Dual Zone Wireless Pulp Washer
A wireless dual zone pulp washer with rotating concentric filters for creating centrifugal force against feedstock in order to expel liquid contained in the feedstock before further processing of the stock. A secondary filter surrounds the primary filter to capture viable pulp fibers expelled from the feedstock by the dewatering process.
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This application claims the priority benefit of U.S. Provisional Patent Application 60/563,066 filed Apr. 16, 2004.
FIELD OF THE INVENTIONThe present invention is related to the washing and/or thickening of pulp and more particularly to a washer with a two stage dewatering zone without a wire belt.
BACKGROUND OF THE INVENTIONThe pulp and paper making industry has for many years made regular use of apparatus for washing and/or thickening pulp and paper stock. One apparatus commonly used in the prior art practice, described in U.S. Pat. No. 5,382,327 by Seifert et al., is known as a double nip thickener (DNT) or simply a washer and is relatively closely comparable in structure and mode of operation with a cylinder type paper forming machine in that its main components are a pair of wire-covered cylinders and a vat in which the cylinders rotate.
The DNT may be used as an extraction device, to thicken the stock, or may be used primarily for washing of the pulp fibers. In operation, the pulp stock is fed to the nip between a rotating breast cylinder and wire entrained thereover. The pulp is dewatered by centrifugal force and travels on the wire to a second or couch roller for further dewatering. The pulp is removed from the couch roller by gravity and a doctor blade and collected on a conveyor which moves the dewatered pulp downstream from the DNT.
In many of these prior art devices, an endless belt or loop of foraminous “wire” is trained around the rolls and defines therewith a space in which the other operating parts of the washer are located. The wire may consist preferably of a plastic material, i.e., polyester. Since the product of the machine is pulp, rather than a sheet on which wire marking may be undesirable, the wire may be of the pin seam type wherein the ends of the wire belt include overlapping loops which are releasably fastened together by a metal “pin” inserted through these loops. Use of pin seam wires makes possible the changing of wires after wear without the cantilevering of the rolls which is required if the wire is an endless loop without a seam. In addition, a wire thickener or washer has limited rotational speed due to wire belt and other component wear concerns, thus the hydraulic capacity of the machine is directly related to the rotational speed.
During the dewatering process of the pulp, pulp stock is fed on to the rotating wiring. Centrifugal force throws fluid with contaminants, and usually good fibers from the pulp, outward through the filtered wire.
Accordingly, it would be beneficial to have a pulp thickening or washer device that would eliminate a wire belt as the filtering medium, increase the rotational speed of the thickener to create additional centrifugal force therefore removing more fluid from the pulp, and prevent the waste of good pulp fibers.
SUMMARY OF THE INVENTIONThe present invention provides for a pulp washing or thickening apparatus for removing fluid from pulp stock in a dewatering system. The apparatus includes a feed manifold for supplying the apparatus with pulp stock, a primary cylindrical rotating filter for accepting the pulp stock from the feed manifold and for creating centrifugal force against the pulp stock to expel liquid, and a first doctor blade for assisting the removal of the pulp stock from an inner surface of the primary cylindrical filter after the pulp stock is dewatered.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will be described with reference to the drawings.
Feedstock is delivered to the apparatus 5 similarly to the prior art thickeners or washers. The headbox 20, shown in
The motor 10, shown in
The jet of feedstock from the headbox 20 is directed at a high point onto the inner surface 32 of the primary cylinder 30. Some of the stock is immediately partially dewatered because the force of the jet causes liquid to travel through the meshed body. Accepts material may be scraped from the inside of the cylinder 30 by doctor blade 50 with the accepts collected by the doctor assembly transported away through outlet pipe 51.
Turning to
As shown, the primary and secondary cylindrical filters are attached to a common drive. Alternatively, the two filters could be separately driven for g-force optimization. The primary cylindrical filter is driven with about 30-120 g-forces and the secondary cylindrical filter is driven with about 60-300 g-forces to provide the desired filtrate clarity and capacity. Variable speed drives can also be provided for either or both of the cylindrical filters so that g-loads and washing efficiency can be controlled within a wide range of operating parameters. As stated above, in contradistinction to many of the prior art devices, wires or similar rotating meshes are not trained or disposed around the cylinders in the present invention in order to form a nip with the cylinder to express liquid from the pulp suspension located in the nip region. Accordingly, the apparatus 5 is subjected to lower amounts of loading, can achieve higher rotation speeds, and can result in increased hydraulic capacity and fines separation efficiency.
The continuous application of centrifugal force causes the liquid component of the feedstock to be expressed through the wire meshing of the primary and secondary filters while the pulp materials suspended therein are held by the meshed body and form a layer on the inner surfaces 32, 42 of the primary and secondary cylindrical filters 30, 40. The liquid expressed through the secondary discharge is expelled from the apparatus 5 through port 60. As known to those skilled in the art, the liquid often carries very fine solid particles such as ink, PSA, etc. These solids are desirably discharged through the port also along with the liquid carrier. As shown, secondary accepts material traveling on an inner surface 42 of the cylinder 40 is removed via doctor 52 and travels through egress piping 55.
The function of the foraminous bodies on the cylinders is to serve as a filter medium that holds the fiber from the feedstock and other desired solid constituents of the feedstock on its inner surface against the action of centrifugal force, which is the major factor causing dewatering of the retained pulp. Vanes 35, 33 shown in
The first doctor blade 50 and associated outlet pipe 51 remove the thickened/dewatered pulp from the inner surface 32 of the primary filter. The thickened/dewatered pulp is transferred from the inner surface 32 of the primary cylindrical filter 30 to a downstream process in the papermaking system. A screw like conveyor (not shown) or other transport means may be operatively associated with the pipe 51 to aid in transferring the pulp. When the mat touches the doctor blades, the mat may become airborne. Directional steering jets of air may be employed to keep the mat airborne and blow the mat out of the washer 5 into the doctor collection assembly. Alternatively, a vacuum may be used to pull the pulp from the washer 5. It is noted that the primary accepts may be subjected to an additional thickening operation before removal from the washer 5.
For the dewatered pulp on the inner surface 42 of the secondary cylindrical filter 40, a second doctor blade assembly 52 and associated collection pipe 55 are provided, and the removal process is the same as above. The purpose of the second doctor blade 52 is to clean the filter media and recover any fiber that was plugged on the filter media surface of the secondary filter 42.
To release the mat of pulp from the filter media, a backflush of water at a pressure great enough to exceed the opposing g-force may be used to impinge the cylinder surface just upstream from or at the leading edge of the first doctor blade assembly 50. The pulp not collected by the first doctor blade assembly 50 will be filtered out again on the primary cylindrical filter 30. A second backflush of water at the leading edge of the second doctor blade 52 may be used to collect the pulp that is retained on the secondary cylindrical 40 filter in order that the filter media does not become clogged over time.
In an alternative embodiment of the present invention, non-contacting doctor blades may be used to remove the thickened mat from the filter media of the primary and secondary cylindrical filters 30, 40. For example, a very fine, high pressure jet or fan of water or air that blows from the inside to get under the fiber mat and lift the mat off the filter media or blows from the backside to blow the mat off may be mentioned as exemplary.
In an alternative method of operation, a pulsed system may be used to increase the dewatering levels and thicken the pulp more. This could be achieved by selective, intermittent contact of the first and second doctor blades 50, 52 with their associated rotating cylinders to remove the thickened pulp after every two or more revolutions of the primary and secondary cylindrical filters 30, 40. This would allow a longer period of time for centrifugal force to be applied to the pulp forcing liquid to expel from the pulp.
In the washer 5, the filter media for the primary and secondary cylindrical filters 30, 40 may be replaceable. In one embodiment, the filter media is in the form of a cartridge that inserts into the primary and secondary cylindrical filters 30, 40. In another embodiment, the filter media may be installed and tensioned in place to the primary or secondary cylindrical filters 30, 40.
An elongated nozzle in the form of a slotted opening 78 comprising a generally planar housing surface 76 extends tangentially from the conical body in laterally offset position from axis 95. Pulp suspension exits the cyclone through this slotted opening 78 with the opening positioned adjacent the inner surface 32 of the primary filter 30.
The slotted opening presents an elongated opening with its elongated dimension oriented parallel to the surface of the inner cylinder 32 as this surface is positioned adjacent the opening 78 during its rotation.
As shown in
By employment of the stratified feed shown in
As shown in
In accordance with the embodiment shown in
It is also possible to add wash shower nozzles along either or both of the rotating cylinders.
Preliminary results have indicated that the dual zone washer is effective in removing ash, ink, and stickies, and fines from pulp slurries that may include, for example, copy paper, OCC, and mixed office waste. At present, it is preferred that the inner wire medium be more open than the outer wire medium. Present data suggests that ash removal is optimized with a 60 micron filter medium with fines removal optimized utilizing a 200 micron filter medium. The filter medium may, for example, include nylon, polyester, or other polymer mesh screens having opening from about 30-600 microns. Woven polymer media having square openings are presently preferred. However, a wedgewire filter cartridge may also be mentioned as an acceptable filter medium. For example, a wedgewire cartridge having slot openings of from about 0.001-0.010 inches may be provided with 0.020-0.045 inch thick smooth wires. Preliminary results indicate that the dual zone washer shows improved ash removal while exhibiting minimal fiber loss.
Exemplary operating parameters include inner and outer concentrically disposed cylinders having lengths of about 300 cm. The inner cylinder, in one embodiment, has a diameter of about 250 cm. Thus, the apparatus is compact, leading to decreased floor space requirements. G-forces exerted on the slurry typically may be on the order of about 50-350 G. Initial feed consistency to the dual zone washer may be on the order of about 0.1-10%, preferably about 0.5-5.0%.
Although the invention has been described in detail with reference to certain preferred embodiments thereof, other embodiments are possible. Therefore, the spirit and scope of the appended claims should not be limited to the description of the preferred embodiment contained herein.
Claims
1. A pulp thickening apparatus for removing fluid from pulp stock in a dewatering system comprising:
- a feed manifold for supplying the apparatus with pulp stock;
- a primary cylindrical filter for accepting said pulp stock from said feed manifold and for creating centrifugal force against said pulp stock to expel liquid therethrough, said primary cylinder filter being devoid of any associated wire member in contact therewith; and
- first removal means for removing said pulp stock from a surface of said primary cylindrical filter.
2. The pulp thickening apparatus according to claim 1 further comprising a secondary cylindrical filter surrounding said primary cylindrical filter for collecting pulp fibers that flow through said primary filter, said secondary cylindrical filter being devoid of any associated wire member in contact therewith.
3. The pulp thickening apparatus according to claim 2 further comprising a second removal means for removing said pulp stock from a surface of said secondary cylindrical filter.
4. The pulp thickening apparatus according to claim 2 wherein said secondary cylindrical filter has smaller openings than said primary cylindrical filter.
5. The pulp thickening apparatus according to claim 2 wherein said primary and secondary cylindrical filters are both rotatable around a common axis and create centrifugal force which expels fluid from said pulp stock.
6. The pulp thickening apparatus according to claim 5 further comprising an outlet for discharging fluid from said apparatus.
7. The pulp thickening apparatus as recited in claim 1 further comprising a compression roller adjacent said primary cylinder filter and between said feed manifold and said first removal means.
8. The pulp thickening apparatus as recited in claim 1 further comprising a water wash nozzle adjacent said primary cylinder filter and between said feed manifold and said first removal means.
9. The pulp thickening apparatus as recited in claim 1 wherein said feed manifold and first removal means define a first pair of feed manifold and removal means, said dewatering system further comprising another pair of feed manifold and removal means in operative association with said primary cylindrical filter.
10. A method of dewatering pulp stock comprising the steps of:
- a. delivering pulp stock to a wireless rotating primary filter;
- b. applying centrifugal force to said pulp stock;
- c. expelling fluid, small pulp fibers, and contaminants from said pulp stock through said rotating primary filter;
- d. collecting primary accepts including fibers and other material on said rotating primary filter; and
- e. removing said primary accepts from said primary filter.
11. The method according to claim 10 further comprising the step of receiving said small pulp fibers and contaminants on a rotating wireless secondary filter.
12. A wireless pulp thickening system comprising:
- two cylindrical filters for expelling water and contaminates from pulp stock by centrifugal force with a feed-line for supplying said filters with pulp stock.
13. Method for thickening pulp stock comprising:
- a. providing a first rotatable cylinder carrying a first filter medium;
- b. providing a second rotatable cylinder carrying a second filter medium;
- c. feeding a pulp stock suspension into said first rotatable cylinder;
- d. subjecting said pulp stock suspension to centrifugal force in said first rotatable cylinder to expel liquid, small fibers, and contaminants through said first filter medium and collect primary accepts from said first filter medium;
- e. forwarding said expelled liquid, small fibers, and contaminants into said second rotatable cylinder; and
- f. subjecting said expelled liquid, small fibers, and contaminants to centrifugal force in said second rotatable cylinder to expel liquid through said second filter medium and collect secondary accepts from said secondary filter medium.
14. Method as recited in claim 13, further comprising providing first vane means around the circumference of said first rotatable cylinder to regulate flow of said pulp suspension through said first filter medium.
15. Method as recited in claim 13, further comprising providing second vane means around the circumference of said second rotatable cylinder to regulate flow of said pulp suspension through said second filter medium.
16. Method as recited in claim 13, wherein said second filter medium has a finer mesh than said first filter medium.
17. Method as recited in claim 13, wherein said step (c) comprises feeding a stratified feed of said pulp suspension on an inside surface of said first rotatable cylinder.
18. Method as recited in claim 17 wherein said stratified feed comprises a plural layer arrangement of said pulp suspension having a first layer of short fibers and heavy fines laid contiguous to said inside surface.
19. Method as recited in claim 18 wherein said plural layer arrangement comprises a top layer of long fibers and light fines superposed on said first layer and remote from said inside surface.
20. Method as recited in claim 13, wherein said second rotatable cylinder is concentrically disposed with and surrounds said first rotatable cylinder.
21. Apparatus for thickening a pulp stock suspension comprising:
- a. first rotatable cylinder carrying a first filter medium;
- b. a second rotatable cylinder carrying a second filter medium;
- c. means for feeding a pulp stock suspension into said first rotatable cylinder;
- d. means for rotating said first and second rotatable cylinder for creating centrifugal force therein whereby pulp stock suspension in said first rotatable cylinder will impinge upon said first filter medium with primary accepts forming on one said of said first filter medium and with liquid and other material from said pulp stock suspension being expelled through said first filter medium and into contact with said second filter medium, whereby secondary accepts will gather on said second filter medium;
- e. means for collecting accepts material gathered on said first filter medium;
- f. means for collecting accepts material formed on said second filter medium; and
- g. means for transporting materials passing through said first and second filter media away from said apparatus.
22. Apparatus as recited in claim 21, wherein said second filter medium is of a finer mesh than said first filter medium.
23. Apparatus as recited in claim 21, wherein said second rotatable cylinder is concentric with and surrounds said first rotatable cylinder.
24. Apparatus as recited in claim 21, wherein said first rotatable cylinder comprises a first set of adjustable vane means around the circumference of said first rotatable cylinder for selectively adjusting gaps between individual ones of said vanes to regulate flow of said pulp stock suspension through said first rotatable cylinder.
25. Apparatus as recited in claim 24, wherein said second rotatable cylinder comprises a second set of adjustable vane means around the circumference of said second rotatable cylinder for selectively adjusting gaps between individual ones of said second set of vanes to regulate flow of said pulp suspension through said second filter medium.
26. Headbox feeder adapted for feeding pulp suspension to a filter medium surface, said feeder apparatus comprising a cyclonic separator in the form of an enclosed truncated cone having a central axis, a base end, and a closed apex end, an inlet opening at said base end and laterally offset from said axis to impart a rotational vector to said pulp suspension upon entry into said cone, a feed slot manifold connected to said cone between said base end and said closed apex end providing an exit for said pulp suspension.
27. Headbox feeder apparatus as recited in claim 26 wherein said feed slot manifold comprises a housing portion extending away from truncated cone.
28. Headbox feed apparatus as recited in claim 27 wherein said feed slot manifold is laterally offset from said axis.
29. Headbox feed apparatus as recited in claim 27 wherein said housing has a first leg extending away from said truncated cone and a radiused section terminating in a slot.
30. Method of feeding a pulp suspension to a filter surface comprising:
- a. providing a separator;
- b. admitting said pulp suspension to said separator;
- c. forming a stratified arrangement of said suspension in said separator, including a first layer of heavier fines, short fibers, and contaminants and a second layer of longer fibers and lighter fines; and
- d. feeding said stratified arrangement to said filter surface.
31. Method as described in claim 30 wherein said step (d) comprises placing said first layer contiguous with said filter surface with said second layer superposed over said first layer.
32. Method as described in claim 30 wherein said step (d) comprises placing said second layer of longer fibers and lighter fines contiguous with said filter surface and said first layer superposed over said second layer.
33. Method of feeding a pulp suspension to a filter surface as recited in claim 30 further comprising forming an intermediate layer of fines and fibers, said intermediate layer located intermediate said first and second layers.
34. Method of feeding a pulp suspension to a filter surface as recited in claim 28 wherein said separator is a headbox feeder apparatus.
Type: Application
Filed: Apr 11, 2005
Publication Date: Sep 13, 2007
Applicant: Kadant Black Clawson Inc. (Mason, OH)
Inventor: John Egan (Centerville, OH)
Application Number: 11/578,218
International Classification: D06F 35/00 (20060101);