Control method for high-pressure heating splitting BEST steam feed pump set of double-machine regenerative thermal power plant

Abstract

The invention belongs to the technical field of automatic control of thermal generator sets, and particularly discloses a control method of a BEST steam feed pump set for high-pressure heating and splitting of a double-machine regenerative thermal power plant, which comprises the following steps: determining the pre-action opening degree of a steam inlet regulating valve of a BEST feed pump turbine after high-pressure heating and splitting; the pre-action opening degree of an overflow valve and the pre-action opening degree of a bypass valve on an exhaust header of the BEST feed pump turbine are determined; and after the high-pressure heating splitting signal is triggered, a steam feed pump minimum flow recirculation valve control method is started, a BEST feed pump turbine backpressure control method is determined according to the control method, and a BEST feed pump turbine valve adjusting opening degree control method is determined according to the control method. According to the invention, the stability and safety of the BEST steam feed pump set after high-pressure heating and splitting and the whole set can be improved.

Description

Technical Field

[0001] This invention belongs to the field of automatic control technology for thermal power generating units, and specifically relates to a control method for a BEST steam-driven feedwater pump set in a dual-unit regenerative thermal power plant. Background Technology

[0002] With the large-scale grid connection of new energy units in recent years, the role of thermal power plants as a ballast has become increasingly apparent. To achieve energy conservation and emission reduction, designing a BEST dual-unit regenerative thermal power plant is an effective approach. To reduce the throttling losses of the BEST feedwater pump turbine, the BEST dual-unit regenerative thermal power plant utilizes the remaining power of the BEST feedwater pump turbine and the BEST steam-driven feedwater pump unit when the valves are fully open by setting up a small generator. This achieves the goals of reducing plant power consumption, improving the efficiency of the BEST feedwater pump turbine, and enhancing the unit's economic efficiency.

[0003] When the BEST dual-unit regenerative turbine is running, the BEST feedwater pump turbine inlet regulating valve is fully open, and the pump unit speed is controlled via a converter. During high-pressure heater disconnection, all extracted steam is used for work, which can cause sudden increases in BEST feedwater pump turbine extraction pressure, exhaust pressure, and even over-limit power output of the small generator. Inaccurate control can lead to significant fluctuations in feedwater flow, deaerator safety valve activation, high exhaust pressure tripping of the BEST feedwater pump turbine, and even directly cause the entire turbine generator unit to trip. Furthermore, high-pressure heater disconnection under high load also raises the question of how to control the unit under the RB (regenerative braking) condition of the high-pressure heater. Currently, there is no mature automatic control method for the BEST steam-driven feedwater pump unit to handle high-pressure heater disconnection. Summary of the Invention

[0004] To address the above technical problems, this invention provides a control method for the BEST steam-driven feedwater pump unit in a dual-unit regenerative thermal power plant after the high-pressure heater is disconnected. This method enables safe and stable control of various parameters of the BEST steam-driven feedwater pump unit after the high-pressure heater is disconnected, thereby improving the stability and safety of the steam-driven feedwater pump unit and the entire unit.

[0005] This invention provides a control method for the BEST steam-driven feedwater pump unit in a dual-unit regenerative thermal power plant with a high-pressure heater disconnection. The BEST steam-driven feedwater pump unit includes a steam-driven feedwater pump, a BEST feedwater pump turbine, and a small generator. The control method for the BEST steam-driven feedwater pump unit in a dual-unit regenerative thermal power plant with a high-pressure heater disconnection includes: Step 1: Determine the extraction steam flow rate of each stage of extraction in a dual-unit regenerative thermal power plant; Step 2: Determine the shaft power of the steam-driven feedwater pump Small generator shaft power The potential work capacity of the BEST feedwater pump turbine is determined based on the extraction steam flow rates at each stage. ; Step 3, according to , and After determining the high-pressure heater disconnection, the pre-action opening degree of the BEST feedwater pump turbine inlet steam regulating valve is determined. ; Step 4, according to , , Based on the extraction steam flow rates at each stage, determine the pre-action opening of the BEST feedwater pump turbine exhaust pressure control valve. and according to Determine the pre-action opening degree of the overflow valve on the BEST feedwater pump turbine exhaust header. and the pre-action opening degree of the bypass valve ; Step 5: After the high-pressure heater disconnection signal is triggered, start the minimum flow recirculation valve control method for the steam-driven feedwater pump, and according to... , Determine the BEST feedwater pump turbine back pressure control method, based on Determine the valve opening control method for the BEST feedwater pump turbine.

[0006] Preferably, according to The method for controlling the valve opening of the BEST feedwater pump turbine is determined as follows: In converter master control mode, after the high-pressure heater disconnection signal is triggered, the converter master control is maintained, and the BEST feedwater pump turbine inlet steam regulating valve is pre-closed. ; In MEH master control mode, after the high-pressure heater disconnection signal is triggered, MEH master control is maintained, and the BEST feedwater pump turbine inlet steam regulating valve is pre-closed. Automatically reset afterwards; The actual opening degree of the BEST feedwater pump turbine inlet regulating valve before the high-pressure heater is disconnected.

[0007] Preferably, the method for controlling the minimum flow recirculation valve of the steam-driven feedwater pump is as follows: In the main control mode of the converter, after the high-pressure heater disconnection signal is triggered, when the converter power is greater than the first proportion of its power limit, the steam-driven feedwater pump minimum flow recirculation valve opens at a preset first rate; when the converter power is less than the second proportion of its power limit, the steam-driven feedwater pump minimum flow recirculation valve closes at a preset second rate; until the high-pressure heater disconnection signal is reset. In MEH main control mode, after the high-pressure heater disconnection signal is triggered, the minimum flow recirculation valve of the steam-driven feedwater pump remains in normal control mode.

[0008] Preferably, according to , The back pressure control method for the BEST feedwater pump turbine is determined as follows: After the high-pressure heater disconnection signal is triggered, the overflow valve is opened to... Bypass valve opened to At the same time, the automatic control settings of the relief valve and bypass valve are increased to the target value at a preset third rate. The target value is the minimum value between the upper limit of the exhaust pressure that satisfies the exhaust pressure ratio and the high exhaust pressure alarm value. After the high-pressure heater disconnection signal is reset, the automatic control target values ​​of the relief valve and bypass valve are reduced to the normal exhaust pressure control range at a preset fourth rate.

[0009] Preferably, after step 5, the method further includes: Step 6: When the feedback deviation of the BEST feedwater pump turbine speed command is less than 20 rpm, the exhaust pressure is less than the set value, and the extraction pressure of each stage is within the normal value, restore the normal control mode of the steam-driven feedwater pump minimum flow recirculation valve, the BEST feedwater pump turbine regulating valve, and the BEST feedwater pump turbine back pressure.

[0010] Preferably, the potential work capacity of the BEST feedwater pump turbine is determined based on the extraction steam flow rate at each stage. Specifically: ; In the formula, The enthalpy value of the BEST feedwater pump turbine; Let be the enthalpy of the steam extracted in the i-th stage; Let be the extraction steam flow rate of the i-th stage extraction. The potential work capacity of the i-th stage extraction steam; i is the extraction steam number of each stage of the BEST feedwater pump turbine, excluding the deaerator and exhaust steam.

[0011] Preferably, according to , and After determining the high-pressure heater disconnection, the pre-action opening degree of the BEST feedwater pump turbine inlet steam regulating valve is determined. Specifically: Determine the percentage of steam flow corresponding to the actual opening of the BEST feedwater pump turbine inlet regulating valve before the high-pressure heater is disconnected. ; Based on the shaft power of the steam-driven feedwater pump Small generator shaft power and the percentage of steam flow rate Determine the percentage of flow occupied by the steam-driven feedwater pump and the small generator. ; Based on the percentage of flow occupied by steam-driven feedwater pumps and small generators After determining the high-pressure heater disconnection, the pre-action opening degree of the BEST feedwater pump turbine inlet regulating valve is determined. .

[0012] Preferably, based on the shaft power of the steam-driven feedwater pump Small generator shaft power and the percentage of steam flow rate Determine the percentage of flow occupied by the steam-driven feedwater pump and the small generator. Specifically: ; In the formula, This refers to the shaft power of the steam-driven feedwater pump. For small generator shaft power; The working capacity of the BEST feedwater pump turbine; This represents the percentage of steam flow rate.

[0013] Preferably, according to , , Based on the extraction steam flow rates at each stage, determine the pre-action opening of the BEST feedwater pump turbine exhaust pressure control valve. Specifically: according to , , Based on the extraction steam flow rates at each stage, determine the additional exhaust steam flow rate after the BEST feedwater pump turbine valves are pre-closed. ; according to Specific pressure during high-pressure separation Exhaust pressure Determine the pre-action opening of the BEST feedwater pump turbine exhaust pressure control valve. .

[0014] Preferably, according to , , Based on the extraction steam flow rates at each stage, determine the additional exhaust steam flow rate after the BEST feedwater pump turbine valves are pre-closed. Specifically: ; In the formula, This refers to the shaft power of the steam-driven feedwater pump. For small generator shaft power; To enhance the potential of the BEST feedwater pump turbine; Let i be the extraction steam flow rate of the i-th stage extraction steam, where i is the extraction steam number of each stage of the BEST feedwater pump turbine, excluding the deaerator and exhaust steam. This refers to the extraction steam flow rate corresponding to the deaerator. This represents the extraction steam flow rate corresponding to the low-pressure heater.

[0015] The control method for the BEST steam-driven feedwater pump set of a dual-unit regenerative thermal power plant, as described in this invention, has the following advantages compared to the prior art: This invention clarifies the key points of a control method for the BEST steam-driven feedwater pump group after the high-pressure heater is disconnected in a dual-unit regenerative thermal power plant, and sets them in a reasonable sequence in the control logic, so that the automatic control of the BEST steam-driven feedwater pump group after the high-pressure heater is disconnected is practically operable.

[0016] This invention enables continuous and real-time judgment and control of the BEST steam-driven feedwater pump set after the high-pressure heater of the dual-unit regenerative unit is disconnected, thereby minimizing the significant interference caused by discontinuous control of equipment and systems.

[0017] This invention features reasonable control logic for the BEST feedwater pump turbine valves, automatic control logic for the steam-driven feedwater pump recirculation, and back pressure control logic for the BEST feedwater pump turbine after the high-pressure heater is disconnected. This shortens the disturbance process, reduces the fluctuation range of the boiler inlet feedwater flow, and improves the stability and safety of the BEST steam-driven feedwater pump unit and the entire unit after the high-pressure heater is disconnected.

[0018] This invention fills the gap in the field of automatic control of BEST steam-driven feedwater pump sets under high-pressure heater disconnection conditions in dual-unit regenerative thermal power units, and can be used as a reference for the automatic control of high-pressure heater RB in dual-unit regenerative thermal power units. Attached Figure Description

[0019] Figure 1 This is a flowchart of the control method for the BEST steam-driven feedwater pump group in a dual-unit regenerative thermal power plant according to an embodiment of the present invention. Detailed Implementation

[0020] In the following description, specific details such as particular system architectures and techniques are set forth for illustrative purposes and not for limitation, in order to provide a thorough understanding of the embodiments of the invention. However, those skilled in the art will understand that the invention can be implemented in other embodiments without these specific details. In other instances, detailed descriptions of well-known systems, apparatuses, circuits, and methods are omitted so as not to obscure the description of the invention with unnecessary detail.

[0021] Before controlling the BEST steam-driven feedwater pump set for high-pressure water heater decoupling in this embodiment of the invention, the following automatic control conditions need to be confirmed: (1) The BEST feedwater pump turbine MEH system has a basic feedwater pump turbine inlet steam regulating valve opening module, which can realize the control of the feedwater pump turbine inlet steam regulating valve in the BEST steam-driven feedwater pump group converter main control mode.

[0022] The common approach is to, in the converter master control mode, set the BEST feedwater pump turbine speed to track the actual speed, while slowly opening the control valve at a deviation rate of 2 rpm, eventually increasing the offset by 10 rpm to ensure the control valve is fully open (or reaches the set upper limit of valve opening). This setting mode does not completely abandon the MEH's control over the control valve opening, and can achieve control of the control valve opening in the MEH-side logic in special cases (such as high-voltage heater decoupling).

[0023] (2) The high-voltage splitting signal can be effectively and accurately transmitted to the MEH system.

[0024] The high-voltage generator disconnection signal is transmitted from the DCS cabinet to the MEH cabinet via hardwired connection rather than communication, otherwise delay issues may occur. Furthermore, the DCS is connected to the MEH side via three hardwired connections, and identification is achieved on the MEH side using a two-out-of-three method. This ensures that the MEH side effectively and accurately receives the high-voltage generator disconnection signal after it is initiated on the DCS side.

[0025] (3) The BEST feedwater pump turbine back pressure automatic control module is operating normally and can dynamically adjust the exhaust pressure.

[0026] The DCS or MEH side is designed with BEST feedwater pump turbine back pressure automatic control logic. For example, a back pressure target value is set. When the back pressure is high, the overflow valve opens to the lower-level low-pressure heater. When the back pressure is too high, the bypass valve opens to the condenser. That is, the back pressure control set value is set first. When the back pressure is higher than the set value, the overflow valve acts first. When the back pressure is higher than the set value plus a certain deviation value, the bypass valve acts then.

[0027] (4) It can effectively and accurately acquire the following real-time data: BEST feedwater pump turbine related extraction steam pressure at each stage and temperature High inlet water flow rate Water supply pressure Inlet pressure of water pump and temperature The inlet and outlet water temperatures of each heater \ Steam inlet pressure of each heater and temperature , the condensate temperature of each heater BEST feedwater pump turbine exhaust pressure and temperature Condensate flow rate Condensate pressure Where 'i' corresponds to the extraction steam number.

[0028] The system requires the design of pressure, temperature, and flow measurement points at corresponding locations. The inlet flow rate of the high-pressure heater can be calculated by the relationship between the inlet flow rate of the feed water pump, the boiler feed water flow rate, and the flow rates of the desuperheating water at each stage.

[0029] (5) The flow characteristic curve of the BEST feedwater pump turbine inlet regulating valve has been obtained, and the correlation formula between the valve opening percentage and the valve flow rate percentage has been derived. .

[0030] (6) The overflow valve and bypass valve in the BEST feedwater pump turbine exhaust piping system have been obtained at a specific pressure. Relationship between valve opening percentage and valve flow rate , .

[0031] Valve manufacturers typically provide a table or curve showing the relationship between valve opening and flow rate under the rated exhaust pressure of the BEST feedwater pump turbine.

[0032] (7) It can effectively and accurately acquire the following real-time data: Small generator power BEST steam-driven feedwater pump unit speed Inlet and outlet feedwater parameters of the feedwater pump set (including the inlet feedwater temperature of the steam-driven feedwater pump) Import and export pressure / Pump inlet feedwater mass flow rate ).

[0033] (8) The maximum efficiency of the steam-driven feedwater pump set has been obtained based on the information provided by the manufacturer. Average efficiency of small generator and converter sets .

[0034] The control method for the BEST steam-driven feedwater pump group in a dual-unit regenerative thermal power plant with high-pressure heater disconnection according to an embodiment of the present invention includes a steam-driven feedwater pump, a BEST feedwater pump turbine, and a small generator. The control method for the BEST steam-driven feedwater pump group in a dual-unit regenerative thermal power plant with high-pressure heater disconnection is as follows: Figure 1 As shown, it includes: Step 1: Determine the steam extraction flow rate of each stage of extraction in a dual-unit regenerative thermal power plant.

[0035] In this embodiment of the invention, the feedwater flow rate, condensate flow rate, and the enthalpy value of the medium obtained from the heater inlet steam, condensate, and inlet / outlet water temperature parameters are substituted into the heater heat balance calculation formula to obtain the extraction steam flow rate of each stage of extraction.

[0036] 1. For high-pressure heaters, the steam extraction flow rate for each stage is calculated as follows: 1) When the first stage extraction steam or the upstream heater's normal drain is not open, the extraction steam flow rate must meet the following requirements: (1) In the formula, To ensure high feedwater flow rate at the inlet; Enthalpy value, kJ / kg; Water supply pressure and the outlet water temperature of the heater Seek; Water supply pressure and Seek; The intake pressure of the heater and the heater's inlet temperature Seek; The intake pressure of the heater and the hydrophobic temperature of the heater To obtain.

[0037] 2) For non-first-stage extraction steam and with the upstream heater's condensate drain normally open, the extraction steam flow rate must meet the following requirements: (2) (3) In the formula, The intake pressure of the heater and the hydrophobic temperature of the heater Seek; The valve opening for the emergency drain of the i-1 stage heater. The valve opening is for normal condensation of the i-1 stage heater.

[0038] It should be noted that the calculation It is assumed that the flow capacity of the emergency drain control valve and the normal drain control valve are the same. However, the actual flow capacity of the emergency drain is greater than that of the normal drain, which will cause a certain deviation (too small) in the calculation of the extraction steam flow rate in the next stage. However, this deviation can be compensated for by the content of the next step in this invention. For the sake of configuration implementation, it is simplified to the above calculation formula. In practice, the ratio of the flow capacity of the emergency drain control valve to that of the normal drain control valve can also be used to calculate the flow rate. The calculation formula was modified, but it has little significance for engineering applications.

[0039] 2. For the low-pressure heater, the steam extraction flow rate for each stage is calculated as follows: 1) When the first stage extraction steam or the upstream heater's normal drain is not open, the extraction steam flow rate must meet the following requirements: (4) In the formula, The flow rate of condensate water; Condensate pressure and the outlet water temperature of the heater Seek; Condensate pressure and To obtain.

[0040] 2) For non-first-stage extraction steam and with the upstream heater's condensate drain normally open, the extraction steam flow rate must meet the following requirements: (5) (6) 3. For the deaerator, the extraction steam flow rate is calculated as follows: (7) (8) In the formula, Enthalpy value, kJ / kg; From the inlet pressure of the water pump and feedwater pump inlet temperature Seek; Condensate pressure and the outlet water temperature of the heater To obtain.

[0041] Furthermore, the specific selection of values ​​for the above calculation formula under different operating conditions of the heater is explained as follows: a) If a certain stage heater is in normal operation, the extraction steam electric valve is open and the normal drain regulating valve opening degree is ≥2% as the criterion. When calculating the extraction steam flow rate of this stage, the above process shall be followed.

[0042] b) If a certain stage heater is disconnected, the extraction steam electric valve is closed and (the heater inlet steam pressure is much lower than the corresponding extraction steam pressure or the opening of the normal drain valve and the emergency drain valve are both <2%), the extraction steam flow rate of this stage is directly set to zero.

[0043] c) If a heater stage is activated but uses emergency condensate instead of normal condensate, the extraction steam flow rate for this stage shall be calculated based on the following criteria: the extraction steam electric valve is open, the emergency condensate control valve opening is ≥2%, and the normal condensate control valve opening is <2%. The calculation is based on the inlet steam pressure of this stage heater. Obtain the enthalpy of saturated water directly.

[0044] Because the extraction steam flow rate is calculated using DCS measuring points rather than performance test-specific measuring points in this step, the calculated extraction steam flow rate has a certain deviation. On the one hand, these deviations can be reduced by correcting the DCS measuring point display results through methods such as zero-point adjustment, multiplication by a coefficient, and deviation reduction; on the other hand, in engineering, such small deviations do not affect the reliable implementation of automatic control.

[0045] Step 2: Determine the shaft power of the steam-driven feedwater pump Small generator shaft power The potential work capacity of the BEST feedwater pump turbine is determined based on the extraction steam flow rates at each stage. Specifically: Step 2.1: Determine the shaft power of the steam-driven feedwater pump As shown in formula (9): (9) In the formula, This refers to the mass flow rate of the feedwater at the inlet of the steam-driven feedwater pump. This refers to the inlet pressure of the steam-driven feedwater pump. This refers to the outlet pressure of the steam-driven feedwater pump. This represents the highest efficiency of the steam-driven feedwater pump. The feedwater density inside the steam-driven feedwater pump is kg / m³. 3 It is obtained from the inlet temperature and inlet pressure of the steam-driven feedwater pump.

[0046] In addition, if the booster pump of the steam-driven feedwater pump is also driven by the BEST feedwater pump turbine, its power is also calculated with reference to the above formula and added to the power calculation of the steam-driven feedwater pump.

[0047] Step 2.2: Determine the shaft power of the small generator. As shown in formula (10): (10) In the formula, For small generator power; This represents the minimum efficiency for small generators and converter units.

[0048] Step 2.3: Determine the potential work capacity of the BEST feedwater pump turbine based on the extraction steam flow rates of each stage. As shown in formula (11): (11) In the formula, The enthalpy of the BEST feedwater pump turbine is determined by the BEST feedwater pump turbine exhaust pressure. And BEST feedwater pump turbine exhaust temperature Seek; The enthalpy of the i-th stage extraction steam is given by the pressure of the i-th stage extraction steam from the BEST feedwater pump turbine. and temperature Seek; Let be the extraction steam flow rate of the i-th stage extraction. The potential work capacity of the i-th stage extraction steam; i is the extraction steam number of each stage of the BEST feedwater pump turbine, excluding the deaerator and exhaust steam.

[0049] The calculation is based on the capacity of the extracted steam to perform work instead of heat exchange. It is this potential work that leads to an increase in the shaft power of the BEST steam-driven feedwater pump set.

[0050] Step 3, according to , and After determining the high-pressure heater disconnection, the pre-action opening degree of the BEST feedwater pump turbine inlet steam regulating valve is determined. Specifically: Step 3.1: Determine the actual opening degree of the BEST feedwater pump turbine inlet regulating valve before the high-pressure heater is disconnected. corresponding percentage of steam flow .

[0051] The embodiments of the present invention will Substitution .

[0052] Step 3.2: Based on the shaft power of the steam-driven feedwater pump Small generator shaft power and percentage of steam flow Determine the percentage of flow occupied by the steam-driven feedwater pump and the small generator. Specifically: (12) In the formula, This refers to the shaft power of the steam-driven feedwater pump. For small generator shaft power; The working capacity of the BEST feedwater pump turbine; This represents the percentage of steam flow rate.

[0053] Step 3.3: Based on the percentage of flow occupied by the steam-driven feedwater pump and the small generator. After determining the high-pressure heater disconnection, the pre-action opening degree of the BEST feedwater pump turbine inlet regulating valve is determined. Specifically: Substitution The pre-action opening degree of the BEST feedwater pump turbine inlet regulating valve is calculated by reverse calculation. .

[0054] After the high-pressure heater is disconnected, there is a process in which the exhaust pressure of the feedwater pump turbine increases and the shaft power increases. The pre-closing valve is designed to shorten this process and maintain the shaft power stability of the feedwater pump set and the small generator as accurately as possible.

[0055] Step 4, according to , , Based on the extraction steam flow rates at each stage, determine the pre-action opening of the BEST feedwater pump turbine exhaust pressure control valve. and according to Determine the pre-action opening degree of the overflow valve on the BEST feedwater pump turbine exhaust header. and the pre-action opening degree of the bypass valve Specifically: Step 4.1, according to , , Based on the extraction steam flow rates at each stage, determine the pre-action opening of the BEST feedwater pump turbine exhaust pressure control valve. Specifically: Step 4.1.1, according to , , Based on the extraction steam flow rates at each stage, determine the additional exhaust steam flow rate after the BEST feedwater pump turbine valves are pre-closed. As shown in formula (13): (13) In the formula, This refers to the shaft power of the steam-driven feedwater pump. For small generator shaft power; To enhance the potential of the BEST feedwater pump turbine; Let i be the extraction steam flow rate of the i-th stage extraction steam, where i is the extraction steam number of each stage of the BEST feedwater pump turbine, excluding the deaerator and exhaust steam. This is the sum of the extraction steam flow rates associated with the BEST feedwater pump turbine; This refers to the extraction steam flow rate corresponding to the deaerator. This represents the extraction steam flow rate corresponding to the low-pressure heater.

[0056] Step 4.1.2, according to Specific pressure during high-pressure separation Exhaust pressure Determine the pre-action opening of the BEST feedwater pump turbine exhaust pressure control valve. .

[0057] The embodiments of the present invention firstly include In the middle, we get .

[0058] Secondly, considering the specific pressure during high-pressure separation... Exhaust pressure Sure As shown in formula (14): (14) Finally, the pre-action opening of the BEST feedwater pump turbine exhaust pressure control valve. As shown in formula (15): (15) Step 4.2, according to Determine the pre-action opening degree of the overflow valve on the BEST feedwater pump turbine exhaust header. and the pre-action opening degree of the bypass valve .

[0059] This invention establishes a specific pressure based on the relationship between the flow rate of the relief valve and the bypass valve and the valve opening degree, by opening the relief valve first and then the bypass valve. The relationship between the additional exhaust steam flow rate and the opening degrees of the two valve groups, namely the relief valve and the bypass valve, is as follows: ; ; .

[0060] It should be noted that, to ensure smooth adjustment, and correspond There should be an appropriate degree of overlap.

[0061] In obtaining Then, there is: (16) (17) Step 5: After the high-pressure heater disconnection signal is triggered, start the minimum flow recirculation valve control method for the steam-driven feedwater pump, and according to... , Determine the BEST feedwater pump turbine back pressure control method, based on A method for controlling the valve opening of the BEST feedwater pump turbine is determined. In this embodiment of the invention, the above three control logics are activated simultaneously to achieve control of the BEST feedwater pump turbine.

[0062] Specifically, after the high-voltage release signal is triggered, it is synchronously transmitted to the MEH system and the DCS system; at the same time, the following three automatic control modules are activated: A. The valve opening control module of the BEST feedwater pump turbine. This module realizes the control of valve opening according to... Determine the valve opening control of the BEST feedwater pump turbine.

[0063] During normal operation, the BEST feedwater pump turbine with dual-unit regenerative operation has two speed control modes: converter main control mode and MEH main control mode. In converter main control mode, the opening of the BEST feedwater pump turbine inlet steam regulating valve is maintained at a fixed set value, and the speed is achieved by the converter controlling the change in the power of the small generator. In MEH main control mode, the speed is achieved by the speed control PID in the MEH configuration controlling the change in the opening of the BEST feedwater pump turbine inlet steam regulating valve.

[0064] In converter main control mode, after the high-pressure heater disconnection signal is triggered, the converter main control is maintained, and the BEST feedwater pump turbine inlet steam regulating valve is pre-closed. The valve opening gradually returns to normal when the main control valve of the converter is activated, until the sixth step is triggered.

[0065] In MEH master control mode, after the high-pressure heater disconnection signal is triggered, MEH master control is maintained, and the BEST feedwater pump turbine inlet steam regulating valve is pre-closed. It then automatically resets, and its valve opening is controlled by MEH speed control PID.

[0066] The pre-closing of the BEST feedwater pump turbine inlet regulating valve in MEH main control mode is less than that in converter main control mode because: ① In MEH main control mode, after the high-pressure heater is disconnected, the speed increases, and the valve will close under speed PID control. If an excessive pre-closing amount is added, it can easily lead to overshooting of the BEST feedwater pump turbine speed; ② In order to shorten the adjustment time of the speed PID and reduce the possibility of PID overshooting, a certain pre-closing amount is still required. This pre-closing amount is related to the response of the entire unit's thermal system, including the dual-unit (extraction steam) regenerative system, main reheat steam system, and boiler steam-water system, to the high-pressure heater disconnection, as well as the parameter settings of the speed PID under MEH main control. The pre-closing opening mentioned above... This is just a provisional value, and the pre-shutdown value can be adjusted according to the actual situation of the unit. It can be close to, equal to, or even less than the pre-shutdown value. It can also be close to or equal to (That is, no pre-closing, relying entirely on speed PID regulation). ③ Under the main control of the converter, even if the pre-closing of the BEST feedwater pump turbine inlet regulating valve is too large or too small, stable control can be achieved by reducing the output of the generator.

[0067] B. Minimum Flow Recirculation Valve Control Module for Steam-Driven Feedwater Pump After the high-voltage heater is disconnected, in the main control mode of the converter, when the converter power is greater than the first proportion of its power limit, the steam-driven feedwater pump recirculation valve opens at a preset first rate; when the converter power is less than the second proportion of its power limit, the steam-driven feedwater pump recirculation valve closes at a preset second rate; until the high-voltage heater disconnection action signal is reset.

[0068] After the high-pressure heater is disconnected, in MEH main control mode, the steam-driven feedwater pump recirculation valve maintains its normal control mode. Common normal control modes for the steam-driven feedwater pump recirculation valve include: ① open-loop control mode with a one-to-one correspondence between feedwater pump inlet flow and valve opening; ② closed-loop control with PID control outputting valve opening based on feedwater pump inlet flow as the target value.

[0069] The opening and closing rates of the recirculation system are related to the design and equipment configuration of the feedwater system in a dual-unit regenerative thermal power plant, and need to be determined based on the design flow rate of the recirculation control valve and its flow characteristic curve. Specifically, the valve opening rate is set at opening the feedwater pump recirculation control valve within 10 seconds until its flow rate reaches 40%; the valve closing rate is half the opening rate.

[0070] The main purpose is to prevent the small generator from overloading under the main control mode of the converter after the high-voltage generator is disconnected, which could lead to the expansion of system instability.

[0071] C. BEST feedwater pump turbine back pressure control module, realizing the control based on... , Determine the back pressure control of the BEST feedwater pump turbine.

[0072] The back pressure control of the BEST feedwater pump turbine is generally achieved through a combination of relief valves, bypass valves, and extraction steam pipe valves on its exhaust header. Under normal circumstances, the extraction steam pipe valves remain fully open, and the back pressure of the BEST feedwater pump turbine is controlled by automatically adjusting the opening degrees of the relief valves and bypass valves.

[0073] After the high-pressure heater disconnection signal is triggered, the overflow valve is opened directly to... Bypass valve opened to The pressure is then handed over to BEST for PID control of the steam turbine exhaust pressure of the feedwater pump.

[0074] After the high pressure heater disconnection signal is triggered, the back pressure of the BEST feedwater pump turbine is simultaneously increased at a preset third rate to the lower of the upper limit of the exhaust pressure that meets the exhaust pressure ratio and the high exhaust pressure alarm value. In other words, the automatic control settings of the overflow valve and bypass valve are increased to the target value at the third rate. The target value is the minimum of the upper limit of the exhaust pressure that meets the exhaust pressure ratio and the high exhaust pressure alarm value.

[0075] After the high-pressure heater disconnection signal is reset, the automatic control target values ​​of the relief valve and bypass valve are reduced to the normal exhaust pressure control range at the fourth rate.

[0076] The purpose of setting the pre-opening degree of the bypass valve and the relief valve in this embodiment of the invention is to reduce the control lag and fluctuations caused by pure PID control; the purpose of increasing the back pressure is to suppress the magnitude of the speed increase and shorten the speed fluctuation time; at the same time, changing the set value at a uniform speed is also to stabilize the control process.

[0077] In this embodiment of the invention, the ratio of valve pressure is directly used as the opening correction coefficient of the above-mentioned regulating valve, ignoring the effect of the differential pressure before and after the valve on the flow rate of the regulating valve. This is also for the purpose of simplifying the engineering control configuration. The resulting control deviation can be compensated by other control loops and does not affect the reliability of actual control.

[0078] Step 6: When the feedback deviation of the BEST feedwater pump turbine speed command is less than 20 rpm, the exhaust pressure is less than the set value, and the extraction pressure of each stage is within the normal value, restore the normal control mode of the steam-driven feedwater pump minimum flow recirculation valve, the BEST feedwater pump turbine regulating valve, and the BEST feedwater pump turbine back pressure.

[0079] It should be noted that the set value of the exhaust pressure here is a value between the exhaust pressure alarm value and the trip value in the instruction manual provided by the feedwater pump turbine manufacturer, and is determined according to the actual situation of the unit; the normal value of the extraction pressure of each section should be determined with reference to the heat balance diagram of the high-pressure heater under full shutdown condition.

[0080] Example: This invention takes a 1000MW double reheat dual-unit regenerator unit in Anhui Province as an example. The feedwater pump group shaft system of its BEST dual-unit regenerator unit is composed of feedwater pump - BEST feedwater pump turbine - small generator. The extraction steam regenerator system has the following extraction stages: Stage 1 extraction steam comes from the exhaust steam of the generator turbine's ultra-high pressure cylinder; Stages 2-7 extraction steam comes from the BEST feedwater pump turbine; Stages 1-5 extraction steam supplies steam to the high-pressure heater; Stage 6 extraction steam supplies steam to the deaerator; Stage 7 extraction steam is the exhaust steam of the BEST feedwater pump turbine, which supplies steam to the No. 7 low-pressure heater during normal operation. When the exhaust steam pressure is high, the excess pressure is released to the No. 8 low-pressure heater through the overflow valve; when the exhaust steam pressure is excessively high, the excess pressure is released to the condenser through the bypass valve.

[0081] The automatic control method of the BEST steam-driven feedwater pump set for the high-pressure heater disconnection in a dual-unit regenerative thermal power plant according to the present invention is explained using the operating parameters of the unit at 75% THA.

[0082] A control method for the BEST steam-driven feedwater pump set in a dual-unit regenerative thermal power plant includes the following: (1) Reasonable automatic control method prerequisites; (2) BEST feedwater pump turbine control method for dual-unit regenerative thermal power plant.

[0083] Confirmation of the conditions for a reasonable automatic control method for the BEST feedwater pump turbine control method in the dual-unit regenerative thermal power plant: A. The BEST feedwater pump turbine MEH system has a basic feedwater pump turbine inlet steam regulating valve opening module, which can control the feedwater pump turbine inlet steam regulating valve under the main control mode of the BEST steam-driven feedwater pump group converter.

[0084] In the converter master control mode, the BEST feedwater pump turbine speed setting of this unit tracks the actual speed, while the control valve is slowly opened at a deviation rate of 2 rpm, and finally the offset is increased by 10 rpm to ensure that the control valve is in a fully open state (or reaches the set upper limit of valve opening).

[0085] B. The high-voltage generator disconnection action signal can be transmitted from the converter device to the MEH system and DCS system; The high-voltage disconnection signal of this unit is transmitted from the DCS cabinet to the MEH cabinet through hard-wiring; and on the DCS side, it is connected to the MEH side through three hard-wiring connections respectively, and identification is achieved on the MEH side through a three-out-of-two method.

[0086] C. The feedwater pump turbine back pressure automatic control module operates normally, dynamically adjusting the exhaust pressure according to changes in the feedwater pump turbine inlet steam pressure and final stage pressure ratio. The unit controls the feedwater pump turbine exhaust pressure by automatically controlling the opening of the overflow valve and bypass valve.

[0087] The MEH side of this project is designed with automatic back pressure control logic for the BEST feedwater pump turbine. The back pressure of the BEST feedwater pump turbine is the target value. When the back pressure is higher than the set value, the overflow valve is activated to release pressure to No. 8 low pressure heater; when the back pressure is higher than the set value + 0.1MPa, the bypass valve is activated to release pressure to the condenser.

[0088] The exhaust pressure setpoints for this project are shown in Table 1. Table 1 Exhaust Pressure Setpoints

[0089] D. It can effectively and accurately acquire the following real-time data: BEST feedwater pump turbine related extraction steam pressure at each stage and temperature High inlet water flow rate Water supply pressure Inlet pressure of water pump and temperature Inlet and outlet water temperatures of each heater \ Steam inlet pressure of each heater and temperature , the condensate temperature of each heater BEST feedwater pump turbine exhaust pressure and temperature Condensate flow rate Condensate pressure Where 'i' corresponds to the extraction steam number. See the table below for specific extraction steam parameters: Table 2. Extraction Steam Related Parameters

[0090] Note: a) The steam from the first pump of this unit enters the No. 1 high-pressure heater after passing through the external steam cooler, so the steam pressure and temperature at the No. 1 high-pressure heater vary considerably.

[0091] b) Pressure of the 7th stage extraction steam and temperature This is the exhaust pressure of the BEST feedwater pump turbine. and temperature .

[0092] c) Deaerator outlet water temperature This is the inlet temperature of the water pump. .

[0093] Other data is shown in the table below: Table 3 Other relevant parameters

[0094] E. The flow characteristic curve of the BEST feedwater pump turbine inlet regulating valve has been obtained, and the correlation formula between valve opening and valve flow rate has been derived. It meets the following table: Table 4. Correlation between valve opening degree and valve flow rate

[0095] F. The overflow valve and bypass valve in the BEST feedwater pump turbine exhaust piping system have been obtained at specific pressures. Relationship between valve opening percentage and valve flow rate , .

[0096] The flow characteristic of the relief valve in this project is linear. When =0.7MPa, As shown in the table below: Table 5. Correlation between relief valve opening degree and steam flow rate

[0097] The bypass valve in this project has an equal percentage flow characteristic. When =0.7MPa, As shown in the table below: Table 6. Correlation between bypass valve opening and steam flow rate

[0098] G. It can effectively and accurately acquire the following real-time data when the unit is operating at 75% THA: Small generator power =18741kW, BEST steam-driven feedwater pump unit speed =3843rpm, inlet and outlet water supply parameters of the water supply pump set (including the inlet water temperature of the water supply pump) =190℃, inlet and outlet pressure =3.32MPa / =30.53MPa, pump inlet feed water mass flow rate =1972.8t / h).

[0099] H. The maximum efficiency of the steam-driven feedwater pump set has been obtained based on the information provided by the manufacturer. =86%, average efficiency of small generator and converter sets =98.0%.

[0100] The control method for the BEST steam-driven feedwater pump set of the dual-unit regenerative thermal power plant high-pressure heater disconnection, as described in (2), is as follows: The first step is to determine the extraction steam flow rate of each stage of extraction in a dual-unit regenerative thermal power plant.

[0101] All heaters in this unit operate normally with gravity flow. By substituting the feedwater flow rate, condensate flow rate, and the enthalpy of the medium obtained from the heater inlet steam, condensate, and inlet / outlet water temperature parameters into the heater heat balance calculation formula, the extraction steam flow rate for each stage can be obtained.

[0102] The extraction steam volume is calculated as follows, taking stage 1 / 2 / 3 (i.e., level 1 / 2 / 3) as examples: Calculate the pumping flow rate for stage 1: ; Calculate the air flow rate for the two stages: Since all the condensate flows through the normal condensate drain, therefore =0; Since there is no zero-segment steam extraction, therefore =0.

[0103] ;

[0104] ; Calculate the air flow rate for the three sections: Since all the condensate flows through the normal condensate drain, therefore =0.

[0105] ;

[0106] ; The steam extraction volume for each section is calculated sequentially, and the results are summarized in the table below: Table 7 Summary of Steam Extraction Volume for Each Section

[0107] Step 2: Calculate the shaft power of the steam-driven feedwater pump Small generator shaft power and potential functional abilities .

[0108] Based on the real-time operating data and maximum efficiency of the steam-driven feedwater pump Calculate the shaft power of the steam-driven feedwater pump The shaft power of the steam-driven feedwater pump then satisfies: ; The density of the feed water in the feed pump is kg / m³. 3 It is obtained from the inlet temperature and inlet pressure of the water pump.

[0109] In addition, the booster pump of the steam-driven feedwater pump of this unit is driven independently by the motor and does not require calculation.

[0110] Based on the small generator's power and the minimum efficiency of the small generator and converter set Calculate the shaft power of the converter and small generator. Then the shaft power of the small generator satisfies: ; Calculate the potential work capacity of each stage of extraction steam from the BEST feedwater pump turbine and high-pressure heater.

[0111] Based on the extraction steam pressure and temperature of each section, the corresponding extraction steam enthalpy values ​​are obtained as follows: Table 8. Enthalpy values ​​of steam extraction for each section

[0112] The potential work capacity of each stage of steam extraction is calculated using the following formula: ; The third step is to obtain the pre-action value of the BEST feedwater pump turbine inlet regulating valve after the high-pressure heater is disconnected, based on the distribution of feedwater pump shaft power, small generator shaft power and the potential work capacity of each stage of extraction steam.

[0113] Given the actual opening degree of the BEST feedwater pump turbine inlet regulating valve before the high-pressure heater is disconnected. ,Will Substitution .

[0114] Based on the shaft power distribution of the feedwater pump group before the high-pressure heater is disconnected, the percentage of flow occupied by the feedwater pump is calculated. , satisfy: ; Will Substitution The pre-action opening degree of the feedwater pump turbine inlet regulating valve is calculated by reverse calculation. .

[0115] Step 4: Based on the sum of the extraction steam flow rates of each section of the BEST feedwater pump turbine, and the proportions of the feedwater pump shaft power, the small generator shaft power, and the extractable power, calculate the pre-action value of the BEST feedwater pump turbine exhaust pressure control valve group.

[0116] The specific process for obtaining the pre-action value is as follows: 1) Calculate the additional exhaust steam flow rate after the BEST feedwater pump turbine valves are pre-closed. ,satisfy: ; 2) Based on the relationship between the flow rate of the relief valve and the bypass valve and their valve opening degree, open the relief valve first, then the bypass valve, while ensuring... and correspond Under the premise of appropriate overlap, establish specific pressure. The relationship between the additional exhaust steam flow rate and the opening degree of the relief valve and bypass valve assembly at a pressure of 0.7 MPa, i.e. ; ; .

[0117] Table 9 Pre-action values ​​of exhaust pressure control valve group

[0118] 3) Combined with the exhaust pressure during high-pressure heater disconnection With specific pressure The ratio of to is used to obtain the final pre-opening range, i.e.: ; ; ; ; Step 5: After the high-pressure heater disconnection action of the dual-unit regenerative thermal power unit is triggered, three control logics are activated simultaneously: the minimum flow recirculation valve control logic of the steam-driven feedwater pump, the valve opening control logic of the BEST feedwater pump turbine, and the back pressure control logic of the BEST feedwater pump turbine, thereby realizing the control of the BEST feedwater pump turbine.

[0119] After the high-voltage release signal is triggered, it is synchronously transmitted to the MEH system and DCS system; at the same time, the following three automatic control modules are activated: A. Valve opening control module for BEST feedwater pump turbine In converter main control mode, after the high-pressure heater disconnection signal is triggered, the converter main control is maintained, and the BEST feedwater pump turbine inlet steam regulating valve is pre-closed. The valve opening gradually returns to normal when the converter is in main control mode after the fifth step is triggered.

[0120] In MEH master control mode, after the high-pressure heater disconnection signal is triggered, MEH master control is maintained, and the BEST feedwater pump turbine inlet steam regulating valve is pre-closed. It then automatically resets, and its speed operates normally under the MEH speed control PID.

[0121] B. Minimum Flow Recirculation Valve Control Module for Steam-Driven Feedwater Pump After the high-pressure heater is disconnected, in the main control mode of the converter, when the converter power is greater than 85% of its power limit, the steam-driven feedwater pump recirculation control valve opens at a rate of 2% / s; when the converter power is less than 45% of its power limit, the steam-driven feedwater pump recirculation control valve closes at a rate of 1% / s; until the high-pressure heater disconnection action signal is reset.

[0122] After the high-pressure heater is disconnected, in MEH main control mode, the recirculation control mode remains unchanged. The normal recirculation control mode for this unit is an open-loop control mode with a one-to-one correspondence between the feedwater pump inlet flow and the control valve opening. Details are as follows: Table 10 Relationship between feedwater pump inlet flow rate and regulating valve opening

[0123] C. BEST Feedwater Pump Turbine Back Pressure Control Module After the high-pressure heater is decoupled, the overflow valve is pre-opened to 81.3%, the bypass valve remains fully closed, and then the back pressure control PID is handed over.

[0124] After the high pressure is released, the back pressure of the BEST feedwater pump turbine is simultaneously increased to the lower of the upper limit of the exhaust pressure that meets the exhaust pressure ratio and the high exhaust pressure alarm value at the preset third rate. In other words, the automatic control target values ​​of the overflow valve and bypass valve are increased to the target values ​​at the third rate.

[0125] The high exhaust pressure alarm value for this unit is 1.05 MPa, and the trip value is 1.25 MPa. The pressure ratio of the last stage of the feedwater pump turbine in this project is calculated as: 6 extraction pressure / feedwater pump turbine exhaust pressure (7 extraction). The pressure ratio of the last stage must be controlled to be no less than the following values: Table 11 Relationship between Rotational Speed ​​and Pressure Ratio

[0126] When the unit load is 750MW, the extraction pressure of the 6th stage is 1.32MPa; when the feedwater pump turbine speed is 3843rpm, the pressure ratio of the last stage group is 1.158; therefore, the maximum exhaust pressure is 1.32MPa÷1.158=1.14MPa>1.05MPa. Therefore, after the high-pressure heater is disconnected, the setpoints of the overflow valve and bypass valve increase to 1.05MPa in increments of 0.1MPa / s.

[0127] After the high-pressure heater is disconnected and reset, the automatic control target values ​​of the relief valve and bypass valve are reduced to the normal exhaust pressure control set value at a rate of 0.05 MPa / s.

[0128] Step 6: When the feedback deviation of the BEST feedwater pump turbine speed command is <20 rpm, the exhaust pressure is <1.1 MPa, and the extraction pressure of each section is within the normal value, restore the normal control mode of the steam-driven feedwater pump minimum flow recirculation valve, the BEST feedwater pump turbine regulating valve, and the BEST feedwater pump turbine back pressure control.

[0129] The normal values ​​for the extraction steam pressure of each section of this unit are: Table 12 Normal values ​​of extraction steam pressure for each section

[0130] This invention clarifies the key points of a control method for the BEST steam-driven feedwater pump group after the high-pressure heater is disconnected in a dual-unit regenerative thermal power plant, and sets them in a reasonable sequence in the control logic, so that the automatic control of the BEST steam-driven feedwater pump group after the high-pressure heater is disconnected is practically operable.

[0131] This invention enables continuous and real-time judgment and control of the BEST steam-driven feedwater pump set after the high-pressure heater of the dual-unit regenerative unit is disconnected, thereby minimizing the significant interference caused by discontinuous control of equipment and systems.

[0132] This invention features reasonable control logic for the BEST feedwater pump turbine valves, automatic control logic for the steam-driven feedwater pump recirculation, and back pressure control logic for the BEST feedwater pump turbine after the high-pressure heater is disconnected. This shortens the disturbance process, reduces the fluctuation range of the boiler inlet feedwater flow, and improves the stability and safety of the BEST steam-driven feedwater pump unit and the entire unit after the high-pressure heater is disconnected.

[0133] This invention fills the gap in the field of automatic control of BEST steam-driven feedwater pump sets under high-pressure heater disconnection conditions in dual-unit regenerative thermal power units, and can be used as a reference for the automatic control of high-pressure heater RB in dual-unit regenerative thermal power units.

[0134] The above descriptions are merely a few embodiments of the present invention and are not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any modifications or alterations made by those skilled in the art without departing from the scope of the technical solution of the present invention using the disclosed technical content are equivalent to equivalent implementation cases and fall within the scope of the technical solution.

Claims

1. A control method for a BEST steam-driven feedwater pump set in a dual-unit regenerative thermal power plant, characterized in that, The BEST steam-driven feedwater pump unit includes a steam-driven feedwater pump, a BEST feedwater pump turbine, and a small generator. The control method for the BEST steam-driven feedwater pump unit in a dual-unit regenerative thermal power plant with high-pressure heater disconnection includes: Step 1: Determine the extraction steam flow rate of each stage of extraction in a dual-unit regenerative thermal power plant; Step 2: Determine the shaft power of the steam-driven feedwater pump Small generator shaft power The potential work capacity of the BEST feedwater pump turbine is determined based on the extraction steam flow rates at each stage. ; Step 3, according to , and After determining the high-pressure heater disconnection, the pre-action opening degree of the BEST feedwater pump turbine inlet steam regulating valve is determined. ; Step 4, according to , , Based on the extraction steam flow rates at each stage, determine the pre-action opening of the BEST feedwater pump turbine exhaust pressure control valve. and according to Determine the pre-action opening degree of the overflow valve on the BEST feedwater pump turbine exhaust header. and the pre-action opening degree of the bypass valve ; Step 5: After the high-pressure heater disconnection signal is triggered, start the minimum flow recirculation valve control method for the steam-driven feedwater pump, and according to... , Determine the BEST feedwater pump turbine back pressure control method, based on Determine the valve opening control method for the BEST feedwater pump turbine.

2. The control method for the BEST steam-driven feedwater pump set of a dual-unit regenerative thermal power plant according to claim 1, characterized in that, according to The method for controlling the valve opening of the BEST feedwater pump turbine is determined as follows: In converter master control mode, after the high-pressure heater disconnection signal is triggered, the converter master control is maintained, and the BEST feedwater pump turbine inlet steam regulating valve is pre-closed. ; In MEH master control mode, after the high-pressure heater disconnection signal is triggered, MEH master control is maintained, and the BEST feedwater pump turbine inlet steam regulating valve is pre-closed. Automatically reset afterwards; The actual opening degree of the BEST feedwater pump turbine inlet regulating valve before the high-pressure heater is disconnected.

3. The control method for the BEST steam-driven feedwater pump set of a dual-unit regenerative thermal power plant with high-pressure heater disconnection as described in claim 1, characterized in that, The specific method for controlling the minimum flow recirculation valve of the steam-driven feedwater pump is as follows: In the main control mode of the converter, after the high-pressure heater disconnection signal is triggered, when the converter power is greater than the first proportion of its power limit, the steam-driven feedwater pump minimum flow recirculation valve opens at a preset first rate; when the converter power is less than the second proportion of its power limit, the steam-driven feedwater pump minimum flow recirculation valve closes at a preset second rate; until the high-pressure heater disconnection signal is reset. In MEH main control mode, after the high-pressure heater disconnection signal is triggered, the minimum flow recirculation valve of the steam-driven feedwater pump remains in normal control mode.

4. The control method for the BEST steam-driven feedwater pump set of a dual-unit regenerative thermal power plant according to claim 1, characterized in that, according to , The back pressure control method for the BEST feedwater pump turbine is determined as follows: After the high-pressure heater disconnection signal is triggered, the overflow valve is opened to... Bypass valve opened to At the same time, the automatic control settings of the relief valve and bypass valve are increased to the target value at a preset third rate. The target value is the minimum value between the upper limit of the exhaust pressure that satisfies the exhaust pressure ratio and the high exhaust pressure alarm value. After the high-pressure heater disconnection signal is reset, the automatic control target values ​​of the relief valve and bypass valve are reduced to the normal exhaust pressure control range at a preset fourth rate.

5. The control method for the BEST steam-driven feedwater pump set of a dual-unit regenerative thermal power plant with high-pressure heater disconnection according to claim 1, characterized in that, Step 5 is followed by: Step 6: When the feedback deviation of the BEST feedwater pump turbine speed command is less than 20 rpm, the exhaust pressure is less than the set value, and the extraction pressure of each stage is within the normal value, restore the normal control mode of the steam-driven feedwater pump minimum flow recirculation valve, the BEST feedwater pump turbine regulating valve, and the BEST feedwater pump turbine back pressure.

6. The control method for the BEST steam-driven feedwater pump set of a dual-unit regenerative thermal power plant with high-pressure heater disconnection according to claim 1, characterized in that, The potential work capacity of the BEST feedwater pump turbine is determined based on the extraction steam flow rates at each stage. Specifically: ； In the formula, The enthalpy value of the BEST feedwater pump turbine; Let be the enthalpy of the steam extracted in the i-th stage; Let be the extraction steam flow rate of the i-th stage extraction. The potential work capacity of the i-th stage extraction steam; i is the extraction steam number of each stage of the BEST feedwater pump turbine, excluding the deaerator and exhaust steam.

7. The control method for the BEST steam-driven feedwater pump set of a dual-unit regenerative thermal power plant according to claim 1, characterized in that, according to , and After determining the high-pressure heater disconnection, the pre-action opening degree of the BEST feedwater pump turbine inlet steam regulating valve is determined. Specifically: Determine the percentage of steam flow corresponding to the actual opening of the BEST feedwater pump turbine inlet regulating valve before the high-pressure heater is disconnected. ; Based on the shaft power of the steam-driven feedwater pump Small generator shaft power and the percentage of steam flow rate Determine the percentage of flow occupied by the steam-driven feedwater pump and the small generator. ; Based on the percentage of flow occupied by steam-driven feedwater pumps and small generators After determining the high-pressure heater disconnection, the pre-action opening degree of the BEST feedwater pump turbine inlet regulating valve is determined. .

8. The control method for the BEST steam-driven feedwater pump set of a dual-unit regenerative thermal power plant according to claim 7, characterized in that, Based on the shaft power of the steam-driven feedwater pump Small generator shaft power and the percentage of steam flow rate Determine the percentage of flow occupied by the steam-driven feedwater pump and the small generator. Specifically: ； In the formula, This refers to the shaft power of the steam-driven feedwater pump. For small generator shaft power; The working capacity of the BEST feedwater pump turbine; This represents the percentage of steam flow rate.

9. The control method for the BEST steam-driven feedwater pump set of a dual-unit regenerative thermal power plant with high-pressure heater disconnection according to claim 1, characterized in that, according to , , Based on the extraction steam flow rates at each stage, determine the pre-action opening of the BEST feedwater pump turbine exhaust pressure control valve. Specifically: according to , , Based on the extraction steam flow rates at each stage, determine the additional exhaust steam flow rate after the BEST feedwater pump turbine valves are pre-closed. ; according to Specific pressure during high-pressure separation Exhaust pressure Determine the pre-action opening of the BEST feedwater pump turbine exhaust pressure control valve. .

10. The control method for the BEST steam-driven feedwater pump set of a dual-unit regenerative thermal power plant according to claim 9, characterized in that, according to , , Based on the extraction steam flow rates at each stage, determine the additional exhaust steam flow rate after the BEST feedwater pump turbine valves are pre-closed. Specifically: ； In the formula, This refers to the shaft power of the steam-driven feedwater pump. For small generator shaft power; To enhance the potential of the BEST feedwater pump turbine; Let i be the extraction steam flow rate of the i-th stage extraction steam, where i is the extraction steam number of each stage of the BEST feedwater pump turbine, excluding the deaerator and exhaust steam. This refers to the extraction steam flow rate corresponding to the deaerator. This represents the extraction steam flow rate corresponding to the low-pressure heater.

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