A method and device for balanced distribution of air and coal powder in a coal pulverizing system of a coal-fired unit

Abstract

A wind-powder balanced distribution method and device for coal pulverizing system of coal-fired unit are provided to solve the problem of uneven distribution of wind-powder of each burner caused by the change of coal quality and output of coal mill during unit peak shaving, which comprises M wind-powder pipelines connected with the outlet of coal mill; each pipeline is divided into n sub-pipelines, and the wind resistance of the same group of sub-pipelines is approximately equal by adjusting the path / length; the ends of the same column of sub-pipelines are combined and directly connected with the burner; an on-line detection device and a wind volume adjusting device are arranged on the combined pipeline; the wind volume control device receives the detection signal and controls the adjusting device to make the wind volume of each combined pipeline equal. By splitting and combining the pipeline to recombine the wind-powder flow, the self-adaptive balanced distribution of pulverized coal is realized simultaneously by only controlling the final wind volume balance, and it is not necessary to detect the pulverized coal concentration in real time. The present application has strong resistance to load / coal quality disturbance and fast response speed; there is no spoiler, and the wind resistance loss is small; the structure is simple and easy to implement. The present application is suitable for flexible peak shaving scene of coal-fired unit of direct-fired pulverizing system.

Description

Technical Field

[0001] This invention discloses a method and apparatus for balanced distribution of air and pulverized coal in a coal-fired power unit pulverizing system, and particularly relates to a method and apparatus for balanced distribution of primary air and pulverized coal in a coal-fired power unit pulverizing system. Background Technology

[0002] For coal-fired power generating units using direct-fired pulverizing systems, the same pulverizer typically supplies primary air and pulverized coal to multiple burners. When the unit participates in flexible peak shaving, the balance of air and pulverized coal distribution in the pulverizing system has a crucial impact on the combustion stability of the furnace flame under low load. Under low load, the furnace temperature drops sharply, the pulverized coal combustion rate decreases, and uneven distribution of primary air and pulverized coal in the pulverizing system will cause significant differences in the combustion state of each burner. This results in uneven temperature distribution in the main combustion zone of each burner, affecting the combustion-supporting effect of the burner itself and adjacent burners. Consequently, phenomena such as unstable combustion, uneven furnace burning, and increased NOx concentration occur, which is an important factor limiting the peak shaving depth of the unit.

[0003] During peak-shaving operation of the unit, the output of the coal mill decreases, and the coal feed rate of some coal mills is far lower than the rated output. Under rated load, it is difficult for the leveling mechanism to ensure the balance of primary air volume and coal feed of each burner under low load. Moreover, the coal quality changes during long-term operation, such as uneven coal powder particle size, changes in moisture or viscosity, are random. Wear of bends and constrictions in coal powder pipelines causes changes in pipeline resistance, which will affect the balance of air and coal distribution in the pulverizing system.

[0004] Current methods for adjusting the air-powder balance in powder-making systems mainly include:

[0005] 1) Adjusting the primary air volume of the pulverizing system by installing adjustable orifices on each primary air pulverized coal pipeline can only meet the air-pulverized coal balance of each pipeline when the output of the coal mill is at the rated load. When the output of the coal mill is much lower than the design value, the air-pulverized coal mixing mechanism in the coal mill fails, and the coal powder concentration in each pipeline is different. At this time, controlling the primary air volume by adjusting the orifices alone cannot complete the air-pulverized coal balance adjustment function.

[0006] 2) The static separator at the top of the coal mill achieves rapid separation of coarse coal particles by increasing swirling flow. When the coal mill output is high and the air-coal flow rate is fast, it has a certain balancing effect. However, when the coal mill output is far below the rated load, the turbulence control direction within the static separator is almost perpendicular to the coal mill outlet direction. Therefore, it is difficult to affect the air-coal concentration in the various air-coal pipes at the coal mill outlet. The main function of the dynamic separator is to further adjust the fineness of the coal powder using the centrifugal force of coal powder of different particle sizes, and to a certain extent, it has a mixing effect on the primary air and coal powder at the coal mill outlet.

[0007] 3) Installing a coal pulverizer distributor at the coal mill outlet, such as the compact coal pulverizer designed by Jia Bo et al. of Xi'an Thermal Power Research Institute Co., Ltd., redistributes the coal pulverizer in each primary air duct by changing the coal pulverizer flow trajectory through the baffles inside the distributor. However, this also increases the wind resistance during the operation of the pulverizing system. Furthermore, when the output of the coal mill changes, due to the complex coupling effect between the primary air volume and the coal pulverizer concentration, it is necessary to equip each primary air duct with an online coal pulverizer concentration detection device and repeatedly adjust the air volume regulating valve and the coal pulverizer concentration regulating valve on each air-powder duct to achieve balanced air-powder regulation. Therefore, it is difficult to adapt to the on-site requirements that require frequent changes in the output of the coal mill. Moreover, the operation, installation and maintenance costs of the online coal pulverizer concentration detection device in the primary air duct increase the equipment cost, which limits the promotion of the device.

[0008] 4) Numerous studies on balanced distribution in pulverizing systems exist in relevant papers and patents. For example, in Shi Quancheng et al.'s paper, "Numerical Simulation of Air-Powder Two-Phase Flow Characteristics in an Adjustable Powder Distributor," a special-shaped pipe, a dense-phase regulating valve, and a dilute-phase regulating valve are installed at the bend of the pulverizer outlet. Under CFD simulation and laboratory conditions, the air-powder distribution deviation can be kept below 10%. However, this system has requirements on the pulverizer structure and coal quality / type, requires the installation of online detection devices for primary air and powdered coal concentration, and necessitates modifications to the outlets of most pulverizers before it can be widely applied in the field. Zhou Wentai et al.'s patent, "An Adjustable Air-Powder Two-Phase Powder Distributor and a Method for Regulating Powdered Coal Conveying," patent application number:

[0009] In CN202010193111.4, the principle is similar to that in Shi Quancheng's paper, but the positions of the dense phase regulating valve and the dilute phase regulating valve are different. Similarly, for field applications, additional detection and control devices and complex control methods are required. In their paper "Numerical Simulation and Optimization of Boiler Balance Distribution," Gao Manda et al. used CFD simulation to adjust the air-coal balance of their self-designed air-coal distributor by changing the angle of the guide vanes, achieving some effect. However, this research is related to the structure of the coal mill and pulverizing system, and lacks universality in the face of various complex and changing coal mill and pulverizing system structures in the field.

[0010] In summary, when the unit participates in flexible peak shaving, the output of the coal mill changes frequently, sometimes falling far below the rated load. Furthermore, the coal quality changes unpredictably over long periods of operation, making it difficult to meet the requirements for balanced air-coal distribution during peak shaving operations using the methods described above. Dynamically adjusting the air-coal concentration based on changes in the primary air volume and coal quantity at the coal mill outlet requires real-time monitoring of the primary air volume and coal quantity in each air-coal pipeline. This necessitates balancing the primary air volume and coal quantity in each pipeline while resolving the coupling between air volume and coal quantity, significantly increasing the difficulty of balanced air-coal distribution and limiting the versatility of the adjustment method.

[0011] Ensuring the balanced distribution of air and coal to each burner of the same coal mill during flexible peak shaving, when the output and coal quality of the coal mill change, is a key and challenging issue that urgently needs to be addressed at this stage. Summary of the Invention

[0012] To enable coal-fired power generating units to participate in flexible peak-shaving phases, and to maintain a balanced distribution of primary air and coal feed rate for each burner of the coal mill when the output and coal quality change, this invention provides a method and device for balanced air-coal distribution in the pulverizing system of a coal-fired power generating unit. This invention is mainly applied to the automatic adjustment of the balance of primary air and coal feed rate for each pipeline of the coal mill in a coal-fired power generating unit. The technical solution is as follows:

[0013] A method and apparatus for balanced air-coal distribution in a coal-fired power unit pulverizing system, the method and apparatus comprising:

[0014] 1) Obtain the number M of the coal mill outlet air-coal ducts and the corresponding number N of burners. The coal mill outlet air-coal duct numbers are m1, m2, ... m m Where the subscript m = M;

[0015] 2) Divide each air-coal duct at the coal mill outlet into n ducts, where n = N, and number them m. x n1,m x n2,…m x n n Where 1 ≤ x ≤ M, and the subscript n = N, this will generate m groups of pipes, and the pipes in each group will be numbered as follows:

[0016]

[0017] 3) Organize the pipes in column n1: m1n1, m2n1, ... m m The ends of n1 are merged into one pipe N1, and the pipes in the n2 column are m1n2, m2n2, ... m m The ends of n2 merge into one pipe N2, until n n The column of pipes m1n n m2n n ,…m m n n The ends merge into one pipe N n N1, N2, ...

[0018] N n The ends of the pipes are connected to burners;

[0019] 4) It should be noted that the m groups of pipes in formula (2) should be adjusted according to the pipe structure of the on-site pulverizing system through experiments or numerical simulations to ensure that the air resistance of each pipe in each group is equal as much as possible. For example, the m1 group of pipes is composed of m1n1, m1n2, ... m1nn wind resistance f m1n1 ≈f m1n2 ≈…≈

[0020] f m1nn ;

[0021] 5) In the merged N1, N2, ... N n An online primary air volume monitoring device and an air volume regulating device are installed on the pipeline, and then the air volume control device is connected to N1, N2, ...

[0022] N n The primary air volume online detection device and the air volume regulation device installed on the pipeline are electrically connected. The primary air volume online detection device sends the detected air volume signal to the air volume control device. The air volume control device calculates the air volume regulation control signal based on the air volume signal and sends it to the air volume regulation device. The air volume online detection device can be a Pitot tube flow meter, averaging pitot tube flow meter, orifice plate flow meter or venturi tube flow meter, etc. The air volume regulation device can be an adjustable orifice, valve, baffle, etc. The air volume control device can be a common controller, microcontroller controller, industrial control computer, etc. that can be purchased on the market.

[0023] 6) During coal mill operation, the online primary air volume monitoring device detects N1, N2, ... N... n Primary air volume in ducts, obtain the primary air volume Q of each duct. N1 Q N2 ,…Q Nn And it is sent to the air volume control device, which controls the air volume according to Q. N1 -Q Nn Calculate the average primary air volume μ and variance σ for each duct. 2 Under the condition of satisfying the instrument error of the primary air volume detection device and the control error of the air volume control device, the adjustment variance σ is optimized. 2 With the goal of minimization, an airflow regulation signal is calculated based on the primary air volume of each duct and the average primary air volume μ, and then sent to the airflow regulation device. The airflow regulation device adjusts the airflow of each duct to make N1, N2, ... N n The primary air volume in the duct is equal, i.e., Q N1 =Q N2 =…=Q Nn The pulverized coal in each pipeline is distributed adaptively and evenly through the splitting and merging of the air-coal pipelines in the pulverizing system of this invention, so as to achieve the purpose of balanced distribution of air and coal in each burner.

[0024] The working principle of the balanced air-coal distribution system of the coal-fired power unit of the present invention is as follows:

[0025] If the primary air volume of the coal mill is Q and the coal feed rate is C, then the primary air volumes of each air-coal duct at the coal mill outlet are Q1, Q2, ... Q1, Q2, ... Q3, respectively.m The coal feed rates are C1, C2, ... C m After the air and pulverized coal flow into n pipes in the outlet pipe of the coal mill, the primary air volume in each pipe is represented by q. Then, the primary air volumes in the m groups of pipes in formula (2) are as follows:

[0026]

[0027] in:

[0028]

[0029] Let c represent the amount of coal fed into each pipe, then they are as follows:

[0030]

[0031] in:

[0032]

[0033] After the air and powder flow through the end of m sets of pipes merge into N pipes, the primary air volume in each pipe is Q. N1 Q N2 ,…Q Nn The coal feed rates are C N1 C N2 ,…C Nn ,but:

[0034]

[0035] When the output of the coal mill or the quality of the coal changes, the pulverized coal undergoes grinding, separation, and moisture evaporation within the complex coal mill. After being carried by the primary air to the mill outlet, the primary air volume Q and the coal feed rate C in each pipeline will change. Specifically, the primary air volume Q1, Q2, ... Q in each air-coal pipeline will change. m And coal feed rates C1, C2, ... C m This will result in an imbalance between air and coal, and this imbalance has a certain degree of randomness and uncertainty. If the ends of the outlet pipes of the coal mill are directly connected to the burners, it will inevitably lead to differences in the combustion state of the corresponding burners of the coal mill, and affect the furnace temperature layout. Especially when the boiler is running at low load, it will seriously affect the combustion stability.

[0036] Compared to the complex air-coal flow field inside the coal mill, the diameter of the m air-coal pipes at the coal mill outlet is much smaller than that of the coal mill. The primary air carries the coal powder and flows at high speed and regularly along the axis in each air-coal pipe at the coal mill outlet. Under the influence of turbulence, the coal powder can be distributed relatively evenly in the pipes. At this time, after dividing the air-coal pipes into n pipes with approximately equal air resistance, the coal feed rate in each pipe will be approximately equal, provided that the primary air volume of the pipes is consistent.

[0037] The coal-fired power plant pulverizing system's air-coal equalization distribution device of this invention adjusts the path and length of each pipe in each group of pipes through experiments or numerical simulations, so that the m pipes at the coal mill outlet are evenly divided into n pipes with approximately equal air resistance. After the m groups of pipes are merged into N pipes, the airflow is distributed through N1, N2, ... N... n The primary air volume online detection device, air volume regulation device, and air volume control device electrically connected to the primary air volume online detection device and air volume regulation device installed on the pipeline enable Q N1 =Q N2 =…=Q Nn =Q / n, combined with formula (7), the primary air volume of each pipe after the coal mill outlet air-coal pipeline is divided into n pipes is approximately equal, that is:

[0038]

[0039] Therefore, the coal feed rate within each group of pipes after being divided into n pipes is approximately evenly distributed, that is:

[0040]

[0041] Based on formula (10) and formula (8), C can be derived. N1 ≈C N2 ≈…≈C Nn ≈C / n. Based on the above-described method and device for balanced air-coal distribution in a coal-fired power plant pulverizing system, a balanced distribution of primary air volume and coal feed rate is achieved for each burner corresponding to the same coal mill.

[0042] It should be noted that there are various layout options for the air-coal pulverizer outlet pipes in coal-fired power generating units. Only some pulverizing systems, such as those with four outlet pipes to supply primary air and pulverized coal to four burners, can automatically control the even distribution of air and pulverized coal among the burners of the same coal mill. However, many coal mills have only one or two outlet pipes, or multiple outlet pipes are merged into one pipe and extended near the boiler before being divided into multiple pipes connecting to the burners. In these cases, the diameter of the outlet pipe is relatively large, and uneven distribution of pulverized coal still occurs within the pipes during system operation.

[0043] Therefore, if there is only one air-coal duct at the coal mill outlet, or if multiple air-coal ducts at the coal mill outlet are merged into one duct, one approach is to first divide the air-coal duct at the coal mill outlet section into m' ducts, then divide each of these m' ducts into n ducts, and adjust the path and length of the n ducts in each group to make the air resistance of the n ducts approximately equal. The numbering of each duct is as follows:

[0044]

[0045] Then, divide the pipes in column n1 into m'1n1, m'2n1, ..., m' m The ends of n1 are merged into one pipe N1, and the pipes in column n2 are m'1n2, m'2n2, ..., m' m The ends of n2 merge into one pipe N2, until n n The column of pipes m'1n n ,m'2n n ,…m' m n n The ends merge into one pipe N n N1, N2, ... N n The ends of the pipes are connected to burners. Then, the combined N1, N2, ... N... n An online primary air volume detection device and an air volume regulation device are installed on the pipeline, and electrically connected to the air volume control device. Then, the primary air volume and coal feed of each burner are evenly distributed by the pulverizing system control method with M number of air-coal pipelines at the outlet of the coal mill and N corresponding burners.

[0046] If there are m air-coal ducts at the coal mill outlet, but the ducts are relatively thick, and the air-coal distribution within the ducts is still uneven, another approach can be taken: First, divide each air-coal duct at the coal mill outlet into k ducts, then divide these k ducts into n ducts, and adjust the duct path and length to make the air resistance of the n ducts approximately equal. The ducts are numbered as follows:

[0047]

[0048] Then, connect the pipes in column n1: m1k1n1, m1k2n1, ..., m1k k n1,m2k1n1,m2k2n1,…m m k k The ends of n1 are merged into one pipe N1, and the pipes in column n2 are m1k1n2, m1k2n2, ..., m1k k n2,m2k1n2,m2k2n2,…m m k k The ends of n2 merge into one pipe N2, until n n The column of pipes m1k2n n ,m1k2n n ,…m1k k n n m2k1n n ,m2k2n n ,…m m k k n n The ends merge into one pipe N nIt should be noted that, to avoid merging too many pipes at the end of each column at once, a step-by-step merging method can be used. That is, first divide the m1 pipe in column n1 into k pipes m1k1n1, m1k2n1, ..., m1k k n1 are merged into one m1n1 pipe, m2k1n1, m2k2n1, ..., m2k k n1 is merged into one m2n1 pipe until m m k1n1,m m k2n1,…m m k k n1 merges into 1 root m m pipe n1, then connect m1n1, m2n1, ... m m The ends of n1 are merged into one pipe N1, and then the pipes in column n2 are merged into m1n2, m2n2, ... m in sequence. m n2 pipe, then m1n2, m2n2, ... m m The ends of n2 merge into one pipe N2, until n n The pipelines in the column are merged into one pipeline N. n Then, in N1, N2, ... N n The ends of the pipes are connected to burners. Finally, the combined N1, N2, ... N n An online primary air volume monitoring device and an air volume regulating device are installed on the pipeline, and electrically connected to the air volume control device. This controls N1, N2, ... N n The coal feed rate is evenly distributed in each pipeline by equalizing the primary air volume within the pipeline.

[0049] It should also be noted that, if the length of the air-coal duct at the coal mill outlet is sufficient, a third method can be adopted: the air-coal duct at the coal mill outlet can be progressively divided into multiple ducts (m). x Then, each pipe is divided into n pipes, the same number as the number of burners corresponding to the same coal mill, forming m pipes. x Group n pipes, then split the m pipes into groups. x The n pipes are merged either sequentially or all at once into n pipes equal to the number of burners, denoted as N1, N2, ... N. n Pipeline, then through N1, N2, ... N n The ends of the pipes are connected to burners. Finally, the combined N1, N2, ... N n An online primary air volume monitoring device and an air volume regulating device are installed on the pipeline, and electrically connected to the air volume control device. This controls N1, N2, ... N n The coal feed rate is evenly distributed in each pipeline by equalizing the primary air volume within the pipeline.

[0050] This invention discloses a method and device for balanced distribution of air and coal in a coal-fired power unit pulverizing system, which is applicable to coal-fired power generating units, and is particularly suitable for the automatic control of balanced distribution of primary air volume and coal feed rate of multiple burners corresponding to the same coal mill when a direct-fired pulverizing system coal-fired power generating unit participates in flexible peak shaving.

[0051] Beneficial effects

[0052] The method and apparatus of the present invention have the advantages of being simple to control, versatile, fast in response, simple in structure, and easy to implement.

[0053] 1) Simple control and versatility: The air-coal pulverizing system air-coal equalization distribution method and device of the present invention controls the primary air volume of each pipe after merging to be equal through a primary air volume detection and control device installed on the merged pipeline, thereby achieving the function of equal air-coal distribution for each burner of the same coal mill. When the coal mill output, coal quality, wear of the air-coal pulverizing pipeline, etc., cause changes in the coal powder concentration in the air-coal pulverizing pipeline at the coal mill outlet, the air-coal pulverizing system air-coal equalization distribution device of the present invention reorganizes the air-coal flow in the coal mill outlet pipeline through pipeline splitting and merging to achieve equal coal powder distribution, and has an adaptive equalization distribution function for changes in the coal powder concentration at the coal mill outlet. Since the present invention only needs to control the primary air volume of each pipe after merging to be equal, without the need for additional coal powder concentration adjustment, it can be adapted to almost all direct-fired pulverizing systems, thus having the characteristics of simple control and versatility.

[0054] 2) Fast response speed: Through the coal-fired unit pulverizing system air-coal equalization distribution method and device of the present invention, the equalization distribution of coal powder concentration is completed by the splitting and merging of pipelines to reorganize the air-coal flow. Therefore, the equalization distribution speed of coal powder concentration is synchronized with the primary air velocity in the air-coal pipeline from the coal mill outlet to the burner, and the response speed is fast.

[0055] 3) Low wind resistance loss: The air-coal pulverizing system air-coal equalization distribution method and device of the present invention achieves equal distribution of coal powder concentration by splitting and merging the pipeline to reorganize the air-coal flow. There are no baffles, so there is almost no additional wind resistance. In contrast, the baffles installed in the existing air-coal equalization distributor will increase the wind resistance of the pulverizing system, thereby increasing the power consumption of the coal mill and the wear of the fan.

[0056] 4) Simple structure and easy to implement: The air-coal equalization distribution device for the pulverizing system designed by the method of this invention can modify the air-coal pipeline by splitting and merging the original pulverizing system pipeline path, and install a primary air volume detection and control device on the merged pipeline. During operation, it is only necessary to control the primary air volume of the air-coal pipeline directly connected to each burner after splitting and merging. Therefore, this invention has a simple structure and is easy to implement. Attached Figure Description

[0057] Figure 1 This is a schematic diagram of the air-coal equalization distribution device according to one embodiment of the present invention, which has four air-coal pipes at the outlet of a coal mill corresponding to four burners, and the air-coal pipes are split and merged.

[0058] Figure 2 This is a schematic diagram of the air-coal equalization distribution device for one coal mill outlet air-coal pipeline corresponding to five burner air-coal pipelines, according to one embodiment of the present invention, which involves splitting and merging the air-coal distribution pipelines.

[0059] Figure 3 This is a schematic diagram of the structure of an air-coal equalization distribution device according to one embodiment of the present invention, which has four air-coal pipes at the outlet of a coal mill corresponding to four burners, and the air-coal pipes are split and merged in multiple stages.

[0060] Figure 4 Flowchart for primary air volume control in each air-coal duct connected to the burner

[0061] Among them: 1 coal mill, 2 coal mill outlet air-coal duct, 3 air-coal duct divided into 4 equal parts, 4 air-coal duct connected to the burner after merging, 5 primary air volume online detection device, 6 air volume regulating device, 21 coal mill outlet air-coal duct merged into 1 duct, 22 air-coal duct split into 4 parts at one time, 23 air-coal duct split into 2 parts at one time, 24 air-coal duct split into 4 parts at two times, 25 air-coal duct after multi-stage splitting, 31 air-coal duct divided into 5 equal parts, 32 air-coal duct after initial merging of the equally divided ducts, 33 air-coal duct after further merging, 41 air-coal duct connected to the burner after multiple merging. Detailed Implementation

[0062] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0063] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below.

[0064] Depending on the different pulverizing systems, the coal-fired unit pulverizing system air-coal balanced distribution method and device of the present invention mainly have the following modification methods:

[0065] 1) The most common configuration is that one coal mill supplies pulverized coal to four burners, meaning that four air-coal pipes branch off from the coal mill outlet and connect to the four burners respectively. This is common in boilers with a tangential burner layout. When the air-coal balanced distribution device of the coal-fired unit pulverizing system of this invention is applied to this air-coal system layout, adhering to the principle of minimizing changes to the original air-coal pipes, the four air-coal pipes at the coal mill outlet can be arranged sequentially along the same vertical plane. Then, each pipe is split into four horizontally. Next, the four pipes that are now on the same vertical plane are merged. Finally, an air volume detection and control device is installed on the merged four pipes, such as... Figure 1 As shown;

[0066] 2) The second type involves a single coal mill supplying pulverized coal to 5-8 burners. This is common in front-and-back wall opposed-flow boilers or large coal-fired boilers of 1000MW and above. In this case, the number of outlet pipes of the coal mill does not match the number of corresponding burners. A common layout is to merge the air-coal pulverized coal outlet pipes of the coal mill into one main pipe, and then divide it into 5-8 branches. First, the main pipe can be split into 4 or more branches on the same vertical plane, and then horizontally split into branch pipes equal to the number of burners corresponding to the coal mill. Next, the 4 or more branches on the same vertical plane are merged into one pipe. Finally, an air volume detection and control device is installed on the merged pipe, such as... Figure 2 As shown;

[0067] 3) For cases where the air-coal powder distribution in the pulverizer outlet air-coal powder pipeline is highly uneven, for example, where the pulverized coal powder concentration on the outer side of the bend is significantly higher than on the inner side due to centrifugal force at the bend, the air-coal powder pipeline can be pre-divided into two sections on the same vertical plane. Then, the ends of the pre-divided pipelines can be horizontally split into branch pipelines equal in number to the number of burners. The two pipelines on the same vertical plane after splitting can then be merged. Next, the remaining pipelines on the same vertical plane can be merged into one pipeline. Finally, an air volume detection and control device can be installed on the merged pipeline. Figure 3 As shown, it should be noted that, where the pipeline length allows, the air-coal pulverized coal pipeline at the coal mill outlet can be split and merged in multiple stages to achieve the goal of balanced coal pulverized coal distribution to meet the requirements of variable load on site.

[0068] 4) The air volume control device is based on the average primary air volume μ and variance σ of each duct. 2 Under the condition of satisfying the instrument error of the primary air volume detection device and the control error of the air volume control device, the adjustment variance σ is optimized. 2 With the goal of minimization, an airflow regulation signal is calculated based on the primary air volume of each duct and its average value μ, and then sent to the airflow regulation device. The airflow regulation device adjusts the airflow of each duct to ensure that the primary air volume of each duct connected to the burner is equal after merging. The control process is as follows: Figure 4 As shown.

[0069] Obviously, the accompanying drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without any creative effort.

[0070] The following description, in conjunction with the accompanying drawings, illustrates a method and apparatus for balanced air-coal distribution in a coal-fired power unit pulverizing system according to an embodiment of the present invention.

[0071] The coal-fired power generation unit in this embodiment of the invention is a pulverized coal boiler, preferably applicable to pulverized coal boilers using a direct-fired pulverizing system. Since there are various layout options for the pulverized coal outlet air-air duct of the coal mill in a coal-fired power generation unit, three typical embodiments are selected here for description. Other layout options only require slight modifications to one of these three embodiments to achieve the same function.

[0072] The coal mill outlet is a pulverizing system with four air-coal pipes corresponding to four burners.

[0073] like Figure 1 The diagram shows a schematic of an air-coal equalization distribution device for a coal mill, comprising four air-coal pipes at its outlet corresponding to four burners, according to an embodiment of the present invention. The device includes: 1. a coal mill; 2. air-coal pipes at the mill outlet; 3. air-coal pipes evenly divided into four sections; 4. air-coal pipes connected to the burners after being merged; 5. an online primary air volume detection device; 6. an air volume regulating device; and an air volume control device electrically connected to the online primary air volume detection device (5) and the air volume regulating device (6). The specific implementation steps of this embodiment are as follows:

[0074] 1) According to Figure 1 It can be seen that the number of air-coal ducts at the outlet of the medium coal mill is M=4, corresponding to the number of burners N=4, and the outlet air-coal duct numbers of the two coal mills are m1, m2, m3, m4 respectively;

[0075] 2) Divide each air-coal duct at the coal mill outlet into n ducts. In this embodiment, n = 4, that is, divide 3 ducts into 4 air-coal ducts. This will generate m groups of ducts. Each duct in each group is numbered as follows:

[0076]

[0077] 3) Figure 1 The n pipes in each group are distributed on the same floor. The paths and lengths of each pipe within each group are adjusted through experiments or numerical simulations to make the wind resistance of the same group of pipes approximately equal, i.e., the wind resistance f of group m1. m1n1 ≈f m1n2 ≈f m1n3

[0078] ≈f m1n4m2 group of pipeline air resistance f m2n1 ≈f m2n2 ≈f m2n3 ≈f m2n4 m3 group duct air resistance f m3n1 ≈f m3n2 ≈f m3n3 ≈f m3n4 m4 group pipeline air resistance f m4n1 ≈f m4n2

[0079] ≈f m4n3 ≈f m4n4 ;

[0080] 4) Then merge the evenly divided air-coal pipes into 4 merged air-coal pipes connected to the burner. Specifically, the pipes m1n1, m2n1, m3n1, and m4n1 in column n1 are merged into one pipe N1; the pipes m1n2, m2n2, m3n2, and m4n2 in column n2 are merged into one pipe N2; the pipes m1n3, m2n3, m3n3, and m4n3 in column n3 are merged into one pipe N3; and the pipes m1n4, m2n4, m3n4, and m4n4 in column n4 are merged into one pipe N4. The ends of pipes N1, N2, N3, and N4 are connected to the burner respectively.

[0081] 5) Install a primary air volume online detection device (5) and an air volume regulating device (6) on the merged N1, N2, N3, and N4 pipelines respectively. Then, connect the air volume control device to the primary air volume online detection device (5) and the air volume regulating device (6) installed on the N1, N2, N3, and N4 pipelines. The primary air volume online detection device (5) sends the detected air volume signal to the air volume control device. The air volume control device calculates the air volume regulating control signal based on the air volume signal and sends it to the air volume regulating device (6). The primary air volume online detection device (5) can be a Pitot tube flow meter, averaging pitot tube flow meter, orifice plate flow meter, or venturi tube flow meter, etc. The air volume regulating device (6) can be an adjustable orifice, valve, baffle, etc. The air volume control device can be a common controller, microcontroller controller, industrial control computer, etc. that can be purchased on the market.

[0082] 6) During coal mill operation, the detailed primary air volume control process for each burner's air-coal pipeline is as follows: Figure 4 As shown in Figure 5, the online primary air volume detection device detects the primary air volume in pipelines N1, N2, N3, and N4 respectively, and obtains the primary air volume Q for each pipeline. N1 Q N2 Q N3 Q N4 And it is sent to the air volume control device, which controls the air volume according to Q. N1 Q N2 Q N3 QN4 Calculate the average primary air volume μ and variance σ for each duct. 2 Under the condition of satisfying the instrument error of the primary air volume detection device and the control error of the air volume control device, the adjustment variance σ is optimized. 2 With the goal of minimizing the primary air volume, an airflow adjustment signal is calculated based on the primary air volume of each duct and its average value μ, and then sent to six airflow adjustment devices. These devices adjust the airflow in each duct to ensure that the primary air volume in ducts N1, N2, N3, and N4 is equal, i.e., Q. N1 =Q N2 =Q N3 =Q N4 .

[0083] When the primary air volume in each air-coal duct connected to the burner is equal, i.e. Q N1 =Q N2 =Q N3 =Q N4 At the same time, the pulverized coal in each pipeline is automatically and evenly distributed through the splitting and merging of the air-pulverized coal pipelines in the pulverizing system of this invention. The working principle is as follows:

[0084] When the coal mill is running, the primary air volume is Q, and the coal feed rate is C. Therefore, the primary air volumes of each air-coal duct at the outlet of the second coal mill are Q1, Q2, Q3, Q4, and the coal feed rates are C1, C2, C3, C4. After the air and coal flow within the outlet duct of the second coal mill are evenly divided into n = 4 air-coal ducts, the primary air volume in each duct is represented by q. Then, the primary air volumes in m = 4 groups of ducts are as follows:

[0085]

[0086] in:

[0087]

[0088] Let c represent the amount of coal fed into each pipe, then they are as follows:

[0089]

[0090] in:

[0091]

[0092] When the air-coal flow passes through the end of m=4 sets of pipes and merges into N=4 combined air-coal pipes connected to the burner, the primary air volume in each pipe is Q. N1 Q N2 Q N3 Q N4 The coal feed rates are C N1 C N2 C N3 CN4 ,but:

[0093]

[0094] When the output or coal quality of the coal mill changes, the pulverized coal undergoes grinding, separation, and moisture evaporation within the complex mill. After being carried by the primary air to the mill outlet, the primary air volume Q and coal feed rate C in each pipeline will change. This results in an imbalance between the primary air volume Q1, Q2, Q3, Q4 and the coal feed rates C1, C2, C3, C4 in each air-coal pipeline, exhibiting a degree of randomness and uncertainty. If the ends of the pipelines at the mill outlet are directly connected to burners, it will inevitably lead to differences in the combustion state of the corresponding burners within the mill, affecting the furnace temperature distribution. This will severely impact combustion stability, especially during low-load boiler operation.

[0095] Compared to the complex air-coal flow field inside the coal mill, the diameter of each air-coal duct at the coal mill outlet is much smaller than that of the coal mill. The primary air carries the coal powder and flows at high speed and regularly along the axis in each air-coal duct at the coal mill outlet. Under the influence of turbulence, the coal powder can be distributed relatively evenly in the duct. At this time, after dividing the air-coal duct into n ducts with approximately equal air resistance, the coal feed rate in each duct will be approximately equal, provided that the primary air volume of the duct is consistent.

[0096] This embodiment Figure 1 The m=4 groups of air-coal ducts at the outlet of the medium-sized coal mill are divided into n=4 ducts in 4 layers. The path and length of each duct in each group are adjusted to make the air resistance of the n=4 ducts in each group at the coal mill outlet approximately equal. After the m=4 groups of ducts are merged into N=4 ducts, the air volume is controlled by an online primary air volume monitoring device (5), an air volume regulating device (6), and an air volume control device electrically connected to the online primary air volume monitoring device (5) and the air volume regulating device (6) installed on the N1, N2, N3, and N4 ducts, which controls the air volume Q. N1 =Q N2 =Q N3 =Q N4 =Q / 4, combined with formula (18), the primary air volume of the air-coal pipeline at the outlet of the 2 coal mills can be made equal to n=4 pipelines, that is:

[0097]

[0098] Therefore, after dividing the 3 into 4 air-coal pipes, the coal feed rate in each group of pipes is approximately evenly distributed, that is:

[0099]

[0100] Based on formula (21) and formula (19), C can be derived. N1 ≈C N2 ≈CN3 ≈C N4 ≈C / 4. Based on the above-described method and device for balanced air-coal feeding distribution in a coal-fired power plant pulverizing system, a balanced distribution of primary air volume and coal feed rate is achieved for each burner corresponding to the same coal mill. The pulverizing system has one air-coal feeding pipe at the coal mill outlet corresponding to five burners.

[0101] Figure 2 This is a schematic diagram of an air-coal equalization distribution device according to one embodiment of the present invention, which merges four air-coal pipes at the outlet of a coal mill into one, corresponding to five burner air-coal pipes after splitting and merging. It includes: 1. a coal mill; 2. a coal mill outlet air-coal pipe; 4. a merged air-coal pipe connected to the burners; 5. an online primary air volume detection device; 6. an air volume regulating device; 21. a coal mill outlet air-coal pipe merged into one pipe; 22. an air-coal pipe split into four pipes; and 31. air-coal pipes evenly divided into five pipes.

[0102] When the coal mill boiler burners of a coal-fired power generation unit adopt a front-to-back wall opposed layout, there are usually 5 or 6 burners on one floor, corresponding to one coal mill. In this case, the number of air-coal pulverized coal outlet pipes of the two coal mills is inconsistent with the number of burners. The common layout method is to first merge the air-coal pulverized coal outlet pipes of the two coal mills into one large pipe, extend it to the vicinity of the boiler, and then divide it into multiple pipes to connect each burner. This layout method helps to extend the mixing time of primary air and pulverized coal in the pipe, so as to reduce the difference in pulverized coal concentration in each pipe after being divided into multiple pipes, and improve the air-coal pulverized coal uniformity of each burner to a certain extent. However, due to the large pipe diameter and the primary air velocity usually exceeding 20 m / s, the residence time of primary air and pulverized coal in the merged large pipe is very short, and the mixing effect is limited.

[0103] In this embodiment, the air-coal duct at the coal mill outlet is first divided into m' = 4 pipes, and then each of these 4 pipes is further divided into n = 5 pipes with approximately equal air resistance. The pipes are numbered as follows:

[0104]

[0105] Then, merge the ends of pipes m'1n1, m'2n1, m'3n1, and m'4n1 in column n1 into one pipe N1; merge the ends of pipes m'1n2, m'2n2, m'3n2, and m'4n2 in column n2 into one pipe N2; merge the ends of pipes m'1n3, m'2n3, m'3n3, and m'4n3 in column n3 into one pipe N3; merge the ends of pipes m'1n4, m'2n4, m'3n4, and m'4n4 in column n4 into one pipe N4; and merge the ends of pipes m'1n5, m'2n5, m'3n5, and m'4n5 in column n5 into one pipe N5. Connect the ends of pipes N1, N2, N3, N4, and N5 to the burners respectively. Then, an online airflow monitoring device and an airflow regulating device are installed on the merged N1, N2, N3, N4, and N5 pipelines, respectively, and electrically connected to the airflow control device. Figure 4 The primary air volume control method of each air-coal pipeline connected to the burner shows that the primary air volume of each burner is evenly distributed. The coal powder in each pipeline is adaptively and evenly distributed by splitting and merging the air-coal pipeline of the pulverizing system in this embodiment, so as to achieve the purpose of balanced air-coal distribution.

[0106] Multi-stage splitting and merging air-powder equalization distribution device

[0107] When the outlet air-coal duct of the No. 2 coal mill is relatively large and the air-coal distribution within the duct is still uneven, a multi-stage splitting and merging pulverizing system layout can be adopted. Figure 3 This is a schematic diagram of a multi-stage splitting and merging air-coal equalization distribution device for a coal mill outlet with four air-coal pipes corresponding to four burners, according to one embodiment of the present invention. It includes: 1. Coal mill; 2. Coal mill outlet air-coal pipes; 5. Online primary air volume detection device; 6. Air volume regulating device; 23. Air-coal pipes split into two at the first stage; 24. Air-coal pipes split into four at the second stage; 25. Air-coal pipes after multi-stage splitting; 32. Air-coal pipes after the initial merging of the evenly divided pipes; 33. Air-coal pipes after further merging; 41. Air-coal pipes connected to the burners after multiple merging stages.

[0108] One implementation method in this embodiment is to first divide the m=4 air-coal pipes at the outlet of the 2 coal mills into k=2 pipes, and then divide these two pipes into n=4 pipes each. The numbering of each pipe is as follows:

[0109]

[0110] Then, the k=2 split pipes in formula (23) are merged into 32 equally divided pipes. The initial merged air-powder pipes are numbered as follows:

[0111]

[0112] Next, the pipes in each column of formula (24) are merged into a 33-pipe system. That is, the pipes in column 1 are merged into one pipe N1, the pipes in column 2 are merged into one pipe N2, the pipes in column 3 are merged into one pipe N3, and the pipes in column 4 are merged into one pipe N4. To reduce the complexity of pipe merging or shorten the length of the merged pipe system, the ends of the pipes m1k1n1, m1k2n1, m2k1n1, m2k2n1, m3k1n1, m3k2n1, m4k1n1, m4k2n1 in column n1 can be directly merged into one pipe N1, and the ends of the pipes m1k1n2, m1k2n2, m2k1n2, m2k2n2, m3k1n2, m3k2n2, m4k1n2, m4k2n1 in column n2 can be merged into one pipe N1. The ends of pipes 2n2 are merged into one pipe N2. Similarly, the ends of pipes m1k1n3, m1k2n3, m2k1n3, m2k2n3, m3k1n3, m3k2n3, m4k1n3, and m4k2n3 in column n3 are merged into one pipe N2. Likewise, the ends of pipes m1k1n4, m1k2n4, m2k1n4, m2k2n4, m3k1n4, m3k2n4, m4k1n4, and m4k2n4 in column n4 are merged into one pipe N4. Then, 5 primary air volume online monitoring devices and 6 air volume regulating devices are installed on the merged N1, N2, N3, and N4 pipes, respectively, and electrically connected to the air volume control device. Figure 4 The primary air volume control method of each air-coal pipeline connected to the burner shows that the primary air volume of each burner is evenly distributed. The coal powder in each pipeline is automatically and evenly distributed by splitting and merging the air-coal pipeline of the pulverizing system in this embodiment, so as to realize the function of even distribution of air-coal in the pulverizing system.

[0113] It should also be noted that, assuming the air-coal duct at the coal mill outlet is of sufficient length, it can be adjusted according to... Figure 3 The 25-stage split air-coal duct in the middle adopts the method of splitting the air-coal duct at the coal mill outlet into multiple ducts in stages. x Then, each pipe is divided into n pipes, the same number as the number of burners corresponding to the same coal mill, forming m pipes. x Group n pipes, then split the m pipes into groups. x The n pipes are merged either sequentially or all at once into n pipes equal to the number of burners, denoted as N1, N2, ... N. n Pipeline, then through N1, N2, ... N n The ends of the pipes are connected to burners. Finally, the combined N1, N2, ... N n An online primary air volume monitoring device and an air volume regulating device are installed on the pipeline, and electrically connected to the air volume control device. This controls N1, N2, ... N n The coal feed rate is evenly distributed in each pipeline by equalizing the primary air volume within the pipeline.

[0114] This embodiment only selects three typical embodiments for description. Other layout methods can achieve the same function by making slight modifications to one of the above embodiments.

[0115] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the claimed invention. The scope of protection claimed by the appended claims and their equivalents is defined.

Claims

1. A method for balanced air-coal distribution in a coal-fired power unit pulverizing system, characterized in that, Includes the following steps: Step 1: Obtain the number M of the coal mill outlet air-coal ducts and the corresponding number N of burners. The coal mill outlet air-coal ducts are numbered m1, m2, ... m m Where the subscript m=M; Step 2: Divide each air-coal pulverizer outlet pipe into n pipes, numbered m. x n1,m x n2,…m x n n Where 1≤x≤M, subscript n=N, generating m groups of pipes; the pipe groups are numbered as follows: Step 3: Connect the pipes in column n1, m1n1, m2n1, ... m m The ends of n1 are merged into one pipe N1, and the pipes in the n2 column are m1n2, m2n2, ... m m The ends of n2 merge into one pipe N2, until n n The column of pipes m1n n m2n n ,…m m n n The ends merge into one pipe N n N1, N2, ... N n The ends of the pipes are connected to burners; Step 4: Based on the pipeline structure of the on-site pulverizing system, adjust the path and length of each pipe in each group of m pipelines to ensure that the air resistance of each pipe in each group is equal. Step 5: Merge pipes N1, N2, ... N n Install an online air volume detection device and an air volume adjustment device on the upper part, and connect them to the air volume control device; Step 6: During operation, the primary air volume Q of each duct is obtained through the online air volume monitoring device. N1 Q N2 ,…Q Nn And it is sent to the air volume control device, which controls the air volume according to Q. N1 Q N2 ,…Q Nn The calculated airflow adjustment signal is sent to the airflow regulation device, which then adjusts the airflow in each duct to adjust N1, N2, ... N n The primary air volume is equal in the duct.

2. The method as described in claim 1, characterized in that: In step 4, wind resistance balance is achieved by designing equal-length bend paths.

3. The method as described in claim 1, characterized in that: When there is only one outlet pipe for the coal mill, first divide it into m equal parts, and then proceed with steps 2-6.

4. The method as described in claim 1, characterized in that: When the outlet pipe diameter is too large, it is first split into k secondary pipes, then evenly divided into n sub-pipes, and finally merged into N1-N sub-pipes through multiple stages. n .

5. The method as described in claim 1, characterized in that: The air volume control device uses a PID controller, with Q... N1 -Q Nn Minimizing the variance is the target output adjustment signal.

6. The method as described in claim 1, characterized in that: The primary air volume online detection device is any one of a Pitot tube flow meter, an averaging pitot tube flow meter, an orifice plate flow meter, or a Venturi tube flow meter.

7. The method as described in claim 1, characterized in that: The air volume regulating device can be any one of an adjustable orifice, a valve, or a baffle.

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