Steam turbine shaft seal system based on overflow steam recovery and emergency steam supply method

Abstract

The application relates to a steam turbine shaft seal steam supply technology field, in particular to a steam turbine shaft seal system and an emergency steam supply method based on overflow steam recovery, wherein the system comprises a high-medium pressure shaft seal subsystem, a low pressure shaft seal subsystem, a condenser, a high-medium pressure shaft seal overflow pipeline, an emergency steam supply pipeline which is communicated with the high-medium pressure shaft seal overflow pipeline at one end and communicated with the front end of a low pressure shaft seal steam inlet valve at the other end, and the emergency steam supply pipeline is connected with an overflow isolation valve and an emergency booster pump in series. The application sets up the emergency steam supply pipeline between the high-medium pressure shaft seal overflow pipeline and the low pressure shaft seal steam supply pipeline, and cooperates with a DCS controller to automatically execute preset emergency control logic, so that the high-medium pressure shaft seal overflow steam which is originally discharged to the condenser can be quickly supplied to the low pressure shaft seal after auxiliary steam interruption, manual operation is not needed, the emergency response time is greatly shortened, and the possibility of shaft seal failure accidents caused by operation delay is reduced.

Description

Technical Field

[0001] This application relates to the field of steam turbine shaft seal technology, and in particular to a steam turbine shaft seal system and emergency steam supply method based on overflow steam recovery. Background Technology

[0002] The turbine shaft sealing system is one of the key auxiliary systems for ensuring the safe and stable operation of the unit. Its core functions are: during turbine start-up and shutdown, when the internal pressure of the cylinder is lower than the external atmospheric pressure, it prevents air from leaking into the cylinder through the dynamic and static gap between the rotor and the cylinder, thereby avoiding deterioration of condenser back pressure or even rotor dynamic and static rubbing accidents; during normal turbine operation, when the internal pressure of the cylinder is higher than atmospheric pressure, it prevents high-temperature steam in the cylinder from leaking outward along the shaft end gap, thereby reducing working fluid loss and preventing steam from entering the bearing chamber and causing lubricating oil emulsification.

[0003] Existing turbine shaft sealing systems are mainly divided into high-pressure and intermediate-pressure shaft sealing units and low-pressure shaft sealing units, with some differences in their steam supply modes. The high-pressure and intermediate-pressure shaft sealing units can achieve self-sealing operation by relying on steam leakage from the high-pressure cylinder's own shaft seals during unit operation under load, exhibiting high steam supply redundancy. Excess high-temperature, high-quality steam is mostly discharged directly into the condenser through the overflow pipeline without being recovered and utilized. In contrast, the low-pressure shaft sealing unit relies solely on the external auxiliary steam system for its steam supply. The auxiliary steam from the plant is uniformly pressurized by an external heat source and delivered to the auxiliary steam headers of each unit. If the auxiliary equipment of the auxiliary steam system malfunctions (such as temperature runaway) or the external steam source is interrupted, it will lead to insufficient or even complete interruption of steam supply to the low-pressure shaft seals. This will cause external cold air to directly flow back into the low-pressure cylinder, not only disrupting the condenser vacuum but also potentially causing rapid cooling and deformation of the low-pressure cylinder components, seriously threatening the safe operation of the unit.

[0004] Currently, the main countermeasures for auxiliary steam interruption include: adjusting the unit's operating mode, closing the auxiliary steam inlet valve of the unit-type unit, and breaking the shaft seal vacuum of the standby unit; or modifying the pipeline to extract steam from the intermediate-pressure superheater as a backup steam source. However, these measures involve cumbersome procedures, require complex coordination between control panel and local operations, demand highly skilled operators, and are prone to escalation of accidents due to delays or misoperations. There is a lack of an automatic and rapid emergency steam supply mechanism. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this application provides a turbine shaft seal system and emergency steam supply method based on overflow steam recovery, which solves the technical problems of existing low-pressure shaft seal systems, such as high dependence on external auxiliary steam, lack of rapid switching means when auxiliary steam is interrupted, cumbersome and time-consuming processing steps, and easy occurrence of unit trip accidents.

[0006] This application provides a turbine shaft seal system and emergency steam supply method based on overflow steam recovery, including an intermediate-high pressure shaft seal subsystem, a low pressure shaft seal system, an auxiliary steam supply header, and a condenser. The intermediate-high pressure shaft seal system includes an intermediate-high pressure shaft seal overflow pipeline connected to the condenser. Under normal unit operation, the intermediate-high pressure shaft seal system can achieve self-sealing steam supply through high-pressure cylinder leakage. The system also includes: An emergency steam supply pipeline has one end connected to the high-pressure shaft seal overflow pipeline and the other end connected to the front end of the steam inlet valve of the low-pressure shaft seal subsystem. The emergency steam supply pipeline is equipped with an overflow isolation valve and an emergency booster pump connected in series along its medium flow direction. The high-pressure shaft seal overflow pipeline is equipped with a high-pressure shaft seal overflow valve, and the steam inlet of the emergency steam supply pipeline is located downstream of the high-pressure shaft seal overflow valve. The emergency steam supply pipeline can divert and transport the overflow steam from the high-pressure shaft seal subsystem to the low-pressure shaft seal subsystem in the event of an interruption in the external auxiliary steam supply.

[0007] Preferably, the high-pressure shaft seal overflow pipeline is further provided with an overflow regulating valve, and the overflow regulating valve is located downstream of the emergency steam supply pipeline access point, used to regulate the amount of steam discharged into the condenser under accident conditions, so as to stabilize the pressure in the high-pressure shaft seal subsystem.

[0008] Preferably, the downstream section of the steam inlet valve of the low-pressure shaft seal subsystem is also provided with a low-pressure shaft seal desuperheating pipeline connected to an external cooling water source. A water regulating valve is provided on the low-pressure shaft seal desuperheating pipeline, and the external cooling water source is the unit's self-condensing water network or an external cooling water network.

[0009] Preferably, the steam supply pressure of the high-pressure shaft seal system is 3.5 kPa, and the steam supply temperature is the same as the external auxiliary steam temperature; The steam supply temperature of the low-pressure shaft seal system is 150℃±5℃, and the steam supply pressure is 9kPa. A temperature acquisition transmitter is installed at the steam supply line of the low-pressure shaft seal system, and a pressure acquisition transmitter is installed at the steam supply lines of both the low-pressure shaft seal system and the high- and medium-pressure shaft seal system.

[0010] Preferably, the system further includes a DCS (Distributed Control System) controller, which is configured to automatically execute the following emergency control procedure when the steam supply pressure at the steam supply line of the low-pressure shaft seal subsystem is detected to be lower than a preset trigger threshold: Close the valve connecting the auxiliary steam supply header to the external auxiliary steam system to cut off the external auxiliary steam supply. Increase the operating load of the unit and close the power passage from the high-pressure cylinder shaft seal leakage in the high-pressure and intermediate-pressure shaft seal subsystem to the low-pressure cylinder in the low-pressure shaft seal system; Open the overflow isolation valve and start the emergency booster pump to divert the high- and medium-pressure shaft seal overflow steam that was originally discharged into the condenser to the low-pressure shaft seal subsystem; The operating power of the emergency booster pump and the opening of the high-pressure shaft seal overflow valve and overflow regulating valve are adjusted in conjunction with the temperature and pressure acquisition transmitters. In addition, the steam supply pressure and steam supply temperature of the high-pressure shaft seal subsystem and the low-pressure shaft seal subsystem are stabilized to their respective target set values ​​in conjunction with the water regulating valve. The preset trigger threshold is greater than or equal to zero and less than or equal to half of the steam supply pressure of the low-pressure shaft seal subsystem.

[0011] This application also provides an emergency steam supply method for a turbine shaft seal system based on overflow steam recovery as described in any of the above claims, comprising: The inlet steam pressure of the low-pressure shaft seal subsystem is collected in real time by a pressure acquisition transmitter. When the pressure acquisition transmitter detects that the inlet steam pressure of the low-pressure shaft seal subsystem has dropped to a preset trigger threshold, it will trigger the auxiliary steam interruption program and the DCS controller will control the start of the emergency control program. The unit automatically closes the valve connecting it to the external auxiliary steam system and increases the unit's operating load to full load to increase the steam production at the high and medium pressure shaft seal system. Open the overflow isolation valve and start the emergency booster pump to switch the overflow steam from the high and medium pressure shaft seal from being discharged to the condenser to being discharged to the steam inlet of the low pressure shaft seal subsystem; The system works in conjunction with temperature and pressure transmitters to regulate the operating power of the emergency booster pump and the opening of the high and medium pressure shaft seal overflow valve. It also regulates the pressure of the overflow steam after switching and works with the water regulating valve to control its pressure and temperature to meet the sealing requirements of the low pressure shaft seal. Finally, it supplies steam to the low pressure shaft seal subsystem after the auxiliary steam interruption procedure is triggered.

[0012] Preferably, during the operation of the emergency control program, the valve connecting the unit to the external auxiliary steam system remains closed, and all steam supply to the low-pressure shaft seal subsystem is supplied by the high- and medium-pressure shaft seal overflow steam transported by the emergency steam supply pipeline.

[0013] Preferably, the specific steps for switching the overflow steam from the high-pressure shaft seal to the condenser and then to the inlet of the low-pressure shaft seal subsystem include: Open the overflow isolation valve installed on the emergency steam supply pipeline to switch the discharge route of the overflow steam from the high and medium pressure shaft seal to the condenser and then to the low pressure shaft seal inlet. Start the emergency booster pump to pressurize the overflow steam in the discharge route. Adjust the overflow valve of the high-pressure shaft seal and simultaneously adjust the overflow regulating valve to maintain the stability of the main pipe pressure in the high-pressure shaft seal subsystem; The overflow regulating valve only participates in the regulation after the high-pressure shaft seal overflow valve is adjusted to the preset maximum or minimum opening.

[0014] Preferably, the emergency steam supply method further includes a coordinated steam supply stage, and the DCS controller is also preset with a coordinated steam supply trigger threshold, which is less than the steam supply pressure of the low-pressure shaft seal subsystem and greater than the preset trigger threshold. When the pressure acquisition transmitter detects that the inlet steam pressure of the low-pressure shaft seal subsystem is less than or equal to the coordinated steam supply trigger threshold and greater than the preset trigger threshold, it will enter the coordinated steam supply stage. During the coordinated steam supply phase, only the overflow isolation valve is opened and the emergency booster pump is started. The valve connecting the unit to the external auxiliary steam system is not closed. The remaining operations are the same as the emergency control procedure steps, so as to realize the pre-operation of auxiliary steam failure and avoid complete loss of steam from the low-pressure shaft seal.

[0015] Preferably, the system also includes an emergency exit and system recovery step. When the steam supply parameters of the external auxiliary steam system are detected to have returned to normal and the steam quality is qualified, or when external maintenance is completed, the DCS controller will issue a recovery prompt to indicate the exit from the emergency control program, or automatically execute the emergency exit and system recovery step to exit the emergency control program. The emergency exit and system recovery step includes: Gradually open the valves connecting the unit to the external auxiliary steam system, while gradually closing the overflow isolation valve and reducing the operating power of the emergency booster pump; Once the inlet steam pressure of the low-pressure shaft seal subsystem can be stably supplied by external auxiliary steam, the emergency booster pump is shut down, the overflow isolation valve is closed, and the steam supply to the low-pressure shaft seal subsystem is switched from the high- and medium-pressure shaft seal overflow steam transported by the emergency steam supply pipeline back to the external auxiliary steam supply, switching to normal operating conditions.

[0016] The beneficial effects of this application are as follows: This application discloses a turbine shaft seal system and emergency steam supply method based on overflow steam recovery. By setting up an emergency steam supply pipeline between the high- and intermediate-pressure shaft seal overflow pipeline and the low-pressure shaft seal steam supply pipeline, and cooperating with the DCS controller to automatically execute preset emergency control logic, the overflow steam from the high- and intermediate-pressure shaft seals, which was originally discharged to the condenser, can be quickly directed to the low-pressure shaft seal after an auxiliary steam interruption. This eliminates the need for cumbersome manual operation, greatly shortens the emergency response time, and reduces the possibility of shaft seal failure accidents caused by operational delays. Only a bypass modification is required on the original overflow pipeline, without changing the main process of the original system. Moreover, the principle is universal and can be extended to applications of similar units.

[0017] Furthermore, by utilizing the overflow steam from the high- and intermediate-pressure shaft seals that was originally wasted by being discharged to the condenser as an emergency steam source for the low-pressure shaft seals, the venting loss of high-quality steam is reduced, and the economic efficiency of the unit is improved. By adding an emergency booster pump, the problem of switching when the pressure of the high- and intermediate-pressure shaft seal header is lower than the pressure required by the low-pressure shaft seal is solved, ensuring that the pressure and flow rate of the emergency steam supply meet its sealing requirements. At the same time, in conjunction with the desuperheating water system, the temperature is ensured to be controlled within a safe range. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the specific embodiments of this application or the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0019] Figure 1 A schematic diagram of the overall structure of a turbine shaft seal system based on overflow steam recovery provided in an embodiment of this application; Figure 2 A flowchart illustrating an emergency steam supply method for a turbine shaft seal system based on overflow steam recovery, provided in an embodiment of this application.

[0020] Figure label: 1. High-pressure cylinder; 2. Intermediate-pressure cylinder; 3. Low-pressure cylinder; 4. Condenser; 5. High- and intermediate-pressure shaft seal relief valve; 6. Relief regulating valve; 7. On / off valve for steam leakage from high- and intermediate-pressure shaft seal to low-pressure cylinder; 8. Low-pressure shaft seal inlet valve; 9. Water regulating valve; 10. Relief isolation valve; 11. Emergency booster pump; 12. Shaft seal electric heating unit; 13. Shaft seal fan; 14. Shaft seal electric heating shut-off valve; 15. Cleaning condensate tank; 16. Butterfly valve for steam leakage from high- and intermediate-pressure shaft seal to condenser. Detailed Implementation

[0021] The technical solutions of this application will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0022] The following is combined with Figure 1 and Figure 2 This application describes the turbine shaft seal system and emergency steam supply method based on overflow steam recovery provided in the embodiments of this application.

[0023] Reference Figure 1 As shown, this application provides a turbine shaft seal system based on overflow steam recovery, which mainly includes a high-pressure and intermediate-pressure shaft seal subsystem, a low-pressure shaft seal subsystem, an auxiliary steam supply main pipe, a condenser 4, and an emergency steam supply pipeline.

[0024] The high-pressure and intermediate-pressure shaft seal steam header is connected to the high-pressure and intermediate-pressure shaft seal overflow pipeline. On the high-pressure and intermediate-pressure shaft seal overflow pipeline, a high-pressure and intermediate-pressure shaft seal overflow valve 5 and an overflow regulating valve 6 are sequentially installed along the direction of medium flow. The high-pressure and intermediate-pressure shaft seal overflow valve 5 serves as the main valve, controlling the total amount of overflow steam flowing to the condenser 4; the overflow regulating valve 6 is used to finely adjust the exhaust steam flow to maintain the pressure of the high-pressure and intermediate-pressure shaft seal steam header at approximately 3.5 kPa.

[0025] In addition, the high-pressure and intermediate-pressure shaft seal steam header is also connected to the low-pressure cylinder 3 via a bypass path through the high-pressure and intermediate-pressure shaft seal leakage steam to the low-pressure cylinder on / off valve 7. When the unit is operating under normal load, if the high-pressure and intermediate-pressure cylinder leakage steam parameters meet the requirements, this valve is opened to send some of the leakage steam into the low-pressure cylinder 3 to perform work and recover energy; during the unit startup phase or when the parameters do not meet the requirements, this valve is closed, and the leakage steam is directly discharged into the condenser 4 via another bypass path through the high-pressure and intermediate-pressure shaft seal leakage steam to the condenser butterfly valve 16.

[0026] The low-pressure shaft seal steam inlet valve 8 is installed on the low-pressure shaft seal steam inlet main pipe, which is connected to the shaft seal desuperheating pipeline and the water regulating valve 9. The cooling water source is usually taken from the unit's condensate pipeline network or the external tap water network, and is used to control the low-pressure shaft seal steam temperature at about 150℃ to prevent high temperature damage to the shaft seal bearing.

[0027] After the exhaust steam from the low-pressure shaft seal is collected, it enters the shaft seal electric heating unit 12, and is then extracted by the shaft seal fan 13 to be discharged to the atmosphere, maintaining a slight negative pressure in the shaft seal chamber and preventing steam leakage.

[0028] A pipeline is led out downstream of the high-pressure shaft seal overflow valve 5, upstream of the overflow regulating valve 6, or at a branch point connected in parallel with the overflow regulating valve 6, as an emergency steam supply pipeline.

[0029] The emergency steam supply pipeline is equipped with an overflow isolation valve 10 and an emergency booster pump 11 connected in series along the direction of medium flow. The overflow isolation valve 10 is used to isolate the branch under normal operating conditions to prevent steam backflow or missupply; the emergency booster pump 11 is a variable frequency booster pump used to increase the steam pressure.

[0030] The end of the emergency steam supply pipeline is connected to the low-pressure shaft seal inlet steam main and to the front end of the low-pressure shaft seal inlet steam valve 8, so that the recovered overflow steam can be combined with the original auxiliary steam or independently supplied to the low-pressure shaft seal when the auxiliary steam is interrupted.

[0031] A check valve is preferably installed on the outlet side of the emergency booster pump 11 to prevent steam backflow from impacting the emergency booster pump 11 due to pressure fluctuations on the low-pressure shaft seal side.

[0032] More specifically, this embodiment provides a turbine shaft seal system based on overflow steam recovery, the main body of which includes a high-pressure cylinder 1, an intermediate-pressure cylinder 2, a low-pressure cylinder 3, a condenser 4, an intermediate-high-pressure shaft seal overflow valve 5, an overflow regulating valve 6, an on / off valve for leakage steam from the intermediate-high-pressure shaft seal to the low-pressure cylinder 7, a low-pressure shaft seal inlet valve 8, a water regulating valve 9, an overflow isolation valve 10, an emergency booster pump 11, a shaft seal electric heating unit 12, a shaft seal fan 13, a shaft seal electric heating shut-off valve 14, a cleaning condensate tank 15, a butterfly valve for leakage steam from the intermediate-high-pressure shaft seal to the condenser 16, and a DCS (Distributed Control System) controller.

[0033] Labyrinth-type shaft seal sealing teeth are arranged on both sides of the high-pressure cylinder 1 and on the opposite sides of the intermediate-pressure cylinder 2 and the low-pressure cylinder 3. The steam leakage from the shaft seals at the shaft ends of the high-pressure cylinder 1 and the intermediate-pressure cylinder 2 is collected into the high- and medium-pressure shaft seal steam collection pipeline after passing through the labyrinth-type shaft seal sealing teeth, forming a self-sealing steam source for the high- and medium-pressure shaft seals.

[0034] Downstream of the high-pressure shaft seal steam collection pipeline is a high-pressure shaft seal overflow valve 5. The downstream pipeline of the overflow valve 5 is divided into two paths: one is the original high-pressure shaft seal overflow pipeline, on which an overflow regulating valve 6 is installed and connected to the condenser 4; the other is the emergency steam supply pipeline newly added in this application, and the emergency steam supply pipeline is connected in series with an overflow isolation valve 10, an emergency booster pump 11 and a check valve along its steam flow direction, and the end of the pipeline is connected to the front end of the low-pressure shaft seal steam inlet valve 8.

[0035] The high-pressure and intermediate-pressure shaft seal overflow valve 5 controls the total overflow steam flow in the high-pressure and intermediate-pressure shaft seal overflow pipeline, isolating or connecting the overflow steam source. The overflow regulating valve 6 is used for closed-loop regulation of the high-pressure and intermediate-pressure shaft seal main pipe pressure, maintaining a standard sealing pressure of 3.5 kPa. The steam inlet of the emergency steam supply pipeline is connected downstream of the high-pressure and intermediate-pressure shaft seal overflow valve 5 and upstream of the overflow regulating valve 6, while the steam outlet is connected to the low-pressure shaft seal steam supply main pipe upstream of the low-pressure shaft seal inlet valve 8. The overflow isolation valve 10 is a pneumatic isolation valve, with its upstream section taken from the pipe section after the high-pressure and intermediate-pressure shaft seal overflow valve 5 and before the overflow regulating valve 6, and its downstream section connected to the inlet of the emergency booster pump 11. The overflow isolation valve 10 serves as the isolation gate of the emergency steam supply branch, remaining fully closed under normal operating conditions to prevent overflow steam from entering the low-pressure shaft seal; it is automatically opened by the DCS controller in the event of an auxiliary steam interruption accident. The emergency booster pump 11 is a variable frequency speed control pump, located in the middle section of the emergency steam supply pipeline, between the overflow isolation valve 10 and the low-pressure shaft seal inlet steam main. The emergency booster pump 11 is used to increase the pressure of the overflow steam from the high- and intermediate-pressure shaft seal from approximately 3.5 kPa to the 9 kPa required by the low-pressure shaft seal, thus offsetting pipeline resistance losses and ensuring that the overflow steam pressure meets the sealing requirements of the low-pressure shaft seal. Under normal operating conditions, the emergency booster pump 11 remains shut down. The low-pressure shaft seal inlet steam valve 8 is located on the low-pressure shaft seal inlet steam main at the front end of the low-pressure shaft seal. As the main regulating valve after the convergence of the two steam sources (auxiliary steam and overflow emergency steam source), it is used to regulate the total steam flow to the low-pressure shaft seal and stabilize the shaft seal pressure at 9 kPa.

[0036] The high-pressure shaft seal steam collection pipeline is also equipped with a bypass for high-pressure shaft seal leakage to low-pressure cylinder. This bypass is equipped with a valve 7 for high-pressure shaft seal leakage to low-pressure cylinder. Under normal operating conditions, this valve is open, and a small amount of leakage steam from the high-pressure shaft seal is sent to the low-pressure cylinder 3 to perform work. Under emergency operating conditions, the DCS controller interlocks and closes the valve, converting the shaft seal leakage steam into an overflow backup steam source.

[0037] In some specific embodiments, a low-pressure shaft seal desuperheating pipeline is also provided downstream of the low-pressure shaft seal inlet valve 8. This pipeline is connected to the unit's condensate or external tap water as a cooling water source, and a water regulating valve 9 is installed on the pipeline. Pressure acquisition transmitters and temperature acquisition transmitters are arranged on the low-pressure shaft seal inlet main pipe, and the acquired signals are uploaded to the DCS controller in real time. Pressure acquisition transmitters are also installed in the high- and medium-pressure shaft seal steam collection pipeline to monitor the main pipe pressure in real time.

[0038] The low-pressure shaft seal desuperheating pipeline is connected to the downstream section of the low-pressure shaft seal steam inlet valve 8. Since the overflow steam temperature is usually 260-270℃, which is far beyond the tolerance temperature of the low-pressure shaft seal, it is necessary to adjust the water regulating valve 9 to reduce the shaft seal steam temperature and spray the steam to cool it down, so as to stabilize the low-pressure shaft seal steam supply temperature at 150℃±5℃ and avoid high-temperature steam from damaging the shaft seal.

[0039] The auxiliary steam supply header is connected to the low-pressure shaft seal inlet steam header, serving as the only backup steam source from the original manufacturer, for basic steam supply to the low-pressure shaft seal during unit start-up, shutdown, and normal operation.

[0040] In some specific embodiments, the system also includes an exhaust pipe, a shaft seal electric heating unit 12, a shaft seal fan 13, and a shaft seal electric heating shut-off valve 14. Exhaust steam from the cylinder shaft seal is collected through the exhaust pipe and sent to the shaft seal electric heating unit 12. After heating, it is discharged to the shaft seal fan 13, which then draws it into the atmosphere. The shaft seal electric heating unit 12 heats the exhaust steam from the shaft seal, preventing condensation and avoiding water hammer damage to the equipment. The shaft seal fan 13 is a two-stage parallel exhaust fan used to establish a slight negative pressure in the shaft seal chamber, preventing shaft seal steam from leaking into the bearing housing and emulsifying the lubricating oil. The shaft seal electric heating shut-off valve 14 is located on the lowest point of the low-pressure shaft seal pipe's drain branch, connected downstream to a clean drain tank 15, used to drain condensate from the shaft seal pipe, preventing water hammer damage to the valve and pipes. The cleaning condensate tank 15 is used to collect condensate from the shaft seal pipeline to achieve working fluid recovery.

[0041] The DCS controller is electrically connected to the overflow isolation valve 10, the emergency booster pump 11, the overflow regulating valve 6, the low-pressure shaft seal inlet valve 8, the water regulating valve 9, the high-pressure shaft seal leakage to low-pressure cylinder on / off valve 7, and the high-pressure shaft seal leakage to condenser butterfly valve 16. The signal output terminals of the pressure and temperature acquisition transmitters located at the low-pressure shaft seal inlet main pipe are connected to the signal input terminals of the DCS controller. The DCS controller has a built-in auxiliary steam interruption accident sequence control logic module, which automatically executes the emergency control program when an auxiliary steam interruption is detected.

[0042] During operation, the system has the following three types of normal operating conditions: 1) During the unit start-up and heating phase, the temperature and pressure of the high-pressure and intermediate-pressure shaft seal exhaust steam are low and have no recycling value. The emergency steam supply pipeline should be kept closed. Steam leakage from the high-pressure shaft seal is directly discharged into the condenser 4 via the condenser butterfly valve 16. Once the exhaust steam parameters rise above 260℃ and the pressure matches the requirements of the low-pressure shaft seal, close the butterfly valve 16 for the leakage steam from the high-pressure and intermediate-pressure shaft seal to the condenser, open the on / off valve 7 for the leakage steam from the high-pressure and intermediate-pressure shaft seal to the low-pressure cylinder, and recover the leakage steam to the low-pressure cylinder 3 to perform work.

[0043] 2) Under normal operating conditions, the unit has normal self-sealing and there are no faults in the external auxiliary steam. In this state, the overflow isolation valve 10 is fully closed, and the emergency booster pump 11 is shut down; the high-pressure and intermediate-pressure shaft seal overflow valve 5 is maintained in the 40%–50% half-open range, and the overflow regulating valve 6 is simultaneously in the half-open range; excess steam from the high-pressure and intermediate-pressure shaft seal is discharged into the condenser 4 through the overflow pipeline and overflow regulating valve 6; the low-pressure shaft seal relies entirely on the auxiliary steam supply main pipe for steam supply, and the water regulating valve 9 is slightly adjusted according to the auxiliary steam temperature to stabilize the low-pressure shaft seal steam temperature at 150℃±5℃. At this time, the emergency steam supply branch of this application is in standby mode, and the high-pressure and intermediate-pressure shaft seal leakage steam to the low-pressure cylinder on / off valve 7 is in the open state, and the leakage steam is sent to the low-pressure cylinder 3 to perform work.

[0044] 3) Emergency operating condition: When external auxiliary steam is interrupted, the emergency steam supply pipeline is opened; The DCS controller collects the signal from the low-pressure shaft seal pressure transmitter. When a fault occurs in the external auxiliary steam system, causing the pressure of the auxiliary steam supply header to drop below the preset trigger threshold (0-4.5 kPa), the emergency control program is triggered. It automatically cuts off the external auxiliary steam supply to prevent the fault from spreading or steam backflow, increases the unit to full load, closes the high and medium pressure shaft seal leakage valve 7 to the low-pressure cylinder, and simultaneously opens the overflow isolation valve 10 and starts the emergency booster pump 11. The overflow steam is pressurized through the emergency steam supply pipeline and sent to the low-pressure shaft seal. The DCS controller's closed-loop regulation valve 9 sprays condensate to cool it down, and links the high and medium pressure shaft seal overflow valves 5 and overflow adjustment valve 6 to stabilize the high and low pressure shaft seal pressures to the set values ​​respectively. After the emergency booster pump 11 starts, it uses frequency conversion control to increase the steam pressure to overcome pipeline resistance and ensure that the low pressure shaft seal inlet steam pressure meets the standard.

[0045] In some specific embodiments, such as Figure 2 As shown, this application also provides an emergency steam supply method based on the above-mentioned turbine shaft sealing system, which mainly includes the following steps: (a) Auxiliary steam interruption detection and triggering: The inlet steam pressure of the low-pressure shaft seal subsystem is collected in real time by a pressure acquisition transmitter at the low-pressure shaft seal inlet main pipe. When the pressure acquisition transmitter detects that the low-pressure shaft seal inlet steam pressure continues to drop to the preset trigger threshold, or when the external auxiliary steam supply header pressure is lower than the second preset threshold, the DCS controller determines that an auxiliary steam interruption has occurred and automatically triggers the auxiliary steam interruption emergency control program.

[0046] Furthermore, to reduce false detections caused by steam supply fluctuations and reduce the number of false starts of emergency steam supply pipelines, a judgment time can be added during the detection phase. When the pressure acquisition transmitter detects that the low-pressure shaft seal inlet steam pressure continues to drop to the preset trigger threshold and the duration exceeds the preset judgment time, the emergency control program will be triggered. The preset judgment time can be 3-5 seconds.

[0047] (II) Implementation of emergency control procedures The DCS controller automatically executes the following sequence of actions according to a preset control logic: Step S1: The DCS controller interlocks and closes the valve connecting the auxiliary steam supply header to the external auxiliary steam system, completely cutting off the failed external steam source and interrupting the external auxiliary steam supply to prevent the operating unit from tripping due to a large amount of leakage of shaft seal steam from the accident location.

[0048] Step S2: Issue a load increase command to increase the unit load from the normal operating load to the full load under the current season conditions. The controller will control the increase of unit output to improve the steam production of the high-pressure and intermediate-pressure shaft seal system and ensure sufficient emergency steam supply.

[0049] Generally, the operating load of the unit is 260-350MW in summer and 260-400MW in winter. Under these circumstances, when the emergency control procedure is triggered, the unit will be operated at full load or above full load for that season, such as 350MW in summer and 400MW in winter.

[0050] Step S3: Close the valve 7 for shutting off the leakage steam from the high-pressure shaft seal to the low-pressure cylinder, thereby terminating the power supply path of the leakage steam to the low-pressure cylinder 3, saving steam source and increasing the pressure of the high-pressure shaft seal steam header.

[0051] Step S4: Fully open the overflow isolation valve 10 and start the emergency booster pump 11 to switch the overflow steam from the high and medium pressure shaft seal from being discharged to the condenser 4 to being discharged to the low pressure shaft seal inlet steam main.

[0052] Step S5: Activate the automatic control loop for low-pressure shaft seal pressure. The DCS controller performs closed-loop adjustment based on the real-time pressure and temperature parameters of the high and low-pressure shaft seals. The DCS controller adjusts the operating frequency of the emergency booster pump 11 based on the deviation between the measured pressure of the low-pressure shaft seal steam header and the target set value (9 kPa), thereby finely adjusting the low-pressure shaft seal steam supply pressure. At the same time, it adjusts the opening of the low-pressure shaft seal steam inlet valve 8 to stabilize the low-pressure shaft seal steam header pressure within 9 kPa or its set deviation range.

[0053] Step S6: Activate the automatic control loop for low-pressure shaft seal temperature. The DCS controller automatically adjusts the opening of the water regulating valve 9 based on the deviation between the measured temperature of the low-pressure shaft seal steam header and the target set value (150℃), thereby controlling the low-pressure shaft seal steam supply temperature at 150℃±5℃.

[0054] Step S7: Activate the automatic control loop for the high-pressure shaft seal pressure. The DCS controller automatically adjusts the opening of the high-pressure shaft seal relief valve 5 based on the deviation between the measured pressure value of the high-pressure shaft seal steam header and the target set value (3.5 kPa), so that the high-pressure shaft seal steam pressure is maintained at 3.5 kPa or within its set deviation range.

[0055] During the above process, the overflow regulating valve 6 does not participate in the regulation. When the pressure of the high-pressure and intermediate-pressure shaft seal steam header is too low and the high-pressure and intermediate-pressure shaft seal overflow valve 5 has been adjusted to the preset minimum opening degree, i.e., 40%, the overflow regulating valve 6 is controlled to close slightly, reducing the amount of steam discharged to the condenser 4 and helping to raise the pressure of the high-pressure and intermediate-pressure shaft seal steam header to the normal level. When the pressure of the high-pressure and intermediate-pressure shaft seal steam header is too high and the high-pressure and intermediate-pressure shaft seal overflow valve 5 has been adjusted to 50% of the preset maximum opening degree, the overflow regulating valve 6 is controlled to open wider, increasing the amount of steam discharged to the condenser 4 and reducing the pressure of the shaft seal steam header.

[0056] Furthermore, throughout the entire emergency procedure, the valve connecting the auxiliary steam supply main pipe to the external auxiliary steam system remains closed, and all steam for the low-pressure shaft seal is supplied separately from the overflow steam from the high- and medium-pressure shaft seal, which is transported by the emergency steam supply pipeline.

[0057] It also includes step S8: Emergency Exit and System Recovery Once on-site maintenance is completed or the DCS controller detects that the external auxiliary steam supply parameters have returned to normal, and the steam quality has been qualified and stable for a period of time, it will automatically issue a prompt or automatically execute the exit emergency procedure.

[0058] Exiting the emergency procedure includes the following steps: S81: Slowly open the external auxiliary steam connection valve to gradually increase the external auxiliary steam supply flow rate; S82: Simultaneously and gradually close the overflow isolation valve 10 and reduce the operating frequency of the emergency booster pump 11 to reduce the overflow steam supply. S83: Continuously monitor the low-pressure shaft seal pressure and temperature. When the external auxiliary steam can independently and stably maintain the parameters of 9kPa and 150℃, completely shut down the emergency booster pump 11 and fully close the overflow isolation valve 10. S84: Restore the steam leakage from the high and medium pressure shaft seal to the open state of the low pressure cylinder on / off valve 7, and the system returns to normal self-sealing operation.

[0059] In one preferred embodiment, the DCS controller also has a preset coordinated steam supply trigger threshold, which is less than the steam supply pressure of the low-pressure shaft seal system (9 kPa) and greater than the preset trigger threshold, for example, 6 kPa.

[0060] When the pressure acquisition transmitter detects that the low-pressure shaft seal inlet steam pressure is less than or equal to the coordinated steam supply trigger threshold and greater than the preset trigger threshold, the DCS controller determines that the auxiliary steam system has a fault precursor but has not been completely interrupted, and enters the coordinated steam supply stage.

[0061] During the coordinated steam supply phase, the DCS controller only opens the overflow isolation valve 10 and starts the emergency booster pump 11, without closing the unit's auxiliary steam supply main valve. The remaining operations are the same as the emergency control procedure, enabling the external auxiliary steam and overflow steam to be supplied to the low-pressure shaft seal in a coordinated manner. This buffers the pressure decay of the steam source in advance, preventing the pressure from continuously dropping to the complete steam loss threshold, and further enhancing the system's active defense capability.

[0062] Specifically, the turbine shaft seal system based on overflow steam recovery provided in this application embodiment can be used to perform the above-mentioned emergency steam supply method to achieve the required technical effect, which will not be elaborated here.

[0063] In the description of this application, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc., indicating the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this application.

[0064] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this application, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0065] In this application, unless otherwise expressly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection, an electrical connection, or a connection that allows communication between components; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise expressly limited. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0066] In this application, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0067] Although embodiments of this application have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting this application. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of this application.

Claims

1. A turbine shaft sealing system based on overflow steam recovery, comprising an intermediate-high pressure shaft sealing subsystem, a low pressure shaft sealing subsystem, an auxiliary steam supply header, and a condenser, wherein the intermediate-high pressure shaft sealing subsystem includes an intermediate-high pressure shaft sealing overflow pipeline connected to the condenser, and the intermediate-high pressure shaft sealing subsystem can achieve self-sealing steam supply under normal unit operation, characterized in that... The system also includes: An emergency steam supply pipeline has one end connected to the high-pressure shaft seal overflow pipeline and the other end connected to the front end of the steam inlet valve of the low-pressure shaft seal subsystem. The emergency steam supply pipeline is equipped with an overflow isolation valve and an emergency booster pump connected in series along its medium flow direction. The high-pressure shaft seal overflow pipeline is equipped with a high-pressure shaft seal overflow valve, and the steam inlet of the emergency steam supply pipeline is located downstream of the high-pressure shaft seal overflow valve. The emergency steam supply pipeline can divert and transport the overflow steam from the high-pressure shaft seal subsystem to the low-pressure shaft seal subsystem in the event of an interruption in the external auxiliary steam supply.

2. The turbine shaft sealing system based on overflow steam recovery according to claim 1, characterized in that, An overflow regulating valve is also provided on the high-pressure shaft seal overflow pipeline, and the overflow regulating valve is located downstream of the emergency steam supply pipeline access point. It is used to regulate the amount of steam discharged into the condenser in order to stabilize the pressure in the high-pressure shaft seal subsystem.

3. The turbine shaft sealing system based on overflow steam recovery according to claim 1, characterized in that, The downstream section of the steam inlet valve of the low-pressure shaft seal subsystem is also provided with a low-pressure shaft seal desuperheating pipeline connected to an external cooling water source, and a water regulating valve is provided on the low-pressure shaft seal desuperheating pipeline.

4. The turbine shaft sealing system based on overflow steam recovery according to claim 3, characterized in that, The steam supply pressure of the high-pressure shaft seal system is 3.5 kPa; The steam supply temperature of the low-pressure shaft seal system is 150℃±5℃, and the steam supply pressure is 9kPa. A temperature acquisition transmitter is installed at the steam supply line of the low-pressure shaft seal system, and a pressure acquisition transmitter is installed at the steam supply lines of both the low-pressure shaft seal system and the high- and medium-pressure shaft seal system.

5. The turbine shaft sealing system based on overflow steam recovery according to claim 4, characterized in that, The system also includes a DCS (Distributed Control System) controller, which is configured to automatically execute the following emergency control procedure when the steam supply pressure at the steam supply line of the low-pressure shaft seal subsystem is detected to be lower than a preset trigger threshold: Close the valve connecting the auxiliary steam supply header to the external auxiliary steam system to cut off the external auxiliary steam supply. Increase the operating load of the unit and close the power passage from the high-pressure cylinder shaft seal leakage in the high-pressure and intermediate-pressure shaft seal subsystem to the low-pressure cylinder in the low-pressure shaft seal system; Open the overflow isolation valve and start the emergency booster pump to divert the high- and medium-pressure shaft seal overflow steam that was originally discharged into the condenser to the low-pressure shaft seal subsystem; The operating power of the emergency booster pump and the opening of the high-pressure shaft seal overflow valve and overflow regulating valve are adjusted in conjunction with the temperature and pressure acquisition transmitters. In addition, the steam supply pressure and steam supply temperature of the high-pressure shaft seal subsystem and the low-pressure shaft seal subsystem are stabilized to their respective target set values ​​in conjunction with the water regulating valve. The preset trigger threshold is greater than or equal to zero and less than or equal to half of the steam supply pressure of the low-pressure shaft seal subsystem.

6. The emergency steam supply method for a turbine shaft seal system based on overflow steam recovery according to any one of claims 1-5, characterized in that, include: The inlet steam pressure of the low-pressure shaft seal subsystem is collected in real time by a pressure acquisition transmitter. When the pressure acquisition transmitter detects that the inlet steam pressure of the low-pressure shaft seal subsystem has dropped to a preset trigger threshold, it will trigger the auxiliary steam interruption program and the DCS controller will control the start of the emergency control program. The unit automatically closes the valve connecting it to the external auxiliary steam system and increases the unit's operating load to full load to increase the amount of steam leakage at the high and medium pressure shaft seal subsystem. Open the overflow isolation valve and start the emergency booster pump to switch the overflow steam from the high and medium pressure shaft seal from being discharged to the condenser to being discharged to the steam inlet of the low pressure shaft seal subsystem; The system works in conjunction with temperature and pressure transmitters to regulate the operating power of the emergency booster pump and the opening of the high and medium pressure shaft seal overflow valve. It also regulates the pressure of the overflow steam after switching and works with the water regulating valve to control its pressure and temperature to meet the sealing requirements of the low pressure shaft seal. Finally, it supplies steam to the low pressure shaft seal subsystem after the auxiliary steam interruption procedure is triggered.

7. The emergency steam supply method according to claim 6, characterized in that, During the operation of the emergency control program, the valve connecting the unit to the external auxiliary steam system remains closed, and all steam supply to the low-pressure shaft seal subsystem is provided by the high- and medium-pressure shaft seal overflow steam transported by the emergency steam supply pipeline.

8. The emergency steam supply method according to claim 6, characterized in that, The specific steps for switching the overflow steam from the high-pressure shaft seal to the condenser and then to the inlet of the low-pressure shaft seal subsystem include: Open the overflow isolation valve installed on the emergency steam supply pipeline to switch the discharge route of the overflow steam from the high and medium pressure shaft seal to the condenser and then to the low pressure shaft seal inlet. Start the emergency booster pump to pressurize the overflow steam in the discharge route. Adjust the overflow valve of the high-pressure shaft seal and simultaneously adjust the overflow regulating valve to maintain the stability of the main pipe pressure in the high-pressure shaft seal subsystem; The overflow regulating valve only participates in the regulation after the high-pressure shaft seal overflow valve is adjusted to the preset maximum or minimum opening.

9. The emergency steam supply method according to claim 6, characterized in that, The emergency steam supply method also includes a coordinated steam supply phase. The DCS controller is also preset with a coordinated steam supply trigger threshold. The coordinated steam supply trigger threshold is less than the steam supply pressure of the low-pressure shaft seal subsystem and greater than the preset trigger threshold. When the pressure acquisition transmitter detects that the inlet steam pressure of the low-pressure shaft seal subsystem is less than or equal to the coordinated steam supply trigger threshold and greater than the preset trigger threshold, it will enter the coordinated steam supply stage. During the coordinated steam supply phase, only the overflow isolation valve is opened and the emergency booster pump is started, without closing the valve connecting the unit to the external auxiliary steam system.

10. The emergency steam supply method according to claim 6, characterized in that, It also includes emergency exit and system recovery steps. When the steam supply parameters of the external auxiliary steam system are detected to have returned to normal and the steam quality is qualified, the DCS controller will issue a recovery prompt to indicate the exit from the emergency control program, or automatically execute the emergency exit and system recovery steps to exit the emergency control program. The emergency exit and system recovery steps include: Gradually open the valves connecting the unit to the external auxiliary steam system, while gradually closing the overflow isolation valve and reducing the operating power of the emergency booster pump; Once the inlet steam pressure of the low-pressure shaft seal subsystem can be stably supplied by external auxiliary steam, the emergency booster pump is shut down, the overflow isolation valve is closed, and the steam supply to the low-pressure shaft seal subsystem is switched from the high- and medium-pressure shaft seal overflow steam transported by the emergency steam supply pipeline back to the external auxiliary steam supply, switching to normal operating conditions.

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