Numerical simulation prediction method for full-scale fine superheater tube panel wear in coal-fired boilers

Abstract

The present invention provides a method for numerical simulation prediction of full-size fine superheater tube panel wear of a coal-fired boiler, and belongs to the technical field of coal-fired boiler operation analysis. The method includes constructing a full-size superheater tube panel geometric model of the coal-fired boiler to be predicted; meshing the full-size superheater tube panel geometric model; obtaining the design parameters of the coal-fired boiler; simulating the boiler flow and combustion conditions in the meshed full-size superheater tube panel geometric model based on the design parameters; and determining the wear condition of the partition screen based on the boiler flow and combustion conditions. The present invention considers the connection between "operating parameters-boiler flow and combustion conditions-partition screen wear conditions" and the influence of the structure of the partition screen superheater pipeline itself, and constructs a full-size superheater tube panel geometric model to meet the analysis needs of the full-size superheater tube panel wear condition.

Description

Technical Field

[0001] The invention belongs to the technical field of coal-fired boiler operation analysis, and in particular relates to a full-size fine superheater tube screen wear numerical simulation prediction method for a coal-fired boiler. Background Art

[0002] As one of the main heating surfaces of the boiler, the partition screen superheater not only absorbs the heat in the furnace to generate superheated steam, but also has the function of flue gas rectification, so that the flue gas at the furnace outlet passes through the boiler tail heating surface more evenly for heat exchange. At the same time, due to its special position (located in the front upper part of the furnace, in the area from the flame angle to the furnace top), the partition screen superheater is relatively more affected by the combustion conditions in the furnace than other heating surfaces of the boiler, and the surrounding flue gas temperature is high, and there is a change in the flow area at the bottom of the screen. The flue gas velocity distribution in the nearby area and the wear condition on the pipeline are more complex and changeable. In addition, since the internal working medium is high temperature and high pressure, the harm caused by leakage is very serious.

[0003] During the operation of coal-fired boilers, the collision and wear between solid particles and the wall of the heat exchanger seriously affect the service life of the boiler equipment. In the analysis of the failure of the convection heating surface tube bundle of the boiler, almost 1 / 3 is caused by the erosion and wear of particles such as coal powder and fly ash. In order to ensure the safe and long-term stable operation of the equipment, reduce wear, and improve the wear resistance of the equipment, and then study the collision and wear mechanism of gas-solid two-phase flow on the wall, it is of great significance to verify and predict the theory using numerical simulation methods.

[0004] The combustion conditions and gas-solid flow conditions in the furnace of a pulverized coal boiler are controlled by the operating parameters, which in turn determine the wear condition of the partition screen superheater. At the same time, the pipe arrangement structure of the heating surface will also have a certain impact on the surrounding gas-solid flow and wear conditions. However, most previous studies have ignored the above-mentioned influences, only selecting a single tube or a simplified tube row for research, and the flue gas parameters in the calculation model are disconnected from the actual combustion conditions of the boiler, resulting in few existing three-dimensional superheater tube screen full-scale fine modeling. Summary of the invention

[0005] In view of this, the present invention aims to provide a numerical simulation prediction method for full-size fine superheater tube screen wear of a coal-fired boiler. The method is based on the relationship between operating parameters, boiler flow and combustion conditions, and partition screen wear conditions, and the influence of the partition screen superheater pipe's own structure, and constructs a flue model with a full-size complete partition screen superheater pipe.

[0006] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0007] The present invention provides a numerical simulation prediction method for full-scale fine superheater tube panel wear of a coal-fired boiler, comprising the following steps:

[0008] Construct a full-scale superheater tube panel geometry model of the coal-fired boiler to be predicted;

[0009] Meshing of full-scale superheater tube panel geometry;

[0010] Obtain design parameters of coal-fired boilers;

[0011] Based on the design parameters, the boiler flow and combustion conditions are simulated in the meshed full-scale superheater tube panel geometry model;

[0012] Predict the wear of the partition screen based on boiler flow and combustion conditions.

[0013] Furthermore, the grid division includes: the grid division of the flow field of the partition screen and the grid division of the tube bundle of the partition screen;

[0014] The grid division of the partition screen flow field adopts the unstructured grid division method;

[0015] The grid division of the partition screen tube bundle adopts the expansion layer grid division method.

[0016] Furthermore, the process of dividing the mesh of the partition screen flow field specifically includes:

[0017] Construct a hexagonal face mesh based on the geometry;

[0018] The volume area is calculated based on the area of ​​the surface mesh, and the volume mesh is filled from the outside to the inside.

[0019] Furthermore, the design parameters are specifically:

[0020] Related parameters of the boiler under BMCR maximum continuous output condition, BRL rated condition and ECR rated condition.

[0021] Furthermore, the design parameters specifically include:

[0022] Superheated steam flow rate, superheated steam outlet pressure, superheated steam outlet temperature, reheated steam flow rate, reheated steam inlet pressure, reheated steam outlet pressure, reheated steam inlet temperature, reheated steam outlet temperature, economizer feed water flow rate, economizer feed water temperature and boiler coal combustion amount.

[0023] Furthermore, when simulating the boiler flow and combustion conditions, the discrete phase model is used in the fluid dynamics simulation tool to calculate the physical state of the particles, and the function of surface grid flow average scaling is turned on.

[0024] Furthermore, when simulating the flow and combustion conditions of the boiler, a fluid-solid bidirectional coupling unsteady-state simulation method is adopted. The fluid-solid bidirectional coupling unsteady-state simulation method is that for each time step of the continuous phase of the flow field, the DPM solver calculates the physical state of the current particles and completes a round of fluid-solid coupling iteration.

[0025] Furthermore, the calculation formula for the total number of incident particles is specifically: total number of particles = stop time / (start time*time step).

[0026] Furthermore, the wear condition of the separator screen is determined using the erosion model based on the DNV model and E / CRC, Neilson and Gilchrist and Oka.

[0027] Furthermore, the calculation model expression of the wear condition of the partition screen is as follows:

[0028]

[0029] Where ER is the wear amount, 2×10 -9 is the empirical parameter of the steel pipe; f(θ) is the impact angle function; θ is the degree of the impact angle; u p is the impact velocity of the particle; 2.6 is the velocity index of the steel pipe, 8 is the number of impact model parameters, B i are the shock model parameters.

[0030] In summary, the present invention provides a method for numerical simulation prediction of full-scale fine superheater tube panel wear of a coal-fired boiler, including constructing a full-scale superheater tube panel geometric model of the coal-fired boiler to be predicted; meshing the full-scale superheater tube panel geometric model; obtaining the design parameters of the coal-fired boiler; simulating the boiler flow and combustion conditions in the meshed full-scale superheater tube panel geometric model based on the design parameters; and predicting the wear condition of the partition screen based on the boiler flow and combustion conditions. The present invention considers the connection between "operating parameters-boiler flow and combustion conditions-partition screen wear conditions" and the influence of the structure of the partition screen superheater pipeline itself, and constructs a full-scale superheater tube panel geometric model to meet the analysis needs of the full-scale superheater tube panel wear condition. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0032] Figure 1A flowchart of a method for numerical simulation prediction of full-scale fine superheater tube panel wear of a coal-fired boiler provided in an embodiment of the present invention;

[0033] Figure 2 A schematic diagram of a superheater structure provided by an embodiment of the present invention;

[0034] Figure 3 A schematic diagram of a full-scale superheater tube panel geometric model provided in an embodiment of the present invention;

[0035] Figure 4 A schematic diagram of the flow state of particles in a grid provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0036] In order to make the purpose, features and advantages of the present invention more obvious and easy to understand, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the embodiments described below are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0037] See also Figure 1 This embodiment provides a numerical simulation prediction method for full-size fine superheater tube screen wear of a coal-fired boiler, and is introduced in combination with a subcritical four-corner tangential circle coal-fired boiler as a research object.

[0038] The method comprises the following steps:

[0039] S1: Construct a full-scale superheater tube panel geometry model of the coal-fired boiler to be predicted.

[0040] like Figure 2 As shown, Figure 2 It is based on the SG-1025 / 18.3-M830 coal-fired subcritical single reheat controlled circulation drum boiler. The partition screen superheater is located in the front upper part of the furnace. It can not only absorb the flue gas radiation heat in the upper part of the furnace and reduce the furnace outlet temperature, but also separate the flue gas, reduce the furnace outlet flue gas temperature deviation and reduce the swirl. Its specific structure and size are as follows Figure 2As shown, the partition screen superheater is arranged with four rows of pipes along the width of the furnace, with a horizontal pitch of 171mm. Each row is divided into 2 groups of 3 small pipes. The spacing between the two groups of pipes in the same row is 800mm, and the height of a single piece is 13700mm. The group of 3 pipes closest to the front wall and the right wall is numbered P1, and the positions 1-8 are clockwise. Each small piece consists of 4 W-shaped parallel sleeves, with a single tube outer diameter of 51mm, a tube wall thickness of 6.5mm, and a spacing of 74mm between tubes. The main heat exchange tube section material is 12Cr2MoWVTiB steel pipe. The constructed tube screen geometric model is shown in the figure below. Figure 3 shown.

[0041] Based on the above partition panel prototype, a full-scale superheater tube panel geometry model is constructed as follows: Figure 3 shown.

[0042] S2: Meshing of the full-scale superheater panel geometry.

[0043] It should be noted that the simulation of flue gas outward wear based on ANSYS Fluent calculation has extremely high requirements for the fineness of the grid. Different from the grids used in general flow field calculations, the particle flow of the discrete phase (DPM) model used to calculate fly ash wear is simulated based on the deposition and aggregation of each independent grid. The center of the wear point is determined by the intersection of three grids. The wear distribution within a grid gradually decreases and diffuses from the inside to the outside. The outermost grid of the wear point presents a faded radial shape. Therefore, the wear distribution obtained depends largely on the division accuracy of a single grid.

[0044] In the full-size fine superheater tube bundle model, the balance between the local wear accuracy determined by the mesh fineness and the computing resources required for the overall large flue flow field will be more complicated than the single-tube external wear model. Therefore, the present invention fully utilizes the influence of mesh technology on the mesh division fineness on the basis of considering reasonable simplified geometric modeling, and provides a mesh division method with reference significance.

[0045] S3: Obtain design parameters of the coal-fired boiler.

[0046] S4: Simulate boiler flow and combustion conditions in a meshed full-scale superheater panel geometry based on design parameters.

[0047] It should be noted that ANSYS Fluent fluid dynamics calculation software is used in this embodiment, which is used to model and analyze fluid flow, heat transfer and mass exchange, chemical reaction process, etc. The software is used to simulate the full-scale superheater tube panel geometry model after meshing.

[0048] S5: Predict the wear condition of the partition screen based on the boiler flow and combustion conditions.

[0049] The present embodiment provides a numerical simulation prediction method for full-size fine superheater tube panel wear of a coal-fired boiler. The method takes into account the relationship among "operating parameters-boiler flow and combustion conditions-partition panel wear conditions" and the influence of the partition panel superheater pipeline structure itself, and constructs a full-size superheater tube panel geometric model to meet the analysis needs of the full-size superheater tube panel wear conditions.

[0050] In a further embodiment of the present invention, the meshing includes the partition screen flow field meshing and the partition screen tube bundle meshing.

[0051] For the meshing of the partition screen flow field, the Hexcore mesh can combine the flexibility of tet (triangle), hex (hexagon) and prism (prismatic) meshes, with a smaller number of cells and a higher hex-to-tet ratio. Since the ANSYS Fluent solver uses unstructured grid calculations, and the existing hybrid grid division technology can achieve the division quality of structured grids and use fewer cells, this model uses unstructured grid division.

[0052] The face area and edge area of ​​a geometric object are used to identify the space to be divided. Therefore, by defining the edge area of ​​the object, the characteristics of the geometric object can be captured in any case, making each object independent of each other. The logic of mesh generation is to first build a hexagonal face mesh based on the geometric body by wrapping, connecting and intersecting, and then calculate the volume area based on the area of ​​the surface mesh, fill the partitioned volume mesh from the outside to the inside, and use boundary layer partitioning at all set wall boundaries to improve the calculation accuracy.

[0053] For the meshing of the partition screen tube bundle, since the pipe itself does not participate in the flow field calculation, in order to reduce the number of grids and the amount of calculation, only the pipe wall wrapped by the boundary layer is generated to participate in the wear and flue gas sweep calculation. The expansion layer meshing method is used to generate the boundary layer for the wall. At this time, the grid will grow outward layer by layer based on the generated wall grid, ensuring the uniformity of each layer and each grid division, which is conducive to the uniformity and reasonable deposition of the flow field before the particle collision wall. In this model, the number of boundary layers is set to 3.

[0054] In one embodiment of the present invention, the main design parameters of the boiler are mainly related main parameters under the boiler BMCR maximum continuous output condition, BRL rated condition and ECR rated condition. In a further embodiment, the main design parameters of the boiler are shown in Table 1

[0055] Table 1 Main design parameters of boiler

[0056]

[0057] In one embodiment of the present invention, when ANSYS Fluent is used for simulation, discrete phase model calculation settings need to be performed. The wear law calculated using the discrete phase model is largely based on the fineness of the grid. When solid particles such as coal powder and fly ash are set to enter the calculation domain along the incident surface, the movement trajectory of the particles first depends on their state in each grid, that is, within a single grid, the physical state of the particles will be calculated and passed to the next grid calculation domain. The DPM particle model in Fluent is calculated based on the Lagrangian method, so the incident source of the particles is in the central area of ​​the grid, which results in the more and denser the grids, the greater the flow rate and density of the particles, which is obviously not in line with the actual particle flow state. Therefore, not only should the grid of the calculation domain be divided as evenly as possible, but the face grid flow average scaling option of Scale Flow RateBy Face Area should also be turned on so that the flow rate is proportionally scaled according to the area ratio of the grid where the particles are located to the entire face grid (such as Figure 4 ), thereby obtaining a relatively uniform flow across the surface.

[0058] In a further embodiment, in order to comprehensively consider the influence of the flow field on the particle particles, the patent of the present invention uses a fluid-solid bidirectional coupling non-steady-state simulation, that is, for each time step of the continuous phase of the flow field, the DPM solver calculates the physical state of the current particle and completes a round of fluid-solid coupling iteration. In this process, the mass flow rate of particle injection is a necessary input parameter because it determines the absolute value of the particle source of the DPM model. This mass flow rate can be converted into the number of particles injected per unit time. However, the simulation process does not support tracking the number of particles. The concept used for tracking here is "package". Each package represents a part of the total continuous mass flow rate in the set time step. Each package can be considered as a representative particle with a specific particle diameter, and its trajectory in the flow field is applicable to the relaxation time of a single particle. Therefore, the total number of incident particles can be determined by setting the start injection time and stop time of the particles. The calculation formula is:

[0059]

[0060] The start and stop time of the particles depends on the size of the geometric model. The time required for the particles to flow through the flow field once at the set speed is the injection time. Finally, the particle injection stop time is determined according to the required number of simulated particles.

[0061] In one embodiment of the present invention, the wear model adopts the erosion model based on the DNV model and refers to the E / CRC, Neilson and Gilchrist and Oka erosion model, and obtains the relationship between the impact angle function and the wear amount, and substitutes the UDF empirical equation constructed by the DPM_DEFINE_EROSION macro into the calculation. The specific algorithm is as follows

[0062]

[0063] Where ER is the wear amount, the constant 2×10-9 is the empirical parameter of the steel pipe; f(θ) is the impact angle function; θ is the degree of the impact angle; u p is the impact velocity of the particle; 2.6 is the velocity index of the steel pipe, 8 is the number of impact model parameters, B i are the shock model parameters.

[0064] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A numerical simulation prediction method for full-scale fine superheater tube panel wear of a coal-fired boiler, characterized in that: The steps include: Construct a full-scale superheater tube panel geometry model of the coal-fired boiler to be predicted; Meshing the full-scale superheater tube panel geometric model; Obtaining design parameters of the coal-fired boiler; Based on the design parameters, simulating boiler flow and combustion conditions in the meshed full-scale superheater tube panel geometry model; predicting wear conditions of the partition screen based on the boiler flow and combustion conditions; The calculation model expression of the wear condition of the partition screen is as follows: Where ER is the wear amount, 2×10 -9 is the empirical parameter of the steel pipe; f(θ) is the impact angle function; θ is the degree of the impact angle; u p is the impact velocity of the particle; 2.6 is the velocity index of the particle, 8 is the number of impact model parameters, B i are the shock model parameters.

2. The method for numerical simulation prediction of full-scale fine superheater tube panel wear of a coal-fired boiler according to claim 1 is characterized in that: Meshing includes: meshing of the partition screen flow field and meshing of the partition screen tube bundle; The partition screen flow field grid is divided by using an unstructured grid division method; The partition screen tube bundle grid division adopts the expansion layer grid division method.

3. The method for numerical simulation prediction of full-scale fine superheater tube panel wear of a coal-fired boiler according to claim 2 is characterized in that: The process of dividing the partition screen flow field grid specifically includes: Construct a hexagonal face mesh based on the geometry; The volume area is calculated based on the area of ​​the surface mesh, and the volume mesh is filled from the outside to the inside.

4. The method for numerical simulation prediction of full-scale fine superheater tube panel wear of a coal-fired boiler according to claim 1 is characterized in that: The design parameters are specifically: Related parameters of the boiler under BMCR maximum continuous output condition, BRL rated condition and ECR rated condition.

5. The method for numerical simulation prediction of full-scale fine superheater tube panel wear of a coal-fired boiler according to claim 4 is characterized in that: The design parameters specifically include: Superheated steam flow rate, superheated steam outlet pressure, superheated steam outlet temperature, reheated steam flow rate, reheated steam inlet pressure, reheated steam outlet pressure, reheated steam inlet temperature, reheated steam outlet temperature, economizer feed water flow rate, economizer feed water temperature and boiler coal combustion amount.

6. The method for numerical simulation prediction of full-scale fine superheater tube panel wear of a coal-fired boiler according to claim 1 is characterized in that: When simulating boiler flow and combustion conditions, the discrete phase model is used in the fluid dynamics simulation tool to calculate the physical state of the particles, and the surface grid flow average scaling function is turned on.

7. The method for numerical simulation prediction of full-scale fine superheater tube panel wear of a coal-fired boiler according to claim 6 is characterized in that: When simulating the flow and combustion conditions of the boiler, a fluid-solid bidirectional coupling unsteady-state simulation method is adopted. The fluid-solid bidirectional coupling unsteady-state simulation method is that for each time step of the continuous phase of the flow field iterates, the DPM solver calculates the physical state of the current particles and completes a round of fluid-solid coupling iteration.

8. The method for numerical simulation prediction of full-scale fine superheater tube panel wear of a coal-fired boiler according to claim 7 is characterized in that: The calculation formula for the total number of incident particles is: total number of particles = stop time / (start time*time step).

9. The method for numerical simulation prediction of full-scale fine superheater tube panel wear of a coal-fired boiler according to claim 1 is characterized in that: The wear condition of the separator screens was determined using an erosion model based on the DNV model and the E / CRC, Neilson and Gilchrist and Oka.

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