How to judge the operating condition of a screw press and a screw press

Abstract

To provide a screw press capable of accurately determining an operation state of the screw press.SOLUTION: A screw press SP includes a plurality of pressure sensors 40 that detect a pressure to a filtration cylinder 1 for an object including liquid. The plurality of pressure sensors 40 are arranged in at least two areas of a first screw area Pt, a second screw area Pp, and a switching area Py.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a screw press and a method for determining the operating state of the screw press. [Background technology]

[0002] Screw presses have been known as devices that compress sludge (liquid-containing material) discharged from liquid treatment facilities such as water supply and sewage treatment plants and sewage treatment plants to separate water from the sludge (i.e., dehydrate it).

[0003] This screw press comprises a filter cylinder formed from a screen (perforated plate) and a screw disposed inside the filter cylinder. The screw squeezes and dehydrates the sludge fed into the filter cylinder. The dehydrated sludge (cake) is discharged from the discharge end of the filter cylinder. It is desirable that the cake be discharged from the discharge end of the filter cylinder with its moisture content as low as possible. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2018-51582 Summary of the Invention [Problem to be solved by the invention]

[0005] One possible method for determining the state of sludge introduced into the filter cylinder is to measure the screw torque and current value. However, with this method, the rotation speed of the screw changes depending on the amount of sludge being processed, and as a result, the screw torque and current value also change. Therefore, it is difficult to determine the operating state of the screw press based solely on these physical quantities (i.e., torque and current value). Furthermore, because the amount of change in the screw torque and current value is small, it is difficult to accurately determine the operating state of the screw press.

[0006] Therefore, an object of the present invention is to provide a screw press that can accurately determine the operating state of the screw press, and a method for determining the operating state of the screw press. [Means for solving the problem]

[0007] In one embodiment, a screw press is provided, comprising: a filter cylinder into which a liquid-containing material is introduced; a first screw and a second screw arranged in the filter cylinder and rotating independently of each other; and a plurality of pressure sensors for detecting the pressure of the liquid-containing material against the filter cylinder. When the area of ​​the filter cylinder is divided into a first screw area where the first screw is arranged, a second screw area where the second screw is arranged, and a transition area between the first screw area and the second screw area, the plurality of pressure sensors are arranged in at least two areas among the first screw area, the second screw area, and the transition area.

[0008] In one embodiment, each of the plurality of pressure sensors is disposed in the first screw area, the second screw area, and the switching area. In one embodiment, the first screw has a first screw flight, and any one of the plurality of pressure sensors is arranged in the first screw area within a pitch of the first screw flight adjacent to the changeover area. In one embodiment, the second screw has a second screw flight, and any one of the plurality of pressure sensors is arranged in the second screw area within a pitch of the second screw flight adjacent to the changeover area.

[0009] In one embodiment, any one of the plurality of pressure sensors is disposed in the first screw area adjacent to the liquid-containing material inlet formed at the upstream end of the filter cylinder. In one embodiment, the screw press includes a sensor base for attaching at least one of the plurality of pressure sensors to the filter cylinder, the sensor base being fixed to the outer surface of the filter cylinder. In one aspect, the sensor base has a thickness that prevents a sensor measurement portion of a pressure sensor attached to the sensor base from protruding from the inner surface of the filter cylinder.

[0010] In one embodiment, there is provided a method for determining the operating state of a screw press having a first screw and a second screw that rotate independently of each other and are disposed in a filter cylinder into which a liquid-containing material is introduced. The method for determining the operating state of a screw press includes, when the area of ​​the filter cylinder is divided into a first screw area in which the first screw is disposed, a second screw area in which the second screw is disposed, and a transition area between the first screw area and the second screw area, measuring the pressure of the liquid-containing material against the filter cylinder based on signals detected by a plurality of pressure sensors disposed in at least two areas among the first screw area, the second screw area, and the transition area, and determining the operating state of the screw press based on the measured pressure. [Effects of the Invention]

[0011] The screw press can determine the operating state of the screw press based on a plurality of pressure sensors arranged in at least two areas of the first screw area, the second screw area, and the changeover area. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a schematic diagram illustrating an embodiment of a screw press. [Figure 2] FIG. 10 is a diagram showing a pressure sensor disposed in a first screw area. [Figure 3] FIG. 10 is a diagram showing a pressure sensor disposed in a second screw area. [Figure 4] 4(a) and 4(b) are diagrams showing pressure sensors arranged in the switching area. [Figure 5] FIG. 10 is a diagram showing a pressure sensor disposed in a first screw area. [Figure 6] FIG. 10 is a diagram showing a pressure sensor attached to a screen casing. [Figure 7] FIG. 10 is a view showing another embodiment of the second screw. [Figure 8] FIG. 10 is a diagram showing changes in sludge pressure during operation of the screw press. [Figure 9] FIG. 10 is a diagram showing changes in sludge pressure during operation of the screw press. [Figure 10] FIG. 10 is a diagram showing changes in sludge pressure during operation of the screw press. [Figure 11] FIG. 10 is a diagram showing changes in sludge pressure during operation of the screw press. [Figure 12] FIG. 1 is a diagram showing the correlation between sludge pressure and sludge moisture content. [Figure 13] FIG. 10 is a diagram showing changes in pressure measurements when an abnormality occurs in the operating state of the screw press. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Fig. 1 is a schematic diagram showing one embodiment of a screw press. The screw press SP shown in Fig. 1 includes a cylindrical screen casing (filter cylinder) 1, a first screw 3 and a second screw 4 that are arranged concentrically with the screen casing 1 within the screen casing 1 and transport sludge (liquid-containing material) in a predetermined transport direction D, 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.

[0014] The screen casing 1 is formed from a screen (perforated plate) such as a punched metal screen, and has a double structure having an outer cylinder and an inner cylinder. The structure of the screen casing 1 will be described later.

[0015] A sludge inlet 2 is formed at the upstream end of the screen casing 1. The sludge introduced into the screen casing 1 from the inlet 2 is transported in a predetermined transport direction D within the screen casing 1 by the rotating first screw 3 and second screw 4. The screw press SP further includes a control unit 6 that controls the operation of the first rotation mechanism 7 and the second rotation mechanism 20.

[0016] 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.

[0017] The first screw 3 has a first screw shaft 3A with a truncated cone shape (tapered shape) whose diameter gradually increases downstream in the sludge transfer direction D, and a first screw blade 3B fixed to the outer surface of the first screw shaft 3A. 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 second screw 4 is disposed downstream of the first screw 3 in the sludge transfer direction D.

[0018] The upstream end of the screen casing 1 is sealed by a blocking wall 8. One end of the first screw shaft 3A (the upstream end in the transfer direction D) extends through this blocking wall 8. A water sealing device 10 is installed on this blocking wall 8 to seal the gap between the blocking wall 8 and the first screw shaft 3A. The upstream end of the first screw shaft 3A extending through the blocking wall 8 is rotatably supported by bearings 11 and 12 installed on a base (not shown) while its axial movement is restricted. Note that one of the bearings 11 and 12 may be omitted.

[0019] 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 driving machine (e.g., an electric motor) 14, a sprocket 15 fixed to the rotating shaft of the first driving machine 14, a sprocket 16 fixed to the first screw shaft 3A, and a chain 17 wound around these sprockets 15 and 16.

[0020] Sprocket 16 is located between the bearings 11 and 12. When first driver 14 of first rotation mechanism 7 is driven, sprocket 15 fixed to the rotation shaft of first driver 14 rotates, which in turn rotates sprocket 16 fixed to first screw shaft 3A via chain 17. As a result, first screw 3 is rotated by first rotation mechanism 7. First driver 14 is connected to control unit 6, which is configured to be able to control the operation of first driver 14.

[0021] Although not shown, the rotation shaft of the first driving device 14 may be connected to the first screw shaft 3A via a reducer, or may be connected directly to the first screw shaft 3A.

[0022] The second screw shaft 4A of the second screw 4 is disposed 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 is formed with a reduced diameter portion 4F that extends through the inner wall 33A of the discharge chamber 33. By forming the reduced diameter portion 4F on the second screw shaft 4A, a wall surface 4D perpendicular to the axial direction of the second screw shaft 4A is formed on the second screw shaft 4A.

[0023] The upstream end of the second screw shaft 4A is rotatably supported by the first screw shaft 3A via a plain bearing (not shown), and the downstream end of the second screw shaft 4A is rotatably supported while being constrained from moving in the axial direction by bearings 22 and 23 installed on a base (not shown). Note that the bearing 23 can be omitted.

[0024] The 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 driving machine (e.g., an electric motor) 24, a sprocket 25 fixed to the rotation shaft of the second driving machine 24, a sprocket 26 fixed to the second screw shaft 4A, and a chain 27 wound around these sprockets 25 and 26.

[0025] The sprocket 26 is located between the bearings 22 and 23. When the second driver 24 of the second rotation mechanism 20 is driven, the sprocket 25 fixed to the rotation shaft of the second driver 24 rotates, which in turn rotates the sprocket 26 fixed to the second screw shaft 4A via the chain 27. As a result, the second screw 4 is rotated by the second rotation mechanism 20.

[0026] The second driver 24 is connected to the control unit 6. The second driver 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 driver 24 via the inverter. That is, the control unit 6 can control the rotation speed and rotation direction of the second driver 24 via the inverter. The second driver 24 can rotate the second screw 4 independently of the first screw 3. It is preferable that the first driver 14 also has a built-in inverter that can change the rotation speed and rotation direction of the first driver 14.

[0027] Although not shown, the rotation shaft of the second driving device 24 may be connected to the second screw shaft 4A via a reducer, or may be directly connected to the second screw shaft 4A.

[0028] The first screw blade 3B extends spirally along the axial direction of the first screw shaft 3A, and the second screw blade 4B extends spirally along the axial direction of the second screw shaft 4A. The combined 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 equal to or longer than the axial length of the screen casing 1.

[0029] A small gap is formed between the inner surface of the screen casing 1 (more specifically, the inner cylinder 5B described below) and the first screw blade 3B, allowing the first screw blade 3B to rotate without contacting the screen casing 1. Similarly, a small gap is formed between the inner surface of the screen casing 1 and the second screw blade 4B, allowing the second screw blade 4B to rotate without contacting the screen casing 1.

[0030] The rotating first screw blade 3B and second screw blade 4B can transport sludge that has been introduced into the screen casing 1 from the inlet 2 formed at the upstream end of the screen casing 1 toward the discharge chamber 33 (i.e., in the transport direction D).

[0031] In this embodiment, the winding direction (i.e., helical direction) of the second screw blade 4B is opposite to the winding direction of the first screw blade 3B. Therefore, when the sludge introduced from the inlet 2 is sent to the discharge chamber 33, the second screw 4 is rotated in the opposite direction to the first screw 3, as shown in FIG.

[0032] In one embodiment, 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 the sludge introduced from the inlet 2 is sent to the discharge chamber 33, the second screw 4 is rotated in the same direction as the first screw 3.

[0033] As shown in Figure 1, the screen casing 1 is divided into a dewatering area 1A in which the first screw 3 is disposed, and a plug-forming area 1B in which the second screw 4 is disposed. The space in which the sludge is transported 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.

[0034] As shown in Figure 1, the cross-sectional area of ​​this transfer space gradually decreases along the sludge transfer direction D. Therefore, as the sludge introduced through the inlet 2 is transferred through this transfer space by the first screw blade 3B, the sludge is squeezed and dewatered. The filtrate that passes through the screen (perforated plate) of the screen casing 1 is collected in a filtrate receiver 38 disposed 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 SP via the drain 39.

[0035] The space through which the 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 Figure 1, the cross-sectional area of ​​this transfer space is constant. In the plug formation region 1B, a plug cake is formed from the sludge (i.e., cake) dewatered in the dewatering region 1A.

[0036] As described above, it is difficult to accurately determine the operating state of the screw press SP based on the torque and current values ​​of the first screw 3 and the second screw 4. Therefore, in this embodiment, the screw press SP is provided with a plurality of pressure sensors 40 (40A, 40B, 40C, 40D) that detect the pressure of the sludge against the screen casing 1.

[0037] Each of the multiple pressure sensors 40 is electrically connected to the control unit 6. Therefore, the control unit 6 is configured to measure the pressure of the sludge against the screen casing 1 based on the signal sent from each of the multiple pressure sensors 40, and to determine the operating state of the screw press SP (more specifically, the first screw 3 and the second screw 4) based on the measured pressure.

[0038] As shown in Figure 1, the screen casing 1 is divided into a first screw area Pt where the first screw 3 is arranged, a second screw area Pp where the second screw 4 is arranged, and a transition area Py between the first screw area Pt and the second screw area Pp.

[0039] 1, the pressure sensors 40 are arranged in the first screw area Pt, the second screw area Pp, and the switching area Py, respectively. More specifically, the pressure sensors 40A and 40D are arranged in the first screw area Pt, the pressure sensor 40B is arranged in the second screw area Pp, and the pressure sensor 40C is arranged in the switching area Py.

[0040] In one embodiment, the screw press SP may include at least two pressure sensors 40 arranged in at least two of the first screw area Pt, the second screw area Pp, and the changeover area Py. Even with this configuration, the screw press SP can determine its operating state.

[0041] As a first example, the pressure sensor 40 may be arranged in the first screw area Pt and the second screw area Pp (or the switching area Py). As a second example, the pressure sensor 40 may be arranged in the second screw area Pp and the first screw area Pt (or the switching area Py). As a third example, the pressure sensor 40 may be arranged in the switching area Py and the first screw area Pt (or the second screw area Pp). Details of the mounting position of the pressure sensor 40 will be described below.

[0042] Fig. 2 is a diagram showing a pressure sensor arranged in the first screw area Pt. As shown in Fig. 2, the pressure sensor 40A arranged in the first screw area Pt is arranged in the first screw area Pt within the pitch P (i.e., one blade pitch) of the first screw blade 3B adjacent to the switching area Py.

[0043] Fig. 3 is a diagram showing a pressure sensor arranged in the second screw area. As shown in Fig. 3, the pressure sensor 40B arranged in the second screw area Pp is arranged in the second screw area Pp within the pitch P (i.e., one blade pitch) of the second screw blade 4B adjacent to the switching area Py.

[0044] 4(a) and 4(b) are diagrams showing a pressure sensor disposed in the transition area. As shown in FIG. 4(a), the transition area Py has a fixed width that includes a boundary portion B between the first screw 3 and the second screw 4, and the pressure sensor 40C is disposed in the transition area Py having a fixed width. In one embodiment, the width of the transition area Py is ±100 mm forward and backward from the boundary portion B.

[0045] 4(b), the width of the transition area Py may be zero. In this case, the transition area Py corresponds to the boundary portion B, and the pressure sensor 40C is disposed in the boundary portion B.

[0046] Fig. 5 is a diagram showing a pressure sensor arranged in the first screw area. As shown in Fig. 5, pressure sensor 40D is arranged in the first screw area Pt adjacent to the insertion port 2. More specifically, pressure sensor 40D is arranged in an insertion port side area Pz of the first screw area Pt that has a predetermined width and is adjacent to the insertion port 2. The mounting structure of pressure sensor 40 will be described below.

[0047] Fig. 6 is a diagram showing a pressure sensor attached to a screen casing. As shown in Fig. 6, the screen casing 1 has a double structure composed of an outer cylinder 5A as a perforated plate having a plurality of holes 1a formed therein, and an inner cylinder 5B as a perforated plate having a plurality of holes 1b formed therein and fixed to the inner peripheral surface of the outer cylinder 5A. The inner cylinder 5B is arranged to filter the liquid contained in the sludge, and the outer cylinder 5A is arranged to reinforce the inner cylinder 5B.

[0048] In the embodiment shown in Fig. 6, the screw press SP is provided with a sensor base 50 for attaching at least one of the multiple pressure sensors 40 to the screen casing 1. The sensor base 50 is fixed to the outer surface of the screen casing 1 (i.e., the outer cylinder 5A). The pressure sensor 40 has a measuring unit 41 for detecting the pressure of the sludge, and the measuring unit 41 is inserted into an opening 51 formed in the sensor base 50. The opening 51 communicates with a hole 1a in the outer cylinder 5A and an insertion hole 1c formed in the inner cylinder 5B, into which the measuring unit 41 is inserted.

[0049] In order to more accurately detect the pressure of the sludge against the screen casing 1, it is preferable that the multiple pressure sensors 40 (more specifically, pressure sensors 40A, 40B, 40C, 40D) are positioned at the top of the screen casing 1 (more specifically, at the highest position of the screen casing 1).

[0050] If the pressure sensor 40 is attached to the screen casing 1 so that the measuring part 41 of the pressure sensor 40 protrudes from the inner surface of the screen casing 1 (i.e., the inner cylinder 5B), the measuring part 41 may come into contact with the screw blades 3B, 4B, or the pressure sensor 40 may break down due to the action of excessive pressure. Therefore, the sensor base 50 has a thickness that prevents the measuring part 41 of the pressure sensor 40 from protruding from the inner surface of the screen casing 1. Preferably, the tip of the measuring part 41 has a flat shape. In one embodiment, the size of the gap between the measuring part 41 and the inner surface of the screen casing 1 is 2 to 8 mm.

[0051] On the other hand, if the gap between the measuring unit 41 and the inner surface of the screen casing 1 is large, there is a risk that sludge will become clogged in the gap between the pressure sensor 40 and the insertion hole 1c (and hole 1a) of the screen casing 1. Therefore, it is desirable that the measuring unit 41 of the pressure sensor 40 be arranged in the same plane as the inner surface of the screen casing 1.

[0052] In this embodiment, the relative position of the measuring unit 41 with respect to the inner surface of the screen casing 1 can be adjusted depending on the thickness of the sensor base 50. Therefore, the thickness of the sensor base 50 can be selected so that the measuring unit 41 and the inner surface of the screen casing 1 are arranged in the same plane.

[0053] Fig. 7 is a diagram showing another embodiment of the second screw. In the above-described embodiment, the pitch of the second screw blade 4B of the second screw 4 is the same on the upstream side and downstream side in the sludge transfer direction D. In the embodiment shown in Fig. 7, the pitch of the second screw blade 4B is different on the upstream side and downstream side in the sludge transfer direction D. More specifically, the pitch P1' on the upstream side of the second screw blade 4B is larger than the pitch P1'' on the downstream side of the second screw blade 4B (i.e., P1' > P1'').

[0054] In this way, by making the upstream pitch P1' larger than the downstream pitch P1'', the cake transferred from the dewatering zone 1A to the plug formation zone 1B by the rotation of the first screw 3 can be gradually retained in the plug formation zone 1B. As a result, the back pressure applied to the cake in the dewatering zone 1A does not increase abruptly, which effectively prevents the cake in the dewatering zone 1A from rotating together with the first screw 3. An example of determining the operating state of the screw press SP will be described below.

[0055] 8 to 11 are diagrams showing changes in the pressure of the sludge during operation of the screw press. In FIGS. 8 to 11, the horizontal axis represents time, and the vertical axis represents measured pressure values. FIGS. 8 to 11 show pressure values ​​measured based on signals detected by pressure sensor 40A (i.e., the pressure of the sludge in the first screw area Pt against the screen casing 1), pressure values ​​measured based on signals detected by pressure sensor 40B (i.e., the pressure of the sludge in the second screw area Pp against the screen casing 1), and pressure values ​​measured based on signals detected by pressure sensor 40C (i.e., the pressure of the sludge in the switching area Py against the screen casing 1).

[0056] 8 to 11, the signal detected by each pressure sensor 40 (i.e., the pressure measurement value of the sludge) changes periodically as the first screw blade 3B and the second screw blade 4B rotate. As the rotating screw blades 3B, 4B approach the pressure sensor 40, the pressure measurement value gradually increases, and reaches a peak when the screw blades 3B, 4B are closest to the pressure sensor 40. Thereafter, as the screw blades 3B, 4B move away from the pressure sensor 40, the pressure measurement value gradually decreases.

[0057] FIG. 12 is a diagram showing the correlation between the pressure of the sludge and the moisture content of the sludge. In FIG. 12, the horizontal axis represents the moisture content, and the vertical axis represents the pressure. As shown in FIG. 12, there is a correlation between the pressure of the sludge on the screen casing 1 and the moisture content of the sludge, and the pressure increases as the moisture content decreases. Therefore, the screw press SP can determine the dehydration state of the sludge without adding a sensor such as a moisture content meter.

[0058] First, the control unit 6 drives the first rotation mechanism 7 to rotate the first screw 3 while stopping the second screw 4. Next, sludge is introduced into the screen casing 1 through the inlet 2 (see FIG. 1). The sludge introduced through the inlet 2 does not remain in place, but is transported by the rotating first screw blade 3B toward the second screw 4 (i.e., in the transport direction D).

[0059] As the amount of sludge introduced through the inlet 2 increases, the pressure of the sludge on the screen casing 1 adjacent to the inlet 2 increases. Therefore, by arranging the pressure sensor 40D in the inlet side area Pz adjacent to the inlet 2 (see FIG. 5), the control unit 6 can measure the pressure of the sludge on the screen casing 1 based on the signal detected by the pressure sensor 40D.

[0060] In this embodiment, the control unit 6 stores data relating to the correlation between the sludge pressure based on the signal detected by the pressure sensor 40D and the height of the sludge introduced into the inlet 2. Therefore, the control unit 6 can measure the height of the sludge introduced into the inlet 2 based on the signal detected by the pressure sensor 40D. When the measured sludge height reaches a predetermined threshold, the control unit 6 may increase the rotation speed of the first screw 3 to increase the sludge transport speed, or may stop the introduction of the sludge.

[0061] 8, after the operation of the screw press SP is started, the pressure of the sludge begins to rise as the sludge begins to accumulate in the screen casing 1. In this embodiment, the first screw 3 is rotated while the second screw 4 is stopped, but in one embodiment, the second screw 4 does not necessarily have to be stopped, and the pressure of the sludge gradually increases even when the rotation speeds of the first screw 3 and the second screw 4 are relatively low compared to the amount of sludge input.

[0062] As the sludge is transported through the dewatering area 1A, it is squeezed and the liquid contained in the sludge is filtered by the screen casing 1. While the sludge is transported through the dewatering area 1A of the screen casing 1, the sludge is dewatered to form a cake, which is then sent to the plug forming area 1B where the second screw 4 is located.

[0063] As shown in Figures 9 and 10, as the dehydration of the sludge progresses within the screen casing 1, the peak of the pressure measurement value gradually increases (see the arrow in Figure 9), and when the operation of the screw press SP stabilizes, the peak of the pressure measurement value also stabilizes (see the arrow in Figure 10).

[0064] At the beginning of operation, the second screw 4 is not rotating (or is rotating at a low speed), so the cake in the plug-forming zone 1B is not discharged into the discharge chamber 33 and remains in the plug-forming zone 1B. The cake gradually accumulates on the second screw 4 and is pressed against the second screw blade 4B by the sludge (hereinafter referred to as "subsequent cake") being transferred from the dewatering zone 1A to the plug-forming zone 1B.

[0065] The cake in the plug-forming region 1B is compressed by being prevented from moving by the second screw flight 4B, resulting in a cake with a low moisture content. This cake with a low moisture content forms a plug cake that prevents the movement of subsequent cakes. The plug cake formed around the second screw shaft 4A applies back pressure to the subsequent cakes, further compressing them. The liquid separated from the plug cake in the plug-forming region 1B is collected in a filtrate receiver 38 and discharged from the screw press via a drain 39.

[0066] After the plug cake is formed, the control unit 6 drives the second rotation mechanism 20 to rotate the second screw 4 (or operates the second rotation mechanism 20 to increase the rotational speed of the second screw 4). By rotating the second screw 4 in the direction opposite to the rotational direction of the first screw 3, the plug cake is sent out little by little to the discharge chamber 33 (i.e., discharged). In this way, the plug cake is continuously formed and discharged, so the screw press SP can be operated with a plug cake always present in the plug-forming region 1B.

[0067] 11, in the process of shutting down the screw press SP, that is, when the supply of sludge is stopped, the plug cake inside the screen casing 1 is discharged and the peak of the pressure measurement value gradually decreases. The control unit 6 can determine the discharge (discharge) of the sludge from the screen casing 1 at the point when the peak of the pressure measurement value disappears (in other words, at the point when the amount of change in the pressure measurement value per predetermined time falls below a predetermined threshold value).

[0068] According to this embodiment, the control unit 6 can determine the operating state of the screw press SP based on signals detected by a plurality of pressure sensors 40 arranged in a plurality of areas of the screen casing 1. More specifically, the control unit 6 can accurately determine at least one of the progress of dehydration of the sludge, an estimate of the moisture content of the sludge, and the occurrence of co-rotation between the sludge in the screen casing 1 and the first screw 3 and / or the second screw 4.

[0069] For example, in a screw press SP having a structure in which the pitch P1' on the upstream side of the second screw blade 4B is larger than the pitch P1'' on the downstream side of the second screw blade 4B (see Figure 7), when the screw press SP is operating normally, the relationship (normal relationship) between the peaks of the pressure measurement values ​​in the first screw area Pt, the second screw area Pp, and the switching area Py is as follows. Peak of pressure measurement value in the second screw area Pp > Peak of pressure measurement value in the switching area Py > Peak of pressure measurement value in the first screw area Pt

[0070] When an abnormality occurs in the operating state of the screw press SP, an example of the relationship (abnormal relationship) between the peaks of the pressure measurement values ​​in the above-mentioned multiple areas is as follows. Peak pressure measurement value of the second screw area Pp < Peak pressure measurement value of the switching area Py ≦ Peak pressure measurement value of the first screw area Pt

[0071] In this way, when the relationship between the peaks of the pressure measurement values ​​in multiple areas is disrupted, it is considered that the rotation speed of the first screw 3, the rotation speed of the second screw 4, and the difference between these rotation speeds are inappropriate. When an abnormal relationship such as the one described above occurs, the rotation speed of the second screw 4 is too high, so the control unit 6 reduces the rotation speed of the second screw 4 so that the peaks of the multiple pressure measurement values ​​have a normal relationship.

[0072] Thus, according to this embodiment, the control unit 6 can accurately determine whether the rotational speeds of the screws 3 and 4 and the difference between these rotational speeds are appropriate based on signals detected by multiple pressure sensors 40.

[0073] FIG. 13 is a diagram showing changes in pressure measurements when an abnormality occurs in the operating state of the screw press. In FIG. 13, the horizontal axis represents time, and the vertical axis represents pressure measurements. In the graph shown in FIG. 13, the peaks of the pressure measurements in the first screw area Pt change irregularly. In this case, it is highly likely that the sludge in the screen casing 1 is rotating together with the first screw 3. Therefore, the control unit 6 can prevent the sludge from rotating together with the first screw 3 by increasing the rotation speed of the first screw 3.

[0074] As described above, the control unit 6 can measure the height of the sludge introduced into the inlet 2 based on the signal detected by the pressure sensor 40D. If the measured sludge height is abnormally high or is on an upward trend even when the rotation speeds of the first screw 3 and the second screw 4 are appropriate, the amount of sludge introduced may be inappropriate, or the sludge may not be transported properly due to co-rotation of the sludge with the first screw 3. In this case, reducing the amount of sludge introduced or increasing the rotation speed of the first screw 3 can eliminate the co-rotation of the sludge with the first screw 3, thereby optimizing the operation of the screw press SP. In this way, the control unit 6 can determine whether the sludge is co-rotating with the first screw 3 based on the signal detected by the pressure sensor 40D.

[0075] As described above, there is a correlation between the pressure of the sludge on the screen casing 1 and the moisture content of the sludge (see FIG. 12). Therefore, when the peak of the pressure measurement value is not sufficiently large by comparing it with the past operating conditions of the screw press SP, the control unit 6 can determine that poor sludge coagulation or co-rotation of the sludge has occurred in the coagulation process (a process preceding the dewatering process in the screw press SP).

[0076] The above-described embodiments have been described for the purpose of enabling a person of ordinary skill in the art to practice the present invention. Various modifications of the above-described embodiments would naturally be possible for a person skilled in the art, and the technical concept of the present invention may also be applied to other embodiments. Therefore, the present invention is not limited to the described embodiments, but is to be interpreted in the broadest scope in accordance with the technical concept defined by the claims. [Explanation of symbols]

[0077] 1 Screen casing 1a hole 1b hole 1c Insertion hole 2 Inlet 3 First screw 3A First screw shaft 3B First screw blade 4 Second screw 4A Second screw shaft 4B No. 2 screw blade 4D Wall 4F reduced diameter section 5A outer cylinder 5B Inner cylinder 6 Control Unit 7 First rotation mechanism 8 Blocking wall 10 Water sealing device 11,12 Bearings 14 First Drive Unit 15,16 sprocket 17 Chain 20 Second rotation mechanism 22,23 Bearings 24 Second Drive 25,26 sprocket 27 Chain 33 Exhaust chamber 33A Inner wall 38 Filtrate receiver 39 Drain 40(40A, 40B, 40C, 40D) Pressure sensor 41 Measuring part 50 Sensor base 51 Aperture SP Screw Press Pt 1st screw area Pp Second screw area Py Switching Area Pz insertion area D Transfer direction 1A Dehydration area 1B Plug formation region

Claims

1. A screw press, a filter cylinder into which the liquid content is introduced; a first screw and a second screw arranged in the filter cylinder and rotating independently of each other; a plurality of pressure sensors for detecting the pressure of the liquid-containing substance against the filter cylinder; A control unit that measures the pressure of the liquid-containing material against the filter cylinder based on signals detected by the plurality of pressure sensors, and controls the rotation speeds of the first screw and the second screw based on the measured pressure, When the area of ​​the filter cylinder is divided into a first screw area in which the first screw is arranged, a second screw area in which the second screw is arranged, and a transition area between the first screw area and the second screw area, the plurality of pressure sensors are arranged in the second screw area and at least one of the first screw area and the transition area, The control unit Measure the pressure of the liquid-containing material against the filter cylinder based on signals detected by a plurality of pressure sensors arranged in at least one of the second screw area, the first screw area, and the switching area; The screw press detects an abnormality in the screw press by comparing the magnitude of the measured peak pressure values.

2. The screw press according to claim 1 , wherein each of the plurality of pressure sensors is disposed in the first screw area, the second screw area, and the changeover area.

3. the first screw has a first screw flight, 3. The screw press according to claim 1, wherein any one of the plurality of pressure sensors is disposed in the first screw area within a pitch of the first screw flight adjacent to the changeover area.

4. the second screw has a second screw flight, 3. The screw press according to claim 1, wherein any one of the plurality of pressure sensors is disposed in the second screw area within a pitch of the second screw flight adjacent to the changeover area.

5. 3. The screw press according to claim 1, wherein any one of the plurality of pressure sensors is arranged in the first screw area adjacent to an inlet for the liquid-containing material formed at the upstream end of the filter cylinder.

6. The screw press includes a sensor base for attaching at least one of the plurality of pressure sensors to the filter cylinder, The screw press according to claim 1 or 2, wherein the sensor base is fixed to an outer surface of the filter cylinder.

7. The screw press according to claim 6, wherein the sensor base has a thickness such that a sensor measurement portion of a pressure sensor attached to the sensor base does not protrude from an inner surface of the filter cylinder.

8. A screw press, a filter cylinder into which the liquid content is introduced; a first screw and a second screw arranged in the filter cylinder and rotating independently of each other; a plurality of pressure sensors for detecting the pressure of the liquid-containing substance against the filter cylinder; A control unit that measures the pressure of the liquid-containing material against the filter cylinder based on signals detected by the plurality of pressure sensors, and controls the rotation speeds of the first screw and the second screw based on the measured pressure, When the area of ​​the filter cylinder is divided into a first screw area in which the first screw is arranged, a second screw area in which the second screw is arranged, and a transition area between the first screw area and the second screw area, the plurality of pressure sensors are arranged in the second screw area and at least one of the first screw area and the transition area, The control unit detects an abnormality in the screw press by comparing the magnitude of the measured peak pressure values, the control unit is configured to control the rotational speeds of the first screw and the second screw, or a difference between the rotational speeds, so that a peak value of pressure detected by the plurality of pressure sensors is greater in the second screw area than in the first screw area.

9. A method for determining the operating state of a screw press having a first screw and a second screw that are arranged in a filter cylinder into which a liquid content is introduced and that rotate independently of each other, comprising: When the area of ​​the filter cylinder is divided into a first screw area in which the first screw is arranged, a second screw area in which the second screw is arranged, and a transition area between the first screw area and the second screw area, the pressure of the liquid-containing material against the filter cylinder is measured based on signals detected by a plurality of pressure sensors arranged in the second screw area and at least one of the first screw area and the transition area, A method for detecting an abnormality in the screw press as a method for determining the operating state of the screw press by comparing the magnitude of the measured peak pressure values.

10. A method for determining the operating state of a screw press having a first screw and a second screw that are arranged in a filter cylinder into which a liquid content is introduced and that rotate independently of each other, comprising: When the area of ​​the filter cylinder is divided into a first screw area in which the first screw is arranged, a second screw area in which the second screw is arranged, and a transition area between the first screw area and the second screw area, the pressure of the liquid-containing material against the filter cylinder is measured based on signals detected by a plurality of pressure sensors arranged in the second screw area and at least one of the first screw area and the transition area, A method for determining the operating state of the screw press, based on the results of displaying the change in the measured pressure over time, to determine the progress of dewatering of sludge in the screw press.

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