JP2002282892A - Scale prevention method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a scale prevention method which efficiently conducts a scale prevention within a cooling water system of a heat exchanger for air conditioning in the building, general factories and petrochemical complex, etc. SOLUTION: In a scale prevention method that scale components in cooling water are deposited on calcium carbonate particles and/or silica gel particles by sending at least a part of cooling water circulating between a cooling tower and a heat exchanger to a filling tower filled with calcium carbonate particles and/or silica get particles, the special feature of this scale prevention method is to take out cooling water being sent to the filling tower from the return circulation line to the cooling tower from the heat exchange part.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a scale prevention method. More specifically, the present invention relates to a scale prevention method capable of efficiently preventing scale of a cooling water system of a heat exchanger such as a building air conditioner, a general factory, and a petrochemical complex.

[0002]

2. Description of the Related Art A scale failure occurs on a heat transfer surface or a pipe in contact with water, such as a cooling water system and a boiler water system. In particular, from the standpoint of resource saving and energy saving, when performing high concentration operation with less discharge (blow) of cooling water outside the system,
The dissolved salts are concentrated, and the heat transfer surface is easily corroded, and the scale becomes a hardly soluble salt. The generated scale causes serious obstacles to the operation of the boiler and the heat exchanger, such as a decrease in thermal efficiency and a blockage of piping. The resulting scale species include calcium carbonate, calcium sulfate, calcium sulfite, calcium phosphate, calcium silicate, magnesium silicate, magnesium hydroxide,
There are zinc phosphate, zinc hydroxide, basic zinc carbonate, etc.
Among them, the calcium-based scale and the silica-based scale are particularly hindered, which is a problem. For calcium-based scales, maleic acid, acrylic acid,
A polymer having a carboxyl group obtained by polymerizing itaconic acid or the like is effective, and if necessary, vinyl sulfonic acid,
A copolymer in which a vinyl monomer having a sulfonic acid group such as allylsulfonic acid and 2-acrylamido-2-methylpropanesulfonic acid or a nonionic vinyl monomer such as acrylamide is combined according to the target water quality is generally used as a scale inhibitor. It is used. In addition, inorganic polyphosphoric acids such as sodium hexametaphosphate and sodium tripolyphosphate, and phosphonic acids such as hydroxyethylidene diphosphonic acid and phosphonobutane tricarboxylic acid are also generally used. JP-A-61-107998 proposes a scale inhibitor containing an acrylamide-based polymer and an acrylic acid-based polymer as a scale inhibitor having an excellent effect of preventing silica-based scale. Also, JP-A-2-31894 discloses a scale water preventive containing polyethylene glycol and a phosphonic acid or carboxylic acid-based polymer as a composite water treatment agent having the effects of preventing scale of a cooling water system, preventing corrosion and preventing slime. Agents have been proposed. Japanese Patent Application Laid-Open No. Hei 7-256266 discloses that, irrespective of the quality of cooling water and the operating conditions,
As a water treatment method capable of preventing the occurrence of slime, scale, corrosion damage, and Legionella bacteria, a method of adding a water-soluble cationic polymer, a halogenated aliphatic nitro alcohol, and a phosphonic acid or carboxylic acid-based polymer has been proposed. Further, Japanese Patent Application Laid-Open No. 10-165986 discloses that
As a scale inhibitor having an excellent effect on preventing silica-based and calcium-based scales, having a water-soluble polymer of N-vinylcarboxylic acid amide or a primary amino group obtained by hydrolyzing the polymer. Scale inhibitors containing water-soluble polymers have been proposed. As described above, various polymers are properly used depending on the scale type. The water used in the cooling water system is usually industrial water, tap water, groundwater, and the like, and thus various ionic species are present in the water. Therefore, especially when performing a high concentration operation, a scale inhibitor capable of effectively coping with all scale types is required, but such a scale inhibitor does not yet exist. In recent years, there has been a remarkable movement to use water as effectively as possible for the purpose of saving water and conserving energy. Expectations for a high-concentration operation of cooling water for heat exchangers have been greatly increased. On the other hand, the current scale inhibitor described above has a function of holding down the scale species (ions) dissolved in the cooling water in the water so as not to precipitate as scales, that is, keeping the scale species dissolved. In the case of a further high concentration operation, there is a limit in suppressing the scale deposition. As the operation of high-concentration cooling water becomes more widespread in the future, the development of a high-performance scale prevention method that replaces the current scale prevention method is desired.

[0003]

SUMMARY OF THE INVENTION The present invention relates to a building air conditioner,
An object of the present invention is to provide a scale prevention method capable of efficiently preventing scale of a cooling water system of a heat exchanger such as a general factory or a petrochemical complex.

[0004]

Means for Solving the Problems The present inventors have made intensive studies to solve the above-mentioned problems, and as a result, at least a part of the cooling water of the cooling water system is brought into contact with calcium carbonate particles and / or silica gel particles. This allows the scale components in the cooling water to precipitate on the surfaces of these particles and prevent the scale from adhering to the walls of the vessel.In particular, the cooling water flows from the circulation line returning from the heat exchange section of the cooling water system to the cooling tower. Was found to be able to effectively prevent scale adhesion by passing water through a packed tower filled with calcium carbonate particles and / or silica gel particles, and based on this finding, completed the present invention. Reached. That is, the present invention
At least a part of the cooling water of the cooling water system circulating between the cooling tower and the heat exchange section is passed through a packed tower filled with calcium carbonate particles and / or silica gel particles, and the scale component in the cooling water is converted into calcium carbonate particles and / or Or, in a method of preventing scale by depositing on silica gel particles, there is provided a scale prevention method characterized in that cooling water flowing through a packed tower is taken from a circulation line returning from the heat exchange section to the cooling tower. Things.

[0005]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the scale prevention method of the present invention, at least a part of a cooling water of a cooling water system circulating between a cooling tower and a heat exchange section is filled with a calcium tower particle and / or a silica gel particle. In a method of preventing scale by allowing water to pass through, and allowing scale components in the cooling water to precipitate on calcium carbonate particles and / or silica gel particles,
Cooling water flowing through the packed tower is collected from a circulation line returning from the heat exchange section to the cooling tower. According to the method of the present invention, in a circulating cooling water system of a heat exchanger such as a building air conditioner, a general factory, and a petrochemical complex, a heat exchanger body, a cooling tower, a pit and the like, and a scale attached to a pipe or the like are effectively reduced. Can be prevented. The scale to which the method of the present invention is applied is generally a scale which is generally problematic in a cooling water system, and is a calcium-based scale such as calcium carbonate, calcium sulfate, calcium sulfite, and calcium phosphate, silica, calcium silicate, and silicate. The main target is silica-based scales such as magnesium. FIG. 1 is a process flow chart of an embodiment of the method of the present invention. In this embodiment, a part of the cooling water of the cooling water system circulating between the cooling tower 1 and the heat exchange unit 2 is collected from the circulation line 3 returning from the heat exchange unit to the cooling tower, and the calcium carbonate particles and the silica gel particles are removed. Water is passed through the packed packed tower 4 and returned to the circulation line. FIG. 2 is a process flow chart of another embodiment of the method of the present invention. In this embodiment, a part of the cooling water of the cooling water system circulating between the cooling tower 1 and the heat exchange unit 2 is collected from the circulation line 3 returning from the heat exchange unit to the cooling tower, and the calcium carbonate particles and the silica gel particles are removed. The water is passed through the packed packed tower 4,
It is returned to the cooling tower pit 5. Cooling water of the cooling water system,
By contacting with silica gel particles and / or calcium carbonate particles, the surfaces of these particles become nuclei for crystal growth, and calcium carbonate scale components and silica scale components in the cooling water precipitate as solids. As a result, the calcium carbonate concentration and the silica concentration in the cooling water are reduced, and the adhesion of the calcium carbonate scale and the silica scale can be prevented.

[0006] In the method of the present invention, there is no particular limitation on the location where the cooling water that is passed through the packed tower filled with calcium carbonate particles and / or silica gel particles is a circulation line returning from the heat exchange section to the cooling tower. However, when the cooling water having a higher water temperature is brought into contact with the calcium carbonate particles and / or the silica gel particles, the calcium carbonate scale component and / or the silica scale component more efficiently precipitates as a solid, so that the heat exchanger is used as much as possible. It is preferable to take water at a position close to the outlet. In the method of the present invention, there is no particular limitation on the method of collecting cooling water returning from the heat exchange section to the cooling tower,
For example, a branch can be provided in the circulation line to collect cooling water, or the total amount of cooling water flowing through the circulation line can be directly connected to a packed tower filled with calcium carbonate particles and / or silica gel particles. Can be sampled. The amount of the cooling water in the cooling water system preferably contacts the calcium carbonate particles and / or the silica gel particles at least once a day. There is no particular limitation on the calcium carbonate particles used in the method of the present invention, and three types of calcium carbonate crystals, calcite, vaterite,
Any of the aragonites can be used. Heavy calcium carbonate obtained by crushing natural limestone or chalk is mainly calcite, and precipitated calcium carbonate or light calcium carbonate obtained by adding an aqueous solution of sodium carbonate to an aqueous solution of calcium chloride includes vaterite in addition to calcite. There are also aragonites. There is no particular limitation on the particle size of the calcium carbonate particles used, but 5 μm to 3 mm
And more preferably 20 μm to 1 mm. The smaller the size of the crystal, the larger the surface area and the higher the activity, and the greater the scale prevention effect. However, if the size of the crystal is small, the crystal tends to flow into the cooling water when brought into contact with the cooling water. Crystals can be filtered off with a strainer or the like. However, if a finer strainer with smaller crystals is used, the flow rate will be reduced, and it may be difficult to efficiently contact the cooling water with the crystals. On the other hand, if the crystal is too large, the surface area becomes small, and the scale prevention effect may not be sufficiently exhibited.

The silica gel particles used in the method of the present invention are not particularly limited, and include ordinary silica gel for drying which is not chemically modified as defined in JIS Z 0701, methyl group, butyl group, octyl group, octadecyl group and phenyl group. Such as hydrocarbon groups, amino groups, aminopropyl groups,
Silica gel chemically modified with an ion exchange group such as a quaternary ammonium group or a sulfone group can be used. The shape of the silica gel particles is not particularly limited, and particles having any shape such as spherical particles and crushed particles can be used. There is no particular limitation on the particle size of the silica gel particles,
It can be appropriately selected in consideration of handleability, but usually the average particle size is preferably from 0.1 to 500 µm, more preferably from 10 to 100 µm. The specific surface area of the silica gel particles is not particularly limited.
2,000 m ² / g, preferably 200 to 750
More preferably, m ² / g. The pore size of the silica gel particles is not particularly limited, but is preferably 1 to 50 nm, more preferably 2 to 20 nm.
In the method of the present invention, the packing form of the calcium carbonate particles and the silica gel particles in the packed tower is not particularly limited. For example, calcium carbonate particles and silica gel particles can be mixed and filled in one packed tower, The calcium particles and the silica gel particles can be packed in layers, or the calcium carbonate particles and the silica gel particles can be packed in separate packing towers using two or more packing towers. By passing water through a packed tower filled with calcium carbonate particles and / or silica gel particles, the cooling water of the cooling water system is brought into contact with the calcium carbonate particles and / or silica gel particles, and the scale component in the cooling water is converted into calcium carbonate particles and / or silica gel particles. Alternatively, it can be precipitated on silica gel particles. The direction of water flow to the packed tower is not particularly limited, and may be either an upward flow or a downward flow. In the method of the present invention, there is no particular limitation on the position where the cooling water flowing out of the packed tower filled with calcium carbonate particles and / or silica gel particles is returned to the cooling water system. For example, a circulation line, a top of the cooling tower, a pit of the cooling tower are provided. It can be returned to any position such as. Among these, the pits of the cooling tower are preferable because pressure loss can be reduced.

In the method of the present invention, the filling amounts of the calcium carbonate particles and the silica gel particles are not particularly limited, and may be appropriately selected according to the average particle diameter of the particles, the specific surface area of the particles, the quality of the cooling water in the cooling water system, and the like. it can. As a rough guide, it is preferable that each of the calcium carbonate particles and the silica gel particles is 50 g or more with respect to 1 m ^{3 of the} amount of water held in the cooling water system. Even when the amount of particles is small at the start of operation of the cooling equipment, the amount of particles gradually increases due to crystal growth due to precipitation of scale components in the cooling water, generation of secondary nuclei of crystals during crystal growth, and the like. In the method of the present invention, there is no particular limitation on the method of removing scale components precipitated on the surface of calcium carbonate particles and / or silica gel particles.
It can be replaced with the calcium carbonate particles or silica gel particles packed in the packed tower. When implementing the scale prevention method of the present invention, there are no particular restrictions on water quality conditions, operating conditions such as boilers and heat exchangers, and normal water quality,
It can be operated under boiler and heat exchanger operating conditions. According to the method of the present invention, by contacting calcium carbonate particles and / or silica gel particles with cooling water containing scale components, these particles become nuclei, and the calcium carbonate scale components and silica scale components in the cooling water become Precipitates as a solid and reduces the concentration of the scale component, thereby preventing calcium carbonate scale and silica scale from adhering. In addition, by collecting the cooling water to be brought into contact with the calcium carbonate particles from the circulation line returning from the heat exchange section to the cooling tower, the cooling water having the highest temperature in the cooling water system can be brought into contact with the calcium carbonate particles. Can,
The calcium carbonate scale component in the cooling water easily precipitates as a solid, and efficient calcium carbonate scale prevention is possible. Further, since the calcium carbonate scale component can be efficiently deposited, the amount of the calcium carbonate particles to be filled can be reduced, and the packed tower can be reduced in size and the installation space can be reduced.

[0009]

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 Examples and Comparative Examples, the tests were performed by the following methods. That is, the amount of water possessed by a heat exchanger having a heat transfer area of 0.25 m ² is 0.45 m ^3.
Atsugi City water is used as make-up water in the open circulation cooling water system, and the concentration of the chloride ion in the water is measured.
The operation was controlled by a factor of two. As shown in FIG. 2, a circulation line is branched at a position 10 cm from the heat exchanger outlet, and calcium carbonate particles [heavy calcium carbonate, average particle size 250 μm] and silica gel particles [silica gel for drying,
An acrylic resin column 7 having an inner diameter of 40 mm and a height of 1,500 mm filled with the mixture 6 having an average particle size of 60 μm and a specific surface area of 365 m ² / g] was installed, and cooling water 24 L / h was passed in an upward flow. The particles were contacted with calcium carbonate particles and silica gel particles. The flow rate of water in the column was 0.53 cm / s,
The packed layer of the calcium carbonate particles and the silica gel particles was expanded to a developing rate of about 200% by passing water. The distance of the pipe from the branch to the acrylic resin column was 1 m, and the cooling water in contact with the calcium carbonate particles and the silica gel particles was returned to the cooling tower pit through the pipe. The water quality of Atsugi city water used was pH 7.80, electric conductivity 183 μS /
m, calcium hardness 42mgCaCO ₃ / L, M alkalinity 5
₃ mg CaCO ₃ / L, chloride ion 11 mg Cl ⁻ / L, silica 2
It was 6 mg SiO ₂ / L. The material of the heat exchanger tube is copper and the outer diameter is 19 mm. The hot water temperature was 80 ° C., the cooling water inlet temperature was 30 ° C., the outlet temperature was 40 ° C., and the cooling water flow rate was 1.0 m / s. Two days after the start of operation,
After 4 days, 6 days, 10 days, 20 days and 30 days, the cooling water was sampled, and the calcium hardness and total silica were measured according to JIS K0101. After the operation for 30 days, the scale attached to the heat exchanger tube was sampled, the amount of the attached scale was measured, and in the comparative example, the component analysis of the scale was performed. In the component analysis, the collected scale was calcined at 600 ° C., the calcined residue was dissolved in hydrochloric acid, and the acid-insoluble component was regarded as silica, and the SiO 2 in the scale was analyzed.
_Two minutes were calculated. Further, the calcium concentration of the hydrochloric acid solution of the calcined residue was measured by the flame atomic absorption method, and the calcium in the scale was indicated as the amount of CaO.

Example 1 200 g of calcium carbonate particles were placed in an acrylic resin column.
And 200 g of silica gel particles, and operated for 30 days. The concentration folds at 2, 4, 6, 10, 20, and 30 days after the start of operation were 2.
1, 3.6, 5.7, 10.4, 12.3, and 11.5 times, and the calcium hardness of the cooling water was 81, 12 respectively.
6, 118, 114, 115, and 121 mg CaCO ₃ / L, and the silica concentration was 46, 98, 134, 1, respectively.
27,130 and 136mgSiO was ₂ / L. Scale deposition rate was 0.1mg / cm ^2/30 days. Example 2 400 g of calcium carbonate particles were placed in an acrylic resin column.
And 400 g of silica gel particles, and operated for 30 days. The concentration folds at 2, 4, 6, 10, 20, and 30 days after the start of operation were 2.
2, 3.7, 5.6, 10.3, 12.1, and 11.9 times, and the calcium hardness of the cooling water is 76, 10
8, 111, 106, 109 and 102 mg CaCO ₃ / L, and the silica concentration was 43, 95, 115, 1
18,109 and 121mgSiO was ₂ / L. Scale deposition rate was 0.1mg / cm ^2/30 days.

Comparative Example 1 A column packed with calcium carbonate particles and silica gel particles
Hydroxyethylidene in cooling water without passing water through
Hydroxy is adjusted so that the concentration of diphosphonic acid becomes 20 mg / L.
30 days of operation with the addition of thiethylidene diphosphonic acid
Was done. 2 days, 4 days, 6 days, 10 days
After 20 days and 30 days, the concentration fold was 2.
2, 3.8, 5.5, 10.2, 11.8 and 12.2 times
Yes, the calcium hardness of the cooling water is 77, 13 respectively
2, 129, 126, 133 and 128 mg CaCO_Three/ L
And silica concentrations of 42, 87, 144, 1 respectively.
50, 177 and 165 mg SiO_Two/ L. scale
Adhesion rate is 44mg / cm ^Two/ 30 days. scale
The CaO content is 48.8% by weight,_TwoIs 33.7
% By weight. Comparative Example 2 Column packed with calcium carbonate particles and silica gel particles
Sodium acrylate in cooling water without passing water through
The average molecular weight is 3,000 so that the concentration of
30 days of operation by adding sodium polyacrylate
went. After 2 days, 4 days, 6 days, 10 days,
The fold concentration after 20 days and 30 days was 2.1, respectively.
3.7, 5.6, 10.3, 12.0 and 11.8 times
And the calcium hardness of the cooling water is 76, 11 respectively.
5, 124, 132, 130 and 129 mg CaCO_Three/ L
And silica concentrations of 37, 90, 122, 1 respectively.
31, 137 and 129 mg SiO_Two/ L. scale
The deposition rate is 118 mg / cm^Two/ 30 days. Scale
Of CaO in the reactor is 50.4% by weight._TwoIs 29.
It was 5% by weight. Table 1 shows the results of Examples 1 and 2
Table 2 shows the results of Comparative Examples 1 and 2.

[0012]

[Table 1]

[0013]

[Table 2]

As shown in Table 2, in Comparative Example 1 in which hydroxyethylidene diphosphonic acid was added as a scale inhibitor and in Comparative Example 2 in which sodium polyacrylate was added, the calcium hardness and silica concentration of the cooling water were lower. High, indicating that these scale components were solubilized by the scale inhibitor, but reached almost saturation 6 days after the start of operation, and the subsequent increment of the scale components adhered to the heat exchanger tubes as scale. It is considered something. On the other hand, in Examples 1 and 2 in which the cooling water of the cooling water system was extracted from the circulation line returning from the heat exchange section to the cooling tower, passed through the column, and brought into contact with the calcium carbonate particles and the silica gel particles, Calcium hardness and silica concentration are low, and almost no scale adheres to the heat exchanger tube even after 30 days of operation. This is considered to be because the scale component in the cooling water precipitated on the surfaces of the calcium carbonate particles and the silica gel particles and was removed from the cooling water.

[0015]

According to the scale prevention method of the present invention, the scale components in the cooling water are easily deposited and removed using a simple device, and the heat exchangers for building air conditioning, general factories, petrochemical complexes, and the like are used. Of the cooling water system can be efficiently prevented.

[Brief description of the drawings]

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

FIG. 2 is a process flow chart of another embodiment of the method of the present invention.

FIG. 3 is an explanatory diagram of a column used in an example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Cooling tower 2 Heat exchange part 3 Circulation line 4 Packing tower 5 Cooling tower pit 6 Mixture of calcium carbonate particles and silica gel particles 7 Acrylic resin column

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Ikuko Nishida Kurita Kogyo Co., Ltd., 3-4-7 Nishishinjuku, Shinjuku-ku, Tokyo

Claims (1)

[Claims] At least a part of cooling water of a cooling water system circulating between a cooling tower and a heat exchange part is provided with calcium carbonate particles and / or
Alternatively, water is passed through a packed tower filled with silica gel particles, and scale components in the cooling water are precipitated on calcium carbonate particles and / or silica gel particles to prevent scale. A scale prevention method, wherein water is sampled from a circulation line returning to a cooling tower from an exchange unit.