Low-load boiler flue gas recirculation collaborative control method and system

Abstract

The application discloses a kind of low load boiler flue gas recirculation collaborative control method and system, wherein the method comprises: the flue gas pipeline of boiler output is distributed as two flue gas pipelines;For the first flue gas pipeline, the linear interpolation formula of benchmark flue gas recirculation rate is constructed, and the flue gas recirculation rate is dynamically corrected based on load-steam temperature coupling coefficient and benchmark flue gas recirculation rate;The first flue gas amount calculation value is calculated based on flue gas recirculation rate, and it is input PID controller to control recirculation fan output;For the second flue gas pipeline branch of coal mill, the oxygen content in coal mill is measured to derive the mixed flue gas oxygen content control value, and the oxygen content PID controller is used to switch control mode to realize oxygen content control, and a dynamic risk assessment model is constructed by introducing combustion condition parameters to realize hierarchical control strategy.The application solves the problem that the traditional flue gas recirculation technology does not combine the explosion-proof and collaborative control of the pulverizing system, and is easy to cause low-temperature corrosion and poor oxygen content regulation flexibility.

Description

Technical Field

[0001] This invention belongs to the field of low-load peak shaving and safety control technology for coal-fired power plant boilers, and specifically relates to a method and system for coordinated control of flue gas recirculation in low-load boilers. Background Technology

[0002] Under low-load operation conditions of coal-fired power plant boilers, the furnace flame temperature decreases, and radiative heat transfer weakens, resulting in insufficient heat absorption by the reheater and difficulty in maintaining the reheat steam temperature at its rated value. Simultaneously, to meet the requirements for stable combustion under low load, the oxygen content often needs to be increased, which in turn promotes the formation of thermal nitrogen oxides (NOx). Furthermore, when the oxygen content in the hot primary air is too high, the volatile matter in the pulverized coal silo can easily reach the explosion limit, posing a significant risk of deflagration to the pulverizing system. To address these issues, traditional flue gas recirculation technologies typically focus only on reheat steam temperature regulation or NOx emission control, failing to incorporate the deflagration prevention requirements of the pulverizing system into the synergistic optimization framework. Moreover, directly returning tail-end flue gas to the furnace can exacerbate low-temperature corrosion, and the system's flexibility in adjusting oxygen content is generally insufficient, making it difficult to balance operational safety, economy, and environmental indicators under low load conditions.

[0003] Chinese patent CN112460576A discloses a boiler flue gas system and method adapted for deep peak shaving. The system includes a connecting channel between the boiler forced draft fan outlet duct and the induced draft fan inlet flue, and a flue gas recirculation loop between the economizer outlet flue and the SOFA (Sodium Air Fusion Assembly) box. The connecting channel is located near the forced draft fan outlet and the induced draft fan inlet. The flue gas recirculation loop is located near the economizer outlet. The flue gas recirculation loop includes a flue gas recirculation fan and a flue gas regulating valve. The flue gas recirculation fan inlet is connected to the economizer outlet flue, and the flue gas recirculation fan outlet is connected to the SOFA nozzle. The flue gas recirculation fan outlet is also connected to the boiler main combustion nozzle via a pipeline. This invention focuses on solving the problem of high NOx concentration at the SCR (Sodium Air Refractory) inlet and does not coordinate with the anti-explosion function of the pulverizing system. Summary of the Invention

[0004] The purpose of this invention is to provide a method and system for coordinated control of flue gas recirculation in low-load boilers, in order to solve the problems of traditional flue gas recirculation technology having limited functions, not being combined with anti-explosion and anti-burning control of the pulverizing system, and being prone to low-temperature corrosion and poor oxygen regulation flexibility.

[0005] The technical solution of the present invention is as follows: On the one hand, the present invention provides a method for coordinated control of flue gas recirculation in a low-load boiler, comprising the following steps: The flue gas output from the boiler is divided into two flue gas pipes, including the first flue gas pipe and the second flue gas pipe. For the first flue gas duct, a data matching table of flue gas recirculation rate and load rate is established to construct a linear interpolation formula for the reference flue gas recirculation rate. The flue gas recirculation rate is dynamically corrected based on the designed load-steam temperature coupling coefficient and the reference flue gas recirculation rate. The first flue gas volume is calculated based on the flue gas recirculation rate, and the first flue gas volume is input into the PID controller to control the output of the recirculation fan. For the second flue gas pipeline, which is a branch of the coal mill, the oxygen content control value of the mixed flue gas is derived by measuring the oxygen content inside the coal mill. Based on the oxygen PID controller, the oxygen regulating valve is controlled by switching the control mode to achieve oxygen control. Then, combustion condition parameters are introduced to construct a dynamic risk assessment model to realize the hierarchical control strategy.

[0006] Preferably, the expression for the load-temperature coupling coefficient of the design is:

[0007] In the formula, This is the load-steam temperature coupling coefficient; Weighted by load factor; Load factor; The baseline load factor; Weighting for reheat steam temperature deviation, ; For reheat steam temperature deviation; The baseline reheat steam temperature deviation.

[0008] Preferably, the dynamic correction of the flue gas recirculation rate based on the designed load-temperature coupling coefficient and the reference flue gas recirculation rate specifically involves:

[0009] In the formula, The corrected flue gas recirculation rate; The baseline flue gas recirculation rate; This is the load-temperature coupling coefficient.

[0010] Preferably, the oxygen quantity control based on the oxygen quantity PID controller switching control mode control of the oxygen quantity regulating valve specifically involves: Under steady-state operation, coal quality fluctuation, and coal supply interruption recovery transition conditions, the oxygen PID controller switches to the corresponding PID tracking, feedforward compensation, and enhanced suppression control modes respectively, controlling the oxygen regulating valve to keep the oxygen content in the mixed flue gas oxygen control value within the set oxygen target value.

[0011] Preferably, the dynamic risk assessment model performs risk assessment based on a deflagration risk index, the formula for which the deflagration risk index is calculated is:

[0012] In the formula, The deflagration risk index; This refers to the mill outlet temperature. The reference mill outlet temperature; This is a scaling temperature difference correction factor; Oxygen content; The volatile matter content in coal; The pressure deviation of the coal mill inlet header; This is the scaling pressure deviation correction number; , , , These are the weighting coefficients for each indicator. .

[0013] Preferably, the hierarchical control strategy specifically includes: The calculated deflagration risk index R is divided into three levels of intervals based on a preset interval threshold. When the deflagration risk index R is in the low-risk range, the response of the control strategy is to increase the flue gas blending ratio. When the deflagration risk index R is in the medium-risk range, the control strategy responds by further increasing the flue gas blending ratio, with the increase being higher than the control amplitude in the low-risk range, and simultaneously reducing the output of the coal mill. When the deflagration risk index R is in the high-risk range, the control strategy responds by injecting a set flow rate of CO2.

[0014] On the other hand, the present invention provides a low-load boiler flue gas recirculation collaborative control system, including a flue gas diversion module, a flue gas recirculation control module, and a coal mill branch control module. The flue gas diversion module is used to divide the flue gas output from the boiler into two flue gas pipes, including a first flue gas pipe and a second flue gas pipe. The flue gas recirculation control module is used to establish a data matching table between the flue gas recirculation rate and the load rate for the first flue gas duct to construct a linear interpolation formula for the reference flue gas recirculation rate, dynamically correct the flue gas recirculation rate based on the designed load-steam temperature coupling coefficient and the reference flue gas recirculation rate, calculate the first flue gas volume based on the flue gas recirculation rate, and input the first flue gas volume calculation value into the PID controller to control the output of the recirculation fan. The coal mill branch control module is used for the second flue gas pipeline, which is a branch of the coal mill. It derives the oxygen content control value of the mixed flue gas by measuring the oxygen content inside the coal mill. Based on the oxygen content PID controller, it switches the control mode to control the oxygen content regulating valve to achieve oxygen content control. Then, it introduces combustion condition parameters to build a dynamic risk assessment model to realize a graded control strategy.

[0015] Furthermore, the present invention also provides a low-load boiler flue gas recirculation system, the system comprising a control system, a flue gas extraction unit, a first flue gas duct, and a second flue gas duct. The control system is configured to perform coordinated control of the low-load boiler flue gas recirculation system as described in any embodiment of the present invention. The flue gas extraction unit comprises an economizer, a three-dimensional grid sampling device, an acoustic soot blower, and a cyclone dust collector. The first flue gas duct comprises a secondary burner air box, a swirling diffuser, a PID controller, and a recirculation fan. The second flue gas duct comprises an oxygen regulating valve, a Venturi mixer, a hot primary air duct, a coal mill, an online laser spectrometer for oxygen, and an oxygen PID controller. The economizer receives flue gas discharged from the boiler. The economizer outlet flue is equipped with a three-dimensional grid sampling device and is equipped with an acoustic soot blower and a cyclone dust collector. The recirculation fan is connected to the outlet of the cyclone dust collector. The first flue gas is injected into the secondary air box of the boiler burner through a cyclone diffuser. The second flue gas is sequentially fed into the coal mill through an oxygen regulating valve and a Venturi mixer. The coal mill is equipped with an online laser spectroscopy oxygen meter. The hot primary air duct is connected to the Venturi mixer.

[0016] Preferably, the Venturi mixer is equipped with an inert gas quick-closing valve. When the oxygen content exceeds a set threshold and the duration exceeds a preset time, or when the dynamic risk assessment model assesses that the risk exceeds the limit, the inert gas quick-closing valve automatically injects CO2 into the Venturi mixer.

[0017] In another aspect, the present invention also provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the method described in any embodiment of the present invention.

[0018] Compared with the prior art, the present invention has the following technical effects: This invention achieves zoned coordinated control by dividing the boiler flue gas pipeline into two independent pipelines. The first pipeline determines the baseline flue gas recirculation rate based on the matching relationship between load rate and flue gas recirculation rate and a linear interpolation formula. It then performs dynamic correction by combining the load-steam temperature coupling coefficient and adjusts the recirculation fan output through a closed-loop PID controller. This allows for real-time adaptive optimization of the flue gas recirculation volume based on the boiler's low-load operating conditions, effectively improving the steam temperature regulation accuracy and operating condition adaptability. The second pipeline targets the coal mill branch pipeline. It derives the flue gas oxygen control target based on the measured oxygen content inside the coal mill. It uses an oxygen PID controller to switch control modes and adjust the oxygen regulating valve to flexibly optimize the flue gas mixing effect. Simultaneously, it integrates combustion condition parameters to construct a dynamic risk assessment model and executes a graded control strategy. Overall, this invention overcomes the shortcomings of traditional flue gas recirculation technology, which is limited in function and not integrated with the pulverizing system's anti-explosion measures. It achieves deep synergy between flue gas recirculation, steam temperature regulation, oxygen optimization, and the pulverizing system's anti-explosion measures, avoiding the low-temperature corrosion problem caused by direct flue gas delivery to the furnace. This significantly enhances the safety, stability, and intelligent control level of the boiler during low-load operation. Attached Figure Description

[0019] Figure 1 This is an overall flowchart of the low-load boiler flue gas recirculation coordinated control method described in this invention; Figure 2 This is an overall architecture diagram of the low-load boiler flue gas recirculation system described in this invention. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below in conjunction with specific embodiments of the present application and with reference to the accompanying drawings.

[0021] Example 1 This embodiment provides a low-load boiler flue gas recirculation collaborative control method, applicable to scenarios where uneven pressure distribution in the primary hot air header (e.g., the inlet air pressure of the 2D mill is 15-20% lower than that of other mills) leads to a risk of deflagration in a high-volatile coal pulverizing system. (See also...) Figure 1 As shown, it includes the following steps: The flue gas output from the boiler is divided into two flue gas ducts, including the first flue gas duct and the second flue gas duct.

[0022] For the first flue gas duct, a data matching table of flue gas recirculation rate and load rate is established to construct a linear interpolation formula for the reference flue gas recirculation rate. The flue gas recirculation rate is dynamically corrected based on the designed load-steam temperature coupling coefficient and the reference flue gas recirculation rate. The calculated value of the first flue gas volume is calculated based on the flue gas recirculation rate, and the calculated value of the first flue gas volume is input into the PID controller to control the output of the recirculation fan.

[0023] Specifically, the following is an example of establishing a data matching table between flue gas recirculation rate and load rate in this embodiment to construct a linear interpolation formula for the baseline flue gas recirculation rate: Establish the matching relationship between recirculation rate γ and load rate L (based on test data of a 600MW unit):

[0024] The above test data table establishes a baseline relationship between recirculation rate and steam temperature rise under different loads. The recirculation rate L is determined by referring to the test data table (linear interpolation is required). The interpolation formula is applicable to... ) is represented as:

[0025] In the formula, Baseline recycling rate (in %).

[0026] As a preferred embodiment of this practice, a load-temperature coupling coefficient is designed to dynamically quantify the combined impact of load and temperature deviations on recirculation demand. Its expression is as follows:

[0027] In the formula, This is the load-steam temperature coupling coefficient; Weighted by load factor; The load factor is % The baseline load factor is used, such as c=100; Weighting for reheat steam temperature deviation; The weights a and b are set based on the actual application scenario requirements, such as preferably set as follows: ; The reheat steam temperature deviation is (target value - actual value) °C. The baseline reheat steam temperature deviation is denoted as d=20.

[0028] The design features of the load-temperature coupling coefficient are as follows: load-dominant (preferably 70% weight): at low loads, ((1-L / 100)) increases significantly to ensure an improvement in the basic recirculation rate; temperature fine-tuning (preferably 30% weight): the influence range of (ΔT) is smoothly limited by the (tanh) function (output limited to ([-0.3,0.3]) to avoid over-adjustment.

[0029] In a preferred embodiment of this invention, the dynamic correction of the flue gas recirculation rate based on the designed load-steam temperature coupling coefficient and the baseline flue gas recirculation rate specifically involves:

[0030] In the formula, The corrected flue gas recirculation rate; The baseline flue gas recirculation rate; This is the load-temperature coupling coefficient.

[0031] This formula achieves dual optimization of "load baseline + steam temperature feedback": static matching: through Establish the basic relationship between load and recirculation rate; dynamic correction: through It responds to real-time steam temperature deviations to achieve closed-loop control. The goal is to maximize reheat steam temperature stability under low loads while ensuring combustion safety.

[0032] The core idea is as follows: Under low load (L<50%), boiler combustion weakens, and flue gas volume and velocity decrease, leading to insufficient heat absorption by the reheater and low reheat steam temperature. Flue gas recirculation, by re-injecting some low-temperature flue gas into the furnace, can increase flue gas flow and slow down the combustion process, thereby increasing the reheat steam temperature. However, an excessively high recirculation rate (γ) will reduce the furnace temperature and affect combustion efficiency, requiring dynamic adjustment based on the load. This algorithm dynamically corrects the recirculation rate setpoint through the "load-steam temperature coupling coefficient K," achieving optimized control where "the lower the load, the higher the recirculation rate; when the steam temperature is low, the recirculation rate is further increased."

[0033] For the second flue gas pipeline, which is a branch of the coal mill, the oxygen content control value of the mixed flue gas is derived by measuring the oxygen content inside the coal mill. Based on the oxygen PID controller, the oxygen regulating valve is controlled by switching the control mode to achieve oxygen control. Then, combustion condition parameters are introduced to construct a dynamic risk assessment model to realize the hierarchical control strategy.

[0034] As a preferred embodiment of this practice, the oxygen quantity control method achieved by switching control modes of the oxygen quantity regulating valve based on the oxygen quantity PID controller specifically involves: Under steady-state operation, coal quality fluctuation, and coal supply interruption recovery transition conditions, the oxygen PID controller switches between corresponding PID tracking, feedforward compensation, and enhanced suppression control modes to control the oxygen regulating valve to keep the oxygen content in the mixed flue gas within the set oxygen target value. The following is an example of the preferred control mode switching in this embodiment:

[0035] In a preferred embodiment of this invention, the dynamic risk assessment model performs risk assessment based on a deflagration risk index, the formula for which the deflagration risk index is:

[0036] In the formula, The deflagration risk index; The mill outlet temperature is given in °C. The reference mill outlet temperature can be set based on the actual application scenario requirements; in this embodiment, it is preferably set to 60. The scaling temperature difference correction number is used to scale the temperature deviation to the same numerical range as the risk item. It can be set according to the actual application scenario requirements. In this embodiment, it is preferably set to 10. Oxygen content; The volatile matter content in coal; The pressure deviation of the coal mill inlet header pipe is expressed in kPa. The scaling pressure deviation correction number is used to scale the pressure deviation to the same numerical range as the risk item. It can be set according to the actual application scenario requirements. In this embodiment, it is preferably set to 10. , , , These are the weighting coefficients for each indicator. The weighting coefficients are set based on the actual application scenario requirements, such as preferably being set as follows: .

[0037] As a preferred embodiment of this invention, the hierarchical control strategy is specifically as follows: The calculated deflagration risk index R is divided into three levels of intervals based on a preset interval threshold. When the deflagration risk index R is in the low-risk range, the response of the control strategy is to increase the flue gas blending ratio. When the deflagration risk index R is in the medium-risk range, the control strategy responds by further increasing the flue gas blending ratio, with the increase being higher than the control amplitude in the low-risk range, and simultaneously reducing the output of the coal mill. When the deflagration risk index R is in the high-risk range, the control strategy responds by injecting a set flow rate of CO2.

[0038] The following is an example of switching the preferred control mode in this embodiment:

[0039] Example 2 Accordingly, this embodiment provides a low-load boiler flue gas recirculation collaborative control system for implementing the method described in any embodiment of the present invention, including a flue gas diversion module, a flue gas recirculation control module, and a coal mill branch control module; The flue gas diversion module is used to divide the flue gas output from the boiler into two flue gas pipes, including a first flue gas pipe and a second flue gas pipe. The flue gas recirculation control module is used to establish a data matching table between the flue gas recirculation rate and the load rate for the first flue gas duct to construct a linear interpolation formula for the reference flue gas recirculation rate, dynamically correct the flue gas recirculation rate based on the designed load-steam temperature coupling coefficient and the reference flue gas recirculation rate, calculate the first flue gas volume based on the flue gas recirculation rate, and input the first flue gas volume calculation value into the PID controller to control the output of the recirculation fan. The coal mill branch control module is used for the second flue gas pipeline, which is a branch of the coal mill. It derives the oxygen content control value of the mixed flue gas by measuring the oxygen content inside the coal mill. Based on the oxygen content PID controller, it switches the control mode to control the oxygen content regulating valve to achieve oxygen content control. Then, it introduces combustion condition parameters to build a dynamic risk assessment model to realize a graded control strategy.

[0040] Example 3 This embodiment provides a low-load boiler flue gas recirculation system, such as Figure 2 As shown, the system includes a control system, a flue gas extraction unit, a first flue gas duct, and a second flue gas duct. The control system is configured to perform coordinated control of the low-load boiler flue gas recirculation system as described in any embodiment of the present invention. The flue gas extraction unit includes an economizer, a three-dimensional grid sampling device, an acoustic soot blower, and a cyclone dust collector. The first flue gas duct includes a secondary burner air box, a swirling diffuser, a PID controller, and a recirculation fan. The second flue gas duct includes an oxygen regulating valve, a Venturi mixer, a hot primary air duct, a coal mill, an online laser spectrometer for oxygen, and an oxygen PID controller.

[0041] The economizer receives flue gas discharged from the boiler. The outlet flue gas temperature is moderate, which avoids overheating of the heating surface caused by high-temperature backfire and reduces the risk of condensation when directly mixed with hot primary air. A three-dimensional grid sampling device is installed in the economizer outlet flue, along with an acoustic soot blower and a cyclone dust collector. The recirculation fan is connected to the outlet of the cyclone dust collector. Furthermore, the configuration of the above components can be selected according to the actual application scenario. In this embodiment, the preferred configuration is: a three-dimensional grid sampling device with an aperture of Φ8mm and an opening rate of 35%; an acoustic soot blower frequency of 40kHz with a 10-minute interval; a cyclone dust collector with a dust removal efficiency of ≥85%; and a recirculation fan with a variable frequency speed control design, a temperature resistance rating of ≥300℃, and a wind pressure adjustment range of 5-15kPa.

[0042] The first flue gas is injected into the secondary air boxes of the A, B, and C layers of burners in the boiler via a swirling diffuser, which enhances the mixing of the flue gas with the main airflow. The second flue gas is sequentially fed into the coal mill via an oxygen regulating valve and a Venturi mixer to dry and transport the pulverized coal. The coal mill is equipped with an online oxygen analyzer using laser spectroscopy, and the hot primary air duct is connected to the Venturi mixer. Furthermore, the configuration of the above-mentioned components can be selected according to the actual application scenario requirements. In this embodiment, the preferred configuration is as follows: the Venturi mixer throat speed is 25-30 m / s, the inner wall of the mixer is coated with silicon carbide (thickness ≥200 μm), and the temperature resistance is increased to 300℃; the online oxygen analyzer uses laser spectroscopy (accuracy ±0.2%), with a sampling frequency of 10 Hz. In a preferred embodiment of this invention, the Venturi mixer is equipped with an inert gas quick-closing valve. When the oxygen level exceeds a set threshold and the duration exceeds a preset time, or when the dynamic risk assessment model determines that the risk exceeds the limit (e.g., R>25), the inert gas quick-closing valve automatically injects CO2 into the Venturi mixer. For example, CO2 is automatically injected when the oxygen level continuously exceeds the standard (>12% for more than 30 seconds).

[0043] The working principle of the system is as follows: Low-temperature flue gas (120~250℃) is drawn from the economizer outlet and, after being pressurized by the recirculation fan, is divided into two paths: The first path is injected into the lower combustion zone of the furnace to dilute the combustion oxygen concentration, reduce the peak flame temperature, increase the reheat steam temperature, and reduce NOx generation; The second path is mixed with the primary air of the 2D mill to form low-oxygen hot air (oxygen content ≤10%), which is then transported to the pulverizing system to suppress deflagration.

[0044] A Venturi mixer is installed in the hot primary air duct to dynamically control the oxygen content at the pulverizing system inlet by adjusting the mixing ratio of flue gas and hot primary air; an online oxygen meter with laser spectroscopy and an oxygen regulating valve are configured to automatically switch to carbon dioxide blending mode when the oxygen content exceeds the limit.

[0045] During the low-load phase (load rate ≤ 50%): start flue gas recirculation, prioritize increasing the proportion of the second flue gas (accounting for 40%~60% of the total recirculation volume), and ensure that the oxygen content of the pulverizing system is ≤ 10%; adjust the flow rate of the first flue gas according to the steam temperature deviation at the reheater outlet, and increase the target steam temperature by 5~15℃.

[0046] Example 4 This embodiment provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the method described in any embodiment of the present invention.

[0047] In this application embodiment, "at least one" refers to one or more, and "more than one" refers to two or more. "And / or" describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent the existence of A alone, A and B simultaneously, or B alone. A and B can be singular or plural. The character " / " generally indicates that the preceding and following related objects are in an "or" relationship. "At least one of the following" and similar expressions refer to any combination of these items, including any combination of singular or plural items. For example, at least one of a, b, and c can represent: a, b, c, a and b, a and c, b and c, or a and b and c, where a, b, and c can be single or multiple.

[0048] Those skilled in the art will recognize that the units and algorithm steps described in the embodiments disclosed herein can be implemented using electronic hardware, computer software, or a combination of electronic hardware and software. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of this application.

[0049] Those skilled in the art will understand that, for the sake of convenience and brevity, the specific working processes of the systems, devices, and units described above can be referred to the corresponding processes in the foregoing method embodiments, and will not be repeated here.

[0050] In the several embodiments provided in this application, any function, if implemented as a software functional unit and sold or used as an independent product, can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of this application, in essence, or the part that contributes to the prior art, or a part of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute all or part of the steps of the methods described in the various embodiments of this application. The aforementioned storage medium includes various media capable of storing program code, such as USB flash drives, portable hard drives, read-only memory (ROM), random access memory (RAM), magnetic disks, or optical disks.

[0051] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made based on the content of the present invention's specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A method for coordinated control of flue gas recirculation in a low-load boiler, characterized in that, Includes the following steps: The flue gas output from the boiler is divided into two flue gas pipes, including the first flue gas pipe and the second flue gas pipe. For the first flue gas duct, a data matching table of flue gas recirculation rate and load rate is established to construct a linear interpolation formula for the reference flue gas recirculation rate. The flue gas recirculation rate is dynamically corrected based on the designed load-steam temperature coupling coefficient and the reference flue gas recirculation rate. The first flue gas volume is calculated based on the flue gas recirculation rate, and the first flue gas volume is input into the PID controller to control the output of the recirculation fan. For the second flue gas pipeline, which is a branch of the coal mill, the oxygen content control value of the mixed flue gas is derived by measuring the oxygen content inside the coal mill. Based on the oxygen PID controller, the oxygen regulating valve is controlled by switching the control mode to achieve oxygen control. Then, combustion condition parameters are introduced to construct a dynamic risk assessment model to realize the hierarchical control strategy.

2. The low-load boiler flue gas recirculation coordinated control method according to claim 1, characterized in that, The expression for the load-temperature coupling coefficient of the design is as follows: In the formula, This is the load-steam temperature coupling coefficient; Weighted by load factor; Load factor; The baseline load factor; Weighting for reheat steam temperature deviation, ; For reheat steam temperature deviation; The baseline reheat steam temperature deviation.

3. The low-load boiler flue gas recirculation coordinated control method according to claim 1, characterized in that, The dynamic correction of the flue gas recirculation rate based on the design-based load-steam temperature coupling coefficient and the reference flue gas recirculation rate is specifically as follows: In the formula, The corrected flue gas recirculation rate; The baseline flue gas recirculation rate; This is the load-temperature coupling coefficient.

4. The low-load boiler flue gas recirculation coordinated control method according to claim 1, characterized in that, The method of controlling the oxygen regulating valve based on the switching control mode of the oxygen PID controller to achieve oxygen control is as follows: Under steady-state operation, coal quality fluctuation, and coal supply interruption recovery transition conditions, the oxygen PID controller switches to the corresponding PID tracking, feedforward compensation, and enhanced suppression control modes respectively, controlling the oxygen regulating valve to keep the oxygen content in the mixed flue gas oxygen control value within the set oxygen target value.

5. The low-load boiler flue gas recirculation coordinated control method according to claim 1, characterized in that, The dynamic risk assessment model performs risk assessment based on a deflagration risk index, the formula for which the deflagration risk index is: In the formula, The deflagration risk index; This refers to the mill outlet temperature. The reference mill outlet temperature; This is a scaling temperature difference correction factor; Oxygen content; The volatile matter content in coal; The pressure deviation of the coal mill inlet header; This is the scaling pressure deviation correction number; , , , These are the weighting coefficients for each indicator. .

6. The low-load boiler flue gas recirculation coordinated control method according to claim 5, characterized in that, The hierarchical control strategy is specifically as follows: The calculated deflagration risk index R is divided into three levels of intervals based on a preset interval threshold. When the deflagration risk index R is in the low-risk range, the response of the control strategy is to increase the flue gas blending ratio. When the deflagration risk index R is in the medium-risk range, the control strategy responds by further increasing the flue gas blending ratio, with the increase being higher than the control amplitude in the low-risk range, and simultaneously reducing the output of the coal mill. When the deflagration risk index R is in the high-risk range, the control strategy responds by injecting a set flow rate of CO2.

7. A low-load boiler flue gas recirculation coordinated control system, characterized in that, The system is used to implement the method as described in any one of claims 1 to 6, and includes a flue gas diversion module, a flue gas recirculation control module, and a coal mill branch control module; The flue gas diversion module is used to divide the flue gas output from the boiler into two flue gas pipes, including a first flue gas pipe and a second flue gas pipe. The flue gas recirculation control module is used to establish a data matching table between the flue gas recirculation rate and the load rate for the first flue gas duct to construct a linear interpolation formula for the reference flue gas recirculation rate, dynamically correct the flue gas recirculation rate based on the designed load-steam temperature coupling coefficient and the reference flue gas recirculation rate, calculate the first flue gas volume based on the flue gas recirculation rate, and input the first flue gas volume calculation value into the PID controller to control the output of the recirculation fan. The coal mill branch control module is used for the second flue gas pipeline, which is a branch of the coal mill. It derives the oxygen content control value of the mixed flue gas by measuring the oxygen content inside the coal mill. Based on the oxygen content PID controller, it switches the control mode to control the oxygen content regulating valve to achieve oxygen content control. Then, it introduces combustion condition parameters to build a dynamic risk assessment model to realize a graded control strategy.

8. A low-load boiler flue gas recirculation system, characterized in that, The system includes a control system, a flue gas extraction unit, a first flue gas duct, and a second flue gas duct. The control system is configured to coordinate the control of the low-load boiler flue gas recirculation system as described in claim 7. The flue gas extraction unit includes an economizer, a three-dimensional grid sampling device, an acoustic soot blower, and a cyclone dust collector. The first flue gas duct includes a secondary burner air box, a swirl diffuser, a PID controller, and a recirculation fan. The second flue gas duct includes an oxygen regulating valve, a Venturi mixer, a hot primary air duct, a coal mill, an online laser spectrometer for oxygen, and an oxygen PID controller. The economizer receives flue gas discharged from the boiler. The economizer outlet flue is equipped with a three-dimensional grid sampling device and is equipped with an acoustic soot blower and a cyclone dust collector. The recirculation fan is connected to the outlet of the cyclone dust collector. The first flue gas is injected into the secondary air box of the boiler burner through a cyclone diffuser. The second flue gas is sequentially fed into the coal mill through an oxygen regulating valve and a Venturi mixer. The coal mill is equipped with an online laser spectroscopy oxygen meter. The hot primary air duct is connected to the Venturi mixer.

9. The low-load boiler flue gas recirculation coordinated control method according to claim 8, characterized in that, The Venturi mixer is equipped with an inert gas quick-closing valve. When the oxygen content exceeds the set threshold and the duration exceeds the preset time, or when the dynamic risk assessment model assesses that the risk exceeds the limit, the inert gas quick-closing valve automatically injects CO2 into the Venturi mixer.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by a processor, it implements the method as described in any one of claims 1 to 6.

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