Centrifugal dehydrator

Abstract

To apply sufficient back pressure to sludge with a low moisture content and to prevent the occurrence of poor discharge of sludge even when sludge with a high moisture content is supplied. [Solution] A centrifugal dehydrator (1) has an inner drum rotor (2), an outer drum rotor (3) containing the inner drum rotor (2), and inner drum blades (4) installed on the outer surface of the inner drum rotor, with the outer drum rotor (3) having a convex valve seat (19) protruding from its inner surface. The centrifugal dehydrator (1) also has a valve element (6) having three or more contact areas (22) capable of contacting the valve seat (19) and a constantly open groove (23) formed between two adjacent contact areas (22), and a pressurizing device that applies back pressure to the sludge via the valve element (6). When the contact areas (22) are in contact with the valve seat (19), the discharge passage leading to the dehydrated cake discharge hole (5) is formed only by the space between the constantly open groove (23) and the valve seat (19); when the contact areas (22) are separated from the valve seat (19), the discharge passage is formed by the space between the valve seat (19) and the contact areas (22) and the space between the constantly open groove (23) and the valve seat (19).

Description

Technical Field

[0001] The present invention relates to a centrifugal dewatering device that uses centrifugal force to dewater sludge and discharge the dewatered cake.

Background Art

[0002] There are multiple types of centrifugal dewatering devices for dewatering sludge using centrifugal force. Among them, there is a centrifugal dewatering device including two rotors that rotate around the same rotation axis, that is, an outer cylinder rotor and an inner cylinder rotor that is enclosed by the outer cylinder rotor and has screw-type inner cylinder blades. The centrifugal dewatering device can appropriately separate solid and liquid of sludge by applying back pressure with a valve body pressed by a spring to the sludge supplied between the inner cylinder rotor and the outer cylinder rotor. Then, the sludge conveyed by the inner cylinder blades and solid-liquid separated, that is, the dewatered cake, is discharged from a dewatered cake discharge hole provided in the outer cylinder rotor (see Patent Document 1). In the centrifugal dewatering device, when the pressure of the sludge becomes greater than the back pressure and the valve body moves, not only the opening and closing of the discharge passage through which the sludge goes toward the dewatered cake discharge hole but also the size of the discharge passage changes.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] The moisture content of the sludge supplied to the centrifugal dewatering device is not always constant and may change over time. And when sludge with a large amount of water and soft texture is conveyed near the valve body, the back pressure becomes greater than the pressure with which the sludge pushes the valve body, the valve body closes the discharge passage, and there is a risk of poor discharge of the sludge. When such discharge failure occurs, it is necessary to stop the operation of the centrifugal dehydrator and perform cleaning and maintenance work. Therefore, in order to avoid this, conventionally, the position of the spring support portion that supports the spring was appropriately adjusted to relieve the back pressure. By relieving the back pressure, even if the sludge has a large water content and is soft, the valve body can easily move under the pressure of the sludge and the discharge passage opens, so that the occurrence of such discharge failure can be prevented. However, in principle, when the sludge supplied to the centrifugal dehydrator is sludge with a low water content, exceptionally, that is, for sludge with a large water content that is only supplied temporarily, if the position of the spring support portion is adjusted and set in the direction of relieving the back pressure, the moisture content of the dehydrated cake will increase overall. That is, the water content of the dehydrated cake increases, and the quality of the dehydrated cake may deteriorate.

[0005] The present invention has been made in view of the above problems, and one of the objects is to provide a centrifugal dehydrator that can apply sufficient back pressure to sludge with a low water content and can also avoid the occurrence of poor sludge discharge even when sludge with a large water content is supplied.

Means for Solving the Problems

[0006] The centrifugal dehydrator of the present invention an inner cylinder rotating body into which sludge is supplied and can supply sludge to the outside, and is rotatable around an axis, and a cylindrical outer cylinder rotating body that encloses the inner cylinder rotating body and is rotatable around an axis, and inner cylinder blades installed on the outer surface of the inner cylinder rotating body, for conveying along the axis the sludge supplied from the inside of the inner cylinder rotating body between the inner cylinder rotating body and the outer cylinder rotating body to discharge from the dehydrated cake discharge holes installed on the outer cylinder rotating body, and a valve seat installed on the inner surface of the outer cylinder rotating body between the inner cylinder blades and the dehydrated cake discharge holes and in the vicinity of the dehydrated cake discharge holes, protruding radially inward from the inner surface, and circular in shape when viewed in a plane perpendicular to the axis, and At a position on the axis opposite to the inner cylinder blade with respect to the valve seat, and arranged coaxially with the axis, there are three or more contact portions capable of contacting the valve seat, and a plurality of always-open grooves formed between two adjacent contact portions and always forming at least a part of the sludge discharge passage leading from the valve seat to the dewatered cake discharge hole. A valve body that is movable along the axis and circular in shape when viewed in a plane perpendicular to the axis, It has a pressurizing device that applies a pressure in a direction opposite to the conveying direction to the valve body in order to apply back pressure to the sludge. When the pressure of the sludge pressing the valve body is smaller than the back pressure and the contact portion is in contact with the valve seat, the discharge passage is formed only by the space between the always-open groove and the valve seat. When the pressure of the sludge pressing the valve body is larger than the back pressure and the contact portion is separated from the valve seat, the discharge passage is formed by the space between the contact portion and the valve seat and the space between the always-open groove and the valve seat.

Advantages of the Invention

[0007] According to the centrifugal dewatering device of the present invention, the valve body is provided with three or more contact portions capable of contacting the valve seat, and always-open grooves are respectively provided between adjacent contact portions. For this reason, even when the pressure of the sludge conveyed by the inner cylinder blade pressing the valve body is smaller than the back pressure by the pressurizing device, as in the case where sludge with a large water content is supplied and the contact portion is in contact with the valve seat, at least a part of the discharge passage is always open through the three or more always-open grooves and leads to the dewatered cake discharge hole, and the sludge is discharged from the dewatered cake discharge hole through the discharge passage. Therefore, the occurrence of poor sludge discharge can be avoided. Also, when sludge with a small water content is supplied, when the pressure of the sludge conveyed by the inner cylinder blade pressing the valve body is larger than the back pressure by the pressurizing device and the valve body is pushed by the sludge and moves axially, the discharge passage is formed by the space between the contact portion and the valve seat and the space between the always-open groove and the valve seat. As a result, a large discharge passage can be formed, and the sludge can be smoothly discharged from the dewatered cake discharge hole. At this time, the valve body is not in contact with the valve seat and is moving, but a sufficient back pressure for obtaining a dewatered cake of a predetermined quality can be applied to the sludge by the valve body and the pressurizing device. Therefore, it is possible to provide a centrifugal dehydrator that can apply sufficient back pressure to sludge with a low water content and can also avoid the occurrence of poor sludge discharge even when sludge with a high water content is supplied.

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Embodiments for Carrying Out the Invention

[0009] Hereinafter, with reference to FIGS. 1 to 6, the centrifugal dehydrators according to the embodiments and modified examples of the present invention will be described. In this specification and the drawings, for the sake of simplicity of explanation, a rectangular coordinate system using the X-axis, Y-axis, and Z-axis will be used for explanation as appropriate. The embodiments and modified examples are merely examples, and there is no intention to exclude various modifications and applications of technologies that are not explicitly stated. Except for the essential configurations of the present invention, each configuration of the embodiment can be selected or modified as needed and implemented in various ways. First, the main configurations included in the centrifugal dehydrator 1 of the embodiment will be sequentially described, and then, the structure of the valve body and the pressurizing device, which is one of the features of the present invention, will be described in detail.

[0010] <Centrifugal Dehydrator of the Embodiment> FIG. 1 is a cross-sectional view in the XZ plane showing the overall configuration of the centrifugal dehydrator 1 of the embodiment. The centrifugal dewatering device 1 includes a cylindrical inner cylinder rotating body 2 that is rotatable around an axis O, which is a virtual line extending in the X-axis direction. Near both ends of the inner cylinder rotating body 2 are inner cylinder rotating shafts 8 that are smaller in diameter than other parts of the inner cylinder rotating body 2. Inside one of the two inner cylinder rotating shafts 8, a cylindrical sludge supply pipe 16 coaxial with the axis O is inserted, and sludge is supplied into the inner cylinder rotating body 2 through the sludge supply pipe 16. On a part of the outer surface of the other part of the inner cylinder rotating body 2, screw-type inner cylinder blades 4 are installed. Also, on the wall surface of the other part of the inner cylinder rotating body 2, sludge supply holes 17 are formed, which are through holes for discharging the sludge supplied to the inside of the inner cylinder rotating body 2 to the outside of the inner cylinder rotating body 2, in other words, for supplying sludge to the outside of the inner cylinder rotating body 2 through the inside of the inner cylinder rotating body 2. The centrifugal dewatering device 1 includes a cylindrical outer cylinder rotating body 3 that encloses the inner cylinder rotating body 2 and is rotatable coaxially with the inner cylinder rotating body 2, that is, rotatable around the axis O. Near both ends of the outer cylinder rotating body 3 are outer cylinder rotating shafts 9 that are smaller in diameter than other parts of the outer cylinder rotating body 3. Most of the inner diameter of the other part of the outer cylinder rotating body 3 is designed to be slightly larger than the diameter of the circle obtained by the rotation of the inner cylinder blades 4 as viewed in the XY plane. The sludge supplied between the inner cylinder rotating body 2 and the outer cylinder rotating body 3 from the sludge supply holes 17 of the inner cylinder rotating body 2 is conveyed in the +X-axis direction through the space between the inner cylinder rotating body 2 and the outer cylinder rotating body 3 by the inner cylinder blades 4 when the inner cylinder rotating body 2 on which the inner cylinder blades 4 are installed rotates.

[0011] Note that the inner cylinder rotating body 2 and the outer cylinder rotating body 3 rotate at different speeds. Specifically, the inner cylinder rotating body 2 rotates faster than the outer cylinder rotating body 3. One of the two outer cylinder rotating shafts 9 of the outer cylinder rotating body 3 is connected to the motor 14 by a belt transmission mechanism 15, and the rotation of the motor 14 is transmitted to the outer cylinder rotating shaft 9 by the belt transmission mechanism 15, causing the entire outer cylinder rotating body 3 to rotate. The other inner cylinder rotating shaft 8 and the other outer cylinder rotating shaft 9, which are different from the above-mentioned one, are connected to each other by a rotary joint (not shown) with the outer cylinder rotating shaft 9 enclosing the inner cylinder rotating shaft 8, and the rotation speed of the inner cylinder rotating body 2 is adjusted by a differential speed device 13 so that the inner cylinder rotating body 2 and the outer cylinder rotating body 3 rotate at a preset speed difference. When the inner cylinder rotating body 2 and the outer cylinder rotating body 3 rotate respectively, the sludge is conveyed in the +X-axis direction by the inner cylinder blades 4 in the space between the inner cylinder rotating body 2 and the outer cylinder rotating body 3, and is solid-liquid separated by centrifugal force. The separated liquid after solid-liquid separation is discharged from the separation liquid discharge hole 18 formed at the -X-axis direction end portion at the other location of the outer cylinder rotating body 3, and is conveyed to the outside of the centrifugal dehydrator 1 through the separation liquid chute 7A. On the other hand, the sludge after solid-liquid separation, that is, the dehydrated cake, is discharged from the dehydrated cake discharge hole 5 which is a through hole formed in the wall surface of the outer cylinder rotating body 3, and is conveyed to the outside of the centrifugal dehydrator 1 through the dehydrated cake chute 7B.

[0012] Here, a casing 7 covering the outer cylinder rotating body 3 is arranged outside the outer cylinder rotating body 3. Since the casing 7 prevents the separation liquid and the dehydrated cake from scattering around the centrifugal dehydrator 1, the surrounding environment is not polluted. In addition, outside the casing 7, a sludge supply side support unit 11 and a sludge discharge side support unit 12 that stably support the two outer cylinder rotating shafts 9 between the floor 10, in other words, support the entire centrifugal dehydrator 1 on both sides are arranged.

[0013] The outer cylinder rotating body 3 is provided with a valve seat 19 having the following shape. That is, when viewed in the X-axis direction position, it is installed on the inner surface of the outer cylinder rotating body 3 between the inner cylinder blades 4 and the dehydrated cake discharge hole 5 and in the vicinity of the dehydrated cake discharge hole 5, and has a convex shape protruding radially inward from the inner surface, and is an annular valve seat 19 that is circular and seamless when viewed in a plane perpendicular to the axis O or the X-axis. The convex shape is, for example, a substantially triangular shape having a vertex on the radially inner side of the outer cylinder rotating body 3 as shown in FIG. 1. Since the valve seat 19 protrudes radially from the inner surface of the outer cylinder rotating body 3, the sludge conveyed from the -X-axis direction to the +X-axis direction when viewed at the position of the valve seat 19 is squeezed by the valve seat 19, so that in addition to solid-liquid separation by centrifugal dehydration, further solid-liquid separation is achieved. Then, the sludge conveyed in the +X-axis direction when viewed at the position of the valve seat 19, that is, the dehydrated cake, is discharged from the dehydrated cake discharge hole 5 through the discharge passage formed between the valve seat 19 and the valve body 6a described later.

[0014] Next, the valve body 6a and the pressurizing device that applies pressure to the valve body 6a in the -X-axis direction, i.e., the direction opposite to the above-described conveying direction, will be described. Here, an example in which the pressurizing device is composed of a spring that is an elastic body, specifically a disc spring 20, a spring support portion 21a, and a cylinder 21b for fixing the spring support portion will be described. However, as long as it is a device that presses the valve body 6a in the -X-axis direction, it is not limited to an elastic body, and a device using hydraulic pressure may also be used.

[0015] The valve body 6a is coaxially and inseparably fixed to a cylindrical valve body fixing cylinder 6b. The valve body 6a and the valve body fixing cylinder 6b may be fixed by welding or may be integrally formed from the beginning. As shown in FIG. 1, the shape in which the valve body 6a and the valve body fixing cylinder 6b are integrated is arrow-shaped when viewed in the XZ plane. Taking the arrow as an example, the valve body 6a has a shape corresponding to the arrowhead. That is, at the connection portion between the valve body 6a and the valve body fixing cylinder 6b, the dimensions of the valve body 6a in the direction perpendicular to the X-axis and outward from the connection portion, in other words, the dimensions in the Z-axis direction and the Y-axis direction are the largest. And the dimension is such that the largest dimension portion of the valve body 6a contacts the inner surface of the outer cylinder rotating body 3 and can slide smoothly in the X-axis direction. And from this position, as it proceeds in the -X-axis direction, the dimensions of the valve body 6a in the Z-axis direction and the Y-axis direction gradually become smaller. However, as shown in FIG. 3, in the valve body 6a, there are a contact portion 22 that can smoothly contact the valve seat 19, and a constantly open groove 23 that forms a discharge passage for sludge leading to the dewatered cake discharge hole 5 between the valve seat 19 and the valve body 6a even when the contact portion 22 contacts the valve seat 19. The location where it begins to become smaller and the degree of becoming smaller are different. These locations and degrees are appropriately designed according to the properties of the sludge, but at least it can be said that the constantly open groove 23 has a concave shape when viewed from two adjacent contact portions 22.

[0016] As shown in FIG. 2, when viewed in the YZ plane, the shape of the valve body 6a is circular and annular, in other words, doughnut-shaped. The diameter of the hole of the doughnut is the same as the inner diameter of the cylinder 6b for fixing the valve body. As shown in FIG. 2, when viewed in the YZ plane, three contact portions 22 are formed on the valve body 6a at equal intervals of 120° as an example. Further, a normally open groove 23 is formed between two adjacent contact portions 22. Therefore, three contact portions 22 and three normally open grooves 23 are formed on the valve body 6a at equal intervals. Here, since the contact portion 22 needs to stably contact the valve seat 19, three contact portions 22 are arranged. Since the contact portion 22 and the normally open groove 23 are portions that receive the pressure of the sludge, in order to evenly disperse the pressure and prevent the occurrence of failures such as the valve body 6a, it is desirable to arrange three or more of each of them at equal intervals according to the properties of the sludge when viewed in the YZ plane.

[0017] In the integrated valve body 6a and the cylinder 6b for fixing the valve body, a plurality of disc springs 20 having an inner diameter similar to the outer diameter of the cylinder 6b for fixing the valve body are inserted from the outside of the cylinder 6b for fixing the valve body. Thereafter, the integrated valve body 6a and the cylinder 6b for fixing the valve body are inserted outside the cylindrical spring support portion fixing cylinder 21b via the O-ring 26. The outer diameter of the spring support portion fixing cylinder 21b and the inner diameter of the cylinder 6b for fixing the valve body are designed to have dimensions such that the cylinder 6b for fixing the valve body can slide smoothly on the spring support portion fixing cylinder 21b.

[0018] At the +X-axis direction end of the spring support portion fixing cylinder 21b, a spring support portion 21a is fixed to the outer surface of the spring support portion fixing cylinder 21b in a state where the position can be finely adjusted in the X-axis direction. The spring support portion 21a includes a columnar portion having a dimension that extends vertically and outward from the outer surface of the spring support portion fixing cylinder 21b and does not contact the inner surface of the outer cylinder rotating body 3, and a branched portion that extends in the -X-axis direction from the middle of the columnar portion. Therefore, the plurality of disc springs 20 are sandwiched between the branched portion and the valve body 6a. Of the two inner cylinder rotating shafts 8, the spring support portion fixing cylinder 21b is inserted through a plurality of O-rings 25 from the outside of the other inner cylinder rotating shaft 8. After that, the end portion of the spring support portion fixing cylinder 21b in the +X-axis direction is fixed to the outer cylinder rotating body 3 by screwing or the like. Since the spring support portion fixing cylinder 21b is fixed to the outer cylinder rotating body 3, the spring support portion fixing cylinder 21b, the valve body 6a, the valve body fixing cylinder 6b, and the disc spring 20 will rotate around the axis O at the same speed as the outer cylinder rotating body 3.

[0019] Now, the operation of the valve body 6a and the pressurizing device will be described. FIG. 4 is an enlarged cross-sectional view of the vicinity of the valve body 6a of the centrifugal dehydrator 1 in a state where the contact portion 22 of the valve body 6a is in contact with the valve seat 19. Pressure is applied to the valve body 6a in the -X-axis direction by a pressurizing device. Here, while the spring support portion 21a is fixed to the spring support portion fixing cylinder 21b and is immovable, the valve body 6a is slidable on the spring support portion fixing cylinder 21b. Therefore, the force that the disc spring 20, which is arranged in a compressed state between the valve body 6a and the spring support portion 21a, extends, that is, the elastic force, is applied to the valve body 6a so that the valve body 6a can slide in the -X-axis direction. Accordingly, the contact portion 22 of the valve body 6a contacts the valve seat 19 with a certain force, and the valve body 6a is stopped. In a state where no sludge is supplied to the centrifugal dehydrator 1, that is, in the initial state before the centrifugal dehydrator 1 operates, the contact portion 22 of the valve body 6a is designed to contact the valve seat 19.

[0020] Even when the centrifugal dehydrator 1 is operated and sludge is supplied to the centrifugal dehydrator 1, if there is a large amount of moisture and soft sludge near the valve seat 19, the pressure exerted by the sludge conveyed by the inner cylinder blades 4 to push the valve body 6a in the +X-axis direction is smaller than the back pressure applied in the -X-axis direction by the pressurizing device. Therefore, the positional relationship between the valve body 6a and the valve seat 19 is the same as in the initial state, and the contact portion 22 of the valve body 6a is in contact with the valve seat 19. However, even when the contact portion 22 of the valve body 6a is in contact with the valve seat 19, there is a space between the three always-open grooves 23 and the valve seat 19, and this space serves as a discharge passage for sludge leading to the dewatered cake discharge hole 5. Therefore, sludge with a large water content and soft texture is discharged from the dewatered cake discharge hole 5 through the three discharge passages (see the white arrows in Fig. 4). Therefore, it is possible to prevent the occurrence of the above-described discharge failure, that is, the discharge failure that leads to a failure of the centrifugal dehydrator 1 where the supplied sludge cannot be discharged despite the continuous supply of sludge to the centrifugal dehydrator 1.

[0021] On the other hand, when there is sludge with a low water content in the vicinity of the valve seat 19, the pressure exerted by the sludge conveyed by the inner cylinder blades 4 to push the valve body 6a in the +X-axis direction is greater than the back pressure applied in the -X-axis direction by the pressurizing device. Therefore, the positional relationship between the valve body 6a and the valve seat 19 is such that the contact portion 22 of the valve body 6a is not in contact with the valve seat 19, as shown in Fig. 5. In this case, the valve body 6a slides on the spring support portion 21a in the +X-axis direction, the contact portion 22 of the valve body 6a moves away from the valve seat 19, and the space between the valve seat 19 and the contact portion 22 also serves as a discharge passage for sludge leading to the dewatered cake discharge hole 5. That is, in this case, in addition to the space between the always-open groove 23 and the valve seat 19, the space between the valve seat 19 and the contact portion 22 also serves as a discharge passage for sludge leading to the dewatered cake discharge hole 5 (see the white arrows in Fig. 5). Therefore, even for sludge with a low water content and thus a shape that is less likely to change flexibly compared to sludge with a large water content and soft texture, a large discharge passage is formed by the space between the always-open groove 23 and the valve seat 19 and the space between the valve seat 19 and the contact portion 22, so that it can be smoothly discharged from the dewatered cake discharge hole 5. And even though it has slid in the +X-axis direction, the valve body 6a still applies back pressure to the sludge by the pressurizing device. Therefore, in addition to the solid-liquid separation by the above-described centrifugal dehydration and the solid-liquid separation by squeezing at the valve seat 19, the sludge is squeezed by the back pressure for solid-liquid separation, so that sludge with an even lower water content, that is, high-quality dewatered cake, can be discharged from the dewatered cake discharge hole 5.

[0022] As described above, the centrifugal dehydrator 1 of the embodiment can apply sufficient back pressure to sludge with a small water content, and can also avoid the occurrence of poor sludge discharge even when sludge with a large water content is supplied. In addition, in FIGS. 4 and 5, an example is shown in which the surface of the contact portion 22 and the always-open groove 23 on the -X-axis side of the valve body 6a is an inclined surface that is located radially outward toward the +X-axis side when viewed in the XZ plane. With such an inclined surface, the sludge conveyed in the +X-axis direction can be smoothly guided to the dehydration cake discharge hole 5. Regarding the distance between the valve seat 19 and the always-open groove 23 in the state where the contact portion 22 contacts the valve seat 19, the following experimental results have been obtained by the inventor. That is, in the case of digested sludge, a distance of about 0.5 mm to 1 mm, and in the case of mixed raw sludge, a distance of about 1.5 mm to 2 mm is a distance at which good effects are obtained. Therefore, it is desirable to design the distance to be at least the shortest distance according to the type of sludge. Furthermore, in order to avoid mechanical failures such as cracking of the valve seat 19, the area S (mm 2 ) of the surface where the contact portion 22 contacts the valve seat 19 is designed to satisfy S≧(F / C) / N when the back pressure is F (kgf), the allowable stress of the metal constituting the valve seat 19 is C (kgf / mm 2 ), and the number of contact portions 22 is N (pieces) (however, N≧3).

[0023] <Centrifugal dehydrator of modified example> FIG. 6 is an enlarged cross-sectional view for explaining the valve body 6a' and the valve body fixing cylinder 6b' of the centrifugal dehydrator of the modified example. The difference between the centrifugal dehydrator of the modified example and the centrifugal dehydrator 1 of the embodiment is mainly that the valve body 6a' and the valve body fixing cylinder 6b' are separable, that is, the valve body 6a' is designed as an attachment so that it can be easily attached and detached. Therefore, the description of the same configuration between the centrifugal dehydrator of the modified example and the centrifugal dehydrator 1 of the embodiment is omitted. The cylinder 6b' for fixing the valve body has a circular base 24 with a larger diameter at one end compared to other parts. The base 24 has a circular and annular shape, that is, a donut shape when viewed in the XY plane, and it is a pedestal for easily attaching the valve body 6a' with a screw or the like. The dimension of the base 24 in the YZ plane is designed to be the same as or slightly smaller than that of the valve body 6a' to be attached. The valve body 6a' has the same or similar shape as the aforementioned valve body 6a when viewed in the YZ plane. In the centrifugal dehydrator of the modified example, a plurality of attachments as the valve body 6a' with different numbers of evenly arranged contact parts 22, for example, 3, 4, 5, etc., and more than 3 are prepared in advance. Then, according to the season, weather, room temperature when the centrifugal dehydrator operates, or the properties of the sludge that can vary depending on the type and origin of the sludge, that is, the properties of the sludge supplied to the inner cylinder rotating body 2 of the centrifugal dehydrator, one of these plurality of attachments is selected, attached to the base 24, and used. Thereby, in addition to the effects of the centrifugal dehydrator of the embodiment, the centrifugal dehydrator of the modified example can easily obtain a dehydrated cake of the corresponding quality by appropriately selecting the above-mentioned attachment according to the quality of the dehydrated cake required by the customer.

Explanation of reference numerals

[0024] 1 Centrifugal dehydrator 2 Inner cylinder rotating body 3 Outer cylinder rotating body 4 Inner cylinder blade 5 Dehydrated cake discharge hole 6a, 6a' Valve body 6b, 6b' Cylinder for fixing the valve body 7 Casing 7A Separation liquid chute 7B Dehydrated cake chute 8 Inner cylinder rotating shaft 9 Outer cylinder rotating shaft 10 Floor 11 Sludge supply side support unit 12 Sludge discharge side support unit 13 Differential device 14 Motor 15 Belt transmission mechanism 16 Sludge supply pipe 17 Sludge supply hole 18 Separation liquid discharge hole 19 Valve seat 20 Spring (disk spring) 21a Spring support part 21b Cylinder for fixing spring support part 22 Contact part 23 Always open groove 24 Base part 25, 26 O-ring O axis

Claims

1. An inner cylinder rotating body into which sludge is supplied and can supply the sludge to the outside, and is rotatable around an axis, A cylindrical outer cylinder rotating body that encloses the inner cylinder rotating body and is rotatable around the axis, Installed on the outer surface of the inner cylinder rotating body, the sludge supplied from the inside of the inner cylinder rotating body between the inner cylinder rotating body and the outer cylinder rotating body is conveyed along the axis to be discharged from the dehydration cake discharge hole installed on the outer cylinder rotating body. Inner cylinder blades, Between the inner cylinder blades and the dehydration cake discharge hole, and installed on the inner surface of the outer cylinder rotating body near the dehydration cake discharge hole, convex and circular in a plane perpendicular to the axis protruding radially inward from the inner surface. A valve seat, At a position on the axis opposite to the inner cylinder blades with respect to the valve seat, and arranged coaxially with the axis, three or more contact parts that can contact the valve seat, and formed between two adjacent contact parts And a plurality of always-open grooves that always form at least a part of the sludge discharge passage leading from the valve seat to the dehydration cake discharge hole, and a valve body that is movable along the axis and circular when viewed in a plane perpendicular to the axis, A pressurizing device that applies a pressure in a direction opposite to the conveying direction to the valve body in order to apply back pressure to the sludge having, When the pressure of the sludge pressing the valve body is smaller than the back pressure and the contact part is in contact with the valve seat, the discharge passage is formed only by the space between the always-open groove and the valve seat, When the pressure of the sludge pressing the valve body is greater than the back pressure and the contact part is separated from the valve seat, the discharge passage includes the space between the contact part and the valve seat, and the always-open groove and the valve seat. A centrifugal dehydrator formed by the space therebetween.

2. The centrifugal dehydrator according to claim 1, wherein the pressurizing device applies pressure to the valve body using either a spring or a hydraulic pressure.

3. In a state where the contact part is in contact with the valve seat, the shortest distance between the always-open groove and the valve seat is set to 0.5 mm to 1 mm when the sludge is digested sludge, and 1.5 mm to 2 mm when the sludge is mixed raw sludge. The centrifugal dehydrator according to claim 2, which is set to mm.

4. The valve body is an attachment provided with the contact part and the always-open groove, A plurality of attachments with different numbers of the contact parts are prepared in advance, and any one of the plurality of attachments is used in accordance with the properties of the sludge supplied to the inner cylinder rotating body in the centrifugal dehydrator according to any one of claims 1 to 3.

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