JPH03154654A - Vertical mill - Google Patents

Abstract

PURPOSE:To prevent lowering of grinding efficiency under high loads by providing a powder layer holder in a space defined by grinding rollers near a rotary table shaft, in which the upper part of the holder is open to a raw material feed zone and the lower part thereof is open to a rotary table. CONSTITUTION:There are provided in a casing 14 a rotary table 3 rotating in a horizontal plane about a vertical rotation shaft in the lower region of the casing, a plurality of grinding rollers 8 disposed on the table 3 and an annular space 11 for blowing up air streams provided between the table 3 and the casing 14. And, in a space defined between each roller 8 near a rotary table shaft 4, a powder layer holder 15 having an approximately cylindrical shape is provided so that its upper part is open toward a raw material feed zone 2 and its lower part is open toward the table 3. A plate-like powder feed guide 16 supported by the lower opening of the holder 15, expanding in width toward the table 3, is provided in such a manner that the guide 16 extends, without directly contacting the table 3 and rollers 8, as far as to a gap between a particle engaging part and a fine particle producing part.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a vertical mill equipped with a classifier therein, and particularly to a vertical mill with improved crushing function.

[Conventional technology]

Low-pollution combustion (low N) even in coal-fired boilers.

X, reduction of unburned matter) and rapid load fluctuation operation (change in coal feed amount), and as a result, pulverizers (mills) were also required to have higher performance.

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 one of the representative models.

This type of crusher is located at the bottom of a cylindrical mill housing 114, as shown in FIG. The table 103 includes a table 103 and a plurality of crushing rollers 111 that are rotated by being pressed down by hydraulic pressure or a spring to positions that equally divide the outer peripheral portion of the upper surface in the circumferential direction. The raw material 101 to be crushed is supplied from the raw material supply pipe 102 to the center of the rotary table 103.
The rotation of the rotary table 103 and the centrifugal force cause the rotary table 10 to move toward the outer periphery while drawing a spiral trajectory on the rotary table 103.
It is caught between the grinding race 105 surface of No. 3 and the grinding roller l11 and is crushed. At the base of the mill housing 114, there is hot air 110 sent through a duct (not shown).
is guided, and this hot air 110 is directed to the rotary table 103.
The air is blown up from the air throat 108 between the outer circumference of the mill housing 114 and the inner circumference of the mill housing 114. The powder after pulverization is dried while rising inside the mill housing 114 by hot air 110 blown up from the air throat 108.

The powder particles transported to the upper part of the mill housing 114 are
The powder is classified by a cyclone separator or a rotary classifier provided at the upper part of the mill housing 114, and the fine powder having a predetermined particle size or less is conveyed by hot air 110, and sent to a pulverized coal burner or a fine powder storage bin in a boiler (not shown). Coarse powder having a predetermined particle size or more that does not pass through the classifier falls onto the rotary table 103 and is crushed again together with the raw material to be crushed 101 that has just been supplied into the mill. In this way, the crushing is repeated by the crushing roller 111.

For this purpose, in order to increase the crushing capacity,
An optimal roller or structure of a groove-shaped crushing race 105 carved on the top surface of the rotary table has been proposed. On the other hand, regardless of the shape of the rollers or grinding race, even if they are of the conventional type, the movement of the powder layer on the table can be controlled by '+H'.
This is considered to be effective in increasing the crushing force.

[Problem to be solved by the invention]

In a conventional vertical roller mill, the structure of which is shown in cross-section in Figure 11, the crushing section, especially the 3
If too much granular material, which is the raw material to be crushed, accumulates in the space between the crushing rollers 111,
There was a problem in that this caused resistance to transfer, increased wasted power that was not directly involved in pulverization, and resulted in a decrease in pulverization efficiency.

FIG. 7 shows the experimental results in the pilot mill, and summarizes the thickness of the powder layer under the grinding roller as a change in power consumption. Both fir and horizontal wheels were made dimensionless using the values under standard crushing conditions. When the thickness of the powder layer under the grinding roller reaches a predetermined value, the power consumption increases rapidly.

There is a limit to the amount of coal that can be held as a compressed powder layer between the crushing rollers and the crushing race. Therefore, in this case, as schematically shown in FIG. 8-1, the granular material 120, which is the raw material to be crushed, overflows from between the crushing rollers 111, and this becomes the rolling resistance of the crushing rollers 111. it is conceivable that. The granular material 120 becomes supersaturated between the pulverizing rollers 111, and the granular material 120 becomes supersaturated between the rotating pulverizing rollers 111.
20 overflows, the powder layer is transferred to the adjacent grinding rollers 111A and III rotating in the opposite direction, as shown in FIG. 8-2.
B becomes the shear resistance between the grinding surfaces. This behavior is predicted to be one of the main causes of the rapid power consumption phenomenon shown in FIG. In addition, in this way, the crushing roller IIIA, 11
If the powder 120 overflows between 1B, it becomes caught in the grinding rollers and becomes a resistance to air transportation after the fine powder is generated, and has various adverse effects on the operation of the mill, such as increased pressure loss and vibration of the mill.

Figures 9 and 1O show the basic experimental results of a batch-type mill, and show the fine powder production rate W (200 mesh pass g/mln) and the effective grinding rate ΔS/p e with respect to the coal loading rate in the mill, respectively. This is a summary of changes in MwD (which is obtained by dividing the surface area increase ΔS of the generated fine powder by the effective grinding energy rate μeMwD, which is the net grinding power consumption, and essentially becomes the grinding efficiency). A comparison is made using rollers A and B types with different structures (
Type A: A roller whose crushing surface is approximately arc-shaped; Type B: A two-step roller with a stepped crushing section whose diameter is varied. 9th
From the results in the figure, it can be seen that the B type roller has high crushing capacity under high load rate conditions, but as shown in Figure 1O, when the B type roller is used, the efficiency is lower than that of the A type. Put it away.

This characteristic indicates that the +11 yen structure of the roller strongly affects the flow resistance of the roller as it tries to rotate through the powder group. In other words, in the case of type B rollers, the space between the rollers is small, and unpulverized powder and granules overflow in the roller biting area and the fine powder generation area.
It is predicted that Laura's resistance to transfer has increased.

As an example of the prior art regarding the method of controlling powder supply to the roller crushing section, as shown in FIG.
There is a proposal to feed the powder to the biting part of the crushing roller 212 by providing the crushing roller 212. This method is considered to be effective in promoting entrainment and preventing vibration of the mill under low-load conditions where the number of rollers is small (2) and there is little raw material in the crushing section, but under high-load conditions such as the one being addressed here, This does not meet the demand for improved pulverization efficiency during operation.

In the prior art shown in FIG. 13, a container is provided in the mill, which is a combination of a truncated conical section 1347 that guides the raw material supplied from a chute 1350 and particles returned from the secondary classification section, and a small diameter cylindrical section 1346. It is something. In this technology, particle groups are recirculated from the primary (gravity) classification section to the crushing section,
or when using a rotary classifier, the mill housing 1
The particles that are thrown out to the 340 side and fall into the crushing section are
Gap between roller 1343 and small diameter cylindrical portion 1346, roller 1
343 and the truncated cone portion 1347 or the roller 1
There is also a possibility that the particles may enter the gap between the leveling member 343 and the leveling member 1348 and overflow onto the roller 1343. Particularly when increasing the amount of recirculation within the mill in order to increase particle size under high loads, a series of container members (1346
, 1347, 1348) and the roller 1343, it becomes a rolling resistance of the roller 1343, which may result in an increase in the power of the mill. By the way, the recent trend is to increase C/A (C and A are the mass flow M of coal and primary (mill) air, respectively) in response to lower NOx and higher efficiency in pulverized coal combustion, including in mills. be. Therefore, there is a tendency to try to reduce the mill air as much as possible, and the proportion of recirculated particles returning from the primary (gravity) classification section is
This is considerably higher than the previous method.

The purpose of the present invention is to solve the above-mentioned problems and provide a mill that does not reduce its grinding efficiency even under operating conditions with a large amount of recirculation from the primary classification section or under high load operation. It is in.

(Means for Solving the Problems) The present invention aims to solve the above-mentioned problems, and the purpose is to provide a rotary table that rotates on a horizontal plane around a vertical axis of rotation in a lower part of a casing; In a vertical mill that has a plurality of crushing rollers placed on a rotating table and an annular space for blowing up air between the rotating table and the casing, there is a A nearly cylindrical powder bed holder with its upper part open toward the raw material supply section and its lower part opened toward the rotary table is provided in the space configured as shown in FIG. The plate-shaped powder supply guide, whose width increases as it approaches the rotary table, is extended to the gap between the particle catching part and the fine powder generating part of each crushing roller without directly contacting the rotary table or the crushing rollers. This is achieved by a vertical mill that is characterized by the following:

[Effect]

The raw materials supplied into the mill and the powder returned from the classification section in the mill to the crushing section enter the approximately cylindrical powder holder described above, so the proportion of them that directly contact the rollers is small, and the amount of contact is small. Waste of power due to resistance can be avoided. Also,
Since the powder is supplied to the crushing section of the crushing roller on the crushing race through the plate-shaped powder supply guide mentioned above, the powder overflows between the crushing rollers and the transfer resistance of the crushing roller is reduced. The problem of rapid growth will be solved.

Therefore, according to the present invention, it is possible to minimize the decrease in the crushing efficiency even under high load operation, where the crushing section becomes supersaturated and power is wasted. Moreover, since the powder and granules do not overflow to the fine powder generation/airflow blowing up section of the crushing roller, pressure loss in the crushing section can be reduced. Furthermore, especially under high load conditions, the grinding rollers bite and grind an appropriate amount of raw material under a high load, which improves the particle size of the fine powder.

〔Example〕

1 and 2 show the structure of a vertical mill according to the present invention. FIG. 1 is a longitudinal cross-sectional view passing through the center axis of the mill, and FIG. 2 is a view of the crushing section viewed from above along the line ■-■ in FIG.

The raw material to be crushed 1 is supplied into the mill from a raw material supply pipe 2 provided on the central axis of the upper part of the mill, and a cylindrical powder layer holder 1 is installed in a space sandwiched between three crushing rollers 8.
5, and falls onto a rotary table 3 rotating at a low speed below the mill. Due to centrifugal force, the raw material to be crushed on the rotary table 3 is sent onto the crushing race 7, which has a substantially arc-shaped cross section carved on the upper surface of the annular crushing ring 6 provided on the outer circumferential side of the rotary table 3. be provided. The raw material to be crushed on the crushing race 7 is crushed by a crushing roller 8 that rotates while being pressed on the crushing race 7 . The granular material thus pulverized is transported above the mill by hot air 13 blown from an air throat 11 disposed outside the rotary table 3.

Among the transported powder and granules, those that are quite coarse fall to the crushing section due to gravity (primary classification) and are re-pulverized. - Of the powder and granules that have passed through the secondary classification section, relatively coarse particles are repelled by the rotary classifier to the inner wall of the mill housing 14 by centrifugal force (secondary classification), and are finally sent to the crushing section by gravity. Return to and be re-pulverized. The fine particles that have passed through the secondary classification area of the rotary classifier are transported to the outside of the mill through the product fine powder recovery duct 21 and recovered as a product.

In the case of a mill for a pulverized coal-fired boiler, the pulverized coal is either directly transported to a pulverized coal burner (not shown) and burned, or stored in a pulverized coal bin (not shown).

In the rotary classifier in this embodiment, the rotating cylinder 17 around the raw material supply pipe (center chute) 2 serves as the rotation axis,
At the bottom thereof, a rotary classifier rotor 18 is provided, in which several plate-like blades 19 are arranged at equal intervals in the circumferential direction. In the vertical mill, the rotating direction of the rotary classifier and the rotary table 3 are the same.

A feature of the present invention is that a powder bed holder 15 is provided in the space between the crushing rollers 8 to receive the group of raw material particles to be crushed that accumulate on the rotary table 3.

This powder bed holder 15 has a generally cylindrical shape, and its upper end is located at a higher position than the upper end of the crushing roller 8, forming a truncated conical inlet portion 15A that opens upwardly of the mill.

Further, a container 15B having a cylindrical shape and a bottom opening upwardly from the rotary table 3 is connected to the inlet portion thereof, and the lower end of this container is provided with a gripping portion of the crushing roller 8, as shown in FIG. and three plate-shaped powder supply guides 16 whose width increases toward the space between the fine powder generation section and the fine powder generation section. Note that this powder layer holder 15 is held by a plurality of supports 22 having fixed portions on the mill housing 14. A perspective view of the powder bed holder is shown in FIGS. 14A and 14B. During the crushing operation, powder particles accumulate on the crushing section of the mill, that is, the rotary table 3.

In particular, when the mill is operated under high load (conditions that increase the supply amount), or when the operating conditions of the classifier or the amount of air are changed to increase the amount of circulation inside the mill, a large amount of powder and granules accumulates. ,
The crushing roller 8 is completely buried. The powder bed holder 15 of this embodiment receives the lumpy raw material l supplied from the raw material supply pipe (center chute) 2 and the powder and granular material returned from the primary classification section or the secondary classification section, and This prevents the particles from coming into direct contact with the rotating crushing roller 8 and creating resistance. The powder supply guide 16 also prevents the powder from overflowing to the crushing section (the biting section and the fine powder generating section) of the crushing roller 8, and allows the crushing roller 8 to crush an appropriate amount of the powder and granular material. There is a role. When the coal hold-up in the mill increases, the inside of the powder bed holder 15 is filled with powder and granules, and in extreme cases, there is a possibility that the coal may overflow from above the powder bed holder 15.

However, compared to the conventional vertical mill, where no countermeasures are taken, the particle size is improved by this powder bed holder 15 (
The effects of improving grinding efficiency) and reducing pressure) are remarkable. This will be discussed later.

Regarding the operation method of the mill, it is possible to increase the coal feeding amount beyond the standard coal feeding amount (the limit that satisfies a predetermined grain size), or the mill may increase the coal feed amount to the standard value of the coal hold amplifier in the mill (the coal seam differential pressure in the mill). (judging from the threshold value), the crushing load of the mill is increased to 1.3 times.

FIG. 3 schematically shows the state of powder in the crushing section of the mill according to the present invention. In the crushing section, the raw material to be crushed is powder (feed), primary (gravity) classification and secondary (gravitational) classification.
Most of the circulating particles) 23 from the rotating/classifying section are received in the powder bed holder 15 of the present invention, and are crushed from below the powder supply guide 16 attached to the lower part of the powder bed holder 15. It is fed to the biting position of the roller 8. In this way, the granular material 2 is removed, except for the biting part of the crushing roller 8.
3 is prevented from coming into contact with the crushing roller 8 and creating a large resistance. Therefore, most of the power consumed in the crushing section is spent on actual crushing, ultimately improving the crushing efficiency. Furthermore, since the amount of powder overflowing to the top of the air throat 11 is reduced, pressure loss in the crushing section is reduced.

Figure 4-1 shows the non-dimensional pulverizing power consumption (consuming the power consumption under standard coal feeding conditions as 100%) against the coal feeding load rate (standard coal feeding amount is 100%) under the condition of constant load. This is a comparison of the grinding performance of the mill according to the present invention and the conventional mill. Generally, power increases as the coal feeding load rate increases, but the rate of increase in power in the mill according to the present invention is lower than that of the conventional mill, and the difference increases as the load increases. As shown in FIG. 3, even under high load conditions, the mill according to the present invention provides a more appropriate amount of raw material to be crushed due to the action of the powder bed holder 15 and powder supply guide 16. This is thought to be because the particles were fed to the biting part of the crushing roller 8 and were efficiently crushed. In a mill without countermeasures, the amount of raw material in the gripping area of the grinding roller is too large, resulting in poor biting, or the powder layer under the grinding roller becomes too thick, causing the load pressure on the grinding roller to spread out. There is a possibility that

Figure 4-2 shows the dimensionless fine particle size (2
Based on the grain size of 00 mesh pass.

The graph shows the change in the particle size (which was made dimensionless using the particle size under standard conditions as a 100% standard). However, in this experiment, the crushing load was increased under conditions where the amount of coal fed was larger than the standard amount. At low loads, there is not much difference in particle size between the example of the present invention and the conventional example. However, when the load becomes high, the particle size of the mill according to the present invention decreases little, and the difference between the particle size of the conventional mill and the particle size of the conventional mill, which decreases significantly, increases significantly.

This is because in the mill according to the present invention, the crushing ability is improved because the rollers efficiently bite the appropriate amount of raw material under a high load. The mill according to the present invention has a so-called wide range function with little change in particle size under such a wide range of loads. In this way, when the capacity of the crushing section is increased, the amount of coarse particles that penetrate to the air throat is reduced, and the pressure loss of the mill is also reduced.

Figure 5 shows the non-dimensional coal seam differential pressure (the portion of the total pressure loss in the mill that is related to coal, which is made non-dimensional based on the coal seam differential pressure under standard coal feeding conditions in a conventional mill). It is summarized as a change in coal feeding load factor.

As mentioned above, in the mill according to the present invention, the amount of powder that overflows onto the air throat 11 without being sufficiently pulverized is reduced, so the effect of reducing pressure loss is remarkable, especially under high load conditions. I understand. Such a reduction in pressure loss also produces the effect that the power of the primary blower can be reduced.

Combustion test results of pulverized coal produced with the mill of the present invention are
6th map of NOx concentration in exhaust gas and unburned content in ash
As shown in the figure. The pulverized coal produced by the mill of the present invention is more
It can be seen that both the NOx concentration and the unburned content in the ash are reduced. First, the decrease in unburned content in the ash is due to improved particle size, which improves ignition and flame stability near the burner, greatly expands the combustion zone, and greatly accelerates burnout. on the other hand,
Such improvements in ignition and flame stability also produce the effect of reducing NOx concentration. In other words, in the flame self-denitration type burner, a stable low air ratio combustion region at high temperature is formed in the center of the flame near the burner, and a reducing substance for reducing the generated No to N2 is formed. b is actively generatedb. Therefore, as a result, N in the flame wake
Ox4 degree decreases.

As described above, by using a vertical mill embodying the present invention, not only the performance of the mill is improved, but also the low-pollution operation of a coal-fired power plant becomes possible.

The vertical mill of the present invention is not limited to the mill for pulverized coal-fired or solid fuel-fired boilers such as petroleum coke, which have been taken up as examples and shown in the examples, but also mills for cement finishing, steel slag crushing, or It can also be applied almost directly to blast furnace blow pulverization mills. Particularly in the field of cement, where particularly strict quality control and energy-saving operations have recently been promoted, the vertical mill of the present invention is considered to be particularly effective.

(Effects of the Invention) According to the present invention, since excess particles to be crushed do not enter between the respective crushing rollers, there is less rolling resistance of the rollers, and the crushing power can be reduced.Furthermore, the particles to be crushed can be appropriately supplied. This increases the grinding capacity of the mill and improves the fineness of the product.

[Brief explanation of the drawing]

Figures 1, 2, 14A, and 148 are diagrams showing the structure of the vertical mill according to the present invention, Figure 3 is a functional explanatory diagram of the mill according to the present invention, and Figure 4-1. ~The 6th is an explanatory diagram of experimental results using the mill of the present invention, Figures 7 to 10 are explanatory diagrams of problems in the conventional vertical mill, Figure 11 is a structural diagram of the conventional vertical mill, and the 12th FIG. 13 is an explanatory diagram of the prior art. DESCRIPTION OF SYMBOLS 1... Raw material to be crushed, 2... Raw material supply pipe, 3... Rotating table, 4... Rotating table shaft, 5...
Rotary table rotating shaft, 6... Grinding ring, 7... Grinding race, 8... Grinding roller, 9... Roller shaft, 11... Air throat, 13... Hot air, 14...
... Mill housing, 15 ... Powder bed holder, 16 ...
・Powder supply guide, 21... Product fine powder collection duct,
22...Powder layer holder support.

Claims (1)

[Claims] A rotary table that rotates on a horizontal plane around a vertical axis of rotation below the casing, a plurality of crushing rollers arranged on the rotary table, and an annular space for blowing up air provided between the rotary table and the casing. In a vertical mill having a section, the space is configured to be sandwiched between the respective grinding rollers near the rotary table axis, and the upper section is open toward the raw material supply section, and the lower section is open toward the rotary table. A substantially cylindrical powder bed holder is provided, and a plate-shaped powder supply guide, which is held in the lower opening of the powder bed holder and whose width increases as it approaches the rotary table, is brought into direct contact with the rotary table and the crushing roller. A vertical mill characterized in that the mill extends to the gap between the particle catching part and the fine powder generating part of each crushing roller.