JPS63182049A - Air swept ball mill - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to an air swept ball mill, and particularly to an air swept ball mill suitable for improving the particle size of pulverized coal and reducing the power unit consumption.

(Prior art) Conventionally, as boiler fuel or kiln injection fuel, the mesh size of about 200 mesh (equivalent diameter 74 μm) or less is usually about 65 to 8 mm.
Coal that has been dry-pulverized to a fineness of about 5% is used. Such dry pulverizers include ring roller mills equipped with a rotating ring and crushing rollers, as well as ball mills in which crushed material is crushed by the transfer of crushing balls filled in a rotating cylinder. Ball mills as dry-type pulverized coal machines generally employ an air web system in which high-temperature gas such as high-temperature air is introduced into the mill, and the pulverized coal produced at the same time as the coal is dried is conveyed by airflow to the outside of the mill. For such conventional air swept ball mills, for example, COA7! Grinding Technofog
y, FE-2475-25, Dist, Category
y UC-90, Nationa! ! Techni
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USDept, of Commerce.

FIG. 5 is a diagram showing the configuration of such a conventional air swept ball mill.

This device includes a ball mill 4, a coal feeder 2 connected to the inlet side of the ball mill 4 via an inlet trunnion 3 and a chute 6, and an outlet of the ball mill 4 (usually connected via an outlet trunnion 5 and a duct 17). Connected classifier 7
and a fan 8 connected to the cough classifier 7 via a duct 19. Note that 10 is high pressure gas B
The duct 18 that connects the source and the chute 6 is a duct that connects the classifier 7 and the chute 6. In such a configuration, coal A is supplied from the coal feeder 2 to the inlet trunnion 3 of the ball mill 4 via the chute 6. On the other hand, high-temperature gas B is sucked by a fan 8 installed on the downstream side of the mill, passes through a duct 1°, and is sent to a chute 6 where it is classified with coal A supplied from a coal feeder 2 and a classifier 7. It merges with the coarse coal and is passed through the mill inlet trunnion 3 to the ball mill 4.
be introduced within. The coal powder dried and pulverized in the ball mill 4 is carried by high-temperature gas, and is introduced from the mill outlet trunnion 5 through the duct 17 into the classifier 7 .

In the classifier 7, the coal powder is classified by wind, and the coarse coal is returned to the ball mill 4 from the chute 6 via the duct 18. - The pulverized coal passes through the exhaust fan 8 from the duct 19 and is either directly combusted in a combustor (not shown) or recovered as a product using a separator such as a cyclone. Also the 6th
FIG. A is a sectional view of the ball mill showing the movement of the contents inside the ball mill 4. In the figure, the mill is rotated at a predetermined speed in the direction of the arrow. As the mill rotates, the mixture of balls and coal is lifted along the inner wall of the mill to a certain height, and then ejected in the circumferential direction, repeating the motion of free falling or rolling down the packing surface. At this time, the coal is pulverized by impact force, frictional force, etc. by the balls, and at the same time, it is dried by contact with high-temperature air. Furthermore, the particles discharged into the space inside the mill are classified by high-temperature air flowing from the mill inlet to the outlet, and coal particles whose particle size is smaller than the particle size corresponding to the flow velocity and density of the air are transported by air and discharged from the mill. be done. On the other hand, coarse particles fall onto the packed bed and are ground again by repeating the above-mentioned movement. In such an air swept pole mill, the cross-sectional area of the openings of the mill inlet and outlet trunnions 3 and 5 is designed to be large to a certain extent in order to reduce the flow resistance (pressure loss) of gas within the mill. The trunnion inner diameter is usually 25 to 30% of the mill inner diameter (6 to 9% as a cross-sectional area)
). Because the trunnion opening is large, the amount of balls filled in the mill is kept low to prevent balls from accumulating and clogging the trunnion, and the ratio of the apparent volume of the balls to the mill volume is usually less than 25%. It is said that

Another reason why it is necessary to reduce the amount of ball filling is that as the amount of ball filling increases, the amount of coal particles that stay in the mill also increases, and the amount of coal particles that are ejected into the space per unit time is reduced. As a result, the efficiency of contact with air decreases, that is, the efficiency of drying and classification decreases.

FIG. 6B is a cross-sectional view of the mill when the ball filling amount is increased in this way. In the figure, the mill is rotated in the direction of the arrow to pulverize coal, but the ball filling amount is 6th.
Since the amount of coal powder is considerably larger than that shown in Figure A, the amount of coal powder staying in the mill also increases, and the drying and classification efficiency decreases. On the other hand, regarding the diameter of the balls filled in the mill, balls with a large diameter are efficient in grinding large particles, but are inefficient in grinding small particles, so there are usually several types of balls with different diameters. is filled with a mixture of Furthermore, such a pole mill has a critical speed Nc (rpm) at which the balls inside the mill receive centrifugal force due to the rotation of the mill, rotate along the inner wall, and stop falling. ) D: Mill inner diameter (m) d: Ball diameter (m) It is operated at a rotation speed of approximately 70 to 80% of the mill diameter (m).

The ratio L/D of the mill length to the mill inner diameter is 0.
．． It is about 8 to 1.25. The reason for reducing L/D in this way is that, based on the same throughput, a mill with a larger L/D has a smaller cavity area in the cross-sectional area of the mill. It is conceivable that the particles will be carried out of the system and that the pressure loss will increase as described above.

Furthermore, as a known technology of this type, US Patent No. 2620
No. 987 is mentioned. FIG. 7 is a diagram showing the configuration of a two-chamber ball mill used as an air-swept ball mill in this US patent. This device includes a ball mill 4 and an inlet trunnion 3 on the inlet side of the ball mill 4.
a chute 6 connected to the ball mill 4 via an outlet trunnion 5, a fan 8 connected to the outlet side of the ball mill 4 via an outlet trunnion 5, and a classifier 7 connected to the rear stage of the fan 8 via a duct. It mainly consists of

In addition, 20 is a porous partition plate that partitions the inside of the mill into two chambers,
There is a ball with a large diameter in the room on the entrance side, and a ball with a large diameter on the exit side.
Filled with small diameter balls.

In such a configuration, coal A is fed from chute 6 through
is fed into a ball mill 4 via an inlet trunnion 3;
It is crushed first by a ball with a large diameter and then by a ball with a small diameter. The coal powder thus pulverized is sent to a classifier 7 by a fan 8, and is classified in the classifier 7.

Note that this device also uses the Coaf Grindin.
In order to reduce the flow resistance of the gas in the mill, similar to the prior art shown in ``G Technology'', the cross-sectional areas of the inlet and outlet trunnions are designed to be large, each being 15% or more of the cross-sectional area of the mill.

(Problems to be Solved by the Invention) However, the conventional air swept ball mill described above has (1) poor classification efficiency and pulverization efficiency compared to ring roller mills, which are other representative models as pulverizers; There are drawbacks. In other words, the power required for pulverization is approximately 7 to 15 kWh/ of coal for the ring roller mill, while the power required for pulverization is approximately 15 to 15 kWh for the conventional air swept ball mill.
20kw h/ is coal. As shown in Figures 6A and 6B, this is due to the fact that the coal particles inside the mill come into contact with high-temperature air only when they fly out into the space inside the mill, so the contact efficiency between air and coal particles is reduced. This is because the drying efficiency is low and the pulverizability of the coal particles is also poor. Figure 8 shows the hard globe crushability index of coal (
2 is a graph showing an example of the results of investigating the relationship between H, G, I) and the surface moisture of coal particles. Generally, the higher the water content, the lower the crushability.

Another reason for the poor classification efficiency and pulverization efficiency is that if the drying efficiency is poor, coal particles agglomerate among themselves and adhere to the inside of the pulverizer and the balls as the pulverization progresses. As described above, due to poor classification efficiency, fine particles that should normally be carried out from the crushing section by gas stay in the crushing section and are over-pulverized, resulting in wasted energy.

In addition, (2) there is a drawback that the size of the mill becomes larger for the same amount of grinding compared to other dry or wet ball mills. Generally, if the dimensions of the mill are the same, the power to drive the mill is roughly proportional to the amount of balls filled, and the crushing capacity is said to be proportional to the power. Dry ball mills and wet ball mills are often operated with a pole filling amount of 30 to 35%, but the air swept ball mill mentioned above is operated with a pole filling amount of 2%.
Since the amount is suppressed to 5% or less, the driving power cannot be increased, the crushing capacity is also small, and the mill size becomes relatively large.

In addition, (3) Since the pulverized material is transported by air from the mill, those that are not finely reduced in the mill stay near the exit of the mill, increasing the amount of coal particles held in the mill and increasing the coal/ball ratio. A problem arises in that the pulverization efficiency increases and the pulverization efficiency decreases.

To avoid this, a method is generally adopted in which the grinding noise is monitored using a microphone, etc., and when the amount of hold-up increases, the air volume (i.e., flow velocity) is increased to transport coarse particles out of the mill system. The particle size of the pulverized coal as a final product becomes coarse.

Furthermore, (4) there is a problem in scaling up. For example, FIGS. 9A and 9B are diagrams showing cross sections of air swept ball mills with different mill diameters. In these two mills, the pole filling amount is the same and the mill rotation speed is calculated using the formula (I) above. When operating at 70% of the critical speed specified by The number of cycles through the mill is
The larger the mill diameter, the less. That is, the larger the scale, the lower the contact efficiency between the particles and high-temperature air, the lower the drying rate and the classification efficiency of the particles, and the worse the pulverization efficiency becomes.

An object of the present invention is to overcome the drawbacks of the prior art described above and provide a high-performance air swept ball mill.

(Means for solving the problem) The above purpose is to introduce high-temperature gas for drying and airflow conveyance into the mill inlet and the inner wall of the mill, and to introduce other gases into the outlet side of the mill divided into multiple rooms. This is achieved by placing a ball with a larger maximum diameter than the room.

That is, the present invention introduces an air flow conveying medium into a ball mill that is divided into two or more chambers and is filled with balls with a large diameter on the inlet side and balls with a small diameter on the outlet side, thereby drying the crushed material and drying the crushed material. In an air swept ball mill that simultaneously carries out air flow conveyance, the means for supplying the air flow conveyance medium is provided at the feed port of the crushed material and the inner wall of the mill, and the outlet side of the mill is filled with balls having a larger diameter than the inlet side. This is a characteristic feature.

In the present invention, the air flow conveyance medium supply ports provided on the inner wall of the mill are provided in two directions symmetrically with respect to the center axis of the mill, and when one side is exposed from the packed bed due to rotation of the mill, the other is covered with the packed bed. , it is preferred that the pneumatic transport medium is always supplied from within the packed bed. Further, at this time, the amount of air flow conveying medium supplied from the inner wall of the mill is 5 to 20% of the total amount of air flow conveying medium supplied into the mill. Furthermore, the ratio of the length of the straight body of the mill to the inside diameter of the mill is set to 1.5 or more, and a perforated plate is used as a partition plate to partition the inside of the mill, and the volume of the chamber on the exit side is set to 115 to 115 of the total mill volume. 1
/3 is preferable.

(Function) By introducing the high temperature gas for drying and air flow conveyance from the inner wall of the mill, the high temperature gas passes through the packed bed in the ball mill. This increases the contact efficiency between the coal particles and the drying gas, increases the drying rate of the coal particles, improves the pulverizability of the particles, and increases the pulverization efficiency. Further, the pulverized coal in the packed bed is blown directly from the packed bed into the mill internal space, thereby improving classification efficiency, avoiding over-pulverization, and improving pulverization efficiency. Therefore, the ball filling amount in the mill is 25%
It is no longer necessary to suppress the mill diameter to below, and the grinding efficiency does not decrease as the mill diameter increases.

Furthermore, by arranging balls with a larger diameter on the outlet side than on the mill inlet side, particles with poor pulverization properties that are supplied to the mill inlet, survive, and flow to the mill outlet side are crushed by the large diameter balls. Therefore, it is possible to avoid an increase in the hold-up amount due to the accumulation of coarse particles near the mill outlet.

Therefore, the grinding efficiency does not decrease due to an increase in the hold-up amount.

(Example) Next, the present invention will be explained in detail based on examples.

FIG. 1 is a diagram showing a system of an air swift ball mill that is an embodiment of the present invention. This device includes a ball mill 4, a coal feeder 2 connected to the inlet side of the ball mill 4 via an inlet trunnion 3, a bunker 1 disposed upstream of the coal feeder 2, and an outlet of the ball mill 4. A classifier 7 connected to the side via an outlet trunnion 5 and a duct 17
A heat exchanger 9 is attached to the rotary trunnion 3 containing the ball mill 40.
and a fan 8 for blowing air connected via a duct 10
and a fan 12 for blowing air connected to the inner wall of the ball mill 4 via the heat exchanger 9, a duct 14 having a valve 13, and a duct 16 having a valve 15.

Note that 11 is a duct that has a valve 32 and bypasses the heat exchanger 9 to connect the ventilation fan 8 and the duct 1o;
18 is a duct that connects the classifier 7 and the inlet trunnion 3 of the ball mill 4, 19 is a duct that sends out coal particles from the classifier 7, F is a temperature control needle provided in the duct 19, and E is a duct 16 This is a pressure regulator installed in the In such a configuration, coal A, which has been roughly crushed to a diameter of about 10 m or less, is fed from bunker 1 and then transferred to coal feeder 2.
The coal is cut out in a fixed amount and fed into the ball mill 4 along with the coarse granulated coal which is returned to the ball mill 4 from the classifier 7. On the other hand, air B is supplied to the inlet trunnion 3 of the ball mill 4 by the blowing fan 8, but part of it is heated by the heat exchanger 9 and the rest bypasses the heat exchanger 9 and is sent to the duct l-10. After joining, it is fed to the inlet trunnion 3 of the ball mill 4. At this time, the temperature controller F installed in the duct 19 on the outlet side of the classifier 7 controls the temperature of the duct 19.
The opening degree of the valve 32 is adjusted so that the temperature inside the valve 32 is within a certain range. The air C is heated by a heat exchanger 9 by a blowing fan 12, and then introduced into the ball mill 4 from the mill wall through a duct 14 having a valve 13 or a duct 16 having a valve 15. At this time, duct 1
6 detects the pressure inside the duct 16 and opens and closes the valves 13 and 15.
Air C is introduced into the ball mill 4 through one of the ducts 14 or 16. The coal particles dried and pulverized in the ball mill 4 are carried by heated air and sent to a classifier 7 via a duct 17, where they are classified into coarse particles and fine particles. The classified coarse particles are returned to the ball mill 4 via the duct 18, and the fine particles are air-flow conveyed via the duct 19 to a burner or recovery device (not shown).

Here, the ball mill 4 will be explained in more detail. FIG. 2 is a diagram showing the structure of the ball mill 4 used in the embodiment of the present invention shown in FIG. This ball mill 4 includes a mill shell 31 having a liner 25 stretched on the inner wall via a cushioning material 28, a porous partition plate 20 that divides the inside of the ball mill 4 into two chambers, and a mirror plate 24 provided on the inlet side of the mill shell 31. a duct 23 connected to the duct 14 of high-temperature air C by a joint 21 within the inlet trunnion 3; an outlet trunnion 5 provided on the outlet side of the mill shell 31 via an end plate 26; It mainly consists of a duct 27 connected to the duct 16 of high temperature air C by a joint 22 in the outlet trunnion 5, and the duct 23 is connected to the end plate 24.
The duct 27 is introduced into the ball mill 4 along the liner 25 and along the mill wall to the end plate 26 on the mill outlet side. The ball mill 4 is introduced into the ball mill 4, and is arranged along the mill wall between the liners 25 to the end plate 24 on the mill inlet side.

Note that 29 is a support, and 30 is a bearing.Although not shown in the drawings, the portions of the ducts 23 and 27 disposed in the body of the ball mill 4 are provided with a large number of air ejection holes. . Furthermore, each room is divided into two chambers by a porous partition plate 20, and steel balls with different diameters of 20 to 50 meters are placed on the mill entrance side, and steel balls with different diameters of 20 to 70 meters are placed on the mill outlet side. volume of 3
Filled with an amount equivalent to 0% (apparent density of pole 4.68t/n?). The ratio L/D of the length L of the straight body to the mill inner diameter is 2. In such a configuration, the coal A supplied from the coal feeder 2 shown in FIG. and the diameter is 2
After being crushed by a steel ball of 0 to 50 fi, it is introduced into the exit side chamber. The coarse coal remaining without being atomized in the chamber on the inlet side is further crushed by steel balls with a diameter of 20 to 70 mm in the chamber on the outlet side. On the other hand, duct 2
The high-temperature air C ejected from 3 or 27 into the packed bed in the ball mill 4 promotes drying of the coal particles and improves the pulverization properties, and together with the air B introduced into the ball mill 4 via the inlet trunnion 3, the coal particles are pulverized. The granulated coal and a part of the coarse coal are conveyed by air flow to a classifier 7 via an outlet trunnion 5.

Furthermore, FIG. 3 shows the lll-
In Figure 0, which is a sectional view in the direction of the lff line, the duct 2
3 and 27 are arranged symmetrically between the liners 25 stretched on the inner wall of the mill with the center axis of the ball mill as the axis of symmetry. In such a configuration, when the duct 27 is exposed from the packed bed of balls and coal particles due to the rotation of the mill, the air resistance becomes smaller, so the duct 16 (
The air pressure inside the valve 1) decreases, and the pressure regulator E shown in FIG.
5 and open the valve 13, the high temperature air C introduced from the duct 27 into the ball mill 4 is stopped, and the high temperature air C is introduced from the duct 23 into the packed bed. That is, hot air C is always introduced into the mill through the packed bed from a duct located below the packed bed.

In this example, a part of the high temperature air is blown into the packed bed of balls and coal particles through the duct 23 or 27 arranged along the axial direction of the inner wall of the mill, so that the coal particles and the high temperature air are mixed. In order to improve the contact efficiency of (1)
Good drying efficiency improves coal pulverization (see Figure 8)
At the same time, reduction in pulverization efficiency due to adhesion and agglomeration of pulverized coal is eliminated. In addition, (2) the granulated coal in the packed bed is blown up by air and transported by airflow, so there is little energy loss due to over-grinding; and (3) the ball filling amount is 30% or more of the mill volume. This makes it possible to design the mill dimensions to be smaller than that of a conventional air-swept ball mill at the same amount of grinding. Also,(
4) When using Schenylamp equipment, the rotation speed of the mill must be reduced, but by increasing the amount of air blown into the packed bed as the mill size increases, it is possible to prevent the reduction in grinding efficiency due to the decrease in rotation speed. can be covered. Furthermore, (5) since the amount of air flow conveyed medium can be reduced, pressure loss within the mill does not increase. Therefore, the ratio L/D of the length of the straight body to the mill diameter can be increased, and the residence time of particles at the same amount of grinding is
It is longer than a mill with a small L/D, and particles with poor pulverization properties are also easily pulverized.

On the other hand, coal is a heterogeneous substance, and particles (parts) with poor grindability remain unpulverized and migrate from the mill inlet to the mill outlet and stagnate, increasing the amount of hold-up and reducing the grinding efficiency. In this example, the chamber on the mill outlet side is filled with balls with a larger diameter of 20 to 70 mm compared to the 20 to 50 mm balls on the mill inlet side, and particles with poor pulverizability that survived without being crushed were also included. , this 50-7
The particles are crushed by the impact force of the large-diameter balls of the zero crane, and it is possible to avoid a decrease in the crushing efficiency due to an increase in the amount of hold-up.

Here, FIG. 4 shows that using the air swept ball mill of this example, coals with different grindability were
The relationship between the power unit (including fan power) and the hard glove crushability index (H, G, I) when crushed to 0% is shown in comparison with the conventional technology. From this result, this example It can be seen that the power consumption rate can be reduced by about 20% compared to the conventional technology.

In this example, 20 to 50 balls were filled in the inlet side chamber and 20 to 70 balls in the outlet side chamber, but this may generally vary depending on the type and particle size of the crushed material. Although two ducts are used to blow hot air into the packed bed from the inner wall of the mill, it is also possible to use three or more ducts. Furthermore, it is also possible to use high-temperature compressed air as the high-temperature air.

On the other hand, although this embodiment is an apparatus configuration for dry-pulverizing coal containing about 10% water, it can also be applied to dry-pulverizing crushed materials other than coal with a low water content. Generally, most of the energy used for grinding in a ball mill is converted into heat, so a fluid such as room temperature air is used instead of high temperature air for refrigerant and air flow conveyance. By blowing a portion of the material through the inner wall of the mill, the contact efficiency between the crushed material and air is improved, resulting in improved cooling efficiency, classification efficiency, and crushing efficiency. Also, in dry tube mill grinding of cement clinker, where a part of the ground material is conveyed by air flow and the rest flows by gravity and is discharged outside the mill,
Similar effects are expected by applying the present invention.

(Effects of the Invention) According to the present invention, the contact efficiency between the air flow conveying medium and the pulverized material is improved, drying or cooling of the coal powder is promoted, the classification efficiency is improved, and the pulverizing power consumption rate (kw h , /
It is possible to provide an air-swept ball mill that achieves a reduction in t) and an improvement in particle size.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the configuration of an embodiment of the present invention, FIG. 2 is a diagram showing the detailed structure of the ball mill in FIG. 1, and FIG. The directional sectional view, Figure 4, is
An explanatory diagram showing a comparison of power consumption between the present invention and a conventional method. Figure 5 is a diagram showing the configuration of a conventional air swept pole mill. Figures 6A and 6B are diagrams showing the relationship between particles and airflow in the mill. A diagram showing contact efficiency, FIG. 7 is a diagram showing the configuration of a conventional two-chamber ball mill used as an air swept ball mill, and FIG. 8 is an explanatory diagram showing the relationship between hard glove crushability index and surface moisture. Figures 9A and 9B are
An explanatory diagram showing the contact efficiency between particles and airflow in the mill. l... Bunker, 2... Coal feeder, 4... Ball mill, 7... Classifier, 8... Fan, 9... Heat exchanger, 20... Porous partition plate, 14 .16.23.27...
·duct. Agent Takeshi Kawakita Figure 4 Hard glove crushability index HGI (-) Figure 5 6A IM 6B T3 Figure 7

Claims (4)

[Claims] (1) Introducing an air flow conveying medium into a ball mill that is divided into two or more chambers, filled with large diameter balls on the inlet side and small diameter balls on the outlet side, to dry the crushed material and air flow convey the crushed material. At the same time, in the air swept ball mill,
An air-swept ball mill characterized in that the supply means for the air flow conveying medium is provided at the feed port for the crushed material and at the inner wall of the mill, and balls having a larger diameter are filled on the outlet side of the mill than on the inlet side. (2) An air-swept ball mill according to claim 1, characterized in that the ratio L/D of the length L of the mill to the inner diameter D of the mill is 1.5 or more. (3) The air conditioner according to claim 1 or 2, characterized in that a partition plate is provided so that the volume of the chamber on the mill outlet side is 1/5 to 1/3 of the total mill volume. Swept ball mill. (4) In any one of claims 1 to 3, the amount of air flow conveying medium introduced from the inner wall of the mill is
An air swept ball mill characterized in that it is provided with means for adjusting the amount of air flow to 5 to 20% of the total amount of air conveyed medium introduced into the mill.