JP2023168768A - Screw press operation method and screw press - Google Patents

Abstract

To provide a screw press operation method where steady operation can be quickly attained by avoiding corotation between a plug cake and a second screw.SOLUTION: In a screw press operation method, a low differential velocity operation and a differential velocity adjustment operation are implemented before starting steady operation that a first screw 3 and a second screw 4 are rotated at a predetermined rotation speed. The low differential velocity operation is an operation to lower the hardness of a plug cake in a plug cake formation region 1B in which the second screw 4 is disposed to hardness where the plug cake does not corotate with the second screw 4. The differential velocity adjustment operation is an operation to gradually lower the rotation speed of the second screw 4 at the low differential velocity operation to the rotation speed of the second screw 4 at the steady operation.SELECTED DRAWING: Figure 4

Description

The present invention relates to a screw press operating method for squeezing a liquid-containing material such as sludge to separate a liquid from the liquid-containing material, and a screw press.

Conventionally, screw presses have been used as devices for squeezing sludge (liquid-containing substances) discharged from liquid processing facilities such as water and sewage treatment plants and human waste treatment plants, and separating water from the sludge (that is, dewatering it). Are known. This screw press includes a filtration tube formed from a screen (perforated plate) and a screw placed inside the filtration tube. The screw has a screw shaft arranged concentrically with the filter cylinder and a screw blade fixed to the outer surface of the screw shaft. By rotating the screw blades using a rotation mechanism connected to the screw shaft, the sludge introduced into the filter cylinder is compressed and dehydrated. A back pressure plate that dams up the sludge is placed at the downstream opening end of the filtration tube, and this back pressure plate allows the cake (dehydrated sludge) sent by the rotating screw blades to stay there, and creates a plug (made of cake). form a plug). This plug applies back pressure to the cake that is fed in later, and further compresses the cake, thereby reducing the water content of the sludge in the filter cylinder.

Patent Document 1 describes a screw press having a first screw and a second screw arranged in series within a filtration cylinder. The second screw of this screw press is configured so that it can be rotated by a drive device different from that of the first screw, so that the first screw and the second screw can be rotated at different speeds from each other. And it can be rotated in any direction. Therefore, by individually controlling the rotational speed and direction of the first and second screws, a plug cake can be formed inside the filtration tube without the need for a back pressure plate, and the sludge inside the filtration tube can be efficiently removed. can be squeezed.

JP 2018-51582 Publication

However, as a result of intensive research by the inventors, even with the screw press described in Patent Document 1, depending on the properties of the sludge introduced into the screw press, the plug cake in which the second screw is located may It has been found that there is a possibility that co-rotation may occur between the cake (plug cake) in the formation area and the second screw. In particular, when sludge with few fibrous substances is fed into the screw press, and/or when strong back pressure is applied to the sludge fed into the screw press at once, the plug cake and the second screw rotate together. It was found that the risk of Note that in this specification, the device start-up operation means the operation of the screw press for forming a plug cake having a desired moisture content in the plug forming region. If co-rotation occurs between the plug cake and the second screw when starting up the equipment, it will take a long time to shift to steady operation to discharge the plug cake with the desired moisture content from the screw press. Put it away.

On the other hand, if the water content of the sludge is reduced relatively slowly by continuing to apply a weak back pressure to the sludge fed into the screw press during equipment start-up operation, the water content between the plug cake and the second screw will decrease. It is possible to avoid turning around. However, in this case as well, it takes a long time to reach steady operation from the start-up operation of the device.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a method of operating a screw press that can quickly reach steady operation by avoiding co-rotation of the plug cake and the second screw. Another object of the present invention is to provide a screw press that can implement such an operating method.

In one embodiment, a filtration tube into which a liquid-containing substance is introduced, and a first screw and a second screw that are arranged concentrically with the filtration tube in the filtration tube and transfer the liquid-containing substance in a predetermined transfer direction. A method of operating a screw press, comprising: a first rotation mechanism that rotates the first screw; and a second rotation mechanism that rotates the second screw independently of the first screw. Before starting steady operation in which the first screw and the second screw are rotated at a predetermined rotational speed, a low differential speed operation and a differential speed adjustment operation are performed, and the low differential speed operation is performed when the second screw rotates at a predetermined rotational speed. The hardness of the plug cake in the plug cake forming area where the plug cake is arranged is reduced to such a hardness that the plug cake does not rotate together with the second screw. A method of operating a screw press is provided, which is an operation in which the rotational speed of the second screw is gradually reduced to the rotational speed of the second screw during the steady operation.

In one aspect, before the low differential speed operation, the pressure of the plug cake in the plug formation area is checked, and if the pressure of the plug cake is lower than a predetermined threshold, the sludge filling operation is performed. , the sludge filling operation may include rotating only the first screw at a predetermined rotational speed without rotating the second screw until the pressure of the plug cake exceeds the threshold; This is an operation in which the first screw is rotated at the predetermined rotation speed while rotating the screw at a rotation speed lower than the rotation speed during the low differential speed operation.
In one embodiment, the rotation speed of the second screw during the low differential speed operation is in a range of 0.6 to 0.9 times the rotation speed of the first screw during the steady operation.
In one embodiment, the operating time of the low differential speed operation is in the range of 1 to 20 minutes.

In one embodiment, in the differential speed adjustment operation, the number of stages for reducing the rotational speed of the second screw from the rotational speed during the low differential speed operation to the rotational speed of the second screw during the steady operation is 3 to 10. in range.
In one embodiment, the operating time of each stage of the differential speed adjustment operation is in the range of 1 to 20 minutes.

In one embodiment, a filtration tube into which a liquid-containing substance is introduced, and a first screw and a second screw that are arranged concentrically with the filtration tube in the filtration tube and transfer the liquid-containing substance in a predetermined transfer direction. a first rotation mechanism that rotates the first screw; a second rotation mechanism that rotates the second screw independently of the first screw; and a second rotation mechanism that rotates the first rotation mechanism and the second rotation mechanism. A control unit for controlling the first screw and the second screw, the control unit controlling the low differential speed operation and the differential speed adjustment operation before starting the steady operation in which the first screw and the second screw are rotated at a predetermined rotational speed. and the low differential speed operation is an operation that reduces the hardness of the plug cake in the plug cake forming area where the second screw is arranged to a hardness that does not allow the plug cake to rotate together with the second screw. The screw press is provided, wherein the differential speed adjustment operation is an operation in which the rotational speed of the second screw during the low differential speed operation is gradually reduced to the rotational speed of the second screw during the steady operation. be done.

According to the present invention, in the differential speed adjustment step, the rotational speed of the second screw is reduced stepwise to the target rotational speed which is the rotational speed of the second screw during steady operation. The hardness of the entire plug cake existing between the screw blades is gradually reduced. As a result, the occurrence of co-rotation between the plug cake and the second screw 4 can be effectively prevented.

FIG. 1 is a schematic diagram showing a screw press according to one embodiment. FIG. 2 is a schematic cross-sectional view of the second screw shown in FIG. 1. FIG. 3 is a schematic diagram for explaining the number of turns of the second screw blade. FIG. 4 is a flowchart showing a method of operating a screw press according to one embodiment.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a schematic diagram showing a screw press according to one embodiment. The screw press shown in FIG. 1 includes a cylindrical screen casing (filtration tube) 1, which is arranged concentrically within the screen casing 1, and which transfers sludge (liquid content) in a predetermined transfer direction D. a first screw 3 and a second screw 4 that are transferred to the first screw 3, a first rotation mechanism 7 that rotates the first screw 3, and a second rotation mechanism 20 that rotates the second screw 4 independently of the first screw 3; It is equipped with The screen casing 1 is formed from a screen (perforated plate) such as a punched metal. A sludge inlet 2 is formed at the upstream end of the screen casing 1 . Sludge introduced into the screen casing 1 from the input port 2 is transferred in a predetermined transfer direction D within the screen casing 1 by the rotating first screw 3 and second screw 4. Further, the screw press includes a control section 6 that controls the operations of the first rotation mechanism 7 and the second rotation mechanism 20.

The second screw 4 is connected to the first screw 3 so as to be rotatable independently of the first screw 3. The first screw 3 and the second screw 4 extend through the screen casing 1 and the discharge chamber 33, respectively. The discharge chamber 33 is connected to the screen casing 1. A plug cake, which will be described later, is discharged from the screen casing 1 into this discharge chamber 33 . The axial length of the second screw 4 is shorter than the axial length of the first screw 3. The first screw 3 has a truncated conical (tapered) first screw shaft 3A whose diameter gradually increases toward the downstream side in the sludge transfer direction D, and is fixed to the outer surface of the first screw shaft 3A. It has a first screw blade 3B. The second screw 4 has a cylindrical second screw shaft 4A and a second screw blade 4B fixed to the outer surface of the second screw shaft 4A.

The upstream end of the screen casing 1 is sealed by a closing wall 8. One end (the upstream end in the transfer direction D) of the first screw shaft 3A extends through the closing wall 8. A water sealing device 10 is installed on the closing wall 8 to seal the gap between the closing wall 8 and the first screw shaft 3A. The upstream end of the first screw shaft 3A that extends through the closure wall 8 is rotatably supported while being restrained from moving in the axial direction by bearings 11 and 12 installed on a base (not shown). . Note that one of the bearings 11 and 12 can be omitted.

The upstream end of the first screw shaft 3A is connected to a first rotation mechanism 7 for rotating the first screw 3. In this embodiment, the first rotation mechanism 7 includes a first drive machine (for example, an electric motor) 14, a sprocket 15 fixed to the rotating shaft of the first drive machine 14, and a sprocket fixed to the first screw shaft 3A. 16, and a chain 17 wound around these sprockets 15 and 16. The sprocket 16 is located between the bearings 11 and 12. When the first drive machine 14 of the first rotation mechanism 7 is driven, the sprocket 15 fixed to the rotating shaft of the first drive machine 14 rotates, and the sprocket 16 fixed to the first screw shaft 3A via the chain 17 rotates. Rotate. As a result, the first screw 3 is rotated by the first rotation mechanism 7. The first drive machine 14 is connected to the control unit 6, and the control unit 6 is configured to be able to control the operation of the first drive machine 14.

Although not shown, the rotating shaft of the first driving machine 14 may be connected to the first screw shaft 3A via a speed reducer. Alternatively, the rotating shaft of the first drive machine 14 may be directly connected to the first screw shaft 3A.

FIG. 2 is a schematic cross-sectional view of the second screw 4 shown in FIG. As shown in FIG. 2, the second screw shaft 4A has a hollow structure. A reduced diameter portion 3C that is inserted into the cylindrical second screw shaft 4A is formed at the other end (downstream end in the transfer direction D) of the first screw shaft 3A. By forming the reduced diameter portion 3C on the first screw shaft 3A, a wall surface 3D perpendicular to the axial direction is formed on the first screw shaft 3A. The reduced diameter portion 3C is inserted into the cylindrical second screw shaft 4A, and is rotatably supported by slide bearings 30 and 31 fixed to the inner wall 4C of the second screw shaft 4A. With such a configuration, the first screw 3 is rotatably connected to the second screw 4.

As shown in FIG. 2, in a state where the reduced diameter portion 3C of the first screw shaft 3A is inserted into the second screw shaft 4A, the upstream end of the second screw shaft 4A is connected to the first screw shaft 3A. It is in contact with the wall surface 3D. In one embodiment, a slight gap may be formed between the upstream end of the second screw shaft 4A and the wall surface 3D of the first screw shaft 3A. In this case, a seal structure (for example, a labyrinth structure) that prevents the sludge in the screen casing 1 from passing through the gap between the slide bearing 30 and the reduced diameter portion 3C is installed in the slide bearing 30 and/or the reduced diameter portion 3C. may be provided.

As shown in FIGS. 1 and 2, the second screw shaft 4A of the second screw 4 is arranged concentrically with the first screw shaft 3A. The outer diameter of the second screw shaft 4A is the same as the maximum diameter of the first screw shaft 3A. The second screw shaft 4A extends through the wall 33A of the discharge chamber 33. The upstream end of the second screw shaft 4A is rotatably supported by the first screw shaft 3A via the slide bearings 30 and 31, and the downstream end of the second screw shaft 4A is supported by a base (not shown). ) is rotatably supported while being restrained from moving in the axial direction by bearings 22 and 23 installed in the bearings 22 and 23. Note that the bearing 23 can be omitted.

A downstream end of the second screw shaft 4A is connected to a second rotation mechanism 20 for rotating the second screw 4. In this embodiment, the second rotation mechanism 20 includes a second drive machine (for example, an electric motor) 24, a sprocket 25 fixed to the rotation shaft of the second drive machine 24, and a sprocket fixed to the second screw shaft 4A. 26, and a chain 27 wound around these sprockets 25, 26. Sprocket 26 is located between bearings 22 and 23. When the second drive machine 24 of the second rotation mechanism 20 is driven, the sprocket 25 fixed to the rotating shaft of the second drive machine 24 rotates, and the sprocket 26 fixed to the second screw shaft 4A via the chain 27 rotates. Rotate. As a result, the second screw 4 is rotated by the second rotation mechanism 20.

The second drive machine 24 is connected to the control section 6. The second drive machine 24 has a built-in inverter (not shown), and the control unit 6 is configured to be able to control the operation of the second drive machine 24 via the inverter. That is, the control unit 6 can control the rotation speed and rotation direction of the second drive machine 24 via the inverter. The second drive machine 24 can rotate the second screw 4 independently of the first screw 3. Note that it is preferable that the first driving machine 14 also incorporates an inverter that can change the rotation speed and rotation direction of the first driving machine 14.

Although not shown, the rotating shaft of the second driving machine 24 may be connected to the second screw shaft 4A via a speed reducer. Alternatively, the rotation shaft of the second drive machine 24 may be directly connected to the second screw shaft 4A.

The first screw blade 3B extends helically along the axial direction of the first screw shaft 3A, and the second screw blade 4B spirally extends along the axial direction of the second screw shaft 4A. The total length of the portion of the first screw 3 to which the first screw blade 3B is fixed and the portion of the second screw 4 to which the second screw blade 4B is fixed is the length of the screen casing 1 in the axial direction. Same or longer.

A minute gap is formed between the inner surface of the screen casing 1 and the first screw blade 3B, so that the first screw blade 3B can rotate without contacting the screen casing 1. Similarly, a minute gap is formed between the inner surface of the screen casing 1 and the second screw blade 4B, so that the second screw blade 4B can rotate without contacting the screen casing 1. ing. The sludge introduced into the screen casing 1 from the input port 2 formed at the upstream end of the screen casing 1 is directed toward the discharge chamber 33 (i.e., transferred) by the rotating first screw blade 3B and second screw blade 4B. direction D).

In this embodiment, the winding direction (that is, the helical direction) of the second screw blade 4B is opposite to the winding direction of the first screw blade 3B. Therefore, when sending out the sludge introduced from the input port 2 to the discharge chamber 33, the second screw 4 is rotated in the opposite direction to the first screw 3, as shown in FIG.

The winding direction of the second screw blade 4B may be the same as the winding direction of the first screw blade 3B. In this case, when sending out the sludge introduced from the input port 2 to the discharge chamber 33, the second screw 4 is rotated in the same direction as the first screw 3.

As shown in FIG. 2, the pitch P1 of the second screw blade 4B is smaller than the pitch P2 of the first screw blade 3B (ie, P1<P2). Furthermore, the number of turns of the second screw blade 4B is less than three turns. FIG. 3 is a schematic diagram for explaining the number of turns of the second screw blade 4B. As shown in FIG. 3, the number of turns of the second screw blade 4B that extends spirally is 1 when the second screw blade 4B travels 360° around the first screw shaft 3A from the starting point S1 to the point S2. Count as a roll. In the second screw 4 shown in FIG. 3, the number of turns of the second screw blade 4B is two.

As shown in FIG. 1, the screen casing 1 is divided into a dewatering area 1A where the first screw 3 is placed and a plug forming area 1B where the second screw 4 is placed. A space in which sludge is transferred in the dewatering area 1A is formed by the inner surface of the screen casing 1, the first screw blade 3B, and the first screw shaft 3A. The cross-sectional area of this transfer space gradually decreases along the sludge transfer direction D, as shown in FIG. Therefore, as the sludge introduced from the input port 2 is transferred through this transfer space by the first screw blades 3B, the sludge is compressed and dewatered. The filtrate that has passed through the screen (perforated plate) of the screen casing 1 is collected by a filtrate receiver 38 arranged below the screen casing 1. A drain 39 is connected to the filtrate receiver 38, and the filtrate collected by the filtrate receiver 38 is discharged from the screw press via the drain 39.

The space into which sludge is transferred in the plug formation region 1B is formed by the inner surface of the screen casing 1, the second screw blade 4B, and the second screw shaft 4A. As shown in FIG. 1, the cross-sectional area of this transfer space is constant. In the plug forming region 1B, a plug cake is formed from the sludge (ie, cake) dehydrated in the dewatering region 1A. A method for forming a plug cake will be described later.

As shown in FIG. 1, the screw press has a pressure sensor 29 arranged in the plug forming area 1B. The pressure sensor 29 is a sensor for measuring the pressure of the sludge in the plug forming region 1B, that is, the pressure of the (plug) cake. The pressure sensor 29 is connected to the control unit 6 via a signal line (not shown), and is configured to be able to transmit its measured value to the control unit 6. The control unit 6 can monitor the pressure of the (plug) cake in the plug forming region 1B based on the measured value of the pressure sensor 29.

Next, an example of a method of operating the screw press shown in FIG. 1 will be described. FIG. 4 is a flowchart showing a method of operating a screw press according to one embodiment. More specifically, FIG. 4 is a flowchart mainly showing the start-up operation of the screw press shown in FIG. 1.

As shown in FIG. 4, the control unit 6 first obtains the pressure of the cake (or sludge) in the plug formation region 1B using the pressure sensor 29, and when the pressure of the cake is equal to or higher than a predetermined threshold value, It is determined whether there is one (S101). The predetermined threshold value is a value that is preset according to the properties of sludge introduced into the screw press in order to determine whether or not the entire plug forming area 1B is filled with enough sludge to form a plug cake. For example, it is set to 5 kPa. This predetermined threshold value is stored in the control section 6 in advance.

If the measured value of the pressure sensor 29 is smaller than a predetermined threshold value ("No" in S101), the control unit 6 determines that the plug forming region 1B is not sufficiently filled with sludge, and starts the sludge filling operation. The process is carried out (S102). The sludge filling operation step is a step of filling the plug forming region 1B with sludge. In the sludge filling operation step, the control unit 6 rotates only the first screw 3 at a predetermined rotational speed without rotating the second screw 4 until the measured value of the pressure sensor 29 exceeds a predetermined threshold. . By this operation, the plug forming area 1B is filled with sludge.

In one embodiment, the control unit 6 may rotate the second screw 4 at a relatively low speed in the sludge filling operation process. For example, the control unit 6 may rotate the second screw 4 at a rotation speed lower than the rotation speed during low differential speed operation, which will be described later, in the sludge filling process. Also in this case, the control unit 6 rotates the first screw 3 at a predetermined rotational speed set for the sludge filling process.

If the measured value of the pressure sensor 29 is equal to or higher than a predetermined threshold ("Yes" in S101), or if the sludge filling operation step is completed, the control unit 6 implements the low differential speed operation step (S102). ). The low differential speed operation step is a step of reducing the hardness (or moisture content) of the plug cake formed in the plug cake forming region 1B to such a degree that the plug cake does not rotate together with the second screw 4, This is a process in which the screw press is operated while applying a weak back pressure to the plug cake. Therefore, the low differential speed operation process may be referred to as a low back pressure operation process.

In the low differential speed operation, the rotational speed of the second screw 4 is adjusted so that the plug cake in the plug cake forming region 1B is not excessively dehydrated. Specifically, the control unit 6 controls the rotational speed of the second screw 4 to be within a range of 0.6 to 0.9 times the rotational speed of the first screw 3 at the time of starting steady operation, which will be described later. Adjust to speed. Through this operation, the plug cake in the plug cake forming region 1B is maintained at a water content that is lower than the water content during the sludge filling operation process, but higher to some extent.

The rotational speed of the second screw 4 during low differential speed operation is determined in advance according to the properties of the sludge supplied to the screw press, and is stored in the control unit 6 in advance. For example, the rotational speed of the second screw 4 during low differential speed operation is set such that the moisture content of the plug cake in the plug cake forming region 1B is maintained at 80% or more, preferably in the range of 81 to 84%. The rotational speed is adjusted in a range of 0.6 to 0.9 times, preferably in a range of 0.65 to 0.8 times, the rotational speed of the first screw 3 at the time of starting steady operation. . If the rotation speed of the second screw 4 is high, it will take time for the plug cake to reach the desired hardness, and if the rotation speed of the second screw 4 is slow, there is a risk that the plug cake will become too hard.

The low differential speed operation is performed for a predetermined period of time. The operation time (duration time) of this low differential speed operation is stored in the control section 6 in advance. If the operating time of the low differential speed operation is increased, the plug cake can be made to have the desired hardness, but the time required until the screw press starts steady operation becomes longer. On the other hand, if the operating time of the low differential speed operation is shortened, the hardness of the plug cake may not reach a hardness suitable for starting the differential speed adjustment process described later.

Therefore, the operating time of the low differential speed operation is in the range of 1 to 20 minutes, preferably 5 to 10 minutes, based on experiments and/or simulations conducted depending on the properties of the sludge supplied to the screw press. Set in minutes. Alternatively, the operating time of the low differential speed operation may be determined based on the rotational speed of the second screw 4, the length of the plug cake forming region 1B, the number of turns of the second screw blade 4B, the pitch of the second screw blade 4B, etc. 2 may be set by the rotation speed of the screw 4. For example, the low differential speed operation may be performed only while the second screw 4 makes 1 to 5 rotations, preferably 1.5 to 3 rotations.

When the low differential speed operation is completed, the control unit 6 executes a differential speed adjustment operation step (S104). In the differential speed adjustment operation process, the screw press is operated while gradually reducing the rotational speed of the second screw 4 during low differential speed operation to the target rotational speed, which is the rotational speed of the second screw 4 during steady operation. This is the process of In this differential speed adjustment step, as the rotational speed of the second screw 4 is gradually decreased, the back pressure applied to the plug cake is increased in stages. Therefore, the low differential speed operation process may be referred to as a back pressure adjustment process.

If the rotational speed of the second screw 4 during low differential speed operation is reduced all at once to the target rotational speed, the back pressure applied to the plug cake in contact with the second screw blade 4B will suddenly increase, resulting in , only the plug cake in contact with the second screw blade 4B becomes hard. As a result, there is an increased risk that the second screw blade 4B and the harder plug cake will rotate together with the softer plug cake that exists between the second screw blades 4B that extend spirally. Therefore, in the differential speed adjustment step, the rotational speed of the second screw 4 is gradually reduced to the target rotational speed, thereby reducing the hardness of the entire plug cake existing between the second screw blades 4B that extend in a spiral shape. Reduce gradually. This operation effectively prevents the plug cake and the second screw 4 from rotating together.

When co-rotation occurs between the plug cake and the second screw 4, it takes time to reduce the water content of the plug cake discharged from the plug forming region 1B to a desired value. According to the operating method of the screw press according to the present embodiment, it is possible to effectively prevent the occurrence of co-rotation between the plug cake and the second screw 4, so that the operating state of the screw press can be quickly shifted to a steady state. .

In the differential speed adjustment operation process, the number of stages (hereinafter simply referred to as "number of stages") for reducing the rotational speed of the second screw 4 from the rotational speed during low differential speed operation to the target rotational speed, the operating time of each stage, and the next The amount of reduction in the rotational speed of the second screw 4 (hereinafter simply referred to as the "reduction amount") when transitioning to stage 2 depends on the properties of the sludge supplied to the screw press, the rotational speed during low differential speed operation, and the target. It is set in advance based on the difference with the rotational speed and the operating time at each stage. The number of stages, the operating time of each stage, and the amount of reduction are stored in the control unit 6 in advance.

The inventors conducted extensive research on the differential speed adjustment operation process and found that by setting the number of stages to three or more, it is possible to effectively prevent the plug cake and the second screw 4 from rotating together. Furthermore, it has been found that by setting the operating time of each stage to 1 minute or more, the occurrence of co-rotation between the plug cake and the second screw 4 can be effectively prevented. On the other hand, the more the number of stages is increased, and the longer the operating time of each stage is increased, the more effectively the occurrence of co-rotation between the plug cake and the second screw 4 can be prevented. It takes time to transition to this state. Therefore, the number of stages is preferably set in the range of 3 to 10, preferably in the range of 5 to 8, and the operating time of each stage is in the range of 1 to 20 minutes, preferably 3 to 10 minutes. It is preferable to set it within the range of .

Note that the amount of reduction in the rotational speed of the second screw 4 when moving to the next stage may be the same or may be different. Similarly, the operating time of each stage may be the same or different.

When the differential speed adjustment operation step is completed, the control unit 6 starts steady operation (S105). In steady operation, the rotational speed of the first screw 3 and the rotational speed of the second screw 4 are set so that the plug cake whose water content has been reduced to a desired value or less is discharged from the plug forming region 1B. .

In one embodiment, after the operating state of the screw press shifts to steady operation, the control unit 6 adjusts the amount of plug cake discharged into the discharge chamber 33 by changing the rotational speed of the second screw 4. You may. More specifically, the control unit 6 may reduce the rotational speed of the second screw 4 to reduce the amount of plug cake discharged, or the control unit 6 may increase the rotational speed of the second screw 4. This may increase the amount of plug cake discharged. As the amount of discharged plug cake decreases, subsequent cakes remain in the dewatering area 1A, and the back pressure applied to the subsequent cakes increases. Therefore, when the control unit 6 reduces the rotational speed of the second screw 4, the moisture content of the subsequent cake can be reduced. In one embodiment, the back pressure applied to subsequent cakes may be adjusted by performing intermittent operation in which the second screw 4 is alternately rotated and stopped.

The embodiments described above have been described to enable those skilled in the art to carry out the invention. Various modifications of the above embodiment can be naturally made by those skilled in the art, and the technical idea of the present invention can be applied to other embodiments. Therefore, the invention is not limited to the described embodiments, but is to be construed in the broadest scope according to the spirit defined by the claims.

1 Screen casing (filtration tube)
1A Dehydration area 1B Plug formation area 2 Inlet 3 First screw 3A First screw shaft 3B First screw blade 3C Reduced diameter part 3D Wall surface 4 Second screw 4A Second screw shaft 4B Second screw blade 4C Inner wall 6 Control part 7 First rotation mechanism 8 Closure wall 10 Water seal device 11, 12 Bearing 14 First drive machine 15, 16 Sprocket 17 Chain 20 Second rotation mechanism 22, 23 Bearing 24 Second drive machine 25, 26 Sprocket 27 Chain 29 Pressure sensor 30 , 31 sliding bearing 33 discharge chamber 36 bearing 38 filtrate receiver 39 drain

Claims (7)

a filtration tube into which a liquid content is introduced; a first screw and a second screw that are arranged concentrically with the filtration tube within the filtration tube and transfer the liquid content in a predetermined transfer direction; A method of operating a screw press comprising: a first rotation mechanism that rotates one screw; and a second rotation mechanism that rotates the second screw independently of the first screw,
Before starting steady operation in which the first screw and the second screw are rotated at a predetermined rotational speed, a low differential speed operation and a differential speed adjustment operation are performed,
The low differential speed operation is an operation in which the hardness of the plug cake in the plug cake forming region where the second screw is arranged is reduced to a hardness that the plug cake does not rotate together with the second screw,
The method for operating a screw press, wherein the differential speed adjustment operation is an operation in which the rotational speed of the second screw during the low differential speed operation is gradually reduced to the rotational speed of the second screw during the steady operation. Before the low differential speed operation, check the pressure of the plug cake in the plug forming area,
carrying out a sludge filling operation when the pressure of the plug cake is less than a predetermined threshold;
In the sludge filling operation, only the first screw is rotated at a predetermined rotational speed without rotating the second screw until the pressure of the plug cake exceeds the threshold value, or the second screw is rotated at a predetermined rotational speed. The method of operating a screw press according to claim 1, wherein the first screw is rotated at the predetermined rotational speed while rotating the first screw at a rotational speed lower than the rotational speed during the low differential speed operation. The screw press according to claim 1, wherein the rotation speed of the second screw during the low differential speed operation is in a range of 0.6 to 0.9 times the rotation speed of the first screw during the steady operation. How to drive. The method of operating a screw press according to claim 3, wherein the operating time of the low differential speed operation is in a range of 1 to 20 minutes. In the differential speed adjustment operation, the number of stages for reducing the rotational speed of the second screw from the rotational speed during the low differential speed operation to the rotational speed of the second screw during the steady operation is in the range of 3 to 10. A method of operating a screw press according to claim 1. The method of operating a screw press according to claim 5, wherein the operation time of each stage of the differential speed adjustment operation is in the range of 1 to 20 minutes. a filtration cylinder into which the liquid content is introduced;
a first screw and a second screw that are arranged concentrically with the filter tube within the filter tube and transfer the liquid content in a predetermined transfer direction;
a first rotation mechanism that rotates the first screw;
a second rotation mechanism that rotates the second screw independently of the first screw;
a control unit that controls operations of the first rotation mechanism and the second rotation mechanism,
The control unit performs a low differential speed operation and a differential speed adjustment operation before starting a steady operation in which the first screw and the second screw are rotated at a predetermined rotational speed,
The low differential speed operation is an operation in which the hardness of the plug cake in the plug cake forming region where the second screw is arranged is reduced to a hardness that the plug cake does not rotate together with the second screw,
The differential speed adjustment operation is an operation in which the rotational speed of the second screw during the low differential speed operation is gradually reduced to the rotational speed of the second screw during the steady operation.

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