Processing system and control method thereof

Abstract

To provide a treatment system for adding a coagulant agent to an object to be treated and performing solid-liquid separation in a screw press type solid-liquid separation part, which continues to supply a coagulant to an inlet side storage part or discharge a coagulant from the inlet side storage part without suppression as much as possible, and satisfactorily performs solid-liquid separation while suppressing the sudden change of the state of the coagulant in the solid-liquid separation part.SOLUTION: A treatment system executes: temporal suppression treatment of measuring a liquid level Li in an inlet side storage part of a coagulant S2 in an inlet side storage part 20 of a solid-liquid separation part 10, suppressing supply of the coagulant S2 to the inlet side storage part 20 from the side of a coagulant addition part 2, or discharge of the coagulant S2 to the solid-liquid separation part 10 from the inlet side storage part 20, when the liquid level Li in the inlet side storage part is deviated from a predetermined set range, and returning the liquid level Li in the inlet side storage part to the set range; and screw rotation speed correction treatment of correcting the rotation speed of a screw 12 in the solid-liquid separation part 10 so that the execution frequency of the temporal suppression treatment is lowered on the basis of the execution frequency.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a treatment system comprising an addition unit that adds a flocculant to a material to be treated to form flocs, and a solid-liquid separation unit that separates the flocs into a concentrate by solid-liquid separation, wherein the solid-liquid separation unit is configured in a screw press type that separates the flocs by rotationally driving a screw, and a control method therefor.

Background Art

[0002] As a treatment system for reducing the volume of materials to be treated such as sewage sludge and biomass, a flocculant such as a polymer flocculant is added to the material to be treated to aggregate the solid content of the material to be treated contained therein to form flocculant flocs (also referred to as "coarse flocs"), and the flocs containing such flocculant flocs are separated into a concentrate with a reduced water content by solid-liquid separation using a solid-liquid separation unit configured in a screw press type. In such a treatment system, an inlet-side storage unit such as a hopper for temporarily storing the flocs immediately before being introduced into the solid-liquid separation unit is provided on the inlet side of the flocs solid-liquid separation unit. Then, in order to avoid overflow of the flocs from the inlet-side storage unit while continuously feeding the flocs into the solid-liquid separation unit, it is desirable to maintain the liquid level in the inlet-side storage unit, which is the liquid level of the flocs in the inlet-side storage unit, within an appropriate range. Therefore, as a conventional treatment system, there is known one that controls the rotational speed of the screw in the solid-liquid separation unit based on the liquid level in the inlet-side storage unit (see, for example, Patent Document 1).

[0003] In the processing system described in Patent Document 1 above, when the liquid level in the inlet-side storage section is the reference liquid level, the rotation speed of the screw is set to a reference rotation speed determined in advance at startup. Then, when the liquid level in the inlet-side storage section falls below the reference liquid level, the rotation speed of the screw is decreased from the reference rotation speed, and when the liquid level in the inlet-side storage section exceeds the reference liquid level, the rotation speed of the screw is increased from the reference rotation speed. Further, when the liquid level in the inlet-side storage section drops to a lower limit liquid level lower than the reference liquid level, the rotational drive of the screw is temporarily stopped until the liquid level in the inlet-side storage section returns to the reference liquid level.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In the processing system described in Patent Document 1 above, the rotation speed of the screw when the liquid level in the inlet-side storage section is the reference liquid level is always the reference rotation speed determined in advance, and it is not changed. Therefore, for example, due to fluctuations in the addition rate of the flocculant to the object to be processed, etc., the properties of the flocculent flock formed in the flocculant obtained by adding the flocculant, such as viscosity, fineness, and strength (hereinafter referred to as "flocculent flock properties"), change, and due to the change in the flocculent flock properties, the ease of swallowing the flocculant in the solid-liquid separation section changes. In such a case, even if the rotation speed of the screw is set to the reference rotation speed, the liquid level in the inlet-side storage section is likely to deviate from the reference liquid level, and as a result, the rotation speed of the screw is frequently changed, and the solid-liquid separation performance in the solid-liquid separation section may become unstable. In addition, in the processing system described in Patent Document 1, the reference rotation speed of the screw that can maintain the liquid level in the inlet-side storage section at the reference liquid level at startup is determined. However, in the screw press type solid-liquid separation section, the solid-liquid separation performance gradually improves from startup, and the ingestion of aggregates from the inlet-side storage section also gradually improves. Therefore, after a certain period of time has elapsed since startup, even if the rotation speed of the screw is set to the reference rotation speed, the liquid level in the inlet-side storage section is likely to deviate from the reference liquid level, which may cause the rotation speed of the screw to be frequently changed and the solid-liquid separation performance in the solid-liquid separation section to become unstable. In view of this actual situation, the main problem of the present invention is to provide a technology that can maintain the state during steady operation without suppressing the supply of aggregates to the inlet-side storage section or the discharge of aggregates from the inlet-side storage section as much as possible, and can perform good solid-liquid separation while suppressing sudden changes in the state of aggregates in the solid-liquid separation section in a processing system that adds a flocculant to the object to be processed and performs solid-liquid separation in a screw press type solid-liquid separation section.

Means for Solving the Problems

[0006] A first characteristic configuration of the processing system according to the present invention includes an addition section that adds a flocculant to an object to be processed to form aggregates, and a solid-liquid separation section that separates the aggregates into a concentrate by solid-liquid separation, wherein the solid-liquid separation section is configured in a screw press type that separates the aggregates by rotational driving of a screw. An inlet-side storage section installed on the inlet side of the solid-liquid separation section for storing the aggregates input to the solid-liquid separation section. An inlet-side storage section liquid level measurement section for measuring the liquid level of the aggregates in the inlet-side storage section, which is the liquid level in the inlet-side storage section. When the liquid level in the inlet-side storage section deviates from a predetermined set range, the supply of the agglomerates from the flocculant addition section side to the inlet-side storage section is suppressed, or the discharge of the agglomerates from the inlet-side storage section to the solid-liquid separation section side is suppressed, and a temporary suppression process for returning the liquid level in the inlet-side storage section to within the set range is executed. At the same time, a screw rotation speed correction process is executed to correct the rotation speed of the screw in the solid-liquid separation section so that the execution frequency decreases based on the execution frequency of the temporary suppression process. There is a control unit for this. Further, a characteristic configuration of the control method of the processing system according to the present invention includes an addition section for adding a flocculant to the object to be processed to form agglomerates, and a solid-liquid separation section for solid-liquid separating the agglomerates to form a concentrate. A control method for a processing system in which the solid-liquid separation section is configured as a screw press type that solid-liquid separates the agglomerates by rotationally driving a screw. The liquid level in the inlet-side storage section, which is installed on the inlet side of the solid-liquid separation section and stores the agglomerates input to the solid-liquid separation section, is measured. When the liquid level in the inlet-side storage section deviates from a predetermined set range, the supply of the agglomerates from the flocculant addition section side to the inlet-side storage section is suppressed, or the discharge of the agglomerates from the inlet-side storage section to the solid-liquid separation section side is suppressed, and a temporary suppression process for returning the liquid level in the inlet-side storage section to within the set range is executed. At the same time, a screw rotation speed correction process is executed to correct the rotation speed of the screw in the solid-liquid separation section so that the execution frequency decreases based on the execution frequency of the temporary suppression process.

[0007] According to this configuration, when the liquid level in the inlet-side storage section deviates from a predetermined set range, by executing the above temporary suppression process, the supply of the agglomerates to the inlet-side storage section and the discharge of the agglomerates from the inlet-side storage section are suppressed, so that the liquid level in the inlet-side storage section is returned to within the set range. As a result, the liquid level in the inlet-side storage section can be maintained within the set range as much as possible. And by executing the above screw rotation speed correction process, the rotation speed of the screw in the solid-liquid separation section is gradually corrected to the increasing side or the decreasing side based on the execution frequency of the temporary suppression process, and the execution frequency of the temporary suppression process is decreased. Therefore, according to the present invention, in a treatment system in which a flocculant is added to an object to be treated and then solid-liquid separation is performed in a screw press type solid-liquid separation unit, while maintaining the state during steady operation without suppressing the supply of flocs to the inlet side storage unit or the discharge of flocs from the inlet side storage unit as much as possible, it is possible to provide a technique capable of achieving good solid-liquid separation while suppressing sudden fluctuations in the state of the flocs in the solid-liquid separation unit.

[0008] A second characteristic configuration of the treatment system according to the present invention is that, as the temporary suppression process, the control unit temporarily suppresses the rotational drive of the screw in the solid-liquid separation unit from when the liquid level in the inlet side storage unit falls below the lower limit value of the set range until it reaches a predetermined rotational return determination value within the set range, and executes a screw rotation temporary suppression process. As the screw rotation speed correction process, when the screw rotation suppression frequency, which is the execution frequency of the screw rotation temporary suppression process, reaches a predetermined screw rotation suppression frequency determination value, a screw rotation speed decrease process for decreasing the screw rotation speed by a predetermined decrease correction width is executed.

[0009] According to this configuration, when the liquid level in the inlet side storage unit falls below the lower limit value, the screw rotation temporary suppression process is executed until the liquid level in the inlet side storage unit rises and returns to the rotational return determination value within the set range. The supply of flocs from the flocculant addition unit side to the inlet side storage unit is maintained in the state during steady operation, and the discharge of flocs from the inlet side storage unit to the solid-liquid separation unit side is suppressed. Then, the liquid level in the inlet side storage unit can be maintained within the set range as much as possible. And by executing the screw rotation speed decrease process, the rotation speed of the screw in the solid-liquid separation unit is corrected to the decreasing side based on the execution frequency of the screw rotation temporary suppression process, and the execution frequency of the screw rotation temporary suppression process is reduced. By this, in the solid-liquid separation unit, the screw rotation speed can be gradually corrected to the decreasing side, the residence time of the flocs can be increased, and the water content of the concentrate can be reduced as much as possible.

[0010] The third characteristic configuration of the processing system according to the present invention is that, as the temporary suppression process, the control unit temporarily suppresses the supply of the aggregates to the inlet side storage unit from when the liquid level in the inlet side storage unit exceeds the upper limit value of the set range until it reaches a predetermined supply return determination value within the set range, and executes an aggregate supply temporary suppression process. As the screw rotation speed correction process, when the supply suppression frequency, which is the execution frequency of the aggregate supply temporary suppression process, reaches a predetermined supply suppression frequency determination value, a screw rotation speed increase process of increasing the screw rotation speed by a predetermined increase correction width is executed.

[0011] According to this configuration, when the liquid level in the inlet side storage unit exceeds the upper limit value, the aggregate supply temporary suppression process is executed until the liquid level in the inlet side storage unit decreases and returns to the supply return determination value within the set range. In this state where the discharge of aggregates from the inlet side storage unit to the solid-liquid separation unit side is maintained in the state during normal operation, the supply of aggregates from the flocculant addition unit side to the inlet side storage unit is suppressed. Then, the liquid level in the inlet side storage unit can be maintained within the set range as much as possible. And by executing the screw rotation speed increase process, the rotation speed of the screw in the solid-liquid separation unit is corrected to the increasing side based on the execution frequency of the aggregate supply temporary suppression process, and the execution frequency of the aggregate supply temporary suppression process is decreased. Thus, in the solid-liquid separation unit, the screw rotation speed is gradually corrected to the increasing side to improve the ingestion of aggregates from the inlet side storage unit in the solid-liquid separation unit and avoid the overflow of aggregates from the inlet side storage unit.

Brief Description of the Drawings

[0012]

Figure 1

Figure 2

Figure 3

Modes for Carrying Out the Invention

[0013] An embodiment of a processing system and its control method according to the present invention will be described with reference to the drawings. As shown in FIG. 1, in the processing system 100 according to the present embodiment, a flocculant F is added to organic waste S1 (an example of a material to be processed) containing sludge supplied from a front-stage processing unit 1 such as a sludge storage tank, a sludge supply pump, and a concentration device, to form flocculated sludge S2 (an example of a flocculate). A flocculant supply pump 2 (an example of a flocculant addition unit) is provided, and a solid-liquid separation unit 10 is provided for separating the flocculated sludge S2 to which the flocculant F has been added into concentrated sludge S3 (an example of a concentrate). In the present embodiment, the flocculant F is added to the organic waste S1 being stirred in the sludge flocculation tank 5, but it may be added to the organic waste S1 before being supplied to the sludge flocculation tank 5. Then, by stirring the organic waste S1 to which the flocculant F has been added in the sludge flocculation tank 5, the generation of flocculated flocs is promoted, and the flocculated sludge S2 containing the generated flocculated flocs is supplied from the sludge flocculation tank 5 to the subsequent solid-liquid separation unit 10. As the flocculant F, any known flocculant used for sludge flocculation, such as a cationic, amphoteric, or polyamidine polymer flocculant, can be used. In the processing system 100 of the present embodiment, organic waste S1 containing sludge is used as the material to be processed, but biomass or the like may be used as the material to be processed.

[0014] The solid-liquid separation unit 10 is configured to separate the flocculated sludge S2 supplied from the sludge flocculation tank 5 and discharge the concentrated sludge S3 obtained by separating water through the solid-liquid separation. Depending on the degree of concentration, it may be referred to as a concentration device or a dehydration device. Although there is no specific distinction between the concentration device and the dehydration device, generally, a device that gives a higher solid concentration of the processed material after treatment than the concentration device is called a dehydration device. For example, the solid-liquid separation unit 10 that increases the solid concentration of the solid content from about 1% to about 15% is called a concentration device, and a device that gives a higher solid concentration of the solid content than the concentration device is called a dehydration device. In addition, the concentrated sludge S3 corresponds to the concentrated sludge S3 regardless of the solid concentration as long as it is solid-liquid separated in the solid-liquid separation unit 10. As the treatment system 100, examples of the solid-liquid separation unit 10 include those equipped only with a concentration device, those equipped only with a dehydration device, and those equipped with these concentration devices and dehydration devices arranged in parallel in series. However, the characteristic configuration of the present invention is applicable to both or one of the concentration device and the dehydration device. Further, when the concentration device and the dehydration device are provided as the solid-liquid separation unit 10, a sludge transfer pump may be provided for transferring the sludge discharged from the previous-stage concentration device to the subsequent-stage dehydration device.

[0015] The solid-liquid separation unit 10 is configured as a screw press type in which a screw 12 housed in an outer cylinder screen 11 is rotationally driven by a drive motor 13 to pressurize the flocculated sludge S2 introduced from the inlet-side hopper 20 in a pressurizing chamber 15 formed between the outer cylinder screen 11 and the screw 12 for solid-liquid separation, and the concentrated sludge S3 after the solid-liquid separation is discharged to the outlet-side hopper 23.

[0016] In the solid-liquid separation unit 10, an inlet-side hopper 20 (an example of an inlet-side storage unit) for temporarily storing the flocculated sludge S2 is provided on the inlet side where the flocculated sludge S2 is supplied, and an outlet-side hopper 23 for temporarily storing the concentrated sludge S3 is provided on the outlet side where the concentrated sludge S3 is discharged. That is, the flocculated sludge S2 supplied from the sludge flocculation tank 5 is temporarily stored in the inlet-side hopper 20, and the flocculated sludge S2 stored in the inlet-side hopper 20 is swallowed into the pressurizing chamber 15 by the rotational drive of the screw 12. Further, the concentrated sludge S3 discharged from the pressurizing chamber 15 is temporarily stored in the outlet-side hopper 23, and the concentrated sludge S3 stored in the outlet-side hopper 23 is input to a subsequent treatment unit 30 such as a transfer pump or a dehydration device. Incidentally, the outlet-side hopper 23 is usually equipped in the solid-liquid separation unit 10 itself such as a concentration device, but may be an inlet-side hopper of the treatment unit 30 installed in the subsequent stage.

[0017] Furthermore, the inlet-side hopper 20 is provided with a level sensor 21 that functions as an inlet-side hopper internal liquid level measurement unit (an example of an inlet-side storage unit internal liquid level measurement unit) for measuring the inlet-side hopper internal liquid level li (an example of the hopper internal liquid level of the aggregated sludge S2 in the inlet-side hopper 20) which is the liquid level in the hopper of the aggregated sludge S2 in the inlet-side hopper 20.

[0018] The processing system 100 is provided with a control device 50 that controls the operations of the flocculant supply pump 2, the drive motor 13 of the solid-liquid separation unit 10, and the like. And the control device 50 functions as a control unit that executes a temporary suppression process and a screw rotation speed correction process, which will be described later, by executing a predetermined computer program.

[0019] That is, although details will be described later, when the inlet-side hopper internal liquid level li measured by the level sensor 21 deviates from a predetermined set range, the control device 50 suppresses the supply of the aggregated sludge S2 from the previous processing unit 1 side to the inlet-side hopper 20, or suppresses the discharge of the aggregated sludge S2 from the inlet-side hopper 20 to the solid-liquid separation unit 10 side, and executes a temporary suppression process to return the inlet-side hopper internal liquid level li within the set range. By this, the inlet-side hopper internal liquid level li is returned within the set range. Furthermore, the control device 50 executes a screw rotation speed correction process for correcting the rotation speed of the screw 12 in the solid-liquid separation unit 10 so that the execution frequency decreases based on the execution frequency of the above temporary suppression process. By this, the rotation speed of the screw 12 in the solid-liquid separation unit 10 is gradually corrected to the increasing side or the decreasing side based on the execution frequency of the temporary suppression process, and the execution frequency of the temporary suppression process is decreased. Therefore, while maintaining the state during steady operation without suppressing the supply of the aggregated sludge S2 to the inlet-side hopper 20 or the discharge of the aggregated sludge S2 from the inlet-side hopper 20 as much as possible, it is possible to perform good solid-liquid separation while suppressing a sudden change in the state of the aggregated sludge S2 in the solid-liquid separation unit 10. Furthermore, in the control device 50, as screw control including the above temporary suppression process and the above screw rotation speed correction process, a first screw control (see FIG. 2) and a second screw control (see FIG. 3) are executed. Hereinafter, the details of these respective screw controls will be described in order.

[0020] Further, in the following description, as determination values for the liquid level li in the inlet-side hopper, four determination values Li1, Li2, Li3, and Li4 are set in order from the higher side. Also, the timer times t1 and t2 are variables indicating the elapsed time since being reset to 0, and the initial values are set to 0. The determination times T1a and T2a are constants that are determination values for these timer times t1 and t2. The suppression counts n1 and n2 are variables indicating the number of times the supply of the agglomerated sludge S2 to the inlet-side hopper 20 or the discharge of the agglomerated sludge S2 from the inlet-side hopper 20 is suppressed by suppressing the rotational drive of the screw 12 and the supply of the agglomerated sludge S2 to the inlet-side hopper 20 more than during steady operation by executing the temporary suppression process, and the initial values are set to 0. The suppression count determination values N1a and N2a are constants that are determination values for the suppression counts n1 and n2. The screw rotation speed r is a variable set as the rotation speed of the screw 12, and the initial value (i.e., the rotation speed of the screw 12 at startup) is not limited to a specific value but is appropriately set according to the inflow amount of the agglomerated sludge S2 into the solid-liquid separation unit 10, i.e., the throughput. The constants B1 and B2 regarding the correction width set for the screw rotation speed r are both positive numbers greater than 0.

[0021] 〔First Screw Control〕 The first screw control shown in FIG. 2 executes a screw rotation temporary suppression process as the above temporary suppression process and executes a screw rotation speed reduction process as the above screw rotation speed correction process.

[0022] (Screw Rotation Temporary Suppression Process) In the screw rotation temporary suppression process in the first screw control, a range that is equal to or greater than the determination value Li4 and equal to or less than the determination value Li2 is set as the setting range. After the liquid level li in the inlet side hopper falls below the rotation suppression determination value Li4, which is the lower limit value of the setting range, until it reaches a predetermined rotation return determination value Li2 within the setting range, the rotation drive of the screw 12 in the solid-liquid separation unit 10 is temporarily suppressed. This screw rotation temporary suppression process is composed of step #1-03, step #1-05, step #1-06, and step #1-11 shown in FIG. 2.

[0023] That is, in the screw rotation temporary suppression process, as shown in FIG. 2, when it is determined (yes in step #1-03) that the liquid level li in the inlet side hopper has fallen below the rotation suppression determination value Li4, the operation of the drive motor 13 is stopped, and the rotation drive of the screw 12 in the solid-liquid separation unit 10 is stopped in a form that is more suppressed than during the previous steady operation (step #1-05). Then, while the discharge of the flocculated sludge S2 from the inlet side hopper 20 to the solid-liquid separation unit 10 side is more suppressed than during the steady operation, the supply of the flocculated sludge S2 from the previous processing unit 1 side to the inlet side hopper 20 is maintained in the state during the steady operation. Therefore, the liquid level li in the inlet side hopper rises. And when it is determined (yes in step #1-06) that the liquid level li in the inlet side hopper has risen and become equal to or greater than the rotation return determination value Li2 in the state where the rotation drive of the screw 12 is suppressed (step #1-05), the rotation drive of the screw 12 is restored to the state during the steady operation (step #1-11). In this way, by temporarily suppressing the rotation drive of the screw 12 according to the liquid level li in the inlet side hopper, the liquid level li in the inlet side hopper can be maintained within the setting range that is equal to or greater than the rotation suppression determination value Li4 and includes the rotation return determination value Li2 as much as possible. In the screw rotation temporary suppression process of the present embodiment, when suppressing the discharge of the flocculated sludge S2 from the inlet side hopper 20 to the solid-liquid separation unit 10 side, the rotational drive of the screw 12 in the solid-liquid separation unit 10 is stopped, which is more suppressed than during normal operation. However, within the range where the liquid level li in the inlet side hopper can be increased, the rotational drive of the screw 12 can be continued, for example, at the minimum rotational speed, which is more suppressed than during normal operation. It is also possible to continue discharging a small amount of the flocculated sludge S2 from the inlet side hopper 20 in a form that is more suppressed than during normal operation.

[0024] (Screw rotation speed reduction process) In the screw rotation speed reduction process in the first screw control, when the screw rotation suppression count n1 indicating the execution frequency of the above screw rotation temporary suppression process reaches a predetermined screw rotation suppression count determination value N1a (for example, 2 times), the screw rotation speed r is reduced by a predetermined reduction correction width B1. Regarding this reduction correction width B1, it can be determined based on a ratio with respect to the screw rotation speed r before reduction and the maximum screw rotation speed rmax. This ratio can be set within the range of 1 to 20%, preferably within the range of 1 to 10%, and more preferably within the range of 1 to 5%. The above maximum screw rotation speed rmax is the maximum value within the adjustable range of the screw rotation speed r and indicates different values depending on the type and control method of the drive motor 13 and the screw 12. In addition, when performing so-called inverter control to adjust the screw rotation speed r by operating the frequency applied to the drive motor 13, the above-described reduction correction width B1 for the screw rotation speed r can also be determined as the reduction width of the frequency applied to the drive motor 13. For example, in the above inverter control, in principle, the screw rotation speed r increases as the frequency applied to the drive motor 13 increases, and conversely, the screw rotation speed r decreases as the frequency applied to the drive motor 13 decreases. Therefore, the maximum screw rotation speed rmax corresponds to the screw rotation speed r when the frequency applied to the drive motor 13 is maximum. When the maximum value of the frequency applied to the drive motor 13 is 60 Hz, the reduction width of the frequency applied to the drive motor 13 corresponding to the above reduction correction width B1 can be set within the range of 1 to 10 Hz, preferably within the range of 1 to 5 Hz, and more preferably within the range of 1 to 3 Hz. This screw rotation speed reduction process is composed of step #1-01, step #1-02, step #1-04, step #1-07, step #1-08, step #1-09, and step #1-10 shown in FIG. 2.

[0025] That is, in the screw rotation speed reduction process, as shown in FIG. 2, every time it is determined (yes in step #1-03) that the liquid level li in the inlet side hopper has fallen below the rotation suppression determination value Li4 in the above-described screw rotation temporary suppression process and the rotational drive of the screw 12 is stopped (step #1-05), 1 is added to the screw rotation suppression count n1 (step #1-04). Further, when it is determined (no in step #1-01) that the first timer time t1 has reached the first determination time T1a (for example, 60 min), the screw rotation suppression count n1 is reset to 0 together with the first timer time t1. From this, the screw rotation suppression count n1 becomes a value indicating the frequency of screw rotation suppression in which the rotational drive of the screw 12 is suppressed by executing the screw rotation temporary suppression process during the first determination time T1a.

[0026] When it is determined that the number of screw rotation suppression times n1 is equal to or greater than the screw rotation suppression number determination value N1a (yes in step #1-07), the screw rotation speed r is decreased by the decrease correction width B1 (step #1-09), and the number of screw rotation suppression times n1 is reset to 0 (step #1-10). By doing this, in the solid-liquid separation unit 10, the screw rotation speed r is gradually corrected to the decreasing side, increasing the residence time of the flocculated sludge S2 and making it possible to reduce the water content of the concentrated sludge S3 as much as possible.

[0027] Furthermore, in the screw rotation speed decrease process, even when it is determined that the number of screw rotation suppression times n1 is equal to or greater than the screw rotation suppression number determination value N1a (yes in step #1-07), if there is a supply failure of the flocculated sludge S2 from the previous processing unit 1 (yes in step #1-08), assuming that the cause of the decrease in the liquid level li in the inlet side hopper is not that the screw rotation speed r is too high but the supply failure of the flocculated sludge S2, the number of screw rotation suppression times n1 is reset to 0 (step #1-10) without decreasing the screw rotation speed r (step #1-09). By doing this, it is possible to reasonably avoid unnecessary decrease in the screw rotation speed r.

[0028] 〔Second Screw Control〕 The second screw control shown in FIG. 3 executes the flocculated sludge supply temporary suppression process as the above temporary suppression process and executes the screw rotation speed increase process as the above screw rotation speed correction process.

[0029] (Flocculated Sludge Supply Temporary Suppression Process) In the coagulated sludge supply temporary suppression process in the second screw control, a range of the determination value Li3 or more and the determination value Li1 or less is set as a set range, and after the liquid level li in the inlet side hopper exceeds the supply suppression determination value Li1 which is the upper limit value of the set range, until it becomes a predetermined supply return determination value Li3 within the set range, the supply of the coagulated sludge S2 to the inlet side hopper 20 is temporarily suppressed. This coagulated sludge supply temporary suppression process is composed of step #2-03, step #2-05, step #2-06, and step #2-11 shown in FIG. 3.

[0030] That is, in the coagulated sludge supply temporary suppression process, as shown in FIG. 3, when it is determined (yes in step #2-03) that the liquid level li in the inlet side hopper exceeds the supply suppression determination value Li1, the operation of the sludge supply pump (not shown) in the previous processing unit 1 is stopped, and the supply of the coagulated sludge S2 from the previous processing unit 1 side to the inlet side hopper 20 is suppressed more than in the immediately preceding steady operation in such a form that the supply is stopped (step #2-05). Then, while the supply of the coagulated sludge S2 from the previous processing unit 1 side to the inlet side hopper 20 is in a state of being suppressed more than in the steady operation, since the supply of the coagulated sludge S2 from the inlet side hopper 20 to the solid-liquid separation unit 10 side by the rotational drive of the screw 12 is maintained in the state of the steady operation, the liquid level li in the inlet side hopper decreases. And when it is determined (yes in step #2-06) that the liquid level li in the inlet side hopper has decreased and become equal to or less than the supply return determination value Li3 in the state where the supply of the coagulated sludge S2 is suppressed (step #2-05), the supply of the coagulated sludge S2 to the inlet side hopper 20 is restored to the state of the steady operation (step #2-11). In this way, by temporarily suppressing the supply of the coagulated sludge S2 to the inlet side hopper 20 according to the liquid level li in the inlet side hopper, the liquid level li in the inlet side hopper can be maintained within the set range including the supply return determination value Li3 and being equal to or less than the supply suppression determination value Li1 as much as possible. In the coagulated sludge supply temporary suppression process of the present embodiment, when suppressing the supply of the coagulated sludge S2 from the previous treatment unit 1 side to the inlet side hopper 20, the operation of the sludge supply pump in the previous treatment unit 1 is stopped to stop the supply of the coagulated sludge S2 to the inlet side hopper 20, and the suppression is greater than during steady operation. However, within the range where the liquid level li in the inlet side hopper can be decreased, the supply of the coagulated sludge S2 to the inlet side hopper 20 may be suppressed more than during steady operation by continuing the supply in a smaller amount than during steady operation.

[0031] (Screw rotation speed increase process) In the screw rotation speed increase process in the second screw control, when the number of supply suppression times n2 indicating the execution frequency of the coagulated sludge supply temporary suppression process reaches a predetermined supply suppression number determination value N2a (for example, 1 time), the screw rotation speed r is increased by a predetermined increase correction width B2. Regarding this increase correction width B2, it can be determined at a ratio based on the screw rotation speed r before the increase and the maximum screw rotation speed rmax. This ratio can be set within the range of 1 to 20%, preferably within the range of 1 to 10%, and more preferably within the range of 1 to 5%. The maximum screw rotation speed rmax is the maximum value in the adjustable range of the screw rotation speed r and indicates different values depending on the type and control method of the drive motor 13 and the screw 12. Also, when performing so-called inverter control to adjust the screw rotation speed r by operating the frequency applied to the drive motor 13, the above-described increase correction width B2 for the screw rotation speed r can be determined as the increase width of the frequency applied to the drive motor 13. For example, in the above inverter control, in principle, the screw rotation speed r increases as the frequency applied to the drive motor 13 increases, and conversely, the screw rotation speed r decreases as the frequency applied to the drive motor 13 decreases. Therefore, the maximum screw rotation speed rmax corresponds to the screw rotation speed r when the frequency applied to the drive motor 13 is maximum. When the maximum value of the frequency applied to the drive motor 13 is 60 Hz, the increase width of the frequency applied to the drive motor 13 corresponding to the above increase correction width B2 can be set within the range of 1 to 10 Hz, preferably within the range of 1 to 5 Hz, and more preferably within the range of 1 to 3 Hz. This screw rotation speed increase process is composed of step #2-01, step #2-02, step #2-04, step #2-07, step #2-09, and step #2-10 shown in FIG. 3.

[0032] That is, in the screw rotation speed increase process, as shown in FIG. 3, every time it is determined (yes in step #2-03) that the liquid level li in the inlet side hopper exceeds the supply suppression determination value Li1 in the above-described flocculated sludge supply temporary suppression process and the supply of the flocculated sludge S2 is suppressed (step #2-05), 1 is added to the supply suppression count n2 (step #2-04). Also, when it is determined (no in step #2-01) that the second timer time t2 has reached the second determination time T2a (for example, 60 min), the supply suppression count n2 is reset to 0 together with the second timer time t2. From this, the supply suppression count n2 becomes a value indicating the frequency at which the flocculated sludge supply temporary suppression process is executed and the supply of the flocculated sludge S2 is suppressed during the second determination time T2a.

[0033] When it is determined that the number of supply suppression times n2 is equal to or greater than the supply suppression number determination value N2a (yes in step #2-07), the screw rotation speed r is increased by an increase correction width B2 (step #2-09), and the number of supply suppression times n2 is reset to 0 (step #2-10). By doing this, in the solid-liquid separation unit 10, the screw rotation speed r is gradually corrected to increase, so that the ingestion of the flocculated sludge S2 from the inlet side hopper 20 in the solid-liquid separation unit 10 is improved, and the overflow of the flocculated sludge S2 from the inlet side hopper 20 can be avoided.

[0034] In the present embodiment, both the above-described first screw control (see FIG. 2) and the second screw control (see FIG. 3) are executed. The decrease in the screw rotation speed r due to the screw rotation speed decrease process of the first screw control is for the purpose of reducing the water content of the concentrated sludge S3, while the increase in the screw rotation speed r due to the screw rotation speed increase process of the second screw control is for the purpose of avoiding overflow by improving the ingestion of the flocculated sludge S2 from the inlet side hopper 20 in the solid-liquid separation unit 10. From this, it is desirable to set a higher priority for the increase in the screw rotation speed r due to the screw rotation speed increase process of the second screw control than the decrease in the screw rotation speed r due to the screw rotation speed decrease process of the first screw control (see FIG. 2).

[0035] Therefore, in the present embodiment, in order to ensure that the increase in the screw rotation speed r is executed preferentially over the decrease, the supply suppression number determination value N2a (for example, 1 time) used as the determination criterion for the increase in the screw rotation speed r in the screw rotation speed increase process of the second screw control is set to be smaller than the screw rotation suppression number determination value N1a (for example, 2 times) used as the determination criterion for the decrease in the screw rotation speed r in the screw rotation speed decrease process of the first screw control. Furthermore, the increase correction width B2 of the screw rotation speed r in the screw rotation speed increase process of the second screw control is set to be larger than the decrease correction width B1 of the screw rotation speed r in the screw rotation speed decrease process of the first screw control.

Explanation of Signs

[0036] 2 Coagulant supply pump (coagulant addition section) 10 Solid-liquid separation section 12 Screw 20 Inlet side hopper (inlet side storage section) 21 Level sensor (liquid level measurement section in the inlet side storage section) 50 Control device (control section) 100 Processing system S1 Organic waste (object to be treated) S2 Coagulated sludge (coagulated matter) S3 Concentrated sludge (concentrated matter) F Coagulant li Liquid level in the inlet side hopper n1 Number of screw rotation suppression times (screw rotation suppression frequency) n2 Number of supply suppression times (supply suppression frequency) r Screw rotation speed B1 Decrease correction width B2 Increase correction width Li1 Determination value for supply suppression (upper limit value of the set range) Li2 Determination value for rotation return Li3 Determination value for supply return Li4 Determination value for rotation suppression (lower limit value of the set range) N1a Determination value for the number of screw rotation suppression times (determination value for screw rotation suppression frequency) N2a Determination value for the number of supply suppression times (determination value for supply suppression frequency)

Claims

1. An addition unit that adds a flocculant to the object to be treated to form flocs, and a solid-liquid separation unit that separates the flocs into a concentrate by solid-liquid separation, wherein the solid-liquid separation unit is configured in a screw press type that separates the flocs by rotational driving of a screw, and an inlet-side storage unit that is installed on the inlet side of the solid-liquid separation unit and stores the flocs input to the solid-liquid separation unit, and an inlet-side storage unit liquid level measurement unit that measures the liquid level of the flocs in the inlet-side storage unit, which is the inlet-side storage unit liquid level, and when the inlet-side storage unit liquid level falls below the lower limit value of a predetermined set range, the discharge of the flocs from the inlet-side storage unit to the solid-liquid separation unit side is suppressed, and a temporary suppression process for returning the inlet-side storage unit liquid level that has fallen below the lower limit value of the set range to within the set range is executed, and a screw rotation speed correction process for correcting the rotation speed of the screw in the solid-liquid separation unit to the decreasing side so that the execution frequency decreases based on the execution frequency of the temporary suppression process. A processing system comprising a control unit that executes the above.

2. The control unit, as the temporary suppression process, temporarily suppresses the rotational driving of the screw in the solid-liquid separation unit from when the inlet-side storage unit liquid level falls below the lower limit value of the set range until it reaches a predetermined rotation return determination value within the set range. While executing the screw rotation temporary suppression process, as the screw rotation speed correction process, when the screw rotation suppression frequency, which is the execution frequency of the screw rotation temporary suppression process, reaches a predetermined screw rotation suppression frequency determination value, the screw rotation speed reduction process for reducing the screw rotation speed by a predetermined reduction correction width is executed. The processing system according to claim 1.

3. An addition unit that adds a flocculant to the object to be treated to form flocs, and a solid-liquid separation unit that separates the flocs into a concentrate by solid-liquid separation, wherein the solid-liquid separation unit is configured in a screw press type that separates the flocs by rotational driving of a screw, and an inlet-side storage unit that is installed on the inlet side of the solid-liquid separation unit and stores the flocs input to the solid-liquid separation unit, and an inlet-side storage unit liquid level measurement unit that measures the liquid level of the flocs in the inlet-side storage unit, which is the inlet-side storage unit liquid level, and When the liquid level in the inlet-side storage section exceeds the upper limit value of a predetermined set range, the supply of the agglomerates from the flocculant addition section side to the inlet-side storage section is suppressed, and a temporary suppression process is executed to return the liquid level in the inlet-side storage section that has exceeded the upper limit value of the set range to within the set range. At the same time, a screw rotation speed correction process is executed to correct the rotation speed of the screw in the solid-liquid separation section to the increasing side so that the execution frequency decreases based on the execution frequency of the temporary suppression process. A control unit that performs the above is provided.

4. The control unit, as the temporary suppression process, executes an agglomerate supply temporary suppression process that temporarily suppresses the supply of the agglomerates to the inlet-side storage section from when the liquid level in the inlet-side storage section exceeds the upper limit value of the set range until it reaches a predetermined supply restoration determination value within the set range. At the same time, as the screw rotation speed correction process, a screw rotation speed increase process that increases the screw rotation speed by a predetermined increase correction width is executed when the supply suppression frequency, which is the execution frequency of the agglomerate supply temporary suppression process, reaches a predetermined supply suppression frequency determination value. The processing system control method according to claim 3.

5. An addition section that adds a flocculant to the object to be processed to form agglomerates, and a solid-liquid separation section that separates the agglomerates into a solid-liquid separation to obtain a concentrate, are provided. A control method for a processing system, wherein the solid-liquid separation section is configured in a screw press type that separates the agglomerates by rotationally driving a screw. The liquid level in the inlet-side storage section, which is installed on the inlet side of the solid-liquid separation section and stores the agglomerates input to the solid-liquid separation section, is measured. When the liquid level in the inlet-side storage section falls below the lower limit value of a predetermined set range, the discharge of the agglomerates from the inlet-side storage section to the solid-liquid separation section side is suppressed, and a temporary suppression process is executed to return the liquid level in the inlet-side storage section that has fallen below the lower limit value of the set range to within the set range. At the same time, a screw rotation speed correction process is executed to correct the rotation speed of the screw in the solid-liquid separation section to the decreasing side so that the execution frequency decreases based on the execution frequency of the temporary suppression process. A control method for a processing system, characterized by the above.

6. An addition section that adds a flocculant to the object to be processed to form agglomerates, and a solid-liquid separation section that separates the agglomerates into a solid-liquid separation to obtain a concentrate, are provided. A control method for a processing system configured such that the solid-liquid separation unit separates the aggregates by rotational driving of a screw, the method comprising: measuring a liquid level of aggregates in an inlet-side storage unit that is installed on the inlet side of the solid-liquid separation unit and stores the aggregates to be input into the solid-liquid separation unit, the liquid level being the inlet-side storage unit liquid level; when the inlet-side storage unit liquid level exceeds an upper limit value of a predetermined set range, suppressing the supply of the aggregates from the flocculant addition unit side to the inlet-side storage unit, and executing a temporary suppression process for returning the inlet-side storage unit liquid level exceeding the upper limit value of the set range to within the set range, and executing a screw rotation speed correction process for correcting the rotation speed of the screw in the solid-liquid separation unit to increase the execution frequency based on the execution frequency of the temporary suppression process so that the execution frequency decreases. A control method for a processing system characterized by this.

Images