JP2003275767A - Method for controlling electric deionizer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To control an electric deionizer for the purpose of sure production of produced water of a target concentration. <P>SOLUTION: The rate of silica transfer by potential from a desalting chamber 2 to a concentrating chamber 5 and the rate of silica transfer from the concentrating chamber 5 to the desalting chamber 2 by a concentration gradient are computed and the energizing current value of the electric deionizer is computed in accordance with the flow rate of the desalting chamber, the flow rate of the concentrating chamber, the volume of the circulating concentrate, the concentration of the raw water silica, and the target concentration of the silica, by which the deionizer is controlled. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of controlling an electric deionization apparatus for electrically desalting (deionizing) raw water, and more particularly to a method of controlling an electric current value to the electric deionization apparatus. Regarding

[0002]

2. Description of the Related Art Conventionally, semiconductor manufacturing plants, liquid crystal manufacturing plants,
As shown in FIG. 3, a plurality of deionized water producing devices used in various industries such as the pharmaceutical industry, food industry, electric power industry, or for consumer use or research facilities are provided between electrodes (anode 11, cathode 12). The anion exchange membranes 13 and the cation exchange membranes 14 are alternately arranged to form the concentrating chambers 15 and the desalting chambers 16 alternately, and the desalting chambers 16 are made of an ion exchange resin, an ion exchange fiber or a graft exchanger. An electric deionization device in which an anion exchanger and a cation exchanger are mixed or packed in a multi-layered manner is known (Patent No. 1782943).
No., Japanese Patent No. 2751090, Japanese Patent No. 2699256
issue). In FIG. 3, 17 is an anode chamber and 18 is a cathode chamber.

The electric deionization apparatus uses H ⁺ by water dissociation.
Ions and OH ⁻ ions are generated and the ion exchanger filled in the desalting chamber is continuously regenerated,
Efficient desalination treatment is possible, complete regeneration is possible without the need for regeneration treatment using chemicals such as ion exchange resin devices that have been widely used in the past, and high purity water can be obtained. It has an excellent effect of being obtained.

It has been known that the current value is related to the silica removal performance in such an electric deionization apparatus.
The effects of concentration in the concentration room were not clarified.

Therefore, conventionally, the current control of the electric deionization apparatus has been performed by an operation manual or the like determined based on empirical data such as the relationship between the current value and the silica removal rate.

However, with such a control method, the required current value cannot be accurately obtained when the conditions such as the amount of water and the recovery rate are different, or when the concentration of the water to be treated changes. For this reason, conventionally, the automatic control operation of the current value of the electric deionization apparatus has not been performed at all.

[0007]

SUMMARY OF THE INVENTION It is an object of the present invention to control a current value for desalination in an electric deionization apparatus to produce a product water having a target concentration.

[0008]

A method of controlling an electric deionization apparatus according to the present invention is a method of controlling an electric deionization apparatus for deionizing water, which comprises an anode and It is provided with a cathode and a concentrating chamber and a desalting chamber formed by disposing a cation exchange membrane and an anion exchange membrane between the anode and the cathode, and raw water is passed through the desalination chamber to produce. A method for controlling an electric deionization apparatus, in which concentrated water is taken out as water, the concentrated water is passed through the concentrating chamber, a direct current is passed from a power supply device between the anode and the cathode, and the amount of this current is controlled by a control device. In, the deionization operation model in the electric deionization device is set, and the concentration and flow rate of the raw water introduced into the deionization chamber and the concentration of the target production water are input to the control device to be targeted. Required to achieve the concentration of product water Calculates the a current value, is characterized in that energizing the computed current between the anode and the cathode.

According to the present invention, since the deionization operation model is set and the original concentration and flow rate and the target concentration of the product water are given to the control device to determine the current value, the control can be automated.

According to the present invention, a part of the raw water and a part of the water discharged from the concentration chamber are introduced into the concentration chamber, and the rest of the water discharged from the concentration chamber is discharged to the outside of the electric deionization apparatus. The flow rate Q in the salt chamber, the flow rate s · Q in the concentrating chamber, and the concentrated water amount r · Q to be discharged to the outside of the electric deionization device are set respectively, and these set values are input to the control device in advance to obtain the raw water. By calculating the current value in accordance with the concentration and the target product water concentration, it is possible to reliably produce the target water product concentration. Here, s is the ratio of the concentration chamber flow rate to the deionization chamber flow rate, and r is the ratio of the discharge flow rate from the concentration chamber to the deionization chamber flow rate.

In particular, in the present invention, the deionization operation model in the electric deionization apparatus is such that the transfer amount of ions from the deionization chamber to the concentration chamber is proportional to the ion concentration in the deionization chamber and the current value. Amount of ions transferred from desalination chamber to concentration chamber]
From [the amount of ions transferred from the concentration chamber to the desalting chamber in proportion to the membrane area of the ion exchange membrane and the concentration difference between the ion concentration in the concentration chamber and the ion concentration in the deionization chamber] It is preferable to have the set configuration.

In the present invention, the deionization chamber is provided with an inlet for raw water on one end side and an outlet for production water on the other end side, and the deionization operation model is a predetermined range on this one end side. Since the weak electrolyte is set so as not to move from the deionization chamber to the concentration chamber, the behavioral model can be sufficiently approximated to the actual model. In particular, by setting this predetermined range in proportion to the current efficiency of the electric deionization device,
The motion model can be remarkably approximated to the real model.

[0013]

DETAILED DESCRIPTION OF THE INVENTION Embodiments will be described below with reference to the drawings. FIG. 1 is a schematic model diagram of an electric deionization apparatus to which the control method according to the embodiment is applied, and FIG.
[Fig. 4] is a model diagram in the case of performing motion analysis by a difference equation.

In FIG. 1, raw water is introduced into the desalination chamber 2 from the pipe 1 at a flow rate Q, and is also taken out as product water from the desalination chamber 2 at a flow rate Q via the pipe 3.

A part of the raw water is a pipe 4 branched from the pipe 1.
Is introduced into the concentrating chamber 5 through the pipe, and a part of the concentrating chamber outflow water is discharged from the pipe 6 to the outside of the electric deionization device. The remaining portion of the concentrated chamber outflow water is combined with the branched raw water in the pipe 4 via the pipe 7 branched from the pipe 6 and the pump 8 and circulated to the concentrated chamber 5. The deionization chamber 3 and the concentration chamber 5 have an ion exchange membrane 9
They are separated by (anion exchange membrane in this case).

The flow rate in the concentration chamber is proportional to the flow rate Q in the demineralization chamber by s.
Is the flow rate s · Q, and the flow rate discharged to the outside of the electric deionization apparatus is the flow rate r · which is the deionization chamber flow rate Q multiplied by the ratio r.
Q. Naturally, the total amount of raw water supplied to the electric deionization apparatus is (1 + r) Q, and the concentrated water circulation flow rate flowing through the pipe 7 is expressed as (s−r) · Q.

The dissociative compound to be removed in raw water (this
Embodiment, the silica) concentration is c ₀(Μg / L)
And the target concentration of product water is c_NIs.

At a point at a distance x from the inflow port in the desalination chamber 2, the silica concentration in water is c.

In the concentrating chamber 5, the silica concentration at the inflow port is c ₀ 'and the silica concentration in the outflowing concentrated water is c _N '. At a point at a distance x from the inflow port in the concentration chamber 5, the silica concentration in water is c '.

Further, the amount of silica transferred per unit time from the desalting chamber 2 to the concentrating chamber 5 based on the potential difference between the electrodes of the electrodeionization apparatus is K (μg / Hr), and the desalting chamber 5 is desalted. The amount of silica transferred per unit time to the chamber 2 based on the difference in silica concentration is K ′ (μg / Hr).

The current flowing from the anode of the electric deionization device to the cathode is i (A).

As shown in FIG. 1, the flow direction of water at a point at a distance x from the inlet (the direction connecting the inlet and the outlet).
A minute width in the left-right direction in FIG. 1 is dx. This minute width d
The membrane area of the ion exchange membrane 8 belonging to x is m. The membrane area m is an area obtained by multiplying dx by the width of the deionization chamber. The width of the deionization chamber is the width in the direction orthogonal to the flow direction of water.

The amount of silica migration dK per unit time that permeates the region of the membrane area m belonging to this minute width dx from the desalting chamber 2 to the concentrating chamber 5 due to the potential difference is proportional to the silica concentration c of the desalting chamber and the current value i. Therefore, it is expressed as dK = k · c · i · dx (1) using the proportional constant k.

Similarly, the silica migration amount dK 'per unit time which is used as the silica concentration and permeates the region from the concentrating chamber 5 to the desalting chamber 2 is the silica concentration difference (c'-c) in both chambers and the region. Since it is proportional to the area m of d, it is expressed as dK ′ = k ′ · (c′−c) · m · dx (2) using the proportional constant k ′.

The following equation (3) is derived from the material balance at the point of the distance x in the desalination chamber 2. Q · dc / dx = dK / dx−dK ′ / dx (3) dc / dx on the left side is the concentration gradient in the flow direction of water at a point of distance x from the inlet, and Q · dc / dx
Is the amount of silica that decreases by passing through the cross section of the desalination chamber at the point of this distance x.

DK / dx on the right side of the equation (3) is the amount of migrated silica from the desalting chamber to the concentrating chamber at the point x, and dK '
/ Dx is the amount of migrated silica from the concentrating chamber to the desalting chamber at point x, so the difference between the two (dK / dx-dK '/ d
x) is equal to the above Q · dc / dx.

Similarly, the following equation (4) is derived from the material balance at the point of distance x from the inlet in the concentrating chamber 5. −s · Q · dc ′ / dx = dK / dx−dK ′ / dx (4) Note that, as described above, s · Q on the left side of the equation (4) is the flow rate in the concentrating chamber.

The total silica balance of this electric deionization apparatus, that is, the amount of silica in the total amount of raw water to the electric deionization apparatus per unit time, the product water (flow rate Q) and the discharged concentrated water (flow rate r · Q) The following formula (5) is derived from the fact that the amount of silica brought out by is equal. _{(1 + r) · Q ·} c 0 = Q · c N + r · Q · c N '(5)

Similarly, the following equation (6) is derived from the silica balance at the confluence of the pipe 4 and the pipe 7. As a matter of course, the right side of the equation (6) is the sum of the amounts of silica flowing in from the pipe 4 and the pipe 7, and the left side is the amount of silica after joining. s · Q · c ₀ ′ = r · Q · c ₀ + (s−r) · Q · c _N ′ (6)

The contents of the above equations (1) to (6) and variables / constants are summarized below. dK = k * c * i * dx (1) dK '= k' * (c'-c) * m * dx (2) Q * dc / dx = dK / dx-dK '/ dx (3) -s · Q · dc '/ dx = dK / dx-dK' / dx (4) (1 + r) · Q · c 0 = Q · c N + r · Q · c N '(5) s · Q · c 0' = r · Q · c ₀ + (s−r) · Q · c _N ′ (6) Q: Desalination chamber flow rate (L / min) s · Q: Concentration chamber flow rate (L / min) r · Q: Electrical desorption Discharged concentrated water flow rate (L /
min) K: Amount of movement from the desalting chamber to the concentrating chamber due to potential (μg / m
in) k: Constant c: Desalination chamber concentration (μg / L) i: Current (dx part) (A) K ′: Transfer amount from the concentration chamber to the desalination chamber (μg / L)
min) k ′: Constant c ′: Concentration chamber concentration (μg / L) m: Membrane area (dx part) (cm ² ) The unit of the above flow rate, concentration, etc. is an example, and not limited to this.

In the above equations (1) to (6), it is premised that the current i between the electrodes flows uniformly in the flow direction of water in each chamber (the current density is the same). As a result of various experiments, it was confirmed that the current distribution can be treated as almost uniform.

As a result of the experiment, in the desalting chamber 2, in the vicinity of the inflow port, a large amount of chlorine ions were present, silica was hardly dissociated, and the phenomenon that the silica did not move from the desalting chamber to the concentrating chamber was observed. . Therefore, silica does not move in a predetermined range near the inlet, and silica moves only in the remaining range (permeates the membrane).
It is appropriate to treat it as something to do. In the present invention, the range in which silica migration does not occur is preferably treated as a range obtained by multiplying the total deionization chamber length X by the current efficiency e (%), that is, a range of L = X · (e / 100).

Tap water is treated with activated carbon, reverse osmosis (RO) equipment,
Using water with a silica concentration of 200 μg / L
When I conducted an experiment, Desalination chamber flow rate Q: 13.3 L / min Membrane area: 739.2 cm^Two Concentration chamber Silica average concentration: 2000 μg / L Desalination chamber silica average concentration: 100 μg / L Concentration chamber runoff water silica concentration: 2157 μg / L And substituting these values into the integral formula (2)
By k '= 0.000229 Was calculated. For k, the value of
When simulation was performed and the measured value was compared, k = 1
It was recognized that 20 should be adopted. In addition, this place
In the case of silica, the permeation of silica is in the range of X · (e / 100) on the inflow side.
I treated it as not done. In simulation
Needs to solve equations (1) to (6), and in this case
From equations (1) to (6), the following equation (10) is obtained as follows.
Was derived and solved by the difference method.

That is, from the equations (5) and (6), c ₀ '= (r · c ₀ + (s−r) × ((1 + r) · (c ₀ −c _N ) / r) / s (8 ) Where c ₀ is significantly greater than c _N , ie c ₀ >>
Since it is c _N , c ₀ −c _N = c ₀ (9)

From the equations (8) and (9), the following equation (10) is derived. c ₀ ′ = (r · c ₀ + (s−r) × ((1 + r) · c ₀ ) / r) / s (10)

Here, FIG. 1 is regarded as a difference type in which the concentration distribution of the desalting chamber changes stepwise as shown in FIG. 2, and the equations (1) to (4) are treated as a difference equation, and a difference equation (3) is obtained. , (4) are substituted into the equations (1) and (2), and the following (1
Equations (2) and (13) were derived. _{c n + 1 = c n +} (k · c n · i n -k '· (c n' -c n) · m n) / Q × Δx (12) c n + 1 '= c n' - (k · c n _{· i n -k '· (c} n' -c n) · m n) / (s · Q) × Δx (13)

In equations (12) and (13), the product water concentration can be obtained by making Δx sufficiently small, for example, Δx = 1 cm, and sequentially calculating from c _{0 to} c _N.

It is sufficient to calculate the silica concentration of the product water by changing the current value i variously, select the current value i at which the silica concentration of the product water becomes the target concentration, and energize the electrodeionization device. In practice, it is preferable to carry out energization by multiplying i by a safety factor (for example, 1.2).

In FIG. 2, the silica concentration in the desalting chamber is c ₀ on the inlet side, and c ₁ , c ₂ ,
c ₃ ........., c _n, changes in _c n + 1 _......... and stepped,
The product water silica concentration is c _N. Similarly, in the concentration chamber, the silica concentration from the inlet to the outlet is c ₀ ', c
_{1 ', c 2' .........,} c n ', c n + 1' ......... c N '
And changes like a staircase.

In the present invention, it is preferable that the silica concentration in the raw water is continuously measured by a continuous measuring device. A stabilized power supply device is preferable as a power supply device for the electric deionization device. The electric deionization device may be operated in a single stage or may be connected in series in two or more stages.

In the present invention, the pH condition may be treated as follows. That is, if the raw water is neutral, the ion ratio of silica due to dissociation is almost 0, so there is no migration of silica in the range of L above.
If H = 9.86, calculation is performed so that the movement amount is obtained by multiplying the formula (1) by the ion dissociation rate = 0.5 within the range of L.

[0042]

[Examples] Tap water was treated with activated carbon-RO-deaeration membrane as raw water and passed through the electric deionization apparatus of FIG. The electric deionization device has three deionization chambers and an effective height of 66c.
m × width 11.2 cm × thickness 2.5 mm. As the ion exchange resin, a mixed resin of 60% anion exchange resin and 40% cation exchange resin was filled only in the desalting chamber. Spacers were placed in the concentration chamber.

The water flow rate Q and the like are as follows. Q = 13.3L / Hr (per desalting chamber) r = 0.9 s = 0.3

The computer automatically calculated and controlled the concentration of produced water silica to 10 ppb according to the above equations (9) and (10).

At the beginning of operation, the silica concentration in the feed water is 100 p
When operated at pb, the operation was performed at an automatically calculated current value of 0.3A. Further, when silica was added from the operation for 500 hours and the silica concentration of the feed water was set to 500 ppb, the operation was performed at 0.8 A which was automatically calculated. Run time 1000 hours to 1500 hours, silica concentration 2
When operated at 00 ppb, operation was performed at an automatically calculated current value of 0.4 A.

The result of continuous monitoring of silica in the treated water was 8 to 10 ppb at any time, and it was confirmed that the product water having a low silica concentration can be produced by the automatic control operation.

[0047]

As described above, according to the present invention, the electric deionization apparatus can be controlled so as to reliably produce the target concentration of the product water.

[Brief description of drawings]

FIG. 1 is a schematic diagram of a control method of an electrodeionization apparatus to which a method according to an embodiment is applied.

FIG. 2 is a schematic diagram of a control method of an electrodeionization apparatus to which the method according to the embodiment is applied.

FIG. 3 is a schematic cross-sectional view showing a general configuration of an electric deionization device.

[Explanation of symbols]

2 desalination room 5 Concentration room 8 pumps 9 Ion exchange membrane 10 Ion exchanger 11 Anode 12 cathode 13 Anion exchange membrane 14 Cation exchange membrane 15 Concentration room 16 Desalination chamber 17 Anode chamber 18 Cathode chamber

   ─────────────────────────────────────────────────── ─── Continued front page    F-term (reference) 4D006 GA17 JA30Z KA22 KE02Q                       KE03Q KE04Q KE12P KE13R                       KE18P KE18R PA01 PB02                       PB23 PC01 PC11 PC31 PC42                 4D061 DA01 DB18 DC18 EA09 EB01                       EB04 EB13 EB19 EB37 EB39                       FA08 GA05 GC12 GC18

Claims (5)

[Claims] 1. A method for controlling an electrodeionization apparatus for deionizing water, the electrodeionization apparatus comprising an anode and a cathode, a cation exchange membrane and an anion between the anode and the cathode. It is provided with a concentrating chamber and a desalting chamber formed by disposing an exchange membrane, and raw water is passed through the desalting chamber to be taken out as product water,
Concentrated water is passed through the concentrating chamber, a direct current is passed from a power supply between the anode and the cathode, and the amount of this current is controlled by a controller. The deionization operation model in the ion apparatus is set, and the concentration and flow rate of the raw water introduced into the desalting chamber and the target concentration of the produced water are input to the control device to set the target concentration of the produced water. A method for controlling an electric deionization apparatus, comprising: calculating a current value necessary for achieving the current value; and applying the calculated current between the anode and the cathode. 2. The part of the raw water according to claim 1,
A method of introducing a part of the effluent water of the concentration chamber into the concentration chamber and discharging the rest of the effluent water of the concentration chamber to the outside of the electric deionization device, wherein a flow rate Q in the desalting chamber and a flow rate s · Q in the concentration chamber , The concentrated water amounts r and Q to be discharged to the outside of the electric deionization device are respectively set, and these set values are input to the control device in advance, and the current is changed according to the concentration of the raw water and the target production water concentration. A method for controlling an electric deionization device, which comprises calculating a value. 3. The deionization operation model in the electric deionization device according to claim 1, wherein the amount of ions transferred from the deionization chamber to the concentration chamber is defined by: [ion concentration in the deionization chamber and current The amount of ions transferred from the demineralization chamber to the concentration chamber in proportion to the value] [in proportion to the membrane area of the ion exchange membrane and the concentration difference between the ion concentration in the concentration chamber and the ion concentration in the deionization chamber The amount of ions transferred from the concentration chamber to the deionization chamber] is set as a subtracted amount. 4. The desalination chamber according to claim 1, wherein the demineralization chamber has an inlet for raw water at one end and an outlet for product water at the other end. The operation model is set such that the weak electrolyte does not move from the deionization chamber to the concentration chamber within a predetermined range on the one end side. 5. The method for controlling an electric deionization device according to claim 4, wherein the predetermined range is set in proportion to the current efficiency of the electric deionization device.