JPH09176872A - Corrosion suppression of metal in water system and suppressing method of silica based scale - Google Patents

Abstract

PROBLEM TO BE SOLVED: To effectively suppress the corrosion of a metal in a water system and to prevent the generation of a silica based scale by allowing water to contact with a bicarbonate ion type anion exchange resin and hydroxide ion type basic anion exchange resin. SOLUTION: A part of the water in the water system is let flow from pipings 11 and 11A to an anion exchange tower 1 filled with an HCO3 <-> type anion exchange resin 1A. Residual water is let flow from pipings 11 and 11B to an anion exchange tower 2 filled with an OH<-> type anion exchange resin 1B. An effluent (treated water) of the anion exchange towers 1 and 2 is supplied to the water system via pipins 12A, 12B and 12. The water let flow the anion exchange tower 1 is brought into contact with the HCO3 <-> type anion exchange resin 1A and the incorporated corrosive ion such as Cl<-> and SO4 <-2> is subjected to ion exchange between the HCO3 <-> . The corrosive ion incorporated in the water and let flow the anion exchange tower 2 is subjected to ion exchange with the OH<-> , but silica in the water is also subjected to ion exchange with the OH<-> at this time.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of inhibiting corrosion of a water-based metal and a method of inhibiting a silica-based scale. In particular, it effectively suppresses corrosion of metals such as carbon steel, stainless steel, copper and copper alloy in a water-based system. The present invention relates to a method for preventing the formation of a silica-based scale and enabling highly concentrated operation in a cooling water system in which water is concentrated, without causing pitting corrosion or scale failure.

[0002]

2. Description of the Related Art Carbon steel, stainless steel, copper, copper alloys, etc. are used as a base material for various equipments and pipes used in open water, closed circulating cooling water system, heat storage water system, closed cold / hot water system and other fresh water systems. ing. These substrates, which are used by immersion in fresh water, contain chloride ions (Cl
^- ), Sulphate ion (SO ₄ ^2- ) etc. corrode and generate pitting corrosion. Therefore, as a method for suppressing the corrosion of the metal material in contact with such a fresh water system, conventionally, a method of adding a low molecular weight polymer while contacting an anion exchanger carrying an anticorrosive anion with aqueous water has been proposed. (JP-A-6-158364).

In this method, corrosive ions in water such as Cl ⁻ and SO ₄ ²⁻ are brought into contact with an anion exchanger carrying an anticorrosive anion such as OH ⁻ and HCO ₃ ⁻ to carry out ion exchange. The corrosive ion concentration of is reduced, and the corrosiveness of the water system is mitigated. Further, due to the film formation promoting action of the low molecular weight polymer, HCO ₃ ⁻ etc. eluted by ion exchange and Ca ²⁺ etc. derived from the water system form an anticorrosion film on the metal surface,
Corrosion of metal is suppressed more reliably.

That is, the reduction of Cl ⁻ which is a corrosive anion is effective for suppressing pitting corrosion of carbon steel, stainless steel, copper, brass and the like, and also effective prevention of stress corrosion cracking which often occurs in stainless steel and brass. It will be a countermeasure. Further, the reduction of SO ₄ ²⁻ prevents generation of basic copper sulfate, which causes pitting corrosion, with respect to copper and brass, and suppresses corrosion. on the other hand,
Ca ²⁺ and HCO ₃ ⁻ which are anticorrosive ions form a uniform CaCO ₃ precipitate film on the metal surface in the presence of a low molecular weight polymer to prevent the diffusion of dissolved oxygen which is a factor promoting corrosion. , Suppress corrosion. Silica (SiO ₂ ) that remains in water without being ion-exchanged has the effect of changing the rust of carbon steel to a sticky property and suppressing corrosion.

Further, in a water system in which water is concentrated, scale-forming components such as silica are concentrated to be deposited as scale, and in a remarkable case, a problem such as clogging of a pipe is caused. In particular, once the silica-based scale is generated, it is difficult to remove it. Therefore, prevention of the silica-based scale is extremely important in the operational management of the water system.

[0006] Conventionally, as a method of preventing such a scale disorder of an aqueous system, water is brought into contact with an H-type cation exchanger and an OH-type anion exchanger to remove salts, thereby preventing concentration in the aqueous system. Method (JP-A-48-13936); a method of contacting H-type cation exchanger with water to adjust the pH of the aqueous system to prevent scale (Patent No. 1)
No. 046359) is proposed. A silica-based scale inhibitor has also been proposed (Japanese Patent Laid-Open No. 62-289).
297).

By the way, in the open circulation cooling water system, water is evaporated in the cooling tower and salts in the water are concentrated. The water balance of the open circulation cooling water system is expressed as follows.

M = E + B + W (1) N = M / (B + W) (2) (where M: make-up water amount, E: evaporated water amount, B: forced blow water amount, W: splash loss water amount, N: concentration multiple ) In the above equations (1) and (2), if the operating conditions of the cooling water system are constant, the amount of evaporated water (E) and the amount of dispersed water loss (W) will be constant values that are unique to the water system. Therefore, in order to reduce the amount of makeup water (M) to the cooling water system, it is necessary to reduce the forced blow water amount (B) from the above equation (1). The concentration factor (N) increases. It should be noted that reducing the forced blow water amount (B) to reduce the makeup water amount (M) leads to not only saving water but also reducing the amount of drainage, which is preferable in terms of reducing the load on the wastewater treatment device. In addition, various chemicals (for example, phosphates, phosphonates, zinc salts, low molecular weight polymers, etc.) are used in the cooling water system to prevent metal corrosion and scale, but forced blow water amount (B) There is also an advantage that the reduction of CO2 will lead to the reduction of the amount of chemical substances released to the environment.

[0009]

Problems to be Solved by the Invention Japanese Patent Application Laid-Open No. 6-15836
In the method disclosed in Japanese Patent Publication No. 4, the silica in water cannot be removed when only the bicarbonate ion (HCO ₃ ⁻ ) type anion exchange resin is used as the anion exchanger. Therefore, in a water system in which scale disorder may occur due to concentration, it may not be possible to increase the concentration factor. On the other hand, the hydroxide ion (OH ^-)
When only the type anion exchange resin is used, the silica in the water can be removed, but since the water does not contain silica which is an anticorrosive substance, the anticorrosive property of the water is low and the effect of suppressing corrosion in the water system is sufficient. There is a problem that you can not get it.

Among the conventional scale prevention methods, H
A method of removing salts by contacting water with a cation-type cation exchanger and an OH-type anion exchanger is to remove corrosive anions and silica including hardness components. As above, since the water does not contain water, the corrosion resistance of the water is low, and in order to suppress corrosion, a separate anticorrosive agent that may cause environmental pollution such as phosphates and metal salts is required. There is.

On the other hand, in the method of preventing the scale by bringing the H-type cation exchanger into contact with water to adjust the pH, calcium carbonate and silica-based scale are not saturated in water, and the pH at which scale does not precipitate is pH 7 or less. Since it is in the acidic region of the above, there is a drawback that the corrosion of the metal easily proceeds by adjusting to such an acidic region.

Further, in the prevention of silica-based scale by the silica-based scale inhibitor disclosed in JP-A-62-289297, an allowable silica concentration in water, that is,
The silica concentration capable of obtaining the scale prevention effect (hereinafter, may be referred to as "allowable silica concentration") is 30.
Although it is 0 to 400 mg-SiO ₂ / L, if there is concentration in the water system, the maximum concentration multiple that can be concentrated is limited depending on the silica concentration in the makeup water, and water saving and further wastewater treatment equipment by reducing the amount of forced blow water. In some cases, it is not possible to increase the concentration multiple that leads to a reduction in the load on the environment and a reduction in the amount of chemical substances released to the environment. For example, the silica concentration in the makeup water is 30
mg-SiO ₂ / L, when the allowable silica concentration by the addition of the scale inhibitor is 360 mg-SiO ₂ / L,
The maximum possible concentration factor is 360/30 = 12 times, and in the operation of the water system, the water in the system is forcibly blown down and the water is discharged outside the system to prevent further concentration. It is necessary to supply a considerable amount of water.

The present invention suppresses corrosion of a water-based metal even in a concentrated water system without causing problems such as environmental pollution, and suppresses corrosion of a water-based metal and silica-based system that enables the formation of a silica-based scale. An object is to provide a scale suppression method.

[0014]

A method for inhibiting corrosion of a water-based metal and a method for inhibiting a silica-based scale of the present invention is a method for inhibiting a corrosion of a water-based metal and a method for inhibiting a silica-based scale. It is characterized by being brought into contact with an ion type anion exchange resin and a hydroxide ion type strongly basic anion exchange resin.

The strongly basic anion exchange resin, when loaded with a highly basic anion such as OH ⁻ , has NaCl or N
Not only salts of strong acids such as a ₂ SO ₄ but also weak acids such as silica (silicic acid) can be ion-exchanged. On the other hand, when HCO ₃ ⁻ is supported on the anion exchange resin, the basicity is not so high as to be able to exchange and capture silica, and therefore NaCl or Na ₂ SO _{4 is used.}
Only strong acid salts such as are exchanged.

That is, when water is brought into contact with the HCO ₃ ⁻ type anion exchange resin and the OH ⁻ type strongly basic anion exchange resin, corrosive ions such as Cl ⁻ , SO ₄ ^{2− in} water are converted into both anion exchange resins. However, silica is removed only by the OH ⁻ type anion exchange resin.

[0017] HCO corrosive ions in water ₃ ^- HCO Ion exchange water is as described above, eluted with Ca ²⁺ or the like and an ion exchange from aqueous ^- HCO ₃ in a type anion exchange resin
₃ ^- compound of suppressing corrosion by forming an anticorrosive coating on the metal surface. In addition, since the silica component also remains in this water without being ion-exchanged, silica, which is an anticorrosive substance, serves as an anticorrosive agent. However, since silica remains,
There is a problem of silica-based scale formation due to concentration.

Meanwhile, the corrosive ions OH ^- not included silica on the type strongly basic anion exchange resin with water ion-exchanged, there is no problem of silica scale formation, OH eluted with deionized ^- And water-derived cations such as Ca ²⁺ are unlikely to form insoluble compounds that form an anticorrosion film on the metal surface. Therefore, the anticorrosion effect of water in which corrosive ions are removed only by the OH ^- type strongly basic anion exchange resin Is not high.

In the present invention, since such an HCO ₃ ⁻ -type anion exchange resin and an OH ⁻ -type strongly basic anion exchange resin are used in combination, HCO ₃ ⁻ and water-derived HCO ₃ ⁻ eluted by ion exchange are removed. It is possible to obtain both the effect of inhibiting corrosion due to the formation of an anticorrosive film by Ca ^{2+ and the} like and the effect of preventing silica-based scale by removing silica.

In the present invention, in particular, a portion of the water to be treated HCO ₃ ^- with contacting the mold anion exchange resin,
The rest is contacted with an OH ^- type strongly basic anion exchange resin,
The proportion of water contacted with the HCO ₃ ⁻ type anion exchange resin,
It is preferable to control the proportion of water to be brought into contact with the OH ⁻ type anion exchange resin so that the silica concentration of the water in the water system is equal to or lower than the allowable silica concentration.

In the present invention, the method of contacting aqueous water with the HCO ₃ ⁻ type anion exchange resin and the OH ⁻ type strong basic anion exchange resin is not particularly limited, but HCO ₃ ⁻
Make-up water or circulating water may be brought into water contact with the packed column filled with the type anion exchange resin and the packed column filled with the OH ⁻ type strongly basic anion exchange resin. In this case, the water flow conditions, water flow ratio, etc. are appropriately determined according to the water quality of the water system to be treated.

[0022]

BEST MODE FOR CARRYING OUT THE INVENTION A method for inhibiting corrosion of a water-based metal and a method for inhibiting a silica-based scale according to the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a system diagram showing an embodiment of a method for inhibiting corrosion of a water-based metal and inhibiting a silica-based scale according to the present invention.

In FIG. 1, 1 is an anion exchange column packed with HCO ₃ ⁻ type anion exchange resin 1A (hereinafter referred to as “HCO 3
Sometimes referred to as " ₃ ^-- type anion exchange column". )
Reference numeral 2 is an anion exchange column (hereinafter sometimes referred to as “OH ⁻ type anion exchange column”) filled with the OH ⁻ type strongly basic anion exchange resin 2A.

In the method of the present embodiment, a part of the water (water to be treated) in the water system is passed through the pipes 11 and 11A to the anion exchange tower 1 filled with the HCO ₃ ⁻ type anion exchange resin 1A. , The rest is passed through the pipes 11 and 11B to the anion exchange tower 2 filled with the OH ⁻ type anion exchange resin 2A, and the outflow water (treated water) of each anion exchange tower 1 and 2 is passed through the pipes 12A, 12B and 12. After that, it is supplied to the water system.

In the present embodiment, the water passed through the anion exchange tower 1 comes into contact with the HCO ₃ ⁻ type anion exchange resin 1A so that the corrosive ions such as Cl ⁻ and SO ₄ ²⁻ contained in the HCO ₃ ⁻ type HCO ₃ HCO. ₃ ^- and is ion exchange. On the other hand, anion exchange tower 2
The water that has been passed through is contacted with the OH ⁻ type strongly basic anion exchange resin 2B, and the corrosive ions contained therein are ion-exchanged to OH ⁻ . At this time, silica in the water is also ionized to OH ⁻ . Will be exchanged.

In this method, each anion exchange tower 1,
The flow rate of water to 2 is such that the silica concentration in the water of the water system is equal to or less than the saturation concentration generated by the silica scale, that is, the allowable silica concentration or less, and the valves V ₁ and V ₂ provided in the pipes 11A and 11B are used. It is preferable to adjust the opening degree of.

For example, when the silica concentration in the replenishing water to the water system is 30 mg-SiO ₂ / L and the permissible silica concentration in the water system is 200 mg-SiO ₂ / L, the following concentration factors are used. Anion exchange towers 1 and 2 in such a ratio
By passing water to, it is possible to prevent silica-based scale even during operation at a high concentration factor.

[0029]

[Equation 1]

Incidentally, in the past, under the same conditions,
The highest concentration factor is 200/30 = 6.7, which is 10
It is impossible to operate at a high concentration factor such as double or 20 times.

The formula for calculating the water flow ratio to the anion exchange towers 1 and 2 is represented by the following general formula [A].

[0032]

[Equation 2]

In the present invention, when water is subjected to anion exchange treatment by using an anion exchange tower as shown in FIG. 1, it is preferable to pass makeup water to the water system for treatment. The circulating water in the interior may be passed to make the silica concentration of the water in the system below the allowable silica concentration.

In addition, in an aqueous system in which water is concentrated, such as an open-circulation cooling water system, the silica removal rate by the OH ^- type strongly basic anion exchange resin is small in order to prevent metal corrosion while the concentration is low. Or without silica removal, that is, by reducing the water flow rate to the OH ⁻ type anion exchange column, or not passing water to the OH ⁻ type anion exchange column, and when the concentration becomes high, It is desirable to perform the processing according to the formula [A].

For example, the silica concentration in the water to be treated is 30 m
In the case of g-SiO ₂ / L, if the concentration factor is small,
Since the silica concentration in the water system does not reach the allowable silica concentration, no silica-based scale hindrance occurs. Therefore, in order to enhance the corrosion prevention effect, it is better not to carry out the silica removal by the OH ⁻ type strongly basic anion exchange resin. When the concentration factor becomes large, the silica concentration in water reaches the allowable silica concentration, and the production of silica-based scale is expected, the water flow rate to the OH ^- type anion exchange column is determined based on the above formula [A]. It is possible to sufficiently prevent the silica-based scale failure in the water system by changing it or by starting the passage of water to the OH ⁻ type anion exchange column. In this way, changing the water flow rate to the OH ⁻ type anion exchange column according to the concentration multiple is particularly effective at the start of operation of an aqueous system in which water is concentrated.
It is effective for preventing the corrosion of the metal in the system and for preventing the occurrence of silica-based scale trouble after the concentration factor increases.

According to the present invention, a silica-based scale inhibitor is added especially to an aqueous system by keeping the silica concentration in water according to the above formula [A] so that the silica concentration is equal to or less than the allowable silica concentration at the maximum temperature of the aqueous system. Even without it, it is possible to prevent silica-based scale failures. However, the present invention does not exclude the use of silica-based scale inhibitors, and silica-based scale inhibitors may be used as necessary. In this case, the silica-based scale inhibitor used is not particularly limited, and a conventionally known silica-based scale inhibitor such as a partially hydrolyzed product of polyacrylamide can be used. Such a silica-based scale inhibitor was used. In this case, the silica concentration in the water system may be controlled by setting the water flow rate of the anion exchange column based on the above formula [A] so that the silica concentration is not more than the allowable silica concentration.

Also in the present invention, the above-mentioned JP-A-6-158 is used.
Similar to the method described in Japanese Patent No. 364, a low molecular weight polymer may be added to water. By adding a low molecular weight polymer,
The formation of a uniform anticorrosion film between the anticorrosion anions such as OH ⁻ and HCO ₃ ⁻ dissolved in water by ion exchange and the anticorrosion components such as Ca ²⁺ and SiO ₂ derived from the water system is promoted, and corrosion is more reliable. Suppressed to.

In this case, the low molecular weight polymer has a molecular weight of 500 to 100,000, particularly 1000 to 20.0.
A water-soluble polymer of about 00, specifically, maleic acid-isobutylene copolymer, polyacrylic acid, partial hydrolyzate of polyacrylamide, acrylic acid-allyloxy-
2-hydroxypropanesulfonic acid copolymer, acrylic acid-hydroxyethyl methacrylic acid copolymer, acrylamide and allylsulfonic acid copolymer, acrylic acid-maleic acid copolymer, acrylic acid-styrene copolymer, acrylic acid- Styrene sulfonic acid copolymer, polymaleic acid, polystyrene sulfonic acid, acrylic acid-itaconic acid copolymer, polyitaconic acid, acrylic acid-acrylonitrile copolymer, acrylic acid-vinyl sulfonic acid copolymer, methyl vinyl ether-maleic acid copolymer Known low molecular weight polymers such as polymers are exemplified.

The addition amount of such a low molecular weight polymer varies depending on the water quality of the water to be treated, but in the usual case, it is added in an amount of 0.1 to 500 mg / L with respect to the water to be treated.

There are no particular restrictions on the timing of addition of the low molecular weight polymer, but in the usual case, it is preferably after the treatment with the anion exchange resin.

The method of the present invention as described above is extremely effective in inhibiting corrosion of an aqueous metal containing Cl ⁻ and SO ₄ ²⁻ as a corrosive ion, for example, a fresh water system, in which water is concentrated. is there.

As described above, the present invention can achieve water-based anticorrosion and silica-based scale prevention without causing environmental problems by the above-mentioned constitution.
Inorganic phosphates (orthophosphates and polymeric phosphates), organic phosphates, phosphonic acids, zinc, nickel salts, tungstates, molybdates, nitrites, borates, silicates, oxycarboxylic acids Anticorrosion agents such as acid salts, benzotriazole, mercaptobenzothiazole, and as described above,
Scale inhibitors such as lignin derivatives, tannic acids, and polysaccharides such as starch may be used in combination.

[0043]

The present invention will be described more specifically with reference to the following examples.

Example 1 Water was treated by the method shown in FIG.

2 L of strongly basic anion exchange resin "DIAION SA20A" (manufactured by Mitsubishi Chemical Co., Ltd.) has an inner diameter of 38 m.
1 L each of two acrylic columns each having a length of m and a length of 1000 mm was packed, and one column was filled with 5 wt% NaHCO ₃
An HCO ₃ ⁻ -type anion exchange resin was regenerated with an aqueous solution, and an OH ⁻ -type strongly basic anion exchange resin was regenerated with a 5 wt% NaOH aqueous solution, and then washed with pure water.

Atsugi city water having the water quality shown in Table 1 is passed through each column by the water flow ratio shown in Table 1 (HCO ₃ ⁻ type anion exchange resin column water flow rate: OH ⁻ type strongly basic anion exchange resin column flow rate). Water flow = V _HCO3 : V _OH (water flow SV = 5)
hr ⁻¹ ), and treated water AD having the water quality shown in Table 1 was obtained.

[0047]

[Table 1]

Using Atsugi city water and treated water A to D as test water, a loop corrosion test was carried out by the following method using the apparatus shown in FIG.

Test water is put in the water tank 3, and the heating coil 4 and the temperature sensor 5 are inserted into the test water.
The flow rate of the hot water for controlling the water temperature in the flexible pipe 4 was controlled by the solenoid valve 6 linked with the temperature of the test water was kept at 30 ° C. This test water was passed through the test tube 8 by the pump 7 at a flow rate of 0.3 m / s, and the corrosion rate of the test tube 8 was examined. The test tube 8 is a commercially available carbon steel tube (STB34
0, outer diameter 19 mm, wall thickness (actual measurement 2.2 mm), 20
It was cut to a length of 0 mm, and the oil on the inner surface was degreased with toluene. The test period was 4 days, and the corrosion rate of the test tube was calculated by the following formula.

[0050]

(Equation 3)

The weight of the tube after the test was washed only with 10 wt% hydrochloric acid containing an inhibitor (ivite) on the inner surface,
After removing the deposits, washing with water and drying, the balance was weighed. Since the mill scale on the tube surface is also removed by washing with hydrochloric acid after the test, the average mill scale amount (44 mg) obtained from the weight change before and after the inner surface acid washing of 5 unused test tubes was calculated in the above corrosion rate calculation. Corrected. The inside area of the tube is 19mm in outer diameter and 2.2m in wall thickness
m, length 0.92 calculated from 2000 mm
dm ² was used.

In the test water, a maleic acid-based polymer (“Berklene 20 manufactured by FMC” as a low molecular weight polymer was used.
0 ") was added at 40 mg / L.

The results are shown in Table 2. As is clear from Table 2, the corrosion rate is reduced by the removal of corrosive ions, but when the corrosive ions are removed only by the OH ^- type strongly basic anion exchange resin (treated water D), the anticorrosion effect is ,
HCO ₃ ^- type anion exchange resin alone (treated water A) and HCO
_It is inferior to the case where the ₃ ^-- type anion exchange resin and the OH ^- type strongly basic anion exchange resin are combined (treated water B, C).

[0054]

[Table 2]

Example 2 Using the model cooling water system test apparatus shown in FIG. 3, the scale preventing effect and the corrosion preventing effect were confirmed.

In FIG. 3, 20 is a makeup water pipe, 21 is a cooling tower, 22 is a holding water tank, 23 is a filler, 24 is a fan, 25 is a circulation pump, 26 is a shell side cooling water flow heat exchanger, Reference numeral 27 is a tube side cooling water flow heat exchanger, and 28 is a test piece column. The cooling water is supplied from the water tank 22 to the pipe 2
9, piping 29A, 29B, piping 30A, 30B, piping 3
It circulates through 0.

The operating conditions of the heat exchangers 26 and 27 are as follows.

Shell side cooling water flow heat exchanger 26 Cooling water inlet water temperature: 30 ° C. Cooling water outlet water temperature: 35 ° C. Cooling water flow rate: 0.1 m / s Heat exchange tube length: 1100 mm Tube side cooling water flow water heat exchange Unit 27 Cooling water inlet water temperature: 30 ° C. Cooling water outlet water temperature: 50 ° C. Cooling water flow rate: 0.5 m / s Heat exchange tube length: 2700 mm Both heat exchangers have steam of ² kgf / cm ² on the heating side. Further, as the heat exchange tube, a commercially available carbon steel tube (STB340, outer diameter 19 mm, wall thickness (measured value) 2.2)
mm) and after the toluene degreasing treatment in the same manner as in Example 1,
Two pieces were inserted into each heat exchanger 26, 27.

Regarding the corrosion prevention effect, the appearance of the heat exchange tubes of the heat exchangers 26 and 27 is observed, and if pitting corrosion occurs, the depth of the pitting corrosion is examined, and the carbon steel installed in the test piece column 28 is used. Made test piece (SPCC, 50 mm x 15 mm x
It was investigated by measuring the corrosion rate of 1 mm and a surface area of 15.6 cm ² . In addition, the amount of water held by this model cooling water system is 250
L.

The water quality of the test water used is shown in Table 3. Table 3
Medium, anion exchange water, the raw water in the same manner as in Example 1,
Water was passed through the anion exchange device shown in FIG. 1 at V _CH3 : V _OH = 1: 2 to remove corrosive ions.

The test was carried out using the test starting water No. 1, No. 2
In each test, the replenishing water equivalent to the evaporated water and splash water lost in the cooling tower and the forced blow water to maintain a certain concentration multiple are Anion-exchanged water having the water quality shown in 3 was used. Also,
For comparison, the test starting water No. Tests were also conducted using only No. 1 (supplemented water was also water for starting test No. 1) and other conditions were exactly the same. The test start water No. No. 1 was obtained by passing the entire 250 L of raw water through the HCO ₃ ⁻ type anion exchange resin. In No. 2, 250 L of the raw water was passed through the OH ^- type strongly basic anion exchange resin. This model cooling water system first circulated water at room temperature for one day, then started steam heating to the heat exchanger portion, and started concentrating circulating water. At the start of the test, a maleic acid-based polymer (“Berkulen 200” manufactured by FMC) was used as a low molecular weight polymer.
0 mg / L was added, and the forced blow amount was adjusted so that the concentration factor was 15. After the concentration was increased, an amount corresponding to the total blow amount was continuously added so that the polymer concentration in the cooling water would be 40 mg / L.

[0062]

[Table 3]

Table 4 shows the results. The scale adhesion amount in Table 4 is an average value obtained by cutting the heat exchange tube into a length of 200 mm and then scraping off the scale adhered to each tube piece with a metal brush and measuring the weight.

Although the test period was 31 days, the test starting water No. When only 1 was used, the temperature of the heat exchanger steam drain water, which was judged to be due to scale adherence to the heat exchanger tube, was observed from about 7 days after the start of the test, so the test was completed on the 14th day. The result is shown.

[0065]

[Table 4]

From Table 4, the following is clear. That is,
The water for starting the test No. 3 in which silica was not removed by the treatment with only the HCO ₃ ⁻ type anion exchange resin. When 1 water was used as make-up water, a large amount of scale adhered to the heat exchange tube, although the test period was 14 days shorter than the others. It was confirmed by chemical analysis that the deposit was mainly composed of silica.

On the other hand, according to the present invention, when anion-exchanged water from which silica was partially removed was used as make-up water, the scale adhesion amount in all the test results was the start of the test in which silica in the make-up water was not removed. Water No. Compared with the case where only 1 was used, it was greatly reduced, and a good scale preventing effect was obtained.

In order to prevent silica-based scale, it is advantageous to remove the total amount of silica in the makeup water with an OH ^- type strongly basic anion exchange resin, but as is clear from the results in Table 4, At the start of operation, if the water concentration is low, treat with OH ^- type strongly basic anion exchange resin,
Test start water No. containing no silica When No. 2 is used, the anticorrosion property of water is not sufficient, so that a large amount of corrosion is generated on the heat exchange tube or the test piece. On the other hand, in the initial stage of operation when the concentration of water was small, the test start water No. 1 containing silica was treated with the HCO ₃ ⁻ type anion exchange resin. When 1 was used and anion-exchanged water from which silica was partially removed was replenished after the degree of enrichment increased, the amount of corrosion generated was remarkably small. In order to suppress both scale and corrosion, water containing a certain amount of silica should be used at the beginning of operation when the water concentration is low, and water with partial removal of silica should be replenished when the concentration increases. Furthermore, it is clear that it is effective to control the silica concentration of water in the system according to the concentration factor of water.

[0069]

As described above in detail, according to the method for inhibiting corrosion of a water-based metal and the inhibition of a silica-based scale of the present invention, it is possible to prevent corrosion of a water-based metal and to prevent the corrosion of a water-based metal without causing a silica-based scale failure. The concentration factor can be increased. In particular, by controlling the water flow ratio between the HCO ₃ ⁻ type anion exchange column and the OH ⁻ type anion exchange column according to the concentration multiple of the target water system, it is possible to reliably prevent the scale failure. By increasing the concentration factor of the water system, it is possible to reduce the amount of water used and the amount of blow water (wastewater amount). By changing the silica concentration in the water according to the concentration of the water system, a more stable corrosion-inhibiting effect can be obtained only by using a low-molecular weight polymer having a low environmental load, if necessary. Such an effect can be obtained, and the operation of the water system can be stably and efficiently maintained.

[Brief description of the drawings]

FIG. 1 is a system diagram showing an example method of a method for inhibiting corrosion of a water-based metal and a method for inhibiting silica-based scale according to the present invention.

FIG. 2 is a system diagram showing a test apparatus used in Example 1.

FIG. 3 is a system diagram showing a model cooling water system testing device used in Example 2.

[Explanation of symbols]

1,2 anion exchange column 1A HCO ₃ ^- type anion exchange resin 2A OH ^- type strongly basic anion exchange resin 3 water tank 4 for heating the flexible tube 5 temperature sensor 8 test tube 21 the cooling tower 22 held aquarium 25 circulation pump 26 the shell side cooling water Water flow heat exchanger 27 Tube side cooling water water flow heat exchanger 28 Test piece column

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical indication C02F 5/08 C02F 5/08 A

Claims (3)

[Claims] 1. A method for inhibiting corrosion of an aqueous metal and inhibiting silica scale, which comprises contacting the aqueous water with a bicarbonate ion-type anion exchange resin and a hydroxide ion-type strongly basic anion exchange resin. A method for suppressing corrosion of a water-based metal and a method for suppressing a silica-based scale, characterized by: 2. The method according to claim 1, wherein a part of the water of the water system is brought into contact with a bicarbonate ion type anion exchange resin,
A method for inhibiting corrosion of a water-based metal and inhibiting a silica-based scale, which comprises contacting the balance with a hydroxide ion-type strongly basic anion exchange resin. 3. The proportion of water brought into contact with the bicarbonate ion type anion exchange resin and the proportion of water brought into contact with the hydroxide ion type strongly basic anion exchange resin according to claim 2.
A method for inhibiting corrosion of a water-based metal and a method for inhibiting a silica-based scale, wherein the silica concentration of water in the water-based system is controlled to be equal to or lower than a concentration at which a silica-based scale is generated.