Primary air powder leveling method based on corrected resistance model and thermal generator set

Abstract

The invention discloses a primary air and powder leveling method based on a correction resistance model and a thermal generator set. The primary air and powder leveling method comprises the steps that firstly, a two-phase flow resistance model of each air and powder pipeline is established; secondly, parameters such as flow velocity, pulverized coal concentration and pressure drop of an air-pulverized coal mixture are tested and measured; thirdly, correcting the resistance model in a mode of optimizing model parameters based on actual test data; fourthly, the scale adjustment of the adjustable shrinkage cavity is guided according to the resistance calculation result of the wind powder pipeline; fifthly, the second step to the fourth step are repeated until the purpose of primary air and powder leveling is achieved, operation state adjustment of the throttling element is guided according to the resistance calculation result of the air and powder pipelines, the resistance characteristics of all the air and powder pipelines tend to be consistent so as to reduce the number of test measurement times, and the adjustable shrinkage cavity scale is adjusted according to the resistance calculation result of the air and powder pipelines. And a previous adjustment mode depending on experience is replaced, and the operation blindness can be effectively reduced.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of coal-fired boiler combustion control, and particularly relates to a primary air powder leveling method based on a corrected resistance model and a thermal power generating unit, which is suitable for precise adjustment of the air powder flow rate and flow of a pulverizing system in a thermal power plant. BACKGROUND

[0002] Under the background of continuous expansion of new energy installed capacity and increasing proportion, its inherent output fluctuation and intermittent characteristics, combined with the problem of insufficient breakthrough in consumption bottleneck and energy storage technology maturity, thermal power will still play an important power guarantee function in a long period of time in the future. The rapid development of new energy industry not only does not eliminate the strategic value of thermal power, but also drives the thermal power technology system to accelerate evolution towards efficient and flexible operation, deep peak regulation response and clean and low carbon emission. At the same time, in the transition stage of energy structure transformation, thermal power will gradually transform from main power source to system regulation support function.

[0003] At present, the direct-fired pulverizing system is generally used in 300MW-1000MW coal-fired units in China. For this kind of system, the uniformity of the air volume and the coal powder volume of the primary air powder pipeline connected with the same layer burner has an important influence on the safety and economy of the boiler operation, and is a key control variable affecting the boiler combustion efficiency and stability. When the air powder distribution of the primary air powder pipeline connected with the same layer burner is uneven, it will lead to the deflection of the flame center of the furnace, the slagging of the local area of the furnace and the combustion pulsation of the combustion area of the furnace, which not only will cause unstable combustion, but also will cause uneven distribution of the flue gas velocity field and temperature field in the superheater area, thereby causing the steam temperature deviation and even causing the superheater pipe explosion. Therefore, the primary air powder leveling test of the coal-fired boiler is of great significance for maintaining high combustion efficiency and stable operation of the boiler, and reducing the thermal stress and pollutant generation in the local high temperature area.

[0004] A patent with publication number CN115789693A provides a primary air powder conveying pipeline throttling element calculation and adjustment method; based on the friction resistance, local resistance, equipment and component resistance, loss of primary air coal powder lifting pressure head and pressure head loss of primary air coal powder acceleration of the primary air powder conveying pipeline resistance evaluation method; throttling element resistance deviation and adjustment calculation method. Finally, the resistance of each powder conveying pipeline is balanced, the primary air speed is uniform, the problem of how to realize fine adjustment of the throttling element through the primary air throttling element calculation and adjustment method is solved, and the uniformity of the primary air powder conveying pipeline speed is finally improved. According to the theory of aerodynamics and combined with the design principle of the pulverizing system, the throttling element can be adjusted under the operating state of the unit, the primary air speed data does not need to be measured through the test during the whole adjustment process, and the test workload is greatly reduced; at the same time, the influence of the primary air coal powder concentration on the resistance of the powder conveying pipeline is increased, the pressure drop of each branch pipe is calculated, and the calculation model is not corrected in real time, and the wind powder operating parameters in the pipeline are not collected in real time.

[0005] The primary air powder leveling test realizes two-dimensional balanced control to ensure combustion optimization: one is the uniformity control of the wind powder mixing speed distribution of the primary air powder pipeline in the same layer, and the other is the consistency maintenance of the wind powder mixing ratio of the same layer burner. The conventional process of the primary air powder leveling test applied to the engineering practice at present is as follows: first, a tester holds a standard pitot tube or backrest tube to measure the dynamic pressure and static pressure of the wind powder fluid according to the equal cross-section method; second, a coal powder static pressure zero-speed sampling test is carried out according to the equal cross-section method to obtain the coal powder flow of a single wind powder pipe; third, finally, the flow rate and coal powder concentration of the wind powder mixture are calculated according to the dynamic pressure, static pressure measurement value and coal powder flow; fourth, the operating state of the throttling element is adjusted according to the results, and the first to third steps are repeated until the purpose of primary air powder leveling is achieved. However, there are the following problems in the actual measurement process: the operating state of the throttling element is basically adjusted according to experience, which has a certain blindness; the manual operation intensity is large, the measurement times are many, and the measurement time is long; a large amount of high-altitude operation is involved, and the poor working environment can reduce the safety of personnel and equipment. In addition, the tester is prone to measurement deviation after high-intensity physical work in a poor environment, which affects the data accuracy and reliability. SUMMARY

[0006] In order to overcome the deficiencies of the prior art, the purpose of the present application is to provide a primary air powder leveling method based on a modified resistance model, which adjusts the operating state of the throttling element (such as the scale adjustment of the adjustable orifice) according to the resistance calculation results of the wind powder pipeline, so as to make the resistance characteristics of each wind powder pipeline consistent, thereby reducing the test measurement times and reducing the operation intensity of the tester.

[0007] In order to achieve the above purpose, the present application provides a primary air powder leveling method based on a modified resistance model, comprising the following steps: Based on the data distribution characteristics between the wind-pulverized coal pipe parameters, the local resistance coefficient test data at multiple groups of throttling elements, the pulverized coal concentration, and the operating parameters of the throttling elements, a two-phase flow resistance model of each wind-pulverized coal pipe is established. The flow velocity, the pulverized coal concentration, and the pressure drop of the wind-pulverized coal mixture are measured by the test, and the resistance coefficient at the throttling element of the wind-pulverized coal pipe is calculated. The two-phase flow resistance model is corrected based on the data obtained by the test measurement. The operating parameters of the throttling element are guided according to the resistance coefficient at the throttling element of the wind-pulverized coal pipe, until the deviation of the amount of powder and the wind-pulverized coal mixture velocity in the wind-pulverized coal pipe connected with the same layer burner meets the requirement of primary wind-pulverized coal leveling.

[0008] Further, based on the data distribution characteristics between the wind-pulverized coal pipe parameters, the local resistance coefficient test data at multiple groups of throttling elements, the pulverized coal concentration, and the operating parameters of the throttling elements, the two-phase flow resistance model of each wind-pulverized coal pipe includes: a quantitative relationship formula with parameters between the local resistance coefficient, the pulverized coal concentration, and the operating parameters of the throttling element is constructed based on the data distribution characteristics between the wind-pulverized coal pipe parameters, the local resistance coefficient test data at multiple groups of throttling elements, the pulverized coal concentration, and the operating parameters of the throttling element.

[0009] Further, the wind-pulverized coal pipe parameters include the inner diameter of the wind-pulverized coal pipe, the length of each vertical pipe and horizontal pipe, the vertical height from the pulverized coal distributor to the burner, the number of bend pipes in the wind-pulverized coal pipe, and the angle of each bend pipe, which are obtained according to the design file and the field test method.

[0010] Further, the test measurement of the flow velocity, the pulverized coal concentration, and the pressure drop of the wind-pulverized coal mixture, and the calculation of the resistance coefficient at the throttling element of the wind-pulverized coal pipe includes: The dynamic pressure and static pressure of the pulverized coal gas flow are measured by a Pitot tube or a backrest tube, and a pulverized coal static pressure zero-speed sampling test is performed. The flow velocity of the wind-pulverized coal two-phase flow is calculated according to the data obtained by the pulverized coal static pressure zero-speed sampling test u , density p , and pulverized coal concentration p ; The pressure drop of the pulverized coal gas flow in the horizontal pipe, the vertical pipe, and the bend pipe, and the resistance caused by the vertical lifting of the pulverized coal to overcome the gravity are calculated by the flow velocity of the wind-pulverized coal two-phase flow u , density p , and pulverized coal concentration p , to obtain the local resistance coefficient at the throttling element.

[0011] Further, the form of the quantitative relationship formula between the local resistance coefficient and the pulverized coal concentration and the operating parameters of the adjustable contraction hole is a polynomial or a neural network with more than 2 layers.

[0012] Further, the least square method is used to correct the polynomial when the two-phase flow resistance model is corrected based on the measured data, and the neural network with more than 2 layers is corrected by using the Bayesian optimization algorithm.

[0013] Further, the purpose of the primary air-pulverized coal leveling is to make the deviation of the pulverized coal amount and the air-pulverized coal mixing speed in the pipe connected with the layer burner less than ±5%.

[0014] Further, the local pressure drop of the pulverized coal flow at the throttling element is calculated according to the test total pressure drop, flow speed u , density p and pulverized coal concentration p of each air-pulverized coal pipe from the outlet of the coal mill to the outlet of the burner.

[0015] Further, the local resistance coefficient model of the throttling element of the existing air-pulverized coal pipe is corrected, and the operation parameters of the throttling element are guided according to the model, including: the operation state of the throttling element is adjusted according to the next stage operation parameters of the throttling element; the dynamic pressure and the static pressure of the pulverized coal flow after the operation state of the throttling element is adjusted are measured, and the pulverized coal static pressure zero-speed sampling test is carried out; the flow speed u , density p and pulverized coal concentration p of the air-pulverized coal two-phase flow are calculated according to the data obtained by the pulverized coal static pressure zero-speed sampling test.

[0016] The power generator unit can also be provided, which adopts the primary air-pulverized coal leveling method based on the corrected resistance model to adjust the flow speed and flow of the air-pulverized coal flow of the pulverized coal system.

[0017] Compared with the prior art, the present application has at least the following beneficial technical effects: according to the technical improvement of adjustable orifice scale precision adjustment according to the resistance characteristics of the wind powder pipeline, the traditional experience judgment mode is replaced by the establishment of a systematic calculation model, and the scientific quantification of the adjustment parameters is realized. The optimization scheme is based on the principle of fluid mechanics to construct a dynamic balance equation, and through real-time monitoring of the change of the pipeline pressure gradient to guide the adjustment action, so that the wind powder distribution deviation can be systematically corrected. Compared with the traditional leveling process which relies on periodic tests, the new control mechanism significantly reduces the redundant operation of repeated measurements by establishing a closed-loop feedback system. Under the premise of ensuring system stability, the leveling operation process is simplified to standardized operation, which not only effectively avoids the adjustment oscillation phenomenon caused by human experience deviation, but also reduces the length of time that personnel are exposed to high-risk working conditions by reducing the operation frequency, thereby simultaneously achieving a significant reduction in labor intensity and an improvement in equipment operation safety margin. In the dimension of quality control, the automatic control mode eliminates random errors introduced by human operation, so that the uniformity of the wind powder concentration distribution is systematically guaranteed, and technical support is provided for the efficient and stable operation of the combustion system. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 A flowchart of a primary air powder leveling method based on a modified resistance model is provided for the embodiments of the present application. DETAILED DESCRIPTION

[0019] In order for those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be described clearly and completely below in conjunction with the accompanying drawings of the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, not all. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor should be within the scope of protection of the present application.

[0020] Because the distance from the inlet of each branch of the pulverized coal pipeline to the connected burner, the number and form of the bends in the pipeline are different, the resistance of each pulverized coal pipeline through the same fluid is different. However, for the parallel pipeline, the pressure drop of each branch is always equal, so it will lead to the pulverized coal flow and the primary air flow of each branch of the pulverized coal pipeline being different, which is also the problem to be solved in the primary air pulverized coal leveling test. Taking a tangentially cut pulverized coal boiler as an example, the four primary air pulverized coal pipelines of the same layer of the four-corner burner are provided with pulverized coal from the same coal mill, and the primary air pulverized coal main pipeline is divided into four primary air pulverized coal pipelines through the pulverized coal distributor to reach the four-corner burner. However, if the resistance characteristics of the four branch pulverized coal pipelines are inconsistent, the pulverized coal flow and the primary air flow to the four-corner burner will be different. Therefore, the resistance characteristics of the parallel primary air pulverized coal pipelines reaching balance (referring to the resistance of each branch of the pulverized coal pipeline through the same fluid tending to be consistent) is the key to the primary air pulverized coal leveling test. In order to make the resistance characteristics of the parallel primary air pulverized coal pipelines reach balance, the power plant generally adjusts the scale of the adjustable orifice to adjust the resistance characteristics of the pulverized coal pipeline. Based on the above background, the overall idea of the primary air pulverized coal leveling method based on the modified resistance model is: first, the two-phase flow resistance model of each pulverized coal pipeline is established; second, the flow velocity, pulverized coal concentration and pressure drop and other parameters of the pulverized coal mixture are tested and measured; third, the resistance model is modified in the form of optimizing the model parameters based on the actual test data; fourth, the scale of the adjustable orifice is adjusted according to the resistance calculation result of the pulverized coal pipeline; fifth, the second to fourth steps are repeated until the purpose of leveling the primary air pulverized coal is achieved.

[0021] The total resistance of the pulverized coal pipeline generally includes the pipeline friction resistance (i.e. friction resistance), the resistance caused by the vertical lifting of the pulverized coal to overcome the action of gravity, the local resistance at the bend, and the local resistance at the adjustable orifice installed by the power plant to balance the resistance characteristics of the parallel pipelines. Different from the calculation of the friction resistance of the single-phase fluid, the friction resistance coefficient of the pulverized coal two-phase flow in the straight pipeline not only depends on the Reynolds number (Re) of the fluid and the relative roughness of the pipeline, but also is closely related to the pulverized coal concentration (C) and the spatial orientation of the pipeline. Re p

[0022] The friction resistance of the pulverized coal two-phase flow in the pipeline can be expressed as: (1) In the formula, p μ is the friction resistance coefficient of the pulverized coal two-phase flow; L is the length of the pipeline / m; d e is the equivalent diameter of the pipeline / m; p is the mixed density of the pulverized coal two-phase flow / kg·m -3 ; u is the flow velocity of the pulverized coal two-phase flow / m·s​​-1 It is obvious that the mixing density of the two-phase flow p is closely related to the concentration of the pulverized coal p ; the resistance of the two-phase flow in the burner is considered as a part of the resistance along the pipeline.

[0023] According to the relevant literature, the frictional resistance coefficient of the two-phase flow of the pulverized coal and air p μ is generally calculated according to the following general formula: (2) wherein, p 0 is the frictional resistance coefficient of pure air (for the pipeline of the pulverized coal, the value of p 0 can be taken as 0.015); k is a correction factor. Obviously, for the horizontal pipeline and the vertical pipeline, p μ the value of

[0024] The resistance caused by the vertical lifting of the flow of the pulverized coal can be expressed as: (3) wherein, H is the vertical height of the pulverized coal distributor to the burner, m.

[0025] The local resistance of the two-phase flow of the pulverized coal and air at the elbow can be expressed as: (4) wherein, p 0 is the resistance coefficient of pure air in the elbow. When the pure air flows through the elbow with an angle of p (unit: °), the resistance coefficient p 0 can be expressed as: (5) wherein, R is the radius of the elbow, m; p is the Reynolds number, equal to p e / p ; p is the kinematic viscosity of pure air, m 2 ·s -1 .

[0026] The local resistance of the two-phase flow of the pulverized coal and air at the adjustable orifice can be expressed as: (6) wherein, p sj is the local resistance coefficient at the adjustable orifice. In the flow of the pulverized coal, the local resistance coefficient p sjand the operating state of the adjustable orifice (e.g. the scale of the adjustable orifice x ).

[0027] (7) The total resistance Δ p of the wind-pulverized coal two-phase flow in the wind-pulverized coal pipeline can be expressed as: (8) Further, the total resistance Δ p of the wind-pulverized coal two-phase flow in the wind-pulverized coal pipeline can be expressed as: (9) According to the recommended values recognized by the industry, when p ≤0.5, the value of 1+0.65 k sf is taken; when p >0.5, the value of 1.5 p sf is taken; for a horizontal pipe, k cf the value of 1+0.65 k is taken; and for a curved pipe, p wj the value of 1+5.5 k is taken. p

[0028] Finally, the total resistance Δ p of the wind-pulverized coal two-phase flow in the wind-pulverized coal pipeline is expressed as a simplified form with parameters (the local pressure drop calculation formula of the parameters at the throttling element (e.g. the adjustable orifice) ) : (10) On the right side of the equation, in turn, are the pressure drop of the pulverized coal gas flow in the horizontal pipe, the pressure drop of the pulverized coal gas flow in the vertical pipe, the resistance caused by the vertical lifting of the pulverized coal to overcome the action of gravity, the pressure drop of the pulverized coal gas flow in each curved pipe, and the local resistance of the wind-pulverized coal two-phase flow at the adjustable orifice, in which, L i L is the length of each horizontal pipe, m; L j H is the length of each vertical pipe, m; H H is the vertical height of the pulverized coal distributor to the burner connected to the wind-pulverized coal pipeline, m.

[0029] By measuring the wind speed of the wind-pulverized coal pipeline, the coal powder static pressure zero position, and other test contents, combined with equations (11)-(13), the flow velocity u , the density p , and the pulverized coal concentration p of the wind-pulverized coal two-phase flow can be obtained., and then the pressure drop of the pulverized coal gas flow in the horizontal pipe, the pressure drop of the pulverized coal gas flow in the vertical pipe, the resistance caused by the gravity of the vertically lifted pulverized coal, and the pressure drop of the pulverized coal gas flow in each bend pipe can be obtained in a certain pulverized coal gas pipeline.

[0030] (11) (12) (13) In the formula (11)-(13), M is the mass of the pulverized coal obtained by the constant speed sampling test of the zero static pressure of the pulverized coal, kg; A is the area of the pulverized coal gas flow inlet of the constant speed sampling device of the zero static pressure of the pulverized coal, m 2 ; t is the sampling time of the pulverized coal, s; t 2 is the outlet temperature of the coal mill, ℃; p a is the atmospheric pressure, Pa; p p is the static pressure of the gas flow, Pa; V c is the volume per kilogram of the pulverized coal, which can be taken V c as 0.001 m 3 ·kg -1 ; Δ M is the evaporated moisture of the raw coal in the coal mill, kg·kg -1 ; M ar is the received base moisture, %; M pc is the moisture of the pulverized coal, %.

[0031] If the total pressure drop of each pulverized coal gas pipeline from the outlet of the coal mill to the outlet of the burner is obtained, the local pressure drop of the pulverized coal gas flow at the throttling element (such as an adjustable orifice) can be calculated by the obtained flow velocity u , density p and pulverized coal concentration p . Through the actual measurement data in the early stage, the quantitative relationship between the local resistance coefficient p sj and the pulverized coal concentration p and the operating parameters of the adjustable orifice (such as the scale of the adjustable orifice x ) can be fitted.

[0032] When the obtained local resistance coefficient p sj is less (such as within 20 groups of data), the local resistance coefficient p sjand the quantitative relationship between the coal concentration p and the operating state of the adjustable orifice (such as the scale of the adjustable orifice x ). p sj When there are more test data (such as more than 50 groups of data), the local resistance coefficient p sj and the quantitative relationship between the coal concentration p and the operating state of the adjustable orifice (such as the scale of the adjustable orifice x ).

[0033] The sensitivity of the flow rate of the wind-powder mixture to the operating state of the adjustable orifice is higher than the coal concentration, and the reduction of the deviation of the wind-powder mixture speed of each pipeline of the same layer burner helps to reduce the deviation of the powder amount. The purpose of the primary wind-powder leveling is to make the deviation of the powder amount and the wind-powder mixture speed in the pipeline connected with the same layer burner less than a certain value (such as ±5%). Therefore, the coal concentration and the wind-powder mixture speed required in the sub-pipeline pressure drop model can adopt the coal concentration value measured in the last test and the average value of the wind-powder mixture speed of each sub-pipeline, which are used to calculate the operating parameters (such as the scale of the adjustable orifice x ) of the adjustable orifice in the next stage. After adjusting the adjustable orifice in each sub-pipeline according to the calculation results, the wind speed, the zero-speed sampling of the coal static pressure and other test contents of the wind-powder pipeline of each sub-pipeline are tested again to obtain the flow speed u , the density p and the coal concentration p of the wind-powder two-phase flow. If the deviation of the powder amount and the wind-powder mixture speed still does not meet the requirement of the primary wind-powder leveling, the resistance model is corrected by the test data. The above process is repeated until the deviation of the powder amount and the wind-powder mixture speed in the pipeline connected with the same layer burner meets the requirement of the primary wind-powder leveling.

[0034] In summary, the detailed steps of the primary wind-powder leveling method based on the corrected resistance model provided by the present application are as follows: (1) According to the design file and the site test, the internal diameter of the wind-powder pipeline, the length of each vertical pipeline and horizontal pipeline, the vertical height from the coal powder distributor to the burner, the number of bend pipes in the wind-powder pipeline and the angle of each bend pipe and other parameters are obtained. (2) The dynamic pressure and static pressure of the coal-powder gas flow are measured by the Pitot tube or backrest pipe, and the zero-speed sampling test of the coal static pressure is performed. (3) The flow speed u , the density p and the coal concentration p of the wind-powder two-phase flow are calculated according to the data obtained by the test. (4) Obtain the local resistance coefficient at the throttle element by calculating the pressure drop of the pulverized coal gas flow in the horizontal pipe, vertical pipe and elbow pipe, and the resistance caused by the vertical lifting of the pulverized coal to overcome the action of gravity; (5) Based on the data distribution characteristics between the multiple sets of local resistance coefficient test data and the pulverized coal concentration and the operating parameters (such as the scale x ) of the adjustable throttle, a quantitative relationship formula with parameters among the three is constructed, and the resistance model parameters are fitted or corrected; (6) The pulverized coal concentration and the wind-pulverized coal mixed speed required in the sub-pipe pressure drop model adopt the pulverized coal concentration value measured in the last test and the average value of the wind-pulverized coal mixed speed of each sub-pipe to calculate the operating parameters (such as the scale x ) of the adjustable throttle in the next stage; (7) Adjust the operating state of the adjustable throttle according to the calculated scale x of the adjustable throttle; (8) Measure the dynamic pressure and static pressure of the pulverized coal gas flow again through the Pitot tube or back tube, and perform the coal powder static pressure zero speed sampling test; (9) Calculate the flow speed u , density p and pulverized coal concentration p of the wind-pulverized coal two-phase flow according to the data obtained in the test; (10) Check whether the deviation of the pulverized coal amount and the wind-pulverized coal mixed speed in the pipeline connected with the same layer burner meets the requirement of the primary wind-pulverized coal leveling, and if it meets the requirement, end the primary wind-pulverized coal leveling test; (11) If it does not meet the requirement of the primary wind-pulverized coal leveling, repeat steps (2) to (10).

[0035] In each branch pipeline, the total resistance Δ p of the wind-pulverized coal two-phase flow in the wind-pulverized coal pipeline is expressed in a simple form with parameters (the parameters are in the local pressure drop calculation formula at the adjustable throttle): (14) On the right side of the equation, is the pressure drop of the pulverized coal gas flow in the horizontal pipe, is the pressure drop of the pulverized coal gas flow in the vertical pipe, p is the resistance caused by the vertical lifting of the pulverized coal gas flow to overcome the action of gravity, is the pressure drop of the pulverized coal gas flow in each elbow pipe, is the local resistance of the wind-pulverized coal two-phase flow at the adjustable throttle, wherein, L i is the length of each horizontal pipe, m; L j is the length of each vertical pipe, m; H is the vertical height from the pulverized coal distributor to the burner connected with the wind-pulverized coal pipeline, m.

[0036] By measuring the wind speed of the wind-powder pipeline, the coal-powder static pressure zero, and other test contents, the flow velocity of the wind-powder two-phase flow can be obtained by combining equations (15)-(17) u , density p , and coal-powder concentration p , and then the pressure drop of the coal-powder airflow in the horizontal pipe, the pressure drop of the coal-powder airflow in the vertical pipe, the resistance caused by the gravity of the vertically lifted coal-powder, and the pressure drop of the coal-powder airflow in each elbow pipe can be obtained in a certain wind-powder pipeline.

[0037] (15) (16) (17) In equations (15)-(17), M is the mass of the coal powder obtained by the coal-powder static pressure zero constant-speed sampling test, kg; A is the area of the coal-powder airflow inlet of the coal-powder static pressure zero constant-speed sampling device, m 2 ; t is the coal-powder sampling time, s; t 2 is the outlet temperature of the coal mill, ℃; p a is the atmospheric pressure, Pa; p p is the airflow static pressure, Pa; V c is the volume per kilogram of coal powder, which can be taken as V c 0.001 m 3 ·kg -1 ; Δ M is the evaporation moisture of the raw coal in the coal mill, kg·kg -1 ; M ar is the received base moisture, %; M pc is the coal-powder moisture, %.

[0038] The primary air-powder pipeline resistance model is corrected based on the test data, the least square method, and the Bayesian optimization algorithm. The Bayesian optimization algorithm is suitable for solving black box optimization problems in a limited time, which has the following two characteristics: (1) the target function cannot calculate the gradient of the optimized parameters; (2) the provided parameter optimization time is limited. The main steps of the Bayesian optimization algorithm are: (1) according to a number of initialized parameter points, the target function (in this paper, the local resistance coefficient p sj and the coal-powder concentration pthe quantitative relationship between the adjustable orifice and the operating state (such as the scale of the adjustable orifice x ) of the adjustable orifice the value of each point and the confidence degree corresponding to the point); (2) under the guidance of the acquisition function, let try to approach ; (3) take the minimum value of the approximation as the minimum value of the real function .

[0039] The steps of correcting the primary air-pulverized coal pipeline resistance model based on the Bayesian optimization algorithm are as follows: first, based on the physical mechanism, a prediction formula of the local resistance coefficient of the throttling element in each branch pipe is constructed p sj , and the test value of the local resistance coefficient p sj is obtained through the test content of measuring the air speed, coal powder static pressure zero position, and other speed sampling; secondly, the objective function to be optimized is constructed, such as formula (18). Finally, the Bayesian optimization algorithm is used to identify the model parameters a i ( i =1, 2, 3, …).

[0040] (18) In the formula, RMSE is a function for representing the difference between the predicted value and the test value of the local resistance coefficient of the throttling element in each branch pipe; p sj * is the test value of the local resistance coefficient; p sj is the predicted value of the local resistance coefficient.

[0041] (19) In the formula, a i is the undetermined parameter in the quantitative relationship between the local resistance coefficient p sj and the coal powder concentration p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p and the operating state (such as the scale of the adjustable orifice x ) of the adjustable orifice.

[0042] Based on the above primary air-pulverized coal leveling method based on the corrected resistance model, the present application can also provide a thermal power generating unit, which adopts the above primary air-pulverized coal leveling method based on the corrected resistance model to adjust the flow rate and flow of the pulverized coal system.

[0043] ​​While the application has been described in detail and with reference to specific embodiments thereof, it will be apparent to one skilled in the art that various modifications or changes can be made therein without departing from the spirit and scope thereof. Accordingly, it is intended that all such modifications and changes be included within the scope of the application as claimed.

Claims

1. A method for primary air pulverized fuel leveling based on a modified resistance model, characterized in that, The method comprises the following steps: Based on the data distribution characteristics between the wind-pulverized coal pipe parameters, the local resistance coefficient test data at multiple sets of throttling elements, the pulverized coal concentration, and the operating parameters of the throttling elements, a two-phase flow resistance model of each wind-pulverized coal pipe is established; The flow velocity, the pulverized coal concentration, and the pressure drop of the wind-pulverized coal mixture are measured by experiments, and the resistance coefficient at the throttling element of the wind-pulverized coal pipe is calculated; The two-phase flow resistance model is corrected based on the data measured by the experiments; The operating parameters of the throttling element are guided according to the resistance coefficient at the throttling element of the wind-pulverized coal pipe, until the deviation of the pulverized coal amount and the wind-pulverized coal mixture velocity in the wind-pulverized coal pipe connected with the layer burner meets the requirement of the primary wind-pulverized coal leveling.

2. The modified resistance model based primary air pulverization leveling method of claim 1, wherein, The two-phase flow resistance model of each wind-pulverized coal pipe is established based on the data distribution characteristics between the wind-pulverized coal pipe parameters, the local resistance coefficient test data at multiple sets of throttling elements, the pulverized coal concentration, and the operating parameters of the throttling elements, which comprises: constructing a quantitative relationship formula with parameters between the local resistance coefficient, the pulverized coal concentration, and the operating parameters of the throttling element based on the data distribution characteristics between the wind-pulverized coal pipe parameters, the local resistance coefficient test data at multiple sets of throttling elements, the pulverized coal concentration, and the operating parameters of the throttling element.

3. The modified resistance model based primary air pulverization leveling method of claim 2, wherein, The wind-pulverized coal pipe parameters comprise the inner diameter of the wind-pulverized coal pipe, the length of each vertical pipe and horizontal pipe, the vertical height from the pulverized coal distributor to the burner, the number of bend pipes in the wind-pulverized coal pipe, and the angle of each bend pipe, which are obtained according to design documents and on-site test methods.

4. The modified resistance model based primary air pulverization leveling method of claim 1, wherein, The flow velocity, the pulverized coal concentration, and the pressure drop of the wind-pulverized coal mixture are measured by experiments, and the resistance coefficient at the throttling element of the wind-pulverized coal pipe is calculated, which comprises: The dynamic pressure and static pressure of the pulverized coal gas flow are measured by a Pitot tube or a backrest tube, and a pulverized coal static pressure zero-speed sampling test is performed; The flow velocity of the wind-pulverized coal two-phase flow is calculated according to the data obtained from the coal-pulverized static pressure zero position isokinetic sampling test u , density The quantitative relationship formula between the local resistance coefficient and the pulverized coal concentration and the operating parameters of the adjustable orifice is in the form of a polynomial or a neural network with more than 2 layers. and coal-pulverized concentration When the two-phase flow resistance model is corrected based on the data measured by the experiments, the least square method is used to correct the polynomial, and the Bayesian optimization algorithm is used to correct the neural network with more than 2 layers. ​ The flow velocity of the air-powder two-phase flow u ,density The purpose of the primary wind-pulverized coal leveling is to make the deviation of the pulverized coal amount and the wind-pulverized coal mixture velocity in the pipe connected with the layer burner less than ±5%. and coal powder concentration The existing local resistance coefficient model of the throttling element of the wind-pulverized coal pipe is corrected, and the operating parameters of the throttling element are guided according to the model, which comprises: Calculate the pressure drop of pulverized coal airflow in horizontal pipes, vertical pipes, and bends, as well as the resistance caused by vertically lifting pulverized coal to overcome gravity, and obtain the local resistance coefficient at the throttling element.

5. The modified resistance model based primary air pulverization leveling method of claim 1, wherein, The operating state of the throttling element is adjusted according to the next stage operating parameters of the throttling element; 6. The primary flow pulverizer leveling method based on a modified resistance model according to claim 5, wherein, The dynamic pressure and static pressure of the pulverized coal gas flow after the operating state of the throttling element is adjusted are measured, and a pulverized coal static pressure zero-speed sampling test is performed; 7. The modified resistance model based primary air pulverization leveling method of claim 1, wherein, The primary wind-pulverized coal leveling method based on the corrected resistance model in any one of claims 1-9 is used to adjust the wind-pulverized coal flow velocity and flow rate of the pulverized coal system.

8. The modified resistance model based primary air pulverization leveling method of claim 1, wherein, The local pressure drop of the pulverized coal flow at the throttle element is calculated according to the test total pressure drop, flow velocity u , density ​ and pulverized coal concentration ​ of each wind powder pipeline from the outlet of the coal mill to the outlet of the burner, and then the local resistance coefficient at the throttle element is obtained.

9. The modified resistance model based primary air pulverization leveling method of claim 1, wherein, ​ ​ ​ Flow velocity of the wind-pulverized coal two-phase flow is calculated according to data obtained from the coal-pulverized static pressure zero equal-velocity sampling test u , density ​ and coal-pulverized concentration ​ .

10. A thermal power generating unit, characterized by ​

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