WO1991006704A1

WO1991006704A1 - Method and apparatus for recovering pulp solids from whitewater

Info

Publication number: WO1991006704A1
Application number: PCT/US1990/006496
Authority: WO
Inventors: Peter A. Rodriguez; Glauco Corbellini
Original assignee: Rodriguez Peter A; Glauco Corbellini
Priority date: 1989-11-03
Filing date: 1990-11-02
Publication date: 1991-05-16
Also published as: EP0455784A4; EP0455784A1; JPH04505190A; CA2045515A1; BR9006989A

Abstract

A method of feeding a stream of whitewater (27) from a paper making process into a wedge-shaped zone between horizontal travelling upper and lower converging wire meshes (11, 12), applying a siphon means (10) to the upper mesh (12) in the zone to form a web (71) of solid fibrous material between meshes, separating the upper mesh (12) from the web (71) to leave it supported on the lower mesh (11) as meshes (11, 12) leave the zone; washing all solids from meshes (11, 12) into a receiving vessel (48) recycling the vessel contents to the paper making process; recovering in a pool (56) purified liquid from the siphon means (10), and recycling such liquid for use in showers and the like in the paper making process. Preferably, another stream of an aqueous dispersion of pulp via pipe (66) is introduced adjacently below the upper mesh (12) to cause pulp to form on such mesh (12) which enhances removal of entrained solids from the whitewater. Apparatus to perform the above method is also provided.

Description

METHOD AND APPARATUS FOR RECOVERING PULP SOLIDS FROM WHITEWATER

BACKGROUND OF THE INVENTION

Paper making is accomplished today principally by the process and apparatus involving a Fourdrinier traveling screen or fabric, referred herein as a "wire" or "wire mesh". The wire serves as a receptacle to receive a thin layer of aqueous dispersion of wood pulp and associated fibrous ma¬ terials, which eventually is formed into a sheet of paper on the wire after draining away the water and drying the sheet. Water removed from the wire early in the process is called "Whitewater" and it contains a certain amount of fibrous material that the paper manufacturer prefers to recover and to use in making paper. The method and apparatus of this invention is directed principally at recovering as much as possible of the valuable fibrous material from Whitewater and recycling it to the paper making process. It is to be understood however, that this invention may be used to re¬ cover valuable materials from other process streams than those of a paper making procedure, e.g., dispersions of other vegetable fibers, such as cotton, animal fibers, such as wool, and synthetic fibers, such as nylon, acrylonitrile, polyester and the like. Furthermore, dispersions of non- fibrous materials can also be subjected to this invention if it is desirable to filter those materials from the liquid of the dispersion, regardless of whether the filtered materials are to be recovered or disposed of as waste.

The basic features of the method and apparatus of parts of this invention are described in U.S. Patent No. 4,895,623, dated January 23, 1990.

It is an object of this invention to provide a novel method for treating Whitewater from a paper making process to recover and recycle the fibrous solids and the water therefrom. It is another object to provide an apparatus for performing such a process. It is still another object to provide a method and apparatus for continuously filtering a liquid dispersion of solids by a procedure that continuously prepares the filter medium. Still other objects will become apparent from the more detailed description which follows.

BRIEF SUMMARY OF THE INVENTION This invention relates to a method for removing solid fines from Whitewater containing fine pulp produced in a paper making process and recovering purified water therefrom, the method comprising:

(a) feeding Whitewater containing fine pulp into a wedge-shaped zone between upper and lower horizontal, con¬ tinuously moving, converging wire meshes;

(b) applying a siphon means to the upper wire mesh on the side opposite to the side contiguous to the white- water, as the upper wire mesh passes through the zone so as to form a web of pulp and solid fines on the upper wire mesh and to remove purified water through the web;

(c) recovering purified water from the siphon means;

(d) directing a water spray at the web to dislodge the web from the upper wire and to direct it into an aqueous collection pool; and

(e) recycling the aqueous collection pool into the paper making process.

Preferably, an aqueous dispersion of paper pulp is intro¬ duced adjacently below the upper mesh to enhance the trap¬ ping of the entrained solids in the Whitewater fed into the zone adjacently above the lower mesh.

This invention also relates to an apparatus for sep¬ arating solid fines from water in Whitewater produced in a Fourdrinier paper making process which comprises:

(a) an endless upper and an endless lower Fourdrinier wire mesh arranged to move adjacently parallel to each other in generally horizontal positions through a web-forming zone with the two meshes converging toward each other to define a wedge-shaped space;

(b) drive means and guide means to cause the upper and lower wire meshes to separately maintain the wire meshes adjacently parallel to each other and moving at the same speed;

(c) a feed pipe for introducing Whitewater between the dispersion of pulp in water and the lower wire mesh in a stream substantially evenly distributed across the width of the zone;

(d) a solid fluid flow barrier contiguous to the lower wire mesh on the surface opposite to that which is contacted by the Whitewater stream;

(e) a vacuum suction box in contact with the lower wire mesh immediately downstream from the zone and adapted to pull solids trapped between the wire meshes onto the lower wire mesh and be supported thereon;

(f) water sprays positioned downstream of the suc¬ tion box to wash solid materials from the upper and lower wire meshes into a container to receive spray water and solids washed from the wire meshes;

(g) siphon means to maintain water levels wherein the web-forming zone is continuously submerged in water while water is flowing away from the zone; and

(h) a container to receive the water flowing from the zone through the siphon means.

Preferably, there is provided a feed tray for introducing a dispersion of pulp in water at the entrance and directed to contact the upper wire mesh and be evenly distributed across the width thereof.

BRIEF DESCRIPTION OF THE DRAWINGS The novel features believed to be characteristic of this invention are set forth with particularity in the ap¬ pended claims. The invention itself, however, both as to its organization and method of operation, together with further objects and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying drawings in which: FIG. 1 is a front elevational view of one embodiment of the web-forming portion of the apparatus of this inven¬ tion in which a single filter web is formed;

FIG. 2 is a side elevationsl view of the embodiment shown in FIG. 1;

FIG. 3 is a side elevational view of a second embodi¬ ment of the web-forming portion of the apparatus of this invention in which a double filter web is formed;

FIG. 4 is a schematic front elevational view of the entire assembly of the apparatus of this invention employing the apparatus of FIGS. 1 and 2;

FIG. 5 is a cross section taken at 5—5 of FIG. 4; and

FIG. 6 is a schematic front elevational view of the entire assembly of the apparatus of this invention employing the apparatus of FIG. 3.

DETAILED DESCRIPTION OF THE INVENTION The operation of the apparatus and process of this invention may best be understood by reference to the attached drawings.

In FIGS. 1-3 there is shown the web forming portion of Fourdrinier type apparatus and process of this invention which functions generally as described and claimed in co- pending U.S. Patent No. 4,895,623, dated January 23, 1990. An upper wire mesh 12 is guided around cylinder 25 to pass under a water removal device 10 which operates as a siphon. Correspondingly, a lower wire mesh 11 is guided around cyl¬ inder 26 to travel closely adjacent to wire mesh 12 in a substantially parallel movement with both meshes traveling at the same speed. Lower wire mesh 11 and upper wire mesh 12 actually converge upon each other to define a wedge- shaped space or zone between the two as they travel past water removal device 10. Lower wire mesh 11 is supported on a solid plate 13 which is a fluid flow barrier. Water is removed by a siphon means in a water removal container 10 having a water level 29. Whitewater 27 having fines, etc.. therein is fed from source 28 to the upper surface of lower wire mesh 11. In U.S. Patent No. 4,895,623, an aqueous dis¬ persion of paper pulp is fed in contrast to Whitewater which is the water left after passing through a Fourdrinier type apparatus. As the Whitewater passes under water removal con¬ tainer 10 the water in stock 73 is siphoned away by a system whereby the water level in container 10 is at 29 and is con¬ trolled through a float system 24 to drain water continuously away through valved exits 21 and 22. During this time of water removal the stock 73 on wire mesh 11 is submerged in water so that no air-water meniscus is present at or near wire mesh 11.

In FIG. 2 there is a more detailed showing of the siphon means and the water level controls wherein water from stock 73 flows upward through manifold 15 to a drainage tank 16.

In FIG. 3 there is shown a similar system to that in FIGS. 1 and 2 except that a siphon means is applied both above and below stock 73 simultaneously. A similar con¬ tainer to water removal container 10_. is placed in contact with lower wire mesh 11 instead and plate 13 is removed.

In the process and apparatus of the present invention the same general principles, as set forth in U.S. Patent No. 4,895,623, are involved for the treatment of Whitewater to recover the pulp-solids therein to recycle them to the paper making process, and at the same time, purifying the liquid phase of the Whitewater to produce purified water for use in the paper making process or elsewhere as desired. In FIGS. 4 and 5 there is shown the present invention using the water removal siphon system of FIGS. 1 and 2 and in FIG. 6 there is shown the siphon system of the double sided siphon system of FIG. 3.

With specific reference to FIG. 4 upper wire mesh 12 and lower wire mesh 11 supported on plate 13 approach each other at an angle so as to form a wedge-shaped space 64. Into that space 64 is fed Whitewater through pipe 59 from supply line 62. Between the outlet of pipe 59 and upper wire mesh 12 is preferably fed an aqueous dispersion of paper pulp through pipe 67 as a branch from supply line 66. This dis¬ persion may be the same as that used as feed stock 28 from feed box of U.S. Patent No. 4,895,623 or it may be merely paper pulp in water without the surface active agents, dis- persants, bleach and other additives found in the usual paper pulp stock. Pipe 67 terminates so that the outflowing dispersion contacts upper wire mesh 12 where it approaches the leading edge of water removal container 10. Accordingly, the pulp in the dispersion from pipe 67 is sucked against wire mesh 12 and forms a filter web as wire mesh 12 moves across the siphon mouth 14 of container 10. Water cannot flow downwards from wedge-shaped space 64 because of the presence of fluid flow barrier plate 13 supporting lower wire mesh 11.

After passing beyond the downstream end of container 10 upper wire mesh 12 and lower wire mesh 11 are directed apart from each other so as to be returned to pass through the system again. At this point a suction box 53 pulls the filter web 71 from upper wire mesh 12 to lower wire mesh 11 and then passes under a strong water spray 51 which washes the filter web 71 off mesh 11 and allows it to drop into a pool 49 of concentrated pulp in collection tank 48, from whence it can exit at 47 in the direction of 46 to be re¬ cycled to the paper process. Upper wire mesh 12 passes under another water spray 45 to wash off any remaining pulp fiber clinging thereto.

Whitewater from pipe 59 is sucked through filter web 71 causing any solids (usually fines of fiber and similar materials) to be caught by the filter web 71 and the fil¬ tered water passes through valved outlets 21 to a pool 56 which is conducted out exit 57 in the direction of arrow 58 for use elsewhere, e.g., in sprays 45 and 51 or other places in the paper plant.

In FIG. 5 there is shown a cross section of pipe 59 to show how the Whitewater is directed to be evenly distributed across the entire width of wire meshes 11 and 12 and to break up any large clumps or to restrain extraneous matter from entering between the wire meshes.

In FIG. 6 the same process and apparatus as in FIG. 4 is employed except that fluid barrier 13 is removed and in its place there is put a lower siphon means with a mouth with deflectors and a water removal container (similar to 10 but not shown for the sake of simplicity) . Whitewater is fed from pipe 59 into the center of the wedge-shaped space 64 while a pulp dispersion from supply line 66 is fed through pipe 67 to contact upper wire mesh 12 and also through pipe 167 to contact lower wire mesh 11. In this fashion a filter web 71 is formed on upper wire mesh 12 and a similar filter web 171 is formed on lower wire mesh 11 with white- water fed in between. The siphon system pulls water through both filter webs 71 and 171 to be collected in pool 56 and recycled through exit 57 to the paper making process. The two filter webs 71 and 171 continue in contact with their respective wire meshes 12 and 11 until both are washed off by sprays 45 and 51 into pool 49 of concentrated pulp which is recycled through exit 47 to the paper making process. Suction box 53 (see FIG. 4) is eliminated in this arrange¬ ment because it is not normally needed, although a suction box may, if desired, be included on the lower wire mesh downstream from container 10.

It is to be understood that the system of this inven¬ tion can be used to filter other media than Whitewater. Any dispersion of solids in a liquid (particularly in water) can be treated by the present invention to separate the solids and purify the water and recover or recycle each.

Claims

CLAIMS : _8_

1. Method for removing solid fines from white water con¬ taining fine pulp produced in a paper making process and recovering purified water therefrom, the method comprising:

(a) feeding white water containing paper pulp into a wedge-shaped zone between upper and lower horizontal, con¬ tinuously moving, converging wire meshes;

(b) applying a siphon means to said upper wire mesh on the side opposite to the side contiguous to said white- water as the upper wire passes through said zone so as to form a web of pulp and solid fines on said upper wire mesh and to remove purified water through said web;

(c) recovering purified water from said siphon means;

(d) directing a water spray at said web to dislodge the web from said upper wire and to direct it into an aqueous collection pool; and

(e) recycling said aqueous collection pool into said paper making process.

2. The method of Claim 1 wherein said lower wire mesh is supported from underneath and slides on a solid horizontal fluid barrier while said adjacent upper mesh is subjected to said siphon means.

3. The method of Claim 1 further comprising feeding an aqueous dispersion of pulp adjacently below said upper wire mesh to cause pulp therefrom to form on said upper wire and enhancing the removal of solid fines from said Whitewater.

4. The method of Claim 1 wherein said web on said upper wire mesh is subsequently transferred to said lower wire mesh by applying a suction means to pull said web from said upper wire mesh to said lower wire mesh.

5. The method of Claim 4 wherein said upper wire mesh, after said web is removed therefrom, is washed by a water spray to remove any remaining pulp or fines therefrom and direct them to said pool.

6. The method of Claim 3 wherein step (a) includes a first layer of pulp being fed so as to be contiguous with said upper wire mesh, a second layer of pulp being fed so as to be contiguous with said lower wire mesh, and said white- water being fed between said first and second layers of pulp.

7. The method of Claim 6 wherein step (b) additionally includes applying a siphon means to said lower wire on the side opposite to the side contiguous to said second layer of pulp.

8. An apparatus for separating solid fines from water in Whitewater containing fine pulp after passage through a Four¬ drinier paper making process which comprises:

(a) an endless upper and an endless lower Fourdrinier wire mesh arranged to move adjacently parallel to each other in generally horizontal positions through a web-forming zone with the two meshes converging toward each other to define a wedge-shaped space having a large entrance and a small exit;

(b) drive means to move said upper and lower wire meshes substantially the same speed;

(c) a feed pipe having a width less than the width of said meshes for introducing Whitewater containing fine pulp between said upper and lower wire meshes in a stream substan¬ tially evenly distributed across the width of said zone;

9. The apparatus of Claim 8 further comprising:

(d) siphon means to extract purified water from said Whitewater in said zone through said upper mesh and to main¬ tain water levels wherein said web-forming zone is continu¬ ously submerged in water while purified water is flowing away from said zone;

(e) a first container to receive the purified water flowing from said zone through said siphon means for recycling thereof in the paper making process;

(f) a second container to receive the fine pulp and solid fines recovered from said wire meshes downstream of said zone for recycling thereof into the aqueous dispersion of pulp of the paper making process. (g) a feed tray having a width less than the width of said meshes for introducing an aqueous dispersion of pulp at said entrance and directed to contact said upper wire mesh and be substantially evenly distributed across the width of said zone, said Whitewater from said feed pipe being provided between said aqueous dispersion of pulp and said lower wire mesh.

10. The apparatus of Claim 9 further comprising:

(h) a solid fluid flow barrier contiguous to said lower wire mesh on its lower side;

(i) a vacuum suction box in contact with the lower side of said lower wire mesh immediately downstream from said zone and adapted to pull pulp and solid fines trapped between saie wire meshes onto said lower wire mesh and be supported thereon; and

(j) water sprays positioned downstream of said suction box to wash solid materials from said upper and lower wire meshes into said second container to receive said spray water and solids washed from said wire meshes.

11. The apparatus of Claim 10 wherein said upper and lower wire meshes diverge away from each other after passing said suction box.

12. The apparatus of Claim 9 wherein said upper and lower wire meshes converge toward each other in said web-forming zone sufficiently to produce a compressive force on the solids in said web-forming zone.

13. The apparatus of Claim 9 further comprising:

(h) a second feed tray for introducing a second aqueous dispersion of pulp at said entrance and directed to contact said lower wire mesh and be substantially evenly distributed across the width thereof; said siphon means extracting purified water from said white- water in said zone through said lower mesh and maintaining water levels wherein said web-forming zone is continuously submerged in water while the negative pressure produced by said siphon means causes purified water to flow away from said zone and into said first container.

14. The apparatus of Claim 13 further comprising (i) water sprays positioned downstream of said zone to wash said meshes to remove the pulp and solid fines therefrom and discharging same into said second container.