JP2000246286A - Method for preventing generation of scale - Google Patents

Abstract

PROBLEM TO BE SOLVED: To effectively prevent the generation of scale without wasting a chelating agent by supplying a specific amt. of the chelating agent to water containing alkaline earth metal ions. SOLUTION: A chelating agent is added to water in order to suppress the generation of scale in the piping of a heat exchanger or the like to chelate calcium ions or magnesium ions being scale components to increase the solubility of them. In this case, in order to chelate gradually increasing alkaline earth metal ions, the chelating agent is controlled so as to be supplied in an amt. of 0.001-10 mmol per 1 mmol of alkaline earth metal ions. The chelating agent to be used is a substance having a multidentate ligand bonded to metal ions to form an easily soluble chelate compd. and, concretely, iminodiacetic acid, nitrilotriacetic acid, ethylenediaminetetraacetic acid, cyclohexanediaminetetraacetic acid or the like are designated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for preventing precipitation of scale, particularly calcium carbonate, by chelating alkaline earth metals in water.

[0002]

2. Description of the Related Art Generally, when a heat exchanger is used for a long time,
The scale may precipitate on the pipe and block the pipe. This is because calcium ions and the like dissolved in the water flowing in the pipe precipitate as calcium carbonate and the like.

As a method of suppressing this scale generation,
A method of adsorbing and removing calcium ions, magnesium ions, and the like, which are components of the scale, using an ion-exchange resin is considered. However, the above-mentioned ion exchange resin has a low adsorption amount per unit volume, and soon reaches a saturated adsorption amount. Therefore, the removal effect does not occur thereafter, and the scale is gradually deposited.

Further, a method of dissolving and removing the scale deposited by adding an acid can be considered. However, this method has a problem of corroding the metal part of the inner wall of the pipe.

[0005] On the other hand, a method of adding a chelating agent to chelate calcium components and magnesium ions, etc., which are components of the scale, to increase the solubility can be considered. According to this method, generation of scale can be suppressed, and the piping is not corroded.

[0006] When water is supplied periodically as in a heat exchanger, scale generation cannot be completely suppressed only by initially adding a necessary amount of a chelating agent. This is because alkaline earth metal ions gradually increase. Therefore, in order to chelate the increased amount of alkaline earth metal ions, a necessary amount of a chelating agent must be additionally added.

[0007]

However, since the above-mentioned chelating agents have low solubility, when more than a necessary amount of chelating agents are added at once, not all of them are dissolved depending on the added amount. At this time, the chelating agent not dissolved is wasted.

It is an object of the present invention to easily supply a chelating agent at a constant rate.

[0009]

In order to solve the above-mentioned problems, the present invention relates to a method of preparing an aqueous solution containing alkaline earth metal ions in water containing 0.001 mmol per 1 mmol of alkaline earth metal ions.
It is characterized in that a chelating agent of 1 to 10 mmol / hr is supplied.

In water containing an alkaline earth metal ion,
By supplying the chelating agent at a constant rate, the generation of scale can be effectively prevented without wasting the chelating agent.

[0011]

Embodiments of the present invention will be described below.

The scale generation preventing method according to the present invention comprises:
In this method, a predetermined amount of a chelating agent is supplied to water containing alkaline earth metal ions.

The above-mentioned scale means that inorganic salts such as calcium carbonate contained in water are precipitated by evaporation or scattering of water, and are deposited on the inner wall of a device where water evaporates, such as a heat exchanger, a humidifier, an evaporation can, a boiler, and the like. The solid precipitate is called a can stone.

The above alkaline earth metal ions include calcium ions, magnesium ions, barium ions and the like, and constitute the scale in the form of carbonates, sulfates and the like.

The above-mentioned chelating agent is a substance having a polydentate ligand which binds to a metal ion to form an easily soluble chelating compound. Specifically, iminodiacetic acid, nitrilotriacetic acid, ethylenediaminetetraacetic acid ( Hereinafter, referred to as “EDTA”), cyclohexanediaminetetraacetic acid (hereinafter “C”).
yDTA ". ), Aminocarboxylic acids such as ethyl ether diamine tetraacetic acid, glycol ether diamine tetraacetic acid, propylene diamine tetraacetic acid, diethylene triamine pentaacetic acid, triethylene tetramine hexaacetic acid and the like, metal salts thereof, oxalic acid, polycarboxylic acids such as citric acid or Examples thereof include inorganic salts such as metal salts and phosphoric acid, and metal salts thereof.

The supply amount of the chelating agent is 0.001 to 10 mmol per 1 mmol of alkaline earth metal ion.
/ Hr, preferably 0.01 to 1 mmol / hr. When the amount is less than 0.001 mmol / hr, alkaline earth metal ions that are not chelated remain and scale is generated. When the amount is more than 10 mmol / hr,
This is because the chelating agent itself does not dissolve.

As a method of supplying the chelating agent, when the chelating agent is in a solid state, the chelating agent is continuously intermittently supplied while being measured with a hopper or the like, or the chelating agent is dissolved in water, A method of supplying a fixed amount by a pump may be used.

Further, the above-mentioned chelating agent is kneaded with a hydrophobic substance to form a kneaded composition, and this kneaded composition can be used as a scale preventing material and supplied to water containing alkaline earth metal ions. . Further, the chelating agent is kneaded with a hydrophobic substance, and a composition in which this is supported on a hydrophilic porous body can be used as a scale preventing material, and can be supplied to water containing alkaline earth metal ions. . When using any of the above scale prevention materials,
The amount of the kneaded composition or the composition supported on the hydrophilic porous body to be supplied to the water containing the alkaline earth metal ion is the amount of the kneaded composition or the composition supported on the hydrophilic porous body. It is preferable that the amount of the chelating agent released from the water and supplied to the water containing the alkaline earth metal ion is the same as the supply amount of the chelating agent.

Examples of the above-mentioned hydrophobic substance include substances which are not compatible with water and which are solid under the conditions used. Specific examples include mineral waxes such as ozokerite, petroleum waxes such as paraffin wax and microcrystalline wax, vegetable waxes such as carnauba wax and rice wax, animal waxes such as beeswax and beef wax, and rosins such as gum rosin and wood rosin. Modified rosins such as hydrogenated rosin, disproportionated rosin, polymerized rosin, rosin esters such as rosin methyl ester and hydrogenated rosin glycerin ester, higher fatty acids such as stearic acid and palmitic acid, higher alcohols such as stearyl alcohol, and decolorized shellac And sucrose esters such as sucrose stearic acid ester and sucrose palmitate ester, chicle, solver, gelton, dammar, copal, mastic and the like.

The above-mentioned hydrophilic porous body refers to a hydrophilic carrier having a large number of pores opened on the surface. Examples of the hydrophilic porous body include a hydrophilic polymer porous body and an inorganic porous body.

As the hydrophilic polymer, cellulose,
Cellulose acetate and nitrocellulose, ethyl cellulose, cellulose derivatives such as carboxymethyl cellulose,
Examples include starch, polyvinyl alcohol, alginate, casein, collagen, polyamide, polyacrylic acid and the like.

Examples of the form of the porous body include paper, woven cloth,
Non-woven fabrics, sheets, mats, sponges, powders, particles and the like can be mentioned.

Examples of the inorganic porous material include porous materials such as silicate, silica gel, zeolite, and alumina.

The chelating agent and the hydrophobic substance can be kneaded by any method such as melt mixing. At this time,
The mixing ratio of the two is chelating agent / hydrophobic substance of 0.00
1-10 (weight ratio) is good, and 0.01-5 is preferable.
If it is less than 0.001, the chelating agent may hardly be eluted. If it is more than 10, it may be difficult to adjust the dissolution rate of the chelating agent.

The above-mentioned hydrophobic substance can be embedded in the pores of the hydrophilic porous body by any method. For example, the chelating agent and the hydrophobic substance are melt-mixed, and in this molten state, the hydrophilic porous body is impregnated. Upon cooling, the chelating agent and the like are fixed in the holes. At this time, the amount of the hydrophobic substance supported on the hydrophilic porous body is preferably 0.05 to 10 (weight ratio) of the hydrophobic substance / hydrophilic porous body, and preferably 0.1 to 5. If it is less than 0.05, the hydrophobic substance may not be supported uniformly, and if it is more than 10, the hydrophobic substance may not be completely supported.

As an application example of the above-mentioned scale generation preventing method, there is a method used for a humidifier. That is, the above-mentioned scale preventing material is put in a nonwoven fabric bag and put into a tank of a humidifier. The introduced scale preventive material releases the chelating agent at a constant rate and gradually forms a chelate with the alkaline earth metal ion, so that the generation of scale can be prevented.

[0027]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in more detail with reference to embodiments. In Table 1, the kneading substance means a substance capable of melting and mixing a chelating agent, and the porous body means a carrier having a large number of pores opened on the surface. Also,
The release rate indicates the amount of chelating agent released per unit time when the amount of alkaline earth metal ion is 1 mmol.

(Example 1) EDTA as a chelating agent,
Paraffin wax as a hydrophobic substance was melt-mixed at 90 ° C. to produce a composition. Then, this composition is impregnated with cellulose beads (manufactured by Rengo Co., Ltd., Biscopearl) as a hydrophilic porous body, and then cooled to cool the scale inhibitor (chelating agent: hydrophobic substance: hydrophilic porous body = 1: 1: 1 (weight ratio).

In the humidifier tank, the scale preventing material 3
0g wrapped in a non-woven cloth
/ Liter (total alkaline earth metal ion concentration 0.1m
mol / l) of tap water was evaporated at a rate of 500 ml / hr. The scale deposition state of the humidifier evaporating dish after 100 hours was visually evaluated. Table 1 shows the results.

(Embodiment 2) CyDT instead of EDTA
A scale deposition state was evaluated in the same manner as in Example 1 except that A was used. Table 1 shows the results.

Example 3 A scale deposition state was evaluated in the same manner as in Example 1 except that rosin ester was used instead of paraffin wax. Table 1 shows the results.

Example 4 EDTA as a chelating agent
A sucrose ester as a hydrophobic substance was melt-mixed at 90 ° C. to produce a composition. Cool and solidify the above composition, 5m
By molding into an m square, a scale preventing material (chelating agent: hydrophobic substance = 1: 1 (weight ratio)) was produced.

In the humidifier tank, the scale preventing material 2
0 g was wrapped around a non-woven cloth and charged, and the scale deposition state was evaluated in the same manner as in Example 1. Table 1 shows the results.
Shown in

Comparative Example 1 The scale deposition state was evaluated in the same manner as in Example 1 except that EDTA as a chelating agent was not used. Table 1 shows the results.

(Comparative Example 2) The scale deposition state was evaluated in the same manner as in Example 1 except that agar, which was a hydrophilic substance, was used instead of the hydrophobic substance. Table 1 shows the results.

(Comparative Example 3) The scale deposition state was evaluated in the same manner as in Example 3 except that polyethylene beads, which were hydrophobic porous bodies produced by the following method, were used instead of the hydrophilic porous bodies. . Table 1 shows the results.

Production of polyethylene beads A commercially available polyethylene fiber is entangled in a spherical shape. And
The surface is heated and slightly melted to solidify the surface, forming a porous granular material.

[0038]

[Table 1]

[0039]

According to the present invention, the chelating agent is supplied at a constant rate to the water containing the alkaline earth metal ion, so that the chelating agent can be easily supplied and the alkaline earth metal ion contained in the water can be easily supplied. Since the addition time of the chelating agent may be adjusted in accordance with the amount of ions, a necessary amount of the chelating agent can be easily added.

A chelating agent is kneaded with a hydrophobic substance,
When using a scale preventing material in which this is supported on a hydrophilic porous body, the chelating agent kneaded in the hydrophobic substance is gradually released by the interaction between the hydrophobic substance and the hydrophilic porous body, and the hydrophobic substance is released. The release amount of the chelating agent is adjusted by adjusting the mixing ratio of the hydrophilic substance and the hydrophilic substance. Therefore, a predetermined amount of the chelating agent can be released over a long period of time.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Koichi Taniguchi 1-8-10 Jiyugaoka, Kanazu-cho, Sakai-gun, Fukui Prefecture Inside Rengo Co., Ltd. Fukui Research Laboratory (72) Inventor Shuji Hirohama 1-8-8 Jiyugaoka, Kanazu-cho, Sakai-gun, Fukui Prefecture No.10 Inside Rengo Co., Ltd. Fukui Research Laboratory (72) Inventor Yoshinori Nakano 1-8-10 Jiyugaoka, Kanatsu-cho, Sakai-gun, Fukui Prefecture Inside Rengo Co., Ltd. Fukui Research Laboratory

Claims (3)

[Claims] 1. The method according to claim 1, wherein the water containing the alkaline earth metal ion is added to the water containing 0.001 mmol of the alkaline earth metal ion.
A scale generation preventing method for supplying a chelating agent at 1 to 10 mmol / hr. 2. The method according to claim 1, wherein the water containing the alkaline earth metal ion is added to the water containing 0.001 mmol of the alkaline earth metal ion.
A scale prevention method for supplying a kneaded composition of a chelating agent and a hydrophobic substance so that a chelating agent of 1 to 10 mmol / hr is supplied. 3. The method according to claim 1, wherein the water containing the alkaline earth metal ion is added in an amount of 0.001 mmol per alkaline earth metal ion.
A scale generation prevention method in which a chelating agent is kneaded with a hydrophobic substance so that a chelating agent of 1 to 10 mmol / hr is supplied, and a composition in which this is supported on a hydrophilic porous body is provided.