WO1989011560A1

WO1989011560A1 - A device for discharging a reject from a separation device

Info

Publication number: WO1989011560A1
Application number: PCT/SE1989/000224
Authority: WO
Inventors: Folke Jakobson
Original assignee: Celleco Ab
Priority date: 1988-05-17
Filing date: 1989-04-21
Publication date: 1989-11-30
Also published as: SE8801841L; SE461153C; SE8801841D0; SE461153B

Abstract

A device for discharging a reject containing undesired solid particles from a separation device, in which said reject is separated from a mixture of liquid and solid particles, preferably a fibre suspension, the mixture being subjected to an overpressure during the separation, comprises a housing (1) forming a chamber (2), an inlet (10) in the housing for supplying said reject from the separation device to the chamber, an outlet (13) in the housing for discharging reject from the chamber, and two valves (12, 14) arranged in said reject inlet and reject outlet for opening and closing of the latter. According to the invention the substantial part (17) of the volume of the chamber (2) is situated above the opening of the reject inlet (10) into the chamber, whereby air is prevented from flowing from the chamber into the separation device when discharging reject from the latter into the chamber.

Description

A device for discharging a reject from a separation device

The present invention relates to a device for discharging a reject con¬ taining undesired solid particles from a separation device, in which said reject is separated from a mixture of liquid and solid particles, the mixture being subjected to an overpressure during the separation. The discharge device comprises a housing forming a chamber, an inlet in the housing for supplying said reject from the separation device to the chamber, an outlet in the housing for discharging reject from the cha - ber, and two valves arranged in said reject inlet and reject outlet, respectively, for opening and closing of the latter.

In the cellulose and paper industry wooden fibres are elutriated into a so called fibre suspension for further treatment in various process stages, for instance for producing paper pulp. This fibre suspension often contains undesired solid particles, like wood pieces, rubber frag¬ ments, plastic pieces, metal pieces, bale bands, etc. In order to clean the fibre suspension from these undesired solid particles usually a separation device is used, in which the fibre suspension is rotated, whereby i.a. centrifugal forces are utilized for separating the fibre suspension into an accept fraction containing fibres and a reject frac¬ tion containing the undesired solid particles. If necessary, said centri¬ fugal separation is supplemented by straining the fibre suspension by means of a strainer arranged in the separation device.

Since the fibre suspension because of its rotation is subjected to an overpressure in the separation device, and the discharge opening for reject from the separation device needs to be dimensioned to allow passage of the largest undesired particles, in practice it is impossible to discharge the reject intermittently and directly from the separation device without loosing a large amount of fibres. To decrease the fibre losses when discharging the reject a known discharge device of the kind initially described is utilized for locking the reject from the separa¬ tion device. In this known device the reject is first discharged from the separation device into the chamber of the discharged device, while the reject outlet in the latter is kept closed,.after which the reject inlet of the chamber is closed and the reject outlet of the chamber is opened, so that the chamber in its turn is emptied of reject.

A drawback to the known discharge device is that when discharging reject from the separation device into the chamber of the discharge device, air will force from the latter upstreams into the separation device resulting in a functional disorder in succeeding process stages. The air forcing into the separation device can also entrain light undesired particles, for instance of plastic material, back into the separation device.

The object of the present invention is to provide a new discharge device of the kind here present, by means of which air is prevented from flowing from the discharge device into the separation device when discharging reject from the latter.

This object is obtained by means of a discharge device of the kind initially stated, which mainly is characterized in that a substantial part of the volume of the chamber is situated above the opening of the reject inlet in the chamber.

Hereby, air is prevented from flowing upstreams from the chamber into the separation device when discharging the latter, since a sufficiently strong air pressure in the chamber will not be created for pressing the air upstreams through the reject inlet before the chamber has been filled with reject above the opening of the reject inlet. In addition, the advantage is achieved that the air compressed by the reject in the cham¬ ber may be utilized to rapidly press the reject out of the chamber when the latter is to be emptied.

Suitably, the reject outlet opens into the chamber at the bottom of the latter, whereby the discharge of heavy solid particles from the chamber is guaranteed. According to an embodiment of the device according to the invention the housing forms a filtrate space, which communicates with the bottom part of the chamber via a strainer member, the filtrate space having an outlet in the housing for discharging filtrate, which has flowed from the chamber through the strainer member into the filtrate space. Hereby, the air compressed by the reject in the chamber may be utilized for dewatering the reject before the latter is emptied from the chamber. The reject is dewatered by keeping the reject inlet and reject outlet closed, while said filtrate outlet is kept open, whereby filtrate, substantially consisting of water, because of the pressure from the air in the chamber on the reject will flow through the strainer member into the filtrate space and further out of the latter via the filtrate outlet.

Suitably, the filtrate space has an inlet in the housing for supplying liquid, for instance water, whereby the strainer member can be rinsed and, when necessary, the lower part of the chamber can be filled with liquid, at least partly, before reject is discharged from the separation device.

Preferably, the strainer member is annular and extends around a verti¬ cal axis, so that the interior of the strainer member forms at least a part of the lower part of the chamber, the filtrate space extending around the strainer member in the circumferential direction of the latter.

In order to facilitate pressing of greatly thickened reject out of the strainer member the chamber may suitably be provided with an inlet in the housing for supplying pressurized air.

The reject inlet opens into the chamber suitably below the annular strainer member. Alternatively, the reject inlet may open into the chamber either above the strainer member or within the latter. However, the last mentioned alternative would result in problems in connection with the loosening of the strainer member from the discharge device for inspection and when necessary replacement of the strainer member by a new one. The invention is explained more in detail in the following with reference to the accompanying drawing, in which figure 1 shows a preferred embodi¬ ment of the discharge device according to the invention, and figure 2 shows schematically the discharge device according to figure 1 connected to a separation device.

The discharge device shown in figure 1 comprises a vertically extending elongated housing 1 with circular cross section, which forms an elongated chamber 2. In the vicinity of the lower end of the housing 1 the housing has a radially enlarged portion 3, along which the chamber 1 is formed by the interior of a vertical cylindrical strainer member 4, which is situated coaxially with the housing 1. (Alternatively, the strainer member 4 may be conical with its base directed downwards.) Between the portion 3 and the strainer member 4 a filtrate space 5 is formed, which has an outlet 6 for filtrate and ah inlet 7 for water arranged in the portion 3. The outlet 6 and the inlet 7 are provided with valves 8 and 9, respectively, for opening and closing of the latter.

An inlet 10 for supplying reject to the chamber 1 from a separation device 11 (fig. 2) is arranged in the housing 1 and opens into the chamber 2 below the strainer member 4, about 90 % of the volume of the chamber being situated above the opening of the inlet 10 in the chamber. The reject inlet 10 forms a flow passage extending horizontally to the chamber 2. (Alternatively, the flow passage may decline downwards in direction towards the chamber 2.) A valve 12 is arranged in the reject Inlet 10 for opening and closing of the latter.

An outlet 13 for discharging reject from the chamber 2 is arranged in the lower end of the housing 1 and opens into the chamber 2 at the bottom of the latter. A valve 14 is arranged in the reject outlet 13 for opening and closing of the latter.

At top of the housing 1 an inlet 15 is arranged for supplying pressurized air to the chamber 2. The inlet 15 is provided with a valve 16 for opening and closing of it. The chamber 2 is formed by an upper part 17, which extends from the upper end of the chamber to the strainer member 4, and a lower part 18, which extends from the upper part 17 past the strainer member 4 to the reject outlet 14, the upper part 17 of the chamber being substantially larger than the lower part 18 of the chamber.

The separation device 11, shown in figure 2, comprises a cylindrical chamber 19, to which the fibre suspension is supplied through an inlet not shown. In the chamber 19 the fibre suspension is rotated by means of an entrainment member 20, so that solid particles in the fibre suspen¬ sion separates from the latter and are thrown via a tangential outlet 21, which is connected to the reject inlet 10 of the discharge device, into the chamber 2. The fibres are strained through a central strainer 22 and further out from the separation device 11 via an outlet not shown.

The discharge device shown in the drawing operates in the following way:

When the valve 12 of the reject inlet 10 is completely open and reject from the separation device flows into the chamber 2, the valves 8, 9, 14 and 16 are kept closed. The air in the chamber is compressed by the in- streaming reject until the pressure in the chamber amounts to the same pressure prevailing in the flow passage of the reject inlet 10. Solid undesired particles are separated from the fibre suspension in the separation device and are thrown via the tangential outlet 21 and the reject outlet 10 into the lower part 18 of the chamber 2. After a given period of time, when the reject in the lower part 18 of the chamber has been thickened by solid particles, the valve 12 of the reject inlet 10 is closed. Then the valve 8 of the filtrate outlet 6 is opened, so that the chamber 2 communicates with atmosphere, whereby the overpressure in the chamber will make the air In the latter to expand and to press the filtrate from the reject through the strainer member 4 and further out of the discharge device via the filtrate space 5 and the filtrate outlet 6. When a certain volume of the filtrate has been discharged from the discharge device or the flow of filtrate through the filtrate outlet 6 has ceased, the filtrate outlet 6 is closed, after which the valve 14 of the reject outlet 13 is completely opened. Hereby the air in the chamber 2 expands further and squeezes the thickened reject out of the strainer member 4 through the reject outlet 13. When necessary, the valve 16 in the inlet 15 may be opened a short while for supplying pressurized air to the chamber 2, so that the squeezing of the thickened reject out of the strainer member 4 is facilitated.

When the chamber is completely emptied the strainer member 4 is cleaned, when necessary, by flushing water into the filtrate space 5 via the inlet 9, after which the valves 9 and 14 are closed. Then the valve 12 of the reject Inlet is opened and the operation described above is repeated.

Claims

1. A device for discharging a reject containing undesired solid par¬ ticles from a separation device (11), in which said reject is separated from a mixture of liquid and solid particles, the mixture being subjected to an overpressure during the separation, which discharge device com¬ prises a housing (1) forming a chamber (2), n inlet (10) in the housing for supplying said reject from the separation device to the chamber, an outlet (13) in the housing for discharging reject from the chamber, and two valves (12, 14) arranged in said reject inlet and reject outlet, respectively, for opening and closing of the latter, c h a r a c t e ¬ r i z e d i n that a substantial part (17) of the volume of the chamber is situated above the opening of the reject inlet (10) in the chamber.

2. A device according to claim 1, c h a r a c t e r i z e d i n that the reject outlet (13) opens into the chamber (2) at the bottom of the latter.

3. A device according to claim 1 or 2, c h a r a c t e r i z e d i n that the chamber (2) has an inlet (15) in the housing for supplying pressurized air.

4. A device according to any of claims 1-3, c h a r a c t e r i z e d i n that the housing (1) forms a filtrate space (5), which communicates with a lower part (18) of the chamber (2) via a strainer member (4), the filtrate space (5) having an outlet (6) in the housing (1) for discharging filtrate, which has flowed from the chamber (2) through the strainer member (4) into the filtrate space (5).

5. A device according to claim 4, c h a r a c t e r i z e d i n that the fitrate space (5) has an inlet (7) in the housing (1) for supplying liquid.

6. A device according to claim 4 or 5, c h a r a c t e r i z e d i n that the strainer member (4) is annular and extends around a vertical axis, the interior of the strainer member (4) forming at least a part of said lower part (18) of the chamber (2).

7. A device according to claim 6, c h a r a c t e r i z e d i n that the filtrate space (5) extends around the annular strainer member (4) in the circumferential direction of the latter.

8. A device according to claim 6 or 7, c h a r a c t e r i z e d i n that the reject inlet (10) opens into the chamber (2) below the strainer member (4).