Nuclear power station steam generator cleaning method

Abstract

The invention belongs to the technical field of nuclear power heat exchanger cleaning, and particularly relates to a nuclear power station steam generator cleaning method. Comprising the following steps that 1, drainage is completed on the primary side and the secondary side of the steam generator, and then a bubbling cleaning system is installed, connected and checked; 2, rising the water level for bubbling cleaning; 3, circulating bubbling cleaning is conducted; 4, water level reduction bubbling cleaning is carried out; comprising the steps that 5, bubbling cleaning system equipment is dismantled; and 6, hydraulic flushing equipment is installed on a hand hole in the secondary side of the steam generator, hydraulic flushing and circulating filtration are conducted on the tube plate for 18 h, and deposited sludge on the surface of the tube plate on the secondary side of the steam generator is fully discharged. The method has the beneficial effects that the method is suitable for the sludge of the heat transfer tube bundle of the steam generator of the nuclear power station, can also be used for cleaning sludge attached to other heat exchanger tube bundle components, is not limited by conditions such as narrow gap spaces among the components, and is large in cleaning range and good in cleaning effect.

Description

Technical Field

[0001] The present invention belongs to the technical field of nuclear power heat exchanger cleaning, and particularly relates to a cleaning method for steam generators in nuclear power plants. Background Art

[0002] During the operation of nuclear power plants, surface dirt in the restricted flow area on the secondary side of steam generators and harmful impurity ions in the gaps will be locally concentrated due to the evaporation of water. Most of them will participate in the formation of sludge accumulation layers on the horizontal and vertical solid surfaces inside the secondary side of steam generators, such as the surfaces of secondary side tube sheets, flow distribution plates, support plates, and the outer surfaces of heat transfer tubes. The sludge deposition will cause corrosion of the pipe materials, the scaling will cause a decrease in steam pressure, the clogging of plum blossom holes and unstable water levels, thereby reducing the reliability and heat transfer efficiency of steam generators.

[0003] The structure of steam generators is complex, and cleaning is extremely inconvenient. Some existing cleaning technologies, such as high-pressure water cleaning, have limited cleaning ranges. They mainly clean the tube sheets and flow distribution plates in the lower area of the secondary side tube bundle of steam generators and cannot clean the upper and middle areas of the heat transfer tube bundle, with a small coverage range; chemical cleaning has the potential risk of corroding internal components such as heat transfer tubes, and the treatment of waste liquid after cleaning is relatively complex and costly; the low-pressure spray cleaning technology has unsatisfactory effects and is rarely used alone on steam generators and is generally used in combination with other cleaning methods. In order to meet the cleaning requirements for the sludge attached to the secondary side tube bundle of nuclear power plant steam generators, there is an urgent need for a simple and efficient cleaning method for nuclear power plant steam generators to achieve full-tube bundle cleaning of steam generators, improve the heat transfer efficiency of steam generators, and reduce maintenance and cleaning costs. Summary of the Invention

[0004] The purpose of the present invention is to provide a cleaning method for steam generators in nuclear power plants, which can solve the technical problems of high cost, low cleaning efficiency, and potential corrosion of heat transfer tubes in current cleaning methods, achieve full-tube bundle cleaning of the secondary side of steam generators, effectively remove the corrosion products attached to the components of the secondary side heat transfer tube bundle, reduce the cost of full-tube bundle cleaning, and ensure the safe and stable operation of steam generators.

[0005] The technical solution of the present invention is as follows: A cleaning method for steam generators in nuclear power plants includes the following steps:

[0006] Step 1: Drain the primary and secondary sides of the steam generator. After draining, install, connect, and check the bubbling cleaning system;

[0007] Step 2: Raise the water level for bubbling cleaning;

[0008] Step 3: Circulate for bubbling cleaning;

[0009] Step 4: Lower the water level for bubbling cleaning.

[0010] In the said step 1, first, perform hydraulic flushing on the sludge of the steam generator tube sheet.

[0011] The said step 2 includes filling deionized water into the secondary side of the steam generator. When the water level exceeds the upper surface of the flow distribution plate by no less than 80 mm, start the bubbling generating device to release high-pressure gas into the secondary side of the steam generator. The bubbling pressure is 2 MPa, and the bubbling interval is once every 20 s. Keep filling water and continuously raise the water level. The purpose of the bubbling interval of once every 20 s is to fully diffuse the gas introduced into the steam generator.

[0012] The high-pressure gas in the said S2 is compressed air or nitrogen.

[0013] The said step 3 includes the following:

[0014] When the water level reaches 10 - 20 mm below the first support plate, stop filling water, and perform bubbling cleaning on this layer of support plate. The number of bubbling times is 10 times, and the bubbling pressure is 2.5 MPa. After completion, continue to fill water and raise the water level;

[0015] Gradually clean the second to ninth support plates according to the bubbling cleaning steps of the first support plate. Keep the bubbling pressure increasing by 0.5 MPa for each layer of support plate as the water level rises until the bubbling cleaning of each layer of support plate is completed in sequence, and the bubbling pressure gradually increases to 7 MPa as the water level rises;

[0016] After completing the cleaning of the ninth support plate, continue to fill water and raise the water level until the water level submerges the topmost support plate. The bubbling cleaning stage of raising the water level is completed, and start the bubbling cleaning in the circulation stage. Start the suction pump, adjust the flow rate to match the flow rate of the filling pump, the bubbling generating device performs bubbling once every 20 s, and the bubbling pressure is 7 MPa for 24 h.

[0017] The said step 4 includes the following:

[0018] Adjust the flow rate of the filling pump to be reduced to 1 / 2 of the suction pump, and perform bubbling cleaning in the stage of lowering the water level. When the water level drops to 10 - 20 mm below the ninth support plate, stop filling water and draining water, and perform bubbling cleaning on this layer of support plate. The number of bubbling times is 10 times, and the bubbling pressure is 7 Mpa. After completing the cleaning of the ninth support plate, continuously lower the water level. Keep the bubbling pressure decreasing by 0.5 MPa for each layer of support plate as the water level drops until the bubbling cleaning of each layer of support plate is completed in sequence, and the bubbling pressure gradually decreases to 2 MPa as the water level drops;

[0019] Continuously lower the water level, ensure bubbling cleaning once every 20 s until the water level drops to the upper surface of the flow distribution plate, and then stop bubbling;

[0020] Continuously carry out dewatering and circulating drainage. When the water level drops to 100 - 150 mm above the tube sheet, the flow rate of the charging pump can be appropriately increased to be consistent with the suction pump to stir and extract the sludge on the tube sheet. After 30 - 60 minutes, stop the water inlet of the charging pump until the water on the tube sheet is fully drained.

[0021] Including step 5: Remove the bubbling cleaning system equipment.

[0022] Including step 6: Install a hydraulic flushing device on the handhole of the secondary side of the steam generator, and conduct hydraulic flushing and circulating filtration on the tube sheet for 18 hours to fully discharge the deposited sludge on the surface of the secondary side tube sheet of the steam generator.

[0023] The beneficial effects of the present invention are as follows: This method is applicable to the sludge of the heat transfer tube bundle of the steam generator in a nuclear power plant, and can also be used to clean the sludge attached to other heat exchanger tube bundle components. It is not restricted by conditions such as narrow gap spaces between components, has a large cleaning range, good cleaning effect, can effectively improve the cleanliness of the heat exchanger, improve the heat transfer efficiency, and at the same time, avoid local concentrated corrosion of residual sludge and damage to internal components such as heat transfer tubes, and improve the operating life of the heat exchanger. Description of the Drawings

[0024] Figure 1 It is a schematic installation diagram of the bubbling generating device for the cleaning process of the steam generator in a nuclear power plant;

[0025] Figure 2 It is a flow chart of a cleaning method for a steam generator in a nuclear power plant provided by the present invention.

[0026] In the figure: 1 is the steam generator, 101 is the handhole flange, 102 is the flow distribution plate, 103 is the first support plate, 104 is the eighth support plate, 105 is the ninth support plate, 106 is the heat transfer tube, 2 is the bubbling generating device, and 201 is the nozzle. Detailed Embodiments

[0027] In order to make the purpose, technical solutions and advantages of the present invention clearer, the following further elaborates on the embodiments of the present invention in conjunction with the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of the present invention.

[0028] A cleaning method for a steam generator of a nuclear power plant provided by the present invention. The bubble cleaning equipment used includes a water circulation system, a high-pressure gas source, a bubble generating device, and a centralized control system. The water circulation system includes a suction pump, a buffer filtration water tank, a transfer pump, a main water tank, a water filling pump, and pipelines, which realizes the water filling and draining of the secondary side of the steam generator, and filters and circulates the muddy water after bubble cleaning. The high-pressure gas source can be provided by a compressed nitrogen cylinder group or a high-pressure air compressor. After pressure regulation, the compressed gas is input into the bubble generating device through a high-pressure hose. The bubble generating device is installed on the manhole flange of the secondary side of the steam generator, stores the compressed gas input by the high-pressure gas source, and pulses it into the water-filled secondary side of the steam generator. The rapid expansion of the compressed gas causes violent hydraulic shock to wash the surface of the heat transfer tube bundle and the gaps between components, realizing the cleaning of residual mud in the secondary side of the steam generator. The centralized control system realizes the control, monitoring, and adjustment functions of single electrical components such as the water circulation system, the high-pressure gas source, and the bubble generating device.

[0029] As Figure 1 shown, a bubble cleaning method for a steam generator of a nuclear power plant. The bubble generating device 2 is installed on the manhole flange 101 of the steam generator 1, and the nozzle 201 extends into the internal pipe gallery. To ensure the cleaning efficiency, one set or two sets of bubble generating devices can be used to pulse high-pressure gas into the steam generator to clean the mud on the surface of the tube bundle according to the actual situation. The length of the nozzle can be adjusted according to the size of the steam generator. The front section of the nozzle is slightly inclined downward by 30°, so that the ejected high-speed gas impacts the tube plate and is reflected upward to the support plate, causing more violent hydraulic shock and improving the flushing effect.

[0030] This method is divided into three stages: rising water level bubble cleaning, circulating bubble cleaning, and falling water level bubble cleaning;

[0031] The rise and fall of the water level inside the steam generator are controlled by the flow difference between the water filling pump and the suction pump;

[0032] During the rising water level bubble cleaning stage, the nuclear power plant site ASG system continuously supplies water;

[0033] During the circulating bubble cleaning stage, the water filling flow rate and the suction flow rate are kept similar, and the flow control is realized through the water circulation system, and the mud in the suction discharged water is filtered;

[0034] The working pressure range of the bubble generating device is 2 - 7 MPa. For the cleaning and water level requirements of different support plates, different cleaning pressures are selected. The bubble is generated at 2 MPa from the flow distribution plate to the first support plate. When the water level rises by one layer of the support plate, the bubble pressure increases by 0.5 MPa until the bubble cleaning of each layer of the support plate (a total of 9 layers of support plates) is completed in sequence, and the bubble pressure gradually increases to 7 MPa as the water level rises.

[0035] The maximum bubbling pressure of the bubbling device is not greater than 7 MPa, slightly lower than the operating pressure on the secondary side of the steam generator, to prevent damage to the heat transfer tubes.

[0036] The number of bubbling cleaning times for different support plates can be set according to the operating years and cleaning frequency of the steam generator;

[0037] During the water level lowering and cleaning stage, the discharged liquid is filtered and then discharged on-site, or introduced into the next steam generator for bubbling cleaning.

[0038] After the bubbling cleaning is completed, the tube sheet of the steam generator is hydraulically flushed to remove the sludge and some stubborn sludge that have accumulated on the upper surface of the tube sheet under the action of bubbling.

[0039] The present invention mainly proposes a bubbling cleaning process method for a nuclear power plant steam generator to solve the above problems (but it should not be understood that the technical solution is limited by the drawings):

[0040] (1) Installation, connection and inspection of the bubbling cleaning system;

[0041] (2) Start the charging pump to fill the secondary side of the steam generator with deionized water. The water level in the SG gradually rises. When the water level exceeds the upper surface of the flow distribution plate by no less than 80 mm, start the bubbling device to release high-pressure gas (compressed air or nitrogen) into the secondary side of the steam generator. The bubbling pressure is 2 MPa, and the bubbling interval is once every 20 s;

[0042] (3) During the continuous water level rising period, when the water level reaches 10 - 20 mm below the first support plate, stop filling water and conduct bubbling cleaning on this layer of support plate. The initial number of bubbling times is set to 10 times, and the bubbling pressure is 2.5 MPa;

[0043] (4) After completing the cleaning of the first layer of support plate, continue to raise the water level. Keep the bubbling pressure increasing by 0.5 MPa for each rise of the water level by one layer of support plate until the bubbling cleaning of each layer of support plate (a total of 9 layers of support plates) is completed in sequence. The bubbling pressure gradually increases to 7 MPa as the water level rises;

[0044] (5) Until the water level submerges the uppermost support plate, the rising water level and bubbling cleaning stage is completed, and start the circulating cleaning. Start the suction pump, adjust the flow rate to match the flow rate of the charging pump. The bubbling device conducts bubbling every 20 s, the bubbling pressure is 7 MPa, and it lasts for 24 h.

[0045] (6) Adjust the flow rate of the charging pump to be reduced to 1 / 2 of the suction pump, and conduct bubbling cleaning during the water level lowering stage. When the water level drops to 10 - 20 mm below the ninth support plate, stop filling water and draining water, and conduct bubbling cleaning on this layer of support plate. The initial number of bubbling times is set to 10 times, and the bubbling pressure is 7 MPa;

[0046] (7) After the cleaning of the 9th support plate is completed, continuously lower the water level. Keep the bubbling pressure reduced by 0.5 MPa for each layer of support plate the water level drops until the bubbling cleaning of each layer of support plate (a total of 9 layers of support plates) is completed in sequence, and the bubbling pressure gradually decreases to 2 MPa as the water level drops.

[0047] (8) When the water level drops to the upper surface of the flow distribution plate, stop bubbling and continuously carry out the water level lowering and cyclic drainage.

[0048] (9) When the water level drops to 100 - 150 mm above the tube sheet, appropriately increase the flow rate of the charging pump to be consistent with the suction pump, stir up the sludge on the tube sheet and suck it out of the steam generator. After 30 - 60 min, stop the charging pump from feeding water until the water on the tube sheet is fully drained.

[0049] (10) Remove the bubbling cleaning system equipment, install hydraulic flushing equipment on the secondary side handhole of the steam generator, and carry out hydraulic flushing of the tube sheet for about 18 h to complete the cleaning of the deposited sludge on the surface of the secondary side tube sheet of the steam generator.

[0050] As Figure 1 shown, the bubbling generating device 2 of the cleaning process of the nuclear power plant steam generator is installed on the handhole flange 101 of the steam generator 1. The bubbling generating device 2 adopts a pilot-operated valve body structure to achieve rapid triggering, enhance the energy output of a single bubbling, realize the release of a large amount of high-pressure gas, improve the utilization efficiency of the gas, and then generate a strong hydraulic shock to scour the surface of the heat transfer tube bundle and the gaps between components, effectively improving the cleaning quality and efficiency of the secondary side of the steam generator.

[0051] Combined with Figure 2 the cleaning process method of the nuclear power plant steam generator is described, including the following steps:

[0052] Step 1: Drain the primary and secondary sides of the steam generator. If necessary, first carry out hydraulic flushing of the sludge on the tube sheet of the steam generator. After completion, install, connect and check the bubbling cleaning system.

[0053] Step 2: Bubbling cleaning with rising water level, specifically including:

[0054] Fill the secondary side of the steam generator with deionized water. The SG water level gradually rises. When the water level exceeds the upper surface of the flow distribution plate by no less than 80 mm, start the bubbling generating device to release high-pressure gas (compressed air or nitrogen) into the secondary side of the steam generator. The bubbling pressure is 2 MPa, and the bubbling interval is once every 20 s. Keep filling water and continuously raise the water level.

[0055] When the water level reaches 10 - 20 mm below the first support plate, stop filling water, carry out bubbling cleaning of this layer of support plate, with 10 bubbling times and a bubbling pressure of 2.5 MPa. After completion, continue to fill water and raise the water level.

[0056] Clean the second to the ninth support plates step by step according to the above-mentioned bubbling cleaning steps of the first support plate. Keep the bubbling pressure increasing by 0.5 MPa for each layer of support plate as the water level rises, until the bubbling cleaning of each layer of support plate (a total of 9 layers of support plates) is completed in sequence, and the bubbling pressure gradually increases to 7 MPa as the water level rises. The bubbling generating device increases the air-blowing working pressure as the water level increases, mainly to offset the influence of the weakening of the bubbling pulse power caused by the increase in hydrostatic pressure.

[0057] Step 3: Circulating bubbling cleaning, specifically including:

[0058] After the cleaning of the ninth support plate is completed, continue to fill the water and raise the water level until the water level submerges the topmost support plate. The bubbling cleaning stage of raising the water level is completed, and the circulating stage bubbling cleaning is started. Start the suction pump, adjust the flow rate to match the flow rate of the filling pump, the bubbling generating device blows air every 20 s, the bubbling pressure is 7 MPa, and it lasts for 24 h.

[0059] Step 4: Lowering the water level bubbling cleaning, specifically including:

[0060] Adjust the flow rate of the filling pump to be reduced to 1 / 2 of the suction pump, and perform the bubbling cleaning in the stage of lowering the water level. When the water level drops to 10 - 20 mm below the ninth support plate, stop filling and draining water, and perform bubbling cleaning on this layer of support plate. The number of bubbling times is 10 times, the bubbling pressure is 7 Mpa. After the cleaning of the ninth support plate is completed, continue to lower the water level. Keep the bubbling pressure decreasing by 0.5 MPa for each layer of support plate as the water level drops, until the bubbling cleaning of each layer of support plate is completed in sequence, and the bubbling pressure gradually decreases to 2 MPa as the water level drops;

[0061] Continue to lower the water level, ensure bubbling cleaning once every 20 s, until the water level drops to the upper surface of the flow distribution plate, and then stop bubbling.

[0062] Continue to perform the circulating drainage of lowering the water level. When the water level drops to 100 - 150 mm above the tube sheet, the flow rate of the filling pump can be appropriately increased to be the same as that of the suction pump to stir up and extract the mud on the tube sheet. After 30 - 60 min, stop the filling pump from feeding water until the water on the tube sheet is fully drained.

[0063] Step 5: Dismantle the bubbling cleaning system equipment;

[0064] Step 6: Install hydraulic flushing equipment on the manhole on the secondary side of the steam generator, and perform hydraulic flushing and circulating filtration on the tube sheet for about 18 h to fully discharge the deposited mud on the surface of the secondary side tube sheet of the steam generator.

[0065] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the technical principle of the present invention, several improvements and modifications can be made, and these improvements and modifications should also be regarded as the protection scope of the present invention.

Claims

1. A method for cleaning a steam generator in a nuclear power plant, characterized in that: The following steps are involved: Step 1: Complete the drainage of the primary and secondary sides of the steam generator, and then install, connect and inspect the bubbling cleaning system; Step 2: Raise the water level and perform bubbling cleaning; Step 3: Circulation bubbling cleaning; Step 4: Lower the water level and clean by bubbling.

2. A method for cleaning a steam generator in a nuclear power plant according to claim 1, characterized in that: In the step 1, the steam generator tube sheet sludge is firstly hydraulically washed.

3. A method for cleaning a steam generator in a nuclear power plant according to claim 1, characterized in that: The step 2 includes filling deionized water into the secondary side of the steam generator. When the water level exceeds the upper surface of the flow distribution plate by not less than 80 mm, the bubbling device is started to release high-pressure gas to the secondary side of the steam generator. The blowing pressure is 2MPa, and the blowing interval is once every 20s. The water is kept filled and the water level is continuously raised.

4. A method for cleaning a steam generator in a nuclear power plant according to claim 3, characterized in that: The high-pressure gas in S2 is compressed air or nitrogen.

5. A method for cleaning a steam generator in a nuclear power plant according to claim 1, characterized in that: The step 3 includes the following: When the water level reaches 10-20 mm below the first support plate, stop filling with water, and perform bubbling cleaning on the support plate. The bubbling times are 10 times, and the bubbling pressure is 2.5 MPa. Then continue filling with water to raise the water level. Clean the second to ninth support plates step by step according to the bubbling cleaning step of the first support plate, and keep the bubbling pressure increasing by 0.5MPa for each support plate layer raised by the water level, until the bubbling cleaning of each layer of support plates is completed in sequence, and the bubbling pressure gradually increases to 7MPa as the water level rises; After completing the cleaning of the ninth support plate, continue to fill with water and raise the water level until the water level submerges the uppermost support plate. The water level rising bubbling cleaning stage is completed, and the circulation stage bubbling cleaning begins. Start the suction pump, adjust the flow rate to match the water filling pump flow rate, and the bubbling generating device will inflate for 20 seconds each time, with a bubbling pressure of 7MPa, for 24 hours.

6. A method for cleaning a steam generator in a nuclear power plant according to claim 1, characterized in that: The step 4 includes the following: Adjust the flow rate of the water filling pump to 1 / 2 of the suction pump, and perform bubbling cleaning in the water level reduction stage. When the water level drops to 10-20mm below the 9th support plate, stop filling and draining water, and perform bubbling cleaning on this layer of support plate. The bubbling times are 10 times, and the bubbling pressure is 7Mpa. After the ninth support plate is cleaned, continue to lower the water level, and keep the bubbling pressure reduced by 0.5MPa for each layer of support plate lowered by the water level, until the bubbling cleaning of each layer of support plates is completed in turn, and the bubbling pressure gradually decreases to 2MPa as the water level drops; Continue to lower the water level and ensure bubbling and cleaning every 20 seconds until the water level drops to the upper surface of the flow distribution plate, then stop bubbling; Continue to circulate and drain the water to lower the water level. When the water level drops to 100-150mm above the tube sheet, increase the flow of the water filling pump appropriately to match the suction pump, stir and pump out the sludge on the tube sheet. After 30-60 minutes, stop the water filling pump from entering until the water on the tube sheet is fully discharged.

7. A method for cleaning a steam generator in a nuclear power plant according to claim 1, characterized in that: Includes step 5: dismantling the bubbling cleaning system equipment.

8. A method for cleaning a steam generator in a nuclear power plant according to claim 7, characterized in that: The method comprises the following steps: installing a hydraulic flushing device on the secondary side hand hole of the steam generator, and hydraulically flushing and circulating filtering the tube sheet for 18 hours to fully discharge the deposited sludge on the surface of the secondary side tube sheet of the steam generator.

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