A method and device for switching control of a main route bypass of a boiler feedwater system of a thermal power unit

Abstract

The application discloses a kind of main road bypass switching control methods of thermal power generating unit boiler feedwater system, including obtaining the first real-time load in the process of unit load increase;When the first real-time load reaches the first preset load threshold corresponding to the full opening state of feedwater system bypass regulating valve, gradually increase the water supply of feedwater system main road, while gradually reducing the water supply of feedwater system bypass, until the feedwater system bypass is completely closed;In the process of bypass switching to main road, obtain the first real-time drum water level;According to the value of the first real-time drum water level, the value of feedwater flow is adjusted, can automatically realize the undisturbed automatic switching control of boiler feedwater platform main road and bypass, avoid artificial operation in the process of unit start-stop, improve the automation level of unit, also can maintain the constancy of drum water level and feedwater flow, ensure that unit is safely and stably carried out in main / bypass switching process.The application also discloses a kind of main road bypass switching control device of thermal power generating unit boiler feedwater system.

Description

Technical Field

[0001] This invention relates to the field of thermal power generation technology, and more specifically, to a method and apparatus for switching the main circuit and bypass of the boiler feedwater system of a thermal power unit. Background Technology

[0002] Maintaining the boiler drum water level within the normal range is crucial during generator unit operation, requiring accurate measurement and precise control of the boiler drum water level. During normal operation, a three-impulse control method is used to regulate the boiler drum water level by adjusting the turbine speed of the feedwater pump. During unit start-up and shutdown, when the unit operates at low load and the feedwater pump operates at low speed, feedwater enters the drum through the feedwater platform bypass, and the boiler drum water level is regulated via the feedwater platform bypass regulating valve.

[0003] During boiler drum water level regulation, both excessively high and low water levels can affect the safe operation of the boiler. A low water level can cause uneven boiler water circulation, leading to overheating of the boiler water-cooled walls and, in severe cases, boiler tube leaks. An excessively high water level reduces the steam space within the drum, increases the moisture content of the main steam, causing salt buildup in the superheater, and lowers the main steam temperature, resulting in water hammer in the steam pipelines and turbine, damaging the turbine equipment. Therefore, maintaining the drum water level is crucial during boiler operation, and the boiler's main protection system is equipped with high-high and low-low drum water level protection tripping mechanisms.

[0004] Taking a 300MW drum boiler as an example, the boiler is a subcritical, natural circulation "P"-type drum boiler, equipped with two 50% steam-driven feedwater pumps and one 30% electric feedwater pump. The boiler feedwater platform consists of a main feedwater electric valve, a bypass electric valve, and a regulating valve, completing the feedwater control of the main and bypass feedwater lines. The feedwater flow measurement device is installed on the main feedwater pipeline. The main feedwater flow passes through the main feedwater flow orifice plate, one path through the main feedwater electric valve, and the other path through the feedwater bypass. The bypass electric regulating valve collects the flow at the boiler economizer. The feedwater system is as follows: Figure 1 As shown, Figure 1This is a schematic diagram of the boiler feedwater system, including feedwater pipeline 1, main feedwater line electric valve 2, feedwater bypass regulating valve pre-electric valve 3, feedwater bypass regulating valve 4, feedwater bypass regulating valve post-electric valve 5, economizer 6, superheater 7, boiler drum 8, and boiler drum circulation pipeline 9. Water comes from feedwater pipeline 1, passes through the feedwater platform, and during the low-load phase of the unit, the feedwater system bypasses the feedwater platform, which consists of feedwater bypass regulating valve pre-electric valve 3, feedwater bypass regulating valve 4, and feedwater bypass regulating valve post-electric valve 5. During the high-load phase of the unit, the feedwater flow passes through the main feedwater platform, which is controlled by feedwater main line electric valve 2. After passing through the feedwater platform, it passes through economizer 6, then through boiler drum 8, superheater 7, and also through boiler drum circulation pipeline 9, thus achieving boiler water circulation. During the initial startup phase and when the load is below 30%, the boiler drum water level is controlled by the electric valve 5 after the feedwater bypass regulating valve. The control strategy adopts a single-loop control method. The PID controller receives the boiler drum water level deviation signal and, after PID calculation, obtains the regulating valve opening command to regulate the boiler drum water level.

[0005] Currently, the feedwater control system of the aforementioned steam drum boilers uses a single-impulse bypass regulating valve for low-load and boiler startup phases, and a cascade three-impulse feedwater pump for high-load phases. During unit operation, when the feedwater bypass needs to switch to the main feedwater line or vice versa, most units rely on operator experience to manually adjust the feedwater platform regulating valve to achieve this switching. This switching process easily causes fluctuations in the steam drum water level. Currently, most units rely solely on operator experience to maintain a balanced state during the switching process by controlling the pressure difference before and after the feedwater platform, minimizing large fluctuations in the steam drum water level. Therefore, how to successfully control the switching between the feedwater bypass and the main feedwater line, ensuring minimal steam drum water level disturbance, short switching time, and minimal feedwater flow disturbance during the bypass switching process, directly impacts the smooth start-up and shutdown of the unit and even the safety of the main equipment. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention provides a method and apparatus for controlling the switching between the main and bypass feedwater systems of a thermal power unit boiler. This method enables the automatic, disturbance-free switching between the main and bypass feedwater systems of the boiler feedwater platform, avoiding manual operation during unit start-up and shutdown, improving the automation level of the unit, maintaining constant steam drum water level and feedwater flow, and ensuring the safe and stable operation of the unit during the main / bypass switching process.

[0007] This invention provides a main circuit bypass switching control method for boiler feedwater system of thermal power units, comprising:

[0008] Obtain the first real-time load during the unit's load increase process;

[0009] When the first real-time load reaches the first preset load threshold corresponding to the fully open state of the water supply system bypass regulating valve, the water supply of the main water supply system is gradually increased, while the water supply of the water supply system bypass is gradually decreased until the water supply system bypass is completely closed.

[0010] During the process of switching from the bypass to the main route, the first real-time steam drum water level is obtained;

[0011] Adjust the feedwater flow rate based on the first real-time steam drum water level value.

[0012] Preferably, the above-mentioned main circuit bypass switching control method for boiler feedwater system of thermal power units further includes:

[0013] Acquire the second real-time load during low-load operation or shutdown of the unit;

[0014] When the second real-time load reaches the second preset load threshold corresponding to the fully closed state of the main regulating valve of the water supply system, the water supply of the water supply system bypass is gradually increased, while the water supply of the main water supply system is gradually decreased until the main water supply system is completely closed.

[0015] During the process of switching from the main road to the bypass, the second real-time steam drum water level is obtained;

[0016] Adjust the feedwater flow rate based on the second real-time steam drum water level.

[0017] Preferably, in the above-mentioned control method for switching the main circuit and bypass of the boiler feedwater system of a thermal power unit, the first preset load threshold corresponding to the fully open state of the feedwater system bypass regulating valve is 30% of the unit capacity.

[0018] Preferably, in the above-mentioned control method for switching the main feedwater system and the bypass of the boiler feedwater system in a thermal power unit, the step of gradually increasing the water supply of the main feedwater system and simultaneously gradually decreasing the water supply of the bypass until the bypass is completely closed includes:

[0019] The bypass electric regulating valve is closed at a certain rate within 280s to 300s. The opening feedback of the bypass electric regulating valve corresponds to the command of the main water supply electric valve as (100, 0), (98, 5.9), (95, 11.5), (90, 20), (70, 22), (60, 50), (5, 68), (0, 100), until the main water supply electric valve is fully opened, the bypass electric regulating valve is fully closed, and the bypass electric valves before and after are fully closed.

[0020] Preferably, in the above-mentioned main circuit bypass switching control method for boiler feedwater system of thermal power unit, adjusting the feedwater flow rate based on the value of the first real-time steam drum water level includes:

[0021] When the first real-time steam drum water level is greater than 0 mm, the feedwater flow rate is set to the sum of the main feedwater flow rate, the superheater desuperheating water flow rate, and the reheater desuperheating water flow rate minus 45 t / h to 50 t / h.

[0022] When the first real-time steam drum water level is between -110mm and 0mm, the feedwater flow rate is set to the sum of the main feedwater flow rate, the superheater desuperheating water flow rate, and the reheater desuperheating water flow rate.

[0023] When the first real-time steam drum water level is less than -110mm, the feedwater flow rate is set to the sum of the main feedwater flow rate, the superheater desuperheating water flow rate, and the reheater desuperheating water flow rate plus 45t / h to 50t / h.

[0024] Preferably, in the above-mentioned control method for switching the main feedwater system bypass of a thermal power unit boiler, the second preset load threshold corresponding to the fully closed state of the main feedwater system regulating valve is 30% of the unit capacity.

[0025] Preferably, in the above-mentioned method for switching the main feedwater system bypass of a thermal power unit boiler, the step of gradually increasing the water supply of the feedwater system bypass while gradually decreasing the water supply of the main feedwater system includes:

[0026] The main electric regulating valve is closed at a certain rate within 280s to 300s. The correspondence between the opening feedback of the main electric regulating valve and the command of the bypass electric water supply valve is (100, 0), (98, 5.9), (95, 11.5), (90, 20), (70, 22), (60, 50), (5, 68), (0, 100), until the main electric water supply valve is completely closed, the bypass electric regulating valve is fully opened, and the bypass electric front and rear electric valves are fully opened.

[0027] Preferably, in the above-mentioned main circuit bypass switching control method for boiler feedwater system of thermal power unit, adjusting the feedwater flow rate based on the value of the second real-time steam drum water level includes:

[0028] When the second real-time steam drum water level is greater than 0 mm, the feedwater flow rate is set to the sum of the main feedwater flow rate, the superheater desuperheating water flow rate, and the reheater desuperheating water flow rate minus 45 t / h to 50 t / h.

[0029] When the second real-time steam drum water level is between -120mm and 0mm, the feedwater flow rate is set to the sum of the main feedwater flow rate, the superheater desuperheating water flow rate, and the reheater desuperheating water flow rate.

[0030] When the second real-time steam drum water level is less than -120mm, the feedwater flow rate is set to the sum of the main feedwater flow rate, the superheater desuperheating water flow rate, and the reheater desuperheating water flow rate plus 45t / h to 50t / h.

[0031] The present invention provides a main circuit bypass switching control device for boiler feedwater system of thermal power unit, comprising:

[0032] The first acquisition unit is used to acquire the first real-time load during the unit's load increase process;

[0033] The first water supply regulating unit is used to gradually increase the water supply of the main water supply system and gradually decrease the water supply of the water supply system bypass when the first real-time load reaches the first preset load threshold corresponding to the fully open state of the water supply system bypass regulating valve, until the water supply system bypass is completely closed.

[0034] The second acquisition unit is used to acquire the first real-time steam drum water level during the process of switching from the bypass to the main road;

[0035] The first water flow adjustment unit is used to adjust the water flow rate according to the value of the first real-time steam drum water level.

[0036] Preferably, the above-mentioned main circuit bypass switching control device for boiler feedwater system of thermal power unit further includes:

[0037] The third acquisition unit is used to acquire the second real-time load during the low-load operation or shutdown process of the unit;

[0038] The second water supply regulating unit is used to gradually increase the water supply of the water supply system bypass and gradually decrease the water supply of the water supply system main line when the second real-time load reaches the second preset load threshold corresponding to the fully closed state of the main line regulating valve of the water supply system, until the main line of the water supply system is completely closed.

[0039] The fourth acquisition unit is used to acquire the second real-time steam drum water level during the process of switching from the main road to the bypass.

[0040] The second water flow adjustment unit is used to adjust the feedwater flow rate based on the value of the second real-time steam drum water level.

[0041] As can be seen from the above technical solution, the main circuit bypass switching control method for boiler feedwater system of thermal power units provided by the present invention includes: acquiring the first real-time load during the unit's load increase process; when the first real-time load reaches the first preset load threshold corresponding to the fully open state of the feedwater system bypass regulating valve, gradually increasing the water supply of the main circuit of the feedwater system while gradually decreasing the water supply of the bypass circuit until the bypass circuit is completely closed; acquiring the first real-time steam drum water level during the bypass switching to the main circuit; and adjusting the feedwater flow rate based on the value of the first real-time steam drum water level. Therefore, it can automatically realize the disturbance-free automatic switching control of the main circuit and bypass circuit of the boiler feedwater platform, avoid manual operation during unit start-up and shutdown, improve the automation level of the unit, and maintain the constant steam drum water level and feedwater flow rate, ensuring the safe and stable operation of the unit during the main / bypass switching process. The main circuit bypass switching control device for boiler feedwater system of thermal power units provided by the present invention has the same advantages as the above method. Attached Figure Description

[0042] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0043] Figure 1 A schematic diagram of the composition of the boiler feedwater system;

[0044] Figure 2 This is a schematic diagram of an embodiment of a main circuit bypass switching control method for a boiler feedwater system of a thermal power unit provided by the present invention;

[0045] Figure 3 A schematic diagram illustrating a specific example of a control strategy for switching from bypass to main path;

[0046] Figure 4 A logic diagram for generating the water supply flow rate setpoint when the water supply system bypasses the main line;

[0047] Figure 5 This is a schematic diagram of an embodiment of a main circuit bypass switching control device for a boiler feedwater system of a thermal power unit provided by the present invention. Detailed Implementation

[0048] The core of this invention is to provide a method and device for switching control between the main and bypass feedwater systems of a thermal power unit boiler. This method can automatically achieve disturbance-free automatic switching control between the main and bypass feedwater systems of the boiler feedwater platform, avoiding manual operation during unit start-up and shutdown, improving the automation level of the unit, and maintaining constant steam drum water level and feedwater flow rate, ensuring the safe and stable operation of the unit during the main / bypass switching process.

[0049] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0050] An example implementation of the main circuit bypass switching control method for boiler feedwater system of thermal power unit provided by this invention. Figure 2 As shown, Figure 2 This is a schematic diagram of an embodiment of a main circuit bypass switching control method for a boiler feedwater system in a thermal power unit provided by the present invention. The method may include the following steps:

[0051] S1: Obtain the first real-time load during the unit's load increase process;

[0052] S2: When the first real-time load reaches the first preset load threshold corresponding to the fully open state of the water supply system bypass regulating valve, gradually increase the water supply of the main water supply system and gradually decrease the water supply of the water supply system bypass until the water supply system bypass is completely closed.

[0053] Specifically, the first preset load threshold corresponding to the fully open state of the feedwater system bypass regulating valve can preferably be 30% of the unit capacity. During the unit start-up and load increase phase, as the load continues to rise, the boiler main steam evaporation also increases, and the feedwater flow gradually increases. When the unit load rises to about 30%Pe (90MW), the bypass regulating valve in the feedwater system is fully open, and the bypass feedwater has reached its maximum value. At this time, the feedwater pump speed is also far from the equipment's minimum speed. At this time, the feedwater system bypass can be switched to the feedwater main line. The bypass regulating valve is gradually reduced, and the feedwater main line electric valve is gradually opened. The feedwater system regulation is changed from bypass regulating valve regulation to feedwater pump speed regulation. The above-mentioned gradual increase of the water supply volume of the main water supply system and the gradual decrease of the water supply volume of the bypass water supply system until the bypass water supply system is completely closed can specifically include: closing the bypass electric regulating valve at a certain rate within 280s to 300s, with the corresponding relationship between the opening feedback of the bypass electric regulating valve and the command of the main water supply electric valve being (100, 0), (98, 5.9), (95, 11.5), (90, 20), (70, 22), (60, 50), (5, 68), (0, 100), until the main water supply electric valve is fully open, the bypass electric regulating valve is completely closed, and the bypass electric valves before and after are completely closed.

[0054] S3: During the process of switching from the bypass to the main route, obtain the first real-time steam drum water level;

[0055] S4: Adjust the feedwater flow rate based on the first real-time steam drum water level.

[0056] This step can specifically include: when the first real-time steam drum water level is greater than 0 mm, setting the feedwater flow rate to the sum of the main feedwater flow rate, the superheater desuperheating water flow rate, and the reheater desuperheating water flow rate minus 45 t / h to 50 t / h; when the first real-time steam drum water level is between -110 mm and 0 mm, setting the feedwater flow rate to the sum of the main feedwater flow rate, the superheater desuperheating water flow rate, and the reheater desuperheating water flow rate; when the first real-time steam drum water level is less than -110 mm, setting the feedwater flow rate to the sum of the main feedwater flow rate, the superheater desuperheating water flow rate, and the reheater desuperheating water flow rate plus 45 t / h to 50 t / h.

[0057] Specifically, during this process, attention should be paid to the disturbances in boiler drum water level and feedwater flow. A seamless switching between the feedwater bypass and main feedwater line can be achieved by switching control strategies. This control strategy for switching from the bypass to the main line can be as follows: Figure 3 As shown, Figure 3 A schematic diagram illustrating a specific example of a control strategy for switching from bypass to main path, including:

[0058] 21—Activate the water supply bypass to switch to the main line button;

[0059] 22—Main feedwater flow rate of boiler;

[0060] 23—The main feedwater flow rate of the boiler is less than 450 t / h;

[0061] 24 — Any water supply pump is in automatic mode;

[0062] 25—The main water supply line electric gate is closed;

[0063] 26—The electric gate of the main water supply line is open;

[0064] 27—The electric valve in front of the water supply bypass control valve is closed;

[0065] 28—The electric valve behind the water supply bypass regulating valve is in the closed state;

[0066] 29—Feedback from the electric regulating valve for water supply bypass;

[0067] 210—The water supply bypass electric valve is less than 0.3%, meaning it is already in the closed state;

[0068] 211—Command to open the electric valve before the water supply bypass control valve;

[0069] 212—Instruction to open the electric valve after opening the water supply bypass regulating valve;

[0070] 213—Manual reset logic button for switching water supply bypass to main circuit;

[0071] 214-RS trigger;

[0072] 215 -- Automatic adjustment command for water supply bypass before switching;

[0073] 216—Analog Selection Module;

[0074] 217--LEADLAG lead-lag logic block, which implements the 300s adjustment instruction to change from 100% to 0%;

[0075] 218 -- Feedwater bypass valve command during switching process;

[0076] 219--Feedwater bypass valve feedback;

[0077] The 220--F(x) function implements the correspondence between the bypass control gate feedback and the main electric gate command.

[0078] 221 -- Command for main road electric gate before switching logic is activated;

[0079] 222--Analog quantity selection module;

[0080] 223 -- Main road electric gate opening command.

[0081] This strategy enables one-click automatic switching of the water supply system from bypass operation to main operation, avoiding large disturbances in the steam drum water level and water supply flow, as well as abnormal conditions such as large differential pressure across the water supply platform during the bypass-to-main-operation process. The one-button start-up of the water supply system bypass to main line operation buttons 21, 22, and 23 constitutes the starting conditions for the water supply bypass to main line switchover. These conditions include a water supply flow rate greater than 450 t / h, 24 indicating any water supply pump is in automatic mode, and 25 indicating the main water supply electric valve is closed. After the one-button switching function is activated, the RS trigger function logic block 214, AXSEL logic selection block 216, and LEADLAG advance / lag logic block 217 enable the water supply bypass electric regulating valve to close from 100% to 0% within 300 seconds. Through the water supply bypass electric regulating valve opening feedback 219, F(x) function block 220, and AXSEL logic selection block 222, the logical correspondence between the opening of the water supply bypass electric regulating valve and the opening of the main water supply electric valve during the switching process is achieved. The relationships are (100,0), (98,5.9), (95,11.5), (90,20), (70,22), (60,50), (5,68), and (0,100). Through the fully open state 26 of the main feedwater valve, the fully closed state 27 of the electric valve before the feedwater bypass electric regulating valve, and the fully closed state 28 of the electric valve after the feedwater bypass electric regulating valve, and the opening degree of the feedwater bypass electric regulating valves less than 0.3% in states 29 and 210, a one-button automatic feedwater bypass switching to main feedwater reset logic is formed. Considering that abnormal conditions such as steam drum water level fluctuations, feedwater flow fluctuations, and feedwater platform valve damage may occur during the switching process, 213 is designed as a manual reset function for operators. After the operator resets, the feedwater system bypass switching to main feedwater logic function is automatically exited.

[0082] When the unit is in operation and the bypass to main line switching conditions are met (i.e., the main feedwater electric valve is closed, any feedwater pump is in automatic mode, and the main feedwater flow rate is less than 450 t / h), pressing the bypass to main line switching operation button will cause the bypass electric regulating valve to close at a certain rate within 300 seconds. The opening feedback of the bypass electric regulating valve corresponds to the main feedwater electric valve command in a certain way (100,0), (98,5.9), (95,11.5), (90,20), (70,22), (60,50), (5,68), (0,100), until all feedwater main line electric valves are open, the bypass electric regulating valve is completely closed, and the bypass electric valves before and after are completely closed. At this time, after the RS trigger receives the reset command, the system automatically cuts off the pipeline switching logic, and the feedwater bypass to feedwater main line switching is completed. During the switching process from the bypass to the main line, if abnormal conditions occur such as excessively high or low steam drum water level, abnormal main feedwater flow, large differential pressure across the feedwater platform, or malfunction of the feedwater platform electric valve, the switching logic can be manually reset to exit the switching logic operation. After troubleshooting, the system can be reactivated. The feedwater main line electric valve in the switching control strategy has a stop function and can display the valve opening. The openings of the feedwater main line electric valve and the feedwater bypass regulating valve during the switching process between the feedwater bypass and the main line are shown in Table 1.

[0083] Table 1 Valve Opening Degree During Main / Bypass Switching

[0084]

[0085] During the bypass-to-main-line operation, the automatic water flow rate adjustment setpoint remains in a tracking state, with the tracking control logic as follows: Figure 4 As shown, Figure 4 A logic diagram for generating the water supply flow rate setpoint when the water supply system bypasses the main line is provided, including:

[0086] 31—Superheater desuperheating water flow rate;

[0087] 32—Reheater desuperheating water flow rate;

[0088] 33—Boiler feedwater flow rate;

[0089] 34—Main water supply flow rate setting value before main circuit / bypass switching;

[0090] 35—Steam drum water level;

[0091] The 36-SUM accumulator block adds the flow rates of the desuperheating water and the main feedwater.

[0092] 37—The sum of the flow rates of the desuperheating water and the main feedwater minus 45t / h;

[0093] 38—The sum of the flow rates of the desuperheating water and the main feedwater plus 45t / h;

[0094] 39—Steam drum water level greater than 0 mm;

[0095] 310—The water level in the steam drum is between -110 and 0 mm;

[0096] 311 -- Steam drum water level less than -110mm;

[0097] 312—AXSEL Analog Selection Block;

[0098] 313--AXSEL Analog Selection Block;

[0099] 314--AXSEL Analog Selection Block;

[0100] 315—Imparts an automatic water supply flow adjustment loop and sets the water supply flow rate.

[0101] The total boiler feedwater flow rate is obtained by adding the superheater desuperheating water flow rate 31, reheater desuperheating water flow rate 32, and boiler feedwater flow rate 33 as shown in the diagram. The boiler drum water level is determined to be greater than 0 mm by the analog display 35 and 39. Therefore, the feedwater flow rate is set to the total boiler feedwater flow rate minus 45 t / h using AXSEL logic selection block 312. If the boiler drum water level is determined to be between -110 mm and 0 mm by the analog display 35 and 310, the feedwater flow rate is set to the total boiler feedwater flow rate using AXSEL logic selection block 313. If the boiler drum water level is determined to be less than -110 mm by the analog display 35 and 311, the feedwater flow rate is set to the total boiler feedwater flow rate plus 45 t / h using AXSEL logic selection block 314. Based on the different boiler drum water levels, corresponding feedwater flow rate setpoints are provided, which realizes the constant boiler drum water level during the main / bypass switching process of the feedwater system, and ensures the safe operation of the unit during the main / bypass switching process.

[0102] If the steam drum water level is greater than 0 mm after taking the middle value of three parameters, the feedwater flow rate setting value is the sum of the main feedwater flow rate, the superheater desuperheating water flow rate, and the reheater desuperheating water flow rate minus 45 t / h; if the steam drum water level is between -110 mm and 0 mm, the feedwater flow rate setting value is the sum of the main feedwater flow rate, the superheater desuperheating water flow rate, and the reheater desuperheating water flow rate; if the steam drum water level is less than -110 mm, the feedwater flow rate setting value is the sum of the main feedwater flow rate, the superheater desuperheating water flow rate, and the reheater desuperheating water flow rate plus 45 t / h.

[0103] It is evident that this scheme fully considers the equipment status before switching between the main and bypass feedwater systems, as well as the correspondence between the opening of the feedwater bypass regulating valve and the opening of the feedwater main electric valve during the switching process. This ensures that the drum water level and feedwater flow remain constant during the switching process, and the differential pressure across the feedwater platform is controlled within 2 MPa. It also fully considers the impact of the drum water level on the feedwater flow during the main / bypass switching process. When the drum water level is high, the feedwater flow setpoint is appropriately reduced; when the drum water level is low, the feedwater flow setpoint is appropriately increased to maintain a constant drum water level. This eliminates the safety hazards of abnormal fluctuations in the drum water level and feedwater flow, as well as excessive differential pressure across the feedwater platform, during the main / bypass switching process of the boiler.

[0104] As can be seen from the above technical solutions, in the embodiments of the boiler feedwater system main circuit and bypass switching control method provided by the present invention, the following steps are taken: acquiring the first real-time load during the unit's load increase process; when the first real-time load reaches the first preset load threshold corresponding to the fully open state of the feedwater system bypass regulating valve, gradually increasing the water supply of the feedwater system main circuit while gradually decreasing the water supply of the feedwater system bypass circuit until the feedwater system bypass circuit is completely closed; acquiring the first real-time steam drum water level during the main circuit to bypass switching process; and adjusting the feedwater flow rate based on the value of the first real-time steam drum water level. Therefore, the method can automatically realize the disturbance-free automatic switching control of the boiler feedwater platform main circuit and bypass circuit, avoid manual operation during unit start-up and shutdown, improve the automation level of the unit, maintain the constant steam drum water level and feedwater flow rate, and ensure the safe and stable operation of the unit during the main / bypass switching process.

[0105] In a specific embodiment of the above-mentioned main circuit bypass switching control method for boiler feedwater system of thermal power unit, the following steps may also be included:

[0106] Acquire the second real-time load during low-load operation or shutdown of the unit;

[0107] When the second real-time load reaches the second preset load threshold corresponding to the fully closed state of the main regulating valve of the water supply system, the water supply of the water supply system bypass is gradually increased, while the water supply of the main water supply system is gradually decreased until the main water supply system is completely closed.

[0108] During the process of switching from the main road to the bypass, the second real-time steam drum water level is obtained;

[0109] Adjust the feedwater flow rate based on the second real-time steam drum water level.

[0110] Specifically, the second preset load threshold corresponding to the fully closed state of the main feedwater system regulating valve can preferably be 30% of the unit capacity. During low-load operation or shutdown of the unit, as the load decreases, the boiler's evaporation rate also decreases, and the corresponding feedwater flow rate also decreases. When the unit load is below 30% Pe, the regulating capacity of the feedwater pump can no longer maintain the drum water level at a stable operating condition. At this time, the main feedwater line electric valve should be closed, the feedwater bypass electric regulating valve should be opened, and the automatic operation of the feedwater bypass electric regulating valve should be engaged to regulate the feedwater flow rate, thereby achieving the goal of maintaining a stable drum water level. The switching control strategy is similar to the above-mentioned switch from feedwater bypass to main line operation, and will not be elaborated here.

[0111] In another specific embodiment of the above-mentioned control method for switching the main feedwater system bypass of a thermal power unit boiler, gradually increasing the water supply of the feedwater system bypass while gradually decreasing the water supply of the main feedwater system may include:

[0112] The main electric regulating valve is closed at a certain rate within 280s to 300s. The correspondence between the opening feedback of the main electric regulating valve and the command of the bypass electric water supply valve is (100, 0), (98, 5.9), (95, 11.5), (90, 20), (70, 22), (60, 50), (5, 68), (0, 100), until the main electric water supply valve is completely closed, the bypass electric regulating valve is fully opened, and the bypass electric front and rear electric valves are fully opened.

[0113] Specifically, when the main feedwater flow rate is greater than 265 t / h, any feedwater pump is in automatic mode, the electric valves before and after the feedwater bypass regulating valve are closed, and the load is below 30% Pe, the feedwater main line bypass switching button is pressed to switch the main line to bypass control strategy. During the switching process, the electric valves before and after the feedwater bypass regulating valve are first opened, while the feedwater main line electric valve closes at a certain rate, and the feedwater bypass regulating valve opens at a certain rate. The correspondence is consistent with the bypass to main line switching relationship. When the electric valves before and after the bypass regulating valve are fully open and the valve opening is greater than 60%, a command to close the feedwater system main line electric valve is issued. After the feedwater system main line electric valve is fully closed, the feedwater system completes the main line to bypass switch. Similar to the operation of switching from the water supply bypass to the main line, if abnormal conditions occur during the switching process, such as excessively high or low steam drum water level, abnormal water supply flow, differential pressure across the water supply platform exceeding 2 MPa, or malfunction of the water supply platform electric door, the switching logic can be exited by manually resetting the button, and the system can be put back into operation after troubleshooting.

[0114] In another specific embodiment of the above-mentioned main circuit bypass switching control method for boiler feedwater system of thermal power unit, adjusting the feedwater flow rate based on the value of the second real-time steam drum water level may include the following steps:

[0115] When the second real-time steam drum water level is greater than 0 mm, the feedwater flow rate is set to the sum of the main feedwater flow rate, the superheater desuperheating water flow rate, and the reheater desuperheating water flow rate minus 45 t / h to 50 t / h.

[0116] When the second real-time steam drum water level is between -120mm and 0mm, the feedwater flow rate is set to the sum of the main feedwater flow rate, the superheater desuperheating water flow rate, and the reheater desuperheating water flow rate.

[0117] When the second real-time steam drum water level is less than -120mm, the feedwater flow rate is set to the sum of the main feedwater flow rate, the superheater desuperheating water flow rate, and the reheater desuperheating water flow rate plus 45t / h to 50t / h.

[0118] Specifically, the following measures can be adopted: the setpoint for the feedwater flow rate should uniformly follow the rules of bypass-to-main-circuit operation. That is, if the drum water level is greater than 0 mm, the setpoint for the feedwater flow rate should be the sum of the main feedwater flow rate, the superheater desuperheating water flow rate, and the reheater desuperheating water flow rate minus 45 t / h; if the drum water level is between -120 mm and 0 mm, the setpoint for the feedwater flow rate should be the sum of the main feedwater flow rate, the superheater desuperheating water flow rate, and the reheater desuperheating water flow rate; if the drum water level is less than -120 mm, the setpoint for the feedwater flow rate should be the sum of the main feedwater flow rate, the superheater desuperheating water flow rate, and the reheater desuperheating water flow rate plus 45 t / h.

[0119] In addition, the following should be noted during the switching of the main and bypass lines of the water supply system: Before the switching operation, ensure that the key equipment is free of defects and that the valve operation is reliable, and try to avoid switching failure due to equipment reasons; before and after the switching of the main and bypass lines, ensure that the water supply flow, steam drum water level, and differential pressure across the water supply platform are kept as constant as possible to reduce the disturbance to the system during the switching process.

[0120] An example implementation of the main bypass switching control device for boiler feedwater system of a thermal power unit provided by the present invention. Figure 5 As shown, Figure 5 This is a schematic diagram of an embodiment of a main circuit bypass switching control device for a boiler feedwater system of a thermal power unit provided by the present invention. The device may include:

[0121] The first acquisition unit 501 is used to acquire the first real-time load during the unit's load increase process;

[0122] The first water supply regulating unit 502 is used to gradually increase the water supply of the main water supply system and gradually decrease the water supply of the water supply system bypass when the first real-time load reaches the first preset load threshold corresponding to the fully open state of the water supply system bypass regulating valve, until the water supply system bypass is completely closed.

[0123] The second acquisition unit 503 is used to acquire the first real-time steam drum water level during the process of switching from the main road to the bypass.

[0124] The first water flow adjustment unit 504 is used to adjust the water flow rate according to the value of the first real-time steam drum water level.

[0125] Specifically, the first preset load threshold corresponding to the fully open state of the feedwater system bypass regulating valve can preferably be 30% of the unit capacity. During the unit start-up and load increase phase, as the load continues to rise, the boiler main steam evaporation also increases, and the feedwater flow gradually increases. When the unit load rises to about 30%Pe (90MW), the bypass regulating valve in the feedwater system is fully open, and the bypass feedwater has reached its maximum value. At this time, the feedwater pump speed is also far from the equipment's minimum speed. At this time, the feedwater system bypass can be switched to the feedwater main line. The bypass regulating valve is gradually reduced, and the feedwater main line electric valve is gradually opened. The feedwater system regulation is changed from bypass regulating valve regulation to feedwater pump speed regulation. The above-mentioned gradual increase of the water supply volume of the main water supply system and the gradual decrease of the water supply volume of the bypass water supply system until the bypass water supply system is completely closed can specifically include: closing the bypass electric regulating valve at a certain rate within 280s to 300s, with the corresponding relationship between the opening feedback of the bypass electric regulating valve and the command of the main water supply electric valve being (100, 0), (98, 5.9), (95, 11.5), (90, 20), (70, 22), (60, 50), (5, 68), (0, 100), until the main water supply electric valve is fully open, the bypass electric regulating valve is completely closed, and the bypass electric valves before and after are completely closed.

[0126] When the first real-time steam drum water level is greater than 0 mm, the feedwater flow rate is set to the sum of the main feedwater flow rate, the superheater desuperheating water flow rate, and the reheater desuperheating water flow rate minus 45 t / h to 50 t / h; when the first real-time steam drum water level is between -110 mm and 0 mm, the feedwater flow rate is set to the sum of the main feedwater flow rate, the superheater desuperheating water flow rate, and the reheater desuperheating water flow rate; when the first real-time steam drum water level is less than -110 mm, the feedwater flow rate is set to the sum of the main feedwater flow rate, the superheater desuperheating water flow rate, and the reheater desuperheating water flow rate plus 45 t / h to 50 t / h.

[0127] In a specific embodiment of the above-mentioned main circuit bypass switching control device for boiler feedwater system of thermal power unit, it may further include:

[0128] The third acquisition unit is used to acquire the second real-time load during the low-load operation or shutdown process of the unit;

[0129] The second water supply regulating unit is used to gradually increase the water supply of the water supply system bypass and gradually decrease the water supply of the water supply system main line when the second real-time load reaches the second preset load threshold corresponding to the fully closed state of the main line regulating valve of the water supply system, until the main line of the water supply system is completely closed.

[0130] The fourth acquisition unit is used to acquire the second real-time steam drum water level during the process of switching from the bypass to the main road;

[0131] The second water flow adjustment unit is used to adjust the feedwater flow rate based on the value of the second real-time steam drum water level.

[0132] Specifically, the second preset load threshold corresponding to the fully closed state of the main feedwater system regulating valve can preferably be 30% of the unit capacity. During low-load operation or shutdown of the unit, as the load decreases, the boiler's evaporation rate also decreases, and the corresponding feedwater flow rate also decreases. When the unit load is below 30% Pe, the regulating capacity of the feedwater pump can no longer maintain the drum water level at a stable operating condition. At this time, the main feedwater line electric valve should be closed, the feedwater bypass electric regulating valve should be opened, and the automatic operation of the feedwater bypass electric regulating valve should be engaged to regulate the feedwater flow rate, thereby achieving the goal of maintaining a stable drum water level. The switching control strategy is similar to the above-mentioned switch from feedwater bypass to main line operation, and will not be elaborated here.

[0133] Furthermore, the following measures can be adopted: the setpoint for the feedwater flow rate should uniformly follow the rules of bypass-to-main-circuit operation. That is, if the drum water level is greater than 0 mm, the setpoint for the feedwater flow rate should be the sum of the main feedwater flow rate, the superheater desuperheating water flow rate, and the reheater desuperheating water flow rate minus 45 t / h; if the drum water level is between -120 mm and 0 mm, the setpoint for the feedwater flow rate should be the sum of the main feedwater flow rate, the superheater desuperheating water flow rate, and the reheater desuperheating water flow rate; if the drum water level is less than -120 mm, the setpoint for the feedwater flow rate should be the sum of the main feedwater flow rate, the superheater desuperheating water flow rate, and the reheater desuperheating water flow rate plus 45 t / h.

[0134] In summary, using the above-mentioned method and device, during the load increase phase of the feedwater system, the feedwater bypass is switched to the main feedwater line, and during the low load or load decrease phase of the unit, the main feedwater line is switched to the feedwater bypass. The entire switching process can be automatically achieved through a one-button control strategy. During the switching process, the influence of the boiler drum water level on the feedwater flow rate is fully considered. During the main line bypass switching process, the set value of the feedwater flow rate is determined based on the simulated value of the boiler drum water level. When the boiler drum water level is low, the set value of the feedwater flow rate is increased, and when the boiler drum water level is high, the set value of the feedwater flow rate is decreased. During the entire switching process, the boiler drum water level and feedwater flow rate remain constant, and the differential pressure before and after the feedwater platform is controlled within 2MPa. The switching effect is good, the automation level of the unit is improved, and safety is provided for the unit during the main feedwater line bypass switching process.

[0135] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for switching control between the main circuit and the bypass circuit of a boiler feedwater system in a thermal power unit, characterized in that, include: Obtain the first real-time load during the unit's load increase process; When the first real-time load reaches the first preset load threshold corresponding to the fully open state of the water supply system bypass regulating valve, the water supply of the main water supply system is gradually increased, while the water supply of the water supply system bypass is gradually decreased until the water supply system bypass is completely closed. During the process of switching from the bypass to the main route, the first real-time steam drum water level is obtained; Adjust the feedwater flow rate based on the value of the first real-time steam drum water level; The gradual increase in the water supply volume of the main water supply system, while gradually decreasing the water supply volume of the bypass water supply system until the bypass water supply system is completely closed, includes: The bypass electric regulating valve is closed at a certain rate within 280s to 300s. The opening feedback of the bypass electric regulating valve corresponds to the command of the main water supply electric valve as (100, 0), (98, 5.9), (95, 11.5), (90, 20), (70, 22), (60, 50), (5, 68), (0, 100), until the main water supply electric valve is fully opened, the bypass electric regulating valve is fully closed, and the bypass electric valves before and after are fully closed. The step of adjusting the feedwater flow rate based on the first real-time steam drum water level includes: When the first real-time steam drum water level is greater than 0 mm, the feedwater flow rate is set to the sum of the main feedwater flow rate, the superheater desuperheating water flow rate, and the reheater desuperheating water flow rate minus 45 t / h to 50 t / h. When the first real-time steam drum water level is between -110mm and 0mm, the feedwater flow rate is set to the sum of the main feedwater flow rate, the superheater desuperheating water flow rate, and the reheater desuperheating water flow rate. When the first real-time steam drum water level is less than -110mm, the feedwater flow rate is set to the sum of the main feedwater flow rate, the superheater desuperheating water flow rate, and the reheater desuperheating water flow rate plus 45t / h to 50t / h.

2. The method for switching control between the main circuit and bypass circuit of the boiler feedwater system in a thermal power unit according to claim 1, characterized in that, Also includes: Acquire the second real-time load during low-load operation or shutdown of the unit; When the second real-time load reaches the second preset load threshold corresponding to the fully closed state of the main regulating valve of the water supply system, the water supply of the water supply system bypass is gradually increased, while the water supply of the main water supply system is gradually decreased until the main water supply system is completely closed. During the process of switching from the main road to the bypass, the second real-time steam drum water level is obtained; Adjust the feedwater flow rate based on the second real-time steam drum water level.

3. The method for switching control between the main circuit and bypass circuit of the boiler feedwater system in a thermal power unit according to claim 1, characterized in that, The first preset load threshold corresponding to the fully open state of the water supply system bypass regulating valve is 30% of the unit capacity.

4. The method for switching control between the main circuit and bypass circuit of the boiler feedwater system in a thermal power unit according to claim 2, characterized in that, The second preset load threshold corresponding to the fully closed state of the main regulating valve of the water supply system is 30% of the unit capacity.

5. The method for switching control between the main circuit and bypass circuit of the boiler feedwater system in a thermal power unit according to claim 2, characterized in that, The gradual increase in the water supply volume of the water supply system bypass, while gradually decreasing the water supply volume of the water supply system main line, includes: The main electric regulating valve is closed at a certain rate within 280s to 300s. The correspondence between the opening feedback of the main electric regulating valve and the command of the bypass electric water supply valve is (100, 0), (98, 5.9), (95, 11.5), (90, 20), (70, 22), (60, 50), (5, 68), (0, 100), until the main electric water supply valve is completely closed, the bypass electric regulating valve is fully opened, and the bypass electric front and rear electric valves are fully opened.

6. The method for switching control between the main circuit and bypass circuit of the boiler feedwater system in a thermal power unit according to claim 2, characterized in that, The step of adjusting the feedwater flow rate based on the second real-time steam drum water level includes: When the second real-time steam drum water level is greater than 0 mm, the feedwater flow rate is set to the sum of the main feedwater flow rate, the superheater desuperheating water flow rate, and the reheater desuperheating water flow rate minus 45 t / h to 50 t / h. When the second real-time steam drum water level is between -120mm and 0mm, the feedwater flow rate is set to the sum of the main feedwater flow rate, the superheater desuperheating water flow rate, and the reheater desuperheating water flow rate. When the second real-time steam drum water level is less than -120mm, the feedwater flow rate is set to the sum of the main feedwater flow rate, the superheater desuperheating water flow rate, and the reheater desuperheating water flow rate plus 45t / h to 50t / h.

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