Method and apparatus for treating a fiber suspension

Abstract

A method and apparatus for fibrous suspensions in the wood processing industry and more specifically to a so-called drum cylinder, the basic construction of which comprises a vessel, into which suspension being thickened is supplied and a wire-surface cylinder rotating in the vessel. The drum filter is characterized in that the closure member of the drum filter has a channel for leading gas from the filtrate tubes through the compartments of the distribution chamber to the outside of the closing member. The method is characterized in that the operation phase of the filter cylinder is divided into five separate stages. In the first stage, when the cylinder descends on to the vessel, air and the initial filtrate are discharged from the filtrate components and the formation of the pulp web on the wire surface begins. In the second stage, filtrate is discharged with vacuum and the formation of the pulp web continues. In the third stage, pulp web is dried by means of vacuum when said part of the web has risen with the cylinder from the vessel. In the fourth stage, a so-called removal stage, the pulp web is removed from the wire surface and discharged from the apparatus. In the fifth stage, a so-called washing stage, the wire surface is washed.

Claims

1. An apparatus for removing filtrate from paper pulp comprising:

a wire-surfaced cylinder rotatable about an axis of rotation;

a plurality of filtrate compartments disposed beneath said wire surface;

a distribution chamber mounted within said cylinder for rotation about said axis of rotation;

a plurality of filtrate tubes extending between said filtrate compartments and said distribution chamber for passing gas and filtrate from said compartments to said chamber;

suction conduit for drawing the filtrate from said distribution chamber;

a stationary closure member disposed within said distribution chamber and being in fluid connection with said suction conduit, said closure member comprising a channel for permitting the gas and some filtrate to be discharged from said filtrate tubes to a location outside said closure member.

2. The apparatus of claim 1, wherein said channel is constructed so as to permit the gas and some filtrate to be discharged to a location outside said closure member and outside said suction conduit.

3. The apparatus of claim 1, additionally comprising a cone-shaped member within said closure member, said cone-shaped member being disposed at an end of the closure member and pointing toward said suction conduit for axially guiding the filtrate through the distribution chamber in a spiral flow.

4. The apparatus of claim 1, further comprising a vessel, said wire-surfaced cylinder being arranged within said vessel, said vessel being filled with paper pulp to a predetermined level, said channel of said closure member being located below said level.

5. A method of treating pulp including the formation of a pulp web on the surface of a wire-covered cylinder which rotates in a vessel containing pulp slurry and the removal of filtrate from the slurry through the wire surface by the application of a vacuum, the removal of pump from the wire surface and the discharge of the pulp therefrom, the discharge of the filtrate into filtrate compartments separated by a wall and the further discharge of the filtrate through filtrate tubes and through a closure member out to a suction apparatus, said method comprising the following separate stages:

in a first stage, when the cylinder descends into the slurry, removing air and some filtrate from a filtrate tube and forming the pulp web on the wire surface;

in a second stage, discharge filtrate by application of a vacuum and continuing the formation of the pulp web;

in a third stage, when the cylinder has emerged from the slurry, drying the pulp web by means of a vacuum;

in a fourth stage, removing the pulp web from the wire surface and discharging the removed pulp; and

in a fifth stage, washing the wire surface.

6. The method of claim 5, whereby the pulp web is removed form the wire surface by passing a removal medium comprising substantially air into the filtrate tubes; and discharging the removal medium through the closure member separately from the filtrate.

7. The method of claim 5 wherein.Iadd.removal of the pulp in the fourth stage is practiced by using a wiper having a tip, and wherein.Iaddend.there is a gap between the tip of the wiper and the wire surface.Iadd.;.Iaddend.and comprising the additional step of cleaning the gap by forcing the tip of the wiper into a transverse movement away from the wire surface thereby widening the gap and removing pulp accumulated therebetween.

8. The method of claim 7, wherein the transverse movement is caused by arranging the gap between the tip of the wiper and the wire surface at a distance so that the movement of the wall between the filtrate compartments passed the tip of the wiper upon rotation of the cylinder causes an increase in pressure under the tip of the wiper..Iadd.

9. Apparatus for treating pulp comprising:

a vessel;

a wire-surfaced cylinder rotatable about a shaft, said shaft mounted and tightly sealed at the ends thereof to said vessel;

a source of pressure medium for removing and discharging a pulp web from said wire-surface cylinder;

a plurality of filtrate compartments located adjacent each other to form a shell of said wire-surface cylinder;

filtrate tubes located at at least a first end of said cylinder and each extending inwardly, to an inner end, of a compartment;

a suction source connected to said inner ends of said filtrate tubes; and

a flexible wiper disposed exteriorly of said wire-surface, and constructed, dimensioned, and positioned so as to flex radially toward and away from said wire-surface cylinder..Iaddend..Iadd.10. Apparatus as recited in claim 9 wherein said wiper is caused to flex radially in response to a pressure supplied by said pressure medium..Iaddend..Iadd.11. Apparatus as recited in claim 10 wherein said wiper has a tip; and wherein said wiper is mounted with a clearance between said tip thereof and said wire-surface of said cylinder, said clearance being changed in response to the pressure of said pressure medium..Iaddend..Iadd.12. Apparatus as recited in claim 9 wherein said wiper has a tip; and wherein said wiper is mounted with a clearance between said tip and said wire-surface of said cylinder, said clearance being changed in response to the pressure of said pressure medium..Iaddend..Iadd.13. Apparatus as recited in claim 9 wherein said wiper has a tip, and wherein said filtrate compartments include one or more walls therebetween; and wherein said wiper has sufficient flexibility, and is so mounted, that as said walls of said filtrate compartments rotate past said wiper tip a slight pressure increase causes said wiper tip to bend outwardly from said wire-surface of said cylinder, causing any accumulation of fibers between said wiper tip and said wire surface to loosen and fall into the pulp, and to cause the pulp web to be drawn slightly off of said wire surface of said cylinder..Iaddend..Iadd.14. Apparatus as recited in claim 10 wherein said wiper has a tip, and wherein said filtrate compartments include one or more walls therebetween; and wherein said wiper has sufficient flexibility, and is so mounted, that as said walls of said filtrate compartments rotate past said wiper tip a slight pressure increase causes said wiper tip to bend outwardly from said wire-surface of said cylinder, causing any accumulation of fibers between said wiper tip and said wire surface to loosen and fall into the pulp, and to cause the pulp web to be drawn slightly off of said wire surface of said cylinder..Iaddend..Iadd.15. A method of treating pulp utilizing a wire-surfaced filter cylinder disposed in a vessel surrounding the cylinder and rotatable about an axis, comprising the steps of:

(a) supplying pulp into the vessel surrounding the cylinder;

(b) rotating the cylinder in the vessel to form a pulp web on the wire surface of the cylinder;

(c) removing liquid through the pulp web in the wire surface of the cylinder to form filtrate, which is discharged from the vessel by being fed through filtrate tubes; and

(d) removing the pulp web from the wire surface of the cylinder by providing a flexible wiper having a clearance between a tip thereof and the wire surface of the cylinder by radial flexing of the tip of the flexible wiper with respect to the axis of rotation of the wire-surfaced cylinder..Iaddend..Iadd.16. A method as recited in claim 15 wherein step (d) is practiced by providing pressure pulsations from the interior of the wire surface of the cylinder, the pressure pulsations causing radial movement of the tip of the flexible wiper toward and away from the wire surface of the cylinder..Iaddend..Iadd.17. A method as recited in claim 16 wherein step (d) is further practiced so that any fiber accumulating in the clearance causes the fibers to loosen and be discharged into the pulp..Iaddend..Iadd.18. A method as recited in claim 16 wherein the wire-surfaced cylinder has a plurality of filtrate compartments located adjacent each other with a wall between each adjacent filter compartments, and wherein step (d) is practiced to provide pressure pulsations as each wall is rotated past the tip of the wiper..Iaddend..Iadd.19. A method as recited in claim 15 wherein the wire-surfaced cylinder has a plurality of filtrate compartments located adjacent each other with a wall between each adjacent filter compartments, and wherein step (d) is practiced to provide pressure pulsations as each wall is rotated past the tip of the wiper..Iaddend..Iadd.20. A method as recited in claim 17 wherein the wire-surfaced cylinder has a plurality of filtrate compartments located adjacent each other with a wall between each filter compartment, and wherein step (d) is practiced to provide pressure pulsations as each wall

is rotated past the tip of the wiper..Iaddend.21. A method as recited in claim 15 wherein step (d) is further practiced so as to cause any fiber accumulating in the clearance to loosen and be discharged into the pulp.