A method for automatically converting the steam state at the outlet of a sodium-cooled fast reactor direct current evaporator to a water state
The key technical parameters of the sodium-cooled fast reactor DC evaporator outlet are closed-loop control, which solves the problems of cumbersome manual operation and poor safety and stability, realizes automatic conversion and ensures the safe and stable operation of the system and equipment.
Patent Information
- Application Number
- CN202311248132.1
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2023-09-26
- Publication Date
- 2025-04-04
AI Technical Summary
The steam-to-water state of the existing sodium-cooled fast reactor DC evaporator needs manual operation, which is cumbersome and can easily lead to water shutdown, system oscillation and equipment damage.
The sodium temperature, pressure, front and rear differential pressure of the DC evaporator outlet, and the pressure of the main water supply valve, and the pressure of the start-up expander are controlled by PI to achieve automatic conversion.
The DC evaporator outlet automatically switches from steam to water state, ensuring the safe and stable operation of the system and equipment, and avoiding water shutdown and equipment damage.
Smart Images
Figure CN119755604A_ABST
Abstract
Description
Technical Field
[0001] The invention belongs to the technical field of heat exchange control of a sodium-cooled fast reactor direct current evaporator, and in particular relates to a method for automatically converting a steam state at an outlet of a sodium-cooled fast reactor direct current evaporator into a water state. Background Art
[0002] The outlet of the direct current evaporator of the sodium-cooled fast reactor is in a steam state when it changes from high power to low power. The conversion from the steam state at the outlet of the direct current evaporator to the water state is achieved by gradually and repeatedly increasing the speed of the feedwater pump, increasing the opening of the feedwater regulating valve, reducing the opening of the inlet regulating valve of the start-up expansion vessel, and stabilizing the pressure of the start-up expansion vessel. During this process, the nuclear island power remains unchanged. At present, other domestic fast reactors (except the Xiapu fast reactor) use manual methods to convert the steam state at the outlet of the direct current evaporator to the water state. When manually controlling the steam state at the outlet of the direct current evaporator to the water state, increase the opening of the main feedwater pump scoop pipe by 1%, increase the pump speed, and the sodium temperature at the outlet of the evaporator is reduced. The opening of the start-up expansion vessel inlet regulating valve is quickly reduced by 1-2%. Observe the sodium temperature. If it is still on a downward trend, continue to reduce the start-up expansion vessel inlet regulating valve by 1%. When the sodium temperature stabilizes or shows an upward trend, increase the opening of the main feedwater pump scoop pipe by 1%. In this way, based on maintaining the sodium temperature at the evaporator outlet, the pump scoop tube opening is alternately increased by 1% and the start-up expansion tank water inlet regulating valve opening is reduced by 1-2%. When the water supply regulating valve pressure difference is high (the normal pressure drop of the regulating valve is about 1.5MPa), the flow rate is increased by opening the water supply regulating valve instead of the pump, and the opening amplitude is 1% each time. In this process, the pressure of the start-up expansion tank should be constantly paid attention to to avoid overpressure. If overpressure occurs, the condensate spray valve of the start-up expansion tank is manually opened to reduce the pressure of the start-up expansion tank. After repeated operation of the above steps, the sodium temperature at the evaporator outlet is maintained at 285℃ and the evaporator outlet pressure is 7Mpa. At this time, there should be no positive superheat at the evaporator outlet, indicating the completion of the conversion of the steam state to the water state at the direct current evaporator outlet. This operation method is extremely cumbersome, with many operation steps, and is extremely challenging to the operator's technical level. It is also easy to cause water outage and shutdown, sodium temperature mutation, and start-up expansion tank safety valve action. When the system is disturbed, it is difficult to ensure that the system returns to a stable state, which then causes system shock and damage to the equipment. It is urgent to develop a control scheme for automatically converting the steam state to the water state at the outlet of the direct current evaporator of a sodium-cooled fast reactor to ensure the safe and stable conversion of the steam state to the water state at the outlet of the direct current evaporator and reduce the impact of this process on the system and equipment. Summary of the invention
[0003] The purpose of the present invention is to provide a method for automatically converting the steam state at the outlet of a sodium-cooled fast reactor into a water state. After repeated verifications through on-site debugging, the method meets the requirements for safe and stable operation on site and solves the problems that the steam state at the outlet of a fast reactor is difficult to operate, which easily causes water shortage and reactor shutdown, system oscillation and divergence, and system equipment is easily damaged.
[0004] In order to achieve the above object, the technical solution adopted by the present invention is:
[0005] A method for automatically changing the steam state at the outlet of a sodium-cooled fast reactor direct current evaporator to a water state, during which four key technical parameters need to be controlled, namely, the direct current evaporator outlet sodium temperature, the direct current evaporator outlet pressure, the differential pressure before and after the main feed water valve, and the start-up expansion tank pressure; the closed-loop control target value of the direct current evaporator outlet sodium temperature is 285°C, and the closed-loop control target of the direct current evaporator outlet pressure is increased from 7.0Mpa.g to 10.0Mpa.a at a rate of 0.003Mpa / s; the closed-loop control target of the differential pressure before and after the main feed water valve is 0.95Mpa, and the start-up expansion tank pressure control target is 1.8Mpa.
[0006] PI regulation is used to perform closed-loop control of four key technical parameters.
[0007] The operator clicks the sequential control start-up button, and the closed-loop control target of the DC evaporator outlet pressure increases from the current closed-loop control set value to 10.0 MPa.a at a rate of 0.003 MPa / s. In this process, as the DC evaporator outlet pressure increases, the enthalpy of the outlet water vapor mixture gradually decreases, the heat taken away from the DC evaporator gradually decreases, and the DC evaporator outlet sodium temperature gradually increases. To maintain the sodium temperature at 285°C, the main feed water valve is gradually opened, and the differential pressure before and after the main feed water valve gradually decreases. To maintain the differential pressure before and after the main feed water valve at 0.95 MPa, the feed water pump speed is gradually increased. In this process, the high-pressure auxiliary steam pressure reduction regulating valve controls the start-up expansion tank pressure to stabilize at 1.8 MPa to prevent the start-up expansion tank from overpressure; as the DC evaporator outlet pressure increases to 10.0 MPa.a, the DC evaporator outlet sodium temperature stabilizes at 285°C. According to the energy balance, the DC evaporator outlet has a positive superheat, indicating that the DC evaporator outlet has changed from a steam state to a water state. This sequential control ends, and the sequential control start-up button returns to the cut-off state.
[0008] The beneficial effects achieved by the present invention are:
[0009] By adopting the technical means of sequential control, the technical effect of automatic conversion of the DC evaporator outlet from the steam state to the water state is realized; by adopting the technical means of closed-loop control, the technical effect of stable operation of the sodium temperature at the outlet of the sodium side of the DC evaporator at about 285°C during the conversion of the DC evaporator outlet from the steam state to the water state is realized; by adopting the technical means of closed-loop control, the technical effect of the DC evaporator outlet pressure being controlled and stably increased from 7Mpa.g to 10Mpa.a during the conversion of the DC evaporator outlet from the steam state to the water state is realized; by adopting the technical means of closed-loop control, the technical effect of controlling the start-up expansion tank pressure within 2.0Mpa.g during the conversion of the DC evaporator outlet from the steam state to the water state is realized; by adopting the technical means of sequential control, the technical effect of safe and stable operation of the system and equipment during the conversion of the DC evaporator outlet from the steam state to the water state is realized without shutdown, equipment damage, large shocks and disturbances. BRIEF DESCRIPTION OF THE DRAWINGS
[0010] Figure 1 The present invention is a flow chart of a method for automatically converting the steam state at the outlet of a sodium-cooled fast reactor direct current evaporator to the water state. DETAILED DESCRIPTION
[0011] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments.
[0012] The second loop of the fast reactor is hot sodium, and the third loop of the fast reactor is the water vapor loop flow diagram. Figure 1 The three-circuit has two loops, and each loop has a set of main water supply large valve and main water supply small valve. The process flow starting from the feed water pump is as follows: the feed water pump takes water from the deaerator and sends the feed water of 190℃ to 210℃ to the direct current evaporator. After completing the heat exchange in the direct current evaporator, the feed water is discharged to the start-up expansion tank after the pressure is reduced by the start-up expansion tank inlet regulating valve. In the start-up expansion tank, part of it becomes water, and part of it becomes steam and is discharged to the high-pressure auxiliary steam header. The water in the start-up expansion tank will be discharged to the condenser or deaerator (the water quality meets the requirements). The steam flowing to the high-pressure auxiliary steam header will be discharged to the condenser through the high-pressure auxiliary steam pressure reduction regulating valve. Because the start-up expansion tank is connected to the high-pressure auxiliary steam header, the main task of the high-pressure auxiliary steam pressure reduction regulating valve from the high-pressure auxiliary steam header to the condenser is to maintain the start-up expansion tank pressure within 2Mpa.g during the conversion process of the steam state to the water state at the direct current evaporator outlet. If the start-up expansion tank pressure exceeds 2.4Mpa.g, the operator must manually open the condensate spray valve to reduce the pressure of the start-up expansion tank. Ensure that the start-up expansion tank pressure is within a reasonable range. The sign that the steam state at the outlet of the direct current evaporator changes to the water state is that the evaporator outlet pressure switches smoothly and gradually from 7Mpa.g to 10Mpa.a, the evaporator outlet superheat is less than zero, and the evaporator outlet sodium temperature is stable at around 285℃.
[0013] The automatic control process of the DC evaporator outlet steam state to water state requires the completion of automatic control of four main system parameters, namely, the evaporator outlet sodium temperature, the differential pressure before and after the main feed water valve, the DC evaporator outlet pressure, and the start-up expansion tank pressure. The control systems for the above four parameters are all controlled by PI. For detailed control schemes of the four control systems, see Figure 1 . After on-site debugging, it was found that the differential pressure before and after the feed water regulating valve controlled by the feed water pump is better at 0.95Mpa, and the differential pressure before and after the feed water regulating valve controlled by the feed water pump is set to 0.95Mpa. The evaporator outlet pressure control target value is slowly and automatically set from 7.0Mpa.g in the steam state to 10Mpa.a. This process was completed in about 20 minutes after on-site debugging and was relatively stable. The high-pressure auxiliary steam step-down regulating valve is used to stabilize the pressure of the high-pressure auxiliary steam manifold at 1.8Mpa.g, thereby ensuring that the pressure of the start-up expansion tank is within 2.0Mpa.g, which can effectively ensure that the pressure of the start-up expansion tank is far away from 2.4Mpa.g, avoiding overpressure of the start-up expansion tank, and then causing overpressure of the start-up expansion tank. The sodium temperature at the evaporator outlet is controlled by the main water supply valve of each loop. The water supply pump controls the differential pressure before and after the main water supply valve of each loop, compensates for the control of the main water supply valve of each loop, and strengthens the adjustment characteristics of the main water supply valve. Because when the main water supply valve is closed downward, the water supply flow rate will be reduced, the differential pressure will increase, the water supply pump will reduce the speed, the water supply flow rate will decrease faster, and then the sodium temperature at the DC evaporator outlet will increase faster. When the main water supply valve is opened upward, the water supply flow rate will increase, the differential pressure will decrease, the water supply pump will increase the speed, the water supply flow rate will increase faster, and then the sodium temperature at the DC evaporator outlet will be reduced faster, thereby improving the control effect of the sodium temperature at the DC evaporator outlet and ensuring a rapid response to the sodium temperature at the DC evaporator outlet.
[0014] The normal direct current evaporator outlet steam state to water state sequence control operation process is as follows: the first step is to determine that the direct current evaporator outlet sodium temperature control loop is in automatic state, and the control target value is 285℃; the main water supply valve front and rear differential pressure control loop is in automatic state, and the control target value is 0.95Mpa; the high-pressure auxiliary steam pressure reduction control valve is in automatic state, and the control target value is 1.8Mpa. The second step is that the operator clicks the direct current evaporator outlet steam state to water state sequence control input button. At this time, the rate limiter of the direct current evaporator outlet pressure control loop will gradually change from the current value to 10.0Mpa.a at a rate of 0.003Mpa / s. This process starts the expansion tank inlet control valve for automatic closed-loop regulation. When the rate is too large, it is easy to cause oscillation and violent fluctuations in the evaporator outlet sodium temperature. After debugging and verification, it is confirmed that the 0.003Mpa / s pressure increase rate can ensure the safe and stable operation of the system equipment. In the process of the target pressure set value constantly approaching 10.0Mpa.a, the operator setting corresponding to the expansion tank inlet control valve will continuously track the target pressure set value, and the operator can no longer operate the operator setting station. The main purpose is to ensure that the target pressure set value is consistent with the operator setting station when an unexpected situation occurs or the operator manually cuts off the sequential control, ensuring that there is no disturbance in this process. As the outlet pressure of the direct current evaporator increases, the corresponding enthalpy of the water vapor mixture at its outlet will decrease. On the basis of the unchanged inlet water temperature of the direct current evaporator, the heat taken away from the sodium side of the direct current evaporator will gradually decrease, and the outlet sodium temperature of the direct current evaporator will gradually increase. In order to maintain the outlet sodium temperature at 285℃, the main feed water valve will gradually open the main feed water valve. After opening the main feed water valve, the differential pressure before and after the main feed water valve decreases, and the feed water pump will automatically increase the feed water pump speed. In this process, the high-pressure auxiliary steam step-down regulating valve controls the pressure of the high-pressure auxiliary steam manifold at 1.8Mpa. The steam of the high-pressure auxiliary steam manifold is provided by the start-up expansion tank, thereby ensuring that the pressure of the start-up expansion tank is around 2.0Mpa, and will not cause overpressure. When the outlet pressure of the DC evaporator is stable at 7.0Mpa, the outlet sodium temperature of the DC evaporator gradually stabilizes at 285℃. In order to prevent the water from being cut off during the conversion from water state to steam state at the outlet of the DC evaporator, which affects the stable operation of the DC evaporator, the minimum opening of the main water supply valve is set to 28% according to the valve's own Cv characteristics after calculation and debugging. The nuclear power remains basically unchanged before and after the conversion, and the energy taken away from the DC evaporator by the water supply remains unchanged before and after the conversion. The outlet of the DC evaporator is converted from steam state to water state, the superheat is less than zero, and the outlet of the DC evaporator is converted from steam state to water state. This process has been repeatedly verified by debugging. During the debugging process, the outlet pressure of the DC evaporator changes smoothly, the outlet sodium temperature of the DC evaporator changes stably, the system and equipment fluctuate little during the entire conversion process, and the transition is smooth. There is no system oscillation or disturbance caused by the conversion from steam state to water state at the outlet of the DC evaporator.
[0015] See also Figure 1The outlet of the DC evaporator is automatically converted from the steam state to the water state. After analyzing its process flow, there are 4 key technical parameters that need to be controlled in the process, namely, the outlet sodium temperature of the DC evaporator, the outlet pressure of the DC evaporator, the differential pressure before and after the main water supply valve, and the pressure of the start-up expansion tank. We designed four types of controllers for closed-loop control of these 4 key technical parameters. The algorithm is PI adjustment, and the formula is: valve / water supply pump speed command output The closed-loop control target value of the sodium temperature at the outlet of the direct current evaporator is 285°C, and the closed-loop control target of the direct current evaporator outlet pressure is increased from 7.0Mpa.g to 10.0Mpa.a at a rate of 0.003Mpa / s. The closed-loop control target of the differential pressure before and after the main water supply valve is 0.95Mpa. The pressure control target of the start-up expansion tank is 1.8Mpa.
[0016] See also Figure 1 The conversion process of the DC evaporator outlet steam state automatically changing to the water state is as follows: the operator clicks the sequential control input button, and the DC evaporator outlet pressure closed-loop control target increases from the current closed-loop control constant to 10.0Mpa.a at a rate of 0.003Mpa / s. In this process, as the DC evaporator outlet pressure increases, the enthalpy of its outlet water vapor mixture will gradually decrease, the heat taken away from the DC evaporator will gradually decrease, and the DC evaporator outlet sodium temperature will gradually increase. In order to maintain the sodium temperature at 285°C, the main water supply valve will gradually open, and the differential pressure before and after the main water supply valve will gradually decrease. In order to maintain the differential pressure before and after the main water supply valve at 0.95Mpa, the speed of the feed water pump will gradually increase. In this process, the high-pressure auxiliary steam pressure reduction regulating valve controls the start-up expansion tank pressure to stabilize at 1.8Mpa to prevent the start-up expansion tank from overpressure. As the outlet pressure of the DC evaporator increases to 10.0Mpa.a, the outlet sodium temperature of the DC evaporator sodium side stabilizes at around 285°C. According to the energy balance, the outlet of the DC evaporator will have positive superheat, indicating that the outlet of the DC evaporator has changed from a steam state to a water state. This sequential control ends and the sequential control input button returns to the cut-off state.
[0017] The key points and points to be protected of the present invention are: the method and main ideas for automatically converting the outlet of the direct current evaporator from the steam state to the water state; the selection and setting of the main control parameters for automatically converting the outlet of the direct current evaporator from the steam state to the water state and the control algorithm adopted by the controller; the specific operation method and control steps of the sequential control for automatically converting the outlet of the direct current evaporator from the steam state to the water state; the target constant automatically controlled by the controller and the target pressure setting pressure reduction rate for automatically adjusting the inlet regulating valve of the start-up expansion tank during the sequential control process of automatically converting the outlet of the direct current evaporator from the steam state to the water state; the control ideas for the operator to set the tracking target pressure setting during the sequential control process of automatically converting the outlet of the direct current evaporator from the steam state to the water state, and the setting of the transient working condition cut-off sequential control; the minimum opening of the main water supply small valve automatically adjusted to prevent the direct current evaporator from water outage accidents when the outlet of the direct current evaporator is automatically converted from the steam state to the water state.
[0018] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that modifying the technical solutions described in the aforementioned embodiments, or replacing part or all of the technical features therein by equivalents, does not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.
Claims
1. A method for automatically converting the steam state at the outlet of a sodium-cooled fast reactor direct current evaporator to the water state, characterized in that: There are four key technical parameters that need to be controlled in the process, namely the DC evaporator outlet sodium temperature, DC evaporator outlet pressure, the differential pressure before and after the main water supply small valve, and the start-up expansion tank pressure; the closed-loop control target value of the DC evaporator outlet sodium temperature is 285℃, and the closed-loop control target of the DC evaporator outlet pressure increases from 7.0Mpa.g to 10.0Mpa.a at a rate of 0.003Mpa / s; the closed-loop control target of the differential pressure before and after the main water supply small valve is 0.95Mpa, and the start-up expansion tank pressure control target is 1.8Mpa.
2. The method for automatically converting the steam state to the water state at the outlet of the sodium-cooled fast reactor direct current evaporator according to claim 1, characterized in that: PI regulation is used to perform closed-loop control on four key technical parameters.
3. The method for automatically converting the steam state at the outlet of the sodium-cooled fast reactor direct current evaporator to the water state according to claim 2, characterized in that: The operator clicks the sequential control start-up button, and the closed-loop control target of the DC evaporator outlet pressure increases from the current closed-loop control set value to 10.0 MPa.a at a rate of 0.003 MPa / s. In this process, as the DC evaporator outlet pressure increases, the enthalpy of the outlet water vapor mixture gradually decreases, the heat taken away from the DC evaporator gradually decreases, and the DC evaporator outlet sodium temperature gradually increases. To maintain the sodium temperature at 285°C, the main feed water valve is gradually opened, and the differential pressure before and after the main feed water valve gradually decreases. To maintain the differential pressure before and after the main feed water valve at 0.95 MPa, the feed water pump speed is gradually increased. In this process, the high-pressure auxiliary steam pressure reduction regulating valve controls the start-up expansion tank pressure to stabilize at 1.8 MPa to prevent the start-up expansion tank from overpressure; as the DC evaporator outlet pressure increases to 10.0 MPa.a, the DC evaporator outlet sodium temperature stabilizes at 285°C. According to the energy balance, the DC evaporator outlet has a positive superheat, indicating that the DC evaporator outlet has changed from a steam state to a water state. This sequential control ends, and the sequential control start-up button returns to the cut-off state.