A method for on-line monitoring of the thickness of dust accumulation in a rotary air preheater

Abstract

The application discloses a kind of rotary air preheater's ash deposition thickness layering on-line monitoring method, this method is established to the air preheater rotor of conventional arrangement, make reasonable assumption and simplify model, divide grid and use finite difference method to carry out synchronous calculation to ash deposition, metal and fluid temperature.Air side outlet average temperature obtained by each cycle iteration calculation is compared with measured fluid outlet temperature value and the ash deposition thickness of assumption is layering corrected, to obtain relatively accurate each layer average ash deposition thickness.This method does not need to carry out any modification to preheater body, only through conventional inlet and outlet measuring point data can the calculation of ash deposition thickness be completed, the display of ash deposition thickness is more intuitive, and the number of layering and bin is not limited, and the adaptability and expansibility are strong.

Description

Technical Field

[0001] This invention belongs to the field of boiler ash accumulation monitoring technology, specifically relating to an online monitoring method for stratified ash accumulation thickness in a rotary air preheater. Background Technology

[0002] In coal-fired boilers, rotary air preheaters are widely used for utilizing waste heat from flue gas. However, the presence of ammonia, sulfur oxides, water, and fly ash in the upstream flue gas easily leads to ash accumulation on the surface of the internal corrugated plates, reducing the preheater's heat transfer efficiency and, in severe cases, causing channel blockage, fan overload, and forced shutdown for maintenance. If the thickness distribution of ash accumulation inside the rotary air preheater can be monitored after ash buildup on the heating surface, targeted soot blowing can be performed, effectively reducing the frequency of shutdowns for maintenance.

[0003] Accurate monitoring of the thickness of ash accumulation inside the air preheater is particularly important. Existing patents have proposed solutions for ash accumulation monitoring, but all of them have shortcomings.

[0004] The patent "An Online Monitoring Device for Ash Accumulation on the Surface of a Rotary Air Preheater" uses a "detector rod" to perform segmented ash blowing on the rotary air preheater from the flue gas inlet to the outlet, but it does not describe the specific detection instrument used. Under existing detection methods, this arrangement method cannot obtain the specific ash accumulation distribution, resulting in poor accuracy. Furthermore, this device has a complex structure, with the air preheater arranged horizontally, leading to even more uneven heating and ash accumulation distribution.

[0005] The patent "A Method for Monitoring Ash Layering in Rotary Air Preheaters Based on the Finite Difference Method" calculates the temperature of each layer inside the rotor of a rotary air preheater using known temperature measuring points and assumed heat transfer coefficients. It then compares the measured values ​​to correct the heat transfer coefficient of each layer, thus obtaining the final heat transfer coefficient. While this method can determine the degree of reduction in the heat transfer coefficient, it cannot visually represent the thickness of each ash layer, making it insufficiently helpful for practical applications. Summary of the Invention

[0006] To address the aforementioned problems, this invention provides an online monitoring method for the layered ash thickness of rotary air preheaters. This method simplifies the rotor while maintaining its vertical arrangement, establishes a computational model, divides it into grids, and uses the finite difference method to simultaneously calculate the ash, metal, and fluid temperatures. By comparing this calculation with measured fluid outlet temperatures, assumptions and corrections are made regarding the ash thickness. This method is applicable to multi-layer, multi-compartment rotary air preheaters.

[0007] The present invention is achieved using the following technical solution:

[0008] A method for online monitoring of ash accumulation thickness in a rotary air preheater includes the following steps:

[0009] Step 1: Model the rotor of the rotary air preheater, establish a cylindrical coordinate system, and take a sufficiently small sector-shaped cylindrical micro-element to obtain the heat transfer control volume;

[0010] Step 2: In the controlled volume micro-element, it is divided into three regions according to the types of fluid and solid: the heat storage metal region, the ash accumulation region, and the fluid region.

[0011] Step 3: Establish heat balance equations for the fluid region, the metal region of the heat storage body, and the ash accumulation region within the micro-element, respectively;

[0012] Step 4: Discretize and simplify the three heat balance equations established in Step 3;

[0013] Step 5: Input the rotor speed, layer structure parameters, and compartment operating parameters of the three-compartment air preheater; input the ash accumulation parameters.

[0014] Step 6: Input the assumed ash thickness distribution for each layer and substitute it into the corresponding equations for each layer;

[0015] Step 7: Initialize the fluid inlet temperature of each compartment, and assign initial temperature values ​​to the first node of the heat storage metal and ash accumulation in the first layer of flue gas compartment. Substitute the given boundary temperature conditions, and calculate the node temperature distribution of the compartment by solving the discrete equations of metal, fluid and ash accumulation simultaneously.

[0016] Step 8: Transfer the ash accumulation and metal temperature node values ​​of this compartment to the next compartment in the rotation direction, and calculate the temperature field of all compartments in this layer in turn based on the assumed inlet temperature of the next compartment. Check and iterate the temperature according to the rotational continuity until the accuracy requirements are met.

[0017] Step 9: Transfer the fluid temperature node of this layer to the next layer and calculate it according to the above method until the entire rotor is calculated. Compare the calculated values ​​of all air-side outlet temperature nodes with the assumed temperature and iterate according to the deviation until the overall temperature field deviation meets the accuracy requirements.

[0018] Step 10: Compare the calculated air outlet temperature with the measured value at the node. If the deviation between the two does not meet the accuracy requirements, return to step 7 to re-assume the dust accumulation thickness and calculate until the accuracy requirements are met, and output the temperature and dust accumulation thickness distribution.

[0019] A further improvement of the present invention is that, in step two, the following assumptions are also included: (1) the radial temperature of the rotor is uniformly distributed, and radial heat conduction is ignored.

[0020] A further improvement of the present invention is that, in step two, the following assumption is also included: (2) radiative heat transfer is ignored.

[0021] A further improvement of the present invention is that, in step two, the following assumption is also included: (3) the effect of air leakage is ignored.

[0022] A further improvement of the present invention is that, in step two, the assumption is also included: (4) the temperature and composition of the rotor inlet fluid are uniformly distributed.

[0023] A further improvement of this invention is that, in step three, the heat balance equation established for the fluid region within the micro-element is as follows:

[0024]

[0025] In the formula: ρ g This indicates the fluid density, expressed in kg / m³. 3 ;u g c represents the apparent velocity of the fluid, in m / s. p This represents the specific heat capacity of a fluid at constant pressure, expressed in J / kg·K. -1 ;T g The average temperature of the fluid is represented in K; h represents the convective heat transfer coefficient between the fluid and the ash deposit, in W / m³. 2 ·K -1 σ represents the heat transfer area density, m 2 / m 3 ;T a The value represents the average temperature of the accumulated dust, in K; z represents the rotor axial direction.

[0026] A further improvement of this invention is that, in step three, the heat balance equation established for the metal region of the heat storage body within the micro-element is as follows:

[0027]

[0028] In the formula ρ m This represents the equivalent density of the metal, in kg / m³. 3 ω represents the rotational speed of the heat storage element, in rad / s; C m This represents the specific heat capacity of a metal at constant pressure, expressed in J / kg·K. -1 ;T m λ represents the average temperature of the metal, in K; m The thermal conductivity of a metal is expressed in W / m·K. -1 ;; λ represents the porosity without considering the volume of accumulated ash. a This represents the thermal conductivity of ash accumulation in W / m·K. -1 ;δ a θ represents the average dust accumulation thickness; θ represents the rotor circumferential direction.

[0029] A further improvement of this invention is that, in step three, the heat balance equation established for the ash accumulation region within the micro-element is as follows:

[0030]

[0031] In the formula ρ m This represents the converted density of ash, in kg / m³.3 C a This represents the specific heat capacity of ash at constant pressure, in J / kg·K. -1 ;T a The average temperature of the metal is expressed in K; the left side of the equation represents the energy increase due to ash accumulation, the first term on the right side represents heat exchange with the fluid, and the second term represents heat exchange with the metal of the heat storage body.

[0032] A further improvement of this invention is that, in step four, the three heat balance equations established in step three are discretized and simplified as follows:

[0033] A n T g,i-1 / 2,j +A s T g，i+1 / 2,j +A ss T g,i+3 / 2,j +B a T a,i,j-1 / 2 +B as T a,i+1,j-1 / 2 +B m T m,i,j-1 / 2 =0 (4)

[0034] Where i = 1, j = 1, 2, ..., l;

[0035] A nn T g，i-3 / 2,j +A n T g，i-1 / 2,j +A s T g，i+1 / 2,j +A ss T g，i+3 / 2,j +B an T a,i-1,j-1 / 2 +B a T a,i,j-1 / 2 +B as T a,i+1,j-1 / 2 +B m T m,i,j-1 / 2 =0 (5)

[0036] Where i = 2, 3, ..., k, j = 1, 2, ..., l;

[0037] A nn T g，i-3 / 2,j +A n T g，i-1 / 2,j +A s T g，i+1 / 2,j +B an T a,i-1,j-1 / 2 +B a T a,i,j-1 / 2 +B m T m,i,j-1 / 2 =0 (6)

[0038] Where i = k, j = 1, 2, ..., l;

[0039] T a,i,j+1 / 2 +T a,i,j-1 / 2 =C a,n T g，i-1 / 2,j +C a,s T g，i+1 / 2,j (7)

[0040] Where i = 1, 2, ..., k, j = 1, 2, ..., l; and A n A s A nn A ss B an B a B as B m C a,n C a,s All are equation coefficients; with the grid in the i-th row and j-th column as the center grid, after discretization T g In the subscripts, i+1 / 2 represents the fluid outlet node of the central grid, i-1 / 2 represents the fluid inlet node of the central grid, i+3 / 2 represents the fluid outlet node of the downstream adjacent grid, i-3 / 2 represents the fluid inlet node of the upstream adjacent grid, and the ordinate j represents the ordinate of the central grid; after discretization T a With T m In the subscripts, i represents the horizontal coordinate of the center grid, j+1 / 2 represents the dust accumulation node and metal node at the rotating exit of the center grid, and j-1 / 2 represents the dust accumulation node and metal node at the rotating inlet of the center grid.

[0041] The present invention has at least the following beneficial technical effects:

[0042] 1. The model and algorithm used in this invention are applicable to soft measurement and monitoring of ash accumulation thickness in multi-layer, multi-compartment rotary air preheaters. This method uses different numbers of layers and compartments as variable input parameters. If these numbers increase or decrease, this method is still applicable and has strong scalability. Some air preheaters are modified to reduce air leakage or ash accumulation, resulting in four-compartment or five-compartment rotary air preheaters, i.e., more than 3 compartments. Other air preheaters adopt multi-layer heat storage element arrangement to reduce cold-end corrosion. The cold-end elements are mostly corrosion-resistant enamel-plated elements, i.e., more than 1 layer. For both cases, this calculation method uses the means of transferring temperature and assigning independent values ​​to each compartment to ensure that the number of layers and compartments does not affect the calculation convergence, thus having wide adaptability.

[0043] 2. The model and algorithm used in this invention can directly determine the ash accumulation thickness, which is more intuitive than the indirect variables such as cleaning factors used in other literature and patents. Among the disclosed ash accumulation monitoring methods, most use cleaning factors to indirectly reflect the degree of ash accumulation. The definition of cleaning factors is mostly a dimensionless number based on the inlet and outlet temperatures, pressures, or heat transfer coefficients of the air preheater. Although cleaning factors can reflect the degree of ash accumulation, they do not explain the direct relationship between data such as inlet temperature and ash accumulation-related parameters. For example, the correspondence between heat transfer coefficient and ash accumulation thickness cannot be quantified. However, this method can directly determine the specific ash accumulation thickness, which provides more intuitive guidance for operators and improves soot blowing efficiency.

[0044] 3. The model and algorithm used in this invention are applicable to online monitoring of ash accumulation in any conventionally arranged rotary air preheater, and do not require the addition of any special detection devices. Some methods described in published patents and documents require complex modifications such as adding detection rods and measuring points at special locations when implementing the method. However, this invention does not require any modifications. It only needs to obtain the measuring point data that are commonly provided in conventional air preheaters, such as inlet and outlet temperature, pressure and flow rate measuring points, and complete the calculation and monitoring of ash accumulation thickness on the computing platform. This does not affect the operation of the air preheater and is more economical. Attached Figure Description

[0045] Figure 1 This is a volume diagram of the rotor control system described in this invention.

[0046] Figure 2 This is a flowchart of the calculation process described in this invention. Detailed Implementation

[0047] Exemplary embodiments of the present disclosure will now be described in more detail with reference to the accompanying drawings. While exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided to enable a more thorough understanding of the present disclosure and to fully convey the scope of the disclosure to those skilled in the art. It should be noted that, unless otherwise specified, the embodiments and features described herein can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0048] like Figure 2 As shown, the present invention provides an online monitoring method for ash accumulation thickness stratification in a rotary air preheater, comprising the following steps:

[0049] Step 1: Model the rotor of the rotary air preheater, establish a cylindrical coordinate system, and take a sufficiently small sector-shaped cylindrical micro-element to obtain the heat transfer control volume, such as... Figure 1 As shown.

[0050] Step 2: Within the controlled volume micro-element, the system is divided into three regions based on the types of fluid and solid: the heat storage metal region, the ash accumulation region, and the fluid region. For ease of solution, the following assumptions are made: (1) The rotor radial temperature is uniformly distributed, and radial heat conduction is ignored; (2) Radial heat transfer is ignored; (3) The effect of air leakage is ignored; (4) The rotor inlet fluid temperature and composition are uniformly distributed. The heat balance equation for the fluid region within the micro-element is established as follows:

[0051]

[0052] In the formula: ρ g This indicates the fluid density, expressed in kg / m³. 3 ;u g c represents the apparent velocity of the fluid, in m / s. p This represents the specific heat capacity of a fluid at constant pressure, expressed in J / kg·K. -1 ;T g The average temperature of the fluid is represented in K; h represents the convective heat transfer coefficient between the fluid and the ash deposit, in W / m³. 2 ·K -1 σ represents the heat transfer area density, m 2 / m 3 ;T a Let represent the average temperature of the accumulated ash, in K; z represents the rotor axial direction. The heat balance equation for the metal region of the heat storage body within the micro-element is established as follows:

[0053]

[0054] In the formula ρ m This represents the equivalent density of the metal, in kg / m³. 3 ω represents the rotational speed of the heat storage element, in rad / s; C m This represents the specific heat capacity of a metal at constant pressure, expressed in J / kg·K. -1 ;T m λ represents the average temperature of the metal, in K; m The thermal conductivity of a metal is expressed in W / m·K. -1 ; λ represents the porosity without considering the volume of accumulated ash. a This represents the thermal conductivity of ash accumulation in W / m·K. -1 ;δ a θ represents the average ash accumulation thickness; θ represents the rotor circumferential direction. The following thermal balance equation is established for the ash accumulation region within the micro-element:

[0055]

[0056] In the formula ρ m This represents the converted density of ash, in kg / m³. 3 C a This represents the specific heat capacity of ash at constant pressure, in J / kg·K. -1 ;T aThe value represents the average temperature of the metal, in Kelvin. The left side of the equation represents the energy increase from the accumulation of ash, and the first term on the right side represents heat exchange with the fluid, while the second term represents heat exchange with the metal of the heat storage body.

[0057] Step 3: Discretize and simplify the equation as follows:

[0058] A n T g,i-1 / 2,j +A s T g，i+1 / 2,j +A ss T g,i+3 / 2,j +B a T a,i,j-1 / 2 +B as T a,i+1,j-1 / 2 +B m T m,i,j-1 / 2 =0 (4)

[0059] Where i = 1, j = 1, 2, ..., l;

[0060] A nn T g，i-3 / 2,j +A n T g，i-1 / 2,j +A s T g，i+1 / 2,j +A ss T g，i+3 / 2,j +B an T a,i-1,j-1 / 2 +B a T a,i,j-1 / 2 +B as T a,i+1,j-1 / 2 +B m T m,i,j-1 / 2 =0 (5)

[0061] Where i = 2, 3, ..., k, j = 1, 2, ..., l;

[0062] A nn T g，i-3 / 2,j +A n T g，i-1 / 2,j +A s T g，i+1 / 2,j +B an T a,i-1,j-1 / 2 +B a T a,i,j-1 / 2 +B m T m,i,j-1 / 2 =0 (6)

[0063] Where i = k, j = 1, 2, ..., l;

[0064] T a,i,j+1 / 2 +T a,i,j-1 / 2 =C a,n T g，i-1 / 2,j +C a,s Tg，i+1 / 2,j (7)

[0065] Where i = 1, 2, ..., k, j = 1, 2, ..., l; and A n A s A nn A ss B an B a B as B m C a,n C a,s All are equation coefficients. Using the grid in the i-th row and j-th column as the center grid, after discretization, T... g In the subscripts, i+1 / 2 represents the fluid outlet node of the central grid, i-1 / 2 represents the fluid inlet node of the central grid, i+3 / 2 represents the fluid outlet node of the downstream adjacent grid, i-3 / 2 represents the fluid inlet node of the upstream adjacent grid, and the ordinate j represents the ordinate of the central grid; after discretization T a With T m In the subscripts, i represents the horizontal coordinate of the center grid, j+1 / 2 represents the dust accumulation node and metal node at the rotating exit of the center grid, and j-1 / 2 represents the dust accumulation node and metal node at the rotating inlet of the center grid.

[0066] Step 4: Input the rotor speed, layer structure parameters, and compartment operating parameters of the three-compartment air preheater; input the ash accumulation parameters.

[0067] Step 5: Input the assumed ash thickness distribution for each layer and substitute it into the corresponding equations for each layer.

[0068] Step 6: Initialize the fluid inlet temperature of each compartment, and assign initial temperature values ​​to the first node of the heat storage metal and ash accumulation in the first layer of flue gas compartment. Substitute the given boundary temperature conditions, and calculate the node temperature distribution of the compartment by solving the discrete equations of metal, fluid and ash accumulation simultaneously.

[0069] Step 7: Transfer the ash accumulation and metal temperature node values ​​of this compartment to the next compartment in the rotation direction, and calculate the temperature field of all compartments in this layer in turn based on the assumed inlet temperature of the next compartment. Check and iterate the temperature according to the rotational continuity until the accuracy requirements are met.

[0070] Step 8: Transfer the fluid temperature node of this layer to the next layer and calculate it according to the above method until the entire rotor is calculated. Compare the calculated values ​​of all air-side outlet temperature nodes with the assumed temperature and iterate according to the deviation until the overall temperature field deviation meets the accuracy requirements.

[0071] Step 9: Compare the calculated air outlet temperature with the measured value at the node. If the deviation between the two does not meet the accuracy requirements, return to step 7 to re-assume the dust accumulation thickness and calculate until the accuracy requirements are met, and output the temperature and dust accumulation thickness distribution.

[0072] Example

[0073] Taking an air preheater in operation at a coal-fired power plant as an example, the model and algorithm of this invention are used to perform soft measurement of ash accumulation thickness.

[0074] The preheater rotor has a diameter of 10900mm. The heat storage elements are divided into hot and cold sections with different plate types. The hot section is 1140mm high and 0.5mm thick, while the cold section is 950mm high and 1.05mm thick. The power plant is located at an altitude of 1520m, and the rotor's reference speed is 1 r / min. The air preheater has a three-compartment structure: a flue gas compartment, a primary air compartment, and a secondary air compartment. The nominal compartment angle is 180° for the flue gas compartment, 27.18° for the primary air compartment, and 131.25° for the secondary air compartment. The sealing angle for each compartment is 15°.

[0075] According to the calculation process, the structural parameters of the air preheater are first input into the algorithm, and then the operating parameters are set. In this embodiment, the flue gas inlet temperature of the flue gas chamber is 355℃, and its flow rate is 702000 kg / h; the primary air chamber inlet air temperature is 27.18℃, and its flow rate is 291509 kg / h; the secondary air chamber inlet air temperature is 15.7℃, and its flow rate is 402408 kg / h. The operating parameters are input into the algorithm for iterative calculation. Before the calculation, the ash density, thermal conductivity, and heat capacity are set to 1200 kg / m³ based on the operating conditions and coal quality parameters. 3 0.117 W / m·K -1 and 250J / kg·K -1 .

[0076] First, assuming the ash thickness is 0, i.e., the air preheater rotor is in a clean state, the inlet boundary temperature is input, and the discrete equations for fluid, metal, and ash are solved for each compartment to obtain a converged overall temperature field. At this point, the calculated average air-side outlet temperature is 305.2℃. Simultaneously, the measured average air-side temperature of the air preheater at this moment is 300.9℃, lower than the calculated temperature, meaning the air temperature increase is less than in the clean state, indicating lower actual heat exchange and poorer heat exchange performance, meaning the actual ash thickness is not 0. Then, the ash thickness is increased according to the set step size; in this example, the step size is set to 0.05mm. After several iterations, the average calculated air-side outlet temperature is 310.2℃. Assuming the maximum iteration error is 0.5℃, the iteration deviation meets the accuracy requirements, and the ash thickness is 0.25mm. Therefore, based on this operating condition and measured parameters, the average ash thickness in the hot and cold sections is monitored to be 0.25mm. Using this method, an iterative calculation is completed every 3 seconds, which enables real-time monitoring of the air preheater thickness. The calculation cycle is limited only by the equipment's working capacity. In theory, real-time monitoring can be achieved without considering the computing platform's capabilities.

[0077] Although the present invention has been described in detail above with general descriptions and specific embodiments, modifications or improvements can be made to it, which will be obvious to those skilled in the art. Therefore, all such modifications or improvements made without departing from the spirit of the present invention fall within the scope of protection claimed by the present invention.

Claims

1. A method for online monitoring of ash accumulation thickness in a rotary air preheater, characterized in that, Includes the following steps: Step 1: Model the rotor of the rotary air preheater, establish a cylindrical coordinate system, and take a sufficiently small sector-shaped cylindrical micro-element to obtain the heat transfer control volume micro-element; Step 2: In the controlled volume micro-element, it is divided into three regions according to the types of fluid and solid: the heat storage metal region, the ash accumulation region, and the fluid region. Step 3: Establish heat balance equations for the fluid region, the metal region of the heat storage body, and the ash accumulation region within the micro-element, respectively; the heat balance equation established for the fluid region within the micro-element is as follows: （1） In the formula: ρ g This indicates the fluid density, expressed in kg / m³. 3 ; u g Expresses the apparent velocity of the fluid, in m / s; c p This represents the specific heat capacity of a fluid at constant pressure, expressed in J / kg·K. -1 ; T g The average temperature of the fluid is expressed in Kelvin (K). h The convective heat transfer coefficient between the fluid and the ash deposits, expressed in W / m³. 2 ·K -1 ; σ Represents the heat transfer area density, m 2 / m 3 ; T a Indicates the average temperature of the accumulated ash, in K; z Indicates the rotor axial direction; The heat balance equation established for the metallic region of the heat storage body within the micro-element is as follows: （2） In the formula ρ m This represents the equivalent density of the metal, in kg / m³. 3 ; ω The rotational speed of the heat storage medium is expressed in rad / s. C m This represents the specific heat capacity of a metal at constant pressure, expressed in J / kg·K. -1 ; T m The average temperature of the metal is expressed in K. λ m This represents the thermal conductivity of a metal in W / m·K. -1 ; φ This indicates porosity without considering the volume of accumulated ash. λ a This represents the thermal conductivity of ash accumulation in W / m·K. -1 ; δ a Indicates the average dust accumulation thickness; θ Indicates the circumferential direction of the rotor; The heat balance equation established for the ash accumulation region within the micro-element is as follows: （3） In the formula This represents the converted density of ash, in kg / m³. 3 ; C a This represents the specific heat capacity of ash at constant pressure, in J / kg·K. -1 ; T a The average temperature of the metal is expressed in K; the left side of the equation represents the energy increase due to ash accumulation, the first term on the right side represents heat exchange with the fluid, and the second term represents heat exchange with the metal of the heat storage body. Step 4: Discretize and simplify the three heat balance equations established in Step 3 as follows: （4） in i =1, j =1, 2,…, l ; （5） in i =2, 3,…, k , j =1, 2,…, l ; （6） in i = k , j =1, 2,…, l ; （7） in i =1, 2,…, k , j =1, 2,…, l In the formula A n , A s , A nn , A ss , B an , B a , B as , B m , C a,n , C a,s All are equation coefficients; With the first i Line number j The column's grid is centered on the grid, after discretization T g In the subscript, i +1 / 2 represents the fluid outlet node in the center grid. i -1 / 2 represents the fluid inlet node of the central grid. i +3 / 2 represents the fluid outlet node of the downstream adjacent grid. i -3 / 2 represents the fluid inlet node of the upstream adjacent grid, with the ordinate being... j Indicates the ordinate of the center grid; Discretized T a and T m In the subscript, i Indicates the x-coordinate of the center grid. j +1 / 2 represents the dust accumulation node and metal node at the center grid rotation exit. j -1 / 2 represents the dust accumulation node and metal node at the central grid rotation entrance; Step 5: Input the rotor speed, layer structure parameters, and compartment operating parameters of the three-compartment air preheater; input the ash accumulation parameters. Step 6: Input the assumed ash thickness distribution for each layer and substitute it into the corresponding equations for each layer; Step 7: Initialize the fluid inlet temperature of each compartment, and assign initial temperature values ​​to the first node of the heat storage metal and ash accumulation in the first layer of flue gas compartment. Substitute the given boundary temperature conditions, and calculate the node temperature distribution of the compartment by solving the discrete equations of metal, fluid and ash accumulation simultaneously. Step 8: Transfer the ash accumulation and metal temperature node values ​​of this compartment to the next compartment in the rotation direction, and calculate the temperature field of all compartments in this layer in turn based on the assumed inlet temperature of the next compartment. Check and iterate the temperature according to the rotational continuity until the accuracy requirements are met. Step 9: Transfer the fluid temperature node of this layer to the next layer and calculate it according to the above method until the entire rotor is calculated. Compare the calculated values ​​of all air-side outlet temperature nodes with the assumed temperature and iterate according to the deviation until the overall temperature field deviation meets the accuracy requirements. Step 10: Compare the calculated air outlet temperature with the measured value at the node. If the deviation between the two does not meet the accuracy requirements, return to Step 7 to re-assume the dust accumulation thickness and calculate until the accuracy requirements are met, and output the temperature and dust accumulation thickness distribution.

2. The method for online monitoring of ash accumulation thickness in a rotary air preheater according to claim 1, characterized in that, Step 2 also includes the following assumptions: (1) The radial temperature of the rotor is uniformly distributed, and radial heat conduction is ignored.

3. The method for online monitoring of ash accumulation thickness in a rotary air preheater according to claim 2, characterized in that, Step two also includes the assumption that: (2) radiative heat transfer is ignored.

4. The method for online monitoring of ash accumulation thickness in a rotary air preheater according to claim 3, characterized in that, Step two also includes the assumption: (3) Ignore the effect of air leakage.

5. The method for online monitoring of ash accumulation thickness in a rotary air preheater according to claim 4, characterized in that, Step two also includes the assumption that: (4) the temperature and composition of the fluid at the rotor inlet are uniformly distributed.

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