Steam source undisturbed switching system and control method for steam-driven feed water pump
Patent Information
- Application Number
- CN202610990673.9
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-07-03
- Publication Date
- 2026-10-23
Smart Images
Figure CN122960424A_ABST
Abstract
Description
Technical Field
[0001] This application relates to the field of steam-driven feedwater pump operation control technology, specifically to a steam source-free switching system and control method for a steam-driven feedwater pump. Background Technology
[0002] Steam-driven feedwater pumps are important auxiliary machines in thermal power units. The steam turbine (small unit) driven by the pump is usually equipped with two steam supply sources: under normal operation, it is supplied by the fourth stage extraction steam. When the unit load is lower than 60% of the rated load, the pressure of the fourth stage extraction steam decreases, and it is necessary to switch to auxiliary steam supply.
[0003] In existing technologies, the backup steam supply pipeline is kept in a closed valve state for extended periods, requiring preheating and drainage before activation. The preheating and drainage process typically takes about 30 minutes, and key operational points such as whether preheating is sufficient, drainage is complete, and the timing of switching depend on manual observation and operation. Under operating conditions with frequent fluctuations in grid load, the above methods are difficult to meet the needs of rapid switching, posing a risk of fluctuations in steam-driven feedwater pump output or even water hammer due to insufficient preheating or delayed operation.
[0004] In addition, during the existing steam source switching process, the temperature of the backup steam source pipeline is mainly maintained by the warm-up steam condensate method. The warm-up steam is usually directly condensed to the condenser without heat recovery and utilization. Summary of the Invention
[0005] To address the aforementioned issues, this invention provides a steam source seamless switching system and control method for steam-driven feedwater pumps, achieving long-term hot standby of backup steam sources and automatic seamless control of the switching process.
[0006] In a first aspect, the technical solution of the present invention provides a steam-driven feedwater pump steam source seamless switching system, including a steam-driven feedwater pump driven by a small engine, a main steam source, a backup steam source, and a warm-up branch; The main steam source is connected to the turbine inlet steam header through the main steam source supply pipeline, and the backup steam source is connected to the turbine inlet steam header through the backup steam source supply pipeline. The backup steam supply pipeline is equipped with a check valve and a backup steam source isolation valve in sequence along the steam supply direction. The inlet end of the warming pipe branch is connected to the upstream pipe of the backup steam source isolation valve, and the outlet end is connected to the low-pressure heater. A warming pipe regulating valve is installed on the warming pipe branch. An overheat detection unit is installed on the upstream pipeline of the backup steam source isolation door, a main steam source pressure detection unit is installed on the main steam source supply pipeline, and a small turbine steam inlet header pressure detection unit is installed at the small turbine steam inlet header. The backup steam source isolation door, the warm-up regulating valve, the superheat detection unit, the main steam source pressure detection unit, and the small turbine inlet steam header pressure detection unit are each used to connect to a controller signal.
[0007] As a preferred embodiment of the technical solution of the present invention, the outlet end of the backup steam source supply pipeline is connected to the main steam source supply pipeline, and the connection position is located downstream of the small turbine quick-closing valve and upstream of the small turbine inlet steam regulating valve. After converging at the connection position, the steam enters the small turbine through the small turbine inlet steam regulating valve.
[0008] Connecting the outlet of the backup steam supply pipeline to the main steam supply pipeline, with the merging point located downstream of the turbine's quick-closing valve and upstream of the turbine's inlet steam regulating valve, eliminates the need for the backup steam supply to pass through the quick-closing valve when it is put into operation, reducing steam flow resistance. At the same time, it ensures that the two steam sources enter the turbine together after being regulated by the inlet steam regulating valve, which helps maintain the stability and consistency of the turbine's inlet steam parameters.
[0009] Secondly, the present invention also provides a control method for seamless switching of steam source in a steam-driven feedwater pump, applied to the system described in the first aspect. This method includes the following steps: During the normal steam supply period of the unit from the main steam source, the warm-up branch is opened. By adjusting the warm-up regulating valve on the warm-up branch, steam is continuously flowed through the upstream pipe of the standby steam source isolation valve. The superheat of the steam at this point is detected in real time. The superheat is maintained at no less than the preset superheat threshold by adjusting the opening of the warm-up regulating valve. The pressure and rate of change of the main steam source are monitored in real time. When the rate of decrease of the main steam source pressure is greater than a preset rate threshold and the main steam source pressure is higher than a second preset value, the opening of the warm-up regulating valve is increased to increase the steam flow through the upstream pipeline. When the pressure of the main steam source drops to the second preset value, a steam source switching command is issued; In response to the steam source switching command, the backup steam source isolation door is gradually opened in a segmented and slow-opening manner. During the opening process, the pressure fluctuation value of the small turbine inlet steam header is monitored in real time. When the pressure fluctuation value exceeds the set upper limit, the opening action is paused and the current opening degree is maintained until the pressure fluctuation value falls back below the set upper limit. Once the backup steam source isolation valve is fully opened and the pressure of the turbine inlet steam header is stable within the preset range, the warm-up regulating valve is closed to stop the steam flow in the warm-up branch, thus completing the switch from the main steam source to the backup steam source.
[0010] By continuously supplying steam through the warm pipe branch and regulating the superheat in a closed loop, the backup steam supply pipeline is kept in a hot standby state with a superheat not lower than the preset value, thus resolving the contradiction between rapid load changes and switching preparation time under deep peak shaving conditions.
[0011] By monitoring the rate of decrease in the main steam source pressure and increasing the opening of the warm-up regulating valve in advance before the pressure drops to the switching threshold, predictive active compensation is achieved. Compared with traditional passive response control, this effectively avoids the problem of insufficient backup steam source quality at the moment of switching.
[0012] By gradually opening the backup steam source isolation door in stages, and monitoring the pressure fluctuation of the turbine inlet steam header in real time during the opening process, the opening is suspended until it is restored when the limit is exceeded. This achieves refined control of the steam source switching process, ensuring that the entire switching process is undisturbed and the turbine inlet steam pressure transitions smoothly.
[0013] As a preferred embodiment of the technical solution of the present invention, a reverse cut-back step is also included: During the period when the unit is supplied with steam from the backup steam source, the pressure of the main steam source is monitored in real time. When the pressure of the main steam source rises back to the third preset value, a switchback command is issued. The third preset value is greater than the second preset value. In response to the switchback command, the backup steam source isolation door is gradually closed in a segmented slow-closing manner, and the turbine speed fluctuation value is monitored in real time during the closing process. When the absolute value of the speed fluctuation value exceeds the preset fluctuation threshold, the closing action is paused and the current opening is maintained until the absolute value of the speed fluctuation value falls back below the preset fluctuation threshold. After the backup steam source isolation valve is completely closed, the warm-up regulating valve is reopened, and its opening degree is adjusted to restore the superheat of the upstream pipe of the backup steam source isolation valve to a level not lower than the preset superheat threshold.
[0014] By automatically triggering a reverse switchback command when the main steam source pressure rises to the third preset value, an automatic and seamless switch from the backup steam source to the main steam source is achieved. This allows the system to automatically return to the economical operating mode of main steam source supply after load recovery, without manual intervention. The backup steam source isolation valve is gradually closed using a segmented, slow-closing method. During the closing process, the turbine speed fluctuations are monitored in real time, and the closing is paused until recovery if limits are exceeded. This effectively prevents sudden drops or fluctuations in turbine speed caused by excessively rapid closing rates during the switchback process, ensuring the safety and stability of the switchback process.
[0015] By completely closing the backup steam source isolation valve and then reopening the warm-up regulating valve to restore superheat, the backup steam source pipeline is always in a hot standby state that can be put into use at any time, thus achieving continuous maintenance of the hot standby state.
[0016] As a preferred embodiment of the technical solution of the present invention, the step of gradually opening the backup steam source isolation door in a segmented, slow-opening manner specifically includes: The opening stroke of the backup steam source isolation door is divided into multiple stages, and the opening rate corresponding to each stage is set. The backup steam source isolation door is controlled to perform the opening action of the current stage according to the opening rate. After the current stage is completed, determine whether the pressure fluctuation value of the small turbine steam inlet header is less than the set upper limit; If the pressure fluctuation value is less than the set upper limit, the opening action will continue to be performed according to the opening rate of the next stage; If the pressure fluctuation value is greater than or equal to the set upper limit, the switching action from the current stage to the next stage is paused, and the current opening degree is maintained until the pressure fluctuation value falls back below the set upper limit. Then, the opening action is continued according to the opening rate of the next stage.
[0017] By dividing the opening stroke into multiple stages and setting the opening rate for each stage, refined segmented control of the backup steam source isolation door opening process is achieved, avoiding the steam supply shock caused by traditional full-open / full-close operations. After each stage, the pressure fluctuation value is checked for exceeding limits, and the next stage is only initiated when the conditions are met. This achieves closed-loop control based on real-time feedback, enabling simultaneous opening, judgment, and adjustment. This ensures that the steam supply parameters for each stage are within safe limits before proceeding to the next operation, fundamentally eliminating the risk of sudden pressure changes during the opening process.
[0018] As a preferred embodiment of the technical solution of the present invention, the step of gradually closing the backup steam source isolation door in a segmented slow-closing manner in response to the switchback command specifically includes: During the process of closing the backup steam source isolation door, the pressure values of the main steam source and the backup steam source are simultaneously acquired, and the rate of change of the pressure difference between the two is calculated in real time. The rate of change of the pressure difference is compared with a preset rate of change threshold. When the rate of change of the differential pressure is greater than the preset rate of change threshold, it is determined that the current closing rate is too fast, and a rate reduction intervention is performed: the current closing rate of the backup steam source isolation door is reduced, and the reduced closing rate is maintained until the rate of change of the differential pressure falls back to below the preset rate of change threshold. When the rate of change of the differential pressure is less than or equal to the preset rate of change threshold, the current shutdown rate remains unchanged; Throughout the entire process of the segmented slow-closing method, the closing rate of the backup steam source isolation door is dynamically adjusted based on the real-time feedback of the differential pressure change rate, so as to control the differential pressure between the main steam source and the backup steam source to not exceed the preset safe differential pressure threshold, until the backup steam source isolation door is completely closed.
[0019] By calculating the rate of change of the pressure difference between the main steam source and the backup steam source in real time, predictive control of the steam source switching trend is achieved. This elevates the control dimension from traditional pressure value monitoring to pressure change trend monitoring, improving the predictability and accuracy of the control. When the rate of change of the pressure difference exceeds a threshold, the shut-off rate is actively reduced and maintained until the rate of change falls back. This allows the shut-off rate to be dynamically and adaptively adjusted according to real-time operating conditions, upgrading from passive suspension to active speed reduction prevention, thus avoiding drastic fluctuations in steam supply parameters caused by excessively rapid shut-off rates.
[0020] By limiting the pressure difference within the preset safe pressure difference range, the stability of the steam supply quality of the small turbine throughout the reverse switching process is ensured, effectively preventing steam supply interruption or parameter sudden changes caused by excessive pressure difference between the two steam sources.
[0021] As a preferred embodiment of the technical solution of the present invention, it further includes an anti-condensation intervention step: During the opening of the warm pipe branch, the superheat detection unit is used to obtain the steam temperature and steam pressure of the upstream pipe of the backup steam source isolation valve, and the corresponding saturation temperature is calculated based on the current steam pressure; The difference between the steam temperature and the saturation temperature is calculated as the real-time superheat, and the real-time superheat is compared with a preset superheat safety threshold. When the real-time superheat is lower than the preset superheat safety threshold, it is determined that there is a risk of condensation, and the following graded interventions are performed: If the real-time superheat is lower than the preset superheat safety threshold but higher than the first superheat threshold, then the heating pipe regulating valve is controlled to increase its opening according to the first regulating rate; If the real-time superheat is lower than or equal to the first superheat threshold, the warm pipe regulating valve is controlled to increase its opening at a second regulating rate greater than the first regulating rate until the real-time superheat recovers to above the preset superheat safety threshold, or the warm pipe regulating valve reaches its maximum opening position. When the real-time superheat is greater than or equal to the preset superheat safety threshold, it is determined that the condensation risk is eliminated or there is no condensation risk. The warm-up regulating valve is controlled to maintain its current opening to keep the superheat of the upstream pipeline of the backup steam source isolation valve not lower than the preset superheat safety threshold, until the next real-time detection determines that the real-time superheat is lower than the preset superheat safety threshold.
[0022] By employing a graded intervention mechanism that calculates superheat in real time, different adjustment rates are automatically matched according to the severity of the condensation risk when it occurs. This achieves precise control of condensation risk and prevents condensation from forming in the backup steam source pipeline due to changes in environmental conditions during long-term hot standby. Graded intervention avoids the over-adjustment or under-adjustment problems caused by a single adjustment rate.
[0023] By maintaining the current opening degree after the superheat is restored to above the safe threshold and continuously monitoring to form a closed loop, the backup steam source pipeline is always kept in a safe hot standby state, thus avoiding the occurrence of water ingress accidents in the turbine.
[0024] As a preferred embodiment of the technical solution of the present invention, a step of switching security protection is also included: After issuing the steam source switching command, monitor the speed of the turbine and the pressure of the turbine's steam inlet header; When the turbine speed is lower than the minimum allowable speed, or when the turbine inlet steam header pressure is lower than the minimum protection pressure and continues to reach the preset protection time, the backup steam source isolation valve will be stopped immediately, and the turbine trip protection logic will be triggered; the minimum protection pressure is lower than the set upper limit.
[0025] By monitoring the turbine speed and inlet steam header pressure in real time, the system immediately stops opening the isolation door and triggers trip protection in the event of a serious abnormality during the switching process, providing a final safety net for the seamless switching process. The design, with a minimum protection pressure below the set upper limit, minimizes the risk of false tripping while ensuring safety.
[0026] As a preferred embodiment of the technical solution of the present invention, the step of gradually opening the backup steam source isolation door in a segmented, slow-opening manner further includes differential pressure prediction control: Before opening, obtain the pressure difference on both sides of the backup steam source isolation door; When the pressure difference is greater than the preset safe pressure difference threshold, the backup steam source isolation door is controlled to start the opening action at a first preset opening rate, where the first preset opening rate is less than a preset second preset opening rate. When the pressure difference is less than or equal to the preset safe pressure difference threshold, the backup steam source isolation door is controlled to start the opening action at the second preset opening rate.
[0027] Before opening, different opening rates are selected based on the pressure difference on both sides of the isolation door. Predictive intervention is carried out before the opening action is executed, which avoids the pressure impact on the main pipe caused by the instantaneous steam surge due to excessive pressure difference. This forms a multi-layered protection with the pressure fluctuation suspension control during the opening process.
[0028] As a preferred embodiment of the technical solution of the present invention, it further includes an interlock control step for the warming pipe branch and the backup steam source isolation door: During the process of gradually opening the backup steam source isolation door in a segmented and slow manner, the steam inlet suppression interlock is executed: the opening of the warm-up regulating valve is prohibited from being increased, except when the anti-condensation intervention step is triggered, until the backup steam source isolation door is fully opened and the pressure of the small turbine inlet steam header is stable within the preset range, and then the steam inlet suppression interlock is released. During the process of gradually closing the backup steam source isolation valve in a segmented, slow-closing manner, an anti-backflow interlock is executed: before the backup steam source isolation valve is completely closed, the warm-up regulating valve is kept in the closed state, or the warm-up regulating valve is kept at the safe opening determined by the anti-condensation intervention step, until the backup steam source isolation valve is completely closed. Then, the anti-backflow interlock is released and the warm-up regulating valve is reopened, restoring the control logic of the anti-condensation intervention step.
[0029] By using an inlet steam suppression interlock, the warm-up regulating valve is prevented from opening further during the opening of the standby steam source isolation valve. This prevents excessive steam supply from both steam sources simultaneously, which could cause steam supply parameter instability and ensures the stability of the turbine inlet steam parameters during the switchover process. By using an anti-backflow interlock, the warm-up regulating valve is kept closed or at a safe opening during the closing of the standby steam source isolation valve. This prevents main steam source steam from flowing back into the standby steam source pipeline before the standby steam source isolation valve is fully closed, or prevents steam from the warm-up branch pipeline from interfering with the steam supply during the isolation valve closure process. This ensures the safety of the switchback process and the effectiveness of pipeline isolation.
[0030] As can be seen from the above technical solutions, this application has the following advantages: By setting up a warm-up branch and connecting the outlet end to the low-pressure heater, the backup steam supply pipeline is kept in a hot standby state during non-operational periods, eliminating the need for temporary warm-up condensate drainage and achieving immediate availability of the backup steam source; simultaneously, the heat of the warm-up steam is recovered and utilized, avoiding heat loss associated with traditional condensate drainage methods. The sequential arrangement of the check valve and the backup steam source isolation valve ensures that steam backflow will not occur due to pipeline pressure changes while the isolation valve is closed, improving system safety. Attached Figure Description
[0031] To more clearly illustrate the technical solution of this application, the accompanying drawings used in the description will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0032] Figure 1 A connection block diagram of the system provided in an embodiment of the present invention.
[0033] Figure 2 This is a flowchart illustrating the method provided in an embodiment of the present invention.
[0034] In the diagram, 1-steam-driven feedwater pump, 2-small turbine, 3-small turbine inlet steam header, 4-main steam source, 5-main steam source air supply line, 6-standby steam source, 7-standby steam source air supply line, 8-warming branch line, 9-low-pressure heater, 31-small turbine inlet steam regulating valve, 32-small turbine quick-closing valve, 71-check valve, 72-standby steam source isolation valve, 81-warming regulating valve. Detailed Implementation
[0035] To make the purpose, features, and advantages of this application more apparent and understandable, specific embodiments and accompanying drawings will be used to clearly and completely describe the technical solution protected by this application. Obviously, the embodiments described below are only some embodiments of this application, and not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.
[0036] Unless otherwise defined, all technical and scientific terms used in this application have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used in this application and in the specification of this invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.
[0037] like Figure 1 As shown, this embodiment of the invention provides a steam-driven feedwater pump steam source seamless switching system, including a steam-driven feedwater pump 1 driven by a small engine, a main steam source 4, a backup steam source 6, and a warm-up branch 8; The main steam source 4 is connected to the turbine inlet steam header 3 via the main steam source supply pipeline 5, and the standby steam source 6 is connected to the turbine inlet steam header 3 via the standby steam source supply pipeline 7. The main steam source 4 is the fourth stage extraction steam from the turbine, which supplies steam to the turbine 2 under normal operating conditions. The standby steam source 6 is auxiliary steam, which is switched to supply steam when the unit load decreases or the fourth stage extraction steam pressure is insufficient.
[0038] A check valve 71 and a backup steam source isolation valve 72 are sequentially installed along the steam supply direction on the backup steam source supply pipeline 7. The check valve 71 prevents the steam in the backup steam source supply pipeline 7 from flowing back in the opposite direction, and the backup steam source isolation valve 72 is used to isolate the backup steam source 6 during normal operation.
[0039] The inlet of the warm-up pipe branch 8 is connected to the upstream pipe of the standby steam source isolation valve 72, and the outlet is connected to the low-pressure heater 9 (in this embodiment, it is the No. 5 low-pressure heater, which uses the fifth stage extraction steam of the steam turbine). A warm-up pipe regulating valve 81 is installed on the warm-up pipe branch 8. The steam flow rate of the warm-up pipe branch 8 is controlled by the warm-up pipe regulating valve 81, so that a small amount of steam continuously flows through the upstream pipe of the standby steam source isolation valve 72 to continuously warm up this section of the pipe and keep it in a hot standby state. At the same time, the warm-up steam eventually enters the low-pressure heater 9 to heat the condensate and recover heat.
[0040] An overheat detection unit is installed on the upstream pipeline of the backup steam source isolation valve 72 to detect the superheat of the steam at that location. The overheat detection unit can be a combination of a temperature sensor and a pressure sensor. By detecting the steam temperature and pressure, it calculates the saturation temperature at that pressure to obtain the superheat: Superheat = Steam temperature - Saturation temperature.
[0041] A main steam source pressure detection unit is installed on the main steam source supply pipeline 5 to detect the pressure of the main steam source 4 in real time. A small turbine inlet steam header pressure detection unit is installed at the small turbine inlet steam header 3 to detect the pressure of the steam header entering the small turbine.
[0042] The backup steam source isolation valve, warm-up regulating valve, superheat detection unit, main steam source pressure detection unit, and small turbine inlet steam header pressure detection unit are each connected to a controller. The controller can be a DCS or a PLC, used to receive the detection signals from each detection unit and send control commands to each actuator according to preset logic. In this embodiment, the controller has a pre-stored saturated steam pressure-temperature lookup table based on the IAPWS-IF97 standard, used to calculate the corresponding saturated temperature by interpolation based on the measured current pressure value.
[0043] In one specific implementation, the outlet end of the backup steam supply pipeline 7 is connected to the main steam supply pipeline 5, and the connection point is located downstream of the turbine quick-closing valve 32 and upstream of the turbine inlet regulating valve 31. The steam from the two steam sources merges at this connection point and then enters the turbine 2 via the turbine inlet regulating valve 31. The connection of the outlet end of the backup steam supply pipeline 7 to the main steam supply pipeline 5 means that the backup steam supply pipeline 7 connects to the main steam supply pipeline 5 at the aforementioned connection point, allowing the steam from the backup steam source 6 to merge with the steam from the main steam source 4 at this location. The turbine quick-closing valve 32 is an emergency shut-off valve, normally fully open, and only closes in case of a fault to quickly cut off the steam supply. The turbine inlet regulating valve 31 is a continuous regulating valve used to adjust the steam flow rate entering the turbine to control the turbine speed. The point where the two steam sources converge is located downstream of the small turbine quick-closing valve 32 and upstream of the small turbine inlet steam regulating valve 31. This allows the backup steam source 6 to be put into operation without passing through the quick-closing valve, reducing flow resistance. Furthermore, after the two steam sources converge, they are regulated together by the small turbine inlet steam regulating valve before entering the small turbine, which helps to maintain the stability of the inlet steam parameters.
[0044] like Figure 2 As shown in the figure, this embodiment of the invention also provides a control method for seamless switching of steam source for a steam-driven feedwater pump, applied to the system described in the above embodiment. The method includes the following steps: Step 1: During the normal steam supply period of the unit from the main steam source, open the warm-up branch, and adjust the warm-up regulating valve on the warm-up branch to allow steam to continuously flow through the upstream pipe of the standby steam source isolation valve, and monitor the superheat of the steam at that point in real time, and maintain the superheat not lower than the preset superheat threshold by adjusting the opening of the warm-up regulating valve. By adjusting the warm-up regulating valve on the warm-up branch, a small amount of steam continuously flows through the upstream pipe of the backup steam source isolation valve, continuously warming up this pipe section. The superheat detection unit monitors the superheat of the steam at this location in real time, and the controller maintains the superheat at this location above a preset superheat threshold by adjusting the opening of the warm-up regulating valve. The preset superheat threshold can be set according to the specific operating conditions of the backup steam source pipeline; in this embodiment, it is preferably 50°C. When the detected superheat is below 50°C, the controller issues a command to increase the opening of the warm-up regulating valve, increasing the warm-up steam flow rate, so that the superheat rises back above 50°C; when the superheat is above 50°C, the opening of the warm-up regulating valve can be appropriately reduced to save steam.
[0045] Step 2: Monitor the pressure and rate of change of the main steam source in real time. When the rate of decrease of the main steam source pressure is greater than the preset rate threshold and the main steam source pressure is higher than the second preset value, increase the opening of the warm-up regulating valve to increase the steam flow through the upstream pipeline. The main steam source pressure detection unit continuously collects pressure signals from the main steam source supply pipeline, and the controller calculates the rate of pressure change over time. When the rate of pressure drop in the main steam source exceeds a preset threshold, and the current main steam source pressure is still higher than a second preset value, the controller determines that the unit is about to enter a low-load operating condition and increases the opening of the warm-up regulating valve in advance, thereby increasing the steam flow through the upstream pipeline of the standby steam source isolation valve. The purpose of this pre-compensation measure is to further improve the steam quality and superheat of the standby pipeline before the standby steam source is officially put into operation, in order to compensate for the decrease in standby quality caused by the impending pressure drop.
[0046] Step 3: When the pressure of the main steam source drops to the second preset value, a steam source switching command is issued; Step 4: In response to the steam source switching command, the backup steam source isolation door is gradually opened in a segmented slow-opening manner. During the opening process, the pressure fluctuation value of the small turbine inlet steam header is monitored in real time. When the pressure fluctuation value exceeds the set upper limit, the opening action is paused and the current opening degree is maintained until the pressure fluctuation value falls back below the set upper limit. During the opening process, the pressure detection unit of the turbine inlet steam header monitors the pressure fluctuation value of the turbine inlet steam header in real time. When the pressure fluctuation value exceeds the set upper limit, the controller pauses the opening action and maintains the current opening degree. Opening continues only after the pressure fluctuation value drops below the set upper limit. The segmented slow opening is implemented by dividing the opening stroke of the backup steam source isolation valve into multiple stages. Each stage opens a certain stroke, and the header pressure is checked after each stage is completed. The next stage is only entered after the pressure is confirmed to be stable. This ensures that the backup steam source is gradually activated, avoiding steam supply shock caused by a one-time opening.
[0047] Step 5: After the backup steam source isolation valve is fully opened and the pressure of the turbine inlet steam header is stable within the preset range, close the warm-up regulating valve to stop the steam flow in the warm-up branch and complete the switch from the main steam source to the backup steam source.
[0048] In some embodiments, a reverse cutback step is also included: As the unit load recovers, the main steam source pressure gradually returns to normal. While the unit is supplied with steam from the standby steam source, the controller continuously monitors the main steam source pressure. When the main steam source pressure rises to the third preset value, the controller issues a switchback command, initiating the reverse switchback process. The third preset value is greater than the second preset value.
[0049] In response to the switchback command, the controller gradually closes the backup steam source isolation door using a segmented, slow-closing method. The implementation of segmented, slow-closing is similar to segmented, slow-opening: the closing stroke is divided into multiple stages, each stage closing a certain stroke, and the operating status of the turbine is checked after each stage is completed. Only after confirming stability can the next stage be entered.
[0050] During shutdown, the turbine speed detection unit monitors the turbine speed fluctuation value in real time. When the absolute value of the speed fluctuation value exceeds the preset fluctuation threshold, the controller pauses the shutdown action and maintains the current opening. Shutdown continues only after the absolute value of the speed fluctuation value falls back below the preset fluctuation threshold. This method prevents significant fluctuations in turbine speed caused by steam source switching during shutdown.
[0051] After the backup steam source isolation valve is completely closed, the controller reopens the warm-up regulating valve and adjusts its opening to restore the superheat of the upstream pipeline of the backup steam source isolation valve to a level not lower than the preset superheat threshold, so that the backup steam source pipeline re-enters the hot standby state and waits for the next switchover.
[0052] As a specific implementation of segmented slow opening, the opening stroke of the backup steam source isolation door is divided into multiple stages, and the opening rate corresponding to each stage is set. Specifically, in this embodiment, it is divided into 5 stages: the first stage is 5% / s, the second stage is 8% / s, the third stage is 10% / s, the fourth stage is 12% / s, and the fifth stage is 15% / s.
[0053] The controller controls the standby steam source isolation valve to open according to the opening rate of the current stage. After the current stage is completed, the controller determines whether the pressure fluctuation value of the turbine inlet steam header is less than the set upper limit. If the pressure fluctuation value is less than the set upper limit, the opening action continues according to the opening rate of the next stage; if the pressure fluctuation value is greater than or equal to the set upper limit, the switching action from the current stage to the next stage is paused, and the current opening degree is maintained until the pressure fluctuation value falls below the set upper limit, and then the opening action continues according to the opening rate of the next stage.
[0054] Through the above controls, it is ensured that the pressure of the turbine inlet steam header remains within a safe range throughout the entire opening process of the backup steam source isolation valve, thus achieving seamless switching.
[0055] During the reverse switchback process, the controller synchronously acquires the pressure values of the main steam source and the backup steam source, and calculates the pressure difference ΔP between the two and its rate of change d(ΔP) / dt in real time.
[0056] Compare the rate of change of differential pressure with a preset rate of change threshold: When the rate of change of differential pressure exceeds a preset rate of change threshold, the current closing rate is determined to be too fast, and a rate reduction intervention is executed: the controller reduces the current closing rate of the backup steam source isolation door. In this embodiment, the current rate is reduced to 50%~70% of the original rate, and the reduced closing rate is maintained until the rate of change of differential pressure falls back below the preset rate of change threshold. When the rate of change of differential pressure is less than or equal to the preset rate of change threshold, the current closing rate remains unchanged.
[0057] Throughout the segmented slow-closing process, the controller dynamically adjusts the closing rate of the backup steam source isolation valve based on real-time feedback of the differential pressure change rate, so as to control the differential pressure between the main steam source and the backup steam source to not exceed the preset safe differential pressure threshold, until the backup steam source isolation valve is completely closed.
[0058] By using the aforementioned feedforward control, the control parameter is increased from the traditional pressure value to the rate of pressure difference change, thereby achieving predictive control of the steam source switching trend and avoiding drastic fluctuations in steam supply parameters caused by excessively fast shutdown rates.
[0059] In some embodiments, an anti-condensation intervention step is also included: During the opening of the warm pipe branch, the superheat detection unit is used to obtain the steam temperature and steam pressure of the upstream pipe of the backup steam source isolation valve, and the corresponding saturation temperature is calculated based on the current steam pressure; The controller calculates the difference between the steam temperature and the saturation temperature as the real-time superheat, and compares the real-time superheat with a preset superheat safety threshold. When the real-time superheat is lower than the preset superheat safety threshold, it is determined that there is a risk of condensation, and the following graded interventions are performed: If the real-time superheat is lower than the preset superheat safety threshold but higher than the first superheat threshold, it is determined to be a slight risk of condensation. The warm pipe regulating valve is controlled to increase its opening according to the first regulating rate, and the warm pipe steam flow is slowly increased. If the real-time superheat is lower than or equal to the first superheat threshold, it is determined to be a severe condensation risk. The warm-up regulating valve is controlled to increase its opening at a second regulating rate greater than the first regulating rate to quickly increase the warm-up steam flow until the real-time superheat recovers to above the preset superheat safety threshold, or the warm-up regulating valve reaches its maximum opening position.
[0060] Once the superheat recovers, the controller gradually reduces the opening of the warm-up regulating valve to stabilize the superheat near the preset superheat safety threshold, thus avoiding over-adjustment.
[0061] When the real-time superheat is greater than or equal to the preset superheat safety threshold, it is determined that the condensation risk is eliminated or there is no condensation risk. The controller controls the warm-up regulating valve to keep the current opening unchanged so as to maintain the superheat of the upstream pipeline of the standby steam source isolation valve at no lower than the preset superheat safety threshold until the next real-time detection determines that the real-time superheat is lower than the preset superheat safety threshold.
[0062] Through the aforementioned graded intervention mechanism, different adjustment rates are automatically matched according to the severity of condensation risk, achieving precise control of condensation risk while avoiding over-adjustment or under-adjustment problems caused by a single adjustment rate.
[0063] In some embodiments, a step of switching security protections is also included: After issuing the steam source switching command, monitor the speed of the turbine and the pressure of the turbine's steam inlet header; When the speed of the turbine is lower than the minimum allowable speed, or when the pressure of the turbine's steam inlet header is lower than the minimum protection pressure and continues to reach the preset protection time, the controller immediately stops opening the backup steam source isolation door and triggers the turbine trip protection logic.
[0064] When the minimum protection pressure is lower than the set upper limit, a gradient protection mechanism is formed: when the pressure fluctuation exceeds the limit, the start-up is suspended; when the pressure continues to drop to the minimum protection pressure, the trip protection is triggered, thus avoiding false tripping to the greatest extent possible while ensuring safety.
[0065] In some embodiments, the step of gradually opening the backup steam source isolation door in a segmented, slow-opening manner further includes differential pressure prediction control: Before gradually opening the backup steam source isolation door in a segmented, slow-opening manner, the controller obtains the pressure difference on both sides of the backup steam source isolation door.
[0066] When the differential pressure exceeds the preset safe differential pressure threshold, the controller controls the backup steam source isolation door to start the opening action at a first preset opening rate, which is less than the second preset opening rate during normal opening.
[0067] When the pressure difference is less than or equal to the preset safe pressure difference threshold, the controller controls the backup steam source isolation door to start the opening action at the second preset opening rate.
[0068] By using the above differential pressure prediction control, different opening rates are selected according to the differential pressure before opening, thus avoiding the pressure shock to the main pipe caused by the steam rushing in at the moment of opening due to excessive differential pressure. This forms a multi-layered protection with the pressure fluctuation suspension control during the opening process.
[0069] In some embodiments, an interlock control step is also included between the warm pipe branch and the backup steam source isolation door: During the process of gradually opening the backup steam source isolation valve in a segmented and slow manner, the controller executes the steam inlet suppression interlock: it prohibits increasing the opening of the warm-up regulating valve, except when the anti-condensation intervention step is triggered. That is, when the anti-condensation intervention requires increasing the opening of the warm-up regulating valve, the anti-condensation intervention is executed first until the backup steam source isolation valve is fully opened and the pressure of the small turbine inlet steam header is stable within the preset range, and then the steam inlet suppression interlock is released.
[0070] During the process of gradually closing the standby steam source isolation valve in a segmented, slow-closing manner, the controller performs an anti-backflow interlock: before the standby steam source isolation valve is completely closed, the warm-up regulating valve is kept closed, or the warm-up regulating valve is kept at the safe opening determined by the anti-condensation intervention step, that is, the opening determined by adjusting the real-time superheat in the anti-condensation intervention step, which can maintain the superheat not lower than the safe threshold, until the standby steam source isolation valve is completely closed, the anti-backflow interlock is released and the warm-up regulating valve is reopened, restoring the control logic of the anti-condensation intervention step.
[0071] The above interlock control prevents excessive steam supply from both steam sources at the same time, which could cause steam supply parameter disorder, and prevents steam from the main steam source from flowing back into the backup steam source pipeline before the backup steam source isolation valve is fully closed.
[0072] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.
Claims
1. A steam source seamless switching system for a steam-driven feedwater pump, characterized in that, This includes a steam-driven feedwater pump, main steam source, backup steam source, and warm-up pipe branch line, all driven by a small turbine. The main steam source is connected to the turbine inlet steam header through the main steam source supply pipeline, and the backup steam source is connected to the turbine inlet steam header through the backup steam source supply pipeline. The backup steam supply pipeline is equipped with a check valve and a backup steam source isolation valve in sequence along the steam supply direction. The inlet end of the warming pipe branch is connected to the upstream pipe of the backup steam source isolation valve, and the outlet end is connected to the low-pressure heater. A warming pipe regulating valve is installed on the warming pipe branch. An overheat detection unit is installed on the upstream pipeline of the backup steam source isolation door, a main steam source pressure detection unit is installed on the main steam source supply pipeline, and a small turbine steam inlet header pressure detection unit is installed at the small turbine steam inlet header. The backup steam source isolation door, the warm-up regulating valve, the superheat detection unit, the main steam source pressure detection unit, and the small turbine inlet steam header pressure detection unit are each used to connect to a controller signal.
2. The steam source seamless switching system for the steam-driven feedwater pump according to claim 1, characterized in that, The outlet end of the backup steam supply pipeline is connected to the main steam supply pipeline, and the connection point is located downstream of the small turbine quick-closing valve and upstream of the small turbine inlet steam regulating valve. After converging at the connection point, the steam enters the small turbine through the small turbine inlet steam regulating valve.
3. A control method for seamless switching of steam source in a steam-driven feedwater pump, applied to the system as described in claim 1 or 2, characterized in that, The method includes the following steps: During the normal steam supply period of the unit from the main steam source, the warm-up branch is opened. By adjusting the warm-up regulating valve on the warm-up branch, steam is continuously flowed through the upstream pipe of the standby steam source isolation valve. The superheat of the steam at this point is detected in real time. The superheat is maintained at no less than the preset superheat threshold by adjusting the opening of the warm-up regulating valve. The pressure and rate of change of the main steam source are monitored in real time. When the rate of decrease of the main steam source pressure is greater than a preset rate threshold and the main steam source pressure is higher than a second preset value, the opening of the warm-up regulating valve is increased to increase the steam flow through the upstream pipeline. When the pressure of the main steam source drops to the second preset value, a steam source switching command is issued; In response to the steam source switching command, the backup steam source isolation door is gradually opened in a segmented and slow-opening manner. During the opening process, the pressure fluctuation value of the small turbine inlet steam header is monitored in real time. When the pressure fluctuation value exceeds the set upper limit, the opening action is paused and the current opening degree is maintained until the pressure fluctuation value falls back below the set upper limit. Once the backup steam source isolation valve is fully opened and the pressure of the turbine inlet steam header is stable within the preset range, the warm-up regulating valve is closed to stop the steam flow in the warm-up branch, thus completing the switch from the main steam source to the backup steam source.
4. The control method for seamless switching of steam source in a steam-driven feedwater pump according to claim 3, characterized in that, It also includes a reverse cutback step: During the period when the unit is supplied with steam from the backup steam source, the pressure of the main steam source is monitored in real time. When the pressure of the main steam source rises back to the third preset value, a switchback command is issued. The third preset value is greater than the second preset value. In response to the switchback command, the backup steam source isolation door is gradually closed in a segmented slow-closing manner, and the turbine speed fluctuation value is monitored in real time during the closing process. When the absolute value of the speed fluctuation value exceeds the preset fluctuation threshold, the closing action is paused and the current opening is maintained until the absolute value of the speed fluctuation value falls back below the preset fluctuation threshold. After the backup steam source isolation valve is completely closed, the warm-up regulating valve is reopened, and its opening degree is adjusted to restore the superheat of the upstream pipe of the backup steam source isolation valve to a level not lower than the preset superheat threshold.
5. The control method for seamless switching of steam source in a steam-driven feedwater pump according to claim 3, characterized in that, The steps for gradually opening the backup steam source isolation door in a segmented, slow-opening manner specifically include: The opening stroke of the backup steam source isolation door is divided into multiple stages, and the opening rate corresponding to each stage is set. The backup steam source isolation door is controlled to perform the opening action of the current stage according to the opening rate. After the current stage is completed, determine whether the pressure fluctuation value of the small turbine steam inlet header is less than the set upper limit; If the pressure fluctuation value is less than the set upper limit, the opening action will continue to be performed according to the opening rate of the next stage; If the pressure fluctuation value is greater than or equal to the set upper limit, the switching action from the current stage to the next stage is paused, and the current opening degree is maintained until the pressure fluctuation value falls back below the set upper limit. Then, the opening action is continued according to the opening rate of the next stage.
6. The control method for seamless switching of steam source in a steam-driven feedwater pump according to claim 4, characterized in that, In response to the switchback command, the steps of gradually closing the backup steam source isolation door in a segmented, slow-closing manner specifically include: During the process of closing the backup steam source isolation door, the pressure values of the main steam source and the backup steam source are simultaneously acquired, and the rate of change of the pressure difference between the two is calculated in real time. The rate of change of the pressure difference is compared with a preset rate of change threshold. When the rate of change of the differential pressure is greater than the preset rate of change threshold, it is determined that the current closing rate is too fast, and a rate reduction intervention is performed: the current closing rate of the backup steam source isolation door is reduced, and the reduced closing rate is maintained until the rate of change of the differential pressure falls back to below the preset rate of change threshold. When the rate of change of the differential pressure is less than or equal to the preset rate of change threshold, the current shutdown rate remains unchanged; Throughout the entire process of the segmented slow-closing method, the closing rate of the backup steam source isolation door is dynamically adjusted based on the real-time feedback of the differential pressure change rate, so as to control the differential pressure between the main steam source and the backup steam source to not exceed the preset safe differential pressure threshold, until the backup steam source isolation door is completely closed.
7. The control method for seamless switching of steam source in a steam-driven feedwater pump according to claim 4, characterized in that, It also includes anti-condensation intervention steps: During the opening of the warm pipe branch, the superheat detection unit is used to obtain the steam temperature and steam pressure of the upstream pipe of the backup steam source isolation valve, and the corresponding saturation temperature is calculated based on the current steam pressure; The difference between the steam temperature and the saturation temperature is calculated as the real-time superheat, and the real-time superheat is compared with a preset superheat safety threshold. When the real-time superheat is lower than the preset superheat safety threshold, it is determined that there is a risk of condensation, and the following graded interventions are performed: If the real-time superheat is lower than the preset superheat safety threshold but higher than the first superheat threshold, then the heating pipe regulating valve is controlled to increase its opening according to the first regulating rate; If the real-time superheat is lower than or equal to the first superheat threshold, the warm pipe regulating valve is controlled to increase its opening at a second regulating rate greater than the first regulating rate until the real-time superheat recovers to above the preset superheat safety threshold, or the warm pipe regulating valve reaches its maximum opening position. When the real-time superheat is greater than or equal to the preset superheat safety threshold, it is determined that the condensation risk is eliminated or there is no condensation risk. The warm-up regulating valve is controlled to maintain its current opening to keep the superheat of the upstream pipeline of the backup steam source isolation valve not lower than the preset superheat safety threshold, until the next real-time detection determines that the real-time superheat is lower than the preset superheat safety threshold.
8. The control method for seamless switching of steam source in a steam-driven feedwater pump according to claim 3, characterized in that, It also includes switching security protection steps: After issuing the steam source switching command, monitor the speed of the turbine and the pressure of the turbine's steam inlet header; When the turbine speed is lower than the minimum allowable speed, or when the turbine inlet steam header pressure is lower than the minimum protection pressure and continues to reach the preset protection time, the backup steam source isolation valve will be stopped immediately, and the turbine trip protection logic will be triggered; the minimum protection pressure is lower than the set upper limit.
9. The control method for seamless switching of steam source in a steam-driven feedwater pump according to claim 3, characterized in that, The step of gradually opening the backup steam source isolation door in a segmented, slow-opening manner also includes differential pressure prediction control: Before opening, obtain the pressure difference on both sides of the backup steam source isolation door; When the pressure difference is greater than the preset safe pressure difference threshold, the backup steam source isolation door is controlled to start the opening action at a first preset opening rate, where the first preset opening rate is less than a preset second preset opening rate. When the pressure difference is less than or equal to the preset safe pressure difference threshold, the backup steam source isolation door is controlled to start the opening action at the second preset opening rate.
10. The control method for seamless switching of steam source in a steam-driven feedwater pump according to claim 7, characterized in that, It also includes the interlock control steps between the heating pipe branch and the backup steam source isolation door: During the process of gradually opening the backup steam source isolation door in a segmented and slow manner, the steam inlet suppression interlock is executed: the opening of the warm-up regulating valve is prohibited from being increased, except when the anti-condensation intervention step is triggered, until the backup steam source isolation door is fully opened and the pressure of the small turbine inlet steam header is stable within the preset range, and then the steam inlet suppression interlock is released. During the process of gradually closing the backup steam source isolation valve in a segmented, slow-closing manner, an anti-backflow interlock is executed: before the backup steam source isolation valve is completely closed, the warm-up regulating valve is kept in the closed state, or the warm-up regulating valve is kept at the safe opening determined by the anti-condensation intervention step, until the backup steam source isolation valve is completely closed. Then, the anti-backflow interlock is released and the warm-up regulating valve is reopened, restoring the control logic of the anti-condensation intervention step.