A direct-fired pulverizing system and method

Abstract

The present application relates to a kind of direct-fired pulverizing system, comprising: burner, preheater, primary air fan and several groups of mill group;Each mill group includes raw coal bunker, coal feeder, coal mill;Coal mill includes mill bowl, venturi sleeve, pulverized coal distributor;Primary air fan is connected to coal mill by primary air pipe, preheater, and coal mill is provided with several pulverized coal pipes connected to burner;Primary air pipe is provided with isolation door, regulating door and pressure measuring point, temperature measuring point and wind speed measuring point;The raw coal bunker includes cylindrical first component, inverted conical second component and cylindrical third component;Second component side surface and horizontal plane included angle is 60 degrees.

Description

Technical Field

[0001] This invention relates to a direct-blowing milling system, belonging to the field of milling. Background Technology

[0002] A direct-fired pulverizing system refers to the combination of equipment and connecting pipelines required to directly blow raw coal into the furnace as a two-phase gas-powder fluid carrying qualified fine coal powder. A direct-fired pulverizing system includes a raw coal bunker, coal feeder, coal mill, coarse powder separator, fine powder separator, powder storage silo, screw conveyor, powder feeder, powder discharger, blower, and connecting pipelines.

[0003] Material adhesion and consolidation often cause coal blockage in the raw coal bunker. Once the raw coal bunker is blocked, the unit will be forced to reduce output and reduce load, or the boiler combustion will be unstable, resulting in a large amount of oil injection. In severe cases, it will cause the boiler to shut down and the unit to shut down unexpectedly.

[0004] Therefore, the direct-blown pulverizing system needs to be optimized to reduce the risk of material blockage.

[0005] Existing technologies reduce the risk of material blockage by strengthening the pretreatment of raw coal, optimizing airflow, and installing anti-blocking devices. For example, patent CN214494234U, "A device for clearing coal blockage in a raw coal bunker by adding an air cannon", sets up a rotating mechanism to continuously rotate the mixing block and sets up an air cannon to clean the blocked parts inside, thus avoiding blockage. Summary of the Invention

[0006] To overcome the problems existing in the prior art, this invention designs a direct-fired pulverizing system that reduces the risk of coal blockage by adjusting the inclination of the raw coal bunker's contraction opening.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] Technical Solution 1

[0009] A direct-fired pulverizing system includes: a burner, a preheater, a primary air fan, and several sets of mills; each mill set includes a raw coal bunker, a coal feeder, and a coal mill; the coal mill includes a grinding bowl, a Venturi sleeve, and a pulverized coal distributor; the primary air fan is connected to the coal mill via a primary air duct and the preheater, and the coal mill is provided with several pulverized coal pipes connected to the burner; the primary air duct is provided with an isolation door, a regulating door, and pressure measuring points, temperature measuring points, and wind speed measuring points; the raw coal bunker includes a cylindrical first component, an inverted conical second component, and a cylindrical third component; the side of the second component forms a 60-degree angle with the horizontal plane.

[0010] Furthermore, the first component has a diameter of 10 meters, and the third component has a diameter of 40 meters.

[0011] Furthermore, the raw coal bunker is equipped with a heating and dehumidification system.

[0012] Furthermore, the raw coal bunker is equipped with a coal loosening device.

[0013] Furthermore, one of the several sets of grinding units is a standby unit; the non-standby coal feeders are arranged at equal intervals along a circle, and the standby coal feeder is located at the center of the circle; a raw coal bunker is set above each coal feeder, and the coal drop ports of each non-standby coal feeder are equally distributed on the circumference of the same circle; the coal drop port of the standby coal feeder is located at the center of the circle; the belt of the standby coal feeder can rotate in both directions and can rotate with the coal drop port as the center.

[0014] Technical Solution Two

[0015] A direct-blown powder production method includes the following steps:

[0016] Raw coal is transported to each raw coal bunker, which includes a cylindrical first component, an inverted conical second component, and a cylindrical third component; the side of the second component forms a 60-degree angle with the horizontal plane.

[0017] Raw coal enters the coal feeder from each raw coal bunker; the coal feeder delivers the coal to the coal feeder outlet, and then it falls into the grinding bowl of the coal mill through the coal feed pipe and is ground into powder; the primary air delivered by the primary air fan is heated by the preheater and then enters the coal mill tangentially from the air inlet at the bottom of the coal mill, and mixes with the coal powder overflowing from the edge of the grinding bowl to form an air-powder mixture; after multi-stage separation, the coal powder passes through the Venturi sleeve, the coal powder distributor, the coal mill outlet gate and the throttling regulating orifice, and then enters the burner for combustion through the coal powder pipe.

[0018] Furthermore, the first component has a diameter of 10 meters, and the third component has a diameter of 40 meters.

[0019] Furthermore, the raw coal bunker is equipped with a heating and dehumidification system.

[0020] Furthermore, the raw coal bunker is equipped with a coal loosening device.

[0021] Furthermore, the non-standby coal feeders are arranged at equal intervals along a circle, and the standby coal feeder is located at the center of the circle; a raw coal bunker is set above each coal feeder, and the coal drop ports of each non-standby coal feeder are equally distributed on the circumference of the same circle; the coal drop port of the standby coal feeder is located at the center of the circle; the belt of the standby coal feeder can rotate in both directions and can rotate with the coal drop port as the center.

[0022] Compared with the prior art, the present invention has the following features and beneficial effects:

[0023] This invention reduces the risk of coal blockage by adjusting the inclination of the coal bunker's constriction opening. Furthermore, a heating and dehumidification system is added to the coal bunker to keep the coal dry, and coal loosening devices are installed in four directions on the cylindrical surface for use in case of blockage. Using this invention, the length of the inclined surface of the coal bunker can be shortened by 50-65% (taking an angle of 75-85° between the inclined surface and the horizontal as an example), significantly reducing the area prone to coal blockage.

[0024] This invention designs an arrangement scheme for each grinding mill group. The standby coal feeder can not only supply pulverized coal to its own mill group but also to other mills, making the standby mill group's operation more flexible and more efficient in handling accidents such as coal blockage in the raw coal bunker. Furthermore, this design allows for more flexible coal level adjustment control during furnace shutdowns requiring empty coal bunkers. After adopting this invention, the coal feeder's coal interruption handling time (when a standby mill group needs to be started) in the pulverizing system is reduced from 10-15 minutes to 2-5 minutes, improving accident handling efficiency by 50-80%, and resulting in better performance in terms of furnace combustion safety and unit economy. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of a direct-blown powder-making system;

[0026] Figure 2 , 3 This is a schematic diagram of the grinding unit layout;

[0027] Figure 4 This is a schematic diagram of the standby coal feeder;

[0028] Figure 5-6 This is a schematic diagram of the raw coal bunker.

[0029] In the diagram, 1-milling unit; 101-coal conveyor belt; 102-raw coal bunker; 103-coal feeder; 104-coal mill. Detailed Implementation

[0030] The present invention will now be described in more detail with reference to the embodiments.

[0031] Example 1

[0032] like Figure 1-6 As shown, a direct-fired pulverizing system includes a burner (specifically a boiler), a primary air fan, and four sets of mill units. Figure 1 Only two grinding mill groups are shown in the image; each grinding mill group includes a raw coal bunker, a coal feeder, and a coal mill. Each raw coal bunker outlet pipe is equipped with an electric inlet gate valve for the coal feeder. The primary air fan is connected to the coal mill via a primary air duct, and the coal mill has four pulverized coal pipes connected to the burner. The primary air duct is equipped with an isolation valve, a regulating valve, and pressure, temperature, and air velocity measuring points. The sealing air for the grinding mill group is taken from the cold primary air main duct and pressurized by the sealing fan to provide sealing air for the grinding mill group.

[0033] The working process of the direct-blown pulverizing system is as follows:

[0034] Raw coal from the coal yard is conveyed to each raw coal bunker via a conveyor belt. From the bunker, the coal enters the feeder through the chutes and the electric gate at the feeder inlet. The feeder, equipped with automatic speed control, delivers the coal from the chutes to the feeder outlet via the conveyor belt, and then onto the grinding bowl of the pulverizer. Under centrifugal force, the raw coal is ground and compressed into powder in the grinding area, subsequently overflowing along the edge of the grinding bowl. Primary air from the primary blower, heated by the preheater, enters the pulverizer tangentially from the air inlet at the bottom, mixing with the coal powder overflowing from the grinding bowl to form an air-powder mixture. The coal powder is dried by the hot air and carried upwards. Heavier coal particles collide with the separator liner and return to the grinding bowl (first-stage separation), while smaller particles enter the adjustable deflector. Due to collisions with the top shell of the separator and the centrifugal force of the bend, some coarse particles return to the grinding bowl (second-stage separation), while the fine air-powder mixture enters the inner cone. The function of the deflector blades is to create a swirling flow in the gas-powder mixture and perform centrifugal separation (third-stage separation). Coal powder that does not meet the fineness requirements returns to the mill bowl along the inner wall of the inner cone for further grinding; the qualified coal powder passes through the Venturi sleeve, coal powder distributor, mill outlet gates (1-4), and throttling regulating orifice, and then enters the furnace for combustion through coal powder pipes 1-4. Stones, gangue, iron blocks, and other impurities that are difficult to grind in the raw coal fall through the nozzles into the lower part of the mill due to their own weight, and are finally discharged into the slag hopper through the slag discharge gate by the scraper device rotating with the mill bowl, and finally discharged through the slag outlet gate.

[0035] The direct-fired pulverizing system is equipped with four mill sets, one as a standby and the other three in normal operation. The first, second, and third coal feeders are arranged equidistantly in a circle, with an angle of 90 degrees between adjacent feeders; the standby feeder is located at the center of the circle. Raw coal bunkers are located above each feeder. The placement of the first, second, and third feeders is as follows: Figure 2-3 As shown, the coal inlets of each coal feeder are equally distributed on the circumference of the same circle. The standby coal feeder adopts a central coal feeding method, that is, the coal inlet is located at the center of the circle. The belt of the standby coal feeder can rotate in both directions and can rotate around the coal inlet. The circle is the rotation trajectory of the standby coal feeder. The standby coal feeder can transport raw coal to the first, second, and third coal mills. For example, when coal feeder A stops supplying coal, the standby coal feeder D can reverse its belt to supply raw coal to coal mill A. When coal feeders B and C stop supplying coal, the standby coal feeder D rotates to supply raw coal to coal mills B and C, thereby reducing the coal feeder interruption handling time.

[0036] The advancement of this embodiment lies in the fact that the standby mill feeder can not only supply pulverized coal to its own mill but also to other mills, making the standby mill operation more flexible and more efficient in handling accidents such as coal blockage in the raw coal bunker. Furthermore, this design allows for more flexible coal level adjustment and control during shutdowns requiring the empty coal bunker.

[0037] After adopting this invention, the coal feeder interruption accident handling time of the pulverizing system (when the standby mill needs to be started) is reduced from 10-15 minutes to 2-5 minutes, the accident handling efficiency is improved by 50-80%, and the effect is better in terms of furnace combustion safety and unit economy.

[0038] Example 2

[0039] Furthermore, the coal mill is a bowl-type medium-speed coal mill, and its working process is as follows:

[0040] The electric motor drives the grinding bowl to rotate via a vertical gear transmission device. Three independent grinding rollers, each capable of rotating freely around its axis, are evenly distributed above the grinding bowl at 120-degree intervals, maintaining a certain gap with the grinding bowl liner, forming the coal grinding zone. Coal enters the coal mill through the central coal drop pipe at the top of the mill, falling onto the rotating grinding bowl. Under the action of centrifugal force, the raw coal moves to the periphery of the grinding bowl, entering the grinding zone for grinding and being compressed into powder. The ground coal powder finally overflows along the periphery of the grinding bowl.

[0041] Dry air enters the side chamber tangentially from the lower air inlet of the coal mill, reaching the bottom of the grinding bowl. The air flows through the annular gap around the grinding bowl, across the outer diameter of the rotating grinding bowl, and spirals upward through the impeller device that rotates with the grinding bowl, with the airflow tending to be vertical. Smaller, lighter coal powder particles overflowing from the periphery of the grinding bowl are carried upward by the airflow, while heavier, less easily ground foreign matter and pebbles pass through the airflow and fall into the side chamber. Lighter coal dust particles flying above the grinding bowl are scraped off by a scraper device mounted on a rotating skirt cover and undergo a three-stage separation process: The first stage of separation occurs on the grinding bowl plane. Due to the impeller device installed on the separator body, larger particles after the coal lumps are ground on the grinding bowl return to the grinding bowl for further grinding. The finer particles are carried by the rotating airflow to the top cover of the separator for the second stage of separation. Here, an adjustable deflector device causes the coarser particles in the rotating air-powder mixture to lose momentum and fall into the grinding area on the grinding bowl. The finer particles further enter the vertical insertion tube of the Venturi sleeve to achieve the third stage of separation, achieving the required coal dust fineness. The heavier coal dust particles separated in the deflector device and the Venturi sleeve return to the grinding area of ​​the grinding bowl through the inner cone. The cone separates the coal dust from the turbulent area of ​​the coal mill, while the coal dust from the undisturbed area returns to the grinding bowl under the action of gravity. The air-coal mixture is discharged through the Venturi tube and the multi-outlet valve. The air and coal are first concentrated and then expanded to ensure that the air and coal are evenly distributed in each coal tube. The coal tube introduces the air-coal mixture into the furnace for combustion.

[0042] Example 3

[0043] Through research, the technical personnel of this invention discovered that over 90% of raw coal bunker blockages occur within a range of 1-2 meters above the outlet of the lower raw coal bunker. The main reason for this blockage is that during unloading, the material inside the conical hopper expands horizontally and compresses vertically, resulting in a passive plastic stress state. As the outlet size of the bunker decreases, the pressure increases, leading to greater friction between coal particles and between the coal and the cylinder wall. This causes coal particles to agglomerate, significantly increasing their characteristic size, thus causing blockages primarily in this section.

[0044] like Figure 6 As shown, this embodiment provides a raw coal bunker, including a cylindrical first component, an inverted conical second component, and a cylindrical third component; specifically, the diameter of the first component is 10 meters, the diameter of the third component is 40 meters, and the angle between the side of the second component and the horizontal plane is 60 degrees.

[0045] Currently, most raw coal bunkers have a conical surface with an angle greater than 75° to the horizontal. This embodiment reduces the risk of coal blockage by adjusting the inclination of the bunker's contraction opening. A heating and dehumidification system is also installed to keep the raw coal inside dry, and coal loosening devices are installed in four directions on the cylindrical surface for use in case of blockage.

[0046] Calculations show that by adopting this invention, the length of the inclined plane of the raw coal bunker (i.e., the length of the second component) can be shortened by 50-65% (taking an angle of 75-85° between the inclined plane and the horizontal as an example), greatly reducing the area where coal blockage occurs; at the same time, the handling time for coal feeder failure accidents in the pulverizing system (when a backup mill needs to be started) is reduced from 10-15 minutes to 2-5 minutes, and the accident handling efficiency is improved by 50-80%, resulting in better performance in terms of furnace combustion safety and unit economy.

[0047] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should be able to analyze that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A direct-blown pulverizing system, characterized in that, include: The system comprises a burner, a preheater, a primary air fan, and several sets of grinding mills. Each grinding mill set includes a raw coal bunker, a coal feeder, and a coal mill. The coal mill includes a grinding bowl, a Venturi sleeve, and a pulverized coal distributor. The primary air fan is connected to the coal mill via a primary air duct and a preheater. The coal mill is equipped with several pulverized coal pipes connected to the burner. The primary air duct is equipped with an isolation door, a regulating door, and pressure measuring points, temperature measuring points, and wind speed measuring points. The raw coal bunker includes a cylindrical first component, an inverted conical second component, and a cylindrical third component. The side of the second component forms a 60-degree angle with the horizontal plane. One set of the grinding mills is a standby unit. Non-standby coal feeders are arranged at equal intervals along a circle, with the standby coal feeder located at the center of the circle. A raw coal bunker is located above each coal feeder, and the coal inlets of the non-standby coal feeders are evenly distributed on the circumference of the same circle. The coal inlet of the standby coal feeder is located at the center of the circle. The belt of the standby coal feeder can rotate in both directions and can rotate with the coal inlet as the center.

2. The direct-blown pulverizing system according to claim 1, characterized in that, The first component has a diameter of 10 meters, and the third component has a diameter of 40 meters.

3. The direct-blown pulverizing system according to claim 1, characterized in that, The raw coal storage area is equipped with a heating and dehumidification system.

4. The direct-blown pulverizing system according to claim 1, characterized in that, The raw coal bunker is equipped with a coal loosening device.

5. A direct-blowing powder production method, characterized in that, Includes the following steps: Raw coal is transported to each raw coal bunker, which includes a cylindrical first component, an inverted conical second component, and a cylindrical third component; the side of the second component forms a 60-degree angle with the horizontal plane. Raw coal enters the coal feeders from each raw coal bunker. Non-standby coal feeders are arranged equidistantly in a circle, with the standby coal feeder located at the center of the circle. Raw coal bunkers are located above each coal feeder, and the coal inlets of the non-standby coal feeders are evenly distributed along the circumference of the same circle. The coal inlet of the standby coal feeder is located at the center of the circle. The belt conveyor of the standby coal feeder can rotate in both directions and can rotate around the coal inlet. The coal feeders deliver coal to their outlets, which then fall through the feed pipes into the grinding bowl of the coal mill and are ground into powder. Primary air from the primary air fan is heated by the preheater and then tangentially enters the coal mill from the air inlet at the bottom, mixing with the coal powder overflowing from the edge of the grinding bowl to form an air-powder mixture. After multi-stage separation, the coal powder passes through a Venturi sleeve, a coal powder distributor, the coal mill outlet gate, and a throttling regulating orifice, before entering the burner for combustion via the coal powder pipe.

6. The direct-blowing powder-making method according to claim 5, characterized in that, The first component has a diameter of 10 meters, and the third component has a diameter of 40 meters.

7. The direct-blowing powder-making method according to claim 5, characterized in that, The raw coal storage area is equipped with a heating and dehumidification system.

8. The direct-blowing powder-making method according to claim 5, characterized in that, The raw coal bunker is equipped with a coal loosening device.

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