
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electrodeionization apparatus which can reduce electric resistance, thereby minimizing power consumption, and to an electrodeionization method using such an apparatus. This electrodeionization apparatus can be used for production of deionized water in such applications as electronics, pharmaceutical, nuclear or fossil-fuelea power generation, food and beverage, and laboratory.
2. Description of the Related Art
One conventional method for producing deionized water is to pass the water to be treated through ion exchange resins. In this method, the ion exchange resins must be chemically regenerated when they become exhausted. In order to eliminate this troublesome operation, an electrodeionization (hereinafter abbreviated to EDI) method has been developed and commercialized which does not require chemical regeneration.
FIG. 5
is a cross sectional view of a typical conventional electrodeionization apparatus. As shown in the figure, a series of desalination chambers
104
are formed by alternately providing cation exchange membranes
101
and anion exchange membranes
102
with spaces in between, and by filling every other space with ion exchange materials
103
. One side (front side) of each desalination chamber, from where water to be treated is fed, is filled with an anion exchange resin
103
a
and the other side (back side) of the desalination chamber, where treated water flows out, is filled with a mixed bed
103
b
of cation and anion exchange resins. The sections adjacent to desalination chambers
104
which are formed by anion exchange membrane
102
and cation exchange membrane
101
and which are not filled with ion exchange material
103
act as concentrate chambers
105
where concentrate water flows.
As shown in
FIG. 6
, a deionizing module
106
is formed by a cation exchange membrane
101
, an anion exchange membrane
102
, and ion exchange materials
103
filling the space between these ion exchange membranes.
Specifically, one side of a frame
107
is sealed with a cation exchange membrane
101
. The upper side (front side) of the interior of the frame
107
is filled with an anion exchange resin
103
a
and the lower side (back side) of the frame interior is filled with a mixed ion exchange resins
103
b
. The other side of the frame
107
which is then sealed with an anion exchange membrane
102
. Because ion exchange membranes
101
and
102
are soft and flexible, when frame
107
is filled with the ion exchange materials
103
and sealed with ion exchange membranes on both sides, in a typical frame
107
, a plurality of vertical ribs
108
are provided to prevent nonuniform filling of ion exchange materials
103
due to curving of ion exchange membranes. Although not shown in the figure, inlets for the water to be treated are provided at the upper side of the frame
107
and outlets for the treated water are provided at the lower side of the frame
107
.
FIG. 5
shows a plurality of these deionizing modules
106
provided in parallel with spacers (not-shown) in between. A cathode
109
is provided on one side of the parallel deionizing modules
106
and an anode
110
is provided on the opposite side of the parallel deionizing modules
106
. The spacers are provided between deionizing modules
106
and concentrate chambers
105
. A separating membrane such as a cation exchange membrane
101
, an anion exchange membrane
102
, or a diaphragm which does not have any ion exchange functionality is provided externally on both of the outermost concentrate chambers
105
, as necessary. A cathode chamber
112
and an anode chamber
113
are provided in the sections separated by the above-mentioned separating membranes, which sections come in contact with the cathode
109
and anode
110
. As can be seen, in such a conventional EDI apparatus, the number of the concentrate chambers is larger than the number of desalination chambers by one.
A deionized water producing process using such an EDI apparatus is explained referring to
FIGS. 4 and 5
, where
FIG. 4
schematically shows a relationship between the desalination and concentrate chambers. In
FIG. 4
, cathode chamber
112
and anode chamber
113
are separated from concentrate chambers
105
by cation exchange membrane
101
. Specifically, a direct current is applied between the cathode
109
and anode
110
. Water to be treated is fed from the water to be treated supply line
111
and concentrate water is fed from the concentrate water supply line
115
. Electrode water is supplied from electrode water supply lines
111
and
117
. The water to be treated which has been fed from the water to be treated supply line
111
flows through the desalination chambers
104
. Anions such as chloride and sulfate ions in the water are removed when the water flows through the anion exchange resin
103
a
in the front side and then cations such as magnesium and calcium ions are removed when the water flows through the downstream mixed ion exchange resins
103
b
of the cation and anion exchange resins. The concentrate water fed from the concentrated water supply line
115
flows upward through each concentrate chamber
105
, receives impurity ions via the cation exchange membrane
101
and anion exchange membrane
102
and is discharged from the concentrate water discharge line
116
as concentrate water containing concentrated impurity ions. The electrode water supplied from the electrode water supply lines
117
and
117
is discharged from electrode water discharge lines
118
and
118
. Thus, deionized water can be produced in the deionized water discharge line
114
.
There have been various attempts to reduce the electric resistance of this type of EID apparatus in order to reduce the amount of electric power consumption when such an apparatus is used to remove impurity ions from water to be treated. However, because the filling method and amount of the ion exchange materials used in the desalination chambers depend on the desired quality of treated water, there are restrains on how much the electric resistance at the desalination chamber can be reduced, and measures have often been taken for reducing the electric resistance at the concentrate chambers. For example, Japanese Patent Laid-Open Publication No. Hei 9-24374 discloses a method for reducing the electric resistance at the concentrate chambers by adding electrolytes thereto. A method for reducing electric resistance in the concentrate chamber by circulating concentrate water to promote an increase in its electric conductivity has also been proposed.
However, in the method for reducing the electric resistance in the concentrate chambers by adding electrolytes thereto, a pump for supplying the electrolytes to the concentrate chambers, a chemical storage tank, and supply pipes must be provided, and therefore, both installation area and costs increase. Moreover, chemicals must periodically be supplied and managed, causing a problem that considerable personal attention is required, even though the apparatus is referred to as a continuous electrodeionization unit. The method for reducing the electric resistance in the concentrate chambers by circulating concentrate water, thereby increasing the electrical conductivity in the concentrate chambers has also a disadvantage in that hardness components such as calcium and magnesium within the concentrate water also become highly concentrated and form scales which increase electric resistance.
SUMMARY OF THE INVENTION
One object of the present invention is to provide an EDI apparatus which can reduce electric resistance without adding any chemical to the concentrate water, and a deionized water producing method using such an apparatus.
An apparatus according to the present invention comprises a series of desalination chambers, each of which has one side sealed by a cation exchange membrane and the other side sealed by an anion exchange membrane, wherein an intermediate ion exchange membrane is provided between the cation and anion exch
Organo Corporation
Phasge Arun S,.
Rodenthal & Osha L.L.P.
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