JP2000346307A - Thermal power plant and method for managing its operation - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thermal power plant having excellent corrosion resistance capable of deciding a charging amount of a deoxidizer by using a result by clarifying a necessary deoxidizer concentration by measuring the corrosion electric potential in a boiler circulating water system and a method for managing its operation. SOLUTION: The thermal power plant having a water circulating system including a boiler, a turbine and a condenser comprises a means for measuring a corrosion potential of metal brought into contact with boiler water or feed water, and a means for regulating a concentration of a less toxic deoxidizer than a hydrazine so as to make corrosion potential lower than that of metal when deaerated. The method for managing an operation of the plant comprises the steps of measuring the corrosion potential of the metal brought into contact with boiler water or feed water by using a reference electrode and a potentiometer, and regulating the concentration of the deoxidizer so that its molecular weight is larger than that of the hydrazine and smaller than that of a tunnin and the concentration of the deoxidizer reacted with oxygen in water is lower than the potential of the metal when deaerated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for removing oxygen from circulating water in a closed system including a boiler of a power plant or the like.
The present invention relates to a thermal power plant using water treatment means for adding a deoxidizer to circulating water and an operation management method thereof.

[0002]

2. Description of the Related Art An oxygen scavenger is added to a boiler by measuring the oxygen concentration of feed water or boiler water and adding several times the theoretical amount of the oxygen scavenger required for the measurement. According to Japanese Industrial Standard JIS-B8223, boiler water quality analysis shows that the concentration of oxygen and unreacted oxygen scavenger is more than a certain value. It is recommended that the concentration of the drug be used.

Further, Japanese Patent Application Laid-Open No. Hei 10-325508 discloses a method of injecting a phosphite-based oxygen scavenger into boiler water supply and Japanese Patent Application Laid-Open No. Hei 6-109207. JP 5
Japanese Patent Publication No. 98476 discloses that in a system where a metal and water are in contact, the corrosion potential of the metal is monitored by monitoring the spontaneous potential of the metal and adding a corrosion inhibitor to the system so that the value becomes lower than the pitting potential. A method is disclosed.

Japanese Patent Application Laid-Open No. 6-109207 discloses a method of injecting 0.5 to 1.5 ppm of hydrazine into boiler feed water.

Japanese Patent Application Laid-Open No. 6-109207 discloses an oxygen scavenger comprising a phosphite or a hypophosphite and a complex of platinum. However, concentration control when injecting the oxygen scavenger is performed. There is no disclosure.

[0006]

The amount of the oxygen absorber added during boiler operation is several times the amount theoretically necessary based on past experience, and this is one obstacle to cost reduction.

[0007] Further, when storing the boiler in a state where the operation of the boiler is stopped, the boiler is managed with a higher concentration of the oxygen scavenger than during operation. It is difficult to grasp the concentration of the oxygen absorber when the circulating water is stationary when storing the boiler, so a large amount of oxygen absorber is added to prevent accidents due to lack of oxygen absorber and respond to oxygen leaks. . This is because if more than expected oxygen is mixed into the boiler,
This is because the addition of a certain amount of oxygen scavenger theoretically required may cause corrosion due to residual oxygen after the oxygen scavenger is completely consumed.

At present, hydrazine is mainly used as an oxygen scavenger. Hydrazine is toxic (LD _{50 in} rats)
(59 mg / kg) is strongly restricted by plant design and the like from the viewpoint of safety and health.

Further, when a large amount of hydrazine is added, the hydrazine is decomposed at a high temperature to produce ammonia, which contains a high concentration of ammonia in the condensate passage and raises the pH. Corrosion is accelerated.

In recent years, various oxygen scavengers have been developed in place of the hydrazine. However, among them, the reaction with oxygen is complicated, and based on the substance concentration after reacting with oxygen,
It is often difficult to control the concentration of the oxygen scavenger to be added.

For example, ersorbic acid and the like decompose at a high temperature to generate carbonic acid and nitric acid and lower the pH.

[0012] Therefore, there is a need for a management method that minimizes the amount of oxygen scavenger required at a low cost with less problems on safety and hygiene for the oxygen scavenger instead of hydrazine.

An object of the present invention is to determine the required oxygen scavenger concentration by measuring the corrosion potential by measuring the injection amount of the oxygen scavenger into the boiler circulating water system. It is to provide a management method.

[0014]

SUMMARY OF THE INVENTION The present invention relates to a means for measuring the corrosion potential of metal in contact with boiler water or feedwater in a thermal power plant having a water circulation system including a boiler, a turbine and a water impeller. toxicity, preferably a comprising means for adjusting the concentration of the oxygen scavenger to be lower than the corrosion potential at the time of deaeration of the concentration of the metal of the LD ₅₀ is 100 mg / kg or more oxygen scavenger rats Thermal power plant.

Further, according to the present invention, in a method for managing the operation of a thermal power plant having a water circulation system including a boiler, a turbine and a water cover, the corrosion potential of a metal in contact with boiler water or feedwater is determined by using a reference electrode and a potentiometer. Measure and adjust the concentration of the oxygen absorber so that the molecular weight is larger than hydrazine, smaller than tannin, and the concentration of the oxygen absorber that reacts with oxygen in water is lower than the corrosion potential at the time of degassing the metal. An operation management method for a thermal power plant characterized by the above feature.

The method for managing the operation of a thermal power plant is characterized in that the quality of the water is managed during operation of the boiler or during storage when the circulating water flow is stopped.

In the above invention, the means for adjusting the addition amount of the oxygen scavenger measures the corrosion potential of the metal in contact with the boiler water or feed water using a reference electrode and a potentiometer, and determines the corrosion potential with the potential difference. Controlling or monitoring the addition amount of the oxygen absorber so as to have a corrosion potential corresponding to a predetermined concentration of the oxygen absorber from the relationship of the concentration of the oxygen absorber that is reactive;
The corrosion potential at the time of degassing of the metal is a means for periodically measuring the corrosion potential of the metal in contact with boiler water or feedwater without injecting a deoxidizer, or the corrosion potential at the time of constant degassing is desalination. Using a means to measure the corrosion potential of the part in contact with the deoxidizer-free feedwater at the outlet of the degasifier or deaerator, or by injecting ammonia into the feedwater at the demineralizer outlet and boiler water Or controlling and measuring the corrosion potential of the metal in contact with the feed water to the same temperature as the portion to be measured using a reference electrode and a potentiometer, the oxygen scavenger, sulfite, bisulfite, pyrosulfite, Phosphite, methyl ethyl ketoxime, erythorbic acid, diethylhydroxylamine, hydroquinone, carboxylic acid amine salt,
A method for controlling the operation of a thermal power plant, comprising a compound selected from saccharides, the compound having a higher molecular weight than hydrazine, a lower molecular weight than tannin, and reacting with oxygen in water.

Further, the present invention relates to a thermal power plant having a water circulation system including a boiler, a turbine, and a water flooder, wherein a means for measuring a corrosion potential of a metal in contact with boiler water or feed water and a corrosion potential of the metal are measured. There is provided a thermal power plant having an oxygen scavenger adding means for adjusting the corrosion potential to be lower than the corrosion potential at the time of degassing.

The present invention also relates to an operation management method for a thermal power plant having a water circulation system including a boiler, a turbine and a water cover, wherein the corrosion potential of a metal in contact with boiler water or feed water is measured using a reference electrode and a potentiometer. In addition, there is provided an operation management method for a thermal power plant, wherein an addition amount of a deoxidizer is adjusted so that a corrosion potential of the metal is lower than a corrosion potential at the time of degassing of the metal.

[0020]

FIG. 2 is a system diagram showing a measurement position of a corrosion potential in a thermal power plant according to the present invention.

In the present invention, when the corrosion potential is measured, it is preferable that the corrosion potential is measured at a position downstream of the position where the oxygen scavenger is added in the water supply system. 5, 6, 7).

That is, the corrosion potential measurement position 5 in front of the deaerator 4 on the downstream side where the oxygen scavenger is added downstream of the condenser 3
, A method of measuring at a corrosion potential measurement position 6 in the boiler 1 downstream of the deaerator 4 and just before the boiler, and a method of measuring at a corrosion potential measurement position 7 in the boiler 1.

In front of each corrosion potential measurement position, there are corrosion potential measurement positions 8, 9 and 10 at the time of deaeration, and downstream of the corrosion potential measurement positions 8, 9 and 10, an oxygen absorber injection valve 11 attached to an oxygen absorber injection line. , 12 and 13, and oxygen absorber control devices 14, 15 and 16 are installed at the respective locations to control the injection amount of the oxygen absorber.

Further, the deoxidizer is added to the boiler 1 during storage as well as during operation. In general, storage is a static storage without water circulation, but the corrosion potential can be measured without water flow, and the concentration of oxygen scavenger can be controlled and monitored even when the boiler is stopped and stored. is there.

In the case where the corrosion potential or the corrosion potential at the time of degassing is measured at each of the positions 5, 6, and 7 described above, for example, the following method is available. This is a method of directly measuring the potential of a pipe or the like in a plant, or a method of measuring the water supply or the like after collecting the water and adjusting the water quality and temperature to a predetermined value.

FIG. 3 is a schematic diagram of a method for directly measuring the corrosion potential of the piping 17 in the circulating water path.

In this method, a reference electrode 18 is attached to the pipe 17 or the like, and the corrosion potential of the pipe 17 or the like near the pipe 17 is measured by a potentiometer 19. The reference electrode 18 includes an external reference electrode and an internal reference electrode, and any standard electrode that can be converted to a hydrogen standard potential may be used. The signal of the measured corrosion potential is sent to a control device for controlling the amount of the oxygen scavenger added or a monitoring place. This method is applicable during operation and storage.

FIG. 4 is a schematic diagram of a method for collecting a sample water such as a water supply and controlling and measuring a predetermined environment.

FIG. 4 shows a method of taking out the sample water at the measuring point and measuring the corrosion potential of the metal in the pressure vessel 20.
When the method of FIG. 3 is not possible, the boiler water or feed water to be measured is extracted, introduced into the pressure vessel 20, and the corrosion potential of the test piece 22 is measured using the reference electrode 21 and the potentiometer 23.
The signal measured by the potentiometer 23 is sent to a control device that controls and monitors the amount of the oxygen scavenger added. This method is applicable during boiler operation and storage. When the boiler is stopped and stored, it is necessary to attach a pump or the like to circulate the sample water so that the sample water in the pressure vessel 20 has the same quality as the boiler water. Here, the material of the test piece 22 is not particularly limited as long as its corrosion potential can be measured in high-temperature water.

According to the present invention, the corrosion potential of a metal in contact with boiler water or feedwater is measured, and the potential is controlled to be lower than the corrosion potential at the time of degassing. More specifically, the present invention relates to a boiler operation management method in which the boiler is operated and controlled at an appropriate concentration of an oxygen absorber to suppress corrosion of the boiler by oxygen from the relationship between the potential difference between the time of degassing and the time of addition of the oxygen absorber.

In addition, the oxygen scavenger is added without excessive oxygen scavenger to suppress the cost of the surplus oxygen scavenger, and when the reaction between the oxygen scavenger and oxygen is complicated or when different types of oxygen scavengers are mixed. Even when the concentration of the unreacted substance is difficult to control, for example, when the unreacted oxygen is added, the concentration of the unreacted oxygen absorber can be controlled by the corrosion potential from the relationship between the potential difference between the time of degassing and the time of addition of the oxygen scavenger.

Further, it has been conventionally difficult to grasp the oxygen scavenger concentration at the time of boiler stationary storage. However, it is possible to measure the corrosion potential of pipes and the like at the time of stoppage, and conventionally, a very high oxygen scavenger is added. However, this can be reduced and the price of the oxygen scavenger can be reduced. At this time, any substance used as a deoxidizer reacts with oxygen in water and has a lower corrosion potential than at the time of degassing.

On the other hand, by controlling the corrosion potential according to the present invention so as to be lower than the corrosion potential at the time of degassing, even if the reaction of the oxygen scavenger is complicated, the concentration of the oxygen scavenger can be controlled by the corrosion potential. Can respond.

Also, even if oxygen leaks in the boiler for some reason and the oxygen concentration in the boiler water becomes high, it is possible to control the corrosion potential by immediately increasing the amount of the oxygen scavenger added. And corrosion by oxygen can be avoided.

By measuring the corrosion potential of the metal, the oxidizing atmosphere or the reducing atmosphere of the water in the circulating water system can be detected. If there is an oxidizing substance such as oxygen and corrosion potential measured in an environment where pure water is replaced with an inert gas, the corrosion potential changes to a noble side. Conversely, when a substance having a reducing action such as hydrazine is present, it changes to a lower side.

All oxygen scavengers used for boiler water treatment for the purpose of removing oxygen have the effect of lowering the corrosion potential of metals below that of degassing.

In the present invention, from the relationship between the oxygen scavenger concentration and the corrosion potential difference between the time of deaeration and the time of addition of the oxygen scavenger, it is possible to monitor the corrosion potential at the desired oxygen scavenger concentration and control the amount of addition.

Furthermore, when a small amount of dissolved oxygen as an oxidizing agent is present, the corrosion potential is significantly increased, and it is possible to instantaneously detect the shortage of the deoxidizing agent, thereby enabling safer operation management. That is, it is possible to provide a boiler operation management method that can control or monitor an appropriate deoxygenation concentration by measuring the corrosion potential of piping connected to boiler water or feedwater during operation and storage of the boiler.

In the present invention, examples of the oxygen scavenger having an LD ₅₀ of 100 mg / kg or more in rats having lower toxicity than hydrazine include, for example, methylketyl oxime: LD ₅₀
Is 3100 mg / kg, dihydroxylamine: LD
₅₀ is 2190 mg / kg and sodium sulfite: no toxicity.

[0040]

Examples 1 to 6 and

Comparative Examples 1 to 12 Table 1 shows the types and addition conditions of oxygen scavengers (compounds) and the corrosion potential of carbon steel after 100 hours.

[0041]

[Table 1]

In the corrosion potential measurement test, a circulating autoclave device capable of controlling the water quality of the test section was used. The test piece used was carbon steel (STB-35). Test temperature is 300
C., the pH of the feed water was adjusted to pH 9.5 using ammonia, and the dissolved oxygen concentration was <1 ppb. The results in Table 1 are shown in FIG.

FIG. 1 shows the change in corrosion potential when carbon dioxide is added with a deoxidizer. Comparative Example 1 is a reference value for other measured values, and is a condition where the oxygen concentration of the feedwater is 1 ppb or less and the oxygen scavenger is not added. The value is -481 m after 100 hours.
It was almost stable at V (vs SHE). In the figure, the difference in the reference corrosion potential is 0.

Examples 1 and 2 are cases where sodium sulfite is added. The corrosion potential of Example 2 to which a concentration theoretically reacting with the oxygen concentration of 400 ppb was added was about 180 mV lower than that of Comparative Example 1 at the time of degassing.

Comparative Examples 2 and 3 are cases where hydrazine was added. In the case of Comparative Example 3 in which a concentration that theoretically reacts with the oxygen concentration of 400 ppb was added, compared with Comparative Example_1, about 93
mV lower.

Examples 3 and 4 show the results when carbohydrazide was added. The corrosion potential in Example 4 in which a concentration theoretically reacting with the oxygen concentration of 400 ppb was added was 205 mV lower than that in Comparative Example 1.

Examples 5 and 6 show the results when glucose was added. The corrosion potential in Comparative Example 6 in which a concentration theoretically reacting with an oxygen concentration of 500 ppb was added,
107 mV lower than that of Comparative Example 4 has an oxygen concentration of 35 pp
It is the result of adding and measuring. The corrosion potential is 107 mV higher than that of Comparative Example 1.

From the above results, when the oxygen scavenger is added, it becomes lower than the corrosion potential at the time of deaeration, and the amount of addition and the decreased potential differ depending on the oxygen scavenger. Therefore, when an unreacted oxygen scavenger is present, it shows a value lower than the corrosion potential at the time of degassing, and there is a correlation between the concentration of the oxygen scavenger and the corrosion potential difference between when the oxygen scavenger is added and when it is not added, By measuring the corrosion potential difference, the concentration of the oxygen scavenger can be controlled or monitored.

Further, when dissolved oxygen is present as in Comparative Example 2, the corrosion potential is significantly increased, and the case where the oxygen scavenger is insufficient can be immediately detected.

The above method is a case where the corrosion potential at the time of degassing changes with time. In addition to this method, when the quality of the water to be controlled is always constant and there is no change in the corrosion potential at the time of degassing, the addition of the oxygen scavenger can be controlled so that the potential becomes constant.

Table 2 shows carbon steel (STB-35), low alloy steel (STBA-22), and stainless steel (SUS304).
5 shows the experimental conditions and results of the measurement of the change in corrosion potential with and without the oxygen scavenger using the method.

[0052]

[Table 2]

The test was performed at a temperature of 300 ° C., the pH of the feed water was adjusted to 9.5 with ammonia, and the dissolved oxygen was <1 ppb.
And

Hydrazine was used as the oxygen scavenger, and a consumable oxygen concentration of 200 ppb was added, and the corrosion potential was measured after 100 hours. Comparing the corrosion potential without the addition of the oxygen scavenger, the low alloy steel of Comparative Example 5 was −4610 mV (VS SH), which was approximately 28 mV higher than the carbon steel of Comparative Example 1.
E).

The stainless steel of Comparative Example 7 was -351 mV (VS SHE), which was about 130 mV higher than the carbon steel of Comparative Example 1. Comparing the same material with and without a deoxidizer, Comparative Example 2, which is carbon steel, is 70 mV lower than Comparative Example 1. Comparative Example 6, which is a low alloy steel, is 63 m longer than Comparative Example 5.
V is low. Comparative Example 8, which is stainless steel, is 75 mV lower than Comparative Example 7. From the above, it can be seen that there is not much difference between any of the materials, which is 63 to 75 mV lower than that when no material is added. Further, even if the material is different and the corrosion potential at the time of degassing is different, the corrosion potential is reduced when an oxygen scavenger is added.

Table 3 shows the experimental conditions and the results of examining the change in corrosion potential with and without the oxygen scavenger at different temperatures using carbon steel.

[0057]

[Table 3]

The test temperatures were 100, 200 and 300 ° C., the pH of the feed water was adjusted to pH 9.5 using ammonia, and the dissolved oxygen was <1 ppb. Hydrazine is used as a deoxidizer, and a consumable oxygen concentration of 200 ppb is added.
After 0 hour, the corrosion potential was measured. Test temperature is 100
Comparative Example 10 in which the temperature was 0 ° C. had a corrosion potential lower by 55 mV than Comparative Example 9 in which no additive was added. The corrosion potential is 62 mV lower than that of Comparative Example 12 at a test temperature of 200 ° C. and Comparative Example 11 not added. In Example 2 where the test temperature was 300 ° C., the corrosion potential was lower by 70 mV than in Comparative Example 1 where no additive was added. From the above, when the oxygen scavenger is added in any temperature range, the corrosion potential decreases. However, the lower the temperature, the smaller the corrosion potential when the oxygen scavenger is added.

Table 4 shows the experimental conditions and results obtained by examining the change in corrosion potential with and without the oxygen scavenger using carbon steel while changing the pH.

[0060]

[Table 4]

The test temperature was 300 ° C., and the pH of the feed water was adjusted using ammonia to adjust the dissolved oxygen to <1 ppb. In the test, an oxygen concentration equivalent to 200 ppb capable of consuming hydrazine as a deoxidizer was added, and the corrosion potential was measured after 100 hours. The corrosion potential is 72 mV lower than that of Comparative Example 13 in which the test pH of 8.0 was not added.
Comparative Example 2, which has a test pH of 9.5, has a corrosion potential lower by 70 mV than Comparative Example 1. From the above, when the oxygen scavenger is added in the weakly alkaline region, the corrosion potential is lowered, and the tendency is larger near neutrality.

When the oxygen scavenger is injected from the chemical tank, a substance which reacts quickly at room temperature reacts in the chemical tank due to oxygen leak of the tank and consumes the oxygen scavenger. Concentration may have decreased. Even in such a state, the concentration of the oxygen scavenger can be appropriately controlled by measuring the corrosion potential of the metal in contact with the boiler water or the feed water.

[0063]

According to the present invention, the corrosion potential of a metal in contact with boiler water or feed water is measured in a degassed environment in the absence of oxygen so that the corrosion potential is lower than the corrosion potential. The concentration of the oxygen scavenger can be controlled.

The relationship between the concentration of each oxygen scavenger and the corrosion potential depends on the metal to be measured, its temperature pH, and other substances dissolved in water. Therefore, when applied to an actual machine, measure the corrosion potential at the time of degassing in the same environment as the actual machine, and then add a oxygen scavenger to clarify the relationship between the oxygen scavenger and the corrosion potential and adjust the concentration of the oxygen scavenger to be adjusted. Add the oxygen scavenger to the corresponding corrosion potential. When the relationship between the oxygen scavenger and the corrosion potential is to be measured using an actual machine, the corrosion potential is measured by comparing it with the analysis value of the oxygen scavenger or by actually measuring the corrosion potential at the time of degassing, and then adding the oxygen scavenger to the corrosion potential. This can be achieved by determining the relationship between the potential and the deoxygenation concentration.

According to the present invention, the required oxygen scavenger concentration can be easily determined by measuring the corrosion potential with respect to the injection amount of the oxygen scavenger, which has conventionally depended on experience, and the results can be used to appropriately determine the oxygen scavenger concentration. Provided is a boiler management method capable of determining an injection amount.

[Brief description of the drawings]

FIG. 1 shows a change in corrosion potential at the time of adding a deoxidizer to carbon steel.

FIG. 2 is a system diagram of a thermal power plant showing a measurement position of a corrosion potential in an actual boiler.

FIG. 3 is a schematic diagram showing a method for directly measuring a corrosion potential of a pipe or the like.

FIG. 4 is a schematic diagram showing a method of extracting and measuring boiler water and feedwater.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Boiler, 2 ... Turbine, 3 ... Condenser, 4 ... Deaerator, 5 Corrosion potential measurement position, 6 ... Corrosion potential measurement position, 7 ... Corrosion potential measurement position, 8 ... Corrosion potential measurement position at the time of degassing , 9 ... Corrosion potential measurement position during degassing, 10 ...
Corrosion potential measurement position during deaeration, 11 ... Oxygen absorber tank,
12 ... oxygen absorber tank 13 ... oxygen absorber tank
14: oxygen scavenger concentration control device, 15: oxygen scavenger concentration control device, 16: oxygen scavenger concentration control device, 17: piping, 18: reference electrode, 19: potentiometer, 20: pressure vessel, 21: reference electrode , 22: Test piece for measuring electric potential, 23: Potentiometer.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Hiroshi Yamauchi 7-1-1, Omikacho, Hitachi City, Ibaraki Prefecture Within Hitachi Research Laboratory, Hitachi, Ltd. (72) Inventor Tsuyoshi Kambayashi 3-chome, Sachimachi, Hitachi City, Ibaraki Prefecture No. 1 Hitachi Ibaraki Business Engineering Co., Ltd. (72) Inventor Shigeto Murata 3-1-1 Kochicho, Hitachi City, Ibaraki Prefecture Inside Hitachi, Ltd. Hitachi Plant (72) Inventor Norio Shimono Kure City, Hiroshima Prefecture 6-9 Takaracho Babcock Hitachi Kure Factory F-term (reference) 4K062 AA03 AA05 BA08 BB04 BB06 BB07 BB12 BB15 BB18 CA05 CA10 DA01 EA04 FA05 FA06 GA08

Claims (9)

[Claims] In a thermal power plant having a water circulation system including a boiler, a turbine and a water cover, a means for measuring a corrosion potential of metal in contact with boiler water or feed water and a concentration of a deoxidizer having a lower toxicity than hydrazine are provided. A thermal power plant having means for adjusting the corrosion potential to be lower than the corrosion potential at the time of degassing of the metal. 2. A method for controlling the operation of a thermal power plant having a water circulation system including a boiler, a turbine, and a water cover, wherein the corrosion potential of a metal in contact with boiler water or feedwater is measured using a reference electrode and a potentiometer, and hydrazine is used. Operation management of a thermal power plant characterized by adjusting the concentration of a deoxidizer having a higher molecular weight, a lower molecular weight than tannin and reacting with oxygen in water to be lower than a corrosion potential at the time of degassing of the metal. Method. 3. The method according to claim 1, wherein the means for adjusting the concentration of the oxygen scavenger measures a corrosion potential of a metal in contact with the boiler water or the feedwater using a reference electrode and a potentiometer. Controlling or monitoring the amount of the oxygen scavenger added so that the corrosion potential corresponds to a predetermined concentration of the oxygen scavenger from the relationship between the corrosion potential and the concentration of the unreacted oxygen scavenger. Operation management method for thermal power plants. 4. The method according to claim 1, wherein the corrosion potential of the metal at the time of degassing is measured periodically without introducing a deoxidizer into the metal in contact with the boiler water or the feed water. A means for measuring the corrosion potential at the time of degassing or a means for measuring the corrosion potential at the outlet of the demineralizer or at the part in contact with the water supply containing no oxygen absorber at the outlet of the deaerator. Operation management method for thermal power plants. 5. The corrosion potential at the time of degassing of the metal according to claim 1 or 2, wherein ammonia is injected into the feed water at the outlet of the desalter and the corrosion potential of the boiler water or the metal in contact with the feed water is determined. An operation management method for a thermal power plant, wherein the temperature is controlled and measured at a temperature equivalent to that of a part to be measured using a reference electrode and a potentiometer. 6. The operation management method for a thermal power plant according to claim 1, wherein the water quality is controlled during the operation of the boiler or during storage when the circulation water flow is stopped. 7. The method according to claim 1, wherein the oxygen scavenger comprises sulfite, bisulfite, pyrosulfite, phosphite, methyl ethyl ketoxime, erythorbic acid,
Diethylhydroxylamine, hydroquinone, carboxylic acid amine salt, a compound selected from saccharides,
A method for controlling operation of a thermal power plant, wherein the compound has a higher molecular weight than hydrazine and a lower molecular weight than tannin and reacts with oxygen in water. 8. In a thermal power plant having a water circulation system including a boiler, a turbine, and a water flooder, means for measuring a corrosion potential of a metal in contact with boiler water or feed water, and measuring a corrosion potential of the metal when degassing the metal. A thermal power plant, comprising a deoxidizer adding means for adjusting so as to be lower than the corrosion potential of the fuel cell. 9. An operation management method for a thermal power plant having a water circulation system including a boiler, a turbine, and a water cover, wherein the corrosion potential of a metal in contact with boiler water or feedwater is measured using a reference electrode and a potentiometer. An operation management method for a thermal power plant, comprising adjusting an addition amount of a deoxidizer so that a corrosion potential of a metal is lower than a corrosion potential at the time of degassing the metal.