Control method for relieving blockage of air pre-heater of 600MW unit and anti-pollution spray head

Abstract

The invention discloses a control method for relieving blockage of an air pre-heater of a 600MW unit and an anti-pollution sprayer. The control method comprises the following steps: acquiring unit load, exhaust gas temperature, sulfur trioxide concentration in flue gas and differential pressure data of an inlet and an outlet of the air pre-heater in real time, and judging whether the unit is in a working condition of easily generating ammonium bisulfate or not; preparing a sodium carbonate solution with a certain concentration, and preserving heat and storing. The working condition that ammonium bisulfate is easy to generate is accurately recognized through multi-parameter cooperation, the problem of spraying opportunity deviation caused by working condition misjudgment in a traditional technology is solved, meanwhile, heat preservation storage and concentration stable control are adopted, crystallization of a sodium carbonate solution is avoided, the activity of raw materials for removal reaction is guaranteed, and the removal rate of sulfur trioxide is stabilized to be 85% or above; and dynamic injection adjustment and blockage risk assessment are combined, so that the blockage trend of the air pre-heater is effectively delayed, and the load reduction frequency of the unit due to blockage is reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of 600MW unit air preheater blockage mitigation, and in particular to a control method for mitigating 600MW unit air preheater blockage and a pollution prevention spray head. BACKGROUND

[0002] Under the background of increasing demand for power system peak regulation, 600MW ammonium bisulfate coal-fired units, as the main power generation equipment, need to undertake deep peak regulation tasks in winter and often operate in the 180-300MW ammonium bisulfate deep regulation condition.

[0003] Under this condition, the flue gas temperature of the unit is significantly reduced to 120-130℃ of ammonium bisulfate, and a certain amount of ammonia escape exists during the operation of the denitration system. The escaped ammonia is prone to react with sulfur trioxide generated by coal combustion and denitration catalyst conversion in the flue gas to generate ammonium bisulfate with a melting point of 147℃ of ammonium bisulfate. This substance is in a liquid viscous state at the cold end of the air preheater and can absorb a large amount of fly ash in the flue gas and deposit on the surface of the air preheater heat storage element, resulting in air preheater blockage and resistance rise. In severe cases, shutdown is required for treatment, affecting the unit's peak regulation capacity and operation stability.

[0004] Currently, the industry usually uses steam soot blowing technology to remove the deposits on the surface of the heat storage element through high-frequency steam injection.

[0005] However, steam soot blowing only has a certain cleaning effect on freshly deposited ammonium bisulfate, has little effect on solidified deposits, and the duration of deep regulation condition is long. High-frequency steam soot blowing can aggravate the wear and corrosion of the air preheater heat storage element, reducing the service life of the equipment.

[0006] At the same time, the existing technology lacks active inhibition and precise control means for the generation of ammonium bisulfate. It cannot identify the easy-to-generate condition in advance and reduce the generation of ammonium bisulfate from the source, nor can it dynamically adjust the response strategy according to real-time parameters, resulting in low efficiency and high cost of passive soot removal, which cannot meet the demand for long-term stable operation of the unit under deep regulation condition.

[0007] Therefore, there is an urgent need for a technical solution that can accurately identify the ammonium bisulfate generation condition, inhibit its generation from the source, and dynamically adapt to the change of deep regulation load, ensuring the safety and economy of the unit under deep regulation condition. SUMMARY

[0008] Therefore, the technical problem to be solved by the present application is to provide a technical solution that can accurately identify the ammonium bisulfate generation condition, inhibit its generation from the source, and dynamically adapt to the change of deep regulation load, ensuring the safety and economy of the unit under deep regulation condition.

[0009] The technical problem is solved by the following technical solution: the application provides a control method for relieving air preheater blockage of a 600 MW unit, which comprises the following steps: Real-time collection of unit load, flue gas temperature, sulfur trioxide concentration in flue gas and air preheater inlet and outlet differential pressure data, judgment of whether the unit is in a working condition prone to generating ammonium bisulfate, preparation of a certain concentration of sodium carbonate solution and storage under heat preservation; When the unit is in the working condition and the sulfur trioxide concentration reaches the threshold required for inhibiting deposition, the sodium carbonate solution is started to be injected into the flue; According to the unit load, sulfur trioxide concentration, solution concentration and air preheater differential pressure, the injection amount is dynamically adjusted to maintain the sulfur trioxide removal rate within the target range; Combined with the sulfur trioxide removal rate and the solution consumption, a blockage risk assessment model is established to predict the air preheater blockage trend, and when the unit working condition deviates from the range or the sulfur trioxide concentration is lower than the set value, the injection is stopped; The blockage risk assessment model takes the sulfur trioxide removal rate, differential pressure change trend and solution consumption as input parameters to calculate the blockage risk index of the air preheater, and after the injection is stopped, the solution is maintained under heat preservation and the concentration is checked, and if necessary, the solution is adjusted, and the delivery path is emptied to prevent crystallization blockage.

[0010] In a preferred mode of the control method for relieving air preheater blockage of a 600 MW unit, the working condition prone to generating ammonium bisulfate is determined by the flue gas temperature being in the ammonium bisulfate generation temperature range and the high sulfur trioxide concentration.

[0011] In a preferred mode of the control method for relieving air preheater blockage of a 600 MW unit, the concentration of the sodium carbonate solution is determined according to the expected concentration of sulfur trioxide and the flue reaction conditions, and is maintained within a set temperature range during storage to maintain the reaction activity.

[0012] In a preferred mode of the control method for relieving air preheater blockage of a 600 MW unit, before starting the injection, the mixing reaction time of the solution injected into the flue with the flue gas and the solution atomization particle size are first confirmed to meet the requirements, and then the injection is performed.

[0013] In a preferred mode of the control method for relieving air preheater blockage of a 600 MW unit, the basic injection amount is determined according to the unit load, and the molar ratio required for the reaction of sulfur trioxide and sodium carbonate is met.

[0014] In a preferred mode of the control method for relieving air preheater blockage of a 600 MW unit, the specific way of correcting the sulfur trioxide concentration is to adjust the injection amount according to the deviation of the real-time sulfur trioxide concentration from the target concentration.

[0015] In a preferred mode of the control method for relieving the plugging of the air preheater of a 600 MW unit, the specific mode of the solution concentration correction is: if the actual concentration of the solution is higher than the target concentration, the injection amount is proportionally reduced, and if the actual concentration of the solution is lower than the target concentration, the injection amount is proportionally increased.

[0016] In a preferred mode of the control method for relieving the plugging of the air preheater of a 600 MW unit, the specific mode of the air preheater differential pressure correction is: when the differential pressure exceeds the threshold reflecting the plugging trend, the injection amount is increased, and when the differential pressure falls, the original injection amount is restored.

[0017] The present application has the beneficial effects that: by multi-parameter collaborative accurate identification of the working condition prone to generating ammonium bisulfate, the problem of deviation of injection timing caused by misjudgment of the working condition in the traditional technology is solved, and by using heat preservation storage and concentration stability control, crystallization of sodium carbonate solution is avoided, the effect of the solution is guaranteed The raw material activity of the removal reaction is removed, so that the removal rate of sulfur trioxide is stably above 85%; combined with dynamic injection adjustment and plugging risk assessment, the plugging trend of the air preheater is effectively delayed, and the frequency of reducing the load of the unit due to plugging is reduced.

[0018] The present application also solves the problem that: because the nozzle will determine whether to spray the solution according to the amount of smoke in the channel, when the amount of flue gas is small, the solution does not need to be sprayed, but the previously sprayed solution will remain on the nozzle, which is easy to combine with the pollutants in the flue gas, thereby causing the pollutants to adhere to the nozzle nozzle near the nozzle, which will pollute the solution and affect the effect of the solution.

[0019] The above technical problems are solved by the following technical scheme: the present application provides a pollution-proof nozzle, comprising: The injection device for spraying the solution comprises a fixed seat, a connecting pipe arranged on one side of the fixed seat, and a spray port arranged on the top of the fixed seat; The shielding assembly arranged on the top of the injection device for preventing the spray port from being polluted comprises a movable rod movable relative to the fixed seat, a connecting rod rotatably connected to one side of the movable rod, and a round cover connected to one side of the connecting rod for covering the spray port; wherein When the movable rod moves towards the fixed seat, the round cover covers the spray port, and when the movable rod moves away from the fixed seat, the round cover moves away from the spray port.

[0020] In a preferred mode of the pollution-proof nozzle, one side of the fixed seat is provided with a connecting channel, the movable rod penetrates one side of the fixed seat, and the movable rod can slide in the connecting channel, one side of the movable rod is provided with a piston, and the piston can slide in the connecting channel with the movable rod. The first elastic member is sleeved with the outer wall of the moving rod, one side of the connecting rod is rotationally connected with one side of the circular cover, and the second elastic member is arranged at the connecting position of the connecting rod and the circular cover.

[0021] The beneficial effect of the present application is that the rotation of the circular cover is controlled by the moving rod, so that it is opened when the spray head sprays the solution and closed when the spray head does not spray the solution, thereby avoiding the combination of the residual solution on the spray head with the pollutants when the spray head is not used, so that the pollutants can be prevented from polluting the solution when the spray head sprays. BRIEF DESCRIPTION OF DRAWINGS

[0022] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings of the embodiments of the present application will be briefly introduced below. Obviously, the drawings described below only relate to some embodiments of the present application, but not limit the present application. Among them: Figure 1 A flow chart of a control method for relieving the blockage of the air preheater of a 600MW unit is shown; Figure 2 A whole structure diagram of a pollution-preventing spray head is shown; Figure 3 A structure diagram of a spraying device and a shielding assembly is shown; Figure 4 An internal structure diagram of a pollution-preventing spray head is shown; Figure 5 A sectional view of a pollution-preventing spray head is shown. DETAILED DESCRIPTION

[0023] In order to make those skilled in the art better understand the present application, the present application will be further described in detail below in combination with specific embodiments and drawings.

[0024] The terms used in the present application are those general terms currently widely used in the art in consideration of the functions about the present application, but these terms can be changed according to the intention of those skilled in the art, precedents or new technologies in the art. In addition, specific terms can be selected by the applicant, and in this case, the detailed meaning thereof will be described in the detailed description of the present application. Therefore, the terms used in the specification should not be understood as simple names, but based on the meaning of the terms and the overall description of the present application.

[0025] REFERENCE Figure 1 The present embodiment provides a control method for relieving the blockage of the air preheater of a 600MW unit, comprising the following steps: Real-time acquisition of unit load, flue gas temperature, sulfur trioxide concentration in flue gas and air preheater inlet and outlet differential pressure data to determine whether the unit is in a condition prone to generating ammonium bisulfate, wherein the unit load data is collected by a load transmitter, which can capture fluctuation data in the 180-300 MW deep load range of a 600 MW unit in real time, output a 4-20 mA standard current signal, and provide load basis parameters for condition determination; Flue gas temperature data is collected by a temperature sensor, which adopts a needle-shaped structure and can accurately detect the flue gas temperature range of 120-130℃ under deep tuning conditions, avoiding temperature detection deviation leading to condition misjudgment; Sulfur trioxide concentration data in flue gas is collected by an online analyzer, which uses ultraviolet fluorescence method and has a horizontal cuboid structure, and is provided with an L-shaped sampling probe extending into the 1 / 3 depth of the flue gas duct, which can capture the concentration of 36-40 mg / Nm³ under deep tuning conditions in real time, ensuring that the concentration data match the generation mechanism; The air preheater inlet and outlet differential pressure is collected by an air preheater differential pressure transmitter, which has a capacitance structure, a 0-5 kPa range, and a ±0.2% FS accuracy, and is installed in the straight pipe section of the air preheater inlet and outlet, which can monitor the air preheater resistance change under deep tuning conditions and reflect the initial clogging trend; After collecting the above four groups of data, the DCS control cabinet is used to determine whether the unit is in a condition prone to generating ammonium bisulfate, and the judgment logic is as follows: When the unit load is ≤300 MW (deep tuning condition range), the flue gas temperature is 120-130℃ (ammonium bisulfate generation temperature range), the concentration is ≥30 mg / Nm³, and the three parameters meet the conditions at the same time and last for 30 seconds (excluding transient fluctuations), it is determined that the unit is in a condition prone to generating ammonium bisulfate. This process does not require additional formulas, and the judgment can be completed by matching the parameter range.

[0026] A certain concentration of sodium carbonate solution is prepared and stored, wherein the preparation of a certain concentration of sodium carbonate solution is completed by a sodium carbonate dissolving tank and a storage tank; The sodium carbonate dissolving tank adopts a 316L stainless steel vertical cylindrical structure, is equipped with a 15 kW ring-type electric heating device, and has a 60 r / min paddle-type stirrer, which can mix 300 kg of solid sodium carbonate (purity ≥99%) with 700 L of desalted water at a mass ratio of 3:7, and prepare a uniform solution with a concentration of 30% after 30 minutes of heating and stirring; The liquid storage tank adopts a 316L stainless steel horizontal cylindrical structure, is equipped with a 10 kW segmented electric heating device, and a concentration sensor with a range of 25%-35%. It can receive 30% concentration sodium carbonate solution delivered by the dissolving tank, maintain the solution temperature through the heating device to avoid crystallization below 60℃, and monitor the concentration deviation in real time to achieve solution storage and parameter stability.

[0027] The working condition that is prone to generate ammonium bisulfate is determined by the condition that the flue gas temperature is in the ammonium bisulfate generation temperature range and the sulfur trioxide concentration is high. The concentration of sodium carbonate solution is determined according to the expected concentration of sulfur trioxide and the flue gas reaction conditions, and is maintained within the set temperature range during storage to maintain the reaction activity.

[0028] In summary, through the cooperation of load transmitters, temperature sensors, online analyzers and DCS, the 600MW unit 180-300MW deep regulation working condition can be accurately identified (accuracy ≥99%), avoiding the problem of deviation of injection timing caused by misjudgment of traditional technology; at the same time, through the design of 316L stainless steel dissolving tank and segmented heating liquid storage tank, 30% concentration sodium carbonate solution can be stably prepared and stored, which not only meets the demand of removal rate ≥85%, but also reduces the risk of solution crystallization, provides qualified and stable reaction raw materials for the subsequent sodium carbonate solution injection link, and at the same time, 30% concentration can reduce about 33% of the solution consumption compared with the conventional 15%-25% concentration, which preliminarily reduces the energy consumption of deep regulation working condition.

[0029] As an optional embodiment, how to inhibit the trend of air preheater blockage under deep regulation working condition.

[0030] When the unit is in the working condition prone to generate ammonium bisulfate and the sulfur trioxide concentration reaches the threshold required to inhibit deposition, sodium carbonate solution is injected into the flue, wherein the delivery and injection of sodium carbonate solution are completed through the cooperation of a frequency conversion diaphragm metering pump and a ring main pipe; The frequency conversion diaphragm metering pump adopts a diaphragm structure, has a flow range of 0-100L / h, an outlet pressure of 0.8MPa, and a frequency conversion accuracy of ±0.5%. It can pressurize the 30% concentration sodium carbonate solution in the liquid storage tank to 0.6-0.8MPa, and adapt to the injection requirements of different loads under deep regulation working condition; The ring main pipe adopts a DN803 316L stainless steel pipe with a circular structure, is installed between the denitration reactor outlet and the air preheater inlet, and has 8 nozzle interfaces evenly arranged along the circumference of the pipe body, which can uniformly distribute the solution to each atomizing nozzle. ​Before starting the injection, it is necessary to confirm whether the mixing reaction time of the solution injected into the flue and the flue gas and the atomized particle size of the solution meet the standards, and then the injection is carried out. The confirmation of the mixing reaction time is achieved by matching the installation position of the annular mother pipe with the flue gas flow, and the calculation formula of the mixing reaction time is as follows: Mixing reaction time = 5m ÷ (flue gas flow ÷ flue cross-sectional area) By calculating the accurate mixing reaction time value through the formula, it is ensured that the mixing reaction time is greater than or equal to 1.5s, which provides time guarantee for the sufficient reaction with sodium carbonate.

[0031] The confirmation of the atomized particle size of the solution is completed by the laser particle size instrument in cooperation with the atomizing nozzle. The atomizing nozzle is made of silicon carbide and has a cylindrical structure. The solution will be atomized into small droplets by the atomizing nozzle under a pressure of 0.6-0.8MPa. The laser particle size instrument adopts a cylindrical probe, the probe is inserted obliquely into the flue, and the outside is sleeved with a quartz protection tube, which can detect the atomized particle size in real time.

[0032] It should be noted that after the solution is injected into the flue, it reacts with the sulfur trioxide in the flue gas, The reaction formula is as follows: , The generated is a solid powder, which can reduce the generation of from the source and avoid the adhesion and blockage of the heat storage elements of the air preheater.

[0033] In summary, the combination of precise installation of the annular mother pipe, efficient atomization of the silicon carbide atomizing nozzle and real-time verification of the laser particle size instrument ensures that the mixing reaction time of the solution and the flue gas is greater than or equal to 1.5s, and the atomized particle size D50 is less than or equal to 50μm, so that The reaction rate with sodium carbonate is increased to more than 90%, which lays a foundation for the subsequent removal rate of more than 85%, and at the same time, the atomizing nozzle increases the contact area of the solution and the flue gas, avoids the waste of the solution caused by insufficient local reaction, and effectively inhibits the blockage trend of the air preheater under deep adjustment conditions, which meets the needs of long-term operation under deep adjustment conditions.

[0034] As an optional embodiment, how to correct the injection amount is specifically described.

[0035] The injection amount is dynamically adjusted according to the unit load, sulfur trioxide concentration, solution concentration and air preheater differential pressure, so as to maintain the sulfur trioxide removal rate within the target range. The basic injection amount is determined by the unit load and meets the molar ratio requirement of the reaction of sulfur trioxide and sodium carbonate.

[0036] ​It should be noted that the calculation of the basic injection quantity is completed through the injection quantity calculation module built into the DCS control cabinet. The injection quantity calculation formula is as follows: per hour Total mass: Total = Concentration × flue gas flow rate × 3600 ÷ 1000 (unit: g / h); Need to be removed quality: Remove = Total × 85% (Removal rate target) need Number of moles: =( Remove ÷ 80) × 1.1 ( (Molar mass 80 g / mol, 1.1 times molar redundancy). Mass of 30% concentration solution required: m_solution = ( (×106)÷30% (Molar mass 106 g / mol) Basic spray volume: Q = m solution ÷ 1.28 (density of 30% solution at 60-80℃ is 1.28 kg / L); Based on the above formula, the DCS calculates the basic injection volume for each deep adjustment load and outputs it precisely through the variable frequency diaphragm metering pump.

[0037] The specific method for correcting sulfur trioxide concentration is as follows: The injection volume is adjusted accordingly based on the deviation between the real-time sulfur trioxide concentration and the target concentration. The real-time sulfur trioxide concentration is determined by... The online analyzer collects data, and for every 1 mg / Nm³ fluctuation in concentration, the injection rate is adjusted by 0.6–0.8 L / h. For example, under a 180MW operating condition... When the concentration increased from 38 mg / Nm³ to 39 mg / Nm³, the injection rate increased from 55.2 L / h to 56.0 L / h.

[0038] The specific method for correcting the solution concentration is as follows: if the actual solution concentration is higher than the target concentration, the injection volume is reduced proportionally; if it is lower than the target concentration, the injection volume is increased proportionally. The actual solution concentration is collected by a concentration sensor in the storage tank, and the correction formula is: Corrected injection volume = Base injection volume × 30% ÷ Actual concentration For example, when the solution concentration drops to 28% under 180MW operating conditions, the corrected injection volume is calculated as follows: 55.2 × 30% ÷ 28% ≈ 58.9 L / h A plugging risk assessment model is established by combining the sulfur trioxide removal rate and the solution consumption to predict the air preheater plugging trend, wherein the sulfur trioxide removal rate is calculated by a built-in removal rate calculator of the DCS, and the formula is as follows: Removal rate = (Inlet Concentration - Outlet Concentration) ÷ Inlet Concentration × 100% The solution consumption is collected by a turbine type solution flowmeter; the plugging risk assessment model is calculated according to the following formula: Risk index = 0.3 × insufficient removal rate time length + 0.4 × differential pressure exceeding frequency + 0.3 × (actual consumption amount / basic consumption amount) When the risk index is greater than 80%, the DCS triggers an audible and light warning.

[0039] When the unit operating condition deviates from the deep regulation range or the sulfur trioxide concentration is lower than the set value, the spraying is stopped; after the spraying is stopped, the solution is maintained at a temperature of 70-90 DEG C by a heating device in the solution tank, and the concentration is checked and adjusted if necessary, and the delivery path is emptied to prevent crystallization plugging, wherein the stop control is completed by an electric shut-off valve, the solution is maintained at a temperature of 70-90 DEG C by a heating device in the solution tank, and the delivery path is emptied by a pipeline emptying valve.

[0040] In summary, the embodiment realizes that the SO3 removal rate is stable at ≥85%, the removal rate fluctuation range is reduced from ±10% of the traditional technology to ±3%, the plugging trend is captured in advance by the plugging risk assessment model to reduce the number of unit load reductions, the pipeline crystallization is avoided by blowing and heating after shutdown, and the dynamic adjustment of 30% concentration solution further reduces the solution consumption by 33%, thereby achieving the comprehensive effect of reducing the air preheater plugging risk by 70% and improving the operation economy by 25% under the deep regulation condition.

[0041] With reference Figures 2-5 to the drawings, the embodiment provides a pollution-proof spray head, which comprises, a spraying device 1 for spraying solution, which comprises a fixed seat 11, a connecting pipe 12 arranged on one side of the fixed seat 11, and a spraying port 13 arranged at the top of the fixed seat 11, and a connecting channel 14 is arranged on one side of the fixed seat 11, wherein the fixed seat 11 can be mounted on the inner wall of a flue gas pipeline, and the connecting pipe 12 is connected to a solution delivery pipeline, the solution can be delivered into the fixed seat 11 through the connecting channel 14, the connecting channel 14 and the spraying port 13 are in communication with each other, and the solution is sprayed out of the spraying port 13.

[0042] The shielding assembly 2 arranged on the top of the spraying device 1 for preventing the spraying port 13 from being contaminated comprises a moving rod 21 which can move relative to the fixed seat 11, a connecting rod 22 which is rotatably connected to one side of the moving rod 21, and a round cover 23 which is connected to one side of the connecting rod 22 and used for covering the spraying port 13; when the moving rod 21 moves towards the fixed seat 11, the round cover 23 covers the spraying port 13; when the moving rod 21 moves away from the fixed seat 11, the round cover 23 moves away from the spraying port 13; the moving rod 21 penetrates through one side of the fixed seat 11 and can slide in the connecting channel 14; a piston 24 is arranged on one side of the moving rod 21 and can slide in the connecting channel 14 along with the moving rod 21; a first elastic member 25 is sleeved on the outer wall of the moving rod 21; one side of the connecting rod 22 is rotatably connected to one side of the round cover 23, and a second elastic member 26 is arranged at the connecting position of the connecting rod 22 and the round cover 23 In order to ensure that the solution is sprayed out at a sufficient pressure, the solution is pressurized before entering the connecting channel 14, so that the piston 24 is pushed to move after the solution enters the connecting channel 14, the round cover 23 drives the moving rod 21 to move away from the fixed seat 11, the moving rod 21 pulls one end of the connecting rod 22 to move, the connecting rod 22 drives the round cover 23 to rotate, so that the round cover 23 moves away from the spraying port 13, at this time, the solution pushes the piston 24 to enter the internal channel of the spraying port 13 and is sprayed out of the spraying port 13; the length of the internal channel of the spraying port 13 can be set to be longer, so that the round cover 23 has sufficient time to rotate.

[0043] When the solution is not sprayed, the first elastic member 25 pushes the piston 24 to return to the original position, and the second elastic member 26 pushes the round cover 23 to cover the spraying port 13, so as to prevent the spraying port 13 from being contaminated by contaminants.

[0044] It should be noted that the first elastic member 25 is a threaded spring which is sleeved on the moving rod 21 and arranged between the piston 24 and the connecting channel 14, and the second elastic member 26 is a torsion spring which abuts against the round cover 23 and the connecting rod 22.

[0045] Finally, it should be noted that the above detailed description of the method and device is only an embodiment, and those skilled in the art can modify the embodiment in different ways without departing from the scope of the present application.

Claims

1. A control method for alleviating air preheater blockage in a 600MW unit, characterized in that: Includes the following steps, Real-time data collection of unit load, flue gas temperature, sulfur trioxide concentration in flue gas, and differential pressure at the inlet and outlet of the air preheater is used to determine whether the unit is in a condition that easily generates ammonium bisulfate. At the same time, a sodium carbonate solution of a certain concentration is prepared and stored at a certain temperature. When the unit is under the aforementioned operating conditions and the sulfur trioxide concentration reaches the threshold required to inhibit deposition, sodium carbonate solution is injected into the flue. The injection volume is dynamically adjusted based on the unit load, sulfur trioxide concentration, solution concentration, and air preheater differential pressure to maintain the sulfur trioxide removal rate within the target range. A clogging risk assessment model is established by combining the sulfur trioxide removal rate and solution consumption to predict the air preheater clogging trend. Injection is stopped when the unit operating conditions deviate from the predicted range or the sulfur trioxide concentration falls below a set value. The blockage risk assessment model uses sulfur trioxide removal rate, differential pressure change trend and solution consumption as input parameters to calculate the blockage risk index of the air preheater. After the injection is stopped, the solution is kept warm and the concentration is checked. If necessary, adjustments are made, and the transport path is cleared to prevent crystallization blockage.

2. The control method for alleviating air preheater blockage in a 600MW unit according to claim 1, characterized in that: The conditions for determining the easy formation of ammonium bisulfate are: the flue gas temperature is within the ammonium bisulfate formation temperature range and the sulfur trioxide concentration is high.

3. The control method for alleviating air preheater blockage in a 600MW unit according to claim 1, characterized in that: The concentration of the sodium carbonate solution is determined based on the expected concentration of sulfur trioxide and the flue gas reaction conditions, and is maintained within a set temperature range during storage to preserve reactivity.

4. The control method for alleviating air preheater blockage in a 600MW unit according to claim 1, characterized in that: Before starting the spraying, confirm whether the mixing reaction time between the solution and the flue gas after the solution is injected into the flue and whether the atomized particle size of the solution meets the standards before proceeding with the spraying.

5. The control method for alleviating air preheater blockage in a 600MW unit according to claim 1, characterized in that: The basic injection volume is determined by the unit load, and the molar ratio required for the reaction of sulfur trioxide and sodium carbonate is met.

6. The control method for alleviating air preheater blockage in a 600MW unit according to claim 5, characterized in that: The specific method for correcting the sulfur trioxide concentration is as follows: adjust the injection volume accordingly based on the deviation between the real-time sulfur trioxide concentration and the target concentration.

7. The control method for alleviating air preheater blockage in a 600MW unit according to claim 5, characterized in that: The specific method for correcting the solution concentration is as follows: if the actual solution concentration is higher than the target concentration, the injection volume is reduced proportionally; if it is lower than the target concentration, the injection volume is increased proportionally.

8. The control method for alleviating air preheater blockage in a 600MW unit according to claim 5, characterized in that: The specific method for correcting the differential pressure of the air preheater is as follows: when the differential pressure exceeds the threshold reflecting the blockage trend, the injection volume is increased; when the differential pressure drops, the original injection volume is restored.

9. A pollution-prevention nozzle, characterized in that: Including the control method for alleviating air preheater blockage in a 600MW unit as described in any one of claims 1 to 8, and, The spraying device (1) for spraying solution includes a fixed base (11), a connecting pipe (12) disposed on one side of the fixed base (11), and a spraying port (13) disposed on the top of the fixed base (11). A shielding assembly (2) installed on top of the spraying device (1) to prevent contamination of the spray nozzle (13) includes a movable rod (21) movable relative to the fixed base (11), a connecting rod (22) rotatably connected to one side of the movable rod (21), and a round cover (23) connected to one side of the connecting rod (22) to cover the spray nozzle (13); wherein, When the moving rod (21) moves toward the fixed seat (11), the round cover (23) will cover the spray nozzle (13). When the moving rod (21) moves away from the fixed seat (11), the round cover (23) will move away from the spray nozzle (13).

10. The anti-pollution nozzle according to claim 9, characterized in that: A connecting channel (14) is provided on one side of the fixed base (11), the moving rod (21) passes through one side of the fixed base (11), and the moving rod (21) can slide in the connecting channel (14). A piston (24) is provided on one side of the moving rod (21), and the piston (24) can slide in the connecting channel (14) with the moving rod (21). The outer wall of the movable rod (21) is fitted with a first elastic element (25), one side of the connecting rod (22) is rotatably connected to one side of the round cover (23), and a second elastic element (26) is provided at the connection between the connecting rod (22) and the round cover (23).

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