WO2013074764A1

WO2013074764A1 - Microstickies removal apparatus and method for a screen basket

Info

Publication number: WO2013074764A1
Application number: PCT/US2012/065241
Authority: WO
Inventors: William FINERAN
Original assignee: Voith Patent Gmbh
Priority date: 2011-11-15
Filing date: 2012-11-15
Publication date: 2013-05-23

Abstract

A screening apparatus for recycled paper stock includes a screen basket and at least one microstickies colletor. The screen basket includes a fine perforated screen with a circumference. The at least one microstickies collector is positioned in association with the circumference of the screen. Each microstickies collector is comprised of a polyester material for collecting microstickies.

Description

MICROSTICKIES REMOVAL APPARATUS

AND METHOD FOR A SCREEN BASKET

BACKGROUND OF THE INVENTION

1. Field of the Invention

[0001] The present invention relates to the manufacture of recycled paper, and, more particularly, to apparatus and methods used to remove stickies from such recycled paper.

2. Description of the Related Art

[0002] Considerable environmental pressure exists to increase the use of recycled paper in North America as well as throughout the whole paper making world, but its introduction into processes currently using virgin fibers carry some serious implications to product quality and machine performance. Some of the most difficult problems result from the presence of adhesives, arising from hot melt glues, binders and other thermoplastic materials, for example from book-backs and adhesive tape or from silicone. They tend to be pliable organic materials, such as latex, rubber, vinyl, and hot melts. Under certain conditions, these compounds can become tacky and deposit as "stickies" in the paper machine. Stickies have multiple detrimental effects on paper quality such as sheet marking, sheet structural defects, web breaks and discoloration (e.g. black spots). Experience by the assignee of the present invention has been that ignoring the treatment of stickies increases the likelihood of these problems presenting themselves and will increase a mill's operating costs.

[0003] Once stickies are released by the pulping process in an integrated recovered paper plant, they can accumulate in the recycling plant's white water system. Similarly, non-integrated mill's who purchase their recovered fiber can suffer from a build-up of stickies on the paper making machine. As paper mills are continuing to reduce their fresh water usage to minimize costs, white water recycling is becoming more prevalent, increasing the build-up of stickies and thus making them even more of a problem.

[0004] A paper written by Dipl.-Ing. Lutz Hamann, PTS Heidenau entitled Stickies - Definition, Origin and Characterization presented at the 2nd CTP/PTS Advanced Training Course on Recycling in Grenoble, May 31/June 1 & 2, 2005, describes the types of Stickies present in paper making stock and water streams and defines the two main types of stickies that we deal with as system suppliers - Macrostickes and MicroStickies.

[0005] A simplified explanation of a current approach used to address the concentrations of stickies present in the paper making stock system is that fine slotted screen baskets (slot sizes down to 0.1mm - 0.15 mm (0.004 in - 0.006 in) are operated at low stock consistency in combination with low intensity pressure screen rotors for the effective removal of Macwstickies from the paper making system. Any remaining stickies present in the accepts stream following fine slotted screening are considered Microstickies.

[0006] The stock furnish accepted from the fine slotted screening system is pumped to the paper machine where the sheet is formed and dried. Microstickies in the stock furnish deposit on paper making surfaces, fabrics, felts, press rolls, etc. and are especially detrimental to high quality paper grades that have surface coatings applied. Sheet breaks and off quality paper are the most direct effects of microstickies carry over. Some indirect effects of microstickies are the filling of machine clothing such as fabrics and felts and adherence to paper machine rolls.

SUMMARY OF THE INVENTION

[0007] The present invention provides a static collector of microstickies associated with the fine slotted pressure screen prior to the paper machine.

[0008] The invention in one form is directed to a screening apparatus for recycled paper stock, including a screen basket and at least one microstickies colletor. The screen basket includes a fine perforated screen with a circumference. The at least one microstickies collector is positioned in association with the circumference of the screen. Each microstickies collector is comprised of a polyester material for collecting microstickies.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become more apparent and the invention will be better understood by reference to the following description of an embodiment of the invention taken in conjunction with the accompanying drawings, wherein:

[0010] Fig. 1 is an elevation view of a screen basket with a jacket surrounding the screen basket, with the jacket having microstickies collector strips;

[0011] Fig. 2 is a perspective view of a portion of the fine slotted screen basket with the jacket in place at the circumference thereof;

[0012] Fig. 3 is a perspective view of a portion of the fine slotted screen basket with the jacket in place at the circumference thereof, showing microstickies collected on the collector strips; [0013] Fig. 4 is a more detailed perspective view showing the configuration of one embodiment of the collector strips; and

[0014] Fig. 5 is an end view of the collector strip shown in Fig. 4, taken along line 5-5 shown in Fig. 4.

[0015] Corresponding reference characters indicate corresponding parts throughout the several views. The exemplification set out herein illustrates an embodiment of the invention, in one form, and such exemplification is not to be construed as limiting the scope of the invention in any manner. DESCRIPTION OF THE INVENTION

[0016] The present invention provides a static collector of microstickies associated with the fine slotted pressure screen prior to the paper machine. Referring to Figs. 1 and 2, the present invention, in one form, provides a screen basket assembly 8 with a replaceable shell 10 held in place around the exterior (accepts side of a centrifugal basket 12) that holds a plurality of microstickies collector strips 14 made from a material such as High Density Polyethylene

(HDPE). The article "Quantification of Micro Stickies" by Mahendra Doshi, et. al. Paper

Recycling Challenge, Appleton, WI, Doshi & Associates Inc. 1997-1998, p. 119 - 122, describes how HDPE has been proven to act as a stickies collector. The collector strips 14 arranged in a

"jacket" or shell 10 on the outside of the centrifugal basket statically collect microstickies 16

(Fig. 3) as they pass through the slots 18 of shell 10.

[0017] Each of the collector strips 14 is made from a polyesther material for collecting microstickies. The polyesther material is a manmade hydrophobic material, and preferably is a polyethylene thermoplastic. In one embodiment, the polyethylene thermoplastic is high density polyethylene (HDPE), but other materials acting as a static collector may also be used. Each of the collector strips 14 have a cross sectional profile configured to maximize a surface area over which an accepts stock from the screen passes for collecting the microstickies (see, e.g., Figs. 4 and 5).

[0018] In practice it is anticipated that the mill would need to periodically replace the jacket or shell 10 with a new set of HDPE collector strips 14. The integration concept is that initially, a new screen basket assembly 8 is supplied with a new HDPE shell 10 attached and a spare new shell 10 for the mill to install when the collector material is full of microstickies. A used jacket 10 may be later returned, and the manufacturer installs new HDPE strips on jacket 10 and returns it to the mill for as long as the basket assembly 8 is in the machine. The replacement rate of the new jacket 10 depends on the concentration of microstickies in the feed stock, the stickies removal efficiency and the impact the existing system has on stickies size reduction.

[0019] The collector shell or "jacket" 10 is configured so that the collector's performance is optimized and does not interfere with the normal operation of the pressure screen assembly 8. The jacket 10 is also configured with minimal impact on screen slot velocity in relation to the placement of the collector strips 14, and the impact of rotor speed, operating temperature and consistency on microstickies collection efficiency. In order to withstand some of the forces inside the pressure screen assembly 8 on the accepts side, each individual HDPE collector strip 14 may be reinforced with a support or "backing" (e.g., stainless steel) in order to secure the collector strips 14 in the jacket 10 surrounding the screen or basket 12.

[0020] In the embodiment which is illustrated and described above, microstickies are collected using collector strips 14 which are positioned around the screen 12. However, it also possible to use one or more microstickies collectors which are differently configured. For example, the screening apparatus may generically include one or more microstickies collectors positioned in association with a circumference of the screen, with each microstickies collector being made from a polyester material for collecting the microstickies. The microstickies collector can include a plurality of collector elements which are positioned around a circumference of the screen, or even a coating on the screen. When configured as a coating, the coating may be placed on the screen and/or housing surrounding the screen. When configured as discrete collector elements, the collector elements may have any predefined geometric shape, such as strips, circles, rectangles, squares, or any other suitable shape. The discrete collector elements may be entirely made of the collector material, or coated with the collector material. When configured as strips, the strips may extend generally in the longitudinal or circumferential directions of the screen basket, and may be spaced apart from each other skewed or parallel with any desired spacing therebetween.

[0021] While this invention has been described with respect to at least one embodiment, the present invention can be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.

Claims

What is claimed is:

1. A screening apparatus for recycled paper stock, comprising:

a screen basket including a fine perforated screen with a circumference; and at least one microstickies collector positioned in association with the circumference of the screen, each said microstickies collector being comprised of a polyester material for collecting microstickies.

2. The screening apparatus of claim 1, wherein said at least one microstickies collector includes at least one of:

a plurality of collector elements positioned around a circumference of the screen, said plurality of collector elements being comprised of or coated with said polyester material; and a coating on the screen and/or housing surrounding the screen.

3. The screening apparatus of claim 2, wherein said plurality of collector elements each include a predefined geometric shape.

4. The screening apparatus of claim 3, wherein said predefined geometric shape includes strips, circles, rectangles and/or squares.

5. The screening apparatus of claim 4, wherein said plurality of collector elements are collector strips which extend in a longitudinal or circumferential direction about the screen at a predetermined spacing therebetween.

6. The screening apparatus of claim 5, wherein said collector strips are parallel or skewed relative to each other.

7. The screening apparatus of claim 5, wherein each of said collector strips have a cross sectional profile configured to maximize a surface area over which an accepts stock from the screen passes for collecting the microstickies.

8. The screening apparatus of claim 5, including a jacket surrounding the screen, said jacket holding each of the collector strips.

9. The screening apparatus of claim 1, wherein the polyester material is a manmade hydrophobic material.

10. The screening apparatus of claim 1, wherein said polyester is a polyethylene thermoplastic.

11. The screening apparatus of claim 9, wherein said polyethylene thermoplastic is high density polyethylene (HDPE).

12. The screening apparatus of claim 1, wherein said fine perforated screen includes slots and/or holes.