JP2001259650A - Method for preventing scale and slime - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for preventing scale and slime capable of simultaneously preventing scale trouble and slime trouble by simultaneously performing the removal of a hardness component and the supply of an oxidizing agent without using chemicals in a cooling water system. SOLUTION: In the preventing method of the scale and the slime in which the hardness component in water is stuck and removed as solid on the surface of a cathode by applying voltage to an electrode immersed in the cooling water and also chloride ion is converted into an oxidizing agent on the surface of an anode, at least anode out of electrodes is the electrode having the element or oxide of a platinum group element on the surface.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a method for preventing scale and slime. More specifically, the present invention provides
The present invention relates to a scale and slime prevention method capable of simultaneously removing a hardness component and supplying an oxidizing agent without using a chemical in a cooling water system, thereby simultaneously preventing scale damage and slime damage.

[0002]

2. Description of the Related Art Many chemicals are used in water treatment of a cooling water system in order to prevent scale disturbance and slime disturbance. For example, to prevent scale, water-soluble polymers,
Phosphonic acid, polyphosphate and the like are widely used,
Oxidizing agents such as sodium hypochlorite and aqueous hydrogen peroxide are used to prevent slime. However, if such chemicals are used to prevent scale and slime problems, it takes time and labor to check the stock and place an order, and the transportation of the chemicals by tank lorry, the movement of chemical containers, etc. Carrying effort is required, there is a risk of handling such as damage to the human body due to leakage of chemicals, etc.In addition, analysis is performed and chemical injection speed is adjusted to maintain and control the concentration of water-based chemicals at a predetermined value Work is required. In addition, in the treatment with chemicals, there is a limit in water quality that can prevent scale, and wastewater is generated because blowing is performed so as not to exceed the upper limit. This drainage contains C
Since it contains an OD component, a phosphorus component, etc., it is necessary to perform a wastewater treatment in order to be discharged into a general water system, and a cost burden must be borne according to the amount. For this reason, in order to eliminate the effects on the environmental load caused by the treatment by chemicals and various complications, dangers in handling, etc., it is possible to respond to high concentration operation without using chemicals, There has been a demand for a method capable of simultaneously preventing scale and slime.

[0003]

SUMMARY OF THE INVENTION The present invention relates to a scale capable of simultaneously removing a hardness component and supplying an oxidizing agent in a cooling water system without using a chemical, thereby simultaneously preventing scale obstacles and slime obstacles. And a method for preventing slime.

[0004]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to solve the above-mentioned problems, and as a result, using an electrode having a simple substance or an oxide of a platinum group element on the surface as an anode, By converting chloride ions in water to oxidizing agent and supplying it to the water system, the hardness component in water is attached as a solid on the cathode surface and removed, thereby simultaneously preventing scale and slime problems without using chemicals. They have found that they can be prevented, and have completed the present invention based on this finding. That is, according to the present invention, (1) a voltage is applied to the electrode immersed in the cooling water to remove the hardness component in the water as a solid on the cathode surface and convert chloride ions to an oxidizing agent on the anode surface. A method for preventing scale and slime to be supplied into an aqueous system, wherein at least the anode among the electrodes is a method for preventing scale and slime, which is an electrode having a simple substance or an oxide of a platinum group element on the surface, (2) The method for preventing scale and slime according to (1), wherein both the anode and the cathode are electrodes having a simple substance or oxide of a platinum group element on the surface, and the cathode and the anode are inverted. 3. The method for preventing scale and slime according to item 1 or 2, wherein the element is platinum, ruthenium or iridium, and (4) measuring the oxidizing agent concentration in the cooling water, and determining the measurement result. 4. The method for preventing scale and slime according to claim 1, wherein the current between the electrodes is controlled so that the oxidant concentration in the cooling water is adjusted to a predetermined value. Is what you do.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION The scale and slime prevention method of the present invention is to apply a voltage to an electrode immersed in cooling water to remove a hardness component in water as a solid on a cathode surface and to remove the hardness component from the anode surface. This is a method for preventing scale and slime that converts chloride ions into an oxidizing agent and supplies the oxidizing agent into an aqueous system, wherein at least the anode among the electrodes uses an electrode having a simple substance or oxide of a platinum group element on the surface. . In the method of the present invention, a set of electrodes consisting of an anode and a cathode is immersed in cooling water, and a voltage is applied between the terminals of these electrodes using an external power supply. At this time, water is electrolyzed on the surface of the cathode to generate hydroxide ions. As a result, the pH of the electrode surface locally increases, and hardness components such as calcium carbonate and magnesium silicate precipitate and adhere to the surface. As a result, the concentration of the hardness component in the water decreases, and it is possible to prevent scale from being generated on the heat transfer surface such as a heat exchanger. On the other hand, on the surface of the anode, chloride ions in the cooling water are oxidized, and oxidizing chemical species such as hypochlorite ions are generated and supplied into the aqueous system. By maintaining the generated oxidant in the aqueous system, slime damage can be prevented. From the viewpoint of hypochlorite ion generation efficiency and corrosiveness, the chloride ion concentration in the cooling water is preferably from 10 to 200 mgCl / L.

The anode used in the method of the present invention is an electrode having on its surface a simple substance or an oxide of a platinum group element. As the electrode having a simple substance or oxide of a platinum group element on the surface, an electrode composed entirely of a simple substance or oxide of a platinum group element can be used, or an entire surface of a simple substance or oxide of a platinum group element, or Alternatively, an electrode whose surface is coated at an appropriate ratio may be used. When the electrode surface is coated with a platinum group element element or an oxide, the material of the electrode body is not particularly limited, but is preferably a corrosion-resistant material. Examples of the corrosion-resistant material include titanium, stainless steel, silver, carbon, and aluminum. The materials for the anode and the cathode can be the same material or different materials. Examples of the platinum group element include ruthenium, rhodium, palladium, osmium, iridium, and platinum. Among these, platinum,
Ruthenium and iridium can be particularly preferably used. By using an electrode having a simple substance or an oxide of a platinum group element on the surface, the efficiency of generation of the oxidizing agent can be improved by its catalytic action. There is no particular limitation on the method of incorporating a simple substance or oxide of a platinum group element on the electrode surface, and the ratio of the simple substance or oxide of the platinum group element covering the electrode surface depends on the amount of oxidizing agent required. It can be selected as appropriate.

In the method of the present invention, the voltage applied to the electrode is not particularly limited, but is preferably 40 V or less in consideration of safety for the human body. Also, in order to stably prevent scale and slime, the voltage can be automatically controlled to keep the current flowing between the electrodes constant. Alternatively, the current is measured while measuring the oxidant concentration.
It can be controlled so that this becomes a predetermined value. For example, when the water quality of the cooling water fluctuates greatly, maintenance of the cooling water system can be stably performed by adding a system that automatically controls the current based on the measured value of the oxidant concentration. On the other hand, the current required for removing the hardness component can be calculated from the required hydroxide ion generation rate in accordance with the target removal rate of the hardness component. At this time, if the current required for generating the oxidant exceeds the current for removing the hardness component, the operation can be performed in an optimal state. That is, the hardness component is sufficiently removed while the concentration of the oxidizing agent is maintained at a predetermined value in the system. Generally, the current is preferably between 0.1 and 5 A, more preferably between 1 and 3 A. However, the current required to remove the hardness component is often lower than the calculated value. This is considered to be due to the fact that the hardness component attached to the electrode surface becomes a seed crystal and assists in crystal growth, that is, removal of the hardness component. In the method of the present invention, it is preferable that the hardness component adhering to the cathode is peeled off by reversing the polarity of the electrode, and the peeled-off hardness component is treated by a later-stage recovery and removal means. When the hardness component is deposited and adheres to the cathode surface, the current decreases even when a constant voltage is applied. By inverting the polarity of the electrode and using the cathode on which the hardness component is attached as the anode, hydrogen ions are generated from the surface of the electrode, and the adhesive portion of the attached hardness component with the electrode surface is locally dissolved and peeled off. be able to. When reversing the polarity of the cathode and the anode, it is preferable that both poles have a simple substance or oxide of a platinum group element on the surface, and have the same material and structure.

In the method of the present invention, there is no particular limitation on the interval of the reversal of the polarity of the electrode. However, in order to easily collect and remove the peeled hardness component, the thickness of the hardness component adhering to the cathode is 0.5 mm or more. It is preferable to invert after growing.
Further, in order to prolong the life of the electrode, it is preferable that the interval between the reversal of the polarity of the electrode is one hour or more. In the method of the present invention, the structure of the electrode is not particularly limited, but it is preferable to incorporate the electrode into a container to form an electrolytic cell through which water flows.
Although there is no particular limitation on the location of the electrolytic cell, it is preferable to provide a branch line in the cooling water system, install the electrolytic cell, and return water passing through the electrolytic cell to the cooling tower. In the method of the present invention, it is preferable that the hardness component peeled off from the cathode is removed by a collecting means provided at a later stage. By removing the hardness component separated from the cathode by the recovery means, it is possible to prevent the hardness component from being clogged in a strainer or the like and crushed by a pump or the like to become fine particles and deposited in a heat exchanger or a pipe. In the method of the present invention, there is no particular limitation on the means for recovering the hardness component, but since the hardness component peeled from the cathode is liable to settle, most of the hardness component can be recovered by installing a settling tank at the latter stage of the electrolytic cell. . When the sediment is liable to be clogged in a thin pipe at the time of discharging the sediment, a crusher or the like can be attached to discharge the sediment while crushing the sediment. In addition, by providing a filter at the subsequent stage of the sedimentation tank, fine particles of the hardness component that have not been collected in the sedimentation tank can be collected.

FIG. 1 is a process flow chart of an embodiment of the method of the present invention. The cold water stored in the pit 2 of the cooling tower 1 is sent to the heat exchanger 4 by the circulation pump 3. A part of the cold water is divided into a branch line 5 and passed through a valve 6 to an electrolytic cell 7 having a pair of electrodes. The chloride ions in the water are converted into oxidizing agents and supplied into the aqueous system. Due to the reversal of the polarity of the electrode, the hardness component separated from the surface of the electrode is settled and separated in the settling tank 8. The supernatant water of the sedimentation tank is sent to the filter 9 to remove fine particles of the hardness component remaining in the water, and then returned to the cooling tower. The method of the present invention uses a compact apparatus, is simple and safe, and can greatly reduce the amount of wastewater. Also,
In the method of the present invention, since no chemical is used, no burden is imposed on the environment, and problems such as various complications and dangers in handling the chemical can be solved. Furthermore, it is possible to cope with a high concentration operation as compared with the conventional chemical treatment method.

[0010]

EXAMPLES The present invention will be described in more detail with reference to the following Examples, which should not be construed as limiting the present invention. In the Examples and Comparative Examples, the scale prevention ability and the slime prevention ability were evaluated in a cooling water system having a pilot-scale heat exchanger excluding the filter from the process shown in FIG. This cooling water system has a water volume of 300 L, an outer diameter of 19 mm, and a wall thickness of 1 mm.
Internal heat transfer area with two US304 tubes is 0.
It has a heat exchanger of 32 m ² . Cooling water flow is 1,6
80 L / h, of which 300 L / h was drawn from the branch line into an electrolytic cell provided with two iridium-coated titanium electrodes, and the voltage was controlled so that the residual chlorine concentration became a predetermined value. The anode and cathode were inverted each time. The hardness component separated from the electrode settled and separated in the settling tank. The makeup water has a chloride ion concentration of about 10 mg / L,
The operation was performed using city water having a calcium hardness of about 40 mg CaCO ₃ / L at a concentration ratio of 5 or 10 times. Further, the cooling water inlet temperature at the heat exchanger was maintained at 30 ° C., and the heat exchanger outlet temperature at 50 ° C. After 30 days of operation, the calcium hardness of the cooling water was measured, the amount of scale attached was determined from the increase in the weight of the tubes of the heat exchanger, and the hardness per day was determined from the total amount of the hardness components recovered in the settling tank. The component recovery rate was calculated. Further, the chloride ion concentration and the residual chlorine concentration of the cooling water were measured. Furthermore, from the 20th day after the start of operation, 23
75mm x 25mm x in cold water pit for 3 days until day
Three 1.5 mm rubber plates were immersed, and the slime adhered and grown was collected and dried at 105 ° C. until a constant weight was obtained.
The slime deposition rate was determined from the arithmetic mean of the measured weights. Example 1 Cooling water concentration ratio 5 times, residual chlorine concentration 0.15 mgCl / L
Was operated for 30 days. Cooling water has a calcium hardness of 152 mg CaCO ₃ / L and a scale adhesion rate of 9 mg / c.
m ² / month and the recovery rate of the hardness component were 17 g / day. The chloride ion concentration of the cooling water was 45 mg / L, and the slime deposition rate was 10 mg / dm ² / 3day. Example 2 Cooling water concentration ratio 5 times, residual chlorine concentration 0.60 mgCl / L
Was operated for 30 days. Calcium hardness of cooling water is 138mgCaCO ₃ / L, scale adhesion rate is 7mg / c
m ² / month, and the recovery rate of the hardness component was 23 g / day. The chloride ion concentration of the cooling water was 39 mg / L, and no slime was attached. Comparative Example 1 The flow of cooling water to the branch line was stopped, and the molecular weight was 3,500.
Was added so that the concentration of polymaleic acid became 20 mg / L, and the concentration of residual chlorine became 0.6 mgCl / L, and operation was carried out for 30 days at a cooling water concentration ratio of 5 times. . The calcium hardness of the cooling water is 201mgCaCO ₃ /
L, the scale deposition rate was 13 mg / cm ² / month.
The chloride ion concentration of the cooling water was 69 mg / L, the residual chlorine concentration of the cooling water was 0.62 mgCl / L, and no slime was observed. Comparative Example 2 The cooling water was stopped flowing through the branch line, and the operation was performed for 30 days at a concentration ratio of cooling water of 5 times without adding a chemical. The calcium hardness of the cooling water is 153mgCaCO ₃ / L,
The scale deposition rate was 118 mg / cm ² / month. Chloride ion concentration of the cooling water is 52 mg / L, the residual chlorine concentration of the cooling water is 0.04mgCl / L, the deposition rate of the slime was 30mg / dm ² / 3day. Example 3 Concentration ratio of cooling water 10 times, residual chlorine concentration 0.20 mgCl /
The operation was performed for 30 days under the condition of L. Calcium hardness of cooling water is 138mgCaCO ₃ / L, scale adhesion speed is 13m
g / cm ² / month, and the recovery rate of the hardness component was 20 g / day. The chloride ion concentration of the cooling water was 92 mg / L, and the slime deposition rate was 8 mg / dm ² / 3day. Example 4 Concentration ratio of cooling water 10 times, residual chlorine concentration 0.80 mgCl /
The operation was performed for 30 days under the condition of L. The calcium hardness of the cooling water is 132mgCaCO ₃ / L, the scale adhesion speed is 11m
g / cm ² / month, and the recovery rate of the hardness component was 24 g / day. The chloride ion concentration of the cooling water was 87 mg / L, and the slime deposition rate was 1 mg / dm ² / 3day. Comparative Example 3 The flow of cooling water to the branch line was stopped, and the molecular weight was 3,500.
Was added so that the concentration of polymaleic acid became 20 mg / L, and the concentration of residual chlorine became 0.8 mgCl / L, and operation was performed for 30 days at a cooling water concentration ratio of 10 times. . Calcium hardness of cooling water is 315mgCaCO ₃
/ L, the scale deposition rate was 52 mg / cm ² / month. Chloride ion concentration of the cooling water is 124 mg / L, the residual chlorine concentration of the cooling water is 0.81mgCl / L, slime deposition rate was 1mg / dm ² / 3day. Comparative Example 4 The cooling water was stopped flowing through the branch line, and the operation was performed for 30 days at a concentration ratio of cooling water of 10 times without adding a chemical. The calcium hardness of the cooling water is 158mgCaCO ₃ /
L, the scale deposition rate was 186 mg / cm ² / month. Chloride ion concentration of the cooling water is 104 mg / L, the residual chlorine concentration of the cooling water is 0.02mgCl / L, the deposition rate of the slime was 58mg / dm ² / 3day. Examples 1-4
Table 1 shows the processing conditions and results of Comparative Examples 1 to 4.

[0011]

[Table 1]

As shown in Table 1, in Examples 1 to 4 in which cooling water was passed through an electrolytic cell provided in a branch line and a voltage was applied to an electrode, a hardness component was recovered in a settling tank. Scale is prevented from adhering to the tubes of the heat exchanger, and the residual chlorine concentration in the cooling water increases,
Slime adhesion is also prevented. In particular, a concentration ratio of 10
In the case of twice, it is difficult to sufficiently prevent the adhesion of scale by the conventional method in which polymaleic acid and sodium hypochlorite are added as in Comparative Example 3, but according to the method of the present invention, Examples 3 to 4 are used. As described above, scale adhesion can be prevented. In addition, when the concentration magnification was 10 times, the amount of blow water decreased to に or less of that when the concentration magnification was 5 times.

[0013]

According to the method of the present invention, an oxidizing agent can be generated while removing the hardness component in the cooling water by one electrolytic cell, thereby simultaneously preventing scale and slime of the cooling water system. it can. In addition, scale adhesion can be effectively prevented even under high concentration conditions which cannot be achieved by conventional chemical treatment.

[Brief description of the drawings]

FIG. 1 is a process flow chart of an embodiment of the method of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Cooling tower 2 Pit 3 Circulation pump 4 Heat exchanger 5 Branch line 6 Valve 7 Electrolysis cell 8 Sedimentation tank 9 Filter

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) F28F 19/01 F28G 13/00 A F28G 13/00 F28F 19/00 501D (72) Inventor Akira Iimura Tokyo 3-7-7 Nishi-Shinjuku, Shinjuku-ku, Kurita Kogyo Co., Ltd. (72) Inventor Shinji Sasaki 2-6-1, Nakase, Mihama-ku, Chiba-shi, Chiba WBG Malibu West 19th Floor Asahi Glass Engineering Co., Ltd. (72) Inventor Masanori Oishi 2nd floor, 6-6 Nakase, Mihama-ku, Chiba-shi, Chiba WBG Malibu West 19th floor Asahi Glass Engineering Co., Ltd. F term (reference) 3L044 DB02 HA05 JA06 KA01 KA05 4D061 DA05 DB02 DB05 EA02 EB01 EB05 EB12 GC05 EB37 GC39

Claims (4)

[Claims] 1. A voltage is applied to an electrode immersed in cooling water to remove a hard component in water as a solid on a cathode surface and convert chloride ions into an oxidant on an anode surface to form an aqueous agent. A method for preventing scale and slime to be supplied, wherein at least the anode among the electrodes is an electrode having a simple substance or oxide of a platinum group element on the surface. 2. The method for preventing scale and slime according to claim 1, wherein the anode and the cathode are both electrodes having a simple substance or an oxide of a platinum group element on the surface, and the cathode and the anode are inverted. 3. The method for preventing scale and slime according to claim 1, wherein the platinum group element is platinum, ruthenium or iridium. 4. The method according to claim 1, further comprising measuring an oxidant concentration in the cooling water and controlling a current between the electrodes so as to adjust the oxidant concentration in the cooling water to a predetermined value based on the measurement result. The method for preventing scale and slime according to claim 1, 2, or 3.