JPS5817851A - Solid grinding method - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for comminution of solids, such as coal, which must be comminuted before being fed into a boiler, in a pulverizer.

An object of the present invention is to provide a method for efficiently pulverizing solids.

When a solid such as coal is mixed with a liquid such as water and ground, the mixture has a consistency that depends on the size and shape of the solid particles and the amount of liquid added. In a dry state or in a dry state or in a very wet state, it is almost like a liquid, so it also flows easily. In most liquid-solid mixtures, there exists an intermediate state in which there is little free flow. At this time, the particles in the mixture adhere to each other, i.e., clump together, forming a paste-like appearance.

In this state, the mixture is close to a solid in that it can maintain a certain shape, but close to a liquid in that it has little structural strength. This is the property of a mixture of sand and water that has a consistency suitable for building sand castles on beaches.

In this specification, the solid particles in such mixtures will be described as sticking together, and such mixtures will be described as sticky.

When a mixture is passed through a mill, the amount of time the mixture is in the mill (residence time) is usually an important factor in determining how finely it is ground. When the mixture is in a flowable state, gravity determines how long it takes to pass through the mill. On the other hand, when the mixture is sticky and the mill is equipped with channels that move during operation of the mill,
The residence time of the mixture can be varied. By carefully selecting the speed of the mill and the size and speed of movement of its channels, the sticky mixture can be kept in the mill indefinitely or forced upwards against gravity. It can also be sent downward faster than with gravity alone. In the absence of such channels, even sticky mixtures move through the mill under the action of gravity alone (despite frictional and adhesive resistance).

A mill with movable channels arranged so as to be able to convey a viscous mixture will be described herein as "conveying capable." The channels are also configured to direct the mixture in a direction that will help gravity (or other forces used to move the mixture into and out of the pulverizer) to move the mixture through the pulverizer. Sometimes the transport will be referred to as "positive", and conversely, when the channel transports the mixture against gravity, the transport capacity will be referred to as "negative".

The invention is based on the recognition that viscous mixtures can be milled at low cost by mills with positive conveying capacity. Without positive transport, the mixture will remain in the mill because the solid particles in the mixture will not only stick to each other, but also to the mill itself. Traditionally, some mixtures such as foodstuffs must be ground to an extremely sticky consistency, and in such cases it is necessary to provide the grinder with a positive feed capacity in order to send the mixture out of the grinder. There was a need. This feed capacity, similar to the positive conveyance capacity described above, is used to push or aspirate the mixture from the inlet to the outlet of the crusher when gravity cannot transport the mixture from the inlet to the outlet of the crusher. The ability to apply such pressure to the mixture. However, when trying to use such pressure, there must be no voids in the mixture in order to send the mixture using such pressure.
A new problem arises. To crush it in this way,
While it may be possible and economical for certain foods, such as chocolate, for other mixtures, such as coal and oil, which become extremely hard in a sticky state, such If the mixture is too full in the grinder, the power consumption will be too high.

In the present invention, the mill is provided with a positive conveying capacity, which allows the mill to be used with highly viscous mixtures that will not move within the mill without pressure. Due to its positive conveying capacity, the mixture can be conveyed through the crusher even when the crusher is not full of the mixture.

Even if the mixture is so hard that it cannot be moved by gravity, i.e., has a high viscosity, it can be batch-pulverized, i.e., the batch of mixture is put into the pulverizer while the pulverizer is stopped, and the pulverizer is stopped and taken out after the pulverization is finished. It can be crushed if

According to such batch pulverization, the pulverizer does not need to have feeding or conveying ability, and the inside of the pulverizer does not need to be full during pulverization.

However, batch milling is much less economical than continuous milling, to which the present invention is primarily directed.

Furthermore, the present invention provides that if a solid is ground in a grinder with positive conveying capacity by adding a liquid to the solid to form a sticky mixture, the grinding efficiency is determined by the amount of liquid added to the solid. It is based on the recognition that it depends on In the present invention, it is desirable to grind the solid by mixing the solid with an amount of liquid that maximizes the grinding efficiency.

In the present invention, pulverization efficiency does not refer to a specific efficiency. What is most efficient usually depends on what is most economical, and what is most economical depends on various factors.

Therefore, criteria for efficiency and economic efficiency must be determined on a case-by-case basis. For example, in some cases the criterion of economy may lie in a compromise between the fineness of the ground particles and the power consumption of the grinder (this compromise varies depending on regional differences in electricity prices); , the fineness of the ground particles will be a compromise with the capital expense of the grinder required to obtain that fineness within a given throughput of solids.

Whatever the economics criterion one takes in that case, experiments are conducted in the present invention to determine how the economics of comminution (according to that criterion) changes by varying the throughput of added liquid. Through that experiment,
Once it is determined that there is a throughput of liquid that maximizes economics (on that basis), that throughput is used to perform the milling under the particular conditions of the case.

Of course, there are other factors besides liquid throughput that affect grinding efficiency. It is important to keep other factors constant when varying the throughput of liquid added during an experiment.

In the experiments described below, a measure of efficiency that is particularly emphasized is the proportion of particles that pass through a mesh of a given size after milling. The percentage of particles that pass through a mesh of a given size after grinding divided by the power consumption required to drive the grinder was also investigated as another measure of efficiency.

These experiments showed that the fineness of the ground particles varied with the amount of liquid added to the solids throughput. It was also found that the mixture of solid and liquid was most finely ground when its viscosity was highest, although there was some deviation. Furthermore, it was found that the power required to drive the mill also varied with the throughput of the applied liquid, and was greatest when the mixture was most viscous.

The present invention will be explained in more detail below with reference to the drawings.

1 and 2, a crusher 10 includes a housing 12 having a cylindrical inner surface 14. As shown in FIGS. This housing 1
2 is a part of a fixed frame (not shown) of the crusher 10.

A rotor assembly 16 is disposed within the housing 12. The shaft 18 is rotatably supported by a bearing 20 housed within the fixed frame, and is driven by a motor (not shown). A pair of drive plates 22 (22A, 22B) are fixed to the shaft 18 with keys. The shaft 1 is located between the two drive plates 220.
Three rollers 24 are mounted for free rotation relative to their drive plate 22 about an axis parallel to 8.

As shaft 18 rotates, drive plate 22 rotates with it, causing each roller 24 to roll over inner surface 14 of housing 12. Each roller 24 is supported by a somewhat flexible shaft 26 such that the force with which each roller 24 is pressed against the inner surface 14 is primarily provided by centrifugal force due to rotation of the rotor assembly 16. The point of contact between the roller 24 and the inner surface 14 has only friction and almost no slip, so that the roller 24 rotates in a direction opposite to the rotation of the shaft 18.

In operation, the crusher 1O is mounted with the shaft 18 vertical and the solids to be crushed are placed on the upper drive plate 22A at the top of the crusher 10 using a suitable feeding device such as a vibrating hopper (Fig. (not shown). Liquid is also introduced into the top of the grinder 10 from a pipe (not shown). The mixture includes drive plate 22A and housing 12.
falls into the annular gap 28 between the inner surface 14 of
Finally, it is discharged from the machine through the annular gap between the lower drive plate 22B and the inner surface 14.

The pulverized mixture is collected in a suitable collection means (not shown) such as a hopper located below the pulverizer.

The crusher 10 has a "positive conveyance capability".

That is, each roller 24 is formed with a spiral groove 30 that constitutes the channel. As the rotor assembly 16 rotates, its helical groove 30 tends to direct material within the machine upwardly or downwardly depending on the direction of rotation. The spiral groove 30
Many factors are involved in the amount of force that the aircraft applies to the material inside the aircraft.

The first factor is the consistency of the material.

Both gravity and the spiral grooves 30 affect the rate at which the solid and liquid mixture passes through the grinder 10. When the amount of liquid in the mixture is extremely small, most of the mixture passes through the crusher 10 under the influence of gravity alone, and the spiral groove 30
The effect of this is extremely small. This is especially true for dense materials such as metals and ores.

In the case of light, fluffy materials such as pieces of paper, the spiral grooves 30 have a significant effect on the speed of movement, even when dry. Similarly, when the amount of liquid in a mixture is extremely large, and therefore the mixture is thin and highly fluid, it will fall through the machine almost solely by the action of gravity. On the other hand, if the mixture is highly concentrated and viscous, the mixture can support itself to some extent and has a large influence on setting the residence time of the mixture.

When the consistency of the mixture is such that the residence time is influenced by the presence of the spiral grooves 30, the residence time is
It is also influenced by other factors such as the number of two threads, the lead and pitch of the spiral, the flank angle of the side surface of the spiral groove 30, the diameter of the rollers 24 and 71 and the housing 12, and the rotational speed of the shaft 18 and roller 240.

If the liquid content in the mixture is too high or too low, the mixture cannot remain in the mill for sufficient time to be milled. Also, if the mixture is too sticky, the mixture will remain in the mill almost indefinitely without positive conveying capacity. Will. Therefore, by providing a positive conveying capacity, it is possible to control the crushing of a sticky mixture.

However, when the helical groove 30 exhibits a positive conveying ability, the three helical grooves must not become clogged. Therefore, the rotational speed of roller 240 is $
The height must be such that the mixture can flow out of the groove 30 and at least partially empty the groove 30. This ensures that the mixture in the groove 30 is constantly replaced. When the viscosity of the mixture is extremely high, depending on the structure of the groove 30, the mixture may become completely stuck therein. That is, as the grooves 30 on the rollers 24 roll over a portion of the inner surface of the housing, the mixture flows into the grooves 30.
There is a possibility that the groove 30 may be pushed into the groove 30 with an extremely large force and become unable to be ejected from the groove 30 due to centrifugal force. Such defects cannot be corrected by increasing the speed of the mill, since the greater the centrifugal force, the more firmly the mixture is forced into the grooves 30. In such cases, the grooves 30 must be made larger or the sides of the grooves 30 must be provided with a flank angle (1°). can be considered as the axial screw feed capacity. In other mills the positive carrying capacity may be given somewhat differently, but essentially the A channel is required that moves at a temperature that affects the residence time of the mixture.

When using a crusher according to the method of the present invention, the following experiment is first performed. A certain amount of the solids to be ground is passed in dry form through the grinder at a predetermined speed. Record both the rotational speed of the mill and the power required to maintain that speed. The milled solids are collected and the main particle size is determined.

Then add a certain amount of liquid to the solids to be ground and repeat the process. The speed at which the solids are passed through the pulverizer is the same as before, so that the sum of the amounts of liquid and solids passed through the pulverizer is larger by the amount of liquid. Measure the particle size and power consumption after grinding again.

A similar experiment is carried out by gradually increasing the amount of liquid added.

Figures 3 and 4 are graphs showing the results of the above experiments using a mixture of coal and water. The amount of coal passed through the crusher was maintained at a constant throughput (720K) throughout the entire experiment.
g/hr). Also, the shaft rotational permeability is 1250
rpm. In FIG. 3, the vertical axis represents the predetermined mesh size (100 mesh, 200 mesh) after crushing.

325 mesh). The vertical axis in FIG. 4 is the power consumption of the shaft drive motor.

As is evident from Figure 3, the fineness of the ground coal is maximized when the amount of water added is slightly less than 40% of the amount of coal.

Graphs like Figure 3 can be drawn for all solid-liquid mixtures. In the present invention, when the graph has a maximum value as shown in FIG. This is based on the recognition that it can be used to determine what level of consistency should be used.

In addition to coal and water, we conducted the above experiment on coal and oil, mica and water, zinc and water9 limestone and water, and all of them had the maximum values as shown in Figure 3. It has been found that the verge/stage of the added liquid at which the fineness of the milled particles is maximized varies in a somewhat unpredictable manner. FIG. 6 is a diagram similar to FIG. 3 in the case of a mixture of limestone and water. As is clear from FIG. 6, the position of the maximum value and the shape of the graph around it vary depending on the fineness selected as the scale. The top curve is for 100 mesh or 150μ, the second curve is for 200 mesh or 75μ, and the bottom curve is for 3
This is the case of 25 meshes, that is, 45μ. The consistency of the mixture required to obtain maximum fineness is thus related not only to mill speed, throughput speed, helical shape, etc., but also to the actual measure of fineness itself.

In experiments using a mixture of zinc and water, it was found that if the amount of water was extremely small, the ground zinc particles would agglomerate, making grinding impossible. The zinc needs to be somewhat moist for it to grind properly. These factors affect the position of the maximum value on the graph and the shape of its surroundings. However, it is necessary that there be a maximum value.

Figures 9 and 10 are graphs corresponding to Figures 3 and 5, respectively, when the coal passing speed was increased to 9/h to 1200. It can be seen that the size and position of the peaks have changed. This implies that there are important factors other than liquid content that affect efficiency.

The graph of power consumption, as shown in FIG. 4, also depends on the amount of liquid added and has a maximum value.

The maximum power consumption coincides with the maximum viscosity of the mixture.

The width of the peak in the graph of power consumption versus amount of liquid added (Figure 4) is narrower than the width of the peak in the graph of fineness of ground particles versus amount of liquid added (Figure 3). The mill must be scaled not only by the fineness of the particles within a given throughput, but also by the energy consumption required to achieve that fineness. As mentioned above, since the widths of the peaks are different, by slightly shifting the amount of water added from the rate at which the energy consumption is maximum, it is possible to significantly reduce the energy consumption (and also reduce the fineness that can be obtained). doesn't change much.

FIG. 5 shows this effect. The graph in Figure 5 is derived from the graphs in Figures 3 and 4, and the value at each point in the graph in Figure 5 is calculated by subtracting the value in the graph in Figure 3 corresponding to the water percentage at that point. It is t divided by the value of the graph in the figure.

The peaks in the graph of FIG. 5 therefore represent an effective compromise between power consumption and resulting fineness, both of which depend on the viscosity of the mixture. It is easy to guess if you look at the graphs in Figures 3 and 4, but the 5th
The graph in the figure has two peaks. It is desirable to match the viscosity of the mixture to the peak on the right side of FIG. This is because the peak on the right is not only higher (this may not be the case depending on the type of mixture and conditions), but also because the peak on the right is broader. The broader the peak, the greater the degree of freedom of the control means for controlling the amount of liquid. Furthermore, in the graph of FIG. 5, the peak is reached when the amount of water added is 50%, but even if the amount of water increases, the efficiency decreases extremely slowly. A larger proportion of water is advantageous in that the grooves in the crusher can be emptied more easily. On the other hand, it is also bad to have too much water in the mixture, because if the water is not dried before the coal is fed into the boiler, it will evaporate in the boiler. The water content was determined. In particular, when the water content is approximately 70%, the efficiency begins to drop significantly compared to when the water content is 50%. When the grooves are large enough and there is no risk of the mixture clogging the grooves, the water content is 40%
Even a percentage is acceptable. If it is less than 40%, the efficiency will fall into the valley shown in Figure 5, and the economic efficiency will deteriorate significantly. Experiments have shown that in the case of coal-oil mixtures, the range for maximum efficiency is between 30% and 6% liquid (oil) content.
The range is 0%.

As mentioned above, all of the mixtures subjected to the experiment had peaks in both the fineness graph and the power consumption graph. However, the height and location of the peaks are different. Figure 7.8 shows the change in power consumption and resulting efficiency for the limestone and water mixture shown in Figure 6.
, 5 respectively.

The solid and liquid forming the mixture may or may not be premixed before entering the mill. When solids are in the form of powder or dust before being crushed (as is often the case with coal), liquids may be added before entering the crusher to control the dust, especially if the dust is explosive. It is desirable to add at least a portion of the solid to the solid. However, since the more viscous the mixture, the more likely it is to clog conveyors and conduits, it is usually desirable to introduce the solids and liquids separately into the mill so that all practical mixing takes place within the mill.

Although in the above description the grinder is placed vertically, it is also possible to place it in other planes, for example horizontally. It is clear that the effect of gravity is different when the crusher is placed horizontally than when it is placed vertically. However, even if the mill is placed horizontally, it is possible to force the mixture through the mill using gravity alone. i.e. the "head" of the mixture
may be placed at the inlet so that the pulverized mixture can fall from the outlet. Similarly, the mill can be tilted at different angles to vary the influence of gravity on the throughput speed.

Although the mixture may be introduced into the mill by a pump, the mixtures to which the present invention is primarily concerned are generally very sticky and are often not easy to pump.

Coal and water mixtures and coal and oil mixtures can be pumped except in cases of maximum consistency.

Once the experiment is complete, it is possible to determine from the graph the amount of liquid to add that will give the highest efficiency, which is determined by the fineness of the particles crushed and the power required to obtain that fineness of particles. Efficiency is determined by a scale deemed appropriate depending on the case, such as fineness as a compromise with consumption. After selecting the amount of liquid to be added, production grinding can begin. At this time, the amount of liquid added is controlled manually or automatically.

There are some mixtures in which no peak appears when plotting the effect of the amount of liquid added on the grinding efficiency, and the method of the present invention is not suitable for such mixtures.

Ore and minerals have peaks when mixed with water, oil, or liquid carbohydrates that are lighter than oil. Ceramics and metals also have peaks.

However, in many food materials such as seeds for oil extraction, which contain an oily liquid within the cellular matrix and the liquid comes out as soon as grinding begins, the amount of liquid inside is greater than the amount that provides maximum efficiency. It often does not have a peak because it becomes In other words, even such a product will have a peak if some of the liquid originally contained therein is removed before pulverization, but such a process is completely uneconomical. However, if such materials can be made to peak by drying or freezing before grinding,
The present invention can also be applied to such materials. Furthermore, it is extremely difficult to crush materials such as rubber and resin unless they are frozen beforehand.

Some materials liquefy (i.e., the ratio of solid to liquid changes) as the solid dissolves in the liquid as milling progresses. Also, some materials must be milled with too much liquid added to make them sticky. For example, there is something like this in paint. However, pigment powders used in paints can be made sticky without changing their properties, and the method of the present invention is effective for such pigment powders.

Some materials cannot be used with the method of the invention because they are soluble in water or other inexpensive liquids (eg fertilizers). Furthermore, there are some materials, such as cement, whose chemical properties change when moistened, so that the method of the present invention cannot be used.

The properties of the added liquid can affect the sharpness and position of the peak. For example, oil does not penetrate into the pores of coal as well as water. Therefore, in the case of coal, it is possible to obtain a peak with a smaller amount of oil than with water, and carbon products such as coke, graphite, and carbon blank tend to show similar differences. Such a carbonaceous material can be mixed with a low molecular weight alcohol such as methanol or ethanol, or a mixture of water, oil, and alcohol and then pulverized.

Some mixtures exhibit rheological nonlinearities that can affect peak sharpness and position, such as being pseudoplastic, dilatant, or thixotropic.

[Brief explanation of drawings]

Fig. 1 is a plan view of an example of a crusher used to carry out the method of the present invention, Fig. 2 is a perspective view of a part thereof, and Figs. It is a graph showing the influence of quantity. 10...Crusher 12...Housing 1
4...Inner surface 18...S
Shaft 24...Roller 3o
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Claims (9)

[Claims] (1) A method for pulverizing a solid in a pulverizer, comprising the step of mixing the solid with a liquid in such a proportion that a mixture having a viscous consistency is obtained, the pulverizer displacing the viscous mixture from an inlet to an outlet. A method characterized in that the method comprises a channel means for forcing the channel to the channel. (2) Determine by experiment whether the grinding efficiency changes as a function of the proportion of solid surface liquid in the mixture, and if it changes as a function of the above, adjust the amount of liquid in the mixture to the amount that provides the best grinding efficiency. 2. A method according to claim 1, characterized in that: (3) The amount of the liquid that provides the best pulverization efficiency is an amount that maximizes the proportion of the solid particles that can pass through a mesh of a predetermined size among the solid particles after pulverization. The method according to claim 2. (4) The amount of liquid that provides the best grinding efficiency is sufficient to operate the grinder to obtain the value of the fineness of the ground particles expressed as the percentage of particles that pass through a mesh of a given size. 3. The method according to claim 2, wherein the amount is such that the value divided by the required power is maximized. (5) The method according to any one of claims 1 to 4, wherein the solid is coal and the liquid is water. (6) The method according to any one of claims 1 to 4, wherein the solid is coal and the liquid is oil. (7) The method according to any one of claims 1 to 4, wherein the solid is zinc and the liquid is water. (8) The method according to any one of claims 1 to 4, wherein the solid is mica and the liquid is water. (9) The method according to any one of claims 1 to 4, wherein the solid is limestone and the liquid is water. 6. Process according to claim 5, characterized in that α0) the amount of water added to the coal is approximately 40-70% of the throughput mass of the coal. 7. A method according to claim 6, characterized in that the amount of oil added to the coal is approximately 30-60% of the throughput mass of the coal. 12. A method according to any one of claims 1 to 11, characterized in that the mixture is continuously fed to the grinder.