JP3523864B1 - Water treatment method and water treatment device - Google Patents

Abstract

An object of the present invention is to provide a water treatment method and a water treatment apparatus that can improve the efficiency of removing scale components and reduce the pH without using a chemical. SOLUTION: A water treatment method for applying a voltage to a plurality of electrodes in the water to be treated and attaching scale components in the water to be treated to the electrodes, wherein the water to be treated between the plurality of electrodes has an electrode surface. Flow rate is 0.005 to 0.12 m /
h is a water treatment method in which a carbon dioxide-containing gas is supplied so as to satisfy the condition of h, and the adhesion of scale components to the electrode is promoted.
Further, the electrolytic cell has an electrolytic cell for treating the water to be treated, the electrolytic cell has an inlet and an outlet for the water to be treated, a plurality of electrodes provided between the inlet and the outlet, and a diameter of 0.002 to 2m
m is a water treatment apparatus provided with a carbon dioxide-containing gas supply hole.

Description

Detailed Description of the Invention 【Technical field】

The present invention relates to a water treatment method and a water treatment device. Specifically, it belongs to the technical field of a water treatment method and a water treatment device for purifying cooling water of a cooling tower provided in various factory facilities.

[Background technology]

The cooling water of a cooling tower provided in various factory facilities is circulated and used, and a part of the cooling water is diffused to the outside of the system by evaporation, and the reduced amount is externally supplied as makeup water. It is a mechanism. Therefore, the dissolved salts brought into the makeup water are gradually concentrated, and the salt concentration in the cooling water is increased. As a result, the dissolved salts in the cooling water adhere as scales to the piping in the system, heat exchangers, etc., and hinder heat transfer,
There is a problem that it causes pipe clogging and corrosion.
The components of the adhesion scale were mainly calcium carbonate and magnesium hydroxide, and other various metal salts such as calcium salts, magnesium salts and zinc salts.

Therefore, conventionally, in order to prevent the scale from adhering to pipes and heat exchangers, scale inhibitors such as phosphates, phosphonates, sulfonic acid polymers and carboxylic acid polymers have been used. The method of adding to cooling water was performed. However, the addition of the scale inhibitor has problems such as an increase in environmental load, danger of handling, complexity of drug management, and cost increase. In addition, as another scale adhesion preventing method, there is a method in which concentrated water is blown off and drained to mitigate an increase in the concentration of dissolved salts, but there are problems such as a large consumption of water and an increase in cost.

Therefore, in recent years, a water treatment method and apparatus for removing scale components in cooling water by electrolytic treatment have been proposed. Patent Literature 1 and Patent Literature 2 disclose a water treatment method and a water treatment apparatus in which a voltage is applied to an electrode immersed in cooling water and a scale component in the cooling water is adhered to the electrode surface as a solid.

However, the removal efficiency of the scale component is not sufficient only by the water treatment methods by these electrolytic treatments. Therefore, as shown in Patent Document 3, in order to further improve the scale component removal efficiency,
It was necessary to add agents such as sodium bisulfate, sodium carbonate, sodium citrate, sodium acetate, sodium phosphate. Further, since these chemicals are dissolved in water and show basicity, there is a problem that the pH is increased and the water quality of cooling water after treatment is deteriorated.

[0006]

[Patent Document 1] Japanese Patent Laid-Open No. 2001-259690

[Patent Document 2] Japanese Patent Laid-Open No. 2001-129551

[Patent Document 3] Japanese Patent Application Laid-Open No. 2003-088865

DISCLOSURE OF THE INVENTION [Problems to be Solved by the Invention]

In view of the above conventional circumstances, the present invention provides a water treatment method and a water treatment apparatus capable of improving the removal efficiency of scale components and reducing the pH without using a chemical. With the goal.

[Means for Solving the Problems]

In order to solve the above problems, the present invention provides a water treatment method as claimed in claim 1, in which a voltage is applied to a plurality of electrodes in the water to be treated to adhere scale components in the water to be treated to the electrodes. In the water to be treated between the plurality of electrodes, the flow velocity with respect to the electrode surface is 0.005 to 0.12 m /
The present invention provides a water treatment method in which a carbon dioxide-containing gas is supplied so as to achieve h, and the adhesion of scale components to the electrode is promoted.

According to the above means, the carbon dioxide-containing gas supplied to the water to be treated between the electrodes effectively acts on the scale component in the water to be treated and promotes the adhesion of the scale component to the electrode. The scale component mentioned here includes hardness components such as calcium ions and magnesium ions, and alkali components such as hydroxide ions, hydrogen carbonate ions and carbonate ions. Further, since carbon dioxide that produces an acid in water is supplied, the pH of the water to be treated can be reduced.

A second aspect of the present invention is characterized in that, in the water treatment method according to the first aspect, the carbon dioxide concentration of the carbon dioxide-containing gas is 0.01 to 1 vol%.

According to the above means, the concentration of carbon dioxide is optimized from the viewpoint of promoting the adhesion of scale components to the electrodes and adjusting the pH.

[0012] According to a third aspect of the present invention, there is provided an apparatus for carrying out the water treatment method according to the first or second aspect, which has an electrolytic bath for treating water to be treated, and the electrolytic bath has a treatment target. A water treatment apparatus provided with a water inlet and a water outlet, a plurality of electrodes provided between the water inlet and the water outlet, and a carbon dioxide-containing gas supply hole having a diameter of 0.002 to 2 mm. provide.

According to the above structure, the water treatment apparatus is provided which can efficiently attach the scale component in the water to be treated to the electrode by the carbon dioxide-containing gas and further reduce the pH.

According to a fourth aspect, in the water treatment apparatus according to the third aspect, the distance between the electrodes is 10 to 20 mm.

According to the above construction, the distance between the electrodes is optimized from the viewpoint of promoting the adhesion of scale components to the electrodes.

According to a fifth aspect, in the water treatment apparatus according to the third or fourth aspect, there is provided a dispersion plate having a plurality of holes for passing water to be treated between the inlet and the electrode. It is characterized by having.

According to the above construction, the water to be treated is evenly passed between the electrodes through the dispersion plate, and the flow directions thereof are aligned, so that the scale adhesion speeds to the electrodes are almost the same.

【The invention's effect】

As described above, according to the water treatment method of the present invention, the voltage is applied to the electrodes in the water to be treated and the carbon dioxide-containing gas is supplied to the water to be treated between the electrodes, so that the scale component in the water to be treated is removed. Can be efficiently performed, and further, the pH of the water to be treated can be reduced.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention will be described in detail below. First, an embodiment (1) of a water treatment device according to the present invention will be described with reference to FIGS.
Shown in.

The water treatment device 1 according to the embodiment (1) is
The electrolytic bath 10 includes an electrolytic bath 10 and a settling bath 14 provided at the subsequent stage. The electrolytic bath 10 includes an electrolytic bath case 104, a plurality of electrodes 11 provided in the electrolytic bath case 104, and a gas supply pipe 1.
2 and the dispersion plate 13 are roughly configured.

Into the electrolytic cell case 104, an inlet pipe 101 provided with an inlet 102 for passing the water S to be treated into the electrolytic cell 10 is inserted, and an outlet 103 is opened on the side surface. . In addition, on the side surface of the electrolytic cell case 104, a bubble discharging portion 10 is provided at a position between the electrode and the dispersion plate so that a corrosive bubble gas generated by killing bacteria and the like can be discharged.
6 is provided. Although various materials can be used as the material of the electrolytic cell case 104, SUS or the like is preferably used from the viewpoint of strength and heat resistance.

Further, on the inner peripheral surface of the electrolytic cell case 104,
Insulating holding member 10 for holding the end portion of the electrode 11.
5 are provided. The material of the holding member 105 may be any material as long as it is insulating, and plastic or the like is used.

The electrode 11 is formed in a flat plate shape, and a plurality of electrodes 11 are provided in parallel inside the electrolytic cell 10 at equal intervals. In addition, the cathode 11A and the anode 11B
And are arranged alternately. Further, the surface of the electrode can have various shapes such as a flat surface, a mesh shape, and a concavo-convex shape, but it is preferably a flat surface so that the scale component attached to the electrode is easily peeled off.

The material of the electrode 11 may be any material as long as it is electrically conductive, but in consideration of corrosion resistance, conductivity, etc.,
It is preferable to use a titanium base material plated with a Group VIII metal such as platinum, iridium, palladium, or rhodium. These Group VIII metals have a catalytic effect on the precipitation reaction of the scale component and accelerate the reaction of the scale component. Among the Group VIII metals, a titanium base material plated with platinum metal is particularly preferably used. Platinum has a thermal expansion coefficient almost equal to that of titanium, so that it is thermally stable and the plating is less likely to peel off.

The distance w between the electrodes is preferably 10 to 20 mm. When the inter-electrode distance w is smaller than 10 mm, the space velocity of the carbon dioxide-containing gas G with respect to the inter-electrode volume becomes large, so that the scavenging action by the bubbles works and the adhesion of scale components to the surface of the electrode is prevented. There is. Further, when the attached scale component grows, a short circuit between electrodes may occur. On the other hand, when the electrode distance w is larger than 20 mm, the current density decreases,
The deposition rate of scale components may decrease, and it is necessary to increase the voltage to keep the current density constant.

The gas supply pipe 12 is arranged below the electrode 11, and the gas supply hole 1 for supplying the carbon dioxide-containing gas G to the water S to be treated between the electrodes 11 is provided on the upper surface of the pipe.
21 is provided. The diameter d of the gas supply hole 121 is 0.
It is preferably 002 mm to 2 mm. The diameter d is 0.
If it is smaller than 002 mm, clogging may occur due to sedimented scale components and the like. On the other hand, when the diameter d is larger than 2 mm, the bubbles of the carbon dioxide-containing gas G become large and the contact area between the carbon dioxide and the water S to be treated becomes small, so that the deposition rate of the scale component decreases.

The dispersion plate 13 is for uniformly passing the water S to be treated between the electrodes 11, and is provided in the flow path from the inlet 101 to the electrodes 11. The diameter of the holes 131 of the dispersion plate 13 is preferably about 2 to 20 mm. Hole 13
If the diameter of 1 is smaller than 2 mm, the water S to be treated may cause clogging. On the other hand, when it is larger than 20 mm, the water flow direction of the water S to be treated becomes non-uniform, and turbulent flow may occur. Further, the dispersion plate 13 guides the corrosive foamy gas generated by the killing of microorganisms, bacteria and the like in the electrolytic cell 10 to the bubble discharging section 106. Since the corrosive foam gas is exhausted to the outside of the system of the water treatment device 1 through the exhaust port 107 provided in the exhaust unit 106, the corrosion of the metal member of the electrolytic cell 10 and the power supply connection fitting between the electrode plates is caused. Is suppressed.

Further, a settling tank 14 is provided at the latter stage of the electrolytic cell 10, and at the bottom of the settling tank 14, the scale component separated from the electrode 11 and settling is periodically discharged out of the system. A blow outlet 142 is provided.

A water treatment method for removing scale components in the water S to be treated by using the water treatment apparatus 1 having the above structure will be described.

The water S to be treated is introduced from the introduction pipe 101 into the electrolytic cell 11
Each electrode 11 is introduced into the inside and dispersed by the dispersion plate 13.
Water is evenly distributed in the plate surface direction. The electrode 11 has
A voltage is applied through the power cable, and scale components such as calcium ions and magnesium ions in the water S to be treated are attracted to the cathode 11A. This allows
In the vicinity of the cathode 11A, the scale component becomes supersaturated and forms a scale aggregate containing calcium carbonate, magnesium silicate, etc., and adheres to the cathode 11A.

At this time, the carbon dioxide-containing gas G is supplied to the water S to be treated between the electrodes 11 through the gas supply holes 121 provided in the gas supply pipe 12. The supplied carbon dioxide is dissolved in the water S to be treated, and a part thereof is present as carbonate ion by the reactions shown in (Chemical formula 1) to (Chemical formula 3) below. Then, the carbonate ions promote the reactions shown in (Chemical formula 4) and (Chemical formula 5), and the adhesion rate of the main scale components in the water to be treated S, such as calcium carbonate and magnesium carbonate, to the cathode 11A is improved. . Further, since carbon dioxide becomes an acid in water, the pH of the water S to be treated is also reduced.

[0032]

[Chemical 1]

[0033]

[Chemical 2]

[0034]

[Chemical 3]

[0035]

[Chemical 4]

[0036]

[Chemical 5]

Furthermore, the supply of the carbon dioxide-containing gas promotes the formation of scale aggregates by carbonates such as calcium carbonate and magnesium carbonate, and other scale components are also incorporated in the process, so that hydroxide salts, silica Adhesion of other scale components such as is also promoted.

When the adhered amount of the scale component exceeds a certain amount, problems such as a decrease in the adherence rate of the scale component and difficulty in peeling off the adhered scale component occur. Therefore, in order to remove the scale component attached to the electrode 11, it is preferable to switch the polarities of the cathode 11A and the anode 11B. However, if the polarity is changed frequently, the life of the electrode 11 is shortened. For these reasons, the polarity switching interval is preferably about 12 to 48 hours. The scale component separated from the electrode 11 settles at the bottom of the settling tank 14,
It is discharged to the outside of the system through the blow discharge port 142. By providing the settling tank 14 at the subsequent stage of the electrolysis tank 10, it is possible to remove the scale component more reliably.

At the anode 11B, the chlorine content in the water S to be treated is concentrated and electrolyzed to produce a chlorine-based oxidizer such as hypochlorous acid. The generated chlorine-based oxidizing agent acts on microorganisms such as bacteria and algae in the water S to be treated, and suppresses sterilization or growth.

The water S to be treated is preferably supplied into the electrolytic cell 10 so that the flow velocity with respect to the electrode surface is 0.01 to 0.1 m / h. The flow velocity with respect to the electrode surface represents the supply amount per unit electrode area. When the flow velocity of the water to be treated S is less than 0.01 m / h, the electrode 1
Since the water S to be treated during 1 is heated and the temperature in the electrolytic bath 10 rises, a member having low heat resistance may deteriorate. On the other hand, when the flow velocity of the water S to be treated is higher than 0.1 m / h, the contact time with the electrode is not sufficient, so that the electrode 1
In some cases, the adhesion rate of the scale component to 1 may be reduced, or the peeled scale component may carry over.

The carbon dioxide-containing gas G is preferably supplied so that the flow velocity with respect to the electrode surface is 0.005 to 0.12 m / h. If the flow velocity with respect to the electrode surface is less than 0.005 m / h, the deposition rate of the scale component on the electrode 11 decreases. On the other hand, 0.12m /
When it is larger than h, the scavenging action of bubbles of the carbon dioxide-containing gas G acts on the surface of the electrode 11, and the adhesion of scale components to the electrode 11 is hindered.

The carbon dioxide concentration of the carbon dioxide-containing gas G is preferably 0.01 to 1 vol%. 0.01
If it is less than vol%, the scale removal effect may be reduced. On the other hand, when it is 1 vol% or more, the amount of carbon dioxide dissolved in the water S to be treated increases and the carbon dioxide concentration in the water S to be treated becomes high, which may cause corrosion in the cooling water system.

As a method of applying a voltage to the electrode 11, either a constant current method or a constant voltage method can be adopted, but a constant current method is preferable. According to the constant current method, a constant scale amount can be attached to the electrode 11 regardless of the concentration of the scale component in the water S to be treated.

The DC voltage applied to the electrode 11 is 5 to
20V is preferable. If the voltage is lower than 5 V, the rate of deposition of scale components on the electrode 11 is reduced. On the other hand, when the voltage is higher than 20 V, the scale adhesion efficiency is lower than the applied power.

The current density of the current applied to the electrode 11 is preferably 0.001 to 0.03 A / cm ² . If the current density is less than 0.001 A / cm ^{2, the} rate of deposition of scale components on the electrodes will decrease. On the other hand, when the current density is greater than 0.03 A / cm ^{2, the} water S to be treated between the electrodes 11 is heated and the electrolytic bath 10
May increase in temperature.

In the above embodiment (1), the gas supply pipe 12 is arranged below the electrode 11, but the carbon dioxide containing gas G is supplied to the water S to be treated between the electrodes. It should have been done. In addition to the tubular shape, it is also possible to use ceramic-like pumice stones.

Next, a method of actually using the water treatment device 1 of the present invention in a cooling water system will be described. FIG. 5: is a figure showing the use condition of the water treatment apparatus 1 of this invention.

The cooling water stored in the cooling tower 2 is supplied to the heat exchanger 4 by the circulation pump 3 through the cold water line 5. Subsequently, the cooling water is supplied to the hot water line 6, and a part of the cooling water is introduced into the water treatment device 1 through the branch line 7. The cooling water introduced into the water treatment device 1 is reduced in scale component and pH, and is returned to the hot water line 6. As a result, the scale component and pH of the entire cooling water are reduced, so that scale failure in pipes, heat exchangers, etc. is prevented.

【Example】

Next, the present invention will be described in more detail with reference to examples. (Example 1) Cooling water (concentration of 10 times) was passed through a water treatment device at a flow rate of 0.065 m / h to apply a voltage to the electrodes, and
The cooling water was treated by supplying a carbon dioxide-containing gas to the cooling water between the electrodes. Then, the calcium hardness, M alkalinity, pH and the like before and after the treatment of the cooling water were measured. The voltage was applied to the electrodes by automatically controlling so that a constant current of 100 A would flow between the electrodes. The carbon dioxide-containing gas having a carbon dioxide concentration of 0.04% was used, and the flow velocity was 0.097 m / m with respect to the electrode surface.
It was supplied so that it would be h. As the gas supply hole for supplying the carbon dioxide-containing gas, a ceramic material having a myriad of holes each having a diameter of 0.01 to 0.05 mm was used. The gas supply pressure was 30 kPa. And the electrode has 400
× 350 mm plate-shaped, 1.5 mm thick TiO
Twelve sheets of Pt having a thickness of 1 μm plated on the _two base materials were used. The electrodes were arranged such that the anode and the cathode were alternately arranged so that the distance between the electrodes was 13.5 mm.

(Example 2) The flow rate of the carbon dioxide-containing gas to the electrode surface was 0.02.
The same procedure as in Example 1 was performed except that m / h was set.

Comparative Example 1 Example 1 was repeated except that the carbon dioxide-containing gas was not supplied.
I went the same way.

(Comparative Example 2) The flow velocity of the carbon dioxide-containing gas with respect to the electrode surface was 0.15.
The same procedure as in Example 1 was performed except that m / h was set.

(Reference Example 1) Regarding makeup water, calcium hardness, M alkalinity, pH
Etc. were measured.

Table 1 shows the results of calcium hardness, M alkalinity, pH and the like before and after the treatment of the cooling water measured in Examples, Comparative Examples and Reference Examples. Moreover, SI index (Langeria index) was calculated as evaluation of the cooling water after a process.

The SI index represents the corrosiveness of water and the precipitation tendency of calcium carbonate. As shown in (Equation 1) and (Equation 2), the calcium ion concentration ([Ca ²⁺ ]) and hydrogen carbonate ion are It is calculated from three variables of concentration ([HCO ₃ ⁻ ]) and pH. Further, in the formula, pH _S , K _SP , K
Indicates the saturated pH, the solubility product of calcium carbonate, and the dissociation constant of hydrogen carbonate ion, respectively. If SI = 0, there is no tendency of scale adhesion or corrosion and the state is stable. When SI> 0, calcium carbonate is oversaturated and tends to adhere to scale. On the other hand, in the case of SI <0, the calcium carbonate is unsaturated and there is a tendency for corrosion.

[0056]

[Equation 1]

[0057]

[Equation 2]

[0058]

[Table 1]

As shown in Table 1, it is apparent that in Example 1, the scale component was effectively removed as compared with Comparative Example 1 in which the carbon dioxide-containing gas was not supplied. In particular, calcium ions and alkaline components are effectively removed, and it is clear that the SI value approaches 0 in Example 1 even when compared with the SI value. Further, it can be seen that silica or the like which does not form a carbonate is effectively removed. Further, it is clear that the scale component is effectively removed as compared with Comparative Example 2 in which the flow rate of the carbon dioxide-containing gas is set to 1.5 times.

In Example 2, the flow rate of the carbon dioxide-containing gas is 0.2 times that of Example 1, but compared to Comparative Examples 1 and 2, the removal of scale components is sufficiently promoted. You can see that

From the above results, it is understood that the water treatment method and the water treatment apparatus of the present invention are very effective in removing scale components in cooling water.

[Brief description of drawings]

[0062]

FIG. 1 is a schematic perspective view of a water treatment device according to an embodiment (1).

FIG. 2 is a sectional view taken along line AA of FIG.

FIG. 3 is a sectional view taken along line BB of FIG.

FIG. 4 is a diagram showing scale attachment to electrodes.

FIG. 5 is a diagram showing a usage state of the water treatment device.

[Explanation of symbols]

[0063] 1 Water treatment device 10 Electrolyzer 101 introduction tube 102 inlet 103 outlet 104 electrolyzer case 105 holding member 106 Bubbling unit 107 Bubble outlet 11 electrodes 11A cathode 11B anode 12 gas supply pipe 121 Gas supply hole 13 Dispersion plate 131 holes 14 Settling tank 141 outlet 142 Blow outlet 2 cooling tower 3 circulation pumps 4 heat exchanger 5 cold water line 6 hot water line 7 branch lines 8 makeup water tank G carbon dioxide containing gas S treated water X scale

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Claims (5)

(57) [Claims] 1. A water treatment method for applying a voltage to a plurality of electrodes in treated water to adhere scale components in the treated water to the electrodes, wherein the treated water between the plurality of electrodes is Flow velocity to the surface is 0.005-0.12m /
A water treatment method in which a carbon dioxide-containing gas is supplied so as to attain h, and adhesion of scale components to the electrode is promoted. 2. The water treatment method according to claim 1, wherein the carbon dioxide-containing gas has a carbon dioxide concentration of 0.01 to 1 vo.
A water treatment method characterized by being 1%. 3. An apparatus for carrying out the water treatment method according to claim 1, further comprising an electrolytic bath for treating the water to be treated, wherein the electrolytic bath has an inlet for the water to be treated and An outlet, a plurality of electrodes provided between the inlet and the outlet,
A water treatment device provided with a carbon dioxide-containing gas supply hole having a diameter of 0.002 to 2 mm. 4. The water treatment device according to claim 3, wherein the distance between the electrodes is 10 to 20 mm. 5. The water treatment apparatus according to claim 3 or 4, further comprising a dispersion plate provided between the inlet and the electrode with a plurality of holes for passing water to be treated. And water treatment equipment.