A combined heat and power unit zero output heat supply system based on medium pressure cylinder interstage full extraction and a control method thereof
By using a full extraction steam system between intermediate-pressure cylinder stages, the problems of unstable cooling of the low-pressure cylinder and wear of moving blades in cogeneration units have been solved, achieving safe and stable zero-output heating from the low-pressure cylinder and improving the unit's operational flexibility and heating capacity.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- HUADIAN ELECTRIC POWER SCI INST CO LTD
- Filing Date
- 2026-03-30
- Publication Date
- 2026-05-29
AI Technical Summary
The existing cylinder cutting technology of cogeneration units suffers from unstable and inaccurate cooling steam supply to the low-pressure cylinder, leading to safety hazards. In addition, the exhaust steam grade of the intermediate-pressure cylinder is limited, making it difficult to meet the demand for high-grade industrial steam. Furthermore, traditional regulation methods cause wear and fatigue of the moving blades.
The system employs a medium-pressure cylinder stage full extraction steam system, which, through the cooperation of an axial flow steam ejector and a regulating valve, achieves almost complete steam extraction. Combined with independent low-pressure cylinder cooling steam pipelines and heat recovery pipelines, it ensures the safety of low-pressure cylinder cooling and provides stable heating steam.
It eliminates fretting wear and high-cycle fatigue at the blade root, improves unit safety, enables zero-output operation of the low-pressure cylinder and high-quality heating, avoids repetitive maintenance, and meets the grid's deep peak-shaving needs.
Smart Images
Figure CN122107445A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of cogeneration unit heating technology, specifically relating to a zero-output heating system for cogeneration units based on full extraction of steam between intermediate cylinder stages in medium-pressure systems and its control method. Background Technology
[0002] Improving the operational flexibility of combined heat and power (CHP) units to adapt to the grid's deep peak-shaving requirements is crucial for the current transformation of the thermal power industry. One key technology is low-pressure cylinder shut-off operation, which involves stopping the low-pressure cylinder from working or operating at minimal output, thereby significantly reducing power generation and increasing heating capacity.
[0003] Current mainstream cylinder-cutting technology modifications all revolve around the exhaust steam from the intermediate-pressure cylinder. The principle is to divert most or all of the exhaust steam from the intermediate-pressure cylinder, which originally went entirely to the low-pressure cylinder for work, to the heating system, retaining only a minimal amount of steam for cooling the idling low-pressure cylinder. This method has two inherent drawbacks: First, the cooling steam supply to the low-pressure cylinder is unstable and inaccurate, relying on simple valve throttling, which easily leads to insufficient or excessive cooling when system pressure fluctuates, threatening the safety of the low-pressure cylinder rotor and blades; second, the heating steam source is the low-parameter exhaust steam from the intermediate-pressure cylinder, whose grade is limited and cannot meet the high-grade industrial steam requirements.
[0004] Furthermore, if a traditional rotating baffle device is used to regulate the extraction of steam on the intermediate pressure cylinder, the high-pressure steam will violently impact the partially opened baffle, generating vertical rebound turbulence that continuously impacts the root of the upstream moving blades, leading to fatal fretting wear and high-cycle fatigue cracks. Summary of the Invention
[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a zero-output heating system and control method for a cogeneration unit based on full extraction of steam between intermediate-pressure cylinder stages. By extracting steam from the intermediate-pressure cylinder as the main heat source and achieving almost complete extraction of steam from that stage, the system can achieve true zero-output operation of the low-pressure cylinder while ensuring the cooling safety of the low-pressure cylinder, thus eliminating the damage to the moving blades caused by traditional regulation methods.
[0006] This invention provides the following technical solution: In the first aspect, a zero-output heating system for a cogeneration unit based on full extraction of steam between intermediate cylinder stages of intermediate pressure cylinder is provided, including: intermediate pressure cylinder, extraction steam pipeline, axial flow steam ejector device, regulating valve, connecting pipeline between intermediate and low pressure cylinders, cooling steam pipeline for low pressure cylinder, heat recovery pipeline, low pressure cylinder and control unit. The intermediate pressure cylinder has an extraction steam flow channel after the extraction stage moving blade, and an extraction steam pipe is connected to the extraction steam flow channel to transport the extracted steam to the heat user. The axial flow steam ejector and the regulating valve are both located on the extraction steam pipeline. The axial flow steam ejector is located upstream or downstream of the regulating valve. The axial flow steam ejector and the regulating valve work together to extract steam from the intermediate pressure cylinder to the extraction steam pipeline. The medium and low pressure cylinder connecting pipes are respectively connected to the steam inlet of the low pressure cylinder and the steam outlet of the medium pressure cylinder, and are equipped with adjusting butterfly valves for connecting or disconnecting the medium and low pressure cylinder connecting pipes. Both ends of the low-pressure cylinder cooling steam pipe are connected to the medium and low-pressure cylinder connecting pipes, and are located upstream and downstream of the adjusting butterfly valve, respectively; the low-pressure cylinder cooling steam pipe is equipped with a cooling steam flow regulating valve; The heat recovery pipeline is connected to the exhaust port of the intermediate pressure cylinder; The control unit is connected to an axial flow steam ejector, a regulating valve, an adjusting butterfly valve, and a cooling steam flow regulating valve.
[0007] As an optional technical solution of the present invention, the axial flow steam ejector is provided with a drive motor and an axial flow impeller. The drive motor is used to drive the axial flow impeller to generate ejection power in the same direction as the steam flow in the extraction pipe.
[0008] As an optional technical solution of the present invention, the control unit is connected to the drive motor, and the ejector power is adjusted by controlling the speed of the drive motor.
[0009] As an optional technical solution of the present invention, the low-pressure cylinder cooling steam pipeline is further provided with a cooling steam flow measuring mechanism for measuring the steam flow rate through the low-pressure cylinder cooling steam pipeline.
[0010] As an optional technical solution of the present invention, a heat recovery mechanism is provided on the heat recovery pipeline for heat recovery of the residual steam discharged from the exhaust port of the intermediate pressure cylinder.
[0011] As an optional technical solution of the present invention, the steam extraction channel adopts a smooth channel.
[0012] In a second aspect, a control method is provided for the zero-output heating system of a cogeneration unit based on full extraction of steam between intermediate cylinder stages as described in the first aspect, including a full-cut low-pressure cylinder heating operation control mode. The fully-cut low-pressure cylinder heating operation control mode includes: The axial-flow steam ejector is controlled to generate maximum ejection power, and the regulating valve is adjusted to achieve maximum opening. Control the adjustment butterfly valve to close; Control the opening degree of the cooling steam flow regulating valve to reach a preset opening value, and according to... The obtained low-pressure cylinder exhaust temperature and cylinder metal temperature are used to increase or decrease the opening of the cooling steam flow regulating valve.
[0013] As an optional technical solution of the present invention, it also includes a conventional electrothermal coupling operation control mode; The conventional electrothermal coupling operation control mode includes: Control the opening of the adjusting butterfly valve; The cooling steam flow regulating valve is closed. Adjust the axial steam ejector and regulating valve according to the total extraction steam demand command, the extraction steam flow measurement value, and the pressure measurement value after the extraction stage.
[0014] Compared with the prior art, the beneficial effects of the present invention are: This invention provides a zero-output heating system for a cogeneration unit based on full extraction of steam between intermediate-pressure cylinder stages. It completely removes the rotating baffles that generate harmful impacts, ensuring unobstructed main steam flow. This fundamentally eliminates the periodic impact loads that cause fretting wear and high-cycle fatigue at the blade roots, greatly improving the long-term safety of the extraction stage blades and rotor, and avoiding repetitive maintenance. Furthermore, by using an independent low-pressure cylinder cooling steam pipeline, it provides precise, reliable, and stable cooling for the isolated low-pressure cylinder, overcoming the significant safety hazard of uncontrollable cooling flow in traditional methods. Attached Figure Description
[0015] Figure 1 This is a schematic diagram of the zero-output heating system of the cogeneration unit in an embodiment of the present invention.
[0016] Reference numerals in the attached diagram: 1. Intermediate-pressure cylinder; 2. Extraction stage moving blade; 3. Extraction steam flow channel; 4. Extraction steam pipeline; 5. Axial flow impeller; 6. Axial flow steam ejector; 7. Regulating valve; 8. Extraction steam flow measurement mechanism; 9. Extraction stage downstream pressure measurement mechanism; 10. Control unit; 11. Intermediate and low-pressure cylinder connecting pipeline; 12. Low-pressure cylinder; 13. Adjusting butterfly valve; 14. Low-pressure cylinder cooling steam pipeline; 15. Cooling steam flow measurement mechanism; 16. Cooling steam flow regulating valve; 17. Heat recovery mechanism; 18. Low-pressure cylinder last stage blade; 19. Exhaust steam guide ring; 20. Low-pressure cylinder exhaust steam temperature measuring point; 21. Cylinder body metal temperature measuring point. Detailed Implementation
[0017] The present invention will be further described below with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and should not be used to limit the scope of protection of the present invention.
[0018] Example 1 This embodiment provides a zero-output heating system for a cogeneration unit based on full extraction of steam between intermediate cylinder stages, applied to an extraction-condensing steam turbine. For example... Figure 1As shown, it includes an intermediate-pressure cylinder 1, a steam extraction pipe 4, an axial-flow steam ejector device 6, a regulating valve 7, a connecting pipe 11 between the intermediate and low-pressure cylinders, a cooling steam pipe 14 for the low-pressure cylinder, a heat recovery pipe, a low-pressure cylinder 12, and a control unit 10.
[0019] An extraction steam flow channel 3 is provided after the extraction stage moving blade 2 of the intermediate pressure cylinder 1. The extraction steam pipe 4 is connected to the extraction steam flow channel 3 to transport the extracted steam to the heat user. The extraction steam flow channel 3 is a smooth flow channel. In this embodiment, the extraction stage moving blade 2 is the fifth stage moving blade of the intermediate pressure cylinder. The original rotating diaphragm regulating valve and its complex cavity structure are completely removed, and the flow channel is repaired into a smooth and continuous flow channel. The main steam flow channel is unobstructed, which fundamentally eliminates the periodic impact load that causes fretting wear and high-cycle fatigue at the blade root. This greatly improves the safety of the long-term operation of the extraction stage moving blade and rotor of the unit and avoids related repetitive maintenance.
[0020] The axial-flow steam ejector 6 and the regulating valve 7 are both located on the extraction steam pipe 4. The axial-flow steam ejector 6 is located upstream or downstream of the regulating valve 7. The axial-flow steam ejector 6 and the regulating valve 7 work together to extract steam from the intermediate-pressure cylinder 1 to the extraction steam pipe 4. By setting up the axial-flow steam ejector 6, a powerful suction field that can be actively controlled is created, which is sufficient to remove most of the steam flowing out of the intermediate stage when needed.
[0021] The axial-flow steam ejector 6 is equipped with a drive motor and an axial-flow impeller 5. The drive motor drives the axial-flow impeller 5 to generate ejection power in the same direction as the steam flow in the extraction pipe. The ejection power is adjusted by controlling the speed of the drive motor. In this embodiment, a high-power variable frequency motor 6 is used as the drive motor, and a high-strength alloy axial-flow impeller 5 is used to increase its service life. The control unit 10 is connected to the drive motor and adjusts the ejection power by controlling the speed of the drive motor. It is necessary to ensure that when the adjusting butterfly valve 13 is closed, most of the steam after the fifth stage (e.g., more than 90%) can be extracted. This suction effect naturally achieves a sharp reduction in the downstream steam flow, creating ideal conditions for safe cylinder shut-off.
[0022] The medium and low pressure cylinder connecting pipe 11 is connected to the steam inlet of the low pressure cylinder 12 and the steam outlet of the medium pressure cylinder 1, respectively. It is equipped with an adjusting butterfly valve 13 for connecting or disconnecting the medium and low pressure cylinder connecting pipe 11. The adjusting butterfly valve 13 can achieve zero leakage shut-off and realize the physical isolation of the low pressure cylinder 12.
[0023] Both ends of the low-pressure cylinder cooling steam pipe 14 are connected to the medium-low pressure cylinder connecting pipe 11, and are located upstream and downstream of the adjusting butterfly valve 13, respectively. A cooling steam flow regulating valve 16 is installed on the low-pressure cylinder cooling steam pipe 14. A cooling steam flow measuring mechanism 15 is also installed on the low-pressure cylinder cooling steam pipe 14 to measure the steam flow rate through it. By setting up an independent low-pressure cylinder cooling steam pipe 14 with precise metering and regulating functions, it is ensured that the isolated low-pressure cylinder can obtain a stable and controllable minimum cooling flow rate.
[0024] The heat recovery pipeline is connected to the exhaust port of the intermediate-pressure cylinder 1. A heat recovery mechanism 17 is provided on the heat recovery pipeline for heat recovery of the remaining steam discharged from the exhaust port of the intermediate-pressure cylinder 1. In this embodiment, the heat recovery mechanism 17 is a low-pressure heater or a deaerator.
[0025] In this embodiment, the axial-flow steam ejector 6 extracts almost all of the working steam from the designated intermediate stage of the intermediate-pressure cylinder as the main heating steam source; simultaneously, the adjusting butterfly valve 13 is shut off to isolate the low-pressure cylinder 12. The remaining small amount of exhaust steam from the intermediate-pressure cylinder is precisely introduced into the low-pressure cylinder through the low-pressure cylinder cooling steam pipeline 14 for cooling protection, and the other is introduced into the regenerative system through the heat recovery pipeline to maintain the basic requirements for feedwater reheating.
[0026] The control unit 10 is connected to the axial flow steam ejector 6, the regulating valve 7, the adjusting butterfly valve 13, and the cooling steam flow regulating valve 16.
[0027] Furthermore, the axial flow impeller 5 is made of high-temperature resistant and high-strength alloy material, increasing its service life. The drive motor is a variable frequency motor or a magnetically coupled speed-regulating motor.
[0028] Furthermore, the flow channel within the axial-flow steam ejector 6 is airfoil-shaped to maintain high ejection efficiency over a wide operating range.
[0029] In this embodiment, the low-pressure cylinder 12 is equipped with a low-pressure cylinder last-stage blade 18, an exhaust steam guide ring 19, a low-pressure cylinder exhaust steam temperature measuring point 20, and a cylinder body metal temperature measuring point 21. The low-pressure cylinder exhaust steam temperature measuring point 20 is located on the exhaust steam guide ring 19 to measure the low-pressure cylinder exhaust steam temperature, i.e., the steam temperature after the last-stage blade. The cylinder body metal temperature is obtained by monitoring the thermocouple pre-embedded in the cylinder body metal temperature measuring point 21.
[0030] Example 2 Based on Example 1, this embodiment provides a control method for a zero-output heating system of a cogeneration unit based on full extraction of steam between intermediate cylinder stages, including a fully cut-off low-pressure cylinder heating operation control mode and a conventional electrothermal coupling operation control mode.
[0031] The full-cut low-pressure cylinder heating operation control modes include: Step 1: Control the axial flow steam ejector device 6 to generate maximum ejection power, and adjust the regulating valve 7 to achieve maximum opening.
[0032] Control unit 10 controls the drive motor, causing the axial impeller 5 of the axial steam ejector 6 to smoothly increase its speed from zero to the rated maximum speed within 60 seconds. Simultaneously, regulating valve 7 reaches its maximum opening. A powerful axial suction field is formed in the chamber after the fifth stage, drawing almost all of the steam generated there (0.8 MPa, 360°C) into the extraction pipe 4 and sending it to the industrial steam supply network, instantly reducing the steam flow to the final eighth stage to 10%-15% of its original value. Due to the powerful suction capacity of the axial steam ejector 6, the achievable heating steam flow rate can theoretically approach the flow capacity of this intermediate stage, significantly exceeding the heating limit of traditional intermediate exhaust systems.
[0033] Step 2: Close the adjusting butterfly valve 13.
[0034] Approximately 30 seconds after the axial flow steam ejector 6 is started, the control unit 10 controls the adjusting butterfly valve 13 to slowly close until it is completely shut off, at which point the low-pressure cylinder 12 is isolated.
[0035] Step 3: Control the opening of the cooling steam flow regulating valve 16 to reach the preset opening value, and increase or decrease the opening of the cooling steam flow regulating valve 16 according to the obtained low-pressure cylinder exhaust temperature and cylinder metal temperature.
[0036] In this embodiment, the opening degree corresponding to 5% of the rated exhaust steam flow rate is used as the preset opening degree value, and closed-loop correction is performed according to the following logic: When the low-pressure cylinder exhaust temperature is below 80℃ or the cylinder body metal temperature is below 30℃, it is determined that the cooling is excessive, and the opening of the cooling steam flow regulating valve 16 is gradually reduced. When the low-pressure cylinder exhaust temperature is higher than 120℃ or the cylinder metal temperature is higher than 50℃, it is determined that the cooling is insufficient, and the opening of the cooling steam flow regulating valve 16 is gradually increased. When both the low-pressure cylinder exhaust temperature and the cylinder metal temperature are maintained within the preset range, the current valve position is maintained. If there is a conflict between the low-pressure cylinder exhaust temperature and the cylinder block metal temperature, the low-pressure cylinder exhaust temperature shall prevail.
[0037] During this process, the cooling steam flow rate is monitored in real time by the cooling steam flow measurement mechanism 15 to verify the adjustment effect and assist in control, ensuring that this small stream of steam from the final stage of the intermediate-pressure cylinder, whose parameters have been reduced, is accurately and constantly introduced into the low-pressure cylinder. After flowing through the flow passage of the low-pressure cylinder, the cooling steam is finally discharged in the form of exhaust steam. By monitoring the change in exhaust steam temperature, the cooling effect can be indirectly judged, ensuring that the internal components of the low-pressure cylinder are always maintained within a safe temperature range, and that the cooling flow rate is dynamically stabilized at the minimum safe value required to remove the heat from the blower.
[0038] The remaining steam (approximately 5%-10%) from the exhaust of the intermediate-pressure cylinder enters the heat recovery mechanism 17 to maintain the basic requirements for feedwater reheat.
[0039] Conventional electrothermal coupling operation control modes include: Step 1: Control the opening of the adjusting butterfly valve 13.
[0040] Step 2: Close the cooling steam flow regulating valve 16.
[0041] Step 3: Adjust the axial steam ejector 6 and regulating valve 7 according to the obtained total extraction steam demand command, extraction steam flow measurement value and extraction stage pressure measurement value.
[0042] The total steam extraction demand command and the measured steam extraction flow rate are compared. If the measured steam extraction flow rate is less than the total steam extraction demand command, the opening of the regulating valve 7 is increased. If the measured steam extraction flow rate is less than the total steam extraction demand command when the regulating valve 7 is 100% open, the axial flow steam ejector device 6 is adjusted to increase the measured steam extraction flow rate, thereby achieving shock-free and continuous regulation of the steam extraction flow rate.
[0043] When switching from the fully-cut low-pressure cylinder heating operation control mode back to the conventional electrothermal coupling operation control mode, the reverse sequence operation is performed: first, the adjusting butterfly valve is opened to restore the main passage; then, the power of the axial flow steam ejector is reduced; finally, the cooling steam flow regulating valve is closed.
[0044] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicating orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, are used only for the convenience of describing the invention 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 the invention. Furthermore, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined with "first," "second," etc., may explicitly or implicitly include one or more of that feature. In the description of this invention, unless otherwise stated, "a plurality of" means two or more.
[0045] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art will understand the specific meaning of the above terms in this invention based on the specific circumstances.
[0046] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.
Claims
1. A zero-output heating system for a cogeneration unit based on full extraction of steam between intermediate cylinder stages at medium pressure, characterized in that, include: Medium-pressure cylinder (1), steam extraction pipeline (4), axial flow steam ejector device (6), regulating valve (7), medium and low pressure cylinder connecting pipeline (11), low pressure cylinder cooling steam pipeline (14), heat recovery pipeline, low pressure cylinder (12) and control unit (10); The intermediate pressure cylinder (1) has an extraction steam flow channel (3) after the extraction stage moving blade (2), and the extraction steam pipe (4) is connected to the extraction steam flow channel (3) to transport the extracted steam to the heat user. The axial flow steam ejector (6) and the regulating valve (7) are both located on the extraction steam pipe (4). The axial flow steam ejector (6) is located upstream or downstream of the regulating valve (7). The axial flow steam ejector (6) and the regulating valve (7) work together to extract the steam from the intermediate pressure cylinder (1) to the extraction steam pipe (4). The medium and low pressure cylinder connecting pipe (11) is connected to the steam inlet of the low pressure cylinder (12) and the steam outlet of the medium pressure cylinder (1) respectively, and is provided with an adjusting butterfly valve (13) for connecting or disconnecting the medium and low pressure cylinder connecting pipe (11). Both ends of the low-pressure cylinder cooling steam pipe (14) are connected to the medium and low-pressure cylinder connecting pipe (11), and are located upstream and downstream of the adjusting butterfly valve (13), respectively; the low-pressure cylinder cooling steam pipe (14) is equipped with a cooling steam flow regulating valve (16). The heat recovery pipeline is connected to the exhaust port of the intermediate pressure cylinder (1); The control unit (10) is connected to the axial flow steam ejector (6), the regulating valve (7), the adjusting butterfly valve (13), and the cooling steam flow regulating valve (16).
2. The zero-output heating system for a cogeneration unit based on full extraction of steam between intermediate cylinder stages according to claim 1, characterized in that, The axial flow steam ejector (6) is equipped with a drive motor and an axial flow impeller (5). The drive motor is used to drive the axial flow impeller (5) to generate ejection power in the same direction as the steam flow in the extraction pipe.
3. The zero-output heating system for a cogeneration unit based on full extraction of steam between intermediate cylinder stages according to claim 2, characterized in that, The control unit (10) is connected to the drive motor and adjusts the ejection power by controlling the speed of the drive motor.
4. The zero-output heating system for a cogeneration unit based on full extraction of steam between intermediate cylinder stages according to claim 1, characterized in that, The low-pressure cylinder cooling steam pipe (14) is also equipped with a cooling steam flow measuring mechanism (15) for measuring the steam flow through the low-pressure cylinder cooling steam pipe (14).
5. The zero-output heating system for a cogeneration unit based on full extraction of steam between intermediate cylinder stages according to claim 1, characterized in that, The heat recovery pipeline is equipped with a heat recovery mechanism (17) for heat recovery of the residual steam discharged from the exhaust port of the intermediate pressure cylinder (1).
6. The zero-output heating system for a cogeneration unit based on full extraction of steam between intermediate cylinder stages according to claim 1, characterized in that, The extraction steam channel (3) adopts a smooth channel.
7. A control method for a zero-output heating system of a cogeneration unit based on full extraction of steam between intermediate cylinder stages as described in any one of claims 1-6, characterized in that, Including the full-cut low-pressure cylinder heating operation control mode; The fully-cut low-pressure cylinder heating operation control mode includes: Control the axial flow steam ejector (6) to generate maximum ejection power and adjust the regulating valve (7) to achieve maximum opening; Control the closing of the adjusting butterfly valve (13); Control the opening degree of the cooling steam flow regulating valve (16) to reach the preset opening value, and according to The obtained low-pressure cylinder exhaust temperature and cylinder metal temperature are used to increase or decrease the opening of the cooling steam flow regulating valve (16).
8. The control method for a zero-output heating system of a cogeneration unit based on full extraction of steam between intermediate cylinder stages according to claim 7, characterized in that, It also includes a conventional electrothermal coupling operation control mode; The conventional electrothermal coupling operation control mode includes: Control the opening of the adjusting butterfly valve (13); The cooling steam flow regulating valve (16) is closed. Adjust the axial steam ejector (6) and regulating valve (7) according to the total extraction steam demand command, the extraction steam flow measurement value and the pressure measurement value after the extraction stage.