JP2716491B2 - Vertical mill - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vertical mill for pulverizing, drying, and classifying coal, cement raw materials and the like, and more particularly to a vertical mill suitable for reducing operating power.

[Conventional technology]

BACKGROUND ART A vertical mill is used, for example, in a pulverized coal production device of a coal-fired boiler that uses pulverized coal as a fuel.

A conventional vertical mill will be described with reference to FIG. At the bottom of the vertical mill, there is a disk-shaped grinding table 4.
Is connected to the gear box 5. The grinding table 4
It is configured to rotate at 20 to 40 rpm via a gear (not shown) in the gear box 5 which is driven to rotate by the motor 61. An annular grinding ring 6 having a concave upper surface is fixed on the outer periphery of the upper surface of the grinding table 4. A plurality of crushing rollers 7 are in contact with the upper surface of the crushing ring 6, and a rotating force is applied by the crushing ring 6 through the object to be crushed. The pressure applied to the pressure frame 8 is adjusted by a pressure cylinder 11 via a spring 9 and a spring frame 10. A pulverizing section includes the pulverizing table 4, the pulverizing ring 6, and the pulverizing roller 7. An object to be ground such as coal is introduced between the grinding ring 6 and the grinding roller 7,
It is crushed and crushed into powder. Above the center of the crushing section,
A coal feed pipe 3 is provided, around which the crushed powder and granules are sorted according to their size, those having a predetermined particle size or less are transferred to a burner, and those not reaching a predetermined particle size are returned to the pulverizing section. A vessel 13 is provided, and a circulation flow is created by the vane 14, and the fine particles and the coarse particles are separated by the centrifugal force generated thereby.

Above the cyclone classifier 13, a coal feed pipe 17 for transferring the finely divided particles to a burner of a boiler is provided.
The pulverizing unit and the cyclone classifier 13 are housed in the cylindrical housing 1. The space between the inner wall of the housing 1 and the outer peripheral surface of the pulverizing unit and the outer peripheral surface of the classifier 13 is used to pulverize the pulverized particles. To form a flow path for transfer. The transfer air is supplied from a throat 12 which is an annular flow path formed by the outer periphery of the granulation table 4 and the inner wall of the housing 1. The throat 12 is normally divided into 36 to 45 equal parts by a blade 20 attached to the housing 1 (see FIG. 9).

 Next, the operation will be described with reference to FIG.

5 supplied to the pulverizing table 4 through the coal feed pipe 3
Coal of about 20 mm is pulverized into pulverized coal by a centrifugal force generated by rotation of the pulverizing table 4 while passing through a gap between the pulverizing ring 6 and the roller 7, and is pulverized into a throat upper part 12 a which is an upper part of the throat 12. The air is blown up by the transfer air A.

Coarse particles among the coal particles blown up upward are separated from the airflow and returned to the grinding table 4 again (primary classification).

The particles having a small particle size rise along the housing 1 together with the air, and flow into the classifier 13 via the vane 14.

A swirling flow of air with the crushed particles is generated inside the classifier 13, and the particles receive centrifugal force, descend while rotating around the inner wall of the classifier 13, and fall on the crushing table 4 through the flapper 15, Re-crushed. On the other hand, fine particles subjected to only a small centrifugal force are discharged out of the system together with air without being separated (secondary classification).

The coal thus supplied into the vertical roller mill is circulated through the mill several times until it reaches a predetermined particle size, and is then taken out of the system as a product. The amount of coal circulating in the mill, that is, the amount of coal passing through the pulverizing section composed of the pulverizing table 4, the pulverizing ring 6, the roller 7, and the like varies depending on the product particle size and the like, but is 5 to 10 times the product amount. Approximately half (3 to 6 times the amount of the product) is returned to the pulverizing section by primary classification. The flow velocity of the air passing through the throat is usually 50m / s
Driving back and forth.

Total pressure loss [Delta] P of the mill represented by a pressure difference between the air inlet holes 2 and the mill outlet 18, the throat differential pressure [Delta] P ₁ which occurs when the throat air A passes at high speed, transported in suspension in the throat upper 12a The coal bed differential pressure ΔP ₂ which is a pressure loss generated by the fluidized bed of particles, and the transport differential pressure ΔP generated when the primary classified fine particles are transported to the classifier 13 by airflow.
₃ and a classifier differential pressure ΔP ₄ which is a pressure loss of the classifier 13 (see FIG. 10). Of these, ΔP ₁ accounts for about 25% of the total, and ΔP ₃ is negligible, 3% of the total
It is about.

[Problems to be solved by the invention]

Conventional vertical mills prevent particles from falling from the throat by maintaining the air A passing through the throat at a high speed, but as a result of examining the particles falling from the throat, the falling of the particles is intermittent. It became clear that there was.
Therefore, the flow velocity of the air passing through each throat (hereinafter referred to as the throat flow velocity), the amount of particles falling from the throat, and the like were basically examined. FIG. 11 shows the results of measuring the flow velocity of each throat while maintaining the flow velocity lower than usual. As shown in FIG. 11, the throat flow rate fluctuates, and the magnitude of the fluctuation is larger in the throat located radially outside near the portion X where the particles enter the roller than in the other throats. Also, comparing the throat velocities with the average throat velocities Vavg, the throat near the biting portion X has the lowest value (see FIG. 11). The lowest value of the throat flow velocity near the biting portion X is less than 1/3 to 1/10 of the average value Vavg,
It became clear that particles dropped intermittently and intensively from the throat near the biting portion. Although the air velocity required to prevent the particles from falling from the throat is several m / s is sufficient, the reason why they are usually operated at a high speed of about 50 m / s is as described above. This is because the flow velocity of the throat near the biting portion X is lower than that of the other throats, and the fluctuation of the flow velocity is large.

The conventional vertical mill has a problem in that a large pressure loss occurs in the throat in order to maintain the throat flow velocity at a high speed, and the operating power cost of a blower that sends air A supplied into the mill is increased. Further, since the throat is also heavily worn, there has been a problem that the life of the throat ring 12 is shortened.

Conventionally, in order to reduce the throat differential pressure, (a) a method of correcting the imbalance of the throat flow velocity (Jikken Sho 61-22674)
No., No. 62-21326, No. 60-186030, No. 58-
116055), (b) a method for improving the shape of the throat (Japanese Patent Application Laid-Open No. 62-83052, Japanese Utility Model Application Laid-Open No. 62-123250), and (c) a method for adjusting the opening area of the throat (Japanese Patent Publication No. 61-39850, Kimiaki Jitsu
62-36521, JP-A-61-50648).

By the way, in the method (a), the fluctuation of the throat flow rate cannot be suppressed, and a sufficient effect cannot be obtained.
The method (b) changes the direction of air flow from the throat, but the amount of particles sent from the pulverizing unit onto the throat is about 5 to 10 times the amount of air, and the particles fall from the throat. Prevention is not enough. The method (c) is substantially the same as the method (a), and the fluctuation of the throat flow velocity cannot be suppressed.

An object of the present invention is to provide a vertical mill capable of reducing the throat flow velocity, reducing the throat differential pressure, reducing power costs, and extending the life of the throat ring.

[Means for solving the problem]

The present invention is a rotating pulverizing table provided at the lower part of the housing, a pulverizing unit including a plurality of pulverizing rollers for pressing and pulverizing the solid material supplied on the pulverizing table against the upper surface of the pulverizing table, The present invention is directed to a vertical mill having a carrier gas inlet formed between an inner wall of a housing and an outer peripheral surface of a crushing table to blow up a carrier gas upward from below the crushing table.

And radially outside of the particle biting portion formed on the upstream side of the grinding table rotation direction of each of the grinding rollers,
From the upstream side to the downstream side in the grinding table rotation direction from the particle biting portion, a fall prevention portion for preventing the solid substance from falling below the grinding table is provided for a predetermined length, and the fall prevention portion and the next fall prevention portion are provided. This is achieved by a first means in which the carrier gas inlet is formed between the first and second parts.

In the first means, the carrier gas inlet portion is formed by a blade which is inclined, and the direction of rotation of the carrier gas and the direction in which the carrier gas is blown up from the lower side of the pulverizing table to the upper side by the inclined blade are changed. This is particularly effective in a configuration that is oriented in substantially the same direction.

Further, the present invention is achieved by a third means in the first means, wherein a particle stagnation preventing member is provided on a radially outer side of a portion where the particles enter the roller.

[Action]

The present inventors, in a vertical mill actually operating,
As a result of repeatedly examining where a large amount of solid material falls at the inlet of the carrier gas,. First, solid particles to be pulverized are inevitably collected in a particle biting portion formed on the upstream side in the rotation direction of the pulverizing table of each pulverizing roller. The solid particles collected in the particle bite have not yet been ground or are insufficiently ground so that the individual particles are heavy; And among the collected particles, particles that do not bite into the biting part, that is, particles that do not reach the biting part,
Also, particles that were once tried to be caught in the bite portion but were pushed out of the bite portion by the pressing of the crushing roller, etc., were blown up by the centrifugal force accompanying the rotation of the crushing table and the action of the pushing out of the crushing roller, and the carrier gas was blown up. It has been found that it falls from the inlet of the carrier gas below the grinding table against the force.

In view of such a phenomenon, the present invention is radially outside of the particle entrapment portion formed on the upstream side in the grinding table rotation direction of each pulverizing roller, and from the upstream side in the grinding table rotation direction than the particle entrapment portion. By providing a predetermined length of the solid substance fall prevention portion toward the downstream side, the fall of the particles can be effectively prevented. In addition, even if the throat flow velocity of the carrier gas is reduced, the fluctuation of the throat flow velocity is small, so that the vertical mill can be operated under the condition that the throat flow velocity is kept low, so that there is little wear of parts in the mill. In addition, the operating power cost of the blower can be further reduced.

(Example of the invention)

Hereinafter, embodiments according to the present invention will be described with reference to the drawings.

FIG. 1 is a diagram showing a schematic configuration of a vertical mill according to the present invention. In this figure, the same parts as those of the conventional example shown in FIG. 8 are denoted by the same reference numerals. In FIG. 1, a plurality of crushing rollers 7 and a crushing ring 6 are provided on the bottom of the housing 1.
And a pulverizing section comprising a pulverizing table 4 and an air inlet for supplying hot air for drying and transporting the pulverized material.

At the top of the housing 1, a cyclone classifier 13 for classifying the transported pulverized material is provided, and a coal feed pipe for transferring the pulverized coal classified by the cyclone classifier 13 to the outside of the system.
17 is connected.

The air inlet portion is provided at three places in a flow path formed by the outer periphery of the crushing table 4 and the inner wall of the housing 1, and each is provided by a throat 12 equally divided by an inclined blade 20. It is configured. In the case of this embodiment, as shown in FIGS. 2 and 3, a blowing direction Y of air A blown upward from above the grinding table 4 by the inclined blade 20 and a rotation direction Z of the grinding table 4
And are almost in the same direction. Therefore, the condition is such that particles to be pulverized are particularly likely to accumulate in the particle entrapment portion X formed on the upstream side of the pulverizing roller 7 in the rotation direction of the pulverizing table.

Therefore, it is radially outside of the particle entrapment portion X of each pulverizing roller 7 (outside the particle entrapment portion X of a virtual line extending from the rotation center O of the pulverizing table 4 to the particle entrapment portion X in FIG. 2). From the upstream side to the downstream side of the particle entrapment part X in the grinding table rotation direction Z from the upstream side to the downstream side (in the range of the arrow of the arc), a predetermined length of a fall prevention part 30 for preventing the particles from falling is provided. The inclined blade 20 is disposed between the section 30 and the adjacent drop prevention section 30.

 Next, the operation will be described.

The coal B supplied to the mill by the coal feed pipe 3 enters a pulverizing section provided at a lower portion of the housing 1, and when passing through a gap between the pulverizing ring 6 and the roller 7 on the pulverizing table 4 in the pulverizing section. Crushed, roller 7 and housing 1
It is sent to the throat upper part 12a surrounded by. On the other hand, the transport air A is supplied to the upper throat 12a via the throat 12, and transports the pulverized coal particles sent to the upper throat 12a. The coarse particles are returned to the pulverizing section again by the primary classification and the secondary classification. The pulverized coal adjusted to an appropriate particle size is transferred from the coal feeding pipe 17 to the outside of the system.

In a conventional mill, a larger amount of particles are carried to the throat 12 near the biting portion of the roller 7 than other throats, so that particles tend to fall from the throat near the biting portion. Therefore, had increased throat differential pressure [Delta] P ₁ is an opening giving unnecessary flow rate into the throat 12 to prevent falling of the particles.

In the present invention, no throat is provided near the biting portion as shown in FIG. Further, as shown in FIG. 3, according to the present invention, the throat flow velocity is averaged for each throat, and the fluctuation of the flow velocity is much smaller than that of the conventional mill shown in FIG. Therefore, as shown in FIG. 4, even if the flow rate of the throat is kept low, the amount of particles falling from the throat is reduced as compared with the conventional case. Accordingly, not only the throat differential pressure ΔP ₁ can be reduced by increasing the opening area of the throat, but also the effect of suppressing wear of the throat portion (air inlet portion) can be obtained.

In the case where pulverized coal or the like accumulates in a portion where there is no throat, causing operation inconvenience of the mill, the accumulation of the pulverized coal or the like is prevented by providing a triangular body retention preventing member 21 as shown in FIG. I do.

Another embodiment of the present invention is shown in FIG. In this embodiment,
In the space of the upper part of the throat 12a, a plurality of members 22 for preventing particle accumulation having inclined upper surfaces are provided beside the crushing roller 7 and the crushing roller, and an air inlet portion is provided below each of the members 22. The air inlet is constituted by a throat 12 equally divided by an inclined blade 20. The effect of this embodiment is that the particles carried to the upper part of the throat 12 by providing the member 22 can be smoothly blown up on the upper surface of the member 22 by the air A introduced from the throat 12. In addition, the stagnation area of particles having a high particle concentration generated in the upper part of the throat 12 is removed, and the coal seam differential pressure ΔP ₂ can be reduced. Further, as shown in FIG. 6, no throat is provided in a portion where the particles easily fall.

Result the resistance of the throat upper 12 has been softened, the variation of the reduction at the same time as the throat velocity of coal layer differential pressure [Delta] P ₂ is further reduced (see Figure 7). Therefore, the operation can be performed with the throat flow velocity further reduced as compared with the example shown in FIG. 3, and the throat differential pressure ΔP ₁ can be further reduced. As a result, in the method of the present invention,
ΔP ₁ and ΔP ₂ can be made lower than before, and a vertical mill that can significantly reduce the mill differential pressure can be provided.

FIG. 12 and FIG. 13 are partial perspective views for explaining the mounting structure of the stay preventing member 12. In the case of Fig. 12,
The retention preventing member 21 is directly mounted on the blade 20. In the case of FIG. 13, a stagnation preventing member 21 is attached to the inner wall of the housing 1.

〔The invention's effect〕

The present invention is configured as described above, and is radially outside of the particle entrapment portion formed on the upstream side of the pulverizing table rotation direction of each pulverizing roller, and is more in the direction of rotation of the pulverizing table than the particle entrapment portion. By providing a predetermined length of the solid substance fall prevention portion from the upstream side to the downstream side, it is possible to effectively prevent the particles from falling. Also, even if the throat flow velocity of the carrier gas is lowered, the throat flow velocity does not fluctuate much, so that the vertical mill can be operated under conditions where the throat flow velocity is kept low, and wear of parts inside the mill is reduced. In addition, the operating power cost of the blower can be reduced.

[Brief description of the drawings]

1 is a schematic view of a vertical mill showing one embodiment of the present invention, FIG. 2 is a cross-sectional view taken along the line II of FIG. 1, and FIG. 3 is a throat flow rate of the vertical mill of the present invention. FIG. 4 is a characteristic diagram showing test results of the vertical mill of the present invention and a conventional vertical mill, FIG. 5 is a development view near the upper part of a throat provided with a deposition preventing member in the present invention, FIG. 6 is a development view of the vicinity of the upper part of the throat when a member for preventing particle retention is provided according to another embodiment,
FIG. 7 is an explanatory view of the throat flow velocity in the embodiment of FIG. 6, and FIG.
Fig. 9 is a schematic diagram of a conventional vertical mill, Fig. 9 is a schematic diagram of a throat used in the conventional vertical mill, Fig. 10 is a diagram for explaining the pressure loss of the mill, and Fig. FIG. 8 is an explanatory view of the throat flow velocity of the conventional vertical mill shown in FIG. 8, and FIGS. 12 and 13 are partial perspective views showing the structure of a deposition preventing member. DESCRIPTION OF SYMBOLS 1 ... Housing, 4 ... Pulverizing table, 6 ... Pulverizing ring, 7 ... Pulverizing roller, 12 ... Throat, 13 ... Classifier, 20 ... Blade, 21,22 ... Particle retention prevention member, Three
0: Fall prevention part, A: Air, B: Coal, O: Rotation center of the crushing table, X: Particle biting part, Y:
Air blowing direction, Z: rotating direction of the crushing table.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Tadashi Hasegawa 6-9 Takaracho, Kure City, Hiroshima Pref. Inside the Kure Factory, Kure Plant Co., Ltd. (72) Inventor Yoshinori Taoka 6-9 Takaracho, Kure City, Hiroshima Pref. Inside the Kure Factory Co., Ltd. (72) Inventor Hiroaki Kanemoto 6-9, Takaracho, Kure City, Hiroshima Pref.

Claims (3)

(57) [Claims] 1. A crushing unit comprising a rotating crushing table provided at a lower portion of a housing, and a plurality of crushing rollers for pressing a solid substance supplied on the crushing table against an upper surface of the crushing table to crush the solid material. A vertical mill having a carrier gas inlet formed between the inner wall of the housing and the outer peripheral surface of the crushing table to blow up the carrier gas upward from below the crushing table; Radially outside the particle biting portion formed on the upstream side in the table rotation direction, from the upstream side to the downstream side in the grinding table rotation direction from the particle biting portion, the solid substance falls down the grinding table below. A vertical stopper provided with a predetermined length, wherein the carrier gas inlet is formed between the stopper and an adjacent stopper. . 2. A crushing table according to claim 1, wherein said carrier gas inlet portion is formed by a sloped blade, and said inclined direction of said carrier gas blows upward from below said crushing table by said inclined blade. A vertical mill, characterized in that the rotation direction of the vertical mill is substantially the same. 3. The vertical mill according to claim 1, wherein a particle retention member is provided radially outside of a portion where the particles are engaged with the roller.