JP2012206102A - Method of estimating corrosion of water system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of estimating corrosion of a water system conveniently enabling management of an oxidizing agent-based slime control agent in a job site even when a plurality of oxidizing agents coexist in the water system.SOLUTION: The method of estimating the corrosion of the water system adds a halogen-based oxidizing agent reagent in water sampled from the water system and after addition, obtains free residual halogen concentration after passing a prescribed time. The corrosion of the water system is estimated on the basis of the correlation of the free residual halogen concentration of ORP obtained previously. The prescribed time is normally 5-180 seconds, and does not exceed 5-30 seconds in particular.

Description

  The present invention relates to a water system corrosivity estimation method, and more particularly to a method for estimating the corrosivity of a cooling water system or the like to which an oxidizing agent is added to prevent slime failure.

  Cooling water is used in various industrial fields such as the petrochemical industry and the steel industry for the purpose of cooling workpieces indirectly or directly, or for building air conditioning, air conditioning, and related equipment. It's being used. Furthermore, in order to reduce the amount of cooling water used from the viewpoint of lack of water resources and effective use, advanced use of cooling water is performed, for example, reducing the amount of forced blow in the high concentration operation of an open circulating cooling water system. ing. In this way, when cooling water is used at a high level, the quality of the circulating cooling water deteriorates due to the concentration of dissolved salts and nutrients, etc., and soil, sand, dust, etc. are mixed with microorganisms such as bacteria, mold and algae. The slime formed is generated, which causes a decrease in thermal efficiency and deterioration of water flow in the heat exchanger, and also induces local corrosion of equipment and piping at the lower part of the slime adhesion. On the other hand, in the papermaking water system, the concentration of organic substances such as starch is high, and it is easy to generate slime by entraining fillers, and the slime adhering to the wall surface falls off, causing paper breaks and spots. Obstacles due to slime adhesion are not limited to cooling water systems and papermaking water systems, but include industrial water systems such as metalworking fluid systems, ultrapure water manufacturing systems, wastewater membrane treatment systems, textile manufacturing water systems, household water systems, It occurs in all water systems such as agricultural water systems.

  Various antibacterial agents have been used to prevent such slime damage. As in Patent Document 1, a treatment with an inorganic oxidizing antibacterial agent such as hypochlorous acid is widely used because the material cost is low. When water stains and organic concentrations increase, slime damage increases and the required concentration of antibacterial agents increases, but many inorganic oxidizing antibacterial agents are highly corrosive to metals and there is little room to increase the concentration of additives. . Then, the process which is compatible with a slime prevention capability is implemented, suppressing corrosion by stabilizing an inorganic oxidizing antibacterial agent with hydantoins, sulfamic acid, etc. Furthermore, the process which combined the inorganic oxidizing antibacterial agent and the stabilized oxidizing antibacterial agent is also implemented.

  Various methods have been devised for measuring the residual concentration of an aqueous oxidant to which such an oxidant is added. For example, a technology for measuring the oxidation-reduction potential (ORP) to grasp the corrosivity of the aqueous system and controlling the residual concentration of the aqueous oxidant, or a technology for controlling the residual concentration by measuring the oxidant species with a polarometer and so on. These methods are useful management methods because they can grasp the corrosion tendency of the water system and can analyze the composition of the oxidant species. However, there is a problem in the stability and life of the electrode, and a special device is required and the management is complicated, which is not general.

  In order to measure the residual concentration of the aqueous oxidant, a method of measuring the residual concentration using a reagent that exhibits a color development reaction corresponding to the amount of the oxidant is simple and widely used. As a typical reagent, the orthotolidine method has heretofore been the mainstream, but at present, a method using an N, N'-diphenylphenylenediamine (DPD) reagent is mainly used. According to this method, when one kind of oxidizing agent remains in the aqueous system, the corrosivity of the aqueous system can be estimated by measuring the residual concentration of the free oxidizing agent or measuring the total amount of the oxidizing agent. However, when a plurality of oxidants coexist in the water system, the corrosivity of the water system cannot be accurately estimated only by measuring the total amount of the oxidant or measuring the free oxidant.

JP 7-189192 A

  An object of the present invention is to provide an aqueous corrosiveness estimation method that enables easy management of an oxidant-based slime control agent in the field even when a plurality of oxidants coexist in an aqueous system.

  The method for estimating corrosivity of an aqueous system according to claim 1 is a method for estimating corrosivity in an aqueous system to which a halogen-based oxidant for preventing slime is added, and an oxidant measurement reagent is added to the oxidant-containing water to measure the oxidant. The corrosivity is estimated based on the free residual halogen concentration after a predetermined time has elapsed after the addition of the reagent.

  The aqueous corrosiveness estimation method according to claim 2 is characterized in that, in claim 1, the oxidant measurement reagent is an N, N'-diphenylphenylenediamine (DPD) reagent.

  According to a third aspect of the present invention, there is provided an aqueous corrosiveness estimation method according to the first or second aspect, wherein the predetermined time is a time selected from 5 to 180 seconds.

  According to a fourth aspect of the present invention, there is provided the water-system corrosiveness estimation method according to the first or second aspect, wherein the predetermined time is a time selected from 5 to 30 seconds.

  According to a fifth aspect of the present invention, there is provided a method for managing an oxidant residual concentration in an aqueous system according to any one of the first to fourth aspects, wherein the halogen-based oxidant is a stabilized halogen-based oxidant.

  The management method of the residual oxidant concentration in the aqueous system according to claim 6 is characterized in that, in claim 5, the stabilized halogen-based oxidant is a stabilized chlorine-based oxidant or chlorinated sulfamic acids.

  The aqueous corrosiveness estimation method of claim 7 is characterized in that, in claim 6, the chlorinated sulfamic acid is monochlororosulmic acid or dichlorosulfamic acid.

  When an oxidant measurement reagent such as DPD is added to an oxidant such as chlorine-based oxidant-containing water, the oxidant measurement reagent and the oxidant react immediately after the addition, and this reaction proceeds with time. In this case, the coloring changes with time. When the present inventor conducted various studies, the measured value of free residual chlorine by the measuring reagent and the ORP of water when a predetermined time such as 5 to 180 seconds elapses after addition of the measuring reagent shows a good correlation. Admitted. Since this ORP value is an index value indicating the corrosivity of the water system, according to the present invention, the corrosivity of the water system can be accurately estimated without using the ORP electrode.

It is a graph which shows the relationship between an oxidizing agent density | concentration and ORP. It is a graph which shows the relationship between total residual chlorine concentration and ORP. It is a graph which shows the relationship between free residual chlorine concentration and ORP. It is a graph which shows the relationship between free residual chlorine concentration and ORP. It is a graph which shows the relationship between free residual chlorine concentration and ORP.

  In the present invention, a halogen-based oxidant measurement reagent is added to water collected from an aqueous system, and the free residual halogen concentration after a predetermined time has elapsed after the addition. Then, the corrosivity of the aqueous system is estimated based on the correlation between the free residual halogen concentration and the ORP determined in advance. The predetermined time is usually a fixed time selected from about 5 to 180 seconds, particularly about 5 to 30 seconds.

  Examples of the halogen-based oxidant to be measured in the present invention include chlorine dioxide, hypochlorous acid, hypobromous acid, chloramines, broamines, chlorinated isocyanuric acids, chlorinated dimethylhydantoins and the like. Examples of chloramines and broamines include monochlororosulmic acid, dichlorosulfamic acid, monobromosulfamic acid, dibromosulfamic acid, etc., in which halogen is stabilized with sulfamic acid. These may be used alone or in combination. According to the present invention, even when a plurality of oxidizers are used in combination and the individual oxidizer concentration cannot be specified, the corrosivity of the aqueous system can be accurately estimated. In the present invention, a peroxide oxidizing agent such as ozone, hydrogen peroxide, and peracetic acid may be contained together with the halogen oxidizing agent.

  The oxidant concentration measurement method used in the present invention is preferably a syringaldazine method, o-tolidine method, N, N'-diphenylphenylenediamine (DPD) method or the like, but is not limited thereto. There are two types of DPD methods, one used as a free effective chlorine measurement method and the other used as a total residual chlorine measurement method in the presence of iodine. Further, by combining both of these, it is possible to detect a very wide range of corrosivity from a highly stabilized non-corrosive oxidant to a highly corrosive oxidant having a low degree of stabilization.

  In the case where DPD is added to the chlorine-based oxidizing agent-containing water, the free residual chlorine concentration at the time when a certain time selected from 5 to 180 seconds, particularly from 5 to 30 seconds has elapsed after the addition of DPD is obtained. As can be seen in the examples described later, the free residual chlorine concentration at this time shows a good correlation with the aqueous ORP. Therefore, a correlation between the free residual chlorine concentration and the ORP (for example, a calibration curve or a calibration formula) is obtained in advance, and the ORP is calculated from the measured free residual chlorine concentration at the time of 5 to 180 seconds, particularly 5 to 30 seconds after the addition. Can be estimated. Since this ORP is an estimated corrosivity index value, it is possible to detect aqueous corrosivity from the free residual chlorine concentration.

  It is also possible to obtain a correlation between the free residual chlorine concentration and the corrosiveness after the lapse of the predetermined time without using the ORP value and immediately know the corrosiveness of the aqueous system from the free residual chlorine concentration.

  Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.

[Example 1]
1 L of 100 mM borate buffer (pH 8.6) was placed in a beaker and maintained at 25 ° C. in a thermostatic bath while stirring with a stirrer. A predetermined amount of a sodium hypochlorite solution, a NaBr solution as bromine (Br), an NH ₄ Cl solution and 5,5-dimethylhydantoin (DMH) solution as ammonia (NH ₃ ) were added. After stirring for 10 minutes, ORP (saturated Ag / AgCl-Pt electrode), pH, free residual chlorine (Free), and total residual chlorine (Total) were measured. Residual chlorine concentration was carried out using N, N′-diphenylphenylenediamine (DPD) reagent according to JIS method (K0101, K0102). The results are summarized in Table 1. The relationship between the added oxidant concentration, total residual chlorine concentration, free residual chlorine concentration after 10 seconds of reagent addition, free residual chlorine concentration after 60 seconds of reagent addition and ORP is shown in FIGS.

  Hypochlorous acid generates hypobromous acid having stronger oxidizing power in the presence of bromine ions. Similarly, in the presence of ammonium ions, it becomes chloramine and its oxidizing power decreases. Furthermore, by combining with 5,5-dimethylhydantoin, it becomes stable combined chlorine.

  As shown in FIG. 1, there is a correlation between the additive oxidant concentration and the ORP value in any oxidant, but since the absolute value is greatly different, the additive oxidant concentration is an index of corrosiveness in water. An ORP cannot be analogized. As shown in FIG. 2, the relationship between the total residual chlorine concentration, which is an index of the residual concentration of the total oxidizing agent, and ORP is the same. Although a relative correlation is recognized between the free residual chlorine concentration 60 seconds after the addition of the reagent and the ORP, it can be seen that the behavior varies depending on the oxidant species present in the aqueous system and its ratio. On the other hand, the concentration of free residual chlorine 10 seconds after the addition of the reagent shows a very good correlation with ORP, and it can be seen that it is suitable as an index representing the corrosivity of aqueous systems.

[Example 2]
In the actual cooling water system, free effective chlorine and total residual chlorine were measured using N, N′-diphenylphenylenediamine (DPD) reagent according to JIS method (K0101, K0102) except for the reaction time. . This actual cooling water system was an air conditioning refrigerator cooling water system, and the water balance was as follows.
Retained water volume: 2.0m ³
Circulating water volume: 80m ³ / hr
Cooling tower temperature difference: 5.0 ° C
Concentration multiple: 8 times

In this cooling water system, a monochlororosulfamic acid 5% solution is 200 g / m ³ -blowing water amount, a dimethylhydantoin 1% solution is 100 g / m ³ -blowing water amount, and a sodium hypochlorite 12% solution is 400 mg / L-blowing water amount. Pseudo continuous injection was performed once every 2 hours. After continuously operating for one week, the cooling water was periodically sampled and the free effective chlorine concentration and the total residual chlorine concentration were measured at different times. The results are shown in Table 2 together with the ORP value at the time of sampling. FIG. 5 shows the relationship between the free residual chlorine concentration 5 seconds after addition of the reagent and the ORP.

  As shown in Table 2 and FIG. 5, even when the stabilizer is present in the actual cooling water system and the presence of a plurality of oxidizing agents changes with time due to intermittent injection of sodium hypochlorite, The concentration of free residual chlorine after 30 seconds shows a very good correlation with ORP, and the ORP value, which is an aqueous corrosivity index value, can be accurately estimated from the color change of the reagent. In addition, even if reaction time becomes long, it turns out that it is related to ORP up to about 180 seconds.

Claims (7)

  In a method for estimating corrosivity in an aqueous system to which a halogen-based oxidant for preventing slime is added, an oxidant measurement reagent is added to the oxidant-containing water, and free residual halogen after a predetermined time has elapsed after the addition of the oxidant measurement reagent. A method for estimating corrosivity of an aqueous system, wherein corrosivity is estimated based on concentration.   2. The aqueous corrosiveness estimation method according to claim 1, wherein the oxidizing agent measuring reagent is an N, N′-diphenylphenylenediamine (DPD) reagent.   3. The water-system corrosivity estimation method according to claim 1, wherein the predetermined time is a time selected from 5 to 180 seconds.   3. The water-system corrosivity estimation method according to claim 1, wherein the predetermined time is a time selected from 5 to 30 seconds.   5. The method for managing an oxidant residual concentration in an aqueous system according to any one of claims 1 to 4, wherein the halogen-based oxidant is a stabilized halogen-based oxidant.   6. The method of managing an oxidant residual concentration in an aqueous system according to claim 5, wherein the stabilized halogen-based oxidant is a stabilized chlorine-based oxidant or chlorinated sulfamic acids.   7. The aqueous corrosiveness estimation method according to claim 6, wherein the chlorinated sulfamic acids are monochlororosulmic acid or dichlorosulfamic acid.

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