JP2021127472A - Corrosion suppression method in power-generating plant - Google Patents

Abstract

To provide a corrosion suppression method in a power-generating plant capable of suppressing corrosion in a region other than a liquid phase region in the power-generating plant.SOLUTION: In a method for suppressing corrosion of an apparatus in a gas phase or in a gas-liquid two-phase in a power-generating plant for generating steam in a steam generation part, and generating power by rotating a turbine by steam, an agent is injected, containing a metal element, having a boiling point lower than a temperature of the steam generation part, and having a boiling point higher than a temperature of the apparatus during operation.SELECTED DRAWING: Figure 1

Description

An embodiment of the present invention relates to a method for suppressing corrosion of a power plant.

Corrosion is an event in which metal materials such as equipment structural materials and pipes that make up a power plant change from a metallic state to other chemical forms such as ions and oxides by causing a chemical reaction with a liquid or gas in the environment. , It is one of the aged deterioration events that cause functional deterioration of structural materials. Equation 1 shows a typical corrosion reaction that occurs in the presence of water, taking an iron structural material as an example.
Fe → Fe ²⁺ + 2e ⁻ … (Equation 1)

Equation 1 is an oxidation reaction of Fe and an electron emission reaction at the same time. Since electrons are extremely unstable by themselves, in a corrosion-generating environment, a reaction that consumes electrons occurs at the same time as the reaction of Equation 1. Examples of electron consumption reactions in corrosion in the presence of water are shown in Equations 2 and 3.
2H ₂ O + O ₂ + 4e ⁻ → 4OH ⁻ … (Equation 2)
2H ⁺ + 2e ⁻ → H ₂ … (Equation 3)

As shown in the above formula, the corrosion reaction must generate an electron consumption reaction in the same amount as the amount of electrons generated. Therefore, in an environment such as a power plant where it is necessary to reduce corrosion as much as possible, a treatment for reducing an oxidizing agent such as oxygen that causes an electron consumption reaction is carried out in order to suppress corrosion. Specifically, about 7 to 10 ppm of oxygen is dissolved in water in the atmospheric environment, and by reducing this to about several ppb, corrosion is reduced.

Further, by adding hydrogen, ammonia, etc., the oxidizing property of the environment can be reduced, and the corrosiveness can be further reduced. In an environment with only a liquid phase, components such as hydrogen and ammonia are present in the liquid phase, but in an environment where a gas phase coexists at a high temperature, most of the components shift to the gas phase, and the hydrogen and ammonia concentrations in the liquid phase decrease. .. On the other hand, since hydrogen has the property of easily shifting to the gas phase, the target equipment for hydrogen construction for the purpose of reducing oxidative properties is the condenser of power plants, feed water pipes, feed water heaters, and nuclear reactors. Equipment that has a water environment inside, such as structures inside a reactor, is targeted.

On the other hand, the extraction system piping that connects the turbine and the water supply heater is a two-phase environment of water vapor and condensed water, and components such as hydrogen and ammonia move to the gas phase, so the liquid phase. It is an environment where the oxidizing property of hydrogen is increased and it is highly corrosive. As water treatment technology for this bleed air system, there have been proposals for foreign matter removal, such as a technology related to a removal filter for the purpose of removing impurities, a technology related to the operation method of the removal filter, and a technology related to the removal of foreign matter precipitates in the bleed air system. No technology has been proposed whose main purpose is.

Japanese Unexamined Patent Publication No. 2013-181668

Anticorrosion techniques such as rust preventives and water quality adjustment are effective in the liquid phase region, but anticorrosion of equipment that does not come into contact with the liquid phase such as the gas phase or the gas-liquid two-layer region is insufficient or complicated.

Therefore, an object of the present invention is to provide a method for suppressing corrosion of a power plant capable of suppressing corrosion in a region other than the liquid phase region of the power plant.

The method for suppressing corrosion of a power plant of the embodiment is to suppress the corrosion of equipment in a gas-phase or gas-liquid two-phase environment of a power plant that generates steam by generating steam at a steam generating part and rotating a turbine with the steam to generate power. The method is characterized in that a chemical containing a metal element, having a boiling point equal to or lower than the temperature of the vapor generating portion, and having a boiling point equal to or higher than the temperature of the device during operation is injected.

The figure which shows the structure of the boiling water type nuclear power plant for demonstrating the corrosion suppression method of the power plant which concerns on embodiment.

Hereinafter, a method for suppressing corrosion of a power plant according to an embodiment will be described with reference to the drawings.

FIG. 1 is a diagram schematically showing the configuration of a power plant using a boiling water reactor (BWR) as an example of a power plant.

In FIG. 1, the water returned to water by the condenser 1 is sent by the feed water pump 2, heated through the low pressure feed water heater 3, the deaerator 4, and the high pressure feed water heater 5, and is heated in the reactor pressure vessel. It flows into 6. The water flowing into the reactor pressure vessel 6 is heated by the core to become steam, which is guided to the high-pressure turbine 9 through the main steam pipe 8.

After the energy is extracted from the steam by the high-pressure turbine 9, the moisture is removed by the moisture separator (heater) 10, and then the energy is further guided to the low-pressure turbine 11 and the energy is extracted from the steam by the low-pressure turbine 11. Is done.

The low-pressure turbine 11 is provided with a low-pressure turbine bleed system pipe 12, and steam extracted from the low-pressure turbine 11 is sent to the low-pressure feed water heater 3 and used for heating the feed water. Further, the moisture separator 10 is provided with a moisture separator bleed system pipe 13, and steam extracted from the moisture separator 10 is sent to the deaerator 4 to be used for degassing the water supply. NS. Further, the high-pressure turbine 9 is provided with a high-pressure turbine extraction system pipe 14, and steam extracted from the high-pressure turbine 9 is sent to the high-pressure feed water heater 5 and used for heating the feed water.

Of the above configurations, the inside of the main steam pipe 8 and the like is mainly the gas phase of steam, but the bleed system such as the low pressure turbine bleed system pipe 12, the moisture separator bleed system pipe 13, and the high pressure turbine bleed system pipe 14. The piping has a vapor phase of water vapor and a gas-liquid two-phase environment of condensed water. In this case, the temperature of the low-pressure turbine bleed system pipe 12 is about 75 ° C., the temperature of the moisture separator bleed air pipe 13 is about 120 to 140 ° C, and the temperature of the high-pressure turbine bleed air pipe 14 is about 120 to 140 ° C. It is about 200 ° C.

The condensed water generated in each turbine moves to the drain pipe, exchanges heat with the feed water heater, and then merges with the feed water. Corrosion products such as iron oxides that are corroded in the drain pipe move into the reactor pressure vessel 6 together with the cooling water and accumulate in the reactor structural material. Accumulation of corrosion products on reactor structural materials causes problems such as a decrease in thermal efficiency and an increase in the uptake of radioactive materials, so reduction of corrosion products is required.

In order to deal with this problem, firstly, it volatilizes and does not accumulate in the steam generator (steam generator), secondly, it remains on the surface of the equipment that is the target of corrosion suppression, and thirdly, it suppresses corrosion. It is possible to respond by injecting a drug that has the three characteristics of being able to provide an environment.

In order to prevent deposition at the steam generator (steam generator), which is the first condition, the chemical must move to the vapor phase at the steam generator (steam generator), so the boiling point of the chemical is steam. It is required to be below the temperature of the generator (steam generator). Since the temperature of the steam generator (steam generator) is about 270 ° C., the boiling point of the drug is 270 ° C. or lower in order to satisfy the first condition.

In order for the drug to remain on the surface of the device subject to corrosion suppression, which is the second condition, the drug must exist as a liquid phase or a solid phase. To satisfy the second condition, the drug must have a boiling point above the target device temperature or be decomposed at the target device temperature to become a liquid or solid. Since the temperature of the target device is 75 ° C. to 220 ° C., the boiling point of the drug is above this temperature range and the decomposition temperature is below this temperature range.

Further, in order to provide a corrosion suppressing environment, which is the third condition, it is necessary that the chemical having an effect of suppressing corrosion. The following two can be mentioned as the effect of suppressing corrosion.
1. 1. By using itself as an oxidant or by using oxygen in the environment as an oxidant, a dense film of oxides or hydroxides (passivation film) is formed on the surface of the structural material.
2. It adheres to the surface of the structural material and hinders the contact between the structural material and water or steam.

In order to satisfy the third condition, the drug must have at least one of the above effects.

In addition, in BWR, the water quality is strictly controlled by regulations. For example, Japan's water chemistry management guidelines stipulate standard values for chlorine ion concentration and sulfate ion concentration, and stipulate that each ion concentration in water quality should be less than the standard value. It is desirable that no element is contained. Therefore, it is preferable that the element other than the metal contained in the chemical is composed of oxygen, nitrogen, hydrogen, carbon, phosphorus, etc., which have little influence on the plant.

The metal element contained in the chemical must have the effect of reducing the corrosion rate of the structural material described above by the chemical or its decomposition product remaining on the surface of the structural material.

Examples of the drug satisfying these conditions include osmium oxide (VIII) and the like. Since the boiling point of osmium oxide (VIII) is about 130 ° C, it becomes a gas in the steam generator (steam generator) at 270 ° C, and after migrating to the main steam system, it condenses when the temperature drops below 130 ° C and has a structure. Dissolve in the solution on the surface of the material. Since osmium tetroxide (VIII) acts as an oxidant, this effect forms a film on the surface of the structural material in which the agent is present, and corrosion is suppressed.

Other agents that satisfy the above conditions include ruthenium oxide (VIII) (boiling point 40 ° C), hexacarbonyl tungsten (boiling point 170 ° C), hexacarbonyl molybdenum (boiling point 156 ° C), pentacarbonyl iron (boiling point 103 ° C), and the like. There is a metal carbonyl. In addition, for example, chemicals containing metals such as nickel, titanium, manganese, and chromium can also be used.

Next, the method of applying the chemical will be described. The method of applying the chemical can be injected from any part of the operating plant depending on the nature of the chemical. When the drug dissolves in water, the solution in which the drug is dissolved can be injected into the power plant from a device that comes into contact with water. If the drug is insoluble or sparingly soluble in water, the drug can be heated above its boiling point to a gas, which can be injected into the power plant from equipment in contact with steam or gas-liquid two-phase flow.

Even when the power plant is stopped, injection by the above method is possible, but the temperature of water and steam in the power plant can be set to any temperature during the power plant stop period. By adjusting the temperature of the equipment to be constructed below the boiling point of the chemical, the chemical can be applied to the equipment to be constructed regardless of the temperature of the equipment during operation.

Although some embodiments of the present invention have been described above, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other embodiments, and various omissions, replacements, and changes can be made without departing from the gist of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are also included in the scope of the invention described in the claims and the equivalent scope thereof.

1 ... Condenser, 2 ... Water pump, 3 ... Low pressure feed water heater, 4 ... Degasser, 5 ... High pressure feed water heater, 6 ... Reactor pressure vessel, 8 ... Main steam piping , 9 ... High pressure turbine, 10 ... Moisture separator, 11 ... Low pressure turbine, 12 ... Low pressure turbine extraction system piping, 13 ... Moisture separator extraction system piping, 14 ... High pressure turbine extraction system piping.

Claims (8)

It is a method of suppressing corrosion of equipment in a gas-phase or gas-liquid two-phase environment of a power generation plant that generates steam by generating steam in a steam generating section and rotating a turbine with the steam to generate power.
A method for suppressing corrosion of a power plant, which comprises injecting a chemical containing a metal element, having a boiling point equal to or lower than the temperature of the steam generating portion, and having a boiling point equal to or higher than the temperature of the equipment during operation. The method for suppressing corrosion of a power plant according to claim 1.
A method for suppressing corrosion in a power plant, wherein the chemical is a substance consisting only of the metal element and oxygen, nitrogen, hydrogen, carbon, and phosphorus. The method for suppressing corrosion of a power plant according to claim 1 or 2.
A method for suppressing corrosion of a power plant, wherein the chemical contains at least one of the elements of tungsten, molybdenum, osmium, ruthenium, and iron. The method for suppressing corrosion of a power plant according to any one of claims 1 to 3.
A method for suppressing corrosion of a power plant, which comprises injecting the drug or a solution containing the drug from an apparatus in contact with water in the power plant. The method for suppressing corrosion of a power plant according to any one of claims 1 to 3.
A method for suppressing corrosion of a power plant, which comprises injecting the drug or a solution containing the drug or steam from a device in contact with steam in the power plant. The method for suppressing corrosion of a power plant according to any one of claims 1 to 3.
A method for suppressing corrosion of a power plant, which comprises applying the chemical to the equipment by heating the chemical as a liquid or gas, or by heating a solution or vapor containing the chemical in the plant. The method for suppressing corrosion of a power plant according to claim 6.
A method for suppressing corrosion of a power plant, which comprises adjusting the application target of the chemical by adjusting the temperature of the chemical, water or steam in the plant, or the equipment while the power plant is stopped. The method for suppressing corrosion of a power plant according to any one of claims 1 to 7.
A method for suppressing corrosion of a power plant, wherein the equipment includes bleed air piping.

Images