JPH0889846A - Method of operating screw centrifugal separator - Google Patents

Abstract

PURPOSE: To prevent a liquid from discharging from a solid discharge outlet when a screw centrifuge is stopped. CONSTITUTION: When stopping a centrifuge 1, just before the centrifugal force is reduced to a level corresponding to the gravity and the rotation speed becomes such one as a liquid ring collapses, the rotation speed of the centrifuge drum 2 and/or the rotation speed of the screw drum 4 are changed abruptly in a short time and a liquid having inertia not following this rotation speed change is carried out in spiral by a sending screw 3 so as to be sent to a discharging outlet 5 for light material 11.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method of operating a screw centrifuge.

[0002]

2. Description of the Related Art A centrifuge drum rotatably supported around a vertical axis and a centrifuge drum coaxially arranged inside the centrifuge drum and rotating at a different rotational speed (high speed or low speed) from the centrifuge drum. A screw centrifuge for separating a solid-liquid mixture having a spiral feed screw fixed to a screw drum is well known. In this screw centrifuge, the mixture to be separated is fed along the axis of the centrifuge drum, and the separated light and heavy substances are discharged from outlets provided at both ends of the centrifuge drum. Since the radial distance from the shaft axis of the shaft of the centrifuge drum to the outlet is shorter than the distance from the wall of the centrifuge drum to the above axis, the centrifugal force during operation of the screw centrifuge causes liquid inside the centrifuge drum. You can make a ring.

When a solid-liquid mixture is separated by this screw centrifuge, the centrifugal force reaching several times the gravity generated by the rotation of the screw centrifuge causes the solid-liquid mixture to be separated from the solid-liquid mixture to be separated in the centrifugal separation drum. The resulting liquid ring is formed. The liquid ring consists mainly of separated liquids, the inner diameter of the liquid ring being determined by the radial position of the outlet of the light substance (eg separated liquid). In the liquid ring, a substance having a high specific gravity and a substance having a low specific gravity are separated by the action of centrifugal force. In this case, the material having a high specific gravity (solid) is sent to the outer edge of the liquid ring, that is, the wall side of the centrifuge drum, and the material having a low specific gravity (liquid) comes inside the liquid ring, that is, above the material having a high specific gravity.

The substance having a high specific gravity is captured by a feed screw which is rotated in the same direction as the centrifugal drum at a speed slower or faster than the rotation speed of the centrifugal drum, and is sent to one end of the centrifuge. Is discharged to the outside of the centrifuge. The lighter specific gravity material flows to the outlet provided at the opposite end of the centrifuge drum. In this case, at least a part of the material having a low specific gravity flows in the direction opposite to the feed screw feed direction through the passage formed by the feed screw.

If the centrifuge, which was operating at a high speed, is stopped now, the rotation speed of the centrifuge is gradually reduced, the centrifugal force is also reduced, and finally the centrifuge is stopped. In this case, when the centrifugal force reaches the number of rotations lower than gravity, the liquid ring formed in the centrifuge drum “collapses”, and the filling level in the centrifuge drum is higher than that of the outlet of the substance having a high specific gravity. It goes up to the upper side, and as a result, a substance with a low specific gravity flows out in a wavy form from this outlet for a short time, in other words, it becomes a separation failure and a substance with a high specific gravity must be processed again. Disappear.

[0006]

The problem to be solved by the present invention is to provide a method of operating a screw centrifuge without the above-mentioned drawbacks when the centrifuge is stopped.

[0007]

SUMMARY OF THE INVENTION The present invention comprises a centrifuge drum rotatably supported about a longitudinal axis and a centrifuge drum disposed coaxially with the centrifuge drum and having a different rotation. A spiral feed screw fixed to a screw drum rotating by a number, means for feeding the mixture to be separated along the axis of the centrifuge drum, and a separate light weight provided at opposite ends of the centrifuge drum It has a discharge port for substances and heavy substances, the radial distance from the axis of the centrifuge drum to the discharge port is shorter than the distance from the wall of the centrifuge drum to the above axis, and centrifugal force is applied during operation. In the method of operating a screw centrifuge for separation of a solid / liquid mixture in which a liquid ring is formed inside the drum, when the centrifuge is stopped, the centrifugal force must be low enough to correspond to gravity. Immediately before the rotational speed reaches such a level that the liquid ring collapses, the rotational speed of the centrifuge drum and / or the rotational speed of the screw drum is suddenly changed in a short time, and the inertia is such that the change in rotational speed is not followed. A method is provided, characterized in that the liquid ring is fed by means of a feed screw to the outlet of the lighter substance.

[0008]

The feeding action of the feed screw depends on the difference in rotational speed between the feed screw and the substance to be fed, and the feeding direction is determined by the rotation direction of the feed screw and the spiral direction of the feed screw.

In the case of a screw centrifuge in which the feed screw has a higher speed, the rotation speed of the feed screw is higher than the rotation speed of the transfer material, that is, the heavy material rotating together with the centrifuge drum. Therefore, the substance to be transferred is sent by the feed screw to one end of the centrifuge corresponding to the spiral direction.

Now, when shutting down this centrifuge, more precisely, when the number of revolutions of the centrifuge drum decreases until just before the collapse of the liquid ring begins, the centrifuge drum and / or the feed according to the method of the invention If the number of rotations of the screw is suddenly changed by braking, the following occurs in the centrifuge.

That is, the liquid ring that was rotating with the centrifuge drum held its speed by inertia, which was faster than the damped feed screw. The feed direction of the feed screw is reversed to the other end of the liquid separator. When the liquid ring collapses, the liquid “flows in a spiral” towards the end of the centrifuge, which is provided with a light material outlet so that no liquid flows out of the heavy material outlet. .

In the case of a screw centrifuge in which the feed screw has a lower speed, the rotation speed of the feed screw is smaller than that of the centrifuge drum (the rotation direction of the centrifuge drum and the feed screw or the spiral direction of the feed screw). , As opposed to a screw centrifuge where the feed screw is at a high speed), so that in this case too the transfer of heavy substances towards the outlet takes place.

In order to prevent heavy substances from being discharged from the discharge port when the liquid ring collapses, the transport direction of the feed screw is reversed when the centrifuge is stopped, so that the liquid ring is more than the feed screw. Need to rotate at low speed. This is achieved in the method of the invention by rapidly increasing the rotational speed of the centrifuge drum and / or the feed screw for a short period of time. That is, again, because of its inertia, the liquid ring remains slow for the first predetermined time, so that the collapsing liquid ring "helixes" to the outlet for the light material. Embodiments of the present invention will be described below with reference to the accompanying drawings.

[0014]

EXAMPLE A solid-liquid mixture to be separated is supplied to a screw centrifuge 1 along a rotation axis through a supply device 14 and a separation chamber consisting of a centrifugal drum 2 and a screw drum 13 through an opening 7. Sent to. A centrifugal force acts on the supplied mixture to form a liquid ring. The outer diameter of the liquid ring corresponds to the inner diameter of the centrifuge drum, and the inner diameter of the liquid ring (corresponding to the broken line 9 in FIG. 1) is determined by the position of the dam 8 of the light substance (liquid) discharge port 5.

In the method of the present invention, the centrifuge drum 2 and / or the feed screw 4 is braked when the centrifuge is stopped to rapidly change the rotation speed. In this case, since the liquid ring has inertia and does not follow the above-mentioned change, the direction opposite to the transfer direction of the feed screw 4 (the right side in Fig. 1), that is, the lighter substance, at a rotation speed higher than that of the feed screw 4. “Helix” in the direction of the discharge port 5 (left side in FIG. 1).

Since the volume of light substances 11 that can be discharged from the discharge port 5 is limited, not all liquids can be discharged immediately, so a predetermined time from the start of disintegration (the time until most of the liquid is discharged) During a), the liquid is drawn back from the outlet 6 of the heavy substance 10 and creates a new liquid ring with an inner surface 12 which presses the liquid against the left end wall of the centrifuge drum 2. In this method of the present invention, it is possible to reliably prevent the liquid from being discharged from the discharge opening 6 of the heavy substance 10 when the liquid ring is broken.

The present invention is not limited to the embodiment of the counter-current screw centrifuge shown in the drawings, but other screw centrifuges in which the rotation speed of the feed screw is higher or lower, such as a co-current screw centrifuge. It can also be applied to a separator or a centrifugal screw classifier.

[Brief description of drawings]

FIG. 1 is a conceptual cross-sectional view of a counterflow type completely enclosed screw centrifuge in which a feed screw has a higher speed.

[Explanation of symbols]

1 Centrifuge 2 Centrifuge drum 3 Feed screw 4 Screw drum 5 Light material discharge port 6 Heavy material discharge port

Claims (3)

[Claims] 1. A centrifuge drum rotatably supported around a longitudinal axis, and a screw drum which is arranged inside the centrifuge drum coaxially with the centrifuge drum and which rotates at a different rotational speed from the centrifuge drum. Spiral feed screw, means for feeding the mixture to be separated along the axis of the centrifuge drum, and outlet for separated light and heavy substances provided at opposite ends of the centrifuge drum And the radial distance from the axis of the centrifuge drum to the outlet is shorter than the distance from the wall of the centrifuge drum to the axis, and during operation the centrifugal force creates a liquid ring inside the centrifuge drum. In the operating method of the screw centrifuge for separation of solid-liquid mixture, when the centrifuge (1) is stopped, the centrifugal force is reduced to a level corresponding to gravity and the liquid ring collapses. Just before the rotation speed reaches such a value, the rotation speed of the centrifuge drum (2) and / or the rotation speed of the screw drum (4) is rapidly changed in a short time so that inertia that does not follow this change in rotation speed is set. The liquid ring which has a light substance (11) by means of a feed screw (3)
The method characterized by sending to the discharge port (5). 2. Centrifugal drum in the case of a screw centrifuge (1) in which the screw drum (4) has a higher speed.
The rotation speed is rapidly changed in a short time by an operation of braking the (2) and / or the screw drum (4).
the method of. 3. A centrifuge drum in the case of a screw centrifuge (1) in which the screw drum (4) has a lower speed.
The rotation speed is rapidly changed in a short time by an operation of accelerating the (2) and / or the screw drum (4).
the method of.