JPH08224489A - Roller type pulverizer - Google Patents

Abstract

PURPOSE: To provide a roller type pulverizer capable of restraining self-excited vibration and operating it silently by noticing vibration characteristics of the pivot parts and improving the structure. CONSTITUTION: Rigidities of the pivots 9 are made different for every roller supporting structure, and natural frequencies of the supporting structures of each pulverizing roller 4 are made different from each other, thus respective vibrations are canceled with each other and the vibration be greatly reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a roller type crushing device for finely crushing solid fuel such as coal by the motion of a rotating crushing ring and a crushing roller, and particularly to prevent vibration of the roller type crushing device. It is about the structure of the pivot for that purpose.

[0002]

2. Description of the Related Art Even in a coal-fired boiler, low-pollution (low NOx, low unburned matter) combustion and rapid load change (rapid coal supply amount change) operation are carried out, and the pulverizer (mill) also has high performance. It came to be requested.

As one type of mill for finely crushing lumps such as coal, cement raw material or new raw material, a vertical type roller mill equipped with a pulverizing ring and a plurality of pulverizing rollers is used, and recently it has become a representative model. is there.

FIG. 6 shows an outline of the structure of this type of mill. This mill is driven by a motor connected to a speed reducer (gear box) at the lower part of the cylindrical housing 19, and is a disk-shaped crushing ring 12 that rotates at a low speed on a horizontal plane, and its outer peripheral surface in the circumferential direction. It is provided with a plurality of crushing rollers 4 which are rotated by being hydraulically or pressurized by a spring or the like to a position equally divided into two.

The object 1 to be crushed supplied into the cylindrical housing 19 is bitten by the crushing roller 4 on the crushing ring 12 and crushed. The hot air sent in a duct (not shown) is guided to the base of the cylindrical housing 19, and the hot air blows air between the outer peripheral portion of the grinding ring 12 and the inner peripheral portion of the cylindrical housing 19. It is blowing up from throat 14. The crushed powder particles are dried while rising in the cylindrical housing 19 by the hot air blown from the air throat 14.

[0006] The granular material transported to the upper part of the cylindrical housing 19 falls from the coarse one by gravity (primary classification), and the slightly fine granular material passing there is provided on the upper part of the cylindrical housing 19. It is again classified by the cyclone separator or the rotary classifier 20, and is sent to the pulverized coal burner or the fine powder storage bin in the boiler.

The coarse powder having a predetermined particle size or more, which has been sieved by the rotary classifier 20, falls on the crushing ring 12 and is crushed again together with the object to be crushed 1 just supplied into the mill. In this way, the crushing by the crushing roller 4 is repeated. In the figure, 5'is a shaft, 10 is a pressurizing frame, 11 is a pressing force (hydraulic load), 15 is hot air, 16 is a seal ring, 17 is a crushing raw material, 18 is a compressed powder layer, and 21 is a product fine powder discharge. It is a duct.

When a roller type mill is to be operated in a wide area load, the problem in the load cut-down region is abnormal vibration of the mill. This vibration is considered to be a self-excited vibration caused by the collapse of the raw material powder layer below the crushing roller 4 and the sliding of the crushing roller 4. When the object to be crushed 1 is coal, this vibration becomes severe for many types of coal during low load operation.

FIG. 7 is a cross-sectional view showing the structure of a portion supporting a roller of a conventional mill (hereinafter referred to as a roller supporting structure). The crushing roller 4 is supported via a bracket 6 so that a pendulum motion can be performed around a pivot 9 as a spindle.
Bearings 7, 7 ′ are inserted on the shaft 5.
In this roller support structure, the crushing roller 4 has the shaft 5
It is supported in a cantilever manner.

It is considered that the collapse of the powder layer below the crushing roller 4 or the slip between the crushing roller 4 and the powder layer triggers self-excited vibration of the mill.

It has been inferred from the measurement results of the actual machine that this vibration is caused by the vibration mode as shown in FIG. The dotted line in the figure shows the neutral state. In this vibration mode, the bearings 7, 7'supporting the crushing roller 4 and the portion 26 of the shaft 5 (hereinafter referred to as shaft / bearing system) bend, and the portion 27 composed of the pivot 9 and the pivot block 8 (hereinafter referred to as " This is a mode in which the pivot part) is displaced in the radial direction of the crushing ring 12.

From FIG. 8, the shaft /
The rigidity of the bearing system 26 against bending and the pivot portion 2
It can be seen that the rigidity against displacement deformation of 7 (hereinafter referred to as the rigidity of the pivot part) is closely related.

In the conventional mill, as shown in FIG. 9, all the roller supporting structures arranged on the grinding ring 12 of the grinding table 3 are geometrically and materially the same. Therefore,
The bending rigidity of the shaft / bearing system 26 described above and the rigidity of the pivot portion 27 are equal. Therefore, each roller support structure has the same vibration characteristic, and all the grinding rollers 4 sway at the same frequency and vibration mode during self-excited vibration, and as a result, the entire mill vibrates greatly.

FIG. 10 is a diagram showing the frequency distribution of the conventional pivot portion shown in FIG. 9, that is, the mill having the same shape dimensions and materials such as the pivot radius R ₁ and the radius of curvature R ₂ of the pivot block.

In this figure, the horizontal axis represents the mill frequency when the resonance frequency (natural frequency of the conventional roller support structure) is 1, and the vertical axis represents the acceleration when the frequency is 1. This shows an example of the case. As is clear from this figure, there is a clear dominant frequency, indicating that a grown self-excited oscillation is occurring.

In order to suppress such self-excited vibration, it is necessary to improve the structures of the shaft / bearing system 26 and the pivot portion 27. The applicant has already proposed to improve the structure of the shaft / bearing system 26 to prevent the self-excited vibration of the mill. In this proposal, the diameters and lengths of the shafts 5 and 5'are made different for each crushing roller 4, 4 for each support structure, and the rigidity of the shaft / bearing system 26 and hence the natural frequency are changed for each roller support structure. This prevents vibration from occurring.

[0017]

However, in the above-mentioned proposed technique, the shafts 5, 5'having different diameters and lengths are actually used.
In order to design the crushing roller 4 and make the crushing roller 4 suitable for the shafts 5 and 5 ', it is necessary to make different molds for each roller support structure and select bearings 7 and 7'having different sizes. There was room for improvement in terms of cost and manufacturability.

In general, it is difficult to effectively suppress self-excited vibration of the mill by the conventional technique.

It is an object of the present invention to provide a roller type crushing device which pays attention to the vibration characteristic of the pivot part and suppresses self-excited vibration by improving the structure thereof so that it can be operated silently.

[0020]

The above object can be achieved by making the rigidity of the pivot part different for each roller support structure so as to make the natural frequency of each roller support structure different.

[0021]

When all the roller supporting structures in the cylindrical housing vibrate at the same natural frequency, and when all the roller supporting structures vibrate in the same phase, violent self-excited vibration occurs. On the other hand, in each roller support structure, if the natural frequencies are different, the respective vibrations cancel each other out, the dominant component is dispersed, and the vibration is greatly reduced.

[0022]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram for explaining a pivot unit according to the embodiment.

As shown in FIG. 9, the conventional mill has the same geometrical dimensions and materials such as the radius R _{1 of the} pivot 9 and the radius of curvature R ₂ of the pivot block 8 in all roller supporting structures.

On the other hand, as shown in FIG. 1, the present embodiment is characterized in that the radii R ₁ and R ₃ of the pivot 9 and the radii of curvature R ₂ and R ₄ of the pivot block 8 are different for each roller support structure. Thus, the difference in curvature between the pivot block 8 and the pivot 9, that is, the difference in diameter (hereinafter, referred to as the difference in diameter of the pivot portion) is changed, and the rigidity of the pivot portion and thus the natural frequency of each support structure are made different.

Hereinafter, the diameter difference of the pivot portion, the calculation method of the rigidity of the pivot portion, and the relationship between the diameter difference and the natural frequency of the roller support structure will be described in order.

Of the two roller support structures shown in FIG. 1, for example, the diameter difference Δφ of the left pivot part is expressed by the formula (1).
Can be calculated by

Δφ = 2 (R ₂ −R ₁ ) ... (1) The pivot part rigidity k is the hydraulic load W acting on the pivot part.
(2) as a function that is proportional to and is inversely proportional to the diameter difference Δφ of the pivot portion.

K = C (W / Δφ) (2) Here, C is a constant that does not depend on the diameter difference Δφ of the pivot portion or the hydraulic load W. The formula (2) is an empirical formula derived from the measurement result of the rigidity of the actual pivot part.

When the diameter difference Δφ is constant, FIG. 2 shows the result of comparison between the calculated value and the calculated value of the rigidity of the pivot portion by the equation (2). In the figure, the horizontal axis represents the hydraulic load (value of the actual machine rated load is 1), and the vertical axis represents the rigidity of the pivot part with the rigidity of 1 when the hydraulic load is 1.

From the figure, it can be seen that when the hydraulic load is increased, the measured value of the rigidity of the pivot portion becomes large. Similarly, the calculated value also increases with the hydraulic load, and the calculated value is close to the measured value regardless of the magnitude of the hydraulic load. From this, it is understood that the pivot part rigidity can be calculated with practical accuracy by using the equation (2).

FIG. 3 shows the value of the natural frequency of the roller support structure calculated by changing the diameter difference Δφ of the pivot portion.

The diameter difference Δφ of the pivot part, which is the horizontal axis of the figure.
Shows the standard value of the actual machine as 1, and the natural frequency corresponding to the value is taken as 1 and is shown on the vertical axis. In the calculation of the natural frequency, first, the pivot part stiffness k was calculated using the equation (2). In this calculation, the hydraulic load W
Is the rated load value of the actual machine, and the diameter difference Δφ of the pivot part is the standard value of the actual machine.

After the calculation of the rigidity k of the pivot part, the rigidity of the pivot part, the bending rigidity of the shaft and the rigidity of the bearing were expressed by springs, and a model in which the pressing frame, the bracket, and the roller were replaced by mass points was created. The value of the natural frequency shown in FIG. 3 is obtained as a result of performing the eigenvalue analysis using this model.

As shown in FIG. 3, the diameter difference Δ of the pivot portion is shown.
The natural frequency of the roller support structure can be changed by changing φ. Accordingly, in each roller support structure, the natural frequency of each support structure can be changed by changing the diameter difference Δφ of the pivot portion.
It is described below how much the natural frequency of each support structure should be changed to suppress the self-excited vibration of the mill, in other words, how much the diameter difference Δφ of the pivot part should be.

It is generally said that in order to avoid the resonance of the structure, the natural frequency should be shifted from the resonance frequency by about 20%. Based on this idea, as an example of the method for suppressing the self-excited vibration of the mill, the natural frequencies of the roller support structures are made to differ by 20%. Specifically, in the case of a mill having three roller support structures, the natural frequency of each support structure is + 20%, 0%, -20% from the resonance frequency.
I decided to make a mistake. The natural frequencies thus changed will be referred to as the natural frequencies of the support structures 1, 2, and 3, respectively.

FIG. 4 shows the required diameter difference of each pivot portion with respect to the natural frequency of each support structure.

Similar to FIG. 3, this figure shows the horizontal axis representing the diameter difference Δφ of the pivot when the standard value of the actual machine is 1, and the natural frequency corresponding to this value is set to 1 and shown on the vertical axis. is there.

From the figure, in order to realize a natural frequency that is ± 20% different from the resonance frequency, the diameter difference of the pivot part should be ± 4.
It is understood that the difference should be about 0%. The diameter difference of the pivot part in the actual machine is 1/1000 of the pivot diameter.
It is easy to give a diameter difference of about ± 40% to the actual machine pivot part in designing.

FIG. 5 shows the frequency distribution in the embodiment (FIG. 1) according to the present invention. The vertical axis and the horizontal axis in this figure are the same as in FIG.

As described above, since the difference in the diameter of the pivot is different and the natural frequency is different in each roller support structure, the frequencies showing the peaks are finely divided and scattered, and the levels of the peaks are extremely higher than those in FIG. It is getting smaller.

Therefore, it is a characteristic that it is hard to say that there is a so-called prominent component which clearly shows the highest value. In such a form, it is difficult to say that self-excited vibration having a self-amplifying property is generated, and it can be said that the forced vibration is changed to a non-self-amplifying forced vibration. As a result, according to the present invention, the vibration level is significantly reduced, and the self-excited vibration is suppressed.

Instead of changing the shape of the pivot, the material of the pivot or the pivot block may be changed with the shape kept unchanged, the frictional characteristics at the contact surface between the pivot and the pivot block may be changed, or a combination thereof may be used in the above embodiment ( As in FIG. 1), the natural frequency of the roller support structure can be different.

[0043]

As described above, according to the present invention, since the natural frequencies of the roller supporting structures are made different from each other, the respective vibrations cancel each other, so that the superior components are dispersed and the mill itself is dispersed. Excited vibration can be suppressed. This improves the durability of various peripheral devices including the mill itself.

[Brief description of drawings]

FIG. 1 is a structural diagram of a pivot part of a roller type crushing device according to an embodiment of the present invention.

FIG. 2 is a characteristic diagram comparing measured and calculated values of the rigidity of a pivot part.

FIG. 3 is a characteristic diagram showing a relationship between a diameter difference of a pivot part and a natural frequency of a roller support structure.

FIG. 4 is a characteristic diagram showing a diameter difference of a pivot portion, which is necessary to change the natural frequencies of three roller support structures by 20%.

FIG. 5 is a characteristic diagram showing a frequency response spectrum of a mill equipped with a pivot unit according to the present invention.

FIG. 6 is a schematic view of a conventional mill structure.

FIG. 7 is a schematic view of a conventional roller support structure.

FIG. 8 is a schematic view of a roller support structure for explaining a natural vibration mode of the roller support structure measured by an actual machine.

FIG. 9 is a structural diagram of a conventional pivot part.

FIG. 10 is a characteristic diagram showing a frequency response spectrum of a mill equipped with a conventional pivot unit.

[Explanation of symbols]

 3 Grinding table 4 Grinding roller 6 Bracket 8 Pivot block 9 Pivot 10 Pressure frame 12 Grinding ring 26 Shaft / bearing system

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Eiji Murakami Eiji Murakami 3-36 Takaracho, Kure-shi, Hiroshima Babkotsu Hitachi Co., Ltd. Kure Research Institute (72) Hiroaki Kanemoto 6-9 Takaracho, Kure-shi, Hiroshima Babkotsu Hitachi Stock Company Kure Factory

Claims (2)

[Claims] 1. An object to be crushed by arranging crushing rollers on a crushing ring rotatably supported in a housing at predetermined intervals along the rotation direction of the crushing ring and pressing the crushing roller onto the crushing ring. A roller bracket for rotatably supporting a crushing roller for crushing with the crushing ring, and a pressing frame and a roller bracket so that the crushing roller can integrally perform a pendulum motion in the radial direction of the crushing ring. A roller-type crushing device having a pivot interposed between the roller-type crushing device, wherein the rigidity of the pivot is made different between the roller supporting portions. 2. The roller type crushing device according to claim 1, wherein at least one of the diameter of the pivot and the hole diameter of the pivot block is changed to make the rigidity of the pivot different.