JP2005046810A - Scale prevention apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a scale prevention apparatus capable of stably preventing the precipitation of scale mainly comprising metal ions such as calcium and magnesium or silica which are dissolved in water to be treated. <P>SOLUTION: The scale prevention apparatus electrolyzes water, produces fine particles of carbonates of the metal ions dissolved in the water and produces a scale preventing chemical agent by the electrolysis. An anode 12 which is arranged between a pair of planar cathodes 11, 11 is composed of a square tube shaped particle retainer 12a made of a porous body such as mesh and punching plate, particles 12b made of carbonaceous material which are packed in the particle retainer 12a, and an anode plate 12c which is arranged substantially at the center of the particle retainer 12a. A scale preventing component such as mellitic acid is produced by the oxidation reaction on the anode. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an apparatus for preventing scale generated in a cooling water circulation line, a boiler line or the like in a factory or a building.

  Heat exchangers in open circulation cooling water lines such as cooling towers, boiler towers in boiler towers such as cooling towers and piping, or once-through boilers are mainly composed of metal ions such as calcium and magnesium or silica contained in water. Scales may adhere, resulting in a decrease in heat transfer efficiency, blockage of piping, and the like.

  In order to prevent this scale adhesion, more types of scale preventive agents have been used than before. Recently, devices that prevent scale by applying an electric or magnetic field have been developed and sold.

  Japanese Patent No. 2912809 describes a method of preventing scale generation by treating boiler water with electric and magnetic fields.

In Japanese Patent Publication No. 2001-502229, a pair of electrodes made of graphite is disposed in a cylindrical container, and conductive particles made of a carbonaceous material such as graphite, silica, glass, and plastic are disposed between the electrodes. A method is described in which scale formation is reduced by mixing and filling non-conductive particles such as water and passing water through a cylindrical container while energizing between the electrodes. According to the description of the same issue, alkali is generated by this energization treatment, crystal nuclei are generated by this alkali (page 12, lines 17-18), and the scale generation tendency decreases (page 7, lines 5-6). ).
Japanese Patent No. 2912809 Special table 2001-502229 gazette

  Scale can be prevented by adding an appropriate amount of appropriate chemicals to the open circulating cooling water line or boiler line, but the concentration of circulating water or boiler can water can be accidentally operated above the specified level, or vice versa. If the engine is operated at a significantly lower concentration than specified, or if the load on the heat exchange side is larger than specified, the scale may adhere to the heat exchange section where the temperature is high or the cooling tower where water evaporates. This is because if the operation is continued under the condition exceeding the above-mentioned regulation, it will deviate from the scale prevention ability range of the added drug. In order to avoid such a situation, it is only necessary to always add a drug that can cope with an operating condition such as a high load. However, the cost of the drug becomes enormous and is difficult in practice.

  Furthermore, when the raw water quality is very high, such as calcium hardness, silica, total iron concentration, etc., or when the heat load is high, such as a resin polymerization reaction tower, the currently available anti-scale agents may not be applicable. is there.

  In the apparatus for applying an electric field and a magnetic field of the above-mentioned Japanese Patent No. 2912809, since the scale prevention mechanism is hardly clarified, there is a possibility that scale prevention is insufficient.

  According to the method of JP-T-2001-502229, as the water flow continues, the carbonaceous material particles are selected from the mixed packed bed of the particles made of the carbonaceous material filled between the electrodes and the non-conductive particles. Wears down and the particle size decreases. And for this reason, the particle | grain space | interval of a packed bed becomes small and water flow resistance increases. In addition, when the height of the packed bed decreases as the conductive carbonaceous material particles are depleted, even if a new filler is supplied to the packed bed from above to compensate for this, the lower part of the packed bed is carbon. The material particles are not replenished, and most of them become non-conductive particles, and the effect of reducing the scale generation at the lower part of the packed bed tends to be insufficient.

  Therefore, the present applicant has previously proposed scale prevention devices that can solve such problems (Japanese Patent Application Nos. 2003-066184, 2003-061815, and 2003-100526).

  This scale prevention device exhibits an excellent scale prevention effect over a long period of time, but it is desirable that practically the scale prevention effect can be exhibited more efficiently.

  Accordingly, as a result of various studies on the growth mechanism of the scale by the present inventors, the scale is deposited with carbonates such as calcium carbonate and magnesium in the circulating water, which grows and deposits on or adheres to the inner surface of the device. Therefore, if a high pH region is formed on the cathode side in the electrolysis and the scale component is generated in advance as fine particles, and this is rapidly processed by the scale preventing component to maintain the fine particles, It has been found that even if the hardness component in the circulating water is supersaturated, the fine particles do not grow and do not become scale.

  This invention is made | formed in view of the said subject, and aims at providing the scale prevention apparatus which exhibits the scale prevention effect efficiently over a long period of time.

  The scale prevention device of the present invention is a scale prevention device for preventing scale deposition from water, electrodes having an anode and a cathode made of a carbonaceous material, means for applying a voltage between the electrodes, and water passing between the electrodes. The anode has a filler of particles made of a carbonaceous material. In the present invention, “prevention” includes “suppression”.

  In the device of the present invention, when water is passed between the anode and the cathode, water is electrolyzed to produce fine particles of metal carbonate such as calcium and magnesium dissolved in the water, and a scale preventing agent is added. By generating, scale precipitation from water is sufficiently prevented. Particularly when the carbonaceous material has a carbon six-membered ring structure, the scale-preventing agent is efficiently produced. The reason for this is considered as follows.

  That is, in the apparatus of the present invention, a high pH region is formed near the cathode. When the water passes through this region, carbonates mainly of metal ions such as calcium and magnesium contained therein are deposited. By generating a large amount of the fine particles of the scale component in the water in advance, the solubility calcium hardness in the circulating water is lowered, and the heat exchange part and the cooling tower can pass with less than the solubility, and the scale is formed in the heat exchange part and the cooling tower. It does not precipitate. The generated fine particles of the scale component circulate in the line along the water flow, but do not deposit on the inner surface of the apparatus, and are eventually discharged out of the line together with the blow.

<Mechanism for preventing scale by precipitation of fine particles>
The mechanism for preventing scale by fine particle precipitation in the present invention will be described in detail below based on the theory of scale precipitation from water.

(I) In general, the mechanism of scale precipitation from water (mechanism) is as follows.
As the water temperature increases, the solubility of carbonates such as calcium carbonate decreases. In the heat exchange part of the cooling water system or boiler water system, if the surface temperature is high and the solubility in that part is smaller than the concentration of carbonate such as calcium carbonate in circulating water or can water, that is, if it becomes supersaturated, this high temperature Scale deposits in the heat exchange section. Even if a scale-preventing agent is used, the ability to prevent scale per unit mass of the agent has been determined, and abnormal line management was performed for some reason, resulting in a carbonate concentration such as calcium carbonate in circulating water that exceeded this limit. In this case, the scale is deposited in the high temperature heat exchange part by the same mechanism.

  The filler part of the cooling tower of the circulating cooling water system has a structure that evaporates water in order to reduce the temperature of the circulating water. When water evaporates, the concentration of carbonate such as calcium carbonate in the circulating water increases, and when the concentration reaches a supersaturated state with a solubility or higher, scale is deposited on the filler. Moreover, in the filler part, in order to evaporate water efficiently, the flow-down speed of circulating water is made slow, and a scale tends to deposit on a filler.

(Ii) In the scale prevention apparatus of the present invention, the dissolved calcium hardness in water is reduced by electrolyzing water (hereinafter sometimes referred to as water to be treated) to form fine particles of metal carbonate. , Prevent scale precipitation.

  In general, the solubility of carbonates such as calcium carbonate and magnesium carbonate is affected by pH, and the solubility decreases as the pH increases.

  When the water to be treated is electrolyzed using the apparatus of the present invention, the pH in the vicinity of the cathode becomes high pH, and carbonates of metals such as calcium and magnesium in the water to be treated are deposited in the vicinity of the cathode. These precipitated fine particles circulate in the line along the flow of cooling water and boiler water, and are discharged to the outside of the line along with the blow, so the concentration of hardness components such as calcium and magnesium in the cooling water and boiler system decreases, Scale deposition in the heat exchange section and cooling tower is prevented.

  For example, in the case of the calcium carbonate component, a sufficient number of scale component fine particles are generated, so that the soluble calcium hardness in the circulating water is lowered, and the soluble calcium hardness component concentration is less than the solubility even in the heat exchange section and the cooling tower. Thus, scale deposition in the heat exchange section and cooling tower is prevented.

<Effects of production of anti-scale agent>
In the present invention, even if the hardness component in water is in a supersaturated region, a chemical agent for scale prevention such as melittic acid is generated by the electrolytic reaction at the anode, so that the generated fine particles grow excessively and accumulate on the inner surface of the device. It is prevented that it adheres. The anti-scale agent generated by this anodic reaction and added to the water to be treated is adsorbed by the fine particles. Since the scale component fine particles adsorbing the scale preventive agent hardly grow even when exposed to a supersaturated state in a heat exchange section, a cooling tower or the like, the fine particles exist in the circulating water as fine particles and are discharged out of the line together with the blow.

<Electrolytic substance with scale-inhibiting action produced by reaction at anode>
The electrolytic substance produced by the electrolytic reaction at the anode contains an aromatic carboxylic acid.

  It is known that higher-order carboxylic acids having a large number of carboxyl groups have a scale-dispersing effect, and among them, benzenehexacarboxylic acid (mellitic acid) has been reported to be effective as a scale-preventing agent (The Inhibition of Dicalcium Phosphate Dihydrate Crystal Growth by Polycarboxylic Acids Z. AMJAD Journal of Colloid and Interface Science, Vol. 117, No. 1, May 1987).

  By using a carbonaceous material having a six-membered ring structure as an anode and anodizing it in water, an aromatic carboxylic acid can be produced inexpensively and efficiently.

  The carbonaceous material having a six-membered ring structure constituting the anode is preferably a carbonaceous material having a six-membered ring network plane three-dimensionally laminated and having a carbon content of 80% or more. In particular, in order to produce higher-order carboxylic acids such as melittic acid, it is desirable that the condensation rate of the surface layer is higher. Moreover, if a carbon content rate is high, there exists an advantage that a by-product is hard to produce | generate, and it is preferable. As such a carbonaceous material, graphites such as graphite, calvin, coke, charcoal, activated carbon, anthracite, carbon black, and the like can be used. The electrode may be composed of the carbonaceous material near the surface.

  The cathode material is not particularly limited. However, in the present invention, as described later, it is preferable to perform pole reversal, and therefore, the cathode is preferably composed of a carbonaceous material similar to the anode.

  Although there is no restriction | limiting in particular in the shape of a cathode, It is preferable on the reduction of the pressure loss in an electrolytic cell that it is the flat electrode arrange | positioned facing.

  In a preferred embodiment of the present invention, an anode having a filler of carbonaceous material particles is disposed between a plurality of, particularly preferably two, cathodes. The anode preferably includes a particle holder made of a porous body and particles made of the carbonaceous material filled in the particle holder, and a conductor arranged so as to come into contact with the particles. Particularly preferred are those comprising: With the anode having this structure, even if the particles made of the carbonaceous material are depleted, it is only necessary to replenish the carbonaceous material particles in the particle holder, and a scale preventing effect can be obtained stably over a long period of time.

  The average particle diameter of the particles is preferably 5 to 30 mm, particularly 10 to 20 mm when new.

  The applied voltage between the electrodes is preferably 1.3 V or more, particularly about 5 to 30 V. This voltage may be either alternating current or direct current, and may be an alternating current, but it is preferable from the viewpoint of generation efficiency to apply the voltage so that the current flows in the same direction for 10 minutes or more, more preferably for 1 hour or more. .

  In addition, it is preferable to reverse the polarity from the viewpoint of preventing scale failure due to impurities on the cathode surface.

Although there is no particular limitation on the current value, the amount of electricity input and the amount of melittic acid produced are in a proportional relationship, so it is better to increase the current value in order to increase the production efficiency. However, since there is a limit current density, it is preferable that the range be 5.0 A / dm ² or less.

  According to the electrolytic reaction at the anode, aromatic carboxylic acids such as various benzenecarboxylic acids can be easily generated using mellitic acid as a main product. This product usually contains 30-50% of melittic acid based on the total organic carbon content. In addition, benzenecarboxylic acids having one or more carboxyl groups in the benzene ring, condensation of naphthalene, phenanthrene, etc. Aromatic carboxylic acids having one or more carboxyl groups in the ring are included.

  ADVANTAGE OF THE INVENTION According to this invention, scale precipitation which has as a main component metal ions, such as calcium and magnesium, and silica which are melt | dissolving in to-be-processed water can be prevented stably.

  Hereinafter, embodiments will be described with reference to the drawings.

  FIG. 1 is a schematic longitudinal sectional view of a scale prevention device according to an embodiment.

  A cylindrical chamber 4 is installed between flanges 1a, 3a and 4a between pipes 1 and 3 for passing cooling water, boiler water and the like. Two flat cathodes 11, 11 are disposed facing each other in the chamber 4. An anode 12 is disposed approximately at the center between the cathodes 11 and 11. A voltage is applied from the power source 7 to the anode 12 and the cathode 11 to be energized. Between this anode 12 and the cathode 11, it is the space part for water flow in which a filler does not exist.

  The anode 12 includes a rectangular cylindrical particle holder 12a made of a porous body made of a net, a punching plate, etc., particles 12b made of a carbonaceous material filled in the particle holder 12a, and a particle holder 12a. It consists of an anode plate 12c arranged in the center.

  The particle holder 12a has a bottom lid made of a porous body such as a net or a punching plate so that the particles 12b do not fall. The particle holder 12a may not be provided with an upper lid, but may be provided with an openable / closable upper lid made of a porous material.

  The particle holder 12a is preferably made of a synthetic resin because of the material that does not flow electricity, specifically the ease of processing and the low cost. The anode plate 12c is preferably made of a corrosion-resistant metal such as stainless steel, but may be made of a carbonaceous material.

  In this embodiment, the cathode 11 and the carbonaceous material particles 12a are made of graphite in which six-membered ring network planes are regularly stacked. However, the cathode 11 may be a corrosion-resistant metal such as stainless steel.

  When electricity is passed between the anode 12 and the cathode 11 by the power source 7 while water is passed through the chamber 4 through the pipes 1 and 3, the vicinity of the anode 12 becomes acidic and the vicinity of the cathode 11 becomes alkaline. On the acidic side, oxygen is generated at the same time as the vicinity of the electrode is acidic, and the oxidation of the graphite electrode is promoted. The graphite electrode is decomposed to produce benzene polycarboxylic acid. Since benzene polycarboxylic acids have carboxyl groups like polymaleic acid and polyacrylic acid which are typical scale inhibitors, they have a scale preventing effect.

  In the high pH region near the cathode 11, fine particles of scale components are generated. Thereby, the soluble calcium hardness in the water taken out from the pipe 3 is lowered, and scale deposition is prevented.

  In addition, in order to improve the contact efficiency of the electrodes 11 and 12 and water, it is preferable to set the water flow rate so that the water flow becomes a turbulent flow.

[Example 1]
The scale prevention device 18 of the present invention shown in FIG. 1 was incorporated in the open system circulating cooling water line shown in FIG.

  A scale prevention device 18 was incorporated in a water storage tank 16 installed under the cooling tower 14 to continuously treat the circulating water. The water in the water storage tank 16 is sent to the double-pipe heat exchanger 20 through the pump 17, is heat-exchanged by the hot water flowing outside the double pipe, is cooled in the cooling tower 14, and is circulated. The water in the water storage tank 16 is circulated through the scale prevention device 18 via the pump 19 and processed.

The cathodes 11 and 11 of the device 18 are flat plates, each having an area of 300 cm ² and a distance between the cathodes 11 and 11 of 7.5 cm. The particle holder 12a of the anode 12 is in the shape of an acrylic square tube having a width of 5 cm and a height of 60 cm. The particle holder 12a is filled with graphite particles having an average particle diameter of 10 mm. The anode rod 12c is made of platinum / iridium-coated titanium and has a thickness of 1 mm and a length of 60 cm. The applied voltage is about 10 V, the current density is 0.5 A / dm ² (current value is 1.5 A), the inversion frequency is once / Hr, and the water flow rate (linear velocity) is 2.0 m / sec.

The calcium hardness (CaH) and acid consumption (pH 4.8 / MA) of the circulating water are 300 mg / l as CaCO _{3 and the} surface temperature of the heat exchange part is 80 ° C. This is a condition for precipitating on the heat exchange surface. The apparatus was operated for 96 hours with a residence time of 24 hours.

[Comparative Example 1]
For comparison, the same operation was performed under the same conditions except that the scale prevention device 18 was not operated.

  Table 1 shows the results of water quality analysis. As shown in Table 1, the water quality is maintained in the present invention, and scale precipitation in the system is suppressed.

  Next, Table 2 shows the results of measuring the amount of scale deposited on the heat exchange section.

  As shown in Table 2, according to the scale prevention device of the present invention, scale deposition on the heat exchange part that becomes high temperature is prevented. The energization current value was constant at 1.5 A during the water flow period.

It is a schematic longitudinal cross-sectional view of the scale prevention apparatus which concerns on embodiment. It is a system flow figure of an open system circulation cooling water line to which the present invention is applied.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1,3 Piping 7 Power supply 11 Cathode 12 Anode 12a Particle holder 12b Carbonaceous material particle 12c Anode plate 14 Cooling tower 16 Water storage tank 18 Scale prevention apparatus 20 Double pipe type heat exchanger

Claims (4)

In a scale prevention device that prevents scale deposition from the water,
An electrode comprising an anode and a cathode, a means for applying a voltage between the electrodes, and a water passage means for passing water between the electrodes,
The scale prevention device, wherein the anode has a filler of particles made of a carbonaceous material.   2. The scale prevention apparatus according to claim 1, wherein the anode is disposed between at least two cathodes.   3. The scale prevention apparatus according to claim 1, wherein the anode includes a particle holder made of a porous body and particles made of the carbonaceous material filled in the particle holder.   The scale prevention device according to any one of claims 1 to 3, wherein the carbonaceous material has a carbon six-membered ring structure.

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