JP2873026B2 - Ring roller mill for fine grinding - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a roller mill, and more particularly to a ring roller mill for fine pulverization in which the fine particle size of an object to be pulverized is increased and vibration of the mill during pulverization is reduced.

[Conventional technology]

Low pollution combustion (low NOx combustion,
Unburned fuel reduction combustion and rapid load fluctuation operation (coal supply change) have been implemented, and as a result, high performance has also been required for fine mills (mills).

As one type of pulverizer for finely pulverizing aggregates such as coal, cement raw materials or new raw materials, a vertical roller mill having a rotary table and a plurality of rollers has been used. We are consolidating our position.

This type of crusher is driven by a motor having a speed reducer in the lower portion of a cylindrical casing, and divides a disk-shaped rotary table that rotates at a low speed on a horizontal plane and an outer peripheral portion of the upper surface in a circumferential direction. A plurality of crushing rollers are provided which are rotated by being pressed down to a position by hydraulic pressure or a spring or the like. The material to be ground supplied from the supply pipe (chute) to the center of the rotary table moves to the outer periphery along a spiral locus on the table by centrifugal force due to the rotation of the rotary table,
It is crushed by being entrapped between the crush roller and the ring groove-shaped crush race surface provided on the outer peripheral portion of the upper surface of the table. Hot air sent through the duct is guided to the base of the mill casing, and this hot air blows up from an air throat, which is a gap between the outer periphery of the rotary table and the inner periphery of the mill casing. I have. The pulverized powder is dried while rising in the mill casing by hot air blown from an air throat. The coarse particles fall into the upper part of the mill casing by gravity (primary classification), and the fine particles penetrating therethrough are separated by a cyclone separator or a rotary classifier provided on the upper part of the mill casing. Classified again, the fine powder having a predetermined particle size or less is conveyed to the outside by hot air, and sent to a pulverized coal burner or a fine powder storage bin in the boiler. The coarse powder having a predetermined particle size or more that does not pass through the classifier falls on a rotary table and is pulverized again with the raw material just supplied into the mill. Thus, the crushing is repeated by the crushing roller.

The crushing mechanism in such a rigid roller mill is thought to be based on compression and shear between the crushing race surface on the table and the roller. In order to optimize such crushing conditions, various structures of rollers and races have been proposed.

It is also conceivable to increase the pulverizing force by controlling the movement of the granular material on the rotary table.

[Problems to be solved by the invention]

According to the conventional technology, particles that have not passed through the pulverizing section are instantaneously penetrated to the pneumatic transport section, that is, the upper part of the air throat, without being pulverized sufficiently under the pulverizing roller. As a result, the amount of circulation in the mill increases, the pressure loss in the mill increases, and even if the classification performance has a level higher than the standard, there is a problem that the particle size of the product is reduced. .

Further, when the powder layer under the crushing roller becomes thinner, especially under a low load operating condition, an irregular stick-slip phenomenon between the roller and the powder layer is induced, and a self-excited vibration occurs.

In the prior art shown in FIGS. 10 and 11, a guide member 1030 is provided between the pulverizing rollers 1004 so that the pulverized particles are
Although it is intended to prevent the penetration of the raw material into the fuel cell 14 and increase the residence time of the raw material on the rotary table 1003, thereby improving the pulverizing ability, the problem of the prior art has not yet been solved.

An object of the present invention is to solve the above-mentioned problems of the prior art and the prior art, and to provide a ring roller mill for fine pulverization having a high fine particle size of pulverized particles and a wide load variation range.

[Means for solving the problem]

The above-mentioned object is to provide a rotary table that rotates around a central axis below the inside of a mill housing, a grinding ring inserted into an outer peripheral portion on the rotary table and a grinding race formed of an annular groove on the upper surface, In a ring roller mill having a plurality of crushing rollers that roll under pressure and a roller bracket that supports the crushing rotor, the lower end of the roller bracket that supports the crushing roller faces downward from the fine powder generation side of the crushing roller. The present invention is achieved by a ring roller mill for fine pulverization, wherein an extended member is provided on the rotary table, and the extended member is bent toward the center axis of the rotary table.

[Action]

Fine powder generated under the crushing roller moves so as to be pushed out from the crushing race toward the air throat part by the rotation of the crushing roller, but the inner surface of the roller bracket extends as if the tip is bent toward the center of the rotary table. And collide back into the grinding race. In this way, the residence time of the particles to be crushed on the crushing race increases, more compression and crushing are repeated at the lower part of the crushing roller, and the particles once crushed and generated become finer one after another. Go. It has been confirmed by the inventors that the powder is pulverized in the powder layer below the pulverizing roller, and that if the powder layer is strongly compressed, the fine particles become finer. In this way, as a result, the pulverizing ability is improved, and the particle size of the product fine powder carried out of the mill out of the system is increased. When the residence time of the particles on the grinding race is excessively increased due to the mechanism described above, the powder layer under the roller becomes excessively thick, and the roller is lifted, and it is difficult to roll the roller in a healthy state. There is. In order to prevent this, in the present invention, a notch is provided at a predetermined interval in the circumferential direction of the grinding race on the outer circumferential side of the grinding race, that is, on the air throat side, so that fine powder particles are periodically removed therefrom. It is carried out to.

Further, when the powder layer becomes thicker under the roller, the frictional force between the crushing roller and the powder layer increases, so that the stick-slip phenomenon that triggers self-excited vibration hardly occurs, and the slip vibration can be suppressed.

〔Example〕

1A and 2 show the structure of a ring roller mill for fine pulverization according to the present invention. FIG. 1A is a sectional view in the height direction in which the mill is vertically divided along a plane passing through the center axis 4 of the mill, and FIG. 2 is a view from above of a pulverizing section which is a feature of the present invention. Since the basic configuration of the mill according to the present invention is as described in the prior art, the structure of the pulverizing section, which is a characteristic, will be described.

The crushing roller 8 crushes the raw material to be crushed on the crushing race 7 while rotating around the crushing roller rotation shaft 9. In this embodiment, three crushing rollers 8 are provided at equal intervals in the circumferential direction of the rotary table 3 (every 120 °). The raw material 1 to be pulverized is supplied from a raw material supply pipe (center chute) 2 into a mill and from a coarse raw material feed, a primary classification (gravity classification) part, or a secondary classification (centrifugal classification by a rotary classifier). It is a powder layer in which powder and granules that circulate and fall to the crushing section are mixed. The crushing roller 8 has a shaft support portion on the roller bracket 10. This roller bracket
A roller pivot 12 is inserted above the roller 10 and serves as a support shaft of a so-called swing mechanism of the roller. On the upper part of the roller pivot 12, a lower pressure frame 13, a spring
14 to an upper pressing frame 15 are mounted, and the pressing force applied to the crushing roller 8 is generated by moving the tension rod 16 downward to compress and contract the spring 14. The object to be crushed on the crushing race 7 engraved on the upper surface of the crushing ring 6 constituting the ring-shaped groove provided on the outer periphery of the upper surface of the rotating table 3 is rotated by the rotating table 3 together with the lace, but the crushing roller 8 is It is driven to rotate by frictional force (traction) with the crushed material.

Each roller bracket 10 is provided with a plate-like fine powder receiving extension member 11 corresponding to the fine powder generation side of the crushing roller 8, and its tip is rounded so as not to contact the top of the crushing race 7. It is extended in the shape to have. Further, the inside of the extended member 11 for receiving fine powder,
On the fine powder generation side, a wear-resistant coating material 11a for preventing wear is adhered. The extended member 11 for receiving fine powder receives fine powder generated and soared by the crushing roller 8, forcibly returns the crushed powder to the crushing race 7 again, and is repeatedly crushed by the crushing roller 7. As shown in FIG. 3, in the pulverizing section of the roller mill, fine powder is generally generated in the compressed powder layer below the roller (of course, large particles are pulverized at once by the compressive force). Even if the fine particles are once crushed and formed, if they are re-engaged in the crushing roller 8 and compressed, they are split into finer particles. The particle circulation function of the pulverizing unit according to the present invention is based on the concept of the pulverizing mechanism of such a roller mill. In order to increase the amount of particles retained on the grinding race 7, the outer peripheral wall 26 of the grinding ring is configured to be slightly higher than that of the conventional type, that is, to deepen the race. According to such a means, there is a possibility that the particles to be crushed become too saturated on the crushing race 7 so that the raw material to be crushed is in a so-called saturated state and the crushing section is blocked. As shown in FIG. 2, a notch 27 in the outer peripheral wall of the grinding ring is provided with a notch 27 in the outer peripheral wall of the grinding ring 6 in order to send the fine powder sufficiently fine to a certain degree to the pneumatic transport section of the mill. Six places are provided at equal intervals in the direction. In this notch, the height of the ring outer peripheral wall is about half of that of the other parts. The fine powder, which has been pulverized to become considerably fine, moves to the outer peripheral side of the pulverizing ring so as to be extruded from under the pulverizing roller 8 and sticks to the outer peripheral wall of the pulverizing ring. From the powder layer composed of such fine particles, the powder is sequentially sent out to the air flow transport section of the mill, that is, onto the air throat 19.

In the present embodiment, the notch 27 of the outer peripheral wall of the ring is the same as the outer peripheral wall 26 of the pulverized ring without the notch 27 in FIG.
Further, as shown in (ii), a portion in which the notch 27 is cut in the outer peripheral wall 26 of the crushing ring is provided at six locations at equal intervals in the circumferential direction of the crushing ring 6. Cutout
The circumferential length of the opening 27 is the same as the length of the other portion, that is, the portion without the notch. It should be noted that the crushing race 7 is used for reasons such as easy vibration due to the nature of the raw material.
If it is desired to make the powder layer as thick as possible, the portion (ii) where the notch 27 is cut may be relatively reduced. FIG. 1A shows a perspective view of a roller bracket according to the present invention. From this drawing, it is easy to understand the configuration of the roller bracket.

FIGS. 4A and 4B schematically show the phenomenon of the pulverizing part of the ring roller mill for fine pulverization according to the present invention. FIG.
This shows a state in which a relatively thick powder layer is formed under the pulverizing roller by the particle recirculation or stagnation action of the fine powder receiving extension member. This sketch-like action leads to the production of finer particles in the pulverized layer (I) which is strongly compressed under the rollers or on the race. FIG. 4B shows a state in which the fine particles (II) are discharged from the notch 27 on the outer peripheral wall of the ring and a thinner powder layer is formed under the crushing roller 8 than in the case of FIG. 4A. At the time of grinding, the state of FIG. 4A is changed to the state of FIG.
By periodically repeating the movement from the state of the figure to the state of FIG. 4A, much finer particles are produced than in a conventional mill. Although the drawing is exaggerated in this figure, the change in the thickness of the powder layer below the crushing roller 8 is not so large and does not become a factor for generating the vibration of the mill.

FIG. 5 summarizes the pulverization characteristics in relation to the fineness of the fine powder (200 mesh pass is used as the basis of the particle size) with respect to the amount of coal supplied, and compares the performance of the mill according to the present invention with that of the conventional mill. Both the vertical and horizontal axes are expressed relative to each other based on the amount of coal supplied and the particle size of the fine powder under the standard conditions of the conventional mill. Generally, the particle size decreases with an increase in the amount of coal supplied, but the mill according to the present invention has a higher particle size in the range of the total amount of coal supplied in the experiment. This is, as described above, by the action of the fine powder receiving engraving member 11 according to the present invention.
The amount of staying particles on the pulverizing section, that is, the pulverizing race 7, increases,
It is considered that many fine particles were generated by repeatedly crushing the particles. The method of increasing the amount of particles in the pulverizing portion, that is, the thickness of the powder layer under the pulverizing roller 8 by the fine powder receiving extension member 11 is also effective particularly in suppressing vibration in a low load zone. FIG. 6 shows a change of the dimensionless vibration displacement with respect to the dimensionless coal seam pressure difference (coal seam pressure difference = mill pressure difference−throat pressure difference). The coal seam pressure difference or vibration displacement is dimensionless based on the value of standard coal feeding conditions in a conventional mill. In a conventional mill, severe vibration occurs under conditions of low coal seam differential pressure, that is, pulverization conditions with little coal hold-up in the mill, and vibration displacement increases extremely. However, it can be seen that in the mill according to the present invention, the vibration was well suppressed to the condition that the coal seam differential pressure in the mill became considerably low. This is on crushing race 7,
Alternatively, it is expected that the powder layer below the crushing roller 8 is thick and the roller has become difficult to slip on the powder layer. Incidentally, the vibration of the roller mill is considered to be caused by unstable sliding vibration (stick-slip phenomenon) in which the roller repeatedly slides and rotates on the thinned powder layer.

Comparison of the combustion characteristics of experiments in which the pulverized coal produced by the mill according to the present invention (FIGS. 1A and 2) and the conventional mill (FIGS. 8 and 9) were burned under almost the same conditions. did.
FIG. 7 shows the relationship between the NOx concentration in the exhaust gas and the unburned portion in the fly ash arranged in a map. Both the NOx concentration and the unburned ash content are expressed as relative values based on the measured values during combustion of pulverized coal produced by a conventional mill. When the unburned ash content is compared at the same level, it can be seen that the NOx concentration is lower when the pulverized coal produced by the mill according to the present invention is burned. In this experiment, the low
The use of a NOx burner has made it more effective in reducing NOx. Burner stable low air ratio combustion zone at a high temperature in the vicinity is formed of the NO in the flame to produced many intermediate products for the reduction to N _2, resulting in the combustion exhaust gas
This is probably because the NOx concentration decreased. In order to exert such effects more strongly, it is necessary to significantly improve the flame holding properties of the burner. For the above reasons, it can be seen that finer grinding with the mill according to the present invention is effective for low-pollution combustion or high-efficiency combustion of coal.

The mill according to the present invention is not limited to a pulverized coal-fired boiler or a mill for a solid fuel-fired boiler such as petroleum coke, which has been described above as an example, but also a cement finishing mill, a steel slag crushing mill, or a blast furnace. The present invention can also be applied to a fine grinding mill for a blow burner.

Particularly in the field of cement, recently, particularly strict quality control has been performed.

In order to improve the strength of the product cement, a fine powder having a wide particle size distribution with a large amount of fine powder while reducing coarse particles is required. Since various types of slag are actively used as a raw material for cement, the crushability of calcined cement clinkers is also diversifying. Therefore, managing product granularity is becoming more difficult and more important than before. In addition, by considering contamination (contamination of impurities), application to the production of ultrafine powders of new materials and chemical products can be considered.

〔The invention's effect〕

According to the present invention, the residence time of the particles to be pulverized in the pulverizing section is increased, the particle size of the product fine powder is improved, and the thickness of the powder layer under the pulverizing roller is increased, so that the sliding vibration of the roller can be suppressed. . As a result, the minimum load of the mill can be reduced, and the load change range of the mill can be widened.

[Brief description of the drawings]

FIG. 1A is a vertical sectional view of a ring roller mill according to an embodiment of the present invention, FIG. 1B is a perspective view of a roller bracket of the ring roller mill shown in FIG. 1A, and FIG. −
B sectional view, FIG. 3, FIG. 4A and FIG. 4B are schematic diagrams showing the function and operation of the mill according to the present invention, and FIG. , FIG. 6 is a graph showing the relationship between coal seam differential pressure and vibration differential pressure in the mill of the present invention, FIG. 7 is a diagram showing the combustion test results of pulverized coal produced by the mill of the present invention, and FIGS. , Conventional mill structure drawing, 10th
FIG. 11 and FIG. 11 are explanatory diagrams of the prior art. DESCRIPTION OF SYMBOLS 1 ... Raw material to be ground, 2 ... Raw material supply pipe, 3 ... Rotary table, 5 ... Rotary table shaft, 6 ... Grinding ring, 7 ... Grinding race, 8 ... Grinding roller, 9 ... Grinding roller Rotary shaft, 10 Roller bracket, 11 Extended member for receiving fine powder, 12 Roller pivot, 13 Lower press frame, 14 Spring, 15 Upper press frame, 16 Tension Rod, 17 ... Milhauzig,
19 ... Air throat, 23 ... Rotating classifier blade, 25 ... Product dust discharge duct.

Continued on the front page (72) Inventor Hiroaki Kanemoto 6-9 Takara-cho, Kure-shi, Hiroshima Pref. Inside the Kure Plant of Babcock Hitachi Ltd. (72) Inventor Yoshinori Taoka 6-9 Takara-cho, Kure-shi Hiroshima Pref. Inside the Kure Factory (72) Inventor Tadashi Hasegawa 6-9 Takara-cho, Kure City, Hiroshima Prefecture Inside the Kure Factory, Babcock Hitachi Ltd. (56) References JP-A-63-62557 (JP, A) JP, U) (58) Field surveyed (Int. Cl. ⁶ , DB name) B02C 15/04

Claims (2)

(57) [Claims] 1. A rotary table that rotates around a central axis below a mill housing, a grinding ring inserted into an outer peripheral portion of the rotary table and having a grinding race formed of an annular groove on an upper surface, and a grinding ring. In a ring roller mill provided with a plurality of crushing rollers that roll under pressure and a roller bracket that supports the crushing roller, the lower end of the roller bracket that supports the crushing roller faces downward from the fine powder generation side of the crushing roller. A ring roller mill for fine pulverization, wherein an extended member is provided on the rotary table, and the extended member is bent toward the center axis of the rotary table. 2. A ring roller mill for fine pulverization according to claim 1, wherein a plurality of notches are provided at an upper end of an outer periphery of said annular crushing race at intervals in a circumferential direction.