Hot and cold air duct structure at the inlet of the coal mill

Abstract

The present invention relates to a structure of hot and cold air pipelines at the inlet of a coal mill, which includes a hot air pipeline and a cold air pipeline assembly connected to the inlet of the coal mill. The cold air pipeline assembly includes a cold air main pipe connected to the hot air pipeline, and the cold air pipeline assembly further includes cold air branch pipes. The cold air branch pipes are arranged in the hot air pipeline, one end of each cold air branch pipe is connected to the cold air main pipe, and a plurality of air outlets are formed on the cold air branch pipes. Multiple rows of cold air branch pipes in the present invention form multi-point scattering to introduce air into the hot air pipeline. At the same time, the cold air branch pipes are evenly arranged in the hot air pipeline, which can not only play the role of mixing hot and cold air, but also play the role of flow equalization and flow stabilization of the air flow, making the temperature field and velocity field of the air flow in the pipeline more uniform, creating good conditions for the downstream flow measurement element. The entire transformation design is ingenious, can be smoothly implemented for the compact space position at the power plant site, and basically does not occupy additional space positions, laying a solid foundation for accurate measurement of the inlet air flow of the coal mill.

Description

Technical Field

[0001] The invention relates to the field of coal-fired thermal power generation units, and in particular to a cold and hot air duct structure at an inlet of a coal mill. Background Art

[0002] Medium-speed direct-blowing coal mills have been widely used in large-scale power plant pulverized coal boilers. In practice, the uneven mixing of cold and hot air can easily cause the measurement of coal mill inlet air flow to be distorted, which directly affects the automatic input of coal mill air volume and the safety and economy of boiler combustion, and may even cause operators to operate incorrectly, causing coal mill blockage or tripping, causing accidents to expand. Therefore, the accuracy of coal mill inlet air volume measurement is a very important parameter for power plant operation.

[0003] The main reason for the inaccurate measurement of the air volume at the coal mill inlet is related to the layout of the cold and hot air ducts at the coal mill inlet. Generally, the layout of the cold and hot air ducts at the coal mill inlet is usually as follows: the cold and hot air ducts are simply connected in a T-shape, so that the cold air cannot penetrate the hot air flow. The cold and hot air flow is severely stratified, which directly affects the measurement accuracy of the flow element downstream of the air flow. The main reason is that the air flow stratification affects the measurement accuracy of the air flow pressure on the one hand, and the air flow stratification affects the measurement accuracy of the air flow temperature on the other hand. With the change of the opening of the cold and hot air doors, the air flow pressure and air flow temperature measurement values ​​will change disorderly, which can easily cause the flow measurement value to be distorted, causing the reverse action of the automatic operation instruction or the operator's misoperation. For example, sometimes there will be an abnormal phenomenon that the hot air door is opened wide, the air flow rate is basically unchanged or reduced; the air door is closed, and the air flow rate increases instead.

[0004] From the following coal mill inlet flow calculation formula (1), we can understand that the root cause of this abnormal phenomenon lies in the dynamic pressure collection and temperature collection data of the measuring element. When these two data measurements cannot represent the average values ​​of the dynamic pressure and temperature in the entire cross-section due to the uneven flow field (velocity field, temperature field), the above abnormal results will appear.

[0005] The calculation formula of coal mill inlet air volume is as follows:

[0006]

[0007] Where:

[0008] A—Area of ​​flow measurement surface

[0009] K—Pitot tube flow coefficient

[0010] P d —The average dynamic pressure on the flow measurement surface, Pa, is calculated as:

[0011]

[0012] Where: Pdi —Dynamic pressure at each grid point

[0013] n—Total number of grid points

[0014] ρ—Medium density at the flow measurement location, kg / m 3 , and the calculation formula is as follows:

[0015]

[0016] In the formula: ρ a —Atmospheric density, taking ρ a = 1.293 kg / m 3

[0017] p a —Atmospheric pressure, Pa

[0018] p st —Static pressure at the measurement location, Pa

[0019] t—Medium temperature at the measurement location, °C

[0020] From the flow calculation process of Equation (1), it can be seen that what affects the flow calculation is the dynamic pressure of the fluid and the density of the fluid. The dynamic pressure of the fluid is related to the uniformity and stability of the flow field of the measurement cross-section, and the density is related to the static pressure and temperature of the fluid. The change range of the static pressure of the fluid is basically 5000 Pa to 8000 Pa. It can be deduced from Equation (3) that the influence of the change in static pressure on the density is about 5%. If the mixing is uneven, the temperature change will be relatively large, from 100 °C to 300 °C. It can be deduced from Equation (3) that the influence of the temperature change on the density is about 35%.

[0021] Therefore, the uneven mixing of cold and hot air and the uneven flow field directly affect the measured values of the dynamic pressure and temperature of the flow rate, thereby affecting the calculation of the flow rate. Summary of the Invention

[0022] The purpose of the present invention is to provide a structure for the cold and hot air pipelines at the inlet of a coal mill.

[0023] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0024] A structure for the cold and hot air pipelines at the inlet of a coal mill includes a hot air pipeline and a cold air pipeline assembly that are connected to the inlet of the coal mill. The cold air pipeline assembly includes a cold air main pipe that is connected to the hot air pipeline. The cold air pipeline assembly further includes cold air branch pipes. The cold air branch pipes are arranged inside the hot air pipeline. One end of each cold air branch pipe is connected to the cold air main pipe, and a plurality of air outlets are provided on the cold air branch pipes.

[0025] Preferably, multiple cold air branch pipes are distributed on the cross-section of the hot air duct, and the positions of the air outlets on the multiple cold air branch pipes are staggered. For example, the air outlets on two adjacent cold air branch pipes on the same cross-section are staggered, or the air outlets on all the cold air branch pipes on the same cross-section are staggered.

[0026] Preferably, multiple cold air branch pipes are distributed along the extension direction of the hot air duct, and the positions of the air outlets on the multiple cold air branch pipes are staggered. For example, the air outlets on two adjacent cold air branch pipes in the same row are staggered, or the air outlets on all the cold air branch pipes in the same row are staggered.

[0027] The design of staggering the air outlets ensures that the cold air blows out at multiple points evenly in the hot air duct, enabling the hot and cold air to be evenly mixed.

[0028] Preferably, multiple cold air branch pipes are provided, and the multiple cold air branch pipes are parallel to each other.

[0029] Preferably, the extension direction of the cold air main pipe is perpendicular to the extension direction of the hot air duct.

[0030] Preferably, the extension direction of the cold air branch pipe is consistent with the extension direction of the cold air main pipe.

[0031] Preferably, the opening direction of the air outlet is consistent with the flow direction of the primary hot air in the hot air duct.

[0032] Preferably, the cold air duct assembly further includes an inlet diffuser. The outlet of the cold air main pipe is connected to the inlet of the inlet diffuser, and one end of the cold air branch pipe is connected to the outlet of the inlet diffuser.

[0033] More preferably, the cross-sectional area of the inlet diffuser is larger than the cross-sectional area of the cold air main pipe.

[0034] More preferably, the cross-sections of the inlet diffuser and the cold air main pipe are square.

[0035] More preferably, the diameter of the inlet diffuser remains unchanged from one end to the other end.

[0036] Preferably, the cold air duct assembly further includes a mounting plate and a sealing plate. The mounting plate includes a first mounting plate and a second mounting plate. One end of the cold air branch pipe is connected to the first mounting plate and is communicated with the cold air main pipe; the other end of the cold air branch pipe is connected to the second mounting plate and is sealed by the sealing plate.

[0037] Preferably, the cold air duct assembly further includes an inlet diffuser, a mounting plate, and a sealing plate. The outlet of the cold air main pipe is communicated with the inlet of the inlet diffuser, and one end of the cold air branch pipe is communicated with the outlet of the inlet diffuser. The mounting plate includes a first mounting plate and a second mounting plate. One end of the cold air branch pipe is connected to the first mounting plate and communicated with the cold air main pipe. The other end of the cold air branch pipe is connected to the second mounting plate and sealed by the sealing plate.

[0038] More preferably, the cold air main pipe, the inlet diffuser, the first mounting plate, the cold air branch pipe, the second mounting plate, and the sealing plate are connected as a whole.

[0039] Due to the application of the above technical solution, the present invention has the following advantages compared with the prior art:

[0040] The present invention leads out multiple rows of cold air branch pipes from the cold air main pipe to form multi-point scattered air inlet into the hot air duct. At the same time, the cold air branch pipes are evenly arranged in the hot air duct, which can not only play the role of mixing cold and hot air, but also play the role of air flow equalization and steady flow, making the temperature field and velocity field of the air flow in the duct more uniform, creating good conditions for the downstream flow measurement element. The whole transformation design is ingenious and can be smoothly implemented for the compact space position at the power plant site, basically not occupying additional space position, laying a solid foundation for accurate measurement of the air flow at the inlet of the coal mill. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Attached Figure 1 is a schematic structural diagram of the cold and hot air ducts at the inlet of the coal mill;

[0042] Attached Figure 2 is Figure 1 the schematic view in the A direction of the prior art in

[0043] Attached Figure 3 is Figure 2 the schematic view in the B direction in

[0044] Attached Figure 4 is Figure 1 the schematic view in the A direction of this embodiment in

[0045] Attached Figure 5 is Figure 4 the schematic view in the C direction in

[0046] Attached Figure 6a 、 6b 、6c are Figure 4 the schematic views of the first row, the second row, and the third row of cold air branch pipes in the D direction in

[0047] In the above drawings:

[0048] 1. Hot air duct; 20. Cold air main pipe; 21. Cold air branch pipe; 210. Air outlet; 22. Inlet diffuser; 230. First mounting plate; 231. Second mounting plate; 24. Sealing plate; 3. Coal mill; 4. Cold air duct. Detailed implementation mode

[0049] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of them. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative work belong to the scope of protection of the present invention.

[0050] In the description of the present invention, it should be noted that the orientation or positional relationship indicated by the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the present invention. In addition, the terms "first", "second", "third" are only used for descriptive purposes and cannot be construed as indicating or implying relative importance.

[0051] In the description of the present invention, it should be noted that unless otherwise clearly specified and limited, the terms "installation", "connection", "connection" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected, or indirectly connected through an intermediate medium, and it can be the communication inside two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific situations.

[0052] A structure of the hot and cold air ducts at the inlet of a coal mill includes a hot air duct 1 connected to the inlet of the coal mill and a cold air duct assembly. The cold air duct assembly includes a cold air main pipe 20 connected to the hot air duct 1. Usually, the extending direction of the cold air main pipe 20 is perpendicular to the extending direction of the hot air duct 1, that is, the hot air duct 1 and the cold air main pipe 20 are perpendicular to form a T-shaped duct structure.

[0053] As Figure 4 、 5As shown, in this embodiment: The cold air duct assembly further includes a cold air branch pipe 21. The extending direction of the cold air branch pipe 21 is the same as that of the cold air main pipe 2, that is, the cold air branch pipe 21 is also perpendicular to the extending direction of the hot air duct 1. The cold air branch pipe 21 is disposed inside the hot air duct 1. One end of the cold air branch pipe 21 is communicated with the cold air main pipe 20. A plurality of air outlets 210 are formed in the cold air branch pipe 21, and the opening direction of the air outlets 210 is the same as the flow direction of the primary hot air in the hot air duct 1.

[0054] There are multiple cold air branch pipes 21, and the multiple cold air branch pipes 21 are parallel and evenly distributed. As shown in the figure: There are 9 cold air branch pipes 21 arranged in a 3×3 pattern. Figure 5 、 6a 6a, 6b, and 6c are respectively three rows of cold air branch pipes 21 in the front and back on the same cross-section. For example, three air outlets 210 are respectively formed on the three cold air branch pipes 21 in the first row. The three air outlets 210 of the first cold air branch pipe 21 are located at the lower part shown in the figure, the three air outlets 210 of the second cold air branch pipe 21 are located in the middle shown in the figure, and the three air outlets 210 of the third cold air branch pipe 21 are located at the upper part shown in the figure, so as to achieve the staggering of the air outlets 210. Similarly, the three air outlets 210 on the three cold air branch pipes 21 in the second row are respectively located at the upper, lower, and middle parts of the cold air branch pipe 21 shown in the figure, and the three air outlets 210 on the three cold air branch pipes 21 in the third row are respectively located at the middle, upper, and lower parts of the cold air branch pipe 21 shown in the figure. In this way, not only the air outlets 210 of the multiple cold air branch pipes 21 in the same row are staggered, but also the air outlets 210 of the cold air branch pipes 21 in the front and back between different rows are staggered.

[0055] The cold air duct assembly further includes an inlet diffuser 22. The outlet of the cold air main pipe 20 is communicated with the inlet of the inlet diffuser 22. One end of the cold air branch pipe 21 is communicated with the outlet of the inlet diffuser 22. The cross-sectional area of the inlet diffuser 22 is larger than the cross-sectional area of the cold air main pipe 21. Thus, the inlet diffuser 22 introduces the primary cold air from the cold air main pipe 20 into each cold air branch pipe 21 respectively. In this embodiment: The cross-section of the inlet diffuser 22 is square, and the diameter of the inlet diffuser 22 remains unchanged from one end to the other end. Of course, the inlet diffuser 22 can also adopt other forms, such as a flared opening, etc.

[0056] In addition, the cold air duct assembly further includes a mounting plate and a blocking plate 24. Among them: the mounting plate includes a first mounting plate 230 and a second mounting plate 231. One end of the cold air branch pipe 21 is connected to the first mounting plate 230 and communicates with the cold air main pipe 20; the other end of the cold air branch pipe 21 is connected to the second mounting plate 231 and is blocked by the blocking plate 24. In this embodiment: the cold air main pipe 20, the inlet diffuser 22, the first mounting plate 230, the cold air branch pipe 21, the second mounting plate 231 and the blocking plate 24 are connected as a whole. In this way, when connecting the cold air duct assembly to the hot air duct 1, only the cold air duct assembly as a whole needs to be connected to the hot air duct 1.

[0057] In this embodiment, the original simple T-shaped connection is changed to leading out multiple rows of cold air branch pipes from the cold air main pipe to form multi-point scattering for air intake into the hot air duct. At the same time, the cold air branch pipes are evenly arranged in the hot air duct, which can not only play the role of mixing hot and cold air, but also play the role of air flow equalization and stabilization, making the temperature field and velocity field of the air flow in the duct more uniform, creating good conditions for the downstream flow measurement element. The whole transformation design is ingenious, can be smoothly implemented for the compact space position at the power plant site, and basically does not occupy additional space position, laying a solid foundation for accurate measurement of the air flow at the inlet of the coal mill.

[0058] The above embodiments are only used to illustrate the technical concept and characteristics of the present invention, and their purpose is to enable those familiar with this technology to understand the content of the present invention and implement it accordingly, and cannot be used to limit the protection scope of the present invention. Any equivalent changes or modifications made according to the spirit and essence of the present invention should be covered within the protection scope of the present invention.

Claims

1. A structure of the hot and cold air pipelines at the inlet of a coal mill, comprising a hot air pipeline and a cold air pipeline assembly connected to the inlet of the coal mill. The cold air pipeline assembly includes a cold air main pipe connected to the hot air pipeline. Characterized in that: The cold air pipeline assembly further includes cold air branch pipes. The cold air branch pipes are arranged inside the hot air pipeline. One end of each cold air branch pipe is connected to the cold air main pipe. A plurality of air outlets are formed on each cold air branch pipe. A plurality of cold air branch pipes are distributed on the cross-section of the hot air pipeline, and the positions of the air outlets on the plurality of cold air branch pipes are staggered; a plurality of cold air branch pipes are distributed on the same straight line along the extending direction of the hot air pipeline, and the positions of the air outlets on the plurality of cold air branch pipes are staggered. The opening directions of the air outlets are consistent with the flow direction of the primary hot air in the hot air pipeline; the cold air pipeline assembly further includes an inlet diffuser, a mounting plate and a sealing plate. The outlet of the cold air main pipe is connected to the inlet of the inlet diffuser, and one end of the cold air branch pipe is connected to the outlet of the inlet diffuser; the mounting plate includes a first mounting plate and a second mounting plate. One end of the cold air branch pipe is connected to the first mounting plate and is connected to the cold air main pipe; the other end of the cold air branch pipe is connected to the second mounting plate and is sealed by the sealing plate. The cold air main pipe, the inlet diffuser, the first mounting plate, the cold air branch pipes, the second mounting plate and the sealing plate are connected as a whole.

2. The structure of the hot and cold air pipelines at the inlet of a coal mill according to claim 1, Characterized in that: A plurality of cold air branch pipes are provided, and the plurality of cold air branch pipes are parallel to each other.

3. The structure of the hot and cold air pipelines at the inlet of a coal mill according to claim 1, Characterized in that: The extending direction of the cold air main pipe is perpendicular to the extending direction of the hot air pipeline.

4. The structure of the hot and cold air pipelines at the inlet of a coal mill according to claim 1, Characterized in that: The extending direction of the cold air branch pipe is consistent with the extending direction of the cold air main pipe.

5. The structure of the hot and cold air pipelines at the inlet of a coal mill according to claim 1, Characterized in that: The cross-sectional area of the inlet diffuser is larger than the cross-sectional area of the cold air main pipe.

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