Regulation and control method for opening degree of air door of tangential combustion boiler based on secondary air distribution mode

Abstract

The invention relates to a method for regulating and controlling the opening degree of an air door of a tangential combustion boiler based on a secondary air distribution mode. Comprising the following steps: calculating comprehensive resistance coefficients xic, n under different air door opening degree conditions; calculating the gas flow qn0 of a burner nozzle and the resistance coefficient xiw, n0 of an air bellow according to the air door opening degree initial value theta n0; the average absolute percentage error delta of qn0 and the target gas flow qg, n is judged; if delta is larger than 0.1%, qn0, xic, n and xiw and n0 are imported through a Newton-Rafoson downhill iteration method, and an air door opening degree improvement value theta nm is generated through iteration; qnm and zeta w and nm are calculated; the average absolute percentage error delta of qnm and qg, n is judged; and if delta is less than or equal to 0.1%, outputting the gas flow of the burner nozzle and the corresponding air door opening, and ending the calculation. According to the method disclosed by the invention, the opening degree of the air door of the tangential combustion boiler under any target flow distribution of the secondary air can be regulated and controlled under a thermal state condition.

Description

Technical Field

[0001] The invention relates to the technical field of tangential combustion boiler control, in particular to a method for controlling the air door opening of a tangential combustion boiler based on a secondary air distribution mode. Background Art

[0002] With the rapid development of renewable energy power generation technology and the urgent need to control the environment and reduce pollutant gas emissions, wind power, solar power and other renewable energy power generation technologies have developed rapidly. In order to improve the power grid's ability to absorb renewable energy power generation, thermal power units have gradually changed from a long-term high-load operation mode to a peak-shaving operation mode that cooperates with renewable energy power generation.

[0003] During peak load regulation, the load variation range of thermal power units is large and the load variation rate is fast. It is necessary to quickly adjust the secondary air ratio and distribution method according to the load change by changing the damper opening. In industrial applications, field test methods are usually used to determine the relationship between the damper opening and the secondary air speed under cold conditions, and then apply it to the study of hot boiler performance. Due to the large temperature difference between cold and hot states, there is a certain error in the results obtained.

[0004] When designing a tangentially fired boiler, due to the limitations of floor space and on-site space, the secondary air ducts connected to each burner nozzle are not independent, and are usually composed of structures such as a bellows and branch pipes. Among them, the structural relationship between the bellows and the burner nozzles is a main pipe and a parallel branch pipe. Changes in the damper opening of any layer of burner nozzles will not only affect the secondary air volume of this layer, but also the secondary air volume of burner nozzles on other layers. In addition, when the tangentially fired boiler is operated in peak-shaving mode, the secondary air flow distribution of the burner nozzles on each layer is usually uneven, and the damper opening needs to be adjusted according to the secondary air volume distribution requirements.

[0005] Therefore, for the problem of regulating the damper opening of a tangentially fired boiler under hot conditions, further research is still needed on how to effectively and reasonably adjust the damper opening under any target flow distribution. Summary of the invention

[0006] In view of the deficiencies in the prior art, the present invention provides a method for regulating the air door opening of a tangential combustion boiler based on a secondary air distribution method.

[0007] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0008] The present invention provides a method for controlling the air door opening of a tangential combustion boiler based on a secondary air distribution method, comprising the following steps:

[0009] (1) Calculate different damper openings θ using the finite volume method of numerical simulation n Under the condition, the average gas velocity u at the burner nozzleb，n , Pressure drop ΔP of horizontal branch pipe p，n and the burner nozzle pressure drop ΔP b，n , and obtain the comprehensive resistance coefficient ξ under different damper opening conditions c，n (The symbol ξ in this application c，n The symbol ξ can also be used c，n m express);

[0010] (2) Based on the initial value of the secondary air damper opening θ n 0 , calculate the gas flow rate q of the burner nozzle under the initial value of the air door opening n 0 and bellows resistance coefficient ξ w，n 0 ;

[0011] (3) Calculate the gas flow rate q of the burner nozzle under the initial value of the air damper opening n 0 The target gas flow rate q of the burner nozzle g,n The mean absolute percentage error δ;

[0012] If δ≤0.1%, the burner nozzle flow and the corresponding damper opening are output and the calculation ends; if δ>0.1%, continue with step (4);

[0013] (4) Using the Newton-Raphson downhill iteration method, the gas flow rate q of the burner nozzle is introduced n 0 、Comprehensive resistance coefficient ξ c，n and bellows resistance coefficient ξ w，n 0 , iteratively generates the improved value of the damper opening θ n m ;

[0014] Improve the value θ according to the air door opening n m , using the method in step (2), calculate the gas flow rate q of the burner nozzle under the condition of the improved value of the air door opening n m and the resistance coefficient of the bellows ξ w，n m ;

[0015] (5) Using the method in step (3), calculate the gas flow rate q of the burner nozzle under the condition of the improved value of the air door opening n m The target gas flow rate q of the burner nozzle g,n The mean absolute percentage error δ;

[0016] If δ≤0.1%, the gas flow rate of the burner nozzle and the corresponding air door opening are output, and the calculation ends; if δ>0.1%, the gas flow rate q introduced into the burner nozzle is n m 、Comprehensive resistance coefficient ξ c，n and bellows resistance coefficient ξ w，n m , repeat steps (4)-(5) until δ≤0.1%.

[0017] Preferably, in step (1), each layer of burners and the horizontal branch pipes connected to the burners are used as independent calculation domains, and the pressure drop ΔP of the horizontal branch pipes is calculated. p，n and the burner nozzle pressure drop ΔP b，n The sum of the pressure drop is ΔP cn ; Under different air door opening conditions, the average gas velocity u at the burner nozzle bn and pressure drop ΔP c，n The relationship between and calculates the comprehensive resistance coefficient ξ under different damper opening conditions c，n ; n is any layer of burners, n = 1, 2, 3..., r;

[0018] Preferably, in step (1), the average gas velocity u of the burner nozzle is b，n and pressure drop ΔP c，n The relationship between them is:

[0019] Where: u b，n is the air door opening θ n The corresponding average gas velocity of the burner nozzle is m / s; ρ is the gas density, kg / m 3 ξ c，n for u b，n As the comprehensive resistance coefficient of the burner nozzle and horizontal branch pipe at the qualitative speed; θ n is the air door opening of any layer of burners, %;

[0020] Preferably, in step (2), according to: Calculate the gas flow rate q at the burner nozzle n m ;

[0021] Where: q n m is the gas flow rate of the burner nozzle calculated after the mth iteration, m is the number of iterations, m = 0, 1, 2, 3..., kg / s; A is the outlet area of ​​the burner nozzle;

[0022] Preferably, in step (2), the pressure drop ΔP of the wind box is w，n and pressure drop ΔP c，nThe sum of the pressure drop is recorded as the total pressure drop ΔP t，n ;according to: Calculate the bellows resistance coefficient ξ w，n m ;

[0023] Where: w，n m After the mth iteration, u b，n As the resistance coefficient of the bellows at the qualitative speed, m is the number of iterations, m = 0, 1, 2, 3...; the bellows is the main bellows or the burnout bellows;

[0024] Preferably, in step (3), the calculation formula of the mean absolute percentage error δ is:

[0025]

[0026] In the formula, q g,n is the target gas flow rate of the burner nozzle, that is, the gas flow rate of the burner nozzle under the flow distribution target, kg / s;

[0027] Preferably, in step (4), the air damper opening improvement value is calculated using the Newton-Raphson downhill iteration method according to the relationship between the gas flow rate of the burner nozzle and the air damper opening; the relationship between the gas flow rate of the burner nozzle and the air damper opening is:

[0028]

[0029] Where: g is the functional relationship between different damper openings; A n is the outlet area of ​​any layer of burner nozzle, m 2 , n=1, 2, 3..., r; q n is the gas flow rate of the burner nozzle of any layer, n = 1, 2, 3..., r, kg / s;

[0030] Preferably, in step (4), on the basis of the iteration of the Newton-Raphson iteration method, θ (k+1) With θ k The weighted average is taken as a new approximation to obtain the expression of the Newton-Raphson downhill iteration method;

[0031] The vector expression of the Newton-Raphson iteration method is: θ (k+1) =θ (k) -(J (k) ) -1 G (k) ;

[0032] The vector expression of the Newton-Raphson downhill iteration method is:

[0033] in,

[0034]

[0035] θ (k) =(θ 1,k ,θ 2,k ,…,θ r,k ) T

[0036] θ (k+1) =(θ 1,k+1 ,θ 2,k+1 ,…,θ r,k+1 ) T

[0037] G (k) =(g 1,k ,g 2,k ,…,g r,k ) T

[0038] In the formula, the matrix J (k) is the Jacobi matrix, which consists of the values ​​of the partial derivatives of G at point k; is the result calculated by the Newton-Raphson downhill method; λ is the step size factor, 0≤λ≤1.

[0039] The technical solution of the present invention achieves the following beneficial technical effects:

[0040] The present invention adopts a numerical simulation method to obtain the relationship between the damper opening under hot conditions and the secondary air velocity of each layer of burners, overcoming the error caused by the cold experimental method. The effective combination of numerical simulation and Newton-Raphson downhill iteration method can realize the regulation of the damper opening under arbitrary target flow distribution of secondary air. Therefore, the method of the present invention can realize the regulation of the damper opening of a tangential combustion boiler under arbitrary target flow distribution of secondary air under hot conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 The secondary air system structure and burner nozzle layout diagram of the existing tangentially fired boiler;

[0042] Among them, (a) is the secondary air system structure; (b) burner nozzle arrangement;

[0043] The reference numerals in the figure are as follows: 1-secondary air main duct; 2.1-main air box; 2.2-burnout air box; 3-secondary air inlet; 4-burner nozzle; 5-air box section inlet; 6-air pressure monitoring position; 7-air gate; 7.1-main burner zone air gate; 7.2-burnout air gate; 8-horizontal branch pipe; 8.1-horizontal branch pipe inlet;

[0044] Figure 2 The structure diagram of the burner nozzle of the existing tangentially fired boiler and the horizontal branch pipe connected thereto;

[0045] Figure 3 The model calculation flow chart of the air door opening control method of the present invention;

[0046] Figure 4 It is a relationship diagram between the pressure drop and velocity in the calculation domain of the AA layer burner nozzle in the application example of the present invention;

[0047] Figure 5 It is a curve diagram showing the relationship between the comprehensive resistance coefficient of the burner nozzle calculation domain of the AA layer and the air door opening in the application example of the present invention. DETAILED DESCRIPTION

[0048] Example

[0049] 1. Resistance analysis of secondary air system

[0050] Figure 1 This is a common secondary air system structure and burner nozzle arrangement for tangential burner boilers. When a tangentially fired boiler is in operation, the outlet airflows of the burner nozzles arranged at the four corners of the furnace are all directed toward an imaginary tangent circle at the center of the furnace. Four airflows at the same layer form a strongly rotating torch at the center of the furnace. In order to make the center of the rotating torch located at the center of the furnace, the speeds of the four gases must be equal. For this reason, during the design, the secondary air main duct, main wind box, and burnout wind box structures all adopt symmetrical structures. The main wind box at the same corner and the nozzles at each layer of the main burner area have a structural relationship of a main pipe and parallel branches, and the burnout wind box at the same corner and the burnout air burner nozzles at each layer also have this relationship. The gas flow rate of each layer of burner nozzles is related to the resistance in the burner nozzles and the horizontal branches connected to them. The greater the resistance, the lower the gas velocity and flow rate of the burner nozzles. Since the horizontal branches connected to the burner nozzles at each layer are independent of each other, the burners at each layer and the horizontal branches connected to them can be analyzed as independent calculation domains. Figure 2 It is the structure of one layer of burner nozzles and the horizontal branch pipes connected to it.

[0051] The secondary air for combustion support flows from the inlet of the secondary air system through the secondary air main duct, the main wind box, the burnout wind box, and enters each horizontal branch pipe after distribution, and finally enters the furnace through the burner nozzles of each layer. The total pressure drop of the secondary air flow includes friction pressure drop, acceleration pressure drop, gravity pressure drop and local pressure drop. In order to reduce heat loss, the secondary air system is usually insulated. It can be assumed that there is no heat exchange between the gas and the environment, the temperature of the gas does not change much, and the change in gas density can be ignored. The flow of gas in the pipeline can be considered as a stable single-phase flow. Therefore, the acceleration pressure drop and gravity pressure drop during gas flow can be ignored.

[0052] Figure 1 It can be seen that the straight pipes of the secondary air system are shorter, there are more bends and branch pipes, and the structure of the burner nozzle is complex. Therefore, the local pressure drop of air flow in the secondary air system is much greater than the friction pressure drop. In the study, the local pressure drop is the main factor, and the influence of the friction pressure drop is incorporated into the local pressure drop in the form of a resistance coefficient.

[0053] The burners on each layer and the horizontal branches connected to them are analyzed as independent calculation domains, and the pressure drop in the secondary air duct is recorded as ΔP mp , the pressure drop of the bellows is recorded as ΔP w , the pressure drop of the horizontal branch is recorded as ΔP p , the pressure drop of the burner nozzle is recorded as ΔP b Therefore, the total pressure drop from the secondary air main inlet to the burner nozzle outlet is ΔP s for:

[0054] ΔP s =ΔP mp +ΔP w +ΔP p +ΔP b (1)

[0055] Since the burner nozzles on each layer and the horizontal branch pipes connected to them are in parallel, the total pressure drop from the inlet of the secondary air main duct to the outlet of the burner nozzles on each layer is equal. For the burner nozzles on each layer, the total pressure drop includes the pressure drop ΔP in the secondary air main duct. mp And the values ​​are equal, so ΔP can be ignored mp Influence. That is, from the inlet of the bellows section (such as Figure 1 The pressure drop from the burner nozzle outlet to each layer is also equal, which is denoted as ΔP t , the calculation formula is:

[0056]

[0057] In the formula, u w 、u p 、u b are the average gas velocities of the wind box, horizontal branch pipe and burner nozzle, m / s; ρ is the gas density, kg / m 3 ξ′ w ,ξ′ p ,ξ′ b They are the resistance coefficients of the bellows, horizontal branch pipe and burner nozzle respectively; the bellows is the main bellows or the burnout bellows.

[0058] Since the flow areas of the wind box, horizontal branch pipe and burner nozzle are different, u in formula (2) w 、u p 、u bFor the convenience of calculation and result analysis, the average gas velocity u of the burner nozzle is b As the qualitative speed. Therefore, formula (1) can be rewritten as:

[0059]

[0060] In the formula, ξ w , p , b u b The drag coefficient of the main wind box or burnout wind box, horizontal branch pipe and burner nozzle at the qualitative speed (where ξ w is the resistance coefficient of the main wind box or burnout wind box under different layers of r combinations of air door openings).

[0061] Since the damper arranged in the horizontal branch pipe is very close to the burner nozzle, the change of the damper opening has a greater impact on the resistance coefficient of the burner nozzle. In order to reduce the calculation error, the pressure drop of the horizontal branch pipe and the burner nozzle is combined and recorded as ΔP c The calculation formula is:

[0062]

[0063] ξ c =ξ p +ξ b (5)

[0064] In the formula, ξ c for u b As the comprehensive resistance coefficient of the burner nozzle and horizontal branch pipe at the qualitative speed (that is, the comprehensive resistance coefficient corresponding to each layer of air door at different opening degrees).

[0065] Then formula (2) can be rewritten as:

[0066]

[0067] 2. Calculation of resistance coefficient

[0068] Under hot conditions, the comprehensive resistance coefficient of the burner nozzle and the horizontal branch connected to it is ξ c and bellows resistance coefficient ξ w It is obtained by numerical simulation method.

[0069] Will Figure 1 The burner nozzles at each layer and the horizontal branches connected to them are Figure 2 The pressure drop ΔP of the burner nozzles and the horizontal branches connected to them at each layer corresponding to different air door openings is calculated by numerical simulation method. c The comprehensive resistance coefficient ξ corresponding to different damper openings is calculated using formula (4):c and burner nozzle wind speed u b The relationship between.

[0070] The burner nozzles at each layer and the horizontal branches connected to them are regarded as part of the secondary air system. The total pressure drop ΔP from the secondary air main inlet to the burner nozzle outlet of the secondary air system under different secondary air damper opening combinations is calculated using a numerical simulation method. s (i.e. ΔP t ). Using formula (6) and combining the comprehensive resistance coefficient ξ c , the bellows resistance coefficient ξ is calculated w .

[0071] 3. Air door opening control model

[0072] Take the r-layer burner nozzles at any corner of the furnace as an example, the burner nozzle at the bottom layer is numbered 1. When the structure of the secondary air system and the burner nozzle is constant, the resistance coefficient is a function of the air door opening θ. The gas flow rate q of any layer of burner nozzles (numbered n) is n and total pressure drop ΔP t The relationship between them is:

[0073]

[0074] In the formula, A n is the outlet area of ​​any layer of burner nozzle, m 2 , n=1, 2, 3..., r; q n is the gas flow rate of the burner nozzle of any layer, kg / s, n=1, 2, 3..., r.

[0075] Since the burner nozzles are connected in parallel, the total pressure drop ΔP t are equal, so the flow ratio between any two layers of burner nozzles (numbered n and n') is:

[0076]

[0077] Taking the gas flow rate of burner nozzle No. 1 as the reference, the total secondary air volume q at any corner of the furnace is t The calculation formula is:

[0078]

[0079] The actual gas flow rate of any layer of burner nozzle is denoted as q n The target gas flow after regulation is recorded as q g,n An algebraic function F is established, which is the sum of the absolute values ​​of the deviations between the actual gas flow rate of each layer of burner nozzles and the target gas flow rate. The expression is:

[0080]

[0081] When F=0, it indicates that the actual gas flow rate of each burner nozzle has reached the target gas flow rate.

[0082] In order to solve the corresponding damper opening when the gas flow rate of each layer of burner nozzle reaches the target gas flow rate, according to equations (7) and (8), the equations containing θ1, θ2, ···, θ r A system of equations with r unknowns:

[0083]

[0084] Where: g is the functional relationship between different damper openings; ξ w (θ n ) is the bellows resistance coefficient, that is, ξ w，n , n=1, 2, 3..., r; ξ c (θ n ) is the comprehensive resistance coefficient, that is, ξ c，n , n=1,2,3......,r;

[0085] Formula (11) is the functional relationship between the gas flow rate and the air door opening of each layer of burner nozzle. Through the finite volume method calculation of numerical simulation, it can be known that the resistance coefficient ξ c and the air door opening θ n The present invention adopts the Newton-Raphson downhill iteration method to find the roots of the nonlinear equation group (11). Assume (θ 1,k ,θ 2,k ,…,θ r,k ) is a set of estimated values ​​of the root, and the function of formula (11) is respectively in (θ 1,k ,θ 2,k ,…,θ r,k ) is expanded by the first order Taylor, and we get (θ 1,k+1 ,θ 2,k+1 ,…,θ r,k+1 ) is:

[0086]

[0087] Wherein, k is the number of iterations, k = 0, 1, ….

[0088] Rewrite formula (11) into vector form:

[0089] G(θ)=0 (13)

[0090] In the formula, θ=(θ1,θ2,…,θ r ) T ,G=(g1,g2,…,gr ) T .

[0091] Using matrix and vector notation, formula (12) can be expressed as follows:

[0092] θ (k+1) =θ (k) -(J (k) ) -1 G (k) (14)

[0093] In the formula, the matrix J (k) is the Jacobi matrix, which is composed of the values ​​of the partial derivatives of G at point k, indicating the change of the gas flow through the burner nozzles of each layer due to the change of the damper opening. The expression is:

[0094]

[0095] The remaining vector expressions in formula (14) are:

[0096] θ (k) =(θ 1,k ,θ 2,k ,…,θ r,k ) T (16)

[0097] θ (k+1) =(θ 1,k+1 ,θ 2,k+1 ,…,θ r,k+1 ) T (17)

[0098] G (k) =(g 1,k ,g 2,k ,…,g r,k ) T (18)

[0099] Formula (14) is the Newton-Raphson iterative method in the vector form of the equation group in formula (11). In order to reduce the dependence on the initial value in the iteration process, make the iteration converge faster and the result more accurate, the Newton-Raphson downhill method is based on the iteration of the Newton-Raphson iterative method, and replaces θ (k+1) With θ k The weighted average is used as the new approximation, and the expression is:

[0100]

[0101] In the formula, is the result calculated by the Newton-Raphson downhill method; λ is the step size factor, 0≤λ≤1.

[0102] Therefore, the Newton-Raphson downhill iteration method in the vector form of the equation system in formula (11) is expressed as:

[0103]

[0104] Formula (20) is the Newton-Raphson downhill iteration model in the damper opening control model. According to the initial value of the burner damper opening, each iteration will generate a new damper opening improvement value, and further calculate a new nozzle gas flow improvement value until F=0 is satisfied.

[0105] For the r layers of burner nozzles at any corner of the furnace, it is necessary to determine the openings of r air doors θ1, θ2, …, θ r , so that the flow rate of each burner nozzle is within a certain tolerance range with the corresponding target flow rate. The damper opening is calculated iteratively by formula (20). In the iterative calculation, the comprehensive resistance coefficient ξ corresponding to each damper at different openings is c , the main wind box or burnout wind box resistance coefficient ξ under r air door opening combinations w , gas flow value q of each layer of burner nozzle n , obtained by numerical simulation method.

[0106] Figure 3 The calculation flow chart of the damper opening control model is given, which includes the following steps:

[0107] (1) The finite volume method of numerical simulation is used to obtain the comprehensive resistance coefficient ξ under different damper opening conditions c,n .

[0108] The pressure drop of the horizontal branch pipe ΔP p，n and the burner nozzle pressure drop ΔP b，n The sum of the pressure drop is ΔP c，n ; Under different air door opening conditions, the average gas velocity u at the burner nozzle b，n and pressure drop ΔP c，n The relationship between the two is used to obtain the comprehensive resistance coefficient ξ under different damper opening conditions. c，n (The symbol ξ in this application c，n The symbol ξ can also be used cn m express).

[0109]

[0110] Where: u b，n is the air door opening θ n The corresponding average gas velocity of the burner nozzle is m / s; ρ is the gas density, kg / m 3 ξ c，n for u b，nThe combined resistance coefficient of the burner nozzle and horizontal branch pipe at the qualitative speed.

[0111] (2) Assuming the initial estimate of the damper opening θ n 0 The initial value of the damper opening θ is obtained by numerical simulation method. n 0 The drag coefficient under the condition ξ 0 w,n and the gas flow value q of each layer of burner nozzle n 0 .

[0112] according to: Calculate the gas flow rate q at the burner nozzle n m ;

[0113] Where: q n m is the gas flow rate of the burner nozzle calculated after the mth iteration, m = 0, 1, 2, 3..., kg / s.

[0114] The pressure drop of the bellows ΔP w，n and pressure drop ΔP c，n The sum of the pressure drop is recorded as the total pressure drop ΔP t，n ;according to: Calculate the bellows resistance coefficient ξ w，n m ;

[0115] Where: is; ξ w，n m After the mth iteration, u b，n As the resistance coefficient of the bellows at the qualitative speed, m=0, 1, 2, 3...; the bellows is a main bellows or a burnout bellows.

[0116] (3) Calculate q n 0 With the target flow q g,n The mean absolute percentage error δ.

[0117]

[0118] In the formula, q g,n It is the target gas flow rate of the burner nozzle, that is, the gas flow rate of the burner nozzle under the flow distribution target, kg / s.

[0119] If δ≤0.1%, the gas flow rate of the burner nozzle and the corresponding air damper opening are output, and the calculation ends; if δ>0.1%, continue with step (4);

[0120] (4) According to the target flow qg,n , using the Newton-Raphson downhill iteration method, c,n , w,n 0 and q n 0 The data is made into an Excel data file and imported into the Newton-Raphson downhill iterative model calculation program. The improved value θ of the air door opening of each layer is obtained through iterative calculation. n 1 .

[0121] The numerical simulation method is used again to obtain the improved value of the air door opening θ n 1 The wind box resistance coefficient ξ under the condition 1 w,n and the gas flow value q of each layer of burner nozzle n 1 .

[0122] (5) Calculate q n 1 With q g,n After m numerical simulations and Newton-Raphson downhill iterative model calculations, until q n m and q g,n The error δ between them is less than 0.1%, and the calculation ends.

[0123] Application Examples

[0124] The control model is implemented on a 350MWe supercritical tangentially fired boiler. Figure 1 The secondary air system structure and the layout diagram of the DC pulverized coal burner. Among them, the secondary air system includes the main air duct, the main wind box, the burnout wind box, the horizontal branch pipe and the burner nozzle. The secondary air system has two inlets, which are connected by a connecting pipe in the middle. The main burner area includes five layers of primary air nozzles with peripheral secondary air (A, B, C, D, E) and six layers of auxiliary secondary air nozzles (AA, AB, BC, CD, DE, EE). The overfire air (OFA) includes two layers of compact burnout air nozzles (CCOFA) arranged above the main burner area and three layers of high-position burnout air nozzles (SOFA) away from the main burner area. The air volume of each nozzle in the main burner area is distributed by the main wind box, and the air volume of the SOFA nozzle is distributed by the burnout wind box.

[0125] Taking the calculation domain of the AA layer burner nozzle as an example, the calculation process of the comprehensive resistance coefficient is explained. Figure 4 The inlet and outlet pressure drop ΔP of the AA layer burner nozzle calculation domain is given c (the sum of the pressure drops of the horizontal branch and the burner nozzle), with the inlet velocity u of the horizontal branch pi (Right now, Figure 2The average velocity of the section at position 8.1 in the middle label) and the average gas velocity u at the burner nozzle b According to the change curve of Figure 4 Using the pressure drop data in, the comprehensive resistance coefficient ξ of the AA layer burner calculation domain under different air door opening conditions can be obtained using formula (4): c , the specific data are listed in Table 1, the curve is as follows Figure 5 shown.

[0126] Table 1 Comprehensive resistance coefficient of the calculation domain of the burner nozzle of the AA layer

[0127] Air door opening θ(%) <![CDATA[Comprehensive drag coefficient ξ c > 10 313.79 15 184.00 20 112.12 25 71.64 30 49.90 40 27.67 50 18.69 60 14.84 80 11.81 100 10.91

[0128] right Figure 5 By nonlinearly fitting the curve in the figure, the comprehensive resistance coefficient ξ of the burner nozzle calculation domain of the AA layer can be obtained. c The double exponential decay function relationship between the damper opening θ is as follows:

[0129]

[0130] Table 2 shows the secondary air gas flow rate and secondary air system inlet wind speed corresponding to the boiler load (i.e. Figure 1 Gas flow rate and inlet velocity at position 3).

[0131] Table 2 Boiler load, secondary air gas flow rate and inlet wind speed

[0132] Boiler load (%) Secondary air gas flow rate (kg / s) Secondary air system inlet velocity (m / s) 100 250.1 8.41 75 210.9 7.09 50 130.2 4.38

[0133] Table 3 shows the average gas velocity u of each burner nozzle obtained by numerical simulation when the secondary air volume distribution method of the main burner area is equal. b , burner nozzle calculation domain and wind box pressure drop ΔP w , and the wind box resistance coefficient ξ corresponding to each burner nozzle calculated using formula (6) w .

[0134] Table 3 Burner nozzle wind speed, wind box resistance coefficient ξ w (Take Horn 1 as an example)

[0135]

[0136] In the calculation results of Table 3, the ratio of SOFA flow to total flow is 27%. Target 1 is to increase the SOFA flow ratio to 30%, keep the gas flow of the four-layer burner nozzles AB, BC, CD, and DE equal, and keep other damper openings unchanged. Table 4 gives the coupled calculation results of the numerical simulation method and the Newton downhill iteration method (taking angle 1 as an example). Among them, the damper opening is calculated by the Newton downhill iteration method, and the gas flow of each burner nozzle is calculated by the numerical simulation method. After m2 coupling calculations, the damper openings of each layer corresponding to the target flow 1 are obtained.

[0137] Table 4 Iterative calculation values ​​of air door adjustment for each burner under target 1

[0138]

[0139] The load of target 2 is 50%, and the other target conditions and the results of the coupled calculation of the numerical simulation method and the Newton downhill iteration method are listed in Table 6 (taking corner 1 as an example). After m4 times of coupled calculation, the damper opening of each layer corresponding to the target flow 2 is obtained. The calculation times m4 of target 2 is greater than m2 of target 1.

[0140] Table 6 Iterative calculation values ​​of air door adjustment for each burner under target 2

[0141]

[0142] The damper opening control model proposed in the present invention can realize damper opening control under any target gas flow distribution. If the difference between the gas flow of each burner nozzle between the initial working condition and the target working condition is larger, the number of coupling calculations will be greater.

[0143] Obviously, the above embodiments are merely examples for the purpose of clear explanation, and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived therefrom are still within the scope of protection of the claims of this patent application.

Claims

1. A method for controlling the air door opening of a tangential combustion boiler based on a secondary air distribution method, characterized in that: The steps include: (1) Calculate different damper openings θ using the finite volume method of numerical simulation n Under the condition, the average gas velocity u at the burner nozzle b，n , Pressure drop ΔP of horizontal branch pipe p，n and the burner nozzle pressure drop ΔP b，n , and obtain the comprehensive resistance coefficient ξ under different damper opening conditions c，n ; (2) Based on the initial value of the secondary air damper opening θ n 0 , calculate the gas flow rate q of the burner nozzle under the initial value of the air door opening n 0 and bellows resistance coefficient ξ w，n 0 ; (3) Calculate the gas flow rate q of the burner nozzle under the initial value of the air damper opening n 0 The target gas flow rate q of the burner nozzle g,n The mean absolute percentage error δ; If δ≤0.1%, the gas flow rate of the burner nozzle and the corresponding air damper opening are output, and the calculation ends; if δ>0.1%, continue with step (4); (4) Using the Newton-Raphson downhill iteration method, the gas flow rate q of the burner nozzle is introduced n 0 、Comprehensive resistance coefficient ξ c，n and bellows resistance coefficient ξ w，n 0 , iteratively generates the improved value of the damper opening θ n m ; Improve the value θ according to the air door opening n m , using the method in step (2), calculate the gas flow rate q of the burner nozzle under the condition of the improved value of the air door opening n m and the resistance coefficient of the bellows ξ w，n m ; (5) Using the method in step (3), calculate the gas flow rate q of the burner nozzle under the condition of the improved value of the air door opening n m The target gas flow rate q of the burner nozzle g,n The mean absolute percentage error δ; If δ≤0.1%, the gas flow rate of the burner nozzle and the corresponding air door opening are output, and the calculation ends; if δ>0.1%, the gas flow rate q introduced into the burner nozzle is n m 、Comprehensive resistance coefficient ξ c，n and bellows resistance coefficient ξ w，n m , repeat steps (4)-(5) until δ≤0.1%.

2. The control method according to claim 1, characterized in that: In the step (1), the burners at each layer and the horizontal branches connected to the burners are used as independent calculation domains, and the pressure drop ΔP of the horizontal branches is calculated. p，n and the burner nozzle pressure drop ΔP b，n The sum of the pressure drop is ΔP c，n ; Under different air door opening conditions, the average gas velocity u at the burner nozzle b，n and pressure drop ΔP c，n The relationship between and calculates the comprehensive resistance coefficient ξ under different damper opening conditions c，n ; n is any layer of burners, n = 1, 2, 3...

3. The control method according to claim 2, characterized in that: In the step (1), the average gas velocity u of the burner nozzle is b，n and pressure drop ΔP c，n The relationship between them is: Where: u b，n is the air door opening θ n The corresponding average gas velocity at the burner nozzle, m / s; ρ is the gas density, kg / m 3 ; ξ c，n for u b，n The combined resistance coefficient of the burner nozzle and horizontal branch pipe at the qualitative speed.

4. The control method according to claim 1, characterized in that: In the step (2), according to: Calculate the gas flow rate q at the burner nozzle n m ; Where: q n m is the gas flow rate of the burner nozzle calculated after the mth iteration, m=0, 1, 2, 3..., kg / s; A is the outlet area of ​​the burner nozzle.

5. The control method according to claim 1, characterized in that: In step (2), the pressure drop ΔP of the wind box is w，n and pressure drop ΔP c，n The sum of the pressure drop is recorded as the total pressure drop ΔP t，n ;according to: Calculate the bellows resistance coefficient ξ w，n m ; Where: w，n m After the mth iteration, u b，n The drag coefficient of the bellows at the qualitative speed; the bellows is a main bellows or a burnout bellows.

6. The control method according to claim 1, characterized in that: In step (3), the calculation formula of the mean absolute percentage error δ is: In the formula, q g,n It is the target gas flow rate of the burner nozzle, that is, the gas flow rate of the burner nozzle under the flow distribution target, kg / s.

7. The control method according to claim 1, characterized in that: In the step (4), the improvement value of the damper opening is calculated using the Newton-Raphson downhill iteration method according to the relationship between the gas flow rate of the burner nozzle and the damper opening.

8. The control method according to claim 7, characterized in that: The relationship between the burner nozzle flow and the air door opening is: Where: g is the functional relationship between different damper openings; A n is the outlet area of ​​any layer of burner nozzle, m 2 , n=1,2,3……,r.

9. The control method according to claim 7, characterized in that: In the iterative basis of the Newton-Raphson iterative method, θ (k+1) With θ k The weighted average is taken as the new approximation and the expression of the Newton-Raphson downhill iteration method is obtained.

10. The control method according to claim 9, characterized in that: The vector expression of the Newton-Raphson iteration method is: θ (k+1) =θ (k) -(J (k) ) -1 G (k) ; The vector expression of the Newton-Raphson downhill iteration method is: in, i (k) =(θ 1,k ,i 2,k ,…,θ r,k ) T i (k+1) =(θ 1,k+1 ,i 2,k+1 ,…,θ r,k+1 ) T G (k) =(g 1,k ,g 2,k ,…,g r,k ) T In the formula, the matrix J (k) is the Jacobi matrix, which consists of the values ​​of the partial derivatives of G at point k; is the result calculated by the Newton-Raphson downhill method; λ is the step size factor, 0≤λ≤1.

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