Device for Filtering Fiber Suspensions

Abstract

A vat (1) with an inlet (2) for a suspension. A rotatable inner axial part (5) with peripheral channels (7) and at least one disc-shaped filter (8) mounted to the inner axial part (5). Within the vat the suspension is contained between partition walls (16A) in which the filters rotate. The filter (8) has inner flow channels (42) for transporting filtrate to channels (7) in the inner axial part (5). The filtrate from the channels (7) is combined in one end of the inner axial part (5) into at least one vacuum forming downpipe (12). Sprays (13) (15) detach material deposited on the filters. Mounted to the top of the partition walls (16A), which form receiving chutes (16), are guide plates (14A) for guiding material down into the chutes. Spray nozzles (14B) are located below the guide plate(s) and between the partition walls (16A) to clean the filtering surface (10).

Claims

1. A device for filtering fiber suspensions, comprising: a vat with an inlet for connection to a source of fiber suspension; an inner axial part with peripheral channels mounted within the vat to rotate about a rotational axis; at least one disc-shaped filter element mounted to the inner axial part at an angle to the rotational axis, wherein the at least one disc-shaped filter element has a plurality of filter sectors; wherein the filter element has an external filtering surface and inner flow channels for transporting filtrate, which passes through the filtering surface, to at least one filtrate channel in the inner axial part: devices for detaching material filtered-out of the fiber suspension and deposited on the filtering surface; a chute having partition walls which is arranged on a side of the vat and positioned to receive detaching material filtered-out of the fiber suspension after it is detached from the filtering surface; a washing and deflection device for washing the filtering surface and transporting away the filtered-out material down into the chute; and wherein the washing and deflection device has at least one guide plate and spray nozzles and that the spray nozzles are located below the guide plate.

2. The device of claim 1 wherein the spray nozzles are spaced from the at least one disc-shaped filter element and located in a space formed between a chute partition wall of the chute and the at least one disc-shaped filter element.

3. The device of claim 1 wherein the guide plate and the spray nozzles are integrated in a one-piece structure which forms the washing and deflection device.

4. The device of claim 3 wherein the spray nozzles are located on a bottom surface of the guide plate.

5. The device of claim 1 wherein the washing and deflection device is pivotally mounted to the vat, to rotate for cleaning of the spray nozzles.

6. The device of claim 1 wherein the inlet is arranged on a side of the vat and defines a level at which fiber suspension enters the vat where the filter sectors start to sink down into the suspension.

7. The device of claim 1 wherein the washing and deflection device is positioned on top of an upper edge of the receiving chute.

8. The device of claim 1 wherein the guide plate is located at a distance from the filtering surface.

9. The device of claim 1 wherein the guide plate forms a contactless scraper.

10. A device for filtering fiber suspensions, comprising: a vat with an inlet for connection to a source of fiber suspension, the inlet defining an inlet level at which fiber suspension enters the vat; an inner axial part with a plurality of filtrate channels, the inner axial part mounted within the vat to rotate about a rotational axis; a plurality of disc-shaped filter elements mounted to the inner axial part substantially perpendicular to the rotational axis, wherein each disc-shaped filter element has a plurality of filter sectors; wherein each filter element has two sides covered with an external filtering surface and inner flow channels for transporting filtrate to at least one filtrate channel in the inner axial part: devices for detaching material filtered-out of the fiber suspension and deposited on the filtering surface; a plurality of chutes each having a partition wall with an upper edge spaced from one of the external filtering surfaces of the plurality of disc-shaped filter elements, wherein the upper edges extend above the inlet level, and wherein each chute is positioned to receive detaching material filtered-out of the fiber suspension after it is detached from the filtering surface; washing and deflection devices for washing the filtering surfaces and guiding the filtered-out material down into one of the receiving chutes; wherein each of the washing and deflection devices is mounted to one of the partition wall upper edges; and wherein each washing and deflection device has at least one guide plate and a plurality of spray nozzles, wherein the spray nozzles are located below the at least one guide plate and above the inlet level in a space formed between one of the partition walls and one of the external filtering surfaces, wherein the spray nozzles are directed to clean said one of the external filtering surfaces.

11. The device of claim 10 each washing and deflecting device comprises said at least one guide plate and the spray nozzles integrated in a one-piece structure.

12. The device of claim 10 wherein the washing and deflection devices are pivotally mounted to the vat, to rotate to and away from said one of the partition wall upper edges for cleaning of the spray nozzles.

13. The device of claim 10 wherein the inlet is arranged on a side of the vat.

14. The device of claim 10 wherein the guide plates are closely spaced from and not engaged with the filtering surfaces.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] FIG. I is a schematic partially sectional side view of the filter device according to the invention.

[0023] FIG. II is a cross-sectional view of the apparatus of FIG. I taken along section line A-A.

[0024] FIG. III is an enlarged fragmentary cross-sectional view of the apparatus of FIG. II taken along section line B-B.

[0025] FIG. IV is a fragmentary cross-sectional view of the apparatus of FIG. III taken along section line C-C.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0026] The filter device 32 according to the invention will in the following be described as suited for dewatering and thickening of fiber suspensions, which are comparatively easily dewatered, but the filter device can also advantageously be used for suspensions, which are difficult to dewater.

[0027] The filter device consists of a U-shaped vat 1, shown in FIG. II, with gables and a support structure and an inlet 2 for fiber suspensions. The inlet 2 is arranged along one side of the vat 1. An inlet pipe 3 leads to the inlet 2. The upper part of the vat is sealed with one or more hatches 4, which can be opened.

[0028] In the vat 1 there is arranged an inner axial part 5, shown in FIG. I, which is rotatable about a geometric axis 30 by an actuator 6 and has flow channels 7 and a plurality of external disc-shaped filter elements 8 placed across the geometric axis 30 of the inner axial part 5. The disc-shaped filter elements 8 are orientated substantially perpendicularly to the rotational axis 30 of the axial part 5. The individual disc-shaped filter element 8 extends in a ring-like configuration around the inner rotor part 5. This ring configuration of the disc-shaped filter element 8 is divided into a number of filter sectors 9, as shown in FIG. II. As shown in FIG. IV, each filter sector 9 has an external filtering surface 10, and inner channels 42 formed by in inner perforated metal frame 44 for transporting filtrate i.e., the filtered water, which has passed through the filtering surface 10, e.g., a filter cloth, to one or more flow channels 7 in the inner rotatable axial part 5.

[0029] As shown in FIG. I, the flow channels 7 in the rotatable axial part 5 exit into a device 11 called a filtrate valve, meant to collect the water (filtrate) flow from a number of flow channels 7 into at least one pipe 12 called a downpipe, in which the water falls through and thus creates the necessary vacuum required for the filtering method.

[0030] The filter device comprises devices 13 for detaching filtered out fibers and deposited on the filtering surface 10. The detaching devices 13 consist of spray nozzles placed to remove the layer of filtered out fibers from the filter sectors as they rotate by, with water fed in via a connecting distribution pipe 21.

[0031] The filter device 32 additionally comprises a washing and deflection device 14, which has at least two functions, namely to wash the filtering surface 10 and to steer the filtered-out fiber material 34 into the chutes 16, also called compartments or pulp chutes. As shown in FIG. I, the chutes 16 are formed by partition walls 16A that keep the filtered-out material 34 separate from washing liquid. The washing device 14 comprises a guide plate 14A placed on top of the chutes' 16 upper edge for guiding the filtered-out material 34 towards chutes' opening 17. The washing device 14 is also comprised of spray nozzles 14B below the guide plate 14A, the spray nozzles 14B are placed to wash the filter elements' 8 filtering surface 10 as they are rotated by the washing device 14, primarily by spraying with washing liquid, e.g., water fed via a connecting distribution pipe 22. The spray nozzles 14B are located after guide plates 14A such that washing liquid is guided away from the filtered-out material 34 and thus mixing of the washing liquid and the filtered-out material 34 is avoided. The washing device's main secondary function is to aid in transporting away filtered-out fiber material 34 through the chutes 16 down to the collecting screw conveyor 18 situated below the filter's vat 1 without water from the washing device's nozzles 14B diluting the concentration of the filtered-out fiber material. The spray nozzles 14B clean the filtering surface before the filtering surface sinks down to the suspension 36. By this compact washing device 14 arrangement is possible to increase the fiber suspension level 38 in the vat 1. The washing device 14 is foldable for easier access to its spray nozzles and cleaning of them. Between each disc there are devices made up of spray nozzles 15 placed to flush the filtered-out material down into the chutes 16 with water fed in via a connecting distribution pipe 23.

[0032] The present invention has primarily improved the operational reliability and filtering possibilities when filtering easily dewatered fiber suspensions, partly through placing the triangular stationary washing device 14 on top of the chutes' 16 upper edge 40, which steers the pulp, which ends up on these, toward the chutes' opening 17, and that the chutes' opening 17 has been maximized in order to obtain as free and safe a fall space as possible for the filtered-out material down into the receiving transport member 18 with an actuator 24, for transportation away from the filter device 32.

[0033] Knowing the importance of the filtering method providing an even predetermined outgoing concentration of filtered-out material and that the filtering surface of the filter discs must be kept clean to obtain an optimal filtering opportunity, and further that filtered-out material does not have an opportunity to stick to and cause blockages in the chutes between the filter's rotating discs, the above-mentioned improvements provide the following:

1. A controlled filtering result is obtained when the washing device 14 placement makes possible a controlled and stable outgoing concentration of the outgoing filtered-out material.
2. A more reliable operation is obtained when filtered-out material cannot fall on the spray nozzles placed beneath the washing device 14 and thus cause shutdowns and that the washing device 14 is designed like a guide plate 14A such as a contactless scraper to steer filtered-out pulp down into the chute opening 17. The guide plate 14A is located at a distance from a filtering surface 10.
3. A further increased operational reliability is obtained also when the conventional oscillating spray pipes between the filter's discs are replaced with a stationary spray device 14 placed on top of the receiving chutes' 16 upper edges. Through this placement the filtering surface of the filter's discs are washed completely during only one rotational lap by the discs 8 with the stationary washing device 14, which is of great importance when a clean washed filtering surface 10 is a requirement for obtaining a maximal capacity, which is not possible with the conventional oscillating washing device, with which it can take up to several hours before the entire filtering surface is washed, resulting in loss of capacity. The stationary washing device 14 is also foldable for easy access to the device's spray nozzles for cleaning.
4. Reduced operational disturbances are obtained when the receiving chutes' 16 opening 17 is maximized, which prevents filtered-out material from sticking to and blocking the chutes' opening.
5. Higher production capacity is obtained because the fiber suspension level 38 in the vat can be raised up by this washing device 14 arrangement.

[0034] The above improvements offer an overall controlled filtering method with a controlled concentration of filtered-out fiber material and over time a maintained high capacity and increased operational reliability with minimized operational disturbances.