An ammonia injection control system for SCR zone of coal-fired unit and a control method thereof

Abstract

The application discloses a coal-fired unit SCR zone ammonia injection control system and a control method thereof, and relates to the technical field of flue gas denitration. The system comprises an ammonia injection pipeline system, a resistance parameter preset module, a flow detection module, an ammonia injection adjustment module, a controller and a NOx detection module. The ammonia injection pipeline system adopts fixed type pipe fittings. The resistance parameter preset module obtains a resistance coefficient through pipe fitting type query and fluid mechanics theory calculation, and forms a resistance parameter database. The controller determines total ammonia injection flow according to NOx concentration data, allocates branch target flow, calls resistance data to calculate valve opening initial value, completes initial ammonia injection allocation, and dynamically corrects valve opening in combination with feedback of the flow detection module. The application solves the problems of large regulation deviation, lag and high debugging cost caused by ignoring pipeline resistance difference in traditional ammonia injection control, improves ammonia injection uniformity, guarantees denitration efficiency, and effectively inhibits ammonia escape.

Description

Technical Field

[0001] This application relates to the field of flue gas denitrification technology, and in particular to an ammonia injection control system and control method for the SCR zone of a coal-fired power unit. Background Technology

[0002] In the Selective Catalytic Reduction (SCR) denitrification system of coal-fired power units, the uniformity of ammonia injection is crucial for ensuring denitrification efficiency and suppressing ammonia slip. Existing precision ammonia injection technologies largely revolve around flow regulation, adjusting the opening of valves in each branch to achieve uniform injection by detecting NOx concentration and ammonia flow rate. However, this approach has significant technical shortcomings. Current precision ammonia injection systems do not consider the resistance differences within the ammonia injection pipeline itself. The ammonia injection pipeline system includes numerous elbows, valves, reducers, tees, and other fittings, each with significantly different resistance coefficients. Furthermore, the friction loss along the pipeline is affected by pipe diameter and length. Even if the valve openings in each branch are the same, the actual ammonia flow rate will deviate considerably due to varying resistance. Current technologies rely solely on closed-loop control through flow feedback and opening adjustment, failing to link pipeline resistance to flow demand. This results in lag and deviations in the adjustment process, making it difficult to achieve truly precise ammonia injection. Localized over- or under-injection of ammonia can still occur, leading to problems such as excessive ammonia slip and catalyst blockage. In addition, the existing precision ammonia injection system requires extensive experimental testing to determine the relationship between the flow rate and opening degree of each branch, resulting in high commissioning costs and failing to meet the requirements of efficient and stable operation of the SCR denitrification system in coal-fired power units. Summary of the Invention

[0003] To address the problems existing in the aforementioned related technologies, this application provides an ammonia injection control system for the SCR zone of a coal-fired power unit and its control method.

[0004] According to a first aspect of this application, an ammonia injection control system for the SCR zone of a coal-fired power unit is provided, comprising:

[0005] The system includes an ammonia injection pipeline system, a resistance parameter preset module, a flow detection module, an ammonia injection adjustment module, a controller, and a NOx detection module. The ammonia injection pipeline system includes a main ammonia injection pipe, multiple branch ammonia injection pipes, and multiple ammonia injection pipelines. The outlet end of the main ammonia injection pipe is connected in parallel with the inlet end of each branch ammonia injection pipe. Multiple ammonia injection pipelines branch off from the outlet end of each branch ammonia injection pipe. The outlet ends of all ammonia injection pipelines extend to the ammonia injection grid of the SCR reactor. All pipe fittings in the ammonia injection pipeline system have a fixed model. The resistance parameter preset module is electrically connected to the controller and is used to preset and store the resistance coefficients of all pipe fittings in the ammonia injection pipeline system and the friction resistance parameters of each pipeline to form a resistance parameter database; the resistance coefficients are obtained by querying the pipe fitting model and calculating using fluid mechanics theory. The flow detection module includes flow sensors installed on the main ammonia injection pipe, each ammonia injection branch pipe, and each ammonia injection pipeline, for collecting real-time ammonia injection flow and transmitting it to the controller. The ammonia injection regulating module includes electrically adjustable valves installed on each ammonia injection branch pipe and each ammonia injection pipeline. The electrically adjustable valves are driven by the controller to adjust the opening degree. The NOx detection module is used to collect NOx concentration data at the inlet and outlet of the SCR reactor and transmit it to the controller; The controller is configured to: The total ammonia injection flow rate requirement is determined based on the NOx concentration data and allocated to each ammonia injection branch and ammonia injection pipeline to determine the target ammonia injection flow rate; By calling the resistance data in the resistance parameter database and combining it with the fluid dynamics flow-resistance relationship, the initial value of the electric regulating valve opening required for each ammonia injection branch and ammonia injection pipeline to reach the target ammonia injection flow rate is calculated. Drive the electric regulating valve to reach the initial opening value to complete the initial ammonia injection quantity distribution; The system receives the actual ammonia injection flow rate from the flow detection module, compares it with the target ammonia injection flow rate, and dynamically adjusts the opening of each electric regulating valve.

[0006] Optionally, the resistance calculation formula built into the resistance parameter preset module includes: Friction resistance formula: Local resistance formula: Formula for total resistance of a branch: ; in, For friction resistance, This is the friction coefficient. This refers to the length of the straight pipe section. The inner diameter of the pipe. The ammonia flow rate is... It is the acceleration due to gravity. For local resistance, This is the local drag coefficient. The total resistance of the ammonia injection branch pipe or ammonia injection pipeline. The sum of the frictional resistances along all straight sections of this branch is: This is the sum of the local resistances of all pipe fittings in this branch.

[0007] Optionally, the friction coefficient The local resistance coefficient is determined based on the pipe material and inner wall roughness. Determined based on the pipe fitting model and specifications.

[0008] Optionally, the resistance parameter preset module has a reserved resistance coefficient correction interface for periodically calibrating and updating the resistance parameter database.

[0009] Optionally, the resistance parameter preset module is also used to automatically generate a new resistance parameter database by inputting the pipe fitting model, pipe length and inner diameter parameters of the updated pipe after the ammonia injection pipeline system is upgraded, using the built-in resistance calculation formula.

[0010] Optionally, the controller is a PLC controller with a built-in flow-resistance correlation algorithm and functions for data storage, logic operation, and fault alarm.

[0011] Optionally, the relationship between the opening degree of the electric regulating valve and the flow rate is pre-entered into the controller in conjunction with the resistance data in the resistance parameter preset module.

[0012] Optionally, when dynamically correcting the opening of each electrically adjustable valve, the controller predicts the valve opening adjustment direction by combining the resistance change trend.

[0013] According to a second aspect of this application, a control method for an ammonia injection control system in the SCR zone of a coal-fired power unit is provided, comprising: The controller calculates the total ammonia injection flow rate requirement based on the target values ​​of NOx concentration at the inlet and outlet of the SCR reactor and the unit load, and determines the target ammonia injection flow rate for each ammonia injection branch and each ammonia injection pipeline in conjunction with the denitrification requirements of the SCR reactor area corresponding to each ammonia injection pipeline. The controller calls the resistance parameter database stored in the resistance parameter preset module to obtain the total resistance data of each ammonia injection branch and ammonia injection pipeline. Combining the relationship that the flow rate is inversely proportional to the square root of the resistance in fluid mechanics, it calculates the initial value of the electric regulating valve opening required for each ammonia injection branch and ammonia injection pipeline to reach the target ammonia injection flow rate. The controller drives the electric regulating valves on each ammonia injection branch pipe and ammonia injection pipeline to the initial opening value, thus completing the initial ammonia injection quantity distribution. The controller receives the actual ammonia injection flow rate of each ammonia injection branch and ammonia injection pipeline collected in real time by the flow detection module, compares the actual ammonia injection flow rate with the target ammonia injection flow rate, and dynamically corrects the opening degree of each electric regulating valve in combination with the resistance change trend.

[0014] This application, through the inclusion of a resistance parameter preset module electrically connected to the controller, allows for the preset and storage of resistance coefficients for all pipe fittings in the ammonia injection pipeline system and friction resistance parameters along each pipeline, forming a resistance parameter database. The controller can first determine the total ammonia injection flow demand based on NOx concentration data and allocate target ammonia injection flow rates to each branch. Then, it calls upon resistance data and combines it with the flow-resistance relationship in fluid mechanics to calculate the initial opening value of each electrically controlled regulating valve, completing the initial ammonia injection allocation. Finally, it dynamically corrects the valve opening based on the actual ammonia injection flow rate feedback from the flow detection module. Therefore, it can solve the problems in related technologies where the closed-loop control, relying solely on flow feedback and opening adjustment without considering the resistance differences within the ammonia injection pipeline, results in adjustment lag, large deviations, and uneven ammonia injection. It also addresses the high commissioning costs associated with extensive experimental testing of the flow-opening relationship between each branch. This achieves the technical effects of improving ammonia injection uniformity, reducing adjustment lag and deviations, lowering system commissioning costs, ensuring denitrification efficiency, and suppressing ammonia escape.

[0015] It should be understood that the description in this section is not intended to identify key or essential features of the embodiments of this application, nor is it intended to limit the scope of this application. Other features of this application will become readily apparent from the following description. Attached Figure Description

[0016] To more clearly illustrate the embodiments of this application, the accompanying drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 This is a schematic diagram of the structure of an ammonia injection control system for the SCR zone of a coal-fired power unit, provided in an embodiment of this application. Figure 2 This is a flowchart illustrating a control method for an ammonia injection control system in the SCR zone of a coal-fired power unit, as provided in an embodiment of this application. Detailed Implementation

[0018] The following description, in conjunction with the accompanying drawings, illustrates exemplary embodiments of this application, including various details to aid understanding. These should be considered merely exemplary. Therefore, those skilled in the art will recognize that various changes and modifications can be made to the embodiments described herein without departing from the scope and spirit of this application. Similarly, for clarity and brevity, descriptions of well-known functions and structures are omitted in the following description.

[0019] The following description, with reference to the accompanying drawings, illustrates an embodiment of the ammonia injection control system and control method for the SCR zone of a coal-fired power unit.

[0020] Figure 1 This is a schematic diagram of the structure of an ammonia injection control system for the SCR zone of a coal-fired unit, provided in an embodiment of this application.

[0021] like Figure 1 As shown, the system includes: The ammonia injection pipeline system includes: 1. Resistance parameter preset module; 4. Flow detection module; 2. Ammonia injection adjustment module; 3. Controller; 5. NOx detection module; 6. The ammonia injection pipeline system 1 includes a main ammonia injection pipe, multiple branch ammonia injection pipes, and multiple ammonia injection pipelines. The outlet end of the main ammonia injection pipe is connected in parallel with the inlet end of each branch ammonia injection pipe. Multiple ammonia injection pipelines branch off from the outlet end of each branch ammonia injection pipe. The outlet ends of all ammonia injection pipelines extend to the ammonia injection grid of the SCR reactor. All pipe fittings in the ammonia injection pipeline system 1 have a fixed model. The resistance parameter preset module 4 is electrically connected to the controller 5 and is used to preset and store the resistance coefficients of all pipe fittings in the ammonia injection pipeline system 1 and the friction resistance parameters of each pipeline to form a resistance parameter database; the resistance coefficients are obtained by querying the pipe fitting model and calculating by fluid mechanics theory. The flow detection module 2 includes flow sensors installed on the main ammonia injection pipe, each ammonia injection branch pipe and each ammonia injection pipeline, for collecting real-time ammonia injection flow and transmitting it to the controller 5; The ammonia injection regulating module 3 includes electrically adjustable valves installed on each ammonia injection branch pipe and each ammonia injection pipeline. The electrically adjustable valves are driven by the controller 5 to adjust the opening degree. The NOx detection module 6 is used to collect NOx concentration data at the inlet and outlet of the SCR reactor and transmit it to the controller 5; The controller 5 is configured as follows: The total ammonia injection flow rate requirement is determined based on the NOx concentration data and allocated to each ammonia injection branch and ammonia injection pipeline to determine the target ammonia injection flow rate; By calling the resistance data in the resistance parameter database and combining it with the fluid dynamics flow-resistance relationship, the initial value of the electric regulating valve opening required for each ammonia injection branch and ammonia injection pipeline to reach the target ammonia injection flow rate is calculated. Drive the electric regulating valve to reach the initial opening value to complete the initial ammonia injection quantity distribution; The actual ammonia injection flow rate fed back by the flow detection module 2 is received and compared with the target ammonia injection flow rate to dynamically adjust the opening degree of each electric regulating valve.

[0022] In this embodiment, the ammonia injection control system for the SCR zone of a coal-fired power unit includes an ammonia injection pipeline system 1, a resistance parameter preset module 4, a flow detection module 2, an ammonia injection adjustment module 3, a controller 5, and a NOx detection module 6. These modules work together to achieve precise control of the ammonia injection quantity, ensuring the stable and efficient operation of the denitrification system.

[0023] The ammonia injection pipeline system 1 is the core channel for ammonia gas transportation, comprising a main ammonia injection pipe, multiple branch ammonia injection pipes, and multiple ammonia injection pipelines. The outlet end of the main ammonia injection pipe is connected in parallel to the inlet ends of each branch ammonia injection pipe. Each branch ammonia injection pipe branches into 3-4 ammonia injection pipelines at its outlet end. The outlet ends of all ammonia injection pipelines extend to the ammonia injection grid of the SCR reactor, used to uniformly deliver ammonia gas into the SCR reactor. All fittings in the ammonia injection pipeline system 1 are of fixed specifications, including elbows, valves, reducers, tees, and other fittings, ensuring stable structural parameters for each fitting and providing a reliable basis for preset resistance parameters.

[0024] The resistance parameter preset module 4, electrically connected to the controller 5, is a core innovative component that distinguishes this system from traditional ammonia injection control systems. The resistance parameter preset module 4 is used to preset and store the resistance coefficients of all pipe fittings in the ammonia injection pipeline system 1, as well as the friction resistance parameters of each pipeline, forming a complete resistance parameter database. The resistance coefficients are obtained through pipe fitting model lookup and fluid mechanics calculations, eliminating the need for extensive on-site testing and effectively simplifying the system commissioning process and reducing commissioning costs.

[0025] The flow detection module 2 includes multiple flow sensors, which are respectively installed on the main ammonia injection pipe, each branch ammonia injection pipe, and each ammonia injection pipeline. The flow sensors can collect the total ammonia injection flow of the main ammonia injection pipe, the branch flow of each ammonia injection pipe, and the end ammonia injection flow of each ammonia injection pipeline in real time, and transmit the collected flow data to the controller 5 in real time, providing accurate data basis for the dynamic adjustment of the controller.

[0026] The ammonia injection regulating module 3 includes multiple electrically operated regulating valves, which are respectively installed on each ammonia injection branch pipe and each ammonia injection pipeline. Each electrically operated regulating valve is independently driven by the controller 5, which can precisely adjust the valve opening of the corresponding branch, thereby controlling the ammonia injection flow rate of each ammonia injection branch pipe and ammonia injection pipeline, and realizing the independent distribution and regulation of ammonia injection in each area.

[0027] The NOx detection module 6 includes multiple NOx sensors, which are respectively installed on the inlet and outlet flues of the SCR reactor. The NOx detection module 6 can collect NOx concentration data at the inlet and outlet of the SCR reactor in real time and transmit the concentration data to the controller 5, which serves as the core basis for the controller to determine the total ammonia injection flow rate requirement.

[0028] Controller 5 is the core of the entire system, with built-in control algorithms. It receives data from various modules and implements precise control of ammonia injection according to preset logic. Controller 5 is configured to execute the following steps: First, based on the target values ​​of NOx concentration at the SCR reactor inlet and outlet, and the unit load transmitted by NOx detection module 6, it calculates the total ammonia injection flow rate required by the system. Combining this with the denitrification requirements of the SCR reactor area corresponding to each ammonia injection pipeline, it allocates the total ammonia injection flow rate to each ammonia injection branch and pipeline, determining the target ammonia injection flow rate for each branch. Second, it calls the resistance parameter database stored in resistance parameter preset module 4 to obtain the total resistance data for each ammonia injection branch and pipeline. Combining this with the correspondence between flow rate and resistance in fluid mechanics, it accurately calculates the initial opening value of the electric regulating valves required for each ammonia injection branch and pipeline to reach the target ammonia injection flow rate. Third, it sends control commands to ammonia injection regulation module 3 to drive each electric regulating valve to the calculated initial opening value, completing the initial ammonia injection flow rate allocation. Since the initial opening calculation fully considers the differences in pipeline resistance among each branch, the initial ammonia injection rate can quickly approach the target value, significantly reducing lag during the adjustment process. Finally, the actual ammonia injection flow rate of each branch is received from the flow detection module 2, and compared with the target ammonia injection flow rate. Based on the comparison results, the opening of each electric regulating valve is dynamically adjusted to further improve the control accuracy of the ammonia injection rate, ensuring that the ammonia injection rate of each branch always matches the denitrification requirements.

[0029] This system, through the setting of resistance parameter preset module 4, uses pipeline resistance characteristics as a prerequisite for ammonia injection quantity adjustment. Combined with the real-time feedback from flow detection module 2, it forms a dual control logic, effectively solving the problems of large adjustment deviations and severe lags caused by neglecting pipeline resistance differences in traditional ammonia injection control systems. Furthermore, it eliminates the need for extensive experimental testing of the correspondence between flow rate and opening degree, significantly reducing system commissioning costs. This system enables precise allocation of ammonia injection quantity to each branch, improving ammonia injection uniformity, ensuring denitrification efficiency, and effectively suppressing ammonia escape, avoiding catalyst blockage and other problems, thus enhancing the operational stability and reliability of the SCR denitrification system.

[0030] Compared with related technologies, in this embodiment, by setting a resistance parameter preset module electrically connected to the controller, the resistance coefficients of all pipe fittings in the ammonia injection pipeline system and the friction resistance parameters of each pipeline can be preset and stored through pipe fitting model query and fluid mechanics theory to form a resistance parameter database. The controller can first determine the total ammonia injection flow demand based on NOx concentration data and allocate the target ammonia injection flow to each branch. Then, it calls the resistance data and combines the fluid mechanics flow-resistance relationship to calculate the initial opening value of each electric regulating valve to complete the initial ammonia injection quantity allocation. Finally, it dynamically corrects the valve opening based on the actual ammonia injection flow fed back by the flow detection module. Therefore, it can solve the problems in related technologies caused by the lack of consideration of the resistance difference of the ammonia injection pipeline itself and the reliance on closed-loop control of flow feedback-opening adjustment, such as adjustment lag, large deviation, uneven ammonia injection, and high debugging costs caused by the need to conduct a large number of experiments to test the correspondence between the flow and opening of each branch. It achieves the technical effects of improving ammonia injection uniformity, reducing adjustment lag and deviation, reducing system debugging costs, and ensuring denitrification efficiency while suppressing ammonia escape.

[0031] Optionally, the resistance calculation formula built into the resistance parameter preset module 4 includes: Friction resistance formula: Local resistance formula: Formula for total resistance of a branch: ; in, For friction resistance, This is the friction coefficient. This refers to the length of the straight pipe section. The inner diameter of the pipe. The ammonia flow rate is... It is the acceleration due to gravity. For local resistance, This is the local drag coefficient. The total resistance of the ammonia injection branch pipe or ammonia injection pipeline. The sum of the frictional resistances along all straight sections of this branch is: This is the sum of the local resistances of all pipe fittings in this branch.

[0032] In this embodiment, the resistance parameter preset module 4 has a complete fluid dynamics resistance calculation formula system built in, which is used to accurately calculate the resistance value of each part of the ammonia injection pipeline system, and provides a theoretical calculation basis for the establishment of the resistance parameter database.

[0033] The resistance parameter preset module 4 includes built-in resistance calculation formulas such as the friction resistance formula, the local resistance formula, and the branch total resistance formula. The friction resistance formula is: ; This formula is applicable to the calculation of resistance in the main ammonia injection pipe, branch ammonia injection pipe, and straight sections of the ammonia injection pipeline. The friction factor is Pascal. This is the friction coefficient along the friction path; This refers to the length of the straight section of the pipeline, in meters. This refers to the inner diameter of the pipe, in meters. The ammonia flow velocity inside the pipeline is expressed in meters per second. The acceleration due to gravity is 9.8 m / s².

[0034] The formula for local resistance is:

[0035] This formula is applicable to the resistance calculation of all pipe fittings in ammonia injection pipeline systems, including elbows, valves, reducers, and tees. This is the local resistance, measured in Pascals. This is the local drag coefficient; The ammonia flow velocity at the inlet and outlet of the pipe fitting is expressed in meters per second. This is the acceleration due to gravity, and its value is consistent with that in the friction factor formula.

[0036] The formula for the total resistance of a branch is: ; This formula is used to calculate the total resistance of a single ammonia injection branch pipe or a single ammonia injection pipeline. The total resistance of the ammonia injection branch pipe or ammonia injection pipeline, in Pascals; This is the sum of the frictional resistance along all straight sections of the branch road, in Pascals. This is the sum of the local resistances of all pipe fittings in this branch, expressed in Pascals.

[0037] The resistance parameter preset module 4 can automatically calculate the total resistance value of each ammonia injection branch pipe and each ammonia injection pipeline by calling the above three formulas and combining the pre-input basic parameters such as pipe length, inner diameter, and pipe fitting model. The calculation results are stored to form a resistance parameter database for the controller 5 to call in real time.

[0038] By incorporating a standardized fluid dynamics resistance calculation formula, the system can achieve accurate, rapid, and automatic calculation of pipeline resistance, avoiding human error caused by manual calculation. At the same time, it significantly shortens the configuration time of system resistance parameters, obtains accurate resistance data without the need for on-site experimental testing, further reduces system debugging costs, and provides a reliable theoretical basis for the accurate calculation of valve opening.

[0039] Optionally, the friction coefficient The local resistance coefficient is determined based on the pipe material and inner wall roughness. Determined based on the pipe fitting model and specifications.

[0040] In this embodiment, the friction coefficient is included in the friction parameter preset module 4. and local drag coefficient Standardization is the core prerequisite for ensuring the accuracy of resistance calculation.

[0041] Friction coefficient The roughness of the inner wall is determined based on the pipe material and internal wall roughness. Ammonia injection pipes are typically made of stainless steel, and different grades of stainless steel pipes have distinct differences in internal wall roughness. For example, the internal wall roughness of 304 stainless steel seamless pipes is generally between 0.01 mm and 0.05 mm, corresponding to different friction coefficients. The smaller the roughness of the inner wall of the pipe, the smaller the frictional resistance during ammonia flow, and the lower the friction coefficient. The smaller the inner wall roughness, the greater the friction coefficient; conversely, the greater the inner wall roughness, the greater the friction coefficient. The larger the value, the better. After determining the material and specifications of the ammonia injection pipeline system, the corresponding friction coefficient can be obtained by consulting a fluid mechanics standard manual. , and preset it into the resistance parameter preset module 4.

[0042] Local drag coefficient The local resistance coefficient is determined based on the model and specifications of the pipe fittings. The ammonia injection piping system includes various pipe fittings such as elbows, valves, reducers, and tees. It is directly related to the pipe fitting's structural form, diameter, and connection method. For example, the local resistance coefficient of a 90-degree long-radius elbow. The local resistance coefficient is approximately 0.3 to 0.5, while that of a 90-degree short-radius bend is... Approximately 0.7 to 1.0; Local resistance coefficient of electrically operated regulating valves of different diameters in the fully open state. Significant differences also exist. The local resistance coefficients of various standard pipe fittings... All have corresponding industry standard data, which can be directly obtained by querying the pipe fitting model and specifications, without the need for on-site experimental testing.

[0043] By clarifying the standardized determination method for the friction coefficient and local resistance coefficient, the accuracy and consistency of resistance parameter calculation can be guaranteed, avoiding deviations in resistance calculation caused by improper parameter selection. At the same time, it eliminates the need to experimentally determine the resistance coefficient, further simplifying the system debugging process and improving the efficiency of establishing the resistance parameter database.

[0044] Optionally, the resistance parameter preset module 4 has a reserved resistance coefficient correction interface for periodically calibrating and updating the resistance parameter database.

[0045] In this embodiment, the resistance parameter preset module 4 has a reserved resistance coefficient correction interface for periodically calibrating and updating the resistance parameter database to ensure the accuracy of resistance data during long-term operation of the system.

[0046] During long-term operation, ammonia injection pipeline systems inevitably experience issues such as pipe fitting aging, dust accumulation on the inner walls of pipes, and scaling. These factors cause changes in the actual resistance coefficient of the pipes and fittings, deviating from the initially preset theoretical value. If the original resistance data continues to be used for valve opening calculations, problems such as decreased accuracy in ammonia injection control and worsened uniformity of ammonia injection will gradually emerge. Setting up a resistance coefficient correction interface can effectively solve this problem.

[0047] The resistance coefficient correction interface allows operators to input resistance deviation data measured during actual system operation, and can also connect to a dedicated resistance detection device to obtain real-time resistance data. Operators can periodically calibrate and update the resistance parameter database based on system operating conditions. The calibration cycle can be set according to the unit's operating conditions and pipeline ash accumulation, typically a comprehensive calibration every quarter or semi-annually. Temporary calibration can also be performed through this interface when the system experiences abnormal ammonia injection flow or fluctuations in denitrification efficiency. During calibration, the resistance parameter preset module 4 automatically calculates the corrected resistance coefficient based on the input actual operating data and replaces the corresponding original parameters in the database, ensuring that subsequent valve opening calculations are always based on the latest accurate resistance data.

[0048] By reserving a resistance coefficient correction interface, resistance deviations caused by factors such as pipe fitting aging and pipe dust accumulation during long-term system operation can be corrected in a timely manner, ensuring the real-time accuracy of the resistance parameter database. This enables the system to maintain high ammonia injection control precision over a long period of time, avoiding problems such as uneven ammonia injection and excessive ammonia escape caused by resistance data failure, extending the stable operation cycle of the system, and reducing the workload of later maintenance.

[0049] Optionally, the resistance parameter preset module 4 is also used to automatically generate a new resistance parameter database by inputting the pipe fitting model, pipe length and inner diameter parameters of the updated pipe after the ammonia injection pipeline system 1 is upgraded, using the built-in resistance calculation formula.

[0050] In this embodiment, the resistance parameter preset module 4 also has the function of automatically generating resistance parameters after the ammonia injection pipeline system 1 is updated, which can quickly adapt to the structural changes of the pipeline system without reconstructing the entire control system.

[0051] During the long-term operation of coal-fired power units, the ammonia injection pipeline system 1 may need to be upgraded or replaced based on requirements for improving denitrification efficiency, replacing aging equipment, or upgrading the unit. This may include various scenarios such as changing pipe fitting models, adjusting pipeline layout, adding or removing branch pipelines, and changing pipeline inner diameter. When faced with such pipeline system changes, the existing ammonia injection control system requires extensive on-site flow tests and re-adjusting the correspondence between valve opening and flow rate in each branch. This process is time-consuming, costly, and may even require replacing the entire control program.

[0052] In this system, after the ammonia injection pipeline system 1 is upgraded, the operator only needs to input the basic parameters such as the pipe fitting model, the length of each pipe section, and the inner diameter of the pipe into the resistance parameter preset module 4. The resistance parameter preset module 4 will automatically call the built-in resistance calculation formula to calculate the friction resistance of each pipe section, the local resistance of various pipe fittings, and the total resistance of each ammonia injection branch pipe and the ammonia injection pipeline, automatically generating and storing a complete new resistance parameter database. The entire calculation process is completed automatically by the module, eliminating the need for manual calculation and avoiding errors that may occur during manual calculation. No on-site flow rate testing is required. After the new resistance parameter database is generated, the controller 5 can directly call the new resistance data to calculate the valve opening, and the system can quickly resume normal operation.

[0053] By implementing an automatic resistance parameter generation function for the upgraded ammonia injection pipeline system 1, the system's adaptability and scalability are significantly improved. This completely solves the problem that existing ammonia injection control systems cannot flexibly adapt to pipeline structure changes, requiring re-debugging or even system replacement. This function can significantly shorten the system commissioning cycle after pipeline upgrades, reduce modification costs, and enable the system to flexibly adapt to SCR ammonia injection scenarios of coal-fired units of different sizes and layouts, thereby improving the system's versatility and service life.

[0054] Optionally, the controller 5 is a PLC controller 5, which has a built-in flow-resistance correlation algorithm and has data storage, logic operation and fault alarm functions.

[0055] In this embodiment, controller 5 is a PLC controller 5, which serves as the core control unit of the ammonia injection control system in the SCR zone of the entire coal-fired power plant. It can adapt to the complex industrial operating environment of coal-fired power plants, characterized by high temperature, high dust, and strong electromagnetic interference, ensuring long-term stable and reliable operation of the system. The PLC controller 5 has a built-in dedicated flow-resistance correlation algorithm and also has complete data storage, logic operation, and fault alarm functions, providing comprehensive technical support for the precise control of ammonia injection.

[0056] The flow-resistance correlation algorithm is the core algorithm of PLC controller 5 for achieving precise ammonia injection control. This algorithm establishes a quantitative correspondence between the resistance of the ammonia injection pipeline, the target ammonia injection flow rate, and the opening of the electrically controlled regulating valve. After calling the resistance data in the resistance parameter preset module 4, PLC controller 5 can quickly calculate the initial valve opening value required for each branch to reach the target ammonia injection flow rate through the flow-resistance correlation algorithm, realizing real-time linkage between resistance data and opening parameters, and avoiding the problem of blindly adjusting the valve opening in traditional control methods.

[0057] The PLC controller 5 possesses powerful logic processing capabilities, enabling it to process multi-channel input and output signals in parallel. It can perform a series of complex calculations in real time, including calculating the total ammonia injection flow demand, allocating target flow to each branch, calculating initial valve opening values, and dynamically adjusting and correcting these processes. Its fast response speed meets the real-time ammonia injection adjustment requirements of coal-fired power units under rapid load changes, ensuring stable operation of the denitrification system under various operating conditions.

[0058] The PLC controller 5 is equipped with a large-capacity data storage unit, capable of automatically storing various data during system operation, including NOx concentration data at the SCR reactor inlet and outlet, ammonia injection flow data for each branch, opening data of electrically controlled regulating valves, resistance parameter data, and system operating status data. The data storage period can be set according to actual needs, and can store more than one year of historical operating data, facilitating operators to analyze system operating status, trace faults, and optimize control logic.

[0059] The PLC controller 5 has a complete fault alarm function, which can monitor the operating status of each component of the system in real time. When abnormalities such as abnormal flow sensor signal, NOx sensor failure, electric regulating valve jamming, or excessive resistance parameter deviation are detected, it can immediately trigger an audible and visual alarm and display the specific fault location and fault type on the display screen. At the same time, it automatically records the time of the fault occurrence and related operating data, which makes it easy for maintenance personnel to quickly locate and troubleshoot the fault, ensuring the safe and stable operation of the system.

[0060] Employing a PLC controller 5 as the system's core leverages its high reliability and strong anti-interference capabilities in industrial control, ensuring stable system operation in complex environments. The built-in flow-resistance correlation algorithm achieves precise linkage between resistance data and valve opening, and combined with powerful logic processing capabilities, significantly improves the control accuracy and response speed of ammonia injection. Comprehensive data storage and fault alarm functions not only facilitate daily system maintenance and troubleshooting but also provide data support for subsequent system optimization, effectively enhancing the overall reliability and maintainability of the ammonia injection control system.

[0061] Optionally, the relationship between the opening degree of the electric regulating valve and the flow rate is pre-entered into the controller 5 in conjunction with the resistance data in the resistance parameter preset module 4.

[0062] In this embodiment, the correspondence between the opening degree of the electric regulating valve and the flow rate, combined with the resistance data pre-entered into the controller 5 in the resistance parameter preset module 4, provides a basis for the accurate calculation and rapid adjustment of the valve opening degree.

[0063] In traditional ammonia injection control systems, the relationship between the opening degree and flow rate of electrically controlled regulating valves is usually obtained through on-site experimental calibration. This requires adjusting the valve opening degree of each branch and measuring the corresponding flow rate to plot the opening degree-flow rate curve for each branch. Since the ammonia injection pipeline system contains a large number of branch pipelines, the experimental calibration process is labor-intensive, time-consuming, and easily affected by on-site operating conditions, leading to calibration errors and making it difficult to ensure the consistency of control accuracy across branches.

[0064] In this system, the relationship between the opening degree and flow rate of the electric regulating valve does not need to be calibrated through on-site experiments. Instead, it is generated by combining the total resistance data of each branch obtained in the resistance parameter preset module 4. The total resistance of each ammonia injection branch and ammonia injection pipeline is different, and the actual ammonia injection flow rate under the same valve opening degree varies significantly. The controller 5 generates a unique opening degree-flow rate correspondence table for each branch based on the total resistance parameters of each branch and the inherent flow characteristics of the electric regulating valve itself, and pre-enters it into the storage unit of the controller 5.

[0065] During system operation, when the controller 5 calculates the initial valve opening value, it directly calls the pre-entered opening-flow correspondence table for the corresponding branch. Combined with the target ammonia injection flow rate, it can quickly obtain the accurate initial valve opening value. This correspondence table is linked to the resistance parameter database. When the resistance parameter database is updated through the correction interface or regenerated due to pipeline system upgrades, the controller 5 will automatically update the opening-flow correspondence of each branch synchronously, without the need for recalibration on-site.

[0066] By pre-entering the relationship between the opening degree and flow rate of the electric regulating valve using resistance data, the extensive on-site flow calibration experiments required in traditional systems are completely eliminated, significantly shortening the system commissioning cycle and reducing commissioning costs. Furthermore, the relationship generated based on theoretical resistance data is more accurate, ensuring consistency in the ammonia injection control precision across all branches, further enhancing the overall control performance of the system.

[0067] Optionally, when dynamically correcting the opening of each electrically adjustable valve, the controller 5 predicts the valve opening adjustment direction by combining the resistance change trend.

[0068] In this embodiment, when the controller 5 dynamically corrects the opening of each electric regulating valve, it predicts the valve opening adjustment direction by combining the resistance change trend, further reducing adjustment lag and deviation, and improving the stability and accuracy of ammonia injection quantity control.

[0069] Traditional ammonia injection control systems rely solely on post-event adjustments based on the deviation between actual and target flow rates. When pipeline resistance changes, valve opening adjustments are only triggered after a significant deviation in actual flow, resulting in inherent adjustment lag. This can lead to periodic fluctuations in ammonia injection volume, impacting the stability of denitrification efficiency. In this system, controller 5 continuously records resistance and flow data for each branch. By analyzing resistance changes over multiple consecutive operating cycles, the system identifies resistance trends.

[0070] Controller 5 accurately determines whether the resistance is slowly increasing, slowly decreasing, or stable by fitting historical resistance data to trends. For example, when ash gradually accumulates on the inner wall of the pipe, the resistance will show a continuous, slow upward trend. After identifying this trend, controller 5 will anticipate the direction in which the valve opening needs to be increased when dynamically adjusting the valve opening, and will appropriately increase the adjustment range, rather than waiting until the actual flow rate is significantly lower than the target value before making adjustments. Conversely, when the system completes pipe cleaning or pipe fitting replacement, the resistance shows a downward trend. Controller 5 will anticipate the direction in which the valve opening needs to be decreased to avoid excessive ammonia injection.

[0071] This predictive dynamic correction method can advance the adjustment action before the flow deviation occurs, effectively offsetting the flow fluctuation caused by slow changes in resistance, so that the actual ammonia injection flow of each branch always closely follows the target flow, greatly reducing overshoot and oscillation during the adjustment process.

[0072] By combining the trend of resistance change to predict the direction of valve opening adjustment, the lag problem of traditional feedback regulation can be effectively solved, further improving the dynamic response speed and stability of ammonia injection control, avoiding fluctuations in ammonia injection caused by slow resistance changes, ensuring the continuous stability of denitrification efficiency, and effectively suppressing ammonia escape and extending the service life of the catalyst.

[0073] Figure 2 A flowchart illustrating a control method for an ammonia injection control system in the SCR zone of a coal-fired power unit, as provided in this application embodiment, includes the following steps: Step 701: The controller calculates the total ammonia injection flow rate requirement based on the target values ​​of NOx concentration at the inlet and outlet of the SCR reactor and the unit load, and determines the target ammonia injection flow rate for each ammonia injection branch and each ammonia injection pipeline in conjunction with the denitrification requirements of the SCR reactor area corresponding to each ammonia injection pipeline.

[0074] In some embodiments, this step is the flow requirement determination stage of the ammonia injection control method, which is a prerequisite for achieving precise ammonia injection. The controller 5 first receives the real-time NOx concentration data at the inlet of the SCR reactor collected by the NOx detection module 6, and combines it with the preset target value of NOx concentration at the outlet of the SCR reactor and the real-time load parameters of the unit, and calculates the total ammonia injection flow requirement required by the system through the built-in denitrification reaction stoichiometric ratio algorithm.

[0075] Due to the inherent non-uniformity of flue gas flow and NOx concentration distribution within the SCR reactor, the denitrification requirements vary significantly across different areas. Controller 5, based on the location of each ammonia injection pipe corresponding to the SCR reactor area, combined with historical operating data and real-time flue gas distribution characteristics, finely allocates the calculated total ammonia injection flow requirement, determining the target ammonia injection flow for each ammonia injection branch and each ammonia injection pipe, ensuring that the ammonia injection volume in each area matches the actual denitrification requirements.

[0076] By combining the inlet NOx concentration, the outlet target value, and the unit load to calculate the total ammonia injection flow rate, and then making precise allocations based on the regional denitrification needs, the rationality of the total ammonia injection amount and the targeting of the ammonia injection amount in each region can be ensured from the source. This avoids problems such as excessive or insufficient ammonia injection overall and imbalance of ammonia injection in local areas, laying the foundation for subsequent precise regulation.

[0077] Step 702: The controller calls the resistance parameter database stored in the resistance parameter preset module to obtain the total resistance data of each ammonia injection branch and ammonia injection pipeline. Combining the relationship that the flow rate is inversely proportional to the square root of the resistance in fluid mechanics, the controller calculates the initial value of the electric regulating valve opening required for each ammonia injection branch and ammonia injection pipeline to reach the target ammonia injection flow rate.

[0078] In some embodiments, this step is the core calculation step of the ammonia injection control method and is a key innovation that distinguishes it from traditional ammonia injection control methods. The controller 5 calls the resistance parameter database pre-stored in the resistance parameter preset module 4 to obtain the total resistance data corresponding to each ammonia injection branch and each ammonia injection pipeline.

[0079] Based on fundamental principles of fluid mechanics, controller 5 utilizes the inverse relationship between flow rate and the square root of resistance—that is, the ammonia injection flow rate is negatively correlated with the square root of the total branch resistance. Combined with pre-recorded data on the correspondence between the opening degree of each branch's electrically controlled regulating valve and the flow rate, controller 5 accurately calculates the initial value of the electrically controlled regulating valve opening required for each ammonia injection branch and each ammonia injection pipeline to achieve the target ammonia injection flow rate. This calculation process is completed automatically by controller 5, achieving real-time linkage between resistance data and valve opening parameters.

[0080] By using pipeline resistance data as a prerequisite for valve opening calculation, the influence of differences in pipeline resistance between branches on ammonia injection flow can be eliminated at the source. This allows the calculated initial valve opening value to directly approach the target value, significantly reducing the number and magnitude of subsequent adjustments. This effectively solves the problems of adjustment lag and deviation caused by blindly adjusting the opening in traditional control methods.

[0081] Step 703: The controller drives the electric regulating valves on each ammonia injection branch pipe and ammonia injection pipeline to the initial opening value to complete the initial ammonia injection quantity distribution.

[0082] In some embodiments, this step is the initial adjustment execution stage of the ammonia injection control method. Based on the initial opening values ​​of each branch electric regulating valve calculated in step 702, the controller 5 sends independent control commands to each electric regulating valve in the ammonia injection regulating module 3, driving each electric regulating valve to precisely operate to its corresponding initial opening value.

[0083] Once all electrically operated regulating valves have completed their opening adjustments, the initial ammonia injection rate distribution for the system is complete. Since the initial opening calculations have fully considered the differences in pipeline resistance across branches, the initial ammonia injection rate can quickly approach the target ammonia injection flow rate for each branch, eliminating the need for repeated trial adjustments as required by traditional control methods.

[0084] By performing a one-time initial adjustment based on the initial opening calculated from resistance data, the time it takes for the system to reach a stable ammonia injection state can be significantly shortened, the system's response speed can be improved, and large fluctuations in the amount of ammonia injected may occur during repeated adjustments, thus ensuring the operational stability of the denitrification system during startup and operation mode switching.

[0085] Step 704: The controller receives the actual ammonia injection flow rate of each ammonia injection branch and ammonia injection pipeline collected in real time by the flow detection module, compares the actual ammonia injection flow rate with the target ammonia injection flow rate, and dynamically corrects the opening degree of each electric regulating valve in combination with the resistance change trend.

[0086] In some embodiments, this step is a dynamic closed-loop adjustment link in the ammonia injection control method, used to ensure the ammonia injection control accuracy during long-term system operation. The controller 5 continuously receives the actual ammonia injection flow data of each ammonia injection branch and each ammonia injection pipeline collected in real time by the flow detection module 2, compares the collected actual ammonia injection flow with the predetermined target ammonia injection flow in real time, and calculates the flow deviation value.

[0087] Controller 5 dynamically adjusts the opening of each electric regulating valve based on the magnitude and direction of the flow deviation. Simultaneously, controller 5 combines the resistance data change trends from multiple consecutive operating cycles to predict the direction and magnitude of valve opening adjustments, allowing for proactive adjustments to counteract the impact of slow changes in pipeline resistance on the ammonia injection flow rate, ensuring that the actual ammonia injection flow rate in each branch remains stable near the target ammonia injection flow rate.

[0088] By combining real-time flow feedback with the prediction of resistance change trends, a dynamic correction method can not only eliminate instantaneous flow deviations in a timely manner, but also effectively solve the lag problem of traditional feedback regulation, further improving the stability and accuracy of ammonia injection control, and ensuring that the denitrification system maintains high denitrification efficiency and low ammonia slip level during long-term operation.

[0089] It should be noted that, in this document, relational terms such as "first" and "second" are used merely 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. Unless otherwise specified, 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 the element.

[0090] The above are merely specific embodiments of this application, enabling those skilled in the art to understand or implement 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 these embodiments, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A coal-fired power unit SCR zone ammonia injection control system, characterized in that, include: The system includes an ammonia injection pipeline system, a resistance parameter preset module, a flow detection module, an ammonia injection adjustment module, a controller, and a NOx detection module. The ammonia injection pipeline system includes a main ammonia injection pipe, multiple branch ammonia injection pipes, and multiple ammonia injection pipelines. The outlet end of the main ammonia injection pipe is connected in parallel with the inlet end of each branch ammonia injection pipe. Multiple ammonia injection pipelines branch off from the outlet end of each branch ammonia injection pipe. The outlet ends of all ammonia injection pipelines extend to the ammonia injection grid of the SCR reactor. All pipe fittings in the ammonia injection pipeline system have a fixed model. The resistance parameter preset module is electrically connected to the controller and is used to preset and store the resistance coefficients of all pipe fittings in the ammonia injection pipeline system and the friction resistance parameters of each pipeline to form a resistance parameter database; the resistance coefficients are obtained by querying the pipe fitting model and calculating using fluid mechanics theory. The flow detection module includes flow sensors installed on the main ammonia injection pipe, each ammonia injection branch pipe, and each ammonia injection pipeline, for collecting real-time ammonia injection flow and transmitting it to the controller. The ammonia injection regulating module includes electrically adjustable valves installed on each ammonia injection branch pipe and each ammonia injection pipeline. The electrically adjustable valves are driven by the controller to adjust the opening degree. The NOx detection module is used to collect NOx concentration data at the inlet and outlet of the SCR reactor and transmit it to the controller; The controller is configured to: The total ammonia injection flow rate requirement is determined based on the NOx concentration data and allocated to each ammonia injection branch and ammonia injection pipeline to determine the target ammonia injection flow rate; By calling the resistance data in the resistance parameter database and combining it with the fluid dynamics flow-resistance relationship, the initial value of the electric regulating valve opening required for each ammonia injection branch and ammonia injection pipeline to reach the target ammonia injection flow rate is calculated. Drive the electric regulating valve to reach the initial opening value to complete the initial ammonia injection quantity distribution; The system receives the actual ammonia injection flow rate from the flow detection module, compares it with the target ammonia injection flow rate, and dynamically adjusts the opening of each electric regulating valve.

2. The ammonia injection control system for the SCR zone of a coal-fired power unit according to claim 1, characterized in that, The resistance calculation formula built into the resistance parameter preset module includes: Friction resistance formula: Local resistance formula: Formula for total resistance of a branch: ; in, For friction resistance, This is the friction coefficient. This refers to the length of the straight section of the pipeline. The inner diameter of the pipe. The ammonia flow rate is... It is the acceleration due to gravity. For local resistance, This is the local drag coefficient. The total resistance of the ammonia injection branch pipe or ammonia injection pipeline. The sum of the frictional resistances along all straight sections of this branch is: This is the sum of the local resistances of all pipe fittings in this branch.

3. The ammonia injection control system for the SCR zone of a coal-fired power unit according to claim 2, characterized in that, The friction coefficient The local resistance coefficient is determined based on the pipe material and inner wall roughness. Determined based on the pipe fitting model and specifications.

4. The ammonia injection control system for the SCR zone of a coal-fired unit according to claim 1, characterized in that, The resistance parameter preset module has a reserved resistance coefficient correction interface for periodically calibrating and updating the resistance parameter database.

5. The ammonia injection control system for the SCR zone of a coal-fired unit according to claim 1, characterized in that, The resistance parameter preset module is also used to automatically generate a new resistance parameter database by inputting the pipe fitting model, pipe length and inner diameter parameters of the updated pipeline after the ammonia injection pipeline system is upgraded, using the built-in resistance calculation formula.

6. The ammonia injection control system for the SCR zone of a coal-fired unit according to claim 1, characterized in that, The controller is a PLC controller with a built-in flow-resistance correlation algorithm and functions for data storage, logic operation, and fault alarm.

7. The ammonia injection control system for the SCR zone of a coal-fired power unit according to claim 1, characterized in that, The relationship between the opening degree and flow rate of the electric regulating valve is pre-entered into the controller along with the resistance data in the resistance parameter preset module.

8. The ammonia injection control system for the SCR zone of a coal-fired power unit according to claim 1, characterized in that, When dynamically correcting the opening of each electrically adjustable valve, the controller predicts the direction of valve opening adjustment based on the trend of resistance change.

9. A control method for an ammonia injection control system in the SCR zone of a coal-fired power unit, characterized in that, The method is applied to the ammonia injection control system of the SCR zone of a coal-fired unit as described in any one of claims 1-8, comprising: The controller calculates the total ammonia injection flow rate requirement based on the target values ​​of NOx concentration at the inlet and outlet of the SCR reactor and the unit load, and determines the target ammonia injection flow rate for each ammonia injection branch and each ammonia injection pipeline in conjunction with the denitrification requirements of the SCR reactor area corresponding to each ammonia injection pipeline. The controller calls the resistance parameter database stored in the resistance parameter preset module to obtain the total resistance data of each ammonia injection branch and ammonia injection pipeline. Combining the relationship that the flow rate is inversely proportional to the square root of the resistance in fluid mechanics, it calculates the initial value of the electric regulating valve opening required for each ammonia injection branch and ammonia injection pipeline to reach the target ammonia injection flow rate. The controller drives the electric regulating valves on each ammonia injection branch pipe and ammonia injection pipeline to the initial opening value, thus completing the initial ammonia injection quantity distribution. The controller receives the actual ammonia injection flow rate of each ammonia injection branch and ammonia injection pipeline collected in real time by the flow detection module, compares the actual ammonia injection flow rate with the target ammonia injection flow rate, and dynamically corrects the opening degree of each electric regulating valve in combination with the resistance change trend.

Images