Flexible air distribution system for inlet of medium-speed coal mill in coal-fired boiler

Abstract

The utility model discloses a kind of flexible air distribution systems of medium-speed coal mill in coal-fired boiler, and medium-speed coal mill inlet air duct includes cold primary air pipeline, hot primary air pipeline and mixed pipeline, mixed pipeline is communicated with medium-speed coal mill, cold primary air pipeline and hot primary air pipeline are converged to mixed pipeline, still include bypass hot air pipeline;Cold primary air pipeline is equipped with cold air isolation door and cold air damper;Hot primary air pipeline is equipped with hot air isolation door and hot air damper;The side wall of hot primary air pipeline upstream of bypass hot air pipeline one end and hot air isolation door and hot air damper is communicated, the other end and hot primary air pipeline downstream of hot air isolation door and hot air damper are communicated, bypass hot air pipeline is equipped with bypass damper;Hot primary air pipeline flow cross-sectional area>cold primary air pipeline flow cross-sectional area>the bypass hot air pipeline flow cross-sectional area is recorded as C.The above-mentioned system can safely and reliably configure 80~120 ℃ medium-temperature air, maintain warm grinding state, realize the rapid restart of medium-speed coal mill.

Description

Technical Field

[0001] This utility model relates to a flexible air distribution system at the inlet of a medium-speed coal mill in a coal-fired boiler, belonging to the technical field of flexible operation control for coal-fired power plant boilers. Background Technology

[0002] The pulverized coal preparation system in a coal-fired power plant is often simply referred to as the pulverizing system. The pulverizing system refers to the combination of equipment and related connecting pipes required to grind and dry raw coal into pulverized coal with a certain fineness and moisture content, which is then fed into the boiler furnace for combustion. Common pulverizing systems are divided into two types according to their operating characteristics: direct-fired and intermediate-storage. However, medium and large-sized coal-fired units are generally equipped with direct-fired pulverizing systems.

[0003] In a direct-fired pulverizing system, the pulverized coal produced by the coal mill is sent directly to the boiler furnace for combustion without intermediate storage. Therefore, the normal operation of the boiler depends on the reliability of the pulverizing system. Coal mills with good variable load operating characteristics, such as medium-speed mills, high-speed mills, and double-inlet double-outlet mills, are recommended. Direct-fired pulverizing systems equipped with medium-speed mills have a simple structure, fewer equipment, compact layout, low steel consumption, lower investment, and relatively low power consumption, making them widely used in medium and large-sized coal-fired power plants.

[0004] Large-scale coal-fired power plants typically have 4-6 sets of medium-speed coal mills in their direct-fired pulverizing systems. During significant load increases and decreases in the unit, some coal mills need to be frequently started and stopped. When a coal mill is shut down, it is generally necessary to maintain ventilation to prevent the release of CO from the pulverized coal inside the mill, which could pose an explosion risk. A small amount of air is also needed to cool the shut-down burners. To prevent the spontaneous combustion of small amounts of coal remaining in the shut-down coal mill or the release of large amounts of CO gas, the temperature of the incoming air is generally required to not exceed 120°C. Although medium-speed coal mills are typically equipped with one stream of hot primary air (approximately 300°C) and one stream of cold primary air (close to atmospheric temperature) at the inlet, theoretically, a medium-temperature air of 80-120°C can be produced by mixing them. However, this is difficult to achieve in practice (due to poor damper adjustment characteristics, the large cross-section of the hot primary air duct and the small cross-section of the cold primary air duct, making it suitable only for producing high-temperature air of around 200-300°C), and inflexible adjustment is not convenient. In actual operation, to facilitate operation and ensure that the air temperature does not exceed the upper limit, only the cold primary air at room temperature is generally introduced directly. When the coal mill needs to be restarted, the hot primary air is temporarily mixed in to warm up the mill, and a small amount of coal (cold medium) is added to adjust the outlet air temperature of the coal mill (generally required not to exceed 120°C). It takes 10-15 minutes from the start-up of the coal mill until the operating parameters are relatively stable.

[0005] In the context of carbon neutrality, large-scale and unstable grid connection of new energy sources often requires coal-fired units to significantly increase their load in a short period, necessitating rapid mill start-up. It is advisable to maintain a warm mill state while the mill is shut down to shorten the restart time. Therefore, it is necessary to reliably configure a medium-temperature airflow of 80-120℃ with an adjustable flow rate within a small range, ensuring that the heat carried by the medium-temperature airflow into the mill is not less than the mill's heat dissipation losses. Utility Model Content

[0006] In order to shorten the start-up time of the coal mill and to safely and economically introduce air at a suitable temperature when the mill is stopped, this utility model provides a flexible air distribution system for the inlet of a medium-speed coal mill in a coal-fired boiler.

[0007] To solve the above-mentioned technical problems, the technical solution adopted by this utility model is as follows:

[0008] A flexible air distribution system for the inlet of a medium-speed coal mill in a coal-fired boiler includes a cold primary air duct, a hot primary air duct, and a mixing duct. The mixing duct is connected to the medium-speed coal mill. The cold primary air duct and the hot primary air duct merge into the mixing duct. A bypass hot air duct is also included. The cold primary air duct is equipped with a cold air isolation valve and a cold air regulating valve. The hot primary air duct is equipped with a hot air isolation valve and a hot air regulating valve. One end of the bypass hot air duct is connected to the side wall of the hot primary air duct upstream of the hot air isolation valve and the hot air regulating valve, and the other end is connected to the hot primary air duct downstream of the hot air isolation valve and the hot air regulating valve. The bypass hot air duct is equipped with a bypass regulating valve. The cross-sectional area of ​​the hot primary air duct is denoted as A, the cross-sectional area of ​​the cold primary air duct is denoted as B, and the cross-sectional area of ​​the bypass hot air duct is denoted as C, where A > B > C.

[0009] The above-mentioned flexible air distribution system at the inlet of the medium-speed coal mill in the coal-fired boiler is adopted. When the coal mill stops, the hot air regulating valve is closed and the cold air isolation valve is opened. A portion of the hot primary air is drawn in through the bypass hot air duct and mixed with the cold primary air. By adjusting the opening of the bypass regulating valve and the cold air regulating valve, medium-temperature air of 80~120℃ is configured and introduced into the medium-speed coal mill through the mixing duct to maintain the warm grinding state and realize the rapid restart of the medium-speed coal mill.

[0010] Because the hot primary air duct is relatively thick while the cold primary air duct is relatively thin, it is difficult to configure medium-temperature air with a suitable temperature. This application cleverly sets up a bypass hot air duct with a cross-sectional area smaller than that of the cold primary air duct. After the coal mill stops, a portion of the hot primary air is drawn in and mixed with the cold primary air, which can configure medium-temperature air with suitable temperature and flow rate, maintain the warm mill state, and significantly shorten the restart time of the medium-speed coal mill.

[0011] After the hot primary air and cold primary air are mixed in the mixing pipe, they enter the medium-speed coal mill.

[0012] One end of the aforementioned bypass hot air duct is connected to the side wall of the primary hot air duct upstream of the hot air isolation door and the hot air regulating door, and the other end is connected to the primary hot air duct downstream of the hot air isolation door and the hot air regulating door. That is, the hot air isolation door and the hot air regulating door are located between the two ends of the bypass hot air duct.

[0013] In this application, "connected" means that the two entities are linked and interconnected.

[0014] To further improve the accuracy of medium-temperature wind control, the preferred values ​​are B = 20%~40%A and C = 20%~40%B. Further preferred values ​​are B = 25%~30%A and C = 25%~30%B.

[0015] To reduce heat loss during normal operation of the medium-speed coal mill and facilitate control, both a bypass isolation valve and a bypass regulating valve are installed on the bypass hot air duct.

[0016] To facilitate control, use, and maintenance, and to extend the service life of the hot air control valve, the hot air control valve is located downstream of the hot air isolation door.

[0017] To facilitate control, use, and maintenance, and to extend the service life of the cold air control damper, the cold air control damper is located downstream of the cold air isolation damper.

[0018] To facilitate control, use, and maintenance, and to extend the service life of the bypass control valve, the bypass control valve is located downstream of the bypass isolation valve.

[0019] For ease of manufacturing and installation, the bypass hot air duct is arranged in a U-shape and uses circular pipes.

[0020] To improve the structural strength and service life of the system, the bypass hot air duct, cold primary air duct and hot primary air duct are all made of Q355 steel with a wall thickness of not less than 5mm.

[0021] The upstream-to-downstream direction of this application is consistent with the flow direction of the material or airflow.

[0022] In this application, terms such as top, bottom, high, and low refer to the relative positions shown in the accompanying drawings or when the device is in normal use.

[0023] Any technologies not mentioned in this utility model are based on existing technologies.

[0024] This utility model relates to a flexible air distribution system for the inlet of a medium-speed coal mill in a coal-fired boiler. It can safely and reliably distribute medium-temperature air (80-120℃) and introduce it into the medium-speed coal mill through a mixing pipe to maintain a warm grinding state and enable rapid restart of the medium-speed coal mill. The flow rate is adjustable, which can effectively ensure that the heat carried by the medium-temperature air introduced into the coal mill is not less than the heat loss of the coal mill. The system has a simple and ingenious structure, is stable and controllable, has high safety, is easy to modify, does not require high-precision equipment, is low in cost, and is conducive to promotion. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the flexible air distribution system at the inlet of the medium-speed coal mill in a coal-fired boiler according to this utility model.

[0026] Figure 2 A structural diagram before the bypass hot air duct is installed;

[0027] In the diagram, 1 is a medium-speed coal mill, 2 is a cold primary air duct, 21 is a cold air isolation door, 22 is a cold air regulating door, 3 is a hot primary air duct, 31 is a hot air isolation door, 32 is a hot air regulating door, 4 is a mixing duct, 5 is a bypass hot air duct, 51 is a bypass isolation door, and 52 is a bypass regulating door. Detailed Implementation

[0028] To better understand this utility model, the following embodiments further illustrate the content of this utility model, but the content of this utility model is not limited to the following embodiments.

[0029] Example 1

[0030] like Figure 1 The diagram illustrates a flexible air distribution system at the inlet of a medium-speed coal mill in a coal-fired boiler. The inlet air duct of the medium-speed coal mill includes a cold primary air duct, a hot primary air duct, and a mixing duct. The mixing duct is connected to the medium-speed coal mill. The cold primary air duct and the hot primary air duct merge into the mixing duct. A bypass hot air duct is also included. The cold primary air duct is equipped with a cold air isolation valve and a cold air regulating valve. The hot primary air duct is equipped with a hot air isolation valve and a hot air regulating valve. One end of the bypass hot air duct is connected to the side wall of the hot primary air duct upstream of the hot air isolation valve and the hot air regulating valve, and the other end is connected to the hot primary air duct downstream of the hot air isolation valve and the hot air regulating valve. The bypass hot air duct is equipped with a bypass isolation valve and a bypass regulating valve. The cross-sectional area of ​​the hot primary air duct is denoted as A, the cross-sectional area of ​​the cold primary air duct is denoted as B, and the cross-sectional area of ​​the bypass hot air duct is denoted as C. Therefore, A > B > C.

[0031] The above-mentioned flexible air distribution system at the inlet of the medium-speed coal mill in the coal-fired boiler is adopted. When the coal mill stops, the hot air regulating valve is closed and the cold air isolation valve is opened. A portion of the hot primary air is drawn in through the bypass hot air duct and mixed with the cold primary air. By adjusting the opening of the bypass regulating valve and the cold air regulating valve, medium-temperature air of 80~120℃ is configured and introduced into the medium-speed coal mill through the mixing duct to maintain the warm grinding state and realize the rapid restart of the medium-speed coal mill.

[0032] Example 2

[0033] Based on Example 1, the following improvements were made: In order to further improve the accuracy of medium-temperature air control, B=25%A, C=25%B (through experiments, it can also be B=30%A, C=30%B; or, B=25%A, C=30%B, etc.).

[0034] Example 3

[0035] Based on Example 2, the following improvements were made: In order to facilitate control and use and maintenance, and to extend the service life of the control valves, the hot air control valve is located downstream of the hot air isolation door; the cold air control valve is located downstream of the cold air isolation door; and the bypass control valve is located downstream of the bypass isolation door.

[0036] Example 4

[0037] Based on Example 3, the following improvements were made: To facilitate manufacturing and installation, the bypass hot air duct adopts a circular pipe and is assembled into a U-shaped structure. In order to improve the structural strength and service life of the system, the bypass hot air duct (5), the cold primary air duct (2) and the hot primary air duct (3) are all made of Q355 steel with a wall thickness of not less than 5mm.

[0038] The flexible air distribution system at the inlet of the medium-speed coal mill in the above-mentioned coal-fired boilers can safely and reliably distribute medium-temperature air of 80~120℃, and introduce it into the medium-speed coal mill through a mixing pipe to maintain a warm grinding state and achieve rapid restart of the medium-speed coal mill. Moreover, the flow rate is adjustable, which can effectively ensure that the heat carried by the medium-temperature air introduced into the coal mill is not less than the heat loss of the coal mill. The structure is simple and ingenious, stable and controllable, highly safe, easy to modify, does not require the use of high-precision equipment, is low in cost, and is conducive to promotion.

Claims

1. A flexible air distribution system for the inlet of a medium-speed coal mill in a coal-fired boiler, wherein the inlet air duct of the medium-speed coal mill (1) includes a cold primary air duct (2), a hot primary air duct (3), and a mixing duct (4), the mixing duct (4) being connected to the medium-speed coal mill, and the cold primary air duct (2) and the hot primary air duct (3) converging into the mixing duct (4), characterized in that: It also includes a bypass hot air duct (5); a cold air isolation door (21) and a cold air regulating door (22) are provided on the cold primary air duct (2); a hot air isolation door (31) and a hot air regulating door (32) are provided on the hot primary air duct (3); one end of the bypass hot air duct (5) is connected to the side wall of the hot primary air duct (3) upstream of the hot air isolation door (31) and the hot air regulating door (32), and the other end is connected to the hot primary air duct (3) downstream of the hot air isolation door (31) and the hot air regulating door (32). A bypass regulating door (52) is provided on the bypass hot air duct (5); the flow cross-sectional area of ​​the hot primary air duct (3) is denoted as A, the flow cross-sectional area of ​​the cold primary air duct (2) is denoted as B, and the flow cross-sectional area of ​​the bypass hot air duct (5) is denoted as C. Then A > B > C.

2. The flexible air distribution system at the inlet of the medium-speed coal mill in a coal-fired boiler according to claim 1, characterized in that: B = 20%~40%A, C = 20%~40%B.

3. The flexible air distribution system at the inlet of the medium-speed coal mill in a coal-fired boiler according to claim 2, characterized in that: B = 25%~30%A, C = 25%~30%B.

4. The flexible air distribution system at the inlet of a medium-speed coal mill in a coal-fired boiler according to any one of claims 1-3, characterized in that: The bypass hot air duct (5) is also equipped with a bypass isolation door (51).

5. The flexible air distribution system at the inlet of the medium-speed coal mill in a coal-fired boiler according to claim 4, characterized in that: The bypass gate (52) is located downstream of the bypass isolation gate (51).

6. The flexible air distribution system at the inlet of a medium-speed coal mill in a coal-fired boiler according to any one of claims 1-3, characterized in that: The hot air damper (32) is located downstream of the hot air isolation door (31).

7. The flexible air distribution system for the inlet of a medium-speed coal mill in a coal-fired boiler according to any one of claims 1-3, characterized in that: The cold air damper (22) is located downstream of the cold air isolation door (21).

8. The flexible air distribution system at the inlet of a medium-speed coal mill in a coal-fired boiler according to any one of claims 1-3, characterized in that: The bypass hot air duct (5) adopts a circular duct and is assembled into a U-shaped structure.

9. The flexible air distribution system for the inlet of a medium-speed coal mill in a coal-fired boiler according to any one of claims 1-3, characterized in that: The bypass hot air duct (5), cold primary air duct (2) and hot primary air duct (3) are all made of Q355 steel.

10. The flexible air distribution system at the inlet of a medium-speed coal mill in a coal-fired boiler according to any one of claims 1-3, characterized in that: The wall thickness of the bypass hot air duct (5), the cold primary air duct (2) and the hot primary air duct (3) shall not be less than 5 mm.

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