Method and system for flexibly adjusting powder output of medium-speed coal mill in direct-fired pulverizing system

Abstract

The invention discloses a method and a system for flexibly adjusting the powder output of a medium-speed coal mill in a direct-fired pulverizing system. The method for flexibly adjusting the powder output of the medium-speed coal mill in the direct-fired pulverizing system comprises the following steps of: arranging a powder storage bin outside the coal mill, and storing redundant coal powder in the powder storage bin when the output of the coal mill is excessive and the powder output is greater than the fuel demand of a boiler; and when the output of the coal mill is insufficient and the pulverized coal output amount is smaller than the fuel demand amount of the boiler, the pulverized coal stored in the pulverized coal storage bin is conveyed into a central coal falling pipe of the coal mill, and the pulverized coal enters the coal mill to be recycled and redistributed into each air powder pipe at an outlet of the coal mill. According to the method, rapid, accurate and dynamic matching of a fuel system and a combustion system in rapid peak regulation of a coal-fired power plant boiler is achieved, further, balance control over the pulverized coal concentration in all air powder pipes at an outlet of a coal mill can be achieved, the pulverized coal concentration regulation response speed is high, and control is convenient; and the device is simple in structure, small in size, small in occupied area, easy to modify and arrange on site, convenient to control and easy to popularize.

Description

Technical Field

[0001] This invention relates to a method and system for flexibly adjusting the output of a high-speed coal mill in a direct-fired pulverizing system, belonging to the technical field of flexible operation control of 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 classified into two types according to their operating characteristics: direct-fired and intermediate-storage.

[0003] In a direct-fired pulverizing system, the pulverized coal produced by the coal mill is directly sent to the boiler furnace for combustion without intermediate stops. 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, high-speed, and double-inlet / double-outlet mills, are preferable. Direct-fired pulverizing systems equipped with medium-speed coal 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. 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 consists of a grinding disc driven by the drive unit and three fixed (meaning their positions are fixed) and self-rotating grinding rollers that roll along the grinding ring. The coarse powder separator consists of coarse powder separation baffles and a conical shell, located above the grinding disc. Raw coal falls onto the grinding disc through the central coal drop pipe. The centrifugal force of the rotating grinding disc propels the raw coal onto the grinding track, where it is ground by the grinding rollers. The grinding and drying of raw coal are carried out 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 grinding disc. Stone coal falls into the stone coal box through the nozzle rings. The coal powder mixture is separated from the coarse powder by the coarse powder separation baffles. Qualified fine powder is carried by the primary air and enters the furnace for combustion through the coal mill outlet air-coal pipe. Coarse powder returns to the grinding disc from the bottom of the cone shell under its own gravity for re-grinding. The aforementioned central coal drop pipe is arranged vertically, with raw coal entering from above the medium-speed coal mill. Four to six air-coal pipes are arranged around the central coal drop pipe, allowing coal powder meeting certain fineness and temperature requirements to enter the furnace under the influence of primary air. Primary air enters from the coal mill inlet pipe, passing through nozzle rings to mix with the coal. To regulate the coal mill temperature, a cold primary air pipe is connected to the coal mill inlet pipe, and its flow rate is controlled.

[0004] While direct-fired pulverized coal systems offer numerous advantages, they are somewhat less effective at responding to boiler load changes. When boiler load changes, the coal feed rate responds accordingly, but due to a 3-5 minute lag time in the pulverized coal grinding process, the pulverized coal output does not perfectly match the boiler's required fuel consumption in real time. This limits the load change rate (i.e., ramp-up rate, including both upward and downward ramp-up rates) of the coal-fired unit, typically reaching only around 1.5% Pe / min. Furthermore, due to their compact structure, medium-speed pulverized coal mills often exhibit significant variations in pulverized coal concentration in the air-coal pipes at the mill outlet, negatively impacting furnace combustion, such as causing overheating of some water-cooled walls.

[0005] Centralized coal storage pulverizing systems typically employ slower-speed ball mills. Compared to direct-fired pulverizing systems, they incorporate additional equipment such as fine powder separators, pulverized coal silos, feeders, and screw conveyors. In a centralized coal storage system, raw coal exits the silo, is fed by the feeder controller, and then flows into the downflow drying pipe, where it meets the drying hot air before being fed into the pulverizer. The raw coal is dried and ground in the pulverizer. The ground pulverized coal is carried out of the outlet by the drying air and sent to the coarse powder separator for further processing. Unqualified coarse powder is returned to the pulverizer via the return pipe for re-grinding, while qualified pulverized coal continues to be carried by the drying air into the fine powder separator. In the fine powder separator, approximately 90% of the pulverized coal is separated from the pulverized coal airflow and falls into the pulverized coal silo below, or is conveyed by the screw conveyor to the pulverized coal silos of other boilers. Pulverized coal for boiler combustion is taken from the pulverized coal silo according to the boiler's needs, fed into the primary air duct via an adjustable pulverizer, and then blown into the boiler for combustion by the primary air. Compared to direct-fired pulverized coal systems, intermediate-storage pulverized coal systems have more components, higher investment, larger footprint, higher power consumption, and greater maintenance workload, and are also more dangerous, posing a risk of explosion. However, they also have significant advantages, such as the ability to extract the required amount of fuel from the pulverized coal silo in real time, thus improving the ramp-up rate of coal-fired units.

[0006] Under the backdrop of carbon neutrality, coal-fired power will undergo a transformation from a primary energy source to a basic energy source to a regulating energy source. For boilers with direct-fired pulverized coal systems, after receiving a load increase command, the process of feeding, mixing, and grinding coal is required before fuel can be delivered 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 significant lag. To minimize the lag, some studies have proposed improvement schemes for the aforementioned direct-fired pulverized coal systems, such as adding small pulverized coal silos, aiming to combine the advantages of the two pulverized coal systems. However, small pulverized coal silos are prone to safety and environmental problems (they can easily lead to dead zones of pulverized coal accumulation causing deflagration, and can also easily cause pipe blockages, and the space for on-site modification is limited). It is also difficult to further 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. Summary of the Invention

[0007] To further overcome the bottleneck of rapid and precise dynamic matching between the fuel system and the combustion system in the rapid peak shaving of coal-fired power plant boilers, and to ensure that the pulverizing system operates in a sufficiently economical, safe and environmentally friendly manner, while simplifying the structure and facilitating modification, this invention provides a method and system for flexibly adjusting the output of the high-speed coal mill in a direct-fired pulverizing system.

[0008] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0009] A method for flexibly adjusting the pulverized coal output of a high-speed coal mill in a direct-fired pulverizing system involves setting up an external pulverized coal storage silo for the coal mill. When the coal mill output is excessive and the pulverized coal output exceeds the boiler fuel demand, the excess pulverized coal is stored in the storage silo. When the coal mill output is insufficient and the pulverized coal output is less than the boiler fuel demand, the pulverized coal stored in the storage silo is transported to the central coal drop pipe of the coal mill, allowing it to recirculate inside the coal mill and be redistributed to the air-coal pipes at the coal mill outlet.

[0010] The above-mentioned method for flexibly adjusting the output of the high-speed coal mill in the direct-fired pulverizing system is simple, flexible, and highly effective.

[0011] To improve the uniformity of pulverized coal concentration in the air-coal pipes at the coal mill outlet, a pulverized coal storage bin is installed on each air-coal pipe. Pipes with higher pulverized coal concentrations have more storage bins, while those with lower concentrations have fewer, thus ensuring a more uniform pulverized coal concentration in each pipe. This guarantees a uniform pulverized coal supply to the furnace and stable combustion.

[0012] As one specific implementation scheme, installation ports are reserved on each air-coal pipe at the outlet of the coal mill, the coal storage bins are installed on the installation ports, and coal storage control valves are installed at the installation ports; the coal powder concentration in each air-coal pipe at the outlet of the coal mill is monitored in real time, and the opening of the corresponding coal storage control valve is adjusted in real time according to the coal powder concentration in each air-coal pipe, so that the coal powder concentration in each air-coal pipe tends to be uniform.

[0013] The location on the powder storage bin that connects to the installation port, i.e., the inlet of the powder storage bin, allows the powder storage control valve to be installed on the inlet end face of the powder storage bin, or it can be directly installed on the installation port reserved on the air-powder pipe.

[0014] The above-mentioned coal powder concentration can be monitored using existing conventional methods, such as laser scattering method, electrostatic induction method, etc.

[0015] To save energy and facilitate modification, the coal powder stored in the coal powder storage bin is transported to the central coal drop pipe of the coal mill via cold primary air.

[0016] The aforementioned primary air cooling is a standard concept used in coal-fired power plants and will not be elaborated upon here.

[0017] A flexible adjustment system for the output of a high-speed coal mill in a direct-fired pulverizing system is installed on the coal mill outlet air-powder pipe and includes at least a powder storage bin, a powder feeder, and a powder return pipe.

[0018] The powder storage bin is equipped with an inlet and an outlet. The inlet of the powder storage bin is equipped with a powder storage control valve. The outlet air-powder pipe of the coal mill is equipped with an installation port. The inlet of the powder storage bin is connected to the installation port and intercepts or extracts powdered coal from the air-powder pipe.

[0019] The return powder pipe has two inlet branches: a powder inlet and a conveying air inlet. The conveying air inlet is located upstream of the powder inlet. The inlet of the powder feeder is connected to the outlet of the powder storage bin, and the outlet of the powder feeder is connected to the powder inlet of the return powder pipe. The conveying air inlet of the return powder pipe is connected to the primary cold air, and the outlet of the return powder pipe is connected to the central coal drop pipe of the coal mill.

[0020] When the coal mill output is excessive and the amount of coal powder produced is greater than the boiler fuel demand, the opening of the coal powder storage control valve is adjusted to store the excess coal powder in the coal powder storage bin. The coal powder pipe with a higher coal powder concentration corresponds to the coal powder storage bin with more coal powder, and the coal powder pipe with a lower coal powder concentration corresponds to the coal powder storage bin with less coal powder, so that the coal powder concentration in each coal powder pipe tends to be uniform.

[0021] When the coal mill output is insufficient and the pulverized coal output is less than the boiler fuel demand, the pulverizer is turned on. The pulverizer adds the pulverized coal from the storage bin to the return pulverizer pipe, and then the pulverized coal in the return pulverizer pipe is transported to the central coal drop pipe of the coal mill by the cold primary air. It then enters the coal mill for recirculation and is redistributed to the air-pulverizer pipes at the coal mill outlet, realizing rapid and precise dynamic matching between the fuel system and the combustion system in the rapid peak shaving of the coal-fired power plant boiler.

[0022] The aforementioned control system is small in size, occupies little space, has a simple structure, is easy to modify and deploy on-site, is easy to control, and is easy to promote.

[0023] The aforementioned powder return pipe has an inlet at one end and an outlet at the other end. The inlet of the powder return pipe has at least two branches, namely at least one powder inlet and one conveying air inlet, while the outlet does not have any branches.

[0024] To facilitate the adjustment of pulverized coal concentration in the air-coal pipes at the coal mill outlet, pulverized coal storage bins are installed on each air-coal pipe at the coal mill outlet. (The installation method involves reserving an installation port on each air-coal pipe and then connecting the inlet of each pulverized coal storage bin to the corresponding installation port on the air-coal pipe.) The pulverized coal storage bins intercept or extract pulverized coal from their respective air-coal pipes, thereby achieving the effect of adjusting the pulverized coal concentration in each air-coal pipe (generally 4-6 pipes) at the coal mill outlet. This also makes the pulverized coal concentration in each air-coal pipe more uniform, ensuring uniform pulverized coal supply to the furnace and stable combustion.

[0025] The return coal pipe has two inlet branches: a conveying air inlet and two or more powder inlets, with the conveying air inlet located upstream of each powder inlet. The number of powder inlets, powder storage bins, and feeders is equal and they correspond one-to-one. The feeder inlet is connected to the outlet of the corresponding powder storage bin, and the feeder outlet is connected to the corresponding powder inlet. In this way, the pulverized coal in each powder storage bin can enter the same return coal pipe and be conveyed to the central coal drop pipe by primary air supplied from the conveying air inlet.

[0026] The upstream-to-downstream direction of this application is consistent with the material flow direction.

[0027] For ease of modification, the aforementioned installation port is located at the bottom of the horizontal section of the air-powder duct, and the powder storage bin is located below the air-powder duct. In other words, the powder storage bin is located below the horizontal section of the air-powder duct.

[0028] The inlet of the aforementioned pulverized coal storage silo is located at its top, and its outlet is located at its bottom. The silo has a tapering structure from inlet to outlet. That is, the top of the silo is the larger end, serving as the inlet, and the bottom is the smaller end, serving as the outlet. This facilitates the control of pulverized coal entry and exit.

[0029] For ease of installation and control, the aforementioned powder storage control valve is located at the inlet end face of the powder storage silo, and the powder storage control valve has a multi-blade structure.

[0030] For ease of installation and control, the powder storage control valve is composed of two or more adjusting blades spliced ​​together; each adjusting blade is equipped with a rotating shaft; each rotating shaft is driven to rotate by a motor or pneumatic actuator, which in turn drives the adjusting blade to rotate, thereby controlling the opening degree of the powder storage control valve.

[0031] To improve the efficiency and effectiveness of pulverized coal regulation, each regulating blade is rectangular, and each rotating axis is parallel to the others. The direction perpendicular to the axis of rotation of the regulating blade is considered the width direction, and the direction parallel to the axis of rotation of the regulating blade is considered the length direction. The axis of rotation of the regulating blade is perpendicular to the direction of air-pulverized coal flow in the air-pulverized coal pipe (i.e., from upstream to downstream). Each regulating blade has a different width, and the width of each regulating blade increases sequentially along the direction of air-pulverized coal flow. This facilitates rapid response in pulverized coal regulation and makes control convenient.

[0032] The length and width are two adjacent sides of the rectangle. The width direction of the aforementioned adjusting blade is also the direction in which the width is located, and the length direction is the direction in which the length is located. For ease of description, this application defines the length and width directions based on the axis of rotation, rather than the actual length of the rectangle's sides. Therefore, in this application, it is not limited to the fact that the width of the adjusting blade can only be less than its length.

[0033] For ease of adjustment and control, the rotation shaft of each adjusting blade is located at the downstream end of the blade in the width direction, and / or at the middle position in the width direction of the blade; each rotating shaft is synchronously driven to rotate by a motor or pneumatic actuator through a crank-connecting rod mechanism. One end of the adjusting blade in the width direction is the upstream end, and the other end is the downstream end, with the direction from the upstream end to the downstream end consistent with the air-powder flow direction in the air-powder pipe.

[0034] To further improve the powder storage speed, each regulating blade is equipped with a baffle plate at a 60-150° angle to its front surface. The angle between the regulating blade and the baffle plate refers to the angle between the front surface of the regulating blade and the baffle plate. The front surface of the regulating blade is the side that is flushed by the powder in the powder duct when the powder storage control valve is open. The baffle plate can be located either above or below the rotating shaft. "Above" and "below" refer to the positions of the baffle plate relative to the rotating shaft when the regulating blade is at a 90° opening. The baffle plate is installed away from the rotating shaft, ensuring that its placement does not affect the rotation of the regulating blade.

[0035] During use, the horizontal position of the adjusting blades is set to zero (corresponding to 0°). When all adjusting blades are in the horizontal position, the inlet of the powder storage chamber is closed. Each adjusting blade is adjustable within a range of at least 0-45°, and more preferably, each adjusting blade is adjustable within a range of 0-90°. When all adjusting blades are at 90°, the opening of the powder storage chamber inlet is at its maximum, and the powder storage speed is the fastest.

[0036] When the inlet of the pulverized coal storage silo is closed, the inlet is completely covered and blocked by the pulverized coal storage control valve. The pulverized coal storage control valve can be closed when it is not necessary to adjust the pulverized coal concentration in the air-coal duct.

[0037] To prevent pulverized coal stored in the shrinkage silo from caking, a heating device is installed on the silo, with a heating temperature of 60-100℃.

[0038] To further prevent pulverized coal stored in the shrinkage silo from caking, a fluidizing air inlet pipe is installed at the bottom of the silo to introduce fluidizing air from the bottom of the silo.

[0039] As one preferred implementation, the fluidizing air inlet pipe is connected to the nitrogen outlet of the nitrogen generator via a pipeline. That is, nitrogen is used as the fluidizing air.

[0040] To prevent the stored pulverized coal from exploding, an explosion-proof gas inlet pipe is installed on the top of the pulverized coal storage silo. Inert gas with an oxygen content of less than 12% is introduced into the silo, and an oxygen measuring point is installed on the top of the silo.

[0041] To improve the reliability of pulverized coal conveying, a silo wall vibrator is installed at the outlet of the pulverized coal storage silo. A level gauge is installed on the silo to monitor the amount of pulverized coal in it.

[0042] For the specific installation of the aforementioned heat tracing devices, oxygen measurement points, silo wall vibrators, level gauges, etc., please refer to the product manual or existing mature technologies.

[0043] Any techniques not mentioned in this invention are based on existing technologies.

[0044] This invention relates to a method and system for flexibly adjusting the output of a high-speed coal mill in a direct-fired pulverizing system. This system enables rapid and precise dynamic matching between the fuel system and the combustion system in the rapid peak shaving of coal-fired power plant boilers. Furthermore, it enables balanced control of the coal powder concentration in each air-coal pipe at the coal mill outlet. The coal powder concentration adjustment has a fast response speed and is easy to control. Moreover, it has a simple structure, small size, small footprint, is easy to modify and lay out on site, is easy to control, and is easy to promote. Attached Figure Description

[0045] Figure 1 This is a schematic diagram of the flexible adjustment system for the output of the high-speed coal mill in the direct-fired pulverizing system of Embodiment 3 of the present invention;

[0046] Figure 2 This is a schematic diagram of the flexible adjustment system for the output of the high-speed coal mill in the direct-fired pulverizing system of Embodiment 4 of the present invention;

[0047] Figure 3 This is a system flowchart of the powder storage bin in Embodiment 11 of the present invention.

[0048] In the diagram, 1 is the raw coal bunker, 2 is the coal feeder, 3 is the coal mill, 4 is the air-coal pipe, 5 is the coal powder storage silo, 501 is the explosion-proof gas interface control valve, 502 is the coal powder storage control valve, 503 is the flow-shielding rib, 504 is the heating device, 505 is the silo wall vibrator, 506 is the fluidizing air inlet pipe, 507 is the fluidizing air control valve, 508 is the oxygen measurement point, 509 is the material level gauge, 6 is the coal powder concentration monitor, 7 is the coal feeder, 8 is the return coal pipe, 9 is the central coal drop pipe, and 10 is the nitrogen generator. Detailed Implementation

[0049] To better understand the present invention, the following embodiments further illustrate the content of the present invention, but the content of the present invention is not limited to the following embodiments.

[0050] The directional terms used in this application, such as "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," and "counterclockwise," are based on the orientation or positional relationship shown in the accompanying drawings or in the usage state, and are only for the convenience of describing this application. They are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as limiting this application.

[0051] Example 1

[0052] like Figure 1 As shown, a method for flexibly adjusting the pulverized coal output of a high-speed coal mill in a direct-fired pulverizing system is described. An external pulverized coal storage silo is installed on the coal mill. When the coal mill's output is excessive and the pulverized coal output exceeds the boiler's fuel demand, the excess pulverized coal is stored in the storage silo. When the coal mill's output is insufficient and the pulverized coal output is less than the boiler's fuel demand, the pulverized coal stored in the storage silo is transported to the central coal drop pipe of the coal mill via cold primary air, allowing it to recirculate inside the coal mill and be redistributed to the air-coal pipes at the coal mill outlet.

[0053] Example 2

[0054] like Figure 2 As shown, based on Example 1, the following improvements were made: To improve the uniformity of pulverized coal concentration in each air-coal pipe at the coal mill outlet, a pulverized coal storage bin was installed on each air-coal pipe at the coal mill outlet. Air-coal pipes with higher pulverized coal concentrations correspond to pulverized coal storage bins with larger storage volumes, while air-coal pipes with lower pulverized coal concentrations correspond to pulverized coal storage bins with smaller storage volumes, thus making the pulverized coal concentration in each air-coal pipe more uniform. In this example, installation ports were reserved on each air-coal pipe at the coal mill outlet, and the pulverized coal storage bins were installed at these ports, along with pulverized coal storage control valves. The pulverized coal concentration in each air-coal pipe at the coal mill outlet was monitored in real time, and the opening of the corresponding pulverized coal storage control valve was adjusted in real time based on the monitored pulverized coal concentration in each air-coal pipe, thus making the pulverized coal concentration in each air-coal pipe more uniform.

[0055] Example 3

[0056] like Figure 1 As shown, a flexible adjustment system for the output of a high-speed coal mill in a direct-fired pulverizing system is installed on the coal mill outlet air-coal duct and includes at least a coal storage bin, a coal feeder, and a return coal pipe.

[0057] The powder storage bin is equipped with an inlet and an outlet. The inlet of the powder storage bin is equipped with a powder storage control valve. The outlet air-powder pipe of the coal mill is equipped with an installation port. The inlet of the powder storage bin is connected to the installation port and intercepts or extracts powdered coal from the air-powder pipe.

[0058] The return powder pipe has two inlet branches: a powder inlet and a conveying air inlet. The conveying air inlet is located upstream of the powder inlet. The inlet of the powder feeder is connected to the outlet of the powder storage bin, and the outlet of the powder feeder is connected to the powder inlet of the return powder pipe. The conveying air inlet of the return powder pipe is connected to the primary cold air, and the outlet of the return powder pipe is connected to the central coal drop pipe of the coal mill.

[0059] When the coal mill output is excessive and the amount of coal powder produced is greater than the boiler fuel demand, the opening of the coal powder storage control valve is adjusted to store the excess coal powder in the coal powder storage bin. The coal powder pipe with a higher coal powder concentration corresponds to the coal powder storage bin with more coal powder, and the coal powder pipe with a lower coal powder concentration corresponds to the coal powder storage bin with less coal powder, so that the coal powder concentration in each coal powder pipe tends to be uniform.

[0060] When the coal mill output is insufficient and the pulverized coal output is less than the boiler fuel demand, the pulverizer is turned on. The pulverizer adds the pulverized coal from the storage bin to the return pulverizer pipe, and then the pulverized coal in the return pulverizer pipe is transported to the central coal drop pipe of the coal mill by the cold primary air. It then enters the coal mill for recirculation and is redistributed to the air-pulverizer pipes at the coal mill outlet, realizing rapid and precise dynamic matching between the fuel system and the combustion system in the rapid peak shaving of the coal-fired power plant boiler.

[0061] The aforementioned control system is small in size, occupies little space, has a simple structure, is easy to modify and deploy on-site, is easy to control, and is easy to promote.

[0062] Example 4

[0063] like Figure 2 As shown, based on Example 3, the following improvements were made: To facilitate the adjustment of pulverized coal concentration in each air-coal pipe at the coal mill outlet, pulverized coal storage bins were installed on each air-coal pipe at the coal mill outlet (the installation method involves reserving installation ports on each air-coal pipe, and then connecting the inlet of each pulverized coal storage bin to the corresponding installation port on the air-coal pipe). The pulverized coal storage bins intercept or extract pulverized coal from their respective air-coal pipes. The return pulverized coal pipe has inlet branches for conveying air and two or more pulverized coal inlets, with the conveying air inlet located upstream of each pulverized coal inlet. The number of pulverized coal inlets, pulverized coal storage bins, and pulverized coal feeders are equal and correspond one-to-one. The inlet of the pulverized coal feeder is connected to the outlet of the corresponding pulverized coal storage bin, and the outlet of the pulverized coal feeder is connected to the corresponding pulverized coal inlet. In this way, the pulverized coal in each pulverized coal storage bin can enter the same return pulverized coal pipe and be sent to the central coal drop pipe by the primary air connected from the conveying air inlet.

[0064] Example 5

[0065] Based on Example 4, the following improvements were made: To facilitate modification, the installation port is located at the bottom of the horizontal section of the air-powder duct, and the powder storage bin is located below the air-powder duct. That is, the powder storage bin is located below the horizontal section of the air-powder duct. The powder storage bin has an inlet at the top and an outlet at the bottom, and the bin has a gradually narrowing structure from the inlet to the outlet.

[0066] Example 6

[0067] Based on Example 5, the following improvements were made: To facilitate installation and control, the powder storage control valve is located at the inlet end face of the powder storage silo, and the powder storage control valve has a multi-blade structure. To facilitate installation and control, the powder storage control valve is composed of two or more adjusting blades spliced ​​together; each adjusting blade is equipped with a rotating shaft; each rotating shaft is driven to rotate by a motor or pneumatic actuator, thereby driving the corresponding adjusting blade to rotate, thus realizing the control of the opening degree of the powder storage control valve.

[0068] Example 7

[0069] Based on Example 6, the following improvements were made: To improve the adjustment efficiency and effect of pulverized coal, each adjustment blade is rectangular, and each rotation axis is parallel to the others; the direction perpendicular to the rotation axis of the adjustment blade is considered the width direction, that is, the direction parallel to the rotation axis of the adjustment blade is considered the length direction. The rotation axis of the adjustment blade is perpendicular to the air-pulverized coal flow direction in the air-pulverized coal pipe (that is, from upstream to downstream). Each adjustment blade has a different width, which increases sequentially along the air-pulverized coal flow direction. This facilitates rapid response in pulverized coal adjustment and is easy to control. For ease of adjustment and control, the rotation axis of each adjustment blade is located at the downstream end of the width direction of the blade, and / or at the middle position of the width direction of the blade, such as... Figure 3 As shown, in this example, the downstream rotating shaft is located at the middle position in the width direction of the adjusting blade, and the remaining rotating shafts are located at the downstream end in the width direction of the adjusting blade; each rotating shaft is synchronously driven to rotate by a motor through a crank-connecting rod mechanism.

[0070] During use, the horizontal position of the adjusting blades is set to zero. When all adjusting blades are in the horizontal position, the inlet of the powder storage chamber is closed. Each adjusting blade is adjustable within the range of 0-90°. When all adjusting blades are at 90°, the opening of the powder storage chamber inlet is at its maximum, and the powder storage speed is the fastest.

[0071] Example 8

[0072] Based on Example 7, the following improvements were made: To further increase the coal powder storage speed, each regulating blade's upstream surface is equipped with a flow-blocking rib plate at a 120° angle (experimentally, it could also be 100°, 150°, etc.) to the regulating blade. In this example, the flow-blocking rib plate is located on the upper side of the rotating shaft, that is, when all regulating blades are at a 90° opening, the flow-blocking rib plate is located above the rotating shaft. To prevent the coal powder stored in the shrinking coal silo from caking, a heating device is installed on the coal powder storage silo, with a heating temperature of 60-100°C.

[0073] Example 9

[0074] Based on Example 8, the following improvements were made: To further prevent pulverized coal stored in the coal silo from caking, a fluidizing air inlet pipe was installed at the bottom of the silo to introduce fluidizing air. In this example, the fluidizing air inlet pipe is connected to the nitrogen outlet of the nitrogen generator via a pipeline, and a fluidizing air control valve is installed on the pipeline. That is, nitrogen is used as the fluidizing air.

[0075] Example 10

[0076] Based on Example 9, the following improvements were made: To prevent the stored pulverized coal from exploding, an explosion-proof gas inlet pipe was installed at the top of the pulverized coal storage silo, and an inert gas with an oxygen content of less than 12% was introduced into the silo. An oxygen measurement point was also installed at the top of the silo. In this example, as... Figure 3 As shown, the pipe connecting the top of the powder storage silo to the air-powder pipe is considered a component of the air-powder pipe, and the explosion-proof gas inlet pipe is located on the air-powder pipe at the top of the powder storage silo. The explosion-proof gas is also nitrogen. The nitrogen generator has two outlet branches: a first outlet and a second outlet. The first outlet is connected to the fluidizing air inlet pipe via a first pipe, which is equipped with a fluidizing air control valve. The second outlet is connected to the explosion-proof gas inlet pipe via a second pipe, which is equipped with an explosion-proof gas interface control valve.

[0077] Example 11

[0078] Based on Example 10, the following improvements were made: To improve the reliability of pulverized coal conveying, a silo wall vibrator was installed at the outlet of the pulverized coal storage silo. To monitor the amount of pulverized coal in the silo, a level gauge was installed on the silo.

[0079] In this example, each powder storage control valve is composed of 6 adjusting blades spliced ​​together. The length of each adjusting blade is 800mm, and the width of each adjusting blade along the powder flow direction is 100mm, 150mm, 200mm, 250mm, 300mm, and 700mm respectively.

[0080] The above scheme was applied to a 1000MW coal-fired power generating unit, which was equipped with 6 medium-speed coal mills, five in operation and one on standby. Two of the coal mills (mill B and mill E) were equipped with a flexible adjustment system for the output of the medium-speed coal mill in the direct-fired pulverizing system. The total coal storage capacity was not less than 5 tons. Through flexible adjustment, the unit's ramp-up rate exceeded 4% Pe / min in the 50%-100% load range. During this period, the temperature and pressure fluctuations of the main steam and reheat steam of the coal-fired boiler were within the allowable range of the operating procedures, and there were no local overheating problems in the water-cooled walls.

[0081] The above-mentioned direct-fired pulverizing systems demonstrate flexible methods and systems for adjusting the output of high-speed coal mills. These systems enable rapid and precise dynamic matching between the fuel system and the combustion system during rapid peak shaving in coal-fired power plant boilers. Furthermore, they allow for balanced control of the coal powder concentration in each air-coal pipe at the coal mill outlet. The coal powder concentration adjustment response is fast and the control is convenient. Moreover, the system is simple in structure, small in size, and occupies little space. It is easy to modify and arrange on-site, convenient to control, and easy to promote.

Claims

1. A method for flexibly adjusting the output of a high-speed coal mill in a direct-fired pulverizing system, characterized in that: An external pulverized coal storage bin is installed on the coal mill. When the coal mill output is excessive and the pulverized coal output exceeds the boiler fuel demand, the excess pulverized coal is stored in the storage bin. When the coal mill output is insufficient and the pulverized coal output is less than the boiler fuel demand, the pulverized coal stored in the storage bin is transported to the central coal drop pipe of the coal mill, so that it enters the coal mill for recirculation and is redistributed to the air and pulverized coal pipes at the coal mill outlet.

2. The method for flexibly adjusting the output of the high-speed coal mill in the direct-fired pulverizing system according to claim 1, characterized in that: A set of pulverized coal storage bins is installed on each air-coal pipe at the outlet of the coal mill. The air-coal pipe with a higher pulverized coal concentration corresponds to a pulverized coal storage bin with more pulverized coal, while the air-coal pipe with a lower pulverized coal concentration corresponds to a pulverized coal storage bin with less pulverized coal, so that the pulverized coal concentration in each air-coal pipe tends to be uniform.

3. The method for flexibly adjusting the output of the high-speed coal mill in the direct-fired pulverizing system according to claim 2, characterized in that: Installation ports are reserved on each air-coal pipe at the outlet of the coal mill. The coal storage bins are installed on the installation ports, and coal storage control valves are installed at the installation ports. The coal powder concentration in each air-coal pipe at the outlet of the coal mill is monitored in real time. The opening of the corresponding coal storage control valve is adjusted in real time according to the coal powder concentration in each air-coal pipe, so that the coal powder concentration in each air-coal pipe tends to be uniform.

4. The method for flexibly adjusting the output of the high-speed coal mill in a direct-fired pulverizing system according to any one of claims 1-3, characterized in that: The pulverized coal stored in the pulverized coal storage bin is transported to the central coal drop pipe of the coal mill by a cold primary air supply.

5. A flexible adjustment system for the output of a high-speed coal mill in a direct-fired pulverizing system, installed on the coal mill outlet air-coal duct, characterized in that: It should include at least a powder storage silo, a powder feeder, and a powder return pipe; The powder storage bin is equipped with an inlet and an outlet. The inlet of the powder storage bin is equipped with a powder storage control valve. The outlet air-powder pipe of the coal mill is equipped with an installation port. The inlet of the powder storage bin is connected to the installation port and intercepts or extracts powdered coal from the air-powder pipe. The return coal pipe has two inlet branches: a powder inlet and a conveying air inlet. The conveying air inlet is located upstream of the powder inlet. The inlet of the feeder is connected to the outlet of the powder storage bin, and the outlet of the feeder is connected to the powder inlet of the return coal pipe. The conveying air inlet of the return coal pipe is connected to the primary air, and the outlet of the return coal pipe is connected to the central coal drop pipe of the coal mill. The coal powder in the powder storage bin is added to the return coal pipe by the feeder, and then the coal powder is conveyed to the central coal drop pipe by the primary air.

6. The flexible adjustment system for the output of the high-speed coal mill in the direct-fired pulverizing system according to claim 5, characterized in that: A pulverized coal storage bin is installed on each air-coal pipe at the outlet of the coal mill. The pulverized coal storage bin intercepts or extracts pulverized coal from its respective air-coal pipe. The return powder pipe has two or more inlet branches: a conveying air inlet and two or more powder inlets, with the conveying air inlet located upstream of each powder inlet. The powder inlets, powder storage bins, and powder feeders are equal in number and correspond one-to-one. The inlet of the powder feeder is connected to the outlet of the corresponding powder storage bin, and the outlet of the powder feeder is connected to the corresponding powder inlet.

7. The flexible adjustment system for the output of the high-speed coal mill in the direct-fired pulverizing system according to claim 5 or 6, characterized in that: The installation port is located at the bottom of the horizontal section of the air-powder duct, and the powder storage bin is located below the air-powder duct. The inlet of the powder storage bin is at the top and the outlet is at the bottom, and the powder storage bin has a structure that gradually narrows from the inlet to the outlet. And / or the powder storage control valve is located on the inlet end face of the powder storage bin, and the powder storage control valve has a multi-blade structure; The powder storage control valve is composed of two or more adjusting blades; each adjusting blade is equipped with a rotating shaft; each rotating shaft is driven to rotate by a motor or pneumatic actuator, which in turn drives the adjusting blade to rotate, thereby controlling the opening degree of the powder storage control valve.

8. The flexible adjustment system for the output of the high-speed coal mill in the direct-fired pulverizing system according to claim 7, characterized in that: Each adjusting blade is rectangular, and each rotating axis is parallel to the other. The direction perpendicular to the axis of rotation of the adjusting blade is regarded as the width direction. The axis of rotation of the adjusting blade is perpendicular to the direction of air and powder flow in the air and powder pipe. Each adjusting blade has a different width, and the width increases sequentially along the direction of air and powder flow. And / or the rotation axis of each adjusting blade is located at the downstream end of the width direction of the adjusting blade, and / or at the middle position of the width direction of the adjusting blade. And / or each regulating blade has a flow-blocking rib plate at an angle of 60-150° to the flow-facing surface of the regulating blade; And / or each rotating shaft is synchronously driven to rotate by a motor or pneumatic actuator through a crank-connecting rod mechanism; And / or the horizontal position of the adjusting blades is zero. When all adjusting blades are in the horizontal position, the inlet of the powder storage bin is closed. Each adjusting blade is adjustable within a range of at least 0-45°.

9. The flexible adjustment system for the output of the high-speed coal mill in the direct-fired pulverizing system according to claim 5 or 6, characterized in that: The powder storage silo is equipped with a heating device with a heating temperature of 60-100℃. The bottom of the powder storage bin is equipped with a fluidizing air inlet pipe, which is connected to the nitrogen outlet of the nitrogen generator through a pipeline, using nitrogen as the fluidizing air. The powder storage silo is equipped with an explosion-proof gas inlet pipe at the top, which fills the powder storage silo with an oxygen content of less than 12% and installs an oxygen measuring point at the top of the powder storage silo. The outlet of the powder storage silo is equipped with a silo wall vibrator; the powder storage silo is equipped with a level gauge.

10. A method for flexibly adjusting the output of a high-speed coal mill in a direct-fired pulverizing system, comprising using the flexible adjustment system for the output of a high-speed coal mill in a direct-fired pulverizing system as described in any one of claims 5-16, characterized in that: When the coal mill output is excessive and the amount of coal powder produced is greater than the boiler fuel demand, the opening of the coal powder storage control valve is adjusted to store the excess coal powder in the coal powder storage bin. The coal powder pipe with a higher coal powder concentration corresponds to the coal powder storage bin with more coal powder, and the coal powder pipe with a lower coal powder concentration corresponds to the coal powder storage bin with less coal powder, so that the coal powder concentration in each coal powder pipe tends to be uniform. When the coal mill output is insufficient and the pulverized coal output is less than the boiler fuel demand, the pulverizer is turned on. The pulverizer adds the pulverized coal from the storage bin to the return pulverizer pipe, and then the pulverized coal in the return pulverizer pipe is transported to the central coal drop pipe of the coal mill by the cold primary air. It then enters the coal mill for recirculation and is redistributed to the air-pulverizer pipes at the coal mill outlet, realizing rapid and precise dynamic matching between the fuel system and the combustion system in the rapid peak shaving of the coal-fired power plant boiler.

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