GAS FREE VALVE FOR PULP VACUUM WASHER AND METHOD

Abstract

In a rotary drum for condensing pulp from a pulp slurry vat, the drum including radial conduits delivering filtrate from a pulp mat on an outer surface of the drum to at least one filtrate conduit coaxial with a drum rotational axis, a valve segment in the filtrate conduit including: an outer surface juxtaposed against drainage outlets of the radial conduits as the conduits pass through an angular range extending from an upper drum position to an immersed in a vat position, wherein the valve segment does not block the drainage outlets during a majority of the rotation of the drum; at least one inlet aperture on the outer surface aligned with the drainage outlets, said inlet aperture extending at least a majority of a width of the valve segment, and a closed passage extending from the inlet aperture to a gas vent external to the filtrate conduit, wherein the closed passage is offset from and below a centerline of the filtrate conduit.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of a conventional rotary vacuum drum filter wherein the housing is shown in cross-section to expose the drum, vat and other interior components of the drum filter.

FIG. 2 is a side, perspective view of a conventional rotary drum filter with the trunnion conduit, elbow and drop leg conduits shown in exploded view.

FIG. 3 is a side view of a front side of a valve segment and support mounted on an elbow conduit.

FIG. 4 is a perspective view of a front side of a valve segment and support mounted on the elbow conduit shown in FIG. 3.

FIG. 5 is a perspective view of a rear side of the valve segment and segment support mounted on the elbow conduit shown in FIG. 3.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 3 is a perspective view of a front side of a valve segment 50 mounted on a cantilevered support 51 which extends from the inlet to an elbow conduit 52. The elbow and conduit are stationary and coupled to a trunnion conduit 34, such as is shown in FIG. 2. The elbow has a mounting bracket 53 that couples to the stationary drive and bearing unit, in a conventional manner. The discharge of the elbow is connected to a down leg conduit 32 that extends to a filtrate collection vessel that is preferably at least 30 feet (10 meters) below the drum filter washer.

The valve segment 50 may be a plate having an arc shaped in cross section. The valve segment 50 forms an arc of preferably about 130 degrees and extends preferably from the 1:00 to 5:00 positions with respect to the rotation of the vacuum drum. The valve segment is juxtaposed with the drainage outlets of the ribs 20 and extends into the filtrate chamber 28 in the drum 12. The valve segment is off-set from the centerline 54 of the trunnion conduit 34. The plate that forms the valve segment 50 includes one or more gas inlet apertures 58 arranged to be in alignment with the discharge of the ribs 20 in the drum. In the arrangement shown in FIG. 3, the gas aperture 58 is positioned at or near a distal end (opposite to the elbow) of the valve segment support 51.

The cantilever support 51 for the valve segment has a closed passageway 56 that extends from the valve segment plate 50 through the trunnion conduit 34 and into the elbow conduit 52. The passageway 56 allows gas and foam collected from the ribs 20 to be exhausted out of the filtrate drum and out of the elbow. The outlet of the passageway 56 includes an upper gas vent 68 and a liquid filtrate drain 70.

The gas aperture(s) 58 of the valve segment preferably extend collective a majority of the arc of the valve segment 50, as is shown in FIG. 3. In the embodiment shown here, the gas aperture(s) 58 collectively form an opening that extends up to about 100 degrees of the 130 degree arc formed by the valve segment. It is preferred that the aperture(s) 58 extend collectively at least 65 degrees.

Further, the gas aperture(s) 58 may extend from a near top drum position of the valve segment 50 to a lower position 60 on the valve segment that corresponds to where the ribs have been fully vented of gas and foam, and are entirely filled with liquid filtrate. The elevation of the liquid level in the vat typically corresponds to the centerline 54 of the drum 12. As the drum surface moves further into vat, liquid filtrate fills the ribs 20 and forces air and foam out of the ribs and into the aperture 58 of the valve segment. Preferably, the lower edge 60 of the aperture(s) 58 is at or below the angular drum position at which the ribs have been purged of air and foam. As shown in FIG. 3, the lower edge of the aperture 60 is at about the 4:00 position, plus or minus 5 degrees. The lower edge 60 may be determined for each drum based on the rotational drum position at which the ribs are filled with filtrate and no longer exhausting gas and foam.

The large cross-sectional area of the gas aperture(s) 58 in the valve segment 50 ensures that substantially all gases vented from the ribs enter the gas passage 56 in the valve segment even for relatively fast rotating drums. The aperture(s) 58 are relatively long (AW) in the direction of drum rotation. This length facilitates the venting of gases from the ribs 20 into the passage 56 as the ribs move across the length (AW) of the aperture 50. The low position, e.g., 4:00 to 5:00 position, of the lower edge 60 of the aperture 58 ensures that all air and foam are discharged from the ribs and into the passage 56.

The plate of the valve segment 50 may be mounted on an outer plate 64 of the valve segment support 51. The outer plate may have an arc cross-sectional shape that faces and conforms to the inside wall surface of the trunnion conduit. The valve segment 50 may be a plate that has an arc cross-sectional shape that conforms to the outer plate 64. The valve segment 50 is mounted, e.g., bolted, to the outer plate 64 and fits over an opening (not shown) in the outer plate 64.

The position of the valve segment 50 on the outer plate 64 may be adjustable, such as thorough the use of oval or race-track slots 66 in the plate that receive the bolts that attach the plate 62 to the outer plate 64 of the valve segment support 51. Alternatively, the valve segment 50 may be welded to the outer plate 64 once the valve segment has been properly positioned with respect to the outlets to the ribs 20 in the drum.

By adjusting the position of the valve segment 50 on the outer plate 64, the apertures 58 can be optimally positioned with respect to the angular movement of the drum and the outlet of the ribs 20. The ribs pass filtrate from the drum surface to a filtrate chamber 28. The ribs serve as drainage pipes for the drum. For example, the valve segment 50 may be moved slightly up or down on the support plate 64 to align the lower edge 60 of the aperture 58 to be sufficiently below the elevation at which the ribs 20 have fully discharged air and foam, and are discharging liquid filtrate. The valve segment 50 may also be positioned laterally, e.g., parallel to the axis 54 of the drum axis, to be aligned with the discharge of the ribs 20.

The valve segment 50 may include a plurality of openings that define the gas aperture 58. Between the openings may be a support bar 66 integral with the plate of the valve segment and bisecting the plate. The support bar 66 provides structural stiffness for the valve segment and the apertures 58. The solid portions 65 of the valve segment (including the support bar) are relatively narrow (in the direction of AW) and have a relatively small cross-sectional area. Reducing the solid areas 65, 66 of the valve segments avoids unduly reducing the area of the aperture 58 or adversely disrupt the flow of gases into the gas vent passage 56.

The internal passage 56 in the valve segment support 51 vents gases that pass through the aperture(s) 58 of the valve segment and are from the ribs and filtrate chambers. The passage 56 is offset from and extends above and below the centerline 54 of the trunnion conduit and drum axis. The lower portion of the passage is preferably at or just below the bottom edge 60 of the apertures 58. Similarly, the lower portion of the passage 56 should be at or just below the angular position of the drum in which the ribs are filled with filtrate and gases and foam have been exhausted from the ribs.

The internal passage 56 may extend from the inlet aperture(s) 58 of the valve segment 50 and to the elbow 52. The passage 56 may have a gas vent 68 at an upper end of the passage and elbow, e.g., above the centerline 54. The passage 56 also has a filtrate drain 70 extending out of the passage and through the elbow. The filtrate drain is at a lower portion of the passage 56 and below the centerline 54 of the trunnion conduit and drum axis and preferably below the elevation of the lower edge 60 of the aperture(s) 58. A substantial amount of filtrate may pass through the passage 56 as air and foam are discharged from the ribs into the passage. Further, liquid filtrate in the ribs may serve a purging action to push out air and foam from the ribs and the pushing liquid filtrate may flow into the passage 56.

Alternatively, the valve segment 50 may be integrated into the valve segment support such that the distal end of the outer plate constitutes the valve segment and openings in the outer plate constitute the gas apertures leading to the gas passage 56. Further, the outer plate 64 and valve segment support 51 may be formed by a sturdy tube having a relatively large cross-sectional area and offset from and lower than the axis 54 of the drum. The tube may have an oval or kidney shaped cross-section to reduce the blockage to fluid flow in the trunnion conduit and conform to the inside wall surface of the trunnion conduit.

FIG. 4 is a perspective view of a valve segment 50 supported by a valve segment support 51. The valve segment is mounted on an outer plate 64 of the support. The support 51 is attached to the elbow conduit 52 and extends as a cantilever to the segment. A mounting bracket 53 provides a coupling for the elbow to the stationary drive and bearing unit.

FIG. 5 is a perspective view of a rear plate 72 of the valve segment support 51. The valve segment support may be formed by welding together the pair of plates 64, 72 along their respective upper and lower edges. The outer plate 64 forms the front surface of the valve segment support and may have an arc shape that generally conforms to the inner wall of the trunnion conduit. The rear plate 72 may be an arc, flat or bent inward along a crease line (as shown in FIG. 5).

The rear plate 72 and outer plate 64 of the valve segment support 51 form a sturdy support and the gas vent passage 56. The valve segment support may extend as a cantilever from the inlet of the elbow 52 into the trunnion conduit. A cylindrical post 78 on the distal end of the valve segment support may fit into a bushing 79 (FIG. 3) in the drum axle and inward of the axial filtrate chamber. Further, a triangular brace 80 may be welded to an inside surface of the rear plate 72 to provide additional support for the valve segment support.

The internal gap between the front and rear plates of the valve segment support defines the gas passage 56. End caps 82 welded to opposite longitudinal ends of the plates seal the ends of the passage. The passage 56 may alternatively be a tube extending along a back surface of the outer front plate and thereby render the rear plate optional.

The valve segment 50 provides a means for removing the air from filter drum before the air enters the drop leg. The valve segment allows the ribs to vent gases into the passage 56 for substantially the entire rotational period during which the suction is not applied to the ribs. Further, the valve segment allows gas and foam from the ribs to vent entirely into the passage 56 (along with a substantial amount of liquid filtrate) to minimize air entering the elbow and down leg conduits. These features are contrary to the conventional approach of blocking liquid fluid flow through the ribs during most of the portion of the rotational in which suction is not applied to the ribs.

While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.

Claims

1. In a rotary drum for condensing pulp from a pulp slurry vat, the drum including radial conduits delivering filtrate from a pulp mat on an outer surface of the drum to at least one filtrate conduit coaxial with a drum rotational axis, a valve segment in the filtrate conduit comprising: an outer surface juxtaposed against drainage outlets of the radial conduits as the conduits pass through an angular range extending from an upper drum position to an immersed in a vat position, wherein the valve segment does not block the drainage outlets during a majority of the rotation of the drum;at least one inlet aperture on the outer surface aligned with the drainage outlets, said inlet aperture extending at least a majority of a width of the valve segment, anda closed passage extending from the inlet aperture to a gas vent external to the filtrate conduit, wherein the closed passage is offset from and extends above and below the horizontal centerline of the filtrate conduit.

2. The valve segment of claim 1 wherein a lower edge of the inlet aperture is at an elevation no higher than an elevation at which the drainage outlets begin discharging solely liquid filtrate and below a liquid level of the slurry vat.

3. The valve segment of claim 1 wherein the valve segment is mounted on a non-rotating cantilever valve segment support extending into the filtrate conduit coaxial.

4. The valve segment of claim 3 wherein the valve segment support includes an outer plate having an arc shape and conforming substantially to an inner wall of the filtrate conduit.

5. The valve segment of claim 4 wherein the valve segment support further includes an inner plate attached to the outer plate, wherein the closed passage is formed between the plates.

6. The valve segment of claim 5 wherein the inner plate bends inward towards the outer plate.

7. The valve segment of claim 1 wherein the valve segment is a plate attached to a valve segment support and the plate includes the inlet aperture and the valve segment support includes the closed passage.

8. A rotary drum filter for removing filtrate from paper pulp comprising: a housing including a chamber to receive a vat of a pulp slurry;a rotatable drum cylinder mounted in the housing wherein a portion of the drum cylinder extends down into the vat, the drum cylinder including a screen surface to receive a mat of pulp as the drum rotates through the vat;an array of filtrate conduits in the drum in fluid communication with the screen surface and having outlets at a filtrate chamber in the drum, wherein the chamber rotates with the drum;a stationary suction conduit coupled to the filtrate chamber and the suction conduit receiving the filtrate flowing through the screen surface, filtrate conduit and filtrate chamber, wherein the suction conduit extends to an elevation below the vat to create a suction in the filtrate chamber, filtrate conduit and at the screen surface;a stationary valve segment in the filtrate conduit including an outer surface juxtaposed to block the outlets of the filtrate conduits only while the filtrate conduits are rotated from an elevated position to a position down to the vat and said stationary valve segment includes an inlet aperture aligned with the outlets of the filtrate conduits, anda stationary gas passage extending from the inlet aperture to a gas vent external to the filtrate conduit, wherein the passage is offset from and extends above and below the horizontal centerline of the filtrate conduit.

9. A rotary drum filter as in claim 8 wherein a lower edge of the inlet aperture is at an elevation no higher than an elevation at which the drainage outlets begin discharging solely liquid filtrate and below a liquid level of the slurry vat.

10. A rotary drum filter as in claim 8 wherein the passage is included in a valve segment support mounted on and extending from the stationary suction conduit and into the filtrate conduit.

11. A rotary drum filter as in claim 10 wherein the valve segment support includes an outer plate having an arc shape and conforming substantially to an inner wall of the filtrate conduit.

12. A rotary drum filter as in claim 11 wherein the valve segment support further includes an inner plate attached to the outer plate, wherein the closed passage is formed between the plates.

13. A rotary drum filter as in claim 12 wherein the inner plate bends inward towards the outer plate.

14. A rotary drum filter as in claim 8 wherein the valve segment includes an aperture plate including the inlet aperture and the aperture plate mounted on the outer surface.

15. A rotary drum filter as in claim 8 wherein said passage in the valve segment exhausts gas and filtrate through the passage and external to the suction conduit.

16. A method of treating pulp including the formation of a pulp web on a porous surface of a rotating drum cylinder having a lower drum portion in a vat of pulp slurry and a radial array of filtrate conduits draining filtrate passing through the porous surface to an axial filtrate chamber, the method comprising: as the porous surface of the drum rotates through the vat, drawing filtrate from the slurry through the porous surface by the application of a suction to the filtrate conduits vacuum;draining the filtrate from the filtrate conduits into the filtrate chamber and to a filtrate suction conduit extending to an elevation below the vat;forming a pulp mat on the porous surface which passes filtrate and substantially blocks fibers;removing the pulp mat from the vat by rotating the porous surface of the drum rotates up and out of the vat;continuing the draining of filtrate from the filtrate suction conduit as the filtrate conduits are rotated through angular positions during which liquid filtrate applied to the surface of the pulp is sufficient to fill the conduits;after liquid filtrate is no longer applied to the pulp mat and before excessive gases passing through the porous surface enter the filtrate conduits, switching a fluid flow downstream of the filtrate conduits from the filtrate conduits from a path directed through the filtrate suction conduit and to a gas vent passage, wherein the gas vent passage is offset and below from a drum rotational axis.

17. A method as in claim 16 wherein the switch from the path directed to the filtrate suction conduit and to the gas vent passage occurs at substantially a 1:00 rotational position of the drum and said method further comprising switching the fluid flow from the gas vent passage to the filtrate suction conduit as the drum rotates through substantially a 5:00 position.

18. A method as in claim 16 wherein the gas vent passage includes a gas vent and a filtrate drain, wherein the filtrate drain is below a liquid elevation of the vat.

19. A method as in claim 16 further comprising switching said method further comprising switching the fluid flow from the gas vent passage to the filtrate suction conduit as the filtrate conduits become substantially filled with filtrate.

20. A method as in claim 16 wherein gases vent to the gas vent passage from the filtrate conduits during at least one half of the angular position in which the filtrate conduits are substantially filled with air.