JP2021121442A - Back-pressure control method in screw press - Google Patents

Abstract

To provide a back-pressure control method in a screw press which can maintain safe operation for a long time by properly controlling back-pressure at an exhaust side, with respect to an operation control method of the screw press.SOLUTION: A condition of sludge in a filtering chamber is estimated in real time from a supply flow rate, torque and a water content ratio of a screw shaft and a cake thickness and back-pressure of an exhaust port is controlled, along with pressure-constant control by a raw liquid supply pump, so that the inside of the filtering chamber can be usually maintained at a state optimal for dehydration, which can quickly respond to fluctuation in property of the sludge and prevent operation of a dehydrator from changing rapidly.SELECTED DRAWING: Figure 5

Description

The present invention relates to a screw press operation control method, and relates to a back pressure control method in a screw press that maintains stable operation for a long time by appropriately controlling the back pressure on the discharge side.

Conventionally, a screw press for concentrating and dehydrating organic sludge such as sewage, human waste, or food production processed wastewater is generally known. A screw press is a device that continuously concentrates and dehydrates sludge. Since the properties of sludge change according to the season, time, weather, etc., it is necessary to control the screw shaft rotation speed, press-fitting pressure, coagulant supply amount, etc. in order to maintain stable performance with a screw press. do.

For example, Patent Document 1 describes a method of adjusting a stock solution supply pump to control a supply flow rate in order to control a constant press-fitting pressure when supplying sludge to a screw press.

Further, Patent Document 2 describes a method of controlling the press-fitting pressure of sludge supplied to the screw press and the chemical injection rate of the coagulant in order to appropriately control the torque of the screw shaft.

Further, Patent Document 3 describes a control method for detecting the opening degree between the discharge port of the screw press and the back pressure valve and supplying the pressure according to the opening degree to the back pressure valve.

Japanese Patent No. 4862562 JP-A-2018-001075 Japanese Patent No. 3576492

The constant press-fitting pressure control method of Cited Document 1 has a problem that the response speed of dehydration control is slowed down and the control range for keeping the press-fitting pressure constant is widened. Further, even if the press-fitting pressure is within the reference value, the solids are not properly compacted in the filtration chamber, and the dehydration operation may be continued in a state where the water content and the cake thickness are insufficient.

Patent Document 2 controls the torque of the screw shaft within an appropriate range to keep the water content of the dehydrated cake constant. However, the water content of the dehydrated cake dehydrated and discharged from the screw press is the back pressure on the discharge side (the back pressure on the discharge side ( Since it is greatly affected by the aperture ratio), the effect of controlling other factors (pressure, chemical injection rate of coagulant) for controlling the torque to be constant is low when the back pressure is constant.

Patent Document 3 adjusts the opening / closing pressure of the back pressure valve that opposes the pressure applied to the back pressure valve by the dehydrated cake dehydrated in the filtration chamber. However, if only the back pressure valve is controlled, the dehydrated cake contains water. It is not realistic because the rate fluctuates greatly and requires very severe control. In general, when the pressure applied to the back pressure valve is increased, the water content of the dehydrated cake decreases, but the amount supplied to the dehydrator also decreases, and the water content is high when the consolidation in the filtration chamber is insufficient. Dehydrated cake was sometimes discharged.

The present invention is a spine in a screw press that adjusts the pressure to press a presser (back pressure plate) based on the supply flow rate and the torque of the screw shaft in order to respond to fluctuations in sludge properties in real time while controlling the press-fitting pressure to be constant. A pressure control method is provided.

The present invention is a back pressure control method in which the presser of the screw press is controlled while controlling the press-fitting pressure of the sludge supplied to the screw press by adjusting the supply flow rate by the undiluted solution supply pump. Set the reference water content, the reference cake thickness, the initial flow rate, the reference pressure of the back pressure of the press, and the pressure range of the back pressure of the press to be gradually increased or decreased.
<A>
When at least one of the torque measurement value, moisture content measurement value, and cake thickness measurement value is within the range of the standard torque, standard moisture content, and standard cake thickness, the screw press operation is continued in the current state. , Repeat the control method of <a>,
If the measured torque value is outside the standard torque range and the measured water content is lower than the standard water content, the pressure applied to the presser is reduced by the pressure range, and then the screw press operation is continued.
If the measured torque value is outside the standard torque range, the measured water content is higher than the standard water content, and the measured cake thickness is higher than the standard cake thickness, the pressure applied to the presser is increased by the pressure width. After that, shift to the control method of <b>,
If the measured torque value is outside the standard torque range, the measured water content is higher than the standard water content, and the measured cake thickness is lower than the standard cake thickness, the pressure applied to the presser is reduced by the pressure width. After that, shift to the control method of <c>,
<B>
(B1)
If the flow rate is greater than or equal to the flow rate measured immediately before, continue the operation of the screw press in the current state and shift to the control method of <a>.
If the flow rate is lower than the flow rate measured immediately before, the pressure applied to the presser is reduced by twice the pressure width, and then the control method (b2) is started.
(B2)
If the flow rate is less than or equal to the flow rate measured immediately before, adjust the back pressure of the presser to the reference pressure, and then shift to the control method of <a>.
If the flow rate is higher than the flow rate measured immediately before, the pressure applied to the presser is reduced by the pressure width, and then the control method (b2) is repeated.
<C>
(C1)
If the flow rate is greater than or equal to the flow rate measured immediately before, continue the operation of the screw press in the current state and shift to the control method of <a>.
If the flow rate is lower than the flow rate measured immediately before, the pressure applied to the presser is increased by twice the pressure width, and then the control method (c2) is started.
(C2)
If the flow rate is less than or equal to the flow rate measured immediately before, adjust the back pressure of the presser to the reference pressure, and then shift to the control method of <a>.
When the flow rate is higher than the flow rate measured immediately before, the pressure applied to the presser is increased by the pressure width, and then the control method (b2) is repeated. Since the pressure is controlled, a dehydrated cake that is stable against changes in sludge properties can be discharged.

In the present invention, in parallel with the constant pressure control by the undiluted solution supply pump, the sludge condition in the filtration chamber is estimated in real time from the supply flow rate and the torque of the screw shaft, and the back pressure of the discharge port is controlled. It can be maintained in the optimum state for dehydration. In addition, the response speed to changes in sludge properties is fast, and there is no sudden change in the operation of the dehydrator.

It is a vertical sectional view of the screw press which concerns on this invention. Similarly, it is an operation control system for a dehydrator. Similarly, it is a schematic flowchart of the control method. Similarly, it is a flowchart of a press-fitting pressure constant control method. Similarly, it is a flowchart of a presser control method.

FIG. 1 is a vertical cross-sectional view of a screw press. The screw press 1 is a screw shaft in which a screw blade 6 is wound around an outer cylinder screen 5 having a filtration surface at the peripheral portion between frames 3 and 4 before and after the gantry 2. 7 is installed internally. The screw shaft 7 arranged inside the outer cylinder screen 5 is tapered in diameter from the start end side to the end side, and the outer cylinder screen 5 and the screw shaft 7 are relatively spaced from each other in the extending direction. I try to reduce it. A sludge supply pipe 8 is connected to the front end of the screw shaft 7, and the supply pipe 8 communicates with the supply hole 9 of the screw shaft 7 opened on the starting end side of the outer cylinder screen 5. A screw drive shaft 10 is connected to the rear end of the screw shaft 7, and a drive sprocket 11 is fitted to the screw drive shaft 10. The sprocket 11 is driven by the 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 side by the screw blade 6, and is concentrated and dehydrated while separating the filtrate from the outer cylinder screen 5. If necessary, the outer cylinder screen 5 may be rotatable.

Then, in the screw press 1, the dewatered cake discharging portion 13 that discharges the sludge (dehydrated cake) immediately after the dewatering treatment to the outside has a tapered cone shape for applying back pressure to the discharged dewatered cake. Presser (pressing plate) 14 is provided. The presser 14 is provided so as to be reciprocally reciprocating in the axial direction (left-right direction in FIG. 1) by a fluid pressure cylinder 15 such as an air cylinder or a hydraulic cylinder. A pressure is applied to the fluid pressure cylinder 15 by using a known presser pump 16.

The sludge in the filtration chamber of the screw press 1 presses the presser 14 toward the discharge side, so that the dehydrated cake is discharged from the discharge unit 13. The balance between the pressure applied to the presser 14 by the sludge and the pressure applied to the presser 14 by the fluid pressure cylinder 15 forms an appropriate discharge portion 13, and a dehydrated cake having a stable moisture content and a cake thickness is produced.

The screw press 1 can continuously dehydrate the coagulated slurry, and is smaller and more compact than conventional continuous dehydrators such as belt type dehydrators and centrifugal dehydrators, and has a small motor capacity and saves power. Is. Further, the screw press 1 can exhibit a stable filtration action by maintaining the filtration chamber at an optimum pressure, and can perform continuous dehydration at an optimum water content.

FIG. 2 is an operation control system for the dehydrator according to the present invention, and an operation control method thereof will be described. The undiluted solution for treating sludge and the like stored in the sludge storage tank 20 is supplied to the coagulation mixing tank 23 through the undiluted solution supply pipe 22 at a predetermined flow rate QS by the undiluted solution supply pump 21. Then, in the middle of the stock solution supply pipe 22, a flow meter 24 for measuring the stock solution flow rate QS of the processed stock solution is provided between the stock solution supply pump 21 and the agglutination mixing tank 23. A densitometer may be provided if necessary.

Further, a chemical solution supply pipe 27 for supplying a polymer flocculant is connected in the middle of the stock solution supply pipe 22 between the flow meter 24 and the coagulation mixing tank 23. The chemical solution supply pipe 25 may be directly connected to the coagulation mixing tank 23.

The end of the stock solution supply pipe 22 is connected to the lower part of the closed type coagulation and mixing tank 23, and sludge to which a polymer coagulant is added is press-fitted from below the coagulation and mixing tank 23, mixed and stirred by a stirrer 26 to coagulate. Generate a slurry. A slurry supply pipe 27 is connected to the upper part of the coagulation mixing tank 23, and the other end of the slurry supply pipe 27 is connected to the screw press 1 and coagulates to the supply pipe 8 of the screw press 1 shown in FIG. The slurry is press-fitted and supplied at the tank pressure of the coagulation mixing tank 23.

FIG. 3 is a schematic flowchart of the control method according to this embodiment.
The operation control method according to the present invention includes a method of controlling the press-fitting pressure to be constant in order to operate the screw press 1 stably, a stock solution flow rate Q fluctuating by this control, a torque T of the screw shaft, and water content of the dehydrated cake. Simultaneously control two systems of the method of adjusting the back pressure of the presser 14 according to the fluctuation of the rate W and the cake thickness D, respond to the fluctuation of the sludge properties in the filtration chamber in real time, and make the screw press 1 more stable. It makes it possible to drive.

(Constant press-fitting pressure control)
FIG. 4 is a flowchart of a press-fitting pressure constant control method according to this embodiment.
A pressure gauge 28 is arranged in the slurry supply pipe 27 to measure the press-fitting pressure P of the aggregated slurry supplied to the screw press 1. The press-fitting pressure P increases or decreases due to fluctuations in sludge properties, and the undiluted solution flow rate supplied so as to be the reference pressure P0 by comparing and judging the pressure P measured by the pressure gauge 28 and the preset reference pressure P0. Adjust Q.

Specifically, a command is given to the stock solution supply pump 21 to increase or decrease the stock solution flow rate Q to perform a constant press-fitting pressure control operation. Actually, the detection signal measured by the pressure gauge 28 is transmitted to the control device 29, the control device 29 makes a comparative judgment, and the control device 29 gives a command to the stock solution supply pump 21.

The control of the undiluted solution flow rate Q by the undiluted solution supply pump 21 mainly affects the press-fitting pressure to the screw press 1, and the press-fitting pressure P increases or decreases in proportion to the undiluted solution flow rate Q.

In this way, by controlling the stock solution supply pump 21 and operating the screw press 1 so that the pressure in the filtration chamber is always constant, stable dehydration processing can be performed.

(Presser back pressure control)
In the operation of controlling the press-fitting pressure to be constant, the water content W and the cake thickness D of the dehydrated cake discharged from the screw press 1 fluctuate, and the undiluted solution flow rate Q and the torque T of the screw shaft 7 press-fitted and supplied to the screw press 1 change. fluctuate. Therefore, while performing constant press-fitting pressure control, the real-time sludge state inside the filtration chamber is estimated from the above-mentioned fluctuation factors, and back pressure control (presser aperture ratio adjustment) of the screw press 1 is performed in order to further stabilize the dehydration process. ..

FIG. 5 is a flowchart of the presser control method according to this embodiment.
A torque meter 30 is arranged in the drive shaft system (for example, the screw drive shaft 10) of the screw press 1 to measure the torque T of the screw shaft 7 that increases or decreases due to fluctuations in sludge properties.

Similarly, in the vicinity of the discharge unit 13 of the screw press 1, a water content meter 32 for measuring the water content of the dehydrated cake discharged from the discharge unit 13 and a cake thickness meter 33 for measuring the cake thickness of the dehydrated cake are arranged. The water content W and cake thickness D of the dehydrated cake, which increases or decreases due to fluctuations in sludge properties, are measured.

If the torque T, the water content W, and the cake thickness D deviate from the reference values, it is determined that the sludge in the filtration chamber is not in a state suitable for dehydration, and the pressure (back pressure) of the presser 14 is adjusted.
Specifically, when the torque T is outside the reference value and the water content W is lower than the reference value, the back pressure of the presser 14 is reduced in order to prevent the sludge in the filtration chamber and the screw shaft 7 from rotating. The pressure received by the sludge in the filtration chamber from the presser 14 is reduced, and the solid-liquid separation action is suppressed, so that the sludge having an appropriate water content is discharged.

When the torque T is outside the reference value, the water content W is higher than the reference value, and the cake thickness D is higher than the reference value, the back pressure of the presser 14 is increased in order to throttle the discharge portion 13 of the screw press 1.
On the contrary, when the torque T is outside the reference value, the water content W is higher than the reference value, and the cake thickness D is lower than the reference value, the back pressure of the presser 14 is reduced in order to expand the discharge portion 13 of the screw press 1. ..

After adjusting the back pressure of the presser 14 based on the torque T, the water content W, and the cake thickness D, the back pressure of the presser 14 is adjusted according to the flow rate of the undiluted solution supplied to the screw press 1 measured by the flow meter 24. ..
Specifically, if the stock solution flow rate Q tends to decrease after increasing the back pressure of the presser 14, it is determined that the sludge in the filtration chamber is excessively compact, and the back pressure of the presser 14 is reduced to reduce the back pressure of the presser 14. If the stock solution flow rate Q tends to decrease after the pressure is reduced, it is determined that the dehydrated cake is discharged in a state where the dehydration is insufficient, and that the transport efficiency is lowered by the screw blades 6 and the stock solution flow rate Q is lowered. Increases the back pressure of the presser 14.

The torque T of the screw shaft 7, the water content W of the dehydrated cake, the cake thickness D and the undiluted solution flow rate Q are measured at predetermined predetermined intervals, and the presser 14 is compared with the predetermined reference value and the data measured immediately before. By controlling the back pressure, the sludge consolidation state in the filtration chamber of the screw press 1 is controlled to approach the optimum value for the dewatering operation.

The flowchart of FIG. 5 will be described in detail.
A. Initial setting The reference press-fitting pressure P0, the initial flow rate Q0, the reference torque T0 of the screw shaft 7, the reference moisture content W0, and the reference cake thickness D0 when press-fitting and supplying to the screw press 1 are set.
Further, the reference pressure PP0 of the back pressure of the presser 14 that determines the opening ratio of the discharge portion 13 of the screw press 1 and the pressure width p of the back pressure of the presser 14 that is gradually increased or decreased are set.
In this embodiment, each reference value has a certain range.

B. Start of operation Each device is operated with the above reference values and initial values, and sludge is supplied to the screw press 1. In this control, the rotation speed of the screw shaft 7 is operated at a predetermined rated rotation speed.
Each measured value is compared with the reference value in a state where the operation of the screw press 1 is started and the operation is stable. The flow rate of the sludge supplied to the screw press 1 is to transmit and store the initial flow rate Q0 to the controller, comparing the initial flow rate Q0 and initial flow rate Q after the _n-1 flow rate Q _n.

C. Constant press-fitting pressure control (flow rate control)
When the operation of the screw press 1 is started, the press-fitting pressure P of the sludge supplied to the screw press 1 is detected by the pressure gauge 28 and sent to the control device 29.
During operation of the screw press 1, if the load on the screw press 1 increases due to an increase in the concentration of supplied sludge due to changes in the properties of sludge, deterioration of the filterability (dehydration) of the outer cylinder screen 5, etc., press-fitting of the supplied sludge The pressure P rises. On the other hand, when the load on the screw press 1 is reduced due to a decrease in the concentration of the supplied sludge due to a change in the properties of the sludge, a recovery of the filterability (dehydration) of the outer cylinder screen 5, and the like, the press-fitting pressure P of the supplied sludge is reduced.
Therefore, in the control device, the pressure measurement value P of the pressure gauge 28 and the preset reference pressure P0 are compared and judged, and if the pressure is higher than the reference pressure P0, the stock solution supply pump 21 is used to reduce the rotation speed of the stock solution supply pump 21. Is given a command to reduce the undiluted solution flow rate Q. On the other hand, when the measured pressure value P is lower than the reference pressure P0, a command is given to the stock solution supply pump 21 to increase the stock solution flow rate Q in order to increase the rotation speed of the stock solution supply pump 21.

D. Back pressure control of presser In the operation control method according to the present invention, in order to operate the screw press 1 stably, the undiluted solution supply pump 21 is adjusted to constantly control the press-fitting pressure of the screw press 1, and the torque, flow rate, and pressure are controlled. The back pressure of the presser 14 is also controlled at the same time based on the water content and cake thickness of the dehydrated cake.

Let the flowcharts D1 to D6 be the process <a>.
<D1>
When the operation of the screw press 1 is started, the torque of the screw shaft 7 measured by the torque meter 30 is transmitted to the control device 29 in real time, and the torque T measured by the torque meter 30 by the control device 29 and a preset reference. Compare with torque T0.
When the torque measurement value T of the torque meter 30 is within the reference torque T0, the operation of each device is maintained in the current state and the torque is measured again.
When the torque measurement value T of the torque meter 30 is outside the reference torque T0, that is, when it is lower or higher than the reference torque T0, the process proceeds to the flowchart D2, and the water content W of the dehydrated cake discharged from the screw press 1 is determined in advance. Compare with the set standard moisture content W0.

<D2>
The moisture content of the dehydrated cake measured by the moisture content meter 32 is transmitted to the control device 29 in real time, and the moisture content W measured by the moisture content meter 32 by the control device 29 is compared with the preset reference moisture content W0.
When the water content measurement value W of the water content meter 32 is within the reference water content W0, the operation of each device is maintained in the current state and the process proceeds to the flowchart D1.
When the moisture content measurement value W of the moisture content meter 32 is higher than the reference moisture content W0, the process proceeds to the flowchart D3, and the cake thickness D of the dehydrated cake discharged from the discharge unit 13 is compared with the preset reference cake thickness D0. do.
If the moisture content measurement value W of the moisture content meter 32 is lower than the reference moisture content W0, the process proceeds to flowchart D6, and a command is given to the presser pump 16 that applies pressure to the presser 14 in order to reduce the back pressure of the presser 14. ..

<D3>
The cake thickness of the dehydrated cake measured by the cake thickness meter 33 is transmitted to the control device 29 in real time, and the cake thickness D measured by the cake thickness meter 33 by the control device 29 is compared with the preset reference cake thickness D0.
When the cake thickness measurement value D of the cake thickness meter 33 is within the reference cake thickness D0, the operation of each device is maintained in the current state and the process proceeds to the flowchart D1.
When the cake thickness measurement value D of the cake thickness meter 33 is higher than the reference cake thickness D0, the process proceeds to the flowchart D4, and a command is given to the presser pump 16 that applies pressure to the presser 14 in order to increase the back pressure of the presser 14. ..
When the cake thickness measurement value D of the cake thickness meter 33 is lower than the reference cake thickness D0, the process proceeds to the flowchart D5, and a command is given to the presser pump 16 that applies pressure to the presser 14 in order to reduce the back pressure of the presser 14. ..

<D4>
The control device 29 gives a command to the presser pump 16 to increase the pressure by a preset pressure width p, and increases the pressure of the presser 14. After that, the process proceeds to the flowchart D7, and the flow rate is measured in real time.

<D5>
The control device 29 gives a command to the presser pump 16 to reduce the pressure by a preset pressure width p, and reduces the pressure of the presser 14. After that, the process proceeds to the flowchart D12, and the flow rate is measured in real time.

<D6>
The control device 29 gives a command to the presser pump 16 to reduce the pressure by a preset pressure width p, and reduces the pressure of the presser 14. After that, the process shifts to the flowchart D1 and the torque is measured in real time.

The flowcharts D7 to D11 are referred to as steps <b>, of which the flowcharts D7 and D8 are referred to as (b1) and the flowcharts D9 to D11 are referred to as (b2).
<D7>
The flow rate measured by the flow meter 24 is transmitted to the control device 29 in real time, and the flow rate Q _n measured by the flow meter 24 by the control device 29 is compared with the flow rate Q _{n-1 measured immediately before.
If the flow rate measurement value Q n} of the flow meter 24 is equal to _{or greater than the flow rate Q n-1} measured immediately before, it is judged that the sludge consolidation state in the filtration chamber is appropriate, and the operation of each device is maintained in the current state. The process proceeds to the flowchart D1 and the same process is repeated.
If the flow rate measurement value Q _{n of the flow meter 24 is lower than the flow rate Q n-1} measured immediately before, it is determined that the increase in the presser pressure was inappropriate, and the process shifts to the flowchart D8 to reduce the increase including the increase. ..

<D8>
The control device 29 gives a command to the presser pump 16 to reduce the pressure by twice (2p) of the preset pressure width p, and reduces the pressure of the presser 14. After that, the process proceeds to the flowchart D9, and the flow rate is measured in real time.

<D9>
The flow rate measured by the flow meter 24 is transmitted to the control device 29 in real time, and the flow rate Q _n measured by the flow meter 24 by the control device 29 is compared with the flow rate Q _{n-1 measured immediately before.}
When the flow rate measurement value Q _{n of the flow meter 24 is equal to or less than the flow rate Q n-1} measured immediately before, the process proceeds to the flowchart D10, and pressure is applied to the presser 14 to set the back pressure of the presser 14 to the reference pressure PP0. Give a command to the presser pump 16.
When the flow rate measurement value Q _{n of the flow meter 24 is higher than the flow rate Q n-1} measured immediately before, the process proceeds to the flowchart D11, and the presser pump 16 applies pressure to the presser 14 in order to reduce the back pressure of the presser 14. Give a command to. This flow is repeated until the number of revolutions tends to increase.

<D10>
The control device 29 gives a command to the presser pump 16 to set the reference pressure PP0 set in advance, and adjusts the pressure of the presser 14. After that, the operation of each device is maintained in the current state, and the process shifts to the flowchart D1.

<D11>
The control device 29 gives a command to the presser pump 16 to reduce the pressure by a preset pressure width p, and reduces the pressure of the presser 14. After that, the process proceeds to the flowchart D9, and the flow rate is measured in real time.

Let the flowcharts D12 to D16 be the process <c>, of which the flowcharts D12 and D13 are (c1) and the flowcharts D14 to D16 are (c2).
<D12>
The flow rate measured by the flow meter 24 is transmitted to the control device 29 in real time, and the flow rate Q _n measured by the flow meter 24 by the control device 29 is compared with the flow rate Q _{n-1 measured immediately before.
If the flow rate measurement value Q n} of the flow meter 24 is equal to _{or greater than the flow rate Q n-1} measured immediately before, it is judged that the sludge consolidation state in the filtration chamber is appropriate, and the operation of each device is maintained in the current state. The process proceeds to the flowchart D1 and the same process is repeated.
If the flow rate measurement value Q _{n of the flow meter 24 is lower than the flow rate Q n-1} measured immediately before, it is determined that the decrease in the presser pressure was inappropriate, and the process shifts to the flowchart D13 in order to increase the decrease including the decrease. ..

<D13>
The control device 29 gives a command to the presser pump 16 to increase the pressure by twice (2p) of the preset pressure width p, and increases the pressure of the presser 14. After that, the process proceeds to the flowchart D14, and the flow rate is measured in real time.

<D14>
The flow rate measured by the flow meter 24 is transmitted to the control device 29 in real time, and the flow rate Q _n measured by the flow meter 24 by the control device 29 is compared with the flow rate Q _{n-1 measured immediately before.}
If the flow rate measurement value Q _{n of the flow meter 24 is equal to or less than the flow rate Q n-1} measured immediately before, the process proceeds to the flowchart D15, and pressure is applied to the presser 14 to set the back pressure of the presser 14 to the reference pressure PP0. Give a command to the presser pump 16.
When the flow rate measurement value Q _{n of the flow meter 24 is higher than the flow rate Q n-1} measured immediately before, the process proceeds to the flowchart D16, and the presser pump 16 applies pressure to the presser 14 in order to increase the back pressure of the presser 14. Give a command to. This flow is repeated until the number of revolutions tends to increase.

<D15>
The control device 29 gives a command to the presser pump 16 to set the reference pressure PP0 set in advance, and adjusts the pressure of the presser 14. After that, the operation of each device is maintained in the current state, and the process shifts to the flowchart D1.

<D16>
The control device 29 gives a command to the presser pump 16 to increase the pressure by a preset pressure width p, and increases the pressure of the presser 14. After that, the process proceeds to the flowchart D14, and the flow rate is measured in real time.

Here, the interval of each measurement time is appropriately determined from the model of the dehydrator, the property of sludge, and the treatment amount.
Further, the measured value immediately before the rotation speed of the screw shaft 7 may be a single measured value or an average of a plurality of measured values.

The back pressure control method in the screw press of the present invention controls the back pressure of the presser in real time according to the sludge properties in the filtration chamber of the screw press, and can maintain stable dehydration performance. Therefore, it can be applied to various solid-liquid separation devices for solid-liquid separation of sewage sludge whose properties of the undiluted solution fluctuate momentarily depending on the season, weather, etc., particularly a continuous screw press.

1 Screw press 14 Presser 21 Undiluted solution supply pump T Screw shaft torque W Moisture content D Cake thickness Q Supply flow rate p Presser back pressure pressure width

Claims (1)

In the back pressure control method in which the presser (14) of the screw press (1) is controlled while the press-fitting pressure of the sludge supplied to the screw press (1) is controlled to be constant by adjusting the supply flow rate by the undiluted solution supply pump (21).
The reference torque (T0) of the screw shaft (7), the reference moisture content (W0), the reference cake thickness (D0), the initial flow rate (Q0), and the reference pressure (PP0) of the back pressure of the presser (14) in advance. And the pressure width (p) of the back pressure of the presser (14) that is gradually increased or decreased.
<A>
At least one of the torque measurement value (T), the water content measurement value (W), and the cake thickness measurement value (D) is the reference torque (T0), the reference moisture content (W0), and the reference cake thickness (D0), respectively. When it is within the range, the operation of the screw press (1) is continued in the current state, and the control method of <a> is repeated.
When the measured torque value (T) is outside the range of the reference torque (T0) and the measured water content (W) is lower than the standard water content (W0), the pressure applied to the presser (14) is applied to the pressure width (14). After reducing by p), continue the operation of the screw press (1),
The measured torque value (T) is outside the range of the standard torque (T0), the measured water content (W) is higher than the standard water content (W0), and the measured cake thickness (D) is the standard cake thickness (D). If it is higher than D0), the pressure applied to the presser (14) is increased by the pressure width (p), and then the control method of <b> is started.
The measured torque value (T) is outside the range of the standard torque (T0), the measured water content (W) is higher than the standard water content (W0), and the measured cake thickness (D) is the standard cake thickness (D). If it is lower than D0), the pressure applied to the presser (14) is reduced by the pressure width, and then the control method of <c> is started.
<B>
(B1)
When the flow rate (Q _{n) is equal to} or higher than the flow rate (Q _n-1 ) measured immediately before, the operation of the screw press (1) is continued in the current state, and the control method of <a> is started.
When the flow rate (Q _n ) is lower than the flow rate (Q _n-1 ) measured immediately before, the pressure applied to the presser (14) is reduced by twice the pressure width (p), and then the control method (b2) is performed. Migrate to
(B2)
When the flow rate (Q _n ) is equal to or less than the flow rate (Q _n-1 ) measured immediately before, the back pressure of the presser (14) is adjusted to the reference pressure (PP0), and then the control method of <a> is started.
When the flow rate (Q _n ) is higher than the flow rate (Q _n-1 ) measured immediately before, the pressure applied to the presser (14) is reduced by the pressure width (p), and then the control method of (b2) is repeated.
<C>
(C1)
When the flow rate (Q _{n) is equal to} or higher than the flow rate (Q _n-1 ) measured immediately before, the operation of the screw press (1) is continued in the current state, and the control method of <a> is started.
When the flow rate (Q _n ) is lower than the flow rate (Q _n-1 ) measured immediately before, the pressure applied to the presser (14) is increased by twice the pressure width (p), and then the control method of (c2) is performed. Migrate to
(C2)
When the flow rate (Q _n ) is equal to or less than the flow rate (Q _n-1 ) measured immediately before, the back pressure of the presser (14) is adjusted to the reference pressure (PP0), and then the control method of <a> is started.
When the flow rate (Q _n ) is higher than the flow rate (Q _n-1 ) measured immediately before, the pressure applied to the presser (14) is increased by the pressure width (p), and then the control method of (b2) is repeated. A method for controlling back pressure in a screw press.

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