JP2015020088A - Classification method and classification system for coal powder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a classification method and a classification system for coal powder, by which low-dusting coal powder can be obtained with a simple facility, without lowering heating value.SOLUTION: A classification method for coal powder includes the steps of: dropping the coal powder; blowing the air to the coal powder while the coal powder is dropping; and recovering the coal powder according to a dropped position. In the method, coal coarse powder is recovered, which has lower content of powder having a powder diameter of 75 μm or less than the coal powder before dropping. It is preferable that in the dropping step, the coal powder has a horizontal velocity component at the start of the drop, and in the air-blowing step, a direction of the blown air opposes to the horizontal velocity component of the coal powder at the start of the drop. A relative velocity, which is obtained by subtracting the horizontal velocity of the coal powder at the start of the drop from the velocity of the blown air, is preferably be 0.5 m/s or more and 10 m/s or less. A difference of elevation between a position of starting to drop the coal powder and a position of blowing the air to the coal powder is preferably be 10 mm or more and 350 mm or less.

Description

  The present invention relates to a coal powder classification method and classification system.

  It is not preferable from the viewpoint of the working environment and the like that dust is generated due to the scattering of fine powder during the transport of coal powder. Therefore, it is desired to suppress such dust generation as much as possible. For example, although it is possible to collect fine powder by providing a dust collector in the coal powder conveyance path, large facilities such as a suction pipe, a dust collector, and an exhaust tower covering the conveyance path are required. Therefore, in order to easily suppress the dust generation of the coal powder, spraying the coal powder with water is performed in the prior art (see, for example, JP 2011-241050 A).

  As another dust generation suppression means, there is an inertia classification for separating particles of several tens of μm or less, which are the source of dust generation, from coal powder. In this inertia classification, fine powder is separated and removed using, for example, an elbow jet classifier, thereby reducing dust generation of the coal powder.

  However, when watering as described above is performed, the calorific value is reduced due to the adhesion of water to the coal powder, and there is a demerit of reducing the quality of the coal powder. Moreover, since the above-mentioned elbow jet classifier generally has a processing amount of about several t / h, it is not suitable for processing a large amount of coal powder generated in a commercial plant.

JP 2011-241050 A

  The present invention has been made based on the above-described circumstances, and a coal powder classification method capable of obtaining coal powder having low dusting properties with simple equipment without reducing the calorific value of the coal powder. And to provide a classification system.

  The invention made to solve the above problems comprises a step of dropping coal powder, a step of blowing wind in the middle of dropping of the coal powder, and a step of collecting the coal powder according to the dropping position, Is a coal powder classification method for recovering coarse coal powder in which the proportion of powder of 75 μm or less is lower than that of the coal powder before dropping.

  In the coal powder classification method, the coal powder falls to different positions for each particle diameter by blowing wind on the coal powder in the middle of dropping. In other words, fine coal powder with a particle size of 75 μm or less, which is likely to generate dust, flies by the wind and falls far from the wind supply point, so the coal powder is selected and collected at a drop position close to the wind supply point. Thus, it is possible to easily recover the coarse coal powder in which the proportion of the powder having a particle size of 75 μm or less is reduced. As a result, the coal powder classification method can obtain coarse coal powder that is low dusting coal powder with simple equipment without reducing the calorific value of the coal powder.

  In the dropping step, the coal powder has a horizontal speed component at the start of dropping, and in the wind blowing process, the direction of the wind is opposite to the direction of the horizontal speed component at the start of the falling of the coal powder. Good. In this way, in the dropping process, by blowing the wind in the direction opposite to the horizontal velocity component at the start of the coal powder falling, the particles having a large particle diameter that is hardly affected by the wind are approaching the wind supply point. On the other hand, the particles having a small particle diameter fall while moving away from the wind supply point due to the influence of the wind, so that the difference in the drop position for each particle diameter can be further increased. As a result, a coal powder having a low dusting property can be obtained more reliably by the coal powder classification method.

  The relative speed obtained by subtracting the horizontal speed at the start of dropping of the coal powder from the wind speed is preferably 0.5 m / s or more and 10 m / s or less. By making the relative speed within the above range, the difference in the drop position for each particle diameter described above can be further increased, so that the coal powder having a low dusting property can be obtained more reliably by the coal powder classification method. be able to.

  The height difference between the coal powder drop start position and the wind blowing position on the coal powder is preferably 10 mm or more and 350 mm or less. By making the height difference within the above range, it is possible to increase the fluctuation range of the fall position by blowing the wind of the coal powder, so that the coal powder having a low dusting property more reliably by the coal powder classification method. Can be obtained.

  You may repeat the said dropping process, a wind spraying process, and a collection | recovery process in multiple times. By repeating these steps a plurality of times, the proportion of coal powder having a particle diameter of 75 μm or less in the coarse coal powder can be further reduced. As a result, a coal powder having a low dusting property can be obtained more reliably by the coal powder classification method.

  The coal powder classification method may be used for modified low-grade coal powder. Here, “modified low-grade coal” refers to coal obtained by drying and improving the quality of low-grade coal such as lignite and subbituminous coal. Since modified low-grade coal is more brittle than ordinary coal, it is more important to control dust generation, so it is more effective to classify dust by classifying it using the coal powder classification method. Can be reduced.

  Another invention made in order to solve the above-mentioned problems includes a device for dropping coal powder, a device for blowing wind on the coal powder in the middle of dropping, and a device for collecting the coal powder according to the dropping position, This is a coal powder classification system that collects coarse coal powder having a particle diameter of 75 μm or less that is lower than that of the coal powder before dropping.

  As described above, the coal powder classification system can easily collect coarse coal powder in which the proportion of powder having a particle diameter of 75 μm or less is reduced by selecting and collecting coal powder at the dropping position. In other words, the coal powder classification system has a simple configuration, and can obtain coarse coal powder that is low dusting coal powder without reducing the calorific value of the coal powder.

  Here, the “powder having a particle size of 75 μm or less” means coal powder that passes through a sieve having an opening of 75 μm according to JIS Z8801-1 (2006). “Wind speed” means the average speed immediately before the wind hits the falling coal powder. The “wind blowing position” means the highest position in the region where the wind hits the falling coal powder.

  According to the classification method and classification system of coal powder of the present invention, coal powder with low dusting property can be obtained with simple equipment without reducing the calorific value of coal powder.

Schematic explanatory drawing which shows one Embodiment of the classification system of the coal powder of this invention Schematic explanatory drawing which shows the classification system of the coal powder of embodiment different from FIG.

  Hereinafter, embodiments of the coal powder classification method and classification system of the present invention will be described in detail.

  The method for classifying coal powder according to the present invention includes a step of dropping coal powder (falling step), a step of blowing wind in the middle of dropping of the coal powder (wind blowing step), and the coal powder according to a dropping position. A step of collecting (recovery step) is provided, and the coarse coal powder having a particle size of 75 μm or less is lower than that of the coal powder before dropping.

  Moreover, as shown in FIG. 1, the classification system of the coal powder of this invention is the inclination board 1 which is an apparatus which drops coal powder, the air blower 2 which is an apparatus which blows wind to the said coal powder in the middle of dropping, and the said A recovery pan 3 is provided which is a device for recovering coal powder according to the dropping position.

<Coal powder>
It does not specifically limit as coal powder used for this invention, For example, the coal powder which consists of particle | grains whose particle diameter is 10 mm or less can be used. Moreover, although the kind of coal is not specifically limited, this invention can exhibit the effect suitably with respect to the modified low grade coal which dried low quality coal, such as lignite and subbituminous coal, and made it high quality. In other words, modified low-grade coal is more fragile than ordinary coal, so it is more important to suppress dust generation, and it can be generated more effectively by classification using the coal powder classification method. Dust can be reduced.

  The low-grade coal refers to a naturally occurring coal containing 20% by mass or more of moisture. Examples of the low-grade coal include brown coals such as Victoria coal, North Dakota coal, and Belga coal; sub-bituminous coals such as West Banco coal, Vinungan coal, and Saramangau coal.

<Drop process>
In the dropping process, the coal powder is naturally dropped from the inclined plate 1. At this time, the horizontal velocity is applied to the coal powder at the start of dropping according to the inclination angle of the inclined plate 1. For the inclined plate 1, a conveyor or the like that gives the coal powder a horizontal speed can be used in addition to the inclined plate. When using a conveyor, it is not necessary to be inclined, but it may be inclined. Although the coal powder may be dropped at a vertical speed, the classification effect may be insufficient because the time until the coal powder reaches the recovery pan 3 may be shortened. It is preferable to drop.

  The horizontal speed at the start of dropping of the coal powder can be, for example, 0.1 m / s or more and 2 m / s.

  The lower limit of the height h1 from the bottom surface (collection position) of the recovery pan 3 at the coal powder drop start position is preferably 300 mm, and more preferably 500 mm. When the height h1 is less than the lower limit, the coal powder classification effect may be insufficient. On the other hand, the upper limit of the height h1 from the bottom surface of the recovery pan 3 at the coal powder dropping start position is preferably 5000 mm, and more preferably 2000 m. When the height h1 exceeds the above upper limit, the coal powder classification system is increased in size, and when the present invention is carried out outdoors, there is a risk of being easily affected by airflow.

<Air blowing process>
In the wind blowing process, wind is blown by the blower 2 during the fall of the coal powder dropped in the dropping process. The direction of the wind is not particularly limited, but a direction parallel to the horizontal direction is preferable from the viewpoint of enhancing the classification effect. Further, the direction of the wind in the horizontal plane is preferably the same direction as or opposite to the direction of the horizontal speed component at the start of the coal powder fall, and the horizontal speed at the start of the coal powder fall. The direction opposite to the direction of the component is more preferable. By applying the wind to the coal powder that is in the process of falling in such a direction, the difference in the drop position for each particle diameter of the coal powder can be increased, and coal coarse powder with low dusting properties is more reliably recovered. be able to.

  The lower limit of the relative speed obtained by subtracting the horizontal speed at the start of dropping of the coal powder from the wind speed is preferably 0.5 m / s, more preferably 2 m / s, and further preferably 3 m / s. When the relative speed is less than the lower limit, the classification effect may be insufficient. On the other hand, the upper limit of the relative speed is preferably 10 m / s, more preferably 6 m / s, and even more preferably 4 m / s. When the relative speed exceeds the upper limit, coal powder may be scattered more than necessary, making recovery difficult, and the equipment of the coal powder classification system may be increased in order to increase the wind speed. The speed of the wind means an average speed immediately before the wind hits the falling coal powder, and adjusts the output of the blower 2, the horizontal distance from the blower opening of the blower 2 to the start position of the fall of the coal powder, and the like. Can be set.

  The upper limit of the height difference h2 between the coal powder drop start position and the wind blowing position on the coal powder is preferably 350 mm, more preferably 270 mm, and even more preferably 200 mm. When the height difference h2 exceeds the above upper limit, the falling speed of the coal powder when the wind is applied by gravitational acceleration is increased, so that the difference in the falling position is decreased and the classification effect may be insufficient. On the other hand, the lower limit of the height difference h2 between the coal powder fall start position and the wind blowing position on the coal powder is preferably 10 mm, more preferably 20 mm, and even more preferably 30 mm. When the height difference h2 is less than the lower limit, the classification effect may be insufficient due to wind hit before the coal powder is sufficiently diffused.

  The upper limit of the ratio of the height difference h2 to the height h1 from the bottom surface of the recovery pan 3 at the coal powder drop start position is preferably 70%, more preferably 40%, and even more preferably 10%. When the ratio of the height difference h2 to the height h1 exceeds the upper limit, the falling distance of the coal powder after hitting the wind becomes small, so the difference in the falling position becomes small and the classification effect may be insufficient. . On the other hand, the lower limit of the ratio of the height difference h2 to the height h1 is preferably 1%, more preferably 2%, and even more preferably 3%. When the ratio of the height difference h2 with respect to the height h1 is less than the lower limit, the classification effect may be insufficient due to wind hit before the coal powder is sufficiently diffused.

  As the blower 2, a known fan, blower, air compressor, or the like can be used. The size of the blower 2 of the blower 2 can be appropriately designed according to the amount of falling coal powder to be classified. For example, the height (vertical length) is 10 mm or more and 300 mm or less, and the width (horizontal length). Can be 10 mm or more and 3000 mm or less.

  The horizontal distance from the air outlet of the blower 2 to the coal powder drop start position can be, for example, 100 mm or more and 3000 mm or less.

<Recovery process>
In the recovery step, the coal powder that has undergone the dropping step and the wind blowing step is recovered according to the dropping position. Specifically, as shown in FIG. 1, a recovery pan 3 is laid in a region below the coal powder fall start position and on the blower 2 side of the fall start position, and the coal powder dropped on the recovery pan 3 is recovered. By doing so, it is possible to easily and reliably collect the coarse coal powder having a small particle size of 75 μm or less and a low dusting property.

  The collection pan 3 may be composed of a plurality of pans, or may be divided into a plurality of regions by a partition. By configuring the recovery pan in this way, the coal coarse powder can be further recovered by being divided into coarse powder groups having different particle size distributions. The width w of the wind direction (left-right direction in the figure) applied to the coal powder of the recovery pan 3 can be designed according to the classification conditions of the coal powder (wind speed, coal powder fall height, etc.) as appropriate. For example, it can be set to 100 mm or more and 4000 mm or less. Also, the position of the recovery pan 3 relative to the coal powder drop start position can be appropriately designed according to the above classification conditions, and the recovery pan 3 is disposed at a position such that the recovery pan 3 includes the drop start position in plan view. Also good.

  In the coal coarse powder recovered by the coal powder classification method, the proportion of the powder having a particle size of 75 μm or less is reduced with respect to the coal powder before classification (before dropping). In this coarse coal powder, the proportion of the powder having a particle size of 75 μm or less is preferably 1.65% by mass or less, more preferably 1% by mass or less, further preferably 0.5% by mass or less, and 0.2% by mass. The following are particularly preferred: By making the said ratio below the said upper limit, the coal coarse powder which was more excellent in dust generation suppression can be collect | recovered. Moreover, as a difference which subtracted the powder ratio whose particle diameter of the said coal coarse powder is 75 micrometers or less from the powder ratio whose particle diameter of the coal powder before classification is 75 micrometers or less, 0.1 mass% or more is preferable, 0.5 More preferably, it is more preferably 1% by mass or more.

  The coal powder that has not been collected as the coarse coal powder (hereinafter referred to as coal fine powder) is preferably separately collected by fine powder collection means 4 such as a bag filter installed on the leeward side of the collection pan 3. . The coal fine powder collected in this way is used after being subjected to dust generation countermeasures such as watering. A collection pan may be used as the fine powder collection means 4.

  The above dropping step, wind blowing step and recovery step may be repeated a plurality of times. In other words, by supplying the coarse coal recovered in the recovery step to the dropping step again, the ratio of fine particles is further reduced through the air blowing step and the recovery step, and the coarse coal powder that is superior in suppressing dust generation. Can be obtained.

<Advantages>
In the coal powder classification method, the coal powder falls to different positions for each particle diameter by blowing wind on the coal powder in the middle of dropping. In other words, fine coal powder with a particle size of 75 μm or less, which is likely to generate dust, flies by the wind and falls far from the wind supply point, so the coal powder is selected and collected at a drop position close to the wind supply point. Thus, it is possible to easily recover the coarse coal powder in which the proportion of the powder having a particle size of 75 μm or less is reduced. As a result, the coal powder classification method can obtain coarse coal powder that is low dusting coal powder with simple equipment without reducing the calorific value of the coal powder.

<Other embodiments>
The coal powder classification method and classification system of the present invention are not limited to the above embodiment. In the above embodiment, the coal powder is dropped so that the coal powder has a horizontal velocity component at the start of dropping, but the coal powder is dropped so as not to substantially have a horizontal velocity component at the start of dropping. May be. That is, the coal powder may be naturally dropped in a substantially vertical direction, that is, in a direction having an angle with respect to the vertical direction of -5 degrees or more and 5 degrees or less. However, from the viewpoint of improving the classification effect, it is preferable to drop the coal powder so that the coal powder has a velocity component in the horizontal direction at the start of dropping.

  Further, as shown in FIG. 2, a belt conveyor 11 may be used as a dropping device, and a belt conveyor 13 may be used as a collecting device instead of a collecting pan. In this way, classification can be performed during the transfer of the coal powder by dropping the coal powder directly on the belt conveyor and collecting the coarse coal powder. Moreover, the coal powder classification equipment can be simplified or miniaturized.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated more concretely, this invention is not limited to these.

[Examples 1 to 14]
The coal powder was classified using the apparatus shown in FIG. Hereinafter, the used coal powder and each process are explained in detail.

(Coal powder)
Modified brown coal (UBC) was used as the coal powder to be dropped. The modified lignite is one of the modified low-grade coals, which means that the lignite is dried (dehydrated). In this embodiment, modified lignite containing 7.0% by mass of moisture was used.

(Drop process)
2 kg of the above coal powder was naturally dropped in 10 seconds from an inclined plate having a guide on the surface. The said inclination board was installed in the position where the height from the collection pan grounding surface of the lower end of the inclination board surface used as the coal powder fall start position becomes 1000 mm, and the inclination angle with respect to the horizontal surface of an inclination board was 25 degrees. The horizontal speed of the coal powder at the drop start position is about 0.3 m / s.

(Wind blowing process)
Using a blower having an output of 24 W, a blower having a rectangular shape with a height of 350 mm and a width of 850 mm, the wind is blown against the coal powder that is being dropped in a direction opposite to the direction of the velocity component in the horizontal direction of the coal powder at the start of dropping. It was. In each Example, the wind speed was adjusted by the position of the wind turbine switch and the blower. The wind speed was measured using an anemometer (custom “CUSTOM WS-01”). In each example, the start position of the coal powder fall (lower end of the inclined plate surface) and the wind on the coal powder. The height difference h2 from the blowing position and the wind speed were the values shown in Table 1, respectively.

(Recovery process)
As shown in FIG. 1, a recovery pan was laid below the coal powder drop start position and in a region closer to the blower than the drop start position, and the coal powder dropped on the recovery pan was recovered as coal coarse powder. Moreover, the coal powder (coal fine powder) which fell to the leeward side from the collection pan for the coarse coal powder was also collected by the collection pan for the same size coal fine powder. In addition, the recovery pan for the coal coarse powder was laid so that one end thereof was positioned substantially directly below the position where the coal powder started to fall. Moreover, the width | variety of the direction (left-right direction in a figure) of the wind applied to the coal powder of the collection | recovery pan for coarse coal powder was 550 mm.

[Comparative Example 1]
The coal powder used in Examples 1 to 14 was directly recovered as coal coarse powder without classification.

[Evaluation 1]
After measuring the mass of the coal coarse powder and coal fine powder recovered in Examples 1 to 14 and Comparative Example 1, respectively, using a metal sieve having a mesh size of 75 μm in accordance with JIS Z8801-1 (2006), each sieve was used. Divided. The coal powder having passed through the sieve is defined as coal powder having a particle diameter of 75 μm or less, and the ratio of the coal powder having a particle diameter of 75 μm or less in the coal coarse powder and the ratio of the coal powder having a particle diameter of 75 μm or less in the coal fine powder in mass%. Asked. Further, the mass ratio (recovery rate) of the coal coarse powder to the coal powder before classification is W1, the mass ratio of the coal powder having a particle diameter of 75 μm or less in the coal coarse powder is w1, and the particle diameter of the coal fine powder is 75 μm or less. When the mass ratio of the coal powder is w2, the value obtained by {(100−W1) × w2} / {(100−W1) × w2 + W1 × w1} is a coal powder having a particle diameter of 75 μm or less with respect to the coarse coal powder. The removal rate was determined. These results are shown in Table 1. The recovery rate is an indicator of whether or not the available coal powder can be recovered effectively.

  Furthermore, about the coarse coal powder, the drop test was performed in the state before sieving the coal powder having a particle diameter of 75 μm or less, and the dust generation state was visually evaluated. That is, for each of the examples and comparative examples, the dust generation level was evaluated in seven stages from A to H, with A being the least dust generation level and H being the most dust generation level.

  From the results of Table 1, the coarse coal powder obtained in Examples 1 to 14 that was classified from the dropping process, the wind blowing process, and the recovery process was compared with the coal powder of Comparative Example 1 that was not classified. It can be seen that the dust generation is reduced.

[Evaluation 2]
About the said Examples 5-7 and the comparative example 1, the particle size distribution of the collect | recovered coal coarse powder was calculated | required. The particle size distribution is sieved by using a metal sieve conforming to JIS Z8801-1 (2006) with openings of 2.00 mm, 1.00 mm, 500 μm, 250 μm, 150 μm, and 75 μm, respectively, and the sieved coal It calculated | required by measuring the mass of each powder. These results are shown in Table 2.

  From the results shown in Table 2, the coarse coal powder recovered in Examples 5 to 7 is smaller than the comparative example 1 in which classification is not performed, and the proportion of coal powder having a particle size of 75 μm or less is reduced. It turns out that the ratio increased and the coarse coal powder which can be easily used was recovered.

[Examples 15 to 19]
In Examples 15 to 19, the height difference h2 between the coal powder fall start position (the lower end of the inclined plate surface) and the wind blowing position on the coal powder and the wind speed were set to the values shown in Table 3, respectively. Were the same conditions as in Examples 1 to 14, and the dropping process, the wind blowing process and the collecting process were repeated as many times as shown in Table 3 to collect the coarse coal powder. For example, in Example 15, the dropping process, the wind blowing process, and the recovery process were performed again under the same conditions using the coarse coal powder recovered in Example 1. Evaluation similar to the said evaluation 1 was performed with respect to the collect | recovered coal coarse powder. These results are shown in Table 3.

  From the results of Table 3, it can be seen that the dust generation level of the recovered coal coarse powder can be further reduced by repeating the dropping step, the wind blowing step and the recovery step a plurality of times.

[Examples 20 to 28]
Using the apparatus used in Examples 1 to 14 above, coal powder was classified by the wind direction and speed shown in Table 4, and recovered in a recovery pan installed leeward than the coal powder drop start position. The mass ratio of powder having a particle size of 0.5 mm or less was determined. The height difference h2 between the coal powder fall start position (lower end of the inclined plate surface) and the wind blowing position on the coal powder was 225 mm. The results are shown in Table 4. In addition, “head wind” in the table means that the wind was blown in the direction opposite to the direction of the velocity component in the horizontal direction of the coal powder at the start position of fall as in Examples 1 to 14, ”Means that the wind was blown in the same direction as the direction of the speed component, and“ cross wind ”means that the wind was blown in a direction perpendicular to the direction of the speed component in the same horizontal plane. Means.

  As shown in Table 4, Examples 20 to 22 in which the wind was blown in the direction opposite to the direction of the velocity component in the horizontal direction of the coal powder at the falling start position were more effective in classifying the particles than the other examples. I understand that it is expensive.

  According to the classification method and classification system of coal powder of the present invention, coal powder with low dusting property can be obtained with simple equipment without reducing the calorific value of coal powder. Therefore, the coal powder classification method and classification system of the present invention can be suitably used in, for example, facilities that transport and load coal.

DESCRIPTION OF SYMBOLS 1 Inclined board 2 Blower 3 Collection pan 4 Fine powder collection means 11, 13 Belt conveyor

Claims (7)

A step of dropping coal powder,
A step of blowing wind in the middle of the dropping of the coal powder, and a step of collecting the coal powder according to the dropping position, wherein the ratio of the powder having a particle diameter of 75 μm or less is lower than that of the coal powder before dropping. Coal powder classification method for collecting powder. In the dropping step, the coal powder has a horizontal velocity component at the start of dropping,
The method of classifying coal powder according to claim 1, wherein, in the wind blowing step, the direction of the wind opposes the direction of the velocity component in the horizontal direction when the coal powder starts to fall.   The coal powder classification method according to claim 2, wherein a relative speed obtained by subtracting a speed in a horizontal direction at the start of dropping of the coal powder from the wind speed is 0.5 m / s or more and 10 m / s or less.   The method for classifying coal powder according to claim 2 or 3, wherein a difference in height between the position where the coal powder starts to fall and the position where the wind is blown onto the coal powder is 10 mm or more and 350 mm or less.   The coal powder classification method according to any one of claims 1 to 4, wherein the dropping step, the wind blowing step, and the recovery step are repeated a plurality of times.   The coal powder classification method according to any one of claims 1 to 5, wherein the coal powder is a modified low-grade coal powder. Equipment for dropping coal powder,
A device that blows wind onto the coal powder that is in the process of dropping and a device that collects the coal powder according to the position of dropping, the ratio of the powder having a particle diameter of 75 μm or less is lower than that of the coal powder before dropping. Coal powder classification system for collecting powder.

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