JPH0510140B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a pulverizer, and more particularly to a pulverizer configured to significantly reduce the amount of pulverized material falling to the bottom of the device.

Due to recent changes in the fuel situation, the number of large boilers for business use such as large boilers for thermal power plants that use coal as fuel is increasing. Ru. By pulverizing the coal in this way (e.g. 200 mesh passing rate of 70% or more), the surface area of the coal per unit amount increases, improving combustibility, and since it burns in a short time, controllability is also greatly improved. There is an advantage of doing so. FIG. 1 shows a crushing device called a vertical ball mill as an example of a vertical crushing device for crushing this coal. Coal c to be pulverized falls through the coal feed pipe 8 of the pulverizer main body 1 and reaches the pulverizer. The crushing section includes an upper fixed wheel 6 to which a pressing force is applied by the pressurizing device 4, a lower roller 9 rotated by the drive device 41, and a lower roller 9 disposed between the upper fixed wheel 6 and the lower roller 9. It is formed from a plurality of grinding balls 7 which are grinding members that roll together with the rotation of the ball 9. The coal that has reached the crushing section passes through the lower roller 9
Due to the centrifugal force generated by the rotation of the ball, the powder is moved to the crushing ball arrangement section, crushed, and discharged to the outer periphery of the wheel. The pulverized coal is passed through air port 1, which is the gas supply port.
The inside of the device is heated by gas (usually high-temperature air to dry the coal) supplied from 7 and ejected from the slits of an annular plate 15 (hereinafter simply referred to as a porous body) having a plurality of arcuate slits. During this time, the large-diameter particles fall into the crushing section as shown by the arrow 14 and are primarily classified, and the air flow containing the remaining crushed coal is given a swirling force by the guide vanes 12 of the classifier 11, and the air flow inside the classifier 11 is flows into. In the classifier 11, large-diameter particles descend through the classifier due to the swirl of this airflow, fall into the crushing section, and are re-pulverized, while the pulverized coal is transported to the pulverized coal pipe 13 along with the airflow.
The pulverized coal flows into the burner as primary air and is transported to the burner together with the pulverized coal.

2 and 3 relate to the structure of the perforated plate attached to the above apparatus. The perforated plate 15 is the lower roller 9
The perforated plate is formed and arranged in an annular manner along the periphery of the perforated plate, and air injection openings including those having a slit shape are formed in this perforated plate. The air injection opening is formed as a slit as shown in FIG. 3, and air is ejected from the slit 18 and the circumferential gap 19 between the perforated plate 15 and the lower roller 9. in this case,
As shown in FIG. 2, the slit 18 opens perpendicularly to the opening side surface of the perforated plate 15. Also, during operation, there is a flow of pulverized coal along the upper surface of the perforated plate, and it is blown upward by the air injected from the perforated plate. However, when examined in detail, a vortex of the injected gas is generated on the wall of the gas passage of the slit 18, and a part of the pulverized coal is drawn along the wall of the slit as it is attracted by this vortex. It will fall to the bottom.
With the recent increase in the capacity of the lower air chamber due to the increase in the capacity of the crusher, the uneven flow within the air chamber becomes larger, and this uneven flow tends to further increase the amount of pulverized coal that falls.

Fallen powdered coal is heated by high-temperature gas and is dangerous and easily ignites, so it is cooled down by water spraying, etc. However, since the removal of fallen coal relies on manual labor, moisture Discharging coal containing carbon dioxide requires a great deal of effort.

In addition, one method to reduce the fall of pulverized coal is to reduce the width of the slit and increase the injection speed, but this increases the pressure loss in the perforated plate and significantly increases the power cost of the blower. There is a problem with doing so. Furthermore, when the diameter of the hole is reduced, there is a problem that once the pulverized coal becomes clogged, the injection port becomes clogged for a long time.

The present invention has been constructed in view of the above-mentioned problems, and relates to a pulverizer that prevents the pulverized material from falling without increasing the pressure loss of the perforated plate.

In short, the present invention provides a rotating wheel provided in an apparatus, a crushing member provided on the wheel to pressurize the wheel, and an outer circumferential portion of the wheel that is crushed by the wheel and the crushing member. In a vertical crusher equipped with a perforated plate having an opening through which a gas body passes from the bottom to the top in order to classify the crushed material discharged from the
The vertical crushing device is characterized in that the ratio between the depth of the hole in the perforated plate opening and the length of the opening in the radial direction of the rolling wheels is 1.3 or more.

First, prior to carrying out this invention, the inventors conducted the following experiment and determined the depth of the holes in the perforated plate to be T.
The dimension (width) of the slit in the radial direction of the wheel is b
The relationship between T/b and the amount of fallen pulverized coal was investigated in the case where: Note that the side wall of the air injection opening is normally formed to be perpendicular to the surface of the perforated plate. Note that the air injection opening does not necessarily mean one that injects only air, but may also inject a gas mixture with combustion gas or the like depending on the operating conditions of the device.

FIG. 4 shows the results of a pulverized coal drop experiment using air injection openings with different T/b by forming air injection openings with a predetermined dimension b on a plurality of metal plates having different thicknesses. A in the figure is the hole diameter
An air injection opening of 28 mm, B of 20 mm, and C of 15 mm was formed, and the changes in the amount of coal falling at each T/b were measured. As is clear from this figure, the falling amount is maximum when T/b is approximately 1 for air injection openings of any hole diameter, and it can be confirmed that the larger the b dimension of the air injection opening, the greater the falling amount. Ta. However, it was confirmed that for any outer diameter, the amount of falling coal decreases significantly when T/b becomes about 1.3 or more, and the absolute amount of falling coal remains almost the same regardless of the hole diameter. However, mainly due to the need to ensure its strength, perforated plates cannot be made very thin, and the wall thickness is often around 20 to 30 mm. Conventionally, for perforated plates of this thickness, b dimension is 20 to 30 mm.
A 30 mm air injection opening is formed, and the hole length/hole diameter ratio of the conventional perforated plate is approximately 0.7 according to this experiment.
It was found that the value was set to be close to the worst value from the viewpoint of preventing crushed coal from falling.

Next, the reason why the fall of the pulverized coal changes due to the change in T/b will be explained with reference to FIG. The behavior of this pulverized coal was confirmed through experiments by the inventors. During the experiment, the amount of air supplied and therefore the wind speed of the supplied air were made to correspond to the wind speed of the actual crushing device. The inventors changed T/b by forming air injection openings with the same dimension b in perforated plates having different thicknesses. The b dimension of each air injection opening 18 is 28 mm,
The thickness of the perforated plate 20 of A was 5 mm, the thickness of the perforated plate 21 of B was 25 mm, and the thickness of the perforated plate 22 of C was 50 mm.
In other words, A's T/b is about 0.18, B's is about 0.9, and C's is about 1.8.
It is. First, in case A, the crushed coal layer 23 formed on the surface of the perforated plate 20 is scattered by the air A injected from the back surface of the perforated plate 20, but the air injection holes 1
When air passes through 8, a vortex 24 is formed along the side wall of the injection hole, and a part of the pulverized coal is attracted by this vortex 24 and falls to the lower part of the perforated plate. However, since the plate thickness is thin, the side wall portion is short compared to dimension b, and the vortex is small, the amount of pulverized coal that is attracted is not very large. On the other hand, B's T/b
When is about 0.9, the vortex region 25 that is formed is large and attracts the crushed coal with a large attractive force, so that the amount of coal that falls also increases. Furthermore, in the case of C, even if a rectified flow is formed and a small eddy current is formed, the vortex area does not reach the perforated plate surface because the hole length is long.
Therefore, almost no pulverized coal can be attracted.
Therefore, the amount of coal falling to the bottom of the perforated plate will be significantly reduced.

As is clear from the above explanation, the T/b value of the slit, which is the air injection opening formed in the perforated plate, is 1.3.
It is necessary to do more than that.

FIG. 6 shows a configuration in which T/b can be changed more easily. T/b can be increased by decreasing the b dimension of the air injection opening or increasing the wall thickness of the perforated plate, but reducing the b dimension of the air injection opening will significantly increase the power cost of the blower. Furthermore, it is not preferable to make the perforated plate thicker than the required perforated plate strength because it is uneconomical and increases the weight of the device. As a countermeasure for this, a rectifying plate 30 having a length L longer than the wall thickness of the perforated plate 15 is arranged with respect to the air injection opening 18 to increase T/b. This embodiment is effective in cases where it is difficult to increase the wall thickness of the perforated plate when it is desired to increase the b dimension of the injection opening, and in particular, it can be easily applied to the perforated plate of a conventional device. can do. For example, if a straightening plate with a length L of about 55 mm is attached to the air injection hole with a hole diameter of 28 mm, and T/b is about 2, the amount of falling coal will be about 1 compared to when T/b is about 1. It was confirmed that it can be reduced to /35. In addition, the end face on the air inflow side is chamfered or rounded as shown in Figure 5c.
It is effective to curve the surface (FIG. 6, 30a) to prevent the formation of eddies. It is desirable that the radius is approximately 1.5 mm or more.

By carrying out this invention, the amount of falling pulverized material can be significantly reduced without increasing the pressure loss of the perforated plate.

Further, since the present invention is effective simply by setting T/b to an appropriate value, the device does not become complicated and the manufacturing cost of the device does not increase.

[Brief explanation of the drawing]

Figure 1 is a sectional view of the coal crusher, Figure 2 is a sectional view of the perforated plate, Figure 3 is a view taken along line A-A in Figure 2, and Figure 4 is the relative relationship between T/b and the amount of falling coal. Figures 5A to C are cross-sectional views of a perforated plate showing the state of coal falling from the air injection opening, and Figure 6 is a cross-sectional view of a perforated plate showing an embodiment of the present invention. be. 15, 20, 21, 22...perforated plate, 18...
Air injection opening, 30... rectifying plate, 30a... curved surface.

Claims (1)

[Claims] 1. A rotating wheel installed in the device, and a crushing member provided on the wheel in a pressurized state against the wheel,
In a vertical crushing device comprising the above-mentioned wheel and a perforated plate having an opening through which a gas body passes from the bottom to the top in order to classify the crushed material crushed by the crushing member and discharged to the outer periphery of the wheel, The ratio between the depth of the hole in the perforated plate opening and the length of the opening in the radial direction of the rolling wheel is 1.3.
A vertical crusher characterized by the above.