JPH08332413A - Screw decanter type centrifugal separator - Google Patents

Abstract

PURPOSE: To simplify equipment constitution, to reduce running cost as well as equipment manufacturing cost to a lower level, to prolong the life of a bearing and to improve the dehydration (separation) efficiency. CONSTITUTION: A cylindrical bowl 8 is rotated by a main driving motor 58 in one direction, and also a screw conveyor 13 which is coaxial with the bowl 8 and is freely rotatable in the same direction with differential revolutions is rotated in the bowl 8 by the direct drive of an induction electric motor 52 controlled by a vector control inverter and connected to the shaft of the screw conveyor 13 through a flexible coupling 65.

Description

Detailed Description of the Invention

[0001]

INDUSTRIAL APPLICABILITY The present invention occurs in various fields such as water / sewage treatment plants, night soil treatment plants, refuse incineration / disposal plants, food industry, livestock industry, chemical industry, and steel industry. A centrifuge used for dewatering or concentrating sludge and various raw materials or products, especially a cylindrical bowl that rotates in one direction and the same direction in the bowl that is coaxial with and has a rotation difference. The present invention relates to a screw decanter type centrifugal separator (horizontal continuous centrifugal dehydrator) equipped with a screw conveyor.

[0002]

2. Description of the Related Art Generally, a screw decanter centrifuge includes a cylindrical bowl that rotates in one direction and a screw conveyor that rotates in the same direction in the bowl coaxially therewith with a rotational difference. ing. The bowl is constant in order to generate a centrifugal force to dehydrate the fluid feed mixed substance and separate it into a solid-rich component (hereinafter, dehydrated cake) and a non-solid component (liquid). It is rotated at various speeds. Due to the centrifugal force generated by this rotation, the solid matter that is heavier than water is collected on the inner surface side of the bowl. The screw conveyor rotates at a minute relative speed with respect to the bowl. This differential rotation creates relative movement between the series of screws and the wall of the bowl, so that the solids are slowly conveyed axially along the wall of the bowl. The light portion or liquid in the feed mixture separates from the solids as a result of centrifugal forces and moves radially inward. The separated heavy material, dehydrated cake, and light material, liquid, are then typically drained separately from both ends of the bowl.

The differential speed between the screw conveyor and the bowl can be varied during the operation of the centrifuge, based on several parameters and the required quality of the feed mixture in which the solids are to be separated and withdrawn. However, since these conditions are known in the actual operation, it is common to keep the rotation speed constant on the bowl side. on the other hand,
The rotation speed of the screw conveyor is always constant with respect to the rotation speed of the bowl, and the rotation speed of the screw conveyor is changed according to the transport torque of the screw conveyor.

In the operation of the screw decanter type centrifugal separator, it is required that the concentration of the dehydrated cake obtained is constant and the water content is minimized, without causing blockage in the bowl. Mechanical factors that affect the dehydration property include centrifugal force, dehydration time, bowl shape, and compaction action. The compaction action refers to the action of solid substances accumulated on the inner wall of the bowl being compressed under a high centrifugal force by a load applied to itself to increase the density and release water. If the concentration of solids supplied to the centrifuge is high, the amount of solids accumulated in the bowl will be high, and the transport torque of the screw conveyor will be high accordingly, and in some cases the allowable value will be exceeded and the machine will malfunction. .

Therefore, in the system in which the speed of rotation of the screw conveyor is always constant with respect to the speed of rotation of the bowl, even when the amount of substance to be supplied and the concentration of solid matter change and become large, the screw conveyor is conveyed. The differential speed is set large so that the torque does not exceed the allowable value.
For this reason, in this constant differential speed method, the compaction effect is small, and there is a limit to improving the dehydration performance.

On the other hand, in the system in which the number of revolutions of the screw conveyor is changed according to the conveying torque, a constant compaction action can be always ensured even when the amount of substance to be supplied or the concentration of solid matter is changed, and the dehydration performance is improved. Can be improved.
In this case, if the amount of solids on the inner wall of the bowl tends to decrease,
Since the conveying torque of the screw conveyor is reduced, the differential speed is reduced to prevent the reduction of the compaction effect, and the conveying amount of the screw conveyor is reduced to recover the solid content on the inner wall of the bowl to restore the consolidation effect. ing. On the contrary, when the solid content on the inner wall of the bowl is increasing, the differential speed of the screw conveyor is increased to increase the transport amount of the screw conveyor, and as a result, the solid content of the inner wall of the bowl is decreased and the transport of the screw conveyor is decreased. The torque is also reduced.

There are many types of drive systems for generating a differential speed between the bowl and the screw of a centrifuge, but they can be roughly classified into two types. One is a back drive system using an electric motor and a differential gear, and the other is a drive system using a hydraulic motor.

FIG. 2 is a schematic configuration diagram showing an example of a conventional screw decanter type centrifugal separator by an electric motor back drive system disclosed in, for example, Japanese Unexamined Patent Publication No. 5-184973 (conventional example 1). The screw decanter centrifuge 1 using this electric motor drive system has a main drive motor 2 and a back drive motor 3, which are connected to an AC power source 5 via a control device 4. Main drive motor 2
Drives the bowl 8 of the centrifuge 1 via the V-belt 6 and the pulley 7. The back drive motor 3 includes a V-belt 9, a pulley 11, and a gear box (planetary differential gear) 1
The screw conveyor 13 of the centrifugal separator 1 is driven via 2. The control device 4 is the first of the V / F controller 14.
The portion 14A converts alternating current (AC) power into direct current (DC) power, and the second portion 14B converts DC power into a variable voltage AC.
The electric power is converted into electric power, and the main drive motor 2 is controlled at a variable speed. On the other hand, another V / F controller 16 connected to the V / F controller 14 via the common DC bus 15 has a first portion 16A and a second portion 16B similar to those of the V / F controller 14, and the back drive motor 3 Is controlled at a second speed different from that of the main drive motor 2 so that the rotation speed of the screw becomes lower than the rotation speed of the bowl by the speed difference.

The screw conveyor 13 is provided with a plurality of nozzles 17 on the tip side of the shaft portion (right side in the drawing) for supplying the stock solution, which is a mixed material to be supplied, into the bowl 8. Both ends of the bowl 8 are rotatably supported by supports 18A and 18B, and one end is tapered.
9 is formed, and a plurality of discharge ports 21 for the dehydrated cake separated from the stock solution are provided at the taper 19 portion, and a plurality of drain ports 22 for the liquid separated from the stock solution are provided at the other end side. Further, in the control device 4, when the back drive motor 3 generates electric power by braking, this electric power is supplied to the AC power source.
A regenerative package 23 for returning to the power source 5 side is provided.

In the conventional screw decanter type centrifugal separator driven by the electric motor, the screw conveyor 13 tries to rotate at the speed of the bowl 8 due to the torque and friction generated by the rotation of the liquid and the dehydrated cake filled in the bowl 8. To do. Therefore, during operation, the back drive motor 3 receives a torque from the screw conveyor 13 to rotate at a rotational speed lower than the bowl rotational speed by a difference in speed, so that the back drive motor 3 always acts as a brake. Maintain a differential speed.

FIG. 3 is a schematic configuration diagram showing an example of a conventional screw decanter type centrifugal separator using a hydraulic motor drive system disclosed in, for example, Japanese Patent Application Laid-Open No. 4-290562 (conventional example 2). The screw decanter centrifuge 31 using this hydraulic motor drive system includes an electric motor 32 as a main drive motor for driving the bowl 8 and a hydraulic motor 33 as a motor for driving the screw conveyor 13.
And a hydraulic unit 34 for driving the hydraulic motor 33.
The hydraulic motor 33 is directly connected to the shaft of the screw conveyor 13. The driving force of the electric motor 32 is transmitted to the bowl 8 via the V belt 35 and the pulley 36. The hydraulic unit 34 is the hydraulic motor 3
3, a control pump 37 for driving the control pump 3, an electric motor 38 for driving the control pump 37, a control valve 39 for adjusting the discharge amount of the control pump 37, spool position setting means 39a of the control valve 39, and a hydraulic motor 33. A pressure detector 41 for detecting the pressure of the hydraulic pressure sent to the valve, a three-position switching valve 42 for switching the control valve 39 by an output signal from the pressure detector 41, a filter 43 and a tank 44. There is.

In the conventional screw decanter type centrifugal separator driven by this hydraulic motor, since the conveying torque can be set high, the dehydrated cake layer in the bowl can be thickened to increase the pressure density of the dehydrated cake.

Other conventional screw decanter centrifuges using a hydraulic motor drive system include those in which both the main drive motor and the screw conveyor drive motor are hydraulic motors (JP-A-3-60751). Needless to say, a hydraulic unit is necessary in this case as well.

FIG. 4 is a schematic configuration diagram of a decanter centrifuge disclosed in Japanese Patent Laid-Open No. 3-505698 (conventional example 3). This decanter centrifuge has a gear (differential gear) 1
2 and bowl 8 of centrifuge 1 and screw conveyor 1
3 and two joints 4 having bending rigidity and torsional rigidity
5 and 46, and the gear 12 is a bearing of a single gear 47, 4
It was supported by 8. With this configuration, the weight on the centrifuge 1 side is reduced, and the vibration generated from the centrifuge 1 is prevented from being transmitted to the gear 12, so that the maximum allowable rotation of the centrifuge 1 is reached. The number is increasing and the separation effect is improved.

[0015]

However, the screw decanter type centrifuge of the prior art example 1 has the drive motor 3
Since the screw conveyor 13 and the screw conveyor 13 are not directly connected, there are the following problems. B) There is a transmission loss or delay due to slippage of the V-belt 9. B) In consideration of the rotation speed of the bowl 8, the reduction ratio of the gears in the drive system of the screw conveyor 13 cannot be made large,
It is difficult to increase the output. C) The differential speed is a minimum of 3 to 5 rpm, and it is difficult to make it smaller than this. D) Since the carrying load is applied to the bowl 8 side, the capacity of the main drive motor 2 must be increased. E) It is necessary to build a regenerative circuit for energy saving operation. F) Gears (differential gears) are expensive.

G) The V / F control inverter generates a required torque due to the slip of the induction motor, and since the rotation speed of the induction motor fluctuates, independent torque control cannot be performed. Therefore, in the one using the V / F control inverter, the screw conveyor 1
In order to control the conveyance torque of No. 3 to a constant value, a torque detector is provided on the screw conveyor 13 to detect the load torque, the expected rotation speed is calculated by the computer, and the rotation speed is instructed to the screw conveyor drive motor. It must be controlled by repeating trial and error of determining whether it is the set value. Further, because of the reason (1) above, it is difficult for the indicated value and the measured value to coincide with each other, so that it is difficult to control the constant transport load (torque).

H) The gear (differential gear) 12 is mechanically a cantilever structure, and its weight occupies a considerable part of the total rotation weight of the screw decanter type centrifugal separator 1. The radial load of 18A is large, so that the life of the support 18A is short.

Re) Screw Decanter Centrifuge 1
Is an imbalance of the balance between the bowl 8 and the screw conveyor 13, obstruction of smooth rotation of the screw conveyor 13 due to mixing of foreign matter into the bowl 8, and the supports 18A and 18B.
It vibrates due to scratches on its sliding surface, oil film breakage, wear of the gear (differential gear) 12, and the like. The gear (differential gear) 12 transmits torque by meshing of a precisely processed gear, and vibration from the outside is not preferable, and this vibration is relatively heavy (differential gear) 12 May be amplified by the presence of. For these reasons, the life of the gear (differential gear) 12 and the supports 18A and 18B is shortened.

(D) Due to factors (1) and (2) above, the number of rotations of the bowl 8 can be increased or the screw conveyor 1
Even if an attempt is made to increase the carrying torque of No. 3, it is difficult to realize it due to the weight of the gear (differential gear) 12.

Further, the screw decanter type centrifugal separator of the conventional example 2 has the advantages that the above-mentioned problems do not occur and the differential speed can be reduced to 0.5 rpm, but the following new problems occur. Occurs. B) The hydraulic unit 34 is required separately. W) The hydraulic pressure loss is large. W) Hydraulic cooling water is required. F) The device configuration must be complicated. Y) The hydraulic motor 33 and the hydraulic unit 34 are expensive. T) Oil causes a fire.

(D) The hydraulic motor 33 has a cantilever structure mechanically, and its weight is slightly smaller than the weight of the gear (differential gear), but still the total weight of the screw decanter type centrifugal separator 31. Occupies a large part,
Since the radial load of the bearing of the bowl 8 on the hydraulic motor 33 side becomes large, the life of this bearing is short. (D) Due to the above factor (1), it is difficult to increase the number of rotations of the bowl 8 due to the weight of the hydraulic motor 33 being restricted.

Further, the decanter centrifuge of Conventional Example 3 has the following problems. T) The gear (differential gear) 12 is connected to the bowl 8 and the screw conveyor 13 by the two joints 45 and 46 having bending rigidity and torsional rigidity, but the joint has to have a special double structure. , Practically very difficult to manufacture and maintain. D) The bearings 47 and 48 for supporting the gear (differential gear) 12 are additionally required, and the cantilever structure causes a large radial load, resulting in a short life of the bearings 47 and 48.

The present invention has been made in order to solve the problems (1) to (4) described above, and can simplify the structure of the apparatus and keep the running cost as well as the manufacturing cost of the apparatus low. It is also an object of the present invention to obtain a screw decanter type centrifuge capable of extending the life of the bearing and improving the dehydration (separation) performance.

[0024]

A screw decanter centrifuge according to the present invention comprises a cylindrical bowl that rotates in one direction, a main drive motor that drives the bowl, and a coaxial rotation in the bowl. In a screw decanter centrifuge that has a screw conveyor that rotates in the same direction with a difference and a motor that drives the screw conveyor, and that changes the differential speed according to the conveying torque of the screw conveyor, a vector for the screw conveyor drive motor An induction motor controlled by a control inverter is used, which is connected to the shaft of a screw conveyor via a flexible shaft joint.

[0025]

In the present invention, an induction motor is used as a motor for driving the screw conveyor, and the induction motor is connected to the shaft of the screw conveyor through a flexible shaft joint to connect the induction motor to a vector control inverter (three-phase sine wave PWM control
It is controlled by digital vector control).
Vector control refers to the primary current supplied to the induction motor so that the primary current is distributed within the induction motor into an exciting current (current that generates a magnetic flux) and a torque current (current that generates a torque) according to the set values. Controlling magnitude, frequency and phase (ie current vector). There are two types of vector control, a magnetic field orientation method that requires magnetic flux detection of the induction motor and a slip frequency control method that requires rotation speed detection of the induction motor.
Either may be used. Since the vector control can control the exciting current and the torque current independently, it has the following features as compared with the conventional V / F constant control. Torque can be controlled. The speed can be controlled from zero speed, and the speed control range is wide. Control response is good. Good acceleration / deceleration characteristics.

In the induction motor which is not vector-controlled, the slip changes and the number of rotations changes when the load changes, but in the induction motor which is vector-controlled, no additional measuring instrument is necessary and 1/1000. With a very short response time of less than a second, constant rotation speed control is possible even with changes in load.
In addition, since the screw conveyor is driven by a direct drive, there is no transmission delay or loss of the belt, and the load torque and generated torque match. That is, the frequency is 0
Approximately 120 Hz, speed control range can be set to 1: 3000 to 50,000, screw conveyor rotation speed can be controlled at 0 to 3600 rpm with a 4-pole motor, and differential speed between bowl and screw conveyor can be controlled at a pitch of about 0.1 to 1 rpm. . It is possible to further increase the output, which increases the consolidation sedimentation effect,
Dehydration and separation performance are improved.

Utilizing such an advantage, the differential speed ΔN is generally (N + ΔN) with respect to the bowl rotation speed N.
The speed difference is controlled so as to give the rotation speed of the screw conveyor. On the other hand, the rotation speed of the screw conveyor is (N-Δ
It is possible to perform back drive so that the rotation speed becomes N), but in this case, it is not rational because a separate regeneration circuit is required for energy saving operation. When the screw conveyor transfer load (torque) increases simultaneously with the above-mentioned differential speed control, the differential speed is increased, which increases the solid transfer speed to increase the solid discharge amount. Conversely, the screw conveyor transfer load (torque) increases. When it decreases, the differential speed is made small, and thereby the solid conveying speed is made small to reduce the solid discharge amount, and the constant solid load control (torque) control is performed so that the solid retention time in the bowl is extended and the consolidation effect is increased. .

In the present invention, since the screw conveyor can rotate independently of the bowl without any dynamic relation, the gear (differential gear) and the hydraulic motor are unnecessary. It is possible to connect the vector-controlled induction motor and the screw conveyor through the flexible shaft coupling.

[0029]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a schematic configuration showing a screw decanter type centrifuge according to the present invention. In the figure, a conventional example (FIG. 2).
The same symbols are given to the portions corresponding to. The screw decanter type centrifuge 51 of this embodiment uses an induction motor 52 as a motor for driving the screw conveyor 13.
This is connected to the shaft of the screw conveyor 13 via a joint 65 (hereinafter referred to as a flexible shaft joint) having bending rigidity and torsional rigidity, and is connected to the AC power source 5A via the speed / torque control device 53. The speed / torque control device 53 is connected to a tachometer 54 that detects the speed of the induction motor 52 and a tachometer 55 that detects the speed of the bowl 8, and calculates the differential speed based on the detection results of these tachometers 54, 55. , A speed controller 56 for determining the speed of the induction motor 52
Based on the speed command value from the speed controller 56 and the actual speed of the induction motor 52 from the tachometer 54.
The vector controller 57 controls the excitation current and the torque current of No. 2 independently, and can always maintain the target differential speed even when the conveyance torque of the screw conveyor 13 fluctuates.

On the other hand, the main drive motor 58 is directly connected to the AC power source 5B and drives the bowl 8 of the centrifuge 51 via the V belt 59 and the pulley 61, but frequency conversion is performed by VVVF control. Preferably. The bowl 8 has supports 18 at both ends.
It is rotatably supported by A and 18B, and a taper 19 is formed on one end side. One side (left side of the figure)
A stock solution injection pipe 62 is attached to the support 18A, and the end of the injection pipe 62 is inserted into the internal space of the axial portion of the screw conveyor 13. The screw conveyor 13 is provided with a plurality of holes 13 a for introducing the stock solution supplied from the injection pipe 62 into the bowl 8. A discharge port 63 for the dehydrated cake separated from the stock solution is attached to the other support body 18B (on the right side in the drawing). The other configuration is the same as that of the above-mentioned conventional example (FIG. 2).

In the screw decanter type centrifuge of this embodiment, the speed / torque control device 53 gives the screw conveyor 13 a rotational speed of (N + ΔN) so that the differential speed is ΔN with respect to the rotational speed N of the bowl 8. Such differential speed control is performed. At the same time, when the screw conveyor transport load (torque) increases, the differential speed is increased, which increases the solid transport speed and increases the solid discharge amount. Conversely, when the screw conveyor transport load (torque) decreases, the differential speed increases. By setting a small value, the solid transfer speed is set to a small value, the solid discharge amount is reduced, the solid retention time in the bowl is extended, and the constant consolidation load (torque) control is performed to maximize the consolidation effect.

As described above, in the screw decanter type centrifuge of this embodiment, the induction motor 52 controlled by the vector control inverter is used as the motor for driving the screw conveyor 13, and the induction motor 52 is mounted on the shaft of the screw conveyor 13 as a flexible shaft coupling. Since they are connected via 65, the speed and torque of the induction motor 52 are independently controlled by the speed / torque control device 53 so as to make a slight differential speed with respect to the rotation speed of the bowl 8 without using a torque detector or the like. In addition to being controllable, the differential speed can be changed with high accuracy and responsiveness according to the transport torque.

As described above, in the present invention, the screw conveyor 13 is driven independently of the bowl 8 without any mechanical relationship with the bowl 8. Therefore, a gear (differential gear) or A hydraulic motor is not required, and the vector-controlled induction motor 52 and the shaft of the screw conveyor 13 can be connected via a flexible shaft coupling. As a result, the induction motor 52 operates in the centrifuge 5
Since the edge of the support 18B can be cut off and supported separately, the radial load of the support 18B is reduced to only the load on the centrifuge 51 side, and the life of the support 18B can be extended. Further, since the total rotational weight of the centrifuge 1 side becomes small and the vibration generated from the centrifuge 51 side is not transmitted to the induction motor 52, the vibration is suppressed only by the centrifuge 51 and resonates with the other. Vibration is reduced because there is no Therefore, it is easy to increase the rotation speed of the bowl 8 in order to increase the life of the support (bearing) and obtain a larger centrifugal effect, and to increase the conveying torque of the screw conveyor 13 in order to obtain a larger consolidation effect. Therefore, the dehydration (separation effect) function can be improved.

In the case of a relatively small-sized screw type centrifugal separator, the induction motor 52 controlled by a vector control inverter is used as a motor for driving the screw conveyor 13 in place of the rotation generally called an AC servo motor. A brushless motor having a slave position detector that is vector-controlled may be used. The brushless motor here generally uses a permanent magnet for the rotor,
An alternating current or a pulsating current is made to flow through the stator winding to create a rotating magnetic field, thus eliminating the need for a brush and a commutator which are required in a conventional DC motor.

[0035]

As described above, according to the present invention, the induction motor controlled by the vector control inverter is used as the motor for driving the screw conveyor, and the induction motor is connected to the shaft of the screw conveyor via the flexible shaft coupling. , The device configuration is simplified, not only the device manufacturing cost but also the running cost can be kept low, and the speed control and the torque control can be controlled independently.
In addition, the differential speed can be changed with high accuracy and responsiveness according to the transport torque.

Further, since the screw conveyor can be driven independently of the bowl without being mechanically related to the bowl, a gear (differential gear) and a hydraulic motor are not required, and the vector-controlled induction is used. The electric motor and the shaft of the screw conveyor can be connected via a flexible shaft coupling. As a result, the radial load of the support (bearing) is small, the total rotating weight of the screw decanter centrifuge is small, and the vibration generated from the centrifuge is not transmitted to the vector-controlled induction motor. . From these facts, the centrifuge has a structure in which vibration is unlikely to occur, so that the life of the support is extended, the rotation speed of the bowl can be increased, and a greater centrifugal effect can be obtained. Furthermore, since the conveying torque of the screw conveyor can be increased, a larger consolidation effect can be obtained, and by these, the dehydration (separation) function can be significantly improved.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a screw decanter type centrifugal separator according to the present invention.

FIG. 2 is a schematic configuration diagram of a conventional screw decanter type centrifugal separator driven by an electric motor.

FIG. 3 is a schematic configuration diagram of a conventional screw decanter type centrifugal separator driven by a hydraulic motor.

FIG. 4 is a schematic configuration diagram of another conventional example.

[Explanation of symbols]

 8 Bowl 13 Screw Conveyor 52 Induction Motor (Screw Conveyor Drive Motor) 58 Main Drive Motor 65 Flexible Shaft Coupling

Claims (1)

[Claims] 1. A cylindrical bowl that rotates in one direction, a main drive motor that drives the bowl, and a screw conveyor that rotates in the same direction in the bowl coaxially therewith with a rotation difference. With a motor for driving this screw conveyor, in the screw decanter centrifuge that changes the differential speed according to the transport torque of the screw conveyor, using an induction motor controlled by a vector control inverter to the screw conveyor drive motor, A screw decanter centrifuge characterized by connecting this to a shaft of a screw conveyor via a flexible shaft joint.