A boiler flue gas temperature active control system and method based on adjustable flue gas flow area

Abstract

This invention discloses an active control system and method for boiler flue gas temperature based on adjustable flue gas flow area. The system includes a boiler, an air preheater, and a control unit. A flue gas flow area adjustment device is installed in the flue gas side duct of the air preheater. The flue gas flow area adjustment device is signal-connected to the control unit. The control unit acquires the boiler's flue gas temperature signal and compares it with a preset target temperature. When the flue gas temperature is lower than the target temperature, the control unit drives the flue gas flow area adjustment device to reduce the effective flow cross-sectional area of ​​the flue gas side duct. This invention overcomes technical concerns about the reliability of active intervention on the flue gas side by directly adjusting the flue gas flow area, fundamentally solving the problem of low-temperature corrosion and blockage of the air preheater under low load.

Description

Technical Field

[0001] This invention belongs to the technical field of thermal power boilers and large industrial boilers, specifically relating to an active control system and method for boiler flue gas temperature based on adjustable flue gas flow area. Background Technology

[0002] In coal-fired boilers, especially those equipped with SCR denitrification systems, the flue gas temperature drops significantly when the unit operates at low loads during deep peak shaving. Excessively low flue gas temperature causes sulfuric acid vapors in the flue gas to condense on the low-temperature heat exchange elements of the air preheater, forming a viscous sulfuric acid film. This film then combines with fly ash and captures ammonia to form ammonium bisulfate (ABS), resulting in severe ash accumulation, corrosion, and blockage of the air preheater.

[0003] Currently, the industry lacks effective proactive control methods for flue gas temperature. Flue gas temperature is primarily determined by boiler load and coal quality, becoming a passively changing parameter. Faced with the corrosion risks caused by fluctuations in both load and coal quality, existing technologies often prove ineffective or unsuitable due to a lack of proactive intervention capabilities, leading to a continued worsening of air preheater ash accumulation, corrosion, and blockage problems. Existing technologies, such as steam heaters and hot air recirculation, are all "indirect" or "bypass" heating solutions, essentially still passive responses or crude adjustments. They essentially increase temperature by injecting additional energy into the system or sacrificing system efficiency, which not only increases energy consumption but also fails to meet the demands of proactive and precise control in rapidly changing peak-shaving conditions.

[0004] For a long time, there has been a general consensus in this field that severe low-temperature corrosion is highly likely to occur on the flue gas side under low-load operating conditions. Therefore, if a movable regulating mechanism is installed on the flue gas side, its reliability in a highly corrosive environment over a long period is difficult to guarantee, posing a high risk of damage. Based on this technical concern, the technical approach of "installing regulating devices on the flue gas side and implementing active control" has not been considered a feasible solution by the industry. Influenced by this concept, engineers generally tend to adopt indirect control measures on the air side to avoid the potential risks of direct intervention on the flue gas side. This inertia in technical approaches has led to a long-term deviation of research and development from the direct adjustment of flue gas side thermal parameters, leaving a long-standing "direct" control strategy capable of precisely controlling core variables to regulate exhaust gas temperature in a state of flux. Summary of the Invention

[0005] The purpose of this invention is to provide an active control system and method for boiler flue gas temperature based on adjustable flue gas flow area. By actively adjusting the flue gas flow area, it overcomes technical concerns about the reliability of active intervention on the flue gas side and fundamentally solves the problem of low-temperature corrosion and blockage of air preheaters under low load.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] An active control system for boiler flue gas temperature based on adjustable flue gas flow area includes a boiler, an air preheater, and a control unit. A flue gas flow area adjustment device is installed in the flue gas side flue of the air preheater. The flue gas flow area adjustment device is signal-connected to the control unit. The control unit acquires the boiler's flue gas temperature signal and compares it with a preset target temperature. When the flue gas temperature is lower than the target temperature, the control unit activates the flue gas flow area adjustment device to reduce the effective flow cross-sectional area of ​​the flue gas side flue.

[0008] Furthermore, the air preheater contains a rotatable air preheater rotor. The flue gas side duct of the air preheater includes an inlet flue and an outlet flue. The inlet flue is divided into several independent inlet flue gas zones along the radial direction of the air preheater rotor, and the outlet flue is divided into several independent outlet flue gas zones along the radial direction of the air preheater rotor, corresponding to the inlet flue gas zones. A flue gas flow area adjustment device is provided in both the inlet and outlet flues. The flue gas flow area adjustment device has a zoned structure and includes multiple independently controllable baffle mechanisms arranged radially along the air preheater rotor. The baffle mechanism includes an inlet adjustment mechanism set in each independent inlet flue gas zone on the flue gas inlet side and an outlet adjustment mechanism set in each independent outlet flue gas zone on the flue gas outlet side. The control unit is configured to individually control each inlet adjustment mechanism or outlet adjustment mechanism, or to control the inlet and outlet adjustment mechanisms corresponding to the same radial zone in a coordinated manner.

[0009] Furthermore, temperature sensors are installed in different zones of the outlet flue gas zone to collect the temperature at different radial positions of the air preheater rotor. The temperature sensors are connected to the control unit. The control unit is configured to: acquire the temperature sensor signals of different zones in real time when executing control commands, analyze the radial temperature distribution of the air preheater rotor, preferentially select the flue gas channel corresponding to the lowest temperature zone, and drive the flue gas flow area adjustment device corresponding to the target channel to reduce the effective cross-sectional area of ​​the flue gas flow.

[0010] Furthermore, the control unit is configured to: receive boiler load signals in real time; when the control unit detects that the boiler load is higher than a preset load threshold, forcibly restore the flue gas flow area adjustment device to the fully open state and exit the active control mode; when the boiler load is lower than the preset load threshold, drive the flue gas flow area adjustment device to operate, so as to reduce the effective flow cross-sectional area of ​​the flue gas side flue.

[0011] Furthermore, the control unit is configured to: when the boiler load is lower than or equal to a preset load threshold, compare the real-time boiler load with the preset load thresholds of multiple zones, and dynamically adjust the action priority or adjustment range of the flue gas flow area regulating device.

[0012] Furthermore, an SO2 concentration analyzer connected to the control unit is installed on the outlet flue. The control unit is configured to: based on the real-time collected SO2 concentration signal, notify the built-in acid dew point calculation model to calculate the dynamic acid dew point temperature T_dp, and set the target temperature T_target as the sum of T_dp and the preset safety margin ΔT, i.e., T_target = T_dp + ΔT, thus constructing a dynamic safety window with T_target as the lower limit.

[0013] This invention also provides an active control method for boiler flue gas temperature based on adjustable flue gas flow area, comprising the following steps:

[0014] Step S201: After the system is powered on or receives a start command, the control unit enters the running state;

[0015] Step S202: The system enters the real-time data monitoring cycle and starts the active control mode. The control unit continuously collects boiler load signal, flue gas temperature signal, SO2 concentration signal in flue gas and air preheater rotor radial temperature signal.

[0016] Step S203: Perform boiler load safety judgment. The control unit compares the real-time boiler load with the preset load threshold. If the load is higher than the preset load threshold, the control unit forces all flue gas flow area adjustment devices to return to the fully open position and exits the active control mode. If the load is lower than or equal to the preset load threshold, then proceed to step S204.

[0017] Step S204: Calculate the dynamic acid dew point based on the real-time SO2 concentration. The control unit calls its internally stored acid dew point calculation model and calculates the dynamic acid dew point temperature T_dp under the current operating conditions, with the real-time SO2 concentration as the core input parameter.

[0018] Step S205: Construct a dynamic safety window by adding a preset safety margin ΔT to the dynamic acid dew point temperature T_dp to obtain the lower limit value T_target of the dynamic safety window: T_target = T_dp + ΔT;

[0019] Step S206: Perform a safety judgment on the exhaust temperature. The control unit compares the real-time exhaust temperature with the lower limit value T_target of the dynamic safety window. If the real-time exhaust temperature is higher than T_target, proceed to step S207; otherwise, proceed to step S208.

[0020] Step S207: The control unit drives the flue gas flow area adjustment device back to the fully open position, and then returns to step S202;

[0021] Step S208: Execute the optimal zoning combination strategy. The control unit analyzes the radial temperature distribution of the air preheater rotor, identifies the area with the lowest temperature, and then drives the flue gas flow area adjustment device corresponding to the target low temperature area to reduce the flow area of ​​that area through the control action of the control unit.

[0022] The corresponding flue gas flow area adjustment device actions include: individually closing the inlet adjustment mechanism corresponding to the target zone, individually closing the outlet adjustment mechanism corresponding to the target zone, or jointly closing the inlet and outlet adjustment mechanisms corresponding to the target zone.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] This invention overcomes technical concerns about the reliability of proactive flue gas flow area by directly controlling the flue gas flow area. It involves installing a flue gas flow area adjustment device on the flue gas side, where the control unit acquires the boiler's exhaust temperature signal and compares it with a preset target temperature. When the exhaust temperature is lower than the target temperature, the control unit sends a control signal to the flue gas flow area adjustment device, which then reduces the effective cross-sectional area of ​​the flue gas passage. This proactive adjustment of the flue gas flow area overcomes these concerns and fundamentally solves the problems of low-temperature corrosion and blockage in air preheaters under low loads.

[0025] Furthermore, this invention employs a zoned structure for the flue gas passages on the inlet and outlet sides of the air preheater. The control unit can individually control each inlet or outlet regulating mechanism, or it can coordinately control the inlet and outlet regulating mechanisms corresponding to the same radial zone. This configuration provides two differentiated active control strategies: in the individual control mode, the inlet and outlet regulating mechanisms can serve as backups for each other, maintaining regulation by the other mechanism when one side fails, thus significantly improving the system's operational reliability; in the coordinated control mode, a "physical isolation zone" is constructed inside the air preheater through "double-sided coordinated closure of inlet and outlet." This is not a simple superposition of the actions of two dampers, but rather, through a synergistic effect, fundamentally suppresses the lateral airflow that causes traditional solutions to fail, ensuring that the temperature of the shielded low-temperature zone can be effectively and reliably raised.

[0026] Furthermore, this invention, by setting temperature sensors in different zones of the outlet flue gas zoning, allows the control unit to acquire temperature sensor signals from different zones in real time, analyze the radial temperature distribution of the air preheater rotor, prioritize the flue gas channel corresponding to the lowest temperature zone, and drive the flue gas flow area adjustment device corresponding to the target channel to reduce the effective cross-sectional area of ​​the flue gas flow. Through zoned control and the strategy of prioritizing the shielding of the lowest temperature zone, the most effective flue gas temperature rise can be achieved with minimal increase in ventilation resistance and minimal impact on the induced draft fan's power consumption, demonstrating intelligent and precise control. While ensuring corrosion safety is fundamentally addressed, this invention introduces a dynamic safety window based on SO2 concentration, enabling the system to adapt to changes in coal quality, avoiding energy waste caused by maintaining excessively high flue gas temperatures at low sulfur content, and achieving an optimal balance between safety and economy. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the overall architecture of the boiler flue gas temperature active control system of the present invention;

[0028] Figure 2 This is a schematic diagram of the dynamic security window construction module used in this embodiment of the invention.

[0029] In the diagram: 100-Boiler; 200-Air preheater; 201-Air preheater rotor; 300-Control unit; 400-Inlet flue; 401-First inlet flue gas zone, 402-Second inlet flue gas zone, 403-Third inlet flue gas zone; 501-First zone flue gas inlet regulating mechanism, 502-Second zone flue gas inlet regulating mechanism, 503-Third zone flue gas inlet regulating mechanism; 600-Outlet flue; 601-First outlet flue gas zone, 602-Second outlet flue gas zone, 603- Third outlet flue gas zone; 604-First zone flue gas outlet temperature sensor, 605-Second zone flue gas outlet temperature sensor, 606-Third zone flue gas outlet temperature sensor; 609-SO2 concentration analyzer; 701-First zone flue gas outlet regulating mechanism, 702-Second zone flue gas outlet regulating mechanism, 703-Third zone flue gas outlet regulating mechanism; 801-Primary air inlet duct; 802-Secondary air inlet duct; 803-Primary air outlet duct; 804-Secondary air outlet duct. Detailed Implementation

[0030] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0031] like Figure 1As shown in this embodiment, a boiler flue gas temperature active control system based on adjustable flue gas flow area includes a boiler 100, an air preheater 200, and a control unit 300. The air preheater 200 serves as the core heat exchange device, and its interior contains a rotatable air preheater rotor 201. A flue gas flow area adjustment device is installed in the flue gas side duct of the air preheater 200. The flue gas flow area adjustment device is signal-connected to the control unit 300. The control unit 300 uses a distributed control system (DCS) or a dedicated programmable logic controller (PLC) to implement the control function. The implementation of the "control command" includes, but is not limited to, the following two modes: 1. Automatic control mode, in which the control unit 300 directly sends a drive signal to the electric or pneumatic actuator of the flue gas flow area adjustment device; 2. Monitoring and command mode, in which the control unit 300 displays the flue gas temperature status, target temperature, and control suggestions to the operator through a human-machine interface (HMI), and receives the operation signal manually issued by the operator according to the command, thereby completing the control of the adjustment device. Regardless of the mode used, the active regulation of the flue gas temperature is achieved through the core control function of the control unit 300. The control unit 300 acquires the flue gas temperature signal of the boiler 100 and compares it with the preset target temperature. When the flue gas temperature is lower than the target temperature, the control unit 300 sends a control signal to the flue gas flow area adjustment device, which reduces the effective flow cross-sectional area of ​​the flue gas channel, thereby increasing the flue gas temperature.

[0032] The flue gas side duct of the air preheater 200 includes an inlet flue gas duct 400 and an outlet flue gas duct 600. The inlet flue gas duct 400 is radially divided into several independent inlet flue gas zones along the air preheater rotor 201: a first inlet flue gas zone 401, a second inlet flue gas zone 402, and a third inlet flue gas zone 403. The outlet flue gas duct 600 is radially divided into several independent outlet flue gas zones along the air preheater rotor 201: a first outlet flue gas zone 601, a second outlet flue gas zone 602, and a third outlet flue gas zone 603, and these zones correspond spatially to the inlet flue gas zones.

[0033] Both the inlet flue duct 400 and the outlet flue duct 600 are equipped with flue gas flow area regulating devices. These devices have a zoned structure, comprising multiple independently controllable baffle mechanisms arranged radially along the air preheater rotor 201. A "zone" refers to a region divided radially along the air preheater rotor; its shape can be fan-shaped, annular, or a combination of both. The baffle mechanism includes inlet regulating mechanisms located within each independent inlet flue gas zone on the inlet side: a first zone flue gas inlet regulating mechanism 501, a second zone flue gas inlet regulating mechanism 502, and a third zone flue gas inlet regulating mechanism 503, used to independently control the flue gas intake of each zone; and outlet regulating mechanisms located within each independent outlet flue gas zone on the outlet side: a first zone flue gas outlet regulating mechanism 701, a second zone flue gas outlet regulating mechanism 702, and a third zone flue gas outlet regulating mechanism 703, which operate in conjunction with the inlet regulating mechanisms for inlet flue gas control and outlet flue gas monitoring and control, respectively.

[0034] The control unit 300 is configured to individually control each inlet or outlet regulating mechanism, or to control the inlet and outlet regulating mechanisms corresponding to the same radial zone in a coordinated manner. This configuration provides two differentiated active control strategies: in the individual control mode, the inlet and outlet regulating mechanisms can serve as backups for each other, with the other mechanism maintaining regulation in case of failure on one side, thus significantly improving the system's operational reliability; in the coordinated control mode, a "physical isolation zone" is constructed inside the air preheater rotor 201 through "dual-sided coordinated closure of inlet and outlet." This is not a simple superposition of the actions of two baffles, but rather, through a synergistic effect, fundamentally suppresses the lateral airflow that causes traditional solutions to fail, ensuring that the temperature of the shielded low-temperature zone can be effectively and reliably raised.

[0035] The "dual-sided shut-off of inlet and outlet" strategy aims to artificially create a relatively sealed "isolation chamber" inside the air preheater rotor 201. This mechanism fundamentally suppresses lateral internal airflow from adjacent high-temperature zones to the target low-temperature zone caused by pressure differential. Lateral airflow is a key reason for localized low-temperature corrosion in the air preheater and the failure of traditional single-sided regulation methods. Through physical isolation, the heat of the target low-temperature zone is effectively prevented from being continuously carried away by the interfering flue gas (i.e., heat dilution), allowing the heat energy of the flue gas flowing through the other open high-temperature zones to be efficiently and specifically used to heat the low-temperature heat exchange elements in the isolation zone, thereby enabling their temperature to be rapidly and reliably raised to a safe level. This is an effect that cannot be achieved by single-sided regulation or simple action superposition.

[0036] Temperature sensors are installed in different zones of the outlet flue gas section to collect the temperature at different radial positions of the air preheater rotor 201: a first zone flue gas outlet temperature sensor 604, a second zone flue gas outlet temperature sensor 605, and a third zone flue gas outlet temperature sensor 606. The temperature sensors are connected to the control unit 300. The control unit 300 is further configured to: acquire the temperature sensor signals of different zones in real time when executing control commands, analyze the radial temperature distribution of the air preheater rotor 201, prioritize the flue gas channel corresponding to the lowest temperature area (the heat exchange element in this area is the coldest and has the highest corrosion risk), and drive the flue gas flow area adjustment device corresponding to the target channel to reduce the effective cross-sectional area of ​​the flue gas flow.

[0037] An SO2 concentration analyzer 609, which is connected to the control unit 300, is installed on the outlet flue 600 to continuously and in real time measure the SO2 concentration signal in the flue gas. The control unit 300 is further configured to: based on the real-time collected SO2 concentration signal, notify the built-in acid dew point calculation model to calculate the dynamic acid dew point temperature T_dp, and set the target temperature T_target to the sum of T_dp and the preset safety margin ΔT, that is, T_target = T_dp + ΔT.

[0038] The control unit 300 is further configured to receive boiler load signals in real time, which originate from key feedforward signals of the power plant's main control system. When the control unit 300 detects that the boiler load is higher than a preset load threshold, it forcibly restores the flue gas flow area regulating device to its fully open state and exits the active control mode. When the boiler load is lower than the preset load threshold, it drives the flue gas flow area regulating device to operate, thereby reducing the effective flow cross-sectional area of ​​the flue gas side duct. Furthermore, when the boiler load is lower than or equal to the preset load threshold, the real-time boiler load is compared with the preset load thresholds of multiple zones, and the operating priority or adjustment range of the flue gas flow area regulating device is dynamically adjusted.

[0039] The control unit 300 continuously receives boiler load signals, outlet temperature sensor signals from each zone, and SO2 concentration signals from the outlet flue 600. Based on the real-time SO2 concentration, it calculates the dynamic acid dew point temperature in real time and adds a safety margin to construct a dynamic safety window with T_target as the lower limit.

[0040] The acid dew point calculation model can be performed using a modified form of the Haase & Borgmann empirical formula, which is well-known to those skilled in the art.

[0041] T_dp = 203.25 + 27.6 * log(P H2O ) + 10.83 * log(P SO3) + 1.06 * (log(P SO3 )+ 8)^2.19

[0042] Among them, P H2O P is the partial pressure of water vapor. SO3 This represents the partial pressure of sulfur trioxide. P SO3 The acid dew point temperature can be estimated using real-time measurements of SO2 concentration, excess air coefficient (oxygen signal), and fuel characteristic parameters (such as sulfur content). Alternatively, other empirical formulas, pre-defined lookup tables, or machine learning models trained based on historical unit data can be used to calculate the dynamic acid dew point temperature.

[0043] The active control system for flue gas temperature also includes an air-side system installed on the air side of the air preheater rotor 201. The air-side system includes a primary air system and a secondary air system. The primary air system includes a primary air inlet duct 801 and an outlet duct 803, and the secondary air system includes a secondary air inlet duct 802 and an outlet duct 804.

[0044] An active control method for boiler flue gas temperature based on adjustable flue gas flow area operates in the control unit 300 of the intelligent control layer, and its logic flow is as follows:

[0045] Step S201: After the system is powered on or a start command is received, the control unit 300 enters the running state;

[0046] Step S202: The system enters the real-time data monitoring cycle and starts the active control mode. The control unit 300 continuously collects the boiler load signal, flue gas temperature signal, SO2 concentration signal in flue gas and radial temperature signal of air preheater rotor.

[0047] Step S203: Perform boiler load safety judgment. The control unit 300 compares the real-time boiler load with the preset load threshold (e.g., 70% of the rated load). If the load is higher than the preset load threshold, the control unit 300 forces all flue gas flow area adjustment devices to return to the fully open position and exits the active control mode. If the load is lower than or equal to the preset load threshold, then proceed to step S204.

[0048] Step S204: Calculate the dynamic acid dew point based on the real-time SO2 concentration. The control unit 300 calls its internally stored acid dew point calculation model and calculates the dynamic acid dew point temperature T_dp under the current operating conditions with the real-time SO2 concentration as the core input parameter.

[0049] Step S205: Construct a dynamic safety window by adding a preset safety margin ΔT (e.g., 15℃) to the dynamic acid dew point temperature T_dp to obtain the lower limit value T_target of the dynamic safety window: T_target = T_dp + ΔT;

[0050] Step S206: Perform a safety judgment on the exhaust temperature. The control unit 300 compares the real-time exhaust temperature with the lower limit value T_target of the dynamic safety window. If the real-time exhaust temperature is higher than T_target, then proceed to step S207; otherwise, proceed to step S208.

[0051] Step S207: The control unit 300 drives the flue gas flow area adjustment device back to the fully open position, and then returns to step S202;

[0052] Step S208: Execute the optimal zoning combination strategy. The control unit 300 analyzes the radial temperature distribution of the air preheater rotor, identifies the area with the lowest temperature, and then drives the flue gas flow area adjustment device corresponding to the target low temperature area to reduce the flow area of ​​that area through the control action of the control unit 300.

[0053] The corresponding flue gas flow area adjustment device actions include: individually closing the inlet adjustment mechanism corresponding to the target zone, individually closing the outlet adjustment mechanism corresponding to the target zone, or jointly closing the inlet and outlet adjustment mechanisms corresponding to the target zone.

[0054] It should be noted that the control unit 300 achieves active and adaptive control of the flue gas temperature through "feedforward (based on load and SO2 concentration) + feedback (based on flue gas temperature)" by cyclically executing the above steps. This complete process confirms the feasibility of this invention as a "direct" and "active" solution. Through zoned and refined active intervention, it proactively, safely, and economically solves the industry-wide problem of low-temperature corrosion in air preheaters in a way that minimizes the impact on the overall system operation.

[0055] The core controller of control unit 300 has a pre-stored acid dew point calculation subroutine. The calculation logic flow executed by this subroutine is as follows: Figure 2 As shown.

[0056] Combination Figure 2 The process for building a dynamic security window is explained below:

[0057] Step S301: Start building the dynamic security window. This process is triggered by step S204.

[0058] Step S302: Read real-time input parameters. The control unit 300 reads the real-time collected SO2 concentration signal and oxygen signal from the cache or direct interface as the core calculation basis.

[0059] Step S303: The acid dew point calculation model is invoked, and the control unit 300 prepares to execute the calculation;

[0060] Step S304: Perform model type determination. Based on system preset or adaptive selection, determine which model to use for calculation. This invention is compatible with multiple models to achieve flexibility.

[0061] Step S305: If it is determined that an "empirical formula" is to be used, then substitute the parameters such as SO2 concentration and oxygen content into the preset empirical formula (such as the Belman formula or its modified formula) for calculation;

[0062] Step S306: If it is determined that a "lookup table" is used, the SO2 concentration is used as the main index to query the dew point temperature lookup table compiled in advance based on experimental data or typical operating conditions to obtain the corresponding T_dp estimate.

[0063] Step S307: If it is determined that a "machine learning model" is used, the input parameters (SO2 concentration, oxygen content, etc.) are fed into the trained machine learning model (such as neural network, support vector machine, etc.) for inference, and the model outputs the predicted dew point temperature;

[0064] Step S308: Obtain the final dynamic acid dew point temperature T_dp through any of the above paths.

[0065] Step S309: Read the preset safety margin ΔT. This value can be a fixed value (such as 15℃) or it can be finely adjusted according to the working conditions.

[0066] Step S310: Calculate the lower limit of the dynamic safety window and perform the operation using an adder: T_target = T_dp + ΔT;

[0067] Step S311: Output the lower limit of the dynamic safety window T_target. This result will be sent to the main process of the intelligent control method for boiler flue gas temperature, serving as the output of step S205 and the judgment criterion for step S206.

[0068] This process ensures that the dynamic safety window is always based on the most reliable real-time SO2 concentration signal and can be adapted to the configuration and accuracy requirements of different power plants through various modeling methods.

[0069] Example of running:

[0070] When the unit is running, the SO2 concentration analyzer measures an SO2 concentration of 2000 mg / m³ in the flue gas. Based on this concentration and the current oxygen level, the control unit 300 calculates the dynamic acid dew point T_dp to be approximately 118°C using a built-in model (e.g., executing the path S304→S305). With a safety margin ΔT = 15°C, the lower limit T_target of the dynamic safety window is set to 133°C.

[0071] At this time, if the actual exhaust temperature is 125℃, the control unit 300 immediately determines that it has left the dynamic safety window, and then starts the control program to close the flue gas baffle, reduce the heat transfer area, and successfully raise and stabilize the exhaust temperature at 135℃, so that it returns to the dynamic safety window.

[0072] Several hours later, the coal combustion in the unit changed, and the SO2 concentration dropped to 800 mg / m³. The control unit 300 recalculated (called again). Figure 2 (Process) The dynamic acid dew point T_dp drops to approximately 105°C. Correspondingly, the dynamic safety window shifts downwards, and T_target is dynamically adjusted to 120°C. The control unit 300 then instructs the flue gas damper to open wider, allowing more heat exchange and relaxing the control of the exhaust gas temperature to 122°C. This ensures safety while maximizing the recovery of waste heat from the flue gas, thus improving the unit's economic efficiency.

[0073] This embodiment fully demonstrates the significant advantages of the present invention compared to fixed temperature control: by moving the dynamic safety window, it can ensure equipment safety at high SO2 concentrations and avoid unnecessary energy waste at low SO2 concentrations, thus achieving a balance between safety and economy.

[0074] Optimal partition combination and two-sided linkage strategy:

[0075] When the unit is operating at low load and the control system calculates that the exhaust gas temperature needs to be increased, the control unit 300 first analyzes the outlet temperature signal from the rotor radial direction.

[0076] Taking a single control process as an example, the analysis results show that the temperature of the second outlet flue gas zone 602 is the lowest, at only 110℃, while the temperatures of the outer first outlet flue gas zone 601 and the third outlet flue gas zone 603 are 125℃ and 135℃, respectively.

[0077] At this point, the control unit 300 activates the "precision strike" mode:

[0078] Diagnosis: The low-temperature outlet zone was identified as the second outlet flue gas zone 602;

[0079] Decision: It was determined that intervention was needed for the entire annular channel corresponding to the low-temperature zone (i.e., the second inlet flue gas zone 402 and the second outlet flue gas zone 602);

[0080] Execution: The control unit 300 issues a coordination command to simultaneously shut down the second zone flue gas inlet regulating mechanism 502 and the second zone flue gas outlet regulating mechanism 702 corresponding to the target channel.

[0081] This "dual-sided shut-off of inlet and outlet" strategy artificially constructs a relatively sealed "isolation chamber" inside the air preheater rotor 201, fundamentally suppressing lateral internal airflow from adjacent high-temperature zones to the target low-temperature zone caused by pressure differential. Through physical isolation, the dilution of heat by crossflow is effectively prevented, allowing the flue gas heat energy flowing through the other open high-temperature zones to be efficiently and specifically used to heat the low-temperature heat exchange elements in the isolation zone, rapidly and reliably raising their temperature to a safe level.

[0082] In this embodiment, the system achieves the goal of raising the flue gas temperature from 120°C to 132°C by selectively shielding one zone (one-third of the zone), resulting in a significant temperature increase. Simultaneously, because the channels in other high-temperature zones remain largely open, the overall ventilation resistance of the boiler and the increase in induced draft fan power consumption are minimized.

[0083] This embodiment fully demonstrates the intelligence and precision of the control strategy of the present invention. It not only solves the safety problem, but also achieves the most effective temperature rise at the lowest cost through the "asymmetric" adjustment and "dual-sided linkage isolation" mechanism.

[0084] It should be noted that the method of increasing exhaust gas temperature by adjusting the flue gas flow area described in this invention is essentially based on the following: when the flue gas flow rate remains essentially constant, reducing the flow area directly leads to an increase in flue gas velocity and a change in heat transfer intensity per unit area; simultaneously, the air preheater heat transfer area corresponding to the adjusted zone is effectively isolated, reducing the total effective heat transfer area. The combined effect of increased flow velocity and reduced heat transfer area ultimately results in a decrease in the overall heat release on the flue gas side, thereby achieving an increase in exhaust gas temperature.

[0085] Therefore, regardless of whether the control system's direct judgment is based on flue gas temperature, boiler load, or other parameters, as long as its technical means involves changing the effective flow cross-sectional area by driving the zonal flue gas flow area adjustment device, it will ultimately affect the flue gas temperature and the low-temperature zone temperature of the air preheater through the aforementioned physical process. Any technical solution based on this core means to adjust the thermal state of the boiler tail flue gas (including but not limited to increasing flue gas temperature, preventing low-temperature corrosion, and alleviating ash accumulation) is an application of the zonal adjustment system and its core principles provided by this invention.

Claims

1. A boiler flue gas temperature active control system based on adjustable flue gas flow area, characterized in that, The system includes a boiler (100), an air preheater (200), and a control unit (300). A flue gas flow area adjustment device is installed in the flue gas side flue of the air preheater (200). The flue gas flow area adjustment device is connected to the control unit (300) by signal. The control unit (300) obtains the flue gas temperature signal of the boiler (100) and compares it with the preset target temperature. When the flue gas temperature is lower than the target temperature, the control unit (300) controls the flue gas flow area adjustment device to reduce the effective flow cross-sectional area of ​​the flue gas side flue. The air preheater (200) contains a rotatable air preheater rotor (201). The flue gas side duct of the air preheater (200) includes an inlet flue (400) and an outlet flue (600). The inlet flue (400) is radially divided into several independent inlet flue gas zones along the air preheater rotor (201), and the outlet flue (600) is radially divided into several independent outlet flue gas zones along the air preheater rotor (201), corresponding to the inlet flue gas zones. A flue gas flow area adjustment device is provided in both the inlet flue (400) and the outlet flue (600). The flue gas flow area adjustment device is a partitioned structure, including multiple independently controllable baffle mechanisms arranged radially along the air preheater rotor (201). The baffle mechanism includes an inlet adjustment mechanism set in each independent inlet flue gas zone on the flue gas inlet side, and an outlet adjustment mechanism set in each independent outlet flue gas zone on the flue gas outlet side. The control unit (300) is configured to control the inlet and outlet adjustment mechanisms corresponding to the same radial zone in a coordinated manner. Temperature sensors are installed in different zones of the outlet flue gas zone to collect the temperature of the air preheater rotor (201) at different radial positions. The temperature sensors are connected to the control unit (300) by signal. The control unit (300) is configured to reduce the effective flow cross-sectional area of ​​the flue gas side duct as follows: when executing the control command, the temperature sensor signals of different zones are acquired in real time, the radial temperature distribution of the air preheater rotor (201) is analyzed, the flue gas channel corresponding to the lowest temperature area is selected, and the flue gas flow area adjustment device corresponding to the target channel is driven to operate: the inlet and outlet adjustment mechanisms corresponding to the target zone are closed in conjunction.

2. The boiler flue gas temperature active control system based on adjustable flue gas flow area according to claim 1, characterized in that, The control unit (300) is configured to receive boiler load signals in real time, and when the control unit (300) detects that the boiler load is higher than the preset load threshold, it forcibly restores the flue gas flow area adjustment device to the fully open state and actively exits the control mode in a safety interlock manner. When the boiler load is lower than the preset load threshold, the flue gas flow area adjustment device is activated to reduce the effective flow cross-sectional area of ​​the flue gas side duct.

3. The boiler flue gas temperature active control system based on adjustable flue gas flow area according to claim 2, characterized in that, The control unit (300) is configured to: when the boiler load is lower than or equal to a preset load threshold, compare the real-time boiler load with the preset load thresholds of multiple zones, and dynamically adjust the action priority or adjustment range of the flue gas flow area adjustment device.

4. The boiler flue gas temperature active control system based on adjustable flue gas flow area according to claim 3, characterized in that, An SO2 concentration analyzer (609) connected to the control unit (300) is installed on the outlet flue (600). The control unit (300) is configured to: based on the real-time collected SO2 concentration signal, notify the built-in acid dew point calculation model to calculate the dynamic acid dew point temperature T_dp, and set the target temperature T_target to the sum of T_dp and the preset safety margin ΔT, i.e., T_target = T_dp + ΔT, to construct a dynamic safety window with T_target as the lower limit.

5. A method for active control of boiler flue gas temperature based on adjustable flue gas flow area, characterized in that, Applied to the system of claim 4, the method includes the following steps: Step S201: After the system is powered on or receives a start command, the control unit (300) enters the running state; Step S202: The system enters the real-time data monitoring cycle and starts the active control mode. The control unit (300) continuously collects the boiler load signal, flue gas temperature signal, SO2 concentration signal in flue gas and radial temperature signal of air preheater rotor. Step S203: Perform boiler load safety judgment. The control unit (300) compares the real-time boiler load with the preset load threshold. If the load is higher than the preset load threshold, the control unit (300) forces all flue gas flow area adjustment devices to return to the fully open position and exits the active control mode. If the load is lower than or equal to the preset load threshold, then step S204 is executed. Step S204: Calculate the dynamic acid dew point based on the real-time SO2 concentration. The control unit (300) calls its internally stored acid dew point calculation model and calculates the dynamic acid dew point temperature T_dp under the current operating conditions with the real-time SO2 concentration as the core input parameter. Step S205: Construct a dynamic safety window by adding a preset safety margin ΔT to the dynamic acid dew point temperature T_dp to obtain the lower limit value T_target of the dynamic safety window: T_target = T_dp + ΔT; Step S206: Perform a safety judgment on the exhaust temperature. The control unit (300) compares the real-time exhaust temperature with the lower limit value T_target of the dynamic safety window. If the real-time exhaust temperature is higher than T_target, then proceed to step S207; otherwise, proceed to step S208. Step S207: The control unit (300) drives the flue gas flow area adjustment device back to the fully open position, and then returns to step S202; Step S208: Execute the optimal partition combination strategy. The control unit (300) analyzes the radial temperature distribution of the air preheater rotor, identifies the area with the lowest temperature, and then drives the flue gas flow area adjustment device corresponding to the target low temperature area to reduce the flow area of ​​that area through the control action of the control unit (300). The corresponding flue gas flow area adjustment device operates by: shutting down the inlet and outlet adjustment mechanisms corresponding to the target zone.

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