Back pressure control system and control method of extraction back pressure feed water pump turbine

Abstract

The application discloses a back pressure control system of a steam extraction back pressure type feed water pump turbine. The system comprises a main turbine, a feed water pump turbine and a regenerative system. The regenerative system comprises a condenser, a steam extraction-condensate heat exchanger, a low-pressure heater, a deaerator and a high-pressure heater which are sequentially connected. The feed water pump turbine is connected with the high-pressure heater and the deaerator. The feed water pump turbine is provided with a sixth steam extraction port and a sixth steam extraction port bypass which are respectively connected with the low-pressure heater and the steam extraction-condensate heat exchanger. The two paths are respectively provided with a first steam extraction valve and a second steam extraction valve and are controlled by a controller. The back pressure control method of the steam extraction back pressure type feed water pump turbine directly stabilizes the back pressure of the feed water pump turbine by adjusting the opening degree of the second steam extraction valve to control the bypass steam exhaust capacity, does not affect the operation of the main machine, is accurate in adjustment, simple in structure, can reduce throttling loss and improve the economy and safety of the unit.

Description

Technical Field

[0001] This invention belongs to the technical field of steam turbine equipment, specifically relating to the back pressure control system of an extraction steam back pressure feedwater pump turbine, and also to the back pressure control method of an extraction steam back pressure feedwater pump turbine. Background Technology

[0002] As the need to further reduce unit coal consumption and improve cycle thermal efficiency grows, the requirements for unit steam parameters are constantly increasing. However, with the increase in steam parameters, the superheat of the extraction steam gradually increases, which can easily lead to an increase in irreversible heat exchange losses on the steam and water sides of the regenerative system heater, thereby weakening the benefits brought by the increase in steam parameters. Therefore, reducing the superheat of the heater heat source steam and improving its efficiency, thereby ensuring the improvement in benefits brought by steam parameters, is one of the primary tasks in the future development of high-parameter units. As a result, the extraction back-pressure feedwater pump turbine has been proposed and widely used.

[0003] Typically, the exhaust steam from feedwater pump turbines in units employing extraction back-pressure feedwater pump turbines is directed to the low-pressure heater (surface heat exchanger). However, in actual operation, considering the possibility of the low-pressure heater being disconnected during an accident, this disconnection would affect the steam balance and exhaust steam destination of the feedwater pump turbine. Therefore, the exhaust steam from the feedwater pump turbine also goes to the deaerator.

[0004] Back-pressure extraction steam turbines require simultaneous control of power generation, back pressure, and extraction steam volume. These variables interact with each other, making control more demanding. The flexible and reliable operation of back-pressure extraction steam turbines is fundamental to ensuring the safety and economy of the entire unit.

[0005] To address the above situation, the invention patent "Thermal System and Control Method for Back Pressure Control of Dual-Unit Regenerative Small Steam Turbine" (Publication No.: CN117211912A, Publication Date: 2023-12-12) discloses a thermal system and control method for back pressure control of a dual-unit regenerative feedwater pump turbine. It proposes two control measures, and by employing one or a combination of these measures, multiple control methods for feedwater pump turbine back pressure can be achieved, increasing the means of feedwater pump turbine back pressure regulation. Due to the combination of multiple control measures, compared to the control method of simply adjusting the overflow pipe regulating valve group, this invention can respond more quickly to changes in feedwater pump turbine back pressure, improving system flexibility and reliability, and reducing the design capacity requirements for the overflow pipe and overflow regulating valve group. However, the heat exchanger in this invention is designed before the low-pressure heater and after the deaerator, where the condensate temperature is high and the heat exchange temperature difference is small, requiring a larger heat exchanger and resulting in higher investment costs.

[0006] The patent "Thermal System and Control Method for Back Pressure Control of Small Steam Turbine" (Publication No.: CN109404075A, Authorization Date: 2019-03-01) discloses a thermal system and control method for back pressure control of a feedwater pump turbine. This invention adjusts the condensate temperature by regulating the extraction steam from the main steam turbine, thereby adjusting the back pressure of the feedwater pump turbine. This invention eliminates the need for an overflow pipe at the exhaust port of the feedwater pump turbine, achieving back pressure control while simultaneously reducing steam piping and simplifying the thermal system design, which is beneficial for simplifying the selection of heaters and ensuring safe operation in the regenerator unit. However, this invention directly adjusts the extraction steam from the main steam turbine, which may have a significant impact on the main steam turbine.

[0007] The patent "A Back Pressure Regulation System and Method for a Steam Turbine with Extraction Back Pressure" (Publication No.: CN110905616A, Publication Date: 2020-03-24) discloses a back pressure regulation system and method for a steam turbine with extraction back pressure. This system coordinates the control of three valves via a back pressure controller, achieving stable back pressure regulation while the small turbine drives the feedwater pump and extracts steam to connect to the regenerative heater. However, this invention has a complex system structure, requiring the three regulating valves to operate synchronously and in coordination, placing high demands on the controller and valve response speed, and making debugging difficult. Furthermore, when the back pressure is abnormal, steam is discharged to the condenser, resulting in wasted steam energy and reduced short-term economic efficiency. Summary of the Invention

[0008] The purpose of this invention is to provide a back pressure control system for a steam extraction back pressure feedwater pump turbine, which solves the problems of single adjustment methods and poor operational stability in the prior art, and realizes precise and stable control of the back pressure of the steam extraction back pressure feedwater pump turbine.

[0009] Another objective of this invention is to provide a back pressure control method for a steam turbine with extraction back pressure feedwater pump.

[0010] The technical solution of the present invention is a back pressure control system for a steam extraction back pressure feedwater pump turbine, comprising a main steam turbine, a feedwater pump turbine, and a regenerative system. The regenerative system includes a condenser, a steam extraction-condensate heat exchanger, a low-pressure heater, a deaerator, and a high-pressure heater connected in sequence. The feedwater pump turbine is connected to the high-pressure heater and deaerator. The feedwater pump turbine is equipped with a sixth extraction port and a sixth extraction port bypass, which are respectively connected to the low-pressure heater and the extraction steam-condensate heat exchanger. The two paths are respectively equipped with a first extraction steam valve and a second extraction steam valve and are controlled by a controller.

[0011] The invention is further characterized in that, A condensate pump is installed between the condenser and the extraction steam-condensate heat exchanger to pressurize the condensate and send it into the heat exchanger.

[0012] The main steam turbine is equipped with a first extraction port, a second extraction port, and a third extraction port, which are respectively connected to the high-pressure heater, the low-pressure heater, and the condenser.

[0013] The steam turbine of the extraction back pressure feedwater pump is equipped with a fourth extraction port and a fifth extraction port, which are respectively connected to the high-pressure heater and the deaerator.

[0014] The extraction steam-condensate heat exchanger is a surface heater with an internal superheated steam cooling section and a condensate cooling section.

[0015] The condensate from the extraction steam-condensate heat exchanger flows into the condenser via a condensate drain pipe.

[0016] Both the first and second extraction valves are electrically connected to the controller, and their openings are synchronously adjusted by the controller.

[0017] Another technical solution adopted in this invention is a back pressure control method for an extraction back pressure feedwater pump turbine, using the aforementioned back pressure control system for the extraction back pressure feedwater pump turbine, with the following steps: While the feedwater pump turbine drives the feedwater pump, it also extracts steam into the high-pressure heater, deaerator, and low-pressure heater to ensure normal reheating. The bypass exhaust steam from the sixth extraction port enters the extraction steam-condensate heat exchanger through the sixth extraction port bypass. The controller controls the opening of the second extraction steam valve to adjust the bypass exhaust steam volume, thereby adjusting the back pressure of the feedwater pump turbine.

[0018] Another feature of the present invention is that: During normal operation, the second extraction valve maintains a preset opening. When the back pressure of the feedwater pump turbine increases, the controller controls the second extraction valve to open wider. When the back pressure of the feedwater pump turbine decreases, the controller controls the second extraction valve to close less.

[0019] The bypass steam from the sixth extraction port enters the extraction-condensate heat exchanger to exchange heat with the condensate. After cooling, it flows into the condenser via a drain, thus achieving waste heat recovery.

[0020] The beneficial effects of this invention are: The back pressure control system of the extraction steam back pressure feedwater pump turbine of the present invention places the extraction steam-condensate heat exchanger at the outlet of the condensate pump, which can increase the heat exchange temperature difference, improve heat exchange efficiency, recover part of the energy, and reduce the investment cost of the equipment. The exhaust steam volume can be directly adjusted by the bypass extraction steam valve, resulting in precise back pressure regulation, fast response, and high stability. The system has a simple structure, fewer pipelines, and is easy to debug, reducing steam throttling losses, simplifying the thermal system, and improving the unit's economy; Not interfering with the main steam turbine's steam extraction and operation is beneficial to the safe operation of the unit; It can recover steam waste heat, reduce energy loss, and meet the high-efficiency and safe operation requirements of high-parameter units; The back pressure control method of the extraction back pressure feedwater pump turbine of the present invention controls the exhaust steam volume of the feedwater pump turbine by controlling the opening degree of the second extraction steam valve, thereby achieving the effect of controlling the back pressure of the feedwater pump turbine; ensuring stable control of the back pressure of the feedwater pump turbine during operation, and reducing the throttling loss at the inlet of the feedwater pump turbine during the adjustment process. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the back pressure control system of the steam turbine for the extraction back pressure feedwater pump of the present invention.

[0022] In the diagram, 1. Main steam turbine, 2. Feedwater pump turbine, 3. Fourth extraction port, 4. Fifth extraction port, 5. Sixth extraction port, 6. Sixth extraction port bypass, 7. Second extraction port, 8. Third extraction port, 9. Small steam turbine generator, 10. Main steam turbine generator, 11. High-pressure heater, 12. Deaerator, 13. Low-pressure heater, 14. Extraction steam-condensate heat exchanger, 15. Condensate pump, 16. Condenser, 17. First extraction valve, 18. Second extraction valve, 19. Water supply pipeline, 20. First extraction port, 21. Controller. Detailed Implementation

[0023] The technical solutions in the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0024] Example 1 The back pressure control system of the extraction back pressure feedwater pump turbine of the present invention has the following structure: Figure 1 As shown, it includes a main steam turbine 1, an extraction back-pressure feedwater pump turbine 2, and a regenerative system; The regenerative system includes a condenser 16, an extraction steam-condensate heat exchanger 14, a low-pressure heater 13, a deaerator 12, and a high-pressure heater 11 connected in sequence. The main steam turbine 1 is equipped with a first extraction port 20, a second extraction port 7, and a third extraction port 8, which are respectively connected to the high-pressure heater 11, the low-pressure heater 13, and the condenser 16.

[0025] The extraction back-pressure feedwater pump turbine 2 is connected to the high-pressure heater 11 and the deaerator 12. The feedwater pump turbine 2 is provided with a sixth extraction port 5 and a sixth extraction port bypass 6, which are respectively connected to the low-pressure heater 13 and the extraction steam-condensate heat exchanger 14. The sixth extraction port 5 is provided with a first extraction valve 17, and the sixth extraction port bypass 6 is provided with a second extraction valve 18. The opening degree of both the first extraction valve 17 and the second extraction valve 18 is controlled by the controller 21.

[0026] The back pressure control system of the extraction steam back pressure feedwater pump turbine of the present invention places the extraction steam-condensate heat exchanger at the outlet of the condensate pump, which can increase the heat exchange temperature difference, improve heat exchange efficiency, recover part of the energy, and reduce the investment cost of the equipment. The opening degree of the second extraction valve 18 is controlled by the controller, thereby controlling the steam discharge rate of the feedwater pump turbine and thus controlling the back pressure of the feedwater pump turbine. A larger opening degree of the second extraction valve 18 results in more steam flowing through the extraction-condensate heat exchanger 14, increasing the extraction rate and decreasing the back pressure of the extraction-back-pressure feedwater pump turbine 2. Conversely, a smaller opening degree of the second extraction valve 18 results in less steam flowing through the extraction-condensate heat exchanger 14, decreasing the extraction rate and increasing the back pressure of the extraction-back-pressure feedwater pump turbine 2. Direct adjustment of the steam discharge rate via the bypass extraction valve provides precise back pressure regulation with fast response and high stability.

[0027] Example 2 Based on Example 1, a condensate pump 15 is further provided between the condenser 16 and the extraction steam-condensate heat exchanger 14 to pressurize the condensate and send it into the heat exchanger.

[0028] The condensate flows from the condenser 16 to the condensate pump 15, where it is pressurized, and then flows sequentially through the extraction steam-condensate heat exchanger 14, the low-pressure heater 13, the deaerator 12, and the high-pressure heater 11.

[0029] Example 3 Based on Embodiment 2, the main steam turbine 1 is further provided with a first extraction port 20, a second extraction port 7, and a third extraction port 8. The first extraction port 20 is connected to the high-pressure heater 11, the second extraction port 7 is connected to the low-pressure heater 13, and the third extraction port 8 is connected to the condenser 16.

[0030] The steam turbine 2 of the extraction back pressure feedwater pump is equipped with a fourth extraction port 3 and a fifth extraction port 4, which are respectively connected to the high-pressure heater 11 and the deaerator 12.

[0031] Example 4 Based on Example 3, the extraction steam-condensate heat exchanger 14 is further a surface heater, with an internal superheated steam cooling section and a condensate cooling section.

[0032] Steam extracted from the sixth extraction port bypass 6 is cooled by the extraction-condensate heat exchanger 14, and the condensate flows into the condenser 16 through the condensate pipe 19.

[0033] Example 5 Based on Example 4, both the first extraction valve 17 and the second extraction valve 18 are electrically connected to the controller 21, and the controller 21 synchronously adjusts their opening.

[0034] The main steam turbine 1 is connected to the main steam turbine generator 10, and the feedwater pump turbine 2 is connected to the small steam turbine generator 9 to ensure power supply for the equipment.

[0035] Existing technologies typically stabilize exhaust back pressure indirectly by adjusting the opening of the steam inlet regulating valve of the feedwater pump turbine to change the steam flow rate, which cannot simultaneously achieve both efficiency and stability. This invention, based on the original extraction back pressure feedwater pump turbine back pressure control, adds an extraction-condensate heat exchanger, along with related piping and control systems, to change the exhaust steam flow of the feedwater pump turbine, thereby achieving the purpose of controlling the feedwater pump turbine back pressure. The system has a simple structure, fewer piping, and is easy to debug, reducing inlet steam throttling losses, simplifying the thermal system, and improving the unit's economic efficiency.

[0036] Example 6 The back pressure control method for the extraction back pressure feedwater pump turbine of the present invention uses the back pressure control system of the extraction back pressure feedwater pump turbine of Embodiment 5 above, and the steps are as follows: Step 1: While the steam turbine 2 drives the feedwater pump, the steam is extracted into the high-pressure heater 11, deaerator 12, and low-pressure heater 13 to ensure normal reheat. Step 2: The bypass exhaust steam from the sixth extraction port 5 enters the extraction steam-condensate heat exchanger 14 via the sixth extraction steam port bypass 6, where it exchanges heat efficiently with the low-temperature condensate at a large temperature difference, recovering some energy. The controller 21 synchronously sends commands to open or close the second extraction steam valve 18 to control the bypass exhaust steam volume and regulate the back pressure of the extraction steam back pressure feedwater pump turbine 2.

[0037] When the back pressure of the extraction back pressure feedwater pump turbine 2 increases, the controller 21 controls the opening of the second extraction steam valve 18. The larger the opening of the second extraction steam valve, the more steam flows through the extraction steam-condensate heat exchanger 14, the more steam is extracted, and the back pressure of the feedwater pump turbine 2 decreases.

[0038] Conversely, when the back pressure of the extraction back pressure feedwater pump turbine 2 decreases, the controller 21 controls the second extraction valve 18 to close less. The smaller the opening of the second extraction valve, the less steam flows through the extraction-condensate heat exchanger 14, the less steam is extracted, and the back pressure of the feedwater pump turbine 2 increases.

[0039] By coordinating and precisely controlling the back pressure through controller 21, the control performance of the feedwater pump turbine 2 can be improved, ensuring its economical and reliable operation.

[0040] The back pressure control method of the extraction back pressure feedwater pump turbine of the present invention does not interfere with the extraction of steam from the main turbine 1 throughout the entire process, does not affect the operation of the main unit, simplifies the system, reduces equipment investment, and takes into account the regenerative efficiency, operational safety and economy of high-parameter units.

[0041] Example 7 Using the back pressure control method of the extraction back pressure feedwater pump turbine in Embodiment 6 of the present invention, when the back pressure of the extraction back pressure feedwater pump turbine is not adjusted, the opening degree of the second extraction valve is set to 50%. At this time, the back pressure of the feedwater pump turbine is 8.02 bar.

[0042] When the back pressure of the extraction back pressure feedwater pump turbine needs to be increased, the opening of the second extraction valve is reduced by 25%. At this time, the back pressure of the feedwater pump turbine is 8.90 bar.

[0043] When the back pressure of the extraction back pressure feedwater pump turbine needs to be reduced, the opening of the second extraction valve is increased by 25%. At this time, the back pressure of the feedwater pump turbine is 7.46 bar.

[0044] The back pressure control system of the extraction back pressure feedwater pump turbine of the present invention has the following advantages: Placing the extraction steam-condensate heat exchanger at the outlet of the condensate pump can increase the heat exchange temperature difference, improve heat exchange efficiency, recover some energy, and reduce equipment investment costs. The exhaust steam volume can be directly adjusted by the bypass extraction steam valve, resulting in precise back pressure regulation, fast response, and high stability. The system has a simple structure, fewer pipelines, and is easy to debug, reducing steam throttling losses, simplifying the thermal system, and improving the unit's economy; Not interfering with the main steam turbine's steam extraction and operation is beneficial to the safe operation of the unit; It can recover steam waste heat, reduce energy loss, and meet the high-efficiency and safe operation requirements of high-parameter units; The back pressure control method of the extraction back pressure feedwater pump turbine of the present invention controls the exhaust steam volume of the feedwater pump turbine by controlling the opening degree of the second extraction steam valve, thereby achieving the effect of controlling the back pressure of the feedwater pump turbine; ensuring stable control of the back pressure of the feedwater pump turbine during operation, and reducing the throttling loss at the inlet of the feedwater pump turbine during the adjustment process. It has precise adjustment, simple structure, high heat exchange efficiency, and low investment, and can reduce throttling losses and improve the economy and safety of the unit.

[0045] Finally, it should be noted that in this application, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0046] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0047] The above description of the disclosed embodiments enables those skilled in the art to make or use this application. 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 this application. Therefore, this application 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 back pressure control system for a steam turbine turbine with extraction back pressure, characterized in that, It includes the main steam turbine (1), the feedwater pump turbine (2), and the regenerative system; The regenerative system includes a condenser (16), a steam extraction-condensate heat exchanger (14), a low-pressure heater (13), a deaerator (12), and a high-pressure heater (11) connected in sequence. The feedwater pump turbine (2) is connected to the high-pressure heater (11) and the deaerator (12). The feedwater pump turbine (2) is equipped with a sixth extraction port (5) and a sixth extraction port bypass (6), which are respectively connected to the low-pressure heater (13) and the extraction steam-condensate heat exchanger (14). The two paths are respectively equipped with a first extraction steam valve (17) and a second extraction steam valve (18) and are controlled by a controller (21).

2. The back pressure control system for the extraction back pressure feedwater pump turbine according to claim 1, characterized in that, A condensate pump (15) is provided between the condenser (16) and the extraction steam-condensate heat exchanger (14) to pressurize the condensate and send it into the heat exchanger.

3. The back pressure control system for the extraction back pressure feedwater pump turbine according to claim 1, characterized in that, The main steam turbine (1) is provided with a first steam extraction port (20), a second steam extraction port (7), and a third steam extraction port (8), which are respectively connected to the high-pressure heater (11), the low-pressure heater (13), and the condenser (16).

4. The back pressure control system for the extraction back pressure feedwater pump turbine according to claim 1, characterized in that, The feedwater pump turbine (2) is provided with a fourth steam extraction port (3) and a fifth steam extraction port (4), which are respectively connected to the high-pressure heater (11) and the deaerator (12).

5. The back pressure control system for the extraction back pressure feedwater pump turbine according to claim 1, characterized in that, The extraction steam-condensate heat exchanger (14) is a surface heater with an internal superheated steam cooling section and a condensate cooling section.

6. The back pressure control system for the extraction back pressure feedwater pump turbine according to claim 1, characterized in that, The condensate from the extraction steam-condensate heat exchanger (14) flows into the condenser (16) via the condensate drain pipe (19).

7. The back pressure control system for the extraction back pressure feedwater pump turbine according to claim 1, characterized in that, The first extraction valve (17) and the second extraction valve (18) are both electrically connected to the controller (21), and the controller (21) adjusts their openings synchronously.

8. A back pressure control method for a steam turbine with extraction back pressure feedwater pump, characterized in that, Using the back pressure control system of the extraction back pressure feedwater pump turbine as described in any one of claims 1-7, the steps are as follows: While the feedwater pump turbine (2) drives the feedwater pump, it extracts steam into the high-pressure heater (11), deaerator (12), and low-pressure heater (13) to ensure normal reheating. The bypass exhaust steam from the sixth extraction port (5) enters the extraction steam-condensate heat exchanger (14) through the sixth extraction port bypass (6). The controller (21) controls the opening of the second extraction steam valve (18) to adjust the bypass exhaust steam volume, thereby adjusting the back pressure of the feedwater pump turbine (2).

9. The back pressure control method for an extraction back pressure feedwater pump turbine according to claim 8, characterized in that, During normal operation, the second extraction valve (18) maintains a preset opening. When the back pressure of the feedwater pump turbine (2) increases, the controller (21) controls the second extraction valve (18) to open wider. When the back pressure of the feedwater pump turbine (2) decreases, the controller (21) controls the second extraction valve (18) to close less.

10. The back pressure control method for a steam extraction back pressure feedwater pump turbine according to claim 8, characterized in that, Steam from the sixth extraction port bypass (6) enters the extraction-condensate heat exchanger (14) to exchange heat with the condensate. After cooling, it flows into the condenser (16) through the drain, thus realizing waste heat recovery.

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