JP2003205391A - Method for controlling back pressure of screw press - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for controlling the back pressure of a screw press which prevents any occurrence of co-rotation phenomenon of a dehydration cake. <P>SOLUTION: A back pressure plate device 9 to apply the pressure in the direction opposite to the sewage feeding direction as the back pressure is provided on a discharge port 7 of a filter cylinder 1, and the back pressure plate device 9 comprises a back pressure plate 10 and a pneumatic cylinder device 11 to press the back pressure plate 10 toward the discharge port 7 side. A pressure regulator 22 to regulate the pressure of air to be fed from a compressor 21 to the cylinder device 11, and a control device 23 are arranged. The control device 23 fluctuates the back pressure given by the back pressure plate 10 to the reference back pressure and the predetermined low level back pressure lower than the reference back pressure alternately in a time series manner by controlling the pressure regulator 22. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a screw press back pressure control method for squeezing and squeezing sewage sludge, industrial wastewater sludge and the like to be pressed.

[0002]

2. Description of the Related Art Conventionally, as a screw press of this type, as shown in FIG. 5, for example, a rotatable screw shaft 2 is concentrically inserted into a cylindrical filter cylinder 1 arranged horizontally. Has been done. The filter cylinder 1 is composed of a thin filter medium 3 made of punching metal or the like, and a protective cylinder body 4 having a larger hole than the filter medium 3 and protecting the outside of the filter medium 3. Further, the screw shaft 2 is formed in a taper shape having a small diameter on the supply side and a large diameter on the discharge side, and is rotationally driven by a driving device such as a motor 12.

A supply pipe 5 for supplying sludge (object to be squeezed) into the filter cylinder 1 is connected to one end of the screw shaft 2 through a joint (not shown). Further, at one end of the screw shaft 2, there is formed a supply port 6 which opens to the outer peripheral surface of the screw shaft 2 and communicates with the inside of the supply pipe 5.
Further, at the other end of the filter cylinder 1, a discharge port 7 for discharging dehydrated sludge from the inside of the filter cylinder 1 is formed. On the outer periphery of the screw shaft 2, screw blades 8 are provided to feed the sludge supplied from the supply port 6 into the filter cylinder 1 to the discharge port 7.

Behind the discharge port 7, there is provided a back pressure plate device 9 for causing the pressure in the discharge port 7 in the direction opposite to the sludge feeding direction to act as back pressure. The back pressure plate device 9 includes an annular back pressure plate 10 having a tapered surface facing the discharge port 7, and a pneumatic cylinder device 11 that presses the back pressure plate 10 toward the discharge port 7. The other end of the screw shaft 2 penetrates the central opening of the back pressure plate 10.

According to this, the supply port 6 is passed through the supply pipe 5.
The sludge supplied from the inside to the inside of the filter cylinder 1 is sent to the discharge port 7 side by the screw blade 8 that rotates together with the screw shaft 2. Since the screw shaft 2 has a larger diameter on the discharge side, the distance between the outer peripheral surface of the screw shaft 2 and the inner peripheral surface of the filter cylinder 1 (that is, the internal volume) gradually decreases as it approaches the discharge port 7 side. , The sludge is squeezed. The dehydrated separated liquid separated from the sludge by such pressing passes through the filter cylinder 1 and is discharged below the filter cylinder 1. When the dehydrated cake after the sludge has been dehydrated reaches the discharge port 7, the back pressure plate 10 is pushed back, and the tapered surface of the back pressure plate 10 and the discharge port 7 (the filter cylinder 1
(The end portion on the discharge side) is pushed out to the outside.

At this time, the back pressure plate 10 is a cylinder device 11
When the dewatering cake is pressed and squeezed by a constant reference back pressure S, the dewatering cake is pressed and the pressing force of the dewatering cake becomes higher than the reference back pressure S of the back pressure plate 10. The dehydrated cake pushes back the back pressure plate 10 and is discharged from the discharge port 7.

The above-mentioned standard back pressure S is set to an appropriate value in accordance with various conditions such as the type of sludge, the water content and the treatment amount. Therefore, when the standard back pressure S is set low, the drainage of the dehydrated cake from the outlet 7 is promoted, so that the amount of dehydration treatment is improved, but the pressing is insufficient and the moisture content of the dehydrated cake is increased. On the contrary, when the standard back pressure S is set to be high, the dehydration cake is suppressed from being discharged from the discharge port 7, so that the dehydration treatment amount is reduced, but the water content of the dehydration cake is reduced and the sludge is sufficiently removed. It can be dehydrated.

[0008]

SUMMARY OF THE INVENTION In the above conventional format,
The dehydrated cake slides (slips) in the circumferential direction with respect to the rotating screw blades 8, and the screw shaft 2
It moves to the discharge port 7 side along the axial direction of. Then, as the dehydrated cake is compressed and the pressure increases as it approaches the discharge port 7, the dehydrated cake is strongly pressed and attached to the screw shaft 2 and the screw blades 8, and together with the screw shaft 2 and the screw blades 8. There was a problem that a co-rotation phenomenon such as rotation occurred. When such a co-rotation phenomenon occurs, the dehydrated cake only rotates on the spot and does not move to the discharge port 7 side, which hinders the discharge of the dehydrated cake.

Further, when the reference back pressure S of the back pressure plate 10 is set to be excessively high in order to improve the dehydration efficiency, the discharge port 7
The nearby dewatered cake cannot be smoothly discharged from the discharge port 7, and the undewatered sludge on the upstream side (supply side) in the filter cylinder 1 short-passes (jumps) to the downstream side (discharge side). However, there is also a problem that the water content of the dehydrated cake cannot be lowered sufficiently.

An object of the present invention is to provide a screw press back pressure control method capable of preventing the co-rotation phenomenon and the short pass phenomenon of a dehydrated cake.

[0011]

In order to solve the above-mentioned problems, a back pressure control method for a screw press according to a first aspect of the present invention is such that a rotatable screw shaft is provided in a filtration cylinder, and the screw shaft is provided. The outer periphery of is provided with a screw blade that feeds the object to be squeezed supplied into the filter tube to the outlet, and at the outlet of the filter tube, the pressure in the direction opposite to the feeding direction of the object to be squeezed is used as back pressure. A back pressure control method of a screw press provided with a back pressure plate device to act, the back pressure given by the back pressure plate device, a reference back pressure, and a predetermined lower back pressure lower than this reference back pressure, It is to change alternately in time series.

According to this, the object to be squeezed supplied into the filter cylinder is squeezed while being sent to the outlet side by the screw blades which rotate integrally with the screw shaft to be a dehydrated cake, which presses the back pressure plate device. It is discharged from a gap formed between the back pressure plate device and the discharge port.

When the back pressure applied by the back pressure plate device is the reference back pressure, there is a predetermined gap between the back pressure plate device and the discharge port. Further, when the back pressure applied by the back pressure plate device changes from the standard back pressure to the lower back pressure, the gap between the back pressure plate device and the discharge port becomes larger than the predetermined gap, and therefore, when discharging. The resistance is reduced and the drainage of the dehydrated cake from the outlet is promoted. As a result, the pressure of the dehydrated cake in the filtration cylinder becomes lower than that in the case of the above-mentioned reference back pressure, so that the force when the dehydrated cake is pressed against the screw shaft or the screw blade is weakened, and the screw shaft or screw blade of the dehydrated cake is reduced. It is possible to prevent the adhesion of the dehydrated cake to the co-rotation phenomenon.

After that, when the back pressure of the back pressure plate device returns from the low back pressure to the reference back pressure, the gap between the back pressure plate device and the discharge port is reduced and returns to a predetermined gap. According to a second aspect of the present invention, there is provided a back pressure control method for a screw press, wherein a rotatable screw shaft is provided in a filtration cylinder, and an object to be squeezed supplied into the filtration cylinder is discharged at an outer periphery of the screw shaft. In the back pressure control method of the screw press, which is provided with a screw blade for feeding to the outlet of the filtration cylinder, a back pressure plate device that acts as a back pressure with a pressure in a direction opposite to the feeding direction of the object to be squeezed is provided. Therefore, the back pressure applied by the back pressure plate device is alternately varied in time series between the reference back pressure and a predetermined high back pressure higher than the reference back pressure.

According to this, the object to be squeezed supplied into the filter cylinder is squeezed while being sent to the discharge port side by the screw blades which rotate integrally with the screw shaft to become a dehydrated cake, which presses the back pressure plate device. It is discharged from a gap formed between the back pressure plate device and the discharge port.

When the back pressure provided by the back pressure plate device is the reference back pressure, a predetermined gap is provided between the back pressure plate device and the discharge port. Further, when the back pressure applied by the back pressure plate device changes from the reference back pressure to the high level back pressure, the gap between the back pressure plate device and the discharge port becomes smaller than the predetermined gap, and therefore, when discharging. The resistance increases, and the discharge of the dehydrated cake from the discharge port is suppressed. As a result, the dehydrated cake in the filter cylinder is squeezed at a higher pressure than in the case of the standard back pressure, so that the dehydration efficiency is improved.

In this state, the dehydrated cake in the vicinity of the discharge port cannot be discharged smoothly and a short pass phenomenon occurs, but thereafter, the back pressure applied by the back pressure plate device changes from the high back pressure to the reference back pressure. By changing the pressure, the gap between the back pressure plate device and the discharge port returns to a predetermined gap, so that the dehydrated cake near the discharge port is smoothly discharged from the gap between the back pressure plate device and the discharge port. It is possible to prevent the pass phenomenon from occurring.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION A first embodiment of the present invention will be described below with reference to FIGS. The same components as those of the conventional one described above are designated by the same reference numerals, and the description thereof will be omitted.

A compressor 21 (compressed air supply device) for supplying compressed air for operation to each cylinder device 11 and a pressure adjusting device 2 for adjusting the pressure of the air supplied from the compressor 21 to each cylinder device 11.
2 (regulator) is connected. Also, FIG.
As shown in (a), the control device 23 controls the pressure adjusting device 2
By controlling 2, the back pressure applied by the back pressure plate 10 is alternately changed in time series between the reference back pressure S and a predetermined lower back pressure A lower than the reference back pressure S. is there. Furthermore, the fluctuation cycle of the back pressure of the back pressure plate 10 is set to T1,
When the time required for the screw shaft 2 to make one rotation is T2, the control device 23 controls the pressure adjusting device 22 so that T1 ≦ T2. The fluctuation period T1
Is the sum of the time ts during which the reference back pressure S continues and the time ta during which the low back pressure A continues. In addition, the fluctuation cycle T1
The time T2 is measured by the timer 24 attached to the control device 23, and the control device 23 controls the back pressure to be switched based on the measured value.

The operation of the above structure will be described below.
The sludge (an example of an object to be squeezed) supplied from the supply port 6 into the filtration cylinder 1 through the supply pipe 5 is squeezed while being sent to the discharge port 7 side by the screw blade 8 that rotates integrally with the screw shaft 2. As a result, the cake becomes dehydrated cake, and the back pressure plate 10 is pressed to be discharged from the gap formed between the back pressure plate 10 and the discharge port 7 (the discharge side end of the filter cylinder 1).

At this time, as shown in FIG. 3 (a), the back pressure plate 10 is pressed toward the discharge port 7 side by the cylinder device 11 with the reference back pressure S for a predetermined time ts.
A predetermined gap is formed between the back pressure plate 10 and the discharge port 7.

After the elapse of the fixed time ts, the back pressure plate 10 is pressed toward the discharge port 7 side by the low back pressure A by the cylinder device 11 for a constant time ta, so that the back pressure plate 10 and the discharge port 7 are discharged. Since the gap between and becomes larger than the above-mentioned predetermined gap, the resistance at the time of discharging the dehydrated cake is reduced, and the discharge of the dehydrated cake from the discharge port 7 is promoted. As a result, the pressure of the dehydrated cake in the filter cylinder 1 becomes lower than that in the case of the above-mentioned reference back pressure S, so that the force when the dehydrated cake is pressed by the screw shaft 2 and the screw blades 8 is weakened. Therefore, the adhesion of the dehydrated cake to the screw shaft 2 and the screw blade 8 is eliminated, and the co-rotation phenomenon of the dehydrated cake can be prevented.

When the low back pressure A is set, the water content of the dehydrated cake discharged from the discharge port 7 increases. However, after the elapse of the predetermined time ta, the back pressure of the back pressure plate 10 becomes low. When the back pressure S is returned to the reference back pressure S, the gap between the back pressure plate 10 and the discharge port 7 is reduced and returns to a predetermined gap, so that the water content of the dehydrated cake is reduced and returned to the original value.

By rotating the screw shaft 2 once, the sludge in the filter cylinder 1 is sent in the axial direction of the screw shaft 2 by one pitch of the screw blades 8, as shown in FIG. 3 (a). As shown, based on the relationship of T1 ≦ T2, while the sludge moves by one pitch, the back pressure plate 10
Since the back pressure changes to the reference back pressure S and the lower back pressure A alternately, it is possible to prevent the co-rotation phenomenon of the dehydrated cake from occurring in small increments every one pitch.

An example of numerical values of the reference back pressure S, the low back pressure A, the fluctuation period T1, and the times T2, ts, and ta will be described below. S = 50 kPa, A = 30 kPa ts = 120 seconds, ta = 15 seconds T1 = 120 + 15 = 135 seconds, T2 = 180 seconds Next, a second embodiment of the present invention will be described with reference to FIG.

As shown in FIG. 4A, the controller 23
By controlling the pressure adjusting device 22, the back pressure plate 1
The back pressure given by 0 is the reference back pressure S and this reference back pressure S
The predetermined higher back pressure B which is higher than the predetermined higher back pressure B is alternately changed in time series. Further, when the fluctuation period of the back pressure of the back pressure plate 10 is T1 and the time required for the screw shaft 2 to make one rotation is T2, the control device 23 uses T1 ≦ T.
The pressure adjusting device 22 is controlled so as to be 2. still,
The fluctuation period T1 is the time ts during which the reference back pressure S continues.
And the time tb during which the high back pressure B continues.

The operation of the above structure will be described below.
The sludge (an example of an object to be squeezed) supplied from the supply port 6 into the filtration cylinder 1 through the supply pipe 5 is squeezed while being sent to the discharge port 7 side by the screw blade 8 that rotates integrally with the screw shaft 2. As a result, a dehydrated cake is formed, which is pressed against the back pressure plate 10 and is discharged from a gap formed between the back pressure plate 10 and the discharge port 7.

At this time, as shown in FIG. 4 (a), the back pressure plate 10 is pushed toward the discharge port 7 side by the reference back pressure S by the cylinder device 11 for a predetermined time ts,
A predetermined gap is formed between the back pressure plate 10 and the discharge port 7.

After the elapse of the fixed time ts, the back pressure plate 10 is pressed toward the discharge port 7 side by the high back pressure B by the cylinder device 11 for a constant time tb, whereby the back pressure plate 10 and the discharge port 7 are discharged. Since the gap between and is smaller than the predetermined gap, the resistance at the time of discharging the dehydrated cake is increased, and the discharge of the dehydrated cake from the discharge port 7 is suppressed. As a result, the dehydrated cake in the filter cylinder 1 has a standard back pressure S
Since it is squeezed at a higher pressure than in the above case, the dehydration efficiency is improved.

In this state, the dehydrated cake in the vicinity of the discharge port 7 cannot be discharged smoothly and a short pass phenomenon occurs, but after the elapse of the above-mentioned certain time tb, the back pressure plate 10 is generated.
By returning the back pressure from the high back pressure B to the reference back pressure S,
Since the gap between the back pressure plate 10 and the discharge port 7 expands and returns to a predetermined gap, the dehydrated cake near the discharge port 7 is smoothly discharged from the gap between the back pressure plate 10 and the discharge port 7, and It is possible to prevent the occurrence of the short pass phenomenon.

Further, when the screw shaft 2 makes one rotation, the sludge in the filter cylinder 1 is sent in the axial direction of the screw shaft 2 by one pitch of the screw blades 8, depending on the relationship of T1≤T2. While the sludge moves by one pitch, the back pressure of the back pressure plate 10 fluctuates between the standard back pressure S and the high-order back pressure B, so that the occurrence of the short pass phenomenon of the dehydrated cake is prevented in small steps every one pitch. can do.

In the first embodiment, as shown in FIG. 3 (a), the relationship between the reference back pressure S and the low back pressure A is changed so as to form a square graph. As shown in (b), the graph may have a triangular waveform, and the graph may be gradually increased or decreased and changed. Similarly, in the second embodiment, as shown in FIG. 4A, the relationship between the reference back pressure S and the high back pressure B is changed so as to form a square graph. As shown in (b), the graph may have a triangular waveform, and the graph may be gradually increased or decreased and changed.

In the first and second embodiments, the back pressure plate 10 is constructed by using the pneumatic cylinder device 11.
However, by using a spring instead of the cylinder device 11 and changing the compression allowance of the spring, the back pressure of the back pressure plate 10 becomes a standard back pressure S, a low back pressure A, and a high back pressure B. It may be changed.

In the first and second embodiments described above, the sludge (organic sludge) is mentioned as an example of the object to be squeezed, but it is not limited to sludge.

[0035]

As described above, according to the first aspect of the present invention, the back pressure applied by the back pressure plate device is changed to the reference back pressure and the lower back pressure, so that the screw shaft and the screw blade of the dehydrated cake are fed. It is possible to prevent the adhesion of the dewatering cake and prevent the co-rotation phenomenon of the dehydrated cake.

According to the second aspect of the present invention, the back pressure applied by the back pressure plate device varies between the reference back pressure and the high back pressure, thereby improving the dehydration efficiency and preventing the occurrence of the short pass phenomenon. be able to.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a screw press according to a first embodiment of the present invention.

FIG. 2 is an enlarged view of the vicinity of a back pressure plate of the screw press.

FIG. 3 is a graph showing a relationship between a back pressure by a back pressure plate of a screw press and time, (a) shows a case where the back pressure is changed so as to have a rectangular shape, and (b) shows (b). The case where the back pressure fluctuates so as to form a triangular wave graph is shown.

FIG. 4 is a graph showing the relationship between the back pressure by the back pressure plate of the screw press and the time in the second embodiment of the present invention, (a) shows the back pressure varied so as to be a square graph. The case is shown, and (b) shows the case where the back pressure is changed so as to form a triangular wave graph.

FIG. 5 is a configuration diagram of a conventional screw press.

[Explanation of symbols]

1 Filter cylinder 2 screw shaft 7 outlet 8 screw blades 9 Back pressure plate device S standard back pressure A low back pressure B High back pressure

Claims (2)

[Claims] 1. A rotatable screw shaft is provided in a filtration cylinder, and a screw blade is provided on the outer periphery of the screw shaft for feeding the object to be compressed supplied into the filtration cylinder to a discharge port. At the discharge port, a method of controlling the back pressure of a screw press provided with a back pressure plate device that acts as a back pressure in a direction opposite to the feeding direction of the object to be squeezed, wherein the back pressure given by the back pressure plate device is A back pressure control method for a screw press, wherein the back pressure and a predetermined lower back pressure lower than the reference back pressure are alternately varied in time series. 2. A rotatable screw shaft is provided in the filtration cylinder, and a screw blade is provided on the outer periphery of the screw shaft for feeding the object to be compressed supplied into the filtration cylinder to a discharge port. At the discharge port, a method of controlling the back pressure of a screw press provided with a back pressure plate device that acts as a back pressure in a direction opposite to the feeding direction of the object to be squeezed, wherein the back pressure given by the back pressure plate device is A back pressure control method for a screw press, characterized in that the back pressure and a predetermined high back pressure higher than the reference back pressure are alternately varied in time series.