JPH022830A - Electric dialysis device - Google Patents

Abstract

PURPOSE:To obtain the electric dialysis device suitable for the area where the acid is difficult to be available by generating the acid to be supplied to the cathode chamber of electric dialysis vessel using the gas generated in the device without the need of supplying the acid from outside of the device. CONSTITUTION:The electric dialysis vessel 1 which numbers of cation exchange membranes and anion exchange membranes are alternatively disposed in and has an anode chamber 8 and the cathode camber 4 on its both ends is provided, and direct electric current is impressed to the electric dialysis vessel 1 to make desalted water 12 and concentrated water 13. An electrolysis unit 21 and a hydrochloric acid generating reactor 27 are provided in the vicinity of the electric dialysis vessel 1 to electrolyze the concentrated water 13 sent from the electric dalysis vessel 1. Hydrochloric acid is produced in the hydrochloric acid generating reactor 27 using the chlorine gas and hydrogen gas produced there as the raw materials, and the hydroric acid is introduced into the cathode chamber 4 of the electric dialysis vessel 1. As a result, the electric dialysis device suitable for the area where the acid is difficult to be available is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an electrodialysis apparatus suitable for eliminating the need to supply acid from outside the apparatus to the cathode chamber, which is originally required as a utility.

[Conventional technology]

As shown in FIG. 5, a conventional electrodialysis apparatus is comprised of an electrodialysis tank 1, an acid tank 7, a DC power source 6, and the like. The electrodialysis apparatus 1 includes a dialysis chamber block 2 in which a large number of cation exchange membranes that selectively permeate cations and anion exchange membranes that selectively permeate anions are laminated alternately, an anode chamber 3 and a cathode chamber at both ends. It has a structure with 4.

The electrodialysis tank 1 is supplied with raw water 14 which is an electrolyte solution (for example, seawater, underground shrubs, industrial wastewater, domestic wastewater). When a direct current is passed between the anode chamber 3 and the cathode chamber 4, the cations in the raw water move toward the cathode chamber 4, and conversely, the anions move toward the anode chamber 3. do. Due to the movement of this ion and the cation exchange membranes and anion exchange membranes that are stacked alternately, a large number of demineralization chambers and concentration chambers are formed alternately, and the raw water that has passed through the demineralization chamber becomes demineralized water 12 and is concentrated. The raw water that has passed through the chamber becomes concentrated water 13. Desalinated water 12 is used as domestic water, and concentrated water 13 is used as raw water for salt production.

The following reactions occur in the anode chamber 3 and cathode chamber 4 of the electrodialysis cell 1, generating chlorine gas and hydrogen gas, respectively.

(Anode chamber) 2Cj2- →C7! z +2 e-・”
-(1) (Cathode chamber) 2 H" + 2 e --Hz
・”-(2) In the cathode chamber 4, the reaction of equation (2) causes an increase in pH, and in order to prevent this pH increase, it is necessary to supply an acid (for example, sulfuric acid, hydrochloric acid). If the supply is not carried out, the cation exchange membrane and anion exchange membrane near the cathode chamber 4 will not only be deteriorated due to the increase in pH (alkaline earth metal salts, and alkaline earth hydroxides [e.g., CaCO .

For this reason, in the conventional apparatus, commercially available industrial sulfuric acid is regularly purchased and stored in the acid tank 7, and a predetermined amount of sulfuric acid is injected into the cathode chamber 4 using the acid supply pump 8.

[Problem to be solved by the invention]

The above conventional technology does not take into account electrodialysis equipment installed in areas where it is difficult to obtain acid. Therefore, in these areas, it is either impossible to install electrodialysis equipment, or even if it is installed, transportation costs are too high. High acid will be used,
There were problems that made it an economical electrodialysis device.

An object of the present invention is to solve the problems of the prior art described above and to provide an electrodialysis device suitable for areas where low-cost acid is not available.

[Means to solve the problem]

The above purpose is to supply the concentrated water produced in the electrodialysis tank to an electrolysis device installed close to the electrodialysis tank, and use the chlorine gas and hydrogen gas generated here as raw gas to produce hydrochloric acid in a hydrochloric acid bioreactor. This is achieved by generating hydrochloric acid and introducing this hydrochloric acid into the cathode chamber of the electrodialyzer.

[Effect]

The concentrated water discharged from the electrodialysis tank is a liquid with a high concentration of cations and anions. When seawater, underground shrubs, etc. are used as raw water, the cations and anions of the concentrated water are Na'' ions and Cff1- ions, respectively.

When concentrated water containing a high concentration of these ions is electrolyzed using an electrolysis device, electrical resistance can be reduced and running costs can be reduced. Hydrochloric acid produced in a hydrochloric acid generation reactor attached to the electrodialysis tank is introduced into the cathode chamber of the electrodialysis tank, thereby preventing an increase in pH near the cathode chamber.

〔Example〕

Embodiments of the present invention will be described below based on the drawings.

FIG. 1 is a schematic diagram showing a first embodiment of the electrodialysis apparatus of the present invention.

This electrodialysis apparatus is mainly composed of an electrodialysis tank 1, an electrolysis device 21, a hydrochloric acid production reactor 27, a DC power supply 6 for the electrodialysis tank 1, and a DC power supply 30 for the electrolysis device 21.

The electrodialysis tank 1 consists of a dialysis chamber block 2 in which a large number of cation exchange membranes and anion exchange membranes are alternately stacked and a large number of demineralization chambers and concentration chambers, an anode chamber 3 and a cathode chamber 4. ing. A line is provided for supplying demineralized water 13 from the dialysis block 2 to the anode chamber 22 of the electrolyzer 21. In addition, a line that supplies chlorine gas 24 generated in the anode chamber 22 of the electrolyzer 21 to the hydrochloric acid generation reactor 27;
A line is installed to supply hydrogen gas 25 generated in the cathode chamber 23 of the electrolyzer 21 to the hydrochloric acid producing reactor 27.

Furthermore, a line is provided for supplying hydrochloric acid produced in the hydrochloric acid production reactor 27 to the cathode chamber 4 of the electrodialysis tank 1.

Note that a line for introducing raw water 28 into the hydrochloric acid producing reactor 27 is provided.

Next, the operation of the electrodialysis apparatus configured as described above will be explained.

The raw water 14 is divided into anode, cathode, desalination, and concentration in one electrodialysis tank, and is divided into anode chamber 3,
It is supplied to the hydrochloric acid production reactor 27, the desalination chamber in the dialysis chamber block 2, and the 'a condensation chamber. The raw water supplied to the anode chamber 3 participates in the anode reaction shown in equation (1), and then is discharged from the apparatus. The raw water supplied to the hydrochloric acid production reactor 27 absorbs hydrochloric acid (hydrogen chloride), is then supplied to the cathode chamber 4, participates in the cathode reaction shown in equation (2), and is then discharged from the apparatus. The raw water supplied into the demineralization chamber in the dialysis room block 2 is desalinated by dialysis, and then turned into demineralized water 12 and supplied outside the apparatus.

The raw water supplied into the concentration chamber in the dialysis room block 2 is concentrated by dialysis and then turned into concentrated water 13 and supplied to the electrolyzer 21 . Concentrated water 1 supplied to electrolyzer 21
3 is used as an electrolytic solution in each of the anode chamber 22 and the cathode chamber 23, and then is discharged to the outside of the apparatus. At this time, the concentrated water 13 needs to flow through the anode chamber 22 and the cathode chamber 23 in this order.

When flowing in the reverse order, NaOH generated in the cathode chamber 23 is supplied to the anode chamber 22, reacts with the chlorine gas C12, and NaOH is generated in the cathode chamber 23.
Generate OCl z. And chlorine gas will no longer be generated.

The electrolytic reaction within the anode chamber 22 is the same as the reaction of equation (1) above, and generates chlorine gas 24. The electrolytic reaction within the cathode chamber 23 is equivalent to the reaction of equation (2) above, and generates hydrogen gas 25. Chlorine gas 24 and hydrogen gas 25 generated in the electrolysis device 21 are supplied to a hydrochloric acid generation reactor 27, and are irradiated with ultraviolet rays 40 to cause a reaction, thereby generating hydrochloric acid. The generated hydrochloric acid is absorbed into the raw water 28 supplied to the hydrochloric acid generation reactor 27.

The production of hydrochloric acid in the hydrochloric acid production reactor 27 is performed by a synthetic hydrochloric acid production method, and the reaction at that time is expressed by the following formula (
3).

Ht +C1,=2 HC1+44 k c a Il
-...C3) According to the above first embodiment, chlorine gas and hydrogen gas, which are raw materials for hydrochloric acid production, are produced in the electrolyzer 21, and hydrochloric acid is produced by a synthesis reaction in the hydrochloric acid production reactor 27. do. Since this hydrochloric acid is used for the reaction in the cathode chamber 4 of the electrodialyzer 1, an increase in pu in the cathode chamber 4 can be prevented, eliminating the need to purchase and inject acid from outside as in conventional devices. . therefore,
This has the effect of providing an economical electrodialysis device to areas where it is difficult to obtain acid at low cost.

Note that an increase in pH is also observed in the cathode chamber 23 of the electrolyzer 21 due to the reaction shown in equation (2). However, since the flow rate of the concentrated water 13 supplied to the cathode chamber 23 is large, the increase in pH is small, and therefore the precipitation of alkaline earth metal salts and hydroxides is extremely small. On the other hand, the dialysis room block 2 is often composed of several hundred sets of desalination chambers and concentration chambers.
It is several hundred times more.

FIG. 2 is a schematic configuration diagram showing a second embodiment of the present invention. In the electrodialysis apparatus of this embodiment, chlorine gas and hydrogen gas generated from the anode chamber 3 and cathode chamber 4 of the electrodialysis tank 1 are separated from the anolyte IO and catholyte 11, and It is supplied to the hydrochloric acid producing reactor 27 together with chlorine gas and hydrogen gas generated from the cathode chamber 23.

In this embodiment, the chlorine gas and hydrogen gas supplied to the hydrochloric acid generation reactor 27 are supplied from the electrodialysis tank 1 in addition to the electrolysis device 21, so that the chlorine gas and hydrogen gas to be generated in the electrolysis device 21 are generated. This has the effect of reducing the capacity and power consumption of the electrolyzer 21.

FIG. 3 is a schematic configuration diagram showing a third embodiment of the present invention, in which the electrolytic device 21 in FIGS. 1 and 2 is
And the piping etc. attached to it are omitted.

In FIG. 3, the piping that supplies raw water 14 to the electrodialysis tank 1 is installed in a hydrochloric acid producing reactor 27 on the way, and part of the raw water 28 that has passed through the piping inside the hydrochloric acid producing reactor 27 undergoes a hydrochloric acid producing reaction. It is designed to be introduced into a container 27.

In this embodiment, the reaction heat generated during the hydrochloric acid production reaction in the hydrochloric acid production reactor 27 is absorbed by the raw water 14. As a result, the temperature inside the hydrochloric acid production reactor 27 due to the reaction of equation (3) exceeds 1000°C if it is not cooled;
Cooling at step 4 makes it possible to maintain the temperature near room temperature. In addition, the raw water 14 is heated and its temperature increases, and its electrical conductivity increases. When this raw water 14 is supplied to the electrodialysis tank 1, the electrical resistance between the anode and the cathode of the electrodialysis tank 1 is reduced, and therefore, the effect of reducing the energy consumed in dialysis can be obtained. Note that the electrical conductivity of a liquid is generally determined at a temperature of 1°
Increases by 2% when C rises.

Next, specifications and operating conditions of the electrodialysis apparatus when the present invention shown in FIGS. 1 and 3 are applied are shown.

(Raw water, manufactured water) (1) Salt concentration of raw water (ppm, as Na
Cj! ) 1200 (2) Salt concentration of produced desalinated water (pp
m, as NaCj! ) 400(3) Salt concentration of produced concentrated water (ppm, as NaCl2) 4400(4
) Flow rate of produced desalinated water (m”/h) 4 (5) Flow rate of produced/concentrated water (m”/h) 1 (6) Flow rate of raw water (m3/h) 5.1 (7) Raw water temperature
(''C) 20.0 (8) Hydrochloric acid consumption (maj! /h) 0.4 (electrodialysis machine) (1) Dialysis chamber dimensions (IIIm) 200X 1800
(2) Ion exchange membrane spacing (mm) 0.75 (
3) Desalination room/concentration room logarithm (pair) 500 (4) DC power consumption for dialysis tank (kW) 0.84 (5) DC power consumption for electrolyzer (kW) 0.03 (6) Electrodialysis Tank inlet raw water temperature ("C)" 20.2 Note that when raw water is directly supplied to the electrolyzer 21, the power consumption of the DC power supply for the electrolyzer is approximately proportional to the salt concentration, and is about 3. It becomes 5 times.

FIG. 4 is a schematic configuration diagram showing a fourth embodiment of the present invention.

In FIG. 4, a polarity exchanger 16 is installed to switch the polarity between each electrode of the electrolyzer 21. Other components in FIG. 4 are the same as in FIG. 1, and are designated by the same reference numerals.

The anode chamber 3 and cathode chamber 4 of the electrodialysis tank 1 generate gases mainly composed of chlorine gas 35 and hydrogen gas 37, respectively, through electrode reactions and are released into the atmosphere. (Chlorine gas and hydrogen gas may be introduced into the hydrochloric acid generation reactor 27)
The direct current applied to this electrodialysis tank l is carried out using a direct current type #6.

Application of direct current to the electrolyzer 21 is performed using a current from a direct current power supply 30 via a polarity converter 16. Chlorine gas 24 is supplied from the anode chamber 22, and hydrogen gas 2 is supplied from the cathode chamber 23.
The generated chlorine gas 24 and hydrogen gas 25 are led to a hydrochloric acid producing reactor 27, are irradiated with ultraviolet light and react, and become hydrochloric acid gas. The generated hydrochloric acid gas is absorbed into the raw water supplied to the cathode chamber 4 of the electrodialysis tank 1.

The polarity converter 16 switches the polarity when the electrical resistance between the electrodes in the anode chamber 22 and cathode chamber 23 of the electrolysis device 21 exceeds a threshold value.

For example, a method of applying a constant voltage between these electrodes and switching the polarity when the current value becomes below a threshold value,
A method of applying a constant current between the electrodes and switching the polarity when the voltage between the electrodes exceeds a threshold value, or measuring the applied voltage and current and calculating the electrical resistance from this voltage and current. However, there is a method of switching the polarity when this electrical resistance exceeds a threshold value. There is also a method in which the time required to dissolve and remove the precipitates is set in advance, and the polarity is periodically switched at each set time.

In the vicinity of the cathode chamber 23 of the electrolyzer 21, the above-mentioned (1st
) The pH rises due to the cathode reaction, and at this time, Mg and Ca'' in the solution are precipitated by the following reaction, and a portion is accumulated on the electrode surface.

Mg” + 20 H-→Mg(OH)z・・・・
・・(4)Ca”+CO,” →CaCO5−・−・・
・(s) Mg (OH) z accumulated on the electrode surface,
Ca COI is dissolved again by the respective next reaction when the polarity of the electrode is switched, thus removing the accumulation on the electrode surface.

Mg(OH)z +C1z→ Mg (OCI!,)z +Ht O・・・・・・(6
) Ca COs + 2 Cl z + 2 Hz
O → Ca (ocp), +2 HC1! , +Hz CO
z ・・・・・・(7) Thus, according to the fourth embodiment, alkaline earth metal salts such as calcium carbonate and magnesium hydroxide deposited on the electrode surface in the cathode chamber 23 of the electrolyzer 21 or Since hydroxide can be removed periodically, the effect of suppressing the decrease in the amount of hydrochloric acid produced over time can be obtained.

In the electrodialysis apparatus shown in the fourth example, the electrodialysis tank had a current carrying area of 0.22 rrr, a logarithm of the cation exchange membrane and anion exchange membrane of 200, and a membrane spacing of 0°75 mm. The concentration of electrolyte in raw water, desalinated water, and concentrated water is 1°200ppm in terms of Na CI2 weight 300
ppm, 2. It is OOOppm.

The electrolysis device has an electrode area of 0.01 nf. The average current applied was 3 A for the electrodialysis tank and 6 A for the electrolyzer, and 4 rrr of demineralized water was produced per hour.

At this time, the polarity of the electrolyzer was changed every 2 hours, and the fluctuation in the current flowing through the electrolyzer was 5% or less of the average value.

〔Effect of the invention〕

As described above, according to the present invention, the acid to be supplied to the cathode chamber of the electrodialysis tank can be generated using the gas generated within the device without requiring the supply of acid from outside the device. We can supply electrodialysis equipment suitable for areas where it is difficult to obtain.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram showing a first embodiment of the present invention, and FIG.
The figure is a schematic block diagram showing a second embodiment of the present invention, Figure 3 is a schematic block diagram of main parts showing a third embodiment of the present invention, and Figure 4 is a schematic diagram showing a fourth embodiment of the present invention. FIG. 5 is a schematic diagram of a conventional electrodialysis apparatus. 1... Electrodialysis tank, 2... Dialysis room block, 3... Anode chamber, 4... Cathode chamber,
10...Anolyte 11...Catholyte, 12
...Demineralized water, 13... Concentrated water, 21.
... Electrolyzer, 22 ... Anode chamber, 23.
...Cathode chamber, 24.35...Chlorine gas,
25.37... Hydrogen gas, 27... Hydrochloric acid production reactor. Figure 1

Claims (3)

[Claims] (1) A large number of cation exchange membranes and anion exchange membranes are installed alternately, and an electrodialysis tank having an anode chamber and a cathode chamber is provided at both ends, and direct current is applied to this electrodialysis tank to demineralize water. In an electrodialysis device that produces water and concentrated water, an electrolysis device and a hydrochloric acid generation reactor are installed adjacent to the electrodialysis tank, and the concentrated water from the electrodialysis tank is electrolyzed by the electrolysis device to generate chlorine gas. and a means for producing hydrochloric acid in the hydrochloric acid production reactor using hydrogen gas as a raw material gas, and introducing the hydrochloric acid into the cathode chamber of the electrodialysis tank. (2) Separate chlorine gas from the anolyte generated from the anode chamber of the electrodialysis tank, separate hydrogen gas from the catholyte generated from the cathode chamber of the electrodialysis tank, and transfer these chlorine gas and hydrogen gas to the The electrodialysis apparatus according to claim 1, further comprising means for introducing the hydrochloric acid into the reactor for producing hydrochloric acid. (3) A pipe for supplying raw water to the electrodialysis tank is installed in the hydrochloric acid production reactor midway through the pipe, and the raw water is heated by the heat generated during hydrochloric acid production. (4) The electrodialysis apparatus according to claim 1, further comprising piping for supplying concentrated water from the electrodialysis tank to an anode chamber in the electrolyzer. .