JPH02115052A - Rotary classification type pulverizer - Google Patents

Abstract

PURPOSE:To improve operation efficiencies at high load operations by bending the end of a rotary classification vane toward the rotary direction of a classifier. CONSTITUTION:In a classifier comprising a cylindrical rotary classifier shaft 14 rotating around a raw material feed pipe 2, a rotary classifier rotor 15 mounted on the lower end of the shaft 14, and plate-like rotary classification vanes 16, the ends of which are bent in an arc shape in the direction of rotation, whereby coarse particles are prevented from flowing into spaces between the vanes 16, 16, whereas particles being transferred from the lower region of the rotary classifier are caused to flow into between the vanes 16, 16 from the bent parts of the ends of vanes 16 and pass through the rotary classifier to be collected as products of fine particle. As a result, the generation of a stagnant region of particle caused in an inlet of a rotary classifier can be avoided.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a rotary classification type pulverizer that is equipped with a crushing section and a classification section, and has a rotary classification function in which a plurality of blades are attached to the classification section. .

Even in coal-fired boilers, low-pollution combustion (low N and Ox).

(reduction of unburned content) and rapid load fluctuation operations (changes in the amount of coal fed) were implemented, and as a result, higher performance pulverizers (mills) were required.

A vertical roller mill equipped with a crushing table and multiple rollers is used as a type of crusher to finely crush lumps such as coal, cement raw materials, or new material raw materials.
Recently, it has been solidifying its position as a representative model.

The structure of the vertical roller mill is shown in Figure 12. The vertical roller mill includes a disc-shaped rotary table 55 that is located at the lower part of the mill casing 65 and rotates at low speed on a horizontal plane by a motor having a speed reducer (not shown), and a rotary table 55 that rotates at a low speed on a horizontal surface, and a rotary table 55 that rotates at a low speed on a horizontal surface. A plurality of crushing rollers 59 are provided which are rotated by being pressed into equal parts by hydraulic pressure or a spring. The raw material 50 to be crushed, which is supplied to the center of the rotary table 55 from the raw material supply pipe 51, moves to the outer periphery of the rotary table 55 in a spiral trajectory due to the centrifugal force caused by the rotation of the rotary table 55, and is rotated. It is caught between the crushing race surface 58 of the table 55 and the crushing roller 59 and is crushed.

Hot air 64 sent through a duct (not shown) is guided to the base of the mill casing 65, and this hot air flows between the outer circumference of the rotary table 55 and the inner circumference of the mill casing 65.・It is blowing up from the throat 62.

The powder after pulverization is dried while rising inside the mill casing 65 by the hot air 64 blown up from the air throat 62. The powder and granules transported to the upper part of the mill casing 65 are classified by a cyclone separator or a rotary classifier 68 provided at the upper part of the mill casing 65, and fine powder with a predetermined particle size or less is transported through a product fine powder duct 67 by hot air. In a boiler (not shown), the coal is sent to a pulverized coal burner or to a pulverized storage bin. Coarse powder having a predetermined particle size or more that does not pass through the rotary classifier 68 falls onto the rotary table 55 and is crushed again together with the raw material that has just been fed into the mill. In this way, crushing is repeated by the crushing roller 59.

In addition, 51 in the figure is a raw material supply pipe (center chute),
52 is a rotary classifier shaft, 53 is a rotary classifier rotor,
54 is a rotary classifier blade, 56 is a rotary table shaft,
57 is a rotary table rotation shaft, 60 is a crushing roller shaft, 61 is a crushing roller shaft rotation axis, 63 is an air throat vane, and 66 is a dam ring.

Now, as mentioned above, most vertical mills have an internal circulation closed circuit grinding system with a classification section at the top of the mill, and the performance of not only the grinding section but also the classification section has a strong relationship with the grinding section. has a great influence on the properties of

Recently, a rotary classifier 68 has been increasingly used as a classifier instead of a cyclone separator. The rotary classifier 68 includes a rotary classifier rotor 53 provided at the center shaft of the mill.
A plurality of rotary classification blades 54 are arranged at equal intervals in the circumferential direction, and are rotated by a drive system independent of the rotation drive system of the rotary table 55.

The powder particles blown up by the hot air 64 from the mill grinding section fall back into the grinding section due to the centrifugal force of the airflow generated by the rotating rotary classification blades 54. On the other hand, a zero-rotation classifier 68 has come into widespread use, in which fine powder smaller than a predetermined particle size passes between the rotary classification blades fli 54 and is discharged from a product fine powder duct 67 to the outside of the mill as product fine powder. The main reasons behind this are the following two points.

i) Product fine powder with sharp particle size is now required more than ever before. This requirement is particularly strong in the fields of cement and new materials.

ii) Improved responsiveness to load fluctuations is required. This is mainly for handling load fluctuations in pulverized coal-fired boilers, and is advantageous over cyclone classifiers in that it allows rotation speed control.

The rotary classifier 68 is a rotary classifier rotor 53 equipped with a plurality of plate-shaped rotary classification blades 54, and the rotation speed is adjusted according to the required particle size of the product fine powder, the sharpness of classification, or the rate of change of load. The shape, specifications, rotation speed, etc. of the classification blade 54 are changed to design or to set an operating method.

[Problem to be solved by the invention]

In conventional rotary classification mills, when trying to increase the coal feeding (pulverization) capacity or increase the rotation speed of the rotary classifier 68 to improve classification performance, the coal tends to rise from the crushing section to the classification section. There was a problem in that the airflow containing a high concentration of particles collided with the airflow descending from the classification section to the crushing section and coming back, creating a stagnation area in the mill casing 65 at the position shown by diagonal lines in Figure 12. . When such areas where particles and airflow accumulate, not only does the pressure loss inside the mill increase and the blowing power increases, but also the sufficient fineness required for combustion cannot be obtained, leading to high-load operation of the mill. becomes impossible.

9 and 10 show the structure of a conventional rotary classification mill equipped with radial vanes. FIG. 11 shows a structure with inclined blades, and this type of rotary classifier has also been widely used up to now. FIG. 12 schematically depicts a flow pattern in a conventional rotary classification mill, and particles accumulate at an intermediate position between the crushing section and the classification section.

Some prior art attempts have been made to forcibly separate the upward flow and downward flow within the mill casing 65, but no decisive or sufficient effect has been achieved.

In the prior art Japanese Patent Application Laid-Open No. 62-241559 shown in FIG. 13, the horizontal cross-sectional shape of the rotating blade 315 is in the shape of an abbreviated letter, and the rotating blade pocket is provided at the edge.
This is a device that attempts to reliably return the coarse particles 317 that form 5c and are trapped in the mill to the mill grinding section. This concept is considered to be effective in preventing particles 317 and rotating blades 315 from being re-scattering due to collisions. Note that 316 in the figure is a corner, and 318 is a particle trajectory.

However, providing the rotating blade pockets 315 a and 315 c in a nearly right-angled bent state as in this configuration not only promotes the generation of hydrodynamic airflow resistance but also prevents the particles 317 from staying in the rotating blade area. There is also a tendency to promote That is, the pressure loss in the classification section increases, and the grinding ability of the mill may also decrease due to an excessive increase in returned coal.

An object of the present invention is to provide a rotary classification type pulverizer of air flow transport classification type that eliminates the above-mentioned problems and can obtain high-quality product fine powder even during high-load operation.

[Means to solve the problem]

The problem mentioned above is that the radial tip of the rotating classification blade is
This can be easily achieved by bending it in the direction of rotation of the classifier.

Preferably, a plurality of classification blades are installed on the classifier rotor at equal intervals in the circumferential direction, and the diameter of the tip increases in the radial direction toward the top of the mill. The bending section is approximately 173 degrees of the blade radius from the tip of the classification blade to the direction of the rotation axis of the classifier.
A structure that follows is particularly effective.

[For production]

In the rotary classification blade according to the present invention, since its tip is inclined or bent with respect to the rotation direction, the powder and granules present near the tip of the classification blade are forcibly absorbed into the center of the rotary classifier. becomes possible. As a result, the particle retention area generated within the mill casing can be significantly reduced. The bending part of the classification blade is located in the classification blade whose diameter increases toward the top of the mill (in such a case, as you move from the bottom of the classifier to the top, it begins to classify coarse particles and gradually changes to separation of fine particles. ), located at the tip of the classifier in both the height and radial directions. This makes it possible to prevent coarse particles from entering the classifier blade row as much as possible, and to feed only minute particles into the classifier.

[Embodiments of the invention]

FIG. 1 is an axial sectional view of a rotary classifier-type pulverizer (hereinafter referred to as a mill) embodying the present invention, and FIG. 2 is a parent view from above of the classifier, which is the main part of the present invention.

A raw material 1 to be crushed, such as coal, is fed from above the raw material supply pipe (center chute) 2 on the center axis of the mill, falls onto the rotary table 3, and is attached to the circumference of the rotary table 3 by centrifugal force. It is guided to the grinding ring 6a. An arc-shaped crushing race 6b is carved on the upper surface of the crushing ring 6a, and three crushing rollers 7 that roll on this crushing race 6b while being compressed are rotated in the circumferential direction of the rotary table 3, etc. They are provided at divided positions (120 degrees each). The raw material 1 to be pulverized is pulverized into pulverized coal between the pulverizing race 6b and the pulverizing roller ruff by the compression and plunging action of both machines.

The raw material to be crushed l in the form of granules is heated by hot air 12 blown out from the air throat IO provided on the outer periphery of the rotary table 3.
is aerodynamically transported to the upper part of the mill casing 13. Among these granules, fairly large coarse particles fall onto the rotary table 3 by gravity without reaching the rotary classifier and are re-pulverized (primary classification). The particle group that has passed through the primary classification section reaches the rotary classifier, but relatively coarse particles are driven to the outer periphery of the classifier by aerodynamic centrifugal action.

On the other hand, minute particle groups are collected by the rotary classification blade 16 of the rotary classifier.
In FIG. 1, 4 is a rotary table shaft, and 5 is a rotary table shaft.
8 is a rotary table rotating shaft, 8 is a crushing roller shaft, 9 is a crushing roller rotating shaft, 11 is an air throat vane, and 17 is a dam ring.

The rotary classifier according to the present invention includes a cylindrical rotary classifier shaft 14 that rotates around a raw material supply pipe 2, a rotary classifier rotor 15 attached to the lower end of the shaft 14, and a rotary classifier rotor 15 that is installed equally between these in the circumferential direction. It consists of a plate-shaped rotary classifier 116.

As shown in FIG. 2, the rotary classification blade 16 has a tip portion curved in an arc shape in the rotation direction. This corresponds to a receiving part' for causing the fine powder group staying at the tip of the classifier to flow into the center of the rotary classifier. In this way, we tend to think that structures that curve in the direction of rotation induce resistance;
In fact, the opposite is true; flow resistance due to aerodynamic drag or the presence of particle groups is definitely reduced.

As shown in FIG. 3, the curve starting point of the rotary classification blade 16 is expressed as the ratio of the distance r in the outer circumferential direction from the central axis to the span R from the central axis of the rotary classifier to the tip of the rotary classifier 116. Corresponds to the position /R to 2/3. The starting point of the curve in the height direction of the rotary classification blade 16 is exactly half way from the lower end of the rotary classification blade 16, that is, the point where the relationship h/H=1/2 holds true in FIG.

The reason why the upper part of the rotary classification blade 16 is curved in this manner is to prevent coarse particles from flowing into between the rotary classification blades 16.16. In a rotary classifier, large particles begin to be classified from the bottom of the classifier, and as they move upward, they are gradually classified into minute particles. If the lower ends of the rotary classification blades 16 are curved, even coarse particles will enter between the rotary classification blades 16, 16, which will be extremely counterproductive to the purpose of improving particle size.

FIG. 3 schematically (two-dimensionally) depicts the flow pattern of the airflow between the rotary classification blades 16 as a horizontal sectional view of the classifier from above.

As in the present invention, due to the action of the angle of attack provided at the tip of the rotary classification blade 16, the airflow flows from the tip of the rotary classification blade 16 toward the central axis of the classifier so as to be enclosed. Naturally, it is expected that many of the particles carried by the airflow will also flow between the rotating classification vanes 16.16. Figure 4 shows such a phenomenon as a trajectory of particles from the side of the rotary classifier. It flows between the blades 16, 16, passes through the rotary classifier, and is recovered as a product fine powder. Due to the above action, the particle group is transferred to the rotating classification blade 16. ．． Since the particles flow so as to be enclosed between the particles 16, it is possible to prevent the formation of a particle retention area at the inlet of the rotary classifier. This prevents excessive circulation and over-grinding of particles within the mill, allowing the mill to operate effectively.

Figure 5 shows test results (pilot mill) showing changes in mill differential pressure (pressure loss) with respect to coal feeding load rate, and compares the performance of the rotary classifier of the present invention and the conventional rotary classifier. be.

When compared at the same coal feeding load rate, the mill equipped with the rotary classifier according to the present invention has a lower mill differential pressure.

This tendency was observed over the entire range of coal feeding loads in which the experiment was conducted. In particular, the difference in the mill differential pressure between the two mills increases under conditions of high coal feeding load rate, and from this, the rotary classifier of the present invention is effective under grinding and classification conditions where the inside of the mill is more concentrated. I know what I can do.

FIG. 6 shows the change in mill differential pressure with respect to the classifier rotation speed ratio. In this case, the coal feeding load was assumed to be constant.

In conventional rotary classifiers, when the rotational speed is increased, the amount of particle circulation within the mill increases and the mill differential pressure increases rapidly. On the other hand, in the rotary classifier according to the present invention, due to the effect of the angle of attack of the rotary classification blades 16, no particle retention area is generated, and the mill differential pressure increases little even under classification conditions with a high rotational speed.

Figure 7 shows the product fine particle size (20
The performance of the conventional rotary classifier and the rotary classifier according to the present invention are compared based on changes in the 0 mesh pass survival rate). In general, the fine particle size improves as the classifier rotation speed increases, but at the rotation speed within the test range, the particle size of the classifier of the present invention is higher.As mentioned above, this is due to the extra circulation in the mill. This is thought to be because it was prevented.

FIG. 8 shows the results of a combustion experiment using crushed pulverized coal, demonstrating the effects of the present invention.

It can be seen that under the conditions using the classifier of the present invention, both NOx and unburned content in the ash were lower, and a significant combustion improvement effect was produced. This is because flame holding is strengthened by improving the fine particle size, and a high-temperature combustion region with a low air ratio is stably formed near the burner. In other words, not only has combustion been accelerated and the amount of unburned matter in the ash has been reduced, but also the amount of unburned matter in the ash has been reduced.
This is thought to be due to the active release of intermediate products for reduction to by rapid thermal decomposition.

As described above, the use of the rotary classifier of the present invention not only improves the performance of the mill and improves its operability, but also achieves low-pollution and highly efficient combustion.
Functional improvements will be achieved throughout the thermal power plant.

The pulverizer having a rotary classifier according to the present invention is not limited to the pulverized coal-fired or solid fuel-fired boiler mills such as petroleum coke, which have been taken as examples up to this point, but also the mills for cement finishing, steel slag mills, etc. For special purposes, it can be directly applied to mills for finely pulverizing ceramic raw materials and for producing pigments and talwa. Particularly in the field of cement, where particularly strict quality control and energy-saving operations have recently been promoted, the rotary classification type pulverizer of the present invention is considered to be particularly effective.

〔Effect of the invention〕

The effects of embodying the present invention can be summarized as follows.

(1) The maximum particle size decreases and the amount of fine powder increases. In other words, the particle size of the product fine powder is improved.

(2) Related to the above effect (1), the crushing capacity that satisfies a predetermined particle size increases. This creates a compact mill.

(3) Related to the above effect (1), it becomes possible to finely crush a wide variety of raw materials with significantly different hardness and crushability, and to control the fine powder particle size.

(4) The amount of circulation within the mill is reduced, and the pressure loss within the mill is reduced.

(5) The flow of particles between the classification blades becomes smoother, the residence time of particles near the tips of the blades and the wall surface of the mill housing is shortened, and the amount of wear on equipment materials can be significantly reduced.

As described above, according to the present invention, a mill particularly suitable for improving the fine particle size and energy-saving operation is provided.

[Brief explanation of drawings]

FIG. 1 is a schematic configuration diagram of a rotary classification type pulverizer according to an embodiment of the present invention, and FIG. 2 is a plan view of a rotary classification section of the pulverizer.
FIGS. 3 and 4 are explanatory diagrams showing the mechanism of the rotary classification section, and FIGS. 5 and 6. Figures 7 and 8 are characteristic diagrams, Figures 9 and 10.
The figure shows a plan view and a sectional view of a conventional rotary classifier, Figure 11 is a plan view of another conventional rotary classifier, Figure 12 is a schematic configuration diagram of a pulverizer, and Figure 13 is a conventionally proposed classification FIG. 1... Raw material to be crushed, 3... Rotary table, 7...
Grinding roller, 15...Rotating classifier rotor, 16...
Rotating classification blade. Fig. 1: [] $'t, 7f'i Fig. (0m) No. 1 Figure 11 Figure 10 Figure 13 0 shots 0 shots 6-9 Takaracho, Kure City, Hiroshima Prefecture Babcock Hitachi Co., Ltd. Kure Factory Babcock Hitachi Co., Ltd. 6-9 Takaracho, Kure City, Hiroshima Prefecture Kure factory

Claims (1)

[Claims] The crushed material is crushed in the crushing section installed at the bottom of the mill casing and transported with the upward airflow. A rotating system in which multiple plate-shaped blades whose diameter increases toward the top of the mill are installed radially or tangentially to incline the crushed material. In a rotary classification type pulverizer that uses classification blades to classify coarse powder and fine powder, and collects the fine powder from an outlet formed in the upper part of the mill casing, the tip of the rotary classification blade is moved in the direction of rotation of the classifier. A rotary classification type pulverizer characterized by a bent structure.