A denitration control method and device

Abstract

The application discloses a denitration control method and device, which can be applied to a control module of a denitration control system, obtains a NOx concentration parameter value and a concentration influence parameter of current exhaust flue gas of a boiler, calls a PID controller after adjusting a proportional gain, determines a nitrogen oxide deviation value between a real-time adjusted NOx concentration set value and a concentration value, and determines a first valve opening value of a urea flow regulating valve of a hand controller based on the nitrogen oxide deviation value; determines a second valve opening value meeting a first preset threshold range based on a preset function and the concentration influence parameter; and determines a target valve opening value meeting a second preset threshold range based on the first valve opening value and the second valve opening value, and controls the hand controller to open the valve of the urea flow regulating valve at the target valve opening value. The application can realize automatic control of the denitration control system, and also can realize advance adjustment, and improve the stability of the denitration control system.

Description

Technical Field

[0001] This application relates to the field of automatic control technology, and more specifically, to a denitrification control method and apparatus. Background Technology

[0002] Circulating fluidized bed (CFB) boilers utilize the most advanced clean coal combustion technology in industrial applications. Due to their numerous advantages, including wide fuel adaptability, high combustion efficiency, large adjustable capacity, and low pollution emissions, they have been rapidly promoted and developed. To ensure emissions meet standards, CFB boilers typically employ SNCR (selective non-catalytic reduction) technology after combustion to denitrify nitrogen oxides (NOx) in the emissions. This is achieved by injecting a suitable reducing agent, such as urea, into the furnace. The urea reduces NOx in the furnace to nitrogen, water, and carbon dioxide, thereby reducing the concentration of NOx in the emissions and enabling them to meet emission standards.

[0003] Currently, commonly used denitrification control methods typically employ proportional-integral-derivative (PI) controllers (or PID controllers). The function of these controllers is to adjust parameters to bring the nitrogen oxide concentration after treatment closer to emission standards. However, this usually requires operators to manually set the parameters of the PI controller and other system modules, introducing subjective factors that can lead to non-compliance with emission standards or unstable emissions. Furthermore, sudden changes in boiler operating conditions can result in delayed human intervention, leading to excessive nitrogen oxide emissions or excessive urea injection, making precise control and stable operation of CFB boiler denitrification impossible. Summary of the Invention

[0004] In view of this, this application provides a denitrification control method and apparatus to solve the problem of low automation in existing denitrification methods.

[0005] To achieve the above objectives, the following solution is proposed:

[0006] A denitrification control method is applied to the control module of a denitrification control system, wherein the denitrification control system further includes at least: a proportional-integral-derivative controller and a handheld device, and the denitrification control method includes:

[0007] The concentration parameters and concentration influence parameters of nitrogen oxides in the flue gas discharged from the boiler are obtained. The concentration parameters include at least: concentration value, hourly average concentration, and concentration change rate. The concentration change rate is the rate of change of the concentration value of nitrogen oxides within a preset time range. The concentration influence parameters are parameters that affect the generation of nitrogen oxides in the flue gas discharged from the boiler at the next moment. The concentration influence parameters include at least: unit load of the thermal power plant unit, unit load command, and oxygen content inside the boiler.

[0008] The nitrogen oxide concentration setpoint is determined based on the hourly average concentration and the concentration change rate.

[0009] The proportional-integral-derivative controller with adjusted proportional gain is invoked to determine the nitrogen oxide deviation value between the nitrogen oxide concentration setpoint and the concentration value, and the first valve opening value of the urea flow regulating valve of the hand-held device is determined based on the nitrogen oxide deviation value.

[0010] Obtain a pre-established characteristic function that characterizes the relationship between the valve opening value of the urea flow regulating valve of the hand-held device and the concentration influence parameter;

[0011] Based on the preset function and the concentration influence parameter, a second valve opening value that meets the first preset threshold range is determined;

[0012] Based on the first valve opening value and the second valve opening value, a target valve opening value that meets the second preset threshold range is determined, and the handheld device is controlled to open the urea flow regulating valve with the target valve opening value.

[0013] Optionally, the process of adjusting the proportional gain of the proportional-integral-derivative controller includes:

[0014] Based on a preset curve function, the proportional gain of the proportional-integral-derivative controller corresponding to the concentration value of nitrogen oxides at the current moment is determined. The preset curve function is used to characterize the relationship between the concentration value of nitrogen oxides and the proportional gain.

[0015] Optionally, determining the nitrogen oxide concentration setpoint based on the hourly average concentration and the concentration change rate includes:

[0016] The nitrogen oxide concentration setpoint of the proportional-integral-derivative controller at the previous moment is obtained and used as the original setpoint.

[0017] Determine whether the hourly average concentration of nitrogen oxides at the current moment is greater than a first preset threshold;

[0018] If the hourly average concentration is greater than the first preset threshold, and the concentration value and the concentration change rate respectively meet preset conditions, the original set value is adjusted to decrease based on the preset change range to obtain the nitrogen oxide set value at the current moment.

[0019] If the hourly average concentration is not greater than the first preset threshold, the nitrogen oxide setpoint at the current moment is determined according to the unit load command and the preset characteristic function, wherein the preset characteristic function is used to characterize the characteristic relationship between the unit load command and the nitrogen oxide setpoint.

[0020] Optionally, determining the second valve opening value that satisfies the first preset threshold range based on the preset function and the concentration influence parameter includes:

[0021] The initial valve opening value corresponding to the current unit load is determined based on a first preset function that characterizes the relationship between the unit load and the valve opening value of the urea flow regulating valve on the hand controller.

[0022] Based on the adjustment direction of the unit load corresponding to the unit load command, and the changing trend of the oxygen content inside the boiler, the initial valve opening value is adjusted to obtain the intermediate valve opening value, and the changing trend includes increase or decrease.

[0023] Determine whether the opening value of the intermediate valve is within the first preset threshold range, where the first preset threshold range is the interval range defined by the first upper limit value and the first lower limit value;

[0024] When the opening value of the intermediate valve is within the range of the first preset threshold, the opening value of the intermediate valve is determined as the opening value of the second valve.

[0025] When the opening value of the intermediate valve is not within the first preset threshold range, and the opening value of the intermediate valve is greater than the first upper limit value, the first upper limit value is determined as the opening value of the second valve.

[0026] When the opening value of the intermediate valve is not within the first preset threshold range and the opening value of the intermediate valve is less than the first lower limit value, the first lower limit value is determined as the second valve opening value.

[0027] Optionally, determining the initial valve opening value corresponding to the current unit load based on a first preset function characterizing the relationship between the unit load and the valve opening value of the urea flow regulating valve on the handheld device includes:

[0028] Obtain the total air volume in the furnace of a thermal power plant;

[0029] Based on the total furnace air volume and the second preset function, a first reference value for valve opening corresponding to the total furnace air volume is determined. The second preset function is used to characterize the characteristic function relationship between the total furnace air volume and the valve opening of the urea flow regulating valve of the hand-held device.

[0030] Based on the unit load and the first preset function, determine a second reference value for the valve opening corresponding to the unit load;

[0031] The valve opening second reference value is corrected based on the first reference value of valve opening, and the corrected second reference value of valve opening is used as the initial valve opening value corresponding to the current unit load.

[0032] Optionally, determining the target valve opening value that satisfies the second preset threshold range based on the first valve opening value and the second valve opening value includes:

[0033] The valve opening value to be determined is obtained by weighting the first valve opening value and the second valve opening value.

[0034] Determine whether the valve opening value to be determined is within the range of the second preset threshold, where the range of the second preset threshold is the interval defined by the second upper limit value and the second lower limit value;

[0035] When the undetermined valve opening value is within the range of the second preset threshold, the undetermined valve opening value is determined as the target valve opening value;

[0036] When the valve opening value to be determined is not within the range of the second preset threshold, and the valve opening value to be determined is greater than the second upper limit value, the second upper limit value is determined as the target valve opening value;

[0037] When the valve opening value to be determined is not within the range of the second preset threshold, and the valve opening value to be determined is less than the second lower limit, the second lower limit is determined as the target valve opening value.

[0038] Optionally, the process of obtaining the first preset threshold range includes:

[0039] Based on the significant impact of the oxygen content inside the boiler and the unit load command on the concentration value of nitrogen oxides, respectively, an oxygen feedforward upper limit value corresponding to the oxygen content inside the boiler and a load feedforward upper limit value corresponding to the unit load command are set.

[0040] The upper limit of oxygen feedforward and the upper limit of load feedforward are summed to obtain the first upper limit of the valve opening of the urea flow regulating valve of the hand-held device;

[0041] Based on the relationship between the concentration value of nitrogen oxides and the nitrogen oxide emission standard, a first lower limit value for the valve opening of the urea flow regulating valve of the hand-held device within a preset lower limit value range is determined.

[0042] The range between the first upper limit and the first lower limit of the valve opening of the urea flow regulating valve of the hand-held device is determined as the first preset threshold range.

[0043] Optionally, the process of obtaining the second preset threshold range includes:

[0044] When the hourly average concentration meets the preset threshold condition, according to the unit load command and the preset limit function, the second upper limit value of the valve opening of the urea flow regulating valve of the hand controller corresponding to the hourly average concentration is determined. The preset limit function is used to characterize the characteristic function relationship between the unit load command and the upper limit value of the valve opening of the urea flow regulating valve of the hand controller.

[0045] Based on the unit load command and the third preset function, a second initial lower limit value corresponding to the unit load is determined. The third preset function is used to characterize the characteristic function relationship between the unit load command and the lower limit value of the valve opening of the urea flow regulating valve of the hand controller.

[0046] Based on the relationship between the hourly average concentration and the nitrogen oxide emission standard, and the soot blowing situation of the boiler flue gas online monitoring system, the initial lower limit value is numerically adjusted to obtain the second lower limit value of the valve opening of the urea flow regulating valve of the hand-held device.

[0047] The range between the second upper limit and the second lower limit of the valve opening of the urea flow regulating valve of the hand-held device is determined as the second preset threshold range.

[0048] Optionally, the method may further include:

[0049] Obtain the valve opening value of the urea flow regulating valve of the hand-held device at the previous moment, and use it as the original urea valve opening value;

[0050] Determine the difference between the original urea valve opening value and the target valve opening value;

[0051] When the difference is within the preset dead zone range, the handheld device is controlled to open the urea flow regulating valve at the original urea valve opening value.

[0052] A denitrification control device is applied to the control module of a denitrification control system, wherein the denitrification control system further includes at least: a proportional-integral-derivative controller and a handheld device, and the denitrification control device includes:

[0053] The parameter acquisition unit is used to acquire the concentration parameter value and concentration influence parameter of nitrogen oxides in the flue gas discharged from the boiler at the current time. The concentration parameter value includes at least: concentration value, hourly average concentration value and concentration change rate. The concentration change rate is the rate of change of the concentration value of nitrogen oxides within a preset time range. The concentration influence parameter is a parameter that affects the concentration of nitrogen oxides in the flue gas discharged from the boiler at the next moment. The concentration influence parameter includes at least: the unit load of the thermal power plant unit, the unit load command and the oxygen content inside the boiler.

[0054] The setpoint determination unit is used to determine the nitrogen oxide concentration setpoint based on the hourly average concentration and the concentration change rate;

[0055] The first valve opening value determination unit is used to call the proportional-integral-derivative controller after adjusting the proportional gain, determine the nitrogen oxide deviation value between the nitrogen oxide concentration set value and the concentration value, and determine the first valve opening value of the urea flow regulating valve of the hand-held device based on the nitrogen oxide deviation value.

[0056] The function acquisition unit is used to acquire a pre-established preset function that characterizes the valve opening of the urea flow regulating valve of the hand controller with the unit load, the unit load command and the oxygen content inside the boiler.

[0057] The second valve opening value determination unit is used to determine the second valve opening value that meets the first preset threshold range based on the preset function and the concentration influence parameter.

[0058] The target control unit is used to determine a target valve opening value that meets a second preset threshold range based on the first valve opening value and the second valve opening value, and to control the handheld device to open the urea flow regulating valve with the target valve opening value.

[0059] This application automatically adjusts the setpoint in real time based on the current nitrogen oxide concentration, hourly average concentration, and a preset function, eliminating the need for operator intervention, reducing the impact of subjective factors, and making the setpoint more consistent with the current boiler emission conditions. Furthermore, in addition to improving the accuracy of valve opening control by adjusting the PID controller setpoint and proportional gain, this application also considers the impact on the nitrogen oxide concentration emitted by the boiler at the next moment. Based on the concentration influence parameter, a second valve opening value is determined for the current moment, avoiding sudden changes or repeated valve opening jumps in the event of unforeseen circumstances, which could affect the stability of the denitrification control system. By combining the first and second valve opening values, a target valve opening value that meets a preset threshold range is determined. This ensures that the amount of urea sprayed at the target opening value not only meets the current emission standard requirements but also prepares for the next nitrogen oxide emission conditions, achieving proactive adjustment and improving the stability of the denitrification control system. Attached Figure Description

[0060] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of this application. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0061] Figure 1 This is a schematic flowchart illustrating a denitrification control method provided in an embodiment of this application.

[0062] Figure 2 An optional application example diagram of a denitrification control system provided in an embodiment of this application;

[0063] Figure 3 This is a schematic diagram of a denitrification control device provided in an embodiment of this application. Detailed Implementation

[0064] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0065] With increasingly stringent controls on nitrogen oxide (NOx) emissions from thermal power plant boilers, most thermal power units have completed low-emission retrofits, such as installing SNCR denitrification devices at the tail end of the flue gas system. By spraying an appropriate amount of reducing agent, such as urea, the urea reduces NOx in the furnace into nitrogen, water, and carbon dioxide, thereby reducing the concentration of nitrogen oxides in the emissions and enabling them to meet emission standards.

[0066] However, the current SNCR denitrification process suffers from problems such as large delay, large inertia, nonlinearity, and multi-factor coupling, meaning that the NOx generation varies greatly and is unmeasurable. Under the condition of manual operation of the denitrification control system, it is impossible to meet the emission requirements. This makes it impossible to accurately and timely control the denitrification control system so that it can automatically and precisely adjust the various parameters of the denitrification control system, so that the flue gas treated by the denitrification control system meets the nitrogen oxide emission standards and improves the stability of the denitrification control system.

[0067] To address the aforementioned issues, this application provides a denitrification control method. This method can be applied to the control module of a denitrification control system. The denitrification control system may further include at least a proportional-integral-derivative controller (or a PID controller) and a handheld device, wherein the handheld device can control the valve opening of the urea flow regulating valve.

[0068] Reference Figure 1 It shows a flowchart of a denitrification control method provided in an embodiment of this application. The specific steps of the process may include:

[0069] Step S110: Obtain the concentration parameter value and concentration influence parameter of the nitrogen oxides in the flue gas currently discharged from the boiler.

[0070] In this embodiment, the concentration parameter values ​​include at least: a concentration value, an hourly average concentration, and a concentration change rate. The concentration change rate is the rate of change of the nitrogen oxide concentration value within a preset time range, and the hourly average concentration is the average concentration of nitrogen oxides in the boiler exhaust gas over one hour. The concentration influence parameter is a parameter that affects the generation of nitrogen oxides in the boiler exhaust gas at the next moment. The concentration influence parameter may include at least: the unit load of the thermal power plant unit, the unit load command, and the oxygen content inside the boiler.

[0071] In this embodiment, the NOx concentration in the exhaust gas is measured and acquired in real time by a CEMS (Continuous Emission Monitoring System) installed at the flue gas outlet, and the hourly average concentration and concentration change rate are calculated based on the NOx concentration values ​​acquired over a period of time.

[0072] The unit load command is an instruction issued by the power dispatching and trading agency. The thermal power plant units adjust their power output in real time at a certain rate to meet the power generation requirements of the power system. Therefore, the unit load command can affect the load and operation of the thermal power plant units. Based on the unit load command, it can be preliminarily determined whether it can affect the current operating conditions of the thermal power plant units and boilers.

[0073] Step S120: Determine the set value of nitrogen oxide concentration based on the hourly average concentration and the concentration change rate.

[0074] The nitrogen oxide concentration setpoint is applied to the PID controller. Based on the principle of the PID controller, through the weighted output of the proportional (P), integral (I), and derivative (D) functions in the controller, the nitrogen oxide concentration value output by the denitrification control system gets closer and closer to the nitrogen oxide concentration setpoint, thereby achieving the goal of stable operation of the denitrification control system according to the nitrogen oxide concentration setpoint.

[0075] Assuming a PID controller is used to control the NOx concentration emitted from a circulating fluidized bed boiler (CFB), and the known NOx emission standard for coal-fired boilers is 50 mg / Nm³, then... 3 However, the current NOx concentration detected in the flue gas discharged from the CFB boiler is 200 mg / Nm³. 3 To ensure that the NOx emission concentration meets emission standards, the nitrogen oxide setpoint of the PID controller can be set to 45 mg / Nm³. 3 This is to ensure that the NOx concentration output by the denitrification control system is lower than the emission standard.

[0076] Typically, the setpoints of PID controllers are manually set by operators. However, the flue gas conditions emitted by the boiler change in real time with the boiler's operating status, and the PID controller setpoints simultaneously affect the denitrification control system's ability to handle nitrogen oxide concentrations. Therefore, operators need to closely monitor the NOx concentration values ​​emitted by the boiler and frequently adjust the NOx concentration setpoints accordingly.

[0077] Given the subjectivity and lag inherent in human operation, this embodiment of the application can determine the NOx concentration setpoint of the PID controller in real time based on the hourly average concentration and the rate of change of concentration. Optionally, it can perform self-learning judgment based on the hourly average NOx concentration, NOx concentration value, and NOx concentration change rate to learn the specific relationship between the hourly average NOx concentration, NOx concentration value, and NOx concentration change rate and the NOx concentration setpoint of the PID controller under various past values. Based on the learned specific relationship, the NOx concentration setpoint corresponding to the current hourly average NOx concentration, NOx concentration value, and NOx concentration change rate is determined.

[0078] Alternatively, the NOx concentration setpoint can be adjusted based on preset adjustment rules, according to the hourly average NOx concentration, the NOx concentration value, and the NOx concentration change rate. In this embodiment, the process may include: obtaining the NOx concentration setpoint of the proportional-integral-derivative controller at the previous moment as the original setpoint; determining whether the hourly average NOx concentration at the current moment is greater than a first preset threshold; if the hourly average concentration is greater than the first preset threshold, and the concentration value and the concentration change rate respectively meet preset conditions, adjusting the original setpoint to decrease it based on a preset change range to obtain the NOx setpoint at the current moment; if the hourly average concentration is not greater than the first preset threshold, determining the NOx setpoint at the current moment according to the unit load command and a preset characteristic function, wherein the preset characteristic function is used to characterize the characteristic relationship between the unit load command and the NOx setpoint.

[0079] The first preset threshold can be set according to the NOx emission standard. In this embodiment, the NOx emission standard can be set to 50 mg / Nm³. 3 The first preset threshold can then be set to 45 mg / Nm³. 3 .

[0080] When the hourly average NOx concentration is low, less than 45 mg / Nm³ 3 At that time, the NOx concentration setpoint can be determined based on a pre-established function F(x) relating unit load commands and NOx concentration setpoints, to determine the specific value of the NOx concentration setpoint corresponding to the unit load command at the current moment. Specifically, the function F(x) can be obtained by pre-collecting all corresponding unit load commands and NOx concentration setpoints when the NOx concentration in the exhaust gas meets emission standards, serving as function reference values. Further, a function is established based on the correspondence between unit load commands and NOx concentration setpoints in the function reference values, resulting in a function F(x) that characterizes the relationship between unit load commands and NOx concentration setpoints. Based on function F(x), the NOx concentration setpoint corresponding to the known unit load command can be determined.

[0081] When the hourly average NOx concentration is high, greater than or equal to 45 mg / Nm³ 3 If the NOx concentration is high, and the rate of change indicates an upward trend in NOx concentration, the NOx concentration setpoint is adjusted based on the previous setpoint to determine the current setpoint. For example, if the NOx concentration is not less than 50 mg / Nm³. 3 If the NOx concentration change rate is greater than 1 within one minute, then subtract 9 from the original set value to obtain the NOx concentration set value at the current moment.

[0082] Based on this, the embodiments of this application can realize the automated setting of the NOx concentration setpoint applied to the PID controller while ensuring that NOx emissions meet the standards, reducing the workload of operators, and enabling accurate control in real time based on NOx emission conditions.

[0083] Step S130: Call the proportional-integral-derivative controller after adjusting the proportional gain, determine the nitrogen oxide deviation value between the nitrogen oxide concentration set value and the concentration value, and determine the first valve opening value of the urea flow regulating valve of the hand-held device based on the nitrogen oxide deviation value.

[0084] The handheld controller in the denitrification control system can adjust based on the deviation between the NOx concentration setpoint output by the PID controller and the actual NOx concentration, outputting a corresponding control quantity to drive the urea flow regulating valve. Therefore, it is necessary to invoke the PID controller to determine the deviation between the NOx concentration setpoint and the actual NOx concentration determined in step S120, in order to determine the control quantity output by the handheld controller. In this embodiment, the control quantity can be the valve opening value of the urea flow regulating valve. Optionally, the control quantity can also be parameters related to the reducing agent dosage control, such as the urea flow rate or total urea volume of the urea flow regulating valve.

[0085] Considering the response speed of the PID controller and the stability of the system, in this embodiment of the application, before calling the PID controller to implement the corresponding control, the proportional gain of the PID controller needs to be adjusted according to the NOx concentration to make the PID controller more adaptable to the current NOx generation situation.

[0086] Specifically, the proportional gain (P) of the PID controller calculates the operational quantity (such as the valve opening value of the urea valve) based on the current deviation value, providing a rapid short-term supplement to the output of the denitrification control system to bring the final NOx concentration close to the set NOx concentration value. The proportional gain in the P control loop determines the proportional relationship between the amplitude of the output operational quantity and the amplitude of the input deviation value. A larger proportional gain amplifies the deviation value more, thus increasing the PID controller's sensitivity and response speed to NOx emission control. Conversely, a smaller proportional gain results in a weaker response to the input deviation value, improving the stability of the PID controller's NOx emission control and reducing oscillations or divergences.

[0087] For example, with a high proportional gain, the NOx deviation corresponds to a larger valve opening value. This larger valve opening allows for a larger amount of urea to be sprayed, reducing the NOx concentration to below the set NOx concentration, thus ensuring the emitted NOx concentration meets emission standards. However, maintaining a high proportional gain for an extended period when NOx concentration is low leads to urea waste and over-adjustment. Conversely, maintaining a low proportional gain results in insufficient output to effectively reduce NOx concentration when it is high, causing the emitted NOx concentration to fail to meet emission standards.

[0088] Therefore, the proportional gain needs to be adaptively adjusted according to different situations. Optionally, the process of adjusting the proportional gain of the PID controller in real time in this application embodiment may include: determining the proportional gain of the proportional-integral-derivative controller corresponding to the concentration value of nitrogen oxides at the current moment based on a preset curve function, wherein the preset curve function is used to characterize the characteristic relationship between the concentration value of nitrogen oxides and the proportional gain.

[0089] The preset curve function can determine the optimal proportional gain corresponding to different NOx concentration values ​​by using the characteristics of the PID controller and by conducting experiments on the PID controller, thereby determining the characteristic relationship between NOx concentration value and proportional gain.

[0090] The relationship between the NOx concentration value and the proportional gain represented by the preset curve function can be summarized as follows: when the NOx concentration value is high, the corresponding proportional gain is large to accelerate the response speed of the denitrification control system; when the NOx concentration value is low, the corresponding proportional gain is small to prevent overshoot of the denitrification control system and improve the stability of the denitrification control system.

[0091] Based on this, the PID controller with adjusted proportional gain is invoked to determine the NOx deviation between the NOx concentration setpoint and the concentration value. The PID controller combines the proportional (P), integral (I), and derivative (P) functions within the controller to perform control adjustment, determine the valve opening value of the urea flow regulating valve of the handheld device, and use this valve opening value as the first valve opening value, so that the NOx deviation value of the denitrification control system becomes smaller and smaller, thereby ensuring that the NOx concentration in the flue gas treated by the denitrification control system meets the emission standards.

[0092] Step S140: Obtain a pre-established preset function that characterizes the relationship between the valve opening value of the urea flow regulating valve of the hand-held device and the concentration influence parameter.

[0093] In this embodiment of the application, the process of establishing the preset function requires obtaining a large number of concentration-affecting parameters and the valve opening value of the urea flow regulating valve corresponding to the concentration-affecting parameters as function reference data. Based on the function reference data, the functional relationship between the concentration-affecting parameters and the valve opening value is determined. The functional relationship can be a non-linear functional relationship.

[0094] In this embodiment of the application, the preset function pre-established based on the above-described method includes at least a first preset function characterizing the relationship between the unit load and the valve opening value of the urea flow regulating valve of the hand-held device.

[0095] Step S150: Based on the preset function and the concentration influence parameter, determine the second valve opening value that meets the first preset threshold range.

[0096] Understandably, the physical distance between the urea-NOx reaction zone and the NOx generation zone in the boiler within the denitrification control system is relatively large, causing a delay in the reaction zone's acquisition of NOx concentration parameters. This results in the denitrification control system being unable to predict NOx generation in a timely manner. Suppose that the NOx concentration generated in the generation zone suddenly changes compared to the previous period, but the reaction zone cannot detect this change in time. When the flue gas with this concentration change is transmitted to the reaction zone, all parameters in the denitrification control system need to be adjusted abruptly, affecting the stability of the denitrification control system.

[0097] Furthermore, due to the high-temperature environment in the reaction zone, it is impossible to accurately collect NOx concentration parameters. Therefore, this scheme collects parameters affecting NOx generation or concentration in the generation zone to predict the trend of NOx concentration or generation in advance. Based on the trend, a valve opening value is determined as a feedforward value. This allows for the determination of the final output valve opening value by combining the feedforward value and the first valve opening value. This ensures that the final output valve opening value not only meets the requirements for controlling the current NOx concentration in the reaction zone but also, in conjunction with the feedforward value, enables proactive adjustment of the denitrification control system in response to changes in NOx concentration, thereby improving the stability of the denitrification control system.

[0098] Assume the current NOx concentration in the NOx reaction zone is 45 mg / Nm³. 3 The corresponding first valve opening value is determined to be 5%, while the predicted NOx concentration generated in the NOx generation zone is 45 mg / Nm³. 3The NOx concentration tends to increase, and the valve opening value determined for the increased NOx concentration is 10%. An intermediate value is determined by combining the valve opening values ​​of 5% and 10%, such as a final valve opening value of 6%. The next valve opening value, combined with the feedforward value, is determined to be 7%, until a high concentration of NOx is transferred to the reaction zone. The valve opening value may then be gradually increased from a value higher than 5% to 10%, such as increasing the valve opening value from 9% to 10%. Increasing the valve opening value from 9% to 10% is more beneficial to the stability of the denitrification system than increasing it from 5% to 10%.

[0099] Considering that the factors affecting NOx generation are not limited to the few referenced in this application embodiment, in order to avoid the inaccuracy of the second valve opening value determined based on the concentration influence parameter, resulting in over-adjustment or excessive emissions, this application embodiment sets a safe range for the second valve opening value, namely a first preset threshold range. When the second valve opening value is within the first preset threshold range, the above-mentioned over-adjustment and excessive emissions can be avoided as much as possible.

[0100] Optionally, the first preset threshold range can be set based on the operator's experience in setting control parameters, or it can be adjusted in real time based on influencing factors such as NOx concentration parameters or boiler operating conditions.

[0101] The preset function may include characteristic functions that characterize the relationship between unit load, unit load command, and boiler oxygen content and the valve opening value of the urea flow regulating valve, respectively. Based on the preset function, the valve opening values ​​corresponding to the current unit load, unit load command, and boiler oxygen content are determined and calculated to determine the final predicted valve opening value.

[0102] Optionally, the specific process of determining the predicted feedforward value, i.e., determining the second valve opening value that meets the first preset threshold range, based on a preset function and concentration influence parameters in this application embodiment may include: determining the initial valve opening value corresponding to the current unit load according to a first preset function characterizing the relationship between the unit load and the valve opening value of the urea flow regulating valve on the hand controller; adjusting the initial valve opening value based on the adjustment direction of the unit load corresponding to the unit load command and the changing trend of the oxygen content inside the boiler to obtain an intermediate valve opening value, wherein the changing trend includes increase or decrease; and determining whether the intermediate valve opening value is within the first preset threshold range, wherein the first preset threshold range is the interval range defined by a first upper limit value and a first lower limit value.

[0103] When the opening value of the intermediate valve is within the first preset threshold range, the opening value of the intermediate valve is determined as the second valve opening value; when the opening value of the intermediate valve is not within the first preset threshold range and the opening value of the intermediate valve is greater than the first upper limit value, the first upper limit value is determined as the second valve opening value; when the opening value of the intermediate valve is not within the first preset threshold range and the opening value of the intermediate valve is less than the first lower limit value, the first lower limit value is determined as the second valve opening value.

[0104] The unit load, unit load command, and concentration parameters such as the oxygen content inside the boiler in thermal power plants all affect NOx generation. Changes in NOx generation also affect the adjustment of control parameters in the reaction zone (such as the valve opening value of the urea flow regulating valve) to adapt to changes in NOx generation. Based on the above idea, this application directly establishes a function between the concentration-affecting parameters and the valve opening value of the urea flow regulating valve, omitting the function calculation of the relationship between intermediate generation and valve opening value, thus simplifying the prediction process.

[0105] In this embodiment of the application, a line graph that can characterize the relationship between the unit load and the valve opening value of the urea flow regulating valve can be determined according to a first preset function. When the unit load at the current moment is determined, a valve opening value corresponding to the unit load can be determined from the line graph as the initial valve opening value.

[0106] Furthermore, the influence of other factors on the valve opening of the urea valve needs to be considered. Optionally, considering that when the adjustment direction of the unit load corresponding to the unit load command is to increase the unit load, the corresponding NOx generation will increase. When the trend of oxygen change in the boiler is increasing, the NOx generation in the generation zone will increase based on the boiler's operating inertia. As the NOx generation increases, it is necessary to control the reaction zone to spray more urea in the next moment (i.e., increase the valve opening value of the urea valve) to react with the NOx.

[0107] Based on the adjustment direction of the unit load corresponding to the unit load command, and the changing trend of the oxygen content inside the boiler, the initial valve opening value is adjusted. If both the adjustment direction and the changing trend are increasing, the valve opening value is increased by an appropriate amount based on the initial valve opening value to obtain an intermediate valve opening value. Conversely, if both the adjustment direction and the changing trend are decreasing, the valve opening value is decreased by an appropriate amount based on the initial valve opening value to obtain an intermediate valve opening value.

[0108] To avoid the intermediate valve opening value being inaccurate, the intermediate valve opening value is compared with a first preset threshold range to determine a second valve opening value as the final predicted value.

[0109] Based on the comparison between the intermediate valve opening value and the first preset threshold range, if the intermediate valve opening value is greater than the upper limit of the first preset threshold range, the upper limit value is used as the second valve opening value to avoid setting the valve opening value too large, which could lead to overshoot. Conversely, if the intermediate valve opening value is less than the lower limit of the first preset threshold range, the lower limit value is used as the second valve opening value to avoid setting the valve opening value too small, which could result in the final NOx emission concentration failing to meet emission standards. Therefore, by using the first preset threshold as a safe reference range, the inaccuracy of predictions based on concentration-related parameters is further reduced.

[0110] Step S160: Based on the first valve opening value and the second valve opening value, determine a target valve opening value that meets the second preset threshold range, and control the handheld device to open the urea flow regulating valve with the target valve opening value.

[0111] This embodiment combines the NOx deviation value determined by the PID controller, the first valve opening value, and the second valve opening value predicted based on concentration influence parameters to determine the final target valve opening value of the urea flow regulating valve of the manual controller. This allows for the prediction of changes in NOx generation at the next moment, based on the current NOx concentration. The final determined target valve opening value corresponds to the amount of urea sprayed, which can not only meet the current demand for denitrification treatment but also adjust the valve opening value of the denitrification control system in advance according to the trend of NOx generation, avoiding disturbances caused by the inertia of the denitrification control system and ensuring the stability of the denitrification control system in regulating NOx concentration.

[0112] Understandably, to avoid any calculation errors or inaccurate predictions in the above steps, which could lead to excessive or insufficient urea spray corresponding to the final determined target valve opening value, resulting in urea waste or emissions that do not meet emission standards, the second preset threshold range serves the same purpose as the first preset threshold range, acting as a safe range for the target valve opening value.

[0113] Optionally, the target valve opening value can be determined based on the first valve opening value and the second valve opening value. If the target valve opening value is within the range of the second preset threshold, the target valve opening value is output. If the target valve opening value is not within the range of the second preset threshold, the upper or lower limit of the second preset threshold range can be used as the target valve opening value for control.

[0114] Optionally, considering that the current NOx concentration parameter has a significant impact on the denitrification control system at the current moment, this embodiment of the application may use a weighted summation method to determine the target valve opening value based on the first valve opening value and the second valve opening value. The process may include: performing weighted processing based on the first valve opening value and the second valve opening value to obtain the valve opening value to be determined; determining whether the valve opening value to be determined is within the range of the second preset threshold value, wherein the second preset threshold value is the interval range defined by the second upper limit value and the second lower limit value.

[0115] When the valve opening value to be determined is within the range of the second preset threshold, the valve opening value to be determined is determined as the target valve opening value; when the valve opening value to be determined is not within the range of the second preset threshold and the valve opening value to be determined is greater than the second upper limit value, the second upper limit value is determined as the target valve opening value; when the valve opening value to be determined is not within the range of the second preset threshold and the valve opening value to be determined is less than the second lower limit value, the second lower limit value is determined as the target valve opening value.

[0116] During the weighted processing, the weight parameter values ​​assigned to the first valve opening value and the second valve opening value can be set according to the significance of the influence of the denitrification control system on the predicted value and the current value.

[0117] The weighted valve opening value obtained needs to be further compared with the second preset threshold range. If the value is greater than the upper limit of the second preset threshold range, the upper limit is used as the target valve opening value to avoid setting the valve opening value too high, which could lead to overshoot. Conversely, if the value is less than the lower limit of the second preset threshold range, the lower limit is used as the target valve opening value to avoid setting the valve opening value too low, which could result in the final NOx emission concentration not meeting emission standards. This also allows for a certain amount of reducing agent margin, preventing oscillations in the NOx concentration adjustment of the denitrification control system, ensuring good robustness and stability of the denitrification control system.

[0118] In summary, this embodiment of the application achieves automatic real-time adjustment of the setpoint based on the current nitrogen oxide concentration and a preset function, eliminating the need for operator intervention, reducing the influence of subjective factors, and making the setpoint more consistent with the current boiler emission conditions. Furthermore, in addition to improving the accuracy of valve opening control by adjusting the PID controller's setpoint and proportional gain, this embodiment also considers the impact of the nitrogen oxide concentration emitted by the boiler at the next moment. Based on the concentration influence parameter, it determines the second valve opening value at the current moment, avoiding sudden changes or repeated jumps in valve opening during unexpected situations, which could affect the stability of the denitrification control system. Combining the first and second valve opening values, a target valve opening value that meets the preset threshold range is determined. This ensures that the amount of urea sprayed at the target opening value not only meets the current emission standard requirements but also prepares for the next nitrogen oxide emission conditions, allowing for timely adjustments and improving the stability of the denitrification control system.

[0119] The denitrification control method of this application embodiment will be further described below.

[0120] It is understandable that many factors influence NOx generation. Where feasible, as many parameters affecting NOx generation as possible should be referenced to predict the valve opening value of the urea flow regulating valve. Optionally, in addition to referencing the unit load, unit load command, and oxygen content inside the boiler, this embodiment of the application can also refer to the total furnace air volume to predict the valve opening value. The specific process may include: obtaining the total furnace air volume of the thermal power plant; determining a first reference value for the valve opening corresponding to the total furnace air volume based on the total furnace air volume and a second preset function, where the second preset function is used to characterize the characteristic function relationship between the total furnace air volume and the valve opening of the urea flow regulating valve of the hand-held device; determining a second reference value for the valve opening corresponding to the unit load based on the unit load and the first preset function; correcting the second reference value for the valve opening based on the first reference value for the valve opening, and using the corrected second reference value for the valve opening as the initial valve opening value corresponding to the current unit load.

[0121] Understandably, changes in the total furnace air volume precede changes in the unit load, allowing for earlier prediction of NOx generation. Given the relationship between NOx generation and valve opening values, valve opening values ​​can also be predicted earlier. A valve opening value can be predicted using the total furnace air volume as an auxiliary variable, correcting the initial valve opening value determined based on the unit load, thus improving the accuracy of valve opening prediction based on concentration-related parameters.

[0122] Specifically, a function can be pre-established to characterize the relationship between the total furnace air volume and the valve opening value of the urea flow regulating valve, namely the second preset function in this application embodiment. Based on the second preset function and the total furnace air volume of the current generation zone, a first reference value for the valve opening value of the urea flow regulating valve at the next moment is determined.

[0123] Furthermore, based on the first preset function and the current unit load in the generation zone, a second reference value for the valve opening of the urea flow regulating valve at the next moment is determined. The second reference value is then corrected based on the first reference value. This correction can be understood as adjusting the second reference value to reduce the deviation between the two when the deviation is large, until the deviation is reduced to a certain range, at which point no further adjustment is made. The corrected second reference value is then used as the initial valve opening value corresponding to the current unit load for subsequent processing to determine the final second valve opening value.

[0124] The second valve opening value needs to meet the first preset threshold range. In this embodiment, the first preset threshold range is the range defined by the first upper limit value and the first lower limit value. The first upper limit value and the first lower limit value can be set manually by the operator. In order to improve the automation of the denitrification process, this embodiment can determine the first upper limit value or the first lower limit value based on the significance of the influence of nitrogen oxide concentration parameters on the denitrification control system and the relationship between nitrogen oxide concentration value and nitrogen oxide emission standards.

[0125] Taking the setting of the first lower limit as an example, based on the statistical analysis of the valve opening values ​​of the urea valve under normal circumstances, a minimum or minimum average value is determined as the fixed value of the first lower limit. When special circumstances are detected, such as a high NOx concentration and an increasing trend reflected by the concentration change rate, the first lower limit is increased based on the fixed value. Furthermore, if the oxygen content in the boiler shows a decreasing trend, according to the above method, the NOx generation will decrease, thus reducing the predicted second valve opening value, causing the target valve opening value to also decrease. However, when the NOx concentration shows an increasing trend, reducing the target valve opening value is not allowed. Therefore, the first lower limit needs to be adjusted so that the output second valve opening value does not affect the target valve opening value.

[0126] In this embodiment, the relationship between the NOx concentration-related parameter value specified in the nitrogen oxide emission standard and the current NOx concentration parameter value can be used to determine whether the current NOx concentration meets the nitrogen oxide emission standard. This indirectly determines whether the current NOx concentration treatment level needs to be increased or decreased, thereby adaptively adjusting the first upper limit and the first lower limit values ​​to avoid unnecessary cost input. Alternatively, a threshold can be directly set according to the nitrogen oxide emission standard, and this threshold can be used to determine the relationship between the current NOx concentration-related parameter and the emission standard.

[0127] This application uses an example to illustrate how to determine the relationship between NOx concentration parameters at the current moment and emission standards based on a threshold. It is assumed that the current nitrogen oxide emission standard allows NOx concentrations below 50 mg / Nm³. 3 The flue gas is treated, but the NOx concentration after denitrification is usually required to be less than 50 mg / Nm³. 3 To avoid uncontrollable factors during the denitrification process that could cause the NOx concentration after treatment to not exactly equal 50 mg / Nm³ 3 Therefore, the threshold set in the embodiments of this application may not necessarily be equal to the NOx concentration corresponding to the nitrogen oxide emission standard.

[0128] Optionally, embodiments of this application may also determine a first upper limit and a first lower limit for limiting a first preset threshold range based on the relationship between the NOx concentration parameter value and emission standards and concentration influence parameters, respectively. The process may include: setting an oxygen feedforward upper limit corresponding to the boiler's internal oxygen level and a load feedforward upper limit corresponding to the unit load command, respectively, based on the significant impact of the boiler's internal oxygen level and the unit load command on the concentration of nitrogen oxides; summing the oxygen feedforward upper limit and the load feedforward upper limit to obtain a first upper limit for the valve opening of the urea flow regulating valve of the hand-held device; determining a first lower limit for the valve opening of the urea flow regulating valve of the hand-held device within a preset lower limit range based on the relationship between the nitrogen oxide concentration and the nitrogen oxide emission standard; and defining the range corresponding to the first upper limit and the first lower limit for the valve opening of the urea flow regulating valve of the hand-held device as the first preset threshold range.

[0129] Understandably, the determination of the first upper limit is based on the influence of the oxygen content inside the boiler and the unit load on the NOx concentration. Generally, an increase in oxygen content leads to an increase in NOx concentration, and a decrease in oxygen content leads to a decrease in NOx concentration. Conversely, a higher unit load leads to an increase in NOx concentration, and a lower unit load leads to a decrease in NOx concentration.

[0130] Therefore, it is necessary to consider multiple NOx concentration influencing parameters when determining the first upper limit value to avoid inaccurate setting of the first upper limit value due to a single factor consideration, which would affect the opening degree of the urea valve of the final hand-held device. In the embodiments of this application, multiple NOx concentration influencing parameters can be analyzed together to determine a first upper limit value, or the upper limit value corresponding to each NOx concentration influencing parameter can be determined separately, and then the upper limit values ​​corresponding to each NOx concentration influencing parameter can be added together to obtain a first upper limit value.

[0131] In this embodiment, the first upper limit value is determined based on the unit load and the oxygen content inside the boiler as analytical factors. In practical applications, operators can set up multiple NOx concentration influence parameter analysis programs for deoxygenation and unit load in the control module to jointly determine the first upper limit value, thereby improving the accuracy of the first upper limit value.

[0132] In this embodiment, the upper limit of the current oxygen level is determined based on the significance of the oxygen level's influence on the NOx concentration. This significance can be determined by pre-establishing a functional relationship between oxygen level and NOx concentration, which assesses the impact of the current oxygen level change compared to the previous moment on the NOx concentration, and the magnitude of the change in oxygen level compared to the previous moment on the NOx concentration. Based on this, the significance of the unit load's influence on the NOx concentration can also be determined using the same method.

[0133] The significance of the impact of oxygen level can be correlated with a set upper limit for oxygen feedforward. This upper limit represents the upper limit of the valve opening of the urea flow control valve on the handheld device under the current oxygen level. This upper limit can be a value within a range of upper limits preset by the operator or control module; alternatively, it can be determined based on the NOx concentration corresponding to the oxygen level. The upper limit for load feedforward, determined by the significance of the impact of unit load, can also be determined using the same method as the oxygen feedforward upper limit, and will not be elaborated further here.

[0134] The first upper limit value is determined by the combined influence of multiple NOx concentration influencing factors. Therefore, in this embodiment, the relationship between the oxygen feedforward upper limit value and the load feedforward upper limit value is additive. However, considering that different influencing factors have different degrees of influence on NOx concentration, weights can be allocated based on the relative importance of different influencing factors to NOx concentration, and the feedforward upper limit values ​​can be weighted and summed. Based on this, the oxygen feedforward upper limit value and the load feedforward upper limit value can be summed or weighted to obtain the first upper limit value.

[0135] Optionally, based on the significance of the influence of the nitrogen oxide concentration parameter on the NOx concentration value, a fixed value can be directly set as the first upper limit. In this embodiment, the first upper limit is determined to be 30. It can be understood that the first lower limit can be determined based on the relationship between the nitrogen oxide concentration value and the nitrogen oxide emission standard.

[0136] Taking the following example, based on the nitrogen oxide emission standard of 50 mg / Nm³... 3 Set a threshold of 40 mg / Nm 3 When the NOx concentration is less than 40 mg / Nm 3 When the NOx concentration shows a decreasing trend, the first lower limit can be appropriately reduced to avoid excessive valve opening, which could lead to urea waste or overshoot. For adjusting the first lower limit, a value lower than the previous first lower limit within a preset range can be selected as the current first lower limit. However, if the NOx concentration is greater than 40 mg / Nm³, the lower limit can be adjusted accordingly. 3 When the NOx concentration is at a high level and the NOx concentration is increasing, the first lower limit value can be appropriately increased to avoid the valve opening being too small, resulting in an insignificant denitrification effect.

[0137] Based on the first upper limit and the first lower limit determined by the above optional method, a first preset threshold range is determined, and a second valve opening value is determined based on the first preset threshold range.

[0138] In addition, this application embodiment also has a second preset threshold range, which is also a valve safety range. The second preset threshold range is used to constrain the target valve opening value to avoid the target valve opening value being too high or too low due to other uncontrollable factors such as inaccurate NOx concentration detection or inaccurate prediction of the second valve opening value by concentration influence parameters, so as to achieve the denitrification requirement.

[0139] The second upper limit and the second lower limit of the second preset threshold range can be determined by self-learning based on the hourly average NOx concentration. The second upper limit or the second lower limit can be set directly, or the second upper limit or the second lower limit of the previous moment can be adaptively adjusted to determine the second upper limit and the second lower limit of the current moment.

[0140] Optionally, in this application embodiment, the second upper limit and the second lower limit can be determined using the following process, specifically including: when the hourly average concentration meets a preset threshold condition, determining a second upper limit value for the valve opening of the urea flow regulating valve of the handheld device corresponding to the hourly average concentration, based on the unit load command and a preset limit function, wherein the preset limit function is used to characterize the characteristic function relationship between the unit load command and the upper limit value of the valve opening of the urea flow regulating valve of the handheld device; and determining a second initial lower limit corresponding to the unit load based on the unit load command and a third preset function. The third preset function is used to characterize the characteristic function relationship between the unit load command and the lower limit value of the urea flow regulating valve opening of the hand-held device; based on the relationship between the hourly average concentration and the nitrogen oxide emission standard, and the soot blowing situation of the boiler flue gas online monitoring system CEMS, the initial lower limit value is numerically adjusted to obtain the second lower limit value of the urea flow regulating valve opening of the hand-held device; the range between the second upper limit value and the second lower limit value of the urea flow regulating valve opening of the hand-held device is determined as the second preset threshold range.

[0141] It is understandable that when the hourly average NOx concentration is less than a certain value, the demand for reducing agent in the denitrification process will decrease accordingly. Therefore, in this embodiment, the second upper limit value corresponding to the current hourly average concentration can be determined according to the unit load command and the preset limit function that characterizes the relationship between the hourly average concentration and the second upper limit value. This prevents the valve opening value of the urea flow regulating valve from being too large, thus preventing excessive urea from being sprayed and reducing ammonia escape.

[0142] In this embodiment of the application, the second lower limit value can be determined by self-learning based on the NOx concentration value, the hourly average concentration value and the CEMS purging situation, and the second lower limit value can be adjusted based on the self-learning determination result.

[0143] Alternatively, a third preset function can be established in advance to characterize the relationship between the unit load command and the second lower limit value. Based on the third preset function, the second initial lower limit value corresponding to the unit load command at the current moment can be determined. The second initial lower limit value can be adjusted numerically according to the NOx concentration parameter value and the CEMS purging situation. Based on this, the reference factors are more comprehensive when setting the second lower limit value, thus improving the accuracy of the second lower limit value.

[0144] Optionally, when the NOx concentration remains low for an extended period and the second initial lower limit is greater than a certain value, or when the second lower limit set by the current denitrification control system is greater than a certain value, the second lower limit needs to be further reduced. Conversely, when CEMS purging is detected and the hourly average NOx concentration is high, the second lower limit needs to be further increased. Furthermore, when adjusting the second lower limit, a certain margin can be allowed to prevent oscillations in the denitrification control system, while also ensuring good robustness and stability.

[0145] Taking the example below, the second initial lower limit value corresponding to the current unit load command is first determined based on the third preset function of the relationship between the unit load command and the second lower limit value. Then, it is further determined whether the current NOx concentration hourly average is ≤41 mg / Nm³. 3 And the NOx concentration is ≤35mg / Nm³. 3 If it is determined that the current situation is as described above, and the second initial lower limit value is greater than 10, then 5 is subtracted from the second initial lower limit value to obtain the final second lower limit value.

[0146] However, if it is determined that the current hourly average NOx concentration is <45 mg / Nm³ 3 And the NOx concentration is ≥50 mg / Nm³ 3 In this case, the second initial lower limit value can be determined as the final second lower limit value. Furthermore, if the current NOx concentration is ≥50 mg / Nm³,... 3 And the decrease in NOx concentration within 2 seconds is greater than 15 mg / Nm³. 3 (or NOx concentration change rate > 7.5 mg / Nm³) 3 In the case of / s), that is, during CEMS purging, 5 is added to the second initial lower limit value to obtain the final second lower limit value.

[0147] Based on the above method, the second upper limit and second lower limit values ​​are reset, or numerical adjustments are made to the original second upper limit and second lower limit values ​​of the denitrification control system to determine the applicable second upper limit and second lower limit values ​​for the current moment, and the second preset threshold range is determined accordingly. The target valve opening value is determined based on the preset threshold range to avoid the valve opening value determined by combining the first valve opening value and the second valve opening value from exceeding the second preset threshold range, which could lead to overshoot or denitrification not meeting requirements.

[0148] Furthermore, in order to avoid repeated adjustments to the urea valve, and to prevent frequent adjustments to the valve opening when the difference between the valve opening value at the previous moment and the required valve opening value at the current moment is small, which would have an adverse effect on the equipment life and the denitrification control system.

[0149] Therefore, this embodiment of the application determines whether it is necessary to adjust the urea flow regulating valve by detecting the difference between the valve opening value at the previous moment and the target valve opening value at the current moment. Optionally, the specific process may include: obtaining the valve opening value of the urea flow regulating valve of the hand-held device at the previous moment as the original urea valve opening value; determining the difference between the original urea valve opening value and the target valve opening value; when the difference is within a preset dead zone range, controlling the hand-held device to open the urea flow regulating valve with the original urea valve opening value.

[0150] In this embodiment, a dead zone is designed for the difference between the target valve opening value and the original urea valve opening value before outputting the target valve opening value. When the difference is within the dead zone, the urea flow regulating valve of the denitrification control system is opened with the original urea valve opening value at the previous moment, so as to avoid frequent adjustment of the urea flow regulating valve.

[0151] The preset dead zone range can be determined based on the operator's experience or the performance characteristics of the urea flow regulating valve. For example, based on the operator's experience, if the deviation of the valve opening value is within 1%, the amount of urea sprayed will not have a significant effect on the denitrification treatment. In this case, the dead zone range can be set to 0-1%. If the difference between the target valve opening value and the original urea valve opening value does not exceed 1%, the valve opening of the urea flow regulating valve will not be adjusted.

[0152] Reference Figure 2 The diagram illustrates an optional application example of a denitrification control system, providing an exemplary description of the aforementioned denitrification control method to aid understanding. (Refer to...) Figure 2 The denitrification control system includes a PID controller 9 and an ALGMAN handheld device 10. The PID controller 9 and the ALGMAN handheld device 10 are connected via an interface to enable the output of the PID controller 9 to control the urea flow regulating valve 11.

[0153] in, Figure 2 The numbers in the table represent the following: 1-NOx concentration emission value, 2-proportional band function F(x), 3-automatic status of urea flow control valve, 4-opening command of urea flow control valve, 5-NOx setpoint module, 6-feedforward command module, 7-upper limit module of reducing agent, and 8-lower limit module of reducing agent.

[0154] exist Figure 2In the example shown, the steps executed by the control module of the denitrification control system are distributed among the proportional band function F(x)2, urea flow regulating valve opening command 4, NOx setpoint module 5, feedforward command module 6, reducing agent upper limit module 7, and reducing agent lower limit module 8. The steps corresponding to each module can be referred to the following description:

[0155] NOx emission value 1 transmits the NOx concentration value measured by the CEMS at the flue gas outlet to the PID controller via the PV interface, and according to... Figure 2 As shown in the connection between the NOx emission value 1 and the proportional band function F(x)2, the proportional band function F(x)2 adjusts the proportional gain of the PID controller based on the NOx concentration value transmitted from the NOx emission value 1 and other concentration parameter values. For example, when the NOx concentration value is high, the proportional gain is increased to speed up the system response; when the NOx concentration value is low, the proportional gain is reduced to prevent overshoot and improve system stability. The adjusted proportional gain is then input to the PID controller 9 to adjust the proportional gain of the PID controller 9.

[0156] The NOx setpoint module 5 can adjust the setpoint of the PID controller 9 based on the hourly average NOx concentration, the NOx concentration emission value, and the rate of change. For example, when the hourly average NOx concentration is low, the setpoint can be adjusted based on a function established by expert experience between the unit's AGC load command and the setpoint. When the hourly average NOx concentration is high, the NOx concentration value is high, and it shows an upward trend, the setpoint is further reduced to obtain the NOx concentration setpoint. Then, the PID controller's setpoint is adjusted to the NOx concentration setpoint via the SP interface, and the deviation value is calculated from the input of the PV interface to obtain the nitrogen oxide deviation value. This ensures that the hourly average NOx concentration meets the standard, improves the automatic operation rate of the denitrification system, and reduces the workload of operators.

[0157] The feedforward instruction module 6 is used to implement the execution steps corresponding to steps S140 and S150 above. Specifically, the actual load of the unit, the unit AGC load instruction, and the oxygen content can be selected as the feedforward instruction influencing variables. Since the above influencing variables can predict the amount of NOx generated earlier, the relationship between the above influencing variables and the valve opening value of the urea flow regulating valve is established and determined. Based on the relationship, the valve opening value of the urea flow regulating valve corresponding to the current influencing variable is determined. The valve opening value is used as the feedforward instruction 6 to input the feedforward value to the PID controller through the OC interface, so as to achieve more accurate advance regulation, improve the dynamic characteristics of the system, and ensure the stability of regulation.

[0158] In this example, the influencing variables of the feedforward instruction module 6—the actual load of the unit and the total air volume of the furnace—have similar trends. However, the change in the total air volume of the furnace precedes that of the actual load of the unit. By using the total air volume of the furnace as an auxiliary variable to correct the valve opening value determined based on the actual load of the unit, the amount of NOx generated can be predicted earlier, which is beneficial to the optimization of the system.

[0159] In addition, the feedforward instruction module 6 is also set with an upper limit value and a lower limit value for the feedforward value. These can be understood by referring to the first upper limit value and the first lower limit value of the first preset threshold range described above. This ensures that the feedforward value input by the feedforward instruction module 6 to the PID controller 9 is within the range defined by the upper limit value and the lower limit value for the feedforward value, thus preventing the feedforward instruction module 6 from overshooting due to inaccurate prediction.

[0160] The reducing agent upper limit module 7 can adjust the reducing agent upper limit based on the hourly average NOx concentration emission. In this example, the reducing agent upper limit can be the upper limit of the valve opening value of the urea flow regulating valve. If the hourly average NOx concentration is less than a certain value, the reducing agent upper limit is adjusted according to a pre-established function of the unit AGC load command and the upper limit value, which can prevent excessive reducing agent injection, reduce ammonia slip, and ensure economic benefits.

[0161] The reducing agent lower limit module 8 can adjust the reducing agent lower limit based on the NOx concentration, the hourly average NOx concentration, and the CEMS purging status. In this example, the reducing agent lower limit can be the lower limit of the valve opening value of the urea flow regulating valve. If the NOx concentration is low for a long time and the lower limit is greater than a certain value, the reducing agent lower limit is further reduced; if the CEMS is purged and the hourly average NOx concentration is high, the reducing agent lower limit is further increased. The reducing agent lower limit can leave a certain reducing agent margin to prevent system regulation from oscillating, while also having good robustness and ensuring system stability.

[0162] The upper and lower limits of the reducing agent can be understood by referring to the explanation of the second upper and lower limits corresponding to the second preset threshold range described above. The upper and lower limits of the reducing agent are input to the PID controller 9 through the OT and OB interfaces, respectively.

[0163] The PID controller 9 performs calculations based on the acquired feedforward value and NOx deviation value to determine the target valve opening value of the urea flow regulating valve 11 for output, and the target valve opening value needs to be within the range defined by the upper limit value and the lower limit value of the reducing agent.

[0164] The urea flow regulating valve in automatic mode 3 is connected to the tracking switch of the PID controller 9, and the urea flow regulating valve opening command 4 is connected to the tracking point of the PID controller 9. When in manual mode, the output of the PID controller 9 tracks the output of the handheld device 10; when in automatic mode, the handheld device 10 tracks the output of the PID controller 9 to achieve automatic tracking, enabling seamless switching between manual and automatic modes.

[0165] Based on this, the embodiments of this application can realize automatic adjustment in the denitrification process, improve the operation rate of the control strategy, and enable the denitrification control system to achieve fully automatic control and switch control strategies.

[0166] The denitrification control device provided in the embodiments of this application is described below. The denitrification control device described below can be referred to in correspondence with the denitrification control method described above.

[0167] First, combined Figure 3 This paper introduces the denitrification control device used in the control module of a denitrification control system. The denitrification control system includes at least a proportional-integral-derivative controller and a handheld device. For example... Figure 3 As shown, the denitrification control device may include:

[0168] The parameter acquisition unit 100 is used to acquire the concentration parameter value and concentration influence parameter of nitrogen oxides in the flue gas discharged from the boiler at the current time. The concentration parameter value includes at least: concentration value, hourly average concentration value and concentration change rate. The concentration change rate is the rate of change of the concentration value of nitrogen oxides within a preset time range. The concentration influence parameter is a parameter that affects the generation of nitrogen oxides in the flue gas discharged from the boiler at the next moment. The concentration influence parameter includes at least: the unit load of the thermal power plant unit, the unit load command and the oxygen content inside the boiler.

[0169] The setpoint determination unit 200 is used to determine a setpoint for nitrogen oxide concentration based on the hourly average concentration and the concentration change rate;

[0170] The first valve opening value determination unit 300 is used to call the proportional-integral-derivative controller after adjusting the proportional gain, determine the nitrogen oxide deviation value between the nitrogen oxide concentration set value and the concentration value, and determine the first valve opening value of the urea flow regulating valve of the hand-held device based on the nitrogen oxide deviation value.

[0171] The function acquisition unit 400 is used to acquire a pre-established preset function that characterizes the relationship between the valve opening value of the urea flow regulating valve of the hand-held device and the concentration influence parameter.

[0172] The second valve opening value determination unit 500 is used to determine the second valve opening value that meets the first preset threshold range based on the preset function and the concentration influence parameter.

[0173] The target control unit 600 is used to determine a target valve opening value that meets a second preset threshold range based on the first valve opening value and the second valve opening value, and to control the handheld device to open the urea flow regulating valve with the target valve opening value.

[0174] In summary, this embodiment of the application achieves automatic real-time adjustment of the setpoint based on the current nitrogen oxide concentration and a preset function, eliminating the need for operator intervention, reducing the influence of subjective factors, and making the setpoint more consistent with the current boiler emission conditions. Furthermore, in addition to improving the accuracy of valve opening control by adjusting the PID controller's setpoint and proportional gain, this embodiment also considers the impact on the nitrogen oxide concentration emitted by the boiler at the next moment. Based on the concentration influence parameter, it determines the second valve opening value at the current moment, avoiding sudden changes or repeated valve opening jumps in the event of unexpected conditions, which could affect the stability of the denitrification control system. Combining the first and second valve opening values, a target valve opening value that meets the preset threshold range is determined. This ensures that the amount of urea sprayed at the target opening value not only meets the current emission standard requirements but also prepares for the next nitrogen oxide emission conditions, allowing for timely adjustments and improving the stability of the denitrification control system.

[0175] Optional, also includes:

[0176] The proportional gain adjustment unit is used to determine the proportional gain of the proportional-integral-derivative controller corresponding to the concentration value of nitrogen oxides at the current time based on a preset curve function, wherein the preset curve function is used to characterize the relationship between the concentration value of nitrogen oxides and the proportional gain.

[0177] Optionally, the setpoint determination unit 200 includes:

[0178] The original set value acquisition subunit is used to acquire the nitrogen oxide concentration set value of the proportional-integral-derivative controller at the previous moment as the original set value;

[0179] The concentration value determination subunit is used to determine whether the hourly average concentration of the nitrogen oxides at the current moment is greater than a first preset threshold.

[0180] The first setting value determination subunit is used to adjust the original setting value to decrease it based on a preset change range when the hourly average concentration is greater than the first preset threshold and the concentration value and the concentration change rate respectively meet preset conditions, so as to obtain the nitrogen oxide setting value at the current moment.

[0181] The second setting value determination subunit is used to determine the nitrogen oxide setting value at the current time based on the unit load command and a preset characteristic function, provided that the hourly average concentration is not greater than the first preset threshold. The preset characteristic function is used to characterize the characteristic relationship between the unit load command and the nitrogen oxide setting value.

[0182] Optionally, the second valve opening value determination unit 500 includes:

[0183] The initial valve opening determination subunit is used to determine the initial valve opening value corresponding to the current unit load based on a first preset function that characterizes the relationship between the unit load and the valve opening value of the urea flow regulating valve of the hand controller.

[0184] The initial valve opening adjustment subunit is used to adjust the initial valve opening value based on the adjustment direction of the unit load corresponding to the unit load command and the changing trend of the oxygen content inside the boiler, so as to obtain an intermediate valve opening value. The changing trend includes increase or decrease.

[0185] The opening value judgment subunit is used to determine whether the opening value of the intermediate valve is within the first preset threshold range, where the first preset threshold range is the interval range defined by the first upper limit value and the first lower limit value.

[0186] The second valve opening value first determination subunit is used to determine the intermediate valve opening value as the second valve opening value when the judgment result of the opening value judgment subunit is yes;

[0187] The second valve opening value determination subunit is used to determine the first upper limit value as the second valve opening value when the judgment result of the opening value judgment subunit is negative and the intermediate valve opening value is greater than the first upper limit value.

[0188] The second valve opening value third determination subunit is used to determine the first lower limit value as the second valve opening value when the judgment result of the opening value judgment subunit is negative and the intermediate valve opening value is less than the first lower limit value.

[0189] Optionally, the initial valve opening determination subunit includes:

[0190] The air volume acquisition subunit is used to acquire the total air volume in the furnace of a thermal power plant.

[0191] The first reference value determination subunit is used to determine a first reference value of valve opening corresponding to the total furnace air volume based on the total furnace air volume and a second preset function. The second preset function is used to characterize the characteristic function relationship between the total furnace air volume and the valve opening of the urea flow regulating valve of the hand-held device.

[0192] The second reference value determination subunit is used to determine the second reference value of valve opening corresponding to the unit load based on the unit load and the first preset function;

[0193] The reference value correction subunit is used to correct the valve opening second reference value based on the valve opening first reference value, and use the corrected valve opening second reference value as the initial valve opening value corresponding to the current unit load.

[0194] Optionally, the target control unit 600 includes:

[0195] The weighted processing subunit is used to perform weighted processing based on the first valve opening value and the second valve opening value to obtain the valve opening value to be determined.

[0196] The valve opening value range determination subunit is used to determine whether the valve opening value to be determined is within the range of the second preset threshold value, where the second preset threshold value range is the interval range defined by the second upper limit value and the second lower limit value.

[0197] The first subunit for determining the target valve opening value is used to determine the undetermined valve opening value as the target valve opening value when the judgment result of the opening value range judgment subunit is yes.

[0198] The second subunit for determining the target valve opening value is used to determine the second upper limit value as the target valve opening value when the judgment result of the opening value range judgment subunit is negative and the valve opening value to be determined is greater than the second upper limit value.

[0199] The third subunit for determining the target valve opening value is used to determine the second lower limit value as the target valve opening value when the judgment result of the subunit for judging the opening value range is negative and the valve opening value to be determined is less than the second lower limit value.

[0200] Optionally, the device may also include:

[0201] The feedforward upper limit determination unit is used to set an oxygen feedforward upper limit corresponding to the oxygen content inside the boiler and a load feedforward upper limit corresponding to the unit load command, respectively, based on the significant influence of the oxygen content inside the boiler and the unit load command on the concentration value of nitrogen oxides.

[0202] The first upper limit value determination unit is used to sum the oxygen feedforward upper limit value and the load feedforward upper limit value to obtain the first upper limit value of the valve opening of the urea flow regulating valve of the hand-held device;

[0203] The first lower limit value determination unit is used to determine the first lower limit value of the valve opening of the urea flow regulating valve of the hand-held device within a preset lower limit value range based on the relationship between the concentration value of the nitrogen oxides and the nitrogen oxide emission standard.

[0204] The first preset threshold range determination unit is used to determine the range corresponding to the first upper limit value and the first lower limit value of the valve opening of the urea flow regulating valve of the hand-held device as the first preset threshold range.

[0205] Optionally, the device may also include:

[0206] The second upper limit value determination unit is used to determine the second upper limit value of the valve opening of the urea flow regulating valve of the hand-held device corresponding to the hourly average concentration when the hourly average concentration meets the preset threshold condition, based on the unit load command and the preset limit function. The preset limit function is used to characterize the characteristic function relationship between the unit load command and the upper limit value of the valve opening of the urea flow regulating valve of the hand-held device.

[0207] The second initial lower limit value determination unit is used to determine the second initial lower limit value corresponding to the unit load based on the unit load command and the third preset function. The third preset function is used to characterize the characteristic function relationship between the unit load command and the lower limit value of the valve opening of the urea flow regulating valve of the hand controller.

[0208] The second lower limit determination unit is used to adjust the initial lower limit value based on the relationship between the hourly average concentration and the nitrogen oxide emission standard, as well as the soot blowing status of the boiler flue gas online monitoring system CEMS, to obtain the second lower limit value of the valve opening of the urea flow regulating valve of the hand-held device.

[0209] The second preset threshold range determination unit is used to determine the range corresponding to the second upper limit value and the second lower limit value of the valve opening of the urea flow regulating valve of the hand-held device as the second preset threshold range.

[0210] Optionally, the device may also include:

[0211] The original valve opening value acquisition unit is used to acquire the valve opening value of the urea flow regulating valve of the hand controller at the previous moment, as the original urea valve opening value;

[0212] The difference determination unit is used to determine the difference between the original urea valve opening value and the target valve opening value;

[0213] The valve control unit is used to control the handheld device to open the urea flow regulating valve with the original urea valve opening value when the difference is within a preset dead zone range.

[0214] Finally, it should be noted that in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0215] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0216] The above description of the disclosed embodiments enables those skilled in the art to make or use this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A denitrification control method, characterized in that, The control module is applied to the denitrification control system, which at least includes: a proportional-integral-derivative controller and a handheld device; the denitrification control method includes: The concentration parameters and concentration influence parameters of nitrogen oxides in the flue gas discharged from the boiler are obtained. The concentration parameters include at least: concentration value, hourly average concentration, and concentration change rate. The concentration change rate is the rate of change of the concentration value of nitrogen oxides within a preset time range. The concentration influence parameters are parameters that affect the generation of nitrogen oxides in the flue gas discharged from the boiler at the next moment. The concentration influence parameters include at least: unit load of the thermal power plant unit, unit load command, and oxygen content inside the boiler. The nitrogen oxide concentration setpoint is determined based on the hourly average concentration and the concentration change rate. The proportional-integral-derivative controller with adjusted proportional gain is invoked to determine the nitrogen oxide deviation value between the nitrogen oxide concentration setpoint and the concentration value, and the first valve opening value of the urea flow regulating valve of the hand-held device is determined based on the nitrogen oxide deviation value. Obtain a pre-established characteristic function that characterizes the relationship between the valve opening value of the urea flow regulating valve of the hand-held device and the concentration influence parameter; Based on the preset function and the concentration influence parameter, a second valve opening value that meets the first preset threshold range is determined. The second valve opening value is a feedforward value that is predicted based on the concentration influence parameter and used to perform advance adjustment of the urea flow regulating valve. Based on the first valve opening value and the second valve opening value, a target valve opening value that meets the second preset threshold range is determined, and the handheld device is controlled to open the urea flow regulating valve with the target valve opening value.

2. The denitrification control method according to claim 1, characterized in that, The process of adjusting the proportional gain of the proportional-integral-derivative controller includes: Based on a preset curve function, the proportional gain of the proportional-integral-derivative controller corresponding to the concentration value of nitrogen oxides at the current moment is determined. The preset curve function is used to characterize the relationship between the concentration value of nitrogen oxides and the proportional gain.

3. The denitrification control method according to claim 1, characterized in that, The determination of the nitrogen oxide concentration setpoint based on the hourly average concentration and the concentration change rate includes: The nitrogen oxide concentration setpoint of the proportional-integral-derivative controller at the previous moment is obtained and used as the original setpoint. Determine whether the hourly average concentration of nitrogen oxides at the current moment is greater than a first preset threshold; If the hourly average concentration is greater than the first preset threshold, and the concentration value and the concentration change rate respectively meet preset conditions, the original set value is adjusted to decrease based on the preset change range to obtain the nitrogen oxide set value at the current moment. If the hourly average concentration is not greater than the first preset threshold, the nitrogen oxide setpoint at the current moment is determined according to the unit load command and the preset characteristic function, wherein the preset characteristic function is used to characterize the characteristic relationship between the unit load command and the nitrogen oxide setpoint.

4. The denitrification control method according to claim 1, characterized in that, The step of determining the second valve opening value that satisfies the first preset threshold range based on the preset function and the concentration influence parameter includes: The initial valve opening value corresponding to the current unit load is determined based on a first preset function that characterizes the relationship between the unit load and the valve opening value of the urea flow regulating valve on the hand controller. Based on the adjustment direction of the unit load corresponding to the unit load command, and the changing trend of the oxygen content inside the boiler, the initial valve opening value is adjusted to obtain the intermediate valve opening value, and the changing trend includes increase or decrease. Determine whether the opening value of the intermediate valve is within the first preset threshold range, where the first preset threshold range is the interval range defined by the first upper limit value and the first lower limit value; When the opening value of the intermediate valve is within the range of the first preset threshold, the opening value of the intermediate valve is determined as the opening value of the second valve. When the opening value of the intermediate valve is not within the first preset threshold range, and the opening value of the intermediate valve is greater than the first upper limit value, the first upper limit value is determined as the opening value of the second valve. When the opening value of the intermediate valve is not within the first preset threshold range and the opening value of the intermediate valve is less than the first lower limit value, the first lower limit value is determined as the second valve opening value.

5. The denitrification control method according to claim 4, characterized in that, The step of determining the initial valve opening value corresponding to the current unit load based on a first preset function characterizing the relationship between the unit load and the valve opening value of the urea flow regulating valve on the handheld device includes: Obtain the total air volume in the furnace of a thermal power plant; Based on the total furnace air volume and the second preset function, a first reference value for valve opening corresponding to the total furnace air volume is determined. The second preset function is used to characterize the characteristic function relationship between the total furnace air volume and the valve opening of the urea flow regulating valve of the hand-held device. Based on the unit load and the first preset function, determine a second reference value for the valve opening corresponding to the unit load; The valve opening second reference value is corrected based on the first reference value of valve opening, and the corrected second reference value of valve opening is used as the initial valve opening value corresponding to the current unit load.

6. The method according to claim 1, characterized in that, The step of determining the target valve opening value that meets the second preset threshold range based on the first valve opening value and the second valve opening value includes: The valve opening value to be determined is obtained by weighting the first valve opening value and the second valve opening value. Determine whether the valve opening value to be determined is within the range of the second preset threshold, where the range of the second preset threshold is the interval defined by the second upper limit value and the second lower limit value; When the undetermined valve opening value is within the range of the second preset threshold, the undetermined valve opening value is determined as the target valve opening value; When the valve opening value to be determined is not within the range of the second preset threshold, and the valve opening value to be determined is greater than the second upper limit value, the second upper limit value is determined as the target valve opening value; When the valve opening value to be determined is not within the range of the second preset threshold, and the valve opening value to be determined is less than the second lower limit, the second lower limit is determined as the target valve opening value.

7. The denitrification control method according to claim 1, characterized in that, The process of obtaining the first preset threshold range includes: Based on the degree of influence of the oxygen content inside the boiler and the unit load command on the concentration value of nitrogen oxides, respectively, an upper limit value for oxygen feedforward corresponding to the oxygen content inside the boiler and an upper limit value for load feedforward corresponding to the unit load command are set. The upper limit of oxygen feedforward and the upper limit of load feedforward are summed to obtain the first upper limit of the valve opening of the urea flow regulating valve of the hand-held device; Based on the relationship between the concentration value of nitrogen oxides and the nitrogen oxide emission standard, a first lower limit value for the valve opening of the urea flow regulating valve of the hand-held device within a preset lower limit value range is determined. The range between the first upper limit and the first lower limit of the valve opening of the urea flow regulating valve of the hand-held device is determined as the first preset threshold range.

8. The denitrification control method according to claim 1, characterized in that, The process of obtaining the second preset threshold range includes: When the hourly average concentration meets the preset threshold condition, according to the unit load command and the preset limit function, the second upper limit value of the valve opening of the urea flow regulating valve of the hand-held device corresponding to the hourly average concentration is determined. The preset limit function is used to characterize the characteristic function relationship between the unit load command and the upper limit value of the valve opening of the urea flow regulating valve of the hand-held device. Based on the unit load command and the third preset function, a second initial lower limit value corresponding to the unit load is determined. The third preset function is used to characterize the characteristic function relationship between the unit load command and the lower limit value of the valve opening of the urea flow regulating valve of the hand controller. Based on the relationship between the hourly average concentration and the nitrogen oxide emission standard, and the soot blowing status of the boiler's flue gas online monitoring system (CEMS), the initial lower limit value is numerically adjusted to obtain the second lower limit value of the valve opening of the urea flow regulating valve of the hand-held device. The range between the second upper limit and the second lower limit of the valve opening of the urea flow regulating valve of the hand-held device is determined as the second preset threshold range.

9. The denitrification control method according to claim 1, characterized in that, Also includes: Obtain the valve opening value of the urea flow regulating valve of the hand-held device at the previous moment, and use it as the original urea valve opening value; Determine the difference between the original urea valve opening value and the target valve opening value; When the difference is within the preset dead zone range, the handheld device is controlled to open the urea flow regulating valve at the original urea valve opening value.

10. A denitrification control device, characterized in that, The control module is applied to the denitrification control system, which further includes at least: a proportional-integral-derivative controller and a handheld device; the denitrification control device includes: The parameter acquisition unit is used to acquire the concentration parameter value and concentration influence parameter of nitrogen oxides in the flue gas discharged from the boiler at the current time. The concentration parameter value includes at least: concentration value, hourly average concentration value and concentration change rate. The concentration change rate is the rate of change of the concentration value of nitrogen oxides within a preset time range. The concentration influence parameter is a parameter that affects the concentration of nitrogen oxides in the flue gas discharged from the boiler at the next moment. The concentration influence parameter includes at least: the unit load of the thermal power plant unit, the unit load command and the oxygen content inside the boiler. The setpoint determination unit is used to determine the nitrogen oxide concentration setpoint based on the hourly average concentration and the concentration change rate; The first valve opening value determination unit is used to call the proportional-integral-derivative controller after adjusting the proportional gain, determine the nitrogen oxide deviation value between the nitrogen oxide concentration set value and the concentration value, and determine the first valve opening value of the urea flow regulating valve of the hand-held device based on the nitrogen oxide deviation value. The function acquisition unit is used to acquire a pre-established preset function that characterizes the valve opening of the urea flow regulating valve of the hand controller with the unit load, the unit load command and the oxygen content inside the boiler. The second valve opening value determination unit is used to determine a second valve opening value that meets the first preset threshold range based on the preset function and the concentration influence parameter. The second valve opening value is a feedforward value that is predicted based on the concentration influence parameter and used to perform advance adjustment of the urea flow regulating valve. The target control unit is used to determine a target valve opening value that meets a second preset threshold range based on the first valve opening value and the second valve opening value, and to control the handheld device to open the urea flow regulating valve with the target valve opening value.

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