JPH08229434A - Screw type decanter and method for controlling it - Google Patents

Abstract

PURPOSE: To provide a screw type decanter which can discharge a concentrated liq. such as a sludge at a specified concn. and stably and a method for controlling it. CONSTITUTION: This decanter is provided with a rotating bowl 1 having a solid matter discharging hole 4 and an opening 3 for a separated liq., a screw conveyer 2 rotating at a different speed from the speed of the rotating bowl 1, a room 5 for the separated liq. in which the separated liq. overflowing the opening 3 for the separated liq. is retained, a control valve 16 disposed in a flow path 11 on the discharging side of a centripetal impeller 6 and a control means 17 for actuating the control valve 16. In addition, the control means 7 controls the control value 16 so as to elevate the injection pressure of the centripetal impeller 6 always higher than a specified pressure.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a screw type decanter and a method for controlling the screw type decanter, and more particularly to a screw type decanter for concentrating sludge and the like, which has a predetermined concentration and a stable flow rate. The present invention relates to a screw type decanter capable of discharging air and a control method thereof.

[0002]

2. Description of the Related Art Centrifugal concentrating method is used for concentrating raw sludge and surplus sludge generated in sewage treatment plants from the viewpoints of volume reduction efficiency, recovery rate of suspended solids, installation area and environmental problems. A screw type decanter is used. The screw type decanter includes a rotating bowl that rotates at a high speed, and a screw conveyor that is coaxially mounted in the rotating bowl and rotates at a constant differential speed with respect to the rotating bowl. The solid content with a high specific gravity, which was separated on the outer diameter side (inner wall side) of the rotating bowl, is moved by a screw conveyor and discharged from the frustoconical side of the rotating bowl as a concentrated liquid to remove sludge-removed water. Is a device for discharging as a separated liquid from the other end side.

What is important in the screw type decanter is the control of the concentration and the discharge amount of the concentrated liquid. The present inventors
First, using the above screw type decanter for sewage sludge, for the purpose of stabilizing the concentration of the concentrate,
A method for concentrating sewage sludge has been proposed, which aims at adjusting the flow rate of the separated liquid discharged from the rotating bowl (see Japanese Patent Laid-Open No. 6-320198).

[0004]

However, in the method disclosed in Japanese Patent Laid-Open No. 6-320198, since the PID control of the flow rate of the separated liquid is simply performed by using the flow rate control valve, the concentrated liquid has a predetermined concentration. Moreover, it may not be possible to stably discharge. Specifically, unexpectedly high-concentration sludge may be intermittently and collectively discharged, which causes a problem in the subsequent process. Therefore, in the screw type decanter, an improved means capable of discharging the concentrate at a more stable concentration and flow rate is desired.

[0005]

Means for Solving the Problems As a result of various studies to solve the above problems, the present inventors have obtained the following findings. In other words, in the past, since the discharge flow rate of the separated liquid was adjusted by paying attention to the concentration of the concentrated liquid, it was not possible to sufficiently follow the flow rate of the stock liquid that changes from moment to moment, and in the rotary bowl of the screw type decanter, the stock liquid was discharged for a short time. The liquid surface (free surface) changes due to the change in the flow rate at. In particular, when the supply amount of the stock solution is temporarily reduced, the discharge of the concentrated solution is stopped, and sludge having an extremely high concentration is scraped up by the screw conveyor and intermittently discharged in the form of a block.

As a result of further studies based on the above findings, the present inventors have found that in screw type decanters,
By appropriately adjusting the discharge pressure of the separated liquid according to the irregular flow rate change of the undiluted liquid, the fluctuation of the undiluted liquid flow rate is buffered and the liquid level in the rotating bowl is always maintained in the overflow state, and the rotating bowl If the concentrated component is discharged using the flow of liquid overflowing from the liquid, it will not scratch the concentrated liquid of high concentration intermittently, and as a result, it will be continuous and stable without causing an extreme concentration change in the concentrated liquid. It became clear that the present invention was completed and the present invention was completed.

That is, the present invention comprises two main points,
The first gist of the invention is to provide a rotary bowl having one end with a frustoconical portion having a solid material discharge port and the other end having a large-diameter end portion having a separation liquid port, and coaxially arranged inside the rotary bowl. And a screw conveyor that rotates at a speed different from that of the rotating bowl, a separation liquid chamber that is provided adjacent to the large-diameter end of the rotation bowl and that overflows the separation liquid port and retains the separation liquid, A centripetal impeller attached to the separation liquid chamber and having an outer peripheral portion immersed in the separation liquid, a control valve provided in a discharge side flow path of the centripetal impeller, and a control means for operating the control valve are included. , The control means,
The control pressure is set so that the discharge pressure of the centripetal impeller is higher than the reference pressure, with the discharge pressure of the centripetal impeller previously determined as the minimum pressure at which the liquid flows out from the solid matter discharge port. The screw type decanter is characterized in that it has a function of adjusting the value in a predetermined adjusting region.

In the screw type decanter, the control means discharges the solid matter from the solid matter discharge port based on the flow rate of the stock solution obtained by continuous measurement, the concentration of the solid matter in the stock solution, the concentration of the solid matter in the separated solution and the mass balance. A function to calculate the flow rate of the separated liquid so that the concentration of the concentrated liquid becomes a predetermined concentration, and use the calculated flow rate of the separated liquid as the reference flow rate to adjust the control valve so that the discharge flow rate of the centripetal impeller approaches the reference flow rate. Must be included.

The second gist of the present invention is to provide a rotary bowl having a frustoconical part having one end having a solid material discharge port and the other end having a large diameter end part having a separation liquid port, and the rotating bowl. A screw conveyor arranged coaxially inside the bowl and rotating at a speed different from that of the rotary bowl, and a screw conveyor provided adjacent to the large-diameter end of the rotary bowl and overflowing the separation liquid port to retain the separation liquid. A separating liquid chamber, a centripetal impeller attached to the separating liquid chamber and having its outer peripheral portion immersed in the separating liquid, a control valve provided in a discharge side flow path of the centripetal impeller, and the control valve. When operating a screw type decanter including a control means for operating the centripetal type decanter, the discharge pressure of the centripetal type impeller previously determined as the minimum pressure at which the liquid flows out from the solid matter discharge port is used as a reference pressure. While adjusting the control valve in a predetermined adjustment region so that the discharge pressure of the peller is higher than the reference pressure, the flow rate of the stock solution obtained by continuous measurement, the solid concentration in the stock solution, and the solid content in the separated solution Based on the concentration and the mass balance, the flow rate of the separated liquid at which the concentration of the concentrated liquid discharged from the solid matter discharge port becomes a predetermined concentration is calculated, and the calculated flow rate of the separated liquid is used as a reference flow rate, and the centripetal impeller A control method for a screw type decanter is characterized in that the control valve is adjusted in the adjustment region so that the discharge flow rate approaches the reference flow rate.

The present invention will be described in more detail below with reference to FIG. FIG. 2 is an explanatory view schematically showing a main part of the screw type decanter. That is, in the illustrated rotating bowl (1), when the separated liquid is pumped out by the centripetal pump (6) composed of the fixed impeller mounted in the separated liquid chamber (5), the following relation is established. To do. (See "Theory and Calculation of Chemical Machines," edited by Sangyo Tosho Publishing, 1970, p. 427.)

[0011]

## EQU1 ## The state in which the liquid in the rotating bowl (1) overflows the ring dam: Normal state (the liquid surface is located at the level shown by the dotted line in FIG. 2) Pn = (γ / 2g) ω ² (Rp ² −Rn ² ) ... (1) Pn: Discharge pressure of impeller ω: Angular velocity of liquid in separation liquid chamber Rp: Outer radius of impeller Rn: Free surface radius of liquid in rotating bowl γ: Specific gravity of liquid g: Gravity acceleration

The liquid level in the rotating bowl (1) is controlled by the control valve (1
When the back pressure of the valve is increased by throttling 6), the valve moves to the inner diameter side (upward in FIG. 2). Then, when the liquid in the rotary bowl (1) flows out from the solid matter discharge port (4), it is shown as follows.

[0013]

[Equation 2] The liquid in the rotating bowl (1) is the solid matter discharge port (4).
State flowing out from: overflow state (state in which the liquid surface is located at the level indicated by the chain double-dashed line in FIG. 2) Po = (γ / 2g) ω ² (Rp ² −Ro ² ) ... (2) Po: Discharge pressure of impeller Ro: Free surface radius of liquid in rotating body

From the comparison of equations (1) and (2), Po> Pn
It turns out that Then, in order to stably flow out the concentrated sludge from the solid matter discharge port (4), it is necessary to bring the liquid level in the rotating bowl (1) into an overflow state and discharge it using the liquid flow. is there. Therefore, first, the pressure gauge (14) is installed on the discharge side flow path (11) of the centripetal impeller, and on the upstream side of the control valve (16), and the liquid level in the rotating bowl (1) is the above formula ( The pressure of the pressure gauge (14) in the overflow state represented by Po of 2) is measured in advance. Then, in the actual operation, the control valve (16) is operated to discharge the separated liquid so that the pressure of the pressure gauge (14) is maintained within a predetermined range. As a result, the liquid level in the rotating bowl can be constantly maintained in an overflow state by buffering the fluctuations in the flow rate of the stock solution and other fluctuations.
The concentrated component can be smoothly discharged by utilizing the flow of the liquid in the rotating bowl, and the concentrated liquid can be stably discharged.

[0015]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is an explanatory diagram showing the structure and control system of the screw type decanter of the present invention. In this embodiment, the screw type decanter is abbreviated as "decanter".

First, the decanter of the present invention will be described. The decanter of the present invention, as shown in FIG. 1, has a frustoconical part having one end having a solid material discharge port (4) and the other end having a large diameter end part having a separation liquid port (3). Bowl (1),
A screw conveyor (2) arranged coaxially inside the rotating bowl (1) and rotating at a slightly different speed from the rotating bowl, and a separation liquid port provided adjacent to the large diameter end of the rotating bowl (1). A separation liquid chamber (5) to which the separation liquid is supplied via (3), and a centripetal impeller (6) mounted in the separation liquid chamber (5) and having its outer peripheral portion immersed in the separation liquid,
It is provided with a control valve (16) provided in the discharge side flow path (11) of the centripetal impeller (6) and a control means (17) for operating the control valve (16).

The frusto-conical portion of the rotating bowl (1) is provided with a screw conveyor (2) through which solid components such as heavy sludge having a large specific gravity centrifugally separated from the inner peripheral surface of the rotating bowl (1) are discharged by a screw conveyor (2). When it is moved to the 4) side, it functions so as to further concentrate the solid component in cooperation with the scraping action by the screw conveyor (2). Also, the rotating bowl (1)
A partition is disposed at the large-diameter end of the partition in a state orthogonal to the axis of the rotating bowl, and a plurality of separation liquid ports (3) are provided in the partition. A separation liquid chamber (5) is formed outside the partition wall, and the rotating bowl (1) is formed in the separation liquid chamber.
A centripetal impeller (6) that rotates relative to is mounted.

The shaft of the screw conveyor (2) is a hollow shaft, and the hollow end thereof has an open end of a liquid supply pipe (7) coaxially inserted from the other end of the rotating bowl (1). Part is inserted. A plurality of openings communicating with the hollow portion are provided on the peripheral surface of the shaft of the screw conveyor (2).

On the other hand, a stock solution line (13) is connected to the liquid supply pipe (7), and a concentration meter (9) and a flow meter (10) are attached to the stock solution line. Further, a separation liquid pipe (11) as a discharge side flow passage is connected to the discharge port of the centripetal impeller (6), and the pressure gauge (14) and the flow meter (15) are connected to the separation liquid pipe. , A control valve (16) and a densitometer (12) are sequentially attached from the upstream side. A concentration meter (8) for confirming the sludge concentration of the concentrated liquid is arranged in the concentrated sludge storage tank below the solid matter discharge port (4).

In the present invention, a control means (17) including an arithmetic processing unit such as a microcomputer is provided, and the control means (17) has a specific function. That is, the control means (17) uses the discharge pressure of the centripetal impeller (6) obtained during the test operation as the minimum pressure at which the clearing liquid flows out from the solid matter discharge port (4) as a reference pressure, and the centripetal impeller (6). ) Has a function of adjusting the control valve (16) in a predetermined adjustment region so that the discharge pressure of (1) becomes higher than the reference pressure. As a result, even if the flow rate of the stock solution supplied into the rotating bowl (1) changes irregularly, the liquid level in the rotating bowl (1) can be maintained constant and stable discharge of the concentrated liquid can be achieved. It will be possible.

Further, in the present invention, the control means (1
7) is based on the flow rate of the undiluted solution obtained by continuous measurement, the concentration of solids in the undiluted solution, the concentration of solids in the separated liquid and the mass balance, the concentration of the concentrated liquid discharged from the solids discharge port (4) is The control valve (16) calculates a flow rate of the separated liquid having a predetermined concentration, and uses the calculated flow rate of the separated liquid as a reference flow rate so that the discharge flow rate of the centripetal impeller (6) approaches the reference flow rate.
Also includes the function of adjusting. Therefore, in the decanter of the present invention, the concentration of the concentrated liquid discharged can be further stabilized.

In the decanter of the present invention, the stock solution line (1
The undiluted solution containing sludge introduced into the liquid supply pipe (7) through 3) is supplied into the rotating bowl (1) through the shaft of the screw conveyor (2). The supplied undiluted solution is moved to the outer diameter side, that is, to the inner peripheral wall side of the rotating bowl (1) by the high speed rotation of the rotating bowl (1), and is separated into solid content and water by centrifugal force. And the separated solids,
That is, the sludge is moved to the solid matter discharge port (4) side by the rotation of the screw conveyor (2). At that time, one end of the rotating bowl (1) is a truncated cone, and the solid matter is dehydrated while being scraped up by the screw conveyor (2) on the inclined surface. As a result, the concentrated slurry-like concentrated liquid is discharged from the solid matter discharge port (4).

Next, the decanter control method of the present invention will be described together with the function of the control means (17). In the control method of the present invention, in the above decanter, the centripetal type is set with the discharge pressure of the centripetal impeller (6) obtained at the time of test operation as the reference pressure as the minimum pressure at which the clarified liquid starts to flow out from the solid matter discharge port (4). The control valve (16) is adjusted in a predetermined adjustment region so that the discharge pressure of the impeller (6) becomes higher than the reference pressure, and the flow rate of the undiluted solution obtained by continuous measurement, the solid concentration in the undiluted solution, the separation Based on the concentration of solid matter in the liquid and the mass balance, calculate the flow rate of the separation liquid at which the concentration of the concentrated liquid discharged from the solid matter discharge port (4) reaches a predetermined concentration, and use the calculated flow rate of the separation liquid as the reference flow rate. As a result, the control valve (16) is adjusted in the adjustment region so that the discharge flow rate of the centripetal impeller (6) approaches the reference flow rate.

By the way, in the above decanter, the amount of the undiluted solution supplied to the rotating bowl (1) (Q), the concentration of the solid matter in the undiluted solution (Ci), and the flow rate of the separated solution discharged from the separated solution pipeline (Q).
l), the concentration of solids in the separated liquid (Cl), the flow rate of the concentrated liquid discharged from the solids discharge port (4) (Qs), the concentration of solids in the concentrated liquid (Cs), etc. The formula holds.

[0025]

[Formula 3] From material balance: Amount of undiluted solution supply: Q = Ql + Qs Amount of solids: Q ・ Ci = Ql ・ Cl + Qs ・ Cs When Q, Ql, Ci, Cl is measured Concentrated liquid flow rate: Qs = Q-Ql solid Amount of substance: Qs.Cs = Q.Ci-Ql.Cl Concentration of solid matter in concentrated liquid: Cs = (Q.Ci-Ql.Cl) / (Q-Ql) ... (3)

The above equation (3) means that the solid content concentration (Cs) in the concentrated liquid can be set to a predetermined value by controlling the flow rate (Ql) of the separated liquid.

In the above decanter, the stock solution line (1
The flow rate of the undiluted solution containing sludge supplied in 3) is measured by the flow meter (10), and the control means (1) outputs the signal (Q).
Input to 7). When the sludge concentration in the stock solution changes, the stock solution concentration is continuously measured by the densitometer (9) and input to the control means (17) as a signal (Ci). on the other hand,
The pressure of the separation liquid separated from the sludge and sent to the separation liquid pipe (11) is used as the back pressure of the control valve (16) and the pressure gauge (1
4) and the flow rate of the separated liquid is measured by a flow meter (1
Control means (17) as a signal (Ql) measured in 5)
Is input to The sludge concentration in the separated liquid, that is, the solids concentration, is continuously measured by a densitometer (12) and the signal (Cl)
Is input to the control means (17).

Using the various data input to the control means (17), the solid concentration (CS) of the concentrated liquid is calculated by the above equation (3). Further, the flow rate (Ql) of the separation liquid at which the solid matter concentration (CS) becomes a predetermined concentration can also be obtained from the equation (3). Regarding the solids concentration (CS) of the concentrated liquid, if the solids concentration (Ci) in the undiluted liquid and the solids concentration (Cl) in the separated liquid can be accurately measured, control the flow rate (Ql) of the separated liquid. Allows you to set the desired value relatively accurately,
There is no need for continuous measurement at all times. However, if the concentration of the concentrated liquid is very important, or if the solids concentration (Ci) in the undiluted liquid or the solids concentration (Cl) in the separated liquid cannot be accurately measured, install a concentration meter, The data is input to the control means (17) and used for setting the separated liquid flow rate (Ql). The control valve (16) is adjusted by using the calculated separated liquid flow rate (Ql) as a reference flow rate and bringing the value of the flow meter (15), that is, the discharge flow rate of the centripetal impeller (6) close to the reference flow rate. Is done. The control valve (16) is adjusted in the above-mentioned predetermined adjustment region.

As described above, in the present invention, the centripetal impeller is set with the discharge pressure of the centripetal impeller (6), which is previously determined as the minimum pressure at which the liquid flows out from the solid matter discharge port (4), as a reference pressure. Since the control valve (16) is adjusted in a predetermined adjustment region so that the discharge pressure of (6) becomes higher than the reference pressure, the flow rate of the stock solution supplied into the rotating bowl (1) changes irregularly. Even in such a case, the liquid level in the rotating bowl (1) can be maintained constant, and the stable concentrated liquid can be discharged. Then, based on the flow rate of the undiluted solution obtained by continuous measurement, the solid concentration in the undiluted solution, the solid concentration in the separated solution, and the mass balance, the flow rate of the separated solution in which the concentration of the discharged concentrated solution becomes a predetermined concentration The calculated concentration of the separated liquid is used as a reference flow rate, and the control valve (16) is adjusted in the above-mentioned adjustment region so that the discharge flow rate of the centripetal impeller (6) approaches the reference flow rate. The liquid concentration can be further stabilized.

[0030]

As described above, according to the present invention, in the screw type decanter for concentrating sludge and the like,
The liquid level in the rotating bowl is always maintained in the overflow state, and the concentrated component is discharged using the flow of the liquid overflowing from the rotating bowl, so that a high-concentration concentrated liquid can be stably discharged at a predetermined concentration. .

[Brief description of drawings]

FIG. 1 is an explanatory view showing a structure and a control system of a screw type decanter of the present invention.

FIG. 2 is an explanatory view schematically showing a main part of a screw type decanter.

[Explanation of symbols]

 1: Rotating bowl 2: Screw conveyor 3: Separation liquid port 4: Solids discharge port 5: Separation liquid chamber 6: Centripetal impeller 11: Discharge side flow path 16: Control valve 17: Control means Q: Stock solution supply amount (stock solution) Flow rate) Ci: concentration of solid matter in stock solution Ql: flow rate of separated solution Cl: concentration of solid matter in separated solution Qs: flow rate of concentrated solution Cs: concentration of solid matter in concentrated solution (concentration of concentrated solution)

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Katsuo Inoue 2-1, Okawa-cho, Kawasaki-ku, Kawasaki-shi, Kanagawa Sanryo Koki Co., Ltd. (72) Hirotaka Mori 2 Okawa-cho, Kawasaki-ku, Kawasaki-shi, Kanagawa No. 1 Sanritsu Kakoki Co., Ltd.

Claims (3)

[Claims] 1. A rotating bowl having a frusto-conical part having one end having a solid material discharge port and another end having a large diameter end having a separation liquid port, and a coaxially arranged inside of the rotating bowl. A screw conveyor that rotates at a speed different from that of the rotating bowl, a separation liquid chamber that is provided adjacent to the large-diameter end of the rotation bowl, and overflows through the separation liquid port to retain the separation liquid, and the separation liquid. A centripetal impeller mounted on the chamber and having its outer peripheral portion immersed in the separated liquid; a control valve provided in a discharge side flow path of the centripetal impeller; and a control means for operating the control valve, The control means uses the discharge pressure of the centripetal impeller previously determined as the minimum pressure at which the liquid flows out from the solid matter discharge port as a reference pressure, and the discharge pressure of the centripetal impeller becomes higher than the reference pressure. A screw type decanter having a function of adjusting the control valve in a predetermined adjusting region. 2. The control means controls the concentration of the concentrated liquid discharged from the solid discharge port based on the flow rate of the undiluted solution obtained by continuous measurement, the solid concentration in the undiluted liquid, the solid concentration in the separated liquid, and the mass balance. Calculate the flow rate of the separation liquid that gives a predetermined concentration,
The screw type decanter according to claim 1, further comprising a function of adjusting a control valve such that a calculated flow rate of the separated liquid is used as a reference flow rate so that a discharge flow rate of the centripetal impeller approaches the reference flow rate. 3. A rotating bowl having a frusto-conical portion having one end having a solid material discharge port and the other end having a large diameter end having a separation liquid port, and arranged coaxially inside the rotating bowl. A screw conveyor that rotates at a speed different from that of the rotating bowl, a separation liquid chamber that is provided adjacent to the large-diameter end of the rotation bowl, and overflows through the separation liquid port to retain the separation liquid, and the separation liquid. A screw type including a centripetal impeller mounted in a chamber and having its outer peripheral portion immersed in a separation liquid, a control valve provided in a discharge side flow path of the centripetal impeller, and control means for operating the control valve. When operating the decanter, the discharge pressure of the centripetal impeller previously determined as the minimum pressure at which the liquid flows out from the solid matter discharge port is set as a reference pressure, and the discharge pressure of the centripetal impeller is set as the reference pressure. While adjusting the control valve in a predetermined adjustment region so as to be higher than the pressure, based on the flow rate of the stock solution obtained by continuous measurement, the solid content concentration in the stock solution, the solid content concentration in the separation liquid, and the mass balance, The flow rate of the separated liquid at which the concentration of the concentrated liquid discharged from the solid matter discharge port reaches a predetermined concentration is calculated, and the calculated flow rate of the separated liquid is used as a reference flow rate, and the discharge flow rate of the centripetal impeller is set to the reference flow rate. A method of controlling a screw type decanter, characterized in that the control valve is adjusted in the adjustment region so as to approach.