A coal drop pipe concentric air ring and a system for increasing the output of a medium-speed coal mill by using central air for a short time
By introducing central air into the central coal drop pipe of the medium-speed coal mill, the problem of mismatch between the coal output of the medium-speed coal mill and the boiler load was solved. This enabled rapid and precise dynamic matching between the fuel system and the combustion system for rapid peak shaving in coal-fired power plant boilers, simplifying the modification and control and reducing costs.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- Filing Date
- 2025-08-19
- Publication Date
- 2026-07-24
AI Technical Summary
In direct-fired pulverizing systems, the output of medium-speed coal mills does not match the changes in boiler load, resulting in a lag in the dynamic matching of the fuel system and combustion system during rapid peak shaving in coal-fired power plant boilers, making it difficult to achieve rapid and precise adjustment.
By introducing central air into the central coal chute of the medium-speed coal mill, the jet pattern accelerates the flow and crushing of raw coal, increases the output of pulverized coal, increases the coal feed rate, and achieves real-time response to changes in boiler load.
It effectively overcomes the lag in combustion system regulation, realizes rapid and accurate dynamic matching between the fuel system and combustion system in rapid peak shaving of coal-fired power plant boilers, simplifies modification and control, and reduces costs.
Smart Images
Figure CN224541861U_ABST
Abstract
Description
Technical Field
[0001] This utility model relates to a concentric air ring for a coal chute and a system for temporarily increasing the output of a medium-speed coal mill by utilizing the central airflow, belonging to the field of flexible operation control technology 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 directly fed into the boiler furnace for combustion without intermediate stops. Therefore, the normal operation of the boiler depends on the reliability of the pulverizing system. Pulverizers with good variable load operating characteristics, such as medium-speed, high-speed, and double-inlet / double-outlet mills, are preferable. 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 commonly used in medium and large-scale coal-fired power plants. While direct-fired pulverizing systems have many advantages, they are still relatively inferior in responding to boiler load changes. When the boiler load changes, the coal feed rate changes accordingly, but due to the 3-5 minute lag time in the pulverized coal grinding process, the pulverized coal output does not perfectly match the boiler's fuel consumption in real time. This limits the load change rate (i.e., the ramp rate, including upward and downward ramp rates) of the coal-fired unit, generally only reaching about 1.5% Pe / min.
[0004] A medium-speed coal mill consists of at least three parts: a drive unit, a grinding unit, and a coarse powder separator. The grinding unit typically comprises a grinding disc driven by the drive unit and three fixed (meaning their positions are fixed) and rotatable grinding rollers that roll along the grinding ring. The coarse powder separator, consisting of a coarse powder separation baffle and a conical shell, is located above the grinding disc. Raw coal falls onto the grinding disc through the central coal chute. The centrifugal force of the rotating disc propels the coal onto the grinding track, where it is ground by the grinding rollers. Grinding and drying of the raw coal occur simultaneously. High-temperature primary air enters relatively evenly around the grinding disc through nozzle rings, drying the coal powder mixture tangentially ejected from the grinding disc and conveying it to the coarse powder separator above the disc. Stone coal falls into the stone coal box through the nozzle rings. The coal powder mixture is separated into fine and coarse powder by the coarse powder separation baffle. The qualified fine powder is carried into the furnace for combustion by the primary air, while the coarse powder returns to the grinding disc from the bottom of the conical shell under its own gravity for re-grinding.
[0005] The aforementioned central coal drop pipe is arranged vertically, with raw coal entering from above the medium-speed coal mill. Four to six pulverized coal discharge pipes are arranged around the central coal drop pipe, allowing pulverized coal meeting certain fineness and temperature requirements to enter the furnace under the influence of primary air. Primary air is introduced from the coal mill inlet pipe, passing through nozzle rings to mix with the coal inside the coal mill. To regulate the temperature of the coal mill, a cold primary air pipe is connected to the coal mill inlet pipe, and its flow rate is controlled.
[0006] Under the background of carbon neutrality, coal-fired power will undergo a transformation from a primary energy source to a basic energy source to a regulatory energy source. For boilers with direct-fired pulverized coal systems, after receiving a load increase command, the process of feeding coal, mixing coal, and grinding is required before the fuel can be sent into the furnace. The load response of the fuel system has a long periodicity, while combustion in the furnace is instantaneous. After receiving the command, the control of the combustion system will have a large lag. Even with the optimization of control strategies, it is difficult to overcome the bottleneck of rapid and accurate dynamic matching between the fuel system and the combustion system in the rapid peak shaving of coal-fired power plant boilers. Utility Model Content
[0007] In order to further overcome the bottleneck of rapid and accurate dynamic matching of fuel system and combustion system in rapid peak shaving of coal-fired power plant boilers, and to fully tap the coal powder storage and supply potential of medium-speed coal mill, this utility model provides a concentric air ring for coal drop pipe and a system for temporarily increasing the output of medium-speed coal mill by utilizing the central air.
[0008] To solve the above-mentioned technical problems, the technical solution adopted by this utility model is as follows:
[0009] A method for temporarily increasing the output of a medium-speed coal mill by utilizing central air: when the output of the medium-speed coal mill does not meet the rapidly increasing load requirements of the boiler, a stream of central air is drawn from the inlet air duct of the coal mill to the central coal drop pipe of the coal mill, so that the central air blows downward along the central coal drop pipe to sweep the central area of the grinding disc, accelerating the flow, crushing and dispersion of raw coal, increasing the output of the coal mill, and increasing the coal feed rate during this process (during the introduction of central air).
[0010] When the output of the medium-speed coal mill meets the rapidly increasing load requirements of the boiler, the introduction of central air is stopped.
[0011] The applicant's research revealed that as the central airflow flows downward along the central coal drop pipe, it pre-dries the raw coal, facilitating its rapid crushing and grinding into qualified coal powder. Simultaneously, the downward-flowing central airflow accelerates the descent of the raw coal, making it easier to crush upon impact with the central area of the mill. Furthermore, the central airflow causes the coal powder or smaller raw coal particles in the central area of the mill to quickly disperse outwards, which on the one hand rapidly discharges the stored coal powder from the mill, and on the other hand accelerates the grinding process of qualified coal powder.
[0012] The above method can respond to changes in boiler load in real time, effectively overcoming the lag in combustion system regulation and the series of problems caused by it, and realizing rapid and accurate dynamic matching of fuel system and combustion system in rapid peak shaving of coal-fired power plant boilers; it is simple, ingenious, easy to modify and control, and low in cost.
[0013] To improve the response, the central airflow flows downward in a jet pattern, accelerating the raw coal by directly impacting and carrying the raw coal particles.
[0014] To further improve the response effect, the central air is directed to the central coal drop pipe above the coal mill.
[0015] As one preferred implementation, the central air is drawn from the pipeline after the cold and hot air are mixed at the coal mill inlet. The central air drawn from the pipeline after the cold and hot air are mixed at the coal mill inlet generally has a temperature between 150-300℃ and a static pressure of 6-8kPa, and can flow by gravity to the central coal drop pipe of the coal mill.
[0016] As an alternative solution, the aforementioned central air is drawn from the hot primary air duct at the inlet of the coal mill. The temperature of this central air is generally between 260-360℃, and the static pressure is generally 7-10 kPa. It can also flow by gravity to the central coal drop pipe of the coal mill.
[0017] A concentric air ring for a coal chute includes an outer pipe, an inner pipe, an upper contraction pipe, and a lower contraction pipe;
[0018] The inner pipe is located inside the outer pipe, and there is a gap between the outer pipe and the inner pipe (the inner diameter of the outer pipe is larger than the outer diameter of the inner pipe); the bottom of the upper contraction pipe is connected to the top of the outer pipe along the periphery (welded or the upper contraction pipe and the outer pipe are directly integrated into a single structure), and the top of the upper contraction pipe is connected to the top of the inner pipe along the periphery (welded) to form the upper interface of the coal drop pipe; the top of the lower contraction pipe is connected to the bottom of the outer pipe along the periphery, and the bottom of the lower contraction pipe extends beyond the bottom of the inner pipe to form the lower interface of the coal drop pipe (that is, the bottom of the inner pipe is surrounded by the inner side of the lower contraction pipe), and there is a gap between the periphery of the bottom of the inner pipe and the lower contraction pipe to form an annular air outlet; the space between the inner pipe and the outer pipe, the upper contraction pipe and the lower contraction pipe forms an annular cavity; a central air interface is provided on the side wall of the outer pipe.
[0019] The bottom diameter of the upper shrink tube is equal to the top diameter of the outer tube, and the top diameter of the lower shrink tube is equal to the bottom diameter of the outer tube, which facilitates splicing and manufacturing.
[0020] The outer tube, inner tube, upper contraction tube, and lower contraction tube are all concentrically arranged (with their central axes coinciding).
[0021] To better ensure the acceleration effect on raw coal, the cross-sectional area of the annular air outlet is 1 / 10 to 1 / 2 of the cross-sectional area of the central coal drop pipe.
[0022] To enhance the jet effect of the central airflow, a first accelerating protrusion is provided at the bottom inner side of the outer tube, and a second accelerating protrusion is provided on the outer wall of the inner tube directly opposite the first accelerating protrusion. A gap is left between the first and second accelerating protrusions, forming an annular accelerating port. The cross-sectional area of the annular accelerating port is 1-5 times the cross-sectional area of the annular air outlet. The central airflow is introduced through the central airflow inlet, enters the annular cavity, undergoes initial acceleration at the annular accelerating port, and secondary acceleration at the annular air outlet, thereby improving the acceleration effect on the raw coal and the response speed to boiler load increases.
[0023] The upper contraction tube is a trumpet-shaped tube structure that gradually narrows from bottom to top; the lower contraction tube is a trumpet-shaped tube structure that gradually narrows from top to bottom, with the inner diameter of the bottom of the lower contraction tube being smaller than the outer diameter of the bottom of the inner tube.
[0024] To improve the structural stability of the device, the top of the upper contraction tube and the top of the inner tube are welded together along the perimeter.
[0025] To ensure the stability of the device, the outer tube, upper shrink tube, and lower shrink tube can be fabricated as an integral structure.
[0026] To facilitate fabrication and ensure the stability of the device, as an alternative implementation, the bottom of the upper shrink tube is welded to the top of the outer tube along the periphery; the top of the lower shrink tube is welded to the bottom of the outer tube along the periphery.
[0027] A system for temporarily increasing the output of a medium-speed coal mill by utilizing central airflow includes at least a central airflow duct, a central airflow regulating valve, and a concentric air ring for the coal drop pipe.
[0028] The concentric air ring of the coal chute is installed on the central coal chute above the coal mill, and is connected to the central coal chute above the coal mill through the upper and lower interfaces of the coal chute.
[0029] One end of the central air duct is connected to the inlet air duct of the coal mill, and the other end is connected to the central air interface on the concentric air ring of the coal drop pipe; the central air regulating valve is installed on the central air duct.
[0030] The aforementioned concentric air ring of the coal chute is concentrically set with the central coal chute above the coal mill.
[0031] As a specific implementation scheme, the central coal drop pipe above the coal mill is divided into two sections, namely the upstream coal drop pipe and the downstream coal drop pipe. The concentric air ring of the coal drop pipe is located between the upstream coal drop pipe and the downstream coal drop pipe. The upper interface of the coal drop pipe on the concentric air ring is connected (welded) to the bottom of the upstream coal drop pipe along the periphery, and the lower interface of the coal drop pipe on the concentric air ring is connected (welded) to the top of the downstream coal drop pipe along the periphery.
[0032] The upstream coal chute, the concentric air ring of the coal chute, and the downstream coal chute are all concentrically arranged (the central axes coincide).
[0033] To further improve the response to boiler load increases, the cross-sectional area of the annular air outlet on the concentric air ring of the coal chute is 1 / 10 to 1 / 2 of the cross-sectional area of the downstream coal chute. More preferably, the cross-sectional area of the annular air outlet on the concentric air ring of the coal chute is 1 / 7 to 1 / 5 of the cross-sectional area of the downstream coal chute, and more preferably 1 / 6.
[0034] The inlet air duct of the medium-speed coal mill includes a cold air duct, a hot primary air duct, and a mixing duct (cold and hot air mixing duct). The cold air duct and the hot primary air duct merge into the mixing duct, which is connected to the medium-speed coal mill.
[0035] One end of the aforementioned central air duct is connected to the cold and hot air mixing duct or the hot primary air duct at the inlet of the coal mill.
[0036] To accurately regulate the central airflow, it is preferable to install a central airflow meter on the central air duct upstream of the central airflow regulating valve.
[0037] The upstream-to-downstream direction of this application is consistent with the flow direction of the material or airflow.
[0038] When the output of the medium-speed coal mill meets the requirements of the boiler's rapid load increase, the aforementioned central air regulating valve is closed. When the output of the medium-speed coal mill does not meet the requirements of the boiler's rapid load increase, the opening of the aforementioned central air regulating valve is gradually increased (the opening is adjusted from 0-100%), and central air is introduced from the coal mill inlet duct into the coal mill's central coal drop pipe, causing it to blow downwards along the central coal drop pipe to sweep the central area of the grinding disc, accelerating the flow, crushing, and dispersion of raw coal, increasing the coal mill's output, and increasing the coal feed rate during this process (during the central air introduction).
[0039] 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.
[0040] Any technologies not mentioned in this utility model are based on existing technologies.
[0041] This invention relates to a method and system for increasing the output of a medium-speed coal mill by utilizing central airflow in a short time. Through a simple and ingenious design, the output of the medium-speed coal mill can respond in real time to changes in boiler load, effectively overcoming the lag in combustion system regulation and the series of problems caused by it. It achieves rapid and accurate dynamic matching between the fuel system and the combustion system in the rapid peak shaving of coal-fired power plant boilers; it is easy to modify and control, and has low cost. Attached Figure Description
[0042] Figure 1 Schematic diagram of the structure of the system for short-term increase of output of medium-speed coal mill by utilizing central wind. Figure 1 (Mixed air).
[0043] Figure 2 Schematic diagram of the structure of the system for short-term increase of output of medium-speed coal mill by utilizing central wind. Figure 2 (Hot air).
[0044] Figure 3 Schematic diagram of the structure of the system for short-term increase of output of medium-speed coal mill by utilizing central wind. Figure 3 (Mixed air).
[0045] Figure 4 Schematic diagram of the structure of the system for short-term increase of output of medium-speed coal mill by utilizing central wind. Figure 4 (Hot air).
[0046] Figure 5 This is a schematic diagram of the concentric air ring structure of the coal chute of this utility model.
[0047] In the diagram, 1 is a medium-speed coal mill, 2 is the powder outlet pipe, 3 is the concentric air ring of the coal drop pipe, 31 is the upper interface of the coal drop pipe, 32 is the central air interface, 33 is the lower interface of the coal drop pipe, 34 is the inner pipe, 35 is the outer pipe, 36 is the first acceleration convex ring, 37 is the second acceleration convex ring, 38 is the annular acceleration port, 39 is the annular air outlet, 4 is the central coal drop pipe, 5 is the central air duct, 51 is the central air regulating valve, 52 is the central air flow meter, 6 is the hot primary air duct, 7 is the cold and hot air mixing duct, and 8 is the cold air duct. Detailed Implementation
[0048] 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.
[0049] Example 1
[0050] A method for temporarily increasing the output of a medium-speed coal mill by utilizing central air: when the output of the medium-speed coal mill does not meet the rapidly increasing load requirements of the boiler, a stream of central air is drawn from the inlet air duct of the coal mill to the central coal drop pipe of the coal mill, so that it blows downward along the central coal drop pipe to sweep the central area of the grinding disc, accelerating the flow, crushing and dispersion of raw coal, increasing the output of the coal mill, and increasing the coal feed rate during this process (during the introduction of central air);
[0051] When the output of the medium-speed coal mill meets the rapidly increasing load requirements of the boiler, the introduction of central air is stopped.
[0052] Experiments showed that as the central airflow flows downward along the central coal drop pipe, it pre-dries the raw coal, facilitating its rapid crushing and grinding into qualified coal powder. Simultaneously, the downward-flowing central airflow accelerates the descent of the raw coal, making it easier to crush upon impact with the central area of the mill. Furthermore, the central airflow causes the coal powder or smaller raw coal particles in the central area of the mill to quickly disperse outwards, thus rapidly discharging the stored coal powder from the mill and accelerating the grinding process of qualified coal powder.
[0053] The above method can respond to changes in boiler load in real time, effectively overcoming the lag in combustion system regulation and the series of problems caused by it, and realizing rapid and accurate dynamic matching between the fuel system and the combustion system in the rapid peak shaving of coal-fired power plant boilers.
[0054] Example 2
[0055] Based on Example 1, the following improvements were made: To enhance the response effect, the central airflow flows downward in a jet pattern, accelerating the raw coal by directly impacting and carrying the raw coal particles. To further improve the response effect, the central airflow is directed into the central coal drop pipe above the coal mill.
[0056] Experiments have shown that the central air can be drawn from the pipeline after the cold and hot air are mixed at the coal mill inlet. The central air introduced from the pipeline after the cold and hot air are mixed at the coal mill inlet has a temperature generally between 150-300℃ and a static pressure generally reaching 6-8kPa, and can flow by gravity to the central coal drop pipe of the coal mill.
[0057] The central air can also be drawn from the hot primary air duct at the inlet of the coal mill. The temperature of this central air is generally between 260-360℃, and the static pressure is generally 7-10 kPa. It can also flow by gravity to the central coal drop pipe of the coal mill.
[0058] Example 3
[0059] like Figure 5 As shown, a concentric air ring for a coal chute includes an outer pipe, an inner pipe, an upper contraction pipe, and a lower contraction pipe arranged concentrically.
[0060] The inner tube is located inside the outer tube, and there is a gap between the outer tube and the inner tube; the bottom diameter of the upper contraction tube is equal to the top diameter of the outer tube, and the bottom of the upper contraction tube is welded to the top of the outer tube along the periphery (as another implementation, the upper contraction tube and the outer tube can be directly integrated into a single structure), and the top of the upper contraction tube is welded to the top of the inner tube along the periphery to form the upper interface of the coal drop pipe; the top diameter of the lower contraction tube is equal to the bottom diameter of the outer tube, and the top of the lower contraction tube is welded to the bottom of the outer tube along the periphery (as another implementation, the lower contraction tube and the outer tube can be directly integrated into a single structure), the bottom of the lower contraction tube extends beyond the bottom of the inner tube to form the lower interface of the coal drop pipe (that is, the bottom of the inner tube is wrapped inside the lower contraction tube), and there is a gap between the periphery of the bottom of the inner tube and the lower contraction tube to form an annular air outlet; the space between the inner tube and the outer tube, the upper contraction tube and the lower contraction tube forms an annular cavity; a central air interface is provided on the side wall of the outer tube.
[0061] Example 4
[0062] Based on Example 3, the following improvements were made: In order to improve the jet effect of the central wind, such as Figure 5 As shown, a first accelerating protrusion is provided on the bottom inner side of the outer tube, and a second accelerating protrusion is provided on the outer wall of the inner tube directly opposite the first accelerating protrusion. A gap is left between the first and second accelerating protrusions, forming an annular accelerating port. The central air inlet is positioned higher than the annular accelerating port, and the cross-sectional area of the annular accelerating port is four times the cross-sectional area of the annular air outlet (verified to be 1.5, 2, or 3 times, etc.). The central air is introduced through the central air inlet, enters the annular cavity, undergoes initial acceleration at the annular accelerating port, and secondary acceleration at the annular air outlet, thereby improving the acceleration effect on the raw coal and the response speed to boiler load increases.
[0063] Example 5
[0064] Based on Example 4, the following improvements were made: In order to improve the jet effect of the central wind, such as Figure 5 As shown, the upper contraction tube is a trumpet-shaped tube structure that gradually contracts from bottom to top; the lower contraction tube is a trumpet-shaped tube structure that gradually contracts from top to bottom, and the inner diameter of the bottom of the lower contraction tube is smaller than the outer diameter of the bottom of the inner tube.
[0065] Example 6
[0066] like Figure 1 and Figure 3 As shown, a system for temporarily increasing the output of a medium-speed coal mill by utilizing central airflow includes at least a central air duct, a central airflow regulating valve, and a concentric air ring for the coal drop pipe.
[0067] The central coal drop pipe above the coal mill is divided into two sections: the upstream coal drop pipe and the downstream coal drop pipe. A concentric air ring is located between the upstream and downstream coal drop pipes. The upstream coal drop pipe, the concentric air ring, and the downstream coal drop pipe are concentrically arranged. The upper interface of the coal drop pipe on the concentric air ring is welded to the bottom edge of the upstream coal drop pipe along the perimeter, and the lower interface of the coal drop pipe on the concentric air ring is welded to the top edge of the downstream coal drop pipe along the perimeter.
[0068] One end of the central air duct is connected to the cold and hot air mixing duct at the inlet of the coal mill, and the other end is connected to the central air interface on the concentric air ring of the coal drop pipe; the central air regulating valve is installed on the central air duct.
[0069] Example 7
[0070] Unlike Example 6, as follows: Figure 2 and Figure 4 As shown, one end of the central air duct is connected to the hot primary air duct at the inlet of the coal mill.
[0071] Example 8
[0072] Based on embodiment 6 or 7, the following improvements are made: a central air flow meter is installed on the central air duct upstream of the central air regulating valve; the cross-sectional area of the annular air outlet on the concentric air ring of the coal chutes is 1 / 6 of the cross-sectional area of the downstream coal chutes (it has been verified that it can also be 1 / 5, 1 / 7, etc.).
[0073] When the output of the medium-speed coal mill meets the requirements of the boiler to rapidly increase its load, the aforementioned central air regulating valve is in the closed state.
[0074] When the output of the medium-speed coal mill does not meet the requirements of the boiler to rapidly increase the load, the opening of the aforementioned central air regulating valve is gradually increased. Central air is introduced from the coal mill inlet air duct (the cold and hot air mixing duct at the coal mill inlet, or the hot primary air duct at the coal mill inlet) into the central coal drop pipe of the coal mill. The central air enters the annular cavity of the concentric air ring of the coal drop pipe from the central air duct, flows downward, undergoes a first acceleration at the annular acceleration port, and a second acceleration at the annular air outlet. The central air enters the central coal drop pipe in a jet form and continues to flow downward along the central coal drop pipe, sweeping the central area of the grinding disc, accelerating the flow, crushing and dispersion of raw coal, increasing the output of the coal mill, and increasing the coal feed rate during this process (during the introduction of central air).
[0075] This example is used for a 1050MW coal-fired power generation unit. Before the modification, the load change rate from 50% to 100% was less than 1.5% Pe / min. After the modification, the central air is drawn from the cold and hot air mixing pipe at the inlet of the coal mill. When a load increase command is received, the coal mill quickly adds coal (matching the boiler load) and simultaneously opens the central air regulating valve to 100% (the process lasts about 140 seconds). At this time, the central air accounts for about 20% of the total primary air volume entering the coal mill. The pulverized coal stored in the coal mill is gradually carried out, realizing rapid and accurate dynamic matching between the fuel system and the combustion system in the rapid peak shaving of the coal-fired power plant boiler. The load change rate of the coal-fired unit from 50% to 100% reaches more than 2.2% Pe / min.
[0076] Comparative Example 1
[0077] Unlike Example 8, this example does not include a system for temporarily increasing the output of the medium-speed coal mill using central airflow; all other aspects are the same as in Example 8. The coal mill's output cannot match the boiler's fuel consumption in real time. Upon receiving a load increase command, coal is rapidly added to the coal mill, causing a significant increase in mill resistance. Consequently, the primary airflow entering the coal mill decreases, limiting the load change rate of the coal-fired unit to approximately 1.2% Pe / min.
Claims
1. A concentric air ring for a coal chute, characterized in that: Includes an outer tube, an inner tube, an upper contraction tube, and a lower contraction tube; The inner pipe is located inside the outer pipe, and there is a gap between the outer pipe and the inner pipe; the bottom of the upper contraction pipe is connected to the top of the outer pipe along the periphery, and the top of the upper contraction pipe is connected to the top of the inner pipe along the periphery to form the upper interface of the coal drop pipe; the top of the lower contraction pipe is connected to the bottom of the outer pipe along the periphery, and the bottom of the lower contraction pipe extends beyond the bottom of the inner pipe to form the lower interface of the coal drop pipe; there is a gap between the periphery of the bottom of the inner pipe and the lower contraction pipe to form an annular air outlet; the space between the inner pipe and the outer pipe, the upper contraction pipe and the lower contraction pipe forms an annular cavity; a central air interface is provided on the side wall of the outer pipe.
2. The concentric ventilation ring for the coal chute according to claim 1, characterized in that: The bottom inner side of the outer tube is provided with a first acceleration protrusion ring, and the outer side wall of the inner tube directly opposite the first acceleration protrusion ring is provided with a second acceleration protrusion ring. There is a gap between the first acceleration protrusion ring and the second acceleration protrusion ring to form an annular acceleration port. The cross-sectional area of the annular acceleration port is 1-5 times the cross-sectional area of the annular air outlet.
3. The concentric ventilation ring of the coal chute according to claim 1 or 2, characterized in that: The cross-sectional area of the annular air outlet is 1 / 10 to 1 / 2 of the cross-sectional area of the central coal chute.
4. The concentric ventilation ring for the coal chute according to claim 1 or 2, characterized in that: The upper contraction tube is a trumpet-shaped tube structure that gradually narrows from bottom to top; the lower contraction tube is a trumpet-shaped tube structure that gradually narrows from top to bottom, with the inner diameter of the bottom of the lower contraction tube being smaller than the outer diameter of the bottom of the inner tube; the outer tube, inner tube, upper contraction tube, and lower contraction tube are all concentrically arranged.
5. The concentric ventilation ring for the coal chute according to claim 1 or 2, characterized in that: The top of the upper shrink tube is welded to the top of the inner tube along the perimeter.
6. The concentric ventilation ring for the coal chute according to claim 1 or 2, characterized in that: The outer tube, upper contraction tube, and lower contraction tube are all integral structures; or, the bottom of the upper contraction tube is welded to the top of the outer tube along the periphery, and the top of the lower contraction tube is welded to the bottom of the outer tube along the periphery.
7. A system for temporarily increasing the output of a medium-speed coal mill by utilizing central airflow, characterized in that: It includes at least a central air duct, a central air regulating valve, and a concentric air ring for the coal chute as described in any one of claims 1-6; The concentric air ring of the coal chute is installed on the central coal chute above the coal mill, and is connected to the central coal chute above the coal mill through the upper and lower interfaces of the coal chute. One end of the central air duct is connected to the inlet air duct of the coal mill, and the other end is connected to the central air interface on the concentric air ring of the coal drop pipe; the central air regulating valve is installed on the central air duct.
8. The system for temporarily increasing the output of a medium-speed coal mill by utilizing central airflow as described in claim 7, characterized in that: The cross-sectional area of the annular air outlet on the concentric air ring of the coal chute is 1 / 10 to 1 / 2 of the cross-sectional area inside the central coal chute.
9. The system for temporarily increasing the output of a medium-speed coal mill by utilizing central airflow as described in claim 7 or 8, characterized in that: The central coal drop pipe above the coal mill is divided into two sections: the upstream coal drop pipe and the downstream coal drop pipe. The concentric air ring of the coal drop pipe is located between the upstream coal drop pipe and the downstream coal drop pipe. The upper interface of the coal drop pipe on the concentric air ring is connected to the bottom of the upstream coal drop pipe along the periphery, and the lower interface of the coal drop pipe on the concentric air ring is connected to the top of the downstream coal drop pipe along the periphery.
10. The system for temporarily increasing the output of a medium-speed coal mill by utilizing central airflow as described in claim 7 or 8, characterized in that: One end of the central air duct is connected to the cold and hot air mixing duct or the hot primary air duct at the inlet of the coal mill; a central air flow meter is installed on the central air duct upstream of the central air regulating valve; the concentric air ring of the coal drop pipe is set concentrically with the central coal drop pipe above the coal mill.