CENTRIFUGAL SEPARATOR AND CENTRIFUGAL SEPARATION METHOD

Abstract

 The present invention provides a centrifugal separator including a cylindrical basket (2) that has a body part provided with a filtration screen (2a) and is configured to rotate about an axis of the basket (2) and a pushing plate (7) that is accommodated inside the basket (2) and is provided to be rotatable integrally with basket and movable relatively in an axis (O) direction of the basket (2). When a cake, which is filtered by the filtration screen (2a) from a substance to be processed supplied inside the basket (2), is discharged by pushing the cake to an open end (2b) side of the basket (2) by the pushing plate (7), a relative movement speed between the pushing plate (7) and the basket (2) in the axis (O) direction is set such that a relative movement speed in a direction where an interval (D) between the pushing plate (7) and an open end (2b) of the basket (2) in the axis (O) direction becomes large is lower than a relative movement speed in a direction where the interval (D) becomes small.

Description

Technical Field

[0001] 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.

[0002] Priority is claimed on Japanese Patent Application No. 2016-133665, filed on July 5, 2016, the content of which is incorporated herein by reference.

Background Art

[0003] 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.

[0004] 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 Literature

[0005] [Patent Document 1] Japanese Unexamined Patent Application, First Publication No. 2014-091093

Summary of Invention

Technical Problem

[0006] 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, a movement speed at the time of forward movement and a movement speed at the time of backward movement are the same in general. In addition, a supply amount of a substance to be processed from the supply pipe is also a fixed amount per unit time in general.

[0007] When the inner basket moves forward with respect to the pushing plate, a substance to be processed is supplied to the filtration screen, through which the substance to be processed is relatively likely to be filtered, after the substance to be processed accumulated on an inner circumferential surface of the filtration screen of the inner basket is pushed by the pushing plate. On the other hand, when the inner basket moves backward with respect to the pushing plate, a substance to be processed is supplied so as to be added onto a cake of a substance to be processed, which is accumulated on the inner circumferential surface of the filtration screen of the inner basket and is being pushed by the pushing plate. Thus, the substance to be processed is unlikely to be filtered.

[0008] For this reason, in particular, in a case where a substance to be processed which is unlikely to be filtered is supplied, the filtration of the substance to be processed is insufficient at the time of backward movement of the inner basket, or it is difficult to form a uniform cake unless the size of the centrifugal separator is increased by making the capacity of the basket large. Thus, there is a possibility that a supply amount of a substance to be processed has to be limited.

[0009] Contrary to the centrifugal separator disclosed in Patent Document 1, a centrifugal separator in which a position where a basket rotates is fixed in an axis direction and a pushing plate accommodated inside the basket is movable by moving forward and backward inside the basket with respect to the axis direction of the basket is also known. In such a centrifugal separator, when the pushing plate moves backward, a substance to be processed is supplied to a filtration screen which is likely to filter the substance to be processed after a cake of the substance to be processed is pushed. On the other hand, when the pushing plate moves forward, a supplied substance to be processed is added onto a cake of a substance to be processed which is being pushed by the pushing plate. For this reason, filtration or cake formation is insufficient.

[0010] 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 cause efficient filtration of a substance to be processed and to achieve an increase in a processing amount and uniform cake formation without increasing the size of the centrifugal separator by making basket capacity large.

Solution to Problem

[0011] 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 configured to rotate about an axis of the basket and 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. A cake, which is filtered by the filtration screen from a substance to be processed supplied inside the basket, is discharged by pushing the cake to an open end side of the basket by the pushing plate. A relative movement speed between the pushing plate and the basket in the axis direction is set such that a relative movement speed in a direction where an interval between the pushing plate and an open end of the basket in the axis direction becomes large is lower than a relative movement speed in a direction where the interval between the pushing plate and the open end of the basket in the axis direction becomes small.

[0012] 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 rotates about an axis of the basket, and a cake filtered by the filtration screen from the substance to be processed is discharged by pushing the cake to an open end side of the basket by a pushing plate that is accommodated inside the basket and is rotatable integrally with the basket and movable relatively in an axis direction of the basket. The centrifugal separation method includes setting a relative movement speed between the pushing plate and the basket in the axis direction such that a relative movement speed in a direction where an interval between the pushing plate and an open end of the basket in the axis direction becomes large is lower than a relative movement speed in a direction where the interval between the pushing plate and the open end of the basket in the axis direction becomes small.

[0013]  In the first aspect of such a centrifugal separator and the first aspect of such a centrifugal separation method, a direction where an interval between the pushing plate and the open end of the basket in the axis direction becomes large is a direction when basket moves forward, and a direction where the interval becomes small is a direction when the basket moves backward, 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, a direction where the interval between the pushing plate and the open end of the basket in the axis direction becomes large is a direction when the pushing plate moves backward, and a direction where the interval becomes small is a direction when the pushing plate moves forward.

[0014] That is, in the first aspect of the centrifugal separator and the first aspect of the centrifugal separation method, which have the above-described configuration, when one of the basket and the pushing plate relatively moves with respect to the other, a relative movement speed when a substance to be processed is supplied to the filtration screen which is in a state of being relatively likely to filter the substance to be processed after the substance to be processed accumulated on the inner circumferential surface of the filtration screen of the basket is pushed by the pushing plate is lower than a relative movement speed when a substance to be processed is supplied to the filtration screen, which is in a state of being unlikely to filter the substance to be processed with the substance to be processed being left thereon.

[0015]  For this reason, even when a supply amount of a substance to be processed is increased in a case where the capacity of the basket is the same, a larger amount of the substance to be processed can be supplied to the filtration screen of the basket, which is in state of likely to filter the substance to be processed. On the other hand, in a case where relative movement speeds are respectively set at the time of forward movement of relative movement and at the time of backward movement of relative movement as described above and time taken for one forward and backward stroke is the same, a relative movement speed when a substance to be processed is supplied to the filtration screen, which is in a state of being unlikely to filter the substance to be processed, is higher than a relative movement speed when a substance to be processed is supplied to the filtration screen, which is in a state of being likely to filter the substance to be processed. For this reason, the supply amount of a substance to be processed added onto a cake of a substance to be processed left on the filtration screen becomes small, and thus a uniform cake can be formed.

[0016] Therefore, in the centrifugal separator and the centrifugal separation method, which have the above-described configuration, a larger amount of a substance to be processed can be supplied to the filtration screen which is in a state of being likely to filter the substance to be processed, and a supply amount of a substance to be processed to the filtration screen which is in a state of being unlikely to filter the substance to be processed can be controlled without increasing the size of the centrifugal separator by making basket capacity large or without making time taken for one forward and backward stroke long. For this reason, a processing amount can be increased by achieving efficient filtration of a substance to be processed, and thus it is possible to cause uniform cake formation.

[0017] In a case where a relative movement speed of the pushing plate with respect to the basket in the axis direction is set such that a relative movement speed in the direction where the interval between the pushing plate and the open end of the basket in the axis direction becomes large is lower than a relative movement speed in the direction where the interval becomes small and if a ratio therebetween is excessively high, it is difficult to set a relative movement speed of one of the basket and the pushing plate with respect to the other. For this reason, a possibility that a large amount of a substance to be processed cannot be reliably supplied to the filtration screen, which is in a state of being likely to filter the substance to be processed, arises.

[0018] For this reason, it is desirable to set the relative movement speed in the direction where the interval between the pushing plate and the open end of the basket in the axis direction becomes large to a speed which is 1/4 or more of the relative movement speed in the direction where the interval between the pushing plate and the open end of the basket in the axis direction becomes small. However, when the ratio between the relative movement speeds approaches 1 and a speed difference is excessively small, there is a possibility that the effects described above cannot be effectively achieved. For this reason, it is more desirable to set the relative movement speed in the direction where the interval becomes large to a speed which is 2/3 or less of the relative movement speed in the direction where the interval becomes small.

[0019] Setting a relative movement speed of forward and backward movement can also be applied to a case where one of the basket and the pushing plate is moved forward and backward with respect to the other, for example, by hydraulic drive by a hydraulic piston of the related art. At this time, a difference in a hydraulic oil discharging speed may be provided 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 bypassing a cylinder discharging side flow path. 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 set to a predetermined relative movement speed.

[0020] In order to drive one of the basket and the pushing plate, 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. Alternatively, it is desirable to use an electric motor having high responsiveness such as a so-called fastener type actuator that causes the piston rod to linearly move or the like. 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.

Advantageous Effects of Invention

[0021] As described above, in the present invention, an increase in a processing amount can be achieved by achieving efficient filtration of a substance to be processed, and a uniform cake can be formed, without increasing the size of the centrifugal separator by making basket capacity large or without making time taken for one forward and backward stroke long. Therefore, it is possible to achieve reduction in costs of the centrifugal separator itself, reduction in a mounting space of the centrifugal separator, and simplification of mounting basis caused by a decrease in the weight of the centrifugal separator, and it is also possible to stably and easily perform post-processing of a cake.

Brief Description of Drawings

[0022] 

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 (a state where an interval between the pushing plate and an open end of the basket in an axis direction is small) 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 (a state where the interval between the pushing plate and the open end of the basket in the axis direction is large) 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 (a state where an interval between the pushing plate and an open end of the basket in an axis direction is small) 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 (a state where the interval between the pushing plate and the open end of the basket in the axis direction is large) according to the embodiment shown in FIG. 4.

Description of Embodiments

[0023] FIGS. 1 to 3 show a first embodiment of a centrifugal separator of the present invention, and show 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.

[0024] 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.

[0025] 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.

[0026] 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.

[0027]  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.

[0028] 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 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.

[0029] 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 shown) 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.

[0030] 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 illustrated) disposed so as to extend in the axis O direction inside a cylinder box 11b. A nut coaxially attached to a piston rod (not illustrated) 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.

[0031] A relative movement speed between the inner basket 2 and the pushing plate 7 in the axis O direction accompanying forward and backward movement of the pushing shaft 6 by such a forward and backward drive unit 11 is set as follows. That is, a relative movement speed in a direction where an interval D between the pushing plate 7 and the open end 2b of the inner basket 2 in the axis O direction becomes large is set to be lower than a relative movement speed in a direction where the interval D between the pushing plate 7 and the open end 2b of the inner basket 2 in the axis O direction becomes small. In order to set a relative movement speed in such a manner, a relative movement speed may be controlled to be adjusted as appropriate during operation of the centrifugal separator, or such control may be set in advance so as to be performed before operation. Such control can be easily performed in an automatic manner 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.

[0032] Specifically, in the embodiment, 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, and the inner basket 2 moves forward and backward in the axis O direction via the pushing shaft 6. For this reason, by moving the inner basket 2 forward to the one end side of the axis O direction from a state where the inner basket 2 has moved backward as shown in FIGS. 1 and 2, the open end 2b of the inner basket 2 is spaced apart from the pushing plate 7 and the interval D becomes large as shown in FIG. 3. A relative movement speed between the outer basket 1 and the inner basket 2 in the direction where the interval D becomes large is set to be lower than a movement speed in a direction where the open end 2b approaches the pushing plate 7 and the interval D becomes small by moving the inner basket 2 backward to the other end side from a state shown in FIG. 3.

[0033] 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 in a fixed amount per unit time 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, and sticks to the inner circumferential surface of the inner filtration screen 2a of the inner basket 2. While the substance to be processed is being supplied in such a manner, the inner basket 2 is moved forward from a state where the inner basket 2 has moved backward as shown in FIGS. 1 and 2. Then, the substance to be processed is filtered by centrifugal force while also being continuously accumulated on the inner circumferential surface of the inner filtration screen 2a of the inner basket 2, which moves forward, in the axis O direction, and thereby a cake of the substance to be processed (cake) is formed.

[0034] Next, when the inner basket 2 which has moved forward 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 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.

[0035] The cake, 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 shown) 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 discharged from the outlet 3b of the casing 3 via the chute as described above.

[0036] When a substance to be processed is filtered by being centrifuged and a cake is formed in such a manner, a relative movement speed between the inner basket 2 and the pushing plate 7 in the axis O direction is set as follows in the centrifugal separator and the centrifugal separation method. That is, a movement speed of the inner basket 2 in a forward direction where the interval D between the pushing plate 7 and the open end 2b of the inner basket 2 in the axis O direction becomes large is set to be lower than a movement speed of the inner basket 2 in a backward direction where the interval D between the pushing plate 7 and the open end 2b of the inner basket 2 in the axis O direction becomes small. That is, since the embodiment has the same time taken for one forward and backward stroke as in the centrifugal separator and the centrifugal separation method of the related art, in which a movement speed of the inner basket moving forward and a movement speed of the inner basket moving backward are the same, a movement speed of the inner basket 2 in the forward direction in the embodiment is lower than that of the related art.

[0037] Therefore, when the inner basket 2 moves forward, a large amount of a substance to be processed supplied from the supply pipe 9 is accumulated slowly, with more time taken than when the inner basket 2 moves backward, onto the inner circumferential surface of the inner filtration screen 2a that is in a state where the amount of the accumulated substance to be processed is small after the substance to be processed is pushed by the pushing plate 7 by the previous backward movement of the inner basket 2. For this reason, even when the capacity of the inner basket 2 is the same as in the related art, a larger amount of a substance to be processed can be supplied to the inner circumferential surface of the inner filtration screen 2a, which is in state where the amount of the accumulated substance to be processed is small and is likely to filter the accumulated substance to be processed.

[0038] In the centrifugal separator and the centrifugal separation method, which have the above-described configuration, a movement speed of the inner basket 2 when a substance to be processed, which is accumulated on the inner circumferential surface of the inner filtration screen 2a, is pushed by the pushing plate 7 by the inner basket 2 moving backward, becomes high compared to a case of the related art, in which time taken for one stroke is the same and a forward movement speed and a backward movement speed are the same. For this reason, the amount of a substance to be processed that is further added onto the substance to be processed accumulated on the inner circumferential surface of the inner filtration screen 2a, which is directly on the one end side of the pushing plate 7 in the axis O direction, can be made small. For this reason, it is possible to suppress an increase in a supply amount of a substance to be processed to the inner filtration screen 2a, which is in a state where the substance to be processed remains being accumulated and is unlikely to be filtered.

[0039] Therefore, in the centrifugal separator and the centrifugal separation method, which are configured in such a manner, it is not necessary to achieve an increase in the size of the centrifugal separator by making the capacity of the inner basket 2 (basket) large, or to make time taken for one forward and backward stroke caused by the relative movement of the inner basket 2 with respect to the pushing plate 7 long. A larger amount of a substance to be processed can be reliably and efficiently processed with one stroke by increasing a supply amount of a substance to be processed to the inner filtration screen 2a, which is in a state of being likely to filter the substance to be processed. It is possible to form a uniform cake over the entire length of the inner basket 2 by controlling the supply of a substance to be processed to the inner filtration screen 2a which is in a state of being unlikely to filter the substance to be processed. Therefore, it is possible to achieve reduction in costs of the centrifugal separator and in a mounting space and simplification of mounting basis caused by a decrease in the weight of the centrifugal separator, and it is also possible to stably and easily perform post-processing of a filtered cake.

[0040] In addition, in the embodiment, in order to set a movement speed of the inner basket 2 with respect to the pushing plate 7 in such a manner, the electric motor 11a is used as the forward and backward drive unit 11 which moves the inner basket 2 forward and backward via the pushing shaft 6. However, even in a case where the pushing shaft 6 and the inner basket 2 are moved forward and backward by hydraulic drive as in the related art, it is possible to provide a difference in a hydraulic oil discharging speed and to set a 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 bypassing a cylinder discharging side flow path. However, in this case, there is a problem that a hydraulic pressure becomes unstable when switching between forward movement and backward movement, which is characteristic of hydraulic drive, and thus there is a possibility that it is difficult to reliably set to a predetermined relative movement speed.

[0041] On the other hand, the forward and backward drive unit 11 in which the electric motor 11a is used as in the embodiment has high responsiveness, and can quickly change a movement direction even when switching between forward movement and backward movement. It is possible to reliably and stably set a movement speed as well, and the forward and backward drive unit 11 is particularly preferable in a case where a relative movement speed of the inner basket 2 with respect to the pushing plate 7 is set to a different level as in the centrifugal separator and the centrifugal separation method, which have the above-described configuration.

[0042] An 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 can be used as the forward and backward drive unit 11 in which such an electric motor 11a is 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. It is also possible to use a so-called fastener type actuator that causes the piston rod to linearly move or the like. 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.

[0043] 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.

[0044] 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.

[0045] 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 positions 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.

[0046] 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 an interval between the pushing plate 22 and the open end 21b of the basket 21 in the axis O direction becomes large is a direction when the pushing plate 22 moves backward, and a direction where the interval becomes small is a direction when the pushing plate 22 moves forward.

[0047] A relative movement speed between the pushing plate 22 and the basket 21 in the axis O direction is set as follows also in the present embodiment. That is, a relative movement speed in 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 as shown in FIG. 5, that is, a direction where the pushing plate 22 moves backward from a state where the pushing plate 22 moves forward with respect to the basket 21 and the interval D between the pushing plate 22 and the open end 21b of the basket 21 in the axis O direction is small as shown in FIG. 4 is set to be lower than a relative movement speed in the direction where the interval D becomes small as shown in FIG. 4 from a state where the interval D between the pushing plate 22 and the open end 21b in the axis O direction is large as shown in FIG. 5.

[0048] For this reason, also in the present embodiment, when the pushing plate 22 moves backward after a substance to be processed accumulated on the inner circumferential surface of the filtration screen 21a is pushed, a large amount of a substance to be processed that is newly supplied from the supply pipe 9 is accumulated slowly with taking time onto the inner circumferential surface of the filtration screen 21a which is in a state where the amount of accumulation after the substance to be processed is pushed is small and the substance to be processed is likely to be filtered. For this reason, a large amount of a substance to be processed can be efficiently filtered. On the other hand, when the pushing plate 22 moves forward and the interval D between the pushing plate 7 and the open end 21b becomes small at the time of pushing an accumulated substance to be processed, a movement speed is high, and the amount of the substance to be processed to be added onto the already accumulated substance to be processed can be made small. For this reason, a uniform cake can be formed over the entire length of the basket 21.

[0049] As in the first and second embodiments, in a case where a relative movement speed of the pushing plate 7 or 22 with respect to the basket 2 or 21 in the axis O direction is set such that a relative movement speed in the direction where the interval D in the axis O direction becomes large is lower than a relative movement speed in the direction where the interval D becomes small and if a ratio therebetween is excessively high, it is difficult to set a movement speed of the moving basket (the inner basket 2) or the pushing plate 22. For this reason, a possibility that a large amount of a substance to be processed cannot be reliably supplied to the filtration screen 2a or 21a, which is in a state of being likely to filter the substance to be processed, or a large amount of a substance to be processed is added onto the filtration screen 2a or 21a, which is in a state of being unlikely to filter, arises.

[0050] For this reason, it is desirable to set a relative movement speed in the direction where the interval D between the pushing plate 7 or 22 and the open end 2b or 21b of the basket 2 or 21 in the axis O direction becomes large to be lower than a speed which is 1/4 or more of a relative movement speed in the direction where the interval D becomes small. However, when a difference between the relative movement speeds is small, there is a possibility that the effects described above cannot be effectively achieved. For this reason, it is more desirable to set a relative movement speed in the direction where the interval D becomes large to a speed which is 2/3 or less of a relative movement speed in the direction where the interval becomes small. 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. However, it is evident that is also possible to apply the present invention to a centrifugal separator and a centrifugal separation method in which three or more baskets are included.

Industrial Applicability

[0051]  In the centrifugal separator and the centrifugal separation method of the present invention, an increase in a processing amount can be achieved by achieving efficient filtration of a substance to be processed, and a uniform cake can be formed without increasing the size of the centrifugal separator by making basket capacity large or without making time taken for one forward and backward stroke long. Therefore, it is possible to achieve a reduction in costs of the centrifugal separator itself, a reduction in a mounting space of the centrifugal separator, and a simplification of mounting basis caused by a decrease in the weight of the centrifugal separator, and it is also possible to stably and easily perform post-processing of a cake.

Reference Signs List

[0052] 

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

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

1. 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; and

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,

wherein a cake, which is filtered by the filtration screen from a substance to be processed supplied inside the basket, is discharged by pushing the cake to an open end side of the basket by the pushing plate, and

a relative movement speed between the pushing plate and the basket in the axis direction is set such that a relative movement speed in a direction where an interval between the pushing plate and an open end of the basket in the axis direction becomes large is lower than a relative movement speed in a direction where the interval between the pushing plate and the open end of the basket in the axis direction becomes small.

2. The centrifugal separator according to Claim 1,
wherein the relative movement speed in the direction where the interval between the pushing plate and the open end of the basket in the axis direction becomes large is set to a speed which is 1/4 or more of the relative movement speed in the direction where the interval between the pushing plate and the open end of the basket in the axis direction becomes small.

3. The centrifugal separator according to Claim 1 or 2,
wherein the relative movement speed in the direction where the interval between the pushing plate and the open end of the basket in the axis direction becomes large is set to a speed which is 2/3 or less of the relative movement speed in the direction where the interval between the pushing plate and the open end of the basket in the axis direction becomes small.

4. 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 discharged by pushing the cake 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:
setting a relative movement speed between the pushing plate and the basket in the axis direction such that a relative movement speed in a direction where an interval between the pushing plate and an open end of the basket in the axis direction becomes large is lower than a relative movement speed in a direction where the interval between the pushing plate and the open end of the basket in the axis direction becomes small.

5. The centrifugal separation method according to Claim 4,
wherein the relative movement speed in the direction where the interval between the pushing plate and the open end of the basket in the axis direction becomes large is set to a speed which is 1/4 or more of the relative movement speed in the direction where the interval between the pushing plate and the open end of the basket in the axis direction becomes small.

6. The centrifugal separation method according to Claim 4 or 5,
wherein the relative movement speed in the direction where the interval between the pushing plate and the open end of the basket in the axis direction becomes large is set to a speed which is 2/3 or less of the relative movement speed in the direction where the interval between the pushing plate and the open end of the basket in the axis direction becomes small.

Drawing