Energy-saving operation method for feedwater temperature rise in start-up stage of thermal power generating unit

Abstract

The application discloses a power plant start-up stage feedwater heating energy-saving operation method, which is applied to a self-adaptive feedwater regenerative system in a thermal power plant; the self-adaptive feedwater regenerative system comprises a high-pressure heater group and a bypass steam supply branch; the bypass steam supply branch is respectively communicated with a condenser in the thermal power plant and a steam side of at least one high-pressure heater in the high-pressure heater group; during the start-up stage of the thermal power plant, the pressure value change of main steam is acquired and monitored in real time, so as to judge whether the pressure value is in a preset operation range; if yes, the bypass steam supply branch is opened, part of the main steam is introduced into the steam side of the at least one high-pressure heater in the high-pressure heater group, the feedwater flowing through the water side of the high-pressure heater is heated, and meanwhile, the remaining part of the main steam is introduced into the condenser; after the thermal power plant meets preset normal operation conditions, the bypass steam supply branch is closed, and a normal feedwater heating mode is switched synchronously.

Description

Technical Field

[0001] This application relates to the field of thermal power generation technology, and in particular to a method for energy-saving operation of feedwater heating during the start-up phase of a thermal power generating unit. Background Technology

[0002] Thermal power generating units are the backbone power source of modern power grids, undertaking base load and peak shaving tasks. A typical thermal power generating unit mainly includes: boiler, steam turbine, condenser, feedwater regeneration system, and bypass system.

[0003] During normal operation, the coordinated process of each component is as follows: the boiler converts the chemical energy of the fuel into the thermal energy of the steam, generating high-temperature and high-pressure main steam; the main steam drives the turbine to rotate, converting thermal energy into mechanical energy, driving the generator to generate electricity; the exhaust steam after doing work enters the condenser, is cooled and condensed into water by the circulating water, and at the same time establishes and maintains a vacuum; after the condensate is pressurized by the condensate pump, it flows through the low-pressure heater, deaerator, feedwater pump, and high-pressure heater in sequence, and is gradually heated before being sent back to the boiler to complete the thermodynamic cycle.

[0004] The feedwater regeneration system is a core component for improving the unit's thermal efficiency. During normal operation, this system extracts a portion of steam from each stage of the turbine (called extraction steam) and sends it to the corresponding high-pressure or low-pressure heaters to heat the feedwater or condensate flowing through it. Specifically, the low-pressure heater uses extraction steam from the turbine's low-pressure cylinder to heat the condensate from the condenser; the deaerator uses exhaust steam from the intermediate-pressure cylinder to deaerate and heat the condensate; and the high-pressure heater uses extraction steam from the high-pressure and intermediate-pressure cylinders to further heat the feedwater. Through this staged heating method, the temperature of the feedwater entering the boiler is significantly increased, thereby reducing boiler fuel consumption and improving the overall thermal economy of the unit.

[0005] With the large-scale grid connection of new energy sources (wind power, photovoltaics, etc.), the power grid has placed higher demands on the peak-shaving capacity and rapid start-up and shutdown performance of thermal power units. Frequent start-up and shutdown have become the norm for the operation of thermal power units, and the existing water heating methods during the start-up phase have revealed a series of problems: 1. Low feedwater temperature and increased energy consumption: During startup, the boiler relies mainly on deaerator heating, making it difficult to quickly raise the feedwater temperature. This prolongs the boiler's heating and pressurization process, significantly increasing fuel consumption. Furthermore, low-temperature feedwater causes substantial thermal stress on the boiler's heating surfaces, affecting the equipment's lifespan.

[0006] 2. Low energy efficiency: The high-pressure heater was put into operation late, and a large amount of low-grade steam was not effectively utilized during the start-up phase. It was directly discharged into the condenser through the bypass system, resulting in energy waste.

[0007] 3. Poor peak-shaving adaptability: Long start-up times and high energy consumption result in slow response times to grid peak-shaving commands, making it difficult to flexibly match the rapidly changing demands of grid load. With a high proportion of renewable energy integration, the rapid start-up and shutdown capability of thermal power units has become a key constraint affecting the grid's absorption capacity.

[0008] 4. Equipment safety risks exist: Some power plants attempt to put high-pressure heaters into operation in advance to increase feedwater temperature. However, due to improper control of main steam parameters during the start-up phase, problems such as overpressure on the water side of the high-pressure heater and poor drainage on the steam side can easily occur, affecting the safe operation of the equipment.

[0009] In summary, the existing technology suffers from a problem during the start-up phase where the feedwater temperature is significantly too low, resulting in high energy consumption, long start-up time, and significant thermal stress, which endangers equipment safety. Summary of the Invention

[0010] In view of this, the present application provides a method for energy-saving operation of feedwater heating during the start-up phase of a thermal power generating unit.

[0011] According to one aspect of this application, a method for energy-saving operation of feedwater heating during the start-up phase of a thermal power generating unit is provided. The method is applied to an adaptive feedwater regeneration system in the thermal power generating unit. The adaptive feedwater regeneration system includes a high-pressure heater group and a bypass steam supply branch. The bypass steam supply branch is connected to the steam side of the condenser in the thermal power generating unit and at least one high-pressure heater in the high-pressure heater group. The method includes: During the startup phase of the thermal power generating unit, the pressure change of the main steam is acquired and monitored in real time to determine whether the pressure of the main steam is within the preset operating range; wherein, the pressure of the main steam refers to the steam pressure at the outlet of the boiler superheater in the thermal power generating unit. If so, the bypass steam supply branch is opened, and part of the main steam is introduced into the steam side of at least one high-pressure heater in the high-pressure heater group to heat the feedwater flowing through the water side of the high-pressure heater, so that the feedwater temperature is raised to the preset target range, while the remaining part of the main steam is introduced into the condenser. After the thermal power generating unit meets the preset normal operating conditions, the bypass steam supply branch is shut down and the normal feedwater heating mode is switched simultaneously.

[0012] Compared with existing technologies, this system has significant advantages: To address the aforementioned problems in the startup phase of existing thermal power generating units, this application provides a method for energy-saving operation of feedwater heating during the startup phase of thermal power generating units. By real-time monitoring of the main steam pressure at the boiler superheater outlet, when the main steam pressure is within a preset operating range, the bypass steam supply branch is opened to introduce part of the main steam into the steam side of the high-pressure heater to heat the feedwater, raising the feedwater temperature to a preset target range. Simultaneously, the remaining main steam is introduced into the condenser. After the unit meets the preset normal operating conditions, the bypass steam supply branch is closed and the unit switches to normal feedwater heating mode. This allows for a significant increase in feedwater temperature during the startup phase of the thermal power generating unit, effectively shortening the boiler heating and pressurization time, reducing fuel consumption, decreasing equipment thermal stress, and improving energy utilization efficiency and unit peak-shaving response speed.

[0013] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, the following are specific embodiments of this application. Attached Figure Description

[0014] The accompanying drawings, which are included to provide a further understanding of this application and form part of this application, illustrate exemplary embodiments and are used to explain this application, but do not constitute an undue limitation of this application. In the drawings: Figure 1 A schematic flowchart of a method for energy-saving operation of feedwater heating during the start-up phase of a thermal power generating unit, provided in an embodiment of this application, is shown. Figure 2 A schematic diagram showing the structural connection of the high-pressure heater group and the low-pressure heater group in the thermal power generator set provided in the embodiment of this application is shown. Detailed Implementation

[0015] The present application will be described in detail below with reference to the accompanying drawings and embodiments. It should be noted that, unless otherwise specified, the embodiments and features described in the embodiments of the present application can be combined with each other.

[0016] It should be understood that low feedwater temperature during the startup phase is a core issue restricting the rapid startup and energy-saving operation of thermal power generating units. Low feedwater temperature not only directly prolongs the boiler's heating and pressurization process and increases fuel consumption, but also generates significant thermal stress due to excessive temperature differences, jeopardizing the service life of the heating surfaces. The focus of this application is to solve the above problems by improving the connectivity and operation of some equipment in the feedwater regeneration system to achieve a rapid increase in feedwater temperature during the startup phase. In other words, the technical solution of this application can be implemented without changing the existing main equipment structure of the power plant (boiler, turbine, condenser, high-pressure heater group, low-pressure heater group, deaerator, feedwater pump, and bypass system, etc.), simply by adding or adjusting some pipelines and control logic, demonstrating good compatibility and economy.

[0017] This embodiment provides a method for energy-saving operation of feedwater heating during the start-up phase of a thermal power generating unit, such as... Figure 1 As shown, the method is applied to an adaptive feedwater regeneration system in a thermal power generating unit. The adaptive feedwater regeneration system includes a high-pressure heater group and a bypass steam supply branch. The bypass steam supply branch is connected to the steam side of the condenser in the thermal power generating unit and at least one high-pressure heater in the high-pressure heater group.

[0018] It should be noted that the "bypass steam supply branch" mentioned here is not the bypass system in existing equipment. This bypass steam supply branch is an additional steam supply channel added or formed by modifying existing pipelines. One end of this bypass steam supply branch is connected to the main steam pipeline or the steam pipeline of the conventional bypass system, and the other end is connected to the steam side of the high-pressure heater. It is specifically used to introduce a portion of the main steam into the high-pressure heater during the start-up phase. The conventional bypass system and the bypass steam supply branch of this application can work together, but they are functionally independent.

[0019] It should be noted that during the startup phase of a thermal power generating unit, the steam turbine has not yet started running, therefore there is no steam extraction from the turbine. Specifically, during the unit startup phase (from boiler ignition to before the turbine starts running), the turbine is stationary, its rotor has not yet rotated, and there is no steam flow in the cylinders. Since steam extraction is steam drawn from the impellers of each stage of the turbine, its generation requires that the turbine has started running and the rotor is rotating and doing work. When the turbine is stationary, there is naturally no steam available for use in the extraction pipes at each stage.

[0020] like Figure 1 As shown, the method includes S110-S130, specifically: S110: During the startup phase of a thermal power generating unit, the pressure change of the main steam is acquired and monitored in real time to determine whether the pressure of the main steam is within the preset operating range; wherein, the pressure of the main steam refers to the steam pressure at the outlet of the boiler superheater in the thermal power generating unit.

[0021] For example, the main steam pressure value can be obtained in real time by a pressure transmitter installed on the main steam pipeline between the boiler superheater outlet and the main steam valve of the turbine high-pressure cylinder. Each time the value is obtained, it is determined whether it is within the preset operating range. To ensure the accuracy of the determination, multiple pressure transmitters can be installed on the main steam pipeline. When the readings of at least two pressure transmitters are within the preset operating range, the subsequent steps are executed.

[0022] It should be noted that the preset commissioning range refers to the range of main steam pressure values ​​pre-set to ensure the safe and efficient introduction of main steam into the high-pressure heater during the start-up phase. Within this pressure range, the main steam has sufficient thermal energy to heat the feedwater, while its pressure and temperature are within the safe range allowed by the design of the high-pressure heater. For example, the preset commissioning range is 0.16 MPa to 0.25 MPa, preferably 0.2 MPa.

[0023] S120: If so, open the bypass steam supply branch and introduce part of the main steam into the steam side of at least one high-pressure heater in the high-pressure heater group to heat the feedwater flowing through the water side of the high-pressure heater, so that the feedwater temperature is raised to the preset target range, while the remaining part of the main steam is introduced into the condenser.

[0024] Here, when the high-pressure heater group includes only one high-pressure heater, that high-pressure heater is high-pressure heater No. 2. High-pressure heater No. 2 refers to the high-pressure heater numbered second in descending order of turbine extraction steam pressure, corresponding to the second extraction stage (i.e., high-pressure cylinder exhaust). In this application, the numbering of high-pressure heater No. 2 follows power industry standards. Different power plants may use different numbering systems (such as high-pressure heater No. 12 in KKS coding), but regardless of the number, all high-pressure heaters whose steam side is connected to the high-pressure cylinder exhaust pipe during normal operation fall within the scope of high-pressure heater No. 2 in this application.

[0025] For cases where the high-pressure heater group includes only one high-pressure heater, the bypass steam supply branch includes a steam supply branch and a condenser branch; wherein, the steam supply branch includes a high bypass steam inlet valve, which is used to introduce part of the main steam into the steam side of at least one high-pressure heater in the high-pressure heater group; the condenser branch includes a low bypass steam inlet valve connected to the condenser in the thermal power generator unit.

[0026] The steam supply branch is an additional or modified steam supply channel added to the conventional bypass system in this application, with its core component being the high-pressure bypass steam inlet valve. This valve is not used to control conventional bypass functions (such as protecting the reheater), but is specifically used to introduce a portion of the main steam into the steam side of the high-pressure heater during the startup phase. By adjusting the opening of this valve, the amount of steam entering the high-pressure heater can be precisely controlled, thereby controlling the feedwater heating rate. It should be noted that the high-pressure bypass steam inlet valve can be a conventional valve in structure, but its functional positioning in this application (for high-pressure heater steam supply) differs from the function of conventional bypass valves in the prior art (protecting the reheater and controlling pressure). Furthermore, the condenser branch is an existing passage in the conventional bypass system, with its core component being the low-pressure bypass steam inlet valve. This valve is connected to the condenser in the thermal power generating unit and is used to introduce the remaining main steam (i.e., steam that has not entered the steam supply branch) into the condenser during the startup phase to maintain condenser vacuum and recover working fluid and heat. The execution method of this branch is basically the same as that of conventional bypass systems in the prior art, and this application does not substantially change its function.

[0027] In another scenario, the high-pressure heater group includes multiple high-pressure heaters connected in series. Correspondingly, the bypass steam supply branch includes at least one steam supply branch and one condenser branch. According to preset requirements, at least one high-pressure heater from the multiple high-pressure heater groups is selected and connected to the steam supply branch. Each steam supply branch includes a high-pressure bypass inlet valve for introducing a portion of the main steam into the steam side of the corresponding high-pressure heater. The condenser branch includes a low-pressure bypass inlet valve connected to the condenser in the thermal power generating unit. Here, the preset requirements include at least one of the following: feedwater temperature rise requirements during startup, the availability of the high-pressure heaters, matching conditions for the main steam pressure, feedwater flow path location, and thermal economy optimization requirements.

[0028] For example, such as Figure 2As shown, the high-pressure heater group includes three high-pressure heaters connected in series: No. 1 (high-pressure heater 11 in the figure), No. 2 (high-pressure heater 12 in the figure), and No. 3 (high-pressure heater 13 in the figure). The steam supply branch connected to No. 2 high-pressure heater is used to introduce part of the main steam into the steam side of No. 2 high-pressure heater during the start-up phase to heat the feedwater flowing through the water side of No. 2 high-pressure heater. The numbering of high-pressure heaters 1, 2, and 3 follows the principle of decreasing turbine extraction steam pressure. High-pressure heater 1 corresponds to the first stage extraction steam with the highest pressure, high-pressure heater 2 corresponds to the second stage extraction steam (high-pressure cylinder exhaust steam), and high-pressure heater 3 corresponds to the third stage extraction steam. High-pressure heaters 1, 2, and 3 are arranged in series according to the feedwater flow. Specifically, the feedwater (from the deaerator and pressurized by the feedwater pump) flows sequentially through the water side of high-pressure heater 3, the water side of high-pressure heater 2, and the water side of high-pressure heater 1, finally entering the boiler economizer. The steam side of each high-pressure heater is connected to the extraction steam pipeline of the corresponding stage of the turbine: the steam side of No. 1 high-pressure heater is connected to a certain stage of extraction steam from the turbine's high-pressure cylinder; the steam side of No. 2 high-pressure heater is connected to the exhaust steam from the high-pressure cylinder (i.e., the cold reheat steam pipeline); and the steam side of No. 3 high-pressure heater is connected to the inlet steam from the intermediate-pressure cylinder or the first stage extraction steam. Furthermore, the condensate from the three high-pressure heaters flows by gravity in stages. Specifically, the condensate from No. 1 high-pressure heater flows by gravity to No. 2 high-pressure heater, the condensate from No. 2 high-pressure heater flows by gravity to No. 3 high-pressure heater, and the condensate from No. 3 high-pressure heater is finally discharged into the deaerator. The "to deaerator" marked in the diagram refers to this condensate pipeline. In addition, the diagram also marks "to emergency condensate expansion" (an emergency discharge pipeline connected to the emergency condensate expansion tank for emergency discharge in case of an accident) and "nitrogen charging header" (a nitrogen charging pipeline connected to the steam side of the high-pressure heater for corrosion protection during shutdown).

[0029] During normal unit operation, the extracted steam from each pressure level of the turbine enters the steam side of the corresponding high-pressure heater, transferring heat to the feedwater flowing through the water-side tube bundle, thus gradually increasing the feedwater temperature. Specifically, the No. 3 high-pressure heater uses steam extracted from the intermediate-pressure cylinder for the first stage of feedwater heating, the No. 2 high-pressure heater uses exhaust steam from the high-pressure cylinder for the second stage, and the No. 1 high-pressure heater uses higher-pressure steam extracted from the high-pressure cylinder for the third stage, raising the feedwater temperature to the higher temperature level required by the boiler (typically above 260°C). This staged heating method effectively utilizes the extracted steam energy from different pressure levels of the turbine, reducing boiler fuel consumption and improving the overall thermal economy of the unit.

[0030] To ensure the safety and efficiency of the feedwater heating process and avoid excessive thermal stress or pressure fluctuations that could affect system stability due to rapid temperature rise, this application, after opening the bypass steam supply branch, also includes: real-time acquisition of feedwater temperature, water level inside the high-pressure heater in the high-pressure heater group, and condensate temperature, in combination with the main steam pressure value, to determine the opening degree of the high bypass steam inlet valve, thereby controlling the feedwater temperature rise rate; and, based on the main steam pressure value, determining the opening degree of the low bypass steam inlet valve, thereby controlling the main steam pressure fluctuation range.

[0031] It should be noted that the real-time acquisition of parameters such as feedwater temperature, internal water level of the high-pressure heater, condensate temperature, and main steam pressure can all be achieved using existing sensors and monitoring systems in thermal power generating units. Specifically, feedwater temperature can be obtained using temperature transmitters installed on the inlet and outlet pipes of the high-pressure heater; the internal water level of the high-pressure heater can be obtained using differential pressure level gauges or electrical contact level gauges mounted on the main casing of the high-pressure heater; condensate temperature can be obtained using temperature transmitters installed on the condensate pipes; and the main steam pressure can be obtained using pressure transmitters installed on the main steam pipe between the boiler superheater outlet and the main steam valve. All of the aforementioned sensors and monitoring equipment are standard configurations already in place in the thermal power generation industry.

[0032] Here, the feedwater temperature, the water level inside the high-pressure heater in the high-pressure heater group, and the condensate temperature, combined with the main steam pressure, have the following specific synergistic effects: (1) Feedwater temperature is positively correlated with the opening of the high bypass steam inlet valve: when the feedwater temperature is too low, the high bypass steam inlet valve needs to be opened wider to increase the steam inlet; when the feedwater temperature is close to the target value, the high bypass steam inlet valve needs to be closed to reduce the steam inlet. Feedwater temperature is the "main demand signal" that drives the adjustment of the high bypass steam inlet valve.

[0033] (2) When the water level inside the high-pressure heater exceeds the safety threshold, regardless of the feedwater temperature requirement, the high-pressure bypass steam inlet valve must be closed or shut off first to cut off the steam source in order to prevent the turbine from being flooded due to excessive water level. That is, water level safety takes precedence over temperature rise requirements.

[0034] (3) When the condensate temperature is too low, it indicates that the steam heat release is sufficient or the steam intake is insufficient. The high bypass steam intake valve can be opened wider. When the condensate temperature is too high, it indicates that the steam heat release is insufficient or the steam intake is too large. The high bypass steam intake valve should be closed wider. The condensate temperature plays a "fine-tuning" role in the opening of the high bypass steam intake valve, rather than being the main control signal.

[0035] (4) When the main steam pressure is lower than the preset lower limit for operation, the high bypass steam inlet valve shall not be opened (lower limit constraint); when the main steam pressure is within the operation range, the opening of the high bypass steam inlet valve is negatively correlated with the main steam pressure. When the pressure is too high, the high bypass steam inlet valve can be opened appropriately to increase steam supply and assist in pressure reduction; when the pressure is too low, the high bypass steam inlet valve should be closed to ensure the boiler steam production.

[0036] That is, among the four parameters, the feedwater temperature requirement is the primary factor, water level safety is the priority constraint, condensate temperature is the correction reference, and main steam pressure is the boundary condition, which together determine the final opening degree of the high bypass steam inlet valve.

[0037] Furthermore, the opening control of the low-side bypass steam inlet valve is based on the main steam pressure, while simultaneously coordinating with the opening of the high-side bypass valve and being constrained by the condenser status. The synergistic influence relationships between the various parameters are as follows: (1) When the main steam pressure rises, the low-pressure bypass valve is opened wider to discharge more steam into the condenser to reduce the pressure; when the main steam pressure drops, the low-pressure bypass valve is closed to reduce the amount of steam discharged to maintain the pressure. The main steam pressure is the "core signal" that drives the regulation of the low-pressure bypass valve.

[0038] (2) After the high-pressure bypass valve opens, a large amount of steam enters the reheater. If the low-pressure bypass valve does not open synchronously, the reheater pressure will rise sharply. Therefore, the opening degree of the low-pressure bypass valve must follow the opening degree of the high-pressure bypass valve—when the high-pressure bypass valve opens wide, the low-pressure bypass valve must also open wide accordingly; when the high-pressure bypass valve closes narrowly, the low-pressure bypass valve must also close narrowly accordingly. A "follow-up linkage" relationship is formed between the two.

[0039] (3) When the condenser vacuum is too low or the exhaust temperature is too high, even if there is a need to reduce the main steam pressure, the low-pressure bypass valve must be restricted or closed to protect the condenser safety. That is, condenser safety takes precedence over pressure regulation.

[0040] It should be understood that the above control logic can be implemented through the existing distributed control system (DCS) or bypass control system of the thermal power generating unit without additional hardware investment. The real-time monitored values ​​of various parameters (feedwater temperature, high-pressure heater water level, condensate temperature, main steam pressure, etc.) serve as input signals to the control system. After calculation by the PID controller, valve opening commands are output, which drive the valves to move through electro-hydraulic or electric actuators, forming a closed-loop automatic control.

[0041] To further improve the overall thermal efficiency of the feedwater regeneration system and provide a complete regeneration channel for the normal operation switch after the feedwater is heated during the start-up phase of this application, the adaptive feedwater regeneration system also includes a low-pressure heater group; the low-pressure heater group includes at least one low-pressure heater; wherein, the low-pressure heater group is located between the condenser and the deaerator in the thermal power generator unit, and is used to heat the condensate from the condenser and deliver the heated water to the deaerator.

[0042] Please continue to refer to Figure 2 The low-pressure heater group includes low-pressure heater No. 5 (15 in the figure), low-pressure heater No. 6 (16 in the figure), and low-pressure heater No. 7 (17 in the figure), connected in series. The numbering of low-pressure heaters No. 5, 6, and 7 follows the principle of decreasing turbine extraction steam pressure (this numbering rule differs from that of high-pressure heaters; a higher number for a low-pressure heater indicates a lower extraction steam pressure and closer proximity to the condenser). Low-pressure heater No. 5 corresponds to extraction steam from the lower-pressure cylinder at a higher pressure, low-pressure heater No. 6 corresponds to extraction steam from the lower-pressure cylinder at a lower pressure, and low-pressure heater No. 7 corresponds to extraction steam from the lowest-pressure cylinder at the lowest pressure (the stage closest to the condenser).

[0043] In terms of connection method, the three low-pressure heaters are arranged in series according to the condensate flow: condensate from the condenser hot well is pressurized by the condensate pump and flows sequentially through the water side of the No. 7 low-pressure heater, the water side of the No. 6 low-pressure heater, and the water side of the No. 5 low-pressure heater, and finally enters the deaerator. The steam side of each low-pressure heater is connected to the extraction steam pipeline of the corresponding level of the turbine low-pressure cylinder.

[0044] Regarding condensate drainage, the three low-pressure heaters employ a staged gravity flow method: condensate from heater #5 flows by gravity to heater #6, condensate from heater #6 flows by gravity to heater #7, and condensate from heater #7 is ultimately discharged into the condenser. The "to exhaust device" marked in the diagram refers to the normal condensate and exhaust pipes of the low-pressure heaters, used to discharge condensate and non-condensable gases to the condenser's exhaust device (condenser throat) to maintain the vacuum state on the steam side of the low-pressure heaters and recover the working fluid. Furthermore, the "to main unit expansion tank" refers to the condensate pipe connected to the main unit expansion tank. The main unit expansion tank is specifically used to collect condensate from the turbine body and main steam and reheat steam pipes. Some condensate from the low-pressure heaters (such as start-up condensate or emergency condensate) can also be discharged into the main unit expansion tank for expansion and cooling. Finally, the "water drain from heater #7" marked at heater #7 in the diagram refers to the drain pipe connected to the water side of heater #7. This drain outlet is used to drain the water accumulated in the water-side pipe bundle when the low-pressure heater is shut down for maintenance, or to drain water during winter shutdown to prevent freezing and cracking.

[0045] During normal operation of the unit, the extracted steam from each pressure level of the turbine's low-pressure cylinder enters the steam side of the corresponding low-pressure heater, transferring heat to the condensate flowing through the water-side tube bundle, thus gradually increasing the condensate temperature. This staged heating method effectively utilizes the energy of the extracted steam from the low-pressure cylinder, reduces boiler fuel consumption, and improves the overall thermal economy of the unit.

[0046] It should be noted that, Figure 2The high-pressure heater group, low-pressure heater group and their respective water-side inlet and outlet valves, steam inlet valves, drain valves, and drain valves are all conventional components already existing in the low-pressure heater system in the thermal power generation industry, and are not improvements in this application. Therefore, this application will not elaborate on them.

[0047] In summary, this application improves the existing feedwater regeneration system in thermal power generating units. Without altering the existing equipment structure such as the boiler, turbine, condenser, high-pressure heater group, and low-pressure heater group, a bypass steam supply branch is added or modified. During startup, a portion of the main steam is introduced to the steam side of the high-pressure heater through this branch, achieving preheating of the feedwater. Simultaneously, by real-time monitoring of parameters such as feedwater temperature, high-pressure heater level, condensate temperature, and main steam pressure, and by implementing coordinated closed-loop control of the high-pressure bypass steam inlet valve and the low-pressure bypass steam inlet valve, the safety, stability, and efficiency of the feedwater heating process are effectively ensured, avoiding problems such as excessive thermal stress and excessive pressure fluctuations caused by rapid temperature rise.

[0048] For example, the preset target range is 60℃~90℃. That is, through the above operation, the feedwater temperature can be increased by 60℃ to 90℃ from the original level. This temperature rise is sufficient to significantly shorten the boiler heating and pressurization time, reduce fuel consumption during startup, and at the same time, it can be controlled within the range that the high-pressure heater and boiler heating surface can safely withstand, avoiding excessive thermal stress caused by excessive temperature rise.

[0049] After completing the water supply heating operation of the above-mentioned start-up phase, when the thermal power generating unit operates to meet the preset normal operating conditions, this application will perform the subsequent exit and switching operations.

[0050] S130: After the thermal power generating unit meets the preset normal operating conditions, the bypass steam supply branch is closed and the normal feedwater heating mode is switched simultaneously.

[0051] Here, the preset normal operating conditions include: (1) The thermal power generating units have been connected to the grid; (2) The pressure value of the main steam is stable within the preset allowable fluctuation range within the preset time period.

[0052] It should be understood that grid connection of a thermal power generating unit means that the unit's transmission lines are connected to the power grid, and the unit begins to output electrical energy to the grid. This signifies that the thermal power generating unit has moved from the "start-up phase" to the "grid-connected operation phase," providing electrical signal basis for subsequently discontinuing the bypass steam supply branch and switching to normal feedwater heating mode.

[0053] Furthermore, the pressure of the main steam remains stable within a preset allowable fluctuation range over a preset time period. This can be understood as follows: the pressure fluctuation of the main steam does not exceed the preset allowable range (e.g., ±0.1MPa, ±0.2MPa, or ±2% of the rated pressure) for a continuous preset time period (e.g., 3 minutes, 5 minutes, or 10 minutes), while the pressure change rate (i.e., the rate of pressure increase or decrease per unit time) is also controlled within a safe range (e.g., not exceeding 0.03MPa / min). This indicates that the boiler's combustion conditions have stabilized, the turbine's inlet steam parameters meet normal operating requirements, the main steam pressure no longer needs frequent adjustment relying on the bypass system, and the unit is ready to safely disconnect from the bypass steam supply branch and switch to normal operating mode.

[0054] Furthermore, S130 specifically includes: during the gradual closure of the bypass steam supply branch, switching the steam source for the high-pressure heaters in the high-pressure heater group from the bypass steam supply branch during the startup phase to turbine extraction steam during the normal phase. Here, to ensure stable main steam pressure, during the process of exiting the bypass steam supply branch, the high-pressure bypass inlet valve and the low-pressure bypass inlet valve are not completely closed instantly or all at once, but rather the valve openings are gradually reduced in stages according to a preset rate or step size until they are completely closed.

[0055] Here, "normal feedwater heating mode" refers to the standard operating mode of a thermal power generating unit under normal grid-connected operation, where the feedwater is heated stage by staged extraction steam from various pressure levels of the turbine. Unlike the startup phase, which relies on bypass steam supply branches, the steam source for the normal feedwater heating mode comes from the extraction steam at each stage during normal turbine operation, eliminating the need for a bypass system. This mode is the standard regenerative heating method in the conventional operation of thermal power units. The high-pressure heater group, extraction steam pipelines, and condensate drainage system in this application all adopt existing conventional configurations, and their specific structures and operating procedures are well known to those skilled in the art, and will not be described in detail here.

[0056] Compared to existing technologies, this system has significant advantages: First, by opening the bypass steam supply branch when the main steam pressure is within the preset operating range during the startup phase, a portion of the main steam is introduced into the steam side of the high-pressure heater, resulting in a significant increase in feedwater temperature, greatly shortening the boiler heating and pressurization time, and reducing fuel consumption during startup. Second, by real-time monitoring of feedwater temperature, internal water level in the high-pressure heater, condensate temperature, and main steam pressure, and by implementing coordinated closed-loop control of the high-pressure bypass steam inlet valve, the feedwater temperature rise rate is precisely controlled, avoiding excessive thermal stress caused by rapid temperature rise, thereby reducing the thermal stress on the boiler heating surface and the high-pressure heater, and extending the service life of core equipment. Third, it does not change the existing main equipment structure of the power plant; it can be implemented simply by adding or modifying the bypass steam supply branch and related control logic, exhibiting good compatibility and facilitating on-site operation by personnel. Fourth, due to the significantly shortened startup time, the unit can respond to grid peak-shaving commands more quickly, enhancing the unit's peak-shaving adaptability. In summary, this application solves the technical problems of low water supply temperature, high energy consumption, slow start-up, and high thermal stress in the equipment during the start-up phase in the prior art, and has significant energy-saving effects and application value.

[0057] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0058] The above embodiments are merely illustrative of several implementation methods of this application, and their descriptions are relatively specific and detailed. However, they should not be construed as limiting the scope of this application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this application should be determined by the appended claims.

Claims

1. A method for energy-saving operation of feedwater heating during the start-up phase of a thermal power generating unit, characterized in that, The method is applied to an adaptive feedwater regeneration system in a thermal power generating unit; the adaptive feedwater regeneration system includes a high-pressure heater group and a bypass steam supply branch, the bypass steam supply branch being connected to the condenser in the thermal power generating unit and the steam side of at least one high-pressure heater in the high-pressure heater group respectively. The method includes: During the startup phase of the thermal power generating unit, the pressure change of the main steam is acquired and monitored in real time to determine whether the pressure of the main steam is within the preset operating range; wherein, the pressure of the main steam refers to the steam pressure at the outlet of the boiler superheater in the thermal power generating unit. If so, the bypass steam supply branch is opened, and part of the main steam is introduced into the steam side of at least one high-pressure heater in the high-pressure heater group to heat the feedwater flowing through the water side of the high-pressure heater, so that the feedwater temperature is raised to the preset target range, while the remaining part of the main steam is introduced into the condenser. After the thermal power generating unit meets the preset normal operating conditions, the bypass steam supply branch is shut down and the normal feedwater heating mode is switched simultaneously.

2. The method for energy-saving operation of feedwater heating during the start-up phase of a thermal power generating unit according to claim 1, characterized in that, The preset operating range is 0.16MPa~0.25MPa.

3. The method for energy-saving operation of feedwater heating during the start-up phase of a thermal power generating unit according to claim 1, characterized in that, The high-pressure heater group includes a No. 2 high-pressure heater; The bypass steam supply branch includes a steam supply branch and a condenser branch; wherein, the steam supply branch includes a high bypass steam inlet valve, which is used to introduce a portion of the main steam into the steam side of at least one high-pressure heater in the high-pressure heater group; the condenser branch includes a low bypass steam inlet valve connected to the condenser in the thermal power generator group.

4. The method for energy-saving operation of feedwater heating during the start-up phase of a thermal power generating unit according to claim 1, characterized in that, The high-pressure heater group includes multiple high-pressure heaters connected in series; the bypass steam supply branch includes at least one steam supply branch and one condenser branch. Specifically, according to preset requirements, at least one high-pressure heater from the multi-stage high-pressure heaters is selected, and the selected high-pressure heater is connected to the steam supply branch. The steam supply branch includes a high-pressure bypass steam inlet valve for introducing part of the main steam into the steam side of the corresponding high-pressure heater. The condenser branch includes a low-pressure bypass steam inlet valve connected to the condenser in the thermal power generator unit.

5. The method for energy-saving operation of feedwater heating during the start-up phase of a thermal power generating unit according to claim 4, characterized in that, The high-pressure heater group includes a No. 1 high-pressure heater, a No. 2 high-pressure heater, and a No. 3 high-pressure heater connected in series. The steam supply branch connected to the No. 2 high-pressure heater is used to introduce part of the main steam into the steam side of the No. 2 high-pressure heater during the start-up phase, so as to heat the feedwater flowing through the water side of the No. 2 high-pressure heater.

6. The method for energy-saving operation of feedwater heating during the start-up phase of a thermal power generating unit according to any one of claims 3 to 5, characterized in that, Also includes: The feedwater temperature, the water level inside the high-pressure heater in the high-pressure heater group, and the condensate temperature are acquired in real time. Combined with the pressure value of the main steam, the opening degree of the high-pressure bypass steam inlet valve is determined, thereby controlling the feedwater temperature rise rate. Furthermore, based on the pressure value of the main steam, the opening degree of the low bypass steam inlet valve is determined, thereby controlling the fluctuation range of the pressure value of the main steam.

7. The method for energy-saving operation of feedwater heating during the start-up phase of a thermal power generating unit according to claim 1, characterized in that, The preset normal operating conditions include: (1) The thermal power generating unit has been connected to the grid; (2) The pressure value of the main steam is stable within a preset allowable fluctuation range within a preset time period.

8. The method for energy-saving operation of feedwater heating during the start-up phase of a thermal power generating unit according to claim 1, characterized in that, The preset target range is 60℃~90℃.

9. The method for energy-saving operation of feedwater heating during the start-up phase of a thermal power generating unit according to claim 1, characterized in that, The adaptive feedwater regeneration system also includes a low-pressure heater group; the low-pressure heater group includes at least one low-pressure heater. The low-pressure heater group is located between the condenser and the deaerator in the thermal power generator set. It is used to heat the condensate from the condenser and deliver the heated water to the deaerator.

10. The method for energy-saving operation of feedwater heating during the start-up phase of a thermal power generating unit according to claim 1, characterized in that, After the thermal power generating unit meets the preset normal operating conditions, the bypass steam supply branch is shut down, and the system is simultaneously switched to normal feedwater heating mode, including: During the gradual closure of the bypass steam supply branch, the steam source for the high-pressure heaters in the high-pressure heater group is switched from the bypass steam supply branch during the startup phase to turbine extraction during the normal phase.

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