Control method of screw press

Abstract

To provide a control method of a screw press that controls an instrument in accordance with pressure supplied to the screw press, and controls a press-fit pressure and a chemical injection ratio of flocculant so that a differential pressure between a plurality of pressures measured in a supply conduit for an undiluted solution is within a predetermined range.SOLUTION: There is provided a control method of a screw press, which adjusts supply amounts of flocculant in order to control a differential pressure between a first pressure P1 and a second pressure P2 measured in a supply conduit for the screw press to a constant pressure. The method can preferentially decrease used amounts of flocculant by washing an outer cylindrical screen as needed. This can quickly cope with environment-related and hardware-related problems such as fluctuation in properties of flow-in sewage sludge and deterioration in filterability of an instrument so as to enable safe operation to be maintained.SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] The present invention relates to a method for controlling the operation of a screw press, and more particularly to a control method for a screw press that controls based on the difference between the pumping pressure of the stock solution and the pressing pressure at the inlet of the dehydrator in order to stably generate a dehydrated cake discharged from the screw press.

Background Art

[0002] Conventionally, screw presses for concentrating and dehydrating organic sludge such as sewage, night soil, or food production and processing wastewater have been generally known. A screw press is a device that continuously concentrates and dehydrates sludge. Since the properties of sludge vary depending on season, time, weather, etc., control methods for the rotation speed of the screw shaft, the pressing pressure, the coagulant supply amount, etc. are required to maintain stable performance with a screw press.

[0003] For example, in order to control the pressing pressure of the stock solution supplied to a screw press to be constant, a screw press that controls the rotation speed of the stock solution supply pump, the rotation speed of the screw shaft, and the chemical injection rate of the coagulant is described in Patent Document 1. Also, in order to keep the moisture content of the dehydrated cake constant, a screw press is provided with a means for detecting the pressing pressure, a means for detecting the torque of the screw shaft, and a means for controlling the rotation speed of the screw shaft, and controls the rotation speed of the screw shaft based on the detection results of the pressing pressure and the torque, as described in Patent Document 2.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] Organic sludge such as sewage, night soil, or food production and processing wastewater, which is concentrated and dewatered by a screw press, varies in properties moment by moment depending on season, weather, time, etc. Various controls have been performed on the operation of the screw press or the conditioning of the sludge in response to this variation.

[0006] The control method of Patent Document 1 determines based only on the injection pressure of the sludge supplied to the screw press. Since the detection position is near the inlet of the screw press, the measured value is greatly affected by factors related to the filterability of the screw press, and it is difficult to determine factors caused by fluctuations in the properties of the raw solution or deterioration of the aggregation state.

[0007] The control method of Patent Document 2 detects not only the injection pressure at the inlet of the screw press but also the torque of the screw shaft to control the equipment, so it is easier to grasp the filtration state inside the filtration chamber. However, since the torque of the screw shaft changes greatly due to the aging deterioration of the rotating equipment and the friction between the screw blades and the filter cylinder, accurate judgment is difficult.

[0008] The present invention provides a control method for a screw press that can quickly respond to environmental and hardware aspects such as fluctuations in the properties of incoming sewage sludge and deterioration of the filterability of the equipment, and maintain stable operation.

Means for Solving the Problems

[0009] In a control method for a screw press that controls the press-fitting pressure supplied to the screw press to be constant, a reference pressure for press-fitting into the screw press in advance, a reference differential pressure between a first pressure and a second pressure measured in the supply pipeline of the stock solution, a reference supply amount of the flocculant, a maximum supply amount that is the maximum value of the supply amount, a minimum supply amount that is the minimum value of the supply amount, and a supply amount width that is increased or decreased step by step are set. When the differential pressure between the first pressure and the second pressure measured in the supply pipeline of the stock solution is within the range of the reference differential pressure, the operation of the screw press is continued. When the differential pressure is smaller than the reference differential pressure, the chemical liquid supply pump is adjusted to decrease the supply amount of the flocculant by the supply amount width, and this operation is repeated until the differential pressure increases within the range of the reference differential pressure. When the differential pressure is larger than the reference differential pressure, the outer cylinder screen is cleaned. Then, when the differential pressure does not decrease within the range of the reference differential pressure, the chemical liquid supply pump is adjusted to increase the supply amount of the flocculant by the supply amount width, and this operation is repeated until the differential pressure decreases within the range of the reference differential pressure. The differential pressure between the first pressure and the second pressure measured in the supply pipeline of the stock solution is controlled within the range of the reference differential pressure. The dehydration status is analyzed from the differential pressure of the supply pipeline, and stable dehydration operation is performed while preferentially reducing the usage amount of the expensive flocculant.

[0010] Also, when a first pressure gauge is installed near the stock solution supply pump in the stock solution supply pipeline of the stock solution to measure the first pressure, and a second pressure gauge is installed immediately before the screw press to measure the second pressure, the dehydration status can be measured in real time from the pressure fluctuations other than the pipe loss.

[0011] Also, when a coagulation mixing tank is provided in the stock solution supply pipeline, a first pressure gauge is installed in the supply pipeline on the upstream side of the coagulation mixing tank to measure the first pressure, and a second pressure gauge is installed in the supply pipeline on the downstream side of the coagulation mixing tank to measure the second pressure, the fluctuations in the environmental aspect and the hardware aspect can be measured in real time with each pressure gauge.

Advantages of the Invention

[0012] Since the present invention is controlled based on the difference between the pressure for pumping the stock solution and the press-fitting pressure at the inlet of the dehydrator, it is possible to detect in real time the deterioration of the environmental aspect (stock solution) or the hardware aspect (dehydration device), and execute the control for the stable operation of the equipment.

Brief Description of the Drawings

[0013]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Modes for Carrying Out the Invention

[0014] FIG. 1 is a longitudinal sectional view of a screw press. The screw press 1 has a screw shaft 7 with screw blades 6 wound around an outer cylinder screen 5 having a filtration surface on its circumference between front and rear frames 3 and 4 of a pedestal 2. The screw shaft 7 disposed inside the outer cylinder screen 5 increases its diameter in a tapered shape from the starting end side to the ending end side, and decreases the relative interval between the outer cylinder screen 5 and the screw shaft 7 in the extending direction. A sludge supply pipe 8 is connected to the front end portion of the screw shaft 7, and the supply pipe 8 communicates with a supply hole 9 of the screw shaft 7 that opens at the starting end side of the outer cylinder screen 5. A screw drive shaft 10 is connected to the rear end portion of the screw shaft 7, and a drive sprocket 11 is fitted on the screw drive shaft 10. This sprocket 11 is driven by a screw drive machine 12 to rotate the screw shaft 7. The sludge supplied from the supply hole 9 is transferred from the starting end side to the ending end side by the screw blades 6, and is concentrated and dehydrated while separating the filtrate from the outer cylinder screen 5. Note that known configurations may be used as necessary, such as directly connecting the screw drive shaft 10 and the screw drive machine 12.

[0015] And in the screw press 1, a taper-cone-shaped presser (pressing plate) 14 for applying back pressure to the discharged dewatered cake is provided in a dewatered cake discharge section 13 that discharges the sludge (dewatered cake) immediately after the dewatering process to the outside. This presser 14 is provided so as to be reciprocally movable in the axial direction (the left-right direction in FIG. 1) by a fluid pressure cylinder 15 such as an air cylinder or a hydraulic cylinder.

[0016] The screw press 1 can continuously dewater the flocculated slurry. Compared with conventional continuous dewatering machines such as belt-type dewatering machines and centrifugal dewatering machines, it is small in size, compact, has a small motor capacity, and is power-saving. Further, the screw press 1 can maintain the filtration chamber at an optimum pressure, exhibit a stable filtration action, and perform continuous dewatering at an optimum moisture content.

[0017] FIG. 2 is a schematic configuration diagram of a control system of the screw press according to the present invention, and its operation control system will be described. The treatment stock solution such as sludge stored in the sludge storage tank 20 is supplied to the flocculation mixing tank 23 through the stock solution supply pipe 22 at a stock solution flow rate Q by the stock solution supply pump 21. And in the middle of the stock solution supply pipe 22, a stock solution flow meter 24 for measuring the stock solution flow rate Q of the treatment stock solution is provided between the stock solution supply pump 21 and the flocculation mixing tank 23. In addition, a concentration meter may be provided as necessary. A first pressure gauge 31 is arranged in the stock solution supply pipe 22, and measures the pressure P1 of the stock solution pumped from the sludge storage tank 20.

[0018] Furthermore, in the middle of the stock solution supply pipe 22 between the stock solution flow meter 24 and the flocculation mixing tank 23, a chemical solution supply pipe 27 that is supplied at a chemical solution flow rate A by a chemical solution supply pump 26 from a polymer dissolution tank 25 in which a polymer flocculant is stored is connected. And in the middle of the chemical solution supply pipe 27, a chemical solution flow meter 28 for measuring the chemical solution flow rate A is provided between the chemical solution supply pump 26 and the stock solution supply pipe 22.

[0019] The end of the stock solution supply pipe 22 is connected below the closed-type agglomeration mixing tank 23. The sludge added with the polymer flocculant is injected from below the agglomeration mixing tank 23 and mixed and stirred by the stirrer 29 to generate an agglomerated slurry. A first pressure gauge 31 is arranged on the stock solution supply pipe 22 to measure the pressure P1 of the treatment stock solution supplied to the agglomeration mixing tank 23. At the upper part of the agglomeration mixing tank 23, a slurry supply pipe 30 is connected. The other end of this slurry supply pipe 30 is connected to the screw press 1, and the agglomerated slurry is pressure-fed to the supply pipe 8 of the screw press 1 shown in Fig. 1 at the tank pressure of the agglomeration mixing tank 23. A second pressure gauge 32 is arranged on the slurry supply pipe 30 to measure the pressure P2 of the agglomerated slurry supplied to the screw press 1.

[0020] Regarding the pressure values measured at multiple locations in the supply pipeline, generally, they gradually decrease according to the piping resistance value of the pipeline. However, due to factors such as changes in the properties of the stock solution and increases or decreases in the filtration resistance on the discharge side (screw press), an unexpected pressure difference may occur.

[0021] In this embodiment, the stock solution supply pipeline is composed of the stock solution supply pipe 22 and the slurry supply pipe 30. The first pressure gauge 31 is installed immediately after the stock solution supply pump 21, and the second pressure gauge 32 is installed immediately before the screw press 1 so that the first pressure gauge 31 is easily affected by the supply pressure of the stock solution and the second pressure gauge 32 is easily affected by the filtration pressure of the screw press 1. That is, it is desirable to install the first pressure gauge 31 and the second pressure gauge 32 while maintaining a certain distance so that the first pressure gauge 31 is hardly affected by the filtration pressure of the screw press 1 and the second pressure gauge 32 is hardly affected by the supply pressure of the stock solution. For example, when agglomerating sludge in the front stage of the screw press 1, it is installed before and after the agglomeration mixing tank 23 arranged in the front stage of the screw press 1. Also, as shown in Fig. 3, when concentrating the agglomerated sludge with a concentrator 33 or the like and supplying it to the screw press 1, the first pressure gauge 31 is installed immediately after the concentrated sludge supply pump 34, and a concentrated sludge supply pipe 35 of a certain length is installed, and the second pressure gauge 32 is installed immediately before the screw press 1.

[0022] Figs. 4 and 5 are flowcharts of the control system according to this embodiment. The flowchart on the left in Figure 4 is a press-fitting pressure constant control system, which measures the second pressure P2 of the agglomerated slurry supplied to the screw press 1 by the second pressure gauge 32 installed immediately before the screw press 1. The second pressure P2 increases or decreases due to fluctuations in sludge properties or deterioration of filterability, etc. The second pressure P2 measured by this second pressure gauge 32 is compared with a preset reference pressure P20, and the equipment is controlled so that the second pressure P2 falls within the range of the reference pressure P20.

[0023] Specifically, a command is given to the screw shaft 7 to change the conveyance speed of the dewatered cake, increase or decrease the pressure in the filtration chamber, and control the press-fitting pressure supplied to the screw press 1 to be constant. Actually, the second pressure P2 measured by the second pressure gauge 32 is transmitted to the control device 36, and the control device 36 compares and judges it with the reference pressure P20, and gives a command from the control device 36 to the screw drive 12.

[0024] The control of the screw shaft 7 by the screw drive 12 mainly affects the press-fitting pressure into the screw press 1, and the pressure P2 increases or decreases in inverse proportion to the rotation speed of the screw shaft 7.

[0025] In this way, by controlling the screw shaft 7 and operating the screw press 1 so that the pressure in the filtration chamber is always constant, it becomes possible to perform stable dewatering treatment.

[0026] Also, instead of controlling the rotation speed of the screw shaft 7, the raw liquid supply pump 21 may be controlled. Specifically, the second pressure P2 is controlled to fall within the range of the reference pressure P20 by increasing or decreasing the raw liquid flow rate Q supplied by the raw liquid supply pump 21 to the supply pipeline and the screw press 1.

[0027] In the operation of controlling the pressing pressure to be constant, it is possible to stabilize the filtration performance in the filtration chamber. However, it was unclear whether the increase or decrease in the second pressure P2 immediately before the screw press 1 was due to fluctuations in the properties of the incoming process stock solution or deterioration of the filtration surface (outer cylinder screen 5) of the screw press 1. Therefore, control is performed while grasping the first pressure that changes greatly under the influence of fluctuations in the properties of the process stock solution and the second pressure that changes greatly under the influence of deterioration of the filtration surface, etc. Specifically, while controlling the second pressure P2 immediately before the screw press 1 to be constant, the sludge state and the filtration property state are appropriately estimated from the pressure difference between the second pressure P2 measured immediately before the screw press 1 and the first pressure P1 measured at a position away from the screw press 1, and differential pressure constant control of the screw press is performed in parallel to further stabilize the dewatering process.

[0028] The right flowchart in Fig. 5 is a differential pressure constant control system, and the equipment is adjusted so that the differential pressure ΔP between the respective measured values measured by the first pressure gauge 31 installed in the stock solution supply pipe 22 and the second pressure gauge 32 installed in the slurry supply pipe 30 becomes the preset reference differential pressure ΔP0.

[0029] Specifically, a command is given to the chemical solution supply pump 26 to control the agglomeration formation of the process stock solution in the agglomeration mixing tank 23, increase or decrease the pressure of the agglomerated slurry in the supply pipeline and the filtration chamber, and perform differential pressure constant control operation. Actually, the pressures P1 and P2 measured by the first pressure gauge 31 and the second pressure gauge 32 are respectively transmitted to the control device 36, the differential pressure ΔP is calculated by the control device 36, and a command is given from the control device 36 to the chemical solution supply pump 26.

[0030] The control of the agglomeration formation by the chemical solution supply pump 26 mainly affects the pressing pressure to the screw press 1. Since the pressure P2 is constantly controlled to be constant by the constant pressing pressure control, as a result, the pressure P1 increases or decreases.

[0031] In this way, by controlling the chemical solution supply pump 26 and operating the screw press 1 so that the differential pressure ΔP between the two pressures P1 and P2 measured in the supply pipeline is always constant, it becomes possible to perform stable dehydration treatment.

[0032] As shown in FIG. 5, when the differential pressure ΔP between the pressures P1 and P2 is large, before controlling the chemical solution supply pump 26, the outer cylinder screen 5 is cleaned to remove the solids adhering to the screen surface. By removing the solids, the filtration pressure decreases, and the raw liquid supply amount increases due to the constant pressure injection control, reducing the first pressure P1 and controlling the differential pressure ΔP within the reference differential pressure ΔP0. After that, when the differential pressure ΔP does not return within the reference differential pressure ΔP0, the chemical solution supply pump 26 is controlled to increase the chemical solution flow rate A, reduce the first pressure P1, and control the differential pressure ΔP within the reference differential pressure ΔP0.

[0033] Also, when the differential pressure ΔP between the pressures P1 and P2 is small, the chemical solution supply pump 26 is controlled to reduce the chemical solution flow rate A to increase the first pressure P1 and control the differential pressure ΔP within the reference differential pressure ΔP0.

[0034] In this way, by combining screen cleaning and control of the chemical solution supply pump 26, it becomes possible to preferentially reduce the supply amount of the flocculant, not only reducing the running cost for sludge treatment, but also expecting to reduce the storage amount of the flocculant and save space in the storage location.

Example

[0035] A flowchart of a differential pressure constant control method that combines the constant pressure injection control shown in FIGS. 4 and 5 and control of the chemical solution supply pump 26 will be described.

[0036] A. Initial setting <Constant pressure injection control> Set the reference pressure P20 when injecting the flocculation slurry into the screw press 1. If necessary, a range can be provided for the reference pressure P20. Set the reference rotational speed N0, maximum rotational speed Nmax, and minimum rotational speed Nmin of the screw shaft 7. Also, set proportional-integral-derivative control (PID control) for adjusting the operation amount according to the difference between the reference value and the measured value of the screw shaft 7.

[0037] Note that instead of adjusting the screw shaft 7, the stock solution supply pump 21 may be adjusted. In that case, set the reference supply amount Q0, maximum supply amount Qmax, and minimum supply amount Qmin of the stock solution. Also, set proportional-integral-derivative control (PID control) for adjusting the operation amount according to the difference between the reference value and the measured value of the supply amount Q.

[0038] <Differential pressure constant control> Set the reference differential pressure ΔP0 between the pressure P1 measured by the first pressure gauge 31 installed in the supply pipeline of the stock solution and the pressure P2 measured by the second pressure gauge 32. The reference differential pressure ΔP0 is appropriately set according to the airport conditions such as the dehydration treatment amount and the piping loss of the supply pipeline. In this embodiment, the reference differential pressure ΔP0 has a width. Set the reference supply amount A0, maximum supply amount Amax, minimum supply amount Amin of the flocculant, and the supply amount width a for stepwise increase and decrease.

[0039] B. Operation start Operate each device with the above reference values P0, ΔP0, A0 and the rated value N.

[0040] <Pressing pressure constant control> The pressing pressure constant control is implemented by the control system shown on the left side of FIG. 4. C. Pressure P2 comparison Measure the second pressure P2 immediately before the screw press 1 and compare it with the preset reference pressure P20. When the measured value P2 measured by the second pressure gauge 32 is within the reference pressure P20, maintain the operation of each device in the current state. When the measured value P2 is smaller than the reference pressure P20, shift to D in the flowchart and compare the rotational speed N considering the rotational speed width n to be decreased by PID control to decrease the rotational speed of the screw shaft 7 to increase the pressure with the minimum rotational speed Nmin. When the measured value P2 of the measurement value is greater than the reference pressure P20, shift to F in the flowchart, and compare the rotation speed N considering the rotation speed width n increased by PID control with the maximum rotation speed Nmax in order to increase the rotation speed of the screw shaft 7 to lower the pressure.

[0041] D. Comparison of the minimum rotation speed of the screw shaft In the above flowchart C, when the measured value P2 of the second pressure P2 is lower than the reference pressure P20, compare the rotation speed N considering the rotation speed width n decreased by PID control with the minimum rotation speed Nmin in order to decrease the rotation speed N of the screw shaft 7 to increase the pressure. When the rotation speed N of the changed screw shaft 7 is equal to or higher than the minimum rotation speed Nmin, shift to E in the flowchart and perform control to decrease the rotation speed of the screw shaft 7. When the rotation speed N of the changed screw shaft 7 is lower than the minimum rotation speed Nmin, shift to V in the flowchart and issue an alarm.

[0042] E. Screw shaft rotation speed (decrease) In the above flowchart D, when the rotation speed N of the changed screw shaft 7 is equal to or higher than the minimum rotation speed Nmin, adjust the screw drive 12 and perform control to decrease the rotation speed of the screw shaft 7.

[0043] Also, as another means, the stock solution supply pump 21 may be adjusted to increase it by a preset stock solution flow rate q. Note that when the stock solution flow rate Q considering the stepwise increased stock solution flow rate q is equal to or higher than the maximum stock solution flow rate Qmax, an alarm is issued, or the operation of the screw press 1 is stopped.

[0044] F. Comparison of the maximum rotation speed of the screw shaft In the above flowchart C, when the measured value P2 of the second pressure P2 is higher than the reference pressure P20, compare the rotation speed N considering the rotation speed width n increased by PID control with the maximum rotation speed Nmax in order to increase the rotation speed N of the screw shaft 7 to lower the pressure. When the rotational speed N of the changed screw shaft 7 is equal to or less than the maximum rotational speed Nmax, the process proceeds to G in the flowchart to perform control to increase the rotational speed of the screw shaft 7. When the rotational speed N of the changed screw shaft 7 is greater than the maximum rotational speed Nmax, the process proceeds to V in the flowchart to issue an alarm.

[0045] G. Screw Shaft Rotational Speed (Increase) In the above flowchart F, when the rotational speed N of the changed screw shaft 7 is equal to or less than the maximum rotational speed Nmax, the screw drive 12 is adjusted to perform control to increase the rotational speed of the screw shaft 7.

[0046] V. Alarm After a certain period of time has passed, the second pressure P2 is measured again, and the above operation is repeated until the measured value returns to the reference pressure P20. If the measured value of the second pressure P2 does not return to the reference value even when the rotational speed N of the screw shaft 7 reaches the maximum rotational speed Nmax or the minimum rotational speed Nmin, an alarm is issued. Check the status of the equipment upon receiving the alarm and appropriately determine whether to continue or stop the operation.

[0047] Also, as another means, the stock solution supply pump 21 can be adjusted to decrease it by a preset stock solution flow rate q. If the stock solution flow rate Q considering the stepwise decreased stock solution flow rate q is equal to or less than the minimum stock solution flow rate Qmin, an alarm is issued or the operation of the screw press 1 is stopped.

[0048] <Differential Pressure Constant Control> The differential pressure constant control is implemented by the control system shown in FIG. 5. H. Differential Pressure ΔP Comparison The differential pressure ΔP between the first pressure P1 and the second pressure P2 measured in the supply pipeline of the screw press 1 is compared with a preset reference differential pressure ΔP0. When the calculated differential pressure ΔP is within the reference differential pressure ΔP0, the operation of each device is maintained in the current state. When the differential pressure ΔP is less than the reference differential pressure ΔP0, shift to J in the flowchart and compare the supply amount A taking into account the supply amount width a to be gradually decreased with the minimum supply amount Amin in order to gradually decrease the supply amount of the flocculant to increase the differential pressure. When the differential pressure ΔP is greater than the reference differential pressure ΔP0, shift to W in the flowchart and perform control to clean the outer cylinder screen 5 of the screw press 1.

[0049] J. Comparison of the Minimum Supply Amount of the Flocculant Supply Amount In the above flowchart H, when the calculated differential pressure ΔP is less than the reference differential pressure ΔP0, compare the supply amount A taking into account the supply amount width a to be gradually decreased with the minimum supply amount Amin in order to gradually decrease the supply amount of the flocculant to increase the differential pressure. When the supply amount A of the flocculant after the change is equal to or greater than the minimum supply amount Amin, shift to K in the flowchart and perform control to gradually decrease the supply amount of the flocculant. When the supply amount A of the flocculant after the change is less than the minimum supply amount Amin, shift to V in the flowchart and perform control to issue an alarm or automatically stop the operation of the screw press 1.

[0050] K. Flocculant Supply Amount (Decrease) In the above flowchart J, when the supply amount A of the flocculant after the change is equal to or greater than the minimum supply amount Amin, adjust the chemical liquid supply pump 26 and perform control to decrease the supply amount of the flocculant by the preset supply amount width a.

[0051] W. Cleaning In the above flowchart H, when the differential pressure ΔP is greater than the reference differential pressure ΔP0, perform control to clean the outer cylinder screen of the screw press 1. By injecting cleaning water for a predetermined time to eliminate clogging of the outer cylinder screen 5, the filterability is improved and the first pressure P1 is decreased using the constant pressure injection pressure control. By injecting cleaning water to eliminate the clogging of the outer cylinder screen 5, the pressure in the filtration chamber of the screw press 1 is reduced to reduce the differential pressure ΔP. Note that this cleaning process is an intermittent cleaning that is performed for a predetermined period of time while continuing the dewatering operation of the screw press 1. After cleaning, proceed to L in the flowchart and compare the differential pressure ΔP between the first pressure P1 and the second pressure P2 measured in the supply pipeline of the screw press 1 with the preset reference differential pressure ΔP0.

[0052] L. Differential Pressure ΔP Comparison After cleaning the outer cylinder screen 5, measure the differential pressure ΔP again after a certain period of time and compare it with the preset reference differential pressure ΔP0. If the calculated differential pressure ΔP is within the reference differential pressure ΔP0, maintain the operation of each device in the current state. If the differential pressure ΔP is greater than the reference differential pressure ΔP0, proceed to M in the flowchart and compare the supply amount A taking into account the supply amount width a for stepwise increase with the maximum supply amount Amax in order to stepwise increase the supply amount of the flocculant to reduce the differential pressure.

[0053] M. Maximum Supply Amount Comparison of Flocculant Supply Amount In the above flowchart L, if the differential pressure ΔP is greater than the reference differential pressure ΔP0, compare the supply amount A taking into account the supply amount width a for stepwise increase with the maximum supply amount Amax in order to stepwise increase the supply amount of the flocculant to reduce the differential pressure. If the supply amount A of the flocculant after change is less than or equal to the maximum supply amount Amax, proceed to N in the flowchart and perform control to stepwise increase the supply amount of the flocculant. If the supply amount A of the flocculant after change is greater than the maximum supply amount Amax, proceed to V in the flowchart and perform control to issue an alarm or automatically stop the operation of the screw press 1.

[0054] N. Flocculant Supply Amount (Increase) In the above flowchart M, when the supply amount A of the coagulant after the change is equal to or less than the maximum supply amount Amax, the chemical liquid supply pump 26 is adjusted, and control is performed to increase the supply amount of the coagulant by a preset supply amount width a.

[0055] V. Alarm After a certain period of time has passed, the differential pressure ΔP is measured again, and the above operation is repeated until the measured value returns within the reference differential pressure ΔP0. If the measured value of the differential pressure ΔP does not return within the reference value even when the supply amount A of the coagulant reaches the maximum supply amount Amax or the minimum supply amount Amin, an alarm is issued. After receiving the alarm, the state of the equipment is checked, and it is appropriately determined whether to continue or stop the operation.

[0056] After controlling the equipment, the pressure P2 and the differential pressure ΔP are measured again after a certain period of time has passed, and the above operation is repeated until the measured values return within the reference pressure P20 and the reference differential pressure ΔP0.

[0057] The cleaning process of this flow is different from the cleaning process that stops the operation of the screw press at the cumulative dehydration process time or a predetermined time. Since cleaning is performed intermittently while continuing the dehydration process, it can respond in real time to fluctuations in the environmental and hardware aspects, enabling stable continuous dehydration.

[0058] In this embodiment, PID control is used for the control of the press-in pressure to be constant, and control is used to increase or decrease by a preset supply amount width for the control of the differential pressure to be constant. However, known control methods such as proportional control can be applied as needed.

Industrial Applicability

[0059] Regarding the pressure values measured at multiple locations in the supply pipeline, when an unexpected pressure difference occurs due to factors other than general piping resistance, the cause is analyzed and the equipment is appropriately controlled, so that the stable dehydration performance of the screw press can be maintained. Therefore, it can be applied to various solid-liquid separation devices for solid-liquid separation of sewage sludge whose properties of the treatment stock solution vary moment by moment due to seasons, weather, etc., particularly continuous screw presses. Also, it is a control method that preferentially reduces the usage amount of expensive coagulants and enables the operation of a dehydrator that takes environmental considerations into account.

Explanation of Symbols

[0060] 1 Screw Press 5 Outer Cylinder Screen 21 Stock Solution Supply Pump 23 Coagulation Mixing Tank 26 Chemical Solution Supply Pump 31 First Pressure Gauge 32 Second Pressure Gauge P1 First Pressure P2 Second Pressure P20 Reference Pressure ΔP Differential Pressure ΔP0 Reference Differential Pressure A0 Reference Supply Amount of Coagulant Amax Maximum Supply Amount of Coagulant Amin Minimum Supply Amount of Coagulant a Supply Amount Width to be Increased or Decreased Step by Step

Claims

1. A method for controlling a screw press (1) that controls a pressing pressure (P2) supplied to the screw press (1) to be constant, comprising: A reference pressure (P20) to be pre-pressed into the screw press (1), a reference differential pressure (ΔP0) between a first pressure (P1) and a second pressure (P2) measured in the supply line of the raw liquid; A standard supply amount (A0) of the flocculant, a maximum supply amount (Amax) which is the maximum value of the standard supply amount (A0), a minimum supply amount (Amin) which is the minimum value of the standard supply amount (A0), and a supply amount width (a) which is increased or decreased in stages are set; When the differential pressure (ΔP) between the first pressure (P1) and the second pressure (P2) measured in the feed line of the raw liquid is within the range of the reference differential pressure (ΔP0), the operation of the screw press (1) is continued, If the differential pressure (ΔP) is smaller than the reference differential pressure (ΔP0), the chemical supply pump (26) is adjusted to reduce the supply amount of the flocculant by the supply amount width (a), and this operation is repeated until the differential pressure (ΔP) increases to within the range of the reference differential pressure (ΔP0), If the differential pressure (ΔP) is greater than the reference differential pressure (ΔP0), the outer cylindrical screen (5) is washed. If the differential pressure (ΔP) does not decrease to within the range of the reference differential pressure (ΔP0), the chemical supply pump (26) is adjusted to increase the supply amount of the coagulant by the supply amount width (a). This operation is repeated until the differential pressure (ΔP) decreases to within the range of the reference differential pressure (ΔP0). The differential pressure (ΔP) between the first pressure (P1) and the second pressure (P2) measured in the supply line of the raw liquid is controlled to be within the range of a reference differential pressure (ΔP0). A method for controlling a screw press.

2. A first pressure gauge (31) is installed in the vicinity of the raw material supply pump (21) in the raw material supply line to measure a first pressure (P1), and a second pressure gauge (32) is installed immediately before the screw press (1) to measure a second pressure (P2).

2. The method for controlling a screw press according to claim 1.

3. A flocculation / mixing tank (23) is provided in the supply pipeline for the raw liquid, a first pressure gauge (31) is provided in the supply pipeline upstream of the flocculation / mixing tank (23) to measure a first pressure (P1), and a second pressure gauge (32) is provided in the supply pipeline downstream of the flocculation / mixing tank (23) to measure a second pressure (P2).

2. The method for controlling a screw press according to claim 1.

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