阅读说明：本技术 一种电站锅炉管蒸汽吹扫参数确定方法 (Method for determining steam blowing parameters of boiler tube of power station ) 是由 徐志远 陈韩青 于 2021-07-19 设计创作，主要内容包括：本发明涉及一种电站锅炉管蒸汽吹扫参数确定方法。它主要是解决现有手段对电站锅炉管进行蒸汽吹扫时,无法准确确定最佳吹扫参数的问题。其技术方案要点是：通过弗劳德相似准则建立在BMCR、BRL和THA三大工况下的等效模型,并引入动量系数K来确定和控制蒸汽吹扫参数。进一步地,设置多组蒸汽流速值,算出相应的动量系数K,在动量系数满足条件的前提下进行EDEM和Fluent联合仿真,考查不同蒸汽流速值对锅炉管弯头处氧化皮堆积量的影响大小。采用L型和U型两种不同形状的奥氏体管进行仿真实验,实验后对堆积在锅炉管弯头处的氧化皮质量进行统计,若某一蒸汽流速值促使氧化皮不再堆积,那么该值即为电站锅炉管蒸汽吹扫的最佳吹扫参数。(The invention relates to a method for determining steam blowing parameters of a boiler tube of a power station. The method mainly solves the problem that the optimal blowing parameters cannot be accurately determined when the steam blowing is carried out on the boiler pipe of the power station by the existing means. The key points of the technical scheme are as follows: an equivalent model under three working conditions of BMCR, BRL and THA is established through a Froude similarity criterion, and a momentum coefficient K is introduced to determine and control steam purging parameters. And further, setting a plurality of groups of steam flow velocity values, calculating a corresponding momentum coefficient K, performing EDEM and Fluent combined simulation on the premise that the momentum coefficient meets the condition, and examining the influence of different steam flow velocity values on the oxide skin accumulation amount at the elbow of the boiler tube. The method comprises the steps of carrying out simulation experiments by adopting austenite pipes in two different shapes of L-shaped and U-shaped, counting the quality of oxide skin accumulated at the elbow of the boiler pipe after the experiments, and if the oxide skin is not accumulated any more due to a certain steam flow velocity value, determining the value as the optimal purging parameter for steam purging of the boiler pipe of the power station.)

1. A method for determining steam purging parameters of a boiler tube of a power station is characterized in that a Froude similarity criterion is adopted to establish an equivalent model of the boiler tube under three working conditions of BMCR, BRL and THA, a discrete element-fluid power combined simulation model based on the Froude similarity criterion is established through EDEM and Fluent software, different steam flow rate values are set as speed inlets, the accumulation conditions of oxide skins at the elbow parts of L-shaped and U-shaped boilers under the action of different steam flow rates are analyzed, and the optimal steam purging parameters are further obtained.

The method for determining the steam purging parameters of the boiler tube of the power station comprises the following specific steps:

step 1, according to a similarity theory, a Froude similarity criterion is adopted to carry out model scaling, and the basic scale is k_l＝0.67。

And 2, establishing an equivalent model of the boiler tube under three working conditions of BMCR, BRL and THA through a Froude similarity criterion.

And 3, under a specific working condition, calculating a steam flow value according to G ═ A × C/V, and then, according to K ═ GC/G₀C₀＝G²V/G₀ ²V₀Calculating a momentum coefficient K, wherein K is required>1. In the formula: a is the cross-sectional area of the pipeline (unit: mm)³)；G、G₀Rated flow (unit: t/h) in the blowing and rated working conditions respectively; C. c₀Respectively the steam flow speed (unit: m/s) under the blowing and rated working conditions; v, V₀Respectively purge andspecific heat capacity (unit: m) of steam under rated working condition³/kg)。

And 4, respectively establishing an L-shaped boiler tube equivalent model and a U-shaped boiler tube equivalent model under the Froude similarity criterion, firstly establishing a discrete phase of oxide skin particles in the EDEM, secondly setting a speed inlet-pressure outlet and boundary conditions in the Fluent, defining the material attributes of the boiler tubes, and setting a plurality of groups of speed gradients meeting the momentum coefficient K condition.

And 5, selecting a plurality of groups of steam flow velocity values as a velocity inlet in the Fluent interface, selecting an Eulerian-Lagrange coupling mode as an Eulerian-Lagrange coupling mode by adopting a Phase Coupled SIMPLE method and an EDEM coupling mode, and selecting an Eulerian double-fluid framework for the interface to perform coupling simulation.

And 6, counting the accumulated quantity of oxide skins at the corners of the L-shaped power station boiler pipe and the U-shaped power station boiler pipe under different steam flow rates, and carrying out data statistics by utilizing Origin and other related drawing software to obtain the optimal steam purging parameter.

2. The method for determining steam sweeping parameters of utility boiler tubes according to claim 1, wherein the scaled model and prototype of boiler tubes in step 1 should satisfy geometric approximation, motion similarity and power similarity simultaneously. Three similar scale length scale k_lSpeed scale k_vDensity scale k_ρThe other parameters can establish a proportional conversion relation according to the basic scale.

3. The method for determining steam blowing parameters of tubes of power station boiler as claimed in claim 1, characterized in that the momentum coefficient K in step 3 is the ratio of the steam momentum under the blowing condition to the steam momentum under the rated condition, and according to the standard specification, the blowing pipe coefficient K is not less than 1, and the steam flow rate is not less than 30 m/s.

4. The method for determining steam sweeping parameters of utility boiler tubes according to claim 1, wherein the L-shape and the U-shape in step 4 are the most basic features of the utility boiler pipeline, and the simulation of the boiler tubes with the two shapes is more suitable for practical situations.

5. The power station boiler tube steam purging parameter determination method as claimed in claim 1, characterized in that the EDEM simulation in step 4 adopts a k-epsilon mode which is selected from a turbulence mode and set as a standard. The model of contact between scale particles was selected from the standard Hertz-Mindin (no slip) and Hertz-Mindlin with heat reduction build-in optimal models.

6. The power plant boiler tube steam purging parameter determination method as claimed in claim 1, characterized in that the discrete element software EDEM and the fluid dynamics software Fluent in step 5 need to be interconnected by using a specially compiled udf interface. The co-simulation time was set to 5s and the initial temperature was set to 698.15K.

Technical Field

The invention relates to a method for determining steam blowing parameters of a tube of a power station boiler, and belongs to the field of power station boilers.

Background

Austenitic boiler tubes have found widespread use in the power generation industry because of their excellent overall performance. However, in the power generation process of the power station, the steam side oxidation phenomenon occurs in the boiler pipe due to the long-term high-temperature and high-pressure operation, and the steam side oxidation phenomenon becomes a bottleneck which is difficult to break through in the power generation of the power station. The steam purging method is usually adopted in engineering to clean the boiler pipeline of the power station. However, the steam purging parameters are difficult to accurately determine, so that the purging period is too long, the purging cost is increased, the start of a large unit is delayed, and the test run period is prolonged. Therefore, the method for determining the steam purging parameters can greatly improve the purging efficiency; on the other hand, the purging parameters are adjusted in time according to different working conditions, the optimal purging working condition can be ensured, and the time and cost for steam purging are greatly reduced.

At present, the selection of the parameters of the steam blowpipe is often obtained through an empirical theoretical calculation formula, and for example, the invention patent application with the publication number of CN104566413A discloses a method for quickly selecting the parameters of the boiler blowpipe. The method comprises the steps that firstly, a pipe blowing formal system and a pipe blowing provisional system are divided into a plurality of small sections, and resistance coefficients lambda L/D of the small sections are respectively calculated, wherein lambda represents an on-way resistance coefficient, L represents the length of a pipeline, and D represents the diameter of the pipeline; then, the flow coefficient alpha under the corresponding total resistance coefficient is found according to the flow ratio curve; according to the formula G ═ 0.0244 α d²P₀(1/T₀)^1/2Calculating the flow rate of the blowing pipe steam, wherein G represents the flow rate of the blowing pipe steam, alpha represents a flow coefficient, and P₀Drum pressure during blow tube, T₀Indicating the pressure P of water₀Lower saturation temperature, d denotes the pipe diameter. After the flow of the blowing pipe steam is calculated, the pressure drop of each section is further calculated, and according to the resistance coefficient and the inlet steam parameter of each section, the pressure drop is sequentially calculated backwards from the inlet of the primary superheater until the pressure drop reaches the outlet of the secondary reheater, and the outlet steam parameter is calculated. In the calculation process, steam pocket parameters are adopted as the inlet steam parameters of the primary superheater, the outlet steam parameters of the previous section are used as the inlet steam parameters of the next section, when the pressure drop of each section is calculated, the outlet pressure is assumed to obtain the average specific volume, then the pressure drop is calculated according to the resistance coefficient to obtain the outlet pressure, and the outlet pressure is iterated for multiple times until the error meets the requirement. Finally, whether the calculated blow pipe coefficient satisfies the blow pipe coefficient K is judged according to the calculated blow pipe coefficient>1, if the pressure does not meet the requirement, adjusting the blow pipe parameter, namely the drum pressure P₀And re-calculating until a proper blow pipe coefficient is obtained. The method has the advantages that not only are more parameters calculated, but also the parameters of each section of pipeline need to be calculated, and when the actual steam blowpipe is used, the corresponding steam parameters can be changed along with the change of the boiler parameters, so that the parameters need to be recalculated, and although reasonable control errors can be mentioned, the process is too complicated and time is consumed.

Also disclosed is a method and a system for debugging the blowpipe of the boiler of the 1045MW ultra-supercritical coal-fired unit, as disclosed in the invention patent application with the publication number of CN 105157047B. After the boiler is subjected to cold state flushing, the superheater and the reheater are subjected to temperature reduction water side pipeline flushing, and the boiler is subjected to hot state flushing. And controlling the boiler to carry out temperature rise and pressure rise operation, putting the boiler into a powder making system to carry out trial blowing treatment, washing the superheater and the reheater by a temperature reduction water vapor side pipeline, and blowing the high-pressure bypass pipeline. And controlling the boiler to carry out heating and boosting operation, carrying out series connection of a primary steam system and a secondary steam system, carrying out pressure reduction purging, and purging a high-pressure bypass pipeline and a boiler blow pipe steam pipeline. And controlling the boiler to heat and boost, connecting a primary steam system and a secondary steam system in series, depressurizing and purging until the target plate is checked to meet preset conditions, and purging the residual body of the boiler, a soot blowing steam pipeline and a small-machine high-pressure steam inlet pipeline. The method needs a powder process system and continuous debugging during cleaning of the blowing pipe, has a long time period, and cannot accurately determine the optimal blowing parameters.

Disclosure of Invention

An object of the present invention is to overcome the above-mentioned deficiencies in the prior art and to provide a method for determining steam purging parameters of tubes of a power station boiler, which has the following advantages: the optimal steam blowing parameters can be determined only through simulation, simulation data of different boiler working conditions can be collected and counted before the steam blowing pipe, the optimal blowing pipe parameters can be utilized for steam blowing pipe by looking up the data during blowing pipe, and therefore the effect of achieving twice with half the effort is achieved.

The invention adopts the following technical scheme for solving the technical problems:

a method for determining steam purging parameters of a boiler tube of a power station comprises the following specific steps:

step 1, according to a similarity theory, performing model scaling by using a Froude similarity criterion in simulation, wherein a basic scale is k_l＝0.67。

The boiler tube scaling model and prototype should satisfy geometric approximation, motion similarity and power similarity simultaneously. Three similar scale length scale k_lSpeed scale k_vDensity scale k_ρThe other parameters can establish a proportional conversion relation according to the basic scale.

And 2, establishing an equivalent model of the boiler tube under three working conditions of BMCR, BRL and THA through a Froude similarity criterion.

And 3, under a specific working condition, calculating a steam flow value according to G ═ A × C/V, and then, according to K ═ GC/G₀C₀＝G2V/G₀2V₀Calculating a momentum coefficient K, wherein K is required>1; wherein A is the cross-sectional area (unit: mm) of the pipe³)；G、G₀Rated flow (unit: t/h) in the blowing and rated working conditions respectively; C. c₀Respectively the steam flow speed (unit: m/s) under the blowing and rated working conditions; v, V₀The specific heat capacity (unit: m) of steam in the blowing and rated working conditions³/kg)。

And 4, respectively establishing an L-shaped boiler tube equivalent model and a U-shaped boiler tube equivalent model under the Froude similarity criterion, firstly establishing a discrete phase of oxide skin particles in the EDEM, secondly setting a speed inlet-pressure outlet and boundary conditions in the Fluent, defining the material attributes of the boiler tubes, and setting a plurality of groups of speed gradients meeting the momentum coefficient K condition.

And 5, selecting a plurality of groups of steam flow velocity values as a velocity inlet in the Fluent interface, selecting an Eulerian-Lagrange coupling mode as an Eulerian-Lagrange coupling mode by adopting a Phase Coupled SIMPLE method and an EDEM coupling mode, and selecting an Eulerian double-fluid framework for the interface to perform coupling simulation.

And 6, counting the accumulated quantity of oxide skins at the corners of the L-shaped power station boiler pipe and the U-shaped power station boiler pipe under different steam flow rates, and carrying out data statistics by utilizing Origin and other related drawing software to obtain the optimal steam purging parameter.

Compared with the prior art, the invention adopting the technical scheme has the following technical effects:

(1) and a joint simulation mode is adopted, so that labor and material resources are saved, and the economic benefit is improved.

(2) The optimal steam purging parameter values of different boiler pipeline parameters under different working conditions can be accurately simulated.

(3) The optimal steam blowpipe parameters of different operating modes can be simulated through the EDEM-Fluent union, the optimal parameter table of the steam blowpipe is manufactured, the table is consulted when the actual steam blowpipe is waited, the steam blowpipe can be carried out according to the optimal blowing parameters, the time is greatly saved, and the efficiency is improved.

Drawings

FIG. 1 is a table showing the correspondence between the parameters of prototype models under three working conditions in Froude model 1

FIG. 2 is a table 2 showing steam compression ratio parameters under standard conditions

FIG. 3 is a table showing the parameters of discrete element desquamation scale model corresponding to the parameters of scale in Table 3

FIG. 4 is a flow chart of the method of the present invention

FIG. 5 is a diagram of a model of a discrete element-fluid dynamic combined simulation L-shaped boiler tube

FIG. 6 is a diagram of a model of a U-shaped boiler tube for discrete element-fluid dynamic combined simulation

FIG. 7 is a K-C (coefficient of momentum-steam flow rate) diagram for different operating conditions

FIG. 8 is a graph of mass-time of oxide skin at the tube bends of a utility boiler

FIG. 9 is a distribution diagram of different mass of oxide skin particles at the elbow

FIG. 10 is a graph of distribution of different mass of scale particles overflowing from the outlet of a tube of a utility boiler

FIG. 11 is a graph of mass of scale-steam flow at L-bend

FIG. 12 is a graph of mass-steam flow rate of scale at a U-bend

Detailed Description

The invention is described in detail below with reference to the following figures and specific examples:

the invention adoptsThe austenite boiler pipeline respectively establishes an L-shaped model and a U-shaped model for simulation analysis, and obtains the optimal steam parameter, and mainly comprises the following specific steps:

step 1, in order to meet the requirements of the EDEM-Fluent combined simulation, coupling analysis is carried out on the simulation by adopting a scaling model based on an original model. According to the similarity criterion of the actual working condition and the fluid, the scaling simulation is carried out by adopting a wide-range Froude model method, and the basic scale is taken as k_l0.67; in the froude model method:

k_v＝k_l ^0.5

from a model prototype with the same material, k_ρ1.0, and satisfy

k_F＝k_l ³

In the formula, k_gIs a gravity scale, k_lIs a linear scale, k_vIs a speed scale, k_ρIs a density scale and V is a flow velocity; g is the acceleration of gravity; l is a characteristic length;is the Froude number; p and m are subscripts and represent a prototype and a model respectively.

And 2, establishing an equivalent model of the boiler pipe under three working conditions of a maximum continuous evaporation capacity (BMCR) working condition, a rated working condition (BRL) and a heat consumption rate acceptance working condition (THA) of the unit through a Froude similarity criterion. And steam flow values of the steam flow under BMCR, BRL and THA working conditions are 2381.44t/h, 2305.65t/h and 2291.87t/h respectively. The corresponding pressure of the steam outlet is 5.75MPa, 5.56MPa and 5.53MPa respectively; the temperature changes corresponding to the steam inlet and the steam outlet are respectively 360-623 ℃, 353-623 ℃ and 353-623 ℃. The unit has a total of 936 pipes, one pipe is simulated in the simulation, and the average steam flow values of the single pipe under the BMCR, BRL and THA working conditions are respectively 2.54t/h, 2.46t/h and 2.45 t/h.

And 3, under a specific working condition, calculating a steam flow value according to G ═ A × C/V, and then, according to K ═ GC/G₀C₀＝G2V/G₀2V₀The momentum coefficient K is calculated, wherein the calculation result of K is shown in fig. 4. Wherein A is the cross-sectional area (unit: mm) of the pipe³)；G、G₀Rated flow (unit: t/h) in the blowing and rated working conditions respectively; C. c₀Respectively the steam flow speed (unit: m/s) under the blowing and rated working conditions; v, V₀The specific heat capacity (unit: m) of steam in the blowing and rated working conditions³/kg)。

And 4, respectively establishing an L-type boiler tube equivalent model and a U-type boiler tube equivalent model under the Froude similarity criterion, setting the sphere radius range of the given oxide scale particles corresponding to the EDEM model parameters to be 0.8-1.8 mm, adopting a particle generation mode of radom, ensuring randomness, reducing errors, and properly increasing the rolling friction coefficient between the particles and the tube wall in order to fit the actual situation, so that the static friction and the rolling friction coefficients between the peeled oxide scale particles and the tube wall are respectively 0.6 and 0.5 in the EDEM software parameter setting, and selecting standard Hertz-Mindin no slice and Hertz-Mindlin with heat reduction build-in optimal models as contact models between the oxide scale particles. Under the condition that the temperature is 353-623 ℃, the fluid in the boiler tube of the power station is equivalent to superheated steam, the density and the viscosity coefficient of the superheated steam are greatly changed compared with the room temperature, the pressure in the superheated pipe is 5.53-5.75Mpa, and the density of the steam is 10.35-11.81kg/m³Viscosity coefficient of 3.28X 10^-5kg/m-s. The values of the power station boiler tubes are assigned in the Fluent operating interface, the Poisson ratio is 0.305, and the shear modulus of elasticity is 7.28 multiplied by 10¹⁰Density of 7930kg/m³The turbulent mode is set to the standard k-epsilon mode. The steam flow rate of the heat transfer pipeline is generally 30-50m/s, and the steam flow rate corresponding to a speed scale is 24.6-41 m/s. Because of the direct proportion of certain steam flow velocity and steam flow of pipe diameter, the steam flow is represented by the change of the steam flow velocity in the EDEM-Fluent coupling simulationInfluence of the size of (2) on the state of scale deposition.

And 5, setting the EDEM-Fluent combined simulation time to be 5s, setting the initial temperature to be 698.15K, setting the inlet and outlet conditions to be a speed inlet and a pressure outlet on a Fluent operation interface, adopting Phase Coupled SIMPLE as a solving method, selecting an Euler-Lagrange coupling mode with the EDEM, and selecting an Eulerian double-fluid frame as an interface.

And 6, in the post-treatment stage, the accumulated amount of oxide skin at the elbow of the boiler pipe under different steam flow rates is mainly counted, and then data statistical analysis is carried out by using related drawing software such as Origin and the like, for example, the data are shown in the attached figures 8 and 9, and the optimal steam flow rate value is obtained.

As described above, the mass of the oxide skin particles passing through the elbow of the boiler tube increases linearly with the time accumulation, which means that under the condition of a certain steam flow rate, the oxide skin particles generated by the particle factory flow from the speed inlet to the pressure outlet, and in the 37g of oxide skin particles generated by the particle factory, most of the oxide skin particles with large diameters are accumulated at the elbow, and a small number of oxide skin particles with small diameters overflow from the outlet, so that the mass of the oxide skin at the elbow is continuously increased along with the increase of the time, but under the condition of continuously increasing the steam flow rate, the mass of the oxide skin accumulated at the elbow is continuously reduced, and the feasibility of steam purging is verified.

As mentioned above, when the steam flow rate is changed at 34-37m/s during steam purging of the L-shaped pipe, the oxide accumulation amount at the elbow is suddenly reduced, and the corresponding flow rate values are slightly different when the flow rate is suddenly reduced under different working conditions. Under BMCR condition, the critical flow rate is 34 m/s-35 m/s, under BRL condition 35 m/s-36 m/s, and under THA condition 36 m/s-37 m/s. And for the U-shaped pipe, when the steam flow rate is changed at 30-31m/s, the oxide accumulation amount at the corner can be suddenly reduced, and under the BMCR working condition, the critical flow rate is between 34m/s and 35m/s, under the BRL working condition, the critical flow rate is between 31m/s and 32m/s, and under the THA working condition, the critical flow rate is between 33m/s and 34 m/s. According to simulation result data, boiler pipes of different shapes have corresponding critical values when working at different steam flow rates, when the critical value is exceeded, less or no oxides are accumulated at the elbow of the pipeline, the flow rate is the optimal steam purging flow rate, and based on the optimal purging flow rate, the optimal purging parameters can be obtained through similar methods in engineering, and the purging efficiency is improved.

The above description is only an embodiment of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art can understand that the modifications or substitutions within the technical scope of the present invention are included in the scope of the present invention, and therefore, the scope of the present invention should be subject to the protection scope of the claims.