A method and system for automatic smooth heat supply withdrawal of a heat supply unit during load reduction

Abstract

The application provides a method and system for automatic and smooth heat supply withdrawal of a heat supply unit during load reduction, and belongs to the technical field of nuclear power heat supply. The method comprises the following steps: the unit enters an automatic load control mode and reduces the load; if the electric load reaches a target electric load and the first-stage pressure of the steam turbine is greater than or equal to a critical value, the load reduction is completed, or the unit enters a heat supply withdrawal mode under the premise of the automatic load control mode until the heat supply is completely withdrawn. The application always keeps the unit in the automatic load control mode during heat supply withdrawal, so that the electric load is always stably within the fluctuation range of the target electric load until the heat supply withdrawal is completed. The whole process has a high degree of automation, a fast operation response, and the unit has a transient response capability during load reduction, and the expected stable reduction of the low-pressure cylinder steam inlet flow, the high-pressure cylinder exhaust pressure, the first-stage pressure of the steam turbine, the opening degree of the main regulating valve of the steam turbine and the reactor power is maintained, and no up and down fluctuation is generated.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of nuclear power heat supply, and particularly relates to a method and system for automatic and smooth heat supply withdrawal of a heat supply unit during load reduction. BACKGROUND

[0002] With the transformation of nuclear power to nuclear energy, nuclear power unit heat supply will become the main direction of nuclear energy comprehensive utilization. The automatic and smooth heat supply withdrawal of a super large-scale nuclear power unit during load variation is of great significance to the safe and stable operation of the reactor and the steam turbine, as well as the stability of the power grid and the heat grid.

[0003] Since the heat supply extraction amount of a single heat supply unit is smaller than that of a super large-scale nuclear power unit, the heat supply withdrawal process has less impact on the external heat grid and the external power grid. The load reduction control mode of a nuclear power reactor is different from that of a thermal power boiler, and the heat supply withdrawal mode of a thermal power boiler does not meet the requirements of linearly reducing the unit power and safely and stably withdrawing the heat supply steam under special working conditions of a nuclear power unit.

[0004] Patent CN114575952A describes how to control the load of a nuclear energy heat supply unit, which improves the control accuracy and avoids fluctuations in the operating parameters of the reactor primary loop system during heat supply load variation, but does not study the heat supply withdrawal scheme during load reduction. Therefore, the research on automatic and smooth heat supply withdrawal of a super large-scale pressurized water reactor heat supply unit during load reduction is still blank.

[0005] In the existing technical scheme of a thermal power unit, if the manual operation is slow during the heat supply withdrawal process, the workload of the operating personnel will be increased. If the unit needs to quickly withdraw heat supply during load reduction, manual or automatic quick heat supply withdrawal will cause the steam flow into the low-pressure cylinder of the steam turbine to first increase and then decrease, the high discharge pressure to fluctuate, and the deviation of the mode of automatic tracking of the unit to adjust the electric load to be large. SUMMARY

[0006] To solve the above problems, the present application provides a method and system for automatic and smooth heat supply withdrawal of a heat supply unit during load reduction.

[0007] To achieve the above purpose, the present application adopts the following technical scheme:

[0008] A method for automatic and smooth heat supply withdrawal of a heat supply unit during load reduction, comprising the following steps:

[0009] The unit enters an automatic load control mode, and the load includes electric load and heat load;

[0010] If the electric load reaches the target electric load and the first-stage pressure of the steam turbine is greater than or equal to the critical value, the load reduction is completed, or the unit enters a heat supply withdrawal mode under the premise of maintaining the automatic load control mode until the heat supply is completely withdrawn;

[0011] If the electric load does not reach the target electric load and the first stage pressure of the steam turbine is less than the critical value, the unit remains in the automatic load control mode and automatically enters the heat supply withdrawal mode until the heat supply is completely withdrawn; after the unit withdraws the heat supply, the unit continues to execute the automatic load control mode until the electric load reaches the target value.

[0012] Preferably, the automatic load control mode comprises the following steps:

[0013] Setting a target electric load and a target rate of the target electric load;

[0014] Based on the target rate, automatically adjusting the main regulating valve of the steam turbine to track the change curve of the target electric load until the electric load decreases to the target value.

[0015] Preferably, the heat supply withdrawal mode comprises the following steps:

[0016] Gradually closing each heat supply regulating valve of the heat network heater inlet one by one under the premise of meeting the first condition, and gradually reducing the heat load until the heat supply is completely withdrawn.

[0017] Preferably, the first condition is:

[0018] (1-2%)Q 目标 ≦Q≦(1+2%)Q 目标 ;

[0019] In the formula, Q represents the electric load; Q 目标 represents the target electric load.

[0020] Preferably, the electric load decreases linearly.

[0021] Preferably, during the gradual reduction of the heat load, the automatic load control mode is maintained based on the first condition.

[0022] Preferably, the first stage pressure is 70% in percentage.

[0023] A system for automatically and smoothly withdrawing heat supply when a heat supply unit reduces load, comprising a control unit, a first execution unit and a second execution unit;

[0024] The control unit is used to control the unit to enter an automatic load control mode and reduce load, wherein the load includes an electric load and a heat load;

[0025] The first execution unit is used to complete load reduction when the electric load reaches a target electric load and the first stage pressure of the steam turbine is greater than or equal to a critical value, or the unit enters a heat supply withdrawal mode under the premise of remaining in the automatic load control mode when the electric load reaches the target electric load and the first stage pressure of the steam turbine is greater than or equal to the critical value until the heat supply is completely withdrawn;

[0026] The second execution unit is used for keeping the unit in an automatic load control mode and automatically entering a heat supply withdrawal mode when the electric load does not reach the target electric load and the first stage pressure of the steam turbine is less than a critical value, until the heat supply is completely withdrawn.

[0027] Preferably, an automatic load control module is included for performing automatic load control, and the automatic load control module includes:

[0028] A setting sub-module is used for setting a target electric load and a target rate of the target electric load.

[0029] An adjusting sub-module is used for automatically adjusting a main regulating valve of the steam turbine based on the target rate to track a change curve of the target electric load until the electric load is reduced to the target value.

[0030] Preferably, a heat supply withdrawal module is included for performing a heat supply withdrawal mode, and the heat supply withdrawal module includes:

[0031] A heat supply withdrawal sub-module is used for gradually closing each heat supply regulating valve of a heat network heater inlet one by one under the premise of satisfying a first condition, and the heat load is gradually reduced until the heat supply is completely withdrawn.

[0032] The present application has the following beneficial effects:

[0033] 1. The present application keeps the unit in an automatic load control mode when the heat supply is withdrawn, so that the electric load is always stabilized in the fluctuation range of the target electric load until the heat supply is withdrawn, the entire process has a high degree of automation, the operation response is fast, the unit has transient response capability when the load is reduced, the expected stable decline of the low-pressure cylinder steam flow, the high-pressure cylinder exhaust pressure, the first stage pressure of the steam turbine, the main regulating valve opening of the steam turbine and the reactor power is maintained, and no up and down fluctuation is generated.

[0034] 2. The method for automatically and smoothly withdrawing heat supply when the unit reduces load in the present application maintains the electric load stable or linearly decreases at a certain rate, does not increase first and then decrease due to the withdrawal of heat supply, does not cause impact on the power grid, and reduces the fluctuation on the power grid.

[0035] 3. The logic for automatically and smoothly withdrawing heat supply in the present application improves the automation degree of the unit, reduces the low-pressure cylinder flow safety problem caused by uncontrolled withdrawal of heat supply, maximally reduces the human error of operators, reduces the workload of operators, and improves the operation stability and safety of the nuclear heat supply unit.

[0036] Additional features and advantages of the present application will be set forth in the description that follows, and in part will be apparent from the description, or can be learned by practice of the application. The objectives and other advantages of the present application will be realized and attained by the structure particularly pointed out in the description and appended claims. BRIEF DESCRIPTION OF DRAWINGS

[0037] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or the prior art description. Obviously, the drawings described below are some embodiments of the present application, and the ordinary skilled in the art can obtain other drawings according to these drawings without any creative effort.

[0038] Figure 1 A flow chart of a method for automatically and smoothly exiting heat supply when a heat supply unit reduces load is shown;

[0039] Figure 2 A system structure diagram of a method for automatically and smoothly exiting heat supply when a heat supply unit reduces load is shown. DETAILED DESCRIPTION

[0040] In order to make the objectives, technical solutions and advantages of the embodiments of the present application clearer, the following will combine the drawings in the embodiments of the present application to make a clear and complete description of the technical solutions in the embodiments of the present application. Obviously, the described embodiments are some of the embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by the ordinary skilled in the art without any creative effort are within the protection scope of the present application.

[0041] A method for automatically and smoothly exiting heat supply when a heat supply unit reduces load, as shown in Figure 1 includes the following steps:

[0042] S1: the unit enters an automatic load control mode, reduces load, and the load includes electric load and heat load;

[0043] S1a: if the electric load reaches the target electric load and the first stage pressure of the steam turbine is greater than or equal to the critical value, the load reduction is completed, or the unit enters a heat supply exiting mode under the premise of keeping the automatic load control mode until the heat supply is completely exited;

[0044] S1a': if the electric load does not reach the target electric load and the first stage pressure of the steam turbine is less than the critical value, the unit keeps the automatic load control mode and automatically enters the heat supply exiting mode until the heat supply is completely exited; after the unit exits the heat supply, the unit continues to perform the automatic load control until the electric load reaches the target value.

[0045] It is to be noted that the first stage pressure is in percentage, and the critical value is 70% which is optional. In step S1a, if it is needed to quit the heat supply, the heat supply quitting button is clicked, and then the unit keeps the automatic load control mode and enters the heat supply quitting mode.

[0046] It is to be noted that the present application firstly considers the safety and stability of the low-pressure cylinder flow, and determines the corresponding total load value of the unit when the heat supply automatic quitting is needed. The total load of the unit includes the electric load and the heat load, and the total load percentage of the unit can be replaced by the first stage pressure (P1st) percentage of the steam turbine. The value is determined according to the design characteristics of the unit and the total amount of heat supply extraction, and the present application takes P1st<70% as an example, as the time when the heat supply starts to be automatically cut off.

[0047] It is to be noted that the heat supply of the present application refers to the high-temperature water being transported to the city secondary heat exchange station, the hot water after heat release being returned to the power plant or the regional boiler room, the circulation being supplied outwards after the pump being pressurized and absorbing the heat released by the steam in the heat network heater.

[0048] Heat supply quitting: the extraction amount of the heat supply unit being decreased from the rated extraction amount to zero,

[0049] Further, the automatic load control mode includes the following steps:

[0050] Firstly, the target electric load and the target rate of the target electric load are set, and then the main regulating valve of the steam turbine is automatically adjusted based on the target rate, the change curve of the target electric load is tracked, and the electric load is reduced to the target value.

[0051] It is to be noted that the electric load of the present application is linearly changed, and the change curve is pre-set.

[0052] Further, the heat supply quitting mode includes the following steps: under the premise of meeting the first condition, the heat supply regulating valve of each heat network heater inlet is closed one by one, the heat load is gradually decreased, and the heat supply is completely quit until the heat supply is completely quit. The first condition is:

[0053] (1-2%)Q 目标 ≦Q≦(1+2%)Q 目标 ;

[0054] In the formula, Q represents the electric load; Q 目标 represents the target electric load.

[0055] It is to be noted that in the process of gradually decreasing the heat load, the automatic load control mode is kept based on the first condition, and the heat load quitting rate is calculated and obtained, which is controlled by the automatic sequence control logic. The heat load decrease rate does not cause the automatic load control mode of the unit to be automatically quit due to the deviation being greater than 2%.

[0056] The heat supply cut-off mode of different unit final states is described in detail as follows:

[0057] Generally, the unit is in rated heat supply condition and runs at full load, then the unit is planned to linearly reduce load or other non-emergency load requirements, then the unit enters the automatic load control mode, which first sets the target electric load and target rate, and then executes load reduction. In the load reduction process, there are two cases: the first stage pressure is greater than or equal to 70% and the first stage pressure is less than 70%, which are as follows:

[0058] (1) If the final total load P1st≥70%, the low-pressure cylinder flow safety can be guaranteed, and the heat supply does not need to be cut off. If further heat supply is required to be withdrawn, the unit is still in the automatic load control mode (ALR) after the above process, and then the opening of the turbine main regulating valve is automatically adjusted to maintain the specified electric load value. If the operator selects to continue to withdraw the heat supply and clicks the heat supply withdrawal button, the unit control mode is automatically judged as follows:

[0059] ① When the unit is not in the automatic load control mode, the heat supply can be withdrawn faster to meet the requirement of rapidly reducing the unit load. However, at this time, the low-pressure cylinder inlet flow, the high-pressure cylinder exhaust pressure, etc. all have fluctuations;

[0060] ② When the unit is in the automatic load control mode, if the electric load does not meet the first condition, the automatic load control mode will automatically exit, so it is necessary to ensure that the heat supply withdrawal rate is not greater than the automatic load control mode automatic exit limit value. According to the characteristics of the unit, the maximum electric load variation rate in the automatic load control mode is 5% / min, so according to the electric load value converted from the heat supply load, the opening reduction rate of each heat exchanger control valve (ECV) is set to ensure that the electric load increase rate corresponding to the heat supply steam reduction rate is ≤5% / min, so as to ensure that the ALR automatic exit is not triggered. The system setting mode of the present application has four ECVs corresponding to four heat exchangers, and the steam extraction amount of each heat exchanger is large, so the sequential control slow withdrawal of the four ECVs is adopted to ensure that the rate of heat supply steam extraction amount reduction does not trigger the automatic load control mode automatic exit.

[0061] During the heat supply sequential control slow withdrawal process, the automatic load control mode still continuously closes the main regulating valve of the steam turbine, the heat load decreases, the electric load remains unchanged, and the reactor power decreases. During the entire load reduction and heat supply withdrawal process, the opening of the main regulating valve of the steam turbine is continuously closed, the high-pressure cylinder exhaust pressure and the low-pressure cylinder inlet flow first decrease and then remain basically unchanged, and the unit stably reduces the load and withdraws the heat supply. After the heat supply is withdrawn, the unit reaches the final state.

[0062] (2) After the unit starts to linearly reduce the load, if the final total load P1st<70%, the heat supply needs to be automatically cut off to ensure the flow safety of the low-pressure cylinder.

[0063] When the first level pressure is less than 70%, the target electric load of the automatic load control mode is triggered automatically, the heat supply is automatically exited, and the first condition needs to be ensured. The same heat supply sequence control slow retreat mode is adopted to ensure that the rate of reducing the heat extraction steam quantity does not trigger the automatic load control mode to automatically exit. In this process, the turbine main regulating valve opening of the unit, the reactor power is reduced, the electric load is maintained, and the high-pressure cylinder exhaust pressure and the low-pressure cylinder inlet flow are basically unchanged.

[0064] After monitoring that the heat supply extraction steam is completely exited, the automatic load control mode automatically inherits the target electric load and the target rate, and automatically continues to execute the power reduction until the target electric load is reached, and the load reduction and heat supply automatic removal process is ended.

[0065] The sequence control slow retreat ECV mode is described as follows:

[0066] The sequence control slow retreat ECV mode needs to comprehensively consider the requirements of not triggering the ALR automatic exit and quickly exiting the heat supply to meet the specific load reduction process of the nuclear power unit. The mode of tracking the drain flow of each heat exchanger and calculating the corresponding heat exchanger steam flow reduction rate is adopted. Taking the maximum load reduction rate of 5% / min in the ALR control mode, the heat supply extraction steam of 1500t / h, the electric load of 80%, and the heat exchanger A outlet drain flow of 300t / h as an example, the calculation is as follows:

[0067] The heat supply extraction steam flow reduction rate that does not trigger the ALR control mode automatic exit is calculated as follows:

[0068] ;

[0069] The heat exchanger A inlet ECV valve closing time is calculated as follows:

[0070] ;

[0071] The above closing time value is assigned to the ECV, and the ECV valve is closed within the above time range.

[0072] It needs to be noted that the nuclear power unit load reduction process has the following requirements for the exit of the heat supply:

[0073] 1) To ensure the safety and stability of the low-pressure cylinder flow, the extraction steam needs to be automatically removed in time after the load is reduced to a certain extent to reduce the low-pressure cylinder water erosion problem and ensure the safety and stability of the low-pressure cylinder flow.

[0074] 2) To maximize the operator human error, the automation level needs to be enhanced, and the automatic logic judgment and automatic heat supply removal mode is adopted.

[0075] 3) Large-scale heat supply has large steam extraction, and when the unit is in an automatic load control mode (tracking the unit electric load, automatically adjusting the opening degree of the steam turbine main steam regulating valve, and it is extremely possible that the heat supply steam will flow back to the steam turbine again when the heat supply is cut off, causing the automatic load control mode process set value and the actual value to deviate too much (such as more than 2%), the automatic load control mode is automatically exited, the unit cannot continue to automatically reduce the load, and manual intervention is required.

[0076] The application adopts a reasonable and controllable means to exit heat supply, ensures the flow safety of the low-pressure cylinder, and avoids problems such as human error, manual intervention after the automatic load control mode is automatically exited, and the like.

[0077] A system for automatically and smoothly exiting heat supply when a heat supply unit reduces load, as shown in Figure 2 , includes a control unit, a first execution unit, and a second execution unit.

[0078] The control unit is configured to control the unit to enter an automatic load control mode and reduce the load of the unit, and the load includes an electric load and a heat load.

[0079] The first execution unit is configured to stop reducing the load (the load reduction is completed) or manually operate the unit to enter a heat supply exit mode without exiting the automatic load control mode when the electric load reaches a target electric load and the first-stage pressure of the steam turbine is greater than or equal to 70% (a critical value), and the heat supply is completely exited.

[0080] The second execution unit is configured to keep the unit in the automatic load control mode and automatically enter the heat supply exit mode when the electric load does not reach the target electric load and the first-stage pressure of the steam turbine is less than 70%, and the heat supply is completely exited.

[0081] Further, the system for automatically and smoothly exiting heat supply when a heat supply unit reduces load further includes an automatic load control module configured to perform automatic load control, and the automatic load control module includes:

[0082] A setting submodule configured to set a target electric load and a target rate of the target electric load.

[0083] An adjusting submodule configured to automatically adjust the main regulating valve of the steam turbine based on the target rate, track a change curve of the target electric load, and reduce the electric load to a target value.

[0084] Further, the system for automatically and smoothly exiting heat supply when a heat supply unit reduces load further includes a heat supply exit module configured to perform a heat supply exit mode, and the heat supply exit module includes:

[0085] The heat supply withdrawal submodule is used to close the heat supply regulating valve at the inlet of each heating network heater one by one, provided that the first condition is met, so that the heat load gradually decreases until the heat supply is completely withdrawn.

[0086] This invention is applicable to nuclear power heating projects. During the unit's load reduction process, the heating can minimize operator intervention and maintain the expected stable decrease in low-pressure cylinder inlet steam flow, high-pressure cylinder exhaust steam pressure, turbine first-stage pressure, turbine main control valve opening, and reactor power without fluctuations.

[0087] Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for automatically and smoothly discontinuing heating supply when a heating unit reduces its load, characterized in that, Includes the following steps: The unit enters automatic load control mode to reduce the load, which includes electrical load and thermal load. If the electrical load reaches the target electrical load and the turbine's first-stage pressure is greater than or equal to the critical value, then the load reduction is complete. Alternatively, if the electrical load reaches the target electrical load and the turbine's first-stage pressure is greater than or equal to the critical value, the unit will enter the heat supply withdrawal mode while maintaining the automatic load control mode, until the heat supply is completely withdrawn. If the electrical load does not reach the target electrical load and the turbine's first-stage pressure is less than the critical value, the unit will maintain the automatic load control mode and automatically enter the heat supply withdrawal mode until the heat supply is completely withdrawn; after the unit withdraws from heat supply, the unit will continue to execute the automatic load control mode until the electrical load reaches the target value.

2. The method for automatically and smoothly shutting down heating supply when a heating unit reduces its load, as described in claim 1, is characterized in that... The automatic load control mode includes the following steps: Set the target electrical load and the target rate of the target electrical load; The main control valve of the steam turbine is automatically adjusted based on the target rate to track the change curve of the target electrical load until the electrical load is reduced to the target value.

3. A method for automatically and smoothly discontinuing heating supply when a heating unit reduces its load, as described in claim 1 or 2, characterized in that... The aforementioned heating withdrawal mode includes the following steps: Under the premise of meeting the first condition, the heating regulating valve at the inlet of each heating network heater is closed one by one, and the heat load gradually decreases until the heating is completely stopped.

4. The method for automatically and smoothly shutting off heating when a heating unit reduces its load, as described in claim 3, is characterized in that... The first condition is: (1-2%)Q 目标 ≦Q≦(1+2%)Q 目标 ; In the formula, Q represents the electrical load; Q 目标 This indicates the target electrical load.

5. The method for automatically and smoothly shutting down heating supply when a heating unit reduces its load, as described in claim 2, is characterized in that... The electrical load decreases linearly.

6. The method for automatically and smoothly discontinuing heating when a heating unit reduces its load, as described in claim 4, is characterized in that... During the gradual decrease of the heat load, the automatic load control mode is maintained based on the first condition.

7. The method for automatically and smoothly discontinuing heating supply when a heating unit reduces its load, as described in claim 3, is characterized in that... The first-level pressure is expressed as a percentage, and the critical value is 70%.

8. A system for automatically and smoothly shutting off heating when a heating unit reduces its load, characterized in that, It includes a control unit, a first execution unit, and a second execution unit; The control unit is used to control the unit to enter the automatic load control mode to reduce the load of the unit, the load including electrical load and thermal load; The first execution unit is used to complete the load reduction when the electrical load reaches the target electrical load and the turbine first-stage pressure is greater than or equal to the critical value, or to enter the heat supply withdrawal mode under the premise that the unit maintains the automatic load control mode when the electrical load reaches the target electrical load and the turbine first-stage pressure is greater than or equal to the critical value, until the heat supply is completely withdrawn. The second execution unit is used to maintain the automatic load control mode and automatically enter the heat supply withdrawal mode when the electrical load does not reach the target electrical load and the turbine first stage pressure is less than the critical value, until the heat supply is completely withdrawn; after the unit withdraws from heat supply, the unit continues to execute the automatic load control mode until the electrical load reaches the target value.

9. A system for automatically and smoothly shutting off heating when a heating unit reduces its load, as described in claim 8, is characterized in that... Includes an automatic load control module for performing automatic load control, the automatic load control module comprising: The setting submodule is used to set the target electrical load and the target rate of the target electrical load; The regulating submodule is used to automatically adjust the main regulating valve of the steam turbine based on the target rate, and track the change curve of the target electrical load until the electrical load is reduced to the target value.

10. A system for automatically and smoothly shutting off heating when a heating unit reduces its load, as described in claim 8, characterized in that, Includes a heating shutdown module for executing the heating shutdown mode, the heating shutdown module comprising: The heat supply withdrawal submodule is used to close the heat supply regulating valve at the inlet of each heating network heater one by one, provided that the first condition is met, so that the heat load gradually decreases until the heat supply is completely withdrawn.

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