Vapor generator chemical cleaning agent and cleaning method based on compound EDTA (Ethylene Diamine Tetraacetic Acid)

Abstract

The invention discloses a steam generator chemical cleaning agent based on composite EDTA and a cleaning method, the steam generator chemical cleaning agent comprises a main cleaning agent, a corrosion inhibitor, a reducing agent, a dissolution promoter, a defoaming agent, a pH regulator and water, by means of the cleaning agent and the cleaning method, the cleaning time of a steam generator can be shortened, the dirt dissolution rate of a heat transfer pipe is high, and the corrosion amount is extremely low.

Description

Technical Field

[0001] The present invention belongs to the technical field of chemical cleaning of steam generators (SGs) in nuclear power plants, and relates to a chemical cleaning agent and a cleaning method for steam generators based on composite EDTA. Background Art

[0002] The steam generator (SG) is one of the key core equipment in a nuclear power plant. It is a physical barrier and heat transfer medium between the primary loop and the secondary loop of the reactor, and plays a crucial role in heat transfer of the nuclear reactor and steam generation. Due to water quality control and the effect of flow-accelerated corrosion of feed water, impurities and various dissolved ions in water will enter the steam generator under the action of feed water carryover. As time goes by, a large amount of dirt and sediment often accumulates inside the SG, resulting in a decrease in heat transfer efficiency, an increase in flow resistance, and even overheating or blockage of the heat transfer tubes, which may cause equipment damage or safety accidents in severe cases.

[0003] Currently known cleaning methods for steam generators mainly include two categories: physical cleaning and chemical cleaning. Physical cleaning usually uses high-pressure water flushing. Although it can remove some large-particle sediments, it has poor removal effects on tiny, tightly attached sediments and corrosion products. This method is generally applied to equipment with a relatively large space such as the steam generator of a pressurized water reactor. For the throttle holes and the inner walls of the heat transfer tubes of a once-through steam generator, the physical cleaning method can only clean some heat transfer surfaces of the heat transfer tubes of the steam generator, and has low cleaning efficiency and long time consumption.

[0004] Traditional chemical cleaning methods can dissolve the scale deposited in the heat transfer tubes of the steam generator well, but may cause secondary corrosion to the heat transfer tubes and pipelines of specific materials. The thickness of the heat transfer tubes of the steam generator in a nuclear power unit is generally 2-3 mm, which is much lower than the thickness of 6-10 mm of the water wall of a thermal power unit. Generally used citric acid cleaning agents or other inorganic acid cleaning agents are difficult to meet the requirements of chemical cleaning of the steam generator in a nuclear power unit. On the one hand, the corrosion amount is relatively large, and on the other hand, the process periods of chemical cleaning, rinsing, passivation, etc. are too long. Therefore, the chemical cleaning agent for the steam generator to be studied needs to take into account the scale dissolution rate of the agent formula, low corrosion amount, and short chemical cleaning period. Summary of the Invention

[0005] The purpose of the present invention is to overcome the above-mentioned disadvantages of the prior art, and provides a chemical cleaning agent and a cleaning method for a steam generator based on composite EDTA. The cleaning agent and the cleaning method can shorten the cleaning time of the steam generator, have a high dirt dissolution rate of the heat transfer tubes, and extremely low corrosion amount.

[0006] To achieve the above purpose, the present invention discloses a chemical cleaning agent for a steam generator based on composite EDTA, which includes a main cleaning agent, a corrosion inhibitor, a reducing agent, a solubilizer, an antifoaming agent, a pH regulator, and water.

[0007] A further improvement of the chemical cleaning agent for steam generators based on composite EDTA according to the present invention lies in:

[0008] Furthermore, the main cleaning agent is EDTA, and the concentration range of the main cleaning agent is 4% - 8% (w / w).

[0009] Furthermore, the corrosion inhibitor is a benzotriazole derivative, and the concentration range of the corrosion inhibitor is 0.3% - 1.0% (w / w).

[0010] Furthermore, the reducing agent is sodium isocitrate or sodium sulfite, and the concentration range of the reducing agent is 0.3% - 0.8% (w / w).

[0011] Furthermore, the solubilizer is DTPA, and the concentration range of the solubilizer is 1% - 2% (w / w).

[0012] Furthermore, the defoamer is a silicone defoamer, and the concentration range of the defoamer is 0.01% - 0.05% (w / w).

[0013] Furthermore, the pH regulator is an ammonia water solution.

[0014] The present invention discloses a chemical cleaning method for steam generators based on composite EDTA, including:

[0015] 1) Weigh EDTA, corrosion inhibitor, reducing agent, solubilizer, defoamer and pH regulator;

[0016] 2) Rinse the evaporator;

[0017] 3) Add EDTA, corrosion inhibitor, reducing agent, solubilizer, defoamer and pH regulator to the system in batches, and then carry out circulating cleaning.

[0018] A further improvement of the chemical cleaning method for steam generators based on composite EDTA according to the present invention lies in:

[0019] Furthermore, the process of adding EDTA, corrosion inhibitor, reducing agent, solubilizer, defoamer and pH regulator to the system is as follows:

[0020] Inject auxiliary steam to start heating the system, with the heating rate ≤ 20°C / h, and heat up to between 70°C and 80°C;

[0021] Add the corrosion inhibitor: Add the corrosion inhibitor to the system, and circulate for no less than 1 hour to ensure the uniformity of the corrosion inhibitor;

[0022] Add the defoamer: Add the defoamer to the system;

[0023] Add ammonia water: Add no more than 50% of the pH regulator to the system;

[0024] Add EDTA: Add no more than 40% of EDTA to the system;

[0025] Add cosolvent: Add cosolvent to the system;

[0026] Add ammonia water: Add no more than 40% of pH regulator to the system;

[0027] Add EDTA: Add no more than 50% of EDTA to the system;

[0028] Add reducing agent: Add reducing agent to the system;

[0029] Add EDTA: Add the remaining EDTA to the system;

[0030] Add ammonia water: Add the remaining pH regulator to the system to adjust the pH value of the system to 8.5 - 9.5.

[0031] Further, the process of circulating cleaning is as follows:

[0032] 321) Heating: Switch the system to a closed - loop system for circulation, input auxiliary steam to start heating the system, the heating rate ≤ 20 °C / h, after the temperature rises to 130 °C, maintain the system temperature at 120 °C - 140 °C;

[0033] 322) Circulating cleaning: Conduct circulating cleaning on the system, take samples of the system water quality at preset intervals to analyze the total iron concentration, pH, and EDTA concentration;

[0034] Circulating cleaning flow rate: The cleaning flow rate is 0.3 - 1 m / s;

[0035] Reverse flushing: Switch the flushing direction at least 1 time during the circulating flushing stage, and the reverse flushing is not less than 1 hour;

[0036] When the EDTA and total iron concentrations are stable and no longer rising, continue circulating flushing for 2 hours until the flushing ends, and stop heating the system;

[0037] The total flushing time does not exceed 24 hours;

[0038] 323) Cooling and passivation;

[0039] Cooling: Cool the system to 65 - 70 °C, the cooling rate ≤ 20 °C / h;

[0040] pH adjustment: Add ammonia water to the system to adjust the pH value of the system to 9.0 - 10.0;

[0041] Passivation: Maintain the system temperature at 65 - 70 °C, and the system circulates for 4 - 6 hours to complete passivation;

[0042] 324) System flushing;

[0043] Drainage: Drain the waste liquid of the system until it is empty;

[0044] Rinsing: Add demineralized water and ammonia water into the system, adjust the pH of the system to be greater than 10.0, and conduct circulating rinsing and dead-end rinsing on the system;

[0045] When the concentration of free EDTA in the cleaning system is less than 0.1% and the total iron concentration is less than 1 mg / L, and the water rinsing after passivation is qualified;

[0046] Empty the system.

[0047] The present invention has the following beneficial effects:

[0048] When the chemical cleaning agent and cleaning method for steam generators based on composite EDTA of the present invention are specifically operated, the cleaning agent includes a main cleaning agent, a corrosion inhibitor, a reducing agent, a solubilizer, an antifoaming agent, a pH regulator and water. Among them, EDTA can be used to remove heavy metal ions in water, such as calcium, magnesium, etc., to prevent them from having an adverse impact on water quality. At the same time, it is combined with a reducing agent, a solubilizer and an antifoaming agent to achieve chemical cleaning of the steam generator. The cleaning time is short, the fouling dissolution rate of the heat transfer tubes is high, and the corrosion amount is extremely low, with extremely strong practicability. Description of the Drawings

[0049] The specification drawings forming a part of the present invention are used to provide a further understanding of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation to the present invention. In the drawings:

[0050] Figure 1 is the process flow chart of the method of the present invention. Detailed Embodiments

[0051] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0052] In the description of the present invention, it should be understood that the terms "include" and "comprise" indicate the presence of the described features, wholes, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, wholes, steps, operations, elements, components and / or their combinations.

[0053] It should also be understood that the terms used in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. As used in the specification of the present invention and the appended claims, unless the context clearly indicates otherwise, the singular forms "a", "an" and "the" are intended to include the plural forms.

[0054] It should be further understood that the term "and / or" used in the specification of the present invention and the appended claims refers to any combination and all possible combinations of one or more of the associated listed items, and includes these combinations. For example, A and / or B can represent three cases: A exists alone, A and B exist simultaneously, and B exists alone. In addition, the character " / " in the present invention generally represents an "or" relationship between the associated objects before and after.

[0055] It should be understood that although the terms first, second, third, etc. may be used in the embodiments of the present invention to describe preset ranges, etc., these preset ranges should not be limited to these terms. These terms are only used to distinguish the preset ranges from each other. For example, without departing from the scope of the embodiments of the present invention, the first preset range may also be referred to as the second preset range, and similarly, the second preset range may also be referred to as the first preset range.

[0056] Depending on the context, the word "if" as used herein can be interpreted as "when", "while", "in response to determining", or "in response to detecting". Similarly, depending on the context, the phrase "if determined" or "if detected (stated condition or event)" can be interpreted as "when determined", "in response to determining", "when detecting (stated condition or event)", or "in response to detecting (stated condition or event)".

[0057] To make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. Usually, the components of the present invention described and shown in the drawings here can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the claimed present invention, but merely represents selected embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts fall within the scope of protection of the present invention.

[0058] Various structural schematic diagrams according to the disclosed embodiments of the present invention are shown in the accompanying drawings. These figures are not drawn to scale, where certain details are enlarged for the purpose of clear expression, and certain details may be omitted. The shapes of various regions and layers shown in the figures, as well as their relative sizes and positional relationships, are merely exemplary, and may deviate in actual practice due to manufacturing tolerances or technical limitations. Those skilled in the art can additionally design regions / layers with different shapes, sizes, and relative positions according to actual requirements.

[0059] The chemical cleaning agent for steam generators based on composite EDTA according to the present invention includes a main cleaning agent, a corrosion inhibitor, a reducing agent, a solubilizer, an antifoaming agent, a pH regulator, and water;

[0060] Among them, the main cleaning agent is EDTA (ethylenediaminetetraacetic acid), and the concentration range of the main cleaning agent is 4% - 8% (w / w). Preferably, the concentration of EDTA (ethylenediaminetetraacetic acid) is 5% (w / w).

[0061] The corrosion inhibitor is an organic amine corrosion inhibitor such as benzotriazole derivatives, and the concentration range of the corrosion inhibitor is 0.3% - 1.0% (w / w); preferably, the concentration of the corrosion inhibitor is 0.5% (w / w).

[0062] The reducing agent is sodium erythorbate or sodium sulfite, and the concentration range of the reducing agent is 0.3% - 0.8% (w / w); preferably, the reducing agent is sodium erythorbate, and preferably, the concentration of the reducing agent is 0.4% (w / w).

[0063] The solubilizer is DTPA (diethylenetriaminepentaacetic acid), and the concentration range of the solubilizer is 1% - 2% (w / w); preferably, the concentration of the solubilizer is 1.0% (w / w).

[0064] The antifoaming agent is a silicone-based antifoaming agent, and the concentration range of the antifoaming agent is 0.01% - 0.05% (w / w); preferably, the concentration of the antifoaming agent is 0.025% (w / w).

[0065] The pH regulator is an ammonia water solution, and the pH regulator is an ammonia water solution with a mass fraction of 25%.

[0066] The water is qualified demineralized water from a power plant.

[0067] Example 1

[0068] The chemical cleaning agent for steam generators based on composite EDTA according to the present invention includes a main cleaning agent, a corrosion inhibitor, a reducing agent, a solubilizer, an antifoaming agent, a pH regulator, and water;

[0069] Among them, the main cleaning agent is EDTA (ethylenediaminetetraacetic acid), and the concentration of the main cleaning agent is 4% (w / w).

[0070] The corrosion inhibitor is a benzotriazole derivative, and the concentration of the corrosion inhibitor is 0.3% (w / w).

[0071] The reducing agent is sodium erythorbate, and the concentration of the reducing agent is 0.3% (w / w).

[0072] The solubilizer is DTPA (diethylenetriaminepentaacetic acid), and the concentration of the solubilizer is 1% (w / w).

[0073] The defoamer is a silicone defoamer, and the concentration of the defoamer is 0.01% (w / w).

[0074] The pH regulator is an ammonia water solution, and the pH regulator is an ammonia water solution with a mass fraction of 25%.

[0075] The water is qualified demineralized water from a power plant.

[0076] Example 2

[0077] The chemical cleaning agent for a steam generator based on composite EDTA according to the present invention includes a main cleaning agent, a corrosion inhibitor, a reducing agent, a solubilizer, a defoamer, a pH regulator and water;

[0078] Among them, the main cleaning agent is EDTA (ethylenediaminetetraacetic acid), and the concentration of the main cleaning agent is 8% (w / w).

[0079] The corrosion inhibitor is an organic amine corrosion inhibitor such as a benzotriazole derivative, and the concentration of the corrosion inhibitor is 1.0% (w / w).

[0080] The reducing agent is sodium sulfite, and the concentration of the reducing agent is 0.8% (w / w).

[0081] The solubilizer is DTPA (diethylenetriaminepentaacetic acid), and the concentration of the solubilizer is 2% (w / w).

[0082] The defoamer is a silicone defoamer, and the concentration of the defoamer is 0.05% (w / w).

[0083] The pH regulator is an ammonia water solution, and the pH regulator is an ammonia water solution with a mass fraction of 25%.

[0084] The water is qualified demineralized water from a power plant.

[0085] Example 3

[0086] The chemical cleaning agent for a steam generator based on composite EDTA according to the present invention includes a main cleaning agent, a corrosion inhibitor, a reducing agent, a solubilizer, a defoamer, a pH regulator and water;

[0087] Among them, the main cleaning agent is EDTA (ethylenediaminetetraacetic acid), and the concentration of the main cleaning agent is 5% (w / w).

[0088] The corrosion inhibitor is a benzotriazole derivative, and the concentration of the corrosion inhibitor is 0.5% (w / w).

[0089] The reducing agent is sodium sulfite, and the concentration of the reducing agent is 0.4% (w / w).

[0090] The solubilizer is DTPA (diethylenetriaminepentaacetic acid), and the concentration of the solubilizer is 1.0% (w / w).

[0091] The defoamer is a silicone defoamer, and the concentration of the defoamer is 0.025% (w / w).

[0092] The pH regulator is an ammonia water solution, and the pH regulator is an ammonia water solution with a mass fraction of 25%.

[0093] The water is qualified demineralized water from a power plant.

[0094] Example 4

[0095] The chemical cleaning agent for a steam generator based on composite EDTA according to the present invention includes a main cleaning agent, a corrosion inhibitor, a reducing agent, a solubilizer, a defoamer, a pH regulator and water. Weigh EDTA, the corrosion inhibitor, the reducing agent, the solubilizer, the defoamer and the pH regulator; wherein, the concentration of EDTA (ethylenediaminetetraacetic acid) is 5% (w / w); the corrosion inhibitor is a benzotriazole derivative, and the concentration of the corrosion inhibitor is 0.5% (w / w); the reducing agent is sodium erythorbate or sodium sulfite, and the concentration of the reducing agent is 0.4% (w / w); the solubilizer is DTPA (diethylenetriaminepentaacetic acid), and the concentration of the solubilizer is 1.0% (w / w); the defoamer is a silicone defoamer, and the concentration of the defoamer is 0.025% (w / w); the pH regulator is an ammonia water solution.

[0096] Among them, the main cleaning agent is EDTA (ethylenediaminetetraacetic acid), and the concentration of the main cleaning agent is 4% (w / w).

[0097] The corrosion inhibitor is a benzotriazole derivative, and the concentration of the corrosion inhibitor is 0.3% (w / w).

[0098] The reducing agent is sodium erythorbate, and the concentration of the reducing agent is 0.3% (w / w).

[0099] The solubilizer is DTPA (diethylenetriaminepentaacetic acid), and the concentration of the solubilizer is 1% (w / w).

[0100] The defoamer is a silicone defoamer, and the concentration of the defoamer is 0.01% (w / w).

[0101] 2) Rinse the evaporator;

[0102] The rinsing medium used for rinsing is demineralized water, the rinsing flow rate ≥ 0.3 m / s, and the larger the rinsing flow rate, the better.

[0103] During the flushing process, closed-loop flushing can be selected. When the water quality is poor, flushing while filling and draining can also be selected.

[0104] The flushing time is greater than 30 minutes, and 1 - 2 hours is optimal.

[0105] When flushing multiple-module steam generators in parallel, adjust the flow rate of each module to ensure that the flow rate deviation does not exceed ±10% of the average value.

[0106] Regular chemical analysis is carried out during flushing. When the light transmittance of the effluent ≥ 90%, turbidity ≤ 10 NTU, chloride ion ≤ 50 ppb, and TOC ≤ 500 ppb, stop the water flushing, empty the system, and then refill with demineralized water. The amount of demineralized water filled is the total water capacity of the system minus the water capacity required for chemical dosing to ensure that the system is just full after the chemical agent is added.

[0107] 3) Chemical agent addition

[0108] 31) Add chemical agents to the system in batches and in sequence according to the pre-calculated dosage.

[0109] Start heating the system by introducing auxiliary steam. The heating rate ≤ 20 °C / h. When the temperature rises to between 70 °C and 80 °C, start adding chemical agents.

[0110] Add corrosion inhibitor: Add corrosion inhibitor to the system and circulate for no less than 1 hour to ensure the corrosion inhibitor is evenly distributed.

[0111] Add defoamer: Add defoamer to the system.

[0112] Add ammonia water: Add ammonia water not exceeding 50% to the system.

[0113] Add EDTA: Add EDTA not exceeding 40% to the system.

[0114] Add co-solvent: Add co-solvent to the system.

[0115] Add ammonia water: Add ammonia water not exceeding 40% to the system.

[0116] Add EDTA: Add EDTA not exceeding 50% to the system.

[0117] Add reducing agent: Add reducing agent to the system.

[0118] Add EDTA: Add the remaining EDTA to the system.

[0119] Add ammonia water: Add ammonia water to the system to adjust the pH value of the system to 8.5 - 9.5. Preferably, the pH value is 8.5 - 9.0.

[0120] 32) Circulating cleaning

[0121] 321) Heating up: Switch the system to a closed system circulation, introduce auxiliary steam to start heating up the system, with the heating rate ≤ 20 °C / h. After the temperature rises to about 130 °C, maintain the system temperature at 120 °C - 140 °C.

[0122] 322) Circulating cleaning: Conduct circulating cleaning on the system. Take samples of the system water quality every 1 hour to analyze the total iron concentration, pH, and EDTA concentration.

[0123] Circulating cleaning flow rate: The cleaning flow rate is 0.3 - 1 m / s. Preferably, the cleaning flow rate is 1 m / s.

[0124] Reverse flushing: Switch the flushing direction at least 1 time during the circulating flushing stage, and the reverse flushing is not less than 1 hour;

[0125] When the EDTA and total iron concentrations are stable and no longer rising, continue circulating flushing for 2 hours until the flushing is completed, and stop heating the system.

[0126] The total flushing time does not exceed 24 hours.

[0127] 323) Cooling and passivation

[0128] Cooling: Cool the system to 65 - 70 °C, with the cooling rate ≤ 20 °C / h.

[0129] pH adjustment: Add ammonia water to the system to adjust the pH value of the system to 9.0 - 10.0.

[0130] Passivation: Maintain the system temperature at 65 - 70 °C, and the system circulates for 4 - 6 hours to complete passivation.

[0131] 324) System flushing

[0132] Drainage: Drain the system waste liquid empty;

[0133] Flushing: Add demineralized water and ammonia water to the system, adjust the system pH to be greater than 10.0, and conduct circulating flushing and dead-end flushing on the system.

[0134] When the free EDTA concentration in the cleaning system is less than 0.1% and the total iron concentration is less than 1 mg / L, the water flushing after passivation is qualified.

[0135] The system is emptied or maintained according to subsequent work.

[0136] 4) Chemical cleaning effect evaluation

[0137] Corrosion amount evaluation: Calculate and evaluate the corrosion rate and total corrosion amount of the heat transfer tubes of the steam generator to confirm that they meet the standards and expectations;

[0138] Scaling removal rate evaluation: Calculate and evaluate the scaling removal rate of the corrosion products in the heat transfer tubes of the steam generator to confirm that it meets the standards and expectations;

[0139] Drug usage and waste liquid generation: Calculate and evaluate the drug usage and waste liquid volume of this chemical cleaning to confirm that they meet the expectations;

[0140] Cleanliness inspection: Use high-definition endoscopes and other equipment to conduct visual inspections on the heat transfer tubes, throttle holes and other parts of the steam generator to confirm that its interior is clean and the protective film formed on the inner surface is intact.

[0141] Example 5

[0142] The steam generator of a nuclear power plant uses the above-mentioned chemical agent formula and method for chemical cleaning. The cleaning time is 24 hours and the passivation time is 4 hours. Under this condition, after the chemical cleaning is completed, the actual measured corrosion rate of the heat transfer tubes is ≤0.094 g / (㎡·h), and the total corrosion amount is ≤2.5 g / ㎡. The corrosion amount is far better than the corrosion amount limited by the standard. The descaling rate reaches 95.4%, and the cleaning effect is excellent.

[0143] After considering the specification and the disclosure of the invention, those skilled in the art will easily think of other embodiments of the present invention. This application aims to cover any variations, uses or adaptations of the present invention, which follow the general principles of the present invention and include the common general knowledge or conventional technical means in the technical field not disclosed in the present invention. The specification and examples are only regarded as exemplary, and the true scope and spirit of the present invention are pointed out by the following claims.

[0144] It should be understood that the present invention is not limited to the precise structures already described and shown in the drawings, and various modifications and changes can be made without departing from its scope. The scope of the present invention is only limited by the appended claims.

[0145] The above are only the preferred embodiments of the present invention, and do not impose any limitations on the present invention. Any simple modifications, changes and equivalent structural changes made to the above embodiments according to the technical essence of the present invention still fall within the protection scope of the technical solution of the present invention.

Claims

1. A steam generator chemical cleaning agent based on composite EDTA, characterized in that: It includes main cleaning agent, corrosion inhibitor, reducing agent, dissolution promoter, defoaming agent, pH adjuster and water.

2. The steam generator chemical cleaning agent based on composite EDTA according to claim 1, characterized in that: The main cleaning agent is EDTA, and the concentration range of the main cleaning agent is 4%-8% (w / w).

3. The steam generator chemical cleaning agent based on composite EDTA according to claim 1, characterized in that: The corrosion inhibitor is a benzotriazole derivative, and the concentration range of the corrosion inhibitor is 0.3%-1.0% (w / w).

4. The steam generator chemical cleaning agent based on composite EDTA according to claim 1, characterized in that: The reducing agent is sodium isotretinoin or sodium sulfite, and the concentration range of the reducing agent is 0.3%-0.8% (w / w).

5. The steam generator chemical cleaning agent based on composite EDTA according to claim 1, characterized in that: The chaotropic agent is DTPA, and the concentration of the chaotropic agent is in the range of 1%-2% (w / w).

6. The steam generator chemical cleaning agent based on composite EDTA according to claim 1, characterized in that: The defoaming agent is an organosilicon defoaming agent, and the concentration range of the defoaming agent is 0.01%-0.05% (w / w).

7. The steam generator chemical cleaning agent based on composite EDTA according to claim 1, characterized in that: The pH adjuster is an aqueous ammonia solution.

8. A steam generator chemical cleaning method based on composite EDTA, characterized in that: include: 1) Weigh EDTA, corrosion inhibitor, reducing agent, solubilizing agent, defoaming agent and pH regulator; 2) flush the evaporator; 3) Add EDTA, corrosion inhibitor, reducing agent, solvent promoter, defoaming agent and pH adjuster to the system in batches, and then perform cyclic cleaning.

9. The steam generator chemical cleaning method based on composite EDTA according to claim 8, characterized in that: The process of adding EDTA, corrosion inhibitor, reducing agent, solvent promoter, defoaming agent and pH regulator to the system in batches is as follows: Add auxiliary steam to start heating the system, with a heating rate of ≤20℃ / h, and raise the temperature to between 70℃ and 80℃; Add corrosion inhibitor: Add corrosion inhibitor to the system and circulate it for no less than 1 hour to ensure that the corrosion inhibitor is evenly distributed; Add defoamer: Add defoamer to the system; Add ammonia: Add no more than 50% of pH adjuster to the system; Add EDTA: Add no more than 40% EDTA to the system; Adding co-solvent: adding co-solvent to the system; Add ammonia: Add no more than 40% of pH adjuster to the system; Add EDTA: Add no more than 50% EDTA to the system; Add reducing agent: add reducing agent to the system; Add EDTA: Add the remaining EDTA to the system; Adding ammonia: Add the remaining pH adjuster to the system to adjust the pH value of the system to 8.5-9.

5.

10. The steam generator chemical cleaning method based on composite EDTA according to claim 8, characterized in that: The cycle cleaning process is: 321) Heating: Switch the system to a closed system cycle, add auxiliary steam to start heating the system, the heating rate is ≤20℃ / h, and after the temperature rises to 130℃, maintain the system temperature at 120℃-140℃; 322) Circulation cleaning: Circulation cleaning of the system, sampling of system water quality at preset intervals, and analysis of total iron concentration, pH and EDTA concentration; Circulation cleaning flow rate: cleaning flow rate is 0.3-1m / s; Back flushing: During the cyclic flushing phase, the flushing direction should be switched at least once, and the reverse flushing should last no less than 1 hour; When the concentrations of EDTA and total iron are stable and no longer increase, continue the cycle flushing for 2 hours and stop heating the system; The total flushing time does not exceed 24 hours; 323) Cooling and passivation; Cooling: Cool the system to 65-70℃, with a cooling rate of ≤20℃ / h; pH adjustment: Add ammonia water into the system to adjust the pH value of the system to 9.0-10.0; Passivation: Maintain the system temperature at 65-70°C and circulate the system for 4-6 hours to complete the passivation; 324) System flushing; Discharge: drain the system waste liquid into the air; Flushing: Add deionized water and ammonia water into the system, adjust the system pH to greater than 10.0, and perform system circulation flushing and dead point flushing; When the free EDTA concentration in the cleaning system is less than 0.1% and the total iron concentration is less than 1 mg / L, the water rinse after passivation is qualified; Drain the system.

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