Treatment system and control method of the same

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 including an addition unit that adds a flocculant to an object to be treated to form a floc, and a solid-liquid separation unit that separates the floc into a concentrate by solid-liquid separation, wherein the solid-liquid separation unit is configured as a screw press type that separates the floc by rotationally driving a screw, and a control method thereof.

Background Art

[0002] As a treatment system for reducing the volume of objects to be treated such as sewage sludge and biomass, a flocculant such as a polymer flocculant is added to the object to be treated to aggregate the solid content of the object to be treated contained therein to form floc flocs (also referred to as "coarse flocs"), and the flocs containing such floc flocs are solid-liquid separated by a solid-liquid separation unit configured as a screw press type to produce a concentrate with a reduced water content. 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 floc 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 desired 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, 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 is known (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 the 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 the lower limit liquid level that is 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, the properties of the flocculant formed in the flocculated matter obtained by adding the flocculant, such as the viscosity, fineness, and strength of the flocculated flocs (hereinafter referred to as "flocculated floc properties"), change. When the ease of swallowing the flocculated matter in the solid-liquid separation section changes due to the change in the flocculated floc properties, 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, resulting in unstable solid-liquid separation performance in the solid-liquid separation section. In addition, in the processing system described in Patent Document 1, the reference rotational 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 a 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 rotational speed of the screw is set to the reference rotational speed, the liquid level in the inlet-side storage section is likely to deviate from the reference liquid level, which may cause the rotational speed of the screw to be frequently changed, resulting in unstable solid-liquid separation performance in the solid-liquid separation section. 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. The solid-liquid separation section is configured as a screw press type that separates the aggregates by rotational driving of a screw, and is a processing system, 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 that measures the liquid level of the aggregates in the inlet-side storage section, which is the inlet-side storage section liquid level, 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. It is characterized in that it includes a control unit for executing the process. Further, the 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 separating the agglomerates into a solid-liquid separation to obtain a concentrate. It is a control method of a processing system in which the solid-liquid separation section is configured in a screw press type in which the agglomerates are solid-liquid separated by the rotational drive of 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 introduced into 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 agglomerates to the inlet-side storage section and the discharge of 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. Then, 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 satisfactorily performing solid-liquid separation while suppressing a sudden change 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 moisture content of the concentrate can be decreased 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 aggregate 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. At the same time, 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, the screw rotation speed is increased by a predetermined increase correction width. That is, the screw rotation speed increase process 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 drops back to the supply return determination value within the set range. In this state, the discharge of the aggregate from the inlet side storage unit to the solid-liquid separation unit side is maintained in the state during normal operation, and the supply of the aggregate 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 increase 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 reduced. Thus, in the solid-liquid separation unit, the screw rotation speed is gradually corrected to the increase side to improve the ingestion of the aggregate from the inlet side storage unit in the solid-liquid separation unit, and the overflow of the aggregate from the inlet side storage unit can be avoided.

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 an object to be processed) containing sludge supplied from a front-stage processing unit 1 such as a sludge storage tank, a sludge supply pump, or 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) and a solid-liquid separation unit 10 that separates the flocculated sludge S2 to which the flocculant F has been added into concentrated sludge S3 (an example of a concentrate) are provided. 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 it is 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 object to be processed, but biomass or the like may be used as the object 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 particular clear distinction between the concentration device and the dehydration device, generally, a device that gives a higher solid concentration of the processed product 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 by the solid-liquid separation unit 10. Note that 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 either 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 once 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 once stored in the outlet-side hopper 23, and the concentrated sludge S3 stored in the outlet-side hopper 23 is introduced into a subsequent treatment unit 30 such as a transfer pump or a dehydration device. Note that 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 a 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. 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. As a result, the inlet-side hopper internal liquid level li is returned within the set range. Further, 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. As a result, 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, it is possible to maintain 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, and to perform good solid-liquid separation while suppressing sudden fluctuations 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 each of these 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 the screw rotation temporary suppression process as the above temporary suppression process and executes the screw rotation speed decrease 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 where the determination value Li4 or more and the determination value Li2 or less is set as a setting range, and 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 becomes a predetermined rotation restoration determination value Li2 within the said setting range, it is a process which temporarily suppresses the rotational drive of the screw 12 in the solid-liquid separation part 10. This screw rotation temporary suppression process is comprised by 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 rotational drive of the screw 12 in the solid-liquid separation part 10 is stopped in a form suppressed more than in the immediately preceding 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 part 10 side is suppressed more than in the steady operation, the supply of the flocculated sludge S2 from the previous treatment part 1 side to the inlet side hopper 20 is maintained in the state during the steady operation, so the liquid level li in the inlet side hopper rises. And in the state where the rotational drive of the screw 12 is suppressed (step #1-05), when it is determined (yes in step #1-06) that the liquid level li in the inlet side hopper has risen to be the rotation restoration determination value Li2 or more, the rotational drive of the screw 12 is restored to the state during the steady operation (step #1-11). Thus, by temporarily suppressing the rotational 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 including the rotation restoration determination value Li2 and being the rotation suppression determination value Li4 or more 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 as a ratio based on 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 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, the residence time of the flocculated sludge S2 is increased, and the water content of the concentrated sludge S3 can be decreased 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 a supply failure of the flocculated sludge S2 from the previous processing unit 1 has occurred (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, an unnecessary decrease in the screw rotation speed r can be reasonably avoided.

[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 inhibition process in the second screw control, a range of not less than the determination value Li3 and not more than the determination value Li1 is set as the setting range, and after the liquid level li in the inlet side hopper exceeds the supply inhibition determination value Li1 which is the upper limit value of the setting range until it reaches a predetermined supply return determination value Li3 within the said setting range, the supply of the coagulated sludge S2 to the inlet side hopper 20 is temporarily inhibited. This coagulated sludge supply temporary inhibition 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 inhibition 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 inhibition determination value Li1, the operation of the sludge supply pump (not shown) in the previous treatment unit 1 is stopped, and the supply of the coagulated sludge S2 from the previous treatment unit 1 side to the inlet side hopper 20 is stopped in a form more inhibited than during the previous steady operation (step #2-05). Then, while the supply of the coagulated sludge S2 from the previous treatment unit 1 side to the inlet side hopper 20 is in a state more inhibited than during the steady operation, 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 during the steady operation, so 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 to not more than the supply return determination value Li3 in the state where the supply of the coagulated sludge S2 is inhibited (step #2-05), the supply of the coagulated sludge S2 to the inlet side hopper 20 is restored to the state during the steady operation (step #2-11). In this way, by temporarily inhibiting 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 setting range including the supply return determination value Li3 and not more than the supply inhibition determination value Li1 as much as possible. In the temporary suppression process of coagulated sludge supply according to the present embodiment, when suppressing the supply of 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 coagulated sludge S2 to the inlet side hopper 20, which is more suppressed than during steady operation. However, within the range where the liquid level li in the inlet side hopper can be lowered, the supply of coagulated sludge S2 to the inlet side hopper 20 may be continued in a smaller amount than during steady operation and be more suppressed than during steady operation.

[0031] (Screw rotation speed increase process) The screw rotation speed increase process in the second screw control is a process of increasing the screw rotation speed r by a predetermined increase correction width B2 when the supply suppression count n2 indicating the execution frequency of the coagulated sludge supply temporary suppression process reaches a predetermined supply suppression count determination value N2a (for example, 1 time). 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 within the adjustable range of the screw rotation speed r and shows 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 increase correction width B2 with respect to the screw rotation speed r can also 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 the increase correction width B2 (step #2-09), and the number of supply suppression times n2 is reset to 0 (step #2-10). As a result, 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 by 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 by 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 make the increase in the screw rotation speed r by the screw rotation speed increase process of the second screw control have a higher priority than the decrease in the screw rotation speed r by the screw rotation speed decrease process of the first screw control (see FIG. 2).

[0035] Therefore, in the present embodiment, in order to preferentially execute the increase in the screw rotation speed r 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 Treatment 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 Screw rotation suppression count (screw rotation suppression frequency) n2 Supply suppression count (supply suppression frequency) r Screw rotation speed B1 Decrease correction width B2 Increase correction width Li1 Judgment value for supply suppression (upper limit value of the set range) Li2 Judgment value for rotation restoration Li3 Judgment value for supply restoration Li4 Judgment value for rotation suppression (lower limit value of the set range) N1a Screw rotation suppression count judgment value (screw rotation suppression frequency judgment value) N2a Supply suppression count judgment value (supply suppression frequency judgment value)

Claims

1. A treatment system comprising an addition unit that adds a flocculant to an 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 as a screw press type that separates the flocs by rotational driving of a screw, 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, 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 a control unit that, when the inlet side storage unit liquid level deviates from a predetermined set range, executes a temporary suppression process of suppressing the supply of the flocs from the flocculant addition unit side to the inlet side storage unit or suppressing the discharge of the flocs from the inlet side storage unit to the solid-liquid separation unit side to return the inlet side storage unit liquid level within the set range, and executes a screw rotation speed correction process of correcting the rotation speed of the screw in the solid-liquid separation unit so that the execution frequency decreases based on the execution frequency of the temporary suppression process.

2. The treatment system according to claim 1, wherein the control unit, as the temporary suppression process, executes a screw rotation temporary suppression process of temporarily suppressing 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, and as the screw rotation speed correction process, executes a screw rotation speed decrease process of decreasing the screw rotation speed by a predetermined decrease correction width 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.

3. The treatment system according to claim 1 or 2, wherein the control unit, as the temporary suppression process, executes a floc supply temporary suppression process of temporarily suppressing the supply of the flocs to the inlet side storage unit from when the inlet side storage unit liquid level exceeds the upper limit value of the set range until it reaches a predetermined supply return determination value within the set range, and as the screw rotation speed correction process, executes a screw rotation speed increase process of increasing the screw rotation speed by a predetermined increase correction width when the supply suppression frequency, which is the execution frequency of the floc supply temporary suppression process, reaches a predetermined supply suppression frequency determination value.

4. An addition section that adds a flocculant to an object to be processed to form flocs, and a solid-liquid separation section that separates the flocs into a concentrate by solid-liquid separation. A control method for a processing system configured in a screw press type in which the solid-liquid separation section separates the flocs by rotationally driving a screw, Measure the liquid level of the flocs in the inlet-side storage section installed on the inlet side of the solid-liquid separation section and storing the flocs to be input into the solid-liquid separation section, that 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, suppress the supply of the flocs from the flocculant addition section side to the inlet-side storage section, or suppress the discharge of the flocs from the inlet-side storage section to the solid-liquid separation section side, and execute a temporary suppression process to return the liquid level in the inlet-side storage section to within the set range. At the same time, execute a screw rotation speed correction process for correcting 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. A control method for a processing system characterized by this.

Images