EDTA soaking and cleaning system and method for the secondary circuit side of a once-through steam generator

Abstract

The invention discloses an EDTA soaking and cleaning system and method for the secondary circuit side of a direct current steam generator, comprising a cleaning box, a steam generator and a waste liquid tank; the cleaning box is provided with a desalted water inlet and a drug adding port, a cleaning box liquid level gauge and a pressure gauge are provided in the cleaning box, a main water supply connecting section of the steam generator is provided with a main water supply temporary blind plate, a main steam connecting section of the steam generator is provided with a main steam temporary blind plate, an outlet of the cleaning box is connected to the water inlet of the main water supply temporary blind plate via a cleaning pump, and the water outlet on the main water supply temporary blind plate is divided into three routes, wherein the first route is connected to the inlet of the waste liquid tank via a drain valve, the second route is connected to the inlet of the cleaning box via a return valve, and the third route is connected to the inlet of the cleaning box via a bypass cooling valve, a chiller and a back pressure valve. The system and method have the characteristics of short cleaning cycle, low consumption of drugs and desalted water, small equipment size and low cost.

Description

Technical Field

[0001] The invention belongs to the field of chemical cleaning of nuclear power plants and relates to an EDTA soaking cleaning system and method for a secondary circuit side of a once-through steam generator. Background Art

[0002] Chemical cleaning technology has been widely used on numerous critical equipment, including steam and water pipelines, in thermal power plants, achieving significant economic and safety benefits. Chemical cleaning is an important method for removing debris from power plant piping systems during manufacturing, transportation, installation, and storage, improving equipment cleanliness and forming a dense oxide film to prevent corrosion damage during operation. It is a crucial step before unit commissioning and during regular maintenance.

[0003] Currently, the feedwater treatment method used for steam generators in nuclear power plants is reductive total volatile treatment (AVT(R)). Based on the operating experience of thermal power once-through boilers, AVT(R) is a common feedwater treatment method for once-through boilers with orifices at the inlet. This can lead to increased temperature deviation at the steam generator outlet and a slow increase in the inlet / outlet pressure differential. To ensure safe steam generator operation, it is necessary to remove scale deposits from the orifices.

[0004] Considering the following drawbacks, comprehensive cleaning methods have the following: First, chemical cleaning cycles are long, especially leading to extended maintenance periods for nuclear power plants, significantly impacting the plant's economic viability. Second, chemical cleaning consumes large amounts of chemicals and desalinated water, generating significant wastewater and high costs. Third, the equipment is bulky and expensive, typically reaching hundreds of thousands of yuan. Summary of the Invention

[0005] The purpose of the present invention is to overcome the shortcomings of the above-mentioned prior art and provide an EDTA immersion cleaning system and method for the secondary circuit side of a once-through steam generator. The system and method have the characteristics of short cleaning cycle, low consumption of chemicals and desalted water, small equipment size and low cost.

[0006] To achieve the above object, the present invention discloses an EDTA soaking and cleaning system for the secondary circuit side of a once-through steam generator, comprising a cleaning tank, a steam generator and a waste liquid tank;

[0007] The cleaning tank is provided with a desalted water inlet and a dosing port, a cleaning tank level gauge and a pressure gauge are provided inside the cleaning tank, and a main water supply temporary blind plate is provided on the main water supply connection section of the steam generator.

[0008] A main steam temporary blind plate is provided on the main steam connection section of the steam generator. The outlet of the cleaning tank is connected to the water inlet on the main water supply temporary blind plate through the cleaning pump. The water outlet on the main water supply temporary blind plate is divided into three routes. Among them, the first route is connected to the inlet of the waste liquid tank through the drain valve, the second route is connected to the inlet of the cleaning tank through the return valve, and the third route is connected to the inlet of the cleaning tank through the bypass cooling valve, the chiller and the back pressure valve.

[0009] The outlet of the cleaning tank is connected to the water inlet on the main water supply temporary blind plate through the cleaning pump inlet valve, cleaning pump, cleaning pump outlet valve, water inlet flange and water inlet valve in sequence.

[0010] The water outlet on the temporary blind plate of the main water supply is divided into three routes after passing through the drain valve and drain flange.

[0011] It also includes a temporary liquid level gauge. The liquid level measuring port on the main water supply temporary blind plate is connected to one end of the temporary liquid level gauge through the upper root valve of the temporary liquid level gauge, and the other end of the temporary liquid level gauge is connected to the liquid level measuring port on the main steam temporary blind plate through the lower root valve of the temporary liquid level gauge.

[0012] The main water supply temporary blind plate is provided with an electric heater, an ultrasonic generator and a thermocouple.

[0013] A nitrogen filling valve is provided at the filling port on the main water supply temporary blind plate.

[0014] The main water supply temporary blind plate is provided with an exhaust port, which is connected to an oxygen meter.

[0015] The waste liquid tank is arranged at the bottom of the steam generator.

[0016] The present invention discloses a method for cleaning the secondary circuit side of a once-through steam generator by soaking with EDTA, comprising:

[0017] 1) Selection of cleaning chemical media;

[0018] 2) System installation, commissioning and water flushing;

[0019] 3) System air tightness check;

[0020] 4) System nitrogen replacement;

[0021] 5) Fill the system with nitrogen;

[0022] 6) Fill the system with protective fluid;

[0023] 7) Perform EDTA cleaning and passivation;

[0024] 8) Rinse with water after passivation;

[0025] 9) Flushing of the entire steam generator.

[0026] The operation process of step 7) is:

[0027] 71) Start the electric heater to increase the temperature of the solution in the steam generator;

[0028] 72) Open the return valve to lower the liquid level of the solution in the steam generator to below the throttling assembly in the steam generator, and then close the return valve;

[0029] 73) Add EDTA cleaning agent to the cleaning tank, start the cleaning pump, and open the return valve to balance the inlet and return water flows, and gradually add the cleaning agent to the steam generator;

[0030] 74) Take samples from the sampling port of the temporary blind plate of the main water supply to test the concentration of the cleaning liquid. When the concentration of the cleaning liquid in the steam generator reaches the process condition, close the return valve and the cleaning pump. At this time, the liquid level should still be below the throttling component;

[0031] 75) Start the electric heater to increase the temperature of the cleaning agent in the steam generator to 120℃-140℃, ensure that the pressure in the system is not less than 0.5MPa, and the heating rate does not exceed 15℃ / h;

[0032] 76) Start the cleaning pump and make the liquid level in the steam generator higher than the position of the temporary blind plate of the main water supply, then stop the cleaning pump;

[0033] 77) Every 0.5-1 hour, open the return valve to lower the liquid level of the solution in the steam generator to below the throttling assembly, then close the return valve and start the cleaning pump. After the liquid level of the solution in the steam generator is higher than the position of the temporary blind plate of the main water supply, stop the cleaning pump.

[0034] 78) Repeat step 77) until the cleaning time reaches 16h-24h;

[0035] 79) At preset intervals, test the Fe ion concentration of the solution in the main water supply connection section and calculate the total iron content in the cleaning solution. The cleaning is completed after the total iron concentration is balanced for 2h-4h;

[0036] 710) activating the ultrasonic generator at a preset time interval, maintaining the ultrasonic generator, and then shutting it down;

[0037] 711) After cleaning, turn off the electric heater, open the bypass cooling valve, put the chiller into operation, and adjust the opening of the back pressure valve to ensure that the cooling rate of the cleaning liquid does not exceed 15°C / h;

[0038] 712) After the temperature of the cleaning liquid drops, open the drain valve and the emptying valve to allow the cleaning waste liquid to be poured into the waste liquid tank;

[0039] 713) draining the waste liquid in the cleaning tank and the waste liquid tank into the transfer barrel and then transferring it to the waste liquid transfer area;

[0040] 714) Add deionized water to the cleaning tank to the preset high liquid level, start the cleaning pump, and inject the flushing solution into the steam generator. After the liquid level in the steam generator is higher than the position of the temporary blind plate of the main water supply, stop the cleaning pump, start the ultrasonic generator, maintain it, and then turn it off;

[0041] 715) Open the drain valve and the emptying valve to allow the cleaning waste liquid in the steam generator to enter the waste liquid tank, drain the waste liquid in the waste liquid tank into the transfer barrel, and then transfer it to the waste liquid transfer area;

[0042] 716) The steam generator is rinsed again and the Fe ion concentration of the solution in the steam generator is tested. When the iron ion concentration of the solution in the steam generator is less than 50 mg / L, EDTA cleaning and passivation are completed. Otherwise, steps 714) and 715) are repeated.

[0043] The present invention has the following beneficial effects:

[0044] The EDTA soaking and cleaning system and method for the secondary circuit side of a direct current steam generator described in the present invention involves covering the main water supply connection section and the main steam connection section with temporary blind plates. A cleaning tank and pump are used to inject chemicals through the temporary blind plates into the secondary side of the steam generator. The throttling component is then soaked and cleaned using a high-temperature EDTA method. The chemical cleaning liquid is heated using an electric heater, and an ultrasonic generator is used to periodically agitate the cleaning liquid. The chemical cleaning liquid is then periodically filled and drained to enhance the cleaning effect. It should be noted that the present invention can significantly shorten the chemical cleaning time, while reducing the consumption of chemical cleaning chemicals and demineralized water, and reducing wastewater generation. The equipment is compact and has a low investment cost, typically ranging from tens to hundreds of thousands of yuan, resulting in significant economic benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 It is a structural diagram of the present invention;

[0046] Figure 2 This is a structural diagram of the temporary blind plate for main water supply in the present invention;

[0047] Figure 3 Top view of the temporary blind plate for the main water supply.

[0048] Among them, 1 is the steam generator, 2 is the throttling component, 3 is the main water supply connection section, 4 is the main water supply temporary blind plate, 5 is the main steam connection section, 6 is the main steam temporary blind plate, 7 is the upper root valve of the temporary liquid level gauge, 8 is the temporary liquid level gauge, 9 is the cleaning tank, 10 is the cleaning tank level gauge, 11 is the desalted water inlet, 12 is the dosing port, 13 is the pressure gauge, 14 is the cleaning pump inlet valve, 15 is the cleaning pump, 16 is the cleaning pump outlet valve, 17 is the drain valve, 18 is the waste liquid tank, 19 is the return valve, 20 is the bypass cooling valve, 21 is the chiller, 22 is the back pressure valve, 401 is the bolt hole, 402 is the water inlet flange, 403 is the water inlet valve, 404 is the electric heater, 405 is the ultrasonic generator, 406 is the nitrogen filling valve, 407 is the thermocouple, 408 is the lower root valve of the temporary liquid level gauge, 409 is the drain flange, and 410 is the drain valve. DETAILED DESCRIPTION

[0049] In order to enable those skilled in the art to better understand the solutions of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only embodiments of a part of the present invention, not all embodiments, and are not intended to limit the scope of the present invention. In addition, in the following description, descriptions of well-known structures and technologies are omitted to avoid unnecessary confusion of the concepts disclosed in the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work should fall within the scope of protection of the present invention.

[0050] The accompanying drawings illustrate schematic diagrams of the structures of the disclosed embodiments of the present invention. These figures are not drawn to scale; for the purpose of clarity, some details are exaggerated and some details may be omitted. The shapes of the various regions and layers shown in the figures, as well as their relative sizes and positional relationships, are merely exemplary and may deviate in practice due to manufacturing tolerances or technical limitations. Those skilled in the art may design regions / layers with different shapes, sizes, and relative positions as needed.

[0051] Example 1

[0052] refer to Figure 1 、 Figure 2 and Figure 3The EDTA soaking and cleaning system for the secondary circuit side of a once-through steam generator of the present invention comprises a steam generator 1, a throttling component 2, a main water supply connection section 3, a main water supply temporary blind plate 4, a main steam connection section 5, a main steam temporary blind plate 6, an upper root valve of a temporary liquid level gauge 7, a temporary liquid level gauge 8, a cleaning tank 9, a cleaning tank liquid level gauge 10, a desalted water inlet 11, a dosing port 12, a pressure gauge 13, a cleaning pump inlet valve 14, a cleaning pump 15, a cleaning pump outlet valve 16, a drain valve 17, a waste liquid tank 18, a return valve 19, a bypass cooling valve 20, a chiller 21, a back pressure valve 22, a bolt hole 401, a water inlet flange 402, a water inlet valve 403, an electric heater 404, an ultrasonic generator 405, a nitrogen filling valve 406, a thermocouple 407, a lower root valve 408 of a temporary liquid level gauge, a drain flange 409 and a drain valve 410;

[0053] The cleaning tank 9 is provided with a desalted water inlet 11 and a dosing port 12 , a cleaning tank level gauge 10 and a pressure gauge 13 are provided inside the cleaning tank 9 , and a main water supply temporary blind plate 4 is provided on the main water supply connection section 3 .

[0054] A main steam temporary blind plate 6 is provided on the main steam connecting section 5 of the steam generator 1. The outlet of the cleaning tank 9 is connected to the water inlet on the main feed water temporary blind plate 4 through the cleaning pump inlet valve 14, the cleaning pump 15, the cleaning pump outlet valve 16, the water inlet flange 402 and the water inlet valve 403 in sequence. The water outlet on the main feed water temporary blind plate 4 is divided into three paths after passing through the drain valve 410 and the drain flange 409. Among them, the first path is connected to the inlet of the waste liquid tank 18 through the drain valve 17, the second path is connected to the inlet of the cleaning tank 9 through the return valve 19, and the third path is connected to the inlet of the cleaning tank 9 through the bypass cooling valve 20, the chiller 21 and the back pressure valve 22. The liquid level measuring port on the main feed water temporary blind plate 4 is connected to one end of the temporary liquid level gauge 8 through the upper root valve 7 of the temporary liquid level gauge, and the other end of the temporary liquid level gauge 8 is connected to the liquid level measuring port on the main steam temporary blind plate 6 through the lower root valve 408 of the temporary liquid level gauge.

[0055] In this embodiment, the main water supply temporary blind plate 4 is provided with an electric heater 404 , an ultrasonic generator 405 and a thermocouple 407 .

[0056] In this embodiment, a nitrogen filling valve 406 is provided at the filling port on the main water supply temporary blind plate 4.

[0057] In this embodiment, the main water supply temporary blind plate 4 is provided with a bolt hole 401 , and the bolt passes through the bolt hole 401 and is inserted into the main water supply connection section 3 to connect the main water supply temporary blind plate 44 with the main water supply connection section 3 .

[0058] In this embodiment, the main water supply temporary blind plate 4 is provided with an exhaust port, and the exhaust port is connected to an oxygen meter.

[0059] In this embodiment, a sampling port is provided on the temporary blind plate 4 for main water supply, and the sampling port is connected to a sampling tube.

[0060] In this embodiment, the design parameters of the cleaning pump 15 are: a lift of 10 m and a flow rate of 60-120 L / min.

[0061] In this embodiment, the temporary pipes and flanges of this device are made of stainless steel.

[0062] In this embodiment, the waste liquid tank 18 is arranged at the bottom of the steam generator 1 for collecting and transporting waste acid and waste water.

[0063] In this embodiment, the four electric heaters 404 are two 6kW and two 3kW electric heaters 404 , which are symmetrically arranged and used to heat the cleaning liquid.

[0064] In this embodiment, the cleaning tank 9, the cleaning pump 15, the valves, and other equipment except the equipment installed on the temporary blind plate 4 of the main water supply are placed in an area with a lower radiation dose as much as possible.

[0065] The EDTA soaking and cleaning method for the secondary circuit side of a once-through steam generator of the present invention comprises the following steps:

[0066] 1) Selection of cleaning chemical media;

[0067] The present invention selects 6.0% EDTA+0.5% auxiliary agent+reducing agent+corrosion inhibitor, pH value is 8.9, and temperature is 120-140°C.

[0068] 2) System installation, commissioning and water flushing;

[0069] After the reactor is shut down and cooled, the main water supply pipe and the main steam pipe are removed, and a temporary main water supply blind plate 4 is installed on the main water supply connection section 3, and a temporary main steam blind plate 6 is installed on the main steam connection section 5 to establish a temporary system. The electric heater 404, ultrasonic generator 405 and cleaning pump 15 are debugged with water to ensure that the equipment is usable, and the temporary system is flushed with water until the drainage is visually clear.

[0070] 3) System air tightness check;

[0071] The temporary system is pressurized with nitrogen to test the system tightness. Nitrogen enters from nitrogen filling valve 406 and is pressurized to no less than 0.5 MPa. The pressure is maintained and it is qualified if the pressure does not drop within 10 minutes.

[0072] 4) System nitrogen replacement;

[0073] Reduce the pressure in the system to normal pressure, and use a nitrogen bottle to fill nitrogen into the steam generator 1 through the nitrogen filling valve 406 to deoxygenate. Use an oxygen meter to measure the oxygen content of the exhaust gas at the exhaust port of the main water supply temporary blind plate 4 to ensure that the oxygen content of the exhaust gas is less than 5%.

[0074] 5) Fill the system with nitrogen to 0.5MPa;

[0075] 6) Fill the system with protective fluid;

[0076] Replenish water to the cleaning tank 9 through the desalted water inlet 11, add ammonia water to the cleaning tank 9 through the dosing port 12 to make the pH value of the solution reach above 10.5, start the cleaning pump 15, inject water into the steam generator 1, calibrate the temporary liquid level gauge 8, and make the liquid level of the solution in the steam generator 1 reach the position of about 2m above the main water supply temporary blind plate 4, and then stop the cleaning pump 15.

[0077] 7) Perform EDTA cleaning and passivation;

[0078] 71) Start the electric heater 404 to raise the temperature of the solution in the steam generator 1 to 90°C. The temperature of the solution is detected by the thermocouple 407;

[0079] 72) Open the return valve 19 to lower the liquid level of the solution in the steam generator 1 to below the throttling component 2 in the steam generator 1, and then close the return valve 19;

[0080] 73) Add EDTA cleaning agent to the cleaning tank 9, start the cleaning pump 15, and open the return valve 19 to balance the inlet and return water flows, and gradually add the cleaning agent to the steam generator 1;

[0081] 74) Take samples from the sampling port of the temporary blind plate 4 of the main water supply to test the concentration of the cleaning liquid. When the concentration of the cleaning liquid in the steam generator 1 reaches the process condition, close the return valve 19 and the cleaning pump 15. At this time, the liquid level should still be below the throttling component 2;

[0082] 75) Start the electric heater 404 to increase the temperature of the cleaning agent in the steam generator 1 to 120°C-140°C, ensuring that the pressure in the system is not less than 0.5 MPa and the heating rate does not exceed 15°C / h;

[0083] 76) Start the cleaning pump 15, and after the liquid level of the solution in the steam generator 1 is 2m higher than the position of the temporary blind plate 4 of the main water supply, stop the cleaning pump 15;

[0084] 77) Every 0.5-1h, open the return valve 19 to lower the liquid level of the solution in the steam generator 1 to below the throttling assembly 2, then close the return valve 19 and start the cleaning pump 15. After the liquid level of the solution in the steam generator 1 is 2m higher than the position of the temporary blind plate 4 of the main water supply, stop the cleaning pump 15.

[0085] 78) Repeat step 77) until the cleaning time reaches 16h-24h;

[0086] 79) Every 1 hour, test the Fe ion concentration of the solution in the main water supply connection section 3, calculate the total iron content in the cleaning solution, and complete the cleaning after the total iron concentration is balanced for 2-4 hours;

[0087] 710) Every 1 hour, start the ultrasonic generator 405, maintain it for 10 minutes, and then turn it off;

[0088] 711) After cleaning is completed, turn off the electric heater 404, open the bypass cooling valve 20, put the chiller 21 into operation, and adjust the opening of the back pressure valve 22 to ensure that the cooling rate of the cleaning liquid temperature does not exceed 15°C / h;

[0089] 712) After the cleaning liquid temperature drops to 60°C, open the drain valve 410 and the emptying valve 17 to allow the cleaning waste liquid to be poured into the waste liquid tank 18;

[0090] 713) draining the waste liquid in the cleaning tank 9 and the waste liquid tank 18 into the transfer barrel and then transferring it to the waste liquid transfer area;

[0091] 714) Add deionized water to the cleaning tank 9 to the preset high liquid level, start the cleaning pump 15, and inject the flushing solution into the steam generator 1. After the liquid level in the steam generator 1 is 2m higher than the position of the main water supply temporary blind plate 4, stop the cleaning pump 15, start the ultrasonic generator 405, maintain it for 10 minutes, and then turn it off;

[0092] 715) Open the drain valve 410 and the emptying valve 17 to allow the cleaning waste liquid in the steam generator 1 to enter the waste liquid tank 18, and drain the waste liquid in the waste liquid tank 18 into the transfer barrel, and then transfer it to the waste liquid transfer area;

[0093] 716) The steam generator 1 is rinsed again and the Fe ion concentration of the solution in the steam generator 1 is tested. When the iron ion concentration of the solution in the steam generator 1 is less than 50 mg / L, the process proceeds to step 8). Otherwise, steps 714) and 715) are repeated.

[0094] 8) Rinse with water after passivation;

[0095] 81) Start the cleaning pump 15 and open the return valve 19 to establish circulation between the cleaning tank 9 and the steam generator 1;

[0096] 82) Add deionized water and ammonia to the cleaning solution, maintain the pH value and liquid level of the flushing water in the cleaning tank 9, continuously sample the steam generator 1, and test the Fe ion concentration. When the Fe ion concentration is less than 10 mg / L, end the water flushing.

[0097] 9) Flushing the entire steam generator 1;

[0098] Continue to add desalted water to the cleaning tank 9, and add ammonia to adjust the pH to above 10, then start the cleaning pump 15 to add water to the secondary side of the steam generator 1, and empty the steam generator 1 after it is full.

[0099] 10) System recovery and maintenance after cleaning;

[0100] 101) Dismantle the temporary system, drain the water in the system, dismantle the temporary system for restoration, and check the cleaning effect of the throttling component 2;

[0101] 102) Perform maintenance on the steam generator 1 according to the maintenance procedure.

[0102] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents. Any modification or equivalent replacement that does not depart from the spirit and scope of the present invention should be covered by the scope of protection of the claims of the present invention.

Claims

1. An EDTA soaking and cleaning system for the secondary circuit side of a once-through steam generator, characterized in that: It includes a cleaning tank (9), a steam generator (1) and a waste liquid tank (18); The cleaning tank (9) is provided with a desalted water inlet (11) and a dosing port (12), a cleaning tank level gauge (10) and a pressure gauge (13) are provided in the cleaning tank (9), and a main water supply temporary blind plate (4) is provided on the main water supply connection section (3) of the steam generator (1); A main steam temporary blind plate (6) is provided on the main steam connection section (5) of the steam generator (1), and the outlet of the cleaning tank (9) is connected to the water inlet on the main water supply temporary blind plate (4) through the cleaning pump (15). The water outlet on the main water supply temporary blind plate (4) is divided into three routes, wherein the first route is connected to the inlet of the waste liquid tank (18) through the emptying valve (17), the second route is connected to the inlet of the cleaning tank (9) through the return valve (19), and the third route is connected to the inlet of the cleaning tank (9) through the bypass cooling valve (20), the chiller (21) and the back pressure valve (22); It also includes a temporary liquid level gauge (8), wherein the liquid level measuring port on the temporary blind plate (4) of the main feed water is connected to one end of the temporary liquid level gauge (8) via the upper root valve (7) of the temporary liquid level gauge, and the other end of the temporary liquid level gauge (8) is connected to the liquid level measuring port on the temporary blind plate (6) of the main steam via the lower root valve (408) of the temporary liquid level gauge; The main water supply temporary blind plate (4) is provided with an electric heater (404), an ultrasonic generator (405) and a thermocouple (407); A nitrogen filling valve (406) is provided at the filling port on the temporary blind plate (4) for main water supply; The main water supply temporary blind plate (4) is provided with an exhaust port, and the exhaust port is connected to an oxygen meter.

2. The EDTA soaking and cleaning system for the secondary circuit side of a once-through steam generator according to claim 1 is characterized in that: The outlet of the cleaning tank (9) is connected to the water inlet on the main water supply temporary blind plate (4) through the cleaning pump inlet valve (14), the cleaning pump (15), the cleaning pump outlet valve (16), the water inlet flange (402) and the water inlet valve (403) in sequence.

3. The EDTA soaking and cleaning system for the secondary circuit side of a once-through steam generator according to claim 2, characterized in that: The water outlet on the temporary blind plate (4) of the main water supply is divided into three routes after passing through the drain valve (410) and the drain flange (409).

4. The EDTA soaking and cleaning system for the secondary circuit side of a once-through steam generator according to claim 1, characterized in that: The waste liquid tank (18) is arranged at the bottom of the steam generator (1).

5. A method for cleaning the secondary circuit side of a once-through steam generator by soaking with EDTA, characterized in that: The EDTA soaking and cleaning system for the secondary circuit side of a once-through steam generator according to claim 1 comprises: 1) Selection of cleaning chemical media; 2) System installation, commissioning and water flushing; 3) System air tightness check; 4) System nitrogen replacement; 5) Fill the system with nitrogen; 6) Fill the system with protective fluid; 7) Perform EDTA cleaning and passivation; 8) Rinse with water after passivation; 9) Flushing of the steam generator (1) as a whole.

6. The EDTA soaking and cleaning method for the secondary circuit side of a once-through steam generator according to claim 5, characterized in that: The operation process of step 7) is: 71) Starting the electric heater (404) to increase the temperature of the solution in the steam generator (1); 72) Open the return valve (19) to lower the liquid level of the solution in the steam generator (1) to below the throttling component (2) in the steam generator (1), and then close the return valve (19); 73) Add EDTA cleaning agent to the cleaning tank (9), start the cleaning pump (15), and open the return valve (19) to balance the inlet and return water flows, and gradually add the cleaning agent to the steam generator (1); 74) Take samples from the sampling port of the temporary blind plate (4) of the main water supply to test the concentration of the cleaning liquid. When the concentration of the cleaning liquid in the steam generator (1) reaches the process condition, close the return valve (19) and the cleaning pump (15). At this time, the liquid level should still be below the throttling component (2); 75) Start the electric heater (404) to increase the temperature of the cleaning agent in the steam generator (1) to 120°C-140°C, ensuring that the pressure in the system is not less than 0.5 MPa and the heating rate does not exceed 15°C / h; 76) Start the cleaning pump (15) until the liquid level of the solution in the steam generator (1) is higher than the position of the main feed water temporary blind plate (4), and then stop the cleaning pump (15); 77) Every 0.5-1h, open the return valve (19) to lower the liquid level of the solution in the steam generator (1) to below the throttling assembly (2), then close the return valve (19), start the cleaning pump (15), and stop the cleaning pump (15) after the liquid level of the solution in the steam generator (1) is higher than the position of the main water supply temporary blind plate (4); 78) Repeat step 77) until the cleaning time reaches 16h-24h; 79) At preset intervals, test the Fe ion concentration of the solution in the main water supply connection section (3) and calculate the total iron content in the cleaning solution. The cleaning is completed after the total iron concentration is balanced for 2h-4h; 710) activating the ultrasonic generating device (405) at predetermined intervals, maintaining the ultrasonic generating device, and then shutting it down; 711) After the cleaning is completed, turn off the electric heater (404), open the bypass cooling valve (20), start the chiller (21), and adjust the opening of the back pressure valve (22) to ensure that the cooling rate of the cleaning liquid temperature does not exceed 15°C / h; 712) After the temperature of the cleaning liquid drops, open the drain valve (410) and the emptying valve (17) to allow the cleaning waste liquid to be poured into the waste liquid tank (18); 713) Drain the waste liquid in the cleaning tank (9) and the waste liquid tank (18) into the transfer barrel and then transfer it to the waste liquid transfer area; 714) Add deionized water to the cleaning tank (9) to a preset high liquid level, start the cleaning pump (15), inject the flushing solution into the steam generator (1), and after the liquid level in the steam generator (1) is higher than the position of the main feed water temporary blind plate (4), stop the cleaning pump (15), start the ultrasonic generator (405), maintain it, and then turn it off; 715) Open the drain valve (410) and the emptying valve (17) to allow the cleaning waste liquid in the steam generator (1) to enter the waste liquid tank (18), and drain the waste liquid in the waste liquid tank (18) into the transfer barrel, and then transfer it to the waste liquid transfer area; 716) The steam generator (1) is rinsed again and the Fe ion concentration of the solution in the steam generator (1) is tested. When the iron ion concentration of the solution in the steam generator (1) is less than 50 mg / L, the EDTA cleaning and passivation are completed. Otherwise, repeat steps 714) and 715).

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