JP2829662B2 - Centrifugal classifier - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention introduces a raw material slurry 9 composed of powder and granules composed of particles having various particle diameters and a liquid into a cylindrical rotary bowl 2 and a centrifugal force. The present invention relates to a wet-type centrifugal classification device for classifying particles by acting on the particles, and more particularly to a device for suppressing the mixing ratio of fine particles into a coarse particle product.

[Prior Art] For the purpose of rapidly classifying powders composed of particles having various particle diameters at an ultra-low particle size in the submicron region, the sedimentation speed of particles in a liquid under normal gravity A centrifugal classification device capable of performing classification in a larger size is used.

Conventional devices of this type are roughly classified into two types: a batch type batch type and a screw decanter type continuous type.

First, a conventional basket-type batch centrifugal classifier will be described with reference to FIG.

In FIG. 3, the raw slurry 9 is supplied to the inside of the rotary bowl 2 through the raw slurry supply pipe 5, and
Through the bottom wall 16 of the rotating bowl.

On the other hand, a part of the stagnation liquid 13 overflows from the inner peripheral surface of the dam ring 17 at the upper part of the rotating bowl 2 in a manner of being pushed out by the raw material slurry 9 flowing into the lower part of the rotating bowl 2, and overflows as an overflow 11. And flows out of the device.

The supplied raw material slurry 9 is accelerated to the same rotation speed as the rotating bowl 2 (usually 500 to 3000 rpm) due to frictional force between the rotating bowl bottom wall 16 and the rotating bowl inner wall 15 of the rotating bowl 2, and as a result, the rotating bowl 2 The centrifugal force of several hundreds to several thousand G acts on the stagnation liquid 13 in the liquid 2, and the powder particles in the stagnation liquid 13 move in the direction of the centrifugal force, that is, the rotating bowl of the rotating bowl 2. Settling to the inner wall 15 side starts.

Here, the sedimentation velocity of the granular material particles in the liquid increases as the particle diameter increases, so that the coarse particles having a high sedimentation velocity settle down to the inner wall 15 of the rotating bowl 2 of the rotating bowl 2 and are captured there. However, the fine particles having a low sedimentation velocity do not settle to the inner wall 15 of the rotating bowl 2 and overflow with the liquid from the inner peripheral surface of the dam ring 17 on the upper part of the rotating bowl 2.

The powder and granules supplied in this way are classified into two products, a fine product in the overflow and a coarse product remaining in the stagnant 13 in the rotating bowl 2 for classification.

In a batch type apparatus, the supply of liquid is stopped before the coarse particles remaining in the retained liquid 13 accumulate and adversely affect the classification performance. (Usually pumping by a discharge pump) is required.

Therefore, the classification is performed by a batch operation including the repetition of two steps of the classification step and the coarse particle product discharging step.

Next, a conventional screw decanter type continuous centrifugal classifier will be described with reference to FIG.

The difference from the above-mentioned batch type apparatus is that coarse products settling on the rotating bowl inner wall 15 side of the rotating bowl 2 can be continuously discharged to the outside of the rotating bowl 2, so that the lower part of the rotating bowl 2 has a conical shape. In addition, a screw conveyor 18 is built in.

Since the screw conveyor 18 is rotated at a slightly lower speed than the rotary bowl 2 by the differential device, the settled coarse-grained product is opposite to the overflow of the fine-grained product while being scraped off by the tip of the screw conveyor 18. And is discharged to the outside of the rotating bowl 2.

Because of the mechanism for continuously discharging the sedimented crude product, the classification operation can be performed continuously, but the basic mechanism of the classification itself is a screw decanter type continuous The device is not much different from the batch device.

Since the present invention has been achieved by improving a classification mechanism common to batch and continuous apparatuses, the classification mechanism of a conventional centrifugal classification apparatus will be described in further detail.

The classification mechanism of a wet centrifugal classification device is already well known and is described in detail in, for example, Chemical Engineering Handbook (Chemical Engineering Association, edited by 4th edition, p1115, 1978-Maruzen).

According to the document, the particle classification mechanism of a parallel flow type classifier including a batch type and a continuous type centrifugal classifier is described as follows.

Here, the description will be given taking a batch type apparatus having a simple structure as an example. (See FIG. 3).

It is assumed that the raw material slurry 9 flows from the lower end of the rotating bowl 2, forms a usable parallel flow (with respect to the rotating shaft), rises in the rotating bowl 2, and overflows from the upper end of the rotating bowl 2.

The granular material particles in the retained liquid 13 in the rotating bowl 2 have the same speed as the slurry in the moving direction of the slurry (here,
While moving u _H and hereinafter), the rate given by the direction of action of centrifugal, i.e. from moving at a settling velocity u _S in a direction perpendicular to the parallel flow, eventually of synthesizing u _H and u _S It moves in the classifier in the direction of u.

Here, the velocity u _H is the same for all particles, but the velocity u _s (the sedimentation velocity of the particles in the liquid) differs depending on the particle size, and the sedimentation velocity increases as the particle diameter increases, In the rotating bowl 2, particles having a larger particle diameter settle down to the rotating bowl inner wall 15 earlier.

Whether or not the particles remain in the rotating bowl 2 is determined by whether or not the particles settle to the rotating bowl inner wall 15 during the time when the slurry moves from the lower end to the upper end of the rotating bowl 2.

Only particles having a low sedimentation velocity that do not settle to the inner wall 15 of the rotating bowl within the time the slurry stays in the rotating bowl 2 flow out of the rotating bowl 2 together with the liquid, whereby classification is achieved.

Therefore, the classification of particles having a certain particle size as a boundary is calculated as follows.

That is, it is considered that the classification is performed when the time required for the particles to settle from the liquid level 14 of the stagnant liquid 13 to the inner wall 15 of the rotating bowl is equal to the time required for the slurry to stay in the rotating bowl 2 of the slurry. First, Equation 1 is obtained.

_{H / u s = V / Q} -1 formula where, H: rotary bowl inner wall from settling distance (retentate liquid surface 14
15), u _S : sedimentation velocity of particles, V: rotating bowl 2
And Q: the liquid supply speed (volume speed) of the raw slurry 9.

Next, the sedimentation velocity u _S of the particles is considered to be equal to the final sedimentation velocity u _m of the particles in the gravitational field multiplied by the centrifugal effect Z according to the Stokes equation, and the following equation 2 is obtained.

_{u s = u m · Z =} (g · (ρ s -ρ L) · D 2 / 18μ) Z -2 formula where, g: gravitational acceleration, [rho _s: the density of the particles, [rho _L: Density of the liquid, D : Particle size of particle, μ: viscosity of liquid. Substituting equation 2 into equation 1 and rearranging yields an equation that gives the separation limit particle size D as shown in equation 3.

D = (18 · H · μ · Q / (V · g · (ρ _s −ρ _L ) · Z)) ^0.5 -3 Formula As shown in Formula 3, the same raw material slurry (therefore, the density and viscosity in Formula 3) Is constant), the sedimentation distance H
When the feed rate Q of the raw material slurry 9 is increased, the value of the separation limit particle diameter D is increased, and the retained liquid in the rotating bowl 2 is increased.
When the capacity V and the centrifugal effect Z of 23 are increased, the value of the separation limit particle diameter D is reduced.

Therefore, by adjusting these factors, a classification operation in which the required particle size becomes a classification point has been performed.

The classification mechanism and the theoretical calculation of the classification point in the conventional apparatus have been described above.

In the actual apparatus, since the flow state of the stagnant liquid 13 in the rotary bowl 2 includes turbulence of the liquid other than the ideal parallel flow, classification is not performed as in the above theoretical calculation and some correction is required. In some cases.

Further, in a screw decanter type continuous centrifugal classifier having a mechanism for inserting the screw conveyor 18 into the retained liquid 13 in the rotating bowl 2 and discharging the settled coarse particles, the turbulence of the liquid caused by scraping of the coarse particles by the conveyor. Therefore, it is generally considered that the classification accuracy is somewhat lower than that of a batch type apparatus.

[Problem to be Solved by the Invention] The conventional technology has the following problems.

However, when such a conventional centrifugal classifier is used to perform a classification test in which a particle size of about 0.6 μm to 2 μm is actually used as a classification point, the particle product has a particle size equal to or larger than the classification point. The proportion of coarse particles mixed is small, and the maximum particle size contained in the fine particle product is not equal to the classification point calculated by the theoretical calculation, but the fine particles having a particle size equal to or smaller than the classification point in the coarse particle product Was found to be very high.

When performing industrial classification, it is ideal that the target particle size (classification point) is completely divided into two products, a fine product with a smaller particle size and a coarse product with a larger particle size, In the case where fine particles are mixed into the coarse product as described above, the coarse product obtained by one classification operation is repeatedly treated under the same classification condition to remove the fine particles mixed into the coarse product. It becomes necessary to overflow the product and increase the recovery rate of the fine particles.

As described above, with the conventional centrifugal classifier, it is impossible to simultaneously satisfy the quality of the fine-grained product and the coarse-grained product obtained by one classification operation, and a large amount of fine particles are mixed in the coarse-grained product. It turned out that there was a problem of coming.

Examining the cause with reference to the classification mechanism as shown in the above-mentioned literature, it is clear that the conventional centrifugal classifier reduces the mixing ratio of fine particles in the coarse product. It was concluded that there was a structural flaw in the classification mechanism.

That is, in the conventional apparatus, the liquid 13
Since the supply direction of the raw slurry 9 and the flow direction of the stagnant liquid 13 are different from each other and are orthogonal to each other, the raw slurry 9 and the stagnant liquid 13 are mixed at the stage where the raw slurry 9 is supplied, and the stagnant liquid level is increased. It is inevitable that a part of the granular material will sink into the liquid having a level of 14 or less.

Extremely speaking, there are fine particles that enter the rotating bowl inner wall 15 at the stage when they are supplied to the rotating bowl 2, and the sedimentation velocity at which the sedimentation starts to overflow if the sedimentation starts from the liquid level 14 of the stagnant liquid. This means that fine particles having a small particle size may be trapped on the inner wall 15 of the rotating bowl at the stage of mixing with the stagnant liquid 13 and may be mixed into the coarse product.

It is considered that the infiltration of the fine particles into the stagnant liquid 13 in the supply stage of the fine particles is the largest cause of the large amount of the fine particles flowing into the coarse product.

This is apparent also from the three equations that give the separation limit particle size in the classification mechanism described above.

When the three equations are arranged by focusing on the sedimentation distance H, the fourth equation is obtained.

D = C · H ^0.5 -4 Equation where C = (18 · μ · Q / (V · g · (ρ _s −ρ _L ) · Z)) ^0.5

Equation 4 shows that when the classification conditions other than the sedimentation distance H are constant,
It is shown that the separation limit particle size D is affected by the settling distance H (D is proportional to H to the 0.5 power).

That is, the remaining liquid level 14 is H = 1, and the rotating bowl inner wall 15
Is set to H = 0, in the conventional centrifugal classifier, a part of the powder and granules sinks into a level below the liquid level of the stagnant liquid 14 in the supply stage, and sedimentation does not start from the position of the constant sedimentation distance H. Since the granules start to settle from almost all positions between H = 0 to 1, a certain separation limit particle size (classification point) cannot be obtained.

Substituting H = 0 and H = 1 into Equation 4, the value of D becomes 0 and C, respectively, and the separation limit particle size of the conventional centrifugal classifier is always the value of the separation limit particle size at the liquid level (H = 1). Is the upper limit and the lower limit is a value having a range of 0.

This is very inconvenient for the purpose of classifying the granular material into two parts at a certain classification point, and the liquid level H =
In the supply stage, even particles having a particle diameter smaller than the separation limit particle diameter C in step 1 fall below the liquid level, and if the particle diameter becomes smaller than the separation limit particle diameter at that level, they settle down to the inner wall 15 of the rotating bowl. Means that they are trapped in the water and are collected as a coarse-grained product.

And the above-mentioned problem of the conventional apparatus, that is, the fact that there are many fine particles in the coarse-grained product is a drawback in the classification mechanism of such a conventional apparatus (part of the granular material particles in the supply stage may be reduced). This is theoretically understood to be due to the fact that the liquid drops below the level of the retained liquid level 14). that's all,
The first problem has been described.

In addition to the above, the second problem is that the flow of the slurry in the rotating bowl 2 in which the ideal flow is ideally ideal in the conventional apparatus is likely to include turbulence.

This is because, as described above, the raw material slurry 9 is used in the conventional apparatus.
And the direction of flow of the slurry in the rotating bowl 2 is orthogonal, and therefore, it is inevitable that the flow of the liquid is disturbed in a region where both liquids are mixed.

The region where the two liquids are mixed is also a region where the supplied raw material slurry 9 is accelerated to the same rotational speed as the rotary bowl 2 due to friction with the inner wall 15 of the rotary bowl and the bottom wall 16 of the rotary bowl. Inner wall 15 and rotating bowl bottom wall
Due to the speed difference between 16 and the liquid flow, the disturbance of the liquid flow in this region is further increased.

Region where classification is performed in a centrifugal classification device (hereinafter, referred to as
(Abbreviated simply as a classification region) can be interpreted as a region where particles settle due to the action of centrifugal force, and it is desired that the flow state in this classification region is close to a parallel flow.

In this sense, in the conventional apparatus, the accumulated liquid 13 in the rotating bowl 2 is
The whole is a classification region, and the turbulence of the flow in the classification region is a second problem of the conventional apparatus.

It is an object of the present invention to eliminate such problems of the conventional centrifugal classifier and to perform high-precision classification so that the ratio of fine particles mixed into a coarse product can be kept low. The object of the present invention is to provide a centrifugal classifier capable of performing the above.

The present application has been made in view of such problems of the related art, and has as its object to provide the following.

In view of the above problems, the centrifugal classifier according to the present invention provides a retentate liquid level 14 of the retentate 13 belonging to the classification area in the rotary bowl 2.
Means for supplying the raw slurry 9 in the flow direction of the stagnation liquid, and supplying the classification liquid 10 in the flow direction of the stagnation liquid 13 in the stagnation liquid 13 belonging to the classification area. The point of having the above means is the gist for solving the problem.

[Means for Solving the Problems] In order to achieve the above object, the present invention is as follows.

FIG. 1 shows an embodiment of the present invention, in which the present invention is applied to a basket-type batch centrifugal classifier.

In order to specifically realize the gist for solving the above-described problems, a classification liquid passage hole 22 is provided at a lower portion, and a ring 20 is fixed to an inner surface immediately above the classification liquid passage 22. Cylinder 19 whose inner surface is in contact with stagnant liquid level 14 of stagnant liquid 13
Is fixed to the bottom wall 16 of the rotating bowl of the rotating bowl 2.

FIG. 2 shows another embodiment of the present invention, in which the present invention is applied to a screw decanter type continuous centrifugal classifier. In this case, in order to realize the gist for solving the above-described problem, the lower end of the cylinder 19 whose inner surface is in contact with the remaining liquid level 14 of the remaining liquid 13, the rotation axis of the screw conveyor 18, In addition, it is fixed to the outer peripheral surface of a ring 20 fixed between the raw material slurry passage hole 21 and the classification liquid passage hole 22 of the rotary shaft of the double shaft structure which is also a supply pipe of the raw material slurry 9 and the classification liquid 10. Such technical measures are taken.

[Action] The thing of the present invention acts as follows.

As described above, the raw slurry 9 is placed at the position of the retained liquid level 14 belonging to the classification area in the rotary bowl 2 and the classification liquid
10 is capable of sedimentation of all the particulate particles only from the retained liquid surface 14 by separately supplying them to the liquid of the retained liquid 13 belonging to the classification area, and a part of the particulate particles are supplied at the supply stage. Can be prevented from penetrating into the liquid below the retained liquid level 14.

Also, by making the supply direction of the raw slurry 9 and the classification liquid 10 into the stagnant liquid 13 belonging to the classification area the same as the flow direction of the stagnant liquid 13, the disturbance of the flow due to the mixing of the liquid at the supply stage is minimized. Can be stopped.

Therefore, in the centrifugal classifier according to the present invention having such a structure, the flow state of the liquid in the rotating bowl 2 is close to an ideal parallel flow, and the above-mentioned equation (3) for calculating the separation limit particle diameter is used. All factors are determined (the value of the sedimentation distance H is also constant for all particles), and ideally such that the raw material particles are bisected at the separation limit particle size calculated from the theoretical formula Classification can be performed.

The operation of the basket-type batch centrifugal classifier to which the present invention shown in FIG. 1 is applied will be described as follows.

1, the raw material slurry 9 is supplied to the upper surface of the ring 20 rotating synchronously with the rotating bowl 2, and is rapidly accelerated by the frictional force with this surface. From the inner surface of the cylinder 19 and flows into the remaining liquid level 14.

Therefore, at the inflow stage, the rotation speed of the raw slurry 9 is almost the same as the rotation speed of the stagnant liquid 13, and the inflow direction is the same as the flow direction of the stagnant liquid 13. There is almost no disturbance.

Then, all the powder particles start sedimentation simultaneously from the liquid level 14 of the retained liquid.

On the other hand, the classification liquid 10 is supplied to the bottom wall 16 of the rotating bowl,
While being rapidly accelerated by the frictional force with this surface, the accumulated liquid passes through the classification liquid passage hole 22 provided in the lower part of the cylinder 19.
Flows into 13.

When flowing into the retained liquid 13, the classification liquid 10 rises in the rotary bowl 2 by changing the flow direction by 90 degrees so as to flow along two parallel surfaces formed by the outer surface of the cylinder 19 and the inner wall 15 of the rotary bowl. And the raw material slurry 9 supplied to the remaining liquid level 14.

In this apparatus, the centrifugal sedimentation of the granular particles starts after the classification liquid 10 and the raw material slurry 9 have joined, and classification is performed. Therefore, all the retained liquid 13 in the rotary bowl 2 belongs to the classification region. Instead, only the stagnation liquid 13 located above the upper end of the cylinder 19 is a classification region in which particles settle.

Therefore, simply arranging such a simple structure combining a perforated cylinder and a ring in a conventional apparatus is extremely important for achieving ideal classification, but is impossible with the conventional apparatus. Can be easily realized.

That is, the retained liquid belonging to the classification area in the rotating bowl 2
The powder particles can be simultaneously centrifugally sedimented only from the liquid surface 14 of the accumulated liquid 13 and the supply liquid can be introduced in the same direction as the flow direction of the accumulated liquid 13 belonging to the classification area. Particles can be classified in a state close to an ideal parallel flow with very few particles.

The operation of the screw decanter-type continuous centrifugal classifier to which the present invention is applied, which is another embodiment of the present invention shown in FIG. 2, will be described as follows.

In the structure as shown in FIG. 2, the inner tube is provided on the rotating shaft of a screw conveyor 18 having a double tube structure in which the inner tube is a supply tube for the raw slurry 9 and the outer tube is a supply tube for the classification liquid. The raw slurry 9 and the classification liquid 10 are separately supplied from the raw slurry passing hole 21 and the classification liquid passage hole 22 located below the raw slurry and are supplied into the rotary bowl 2.

The supplied raw material slurry 9 is supplied to the raw material slurry passage hole 21.
From the upper surface of the ring 20 fixed to the rotating shaft of the screw conveyor 18 between the liquid passage hole 22 for classification and the inner surface of the cylinder 19 fixed to the tip of the ring 20 to flow into the retained liquid surface 14 .

On the other hand, when the classification liquid 10 flows into
The raw material slurry 9 supplied to the retained liquid level 14 rises in the rotary bowl 2 by changing the flow direction by 90 degrees so as to flow along two parallel surfaces formed by the outer surface of the rotary member 19 and the inner wall 15 of the rotary bowl. To join.

Therefore, also in this apparatus, after the classification liquid 10 and the raw material slurry 9 have joined, the centrifugal sedimentation of the granular material particles starts, and only the stagnant liquid 13 located above the upper end of the cylinder 19 becomes the classification area, and the rotating bowl 2 Liquid belonging to the classification area within
The powder particles can be simultaneously centrifugally sedimented only from the liquid surface 14 of the accumulated liquid 13 and the supply liquid can be introduced in the same direction as the flow direction of the accumulated liquid 13 belonging to the classification area. Particles can be classified in a state close to an ideal parallel flow with very few particles.

In the drawing, 1 is a casing, 3 is a rotating shaft, 4 is a rotating means, 5 is a raw material slurry supply pipe, 6 is a classifying liquid supply pipe, 7 is an overflow discharge pipe, 8 is an underflow discharge pipe, and 11 is an overflow. , 12 is an underflow.

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

When a comparison test of classification performance was performed using the apparatus to which the present invention was applied and the conventional apparatus, the following results were obtained.

Example 1 A granular material having a particle size distribution as shown in Table 1 using a basket type batch centrifugal classifier as an embodiment of the present invention shown in FIG. 1 and a conventional apparatus shown in FIG. (Density 3.
5 g / cm ³ ) was classified under the following conditions.

 The results are shown in Table 2.

Classification conditions Example of the present invention: concentration of powder and granules in raw material slurry 1 Wt%: feed rate of raw slurry 60 cm ³ / min: liquid for classification Deionized distilled water: feed rate of liquid for classification 541 cm ³ / min: effective use of rotating bowl Capacity 533cm ³ : Effective settling distance of the rotating bowl 2.3cm: Rotational speed of the rotating bowl 1500rpm: Centrifugal effect on the liquid level of the stagnant liquid 125G: Classification point 1.6μm Conventional example: Concentration of granular material in raw slurry 0.1Wt%: Raw material Slurry supply speed 601 cm ³ / min: Effective capacity of rotating bowl 533 cm ³ : Effective settling distance of rotating bowl 2.3 cm: Number of rotations of rotating bowl 1500 rpm: Centrifugal effect on remaining liquid level 125 G: Calculation classification point 1.6 μm Example 2 A classification test was carried out by changing the conditions of Example 1 as follows, and the results shown in Table 3 were obtained.

Classification conditions Example of the present invention: concentration of powder and granular material in raw material slurry 1 Wt%: supply speed of raw material slurry 34 cm ³ / min: liquid for classification Deionized distilled water: supply speed of liquid for classification 304 cm ³ / min: effective rotating bowl Capacity 533cm ³ : Effective settling distance of the rotating bowl 2.3cm: Number of rotations of the rotating bowl 3000rpm: Centrifugal effect on the liquid level of the stagnant liquid 500G: Classification point of calculation 0.6μm Conventional example: Concentration of granular material in raw slurry 0.1Wt%: Raw material Slurry supply speed 338cm ³ / min: Effective capacity of rotating bowl 533cm ³ : Effective settling distance of rotating bowl 2.3cm: Number of rotations of rotating bowl 3000rpm: Centrifugal effect on remaining liquid level 500G: Calculation classification point 0.6μm Example 3 A screw decanter-type continuous centrifugal classification device as another embodiment of the present invention shown in FIG. 2 and a conventional device shown in FIG. A classification test was performed under the following conditions.

 The results are shown in Table 4.

Classifying conditions present invention e.g. granular material in the raw material slurry concentration 1 Wt%: feed rate 150 cm ³ / min slurry: classifying liquid deionized distilled water: feed rate 1354cm ³ / min of classifying liquid: a rotary bowl effective Capacity 663cm ³ : Effective settling distance of rotating bowl 2.0cm: Number of rotations of screw conveyor 1450rpm: Number of rotations of rotating bowl 1500rpm: Centrifugal effect on remaining liquid level 140G: Calculation classification point 2.0μm Conventional example: Powder and granules in raw material slurry body concentration 0.1 wt%: supply rate of the raw material slurry 1504cm ³ / min: effective capacity of the rotating bowl 663Cm ^3: effective sedimentation distance 2.0cm rotary bowl: rotational speed of the screw conveyor 1450 rpm: revolution speed 1500rpm of rotating bowl: retentate solution Effect on the surface 140G: Classification point 2.0μm As shown in the above Examples 1 to 3, both the centrifugal classifiers according to the conventional example and the present invention can classify in the ultra-fine particle area having a particle size of about 0.6 μm to 2.0 μm as a calculation classification point, and this calculation classification point is almost possible. Although it was confirmed that only the following fine particles were recovered as a fine product, the apparatus according to the present invention was significantly higher when comparing the recovery rates of the fine products, and
Even when the particle size distribution of the coarse product is compared, it can be seen that the content ratio of the fine particles below the calculated classification point is significantly lower in the apparatus according to the present invention.

[Effects of the Invention] The present invention is configured as described above, and has the following effects.

As described above, the present invention centrifugally sediments the powder particles at the same time only from the liquid level for the stagnant liquid belonging to the classification area in the rotating bowl of the centrifugal classifier, and in the liquid. Since the classification liquid is introduced in the same direction as the flow direction of the liquid, it is possible to eliminate the infiltration of the fine particles below the classification point into the liquid during the supply stage. Particles can be classified in a state close to a simple parallel flow.

As a result, it has become possible to perform high-precision classification so that the mixing ratio of fine particles in the coarse-grained product can be kept low.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of a basket type batch centrifugal classifier according to one embodiment of the present invention. FIG. 2 is a longitudinal sectional view of a screw decanter type continuous centrifugal classifier according to another embodiment of the present invention. FIG. 3 is a cross-sectional view of a conventional basket type batch centrifugal classifier, and FIG. 4 is a cross-sectional view of a conventional screw decanter type continuous centrifugal classifier. DESCRIPTION OF SYMBOLS 1 ... Casing, 2 ... Rotating bowl, 3 ... Rotating shaft, 4 ... Rotating means, 5 ... Raw material slurry supply pipe, 6 ... Classification liquid supply pipe, 7 ... Overflow discharge pipe, 8 ... Underflow discharge pipe, 9: Raw material slurry, 10: Classifying liquid, 11: Overflow, 12: Underflow, 13: Retained liquid, 14: Retained liquid level, 15: Rotating bowl inner wall, 16: Rotating bowl bottom wall, 17: Dam ring, 18: Screw conveyor, 19: Cylindrical, 20: Ring, 21: Raw material slurry passage hole, 22: Classification liquid passage hole.

Claims (3)

(57) [Claims] 1. A wet type centrifugal classification in which a raw material slurry 9 composed of a powder and a granular material composed of particles having various particle diameters and a liquid is introduced into a cylindrical rotary bowl 2 and a centrifugal force is applied to classify the particles. In the apparatus, the apparatus is provided with a retentate liquid level 14 of a retentate liquid 13 belonging to a classification area in the rotary bowl 2,
Means for supplying the raw slurry 9 in the flow direction of
A centrifugal classification device having means for supplying the classification liquid 10 in the flow direction of the stagnant liquid 13 in the stagnant liquid 13 belonging to the classification area. 2. Retained liquid belonging to a classification area in a rotating bowl 2.
Means for supplying the raw material slurry 9 in the direction of flow of the retained liquid 13 at the liquid level 14 of the retained liquid 13 and in the direction of flow of the retained liquid 13 in the liquid of the retained liquid 13 belonging to the classification area. The means for supplying the classification liquid 10 has a classification liquid passage hole 22 in the lower part, a ring 20 is fixed on the inner surface immediately above the classification liquid passage hole 22, and the inner surface is 2. The centrifugal classification device according to claim 1, wherein said cylinder belongs to a basket type batch type centrifugal classification device in which said cylinder 19 in contact with said remaining liquid level 14 is fixed to said rotating bowl bottom wall 16 of said rotating bowl 2. 3. Retained liquid belonging to a classification area in a rotary bowl 2.
13 means for supplying the raw material slurry 9 in the direction of flow of the retained liquid 13 in the direction of flow of the retained liquid 13, and in the flow of the retained liquid 13 in the liquid of the retained liquid 13 belonging to the classification area. The means for supplying the classifying liquid 10 is such that the lower end of the cylinder 19 whose inner surface is in contact with the retained liquid level 14 of the retained liquid 13 is the rotating shaft of the screw conveyor 18 and the raw material slurry 9 and the A screw decanter which is fixed to the outer peripheral surface of a ring 20 fixed between the raw slurry passage hole 21 and the classification liquid passage hole 22 of the rotary shaft of the rotary shaft which is also a supply pipe of the liquid 10. The centrifugal classification device according to claim 1, which belongs to a type continuous centrifugal classification device.