JPH07109585A - Treatment of circulating water - Google Patents

Abstract

PURPOSE:To easily prevent the corrosion and scaling of a circulating water system at a low cost. CONSTITUTION:Gaseous CO2 is added to circulating water liable to deposit calcium carbonate. By this addition, calcium carbonate in the water can be maintained in an unsatd. (dissolved) state and the deposition of calcium carbonate-based scale can be prevented. A corrosion preventive coating film of calcium carbonate is formed on the surface of a metal and corrosion is prevented. By the simple operation, scaling and corrosion are easily and efficiently prevented at a low cost.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for treating circulating water. More specifically, it relates to a water treatment method for corrosion prevention and scale prevention of metals used in a water circulation system in which precipitation of calcium carbonate is expected.

[0002]

2. Description of the Related Art In cooling water systems accompanied by water concentration and in dust collection water systems used in steel factories, corrosion and scale are likely to occur due to an increase in salt concentration in water. For example, an increase in corrosive ions such as chloride ions and sulfate ions in water accelerates the corrosion of metals used in the water circulation system, causing problems such as water leakage accidents and shortened equipment life. Moreover, calcium ions and bicarbonate ions in the collected water and the concentrated cooling water cause scale formation, which causes problems such as clogging of pipes and reduction of heat exchange efficiency of the heat exchanger. For this reason, in the conventional cooling water system, in order to prevent damage due to scale, measures are taken to avoid water concentration as much as possible and control the quality of the cooling water, or to use a polymer that has the effect of preventing corrosion and scale formation. A water treatment agent containing it is sometimes added (Japanese Patent Publication No. 55-6439).

[0003]

However, the former method has drawbacks in that it cannot prevent damage due to corrosion and requires a large amount of water.

On the other hand, the method of preventing damage due to scale and corrosion by adding the water treatment agent containing the above-mentioned polymer is an extremely efficient method and is widely applied.
Since the polymer is used, daily drug administration and the like are complicated and economically expensive.

Because of this, daily management is easy,
An inexpensive method of treating circulating water has been desired.

The present invention has been made in view of the above-mentioned conventional circumstances, and is an easy and inexpensive method for treating circulating water for effectively utilizing water resources by preventing damages caused by corrosion and scale of the circulating water system. The purpose is to provide.

[0007]

The method for treating circulating water according to the present invention is characterized by adding carbon dioxide gas to circulating water in which calcium carbonate tends to precipitate.

Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a system diagram showing a method of an embodiment of the method for treating circulating water according to the present invention.

In the figure, 1 is a cooling tower, and the water cooled in the cooling tower 1 is supplied from a pipe 2 equipped with a pump P to a pipe 2A,
After passing through 2B, they are fed to the heat exchangers 3A and 3B for heat exchange. The water whose temperature has risen due to heat exchange is returned to the cooling tower from the pipe 4 via the pipes 4A and 4B, recooled, and reused by circulation. Note that the number of heat exchangers is not limited to two and may be three or more.

In this embodiment, the cooling water supply pipe 2
A carbon dioxide gas blowing pipe 5 is provided at the position to blow carbon dioxide gas into the cooling water flowing into the heat exchanger. Reference numeral 6 is a manual valve, and 7 is an electromagnetic valve, which is configured to open and close in conjunction with the pH controller 8 based on the measured value of the pH sensor 8A provided in the cooling water in the cooling tower 1.

That is, in the present invention, it is important to add carbon dioxide gas so that the calcium carbonate becomes unsaturated at the maximum operating temperature of the water system to be treated, as will be described later in the section of action. Such control of the carbon dioxide gas addition amount can be performed by adjusting the pH of the aqueous system, and the carbon dioxide gas addition amount may be controlled so that the pH becomes 7 to 9.

For this reason, in this embodiment, the opening and closing of the electromagnetic valve 7 is controlled by the pH controller 8 so that the pH measured by the pH sensor 8A becomes unsaturated, and the amount of carbon dioxide gas blown is adjusted. To do. In addition,
9 is a check valve.

In this way, by blowing carbon dioxide into the circulating cooling water in which precipitation of calcium carbonate is expected, scale formation and metal corrosion are effectively prevented.

In the method shown in FIG. 1, blowing of carbon dioxide gas is automatically controlled by pH, but the method of the present invention is based on the measured value of a pH sensor (not shown) as shown in FIG. In addition, the amount of carbon dioxide gas blown in can be controlled by the manual valve 6. Note that the method shown in FIG. 2 is different from the method shown in FIG. 1 only in that the carbon dioxide blowing pipe is not provided with an electromagnetic valve interlocking with the pH controller, and other members having the same function are denoted by the same reference numerals. There is.

In any of the methods, the method of the present invention can be easily carried out by a very simple remodeling work in which a carbon dioxide gas blowing pipe is provided in an appropriate place of the existing equipment, and a good effect is achieved. be able to.

The method of the present invention is not limited to the circulating cooling water system shown in FIGS. 1 and 2, but can be effectively applied to any water system in which calcium carbonate tends to precipitate.
Good effects can be obtained by applying it to dust collection water systems used in steel factories. The method of adding carbon dioxide gas is not particularly limited, and a method of bubbling water in the storage tank or the like can also be adopted.

The carbon dioxide gas used is not limited to high-purity carbon dioxide gas, and waste gas containing a large amount of carbon dioxide gas generated in various factories may be used in some cases. In this case, the amount of waste gas emitted from the factory can be reduced, which is advantageous.

[0019]

The method of treating circulating water according to the present invention effectively utilizes anticorrosive ions such as calcium ions and bicarbonate ions in water to form a protective film on the metal surface in the system to prevent corrosion. It is based on the principle that calcium carbonate in water is maintained in an unsaturated state by contacting with the carbon dioxide gas and the formation of calcium carbonate-based scale is prevented.

The effects of the circulating water treatment method of the present invention will be described in detail below.

Scale Preventive Effect A saturated solution of calcium carbonate has a relationship of the following formula (1), and a carbonate ion and a hydrogen carbonate ion have an equilibrium relationship of the following formula (2).

[0022]

[Chemical 1]

When carbon dioxide gas is blown into a saturated or supersaturated solution of calcium carbonate, the pH of water decreases (H ⁺ increases).
However, as a result of the equilibrium reaction of the above (2) proceeding to the left (←), CO ₃ ²⁻ necessary for the composition of calcium carbonate is reduced, so that calcium carbonate can be maintained in an unsaturated state (dissolved state). That is, it is possible to prevent the precipitation of the calcium carbonate-based scale.

Anticorrosion Effect In the corrosion reaction on the surface of metal such as iron, the elution reaction of iron (anode reaction) and the reduction reaction of oxygen are as follows (3),
It occurs according to the equation (4).

[0025]

[Chemical 2]

The above anode and cathode reactions occur on different iron surfaces. Corrosion can be prevented by suppressing the reaction of either or both of the expressions (3) and (4). As is clear from the above formula (4), the pH is rising (OH ⁻ is increasing) at the place where the cathode reaction is occurring, and even if carbon dioxide gas is blown in, the reaction of the above formula (2) Results in precipitation of calcium carbonate. The precipitated calcium carbonate covers the iron surface not as a bulk but as an extremely thin film different from the scale. When such a calcium carbonate film is formed on the iron surface where the cathodic reaction is occurring, the diffusion of oxygen is hindered, so that the equation (4) becomes difficult to occur. As a result, corrosion can be prevented.

The method of the present invention is easier to carry out on a daily basis and can be carried out at a lower cost than the method using an anticorrosive agent and a scale inhibitor. Moreover, since carbon dioxide gas is used, unlike the pH adjustment with acids such as hydrochloric acid and sulfuric acid, there is no problem of increasing corrosive ions.

[0028]

EXAMPLES The present invention will be described more specifically with reference to Examples and Comparative Examples below.

Example 1, Comparative Examples 1 and 2, carbon dioxide gas was added under the conditions of 45 ° C. and open to the atmosphere so that the pH of the industrial water having the water quality shown in Table 1 was maintained in the range of 7.0 to 8.0. The mixture was concentrated while being blown at a rate of 1 to 5 ml / min, and the change in calcium hardness in water with respect to the concentration multiple was examined (Example 1). For comparison, when carbon dioxide gas was not blown (Comparative Example 1) and a commercial cooling water treatment agent (scale inhibitor and anticorrosive compounded: trademark Kuriroyal 526)
1 A test was also performed when a predetermined amount of Kurita Water Industries Co., Ltd.) was added (Comparative Example 2). As the concentration multiple, a value obtained by dividing the amount of water required for concentration by the amount of water after concentration was used.

The results are shown in FIG. From FIG. 3, when the carbon dioxide gas was not blown, the calcium hardness becomes lower than the theoretical value due to the precipitation of calcium carbonate when the concentration factor becomes 3 times or more, whereas when the carbon dioxide gas is blown, It can be seen that the calcium hardness was maintained in water almost in accordance with the theoretical value as in the case of adding the commercially available cooling water treatment agent.

According to this example, it is apparent that the contact of the concentrated water with the carbon dioxide gas effectively prevents the precipitation of calcium carbonate in the water, and that the method of the present invention is effective in preventing the formation of scale.

[0032]

[Table 1]

Example 2, Comparative Examples 3 and 4 A metal test piece of iron was immersed in the 5-fold concentrated water prepared in Example 1 and the change with time of the weight change amount of the metal was examined under the condition of the water temperature of 45 ° C. (Example 2). During the test period, the blowing of carbon dioxide gas into the concentrated water was continued at a rate of 5 ml / min. For comparison, the 5-fold concentrated water prepared in Comparative Example 1 (Comparative Example 3) and the 5-fold concentrated water prepared in Comparative Example 2 (Comparative Example 4)
Was similarly tested.

The results are shown in FIG. As is clear from FIG. 4, in Example 2, although the initial corrosion weight loss was the same as that of Comparative Example 3 in which carbon dioxide gas was not blown in, the corrosion weight loss became substantially constant after a certain period of time. This indicates that a protective film of calcium carbonate was formed on the iron surface to prevent corrosion. In the case of Comparative Example 3 in which carbon dioxide gas was not blown, the rate of increase in corrosion weight loss tended to decrease with time almost similarly to Example 2 according to the present invention. The declining trend was slow.

On the other hand, in Comparative Example 4 in which a commercially available cooling water treatment agent was added, the initial corrosion weight loss was smaller than that in Example 2, but the increase in corrosion weight loss after a certain period of time was almost the same as in Example 2. It was This result shows that, after forming the protective film in Example 2 according to the present invention, an anticorrosion effect comparable to the case where an anticorrosive agent is used can be expected.
Therefore, it is clear that the method of the present invention is effective for corrosion protection of metals in water.

From the above results, when the carbon dioxide gas is not blown, the scale cannot be prevented even though it is effective in preventing corrosion, whereas the method of the present invention in which the carbon dioxide gas is blown in does not scale. It is clear that comparable scale inhibition and anticorrosion effects can be achieved with the use of inhibitors and anticorrosion agents.

[0037]

As described in detail above, according to the method for treating circulating water of the present invention, scale formation can be prevented and prevented by a very simple operation of bringing carbon dioxide into contact with water in which calcium carbonate is expected to precipitate. It has become possible to easily, efficiently and inexpensively prevent metal corrosion.

According to the present invention, it is possible to make advanced use of water without causing damage such as corrosion and scale, which is extremely advantageous industrially and economically.

[Brief description of drawings]

FIG. 1 is a system diagram showing a method of an embodiment of a method for treating circulating water according to the present invention.

FIG. 2 is a system diagram showing another embodiment method of the circulating water treatment method of the present invention.

FIG. 3 is a graph showing the relationship between concentration factor and calcium hardness in water in Example 1 and Comparative Examples 1 and 2.

FIG. 4 is a graph showing changes over time in corrosion weight loss in Example 2 and Comparative Examples 3 and 4.

[Explanation of symbols]

 1 Cooling Tower 3A, 3B Heat Exchanger 6 Manual Valve 7 Electromagnetic Valve 8 pH Controller 8A pH Sensor

Claims (1)

[Claims] 1. A method for treating circulating water, which comprises adding carbon dioxide gas to circulating water in which calcium carbonate tends to precipitate.