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Title:
METHOD AND APPARATUS FOR PELLETIZING WOOD CHIPS FOR PULP AND PAPER PRODUCTION
Document Type and Number:
WIPO Patent Application WO/1999/009242
Kind Code:
A1
Abstract:
An apparatus for producing wood pellets for pulp and paper production comprising a cutting member (12), a compressor member (14), a long fiber retaining member (104) and a dehydrating member (16). The cutting member (12) cuts the wood into wood chips. The compressor member (14) is capable of compressing and extruding the wood chips. The dehydrating member (16) is associated with the compressor member (14) and facilitates the dehydration of the wood chips. The long fiber retaining member (104) insures that long fibers are not damaged during the compression thereof. The invention additionally comprises a method for producing wood pellets for pulp and paper production.

Inventors:
LINN DAVID D
Application Number:
PCT/US1998/016724
Publication Date:
February 25, 1999
Filing Date:
August 12, 1998
Export Citation:
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Assignee:
STONE CONTAINER CORP (US)
International Classes:
C10L5/44; (IPC1-7): D21B1/04; C10L5/00; C10L5/36; C10L5/44
Foreign References:
US4530700A1985-07-23
US4324561A1982-04-13
US5756098A1998-05-26
Other References:
CHEMICAL ABSTRACTS, 1 January 1900, Columbus, Ohio, US; abstract no. AB5907351, DENCH I D, FARRINGTON A: "New Furnish for Soda and Kraft Pulp Mills" XP002914754
Attorney, Agent or Firm:
Harris, Richard D. (IL, US)
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Claims:
Claims
1. A method for pelletizing wood for pulp and paper production, said wood having a high moisture content and a low density, said method comprising the steps of: cutting said wood into a plurality of wood chips, each of said wood chips including a plurality of preserved long wood fibers; dehydrating said wood chips to eliminate excess moisture therein; compressing a predetermined amount of said plurality of wood chips into wood fibre pellets while increasing the density of same towards compatible digestion by conventional pulp and paper production equipment; and retaining the length of said long wood fibers within said pellets to preserve fiber continuity, to, in turn, prevent damage to said long wood fibers.
2. The method according to Claim 1 wherein said step of compressing the wood chips comprises the steps of: positioning the wood chips between a first end and a second end of a cylinder said second end having an opening therethrough, said cylinder including a piston slidably associated with said cylinder, said piston capable of slidable movement from said first end to said second end; and forwarding the piston from said second end of said cylinder to said first end of said cylinder; and extruding wood pellets through said opening in said second end of said cylinder.
3. The method according to Claim 1 wherein said step of dehydrating comprises the step of heating said wood chips for a predetermined period of time.
4. The method according to Claim 1 further comprising the step of enhancing the adhesion of the wood chips at least one of prior to or during the step of compressing the wood chips, to, in turn, further foster the compression thereof and the adhesion therebetween.
5. The method according to Claim 1 wherein said wood chip comprises a conventional export size wood chip.
6. The method according to Claim 1 wherein said pellets comprise a cube having length and a width between one half inch and three inches.
7. The method according to Claim 6 wherein said resulting wood pellets comprise a cube having a length and width of approximately one inch.
8. The method according to Claim 1 wherein said resulting wood pellets comprise a cylinder having a diameter between one half and three inches.
9. The method according to Claim 8 wherein said resulting wood pellets comprise a cylinder having a diameter of approximately one inch.
10. A method for producing pulp from low density, high moisture content wood, said method comprising the steps of: cutting said wood into a plurality of wood chips, each of said wood chips including a plurality of preserved long wood fibers; dehydrating said wood chips to eliminate excess moisture in said wood chips; compressing a predetermined amount of said plurality of wood chips into wood fiber pellets while increasing the density of same toward an increased digester loading in conventional pulp and paper production equipment; retaining the length of said long wood fibers within said pellets to preserve fiber continuity, to, in turn, prevent damage to said long wood fibers; transporting said pellets to a digester associated with conventional pulp and paper productions equipment; and introducing said wood fiber pellets into said digester without regrinding said wood fiber pellets.
11. The method according to Claim 10 wherein said digester operates at an elevated temperature and pressure relative to ambient temperature and pressure.
12. An apparatus for producing wood pellets for pulp and paper production, said apparatus comprising: means for cutting said wood into wood chips; means for dehydrating said wood chips to eliminate excess moisture in said wood chips; a compressor member associated with said adhesion enhanced means, said compressor member capable of compressing said wood chips into wood fiber pellets while increasing the density of same toward compatible digestion by conventional pulp and paper production equipment; and means for retaining the length of said long wood fibers within said pellets to preserve fiber continuity, to, in turn, prevent damage to said long wood fibers.
13. The apparatus according to Claim 12 wherein said compressor member includes a cylinder having a first end and a second end, said second end including an opening, and, a piston member slidably positioned between said first end and said second end of said cylinder member, capable of forcing said wood chips through said opening in said second end.
14. The apparatus according to Claim 12 wherein said dehydrating means comprises a heater member.
15. The apparatus according to Claim 12 wherein said resulting pellet comprises a cube having a length and width between one half and three inches.
16. The apparatus according to Claim 15 wherein said resulting pellet comprises a cube having a length and width of approximately one inch.
17. The apparatus according to Claim 12 wherein said resulting pellet comprises a cylinder having a diameter between one half and three inches.
18. The apparatus according to Claim 17 wherein said resulting pellet comprises a cylinder having a diameter of approximately one inch.
Description:
TITLE OF THE INVENTION METHOD AND APPARATUS FOR PELLETIZING WOOD CHIPS FOR PULP AND PAPER PRODUCTION BACKGROUND OF THE INVENTION 1. Field of the invention The invention is directed to the preprocessing of raw wood fibers for utilization in the production of pulp and paper, and more particularly to the pelletizing of wood chips for pulp and paper production, to increase the density of low density, high moisture content wood for more efficient transportation thereof and for improved performance in pulp and paper production.

2. Background Art The production of pulp and paper is as old as the written word itself.

Increases in the worldwide consumption of pulp and paper have lead to the use of faster growing and faster developing trees, such as, for instance, the Gmelina tree. Gmelina trees develop quickly; from planting to a fully grown tree 20-25 meters high and having a trunk diameter of 25-30 cm, in only five years. Entire plantations and farms have been established in Central America that plant and harvest the Gmelina trees for pulp and paper production. The use of Gmelina trees from farms and plantations is environmentally friendly, inasmuch as the plantations replant trees and recycle the land, thereby lessening deforestation.

Additionally, due to the relatively short growth cycle, Gmelina trees are relatively inexpensive to plant and harvest.

One drawback of the Gmelina trees, as well as other low density wood, is that the wood is inefficient to transport. This type of wood absorbs and retains a substantial amount of moisture, and per cubic volume, contains less wood fiber than comparable volumes of high density hardwood. Essentially, each cargo load of Gmelina, or other lower density wood, yields less wood fiber per unit volume that is suitable for pulp and paper production than a comparable volume of high density hardwood. In particular, Gmelina trees have a density of only 21.4 Ibs per cubic foot and have a moisture content of 50-60 percent.

Inasmuch as many of the pulp and paper mills that could utilize Gmelina are generally located thousands of miles from the Central American farms and

plantations, the inefficiencies in transportation due to this crop's low density may outweigh the benefits associated with the use of such wood for pulp and paper production.

Additionally, Gmelina trees, and other trees of lower density, encounter certain difficulties during the pulp and paper production process. Due to the low density of Gmelina certain pulp and paper production machinery, such as certain digesters have lower production ratios when processing this type of wood.

Thus, it is an objective of the present invention to increase the density and lower the moisture of the Gmelina, and other low density wood, to improve the stowage factor for transportation.

It is likewise an objective of the present invention to increase the density of the Gmelina, and other low density wood, for improved use in pulp and paper production machinery including increased digester loading; while greatly improving the means and lowering the costs of processing.

These and other objectives will become apparent in light of the present disclosure and claims.

DISCLOSURE OF THE INVENTION The apparatus of producing wood pellets for pulp and paper production comprises means for cutting said wood into wood chips, means for dehydrating said wood chips, a compressor member, and means for retaining the length of long wood fibers. The dehydrating means serves to eliminate excess moisture in the wood chips. The compressor member is associated with the dehydrating means. The compressor member is capable of compressing the wood chips into fiber pellets while increasing the density of the fiber pellets, which increases the digester loading in conventional pulp and paper production equipment. The retaining means serves to preserve fiber continuity which in turn prevents damage to the long wood fibers.

In another preferred embodiment, the compressor member includes a cylinder having a first end and a second end. The second end includes an opening. A piston member slidably positioned between the first end and a second end of the cylinder member. The piston is capable of forcing the wood chips through the opening in the second end.

In yet another preferred embodiment, the dehydrating means comprises a heater member.

In a preferred embodiment, the apparatus may further include adhesion enhancement means associated with the compressor member.

In a preferred embodiment, the resulting pellet is a cube dimensioned to have a length and width between one half inch and three inches, and preferably one inch.

The invention additionally comprises a method for pelletizing wood for pulp and paper production. The wood initially has a high moisture content and a low density. The method comprises the steps of (a) cutting the wood into a plurality of wood chips, wherein each of the wood chips include a plurality of preserved long wood fibers; (b) dehydrating the wood chips to eliminate excess moisture contained therein; (c) compressing a predetermined amount of the plurality of wood chips into wood fiber pellets while increasing the density of same towards compatible digestion by conventional pulp and paper production equipment; and (d) retaining the length of the long wood fibers within the pellets

to preserve fiber continuity, to, in turn, prevent damage to the long wood fibers.

In a preferred embodiment, the step of compressing the wood chips comprises the steps of (a) positioning the wood chips between a first end and a second end of a cylinder where the second end includes an opening therethrough. The cylinder includes a piston slidably associated with the cylinder, and the piston is capable of slidable movement from the first end to the second end; and (b) forwarding the piston from said second end of said cylinder to said first end of the cylinder and extruding wood pellets through the opening in the second end of the cylinder.

In a preferred embodiment, the step of dehydrating comprises the step of heating the wood chips for a predetermined period of time.

In another preferred embodiment, the invention comprises the step of enhancing the adhesion of the wood chips prior to or during the step of compressing the wood chips, to, in turn, further foster the compression thereof and the adhesion therebetween.

In a preferred embodiment, said wood chip comprises a conventional export size wood chip.

In a preferred embodiment, said pellets comprise a cube having a width and height between one half inch and three inches, and preferably one inch. In another preferred embodiment, said resulting wood pellets comprise a cylinder having a diameter between one half and three inches, and preferably one inch.

In a preferred embodiment, the step of producing pulp and paper from low density, high water content wood, comprises the steps of (a) cutting said wood into a plurality of wood chips, each of the wood chips including a plurality of preserved long wood fibers; (b) dehydrating the wood chips to eliminate excess moisture in the wood chips; (c) compressing a predetermined amount of said plurality of wood chips into wood fiber pellets while increasing the density of same toward compatible digestion by conventional pulp and paper production equipment; (d) retaining the length of the long wood fibers within the pellets to preserve fiber continuity, to, in turn, prevent damage to the long wood fibers; (e) transporting the pellets to a digester associated with conventional pulp and paper production equipment; and (f) introducing the wood fiber pellets into the digester without regrinding the wood fiber pellets.

In a preferred embodiment, said digester operates at an elevated temperature and pressure relative to the ambient temperature and pressure.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 of the drawings is an elevated schematic view of the chipping means in operation; Fig. 2 of the drawings is a cross-sectional view of a compressor member; Fig. 3 of the drawings is a cross-sectional view of dehydrating means; Fig. 4 of the drawings is a perspective view of a compressor member; Fig. 5 of the drawings is a perspective view of an individual wood chip; Fig. 6 of the drawings is a perspective view of a series of resulting wood pellets made up of said wood chips; and Fig. 7 of the drawings is an elevated schematic view of the wood pellets of Fig. 6 being fed to a digester in conventional pulp and paper-making equipment.

BEST MODE FOR CARRYING OUT THE INVENTION While this invention is susceptible of embodiment in many different forms, there is shown in the drawings and will herein be described in detail, a specific embodiment with the understanding that the present disclosure can be considered as an exemplification of the principes of the invention and is not intended to limit the invention to the embodiment illustrated.

Apparatus 10 is shown in Figs. 1,2,3 and 7 as comprising cutting means 12, compressor member 14, dehydrating means 16, adhesion enhancement means 18 and digester member 20. Cutting means 12 comprises any one of a multitude of methods for cutting the wood into wood chips of the desired size (as will be explained below), such as special shredding machines, chipping machines and the like, as known in the art. As shown in Fig. 1, once cut, the wood chips are generally stored on a chip pad, or other conventional storage apparatus until needed.

Dehydration means 16 is shown in Fig. 3 as comprising heating chamber 28 and source 49. Heating chamber 28 includes screw advance 71, chip intake 72 and chip exit region 73. The heating chamber is configured to accept wood chips and to heat wood chips to elevated temperatures, which, in turn, dehydrates the wood chips. As will be understood, heater member 28 may be associated with a gas or electric heater source 49 positioned proximate thereto, or, may comprise a forced hot air system. Of course, other types of heaters are likewise contemplated.

Compressor member 14 is shown in Figs. 2 and 4 as comprising cylinder 24, piston 22 and opening 47. Cylinder 24 includes first end 30, second end 32, cross-section 23. Piston 22 includes outer configuration 29 and pusher member 27. Outer configuration 29 corresponds to cross-section 23 so that piston 22 is slidably positionable within cylinder 24 and selectively slidable from second end 32 and first end 30 of cylinder 24. The operation and movement of piston 22 within cylinder 24 may be powered by an electric motor, an internal combustion motor, or other power source. Likewise, the moving force for the piston may comprise a screw advance, as well as hydraulic and/or pneumatic power devices. Additionally, other compression type devices are contemplated

for use.

Opening 47 may be of a multitude of shapes, such as, for example circular or square, among others. Where the opening is square or rectangular the width and height is preferably greater than one half inch (or a one half inch diameter in the case of a circular opening), while a multitude of sizes are contemplated for use. Preferably, having an area greater than one inch assures that the long wood fibers 104 (Fig. 5) will be retained in an undamaged state.

The upper limit of the opening may be as large as desired, however, where the width, height (and/or diameter in the case of a circular opening) exceeds three inches, undesirable air pockets may form within the wood fiber pellet.

Adhesion enhancement means 18 is shown in Fig. 2 as comprising fluid/slurry source 41 and a plurality of openings, such as openings 31, which extend through cylinder 24. As will be explained, during compression, the adhesion enhancement means facilitates pelletizing and adhesion between wood chips during the compression of same. While other means of adhesion enhancement are contemplated, one such means directs water, steam or any combination thereof at a desired velocity and/or pressure from source 41 into cylinder 24. Of course, the use of other fluids/slurries to enhance the adhesion of wood chips is likewise contemplated. Additionally, the quantity of openings, the spacing of openings and the size of the individual openings can vary from application to application and can be determined through testing.

Digester 20 is shown in Fig. 7 as comprising a conventional digester of a conventional pulp and paper production plant operating at an elevated temperature and pressure. Such digesters are known to those of skill in the art.

In operation, the wood is first transformed into wood chips by cutting means 12. Specifically, as shown in Fig. 1, splitting cutter member 21 cuts the wood into wood chips 100 (Fig. 5). Preferably, as shown in Fig. 5, the wood chips comprise standard export wood chips (approximately an 1/4 inch thick, and between a half inch and an inch in width and length). While other sizes of wood chips are contemplated, it is important not to make the wood chips too small, inasmuch as such small wood chips will necessarily result in short and/or damaged wood fibers. It is desirable in the production of pulp and paper to

retain long wood fibers 104, which can be achieved through the use of standard export wood chips (Fig. 5).

Once the wood chips have been cut, the wood may next be dehydrated.

As shown in Fig. 3, the dehydration of the wood is accomplished by placing the wood chips into heater member 28 which removes moisture from the wood chips. Additionally, chips that are either too small or too large may be filtered out prior to or immediately after this step dehydrating in the heater member.

Once dehydrated, the wood chips are placed into the cylinder for compression and, in turn, pelletizing through compression member 14. As shown in Fig. 2, piston 22 is moved from the second end 32 to the first end 30 of cylinder 24. As the piston moves, the wood chips are forced against the first end of the cylinder and, in turn, through smaller opening 47 proximate first end 30 of cylinder 24.

Either before or as the piston advances, adhesion enhancement means is activated to promote adhesion of the wood chips. This further enhances the pelletizing and the attachment of the wood chips to each other. Specifically, water/steam can be forced through opening 31 and can penetrate into the wood chips themselves. Of course, as explained above, other fluids/slurries are likewise contemplated. As the extrusion extends out of opening 47, the extrusion can be broken into pellets, (such as cylinders) or cubes. Preferably, the extrusion is cut so that the thickness of the resulting pellet is between one half and three inches, while other dimensions are also certain contemplated.

Inasmuch as the exiting extrusion/pellet may be at an elevated temperature (depending in part on the adhesion means fluid/slurry utilized), the pellets can be cooled back to ambient temperature either by exposure to ambient or cooler temperature conditions or by other cooling methods such as forced air cooling. Additionally, the wood chips before extrusion, and, the pellets after extrusion can pass through screens and/or filters which will eliminate loose wood chips and wood residue from the pellets and send these "rejects"to reprocessing.

The wood pellet/cube 102 (Fig. 6) comprises a high density wood fiber material substantially free of moisture and air, which can then be transported to

a pulp and paper mill. In the situation of Gmelina wood, the wood is harvested in Central America for processing in the Far East, among other regions.

Subsequently, as the wood pellets are prepared for processing, it is only necessary to introduce the pellets to conventional digester 20. There is no need to regrind the pellets prior to introduction into the digesters. Indeed, the digesters operate at an elevated temperature and pressure, and as such the pellets begin to separate and cook, as desired, upon the introduction into the digester--but in the correct fiber size. It is believed that the pelletized, compressed, wood chips will improve the performance of the digesters, which as explained above, do not typically operate efficiently with lower density wood.

The foregoing description and drawings merely explain and illustrate the invention and the invention is not limited thereto except insofar as the appended claims are so limite, as those skilled in the art who have the disclosure before them will be able to make modifications and variations therein without departing from the scope of the invention.