Centrifugal separator and method for operating the same

Abstract

To achieve optimization of chemical feeding position in a centrifugal separator which adopts a line chemical feeding system for clogged chemical feeding of a coagulant, and applies a centrifugal force to a process liquid containing a solid content to perform solid-liquid separation.SOLUTION: A centrifugal separator comprises: a bowl which rotates to perform solid-liquid separation of a process liquid therein; a screw conveyor which transports a solid content, which has been separated into solid and liquid in the bowl, toward an exhaust port; and chemical feeder which adds a coagulant to the process liquid. The chemical feeder comprises: first clogged chemical feeding means which adds a coagulant to a flow channel of the process liquid before feeding thereof to the bowl at a point where a turbulent flow generates in the process liquid; second clogged chemical feeding means which adds the coagulant on an upstream side of the point where the turbulent flow is formed; and third clogged chemical feeding means which adds the coagulant on a downstream side of the point where the turbulent flow is formed, and is capable of switching in addition of the coagulant from any of the first to third clogged chemical feeding means.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a centrifugal separator that applies centrifugal force to a treatment liquid containing solids to separate it into solid and liquid, and in particular to a technique for supplying a flocculant outside the separator to promote solid-liquid separation of the treatment liquid. [Background technology]

[0002] A centrifugal separator known as a decanter is known as a device for separating solids from a treatment liquid containing solids. Figure 9 shows a schematic diagram of the basic structure of a decanter. A horizontal decanter 1 includes a bowl 11 that rotates around a horizontal axis and a screw conveyor 12. Although not shown, a vertical decanter is also known in which the bowl 11 and screw conveyor 12 rotate around a vertical axis.

[0003] The bowl 11 is a cylindrical body with one or both ends conically shaped. The screw conveyor 12 is a rotary conveying means equipped with screw blades 12a for conveying the solids separated in the bowl 11. The screw conveyor 12 is hollow inside along the central axis of rotation, and a feed tube 13, which is a supply nozzle for the treatment liquid to be centrifuged, is inserted with a slight clearance so as not to come into contact with the screw conveyor 12. The treatment liquid discharged from the tip of the feed tube 13 is supplied to a treatment liquid chamber in the screw conveyor 12, and is then discharged by centrifugal force from supply holes 14 formed on the outer surface and supplied into the bowl 11.

[0004] In this configuration, when separating treated liquid derived from sewage, such as sludge, into dehydrated cake and separated liquid, the treated liquid is continuously supplied into bowl 11 while bowl 11 is rotated at a predetermined rotation speed, and the treated liquid is separated into a solid phase and a liquid phase within bowl 11 by the action of centrifugal force. The centrifuged solids are transported toward one end of bowl 11 by screw conveyor 12, separated from the liquid phase in the conical portion, and discharged as dehydrated cake from solids outlet 15. Meanwhile, the separated liquid overflows and is discharged from separated liquid outlet 16 on the opposite side.

[0005] To obtain a dehydrated cake with a desired moisture content, the centrifugal force (G) applied to the treatment liquid, the torque of the screw conveyor 12, the differential speed between the rotating bowl 11 and the screw conveyor 12, etc., are adjusted. In addition, there is a chemical injection process in which a flocculant is supplied to promote solid-liquid separation (see, for example, Patent Documents 1 to 7).

[0006] Patent Document 1 discloses a centrifugal separator that can control the flow rate ratio between external and internal chemical injection, which the present inventors have realized. The present inventors are considering optimizing external chemical injection as a further improvement. Specifically, external chemical injection often employs a "line chemical injection method" in which a coagulant flow path is connected to the treatment liquid flow path. However, if the external chemical injection location is uniformly designed, for example, the properties of the sludge to be treated vary from one sewage treatment plant to another, and the expected separation performance may not be achieved even if the chemical injection amount is increased. Furthermore, even if the expected separation performance is achieved, the separation performance may not be maintained if the properties of the sludge to be treated change, for example, due to rain. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Patent No. 6230741 [Patent Document 2] Patent No. 3202289 [Patent Document 3] Special Publication No. 8-29268 [Patent Document 4] Patent No. 5650999 [Patent Document 5] Patent No. 5425523 [Patent Document 6] Patent No. 5490442 [Patent Document 7] Patent No. 5619965 Summary of the Invention [Problem to be solved by the invention]

[0008] The present invention was made based on these circumstances, and its purpose is to optimize the external injection of a flocculant in a centrifugal separator that applies centrifugal force to a treatment liquid containing solids to separate the solids from the liquid. [Means for solving the problem]

[0009] The gist of the present invention is as follows. (1) The centrifuge of the present invention is a centrifuge comprising a bowl that rotates to separate the treated liquid inside into solid and liquid, a screw conveyor that transports the solids separated in the bowl toward an outlet, and a chemical feeder that adds a flocculant to the treated liquid, wherein the chemical feeder comprises a first external chemical feeder that adds a flocculant to the flow path of the treated liquid before it is supplied to the bowl at a point where turbulence is formed in the treated liquid, a second external chemical feeder that adds a flocculant upstream of the point where the turbulence is formed, and a third external chemical feeder that adds a flocculant downstream of the point where the turbulence is formed, and is capable of switching between adding the flocculant from any of the first to third external chemical feeders. (2) The point where the turbulent flow is formed is a line mixer disposed in the flow path of the treatment liquid. (3) The point where the turbulent flow is formed is either a joint member of a pipe that constitutes the flow path of the treatment liquid or a valve. (4) The chemical injection device includes an external chemical injection device that adds a flocculant to the treatment liquid before it is supplied into the bowl, and an internal chemical injection device that adds a flocculant to the treatment liquid supplied into the bowl, and variably controls the ratio between the external chemical injection amount and the internal chemical injection amount, and switches between and controls which of the first to third external chemical injection means is used for external chemical injection. (5) The method for operating a centrifuge of the present invention is a method for operating a centrifuge equipped with a bowl that rotates to separate the treated liquid inside into solid and liquid, a screw conveyor that transports the solids separated in the bowl toward an outlet, and a chemical injection device that adds a flocculant to the treated liquid, and is characterized by including the steps of: comparing the solid-liquid separation state when the flocculant is added to a point in the flow path of the treated liquid before it is supplied to the bowl, where the flocculant is formed, at a point where turbulence is formed in the treated liquid; the solid-liquid separation state when the flocculant is added upstream of the point where the turbulence is formed; and the solid-liquid separation state when the flocculant is added downstream of the point where the turbulence is formed; and determining from which point the flocculant should be added based on the results of the comparison. [Effects of the Invention]

[0010] According to the present invention, the flow path of the treatment liquid before it is supplied to the bowl is provided with a first external chemical injection means that adds a flocculant at a point where turbulence is formed in the treatment liquid, a second external chemical injection means that adds a flocculant upstream of the point where turbulence is formed, and a third external chemical injection means that adds a flocculant downstream of the point where turbulence is formed, and by providing a chemical injection device that can switch between adding the flocculant from any of the first to third external chemical injection means, it is possible to optimize the external chemical injection. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a configuration diagram of a centrifugal separator according to a first embodiment of the present invention. [Figure 2] FIG. 2 is a configuration diagram of a chemical injection module of the centrifugal separator. [Figure 3] FIG. 2 is a configuration diagram of a line mixer disposed in the chemical injection module. [Figure 4] 1 is a flow chart showing a method for optimizing the supply of a polymer-based flocculant to the centrifugal separator [Figure 5] FIG. 10 is a configuration diagram of a centrifugal separator according to a second embodiment of the present invention. [Figure 6] FIG. 10 is a configuration diagram of a centrifugal separator according to a third embodiment of the present invention. [Figure 7] FIG. 10 is a configuration diagram of a centrifugal separator according to a fourth embodiment of the present invention. [Figure 8] FIG. 10 is a configuration diagram of a centrifugal separator according to a fifth embodiment of the present invention. [Figure 9] FIG. 1 is a diagram showing the configuration of a conventional centrifugal separator. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, a centrifugal separator according to a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings. However, the technical scope of the present invention is not to be construed as being limited by the following embodiments.

[0013] (First embodiment) As shown in Fig. 1, the decanter 2 of this embodiment includes a casing 2a having a solids outlet 20 and a separated liquid outlet 21 on the underside thereof, a bowl 3 disposed within the casing, a screw conveyor 4 for transporting the solids centrifuged within the rotating bowl 3, and a pipe-like feed tube 5 for supplying the centrifuged treated liquid into the bowl 3. The bowl 3 has both shafts supported by a bearing mechanism 22 such as a bearing disposed outside the casing 2a. Furthermore, the screw conveyor 4 has both shafts supported by a bearing mechanism 23 such as a conveyor bearing. Reference numeral 24 denotes a partition wall that divides the space within the casing 2a.

[0014] When the power of the main motor 25, which is a driving device, is transmitted to the pulley 25b on the bowl 3 side via the rotating belt 25a, the bowl 3 rotates, and the rotational power is transmitted to the screw conveyor 4 via the gear box 26 and spline shaft 26a, which are differential speed generating devices, so that the bowl 3 and the screw conveyor 4 rotate at a relative differential speed. This can be adjusted as appropriate depending on the type and concentration of the processing liquid, but as an example of normal operation, it is set to 500 to 8000 min -1 Rotate bowl 3 at a predetermined rotation speed selected within the range of 0.5 to 50 min for bowl 3. -1For example, when sludge derived from sewage is used as the treated liquid, the rotation speed is set to, for example, 2 to 25 m. 3 / Hr into bowl 3.

[0015] A motor called a backdrive motor 27 is connected to the gearbox 26 via a rotating belt 27a and a pulley 27b. The backdrive motor 27 applies a brake so that the screw conveyor 4 rotates slower than the bowl 3. Regenerative power generated in the backdrive motor 27 by applying the brake can be supplied to the main motor 25. However, the backdrive motor 27 is not necessarily provided. Reference numeral 28 denotes a support frame for the decanter 2, and reference numeral 29 denotes a support member for supporting the feed tube 5.

[0016] Bowl 3 has a conical portion 31 at one end of its cylindrical body, and a disk-shaped member called a front hub 32 at the other end. The body of bowl 3 forms a pool (liquid reservoir) for the treatment liquid supplied into bowl 3. Meanwhile, conical portion 31 forms a beach portion where solids transported by screw conveyor 4 separate from the liquid phase, and is provided with a solids discharge port 33 at its end. Front hub 32 is provided with a separated liquid discharge port 34 through which the separated liquid overflows and is discharged. Separated liquid discharge port 34 is a circular opening that penetrates front hub 32.

[0017] A spiral screw blade 41 for transporting solid content is provided on the outer peripheral surface of the screw conveyor 4. Furthermore, a treatment liquid supply hole 42 is provided on the outer peripheral surface of the screw conveyor 4. The treatment liquid supply hole 42 communicates with a treatment liquid supply chamber 43 formed inside the screw conveyor 4.

[0018] The feed tube 5 approaches or is inserted into the processing liquid supply chamber 43 without coming into contact with the rotating bowl 3 and screw conveyor 4. The processing liquid supply chamber 43 is provided with an upright wall 44 along the circumferential direction, which acts as a liquid barrier to prevent the supplied processing liquid from backflowing. Meanwhile, the base end of the feed tube 5 is connected to a processing liquid flow path 51 (e.g., a pipe) from a processing liquid delivery means (not shown), such as a pump. The processing liquid delivered by the processing liquid delivery means is discharged from the tip of the feed tube 5 into the processing liquid supply chamber 43. The processing liquid supplied into the processing liquid supply chamber 43 is discharged from the processing liquid supply hole 42 by the action of the centrifugal force of the rotating screw conveyor 4 and supplied into the bowl 3.

[0019] Next, the chemical injection device that adds the flocculant will be described. The decanter 2 of this embodiment is equipped with a polymer-based chemical injection device 7 that adds a polymer-based flocculant while controlling the ratio of the chemical injection amounts of external and internal injection. It also has an inorganic-based chemical injection device 6 that supplies an inorganic flocculant. That is, Fig. 1 shows an example of a decanter 2 that adds each flocculant in the following order: a polymer-based flocculant for external injection, a polymer-based flocculant for internal injection, and an inorganic flocculant for internal injection.

[0020] First, the external injection of the polymer-based flocculant will be described. As a preferred example of the external injection, a line injection method is adopted. Specifically, an injection module 70 for the polymer-based flocculant is connected to the middle of the flow path 51 (e.g., piping) of the treatment liquid, and the polymer-based flocculant is added from the injection module 70 to the treatment liquid flowing in the flow path 51.

[0021] FIG. 2 shows a preferred example of a chemical injection module 70. As shown in FIG. 2, the chemical injection module 70 has a line mixer 8 disposed midway through a vertically arranged treatment liquid flow path 51, which serves as a point where turbulence (including vortex flow) is formed in the treatment liquid. The flow path 51 then turns horizontally and connects to a feed tube 5. The chemical injection module 70 branches the polymer flocculant flow path 71 into three paths, one of which is connected to the line mixer 8. A valve 71A is provided in the flow path 71 connected to the line mixer 8, and the addition of the polymer flocculant can be started and stopped by opening and closing the valve 71A. In other words, the chemical injection module 70 has a "first external chemical injection means" that adds the polymer flocculant to the point where turbulence is formed in the treatment liquid.

[0022] One of the three branched flow paths 71 for the polymer flocculant is connected to flow path 51 for the treatment liquid upstream of line mixer 8. Flow path 71 connected upstream of line mixer 8 is provided with valve 71B, which allows the addition of polymer flocculant to be started and stopped by opening and closing valve 71B. In other words, chemical injection module 70 is equipped with a "second external chemical injection means" that adds polymer flocculant upstream of the point where line mixer 8 creates turbulence in the treatment liquid.

[0023] One of the three branched flow paths 71 for the polymer flocculant is connected to the treatment liquid flow path 51 downstream of the line mixer 8. This connection downstream of the line mixer 8 may be to an area where turbulence created by the line mixer 8 remains, or may be after the turbulence created by the line mixer 8 has disappeared. Preferably, it is connected to an area where turbulence created by the line mixer 8 remains. A valve 71C is provided in the flow path 71 connected downstream of the line mixer 8, and the addition of the polymer flocculant can be started and stopped by opening and closing the valve 71C. In other words, the chemical injection module 70 is equipped with a "third external chemical injection means" that adds the polymer flocculant downstream of the point where the line mixer 8 creates turbulence in the treatment liquid.

[0024] The first to third external chemical feed means can be switched to add the polymer flocculant from one of the external chemical feed means by opening and closing valves 71A to 71B. The opening and closing of valves 71A to 71B as switching control can be performed automatically or manually. The polymer flocculant may be added from more than one of the first to third external chemical feed means. In this case, the ratio of the added amounts may be adjusted. Furthermore, the number of external chemical feed means is not limited to three, and additional external chemical feed means may be added upstream and / or downstream. Furthermore, the flow path 71 for the polymer flocculant does not have to be constructed as a three-branched pipe. For example, the downstream side of valve 72 may be a single flexible hose, and the addition position may be switched by connecting a hose to the upstream side of one of valves 71A to 71B.

[0025] The distance L1 from the addition position of the second external chemical feed means to the addition position of the first external chemical feed means (i.e., the length of flow path 51) is, for example, 150 to 500 mm. The distance L2 from the addition position of the first external chemical feed means to the addition position of the third external chemical feed means (i.e., the length of flow path 51) depends on the range of turbulence generated by line mixer 8, but is, for example, 150 to 500 mm. The distances L1 and L2 can be used as parameters for ensuring and adjusting the aggregation reaction time (= length / flow rate).

[0026] Various types of line mixer 8 can be used. There are no particular limitations on the configuration or shape. FIG. 3 shows an example of a line mixer 8. The line mixer 8 has a cylindrical main body 81 connected to the flow path 51, and turbulent flow forming members 82 having arc-shaped convex portions facing each other are fixedly disposed within the main body 81. Discharge ports 83 for the polymer-based flocculant are provided above (i.e., downstream of) the arc-shaped convex portions of the turbulent flow forming members 82 so as to face each other. A static mixer manufactured by JMS Corporation is suitable for this type of line mixer 8.

[0027] Returning to the explanation in FIG. 1, a flow path 71 for a polymeric flocculant connected to chemical injection module 70 is provided with a valve 72 as a flow rate adjusting means, and the flow rate of the chemical injected outside the machine is adjusted by adjusting the opening of valve 72. Furthermore, a flow meter 73 is provided in flow path 71 so that the flow rate of the chemical injected outside the machine can be measured. However, valve 72 is only one example of a flow rate adjusting means, and is not limited to this, and other configurations may be used as long as they are capable of adjusting the flow rate. For example, a metering pump that can variably set the flow rate can be cited as another example.

[0028] A polymer flocculant supply source is connected to the base end of the polymer flocculant flow path 71 via a polymer flocculant supply pump 74 (hereinafter simply referred to as "flocculant pump 74") serving as a liquid supply means. FIG. 1 illustrates a tank 75 storing a solution of the polymer flocculant as an example of the supply source. The polymer flocculant may be an amphoteric polymer, an anionic polymer, or a cationic polymer, or a combination thereof. Preferred examples of polymer flocculants include one or more of dimethylaminoethyl methacrylate, dimethylaminoethyl acrylate, and polyvinylamidine. Another example of a polymer flocculant supply source is a dissolving device that dissolves a solid polymer flocculant in a solvent (e.g., water) to produce a solution.

[0029] Next, the on-board chemical injection of the polymer-based flocculant will be described. On-board chemical injection is performed, for example, using a feed tube 5. The feed tube 5 has a multi-pipe structure with a central flow path 52 through which the treatment liquid flows and a flow path 53 through which the polymer-based flocculant flows, surrounding the central flow path 52. A flow path 76 (e.g., a pipe) from a flocculant pump 74 is connected to the base end of the feed tube 5. A valve 77 is provided as a flow rate control device in the flow path 76 from the flocculant pump 74, and the flow rate is controlled by adjusting the opening of the valve 77. Furthermore, a flow meter 78 is provided in the flow path 76 to measure the flow rate of the on-board chemical injection. However, the valve 77 is merely an example of a flow rate control device, and other configurations capable of controlling the flow rate may be employed. For example, a metering pump capable of variably setting the flow rate is another example. The polymer-based flocculant for on-board chemical injection and that for off-board chemical injection may be the same type or different types from separate supply sources.

[0030] A polymer flocculant outlet is formed at the tip of the feed tube 5, separate from the central treatment liquid outlet. The polymer flocculant outlets are circular openings formed radially through the peripheral surface of the tip of the feed tube 5. Meanwhile, a flocculant supply chamber 45 is formed inside the screw conveyor 4, adjacent to the treatment liquid supply chamber 43, with a partition wall 44 interposed between them. The flocculant supply chamber 45 is a supply chamber with a groove-shaped cross section formed around the entire inner peripheral surface of the hollow of the screw conveyor 4, and is capable of receiving the polymer flocculant discharged radially from the feed tube 5. Furthermore, a flocculant outlet 46 is formed at the bottom of the groove-shaped flocculant supply chamber 45, for supplying the polymer flocculant received in the supply chamber into the bowl 3. The flocculant outlet 46 is a circular opening that radially penetrates the screw conveyor 4. In other words, like the treatment liquid, the polymer flocculant is supplied into the bowl 3 by utilizing the centrifugal force of the rotating screw conveyor 4. The polymer-based flocculant may be supplied to the treatment liquid in the bowl 3 or may be mixed with the treatment liquid while being supplied into the bowl 3 .

[0031] The polymer-based chemical injection device 7 further includes a flow rate ratio control unit 79 that controls the supply rates of external chemical injection and internal chemical injection. As an example, the flow rate ratio control unit 79 can be configured as a computer system including storage devices such as a CPU and memory. The flow rate ratio control unit 79 may be installed near the decanter 2 as a control panel, or may be configured so that its functions are fulfilled by a system installed in a central monitoring room. Of course, instead of automatic control by the flow rate ratio control unit 79, the flow rate ratio control may be manual control in which an operator manually adjusts the openings of the valves 72 and 77 while checking the flow meters 73 and 78.

[0032] The flow rate ratio control unit 79 distributes the total amount of polymeric flocculant supplied to the decanter 2 and executes external chemical feeding and internal chemical feeding at a predetermined flow rate ratio. Controlling the flow rate ratio between external chemical feeding and internal chemical feeding can be achieved, for example, by adjusting the balance of valve openings. More specifically, the opening range of the valves 72 and 77 is first determined in advance, and the closed state within that range is assigned as 0% and the open state as 100%. The valve opening can then be arbitrarily adjusted between 0 and 100% using, for example, an electric actuator with a position meter. The opening range of the valves 72 and 77 may be a range from fully closed to fully open, or may be a range that allows for accurate flow rate adjustment due to the configuration of the valves 72 and 77. The system is then able to transition between a state in which coagulant is supplied with the external chemical injection valve at 100% opening and the internal chemical injection valve at 0%, passing through an intermediate point where both valves are 50% open, and a state in which coagulant is supplied with the external chemical injection valve at 0% opening and the internal chemical injection valve at 100% opening. The external chemical injection valve may start at 0% opening and the internal chemical injection valve at 100% opening. Flow rate ratio control is not limited to balancing the valve openings. As another example, a control model may be employed in which the external chemical injection valve opening and the internal chemical injection valve opening are set in accordance with the magnitude of the centrifugal force (G), which is determined by the rotation speed of the bowl 3.

[0033] Next, the in-machine feeding of the inorganic flocculant will be described. In-machine feeding is performed, for example, using a feed tube 5. The feed tube 5 has a multi-tube structure, with a central flow path 52 through which the treatment liquid flows, a flow path 53 through which the polymer flocculant flows, and a flow path 54 through which the inorganic flocculant flows, surrounding the outer periphery of the central flow path 52. A flow path 61 (e.g., a pipe) for the inorganic flocculant is connected to the base end of the feed tube 5. A valve 62 is provided in the inorganic flocculant flow path 61 as a flow rate control means, and the flow rate of the flocculant is controlled by adjusting the opening of the valve 62. Furthermore, a flow meter 63 is provided midway along the flow path 61 so that the flow rate of the in-machine feeding can be measured. However, the valve 62 is merely an example of a flow rate control means, and other configurations capable of adjusting the flow rate may be used. For example, a metering pump capable of variably setting the flow rate may be used.

[0034] An inorganic flocculant supply source is connected to the base end of the inorganic flocculant flow path 61 via an inorganic flocculant supply pump 64 (hereinafter simply referred to as "flocculant pump 64") serving as a liquid supply means. FIG. 1 illustrates a tank 65 storing a solution of the inorganic flocculant as an example of the supply source. As the inorganic flocculant, for example, one or more types selected from polyferric sulfate (polyiron), PAC, etc. can be used. Among these, polyiron is preferable. Of course, other types of inorganic flocculants may also be used. Furthermore, the flocculants for on-board and off-board injection may be the same type, or may be different types having separate supply sources.

[0035] The tip of the feed tube 5 is provided with an inorganic flocculant outlet, separate from the central treatment liquid outlet and polymer flocculant outlet. The inorganic flocculant outlets are circular openings formed in multiple locations radially penetrating the peripheral surface of the tip of the feed tube 5. Meanwhile, an inorganic flocculant supply chamber 47 is formed inside the screw conveyor 4, adjacent to the polymer flocculant supply chamber 45 via an upright wall 44. The flocculant supply chamber 47 is a supply chamber with a groove-shaped cross section formed around the entire inner peripheral surface of the hollow of the screw conveyor 4, and can receive the inorganic flocculant discharged radially from the feed tube 5. Furthermore, a flocculant outlet 48 is formed at the bottom of the groove-shaped flocculant supply chamber 47, for supplying the inorganic flocculant received in the supply chamber into the bowl 3. The flocculant outlet 48 is a circular opening penetrating the screw conveyor 4 in the radial direction. That is, like the treatment liquid and polymer-based flocculant, the inorganic flocculant is also supplied into the bowl 3 by utilizing the centrifugal force of the rotating screw conveyor 4. However, as a preferred example, the inorganic flocculant is supplied to the solid content near the beach where solid-liquid separation has progressed.

[0036] Next, as an example of a method for operating the decanter 2, a method for optimizing the chemical supply of a polymer-based flocculant when the decanter 2 performs solid-liquid separation of sludge will be described with reference to Figure 4. Note that if this supply optimization method is performed during normal operation, it will be possible to respond to daily changes in sludge properties. It may also be performed during construction or trial operation when a new decanter 2 is installed at a sewage treatment plant, for example.

[0037] First, the chemical supply module 70 selects which of its first to third external supply means to supply chemicals from. As an example, the valves 71A to 71C are opened and closed so that chemicals are supplied from the nth external supply means (n=1) (Act 10). When the solid-liquid separation in the decanter 2 stabilizes, flow rate ratio control is performed (Act 11). As an example of flow rate ratio control, the flow rate ratio control unit 79 changes the opening of the valves 72 and 77 (valve 72: 0% → 100%, valve 77: 100% → 0%), for example, every hour, in 25% intervals, and checks the moisture content of the dehydrated cake (solid content) and / or the state of the separated liquid (SS concentration, color, foam, pH, etc.) each time (Act 12). If the results tend to improve, the opening is further changed; if the results tend to worsen, the opening is reversed. By repeating this cycle, the optimal balance between external and internal chemical supply is achieved.

[0038] Next, n=n+1 (Act13 No, Act14), and the valves 71A-71C are opened and closed to add chemicals from the nth external chemical feed means (n=2) (Act10). Further, flow rate ratio control is executed (Act11), and the moisture content of the dehydrated cake and / or the state of the separated liquid (SS concentration, color, foam, pH, etc.) are checked (Act12). Similarly, n=n+1 (Act13 No, Act14), and the valves 71A-71C are opened and closed to add chemicals from the nth external chemical feed means (n=3) (Act10). Further, flow rate ratio control is executed (Act11), and the moisture content of the dehydrated cake and / or the state of the separated liquid (SS concentration, color, foam, pH, etc.) are checked (Act12).

[0039] When flow rate ratio control is completed for all of the first through third external chemical feeding means (Act 13 Yes), the external chemical feeding means with the best moisture content of the dehydrated cake (the separated solids) and / or the state of the separated liquid (SS concentration, color, foam, pH, etc.) is determined, and for subsequent operations (e.g., throughout the day), the best external chemical feeding means is used for addition (Act 15). It is preferable to continue flow rate ratio control during subsequent operations. More preferably, once the optimal balance point for the flow rate ratio is found, the total flocculant supply rate is reduced, and if the results remain favorable, the total supply rate is further reduced. If the results begin to deteriorate, the total supply rate is increased. Repeating this cycle allows the external chemical feeding and the internal chemical feeding to be optimally balanced and converge to the optimal total supply rate.

[0040] As described above, the decanter 2 of this embodiment is equipped with a first external chemical feeding means that adds a polymer-based flocculant at the point where the line mixer 8 forms a turbulent flow in the treatment liquid, a second external chemical feeding means that adds a flocculant upstream of the point where the line mixer 8 forms a turbulent flow in the treatment liquid, and a third external chemical feeding means that adds a flocculant downstream of the point where the line mixer 8 forms a turbulent flow in the treatment liquid, and is equipped with a polymer-based chemical feeding device 7 that can switch between adding the flocculant from any of the first to third external chemical feeding means, making it possible to optimize the external feeding of the polymer-based flocculant while controlling the ratio of the feeding amounts of the external chemical feeding and the internal chemical feeding.

[0041] (Second embodiment) Next, a decanter 2 according to a second embodiment will be described. The decanter 2 of this embodiment has the same configuration as the decanter 2 of the first embodiment, except that the inorganic flocculant is also configured to control the flow rate ratio between on-board and off-board chemical injection. Therefore, the same components as those in the first embodiment are denoted by the same reference numerals, and detailed description thereof will be omitted.

[0042] As shown in Fig. 5, a preferred example of the external injection of the inorganic flocculant is a line injection method. Specifically, an inorganic flocculant injection module 9 is connected midway through a flow path 51 (e.g., a pipe) for the treatment liquid, and the inorganic flocculant is added from injection module 90 to the treatment liquid flowing through flow path 51. The inorganic flocculant injection module 9 is located upstream of the polymer flocculant injection module 70, and is added to the treatment liquid before the polymer flocculant.

[0043] In the chemical injection module 9, a line mixer 90 is disposed midway through the flow path 51 of the treatment liquid, which serves as a point where turbulence (including vortex flow) is formed in the treatment liquid. The external chemical injection module 9 branches the flow path 71 of the inorganic flocculant into three, one of which is connected to the line mixer 90. A valve 9A is provided in the flow path 66 connected to the line mixer 90, and the addition of the inorganic flocculant can be started and stopped by opening and closing the valve 9A. In other words, the chemical injection module 9 is equipped with a "first external chemical injection means" that adds the inorganic flocculant to the point where turbulence is formed in the treatment liquid.

[0044] One of the three branched inorganic flocculant flow paths 66 is connected to the treatment liquid flow path 51 upstream of the line mixer 90. A valve 9B is provided in the flow path 66 connected upstream of the line mixer 90, so that the addition of the inorganic flocculant can be started and stopped by opening and closing the valve 9B. In other words, the chemical injection module 9 is equipped with a "second external chemical injection means" that adds the inorganic flocculant upstream of the point where the line mixer 90 creates turbulence in the treatment liquid.

[0045] One of the three branched inorganic flocculant flow paths 66 is connected to the treatment liquid flow path 51 downstream of the line mixer 90. This connection downstream of the line mixer 90 may be to an area where turbulence created by the line mixer 90 remains, or may be after the turbulence created by the line mixer 90 has disappeared. Preferably, it is connected to an area where turbulence created by the line mixer 90 remains. A valve 9C is provided in the flow path 66 connected downstream of the line mixer 90, so that the addition of the inorganic flocculant can be started and stopped by opening and closing the valve 9C. In other words, the chemical injection module 9 is equipped with a "third external chemical injection means" that adds the inorganic flocculant downstream of the point where the line mixer 90 creates turbulence in the treatment liquid.

[0046] The first to third external chemical feeding means can be switched to add inorganic flocculant from any one of the external chemical feeding means by opening and closing valves 9A and 9B. The opening and closing of valves 9A and 9B as switching control may be performed automatically or manually. The inorganic flocculant may be added from more than one of the first to third external chemical feeding means, not just one. In this case, the ratio of the added amounts may be adjusted. Furthermore, the number of external chemical feeding means is not limited to three, the first to third external chemical feeding means, but additional external chemical feeding means may be added upstream and / or downstream. Chemical feeding module 9 may have a configuration similar to that of polymer flocculant feeding module 70 shown in Figures 2 and 3.

[0047] A flow path 66 for the inorganic flocculant connected to the chemical injection module 9 is provided with a valve 67 as a flow rate adjusting means, and the flow rate of the chemical injected outside the machine is adjusted by adjusting the opening of the valve 67. Furthermore, a flow meter 68 is provided in the flow path 66 so that the flow rate of the chemical injected outside the machine can be measured. However, the valve 67 is only one example of a flow rate adjusting means, and is not limited to this, and other configurations may be used as long as the flow rate can be adjusted. For example, a metering pump that can variably set the flow rate can be cited as another example.

[0048] The inorganic chemical injection device 6 further includes a flow rate ratio control unit 69 that controls the supply rates of external chemical injection and internal chemical injection. The flow rate ratio control unit 69 can be configured, for example, by a computer system including a CPU, memory, and other storage devices. The flow rate ratio control unit 69 may be installed near the decanter 2 as a control panel, or may be configured so that its functions are fulfilled by a system installed in a central monitoring room. Of course, instead of automatic control by the flow rate ratio control unit 69, the flow rate ratio control may be manual control in which an operator manually adjusts the openings of the valves 62, 67 while checking the flow meters 63, 68.

[0049] By configuring the inorganic chemical injection device 6 in this manner, it is possible to execute the chemical injection optimization method shown in Figure 4, for example, in the same way as the polymer chemical injection device 7. Therefore, with the decanter 2 of the second embodiment, it is possible to optimize the external chemical injection while controlling the ratio of the external and internal chemical injection amounts for both the polymer coagulant and the inorganic coagulant. Note that it is not necessary to pass the chemical through two line mixers 90, 8. For example, a valve and a bypass flow path with a valve may be provided at the base of the line mixer 90 and the line mixer 8, respectively, and only one of the line mixers 90 or 8 may be used by opening or closing the valve.

[0050] (Third embodiment) Next, a decanter 2 according to a third embodiment will be described. The decanter 2 of this embodiment has the same configuration as the decanter 2 of the first embodiment, except that the decanter 2 of this embodiment is configured so that the polymer-based flocculant is only fed externally. Therefore, the same components as in the first embodiment are given the same reference numerals and detailed descriptions will be omitted. The decanter 2 of this embodiment is shown in FIG. 6. Even with this configuration, as with the decanter 2 of the first embodiment, it is possible to optimize the external feeding of the polymer-based flocculant while controlling the ratio of the feeding amounts of the external feeding and the internal feeding.

[0051] (Fourth embodiment) Next, a decanter 2 according to a fourth embodiment will be described. The decanter 2 of this embodiment has the same configuration as the decanter 2 of the first embodiment, except that the addition of flocculant is performed only by external injection of a polymer-based flocculant. Therefore, the same components as those of the first embodiment are designated by the same reference numerals, and detailed description thereof will be omitted. The decanter 2 of this embodiment is shown in FIG. 7. Even with this configuration, it is possible to optimize the external injection of the polymer-based flocculant, as with the decanter 2 of the first embodiment. Note that in-machine injection may be omitted in FIG. 7, and only external injection of the polymer-based flocculant may be performed. In other words, the combination of external injection and / or internal injection of a polymer-based flocculant and / or an inorganic flocculant may be performed as long as external injection is included in at least one of the polymer-based flocculant and the inorganic flocculant, and combination patterns other than those of the first to fourth embodiments are not excluded.

[0052] (Fifth embodiment) Next, a decanter 2 according to a fifth embodiment will be described. The decanter 2 of this embodiment has the same configuration as the decanters 2 of the first to fourth embodiments, except that chemical injection optimization is realized by utilizing a treatment liquid piping (i.e., flow path 51) installed in, for example, a sewage treatment plant, instead of the chemical injection module 70 (including the line mixer 8), an example of which is shown in Fig. 2. Therefore, the same components as those of the first to fourth embodiments are denoted by the same reference numerals, and detailed description thereof will be omitted.

[0053] That is, the size and height of the space in which the decanter 2 is installed, and its relative position to the ancillary equipment (for example, the relative position of the coagulant pump 74) are not always the same, so piping design is performed, including the piping route of the treatment liquid arranged from the coagulant pump 74 to the decanter 2, and the installation positions of piping joints such as elbows and valves. In this embodiment, the piping shape of the treatment liquid is used to realize optimization of the chemical dosing of the polymer coagulant.

[0054] Figure 8 shows an example of a piping system after actual optimization. First, the points where turbulence occurs in the treatment liquid are identified within the piping. In the example shown in Figure 8, it was confirmed that turbulence occurs due to a reducer R, a type of pipe joint. Therefore, addition position A, where turbulence occurs due to reducer R, is set as the point where turbulence is formed in the treatment liquid, and the polymer flocculant piping (i.e., flow path 71) is connected thereto. In other words, this is defined as the "first external chemical supply means" that adds the polymer flocculant to the point where turbulence is formed in the treatment liquid. Addition position A is, for example, 5 m away from decanter 2. As mentioned above, the piping length can be used as a parameter for ensuring and adjusting the flocculation reaction time (= length / flow rate). Therefore, reducer R may be intentionally set at a position 5 m away.

[0055] Next, a pipe for a polymeric flocculant (i.e., flow path 71) is connected to addition position B upstream of reducer R, forming a "second external chemical supply means" that adds the polymeric flocculant upstream of the point where turbulence is formed in the treatment liquid due to reducer R. Addition position B is set, for example, 10 m away from decanter 2 to allow time for the flocculation reaction.

[0056] Next, a pipe for a polymer-based flocculant (i.e., flow path 71) is connected to addition position C downstream of reducer R, forming a "third external chemical supply means" that adds the polymer-based flocculant downstream of the point where turbulence is formed in the treatment liquid due to reducer R. Addition position C is set, for example, 2 m away from decanter 2. Preferably, addition position C is set in the pipe extending from bottom to top toward decanter 2.

[0057] Furthermore, a pipe for a polymeric flocculant (i.e., flow path 71) is connected to addition position D upstream of reducer R, forming a "fourth external chemical supply means" that adds the polymeric flocculant further upstream of the point where turbulence is formed in the treatment liquid due to reducer R. Addition position D is set, for example, 15 m away from decanter 2 in order to secure a long flocculation reaction time. Note that it is preferable that the addition position not be set more than 15 m away.

[0058] The first to fourth external chemical feeding means can switch which external chemical feeding means to add the polymer flocculant from by opening and closing a valve. The opening and closing of the valve as switching control may be performed automatically or manually. The addition of the polymer flocculant is not limited to one of the first to fourth external chemical feeding means, but may be added from multiple means. In this case, the ratio of the amounts added may be adjusted. Furthermore, the number of external chemical feeding means is not limited to four, the first to fourth external chemical feeding means, but additional external chemical feeding means may be added upstream and / or downstream.

[0059] By setting the first to fourth external chemical feeding means in this manner, it is possible to execute, for example, the chemical feeding optimization method shown in FIG. 4. First, one of the first to third external chemical feeding means is selected to be used for chemical feeding. As an example, chemical feeding is performed from the nth external chemical feeding means (n=1) (Act 10). When solid-liquid separation in the decanter 2 stabilizes, flow rate ratio control is executed (Act 11). As an example of flow rate ratio control, the flow rate ratio control unit 79 changes the opening of the above-mentioned valves 72 and 77 (valve 72: 0% → 100%, valve 77: 100% → 0%), for example, every hour, in intervals of 25%, and each time, checks the moisture content of the dehydrated cake (solid content) and / or the state of the separated liquid (SS concentration, color, foam, pH, etc.) (Act 12). If the results tend to improve, the opening is further changed; if the results tend to worsen, the opening is reversed. By repeating this back and forth, the optimal balance between external and internal chemical injection is achieved.

[0060] Next, n=n+1 (Act13 No, Act14) is set, and chemical is added from the nth external chemical feeding means (n=2) (Act10). Further, flow rate ratio control is executed (Act11), and the moisture content of the dehydrated cake and / or the state of the separated liquid (SS concentration, color, foam, pH, etc.) are confirmed (Act12). Similarly, n=n+1 (Act13 No, Act14) is set, and chemical is added from the nth external chemical feeding means (n=3) (Act10). Further, flow rate ratio control is executed (Act11), and the moisture content of the dehydrated cake and / or the state of the separated liquid (SS concentration, color, foam, pH, etc.) are confirmed (Act12). Similarly, n=n+1 (Act13 No, Act14) is set, and chemical is added from the nth external chemical feeding means (n=4) (Act10). Furthermore, the flow rate ratio control is executed (Act 11), and the moisture content of the dehydrated cake and / or the state of the separated liquid (SS concentration, color, foam, pH, etc.) are confirmed (Act 12).

[0061] When the flow rate ratio control is completed for all of the first to fourth external chemical feeding means (Act 13 Yes), it is determined which external chemical feeding means had the best moisture content of the dehydrated cake (the separated solid content) and / or the state of the separated liquid (SS concentration, color, foam, pH, etc.), and the subsequent operation (for example, throughout the day) is started from the external chemical feeding means with the best performance (Act 15). It is preferable to continue the flow rate ratio control in the subsequent operation.

[0062] According to the above-described embodiment, it is possible to optimize the external chemical injection of polymer flocculants by utilizing the piping geometry of the treatment liquid. In this way, by identifying turbulent flow-generating points in the piping and theoretically determining the injection locations, preferably by determining the optimal injection locations according to the flow chart shown in Figure 4, it is possible to efficiently optimize the external chemical injection. As a result, the number of injection locations can be reduced, avoiding situations where no effective injection is obtained despite trial and error. While the point where turbulence occurs due to the reducer R is determined as the point where turbulence occurs in the treatment liquid, this is not limited to this, and it may also be determined as the point where turbulence occurs due to other pipe fittings or valves, such as elbows. In other words, it is preferable to select a point where turbulence occurs frequently in an actual piping system. Furthermore, while a polymer-based flocculant has been described as a preferred example of the fifth embodiment, it may also be applied to inorganic flocculants.

[0063] Although the present invention has been described in detail with reference to specific embodiments, it will be apparent to those skilled in the art that various substitutions, modifications, changes, etc. in form and detail can be made therein without departing from the spirit and scope of the invention as defined by the appended claims. [Explanation of symbols]

[0064] 2 decanters 3 bowls 4. Screw conveyor 6 Inorganic chemical dosing device 7 Polymer-based chemical injection device 70 Chemical injection module 71A, 71B, 71C valves 79 Flow ratio control unit 8 Line Mixer 82 Turbulence forming member

Claims

1. A centrifugal separator including a bowl that rotates to separate a treatment liquid therein into solid and liquid, a screw conveyor that transports solids separated in the bowl toward a discharge outlet, and a chemical feeder that adds a flocculant to the treatment liquid, The chemical injection device comprises a first external chemical injection means that adds the flocculant by a line injection method to the flow path of the treatment liquid before it is supplied to the bowl at a point where turbulence is formed in the treatment liquid, a second external chemical injection means that adds the flocculant by a line injection method to a location upstream of the point where the turbulence is formed but not at the point where the turbulence is formed, and a third external chemical injection means that adds the flocculant by a line injection method to a location downstream of the point where the turbulence is formed but not at the point where the turbulence is formed, and is characterized in that the centrifuge device is capable of switching from which addition position the flocculant is added among the first to third external chemical injection means.

2. 2. The centrifugal separator according to claim 1, wherein the point at which the turbulent flow is formed is a line mixer disposed in the flow path of the treatment liquid.

3. 2. The centrifugal separator according to claim 1, wherein the point at which the turbulent flow is formed is either a joint member or a valve of a pipe that constitutes the flow path of the processing liquid.

4. The centrifuge device according to any one of claims 1 to 3, characterized in that the chemical injection device includes an external chemical injection device that adds the flocculant to the treatment liquid before it is supplied into the bowl, and an internal chemical injection device that adds the flocculant to the treatment liquid supplied into the bowl, and variably controls the ratio between the external chemical injection amount and the internal chemical injection amount, and switches and controls to select an addition position of the first to third external chemical injection means at which the external chemical injection is performed.

5. A method for operating a centrifugal separator including a bowl that rotates to separate a treatment liquid therein into solid and liquid, a screw conveyor that transports solids separated in the bowl toward a discharge outlet, and a chemical feeder that adds a flocculant to the treatment liquid, comprising: a process of comparing the solid-liquid separation state when the flocculant is added by the line injection method to a point where turbulence is formed in the treatment liquid before the treatment liquid is supplied to the bowl, the solid-liquid separation state when the flocculant is added by the line injection method to a point upstream of the point where turbulence is formed but not at the point where turbulence is formed, and the solid-liquid separation state when the flocculant is added by the line injection method to a point downstream of the point where turbulence is formed but not at the point where turbulence is formed; and a step of determining from which addition position the flocculant should be added based on the results of the comparison.

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