Closed-loop control method based on cleaning condition of air preheater and online cleaning device

Abstract

The invention discloses a closed-loop control method based on the cleaning condition of an air preheater and a cleaning device, and relates to the technical field of maintenance of air preheaters of coal-fired power plants. The invention provides a closed-loop control method and an online cleaning device to solve the problems that in the prior art, the cleaning condition of an air preheater cannot be monitored in real time, a closed-loop control method feedback mechanism is lacked, and the cleaning effect is difficult to comprehensively evaluate. According to the closed-loop control method, closed-loop management of cleaning condition monitoring, cleaning action control and economical efficiency evaluation is achieved by measuring key parameters of the air pre-heater, establishing a numerical simulation model, calculating key indexes such as a resistance coefficient and a heat exchange coefficient and combining dynamic wall temperature control and an air energy pulse cleaning technology. The on-line cleaning device adopts an arc-shaped mother pipe and an adaptive flow guide cover, and by optimizing airflow distribution and adjusting the position of the mother pipe, the purging coverage rate and the sweeping effect of heat exchange pieces are improved, efficient and stable operation of the air preheater is guaranteed, and the economical efficiency and the safety of the generator set are improved.

Description

Technical Field

[0001] This invention relates to the field of thermal equipment maintenance technology in coal-fired power plants, specifically to a closed-loop control method and online cleaning device based on the cleanliness status of air preheaters. Background Technology

[0002] Currently, the vast majority of coal-fired power plants have completed denitrification retrofits. Among them, selective catalytic reduction (SCR) denitrification is widely used in the industry due to its mature technology, high denitrification efficiency, and stable operation. However, with the extension of SCR reactor operating time and the increase in ammonia injection under ultra-clean emission requirements, air preheaters commonly experience problems such as ash accumulation, corrosion, and blockage, which seriously affect unit operation.

[0003] The aforementioned problems directly lead to increased resistance in the forced draft fan and induced draft fan, insufficient airflow in the coal mill, and elevated flue gas temperature. In some power plants, the problem of air preheater blockage is particularly serious, even causing induced draft fan stall and tripping, resulting in unplanned temporary shutdowns of the unit. This not only significantly reduces the unit's operating economy but also poses a major threat to operational safety.

[0004] The core cause of air preheater blockage lies in the unavoidable production of ammonium bisulfate during SCR operation. Ammonium bisulfate has a melting point of 147℃ and a boiling point of 350℃, and it can react with alkaline solutions to produce ammonia gas. When it is generated in flue gas, it is usually in a gaseous state with a low concentration. However, as the flue gas temperature gradually decreases, when the temperature drops below the dew point temperature, the gaseous ammonium bisulfate will condense into a liquid state, and the dew point temperature is related to the concentration of ammonium bisulfate. Numerous experimental studies have shown that when the boiler flue gas temperature drops to 220-230℃, the gaseous ammonium bisulfate will transform into a liquid state and condense on the heated surfaces.

[0005] The low-temperature range of the rotary air preheater is exactly 120–230°C, which falls within the condensation temperature range of ammonium bisulfate. Within this temperature range, liquid ammonium bisulfate has extremely high viscosity and will quickly adhere to the surface of the heat exchange elements of the air preheater, and adsorb a large amount of fly ash from the flue gas, ultimately leading to blockage of the air preheater.

[0006] While existing technologies have proposed various solutions to address the problem of ammonium bisulfate clogging in air preheaters, they all have significant drawbacks: they cannot monitor the cleanliness of the air preheater in real time, lack a closed-loop management mechanism of "monitoring-feedback-action," make it difficult to comprehensively evaluate the cleaning effect, and cannot ensure that the air preheater is always in a state of high-efficiency operation; in addition, the existing cleaning devices have complex and unreasonable structures, resulting in poor cleaning effects. Summary of the Invention

[0007] To address the shortcomings of existing air preheater cleaning monitoring and cleaning technologies, the present invention aims to provide a closed-loop control method based on the cleanliness status of the air preheater, enabling real-time monitoring, closed-loop management, and efficient cleaning, thereby ensuring the efficient and stable operation of the air preheater.

[0008] Another objective of this invention is to provide an online cleaning device based on the cleanliness of an air preheater, which has a simple and reasonable structure and a significant cleaning effect.

[0009] To achieve the above objectives, the present invention adopts the following technical solution: a closed-loop control method based on the cleanliness status of an air preheater, comprising the following steps:

[0010] 1) Parameter measurement: Measure and obtain the rotational speed v, rotor radius r, and hot end temperature t1 and cold end temperature t2 of the rotor in the air preheater;

[0011] 2) Model establishment: Establish a single-channel numerical simulation model of the flow gap unit of the heat storage element plate in the air preheater rotor, and set the parameters measured in step 1) as the boundary conditions of the model.

[0012] 3) Calculation of friction resistance coefficient: Based on the single-channel numerical simulation model established in step 2), calculate the friction resistance coefficient of air flowing through the flow gap of the heat storage element plate;

[0013]

[0014] In the formula, Δp is the pressure difference caused by friction resistance; ρ is the air density; v is the flow velocity between the two heat storage elements; r is the hydraulic radius of the flow gap; and l is the length of the heat storage element plate.

[0015] 4) Calculation of convective heat transfer coefficient: Combining the single-channel numerical simulation model in step 2) with the measurement parameters in step 1), calculate the convective heat transfer coefficient of air flowing through the heat storage channel;

[0016]

[0017] In the formula, Q is the heat transfer heat; A is the surface area of ​​the heat storage element plate; Δt is the temperature difference between the fluid and the surface of the heat storage element plate;

[0018] 5) Determine the formation range of ammonium bisulfate: Based on the convective heat transfer coefficient calculated in step 4), obtain the average temperature and temperature distribution of the cold end of the heat storage element plate, and then determine the formation range of ammonium bisulfate on the heat storage element plate.

[0019] 6) Heating parameter calculation: Calculate the heating time and target temperature required for the heat storage element plate in the air preheater rotor to rise;

[0020]

[0021] In the formula, t0 is the crystallization temperature of ammonium hydrogen sulfate; T2 is the average cold end temperature of the heat storage element plate;

[0022] 7) Cleaning parameter calculation: Combining dynamic wall temperature "cold source control" technology, calculate the heat exchange area and time required for the heat storage element plate temperature to reach the target temperature value; at the same time, combining air source pulse cleaning technology, calculate the temperature and time required for pyrolysis and peeling of dirt.

[0023] Heat exchange area A: A=[mc(t) t -t0)] / [KΔt m t]

[0024] In the formula, m is the total mass of the heat storage element, c is the specific heat capacity of the heat storage element, and t is the total mass of the heat storage element. t Temperature control target temperature, t0 initial temperature of the heat storage element, k total heat transfer coefficient (including convective heat transfer between the cold source and the element + heat conduction of the element), Δt m Logarithmic mean temperature difference, t temperature control time;

[0025] Temperature control time calculation t: t = [mc(t)] t -t0)] / [KAΔt av ]

[0026] In the formula, Δt av Average heat transfer temperature difference (°C), which can be taken as Δt for simplified calculation. av = (Δt1 + Δt2) / 2, where Δt1 is the initial temperature difference (t0 - t_cold), and Δt2 is the target temperature difference (t_cold). t -t_cold), where t_cold is the temperature of the cold source.

[0027] pyrolysis stripping temperature T of dirt pγro :

[0028] T pγro =T0+ΔH pYro / c_ash (or directly use the empirical value of the critical temperature for pyrolysis of ash and scale; the formula is derived theoretically)

[0029] In the formula, T0 is the ambient temperature (°C), and ΔH is the ΔH value. pγro Enthalpy of pyrolysis of ash (J / kg), cash: specific heat capacity of ash (J / (kg·℃)).

[0030] pyrolysis stripping time of dirt (t) pγro )

[0031] (Based on unsteady-state heat conduction): t pγro =(δ 2·ρ_ash·c_ash) / (4λ_ash)·ln[(T_air_pulse-T0) / (T_air_pulse-T pγro )]

[0032] In the formula, δ represents the thickness of the scale (m), and ρ_ash represents the density of the scale (kg / m³). 3 The standard value is 1200-1800 kg / m³. 3 λ_ash is the thermal conductivity of the ash (W / (m·℃)), which is usually taken as 0.15-0.3W / (m·℃);

[0033] 8) Impact assessment of the equipment: Quantitatively analyze the impact of the clean production equipment layout on air and flue resistance, as well as the quantitative impact on plant power consumption;

[0034] 9) Comprehensive economic calculation: Based on the evaluation results of step 8), combined with the operating parameters of the air preheater, the comprehensive economic efficiency of the boiler is calculated to form a closed-loop control of "monitoring-calculation-evaluation-feedback".

[0035] The online cleaning device used in the above-mentioned closed-loop control method based on the cleanliness of the air preheater includes an air preheater, a main pipe assembly, and a flow guide assembly. The main pipe assembly is located on one axial side of the heat exchange plates of the air preheater, and is generally arc-shaped. The side adjacent to the air preheater is densely covered with air outlets, and the main pipe assembly also has an air inlet for connecting to an external high-pressure air source. The flow guide assembly covers the outside of the main pipe assembly, and the interior of the flow guide assembly forms a flow guide groove adapted to the shape of the main pipe assembly. The orientation of the flow guide groove is consistent with the axial direction of the heat exchange plates of the air preheater to prevent airflow dispersion and ensure the intensity of the purging airflow. The main pipe assembly and the flow guide assembly are assembled together and moved radially along the air preheater by a reciprocating mechanism, so that all areas of the heat exchange plates can be purged in place.

[0036] Furthermore, the main pipe assembly includes a first main pipe, a second main pipe, and vent pipes, wherein the length of the first main pipe is greater than the length of the second main pipe, the first main pipe and the second main pipe form a concentric arc, and the two are connected and fixed by two vent pipes and are internally connected; both the first main pipe and the second main pipe are densely covered with air outlets on the side adjacent to the air preheater; a three-way pipe joint is provided at the center of the first main pipe, the inlet of the three-way pipe joint is connected to a high-pressure air source, and the other two outlets are respectively connected to the first main pipe, so that two airflows are formed in the first main pipe from the middle to both ends, ensuring that the airflow intensity is uniform in all areas of the entire main pipe assembly.

[0037] The reciprocating mechanism includes a screw assembly and a guide assembly. The guide assembly has two parallel slide rails, and two vent pipes are clamped to the two slide rails by clamps to form a sliding fit, ensuring the stability of the main pipe assembly during radial movement. A nut is hollowly arranged in the central area of ​​the tee pipe joint, and the inner wall of the nut is threaded. The screw assembly includes multiple connecting pipes located between the two vent pipes. A sleeve is attached to the surface of the connecting pipe, and a screw is installed inside the sleeve. The screw extends out of one end of the sleeve and connects to the motor, and passes through the nut at the other end of the sleeve and is threadedly connected to the nut. Both the screw assembly and the guide assembly are arranged radially along the air preheater. By adjusting the screw assembly, the main pipe assembly is driven to move radially along the air preheater, ensuring that all areas of the heat exchange fins are purged.

[0038] The fairing assembly includes a first fairing and a second fairing, which are respectively covered on the outside of the first main pipe and the outside of the second main pipe, and the first fairing and the second fairing are in an arc shape that fits the first main pipe and the second main pipe.

[0039] An air inlet is provided on the second main pipe to further improve the airflow supply efficiency and adapt to different cleaning needs.

[0040] This invention achieves real-time monitoring and dynamic control of the air preheater's cleanliness through a closed-loop control method. Combined with the efficient purging function of an online cleaning device, it solves the problems of non-real-time cleaning monitoring, poor cleaning effect, and lack of closed-loop management in existing technologies. When the air preheater heat exchange fins rotate, the arc-shaped main tube and the guide shroud work together to continuously purge the heat exchange fins within a fixed angle range on the arc surface, increasing the purging time of the heat exchange fins, significantly improving the cleaning effect and heat exchange efficiency, and thus improving the economic performance of the generator set. Attached Figure Description

[0041] Figure 1 This is a schematic diagram of the steps of the closed-loop control method in this invention.

[0042] Figure 2 This is a schematic diagram of the overall structure of the online cleaning device in this invention.

[0043] Figure 3 This is a schematic diagram of the cooperation structure between the main pipe assembly and the flow guide assembly in the online cleaning device of the present invention.

[0044] Figure 4 This is a schematic diagram showing the connection between the tee connector and the first main pipe in the online cleaning device of the present invention.

[0045] Figure 5 This is a schematic diagram showing the connection between the lead screw assembly and the guide assembly in the online cleaning device of the present invention.

[0046] Appendix Figure 2-5In the middle, 1. Air preheater; 2. Main pipe assembly; 3. Clamping device; 4. Air preheater heat exchange plate; 5. T-joint; 7. Slide rail; 8. Sleeve; 9. Lead screw; 10. Connecting pipe; 11. Lead screw assembly; 12. Guide assembly; 21. First main pipe; 22. Second main pipe; 23. Vent pipe; 24. Air outlet; 31. First guide shroud; 32. Second guide shroud; 51. Nut. Detailed Implementation

[0047] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0048] Appendix Figure 1 This is one embodiment of the present invention, disclosing a closed-loop control method based on the cleanliness status of an air preheater, comprising the following steps:

[0049] 1) Parameter measurement: The rotational speed v of the air preheater was measured and obtained by the speed sensor as 1.5 r / min, the rotor radius r was measured as 3.8 m by the laser rangefinder, and the hot end temperature t1 and cold end temperature t2 of the rotor in the air preheater were measured as 380℃ and 135℃ respectively by the thermocouple sensor.

[0050] 2) Model establishment: Establish a single-channel numerical simulation model of the flow gap unit of the heat storage element plate in the air preheater rotor, and set the parameters measured in step 1) as the boundary conditions of the model.

[0051] 3) Calculation of friction resistance coefficient: Based on the single-channel numerical simulation model established in step 2), calculate the friction resistance coefficient of air flowing through the flow gap of the heat storage element plate;

[0052]

[0053] In the formula, Δp is the pressure difference caused by friction resistance; ρ is the air density; v is the flow velocity between the two heat storage elements; r is the hydraulic radius of the flow gap; and l is the length of the heat storage element plate.

[0054] 4) Calculation of convective heat transfer coefficient: Combining the single-channel numerical simulation model in step 2) with the measurement parameters in step 1), calculate the convective heat transfer coefficient of air flowing through the heat storage channel;

[0055]

[0056] In the formula, Q is the heat transfer heat; A is the surface area of ​​the heat storage element plate; Δt is the temperature difference between the fluid and the surface of the heat storage element plate;

[0057] 5) Determine the formation range of ammonium bisulfate: Based on the convective heat transfer coefficient calculated in step 4), obtain the average temperature and temperature distribution of the cold end of the heat storage element plate, and then determine the formation range of ammonium bisulfate on the heat storage element plate.

[0058] 6) Heating parameter calculation: Calculate the heating time and target temperature required for the heat storage element plate in the air preheater rotor to rise;

[0059]

[0060] In the formula, t0 is the crystallization temperature of ammonium hydrogen sulfate; T2 is the average cold end temperature of the heat storage element plate;

[0061] 7) Cleaning parameter calculation: Combining dynamic wall temperature "cold source control" technology, calculate the heat exchange area and time required for the heat storage element plate temperature to reach the target temperature value; at the same time, combining air source pulse cleaning technology, calculate the temperature and time required for pyrolysis and peeling of dirt.

[0062] Heat exchange area A: A=[mc(t) t -t0)] / [KΔt m t]

[0063] In the formula, m is the total mass of the heat storage element, c is the specific heat capacity of the heat storage element, and t is the total mass of the heat storage element. t Temperature control target temperature, t0 initial temperature of the heat storage element, k total heat transfer coefficient (including convective heat transfer between the cold source and the element + heat conduction of the element), Δt m Logarithmic mean temperature difference, t temperature control time;

[0064] Temperature control time calculation t: t = [mc(t)] t -t0)] / [KAΔt av ]

[0065] In the formula, Δt av Average heat transfer temperature difference (°C), which can be taken as Δt for simplified calculation. av = (Δt1 + Δt2) / 2, where Δt1 is the initial temperature difference (t0 - t_cold), and Δt2 is the target temperature difference (t_cold). t -t_cold), where t_cold is the temperature of the cold source.

[0066] pyrolysis stripping temperature T of dirt pγro :

[0067] T pγro =T0+ΔH pγro / c_ash (or directly use the empirical value of the critical temperature for pyrolysis of ash and scale; the formula is derived theoretically)

[0068] In the formula, T0 is the ambient temperature (°C), and ΔH is the ΔH value. pγro Enthalpy of pyrolysis of ash (J / kg), cash: specific heat capacity of ash (J / (kg·℃)).

[0069] pyrolysis stripping time of dirt (t) pγro )

[0070] (Based on unsteady-state heat conduction): t pγro =(δ 2 ·ρ_ash·c_ash) / (4λ_ash)·ln[(T_air_pulse-T0) / (T_air_pulse-T pγro )]

[0071] In the formula, δ represents the thickness of the scale (m), and ρ_ash represents the density of the scale (kg / m³). 3 The standard value is 1200-1800 kg / m³. 3 λ_ash is the thermal conductivity of the ash (W / (m·℃)), which is usually taken as 0.15-0.3W / (m·℃);

[0072] 8) Impact assessment of the equipment: Quantitatively analyze the impact of the clean production equipment layout on air and flue resistance, as well as the quantitative impact on plant power consumption;

[0073] 9) Comprehensive economic calculation: Based on the evaluation results of step 8), combined with the operating parameters of the air preheater, the comprehensive economic efficiency of the boiler is calculated to form a closed-loop control of "monitoring-calculation-evaluation-feedback".

[0074] Appendix Figure 2-5 Another embodiment of the present invention discloses an online cleaning device, including an air preheater 1, a main pipe assembly 2, and a flow guide assembly. The main pipe assembly 2 is disposed on one axial side of the heat exchange plate 4 of the air preheater, and is generally arc-shaped. The side adjacent to the air preheater 1 is densely covered with air outlets 24. The main pipe assembly 2 is also provided with an air inlet for connecting to an external high-pressure air source. The flow guide assembly is disposed on the outside of the main pipe assembly 2. The flow guide assembly forms a flow guide groove inside that is adapted to the shape of the main pipe assembly 2. The orientation of the flow guide groove is consistent with the axial direction of the heat exchange plate 4 of the air preheater to prevent airflow dispersion and ensure the strength of the purging airflow. The main pipe assembly 2 and the flow guide assembly are assembled together and moved radially along the air preheater 1 by a reciprocating mechanism, so that all areas of the heat exchange plate can be purged in place.

[0075] Furthermore, the main pipe assembly 2 includes a first main pipe 21, a second main pipe 22, and a vent pipe 23. The length of the first main pipe 21 is greater than the length of the second main pipe 22. The first main pipe 21 and the second main pipe 22 form a concentric arc and are connected and fixed by two vent pipes 23 and are internally connected. Both the first main pipe 21 and the second main pipe 22 are densely covered with air outlets 24 on the side adjacent to the air preheater 1. A three-way pipe joint 5 is provided at the center of the first main pipe 21. The inlet of the three-way pipe joint 5 is connected to a high-pressure air source, and the other two outlets are respectively connected to the first main pipe 21, so that two airflows are formed in the first main pipe 21 from the middle to both ends, ensuring that the airflow intensity is uniform in all areas of the entire main pipe assembly 2.

[0076] The reciprocating mechanism includes a lead screw assembly 11 and a guide assembly 12. The guide assembly 12 has two parallel slide rails, and two vent pipes 23 are clamped to the two slide rails by clamps 3 to form a sliding fit, ensuring the stability of the main pipe assembly 2 when moving radially. A nut 51 is hollowly provided in the central area of ​​the tee pipe joint 5, and the inner wall of the nut 51 is threaded. The lead screw assembly 11 includes multiple connecting pipes 10 between the two vent pipes 23. A sleeve 8 is attached to the surface of the connecting pipe 10. A lead screw 9 is provided inside the sleeve 8. The lead screw 9 extends out of one end of the sleeve 8 and is connected to the motor. It passes through the nut 51 at the other end of the sleeve 8 and is threadedly connected to the nut 51. Both the lead screw assembly 11 and the guide assembly 12 are arranged radially along the air preheater 1. By adjusting the lead screw assembly 11, the main pipe assembly 2 is driven to move radially along the air preheater 1 to ensure that all areas of the heat exchange fins can be purged.

[0077] The fairing assembly 3 includes a first fairing 31 and a second fairing 32, which are respectively covered on the outside of the first main pipe 21 and the outside of the second main pipe 22, and the first fairing 31 and the second fairing 32 are in an arc shape that is adapted to the first main pipe 21 and the second main pipe 22.

[0078] An air inlet is provided on the second main pipe 22 to further improve the airflow supply efficiency and adapt to different cleaning needs.

[0079] The online cleaning device of the present invention is used to clean the above-mentioned air preheater. The specific structure and application effects are as follows:

[0080] 1. Dimensions of the main pipe assembly and the fairing assembly: The first main pipe has a radius of 3.8m and a length of 6m; the second main pipe has a radius of 3.5m and a length of 5m; the vent pipe has a length of 0.3m and a quantity of 4; the radius of the fairing's arc is adapted to the main pipe, and the width of the guide groove is 80mm;

[0081] 2. Airflow parameters: The high-pressure air source pressure is set to 0.8MPa, and air is supplied to the middle of the first main pipe through a three-way pipe joint. The airflow pressure difference between the two ends of the first main pipe is less than 0.05MPa, and the airflow uniformity is good.

[0082] 3. Position adjustment: The radial position of the main tube is adjusted by the screw mechanism, with an adjustment range of 0-500mm, to ensure that the distance between the air outlet of the main tube and the heat exchange plate is maintained at 150mm (the optimal purging distance), so as to achieve full coverage purging of the heat exchange plate.

[0083] 4. Cleaning effect: After cleaning, the friction coefficient of the air preheater decreased from 0.032 to 0.021, the flue gas temperature decreased from 145℃ to 132℃, the induced draft fan current decreased by 8A, and the unit's coal consumption for power generation decreased by 3g / (kW·h), demonstrating a significant cleaning effect.

Claims

1. A closed-loop control method based on the cleanliness status of an air preheater, characterized in that... Includes the following steps: 1) Parameter measurement: Measure and obtain the rotational speed v, rotor radius r, and hot end temperature t1 and cold end temperature t2 of the rotor in the air preheater; 2) Model establishment: Establish a single-channel numerical simulation model of the flow gap unit of the heat storage element plate in the air preheater rotor, and set the parameters measured in step 1) as the boundary conditions of the model. 3) Calculation of friction resistance coefficient: Based on the single-channel numerical simulation model established in step 2), calculate the friction resistance coefficient of air flowing through the flow gap of the heat storage element plate; In the formula, Δp is the pressure difference caused by friction resistance; ρ is the air density; v is the flow velocity between the two heat storage elements; r is the hydraulic radius of the flow gap; and l is the length of the heat storage element plate. 4) Calculation of convective heat transfer coefficient: Combining the single-channel numerical simulation model in step 2) with the measurement parameters in step 1), calculate the convective heat transfer coefficient of air flowing through the heat storage channel; In the formula, Q is the heat transfer heat; A is the surface area of ​​the heat storage element plate; Δt is the temperature difference between the fluid and the surface of the heat storage element plate; 5) Determine the formation range of ammonium bisulfate: Based on the convective heat transfer coefficient calculated in step 4), obtain the average temperature and temperature distribution of the cold end of the heat storage element plate, and then determine the formation range of ammonium bisulfate on the heat storage element plate. 6) Heating parameter calculation: Calculate the heating time and target temperature required for the heat storage element plate in the air preheater rotor to rise; In the formula, t0 is the crystallization temperature of ammonium hydrogen sulfate; T2 is the average cold end temperature of the heat storage element plate; 7) Cleaning parameter calculation: Combining dynamic wall temperature "cold source control" technology, calculate the heat exchange area and time required for the heat storage element plate temperature to reach the target temperature value; at the same time, combining air source pulse cleaning technology, calculate the temperature and time required for pyrolysis and peeling of dirt. Heat exchange area A: A=[mc(t) t -t0)] / [KΔt m t] In the formula, m is the total mass of the heat storage element, c is the specific heat capacity of the heat storage element, and t is the total mass of the heat storage element. t Temperature control target temperature, t0 initial temperature of the heat storage element, k total heat transfer coefficient (including convective heat transfer between the cold source and the element + heat conduction of the element), Δt m Logarithmic mean temperature difference, t temperature control time; Temperature control time calculation t: t = [mc(t)] t -t0)] / [KAΔt av ] In the formula, Δt av Average heat transfer temperature difference (°C), which can be taken as Δt for simplified calculation. av = (Δt1 + Δt2) / 2, where Δt1 is the initial temperature difference (t0 - t_cold), and Δt2 is the target temperature difference (t_cold). t -t_cold), where t_cold is the temperature of the cold source; pyrolysis stripping temperature T of dirt pγro :T pγro =T0+ΔH pγro / c_ash (or directly use the empirical value of the critical temperature for pyrolysis of ash and scale; the formula is derived theoretically) In the formula, T0 is the ambient temperature (°C), and ΔH is the ΔH value. pγro Enthalpy of pyrolysis of ash and scale (J / kg) c_ash: Specific heat capacity of ash (J / (kg·℃)); pyrolysis stripping time of dirt (t) pγro (Based on unsteady-state heat conduction): t pγro =(δ 2 ·ρ_ash·c_ash) / (4λ_ash)·ln[(T_air_pulse-T0) / (T_air_pulse-T pγro )] In the formula, δ represents the thickness of the scale (m), and ρ_ash represents the density of the scale (kg / m³). 3 The standard value is 1200-1800 kg / m³. 3 λ_ash is the thermal conductivity of the ash (W / (m·℃)), which is usually taken as 0.15-0.3W / (m·℃); 8) Impact assessment of the equipment: Quantitatively analyze the impact of the clean production equipment layout on air and flue resistance, as well as the quantitative impact on plant power consumption; 9) Comprehensive economic calculation: Based on the evaluation results of step 8), combined with the operating parameters of the air preheater, the comprehensive economic efficiency of the boiler is calculated to form a closed-loop control of "monitoring-calculation-evaluation-feedback".

2. The online cleaning device used in the closed-loop control method based on the cleanliness status of the air preheater according to claim 1, characterized in that: The system includes an air preheater, a main pipe assembly, and a flow guide assembly. The main pipe assembly is located on one axial side of the heat exchange plates of the air preheater. It is arc-shaped and has numerous air outlets on the side adjacent to the air preheater. The main pipe assembly also has an air inlet for connecting to an external high-pressure air source. The flow guide assembly covers the outside of the main pipe assembly. The flow guide assembly has a flow guide groove inside that matches the shape of the main pipe assembly. The direction of the flow guide groove is consistent with the axial direction of the heat exchange plates of the air preheater to prevent airflow dispersion and ensure the intensity of the purging airflow. The main pipe assembly and the flow guide assembly are assembled together and moved radially along the air preheater by a reciprocating mechanism, so that all areas of the heat exchange plates can be purged.

3. The online cleaning device used in the closed-loop control method based on the cleanliness status of the air preheater according to claim 2, characterized in that: The main pipe assembly includes a first main pipe, a second main pipe, and vent pipes. The first main pipe is longer than the second main pipe. The first and second main pipes form a concentric arc and are connected and fixed by two vent pipes, which are internally connected. Both the first and second main pipes have densely packed air outlets on the side adjacent to the air preheater. A three-way pipe joint is provided at the center of the first main pipe. The inlet of the three-way pipe joint is connected to a high-pressure air source, and the other two outlets are connected to the first main pipe, so that two airflows are formed in the first main pipe from the middle to both ends, ensuring that the airflow intensity is uniform in all areas of the entire main pipe assembly.

4. The online cleaning device used in the closed-loop control method based on the cleanliness status of the air preheater according to claim 3, characterized in that: The reciprocating mechanism includes a screw assembly and a guide assembly. The guide assembly has two parallel slide rails, and two vent pipes are clamped to the two slide rails by clamps to form a sliding fit, ensuring the stability of the main pipe assembly during radial movement. A nut is hollowly arranged in the central area of ​​the tee pipe joint, and the inner wall of the nut is threaded. The screw assembly includes multiple connecting pipes located between the two vent pipes. A sleeve is attached to the surface of the connecting pipe, and a screw is installed inside the sleeve. The screw extends out of one end of the sleeve and connects to the motor, and passes through the nut at the other end of the sleeve and is threadedly connected to the nut. Both the screw assembly and the guide assembly are arranged radially along the air preheater. By adjusting the screw assembly, the main pipe assembly is driven to move radially along the air preheater, ensuring that all areas of the heat exchange fins are purged.

5. The online cleaning device used in the closed-loop control method based on the cleanliness status of the air preheater according to claim 2, characterized in that: The fairing assembly includes a first fairing and a second fairing, which are respectively covered on the outside of the first main pipe and the outside of the second main pipe, and the first fairing and the second fairing are in an arc shape that fits the first main pipe and the second main pipe.

6. The online cleaning device used in the closed-loop control method based on the cleanliness status of the air preheater according to claim 3, characterized in that: An air inlet is provided on the second main pipe to further improve the airflow supply efficiency and adapt to different cleaning needs.

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