WO2016091968A1

WO2016091968A1 - Method for refining fibres for paper making and apparatus suitable for said process

Info

Publication number: WO2016091968A1
Application number: PCT/EP2015/079156
Authority: WO
Inventors: Mathias Johannes CLUMPKENS
Original assignee: Clumpkens Mathias Johannes
Priority date: 2014-12-10
Filing date: 2015-12-09
Publication date: 2016-06-16
Also published as: EP3230521A1; NL2013950B1

Abstract

The invention relates to a method for compression refining of fibers for papermaking, wherein a slurry of fibers with a consistency of between about 2 wt% and 20 wt% of dry fibers in water is subjected to compression forces in an apparatus comprising at least two rolling surfaces with substantially the same velocity. At least one of the surfaces is curved, such that the surfaces move towards each other to achieve a compression force. The position of smallest distance between the surfaces is a closest position. At least one surface is provided with bars and grooves, the bars being at most 16 mm wide and the grooves being sufficiently large to aid in having water pressed out of the paper slurry. The relative speed of the surfaces to each other is such that water leaves the paper slurry upon reaching the closest position, and wherein the bars compress the fibers.

Description

METHOD FOR REFINING FIBRES FOR PAPER MAKING

AND APPARATUS SUITABLE FOR SAID PROCESS

[0001] The present invention relates to a method for refining fibres for paper making, and apparatus suitable for implementing said process.

Background of the invention

[0002] It has long been known that cellulose fibers must be refined so that the paper subsequently produced therefrom possesses the desired properties, in particular tensile strength, gloss or other properties. The most frequently used refining methods use refining apparatus that are provided with surfaces comprising bars called knives that are moved past one another at high speed. The corresponding machines are usually called knife refiners or disc refiners. For special cases, refining methods are also used in which at least one of the refining surfaces is knifeless. The refining action is transferred by friction forces and shear forces.

[0003] The wood fibres are put through the disc refiner in a dry weight concentration of between 2-6 wt%, the remainder being water.

[0004] The effect of the method can be controlled within a wide range by changing the refining parameters, whereby in addition to the degree of fineness it is especially distinguished as to whether a greater cutting or greater fibrillating refining is desired. If cellulose fibers are refined, their dewatering resistance usually rises with increasing fineness. A common measure for the dewatering resistance is the freeness according to Schopper-Riegler.

[0005] With a disc refiner, a plurality of actions is exerted on the fibres, like shear, compression and cutting. However, for strength increase only compression is required. The shear forces cause the fibres to degrade, which causes fines. The fines, upon recycling of the paper will further degrade and are ultimately removed from the paper making process in the waste water.

[0006] The fines furthermore cause an increase in the freeness value, and negatively effects the sheet formation in the paper machine. Generally, this is tolerated since the above mentioned quality characteristics of the cellulose play a predominant role in its usability.

[0007] The commonly applied disc-refining methods dissipate about 99% of their energy input in the water. Hence, the process generally applied is very inefficient with respect to energy consumption.

[0008] One way to reduce the energy input for the refining process is - potentially - compression refining. Early publications relating to this technique stem from the 1950-1960 period, see e.g.

US2551946, DE894499 and DE959345.

[0009] From US4685623 (1987) a refining method is known that is designed to manage with less energy. The paper fiber suspension to be refined is guided between two surfaces, and depending on the embodiment, into wedge-shaped grooves, that form on a revolving center roll and several outer rolls with nips, rolling thereon. The wedge-shaped center roll is provided with a plurality of circumferential grooves or flutes. The outer rolls are pressed with a defined force against the center roll, so that a dewatering and squeezing of the fibers takes place in the wedge-shaped groove. Part of the suspension and the water pressed out from the nips is thereby guided out crosswise to the direction of movement and in the free space in order to be mixed again later with the already refined thickened fiber stock. In this manner problems in the operation of a machine of this type are to be avoided even with larger throughput. In operation the housing of this apparatus is filled up with suspension, which is pumped through with an adjustable volume flow.

[0010] However, the nipples will catch only few fibers, and it therefore will be difficult to make a refining machine which can be used industrially.

[0011] In 1984, a thesis was published by Richard R. Hartman, on compression refining, showing its theoretical possibilities. However, the refining was done on sheets of fibres, and apparently, it was not possible to use the technique on fibre slurries.

[0012] More recent efforts to implement compression refining can be found in EP-B1702104, US2006/186235, US2007/090209, US2007/006984, WO2006/108555 and WO2008/056978. To the best of the inventor's knowledge, these apparatus never have been put into practice, because no satisfactory results were obtained on commercial scale.

[0013] To date no commercial apparatus is available for compression refining of slurries of fibres with water, while it is long recognized that (i) an improved refining process itself could reduce energy input substantially as only effectively 1 % of the energy is currently used in the disc refiners for actually treating the fibers, and (ii) because the improved dewatering with compression refined fibers, the energy required in the drying step in paper manufacturing would be substantially reduced and (iii) the formation of fines ultimately causes fibers to disappear from the paper making process, reducing the number of times that paper can be recycled.

Summary of Invention

[0014] It would be desirable to provide an industrially acceptable method for treating fiber stock with which it is possible to subject cellulose fibers or paper fibers to compression refining such that the strength of the paper produced therefrom is increased.

[0015] An industrial scale process in the paper industry requires continuous processing, with a throughput of about 200 kg dry weight paper per hour or more, preferably of about 400 kg/hr or more and even more preferably about 500 kg/hr or more. Generally, the capacity will be about 5000 kg/hr of dry weight, or less.

[0016] Alternatively or in addition, it would be desirable to provide a process applicable on an industrial scale, whereby the energy input in the fiber pulp mixture to achieve substantial increase in tensile strength of paper made by the treated fibers, is substantially decreased in comparison to disc refining. It must be noted that this is not self-evident. Pilot scale equipment of prior art compression refining equipment has not been able to show reduced energy input because the efficacy of fibre compression was low to non-existent, and this efficacy decreased with increasing apparatus size. [0017] In certain cases, it may be useful to cut fibers. Generally, fibers originating from wood have a proper length, and cutting is preferably prevented. However, increasingly, fibers are used originating from non-wood origin. Fibers from non-wood, biological origin generally are generated from what is often considered waste. Examples of suitable sources include corn, maize, grass, cotton and remainders of tomato plants, beet-root (sugar beet leaves and left overs) and the like. Fibers originating from these non-wood biological sources generally are relatively long, and it is preferred to have these cut to lengths more comparable to the length of wood fibers. Cutting is different from producing fines.

[0018] Further, it would be desirable to provide a method that allows both fiber crushing and fiber cutting, which process is particularly useful for fresh fibers from sources that provide too long fibers, such as for example from non-wood biological sources.

[0019] Therefore, according to a first aspect of the invention, there is provided a method for compression refining of fibers for paper making

wherein a slurry of fibers with a consistency of between about 2 wt% to 20 wt% of dry fibers in water

is subjected to compression forces

in an apparatus comprising at least two rolling surfaces with substantially the same velocity, at least one of the surfaces being curved, such that the surfaces move towards each other to achieve a compression force

- the position where the distance between the surfaces is smallest being a closest position; at least one surface being provided with bars and grooves

wherein the bars are at most 16 mm wide

and the grooves are sufficiently large to aid in having water pressed out of the paper slurry and wherein the relative speed of the surfaces to each other is such that water leaves the paper slurry upon reaching the closest position, and wherein the bars compress the fibers.

[0020] The very efficient compression refining process according to the present invention allows to have fibers compression refined a very limited number of compression cycles in order to achieve sufficient strength increase. Compression allows an increase in strength, without shearing the fibers, and therefor without producing fines. Generally, not each fiber gets compressed, but bundles of fibers. This means that only the crossing sections within the bundles will get compressed. In order to achieve sufficient tensile strength increase, it is preferred to re-disperse or randomize the fibers, before allowing a next compression cycle.

[0021] Thus, it is possible to have sufficient refining with about 100 revolutions or compression cycles, or less, and preferable about 50 compression cycles or less, and even more preferred about 20 cycles or less, and most preferred about 10 cycles or less. It has been shown that with 5 compression cycles, very good strength increase can be obtained. Hence, the present process preferably uses an average number of cycles of for example, 2, 3, 4, 5, 6, 7, 8, 9 or 10 times before the pulp is used in the next processing step. The upper limit of the number of revolutions is not so fixed, as a higher number of revolutions is possible, but is less advantageous.

[0022] Preferably, the refining cycles take place in the same refiner, and the treated fibers are removed from the refiner after completion of the refining process.

[0023] Preferably, the refining is sufficient to have an increase in paper strength (tensile strength) of 0.5 N/m or more, preferably of about 0.8 N/m or more. In an exemplary test, non-refined paper pulp had a strength of about 2 N/m, while normal disc refining provided about 3 N/m tensile strength. Tests with the invented method showed that a strength of even 4 N/m could be obtained with 5 cycles only. It is even more preferred to perform refining with the method according to the invention to cause an increase of about 1 N/m or more, and even more preferably about 1 .5 N/m or more.

[0024] The fiber slurry used in the process preferably is about 2 wt% to about 20 wt% solids, as the mixture should be transportable, preferably pumpable, and preferably re-dispersable. A preferred characteristic of the mixture is, that in the refiner, the mixture by turbulence randomizes its fibres, such that in a next round of compression, the original cross-over points are changed.

[0025] The fibres obtained with the process of the present invention are very suitable to be used in paper making because the thickening and drying process is much more energy efficient. Hence, the present invention also relates to paper made with the fibres obtained with the process of the present invention.

[0026] The tensile strength of the paper was measured according to standard test methods, ISO 1924.

[0027] Other properties that can be influenced by refining are gloss and folding properties.

Measurement methods for paper are in accordance with ISO; for instance folding endurance of paper, ISO 5626.

[0028] Because the method of the invention provides refining of fibres, without producing fines as in conventional refining, the common test for measuring beating degree (ISO 5267) to test the grinding efficiency, is not suitable to test the progress of treatment according to the present invention. ISO 5267 measures the reduction in removal of water, but this parameter is not changed upon

compression refining. In the method according to the present invention, the improvement in tensile strength is a suitable parameter to measure the progress of the refining.

[0029] It is important, according to this aspect of the present invention, to have water removed from the fiber slurry, while keeping a substantial amount of fibers between the closing surfaces.

[0030] In order for water to be able to leave the paper slurry, the speed of closing the two rolling surfaces needs to be sufficiently low. As will be appreciated, rolling or moving surfaces has the same meaning. The prior art generally shows at least one roll of about 20 cm diameter, or even smaller, while such rolls are - in an industrial scale process - being rotated at a speed of more than 1000 rpm, up to 2000-3000 rpm. In such case, the inventor realized that water is pressed out of the closing bars with such a speed that all the paper fibers are removed as well, which is the cause of the negligent efficacy of the compression processes of the prior art. It was remarkably difficult to reliably find a window of speed, combined with size of the bars and consistency of the fibres, to allow design of a scalable apparatus. With the teaching of the present patent specification, sufficient information is provided to develop efficient compression refiners. For example, US2006/186235 describes 20 m/s as lower limit for the speed of a surface. This means, that for a drum of 20 cm diameter, the drum is rotating at more than 1700 rpm. Another example is US2007/006984, which cites a lower limit of 8 m/s, with a drum of 10 cm diameter, the rotational speed would be more than 1400 rpm.

[0031] According to a second aspect, and in accordance with the advantages and effects described herein above, there is provided an apparatus for performing a method according to the first aspect, wherein the apparatus comprises two surfaces, of which at least one is curved, wherein a length of a surface necessary for closing 7.5 mm distance with respect to a straight plate is about 50 mm or more. Preferably, the length is about 70 mm or more.

[0032] With reference to Fig 1 , according to this second aspect, and in accordance with the advantages and effects described herein above, there is provided an apparatus for performing a method according to the first aspect, wherein the apparatus comprises two surfaces (which are able to move at about the same speed), of which at least one is curved, wherein a length of a surface (L) necessary for closing 7.5 mm distance (H) with respect to a straight plate is about 50 mm or more. Preferably, the length (L) is about 70 mm or more. The length of the curved surface is approximated by the length of the flat (straight) surface 2 of Fig 1 ..

[0033] With two curved surfaces, with both are curved towards the same center, as can be seen in Fig 2, the distance between (h') and (H) of the least curved surface can be taken as length, and the 7.5 mm distance (Η', see Fig 2) is the place where the distance between the two surfaces is 7.5 mm, if a line perpendicular to the least curved surface is drawn between the two surfaces, measured over the elongated radius of the least curved surface. The least curved surface can be approximated to the flat or straight surface.

[0034] In case two cylinders are used, having two surfaces with opposite curvature, like in Fig 4, the distance (H) can be determined with respect to a projected middle line between the two surfaces. The cylinder with the strongest curvature determines the distance (H). Hence, in this case the distance is determined by the projected flat surface. Brief Description of Drawings

[0035] Embodiments will be described by way of example only, with reference to the accompanying schematic drawings in which corresponding reference symbols indicate corresponding parts, and in which:

[0036] Fig. 1 schematically shows parameters for a method of calculating a closing speed of a cylindrical object with respect to a planar surface;;

[0037] Figs. 2-3b schematically depict a laboratory refiner according to an embodiment;

[0038] Figs. 4a-4b show cross-sectional views of a dual-drum refiner according to an embodiment; [0039] Figs. 5a-5c show cross-sectional views of a plates-and-wheels refiner according to an embodiment;

[0040] Figs. 6a-6c show cross-sectional views of a plates-and-wheels refiner according to an alternative embodiment;

[0041] Fig.7 shows a cross-sectional view of an upright refiner according to an embodiment.

[0042] The figures are meant for illustrative purposes only, and do not serve as restriction of the scope or the protection as laid down by the claims.

Description of Embodiments

[0043] the present invention provides for a method for compression refining of fibers for paper making

is subjected to compression forces

- in an apparatus comprising at least two rolling surfaces with substantially the same velocity, at least one of the surfaces being curved, such that the surfaces move towards each other to achieve a compression force

- wherein the bars are at most 16 mm wide

[0044] The method of compression refining can save substantial energy input, as relatively low losses are caused by energy dissipation to water. Further, because only a very small amount of fines is produced, the dewatering step in paper making is more efficient (more water can be removed by filtration), causing lower amounts of energy required to dry the paper. Furthermore, because of the low amount of fines - which are ultimately lost in the paper making process - the paper can be recycled more often.

[0045] The slurry of fibers comprises generally between about 2 to about 20 wt% of fibres.

Preferably, the slurry comprises about 18 wt% or less, more preferably about 16 wt% or less, and even more preferably about 12 wt% of fibers or less, as such consistency allows easier processing. Even more preferable, the consistency is about 8 wt% of fibers or less. Preferably, to increase efficient use of an apparatus, the consistency preferably is about 3 wt% or higher, and even more preferably about 4 wt% or higher. Most common in the paper making industry are consistencies of between about 4 wt% to about 6 wt%.

[0046] Common consistencies of the slurry as currently in use in paper manufacturing for refining over a disc refiner are between 3 and 8 wt%, and even more common 4-6%. However, thicker consistencies can easily be made by thickening the paper slurry. The slurry can be dewatered on webs, like in the first step of paper making, or with specific thickening apparatus. A higher

concentration of fibers allows higher rotating speeds or wider ribs in the compression refiner, as shown in table 2. Hence, even though thickening requires an additional processing step, it can result more efficient processing in the compression refiner.

[0047] In this paragraph, an example of a calculation is provided. In case - for example - a 5% consistency of wood pulp is considered, the free space between the two rolling (moving) surfaces preferably is between 0.15 and 0.25 mm, depending on the fiber length and fiber thickness. The presence of the fibres causes the distance between the two surfaces, In case the machine is empty, the surfaces will be touching each other. When the two rolling surfaces are in the closest position, the consistency of the fibers will be around 50 wt% (e.g. in the range of 40-60 wt%). It is estimated that the fiber mixture of 5% consistency will start to loose water when the distance between the two rolling surfaces is about 7¹/2 mm or less, and probably at least when the distance is about 5 mm or less. With a bar width of 2.4 mm, a velocity of the water of over about 1 m/s will cause the majority of the fibers to be pressed out of the bar region into the free space, and no compression will be exerted. Hence, the velocity of the moving surfaces in this example preferably is such, that the closing speed is less than about 1 m/s. This can easiest be achieved with using two surfaces with relatively small radial difference. A roll with 400 mm diameter relative to a flat surface calculating with 7.5 mm free space or less between the surfaces, that requires water to be removed, allows a radial speeds of about 7.2 m/s (which is about 340 rpm). An 800 mm roll allows in these circumstances a velocity of 10.2 m/s. Hence, larger rolls allow higher speed, and therefore more efficient compression refining.

[0048] In practice, for example, one or more rolls in a drum may be used. In order to allow a relatively high speed, it is preferred that in such an example the difference in radius between the two surfaces is comparable to a roll of 400 mm diameters vs a flat surface or smaller, preferably at about 800 mm and a flat surface or smaller. For example, a 200 mm roll in a 300 mm inner diameter drum will be feasible, e.g. as laboratory apparatus.

[0049] The lengths, which can be used to close a 7.5 mm gap between two moving surfaces, can easily be calculated from goniometric formulas. Closing a gap of 7.5 mm (which is taken as catch length), with a remaining gap of 0.15 mm is given in Table 1 .

Table 1 , length for closing a gap of 7.5 mm, vs diameter of a roll relative to a flat surface:

[0050] Hence, the method according to the present invention preferably has a length of the surfaces necessary for closing 7.5 mm distance of about 50 mm or more, preferably about 70 more. As is shown by the entry of the table, these length values refer to the projected length, relative to a flat surface.

[0051] Table 2 indicates feasible velocities, depending on consistency of the fibers, and bar-width. A 0.15 mm remaining distance for the fibers is assumed (this is the distance between the two surfaces at the closest position), at about 50% consistency, combined with a 7.5 mm catch length. The values in Table 2 are about 30% higher, in case a 5 mm catch length would be applicable. Hence, depending on the precise case, velocities may be somewhat higher or lower, but this is unlikely to be different with more than a factor of 2, although optimization with the given values as starting point, may result in even further improvements. Obviously, higher velocities are preferred, to have higher throughput in an industrial apparatus.

Table 2: allowed velocity (in m/s) of moving surfaces to achieve good fiber catch between the surfaces

[0052] As can be deduced from Table 2, smaller bars allow higher velocities. However, small bars cause some difficulty in apparatus manufacture and maintenance. Generally, the bar width will be about 0.5 mm or larger, preferably about 1 mm or larger. However, for construction purposes, it is preferred to use bars with a width of 2 mm or larger, preferably 3 mm or larger.

[0053] It may be noted, that velocities - as far as reported in the prior art - are generally at least 3 to 10 times higher than appears to be allowed according to the present invention.

[0054] Bars of a width larger than 8 mm can be used, like up to 16 mm. Preferably, the width is 12 mm or less, and more preferably about 10 mm or less, but such wide bars would cause the velocity to be relatively low, and this is not preferred at an industrial scale. However, in case the grooves - between the bars - can be relatively narrow, the capacity of the apparatus may still be good. It is most preferred to have the bars about 8 mm or smaller, and even more preferred about 6 mm or smaller. A suitable width is about 3 times the length of the fibers, which may be for wood fiber about 4 mm or less, and is preferably about 2 mm up to about 3 mm.

[0055] The grooves between the bars are of importance, as each groove lowers the effective compression width. The grooves are important to allow water to be pressed out of the paper slurry on a bar. Both the width, as the depth of the grooves can be optimized. The width preferably is about the same width as a bar, or lower. Preferably, the width is smaller than the width of the bar, like for example about 30% smaller, or about 50% smaller. A smaller width of the groove increases the throughput of the compression refiner. It may also be useful, to have the depth of the groove be about the width of the bar, or less. Preferably, the depth is less than the width of the bar. Preferably, the depth is 2 mm or less, more preferably about 1 mm or less, and may be even only 0.5 mm. A reduced depth causes less untreated fiber passing the nip through the grooves, if the groove is not filled up with water coming from the pressed pulp. A higher depth than necessary causes more untreated fiber passing the nip, hence causing efficiency loss.

[0056] The two surfaces have substantially the same velocity, which means that the surfaces when at the closest position have the same speed. In this way, compression force is present, but no shear forces are exerted on the fibres. This has a further advantage that wear is limited. The surfaces have substantially the same velocity if the difference in speed relative to each other is about 0.1 m/s or less, preferably about 0.05 m/s or less, and/or, the relative velocities are different with about 0.2% or less, preferably about 0.1 % or less, and most preferably about 0.05% or less.

[0057] Next to the compression refining cycle, for a next cycle, fibres need to be randomized at least to some extent. Hence, it is preferred that after one cycle, the fibres are removed from the surfaces and redispersed, preferably by the water which is present in the system.

[0058] It is furthermore preferred to have the surfaces pressed to each other at a certain pressure, which may be variable. The pressure is denoted as the kg force per meter of a first surface, pressing to the second surface. For metal on metal surfaces - which have a sharp edge on the bars -, the pressure generally will be about 10 kN/m or more, preferably about 15 kN/m or more, and most preferably about 20 kN/m or more, like for example about 25 to 27 kN/m. Increased pressure allows more efficient compression refining. Generally, the pressure will be about 60 kN/m or less, preferably about 40 kN/m or less. At lower pressure, only compression will be observed. In case fiber cutting is aimed for, for example because certain long fibers are refined, the pressure can be higher. In case polymer or rubber coated drums or rolls are used, the edge of a bar on a flat surface is less sharp, and the pressure may be substantially higher. For example the pressure may be 150 kN/m or lower, preferably 100 kN/m or lower. A skilled person will be able to determine which pressure is adequate.

[0059] In a preferred method embodiment, the pressure can be exerted in a continuous varying manner, so as to allow thicker parts in the fiber mixture to be pressed at a same pressure, as thinner parts.

[0060] The surface of the roll and the drum may made from steel, like stainless steel. It is equally possible to use ribbed coating layers from rubber, polyurethane or the like, which can be easier replaced after certain time of wear.

[0061] The length of an apparatus, rolls and drums, can vary. For large scale production, a length of 1000 to 5000 mm will be suitable.

Detailed description of figures 1 -3, comparative experiments A through G, and examples 1 -11

[0062] In Fig.1 , a rotating surface 1 is depicted. The local speed of the rotating surface 1 is V_om. A second surface 2 and a fibrous mass 3 supported by the second surface 2 are schematically indicated below the rotating surface 1 . In a process according the invention, the flat surface 2 would move at a speed equal to the speed of the roll 1 , the rotating surface. For a local portion of the rotating surface 1 that is perpendicular to the second surface 2 closing speed V_S| is equal to V_om. For another local portion of the rotating surface 1 that is parallel with the bottom line, the closing speed V_S| has become zero. In general, the closing speed at angle a is V_om ^* sin(a). The relevant speed is the closing speed at the section where the fibrous mass 3 gets compressed. A gap or final height h is defined as a smallest distance between the rotating surface 1 and the second surface 2. Pressing of the fibrous mass 3 starts at an initial height H, and a compression height ΔΗ is defined by AH = H - h. A distance between the points where the rotating surface 1 is at initial height H and where it is at final height h (a is zero), is indicated as projected length L, which is for example given in Table 1 for the specific circumstances calculated. A value for the initial height H can be estimated as follows: the pressed fibres at the closing point have a final height h, which is e.g. 0.15 mm. It is estimated that at this point, about 50% water is present, and 50% fibers. These fibers were in a 3% dispersion, taking 0.15^*50/3 = 2.5 mm. A moving surface will cause flow in an earlier stage, and a safe point to start calculations is about 3 times the height, being 7.5 mm. These values can be optimized in practice. In case only 5 mm would be necessary, the surface speed can be increased with 30%.

Eccentric drum and roll refiner embodiment (figures 2-3b)

[0063] Figs. 2 and 3a schematically depict an embodiment of a laboratory refiner 10. The refiner 10 in fig.2 comprises a plain drum 12, in which a roll 14 with bars 16 separated by grooves 17 is provided. The bars 16 are arranged predominantly in a circumferential direction along an outer perimeter of the roll 14. The drum 12 and the roll 14 are rotatably accommodated in a housing 11 . Both the drum 12 and roll 14 are driven by a frequency regulated motor (not shown). During operation, the drum 12 is caused to rotate via a first drive shaft 42, and the roll 14 is caused to rotate via a second drive shaft 43.

[0064] The drum 12 comprises an inner surface 13. An outer perimeter of the bars 16 on the roll 14 defines an outer surface 15 that faces the inner surface 13 of the drum 12. An inner void is defined between the surfaces 13, 15 of the drum 12 and the roll 14. This inner void is adapted for

accommodating paper slurry 18. The housing 11 comprises a supply opening 22 and a discharge opening 24 for transporting paper slurry 18 into and out of the inner void of the refiner 10.

[0065] During operation of the refiner 10, the paper slurry 18 is introduced via the supply opening 22 and removed via the discharge opening 24, while the drum 12 and the roll 14 are rotated in identical directions. In the exemplary arrangement of fig.2, the drum 12 and the roll 14 are both configured to be rotated in a counter-clockwise direction.

[0066] In fig. 2, an initial height H' is defined between the surfaces 13, 15 at initial location 19. The initial location 19 corresponds to a location where the slurry 18 will start to be compressed by the rotating surfaces 13, 15, and/or pushed away from the surfaces 13, 15. [0067] At a second location 20, which is herein indicated as the "closest surface position", the inner surface 13 and the outer surface 15 are at a smallest mutual distance, thereby defining a gap with a final height h'. The magnitude of the compression forces acting on the slurry 18 during operation is correlated to the closing speed at which the inner surface 13 and the outer surface 15 close in from the initial height H' to the final height h'. The closing speed depends on the local speed of the surfaces 13, 15 that carry the slurry 18 from the initial location 19 towards the gap in the second location 20.

[0068] The slurry 18 is carried along by the moving surfaces 13, 15 through and past the gap at the second location 20. In the closest position, the (local) relative surface speed of the inner surface 13 with respect to the outer surface 15 is about zero. After compression by the surfaces 13, 15, compressed slurry 27 emanates from the gap at the second location 20, and re-disperses in the water that is present in the inner void.

[0069] In this refiner embodiment, the final height h' between the inner and outer surfaces 13, 15 is preferably 0.15 mm for processing a 3% or 5% slurry.

[0070] Here, the discharge opening 24 is provided with a screw (25, not shown) to remove the compressed slurry 27 from the drum 12. Scrapers 26 are provided at or near the discharge opening 24, which are configured to remove compressed slurry 27 from the outer surface 15 of the roll 14 and from the inner surface 13 of the drum 12, for collection and discharge purposes.

[0071] The process described above corresponds with a single compression or refinement cycle of the paper slurry (pulp). Subsequent compression cycles can be obtained by re-introducing the compressed slurry 27 via supply opening 22 into the refiner 10 for a second time. This recycling approach allows precise measurements of effects of any single compression cycle.

[0072] Fig.2 shows that this refiner embodiment 10 also comprises a pressure regulating mechanism, which is configured to adapt a pressure of the drum 12 exerted on the roll 14. The pressure regulating mechanism comprises a pressure line 30, a membrane member 32, a pressure inlet 34, and a back-pressing bias member 36. Pressure P is applied via the pressure inlet (e.g. nipple) 34 on the membrane member 32 to the drum 12 through the pressure line 30. The back-pressing bias member (e.g. a spring) 36 allows adaptation of the final height h' defined by the gap at the second location 20, for example to alleviate the situation wherein a too thick clump of slurry 18 (fibres) travels through the refiner 10.

[0073] As shown in fig.3a, the drum 12 is rotatably supported by drum support 44, which forms a portion of the housing 11 . A roll support 41 defines another portion of the housing 11 , and is fixed to a stationary base plate 40. The drum support 44 is fixed to a slideable baseplate 45, which is slidably arranged with respect to the stationary base plate 40 via linear bearings 46 (e.g. V-grooved bearing blocks). Via pressure-induced repositioning of the drum support 44 with respect to the roll support 41 , a portion of the pressure can be exerted by the drum 12 via the intermediate slurry 18 onto the roll 14.

[0074] Fig.3b schematically shows a structure of the roll 14 in the refiner embodiment 10 shown in figs.2 and 3a. The roll 14 predominantly forms a cylindrical object along axial direction A, and comprises bars 16 and grooves 17 that extend circularly along an outer periphery of the roll 14. Viewed along a radial direction R of the roll 14, the bars 16 project outwards and the grooves 17 recede inwards. In this embodiment, the bars 16 and grooves 17 have a rectangular cross-section viewed in the radial-axial plane. Other cross-sectional shapes are possible, provided that the bars 16 have sufficiently flattened/blunt outer surface portions to jointly define an outer surface 15 suitable for compressing paper slurry 18 (instead of cutting). In the example with rectangular bars 16 and grooves 17, the bars 16 may have bar widths Wb with a value of about 2 mm, and the grooves 17 may have groove widths Wg with a value of about 2 mm.

[0075] In a preferred further embodiment of the refiner 10, the membrane member 32 has a membrane surface of about 100 cm² and is spring-loaded with a 200 N force spring 36 in order to open the nipple 34 for relative repositioning of the drum 12 and the grooved roll 14. In this further embodiment of the laboratory refiner 10 according to the configuration shown in figs.2 and 3a, the drum 12 has an inner diameter of 170 mm, and the roll 14 has an outer diameter of 118 mm. This further embodiment is preferably operated with approximately equal local surface speeds of the inner surface 13 and the outer surface 15, with the local surface speed having a value of about 7.2 m/s with an accuracy of less than 0.05 m/s for the difference in surface speeds. In this further embodiment, a projected length between the initial location 18 and the second location 20 is selected to be 53.7 mm, and a closing speed during operation is about 1 .0 m/s. Here, the pressure P is adaptable by allowing 1 -2 bar pressure via the membrane member 32 of with a surface area of 100 cm² (minus 200 N counter pressure of the spring). Hence, up to 1800 N (180 kg force) can be exerted between the surfaces 13, 15. For this further embodiment, it appeared that a pressure of 1300 N was optimal for refining to increase strength. The roll 14 was 100 mm wide (corresponding with a length defined along an axial direction of the roll 14), with bars 16 having bar widths of 2 mm, and grooves 17 having groove widths of 2 mm. Hence, an effective bar length was 50 mm. An effective optimal pressure (which is calculated as force per meter length, instead of per surface area) was 1300/0.05 N/m, which is 26 kN/m. At 1800 N and hence 36 kN/m, the fibers were cut and this would be a suitable pressure to shorten long biofibers.

[0076] Paper pulp of 3 wt% consistency was processed at two different pressures (16 and 26 kN/m), and for 1 and 5 times. Also, a comparison was made with a commercial disc refining. Paper was tested according to standard procedures ISO 1924, and the average tensile strength was measured. The results are given in Table 3.

Table 3 Ref Ex A Ref Ex B Example 1 Example 2 Example 3 Example 4

Refinement Non- Disc One cycle, Five cycles One cycle, Five cycles, refined refined 16 kN/m 16 kN/m 26 kN/m 26 kN/m

Tensile strength 2.0 3.0 2.2 3.4 2.7 4.1 (N/m) [0077] These results show, that even after 1 compression cycle, measurable differences are found. After 5 cycles, at 16 kN/m pressure, a slightly better tensile strength was found, than in standard refined paper pulp. At 26 kN/m bar pressure and 5 cycles, a clear increase was found, doubling the increase in tensile strength in comparison with standard disc-refined pulp.

[0078] In an analogous way, paper pulp with 5 wt% consistency was processed with comparable results.

[0079] Further experiments were done on Eucalyptus pulp and hardwood pulp. Both the drainability number and tensile strength were measured. Further, standard disc refining was compared with refinement according the present invention. Results are shown in Table 4:

[0080] Further experiments were done with softwood pulp, wherein the effect on tensile index and drainability number is given, relative to the number of compression cycles. The results are given in Table 5.

[0081] Both Table 4 and 5 show that with the compression refinement of the method of the invention the strength of the paper can be substantially increased, while the drainability number is increased only slightly.

[0082] The concept, as proven in Examples 1 -11 with reference to experiments A-G, can be scaled up in apparatuses complying with the rules as set out in the specification above. [0083] In an analogous way to the refiner 10 of Fig 2, a large drum/roll apparatus can for example be provided with an inner diameter of an outer drum of 1200 mm, and an outer diameter of a roll of 1000 mm, and a length of 2000 mm. The surface speed, with reference to the drum, can be 1600 m/min (500 rpm), and the throughput can be calculated to be in the 500-1000 kg/hr region, depending on the thickness of the paper layer compressed (which is related to the consistency of the slurry), and the number of times that the paper needs to go through a compression cycle.

[0084] In a much larger refiner, a plurality of grooved rolls of 100-300 mm diameter can be made rotating over a plain cylinder of e.g. 1200 mm diameter, at a suitable speed and pressure according the present invention. The rotating parts may be enclosed in a housing, with an inlet and outlet at opposite sides of the housing. The length of the cylinder and rolls can be between 1000 and 3000 mm. A refiner according to these specifications may have a refining capacity of 1000-4000 kg dry paper fibers per hour.

Dual roll refiner embodiment (figures 4a-c)

[0085] Figs.4a-4c illustrate an embodiment of a refiner apparatus 10', wherein a first rotatable drum 12a and a second rotatable drum 12b are provided. The first drum 12a is provided with bars 16' and grooves 17' along an outer periphery of the first drum 12a. Small paddle members 47 are included in the grooves 17' at predetermined angular positions, to aid transportation of material along with the periphery of the first drum 12a, if rotated during operation. The second drum 12b has no grooves along its outer periphery.

[0086] According to a method of use of this refiner apparatus 10', fiber slurry 18' is introduced into the refiner 10' through supply opening 22^', and compressed slurry 27' is transported with screw 25' from an inlet region Xi to a discharge opening 24' in an outlet region Xo (see section B— B in Fig. 4b). Depending on the speed of the screw 25', more or less compression cycles may be applied to the fibers in the slurry 18'.

[0087] The drums 12a, 12b can for example be 3000 mm long, with a diameter of 800 mm, allowing a rotation speed of about 240 rpm, and a throughput of between 250-500 kg/hr dry weight to be processed. First plate-and-wheel refiner embodiment (figures 5a-c)

[0088] Figs. 5a-5c depict another embodiment of a refiner apparatus 10". The refiner 10" comprises a housing 11 ", which is mounted on frame 62 with a base plate 40". The housing 11 " accommodates a first plate 50a and a second plate 50b, which comprise respective inner surfaces 51 a, 51 b that face each other. The first and second plates 50a, 50b are suspended inside the housing 11 " in a manner that allows rotations of the plates 50a, 50b in mutually opposite directions. Rotatable members 52 are provided between the first plate 50a and the second plate 50b. In this embodiment, the rotatable members are formed by wheels 52 that are rotatably connected about a corresponding wheel axis 54. The wheels 52 are arranged in between the plates 50a, 50b, and located with an outer perimeter close to each of the plates 50a, 50b.

[0089] Preferably, each one of the wheels 52 is formed by a plurality of separately rotatable wheel plates 52a, 52b, 52c (herein also collectively indicated with reference number 52i). Each wheel plate 52i may for example have a radially outer portion defining a circumferential bar 16", and a radially inner portion that may define a groove 17" in combination with a circumferential bar of an adjacent wheel plate. Each wheel plate 52i may for example be 4 mm thick, and may have a groove 17" having a groove width Wg" of 2 mm and a bar 16" having a bar width Wb" of 2 mm. Each wheel 52 may have a wheel radius Rw of 10-40 cm. One, more, or each of the wheels 52 may for example comprise 5 to 50 individual plates 52i.

[0090] The individual plates 52i comprised by one wheel 52 are preferably connected in an independently rotatable manner about the corresponding wheel axis 54. The refiner 10" may be provided with a compression member (e.g. a spring) 55 for each wheel, the compression member 55 being configured to urge the individual plates 52i of one wheel 52 into a predetermined position along the wheel axis 54.

[0091] It is preferred to have the individual plates 52i in each wheel 52 rotate independently about the corresponding wheel axis 54, because the local rotation speed of a portion of the inner surface 51 a, 51 b of the first or second plate 50a, 50b varies with a radial distance from the center of the first or second plate 50a, 50b and increases along the corresponding wheel axis 54. Independent rotatability of the individual plates 52i allows each plate 52i to rotate with a perimeter speed that (approximately) equals a plate speed of a nearby local portion of the surrounding first and second plates 50a, 50b.

[0092] The first and second plates 50a, 50b are brought into rotational motion by first and second drive axes 56, 57. The first and second drive axes 56, 57 are rotatably accommodated by the fixed housing 11 " by means of gaskets 58. The fixed housing 11 " forms a protective casing for moving parts and comprises discharge opening 24". An inlet for the slurry 18" may be provided by a supply opening 22" and a conduit extending through one or both of the drive axes 56, 57.

[0093] Swivel plates 60 are provided, which are configured to re-disperse the fibers in the slurry 18", by causing a pressure pulse. One or more swivel plates 60 may for example be mounted between the wheels 52, and fixed to the arrangement of wheel axes 54.

[0094] The refiner 10" may be provided with a tensioning arrangement that is configured to urge the first and second plates 50a, 50b towards one another, which during operation will cause a pressure between the inner surfaces 51 a, 51 b of the first and second plates 50a, 50b on the one hand and the wheels 52 on the other hand.

[0095] The refiner 10" according to this embodiment is suitable for continuous use, and its throughput can be calculated to be 500-1000 kg/hr based on dry cellulose fibers. Second plate-and-wheel refiner embodiment (figures 6a-c)

[0096] Figs.6a-6c depict an embodiment of a refiner 10"', which resembles the embodiment shown with reference to figs.5a-5c. In the current embodiment, each of the plates 52i' in a wheel 52' is provided with chamfered edge i.e. a linearly increasing radius Rw' as a function of increasing distance along a respective wheel axis 54'. (The plates 52a', 52b', 52c' are collectively indicated with reference number 52i'). In addition, within one wheel 52', consecutive plates 52i' positioned at increasing distances along the respective wheel axis 54' have increasing wheel radii Rw'. The resulting wheel 52' thereby forms a truncated cone with a tilted outer wheel surface 64. In addition, the first and second plates 50a', 50b' may be provided with tapered (chamfered) surface portions 66a, 66b in a radially outward region of each plate. Each of the tapered surface portions 66a, 66b faces at least partially inwards towards the other plate 50b', 50a' (disregarding the transverse component of the tapered surface portion). A degree of tilt of the surface portions 66a, 66b and the tilted wheel surfaces 64 may be selected in such a manner that the speed of revolution (in rpm) of all the plates 52i' in each wheel 52' will become identical during rotation of the plates and the wheels. Selected ones or all of the wheels 52' in this embodiment may therefore be formed as uni-body wheels, with all plates 52i' in the corresponding wheel 52' being mutually fixed and jointly rotatable about the corresponding wheel axis 54'.

[0097] The configuration according to this embodiment allows construction of longer wheels 52' (e.g. with a length of 400mm to 600 mm defined along a respective wheel axis 54'), while the wheels 52' may additionally be formed with a relatively small wheel radii Rw' . In this way, an embodiment of a refiner may be constructed with up to e.g. twenty wheels 52'. Such a refiner embodiment would employ plate rotation at relatively low speeds. The large contacting surfaces formed by the tapered surface portions 66a, 66b and the tilted wheel surfaces 64 allows for a production of about 2000 kg/hr dry cellulose fiber, or possibly more.

Upright refiner embodiment (figure 7)

[0098] Fig.7 shows another embodiment of a refiner 10"". The refiner 10"" in fig.7 is similar to the refiner 10 shown in fig. 2, but is arranged with rotation axes along a vertical direction Z. A grooved roll 14"" and a plain drum 12"" are arranged in a vertical position inside a housing 11 "" that comprises a mounting bracket 70. The drum 12"" and the roll 14"" are rotatably arranged with respect to the mounting bracket 70, and independently rotatable via drive shafts 42"", 43"".

[0099] During operation, both the drum 12"" and the roll 14"" are rotated in the same direction. Analogous to Fig.2, an outer surface 15"" of the roll 14"" is urged against an inner surface 13"" of the outer drum 12"" by a force exerted on bearings 71 , 72 of the inner roll 14"". If the two surfaces 13"", 15"" are in the closest position, local surface speeds of the outer surface 15"" and of the inner surface 13"" are approximately identical, and local velocity vectors are parallel with each other (resulting is a relative local surface speed of approximately zero). [00100] During operation of the refiner embodiment 10"" of Fig 7, slurry 18"" is entered into the refiner 10 "" at supply opening 22"", and compressed slurry 27"" is removed from the refiner 10"" at discharge opening 24"". The number of compression cycles that the slurry is subjected to is now given by the amount of slurry per minute pumped through the refiner 10"".

[00101] An initial height (H'"\ not shown) at an initial location where the slurry 18"" starts to be compressed preferably has a value comparable to the values discussed with reference to fig.2. A gap with a final height (h"", not shown) is defined between the surfaces 13"", 15"" at the closest position. The final height h is preferably about 0.15 mm if a 3% or 5% slurry 18"" is to be processed.

[00102] The refiner 10"" according to this embodiment is capable of processing a continuous stream of pulp. The refiner may comprise special seals (e.g. gaskets) 73, 74, to account for the eccentric positions of the two drive shafts 42"", 43"". Water lubricated ceramic seals 73, 73 are preferably used.

[00103] Known disc refining machines have a throughput of 500-5000 kg/hr. Hence, with the process according to one aspect of the present invention, it is possible to use compression refining at an industrial scale.

[00104] The descriptions above are intended to be illustrative, not limiting. It will be apparent to the person skilled in the art that alternative and equivalent embodiments of the invention can be conceived and reduced to practice, without departing from the scope of the claims set out below.

Reference Signs List

1 rotating surface

2 second surface

3 fibrous mass

10 refiner

11 housing

12 drum

13 inner surface

14 roll

15 outer surface

16 bars

17 groove

18 slurry

19 initial location

20 second location

22 supply opening

24 discharge opening

25 screw

26 scraper

27 compressed slurry

30 pressure line

32 membrane member

34 pressure inlet (nipple)

36 bias member (spring)

40 base plate

41 roll support

42 first drive shaft

43 second drive shaft

44 drum support

45 moveable base plate

46 linear bearing

47 paddle member

50a first plate

50b second plate

51 a-b inner surface

52 rotatable member (wh

52i wheel plate

54 wheel axis 55 spring

56 first drive axis

57 second drive axis

58 gasket

60 swivel plates

62 frame

64 tilted wheel surface

66 tapered outer surface portion

70 mounting bracket

71 roll bearing

72 further roll bearing

73 seal

73 further seal

H initial height

h gap (final height)

ΔΗ compression height

P pressure

Rw wheel radius

Wb bar width

Wg groove width

Xi inlet region

Xo outlet region

Z vertical direction

Claims

1 . Method for compression refining of fibers for paper making

- wherein a slurry of fibers with a consistency of between about 2 wt% to 20 wt% of dry fibers in water

- is subjected to compression forces;

- the position where the distance between the surfaces is smallest being a closest position;

- at least one surface being provided with bars and grooves

- wherein the bars are at most 16 mm wide

- and the grooves are sufficiently large to aid in having water pressed out of the paper slurry

- and wherein the relative speed of the surfaces to each other is such that water leaves the paper slurry upon reaching the closest position, and wherein the bars compress the fibers.

2. Method according to claim 1 , wherein significant refining is achieved with about 100 revolutions or compression cycles, or less, and preferable about 50 compression cycles or less, and even more preferred about 20 cycles or less, and most preferred about 10 cycles or less.

3. Method according to any one of claims 1 -2, wherein the refining is sufficient to have an

increase in paper strength of 0.5 N/m or more, preferably of about 0.8 N/m or more.

4. Method according to any one of the preceding claims, wherein, after a cycle, the fibers are largely removed from the surfaces and redispersed, preferably by the water which is present in the system.

5. Method according to any one of the preceding claims, wherein the slurry comprises about 16 wt% or less of fibers, preferable about 12 wt% of fibers or less, and the slurry comprises about 3 wt% or higher, and even more preferably about 4 wt% or higher of fibers.

6. Method according to any one of the preceding claims, wherein pressure is applied at the

surfaces of about is 10 kN/m or more, preferably 20 kN/m or more and is about 150 kN/m or lower, preferably about 100 kN/m or lower.

7. Method according to claim 6, wherein the pressure is such, that the compression refining causes refining of fibres, with only little to no cutting of fibers.

8. Method according to claim 6, wherein the pressure is such, that the compression refining also causes a substantial amount of fiber cutting.

9. Method according to any one of the preceding claims, wherein the distance between the

surfaces at the closest position is between 0.1 mm and 2 mm, preferably between 0.15 and 0.5 mm.

10. Method according to any one of the preceding claims, wherein the bar width is about 0.5 mm or larger, preferably 1 mm or larger, preferably 2 mm or larger, and of about 8 mm or smaller.

1 1 . Method according to any one of the preceding claims, wherein the length of the surfaces (L, or the distance between h and H) necessary for closing 7.5 mm distance (H) is about 50 mm or more, preferably about 70 mm or more.

12. Method according to any one of the preceding claims, wherein the relative speed of the

surfaces is about 0.1 m/s or less, and/or about 0.2% or less.

13. Process for preparing paper from refined pulp obtained with a method according to any one of the preceding claims.

14. Apparatus suitable for performing a method according to any one of claims 1 -12, wherein the apparatus comprises two surfaces, of which at least one is curved, wherein a length of a surface necessary for closing 7.5 mm distance with respect to a straight plate, approximated flat surface or projected flat surface is about 50 mm or more, preferably about 70 mm or more.

15. Apparatus according to claim 14, adapted for yielding a throughput of at least 200 kg/hr dry weight in continuous processing.