JP2000288416A - Vertical roller mill - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the grading of pulverized coal and to reduce operating power of a mill by rotating a throat together with a pulverizing table, expanding the pulverizing part housing diameter so that the flow velocity of air passing the upper part of the throat becomes within a range calculated by a specified formula, or reducing the quantity of air fed to the mill. SOLUTION: The diameter of a pulverizing part housing 7 is expanded and/or the quantity of air fed to the mill is reduced so that the flow velocity ν of air passing the upper part of a throat 4 becomes within the range calculated by the following formula. Wa*/[ρa×(π/4)×(DH*2-DT2)]×0.4<=ν<=Wa*/[ρa×(π/4)×(DH*2-DT2)×0.7, in which ν: flow velocity of air passing the upper part of throat (m/s), Wa* and DH*: quantity of air fed to the mill (kg/s) and mill pulverizing housing diameter (m) for conventional vertical roller mill whose pulverizing part housing diameter is set to about 1.2-1.3 times of pulverizing table diameter, ρa: density of air at the temperature in mill (kg/m3), DT: diameter of pulverizing table (m).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vertical roller mill for pulverizing a granular or block-like raw material such as coal to take out fine powder of a predetermined particle size. Means.

[0002]

2. Description of the Related Art FIG. 8 shows an example of a vertical roller mill conventionally used as a fuel pretreatment device in a coal-fired boiler system of a thermal power plant.

[0003] As is apparent from this figure, in the vertical roller mill of this example, a cyclone-type fixed classifier 10 is disposed above a pulverizing section 5 comprising a pulverizing table 2 and a pulverizing roller 3. A rotary classifier 20 is disposed inside the classifier 10.

[0004] The raw coal, which is the material to be pulverized supplied from the coal feed pipe 1, falls into the center of the rotating pulverization table 2, and
Due to the centrifugal force caused by the rotation of the crushing table 2, the crushing table 2 moves to the outer periphery in a spiral locus and is caught between the crushing table 2 and the crushing roller 3 to be crushed. The pulverized coal is blown upward while being dried by hot air introduced from a throat 4 provided around the pulverization table 2.

[0005] Among the blown-up coal powders, those having a large particle size fall by gravity while being conveyed to the fixed classifier 10, and are returned to the pulverizing section 5 (primary classification). The coal powder that has reached the classification section 6 is classified into fine coal having a predetermined particle size or less and coarse coal having a predetermined particle size or more by a fixed classifier 10 and a rotary classifier 20. It falls along the inner wall of the part 11 and is crushed again in the crushing part 5.

On the other hand, the pulverized coal that has exited the classification section 6 is
After that, it is sent to a boiler (not shown). The particle size of the pulverized coal discharged from the coal feed pipe 30 is controlled by adjusting the rotation speed of the rotary classifier 20.

In a coal-fired boiler system, the amount of pulverized coal is from 10 t / h to 100 in accordance with the output of a thermal power plant.
Vertical roller mills of various sizes up to t / h are used. The diameter of the crushing table of such a vertical roller mill ranges from about 1 m in diameter to over 4 m in diameter. In a coal-fired boiler system, a plurality of vertical roller mills are usually provided, and the total amount of coal supplied to each mill is the amount of fuel used in the boiler. Further, the number of mills operated for each fixed boiler load range is determined.

Accordingly, the number of vertical roller mills to be operated also changes with the change in boiler load, and
The amount of coal supplied per unit (coal supply) also changes. The amount of coal supplied to a coal-fired boiler mill of a thermal power plant is usually 40 to
Operated in 100% range. The amount of air introduced into the mill also depends on the amount of coal supplied, and the ratio of the amount of air to the amount of coal supplied is
Although it depends on the coal supply rate, for example, when the coal supply rate is 100%, the weight ratio between the air amount and the coal supply amount is about 2: 1.

In a conventional vertical roller mill (fixed throat type mill) having a throat blade attached to the pulverizing section housing side, the air flow velocity passing through each throat fluctuates greatly and the average flow velocity of each throat also has a large distribution. (Japanese Patent No. 2716491). As a result, the coal is likely to fall from the throat, and in order to suppress the fall, the air velocity passing through the throat must be increased more than necessary.

[0010] Further, the velocity of the air passing through the upper part of the throat is also non-uniform in the circumferential direction, so that the velocity of the coal particles transported in the upper part of the throat also has a distribution in the circumferential direction and is non-uniform. As a result, the particles could not be completely separated at a specific particle size, and the primary classification performance was poor.

In the conventional vertical roller mill, the diameter of the housing of the crushing section is set to be approximately 1.2 to 1.3 times the diameter of the crushing table. This is because, if the diameter of the crushing section housing is made larger than this, the air flow velocity passing through the upper part of the throat decreases, the transport resistance of the coal transported through the upper part of the throat increases, and the differential pressure of the mill increases. Conversely, when the diameter of the crushing unit housing is reduced, the crushing unit housing and the like become more worn.

In recent years, in order to realize high-efficiency operation of a thermal power plant, a vertical roller mill for supplying pulverized coal as a fuel to a coal-fired boiler has been required to reduce the operation power of the mill.

[0013]

As one of means for reducing the motive power of a vertical roller mill, a throat (rotary throat) in which a throat blade is attached to a side edge of a pulverizing table in order to reduce a mill differential pressure. (Japanese Patent No. 2740249, Japanese Patent Laid-Open No. 6-3438)
No. 87).

In the rotary throat type mill, similarly to the fixed throat type mill, the diameter of the pulverizing section housing is set to be approximately 1.2 to 1.3 times the diameter of the pulverizing table. The vertical roller mill equipped with this type of throat not only can reduce the differential pressure of the throat than the vertical roller mill (fixed throat type mill) where the throat blade is attached to the housing side, and the coal particles are uniform on the throat. Therefore, the concentration of the coal layer formed on the throat is evenly distributed, and the coal layer is easily separated at a specific particle size, and the classification performance is improved.

As a result, the coal particles blown up from the throat are transported upward at a high speed, and at the same time, the amount of coal staying in the upper part of the throat is reduced. Becomes thinner, and the coal bed pressure difference, which is the flow resistance, decreases. As described above, in the case of the rotary throat mill, the flow state of the coal particles and the air in the primary classification section in the mill changes completely. As a result, the fluidized bed portion becomes thin and is blown up at a high speed from the pulverizing portion, thereby increasing the diameter of the coal particles sent from the primary classification to the secondary classification. Therefore, when the mill is operated at the same classifier rotation speed, the particle size of the pulverized coal sent to the boiler from the mill outlet becomes coarser than that of a vertical roller mill (fixed throat type mill) having a throat blade attached to the housing side. Disadvantages arise. In order to solve this problem, it is only necessary to increase the number of revolutions of the classifier. However, installation of a classifier motor having a large capacity and an increase in operation power of the classifier are also caused.

SUMMARY OF THE INVENTION The present invention is intended to solve such a conventional disadvantage, and an object of the present invention is to improve the pulverized coal particle size and reduce the operating power of a mill by reducing the speed of particles blown up from a throat. An object of the present invention is to provide a vertical roller mill that can be reduced.

[0017]

In order to solve the above problems, the present invention mainly employs the following configuration.

A crushing section including a crushing table and a crushing roller, a crushing section housing surrounding the crushing section, a classifier installed above the crushing section, and a classifier housing surrounding the classifier. , A throat having a plurality of throat blades attached to an outer peripheral edge of the grinding table, and an annular space formed between the grinding table and the grinding unit housing by the throat. The throat is rotated together with the crushing table, and the flow rate 空 気 of air passing through the upper part of the throat is reduced.

[0019]

(Equation 1)

Wa ^* : Amount of air (kg / s) supplied to a conventional vertical roller mill in which the diameter of the crushing unit housing is set to approximately 1.2 to 1.3 times the diameter of the crushing table. Ρa: Temperature in the mill. Density of air at (kg / m ³ ) D _H ^* : The housing diameter of the crushing section is approximately 1.2 times the diameter of the grinding table
The diameter of the housing of the crushing unit is increased so that the crushing unit housing diameter (m) D _T : the crushing table diameter (m) of the conventional vertical roller mill set to about 1.3 times is calculated. // A vertical roller mill in which the amount of air supplied to the mill is reduced.

Further, a pulverizing section comprising a pulverizing table and a pulverizing roller, a pulverizing section housing surrounding the pulverizing section, a classifier installed above the pulverizing section, and a classifier surrounding the classifier A vertical roller mill provided with a housing, a throat having a plurality of throat blades attached to an outer peripheral edge of the grinding table, and an annular ring formed between the grinding table and the grinding unit housing by the throat. And the throat is rotated together with the pulverizing table to reduce the flow rate 空 気 of air passing through the upper part of the throat.

[0022]

(Equation 1)

Wa ^* : Amount of air (kg / s) supplied to a conventional vertical roller mill in which the diameter of the crushing unit housing is set to approximately 1.2 to 1.3 times the diameter of the crushing table. Ρa: Temperature in the mill. Density of air at (kg / m ³ ) D _H ^* : The housing diameter of the crushing section is approximately 1.2 times the diameter of the crushing table.
Milling housing diameter of the conventional vertical roller mill set to 1.3 times (m) D _T: As the range calculated by the grinding table diameter (m), the milling diameter of the grinding housing 1.35 to 1.55 times the table diameter
Vertical roller mill with double the range.

[0024]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a vertical roller mill according to the present invention will be described with reference to FIGS. FIG. 1 is a schematic view of a vertical roller mill according to the present embodiment. FIG.
FIG. 4 is an explanatory diagram that defines a crushing unit housing diameter _DH and a crushing table diameter _DT . FIG. 3 is an explanatory diagram comparing the primary classification characteristics of the present invention and a conventional vertical roller mill. 4 and 5 are explanatory diagrams comparing the particle size characteristics of fine powder between the present invention and a conventional vertical roller mill. 6 and 7 are explanatory diagrams comparing the pressure loss of the present invention and the conventional vertical roller mill.

Since the structure of the upper part of the throat (primary classifier) is complicated, the air flow velocity at the upper part of the throat is not constant. The value obtained by dividing the amount of air supplied into the mill by the cross-sectional area of the virtual annular flow path between the crushing unit housing and the crushing table was defined as the air flow velocity υ above the throat.

That is,

[0027]

(Equation 2)

Wa: the amount of air supplied to the vertical roller mill of the present invention (kg / s) ρa: the density of air at the temperature inside the mill (kg / m ³⁾
) D _H : Diameter of housing of crushing section of vertical roller mill of the present invention (m) D _T : Diameter of table of crushing section (m) Diameter of housing of crushing section _DH is 1.3 of diameter of crushing table _DT .
The values of 5, 1.45 and 1.55 are adopted.

Air velocity at upper part of throat (primary classification part)
Are 70%, 50%, and 40% of the conventional values, respectively. The pulverizing section 5 includes a pulverizing table 2 and three pulverizing rollers 3, and a throat 4 having a throat blade attached to an outer peripheral edge of the pulverizing table 2 is provided. The throat blade is mounted in the orientation disclosed in Japanese Patent Application Laid-Open No. 3-193142.

A classifier 6 is provided above the pulverizer 5. The classifying unit includes a classifying device 6 (secondary classifier) including a fixed classifier 10 and a rotary classifier 20, and a primary classifier that classifies coarse particles of coal particles blown up from a throat by gravity. .

Hereinafter, the operation of the vertical roller mill configured as described above will be described. The raw coal supplied from the coal feed pipe 1 falls onto the rotating crushing table 2 and is crushed between the crushing table 2 and the crushing roller 3 to be crushed. The air is blown up by the hot air introduced from the throat 4 provided around the periphery 2 and the housing diameter _{DH of the} crushing part is expanded more than before. The particles can be returned to the grinding section.

The solid-gas two-phase flow that has passed through the primary classifier reaches the fixed classifier 10. The solid-gas two-phase flow that has reached the fixed classifier 10 is supplied to the rotating blades 12 provided in the fixed classifier 10.
This gives a centrifugal force to further remove coarse powder in the gas-solid two-phase flow. The removed coarse powder falls along the inner wall of the cone portion 11 while turning, and is pulverized again in the pulverizing section 5.

The solid-gas two-phase flow passing through the fixed classifier 10 reaches the inlet of the rotary classifier 20. In the rotary classifier 20, centrifugal force is again applied by the rotary blades 21, the powder is adjusted to a desired particle size, and discharged from the coal feed pipe 30 to the outside of the system. The coarse powder separated by the rotating blades 21 is returned to the crushing unit 5 via the cone unit 11. Here, when the coal supply rate is 100%, the weight ratio between the air amount and the coal supply amount is about 2: 1.

As described above, when the diameter D _H of the pulverizing portion housing is increased, the flow velocity of the air passing through the upper portion of the throat 4 can be suppressed to a low level. The coarse particles are efficiently separated, and a solid-gas two-phase flow containing almost no coarse particles is conveyed to the classification device 6. As described above, since the solid-gas two-phase flow containing almost no coarse powder is supplied to the classifier, under the condition that the rotation speed of the rotary blades 21 of the rotary classifier 20 is low and the centrifugal force is small. Can also sufficiently separate coarse powder, and pulverized coal having a small particle size can be obtained.

FIG. 3 shows an example of the primary classification performance. FIG.
(A) is an example of the primary classification performance of a conventional vertical roller mill. The performance of a fixed throat type vertical roller mill having a throat blade attached to the pulverizing section housing side and a rotating throat type vertical roller mill having a throat blade attached to the pulverization table side are shown. Comparing fixed and rotating throat mills, for most particle size ranges,
The fixed throat mill has a higher separation efficiency than the rotary throat mill.

For example, the ratio of separating 300 μm coarse particles to the pulverizing section is 50% or more in the case of the fixed throat type mill, but the separation efficiency of the rotary throat type mill is 50% or less. The separation efficiency becomes a straight line on the Rosin-Rammler diagram, and the inclination of this straight line is larger in the rotating throat mill, and the classification performance for separating particles at a specific particle size is good.

In the case of a fixed throat type mill, although the separation efficiency is large as a whole, the classification performance is poor because the inclination of the straight line is small, and the fine powder to be sent from the coal feed pipe 30 to the boiler is also returned to the pulverizing section. Will be. As a result, the amount of coal circulating in the mill increases compared to when the classification performance is good,
This results in an increase in the pressure loss in the mill and an increase in the milling power of the mill.

On the other hand, in the case of a rotary throat type mill, although the classification performance is good, there is a problem that the particle size of the pulverized coal is coarse because the separation diameter is large. Therefore, it is desired to reduce the separation diameter while maintaining good classification performance.

FIG. 3B shows an example of the primary classification performance of the rotary throat type vertical roller mill according to the present invention. The figure also shows the performance of the conventional rotary throat type vertical roller mill shown in FIG. 3A for comparison. From this figure, it can be seen that the separation efficiency of coarse particles of 300 μm or more is significantly improved as compared with the conventional case. In addition, it can be seen that the inclination of the straight line is larger in the present invention than in the related art, and the classification performance is also improved.

When compared under the same operating conditions (the amount of coal supplied, the number of revolutions of the classifier, etc.), the particle size of the pulverized coal is smaller than that of the conventional rotary throat type vertical roller mill. Can also reduce the mill differential pressure and mill power.

The effects of the vertical roller mill according to the present invention are shown in FIGS. FIG. 4 shows the relationship between the pulverized coal particle size (200 mesh pass) and the number of revolutions of the classifier. The conventional rotary throat type mill has a lower value of 200 mesh pass in the low classifier speed range and a higher value in the high classifier speed range as compared with the conventional fixed throat type mill.

On the other hand, the rotary throat type mill of the present invention has a higher value of 200 mesh pass in all the rotation speed ranges of the classifier as compared with the conventional mill, and can make the pulverized coal particle size fine. In addition, the same pulverized coal particle size can be obtained with a classifier rotation speed lower than before, so that the power of the classifier can be reduced.

FIG. 5 shows a comparison between the conventional example and the 200 mesh pass of the present invention at the same classifier rotation speed. In particular, the effect of the present invention is remarkable at a high classifier rotation speed. FIG. 6 shows the relationship between the pressure loss of the mill and the pulverized coal particle size (200 mesh pass), and FIG. 7 shows the comparison between the pressure loss of the conventional example and the pressure loss of the present invention when the 200 mesh pass is 80% (relative value). ). Compared with the same pulverized coal particle size, it can be operated with a lower pressure loss than the conventional mill.

Therefore, the mill of the present invention can reduce the operating power of the ventilator for sending air into the mill. Further, the grinding power of the mill has a correlation with the pressure loss of the mill (see Japanese Patent Publication No. 08-000206), and the mill of the present invention can also reduce the grinding power of the mill. Further, the improved primary classification performance greatly affects the flammability.
It is possible to obtain a fine powder containing no coarse powder of 0 mesh over (150 μm or more).

In this embodiment, an example is described in which the air flow velocity in the primary classifying section (the upper part of the throat) is reduced by enlarging the diameter of the housing of the pulverizing section. Similar effects can be obtained. Since the hot air introduced into the mill plays a role of drying moisture adhering to the coal, the amount of air cannot be extremely reduced in the case of coal having a high moisture content. In this case, the same effect can be obtained by combining the enlargement of the crushing unit housing diameter and the reduction of the air amount, and setting the air flow rate of the primary classification unit in the range of 40 to 70% of the conventional range.

As described above, the embodiments of the present invention include those having the following configuration examples, functions and functions.

In a vertical roller mill equipped with a throat blade on the side of the pulverizing table, the flow velocity 空 気 of the air passing through the upper part of the throat (primary classifier) is determined by

[0048]

(Equation 1)

Wa ^* : The amount of air (kg / s) supplied to a conventional vertical roller mill in which the diameter of the crushing unit housing is set to be approximately 1.2 to 1.3 times the diameter of the crushing table. Ρa: Temperature in the mill Density of air at (kg / m ³ ) D _H ^* : The housing diameter of the crushing section is approximately 1.2 times the diameter of the crushing table.
The diameter of the crushing unit housing (m) _DT : crushing table diameter (m) of the conventional vertical roller mill set to 1.3 times is set to be in the range calculated.

More specifically, the diameter of the housing of the crushing unit is set to be 1.35 to 1.55 times the diameter of the crushing table. Alternatively, the amount of air supplied to the mill is reduced, the diameter of the pulverizing section housing is increased, and the flow rate of the air passing through the upper part of the throat is in the range of 40 to 70% of the conventional.

The coal is pulverized in a pulverizing section of the vertical roller mill with a 200 mesh pass of about 20 to 50%, although it varies depending on the load of the vertical roller mill and the pulverizability of the coal. The pulverized coal is subjected to primary classification before being transported to the classification section, and coarse particles are returned to the pulverization section by gravity. In the primary classification, the particle diameter returned to the pulverizing unit increases as the air flow rate passing through the primary classification unit (upper throat) decreases.
Therefore, by increasing the housing diameter of the pulverizing section and the housing diameter of the classifying section as compared with the prior art, the flow velocity of the primary classifying section is reduced, and coarse particles can be reliably returned to the pulverizing section.

As a result, in the vertical roller mill in which the throat blade is attached to the pulverizing table, the particle size of the pulverized coal sent from the mill outlet to the boiler does not become coarse. Therefore, as compared with a vertical roller mill in which a throat blade is attached to the pulverizing section housing side, not only the mill differential pressure and the pulverizing power of the mill can be reduced, but also the pulverized coal particle size can be reduced, and the pulverized coal is included. The amount of coarse powder can be reduced.

[0053]

As described above, according to the present invention,
Since the throat blade is attached to the pulverizing table side and the air flow velocity in the primary classification section is reduced, the separation efficiency of the primary classification section is improved and the classification performance is improved, so that the particle size of the pulverized coal can be reduced.

Further, when compared with the same pulverized coal particle size, the classifier power, the mill pulverization power and the operation power of the ventilator can be reduced as compared with the conventional mill, which can contribute to the improvement of the efficiency of the thermal power plant. .

Further, since fine powder containing no coarse powder of over 100 mesh can be obtained, unburned components in fly ash can be suppressed.

[Brief description of the drawings]

FIG. 1 is a sectional view of a vertical roller mill according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram showing a crushing unit housing diameter and a crushing table diameter of the vertical roller mill according to the present embodiment.

FIG. 3 is a characteristic diagram showing primary classification performance of the present invention and a conventional vertical roller mill.

FIG. 4 is a graph showing a comparison of the particle size characteristics of fine powder between the present invention and a conventional vertical roller mill.

FIG. 5 is a graph showing a comparison of fine powder particle size characteristics between the present invention and a conventional vertical roller mill.

FIG. 6 is a graph showing a comparison of pressure loss between the present invention and a conventional vertical roller mill.

FIG. 7 is a graph showing a comparison of pressure loss between the present invention and a conventional vertical roller mill.

FIG. 8 is a sectional view of a conventional vertical roller mill.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 coal feed pipe 2 crushing table 3 crushing roller 4 throat 5 crushing unit 6 classifying device 7 crushing unit housing 8 primary classifying unit 10 fixed classifying unit 11 cone unit 12 rotating blade 20 rotary classifying unit 21 rotating blade 30 coal feeding tube

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Kazunori Sato 3-36 Takara-cho, Kure-shi, Hiroshima Prefecture Inside the Kure Research Laboratories Co., Ltd. (72) Inventor Yutaka Yutaka 3-36 Takara-cho, Kure-shi, Hiroshima Babcock-Hitachi Co., Ltd. Kure Research Institute, Inc. (72) Inventor Kotaro Sakoda 6-9 Takaracho, Kure City, Hiroshima Prefecture Inside Babcock Hitachi Kure Factory (72) Inventor Hideo Mitsui 6-9 Takaracho Kure City, Hiroshima Prefecture Babcock Hitachi Kure Factory F term (reference) 4D063 EE04 EE12 EE21 GA08 GC05 GC12 GC19 GC32 GD03 GD11 GD24

Claims (3)

[Claims] A crushing unit including a crushing table and a crushing roller; a crushing unit housing surrounding the crushing unit;
In a vertical roller mill including a classifier installed above the pulverizing unit and a classifier housing surrounding the classifier, a throat having a plurality of throat blades attached to an outer peripheral edge of the pulverizing table. The throat partitions an annular space formed between the pulverizing table and the pulverizing section housing, rotates the throat together with the pulverizing table, and adjusts a flow rate 空 気 of air passing through an upper part of the throat. Equation 1 Wa ^* : The diameter of the housing of the crushing section is approximately 1.2 of the diameter of the crushing table.
Air volume (kg / s) supplied to a conventional vertical roller mill set to ~ 1.3 times ρa: Air density at the temperature in the mill (kg / m ³ ) _DH ^* : Housing diameter of crushing section Approximately 1.2 of the grinding table diameter
The diameter of the housing of the crushing unit is increased so that the crushing unit housing diameter of the conventional vertical roller mill set to about 1.3 times (m) D _T : the diameter of the crushing table diameter (m). A vertical roller mill characterized in that the amount of air supplied to the mill is reduced. 2. A crushing unit comprising a crushing table and a crushing roller; a crushing unit housing surrounding the crushing unit;
In a vertical roller mill including a classifier installed above the pulverizing unit and a classifier housing surrounding the classifier, a throat having a plurality of throat blades attached to an outer peripheral edge of the pulverizing table. The throat partitions an annular space formed between the crushing table and the crushing unit housing, rotates the throat together with the crushing table, and adjusts a flow rate 空 気 of air passing through an upper portion of the throat. Equation 1 Wa ^* : The diameter of the housing of the crushing section is approximately 1.2 of the diameter of the crushing table.
Air volume (kg / s) supplied to a conventional vertical roller mill set to 1.3 times ρa: Density of air at the temperature in the mill (kg / m ³ ) _DH ^* : Housing diameter of crushing section Approximately 1.2 of the grinding table diameter
Milling housing diameter of the conventional vertical roller mill set to 1.3 times (m) D _T: As the range calculated by the grinding table diameter (m), the milling diameter of the grinding housing 1.35 to 1.55 times the table diameter
Vertical roller mill characterized by double the range. 3. A crushing unit comprising a crushing table and a crushing roller, a crushing unit housing surrounding the crushing unit,
In a vertical roller mill including a classifier installed above the pulverizing unit and a classifier housing surrounding the classifier, a throat having a plurality of throat blades attached to an outer peripheral edge of the pulverizing table. The throat partitions an annular space formed between the crushing table and the crushing unit housing, rotates the throat together with the crushing table, and determines the amount of air supplied to the mill to the crushing unit housing diameter. Is smaller than the amount of air supplied to the conventional mill which is set to be approximately 1.2 to 1.3 times the diameter of the crushing table, and / or the housing diameter of the crushing unit is reduced by approximately 1 to the diameter of the crushing table. By increasing the flow rate of the air passing through the upper part of the throat, the diameter of the housing of the pulverizing section is increased by a pulverizing table. 40 of the conventional air flow rate to pass through the throat upper set to approximately 1.2 to 1.3 times the
A vertical roller mill characterized by having a range of 70%.