EP3482830A1

EP3482830A1 - Centrifugal separator and centrifugal separation method

Info

Publication number: EP3482830A1
Application number: EP17824092.5A
Authority: EP
Inventors: Shinpei Kurita; Mitsuhiko Nitta; Ken Abe; Tomonori WATARAI; Yasufumi Otomo; Shinichiro Natori
Original assignee: Tsukishima Kikai Co Ltd
Current assignee: Tsukishima Kikai Co Ltd
Priority date: 2016-07-05
Filing date: 2017-06-28
Publication date: 2019-05-15
Also published as: EP3482830A4; TW201805068A; CN109070099A; KR20190026644A; TWI702985B; KR102325794B1; JP2018001117A; WO2018008486A1; JP6578254B2; CN109070099B

Abstract

The present invention provides a centrifugal separator including a cylindrical basket (2) that is configured to rotate about an axis (O) of the basket (2), a pushing plate (7) that is accommodated inside the basket (2), is provided to be rotatable integrally with the basket (2) and movable relatively in an axis (O) direction of the basket (2), and is configured to push a cake, which is filtered by a filtration screen (2a) from a substance to be processed supplied inside the basket (2), to an open end side (2b) of the basket (2), a forward and backward drive unit (11) that is configured to relatively move the pushing plate (7) and the basket (2) by moving one of the pushing plate (7) and the basket (2) forward and backward in the axis (O) direction with respect to the other, and a measuring unit that is configured to measure a pushing load when pushing a cake by the forward and backward drive unit (11). At least one of a relative movement speed between the pushing plate (7) and the basket (2) and a forward and backward stroke of the pushing plate (7) and the basket (2) is controlled according to the pushing load measured by the measuring unit.

Description

Technical Field

The present invention relates to a push-type centrifugal separator and a centrifugal separation method, in which a substance to be processed that is supplied inside a basket rotating about an axis is filtered by a filtration screen provided on a body part of the basket and a cake filtered from the substance to be processed is discharged from an open end of the basket by a pushing plate that is accommodated inside the basket, is integrally rotatable, and is relatively movable in an axis direction.
Priority is claimed on Japanese Patent Application No. 2016-133666, filed on July 5, 2016 , the content of which is incorporated herein by reference.

Background Art

As such a push-type centrifugal separator, for example, a two-stage basket centrifugal separator that includes an outer basket, which rotates about an axis, and an inner basket, which is coaxially disposed inside the outer basket, integrally rotates with the outer basket, and is moved forward and backward in an axis direction with respect to the outer basket, is disclosed in Patent Document 1. In the two-stage basket centrifugal separator, a substance to be processed, which is filtered by centrifugation, is supplied to a location between a pushing plate that is supported by the outer basket and is disposed inside the inner basket so as to oppose an opening of a substance to be processed supply pipe and an annular distributor that is disposed so as to surround the opening of the substance to be processed supply pipe with an interval placed between the pushing plate and the annular distributor.
In such a centrifugal separator, the substance to be processed that is supplied from the opening of the supply pipe to the location between the pushing plate and the distributor is filtered while being accumulated onto an inner circumferential surface of a filtration screen provided on a body part of the inner basket by centrifugal force, thereby forming a cake. The cake accumulates also in an axis direction of the inner basket by the forward movement of the inner basket facing an open end side of the outer basket. Next, the cake of the substance to be processed is pushed by the pushing plate by the backward movement of the inner basket with respect to the outer basket and is discharged to an inner circumferential surface of the outer basket. In addition, the cake of the substance to be processed that is discharged to the inner circumferential surface of the outer basket in such a manner is further filtered by a filtration screen of the outer basket and is pushed by the forward movement of the inner basket so as to be discharged from an open end of the outer basket.

Citation List

Patent Document

[Patent Document 1] Japanese Unexamined Patent Application, First Publication No. 2014-091093

Summary of Invention

Technical Problem

Relative movement between the basket and the pushing plate in the axis direction in such a centrifugal separator (backward movement of the inner basket with respect to the pushing plate in the centrifugal separator disclosed in Patent Document 1) relies, in general, on hydraulic drive by a hydraulic piston. For this reason, stroke of movement at the time of forward movement and stroke of movement at the time of backward movement are the same, and a movement speed at the time of forward movement and a movement speed at the time of backward movement speed are the same.
A load applied onto the centrifugal separator by a solid of a substance to be processed, which undergoes solid-liquid separation and is dehydrated in such a centrifugal separator, is not limited to being constant at all times, and an increase or decrease in the solid occurs due to a change in a supply amount of a substance to be processed or a solid concentration of a substance to be processed. When a solid content increases by a supply amount or a solid concentration of a substance to be processed being increased and thereby a load increases, the thickness of a cake filtered by the filtration screen from the substance to be processed increases, and the thickness of a cake layer formed on the inner circumferential surface of the filtration screen becomes not uniform. Therefore, there is a possibility that abnormal vibration occurs in the basket rotating at a high speed.
On the contrary, in a case where a relative movement speed between the basket and the pushing plate or stroke of movement is set in advance to be large with respect to a load applied by such a solid, the thickness of the cake formed on the inner circumferential surface of the filtration screen becomes small and also a cake amount held inside the basket becomes small. Therefore, time of stay of a substance to be processed inside the basket shortens. Centrifugal force generated by the rotation of the basket and time of stay inside the basket are main factors affecting the dehydration performance of the centrifugal separator. For this reason, operating in a state where time of stay is short makes the dehydration performance of the centrifugal separator excessive with respect to a load applied by a solid, and the dehydration performance of the centrifugal separator is not sufficiently exhibited.
The present invention is devised under such circumstances, and an object thereof is to provide a centrifugal separator and a centrifugal separation method in which it is possible to respond to an increase or decrease in a load accompanying a change in a supply amount or a solid concentration of a substance to be processed, to prevent the occurrence of abnormal vibration by maintaining a uniform thickness of a cake, and to exhibit dehydration performance without excess or deficiency.

Solution to Problem

According to a first aspect of a centrifugal separator of the present invention, the centrifugal separator includes a cylindrical basket that has a body part provided with a filtration screen and is configured to rotate about an axis of the basket, a pushing plate that is accommodated inside the basket, is provided to be rotatable integrally with the basket and movable relatively in an axis direction of the basket, and is configured to push a cake, which is filtered by the filtration screen from a substance to be processed supplied inside the basket, to an open end side of the basket, a forward and backward drive unit that is configured to relatively move the pushing plate and the basket by moving one of the pushing plate and the basket forward and backward in the axis direction with respect to the other, and a measuring unit that is configured to measure a pushing load of the forward and backward drive unit when the cake is pushed to the open end side of the basket by forward and backward movement of the one of the pushing plate and the basket by the forward and backward drive unit. At least one of a relative movement speed between the pushing plate and the basket by the forward and backward drive unit and a forward and backward stroke of one of the pushing plate and the basket with respect to the other is controlled according to the pushing load measured by the measuring unit.
According to a first aspect of a centrifugal separation method of the present invention, a substance to be processed is supplied into a cylindrical basket that has a body part provided with a filtration screen and is configured to rotate about an axis of the basket, and a cake filtered by the filtration screen from the substance to be processed is pushed and discharged to an open end side of the basket by a pushing plate that is accommodated inside the basket and is provided to be rotatable integrally with the basket and movable relatively in an axis direction of the basket. The centrifugal separation method includes relatively moving the pushing plate and the basket by causing a forward and backward drive unit to move one of the pushing plate and the basket forward and backward in the axis direction with respect to the other, measuring, by a measuring unit, a pushing load of the forward and backward drive unit when the cake is pushed to the open end side of the basket by forward and backward movement of the one of the pushing plate and the basket by the forward and backward drive unit, and controlling at least one of a relative movement speed between the pushing plate and the basket by the forward and a backward drive unit and forward and backward stroke of one of the pushing plate and the basket with respect to the other according to the pushing load measured by the measuring unit.
In the first aspect of such a centrifugal separator and the first aspect of such a centrifugal separation method, at least one of the movement speed of the basket with respect to the pushing plate by the forward and backward drive unit and the forward and backward stroke is controlled, for example, in a case where the pushing plate is at a fixed position in the axis direction and the basket is made movable by being moved forward and backward in the axis direction as in the centrifugal separator disclosed in Patent Document 1. On the contrary, in a case where the basket is at a fixed position in the axis direction and the pushing plate is made movable by being moved forward and backward in the axis direction, at least one of the movement speed of the pushing plate by the forward and backward drive unit and the forward and backward stroke is controlled.
Therefore, in any one of cases, at least one of the relative movement speed and the stroke is controlled to increase when the pushing load increases, that is, there is a possibility that a load of a solid increases and the thickness of a cake becomes large due to an increase in a supply amount of a substance to be processed, a solid concentration of a substance to be processed, or the like. Accordingly, the supply amount of a substance to be processed to the filtration screen decreases per unit length in the axis direction, and thereby cake thickness uniformization can be achieved. For this reason, the occurrence of abnormal vibration or the like caused by a cake having a thickness, which is not uniform, being formed on the filtration screen of the basket rotating at a high speed is prevented and thus stable filtration can be achieved.
Contrary to this case, at least one of the relative movement speed and the stroke is controlled to decrease when a load applied by a solid decreases due to a decline in a supply amount of a substance to be processed, a solid concentration of a substance to be processed, or the like and the pushing load decreases. Accordingly, the supply amount of a substance to be processed to the filtration screen can be increased per unit length in the axis direction. For this reason, a cake having a thickness, which is not uniform, can be prevented from being formed. It is also possible to exhibit the dehydration performance of the centrifugal separator without excess or deficiency by securing long time of stay of a substance to be processed inside the basket and to cause balanced and efficient filtration.
As for controlling a relative movement speed between the pushing plate and the basket in particular, it is possible to control the relative movement speed by making hydraulic oil flow path diameters, for example, at the time of forward movement and at the time of backward movement different from each other, mounting a speed controller, or providing a difference in a hydraulic oil discharging speed by bypassing a cylinder discharging side flow path, for example, even in a case where one of the basket and the pushing plate is moved by being moved forward and backward with respect to the other by hydraulic drive relying on the hydraulic piston of the related art. However, in this case, there is a possibility that a hydraulic pressure becomes unstable when switching between forward movement and backward movement, and it is difficult to control to maintain a predetermined relative movement speed. In addition, it is almost impossible to control the forward and backward stroke of the pushing plate and the basket by hydraulic drive which relies on a general hydraulic piston.
Therefore, it is desirable to drive the forward and backward drive unit by an electric motor, which has high responsiveness when switching between forward movement and backward movement or to movement speed control and can switch between forward movement and backward movement with any stroke, in order to stably control at least one of a relative movement speed between the pushing plate and the basket and the forward and backward stroke of one of the pushing plate and the basket with respect to the other as described above.
As the forward and backward drive unit driven by such an electric motor, for example, a so-called electric cylinder that converts the rotation of an electric motor (servo-motor), which is transmitted to a screw shaft such as a ball screw, to linear motion of a piston rod by a nut coaxially attached to the piston rod being screwed with the screw shaft can be used. In addition, a linear cylinder that directly causes the piston rod to linearly move by means of an electric linear motor can be used as the forward and backward drive unit. A so-called fastener type actuator that causes the piston rod to linearly move or the like is given as an example of the forward and backward drive unit. The piston rod is moved forward by two or more chains being engaged with each other while being drawn in a column shape by an electric motor, and is moved backward by the engagement between the chains being released while being pulled back.
In particular, in a case where the electric motor is driven by the forward and backward drive unit, the measuring unit can measure a pushing load from a current value of the electric motor of the forward and backward drive unit. For this reason, more reliable and stable control can be achieved since a load of a solid substance that actually acts on the forward and backward drive unit can be measured in real time. As such a measuring unit, for example, a load cell included in the forward and backward drive unit can be used not only in a case where the forward and backward drive unit is driven by the electric motor but also a case where the forward and backward drive unit is driven by hydraulic drive.

Advantageous Effects of Invention

In the present invention, it is possible to prevent the occurrence of abnormal vibration by maintaining a uniform thickness of a cake and to exhibit dehydration performance without excess or deficiency regardless of an increase or decrease in a load accompanying a change in a supply amount or a solid concentration of an object to be processed. Therefore, it is possible to cause stable and efficient filtration.

Brief Description of Drawings

FIG. 1 is a cross-sectional view of an outline of a first embodiment of a centrifugal separator according to the present invention.
FIG. 2 is an enlarged cross-sectional view of a vicinity of a basket, which shows a state where an inner basket has moved backward with respect to a pushing plate according to the embodiment shown in FIG. 1.
FIG. 3 is an enlarged cross-sectional view of the vicinity of the basket, which shows a state where the inner basket has moved forward with respect to the pushing plate according to the embodiment shown in FIG. 1.
FIG. 4 is an enlarged cross-sectional view of a vicinity of a basket, which shows a state where a pushing plate has moved forward with respect to a basket according to a second embodiment of a centrifugal separator of the present invention.
FIG. 5 is an enlarged cross-sectional view of the vicinity of the basket, which shows a state where the pushing plate has moved backward with respect to the basket according to the embodiment shown in FIG. 4.

Description of Embodiments

FIGS. 1 to 3 show a first embodiment of a centrifugal separator of the present invention, and illustrate an example in which the present invention is applied to a two-stage basket centrifugal separator including an outer basket and an inner basket as disclosed in Patent Document 1. That is, the centrifugal separator of the embodiment includes a cylindrical outer basket 1 that has a body part, to which an outer filtration screen 1a is attached, and is formed about a horizontal axis O and a cylindrical inner basket 2 that is coaxially accommodated inside the outer basket 1 and has a body part, to which an inner filtration screen 2a is attached. In the first embodiment, the inner basket 2 corresponds to a basket of the present invention. For example, a cylindrical wire screen or a plate screen is used as the outer filtration screen 1a or the inner filtration screen 2a.
The cylindrical outer basket 1 and the inner basket 2 are bottomed cylinders of which one ends in the axis O direction (right ends in an axis O direction in FIGS. 1 to 3) are circular open ends 1b and 2b and the other ends (left ends in the axis O direction in FIGS. 1 to 3) are attached and held by disk- shaped holding plates 1c and 2c. The length of the inner basket 2 in the axis O direction is smaller than the length of the outer basket 1 in the axis O direction. The inner basket 2 is accommodated inside a casing 3 and integrally rotates about the axis O with the outer basket 1. The outer diameter of the open end 2b of the inner basket 2 is set to a size that allows, for example, another annular pushing plate (not shown) provided on the open end 2b and the open end to be in sliding contact with an inner circumferential surface of the outer filtration screen 1a of the outer basket 1.
The holding plate 1c of the outer basket 1 is attached to one end of a hollow main shaft 5, which is rotatably supported by a bearing 4 and is inserted in the casing 3 along the axis O. The outer basket 1 rotates about the axis O by torque of a motor or the like being transmitted to a pulley (not shown) and the main shaft 5 rotating. In addition, a pushing shaft 6 is inserted inside the main shaft 5 via a key (not shown) so as to be integrally rotatable and movable forward and backward in the axis O direction. Also the inner basket 2 is integrally rotatable with the outer basket 1 and is movable forward and backward in the axis O direction on the other end side inside the outer basket 1 by one end portion of the pushing shaft 6 slidably penetrating the holding plate 1c of the outer basket 1 and being attached to the holding plate 2c of the inner basket 2.
A plurality of supporting shafts 1d are attached to the holding plate 1c of the outer basket 1 so as to extend to the one end side in parallel with the axis O at positions spaced apart from the axis O on an outer circumferential side with an interval placed in a circumferential direction. The supporting shafts 1d slidably penetrate the holding plate 2c and protrude inside the inner basket 2. A disk-shaped pushing plate 7 having an outer diameter that allows sliding contact with an inner circumferential surface of the inner filtration screen 2a is attached to one ends of the supporting shafts 1d. Therefore, the pushing plate 7 is coaxially and integrally rotatable about the axis O with the outer basket 1 and the inner basket 2 and is relatively movable in the axis O direction with respect to the inner basket 2.
Further on the one end side of the pushing plate 7, an annular distributing plate (distributor) 8 having an opening at the center is integrally supported with the pushing plate 7 with an interval placed therebetween. In addition, a supply pipe 9 for a substance to be processed is attached and inserted in the casing 3. The supply pipe 9 is inserted in the opening of the distributing plate 8 through the open ends 1b and 2b of the outer basket 1 and the inner basket 2, and a supply port of the supply pipe 9 is opened between the pushing plate 7 and the distributing plate 8.
A substantially U-shaped cake receiving ring 3a of which a cross-section taken along the axis O is opened to an inner circumferential side is disposed on an outer circumference of the open end 1b of the outer basket 1 such that the cake receiving ring 3a is supported by the casing 3 and surrounds the open end 1b. The cake receiving ring 3a is provided with a cake chute (not illustrated). After being received by the cake receiving ring 3a, a cake discharged from the open end 1b of the outer basket 1 is discharged from an outlet 3b provided on a lower side of the casing 3 via the cake chute.
The other end of the pushing shaft 6 protrudes more than the other end of the main shaft 5 does. A forward and backward drive unit 11 that moves the pushing shaft 6 forward and backward in the axis O direction with the inner basket 2 while allowing the rotation of the pushing shaft 6 via a bearing box 10 is connected to the other end portion of the protruding pushing shaft 6. The bearing box 10 is configured to rotatably support the other end portion of the pushing shaft 6 by means of a bearing (not illustrated) or the like and not to rotate with respect to the pushing shaft 6, which integrally rotates with the main shaft 5, and is attached so as to be integrally movable forward and backward in the axis O direction with the pushing shaft 6 via the bearing.
The forward and backward drive unit 11 of the embodiment is driven by an electric motor, and transmits, in particular, the rotation of an electric motor (servo-motor) 11a to a screw shaft such as a ball screw (not shown) disposed so as to extend in the axis O direction inside a cylinder box 11b. A nut coaxially attached to a piston rod (not shown) is screwed with the screw shaft, and the forward and backward drive unit 11 converts the rotation of the electric motor 11a to linear motion of the piston rod via the screw shaft and the nut. Such a forward and backward drive unit 11 is a so-called electric cylinder or servo-cylinder, or an electric actuator.
In one embodiment of a centrifugal separation method of the present invention, in which the centrifugal separator configured in such a manner is used, a substance to be processed (slurry), of which a solid and a liquid are turbid, is supplied from the supply pipe 9 while the outer basket 1 and the inner basket 2 integrally rotate. The supplied substance to be processed reaches the pushing plate 7, disperses to outer circumferential side from a location between the pushing plate 7 and the distributing plate 8 by centrifugal force in the embodiment, and sticks to the inner circumferential surface of the inner filtration screen 2a of the inner basket 2. When the inner basket 2 moves forward from a state where the inner basket 2 has moved backward with respect to the pushing plate 7 as shown in FIG. 2 while the substance to be processed is being supplied in such a manner, the substance to be processed continuously accumulates in the axis O direction while being filtered by centrifugal force. Consequently, a cake of the substance to be processed is formed onto the inner circumferential surface of the inner filtration screen 2a of the inner basket 2 which moves forward.
Next, when the inner basket 2 which has moved forward in such a manner reaches a forward stroke end and shifts backward as shown in FIG. 3, the cake of the substance to be processed accumulated on the inner circumferential surface of the inner filtration screen 2a is pushed to the one end side of the inner basket 2 in turn by the pushing plate 7 which relatively moves forward with respect to the backward moving inner basket 2. The cake of the substance to be processed (cake) accumulated on the one end side is discharged from the open end 2b to the inner circumferential surface of the outer filtration screen 1a of the outer basket 1, and is filtered by centrifugal force while also being continuously accumulated in the axis O direction. In a case where a supply amount or a solid concentration of a substance to be processed to be supplied is stable, a pushing load of the forward and backward drive unit 11 when the inner basket 2 moves forward and a cake of a substance to be processed is pushed is stable as well within a predetermined range.
Next, a cake of a substance to be processed, which is accumulated on the inner circumferential surface of the outer filtration screen 1a in such a manner and is filtered, is pushed to the one end side in turn by the next forward movement of the inner basket 2, which has reached a backward stroke end, by means of the open end 2b of the inner basket 2 or another pushing plate (not illustrated) provided on the open end 2b. Next, the cake of the substance to be processed accumulated on the one end side is discharged to the cake receiving ring 3a from the open end 1b of the outer basket 1, and is further discharged from the outlet 3b of the casing 3 via the cake chute (not shown) as described above.
The centrifugal separator having the configuration includes a measuring unit 15 that measures a pushing load of the forward and backward drive unit 11 when the cake of the substance to be processed is pushed to the open end 2b side of the inner basket 2 by the forward and backward movement of one (the inner basket 2 in the embodiment) of the pushing plate 7 and the inner basket 2, which is the basket of the present invention, by the forward and backward drive unit 11. In the centrifugal separator and the centrifugal separation method in which the centrifugal separator is used, at least one of a relative movement speed between the pushing plate 7 and the inner basket 2 by the forward and backward drive unit 11 and the forward and backward stroke of one of the pushing plate 7 and the inner basket 2 with respect to the other is controlled according to the pushing load measured by the measuring unit 15.
That is, in the centrifugal separator and the centrifugal separation method of the embodiment, when a supply amount or a solid concentration of a substance to be processed changes from a stable state described above and the pushing load increases so as to be larger than the predetermined range, at least one of the relative movement speed and the stroke is controlled to increase. Contrary to this, when the pushing load decreases so as to be lower than the predetermined range, at least one of the relative movement speed and the stroke is controlled to decrease.
In the embodiment, the measuring unit 15 measures a pushing load by measuring a current value of the electric motor 11a of the forward and backward drive unit 11. Such control described above can be easily performed in an automatic manner such that the electric motor 11a is controlled according to the pushing load measured by the measuring unit 15 by installing a program in advance in a control unit of a computer or the like including a known configuring member that controls the electric motor 11a, such as a CPU and a memory.
Specifically, in the embodiment, while the pushing plate 7 is attached to the main shaft 5 via the supporting shafts 1d and the holding plate 1c of the outer basket 1 so as to be fixed in the axis O direction, the inner basket 2 moves forward and backward in the axis O direction via the pushing shaft 6. For this reason, in a case where a relative movement speed is controlled to increase when a pushing load has increased, the relative movement speed is controlled as follows. That is, by moving the inner basket 2 forward to the one end side of the axis O direction, transition occurs from a state where the inner basket 2 has moved backward to the other end side of the axis O direction and an interval D between the open end 2b and the pushing plate 7 in the axis O direction is small as shown in FIG. 2 to a state where the open end 2b of the inner basket 2 has spaced apart from the pushing plate 7 as shown in FIG. 3. Thus, a relative movement speed of the inner basket 2 with respect to the pushing plate 7 in a direction where the interval D becomes large is controlled to become high. Contrary to this, a relative movement speed of the inner basket 2 with respect to the pushing plate 7 in a direction where the interval D becomes small from a state of being large is also controlled to become high.
On the contrary, when a pushing load has decreased so as to be smaller than the predetermined range, a relative movement speed in the direction where the interval D becomes large as shown in FIG. 3 from a state where the interval D is small as shown in FIG. 2 and a relative movement speed in a direction where the interval D becomes small as shown in FIG. 2 from a state where the interval D is large as shown in FIG. 3 are controlled so as to become low.
A case where the forward and backward stroke of one (the inner basket 2 in the embodiment) of the pushing plate 7 and the inner basket 2 with respect to the other (the pushing plate 7 in the embodiment) is controlled will be described. For example, the forward and backward stroke of the inner basket 2 when the pushing load is within the predetermined range is set in advance so as to be smaller than the maximum stroke of the piston rod by the forward and backward drive unit 11. When the pushing load measured by the measuring unit 15 has exceeded the predetermined range and has become larger than the predetermined range, the inner basket 2 is moved forward and backward with stroke larger than the forward and backward stroke of the inner basket 2 when the pushing load is within the predetermined range. On the contrary, when the pushing load has become smaller than the predetermined range, the inner basket 2 is moved forward and backward with stroke smaller than the forward and backward stroke of the inner basket 2 when the pushing load is within the predetermined range.
In a case where a relative movement speed between the pushing plate 7 and the inner basket 2 by the forward and backward drive unit 11 is made high when a supply amount or a solid concentration of a substance to be processed has increased and the pushing load has exceeded the predetermined range, it is possible to obtain the following effects in the centrifugal separator and the centrifugal separation method which are configured in such a manner. That is, when transition occurs from a state where the interval D is small as shown in FIG. 2 to a state where the interval D is large as illustrated in FIG. 3, the amount of a solid included in a substance to be processed supplied to the inner filtration screen 2a after a substance to be processed accumulated on the inner circumferential surface of the inner filtration screen 2a is pushed by the pushing plate 7 becomes small per unit length in the axis O direction. Therefore, the thickness of a cake left on the inner circumferential surface of the inner filtration screen 2a when the substance to be processed is filtered by centrifugation can be made the same as the thickness of a cake when a supply amount or a solid concentration is stable and a pushing load is within the predetermined range.
In addition, it is possible to obtain the following effects when the inner basket 2 moves backward to the other end side of the axis O direction with respect to the pushing plate 7 from a state where the interval D is large as shown in FIG. 3 to a state where the interval D is small as shown in FIG. 2 and a substance to be processed on the open end 2b side of the inner basket 2 is pushed. That is, the substance to be processed supplied from the location between the pushing plate 7 and the distributing plate 8 is added onto (inner circumference) a substance to be processed accumulated on the one end side of the pushing plate 7. Since the relative movement speed of the inner basket 2 with respect to the pushing plate 7 is high also at this time, the amount of a solid in a substance to be processed, which is added per unit length in the axis O direction, becomes small. Thus, it is possible to prevent a cake thickness from becoming excessively large.
In a case where the forward and backward stroke of the inner basket 2 with respect to the pushing plate 7 is made large when a pushing load has exceeded the predetermined range in a state where a supply amount or a solid concentration of a substance to be processed is stable, it is possible to obtain the following effects. That is, even when the interval D becomes large or even when the interval D becomes small, a substance to be processed with a large supply amount or a high solid concentration disperses over a wider area in the axis O direction and is supplied to the inner circumferential surface of the inner filtration screen 2a. Therefore, it is possible to prevent a cake thickness from becoming large. In addition, in a case where the forward and backward stroke of the inner basket 2 is made small when a pushing load has become smaller than the predetermined range, a substance to be processed with a small supply amount or a low solid concentration is supplied to the inner circumferential surface of the inner filtration screen 2a within a relatively small area. Therefore, it is possible to prevent the thickness of a cake from becoming excessively small.
As described above, in a centrifugal separator and the centrifugal separation method, which have the configuration, a supply amount of a substance to be processed or a solid concentration of a substance to be processed increases, a load applied by a solid increases, and accordingly a pushing load increases. At this time, a cake thickness is prevented from becoming excessively large by making at least one of the relative movement speed of the inner basket 2 with respect to the pushing plate 7 and forward and backward stroke of one of the pushing plate 7 and the inner basket 2 with respect to the other large. Thus, cake thickness uniformization can be achieved. On the contrary, when a supply amount or a solid concentration of a substance to be processed decreases and a pushing load has become small, at least one of the relative movement speed and the stroke is made small. Consequently, a partial thickness of a cake is prevented from becoming excessively small. Thus, a cake thickness can also be uniformized.
For this reason, even when a supply amount or a solid concentration of a substance to be processed changes, it is possible to prevent a portion where the thickness of a cake is not uniform from being formed on the inner circumferential surface of the inner filtration screen 2a of the inner basket 2 which rotates at a high speed. For this reason, it is possible to prevent a possibility of the occurrence of abnormal vibration of the inner basket 2 caused by such a cake thickness which is not uniform and to cause filtration by stable centrifugation of a substance to be processed.
In particular, even when a supply amount or a solid concentration of a substance to be processed has decreased, it is possible to secure long time of stay of the substance to be processed inside the inner basket 2 by a relative movement speed or forward and backward stroke becoming small. For this reason, it is possible to achieve efficient filtration by exhibiting the performance of the centrifugal separator without excess or deficiency.
In the centrifugal separator of the embodiment, the electric cylinder converting the rotation of the electric motor 11a to linear motion of the pushing shaft 6 from the piston rod via the screw shaft and the nut is adopted as the forward and backward drive unit 11 that moves the inner basket 2 forward and backward in the axis O direction with respect to the pushing plate 7. The forward and backward drive unit 11, in which such an electric motor 11a is used, shows a quick response in switching between forward movement and backward movement compared to the hydraulic drive of the related art, and can easily and quickly respond by controlling the rotation of the electric motor 11a even in a case of increasing or decreasing a relative movement speed or forward and backward stroke as described above. For this reason, the forward and backward drive unit 11 is particularly effective in a case of performing control as in the centrifugal separator and the centrifugal separation method, which have the above-described configuration.
The forward and backward drive unit 11 having such an electric motor 11a is not limited to the electric cylinder that converts the rotation of the electric motor 11a to the linear motion of the piston rod by means of the screw shaft and the nut as in the embodiment. For example, the forward and backward drive unit 11 may be a linear cylinder that directly causes the piston rod and the pushing shaft 6 to linearly move by means of an electric linear motor. The forward and backward drive unit 11 may be a so-called fastener type actuator that causes the pushing shaft to linearly move. The pushing shaft moves forward by two or more chains connected to the pushing shaft 6 being engaged with each other while being drawn in a column shape by an electric motor, and moves backward by the engagement between the chains being released while being pulled back.
In addition to adopting the centrifugal separator in which the electric motor 11a is used as the forward and backward drive unit 11, the pushing load is measured by the measuring unit 15, which measures a current value of the electric motor 11a of the forward and backward drive unit 11, when measuring the pushing load at the time of pushing a cake of a substance to be processed in the embodiment. Therefore, the pushing load when a cake of a substance to be processed is pushed can be measured in real time and the measured result can be quickly reflected in controlling the forward and backward drive unit 11. Therefore, it is possible to further cause reliable and stable control. In a case where the pushing load measured in such a manner, or at least one of relative movement speed and stroke, which is controlled according to the pushing load, has reached an upper limit value or a lower limit value, which is set in advance, control may be performed such that an alarm is issued as an abnormality or the centrifugal separator stops.
Next, FIGS. 4 and 5 show a second embodiment of a centrifugal separator of the present invention. The same reference signs will be assigned with portions common to the centrifugal separator of the first embodiment and description thereof will be omitted.
Since the other end side portion (not shown) of the centrifugal separator of the second embodiment shown in FIGS. 4 and 5 in the axis O direction is the same as that of the centrifugal separator of the first embodiment, it is not shown in FIGS. 4 and 5.
In the first embodiment, the inner basket 2 is accommodated in the outer basket 1 and is integrally rotatable, the inner basket 2 is attached to the pushing shaft 6 and moves forward and backward in the axis O direction, and the outer basket 1 and the pushing plate 7 supported by the outer basket 1 are held at a fixed position in the axis O direction. Therefore, the pushing plate 7 is relatively movable in the axis O direction with respect to the basket (the inner basket 2). In the second embodiment, a single basket 21, which has a body part provided with a filtration screen 21a and has an open end 21b in one end in the axis O direction, is attached to one end of the main shaft 5 via a holding plate 21c. The basket 21 is held at a fixed position in the axis O direction, and a pushing plate 22 having an outer diameter that allows sliding contact with an inner circumferential surface of the filtration screen 21a is coaxially attached to one end of the pushing shaft 6, which is inserted in the holding plate 21c, and moves forward and backward in the axis O direction. Accordingly, the pushing plate 22 is relatively movable in the axis O direction with respect to the basket 21.
Therefore, in the second embodiment, the pushing plate 22 is movable by being moved forward and backward in the axis O direction with the basket 21 and the open end 21b of the basket 21 being at fixed positions in the axis O direction. For this reason, a direction where the interval D between the pushing plate 22 and the open end 21b of the basket 21 in the axis O direction becomes large is a direction where the pushing plate 22 moves backward as shown in FIG. 5 from a state where the pushing plate 22 has moved forward inside the basket 21 as shown in FIG. 4. In addition, a direction where the interval D becomes small is a direction where the pushing plate moves forward as shown in FIG. 4 from a state where the pushing plate 22 has moved backward as shown in FIG. 5. For this reason, when the pushing plate 22 moves forward, a cake of a substance to be processed accumulated on the inner circumferential surface of the filtration screen 21 a of the basket 21 is discharged from an open end 21b side of the basket 21 to the cake receiving ring 3a.
Also in the second embodiment, at least one of a relative movement speed between the pushing plate 22 and the basket 21 by the forward and backward drive unit 11 and the forward and backward stroke of the pushing plate 22 with respect to the basket 21 is controlled according to a pushing load of the electric motor 11a, which is measured by the measuring unit 15 included in the forward and backward drive unit 11. Specifically, when a pushing load is measured according to a current value of the electric motor 11a and the pushing load increases from a state where a supply amount or a solid concentration of a substance to be processed is stable and also the pushing load is stable, at least one of the relative movement speed and the stroke is controlled to increase. On the contrary, when the pushing load decreases therefrom, at least one of the relative movement speed and the stroke is controlled to decrease.
Also in the second embodiment, it is possible to maintain a uniform thickness of a cake formed on the inner circumferential surface of the filtration screen 21a by controlling at least one of the relative movement speed of the pushing plate 22 with respect to the basket 21 and forward and backward stroke when a supply amount of a substance to be processed or a solid concentration of a substance to be processed has changed. For this reason, it is possible to cause filtration by stable centrifugation of a substance to be processed by preventing the occurrence of abnormal vibration of the basket 21. In addition, even when a supply amount or a solid concentration of a substance to be processed has decreased, it is possible to secure time of stay of the substance to be processed in the basket 21 by making a relative movement speed of the pushing plate 22 with respect to the basket 21 or the forward and backward stroke small. For this reason, it is possible to achieve efficient filtration by exhibiting the performance of the centrifugal separator without excess or deficiency.
Also in the embodiment, the forward and backward drive unit 11 having the electric motor 11a is used and it is possible to easily and quickly control a relative movement speed or forward and backward stroke by controlling the electric motor 11a. In addition, since a pushing load can be measured in real time according to a current value of the electric motor 11a, it is possible to quickly respond to a sudden change in a supply amount or a solid concentration of a substance to be processed.
In addition to adopting the forward and backward drive unit 11 in which the electric motor 11a is used, a pushing load is measured by the measuring unit 15, which measures a current value of the electric motor 11a, in the second embodiment and the first embodiment. Without being limited thereto, for example, a load cell is disposed on the pushing shaft 6 or the like as the measuring unit 15, and a relative movement speed or forward and backward stroke between the pushing plate 7 or 22 and the basket 2 or 21 can be controlled according to a pushing load measured by the load cell.
In a case where a pushing load is measured by the load cell, the present invention may be applied to a centrifugal separator and a centrifugal separation method in which one of the basket and the pushing plate is moved forward and backward with respect to the other by hydraulic drive by a hydraulic piston of the related art particularly when controlling a relative movement speed. It is possible to apply by making hydraulic oil flow path diameters, for example, at the time of forward movement and at the time of backward movement different from each other, mounting a speed controller, or providing a difference in a hydraulic oil discharging speed by bypassing a cylinder discharging side flow path.
However, there is a possibility that a hydraulic pressure becomes unstable when switching between forward movement and backward movement of the pushing plate 7 or 22 and the basket 2 or 21 and it is difficult for the forward and backward drive unit, which relies on such hydraulic drive, to control to maintain a predetermined relative movement speed. In addition, a hydraulic pressure is difficult to be made stable as well since the viscosity of the hydraulic oil changes according to an oil temperature. Cooling water for cooling a hydraulic oil is necessary for oil temperature management, and maintenance, such as oil replacement caused by degradation of the hydraulic oil in long-term operation and periodic replacement of an oil filter, is also cumbersome. It is almost impossible to control the forward and backward stroke of the pushing plate and the basket through hydraulic drive by a general hydraulic piston.
For this reason, it is desirable to adopt the forward and backward drive unit having the electric motor as that of the first and second embodiments of the present invention in controlling at least one of a relative movement speed between the pushing plate and the basket by the forward and backward drive unit and the forward and backward stroke of one of the pushing plate and the basket with respect to the other. Although a case where the present invention is applied to the centrifugal separator and the centrifugal separation method in which two baskets including the outer basket 1 and the inner basket 2 are included in the first embodiment and to the centrifugal separator and the centrifugal separation method in which the single basket 21 is included in the second embodiment has been described, the present invention may be applied to a centrifugal separator and a centrifugal separation method in which three or more baskets are included.

Industrial Applicability

In the centrifugal separator and the centrifugal separation method of the present invention, it is possible to prevent the occurrence of abnormal vibration by maintaining a uniform thickness of a cake and to exhibit dehydration performance without excess or deficiency regardless of an increase or decrease in a load accompanying a change in a supply amount or a solid concentration of a substance to be processed. Therefore, it is possible to cause stable and efficient filtration.

Reference Signs List

1: outer basket
1a: outer filtration screen
1b: open end of outer basket 1
2: inner basket (basket)
2a: inner filtration screen
2b: open end of inner basket 2
3: casing
5: main shaft
6: pushing shaft
7, 22: pushing plate
8: distributing plate
9: supply pipe for substance to be processed
10: bearing box
11: forward and backward drive unit
11a: electric motor
11b: cylinder box
15: measuring unit
21: basket
21a: filtration screen
21b: open end of basket 21
O: axis of rotation of basket 21 (outer basket 1 and inner basket 2)
D: interval between pushing plate 7 or 22 and open end 2b or 21b of inner basket 2 or basket 21 in axis O direction

Claims

A centrifugal separator comprising:
a cylindrical basket that has a body part provided with a filtration screen and is configured to rotate about an axis of the basket;

a pushing plate that is accommodated inside the basket, is provided to be rotatable integrally with the basket and movable relatively in an axis direction of the basket, and is configured to push a cake, which is filtered by the filtration screen from a substance to be processed supplied inside the basket, to an open end side of the basket;

a forward and backward drive unit that is configured to relatively move the pushing plate and the basket by moving one of the pushing plate and the basket forward and backward in the axis direction with respect to the other; and

a measuring unit that is configured to measure a pushing load of the forward and backward drive unit when the cake is pushed to the open end side of the basket by forward and backward movement of the one of the pushing plate and the basket by the forward and backward drive unit,

wherein at least one of a relative movement speed between the pushing plate and the basket by the forward and backward drive unit and a forward and backward stroke of one of the pushing plate and the basket with respect to the other is controlled according to the pushing load measured by the measuring unit.
The centrifugal separator according to Claim 1,
wherein when the pushing load increases, at least one of the relative movement speed and the stroke is controlled to increase.
The centrifugal separator according to Claim 1 or 2,
wherein when the pushing load decreases, at least one of the relative movement speed and the stroke is controlled to decrease.
The centrifugal separator according to Claim 1 or 2,
wherein the forward and backward drive unit is driven by an electric motor.
The centrifugal separator according to Claim 4,
wherein the measuring unit is configured to measure the pushing load from a current value of the electric motor of the forward and backward drive unit.
The centrifugal separator according to any one of Claims 1 to 4,
wherein the measuring unit is a load cell included in the forward and backward drive unit.
A centrifugal separation method in which a substance to be processed is supplied into a cylindrical basket that has a body part provided with a filtration screen and rotates about an axis of the basket, and a cake filtered by the filtration screen from the substance to be processed is pushed and discharged to an open end side of the basket by a pushing plate that is accommodated inside the basket and is provided to be rotatable integrally with the basket and movable relatively in an axis direction of the basket, the method comprising:
relatively moving the pushing plate and the basket by causing a forward and backward drive unit to move one of the pushing plate and the basket forward and backward in the axis direction with respect to the other;

measuring, by a measuring unit, a pushing load of the forward and backward drive unit when the cake is pushed to the open end side of the basket by forward and backward movement of the one of the pushing plate and the basket by the forward and backward drive unit; and

controlling at least one of a relative movement speed between the pushing plate and the basket by the forward and backward drive unit and a forward and backward stroke of one of the pushing plate and the basket with respect to the other according to the pushing load measured by the measuring unit.
The centrifugal separation method according to Claim 7,
wherein when the pushing load increases, at least one of the relative movement speed and the stroke is controlled to increase.
The centrifugal separation method according to Claim 7 or 8,
wherein when the pushing load decreases, at least one of the relative movement speed and the stroke is controlled to decrease.