Method for controlling commissioning of filters of fine treatment system

Abstract

The present invention relates to the technical field of water treatment, and in particular to a method for controlling the commissioning of filters of a fine treatment system. The method comprises: slowly opening valves of backup filters and connecting cation bed filters and mixed bed filters to a fine treatment system; controlling the flow rate of a commissioned filter by means of a decrease in the flow rates of running filters; and opening an inlet regulating valve of each backup filter in a pulsed manner, suspending a valve regulation operation on the commissioned filter when the flow rates of the other four running filters each decrease by 2 kg / s, i.e., a total flow rate decrease of 8 kg / s, waiting for 1 h, then continuing valve regulation until the flow rates of the five filters are equal, and then exiting a failed filter. The slow commissioning process of the present invention eliminates the impact of commissioning and switching operations on cation bed filters and mixed bed filters of a condensed water fine treatment system on the water quality of a secondary loop of a unit; and the slow commissioning operation parameters are accurately and reliably controlled.

Description

A control method for the activation of filters in a fine treatment system Technical Field

[0001] This invention belongs to the field of water treatment technology, specifically relating to a control method for the operation of a filter in a fine treatment system. Background Technology

[0002] The first phase of the Jiangsu Nuclear Power Co., Ltd. project was designed and equipped by Russia, consisting of two VVER-1000 units with a total rated power of 2×1060MW and a design life of 40 years. Each unit is equipped with a condensate polishing system, whose function is to purify the condensate, removing metallic impurities such as corrosion products and ionic impurities to meet the requirements of the unit's feedwater and steam generator wastewater. The condensate polishing system includes a mechanical filtration system (five cation exchange filters), an ion exchange system (five mixed bed filters), an external regeneration system, and a wastewater discharge system.

[0003] The cation bed filter and mixed bed filter of the condensate polishing system are 3.4m diameter cylindrical filters. Normally, four lines operate while one line is on standby, as shown in Figure 1. Condensate from condensers one through four flows through the four operating cation bed and mixed bed filters before returning to the condensate system. The cation bed filter is filled with 14.6 cubic meters of resin. The water quality at the outlet of the cation bed filter must meet the following requirements: conductivity not exceeding 1 μS / cm, sodium ion concentration not exceeding 2 μg / L, and operating pressure differential greater than 0.30 MPa. If the cation bed filter fails, the standby polishing filter is put into operation, and the failed cation bed filter is taken out of operation for regeneration. The polishing cation bed filter undergoes external regeneration, and the system is equipped with a cation bed filter regeneration filter. The mixed bed filter of the polishing system is filled with 16.2 cubic meters of resin, including 9.8 cubic meters of anion resin, 4.8 cubic meters of cation resin, and 1.6 cubic meters of inert resin. When the operating conductivity of the mixed bed filter in the fine treatment system exceeds 0.15 μS / cm, the silicon concentration does not exceed 20 μg / L, and the operating pressure difference of the mixed bed filter exceeds 0.25 MPa, it is considered to have failed. A standby fine treatment mixed bed filter is then put into operation, and the failed fine treatment mixed bed filter is taken out of operation for regeneration. The fine treatment mixed bed filter undergoes external regeneration, and the system is equipped with a mixed bed filter regeneration filter. Regeneration involves exchanging the depleted ion exchange resin with a suitable acid, alkali, or salt solution to convert the resin to the desired form. The chemical reagents used for regeneration of the cation exchange filter and mixed bed filter in the fine treatment system are hydrochloric acid and sodium hydroxide. Before putting the standby cation exchange filter and mixed bed filter into operation, they need to be flushed with demineralized water. Only after the flushing meets the required standards can they be put into operation.

[0004] The requirements for secondary circuit water quality include secondary circuit control indicators and secondary circuit diagnostic indicators. Secondary circuit control indicators are the quality indicators of steam generator feedwater and wastewater. Maintaining these indicators within permissible ranges ensures the safety, reliability, and economic efficiency of the steam generator and secondary circuit equipment, guaranteeing their design lifespan. Secondary circuit diagnostic indicators provide power plant personnel with supplementary information regarding the accuracy of water chemistry conditions of steam generator feedwater and wastewater, saturated steam, and auxiliary systems. Deviations from these indicators indicate abnormal operation of the process systems ensuring proper water chemistry conditions.

[0005] When one or more water quality control indicators of the secondary loop steam generator feedwater and steam generator wastewater deviate from the standard, and these indicators fail to return to normal within the time specified in the standard; or when the pH value, iron, and copper diagnostic indicators of the steam generator feedwater deviate and fail to return to normal within 30 days from the date of discovery of the deviation, the unit needs to take corresponding state-changing operations. This situation is called secondary loop chemical condition failure. The unit has many requirements for water quality during different operating conditions such as startup, operation, and maintenance. Secondary loop chemical condition failure can lead to a reduction in unit power or even shutdown.

[0006] During the operation of the units at full power, both units experienced varying degrees of fluctuation in the conductivity, chloride ion content, and secondary loop pressure of the steam generator effluent. When operators performed the fine treatment cation exchange filter commissioning, it caused fluctuations in the secondary loop water quality and pressure, all of which affected the stable operation of the units, as detailed below:

[0007] (1) The cation bed filter and mixed bed filter of the fine treatment system are in normal operation, but the water quality of the wastewater discharged from the steam generator fluctuates and deviates:

[0008] During full-power operation of the unit, when the condensate polishing cation bed filter reaches its end point, a regenerated cation bed filter needs to be put into operation, and the failed cation bed filter needs to be taken out. During this operation, it was observed that as the flow rate through the newly added cation bed filter rapidly increases, the conductivity of the effluent rises rapidly, and chloride ion levels, as measured by sampling, deviate from the expected water quality. To confirm the conclusion that the cation bed filter in the condensate polishing system causes fluctuations in the steam effluent water quality during switching, the inventors stopped all other operations in the secondary loop before switching the cation bed filter, verifying the conclusion was correct. Similar water quality deviations also occurred during the switching of the mixed bed filter.

[0009] During the startup process, the secondary circuit was put into operation during the power increase period, which increased the fluctuation of water quality. At this time, due to the switching operation of the cation bed filter and the mixed bed filter in the fine treatment system, there were superimposed fluctuations in water quality, and there were instances of water quality deviation.

[0010] The inventors analyzed the system equipment and operating parameters. The condensate polishing cation bed filter and mixed bed filter are 3.4m diameter column tanks. The water distribution device is a cup-within-a-cup type, with 840 holes of 15mm diameter in the inner cup and 1518 holes of 20mm diameter in the outer cup. The system is designed to operate at a flow rate of 250kg / s and a pressure of approximately 1.0-1.1MPa. The pre-commissioning flushing flow rate for the cation bed filter is 13.9kg / s, and for the mixed bed filter it is 27.3kg / s, with a pressure of less than 0.70-0.72MPa. Because the pressure and flow rate of the flushing water are much lower than those of the condensate during operation, uneven water distribution may occur. After flushing, a very small amount of regenerant will remain in the filter. Furthermore, the flushing water is demineralized water, which is of slightly lower quality than the condensate. Therefore, when the cation bed filter and mixed bed filter are put into operation after flushing, the water in the filter enters the secondary loop system, causing the water quality of the steam generator to fluctuate and deviate from the danger zone.

[0011] Currently, there are two types of water sources for flushing before the fine treatment system is put into operation, both domestically and internationally. One is demineralized water, which uses the demineralized water from the unit for flushing; the other is condensate water, which uses condensate water to circulate and flush the filter. Regardless of which water source is used, the quality of the water in the filter is lower than that of the condensate water when connected to the condensate system. After the filter is connected, it will more or less interfere with the water quality of the secondary circuit, causing fluctuations or even deviations.

[0012] (2) The cation bed filter and mixed bed filter of the fine treatment system are in normal operation, and the pressure and water quality of the secondary loop fluctuate:

[0013] When the cation bed filter and mixed bed filter of the condensate polishing system are about to reach the end of their operation, the standby filter is ready to be connected to the condensate system. During the opening of the standby filter valve, the pressure of the condensate system fluctuates, endangering the safe operation of the condensate pump.

[0014] The inventors analyzed and investigated the system equipment structure and on-site pipeline layout. During the operation of the fine treatment cation bed filter and mixed bed filter from failure to shutdown to restoration to standby and commissioning, there were operations such as using compressed air to pour resin and mix grease. These operations would allow air to enter the system. Although subsequent operations included water filling and venting, a small amount of air entered the condensate system, causing fluctuations in the secondary loop pressure. Since the air contains gases such as carbon dioxide, the air entering the system also caused fluctuations in the secondary loop water quality, leading to a dangerous zone.

[0015] (3) The commissioning of the condensate polishing cation bed filter and mixed bed filter after maintenance caused deviations in the unit's water quality:

[0016] The mixed bed filter for condensate polishing has a scheduled maintenance procedure. Before maintenance, the mixed bed filter is in standby mode. For scheduled maintenance, the resin in the mixed bed filter is transferred to a regeneration filter. After maintenance, the resin is returned to the mixed bed. Subsequently, when the mixed bed is put into operation, the conductivity and sulfate levels in the steam generator blowdown increase, while the cation levels are not high, reaching 2.25h. If this deviation reaches 24 hours, the power output must be reduced to the minimum monitorable power.

[0017] The inventors analyzed and investigated the situation on-site, examining aspects such as system operation mode, filter body, resin quality and regeneration, resin degradation and water quality fluctuation reproduction, and instruments. Ultimately, it was confirmed that during the maintenance of the mixed bed filter, the person in charge was also responsible for oil-related work, and introduced oil (containing organic sulfate) into the filter, causing the sulfate level to rise after the filter was put into use, resulting in water quality deviation.

[0018] (4) When the condensate polishing cation bed filter and mixed bed filter are put into operation and flushed, the pressure of the condensate system fluctuates, and the standby pump is interlocked and started.

[0019] The commissioning and flushing operations of the cation bed filter and mixed bed filter in the condensate polishing process are carried out by operating valve switches in the central control room. During a cation bed flushing operation, after the operator opens the drain valve of the filter, the pressure of the condensate system drops sharply, and the standby pump starts.

[0020] The inventor investigated the cause and found that the control of the valves related to the cation exchange filter and the mixed bed filter was on the central control computer. The control screens for the five cation exchange filters and the five mixed bed filters were the same. During the flushing operation, the operator went to the wrong interval and opened the drain valve of the running cation exchange filter, causing condensate to be discharged into the wastewater tank, resulting in pressure and flow loss in the condensate system. Summary of the Invention

[0021] The purpose of this invention is to provide a control method for the operation of filters in a fine treatment system, eliminating the impact of fine treatment system operation on the secondary circuit water quality of the unit. Specifically, it addresses the following: the fluctuation and deviation of steam generator discharge water during normal operation of the cation exchange filter and mixed bed filter in the fine treatment system; the fluctuation of secondary circuit pressure and water quality during normal operation of the cation exchange filter and mixed bed filter in the fine treatment system; the deviation of unit water quality caused by the commissioning of the condensate fine treatment cation exchange filter and mixed bed filter after maintenance; and the pressure fluctuation of the condensate system and the start-up of the standby pump during the flushing of the condensate fine treatment cation exchange filter and mixed bed filter.

[0022] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0023] A control method for activating filters in a fine treatment system involves slowly opening the valve of a standby filter to connect the cation bed filter and the mixed bed filter to the fine treatment system.

[0024] The flow rate of the filter in operation is controlled by the decrease in the flow rate of the filter during operation.

[0025] The pulse opens the inlet regulating valve of the standby filter. When the flow rate of each of the other four operating filters drops by 2 kg / s, i.e. the total flow rate drops by 8 kg / s, the valve operation of the operating filter is suspended and waited for 1 hour. After that, the regulating valve is opened again until the flow rates of the five filters are equal, and then the failed filter is removed.

[0026] During major and minor overhauls of the unit, the cation bed that has reached 30% of the cumulative water production is regenerated, and the mixed bed that has reached 30% of the cumulative water production and has resin output operation is regenerated in preparation for start-up.

[0027] If the filter is not put into operation after flushing, it must be flushed again before it can be put into operation again.

[0028] Pressurize the flushed cation bed filter and mixed bed filter, and vent the system during the pressurization process.

[0029] For any servicing filter, after the servicing is completed, the filter needs to be flushed and sampled. Only after the sample passes the test can the resin be transported back to the servicing filter.

[0030] The valves of the filter in operation are controlled. Except for the filter inlet and outlet valves, which are in an operable state, all other valves are set to an inoperable state.

[0031] If the filter is not put into operation within 3 hours after flushing, it must be flushed again before it can be put into operation again.

[0032] The makeup water system, which is continuously running in the unit, is used to pressurize the flushed cation bed filter and mixed bed filter to 0.7 MPa, and the system is vented during the pressurization process.

[0033] The beneficial effects achieved by this invention are as follows:

[0034] This invention's slow-start process eliminates the impact of switching operations on the cation exchange filter and mixed bed filter in the condensate polishing system on the secondary circuit water quality of the unit; the slow-start operation parameters are precisely and reliably controlled; during major and minor overhauls of the unit, the status of the cation exchange filter and mixed bed filter is controlled, eliminating the impact of cation exchange filter switching on the secondary circuit water quality; the flushing and commissioning time intervals of the condensate polishing cation exchange filter and mixed bed filter are controlled, reducing the impact of water remaining in the filters on the secondary circuit water quality; pressure boosting control before commissioning of the condensate polishing cation exchange filter and mixed bed filter reduces the impact of filter switching on the unit pressure; commissioning control after maintenance of the condensate polishing cation exchange filter and mixed bed filter eliminates the impact of maintenance work on the secondary circuit water quality of the unit; and control of system valves after flushing of the condensate polishing cation exchange filter and mixed bed filter eliminates human error caused by incorrect timing. Attached Figure Description

[0035] Figure 1 is a flow chart of the condensate polishing system. Detailed Implementation

[0036] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0037] (1) The cation bed filter and mixed bed filter of the fine treatment system are put into operation in a slow-dosing manner.

[0038] A new method for slow-release operation of the cation bed filter and mixed bed filter in a fine treatment system has been invented.

[0039] (2) The control method of slow dosing for the cation bed filter and mixed bed filter in the fine treatment system

[0040] Based on the structure of the system equipment, the specific parameters for delayed delivery were determined through experimental verification.

[0041] (3) Control of the flushing and commissioning interval of the cation bed filter and mixed bed filter in the fine treatment system

[0042] To reduce the impact of residual water in the filter on the water quality of the secondary circuit, the operation time is limited after the filter is flushed. If the time requirement is exceeded, the resin in the filter must be flushed again before it can be put back into operation.

[0043] (4) Control of the cation bed filter and mixed bed filter in the fine treatment system during major and minor overhauls of the unit

[0044] To avoid switching between the cation bed filter and the mixed bed filter in the fine treatment system during unit startup, the cation bed and mixed bed filters are controlled when the cumulative water production reaches a certain value during major and minor overhauls of the unit.

[0045] (5) Pressure boosting and exhaust control of the cation bed filter and mixed bed filter in the fine treatment system before commissioning

[0046] Based on the system operating parameters, before the cation bed filter and mixed bed filter of the fine treatment system are put into operation, the existing equipment of the system is used to increase the pressure and exhaust operations of the filters to be put into operation.

[0047] (6) Inspection and control after maintenance of cation bed filter and mixed bed filter in condensate polishing

[0048] After overhauling the cation bed filter and mixed bed filter in the condensate polishing process, water quality testing is added, and resin is only supplied after the test results are qualified.

[0049] (1) The cation bed filter and mixed bed filter of the fine treatment system are put into operation in a slow-dosing manner.

[0050] The inventors analyzed that the cause of water quality fluctuations in the secondary loop system was the inflow of water from the cation bed filter and mixed bed filter in the fine treatment system into the system. If the valve of the standby filter is opened slowly and this part is slowly connected to the system, the water quality fluctuations can be eliminated. That is, the standby filter is put into the system in a "slow-input" manner.

[0051] The control method for the slow-release of the cation bed filter and mixed bed filter in the fine treatment system is as follows: Under normal operation, four lines are running and one line is on standby. The maximum flow rate of each line is 250 kg / s. The dead zone of the flow meter is 25-30 kg / s. Therefore, when the flow rate is below 30 kg / s, the flow meter reading is inaccurate. The inventor verified this conclusion through experiments. Therefore, it is not possible to control the flow rate of the standby filter by the flow meter.

[0052] To precisely control the flow rate during slow deployment, the inventors controlled the flow rate of the operating filters by observing the decrease in the flow rate of the running filters. A pulse opens the inlet regulating valve of the standby filter. When the flow rate of each of the other four operating filters decreases by 2 kg / s (i.e., the total flow rate decreases by 8 kg / s), the valve operation of the operating filters is paused, and the process is allowed to continue for 1 hour. Afterward, the regulating valve is reopened until the flow rates of all five filters are equal, and then the failed filter is deactivated.

[0053] (2) Control of the cation bed filter and mixed bed filter in the fine treatment system during major and minor overhauls of the unit

[0054] To avoid switching between the cation bed filter and the mixed bed filter in the fine treatment system during unit startup, the cation bed filter that has reached 30% of the cumulative water production is regenerated during major and minor overhauls of the unit, and the mixed bed filter that has reached 30% of the cumulative water production and has resin output operation is regenerated in preparation for use during startup.

[0055] (3) Control method for flushing and commissioning time interval of cation bed filter and mixed bed filter in fine treatment system

[0056] To reduce the impact of residual water during the filter period on the water quality of the secondary circuit, if the filter is not put into operation within 3 hours after flushing, it must be flushed again before being put into operation again.

[0057] (4) Pressure boosting and exhaust control of the cation bed filter and mixed bed filter in the fine treatment system before commissioning

[0058] After the cation bed filter and mixed bed filter of the fine treatment system are flushed, the makeup water system of the unit is used to pressurize the flushed filters to 0.7 MPa. During the pressurization process, the system high-point exhaust valve is opened to exhaust the system.

[0059] (5) Inspection and control after maintenance of cation bed filter and mixed bed filter in condensate polishing

[0060] During the maintenance of cation bed and mixed bed filters in condensate polishing, multiple personnel enter the filters. In a past incident, a maintenance worker, who was also responsible for grease-related work in another system, brought grease into the filter, causing sulfate levels to exceed limits. To prevent similar incidents, after any filter has been maintained, it must be flushed and sampled. Only after the sample passes inspection can the resin be returned to the maintained filter.

[0061] (6) Operation control after maintenance of cation bed filter and mixed bed filter in condensate polishing

[0062] The control screens for the five cation bed filters and the five mixed bed filters in the fine treatment system are exactly the same. To prevent operators from going to the wrong interval, the inventor controls the valves of the filters during operation. Except for the filter inlet and outlet valves, which are operable, the other more than ten valves are set to a non-operable state to prevent them from being accidentally opened when going to the wrong interval, which would threaten the stable operation of the unit.

Claims

1. A control method for filter commitment of a polishing system, characterized by: Slowly open the valve of the standby filter and connect the cation bed filter and mixed bed filter to the fine treatment system.

2. The control method of the polishing system filter commitment according to claim 1, characterized in that: The flow rate of the filter in operation is controlled by the decrease in the flow rate of the filter during operation.

3. The control method of claim 2, wherein: The pulse opens the inlet regulating valve of the standby filter. When the flow rate of each of the other four operating filters drops by 2 kg / s, i.e. the total flow rate drops by 8 kg / s, the valve operation of the operating filter is suspended and waited for 1 hour. After that, the regulating valve is opened again until the flow rates of the five filters are equal, and then the failed filter is removed.

4. The control method of claim 1, wherein: During major and minor overhauls of the unit, the cation bed that has reached 30% of the cumulative water production is regenerated, and the mixed bed that has reached 30% of the cumulative water production and has resin output operation is regenerated in preparation for start-up.

5. The control method of claim 1, wherein: If the filter is not put into operation after flushing, it must be flushed again before it can be put into operation again.

6. The control method of the polishing system filter commitment according to claim 1, characterized in that: Pressurize the flushed cation bed filter and mixed bed filter, and vent the system during the pressurization process.

7. The control method of the polishing system filter commitment according to claim 1, characterized in that: For any servicing filter, after the servicing is completed, the filter needs to be flushed and sampled. Only after the sample passes the test can the resin be transported back to the servicing filter.

8. The control method of the polishing system filter commitment according to claim 1, characterized in that: The valves of the filter in operation are controlled. Except for the filter inlet and outlet valves, which are in an operable state, all other valves are set to an inoperable state.

9. The control method of claim 5, wherein: If the filter is not put into operation within 3 hours after flushing, it must be flushed again before it can be put into operation again.

10. The control method for filter commitment of a polishing system according to claim 6, characterized in that: The makeup water system, which is continuously running in the unit, is used to pressurize the flushed cation bed filter and mixed bed filter to 0.7 MPa, and the system is vented during the pressurization process.

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