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 a set value of press-fit pressure 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 the set value of the press-fit pressure 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 an operation control method for 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 raw liquid and the pressing pressure at the inlet of the dehydrator in order to stably generate a dewatered cake discharged from the screw press.

Background Art

[0002] Conventionally, screw presses for concentrating and dewatering 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 dewaters sludge. Since the properties of sludge vary depending on season, time, weather, etc., control methods for the rotational speed of the screw shaft, the pressing pressure, the coagulant supply amount, etc. are required to maintain stable performance in a screw press.

[0003] For example, a screw press that controls the rotational speed of the raw liquid supply pump, the rotational speed of the screw shaft, and the chemical injection rate of the coagulant in order to control the pressing pressure of the raw liquid supplied to the screw press to be constant is described in Patent Document 1. Also, in order to keep the water content of the dewatered cake constant, a screw press 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 rotational speed of the screw shaft, and controlling the rotational speed of the screw shaft based on the detection results of the pressing pressure and the torque is 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] The properties of organic sludge, such as sewage, human waste, or wastewater from food production and processing, which is concentrated and dewatered using a screw press, change from moment to moment depending on the season, weather, time, etc. In response to these fluctuations, various controls have been implemented for the operation of the screw press or the conditioning of the sludge.

[0006] The control method of Patent Document 1 judges only based on the pressure of the sludge being fed into the screw press, and since the detection position is near the inlet of the screw press, the measured value is largely influenced by the filterability of the screw press, making it difficult to judge factors such as fluctuations in the properties of the raw liquid and deterioration of the coagulation state.

[0007] The control method of Patent Document 2 detects not only the pressure at the inlet of the screw press but also the torque of the screw shaft to control the equipment, making it easier to grasp the filtration state inside the filtration chamber. However, the detected value of the torque of the screw shaft changes significantly due to deterioration of the rotating equipment over time and friction between the screw blades and the filter cylinder, making it difficult to make an accurate judgment.

[0008] The present invention provides a method for controlling a screw press that can quickly respond to environmental and hardware issues, such as changes in the properties of inflowing sewage sludge and deterioration of the equipment's filtering ability, and maintain stable operation. [Means for solving the problem]

[0009] The present invention relates to a control method for a screw press that controls the press-fitting pressure supplied to the screw press to be constant. A reference pressure to be press-fitted into the screw press in advance, a maximum reference pressure that is the maximum value of the reference pressure, a minimum reference pressure that is the minimum value of the reference pressure, and a reference differential pressure between a first pressure and a second pressure measured in the supply pipeline of the stock solution 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 set value of the reference pressure is decreased by the pressure width, and this operation is repeated until the differential pressure decreases 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 set value of the reference pressure is increased by the pressure 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 the dehydration operation is stably performed while optimally controlling the press-fitting pressure.

[0010] Also, when a first pressure gauge is installed near the stock solution supply pump in the 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 piping loss.

[0011] Also, when a coagulation mixing tank is provided in the supply pipeline of the stock solution, 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.

Effects of the Invention

[0012] Since the present invention controls based on the difference between the pressure for pumping the stock solution and the press-fitting pressure at the inlet of the dehydrator, it can detect the deterioration of the environmental aspect (stock solution) or the hardware aspect (dehydration device) in real time 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

Mode 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 filtering surface on its circumferential part between front and rear frames 3 and 4 of a gantry 2. The screw shaft 7 disposed inside the outer cylinder screen 5 increases its diameter in a tapered shape from the start end side to the end end side, and reduces 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 opened at the start 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 to 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 start end side to the end end side by the screw blades 6, and is concentrated and dehydrated while separating the filtrate from the outer cylinder screen 5. In addition, a known configuration may be used as necessary, such as directly connecting the screw drive shaft 10 and the screw drive machine 12.

[0015] In the screw press 1, a dehydrated cake discharge section 13, which discharges the sludge (dehydrated cake) immediately after dehydration to the outside, is provided with a tapered cone-shaped presser (pressure plate) 14 for applying back pressure to the discharged dehydrated cake. This presser 14 is provided so as to be reciprocable in the axial direction (left and 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 dehydrate the flocculated slurry, and is smaller and more compact than conventional continuous dehydrators such as belt-type dehydrators and centrifugal dehydrators, and its motor capacity is smaller and more energy-efficient.In addition, the screw press 1 can maintain an optimal pressure inside the filtration chamber, thereby providing stable filtration and enabling continuous dehydration at an optimal moisture content.

[0017] 2 is a schematic diagram of a control system for a screw press according to the present invention, and the operation control system will be described below. A raw liquid to be treated, such as sludge, stored in a sludge storage tank 20 is supplied by a raw liquid supply pump 21 through a raw liquid supply pipe 22 at a raw liquid flow rate Q to a flocculation / mixing tank 23. A raw liquid flow meter 24 for measuring the raw liquid flow rate Q of the raw liquid to be treated is provided midway in the raw liquid supply pipe 22, between the raw liquid supply pump 21 and the flocculation / mixing tank 23. A concentration meter may also be provided if necessary. A first pressure gauge 31 is provided in the raw liquid supply pipe 22, and measures the pressure P1 of the raw liquid being pumped from the sludge storage tank 20.

[0018] Furthermore, a chemical supply pipe 27 is connected to the middle of the raw liquid supply pipe 22 between the raw liquid flow meter 24 and the flocculation mixing tank 23. A chemical supply pipe 27 is connected to the raw liquid supply pipe 22. The chemical supply pipe 27 is supplied with a chemical flow rate A from a polymer dissolving tank 25 in which a polymer flocculant is stored by a chemical supply pump 26. A chemical flow meter 28 for measuring the chemical flow rate A is provided in the middle of the chemical supply pipe 27, between the chemical supply pump 26 and the raw liquid supply pipe 22.

[0019] The end of the stock solution supply pipe 22 is connected below the closed-type flocculation mixing tank 23. The sludge added with the polymer flocculant is pressed in from below the flocculation mixing tank 23 and mixed and stirred by the stirrer 29 to generate a flocculated 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 flocculation mixing tank 23. A slurry supply pipe 30 is connected to the upper part of the flocculation mixing tank 23. The other end of this slurry supply pipe 30 is connected to the screw press 1, and the flocculated slurry is press-fed to the supply pipe 8 of the screw press 1 shown in Fig. 1 at the tank pressure of the flocculation mixing tank 23. A second pressure gauge 32 is arranged on the slurry supply pipe 30 to measure the pressure P2 of the flocculated 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, unexpected pressure differences may occur 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).

[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 flocculating sludge in the front stage of the screw press 1, it is installed before and after the flocculation mixing tank 23 arranged in the front stage of the screw press 1. Also, as shown in Fig. 3, when the flocculated sludge is concentrated by a concentrator 33 or the like and supplied 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 FIG. 4 is a press-fit pressure constant control system that 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. First The second pressure P2 increases or decreases due to fluctuations in sludge properties, 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-fit pressure supplied to the screw press 1 to be constant. In reality, the second pressure P2 measured by the second pressure gauge 32 is transmitted to the control device 36, compared and judged with the reference pressure P20 by the control device 36, and a command is given 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-fit pressure into the screw press 1, and the pressure P2 increases or decreases in inverse proportion to the rotational 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] Alternatively, instead of controlling the rotational speed of the screw shaft 7, the stock solution 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 stock solution flow rate Q supplied by the stock solution 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 inferred 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 the differential pressure constant control of the screw press is performed in parallel to make the dehydration process more stable.

[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, 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 the control is performed by the control device 36. Actually, the setting of the reference pressure P20, which is the basic setting value for the constant pressing pressure control, is changed by the control device 36 to reflect the influence of the constant pressing pressure control on the differential pressure constant control.

[0030] The change in the basic setting value of the constant pressing pressure control mainly affects the pressing pressure to the screw press 1, and the pressure P2 increases or decreases in proportion to the set value of the pressing pressure.

[0031] In this way, by controlling the basic setting value of the constant pressing pressure control and operating the screw press 1 so that the differential pressure ΔP between the two pressures P1 and P, 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 basic set value of the constant pressure injection control, 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 constant pressure injection control increases the raw liquid supply amount to decrease the first pressure P1 and control 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, an instruction is given to the control device to increase the basic set value P20, and the constant pressure injection control decreases the raw liquid supply amount to decrease 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, an instruction is given to the control device to decrease the basic set value P20, so that the filtration pressure increases, and the constant pressure injection control increases the raw liquid supply amount 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 basic set value of the constant pressure injection control, it becomes possible to increase or decrease the differential pressure ΔP in real time, and quickly respond to sudden changes in the properties of the raw liquid.

Example

[0035] A flowchart of a differential pressure constant control method combining the constant pressure injection control shown in Figs. 4 and 5 and control of setting change of the reference pressure P20 will be described.

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

[0037] Instead of adjusting the screw shaft 7, the stock solution supply pump 21 may be adjusted. In that case, the reference supply amount Q0, the maximum supply amount Qmax, and the minimum supply amount Qmin of the stock solution are set. Also, proportional-integral-derivative control (PID control) is set to adjust 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> The reference differential pressure ΔP0 of each of the pressures 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 is set. The reference differential pressure ΔP0 is appropriately set according to the airport, 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. The maximum reference pressure P20max and the minimum reference pressure P20min when press-fitting into the screw press 1 are set. Also, a pressure width p for gradually increasing and decreasing the set value of the reference pressure P20 is set.

[0039] B. Operation start Each device is operated at the above reference values P0, ΔP0, A0 and the rated value N.

[0040] <Press-fitting pressure constant control> The press-fitting pressure constant control is implemented by the control system shown on the left side of FIG. 4. C. Pressure P2 comparison The second pressure P2 immediately before the screw press 1 is measured and compared with the preset reference pressure P20. When the measured value P2 measured by the second pressure gauge 32 is within the reference pressure P20, the operation of each device is maintained in the current state. When the measured value P2 is smaller than the reference pressure P20, the process proceeds to D in the flowchart, and in order to increase the pressure, the rotation speed N considering the rotation speed width n to be decreased by PID control is compared with the minimum rotation speed Nmin. When the measured value P2 is larger than the reference pressure P20, the process proceeds to F in the flowchart, and in order to decrease the pressure, the rotation speed N considering the rotation speed width n to be increased by PID control is compared with the maximum rotation speed Nmax.

[0041] D. Comparison of minimum screw shaft rotation speeds In the above flowchart C, if the measured value P2 of the second pressure P2 is lower than the reference pressure P20, the rotation speed N of the screw shaft 7 is reduced to increase the pressure, and the rotation speed N taking into account the rotation speed range n to be reduced by PID control is compared with the minimum rotation speed Nmin. If the rotation speed N of the screw shaft 7 after the change is equal to or greater than the minimum rotation speed Nmin, the flow chart moves to E, where control is performed to reduce the rotation speed of the screw shaft 7. If the rotation speed N of the screw shaft 7 after the change is smaller than the minimum rotation speed Nmin, the flow chart moves to V and an alarm is issued.

[0042] E. Screw shaft rotation speed (reduction) In the above flow chart D, if the rotation speed N of the screw shaft 7 after the change is equal to or greater than the minimum rotation speed Nmin, the screw driver 12 is adjusted and control is performed to reduce the rotation speed of the screw shaft 7.

[0043] Alternatively, the raw liquid supply pump 21 may be adjusted to increase the raw liquid flow rate q by a preset amount. If the raw liquid flow rate Q, taking into account the stepwise increase in the raw liquid flow rate q, exceeds the maximum raw liquid flow rate Qmax, an alarm is issued or the operation of the screw press 1 is stopped.

[0044] F. Comparison of maximum screw shaft rotation speeds In the above flowchart C, if the measured value P2 of the second pressure P2 is higher than the reference pressure P20, the rotation speed N of the screw shaft 7 is increased to reduce the pressure, and the rotation speed N taking into account the rotation speed range n to be increased by PID control is compared with the maximum rotation speed Nmax. If the rotation speed N of the screw shaft 7 after the change is equal to or less than the maximum rotation speed Nmax, the flow chart moves to G, where control is performed to increase the rotation speed of the screw shaft 7. If the rotation speed N of the screw shaft 7 after the change is greater than the maximum rotation speed Nmax, the flow chart moves to V and an alarm is issued.

[0045] G. Screw shaft rotation speed (increase) In the above flowchart F, when the rotation speed N of the screw shaft 7 after the change is equal to or less than the maximum rotation speed Nmax, the screw drive 12 is adjusted to control the increase in the rotation speed of the screw shaft 7.

[0046] V. Alarm After a certain period of time, 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 rotation speed N of the screw shaft 7 reaches the maximum rotation speed Nmax or the minimum rotation speed Nmin, an alarm is issued. After receiving the alarm, check the state of the equipment and appropriately determine whether to continue or stop the operation.

[0047] Also, as another means, the stock solution supply pump 21 may be adjusted to decrease it by a preset stock solution flow rate q. If the stock solution flow rate Q taking into account the stepwise decreasing 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 [[ID=2s5]]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 smaller than the reference differential pressure ΔP0, the process proceeds to J in the flowchart, and the pressure P20 and the minimum set pressure P20min, taking into account the pressure width p that is decreased stepwise, are compared to decrease the set value of the reference pressure P20 to be press-fitted into the screw press 1. When the differential pressure ΔP is larger than the reference differential pressure ΔP0, the process proceeds to W in the flowchart, and control is performed to clean the outer cylinder screen 5 of the screw press 1.

[0049] J. Comparison of the minimum set pressure of the reference pressure P20 In the above flowchart H, when the calculated differential pressure ΔP is smaller than the reference differential pressure ΔP0, in order to increase the differential pressure, the pressure P considering the pressure width p decreased step by step is compared with the minimum reference pressure P20min to decrease the set value of the reference pressure P20 to be press-fitted into the screw press 1. When the changed reference pressure P20 is equal to or higher than the minimum reference pressure P20min, the process proceeds to K in the flowchart, and control is performed to gradually decrease the set value of the reference pressure P20. When the changed reference pressure P20 is smaller than the minimum reference pressure P20min, the process proceeds to V in the flowchart, and control is performed to issue an alarm or automatically stop the operation of the screw press 1.

[0050] K. Reference pressure P20 (decrease) In the above flowchart J, when the set value of the changed reference pressure P20 is equal to or higher than the minimum reference pressure P20min, control is performed to decrease the set value of the reference pressure P20 by the preset pressure width p.

[0051] W. Cleaning In the above flowchart H, when the differential pressure ΔP is larger than the reference differential pressure ΔP0, control is performed to clean the outer cylinder screen of the screw press 1. By injecting cleaning water for a predetermined time to eliminate the clogging of the outer cylinder screen 5, the filterability is improved, and the first pressure P1 is decreased using the constant press-fitting 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 performed for a predetermined time while continuing the dehydration operation of the screw press 1. After cleaning, the process proceeds to L in the flowchart, and 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 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 a preset reference differential pressure ΔP0. When the calculated differential pressure ΔP is within the reference differential pressure ΔP0, maintain the operation of each device in the current state. When the differential pressure ΔP is greater than the reference differential pressure ΔP0, shift to M in the flowchart and compare the pressure P20 with the maximum set pressure P20max, where P20 is the pressure obtained by adding the pressure width p to be increased step by step to increase the set value of the reference pressure P20 to be press-fitted into the screw press 1.

[0053] M. Comparison of the maximum set pressure of the reference pressure P20 In the above flowchart L, when the differential pressure ΔP is greater than the reference differential pressure ΔP0, compare the pressure P20 with the maximum reference pressure P20max, where P20 is the pressure obtained by adding the pressure width p to be increased step by step to increase the set value of the reference pressure P20 to be press-fitted into the screw press 1 in order to reduce the differential pressure. When the changed reference pressure P20 is less than or equal to the maximum reference pressure P20max, shift to N in the flowchart and perform control to increase the set value of the reference pressure P20 step by step. When the changed reference pressure P20 is greater than the maximum reference pressure P20max, shift to V in the flowchart and perform control to issue an alarm or automatically stop the operation of the screw press 1.

[0054] N. Reference pressure P20 (increase) In the above flowchart M, when the set value of the changed reference pressure P20 is less than or equal to the maximum reference pressure P20max, perform control to increase the set value of the reference pressure P20 step by step.

[0055] V. Alarm Measure the differential pressure ΔP again after a certain period of time and repeat the above operation 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 flocculant reaches the maximum supply amount Amax or the minimum supply amount Amin, issue an alarm. Check the state of the device upon receiving the alarm and appropriately judge whether to continue or stop the operation.

[0056] After controlling the machine, measure the pressure P2 and differential pressure ΔP again after a certain period of time, and repeat the above operation until the measured values return within the reference pressure P20 and 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 and enables stable continuous dehydration.

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

Industrial Applicability

[0059] When an unexpected pressure difference occurs in the pressure values measured at multiple locations in the supply pipeline due to factors other than general piping resistance, by analyzing the cause and appropriately controlling the equipment, 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., especially continuous screw presses. Also, it is a control method that utilizes press-in pressure constant control and enables the operation of a dehydrator considering the environment.

Explanation of Signs

[0060] 1 Screw press 5 Outer cylinder screen 21 Stock solution supply pump 23 Coagulation mixing tank 31 First pressure gauge 32 Second pressure gauge P1 First pressure P2 Second pressure P20 Reference pressure P20max Maximum reference pressure P20min Minimum reference pressure Pressure range that increases and decreases step by step in p ΔP Differential pressure ΔP0 Reference differential pressure

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 pressed into the screw press (1) in advance, a maximum reference pressure (P20max) which is the maximum value of the reference pressure (P20), and a minimum reference pressure (P20min) which is the minimum value of the reference pressure (P20), A reference differential pressure (ΔP0) between a first pressure (P1) and a second pressure (P2) measured in a supply line of the stock solution is 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 set value of the reference pressure (P20) is reduced by the pressure width (p), and this operation is repeated until the differential pressure (ΔP) is reduced 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 cleaned. If the differential pressure (ΔP) does not decrease to within the range of the reference differential pressure (ΔP0), the set value of the reference pressure (P20) is increased by the pressure width (p), and 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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