Abstract:
A refining plate segment for a mechanical refiner of lignocellulosic material including: a convex conical refining surface on a convex conical substrate of the plate, wherein the refining surface is adapted to face a concave conical refining surface of an opposing refiner plate, the convex conical refining surface including bars and grooves formed between adjacent bars, wherein an angle of each bar with respect to a reference line parallel to a rotational axis of the refiner increases at least 15 degrees and the angle is a holdback angle is 10 to 45 degrees at a periphery of the refining surface, and wherein the bars each include a leading sidewall having an irregular surface having protrusions extending outwardly from the sidewall toward a sidewall on an adjacent bar.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application claims the benefit of priority under U.S. Provisional Patent Application No. 61/525,441, having a filing date of Aug. 19, 2011, which is incorporated herein in its entirety by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Technical Field 
         [0003]    The invention relates to conical refiners or disc-conical refiners for lignocellulosic materials, such as refiners used for producing mechanical pulp, thermomechanical pulp and a variety of chemi-thermomechanical pulps (collectively referred to as mechanical pulps and mechanical pulping processes). 
         [0004]    2. Prior Art 
         [0005]    Conical refiners, or conical zones of disc-conical refiners, are used in mechanical pulping processes. The raw cellulosic material, typically wood or other lignocellulosic material (collectively referred to as wood chips), is fed through the middle of one of the refiners discs and propelled outwards by a strong centrifugal force created by the rotation of a rotor disc. Refiner plates are mounted on each of the opposing faces of the refiner discs. The wood chips move between the opposing refiner plates in a generally radial direction to the outer perimeter of the plates and disc section when such a section exists (in disc-conical refiners). In conical refiners (or conical section of disc-conical refiners), the convex rotor element propels the wood chips into the concave stator element. 
         [0006]    Steam is a major component of the feeding mechanism. Steam generated during refining displaces the wood chips through the conical zone. 
         [0007]    In conical and disc-conical refiners, the refiner rotor conventionally operates at rotational speeds of 1500 to 2100 revolutions per minute (RPM). While the wood chips are between the refining elements, energy is transferred to the material via refiner plates attached to the rotor and stator elements. 
         [0008]    The refiner plates generally feature a pattern of bars and grooves, as well as dams, which together provide a repeated compression and shear actions on the wood chips. The compression and shear actions acting on the material separates the lignocellulosic fibers out of the raw material, provides a certain amount of development or fibrillation of the material, and generates some amount of fiber cutting which is usually less desirable. The fiber separation and development is necessary for transforming the raw wood chips into a suitable board or paper making fiber component. 
         [0009]    In the mechanical pulping process, a large amount of friction occurs, such as between the wood chips and the refiner plates. This friction reduces the energy efficiency of the process. It has been estimated that the efficiency of the energy applied in mechanical pulping is in the order of 10% (percent) to 15%. 
         [0010]    Efforts to develop refiner plates which work at higher energy efficiency e.g., lower friction, have been achieved and typically involve reducing the operating gap between the discs. Conventional techniques for improving energy efficiencies typically involve design features on the front face of refiner plate segments that usually speed up the feed of wood chips across the refining zone(s) on the refiner plates. These techniques often result in reducing the thickness of the fibrous pad formed by the wood chips flowing between the refiner plates. When energy is applied by the refiner plates to a thinner fiber pad, the compression rate applied to the wood chips becomes greater for a given energy input and results in a more efficient energy usage in refining the wood chips. 
         [0011]    Reducing the thickness of the fiber pad allows for smaller operating gaps, e.g., the clearance between the opposing refiner plates. Reducing the gap may result in an increase in cutting of the fibers of the wood chips, a reduction of the strength properties of the pulp produced by the discs, an increased wear rate of the refiner plates, and a reduction in the operating life of the refiner plates. The refiner plate operational life reduces exponentially as the operating gap is reduced. 
         [0012]    The energy efficiency is believed to be greatest toward the periphery of the refiner discs, and in general, the same applies for both flat and conical refining zones. The relative velocities of refiner plates are greatest in the peripheral region of the plates. The refining bars on the refiner plates cross each other on opposing plates at a higher velocity in the peripheral regions of the refiner plates. The higher crossing velocity of the refining bars is believed to increase the refining efficiency in the peripheral region of the plates. 
         [0013]    The wood fibers tend to flow quickly through the peripheral region of the conventional refiner plates, regardless of whether they are flat or conical in shape. The quickness of the fibers in the peripheral region is due to the effects of centrifugal forces and forces created by the forward flow of steam generated between the discs. The shortness of the retention period in the peripheral region limits the amount of work that can be done in that most efficient part of the refining surface. 
       BRIEF SUMMARY OF THE INVENTION 
       [0014]    Designing the refiner plates to shift more of the energy input toward the periphery of the refining zone(s) should increase the overall refining efficiency and reduce the energy consumed to refine pulp. The refiner plates are designed to increase the retention period of the fibers in the periphery of the refining zone(s), thereby increasing and improving the refining efficiency. As the energy input is shifted to the periphery of the refining zone(s), operating gap between the refiner plates may be made sufficiently wide so as to provide a long operating life for the refiner plates. 
         [0015]    A novel conical refiner plate has been conceived that, in one embodiment, has enhanced energy efficiency and allows for a relatively large operating gap between discs. The energy efficiency and large operating gap may provide reduced energy consumption to produce pulp, a high fiber quality of the produced pulp, and a long operating life for the refiner plate segments. 
         [0016]    In one embodiment, the refiner plate is an assembly of convex conical rotor plate segments having an outer refining zone with bars that have at least a radially outer section with a curved longitudinal shape and leading sidewalls with wall surfaces that are jagged, serrated, or otherwise irregular. The irregular surface on the leading sidewall may also be embodied as protrusions that are semi-circular, rectangular or curvilinear in shape. 
         [0017]    The curved bars and resulting curved grooves between bars increase the retention time of the wood chip feed material in the outer zone and thereby increase the refining of the material in the outer zone. Further, the jagged surfaces on the leading sidewalls also act to increase the retention time of feed material in the outer zone. 
         [0018]    A refining plate has been conceived with a convex conical refining surface facing another plate; the convex refining surface includes a plurality of bars upstanding from the surface. The bars extend radially outward toward an outer peripheral edge of the plate, and have a jagged or irregular surface on at least the leading sidewall of the bars. The bars are curved, such as with an exponential or in an involute arc. The refining plate may be a convex conical rotor plate, and is arranged in a refiner opposite a concave conical stator plate. 
         [0019]    A refining plate segment has been conceived for a mechanical refining of lignocellulosic material comprising: a convex conical refining surface on a substrate, wherein the refining surface is adapted to face a concave conical refining surface of an opposing refiner plate, the convex refining surface including bars and grooves between the bars, wherein an angle of each bar with respect to a radial line corresponding to the bar increases at least 15 degrees along a radially outward direction, and the angle is a holdback angle in a range of any of 10 to 45 degrees, 15 to 35 degrees, 15 to 45 degrees and 20 to 35 degrees at the periphery of the refining surface, and wherein the bars each include a leading sidewall having an irregular surface, wherein the irregular surface includes protrusions extending outwardly from the sidewall toward a sidewall on an adjacent bar, and the irregular surface extends from at or near the outer periphery of the refining surface, and extends radially inwardly along the bars and may not reach an inlet of the refining surface. 
         [0020]    A refining plate segment has been conceived for a mechanical refiner of lignocellulosic material comprising: a convex conical refining surface on a substrate, wherein the refining surface is adapted to face a concave conical refining surface of an opposing refiner plate, the convex refining surface including bars and grooves between the bars, wherein an angle of each bar with respect to a radial line corresponding to the bar increases at least 15 degrees along a radially outward direction, and the angle is a holdback angle in a range of 10 to 45 degrees or 15 to 35 degrees at the periphery of the refining surface, and wherein the bars each include a leading sidewall having an irregular surface that includes recesses in the bar extending outwardly from the sidewall toward a sidewall on an adjacent bar, and the irregular surface extends from at or near the outer periphery of the refining surface and extends radially inward along the bars and may not reach an inlet of the refining surface. 
         [0021]    The bars may each have a curved longitudinal shape with respect to a radial of the plate extending through the bar. The angles may increase continuously and gradually along the radially outward direction or in steps along the radially outward direction. At the radially inward inlet to the refining surface, the bars may be each arranged at an angle within 10, 15 or 20 degrees of a radial line corresponding to the bar. Further, the refining plate segment may be adapted for a rotating refining disc and to face a rotating refining disc when mounted in a refiner. 
         [0022]    The refining surface may include multiple refining zones, wherein a first refining zone has relatively wide bars and wide grooves and a second refining zone has relatively narrow bars and narrow grooves, wherein the second refining zone is radially outward on the plate segment from the first refining zone, and wherein the holdback angle for the second refining zone may be in a range of any of 10 to 45, 15 to 45 and 20 to 35. 
         [0023]    The irregular surface on the leading sidewall of the bars may include a series of ramps, each having a lower edge at the substrate of each groove, extending at least partially up the leading sidewall. The irregular surface on the leading sidewall may be embodied as protrusions on the semi-circular, rectangular or curvilinear shapes. 
         [0024]    A refiner plate has been conceived for a mechanical refiner of lignocellulosic material comprising: a convex conical refining surface on a substrate, wherein the refining surface is adapted to face a concave conical refining surface of an opposing refiner plate, and the convex refining surface includes bars and grooves between the bars, wherein the bars have at least a radially outer section having an angle of each bar with respect to a corresponding radial line at the inlet of the bar within 10, 15 or 20 degrees of the radial line, and the holdback angle is an angle in a range of any of 10 to 45, 15 to 35, 15 to 45 and 20 to 35 at an outer periphery of the bars, wherein the angle increases at least 10 to 15 degrees from a radially inward inlet of the bars to the outer periphery, and the bars each include a sidewall having an irregular surface in a radially outer section, wherein the irregular surface includes protrusions extending outwardly from the sidewall toward a sidewall on an adjacent bar, wherein the bars each include a leading sidewall having an irregular surface, wherein the irregular surface includes protrusions extending outwardly from the sidewall toward a sidewall on an adjacent bar, and the irregular surface extends from at or near the outer periphery of the refining surface, and extends radially inward along the bars and may not reach an inlet of the refining surface. 
         [0025]    In another embodiment, a refiner plate has been conceived for a mechanical refiner of lignocellulosic material comprising: a convex conical refining surface on a substrate, wherein the refining surface is adapted to face a concave conical refining surface of an opposing refiner plate, and the convex refining surface includes bars and grooves between the bars, wherein the bars have at least a radially outer section having an angle of each bar with respect to a corresponding radial line at the inlet of the bar within 10, 15 or 20 degrees of the radial line, and the holdback angle is an angle in a range of any of 10 to 45, 15 to 35, 15 to 45 and 20 to 35 at an outer periphery of the bars, wherein the angle increases at least 10 to 15 degrees from a radially inward inlet of the bars to the outer periphery, and the bars each include a sidewall having an irregular surface in a radially outer section, wherein the irregular surface includes recesses in the bar extending outwardly from the sidewall toward a sidewall on an adjacent bar, wherein the bars each include a leading sidewall having an irregular surface, wherein the irregular surface includes recesses in the bar extending outwardly from the sidewall toward a sidewall on an adjacent bar, and the irregular surface extends from at or near the outer periphery of the refining surface, and extends radially inward along the bars and may not reach an inlet of the refining surface. 
         [0026]    A refining plate segment has been conceived for a mechanical refiner of lignocellulosic material comprising: a convex conical refining surface on a substrate, wherein the refining surface is adapted to face a concave conical refining surface of an opposing refiner plate; the convex refining surface including bars and grooves between the bars, wherein each bar is at an angle with respect to a radial line corresponding to the bar, and the angle at the inlet to the bars within 10, 15 or 20 degrees of the radial line, the angle increases at least 10 to 15 degrees in a radially outward direction along the bar, and the angle is in a range of any of 10 to 45, 15 to 35, to 45 and 20 to 35 at the periphery of the refining surface, and wherein the bars each include a leading sidewall having an irregular surface, wherein the irregular surface includes protrusions extending outwardly from the sidewall toward a sidewall on an adjacent bar, and the irregular surface extends from at or near the outer periphery of the refining surface, and extends radially inward along the bars and may not reach an inlet of the refining surface. 
         [0027]    In another embodiment, a refining plate segment has been conceived for a mechanical refiner of lignocellulosic material comprising: a convex conical refining surface on a substrate, wherein the refining surface is adapted to face a concave conical refining surface of an opposing refiner plate; the convex refining surface including bars and grooves between the bars, wherein each bar is at an angle with respect to a radial line corresponding to the bar, and the angle at the inlet to the bars is within 10, 15 or 20 degrees of the radial line, the angle increases at least 10 to 15 degrees in a radially outward direction along the bar, and the angle is in a range of any of 10 to 45, 15 to 35, 15 to 45 and 20 to 35 at the periphery of the refining surface, and wherein the bars each include a leading sidewall having an irregular surface, wherein the irregular surface includes recesses in the bar extending outwardly from the sidewall toward a sidewall on an adjacent bar, and the irregular surface extends from at or near the outer periphery of the refining surface, and extends radially inward along the bars and may not reach an inlet of the refining surface. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0028]      FIG. 1  is a schematic diagram of a conical mechanical refiner for converting cellulosic material to pulp, or for developing pulp. 
           [0029]      FIG. 2  is a cross-sectional view of a disc-conical refiner plate arrangement. 
           [0030]      FIG. 3  is a perspective view of a conical rotor refiner plate segment. 
           [0031]      FIG. 4  shows a cross-section of rotor and stator conical zone plates. 
           [0032]      FIG. 5  shows a top view of a convex conical rotor design. 
           [0033]      FIG. 6  shows top view of a conventional concave conical stator plate that could be used opposing the novel rotor design. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0034]    A conical rotor refiner plate has been conceived with a relatively coarse bar and groove configuration, and other features to provide for a long retention time for the fibrous pad in the effective refining zone at a peripheral region of that zone. These features concentrate the refining energy by surface area toward the periphery of the refining surface, together with a lower number of bar crossings (less compression events) and a much longer retention time for the raw material, caused by the specific design of the conical rotor elements or conical rotor refiner plates. This results in a high compression rate of a thick fiber mat, thus maintaining a larger operating gap. Instead of achieving high intensity by reducing the amount of fiber between the opposing plates, high intensity compressions are achieved by lowering the number of bar crossing events and increasing the amount of fiber present at each bar crossing. 
         [0035]      FIG. 1  is a schematic diagram illustrating a conical refiner or disc-conical refiner  10  which converts cellulosic material provided from a feed system  12  to pulp  14 , or which develops wood pulp from the feed system  12  and results in improved pulp  14 . The refiner  10  is a conical or partially conical mechanical refining device. The refiner  10  includes a rotor  16  driven by a motor  18 . Rotor refining plates  20  are mounted on the frustoconical surface of the rotor  16 . Additional rotor refining plates  22  may be optionally mounted on a front planar face of the rotor  16 . These refining plates rotate with the rotor  16 . The rotor refining plates  20  on the frustoconical conical surface of the rotor  16  turn in a generally annular path around the axis  24  of the rotor  16 . The rotor refining plates  20  on the front face of the rotor  16  turn in a plane perpendicular to the rotor axis. 
         [0036]    The refiner  10  includes a conical stator  26  which surrounds the frustoconical portion of the rotor  16 . The stator  26  includes stator refining plates  28  that are opposite the rotor refining plates  20  on the rotor  16 . A narrow gap  30  is between the rotor refining plates  20  and stator refining plates  28 . Similarly, a stator disc  32  faces the front of the rotor  16 . Additional stator refining plates  33  are on the stator disc  32  and are separated by a gap from the additional rotor refining plates  22  on the front of the rotor  16 . 
         [0037]    Cellulosic material, such as wood chips and pulp, flows into a center inlet  36  along the axis  24  of the rotor  16 . As the cellulosic material flows into the gap  34  between the additional rotor and stator refining plates  22  and  33 , the cellulosic material is moved radially outward through the gap  34  by centrifugal forces imparted by the rotating rotor refiner plate  22 . As the cellulosic material reaches the outer perimeter of the additional rotor and stator refiner plates  22  and  33 , it flows into the narrow gap  30  between the rotor and stator refiner plates  20  and  28  on the frustoconical portion of the rotor  16 . The cellulosic material moves axially and radially through the narrow gap  30  due to the centrifugal force applied by the rotor  16 . As the cellulosic material moves through the gaps  34  and  30 , the cellulosic material is subjected to large compression and shear forces which convert the cellulosic material to pulp or further refine the pulp. 
         [0038]      FIG. 2  is cross-sectional view of a disc-conical refiner plate arrangement showing the gaps  34  and  30  between the conical rotor and stator refining plates  20  and  28  and the additional rotor and stator refining plates  22  and  33 . The front face of each refining plate  20 ,  22 ,  28 , and  33  has a refining pattern formed of bars  38  and grooves  40  which extend generally radially across the front surface of each refining plate  20 ,  22 ,  28 , or  33 . The bottoms of the grooves  40  are at the substrate of the each refining plate  20 ,  22 ,  28 , or  33 . Bridges between the grooves extend up from the substrate. The grooves  40  are the volumes between adjacent bars  38  and above the substrate of the plate  20 ,  22 ,  28 , or  33 . 
         [0039]    The pattern of bars  38  and grooves  40  can vary widely in terms of the distance between bars  38 , the length of bars  38 , the longitudinal shape of the bars  38  and other factors. As the plates  20  and  22  move with the rotor  16 , the bars  38  on the rotor refining plates  20  and  22  repeatedly cross over the bars on the stator refining plates  28  and  33 . The pulsating forces imparted to the fiber pad in the gaps  30  and  34  due to the crossing of the bars  38  is a substantial factor in the shear and compression forces applied to the cellulosic material in the fiber pad. 
         [0040]    The refining process applies a cyclical compression and shear to a fibrous pad, formed of cellulosic material, moving in the operating gaps  30  and  34  between the plates of a conical refiner or disc-conical refiner  10 . The energy efficiency of the refining process may be improved by reducing the percentage of the refining energy applied in shear and at lower compression rates. The increased compression rate is achieved with the plate designs disclosed herein by the coarse bars with jagged leading sidewalls at the radially outward regions of the plates. The amount of shearing is reduced by relatively wide operating gaps  30  or  34 , which are wide as compared to conventional higher energy efficiency refiner plates. 
         [0041]    A relatively wide operating gap  30  or  34  between the rotor and stator refining plates  20 ,  22 ,  28 , and in a refiner  10 , results in a thicker pulp pad formed between the plates  20 ,  22 ,  28 , or  33 . 
         [0042]    High compression forces can be achieved with a thick pulp pad using a significantly coarser refiner plate, as compared to conventional rotor plates used in similar high energy efficiency applications. A coarse refiner plate has relatively few bars  38  as compared to a fine refiner plate typically used in high energy efficiency refiners. The fewer number of bars  38  reduces the compression cycles applied as the bars  38  on the rotor  16  pass across the bars  38  on the stator  26 . The energy being transferred into fewer compression cycles increases the intensity of each compression and shear event and increase energy efficiency. 
         [0043]    The rotor refiner plate  20  and  22  designs disclosed herein achieve high fiber retention and high compression to provide high energy efficiency while preserving fiber length and improving wear life of the refiner plates. These designs are to be used in convex conical rotor refiner plates  20  for conical and disc-conical refiners, where any existing or new stator plate design may be used on the concave conical stator refining plates  28 . 
         [0044]      FIG. 3  is a perspective view of a refiner plate  40  for a conical rotor  16 . The refiner plate  40  may have a relatively coarse bar  42  and groove  44  arrangement wherein the separation between bars  42  is greater than with conventional high energy rotor refining plates. The bars  42  may have a back swept angle  46  at their outer perimeter and jagged surfaces on the leading face of the sidewalls in the direction  50  of rotation. These features increase the retention time of the fibrous pad in the radially outward portion  52  the plate  40 . The outward portion  52  is generally the most effective portion for refining because this portion  52  applies much of the energy to the fiber pad in the operating gap  30  or  34 . The back swept angle  46  and jagged surfaces  48  on the sidewall concentrate the refining energy, applied to the pulp in the radially outward portion  52 . These features combine with a coarse bar  42  and groove  44  patterns to reduce the frequency of bar crossings (less compression events) and substantially increase the fiber retention period in the radially outward portion  52  of the refining zone. The lower frequency of compressions applied to the fiber pad, longer period of the pad in the radially outward portion  52 , and relatively wide operating gap  30  or  34  achieve a high compression rate of a thick fiber mat. 
         [0045]    Conventional low energy refining plates may have narrow operating gaps to reduce the amount of fiber between the opposing plates and thereby concentrate the energy on a relatively small accumulation of pulp. In contrast, high intensity compressions are achieved with the refining plate  40  such that the operating gap  30 ,  34  may be relatively wide and thereby increase the amount of fiber present at each bar crossing and the capacity of the refiner to process cellulosic material. 
         [0046]    The refiner plate  40  may have curved bars  42  with jagged surfaces  48  on the leading sidewalls at least in the radially outward portion  52  of the conical refining zone. The curvature  46  and jagged surfaces  48  on the leading sidewalls of the bars  42  slows the fibrous mat and thereby increases the retention of the pulp in the radially outward portion  52  of the refining zone. The increased retention period allows for greater energy input towards the periphery of the refiner where energy input into the pulp is more efficient. 
         [0047]    The jagged surfaces  48  of the leading sidewall may be of various sizes and shapes. The surfaces  48  may include outer protrusions having jagged corners, e.g., points on a saw-tooth shape and corners in a series of “7” shape, that are spaced apart from each other by between 3 mm to 8 mm along the length of the bar. The protrusions of the jagged surfaces  48  on the leading sidewall edge have a depth of, for example, between 1.0 mm to 2.5 mm, where the depth extends into the bar width. The depth of the protrusions may be limited by the width of the bars  42 . A bar  42  may have an average width of between 2.5 mm and 6.5 mm. The bar  42  width varies due to the jagged surface  48  features, particularly the protrusions, on the leading sidewall. 
         [0048]    In another embodiment, recesses in the surface of the bars  42  replace the protrusions. The recesses are not shown in the drawings, but would be in the same locations and have the same dimensions as the protrusions. 
         [0049]    The swept back angle  46  on the bars  42  may be a progressively increasing angle. The angle  46  between a bar  42  and a reference line  49  parallel to the axis and the conical surface of the rotor  16  may be zero or within ten, fifteen or twenty degrees of the reference line  49  at the radially inward inlet  56  region of the refiner plate. The angle  46  may increase at least ten to fifteen degrees as the angle  46  moves radially and axially outward along the bar  42 . At the outer periphery of the refiner plate  40 , the angle  46  is a holdback angle and may be in a range of any of 10 to 45, 15 to 35, 15 to 45 and 20 to 35 degrees. 
         [0050]      FIGS. 4 ,  5  and  6  are a cross-section of rotor and stator conical zone plates, a top view of a convex conical rotor design, and a top view of a conventional concave conical stator plate that could be used opposing the novel rotor design, respectively. A conical rotor plate  140  and a conical stator plate  150 , which are separated by an operating gap  152 , are shown. The rotor plate  140  is described above. The stator plate  150  may include bars  154  and grooves  156  that are parallel to the reference line  148 , or at any angle deemed to be desirable. Dams  158  may be arranged in the grooves  156  to slow the movement of fibers through the grooves  156  and to cause fibers moving deep in the grooves  156  to flow up toward the ridges of the dams  158 . The plate design for the stator plate  150  may be a conventional plate design or a yet to be developed stator plate design, and may still be used with the rotor plate  140  designs disclosed herein. 
         [0051]    The stator and refiner plates  140  and  150  may have a slight convex or concave curvature to seat on the corresponding surface of the stator or rotor. The stator plates  150  are arranged in an annular array on the stator. Similarly, the rotor plates  140  are arranged in an annular array on the frustoconical portion of the rotor. 
         [0052]    While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiments, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.