Air preheater anti-coking system coupled with flue gas recirculation and flue gas regulation method

Abstract

The application provides a kind of coupling flue gas recirculation system's air preheater anti-coking system, including rotary air preheater;Hot end pipe and cold end pipe connected with rotary air preheater;First hot end regulating valve, second hot end regulating valve are provided with on hot end pipe in parallel, first cold end regulating valve, second cold end regulating valve are provided with on cold end pipe in parallel;First variable frequency fan, second variable frequency fan connected with hot end pipe and cold end pipe;Flue gas pipe connected with first variable frequency fan, second variable frequency fan and external boiler flue gas outlet;Flue gas return pipe connected with first variable frequency fan, second variable frequency fan and external boiler hearth, flue gas return pipe is also connected with cold end pipe;First flue gas regulating valve, second flue gas regulating valve on flue gas pipe;First return regulating valve, second return regulating valve on flue gas return pipe;Still include pressure sensor, flow sensor, temperature sensor and the controller of control system operation.

Description

Technical Field

[0001] This application relates to the field of thermal power equipment technology, and in particular to an air preheater anti-ash blockage system and flue gas control method coupled to a flue gas recirculation system. Background Technology

[0002] With the large-scale grid connection of renewable energy sources such as wind power and photovoltaics in my country, the installed capacity and power generation ratio of new energy sources in the power system are constantly increasing. These energy sources are characterized by "randomness, volatility, and uncertainty," making it difficult to maintain stable power output. To ensure grid frequency stability, thermal power units are forced to frequently adjust their load to make way for new energy sources. In situations of "low-valley load + high new energy output," coal-fired units need to reduce their load to a very low level while still maintaining operation. The role of thermal power units as "main power sources" is shifting to that of "regulating power sources," undertaking peak shaving, frequency regulation, and reserve tasks for the power system, which places higher demands on their flexible operation capabilities.

[0003] Deep peak shaving refers to the operation of coal-fired power units below the original design minimum stable combustion load, usually referring to long-term, frequent, or load operation at 50% or even 30%.

[0004] Deep peak shaving leads to inaccurate control of ammonia injection during SCR denitrification, causing some ammonia to escape. This escaped ammonia combines with sulfur trioxide and water in the flue gas to form ammonium bisulfate. Ammonium bisulfate has strong viscosity and some corrosiveness. When the flue gas passes through the medium-low temperature section of the rotary air preheater, the ammonium bisulfate condenses and adheres to the surface of the heat storage elements of the rotary air preheater with dust. Over time, this leads to blockage and corrosion of the rotary air preheater.

[0005] To address this issue, one existing technology employs an air volume split and anti-blockage dust prevention technology for rotary air preheaters. This technology involves periodically blowing hot air through the low- and medium-temperature sections of the rotary air preheater to prevent flue gas condensation, thereby reducing blockage and corrosion in the rotary air preheater.

[0006] Simultaneously, reducing the nitrogen oxide content in the flue gas, thereby decreasing the ammonium bisulfate content, can also alleviate clogging and corrosion of the rotary air preheater. One method is to employ flue gas recirculation (FGR) technology, where the low-temperature, low-oxygen flue gas from the boiler tail is mixed with the hot air from the rotary air preheater outlet, and then enters the furnace burner to be mixed and burned with natural gas. The resulting flue gas then re-enters the boiler for further combustion. This method can reduce the flame temperature in the boiler, thereby reducing the formation of nitrogen oxides.

[0007] Currently, the two systems operate independently, each requiring two fans—one on standby and one in operation. This results in both systems occupying a large area and having numerous pipelines. This causes congestion in the boiler room, affecting employee access and maintenance. When both are used simultaneously in a coal-fired unit, the flue gas exiting the boiler goes to three places: the rotary air preheater flue, the circulation pipeline of the air volume splitting and anti-clogging system, and the boiler furnace. During deep peak shaving, improper distribution of flue gas often leads to problems such as poor anti-clogging effect, low heat utilization rate, and high fan operating energy consumption. For example, when a coal-fired unit operates at 50% load, with the anti-clogging system and flue gas recirculation system running simultaneously, less flue gas is available for heat storage in the rotary air preheater. This results in lower temperatures in the low-temperature section of the rotary air preheater, making it easier for sulfuric acid and ammonium bisulfate in the flue gas to condense and clog the rotary air preheater. The anti-clogging system also requires longer cleaning times, increasing energy consumption. Meanwhile, as the deep peak load changes, the emissions of flue gas also change, resulting in unstable air temperature entering the boiler furnace after being heated by the rotary air preheater. The furnace temperature is prone to disturbance, affecting combustion efficiency and the generation of nitrogen oxides. Summary of the Invention

[0008] In view of this, this application proposes an air preheater anti-clogging system for a coupled flue gas recirculation system with a shared fan, which facilitates flue gas regulation, improves the thermal utilization rate of flue gas, reduces fan energy consumption, and enhances the anti-clogging effect.

[0009] This application also proposes a flue gas control method for an air preheater anti-clogging system based on a coupled flue gas recirculation system. By rationally distributing the flue gas, the thermal utilization rate of the flue gas can be improved, the energy consumption of the fan can be reduced, and the anti-clogging effect can be enhanced.

[0010] An air preheater anti-clogging system for a coupled flue gas recirculation system includes, Rotary air preheater; A hot-end pipe and a cold-end pipe are connected to a rotary air preheater; a first hot-end regulating valve and a second hot-end regulating valve are connected in parallel on the hot-end pipe, and a first cold-end regulating valve and a second cold-end regulating valve are connected in parallel on the cold-end pipe. A first variable frequency fan and a second variable frequency fan connect the hot end pipe and the cold end pipe; a first hot end regulating valve controls the flow of flue gas to the first variable frequency fan, and a second hot end regulating valve controls the flow of flue gas to the second variable frequency fan; a first cold end regulating valve controls the flow of flue gas from the first variable frequency fan to the rotary air preheater, and a second cold end regulating valve controls the flow of flue gas from the second variable frequency fan to the rotary air preheater. The flue gas duct connects the first variable frequency fan, the second variable frequency fan and the flue gas outlet of the external boiler. The flue gas duct is also connected to the flue gas outlet of the rotary air preheater. A flue gas return pipe connects the first variable frequency fan, the second variable frequency fan and the external boiler furnace. The flue gas return pipe is also connected to the cold end pipe. The first flue gas regulating valve and the second flue gas regulating valve on the flue gas duct; The first and second reflux regulating valves on the flue gas reflux duct; Pressure sensor; Flow sensor; Temperature sensor; The controller that controls the operation of the control system.

[0011] A flue gas control method for an air preheater anti-clogging system based on a coupled flue gas recirculation system includes the following steps: Step 1: Acquire characteristic information of the boiler, rotary air preheater, and pipelines in real time; Step 2: Based on the feature information, determine whether it is necessary to actively or passively activate the airflow splitting anti-clogging system. Step 3: Based on the characteristic information, adjust the flue gas flow rate of the air volume splitting and anti-clogging ash system and the flue gas recirculation.

[0012] The flue gas control method of the air preheater anti-clogging system based on the coupled flue gas recirculation system in this application also includes adjusting the power of the first variable frequency fan and the second variable frequency fan according to the characteristic information.

[0013] The technical advantage of this application is that the air preheater anti-clogging system of the coupled flue gas recirculation system combines the two fans of the flue gas recirculation system and the air preheater anti-clogging system into two fans, reducing the number of fans and related pipes, thereby reducing the space occupied by the equipment.

[0014] The air preheater anti-clogging system of the coupled flue gas recirculation system of this application can flexibly allocate flue gas and improve the thermal utilization rate of flue gas by controlling the regulating valve.

[0015] The air preheater anti-clogging system of the coupled flue gas recirculation system of this application can perform thermal purging of the heat storage elements of the rotary air preheater during flue gas recirculation. Compared with the independent flue gas recirculation system and air preheater anti-clogging system, the energy consumption of the blower is significantly reduced.

[0016] The air preheater anti-clogging system of the coupled flue gas recirculation system of this application can significantly reduce the adhesion of fly ash, making the system operate more smoothly and significantly improving the anti-clogging effect of the rotary air preheater.

[0017] The flue gas control method of the air preheater anti-clogging system based on the coupled flue gas recirculation system in this application can improve the thermal utilization rate of flue gas, reduce fan energy consumption, and enhance the anti-clogging effect of rotary air preheaters through reasonable distribution of flue gas. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the air preheater anti-clogging ash system of the coupled flue gas recirculation system of this application; Figure 2 This is a schematic diagram of the control system of the air preheater anti-ash blockage system of the coupled flue gas recirculation system of this application; Explanation of reference numerals in the attached drawings: 1. Rotary air preheater; 101. Hot-end air chamber; 102. Cold-end air chamber; 2. Hot-end pipe; 201. First hot-end regulating valve; 202. Second hot-end regulating valve; 3. Cold-end pipe; 301. First cold-end regulating valve; 302. Second cold-end regulating valve; 4. First variable frequency fan; 5. Second variable frequency fan; 6. Flue gas pipe; 601. First flue gas regulating valve; 602. Second flue gas regulating valve; 7. Flue gas return pipe; 701. First return regulating valve; 702. Second return regulating valve; 8. Pressure sensor; 9. Flow sensor; 10. Temperature sensor; 11. Controller; 12. Diverter valve. Detailed Implementation

[0019] The embodiments of the technical solution of this application will now be described in detail with reference to the accompanying drawings. These embodiments are only used to more clearly illustrate the technical solution of this application and are therefore merely examples, and should not be used to limit the scope of protection of this application.

[0020] Please refer to Figure 1 An air preheater anti-clogging system coupled with a flue gas recirculation system includes, Rotary air preheater 1; A hot end pipe 2 and a cold end pipe 3 are connected to a rotary air preheater 1; a first hot end regulating valve 201 and a second hot end regulating valve 202 are connected in parallel on the hot end pipe 2, and a first cold end regulating valve 301 and a second cold end regulating valve 302 are connected in parallel on the cold end pipe 3. A first variable frequency fan 4 and a second variable frequency fan 5 are connected to the hot end pipe 2 and the cold end pipe 3; a first hot end regulating valve 201 controls the flow of flue gas to the first variable frequency fan 4, and a second hot end regulating valve 202 controls the flow of flue gas to the second variable frequency fan 5; a first cold end regulating valve 301 controls the flow of flue gas from the first variable frequency fan 4 to the rotary air preheater 1, and a second cold end regulating valve 302 controls the flow of flue gas from the second variable frequency fan 5 to the rotary air preheater 1; The flue gas duct 6 connects the first variable frequency fan 4, the second variable frequency fan 5 and the flue gas outlet of the external boiler. The flue gas duct 6 is also connected to the flue gas outlet of the rotary air preheater 1. The flue gas return pipe 7 connects the first variable frequency fan 4, the second variable frequency fan 5 and the external boiler furnace. The flue gas return pipe 7 is also connected to the cold end pipe 3. The first flue gas regulating valve 601 and the second flue gas regulating valve 6 on the flue gas duct 6; The first return regulating valve 701 and the second return regulating valve 702 on the flue gas return pipe 7; Pressure sensor 8; Flow sensor 9; Temperature sensor 10; Controller 11, which controls the operation of the control system.

[0021] In a preferred embodiment, the rotary air preheater 1 includes a flue gas zone, a primary air zone, a secondary air zone, and an ash removal zone with a fan-shaped cross-section. Adjacent zones are separated by fan-shaped plates. The primary air zone is used to dry and preheat pulverized coal, the secondary air zone is used to preheat the air entering the furnace, the flue gas zone is used to heat the heat storage element of the rotary air preheater 1, and the ash removal zone is used to heat the cold end of the heat storage element.

[0022] Part of the flue gas from the boiler passes through the rotor of the rotary air preheater 1 in the flue gas zone, heating the heat storage elements of the rotor.

[0023] Air passes through the rotor from the secondary air zone, is heated by the heat storage element, and then enters the coal mill to mix with pulverized coal to form a "pulverized coal-air mixture", which is finally injected into the furnace through the burner.

[0024] Air passes through the rotor from the primary air zone, is heated by the heat storage element, and is injected into the furnace to fully mix with the pulverized coal carried by the secondary air to maintain combustion.

[0025] Part of the flue gas from the boiler enters the ash removal zone, heating the cold end of the rotor to keep the temperature above the acid dew point. This prevents sulfuric acid and ammonium bisulfate in the flue gas from condensing and forming adhesives that cause dust to stick to the heat storage elements, resulting in blockage or corrosion.

[0026] During the rotation process, the rotor is first heated by the flue gas entering the flue gas zone, then cooled by the secondary air, then cooled by the primary air, and finally heated by the flue gas in the ash removal zone.

[0027] This application provides a first hot-end regulating valve 201 and a second hot-end regulating valve 202 on the hot-end pipe 2, and a first cold-end regulating valve 301 and a second cold-end regulating valve 302 on the cold-end pipe 3. When the first hot-end regulating valve 201, the second hot-end regulating valve 202, the first cold-end regulating valve 301, and the second cold-end regulating valve 302 are closed, the airflow splitting anti-clogging system is shut down. Similarly, when the first hot-end regulating valve 201 and the first cold-end regulating valve 301, or the second hot-end regulating valve 202 and the second cold-end regulating valve 302 are opened, the airflow splitting anti-clogging system is activated.

[0028] The airflow splitting and anti-clogging ash removal system described in this application is an ash removal system that heats and blows the rotor, consisting of an ash removal zone, a hot end pipe 2, a first variable frequency fan 4 or a second variable frequency fan 5, and a cold end pipe 3.

[0029] The flue gas recirculation system described in this application is a flue gas circulation system that reduces the concentration of nitrogen oxides, consisting of flue gas duct 6, first variable frequency fan 4 or second variable frequency fan 5, flue gas circuit duct, and boiler.

[0030] The air volume splitting and anti-clogging ash system and the flue gas recirculation system share the first variable frequency fan 4 and the second variable frequency fan 5.

[0031] The ash removal zone of this application has a hot-end air chamber 101 at the upper end and a cold-end air chamber 102 at the lower end. The hot-end pipe 2 connects to the hot-end air chamber 101, and the cold-end pipe 3 connects to the cold-end air chamber 102. A first variable frequency fan 4 and a second variable frequency fan 5 are connected in parallel to the hot-end pipe 2 and the cold-end pipe 3. After the flue gas enters the cold-end air chamber 102, it heats the cold end of the rotor and flows away from the hot end. The flue gas can circulate within the flue gas zone. The air leakage rate of the flue gas zone is generally 6-8%. After multiple cycles, the flue gas gradually dissipates. Depending on the actual ash removal situation, the flue gas can be replenished in time through the flue gas pipe 6. The flue gas can also be drawn away by the variable frequency fan after heating the rotor.

[0032] This application provides a first flue gas regulating valve 601 and a second flue gas regulating valve 602 on the flue gas duct 6. When the first flue gas regulating valve 601 is open, the flue gas from the boiler enters the first variable frequency fan 4 through the flue gas duct 6; similarly, when the second flue gas regulating valve 602 is open, the flue gas from the boiler enters the second variable frequency fan 5 through the flue gas duct 6.

[0033] The flue gas duct 6 of this application is also connected to the flue gas domain of the rotary air preheater 1 to heat the heat storage element of the rotary air preheater 1. The heat storage element is in the form of a honeycomb or other mesh and is arranged in the form of a rotor inside the shell of the rotary air preheater 1. In the flue gas domain, the rotor is heated from top to bottom by the flue gas while rotating.

[0034] This application provides a first return regulating valve 701 and a second return regulating valve 702 on the flue gas return pipe 7. When the first return regulating valve 701 is open, the flue gas from the first variable frequency fan 4 enters the furnace of the boiler; similarly, when the second return regulating valve is open, the flue gas from the second variable frequency fan 5 enters the furnace of the boiler.

[0035] This application can control the flow direction of flue gas by controlling the opening and closing of the first hot end regulating valve 201, the second hot end regulating valve 202, the first cold end regulating valve 301, the second cold end regulating valve 302, the first flue gas regulating valve 601, the second flue gas regulating valve 602, the first reflux regulating valve 701, and the second reflux regulating valve 702, so that the heat and nitrogen oxides in the flue gas can be fully utilized.

[0036] For example, if the first flue gas regulating valve 601 is open, the first return regulating valve 701 is closed, and the first cold end regulating valve 301 and the first hot end regulating valve 201 are open, then the flue gas exiting the boiler flue enters the air volume splitting and anti-clogging ash system to heat and purge the cold end of the rotary air preheater 1 rotor in the ash removal section. The same method applies to the second flue gas regulating valve 602 and the second return regulating valve 702.

[0037] When the first flue gas regulating valve 601 is closed and the first return regulating valve 701 is closed, and the first cold end regulating valve 301 and the first hot end regulating valve 201 are open, the air volume splitting and anti-clogging ash system performs internal circulation heating and purging of the rotary air preheater 1 rotor. The same method applies to the second flue gas regulating valve 602 and the second return regulating valve 702.

[0038] With the first flue gas regulating valve 601 open, the first return regulating valve 701 closed, the first cold end regulating valve 301 open, and the first hot end regulating valve 201 closed, the second hot end regulating valve 202 open, the second return regulating valve 702 open, and the second cold end regulating valve 302 closed, the flue gas, after purging the rotor of the rotary air preheater 1, will enter the boiler furnace. This flue gas carries ammonium bisulfate and sulfuric acid, which, upon entering the furnace, decompose under high temperature. The resulting ammonia gas burns to generate nitrogen gas. This high-temperature treatment eliminates ammonium bisulfate and sulfuric acid. Compared to existing closed-loop pipe systems for airflow separation and ash prevention, this method effectively dissolves ammonium bisulfate and sulfuric acid. After the ash prevention system stops operating, the ammonium bisulfate and sulfuric acid in the pipes will not re-adhere to the heat storage elements after cooling.

[0039] In a preferred embodiment, expansion joints are also provided on the hot end pipe 2 and the cold end pipe 3 to buffer the pipe deformation caused by thermal expansion and contraction.

[0040] In a preferred embodiment, a diversion valve 12 is installed at the junction of the flue gas duct 6, the cold end duct 3, and the return duct to distribute the flue gas flow. The operation of the first variable frequency fan 4 and the second variable frequency fan 5 is controlled according to the load of the thermal power unit.

[0041] When the thermal power unit load is 80-100%, the flue gas volume is sufficient. Based on the system's anti-ash-clogging requirements, the airflow in the flue gas duct 6 is distributed via the diversion valve 12: 8-15% of the airflow is allocated to the flue gas return duct 7, 5-10% to the airflow within the airflow splitting anti-ash-clogging system, and 75-85% to the airflow passing through the flue gas domain. To maintain a stable thermal field within the boiler furnace, the flue gas within the airflow splitting anti-ash-clogging system can be kept within the flue gas return duct 7.

[0042] When the thermal power unit load is between 60% and 80%, the flue gas volume decreases, and the flue gas is mainly used to heat the rotary air preheater 1. Due to the low load operation, the required air volume is also reduced accordingly. The anti-clogging system is set to timed cleaning. When the rotary air preheater 1 is not purged, the air volume in the flue gas return pipe 7 accounts for 10% to 15%, and the air volume passing through the flue gas domain accounts for 85% to 90%. When the rotary air preheater 1 is purged, the air volume in the flue gas return pipe 7 accounts for 8% to 12%, the air volume in the air volume splitting anti-clogging system accounts for 8% to 12%, and the air volume passing through the flue gas domain accounts for 75% to 85%. When the flue gas entering the boiler furnace is insufficient, some of the flue gas in the air volume splitting anti-clogging system can be supplemented into the boiler.

[0043] When the load of the thermal power unit is less than 60%, the flue gas volume decreases significantly. The anti-ash clogging system is set to passive cleaning. The anti-ash clogging system is activated when the pressure difference across the rotary air preheater 1 exceeds the limit or the rotor temperature of the rotary air preheater 1 is lower than the preset value. The significant reduction in flue gas volume also leads to a decrease in the temperature of the heat storage elements in the rotary air preheater 1, making the flue gas at the cold end of the rotary air preheater 1 more prone to condensation. To ensure that the heat storage elements can reach a sufficient temperature, the flue gas recirculation system is always closed, allowing the flue gas from the boiler to be used to heat the rotary air preheater 1.

[0044] Maintaining a stable temperature in the furnace thermal field of a thermal power unit is beneficial for the complete combustion of fuel and reduces the generation of nitrogen oxides. If flue gas, heated pulverized coal, and air enter the furnace directly, the temperature fluctuation in the furnace will be significant. In a preferred embodiment, the air preheater anti-ash clogging system of the coupled flue gas recirculation system of this application also includes a combustion chamber. The combustion chamber is connected to the flue gas return pipe 7 and also to the external pulverized coal pipe and air pipe. The flue gas is mixed with pulverized coal and air for combustion before entering the furnace. The circulating flue gas contains a large amount of inert gases such as N2, CO2, and water vapor. After mixing with air and fuel, it dilutes the oxygen concentration in the combustion zone, reducing the oxygen concentration from 21% to 18%~20% and absorbing the heat released by combustion. This reduces the peak flame temperature in the furnace from over 1600°C to 1400~1500°C, thus reducing the generation of nitrogen oxides. At the same time, the pre-combustion process significantly increases the temperature of the mixture, reducing the temperature difference between the mixture and the furnace, thereby reducing temperature fluctuations. Nitrogen oxides in flue gas are more likely to decompose into nitrogen gas under anaerobic conditions.

[0045] In addition to detecting pipeline pressure, the pressure sensor 8 of this application also detects the pressure on both sides of the rotor of the rotary air preheater 1, and controls the airflow splitting and anti-clogging ash system to purge the rotor based on the pressure difference. The greater the pressure difference on both sides of the rotor, the more severe the blockage. When the pressure difference reaches a predetermined value, the airflow splitting and anti-clogging ash system is activated.

[0046] The flow sensor 9 of this application is used to detect the flue gas flow rate at the flue gas outlet of the boiler, the flue gas flow rate at the flue gas inlet of the rotary air preheater 1, the flue gas flow rate entering the furnace, and the flue gas flow rate entering the air volume splitting and anti-clogging ash system.

[0047] The temperature sensor 10 of this application is used to detect the temperature inside the boiler furnace, the temperature of the boiler flue gas outlet, and the hot end and cold end temperatures of the heat storage element of the rotary air preheater 1 located in the first air zone, the second air zone, the flue gas zone, and the ash removal zone.

[0048] It should be understood that, please refer to Figure 2 The pressure sensor 8, flow sensor 9, and temperature sensor 10 of this application are electrically connected to the controller 11 to transmit the collected pressure, flow, and temperature information to the controller 11. The controller 11 controls the operation of the first hot-end regulating valve 201, the second hot-end regulating valve 202, the first cold-end regulating valve 301, the second cold-end regulating valve 302, the first variable frequency fan 4, the second variable frequency fan 5, the first flue gas regulating valve 601, the second flue gas regulating valve 602, the first reflux regulating valve 701, and the second reflux regulating valve 702 based on the received information. This improves the thermal utilization rate of the flue gas, reduces the concentration of nitrogen oxides in the flue gas, reduces energy consumption, and simultaneously prevents blockage of the heat storage elements in the rotary air preheater 1, mitigating corrosion of the heat storage elements.

[0049] This application achieves the above-mentioned effect through a flue gas control method based on an air preheater anti-clogging system coupled with a flue gas recirculation system. The specific scheme is as follows.

[0050] The flue gas control method for an air preheater anti-clogging system based on a coupled flue gas recirculation system includes the following steps: Step 1: Acquire the characteristic information of the boiler, rotary air preheater 1, and pipelines in real time; In a preferred embodiment, the feature information specifically includes temperature information, gas flow rate information, pressure difference information across the rotary air preheater 1, and nitrogen oxide concentration information.

[0051] The temperature information is collected by temperature sensor 10. The temperature information includes, but is not limited to, the temperature information inside the boiler furnace, the flue gas temperature information at the boiler flue gas outlet, and the hot end temperature information and cold end temperature information of the heat storage element of the rotary air preheater 1 located in the first air zone, the second air zone, the flue gas zone, and the ash removal zone. Among them, the gas flow information is collected by the flow sensor 9. The flow information collected by the flow sensor 9 includes, but is not limited to, the flue gas flow information at the boiler flue gas outlet, the flue gas flow information at the flue gas inlet of the rotary air preheater 1, the flue gas flow information entering the furnace, and the flue gas flow information entering the air volume splitting and anti-clogging ash system; In a preferred real-time manner, the feature information also includes coal quality information. Coal quality information includes the ash content, sulfur content, and calorific value of the coal. According to the national standard GB / T 17608-2022, "Classification of Coal Products and Grades," the ash content, sulfur content, and calorific value of the coal can be determined based on the grade of the incoming coal. Knowing the coal quality information allows for control of the mixing ratio of pulverized coal, return flue gas, and air entering the furnace, optimizing indicators such as the nitrogen oxide concentration and temperature of the flue gas exiting the boiler.

[0052] Step 2: Based on the feature information, determine whether it is necessary to actively or passively activate the airflow splitting anti-clogging system. The active start-up airflow splitting and anti-ash-clogging system described in this application refers to a situation where the flue gas temperature and flow rate at the boiler outlet exceed predetermined values. Even after heat exchange in the rotary air preheater 1, the flue gas still maintains a high temperature, resulting in heat waste upon discharge. In this case, a portion of the flue gas is diverted to the airflow splitting and anti-ash-clogging system and the flue gas recirculation system to purge and heat the heat storage elements of the rotary air preheater 1, allowing the adhering substances to be blown away. The flue gas entering the boiler furnace through the flue gas recirculation system reduces the generation of nitrogen oxides.

[0053] The passive start-up airflow splitting and anti-clogging ash removal system described in this application refers to the activation of the airflow splitting and anti-clogging ash removal system when the pressure difference between the hot and cold ends of the rotary air preheater 1 exceeds a predetermined value, or when the cold end temperature of the rotary air preheater 1 reaches below the acid dew point. Without heating, the heat storage elements will become clogged or experience increased corrosion. In this case, a portion of the flue gas is introduced into the airflow splitting and anti-clogging ash removal system, allowing the flue gas to circulate within it until the pressure difference between the hot and cold ends of the rotary air preheater 1 returns to the predetermined value, and simultaneously, the cold end temperature reaches the predetermined value, preventing the condensation of sulfuric acid and ammonium bisulfate in the flue gas.

[0054] In a preferred embodiment, when the thermal power unit load is 80-100%, the flue gas volume is sufficient. Based on the system's anti-ash-clogging requirements, the air volume of the flue gas duct 6 is distributed via the diversion valve 12: the air volume of the flue gas return duct 7 accounts for 8-15%, the air volume within the anti-ash-clogging system accounts for 5-10%, and the air volume passing through the flue gas domain accounts for 75-85%.

[0055] When the thermal power unit load is between 60% and 80%, the flue gas volume decreases, and the flue gas is mainly used to heat the rotary air preheater 1. Due to the low-load operation, the required air volume is also reduced accordingly. The anti-clogging system is set to timed cleaning. When the rotary air preheater 1 is not purged, the air volume in the flue gas return duct 7 accounts for 10% to 15%, and the air volume passing through the flue gas domain accounts for 85% to 90%. When the rotary air preheater 1 is purged, the air volume in the flue gas return duct 7 accounts for 8% to 12%, the air volume in the air volume splitting anti-clogging system accounts for 8% to 12%, and the air volume passing through the flue gas domain accounts for 75% to 85%.

[0056] When the load of the thermal power unit is less than 60%, the flue gas volume decreases significantly. The anti-ash clogging system is set to passive cleaning. When the pressure difference across the rotary air preheater 1 exceeds the limit or the rotor temperature is lower than the preset value, the anti-ash clogging system is activated. The significant reduction in flue gas volume also leads to a decrease in the temperature of the heat storage elements in the rotary air preheater 1, making the flue gas at the cold end of the rotary air preheater 1 more prone to condensation. To ensure that the heat storage elements can reach a sufficient temperature, the flue gas recirculation system is shut down, and the flue gas from the boiler is used only to heat the rotary air preheater 1.

[0057] In a preferred embodiment, the power of the first variable frequency fan 4 and the second variable frequency fan 5 is adjusted according to the nitrogen oxide concentration at the flue gas outlet of the boiler, thereby adjusting the flue gas flow rate at the furnace inlet of the boiler and reducing the nitrogen oxide concentration at the flue gas outlet of the boiler.

[0058] Step 3: Based on the characteristic information, adjust the flue gas flow rate of the air volume splitting and anti-clogging ash system and the flue gas recirculation.

[0059] During peak shaving in coal-fired power units, the pulverized coal, air, and flue gas entering the furnace are constantly being adjusted, and the amount of flue gas leaving the boiler also varies. This variation in flue gas volume leads to changes in its calorific value, which in turn affects the temperature of the heat storage elements in the rotary air preheater 1, further impacting the pulverized coal and air temperatures. If the temperature of the heat storage elements decreases, the flue gas is more prone to liquefaction, making the rotary air preheater 1 more susceptible to blockage and corrosion. Simultaneously, the thermal field within the furnace is easily disturbed, affecting the complete combustion of the pulverized coal. This application requires using gas flow rate, temperature, and nitrogen oxide concentration information collected by sensors to determine the combustion status within the furnace, thereby adjusting the airflow separation anti-clogging system and the flue gas flow rate for flue gas recirculation. This maintains a relatively stable temperature within the furnace, achieving energy conservation, emission reduction, and reduced nitrogen oxide generation.

[0060] In a preferred embodiment, when adjusting the flue gas flow rate, the controller 11 trains a PID adaptive adjustment model based on historical operating data to maintain temperature stability during the combustion process.

[0061] In a preferred embodiment, the controller 11 generates a "distribution strategy execution report" daily, which calculates the energy consumption ratio and anti-dust blocking effect of each load segment, and optimizes the threshold parameters iteratively through machine learning.

[0062] In a preferred embodiment, this application also accesses the power plant SIS real-time database to obtain global data such as boiler load, fuel quantity, and oxygen quantity, and adjusts the system of this application based on the global data.

[0063] In a preferred embodiment, when the unit is scheduled to perform deep peak shaving, i.e., operate at 30% load, the anti-ash blockage system is started one hour in advance to preheat the cold end heat storage element, so as to avoid a sudden drop in wall temperature at low load.

[0064] The flue gas control method for an air preheater anti-clogging system based on a coupled flue gas recirculation system presented in this application has a significantly better anti-clogging effect compared to timed cleaning and parameter-based cleaning. It also reduces system energy consumption and the concentration of nitrogen oxides during combustion. Specific embodiments will illustrate this further. Example 1

[0065] When the thermal power unit load is 80~100%, the air volume of flue gas duct 6 is distributed through the regulating valve: the air volume of flue gas return duct 7 accounts for 8~15%, the air volume in the air volume splitting and anti-clogging ash system accounts for 5~10%, and the air volume passing through the flue gas domain accounts for 75~85%.

[0066] When the thermal power unit load is 60-80%, the air volume splitting and anti-ash blockage system is set to purge for five minutes every two hours. Without purging the rotary air preheater 1, the air volume proportion in the flue gas return duct 7 is 10-15%, and the air volume proportion passing through the flue gas domain is 85-90%. When purging the rotary air preheater 1, the air volume proportion in the flue gas return duct 7 is 8-12%, the air volume proportion within the air volume splitting and anti-ash blockage system is 8-12%, and the air volume proportion passing through the flue gas domain is 75-85%.

[0067] When the thermal power unit load is less than 60%, the air volume splitting and anti-clogging ash removal system is set to passive ash removal. The flue gas recirculation system is always running, and the air volume ratio of the flue gas circuit pipeline is 8~15%. When the pressure difference between the two sides of the rotary air preheater 1 exceeds 1.3MPa or the temperature of the rotor of the rotary air preheater 1 is lower than 110℃, the air volume splitting and anti-clogging ash removal system is activated.

[0068] Comparative Example 1 The flue gas recirculation system is always running, and the air volume in the flue gas loop duct accounts for 8-15%. When the pressure difference between the two sides of the rotary air preheater 1 exceeds 1.3MPa or the temperature of the rotor of the rotary air preheater 1 is lower than 110℃, the air volume splitting and anti-clogging system is activated.

[0069] Comparative Example 2 The flue gas recirculation system operates continuously, with the air volume in the flue gas loop duct accounting for 8-15%. The air volume splitting and anti-clogging system is set to purge for five minutes every two hours.

[0070] The air preheater anti-clogging ash system of the coupled flue gas recirculation system of this application was operated for one week according to the ash removal methods of Example 1, Comparative Example 1, and Comparative Example 2. The total energy consumption of the circulating fan, the average concentration of nitrogen oxides in the flue gas emitted by the coal-fired unit, and the mass of ash per square centimeter at the same location of the heat storage element were statistically analyzed. The results are shown in Table 1.

[0071] Table 1: Example 1 265 328 5 Comparative Example 1 321 456 13 Comparative Example 2 368 413 9 As shown in Table 1, the total energy consumption of the fan in Example 1 is 265 kWh, significantly lower than that of Comparative Example 1 (321 kWh) and Comparative Example 2 (368 kWh). The nitrogen oxide concentration in Example 1 is 328 mg / m³. 3 It was significantly lower than the 456 mg / m² of the control group. 3 Compared with Comparative Example 2, 413 mg.m 3 In Example 1, the ash mass per square centimeter was 5g, significantly lower than the 13g in Comparative Example 1 and the 9g in Comparative Example 2. The flue gas control method of the air preheater anti-clogging system based on the coupled flue gas recirculation system of this application has a significant anti-clogging effect compared to timed cleaning and parameter-based cleaning, while also reducing system energy consumption and the concentration of nitrogen oxides during combustion.

[0072] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. An air preheater anti-clogging system for a coupled flue gas recirculation system, characterized in that: include, Rotary air preheater (1); The hot end pipe (2) and the cold end pipe (3) of the rotary air preheater (1) are connected; a first hot end regulating valve (201) and a second hot end regulating valve (202) are connected in parallel on the hot end pipe (2), and a first cold end regulating valve (301) and a second cold end regulating valve (302) are connected in parallel on the cold end pipe (3). A first variable frequency fan (4) and a second variable frequency fan (5) are connected to the hot end pipe (2) and the cold end pipe (3); a first hot end regulating valve (201) controls the flow of flue gas to the first variable frequency fan (4), and a second hot end regulating valve (202) controls the flow of flue gas to the second variable frequency fan (5); a first cold end regulating valve (301) controls the flow of flue gas from the first variable frequency fan (4) to the rotary air preheater (1), and a second cold end regulating valve (302) controls the flow of flue gas from the second variable frequency fan (5) to the rotary air preheater (1); A flue gas duct (6) connects the first variable frequency fan (4), the second variable frequency fan (5) and the flue gas outlet of the external boiler. The flue gas duct (6) is also connected to the flue gas outlet of the rotary air preheater (1). The flue gas return pipe (7) connects the first variable frequency fan (4), the second variable frequency fan (5) and the external boiler furnace. The flue gas return pipe (7) is also connected to the cold end pipe (3). The first flue gas regulating valve (601) and the second flue gas regulating valve (602) on the flue gas duct (6); The first return regulating valve (701) and the second return regulating valve (702) on the flue gas return pipe (7); Pressure sensor (8), the pressure sensor (8) is used to detect pipeline pressure and pressure on both sides of the rotor of rotary air preheater (1); The flow sensor (9) is used to detect the flue gas flow rate at the flue gas outlet of the boiler, and also to detect the flue gas flow rate at the flue gas inlet of the rotary air preheater (1), the flue gas flow rate entering the furnace, and the flue gas flow rate entering the air volume splitting and anti-clogging system. Temperature sensor (10) is used to detect the temperature inside the boiler furnace, the temperature of the flue gas outlet of the boiler, and the hot end temperature and cold end temperature of the heat storage element. The controller (11) that controls the operation of the system has the pressure sensor (8), flow sensor (9), and temperature sensor (10) electrically connected to the controller (11) to transmit the collected pressure information, flow information, and temperature information to the controller (11). The controller (11) controls the operation of the first hot end regulating valve (201), the second hot end regulating valve (202), the first cold end regulating valve (301), the second cold end regulating valve (302), the first variable frequency fan (4), the second variable frequency fan (5), the first flue gas regulating valve (601), the second flue gas regulating valve (602), the first return flow regulating valve (701), and the second return flow regulating valve (702) according to the received information.

2. The air preheater anti-clogging system of the coupled flue gas recirculation system as described in claim 1, characterized in that: The rotary air preheater (1) includes a flue gas zone, a primary air zone, a secondary air zone, and an ash removal zone with a fan-shaped cross section. Adjacent zones are separated by fan-shaped plates. The primary air zone is used to dry and preheat pulverized coal, the secondary air zone is used to preheat the air entering the furnace, the flue gas zone is used to heat the heat storage element of the rotary air preheater (1), and the ash removal zone is used to heat the cold end of the heat storage element.

3. The air preheater anti-ash clogging system of the coupled flue gas recirculation system as described in claim 1, characterized in that: Expansion joints are also provided on the hot end pipe (2) and the cold end pipe (3) to buffer the pipe deformation caused by thermal expansion and contraction.

4. The air preheater anti-ash clogging system of the coupled flue gas recirculation system as described in claim 1, characterized in that: A diversion valve (12) is installed at the junction of the flue gas duct (6), the cold end duct (3), and the flue gas return duct (7) to distribute the flue gas flow.

5. A flue gas control method based on an air preheater anti-clogging system of a coupled flue gas recirculation system as described in claim 1, characterized in that: Includes the following steps: Step 1: Real-time acquisition of characteristic information of boiler, rotary air preheater (1) and pipelines; Step 2: Based on the feature information, determine whether it is necessary to actively or passively activate the airflow splitting anti-clogging system. Step 3: Based on the characteristic information, adjust the flue gas flow rate of the air volume splitting and anti-clogging ash system and the flue gas recirculation.

6. The flue gas control method as described in claim 5, characterized in that: It also includes step 4: adjusting the power of the first variable frequency fan (4) and the second variable frequency fan (5) according to the feature information.

7. The flue gas control method as described in claim 5, characterized in that: In step 3, When the load of the thermal power unit is 80~100%, the air volume of the flue gas duct (6) is allocated; among which, the air volume of the flue gas return duct (7) accounts for 8~15%, the air volume in the air volume splitting and anti-clogging ash system accounts for 5~10%, and the air volume in the flue gas area accounts for 75~85%. When the load of the thermal power unit is 60-80%, the air volume splitting and anti-clogging system is set to timed cleaning; when the rotary air preheater (1) is not purged, the air volume ratio of the flue gas return pipe (7) is 10-15%, and the air volume ratio of the air volume passing through the flue gas domain is 85-90%; when the rotary air preheater (1) is purged, the air volume ratio of the flue gas return pipe is 8-12%, the air volume ratio of the air volume splitting and anti-clogging system is 8-12%, and the air volume ratio of the air volume passing through the flue gas domain is 75-85%. When the load of the thermal power unit is less than 60%, the pressure difference between the two sides of the rotary air preheater (1) exceeds the standard or the temperature of the rotor is lower than the preset value, the air volume splitting and anti-clogging ash system is started; the flue gas recirculation system is always closed.

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