JPH01104355A - Vertical mill - Google Patents

Abstract

PURPOSE: To improve the classification efficiency of pulverized matter and to improve the grain accuracy of products by providing the inside of a classifying device with separate means for introducing gas, exclusive of the gas passing the discharge side of a pulverizing section. CONSTITUTION: Supply ducts 4b, 4c of primary air A are connected to the opposite position of the air introducing side of vane arrays 18 at the inlet 17a of the classifying device 17 of the vertical type mill 4 for pulverizing and classifying ores, such as coal, and to the upper (throat) part 24 of a throat ring 23 of the primary air A. The pulverized coal particles are dried by the hot air introduced via the throat ring 23 from a primary air inlet 22 and are transported up in the vertical type mill 4 by the air of the air supply duct 4c of the throat part 24. The coal particles are subjected to primary classification till a classifying device inlet 17a and are passed together with the air stream through the vane arrays 18 within the classifying device 17 where the coarse coal particles are separated by centrifugal force. The classification efficiency is thus improved and the waste of fan driving powder is eliminated.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a vertical mill for crushing and classifying minerals such as coal, and particularly to a vertical mill that improves classification accuracy.

[Conventional technology]

Vertical mills are used, for example, in pulverized coal production equipment of coal-fired boilers as pulverized coal combustion equipment that uses pulverized coal as fuel.

Hereinafter, a vertical mill in a coal-fired boiler system will be explained as an example.

Figure 4 is a system diagram of a coal-fired boiler system equipped with a vertical mill. In the figure, the coal-fired boiler system includes a boiler 7, a vertical mill 4 that supplies pulverized coal to a pulverized coal bar 7a of the boiler 7, a forced draft fan 1 that supplies air to the boiler 7, and a vertical mill 4 that supplies air to the boiler 7. A forced draft fan 2 for primary air that supplies primary air to the vertical mill 4, a boiler 7, an air preheater 3 that preheats the air supplied to the vertical mill 4, and combustion gas from the boiler 7. It is mainly composed of a dust collector 8 to which is guided, a denitrification device 9, an induced draft alO and a desulfurization device 11.

The forced draft fan 1 supplies combustion air, which is supplied to the combustion chamber of the boiler 7 via the air preheater 3.
A part of the air is pressurized by the forced draft fan 2 for primary air, a part of which passes through the air preheater 3, and the other part is directly supplied to the vertical mill 4. A bunker 5 for charging coal B and a coal feeder 6 for supplying coal B from the bunker 5 to the vertical mill 4 are installed in the upper part of the vertical mill 4, and a necessary amount of coal B is provided.
is supplied into the vertical mill 4.

The pulverized coal pulverized in the vertical mill 4 is supplied to the pulverized boiler 7a, and is combusted in the combustion chamber of the boiler 7 together with secondary air sent directly from the air preheater 3. The exhaust gas generated by combustion is led to a dust collector 8, where dust in the exhaust gas is collected, and subsequently, nitrogen oxides are removed by a denitrification device 9. These exhaust gases pass through the air preheater 3 and are sucked in by the induced draft fan 10, and after heating the air preheater 3, sulfur oxides are removed by the desulfurization device 11 and transferred to the next process.

FIG. 5 shows the structure of the vertical mill 4 in such a coal-fired boiler system. FIG. 5 is a sectional view showing a schematic configuration of a conventional vertical mill 4. As shown in FIG. In the figure, a grinding table 12 is provided at the bottom of the vertical mill 4 and is rotatably driven by a gear (not shown) housed in a gear box 13, and a grinding ring 14 is fixed on top of the grinding table 12. ing. A crushing roller 15 is placed on the top surface of the crushing ring 14.
are in contact with each other under pressure by the upper sprung jig 16, and rotational force is applied by the grinding ring 14 on the grinding table 12 via the object to be crushed. These grinding table 12, grinding ring 14, and grinding roller 15
constitutes the crushing section. Further, a throat ring 23 is disposed on the outer circumferential side of the crushing ring 14, and below the throat ring 23, a primary air port 22 into which the primary air is introduced is provided.

A classifier 17 is provided above the crushing roller 15 for taking out the crushed material as pulverized coal of a predetermined particle size and returning the coarse pulverized coal to the pulverizing table 12 again. A classifier 1 having a circumferential opening is provided at the upper end of the classifier 17.
7 is formed, a variable blade row 18 is provided at the inlet portion 17a, and a flapper 19 is provided at the outlet portion of the bored lower end. A coal feed pipe 20 is provided at the top of the classifier 17 to introduce vertically crushed pulverized coal into the pulverized coal burner 7a. Coal feed pipe 2 serving as a supply unit for supplying coal B from the coal feeder 6 above
1 is provided.

In the vertical mill 4 configured in this way, the raw coal B supplied from the coal feed pipe 21 is rotated at 20 to 40 rpra together with the coarse powdered coal classified by the classifier 17 in the vertical mill 4. The material is sent onto the grinding table 12, which passes through the gap between the grinding ring 14 and the grinding roller 15 by centrifugal force, and is crushed and ground by the grinding roller 15 at this time. On the other hand, 300
Gaseous primary air A heated to around 0.degree. C. is supplied from the primary air supply 22 to the throat upper section 24 via the throat ring 23. Therefore, the coal particles crushed by the crushing roller 15 are transported upward within the vertical mill 4 as shown by the arrow C by the primary air A. Among the transported coal particles, relatively fine pulverized coal passes through the blade row 18 and is transferred to the classifier 17.
sent to. Further, as the air flow velocity decreases, the coarse powder coal is separated from the air flow, passes over the crushing rollers 15, and is returned onto the crushing table 12 as shown by the arrow, where it is subjected to primary classification. Of the coal particles sent into the classifier 17, relatively coarse pulverized coal is separated from the airflow by centrifugal force, falls inside the classifier 17 due to its own weight as shown by arrow E, and moves to the flapper 1.
9, it is returned to the crushing table 12 again (secondary classification)
. On the other hand, the pulverized coal separated in the classifier 17 is taken out as a product from the pulverizer outlet 25 along with airflow as shown by arrow F, and sent to the pulverized coal burner 7a. The particle size of this pulverized coal can be adjusted, for example, by adjusting the angle of the blade row 18.
The particle size is adjusted to about 70% of the mesh pass (particle size of 75 μm or less).

[Problem that the invention seeks to solve]

In recent years, in coal-fired boilers, etc., N
Along with the demand for reducing Ox, the use of flame-retardant coal with a high fuel ratio (ratio of fixed carbon to volatile content in coal) is increasing. In the case of flame-retardant coal, it is difficult to suppress the unburned content in the ash to 5% or less with low NOx combustion even if the pulverized coal burner 7a etc. is improved. As a solution to reducing this, there is a method of reducing the unburned content in the ash by making the coal particle size finer at the outlet of the vertical mill 4. However, the fifth
Vertical mill 4 having a cyclone classifier 17 shown in the figure
In this case, there is a limit to the performance of the classifier 17, and even if the crushing capacity is lowered, it is difficult to obtain a particle size of 85% or more for 200 mesh passes.

Therefore, as a method of reducing the coal particle size at the outlet of the vertical mill 4, it is possible to employ a vertical mill with a built-in rotary classifier. However, in such a vertical mill 4, a part of the classified coarse coal is not returned to the crushing section, but rejoins the pulverized coal being transported and is sent to the classifier, which causes the coarse coal to be re-pulverized. As a result, the pulverization efficiency decreases and the pressure loss of the air flow necessary for transporting the particles increases, resulting in an increase in fan power, etc.
In addition, since the classifier has a mechanical drive unit, maintenance for the classifier increases.

This invention was made in view of the above-mentioned problems, and it is possible to improve the classification efficiency of the pulverized material and improve the particle size of the product without reducing the pulverization efficiency or unnecessary increase in fan power. The purpose is to provide a vertical mill.

[Means for solving problems]

In order to achieve the above object, the present invention includes a classifier, a crushing section in the upper part of the classifier, a supply section that supplies materials to be crushed to the crushing section, and a powder crushed in the crushing section and discharged from a discharge section. In a vertical mill equipped with a first introducing means for introducing gas to be transported to the classifier inlet side or re-transported to the crushing section depending on the particle size, the first introducing means introduces the gas into the classifier. This configuration is provided with a second introducing means for separately introducing a gas other than the gas that has been introduced.

[Effect]

The above means works as follows.

In other words, since the amount of air required to transport the fine powder particles after classification is constant, the amount of air introduced from the first introduction means for transporting the powder crushed in the crushing section and discharged from its outlet upward is equal to the amount of air introduced from the second introduction means. Compared to the case where there is no means, the drag force due to the airflow acting on each pulverized particle is small (becomes).Therefore, the primary classification performance, where the classification force is the gravity acting on each particle that is subjected to the drag force, is improved. , the amount of material to be crushed introduced into the classifier from the classifier inlet is reduced.

On the other hand, since gas is separately introduced into the classifier via the second introducing means, the amount of air supplied into the classifier can be kept constant at the same level as in the prior art, as described above.

Therefore, secondary classification performance, which classifies particles using centrifugal force caused by swirling airflow, reduces the amount of particles carried to the classifier, improves particle dispersion within the classifier, and improves secondary classification performance. Pulverized coal of desired particle size can be classified with high precision.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a sectional view showing a schematic structure of a vertical mill according to a first embodiment of the present invention. In this figure, each part that is the same or can be considered to be the same as that of the conventional example shown in FIG. 5 is given the same reference numeral, and a description of each part will be omitted.

In the figure, the position opposite to the air introduction side of the blade row 18 of the classifier 17 part 17a of the outer body forming the outer wall of the vertical mill 4, and the position where the air is introduced from the primary air population 22 of the supply duct 4a Supply ducts 4b and 4c for the primary air A are connected immediately downstream of the throat ring 23 in the flow direction, that is, to the upper throat 24, respectively. These supply ducts) 4b and 4c are branched from the cold air duct 2b connected to the forced draft fan 2 for primary air.
Cold air duct) 2b is forced ventilation m2 via air preheater 3
It communicates with the hot air duct 2a connected to the duct 2C via the duct 2C. These ducts 2a, 2b, 2c
, 4a, 4b, and 4c are each provided with a damper. Among these, the supply duct 4a of the hot air duct 2a has a damper 26 for controlling the flow rate of the primary air A supplied to the throat ring 23, and the supply duct 4b, 4c
dampers 27.2 for controlling the flow rate of primary air A, respectively.
8 further includes a damper 2 for temperature control in the duct 1-2c.
9 is provided. With this configuration, the supply duct 4b
and 4c, a mixture of hot air branched from the hot air duct 2a and cold air from the cold air duct 2b is guided. The temperature of this air is controlled by the damper 29 to maintain a preset value of, for example, about 80°C.

In the vertical mill configured as described above, the coal particles pulverized by the pulverizing ring 14 and the pulverizing roller 5 are dried by hot air introduced from the primary air intake 22 through the throat ring 23. Further, this hot air and the air introduced from the air supply duct 4c provided in the throat upper part 24 are transported upward inside the vertical mill 4.The speed of the hot air passing through the throat ring 23 is In order to prevent coal particles from falling from the throat ring 23, the speed is maintained at a certain value (for example, 40 m/s) or higher.

Pulverized coal particles flow from the throat upper part 24 to the separator population 17a
In the primary classification that occurs while the particles are being transported, the classification force is the gravity acting on the particles, and the separation diameter X of the particles is determined by the amount of air WA introduced from the throat ring 23 and the air supply duct 4c. is determined.

The partial separation efficiency η4 of the primary classification section can be expressed by the following equation.

77a = 0.98 (1-exp ((0,847
)”” ) ) (1) SO X,, =, W^
(2) where X is the particle size and k is a proportionality constant determined by the size of the device. (1) and (2)
From the equation, it can be seen that the primary classification performance changes greatly depending on the air amount WA. That is, if the primary classification performance is to be improved, the amount of air introduced from the supply duct 4c may be reduced by adjusting the damper 28.

The coal particles sent into the classifier ■7 pass through the blade row 18 along with the airflow, and are given centrifugal force by the swirling of the airflow.
Coarse coal particles are then separated. This secondary classification performance (classifier performance) is determined by the separation diameter X depending on the amount of air WB entering the classifier 17 if the angle of each blade in the blade row 18 is constant.

′ is determined.

The partial separation efficiency η8 of the secondary classification section (classifier 17) can be expressed by the following equation.

Here, k is a proportionality constant set by the separator structure, etc.
C is the coal concentration (b/kg) at the inlet of the classifier. (3)
According to equation (4), if the secondary classification performance is to be improved, the amount of air W8 introduced into the classifier 17 may be increased.

The total amount of air introduced into the mill is set to be the same as the conventional one in order to avoid the concentration of the pulverized coal sent from the pulverized powder outlet 25 to the burner 7a becoming diluted and unstable ignition and combustion. Now, the partial separation efficiency η when the amount of hot air introduced from the throat ring 23 is 70% of the conventional amount and the remaining 30% of the amount of air is introduced from the supply duct 4b to the separator 17a is calculated as follows. Figure 2 shows a comparison with The primary classification performance has been significantly improved as the amount of air passing through the primary classification section WA has been reduced to 70% of the conventional one, and the secondary classification performance (classifier performance) has also improved. result,
Since the coal concentration at the inlet of the classifier is reduced, it is improved compared to the conventional method. As a result of greatly improving the classification performance within the mill, the particle size of the product at the mill exit has also been improved, which was previously unachievable.
00 mesh pass of 90% could be achieved.

Furthermore, in addition to the conventional method of controlling the secondary classification performance by adjusting the angle of the blade row 18, the dampers 27 and 28 are adjusted to adjust the amount of air introduced into the mill from the supply duct 4c to perform the primary classification. Because performance can be controlled, the product particle size at the mill exit can be adjusted over a wider range than previously possible.

Furthermore, even if the combustibility of the supplied coal changes during mill operation and it becomes necessary to adjust the product particle size at the mill outlet, the feed duct 1 - Just adjust the amount of air from 4c and 4b. Therefore, in such a case, labor is greatly reduced.

Next, a second embodiment is shown in FIG. FIG. 3 is a sectional view showing a schematic structure of a vertical mill according to a second embodiment. In the figure, each part that is the same as or can be considered to be the same as that of the conventional example shown in FIG. 5 and the first embodiment shown in FIG.

In this figure, the second embodiment has the same structure as the first embodiment except that the supply duct 4c connected to the upper throat 24 of the first embodiment is omitted.

According to this second embodiment, the primary classification performance and the secondary classification performance can be controlled by adjusting the opening degrees of the dampers 28 and 29, and the same effects as in the first embodiment can be obtained. be able to.

In addition, in this second embodiment, in the case of coal that has a high risk of ignition or ignition within the mill, a supply duct 4b is connected to the air introduction side of the blade row 18 on the classification agricultural outlet side 17a. By directly introducing cold air into the reactor, it is possible to prevent coal from igniting or igniting. Furthermore, in the case of high moisture coal, the dryness of the coal can be increased by introducing hot air into the supply duct 1-4b.

Therefore, according to this second embodiment, in addition to the effects of the first embodiment, it is possible to arbitrarily control the temperature of the supplied air depending on the type of coal, and to maintain the predetermined particle size and dryness without the risk of accidents. The pulverized coal is transferred from the coal pipe 20 to the pulverized coal burner 7.
It can be sent to a.

〔Effect of the invention〕

As is clear from the above description, according to the present invention, which is provided with a second introducing means capable of introducing into the classifier a gas other than the gas passing through the discharge side of the crushing section, the gas is introduced into the classifier inlet. Since the amount of air introduced into the mill can be adjusted separately from the amount of air introduced into the upper part of the throat, it is possible to adjust the product particle size at the mill outlet over a wide range, and the particle size can be adjusted according to the combustibility of the fuel such as coal used. By doing so, over-grinding can be avoided and the mill operating power can be reduced. In addition, by maintaining the same amount of air in the classifier as before and reducing the amount of air introduced into the throat section, it is possible to improve the product particle size at the mill outlet. It has the advantage of being able to operate without reducing grinding efficiency or increasing fan power unnecessarily, unlike conventional mills.

[Brief explanation of the drawing]

Figures 1 to 3 are for explaining the embodiment.
FIG. 1 is a sectional view showing the schematic structure of the vertical mill according to the first embodiment, and FIG. 2 is a characteristic diagram showing the classification performance of the vertical mill according to the first embodiment and the conventional vertical mill. Fig. 3 is a sectional view showing the schematic structure of a vertical mill according to the second embodiment, Figs. 4 and 5 are for explaining the conventional example, and Fig. 4 is a system diagram of a coal-fired boiler system. 5 are cross-sectional views showing the schematic structure of a conventional vertical mill. 4a, 4b, 4c...supply duct, 12...
...Crushing table, 14...Crushing ring, 1
5. Old... Grinding roller, 17... Classifier, 17
a... Classification agricultural outlet side, 21... Coal feeding pipe, 23... Throat ring, 26.27, 28
．． 29...Damper. Figure 1 Figure 2 Figure 2

Claims (4)

[Claims] (1) A classifier, a crushing section at the bottom of the classifier, a supply section that supplies the material to be crushed to the crushing section, and a classifier that collects the powder crushed in the crushing section and discharged to the discharge side according to the particle size. In a vertical mill having a first introducing means for introducing gas to be transported to the inlet side or transported again to the crushing section, a classifier is used to remove gas other than the gas introduced by the first introducing means. A vertical mill characterized in that it is equipped with a second introduction means for guiding the inside. (2) In the statement of claim (1), the second
A vertical mill characterized in that the introduction means comprises an upper introduction means for introducing gas directly to the inlet of the classifier, and a lower introduction means for introducing the gas to the discharge side of the crushing section. (3) In the description of claim (2), the second
A vertical mill characterized in that the introduction means includes control means for respectively controlling the flow rates of the gases introduced from the upper introduction means and the lower introduction means. (4) In the description of claim (1), the first
and a vertical mill characterized in that each of the second introduction means includes control means for controlling the flow rate of the gas introduced.