Dense pulp refining method and plant

Description

11 METHOD AND PLANT FOR REFINING DENSE PULP DESCRIPTION FIELD OF THE INVENTION

[001] The present invention relates to the field of papermaking and, more specifically, relates to a method for refining dense pulp for papermaking.

[002] The present invention also relates to a plant that implements such a method.

[003] In particular, the invention relates to a pulp refiner that is used in such a method. DESCRIPTION OF THE PREVIOUS TECHNIQUE

[004] As is well known, before reaching the machine head, the pulp that will be transformed into paper generally goes through a so-called dense pulp cycle and then a thin pulp cycle.

[005] A typical dense pulp cycle involves pulping suitable fibrous materials in a pulper, the eventual accumulation of the pulp produced by the pulper in a pulped pulp tank, the separation of the pulp from any hard fragments and residual dirt in a centrifugal separator, a refining step in a pulp refiner and, normally, the passage to a refined pulp collection tank.

[006] Again, as is known, the refined pulp goes to the diluted pulp cycle, which involves several vats and several passes of strong dilution with water, degassing, cleaning and stabilization before going to the machine head.

[007] Dense pulp refining is therefore an essential step in the papermaking cycle and is carried out using two main types of refiners: the truncated refiner and the disc refiner. Both apply impulsive shear forces and pressure pulses to the fibrous pulp material, separating the entangled fibers into individual fibers as much as Petition 870250094047, dated 10 / 14 / 2025, page 7 / 26 / 11 possible by impulsive shear forces and achieving an opening of the fibers by repeated pressure forces, thus achieving the desired refinement.

[008] Typical truncated cone refiners are described in documents US5152871, US2016355977, US2019078259 and EP3839134. They involve a truncated conical rotor and stator, having parallel slots with sharp edges that typically run along the generators of the respective conical surfaces. The fluid paste enters and exits in an axial direction to the axis of the rotor and stator, traversing the entire gap, where it undergoes both shear action and high-frequency pressure stresses from the stator and rotor slots in strong relative motion with each other.

[009] Typical disc refiners are described, for example, in documents US5467931, or in US2019203417, and involve a pair of discs facing each other, one of which is fixed and one rotating, separated by a gap. Discs have grooves with sharp edges on their surface. The material to be refined is introduced into the gap, normally from a central entrance, so that the strongly rotating grooves apply pulses of pressure and impulsive shear forces to the material.

[0010] Both the truncated cone refiner and the disc refiner require a high-pressure feed to allow the stock to proceed along the span. In addition, the power required for the rotor to overcome the strong resistance between the truncated cone or disc surfaces is high, so the refining stage with this type of refiner requires several hundred kW of power in total.

[0011] Furthermore, existing refiners do not allow for precise variation in fiber quality as the type of pulp and the type of paper to be produced change. SUMMARY OF THE INVENTION

[0012] It is a feature of the present invention to provide a method Petition 870250094047, dated 10 / 14 / 2025, p. 8 / 26 / 11, regarding dense pulp refining that allows, at least with equal refining quality, reduced energy absorption.

[0013] Another feature of the present invention is to provide a method for refining dense pulp that allows the degree of fiber refining to be precisely modified, achieving high degrees of Shopper-Riegler refining.

[0014] It is also a feature of the present invention to provide a dense pulp refining plant that achieves the purposes described above.

[0015] It is then a feature of the present invention to provide a pulp refiner that achieves the purposes described above.

[0016] These and other objectives are achieved by a dense pulp refining method comprising the following steps: - pre-arrange a stator by having a perforated side wall; - pre-arranging a rotating rotor in said stator, said rotor comprising a plurality of blades having respective shear profiles arranged at a distance d from said perforated side wall, said rotor arranged to be rotated at a peripheral speed v of said shear profiles (22) in relation to said stator; - pre-arrange an inlet duct in said stator and pre-arrange externally to said stator a collection chamber having an outlet duct; - feeding into said stator, through said inlet duct, selected pulp previously subjected to separation of solid parts, so that said blades (21) cause the forced passage of said selected pulp between the cutting profiles of said blades and said perforated side wall, causing a refining action of said selected pulp, and so that the refined fibers pass through said perforated side wall and reach said collection chamber and said outlet duct.

[0017] Advantageously, said stator has a circular opening and said rotor comprises a rotating shaft having a disc flange, connected to said rotating shaft and rotating in said circular opening and a Petition 870250094047, dated 10 / 14 / 2025, page 9 / 26 / 11 plurality of said blades connected to said disc flange.

[0018] Thus, the grazing passage of the blade cutting profiles in relation to the perforated sidewall causes the simultaneous untangling of the fibers from the selected pulp, in the section where the cutting profiles are between one hole and the next hole in the perforated sidewall, cutting these fibers, and the immediate passage of the cut and untangled fibers through the perforated sidewall, in the section where the cutting profiles are in a hole in the perforated sidewall, achieving the ideal fiber refinement.

[0019] Compared to the state of the art, the absence of pressure waves results simultaneously in a drastic reduction in the power required and the achievement of very high peripheral speeds. In fact, the high-speed passages of the cutting profiles scraping the perforated sidewall result in ideal refinement, and the subsequent immediate free passage of the fibers through the perforated wall prevents the creation of pressure waves, thus avoiding a strong braking action on the rotor.

[0020] Advantageously, the said distance d is adjusted between 0.05 mm and 0.5 mm.

[0021] In particular, the said peripheral speed v is adjusted between 3000 rpm and 5000 rpm.

[0022] Advantageously, said blades are configured to cause, with the rotation of said rotor, a suction of the selected pulp from said inlet duct and to cause a flow of refined pulp towards said collection chamber and said outlet duct.

[0023] In this way, the flow from the stator to the collection chamber is caused only by the blades, avoiding overpressure or depressions that could cause defects or non-homogeneity in refining. In addition, there is further energy saving, avoiding the need for a dedicated pump to cause pulp flow through the stator.

[0024] In particular, the said blades of the said plurality are salient Petition 870250094047, dated 10 / 14 / 2025, page 10 / 26 / 11 frontally from said disc flange.

[0025] Advantageously, said blades projecting from said disc flange are configured to generate a suction of selected pulp from said inlet duct and to cause a flow of refined pulp towards said collection chamber and said outlet duct.

[0026] In this way, the disc flange closes the opening with minimal resistance to rotation, so that the blades can reach high rotational speed in the stator, handling a high pulp flow rate for the same power.

[0027] In particular, said inlet duct is arranged in an axial position opposite to said rotor in relation to said stator.

[0028] Thus, the selected pulp encounters the blades of said rotor with axial movement and they immediately receive radial movement towards said perforated side wall, undergoing refining and exiting rapidly through the perforated side wall, with minimal parking in said stator.

[0029] Advantageously, said perforated side wall of said stator has a cylindrical shape and said cutting profiles of said laminations are configured to describe, during their rotation, a cylindrical trajectory that scrapes said perforated side wall.

[0030] Advantageously, said perforated side wall of said stator has a truncated conical shape and said cutting profiles of said laminations are configured to describe, during their rotation, a truncated conical trajectory that scrapes said perforated side wall. Adjustment means are also provided to vary the axial distance between said stator and said rotor, so as to be able to vary said distance d.

[0031] Thus, by axially translating the rotor relative to the stator, the distance d can be varied to adjust the degree of fiber refinement.

[0032] In particular, the said stator is mounted on a support of a Petition 870250094047, dated 10 / 14 / 2025, page 11 / 26 / 11 detachable manner and a plurality of stators with perforated side walls with holes different from each other is provided.

[0033] In this way, different refinements can be made depending on the type of pulp selected.

[0034] According to a further aspect of the invention, a plant for refining dense pulp is claimed to comprise: - an opening for the introduction of said pulp into said plant; - a stator having a perforated side wall and an axial opening communicating with said inlet; - a rotating rotor in said stator, said rotor comprising a plurality of laminations having respective shear profiles arranged at a distance d from said perforated side wall, said rotor arranged to be rotated at a peripheral speed v of said shear profiles relative to said stator; - an external collection chamber attached to said stator and having an outlet duct configured to release refined pulp from said plant.

[0035] Advantageously, said stator has a circular opening and said rotor comprises a rotating shaft having a disc flange, connected to said rotating shaft and rotating in said circular opening and a plurality of said blades connected to said disc flange. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] The invention will now be shown with the following description of some exemplary embodiments, which are illustrative but not limiting, with reference to the accompanying drawings in which: Figure 1 shows a refining stage of selected pulp according to the invention; Figure 2A shows, in perspective, a possible embodiment of the rotor used in the method according to the invention; Figure 2B shows, in plan view, the rotor configuration. Petition 870250094047, dated 10 / 14 / 2025, p. 12 / 26 / 11 in Figure 2A; Figure 3 shows a possible exemplary embodiment of the stator and rotor used in the method according to the invention; Figure 3A shows a detail of Figure 3 in which the distance between the rotor blades and the perforated side wall of the stator is highlighted; Figures 4A-4D show other possible exemplary embodiments of the stator used in the method according to the invention; Figure 5 shows a cross-section of a possible mechanical embodiment of a refining machine used in a refining plant according to the invention, in which the stator has a frustoconical wall. DESCRIPTION OF SOME PREFERRED EXEMPLARY EMBODIMENTS

[0037] With reference to the figures above, the dense pulp refining method according to the present invention involves the pre-arrangement of a stator 10 having a perforated side wall 11, that is, having numerous holes 12 passing through it. The stator 10 and its holes 12 in the side wall 11 can be made in various forms, illustratively and not limitingly represented in Figures 4A to 4D.

[0038] According to the method, a rotor 20 configured to rotatably engage with the stator 10 is then arranged. The rotor 20 includes a plurality of laminations 21 having shear profiles 22. With reference to Figure 3, the laminations 21 are arranged so that their respective shear profiles 22, with the rotation ω of the shaft 25 of the rotor 20 around a common x-axis with the stator 10, describe a surface arranged at a distance d from the side wall 11, so as to be radial to it. Specifically, this distance d is between 0.05 mm and 0.5 mm.

[0039] Rotor 20 is rotated relative to stator 10 by Petition 870250094047, dated 14 / 10 / 2025, p. 13 / 26 / 11 so that the cutting profiles 22 reach a peripheral speed v in relation to the side wall 11. In particular, such peripheral speed v is between 3,000 rpm and 5,000 rpm.

[0040] An inlet duct 15 is provided in the stator 10, while outside the stator 10 there is a collection chamber 30 having an outlet duct 31.

[0041] According to the method, the selected pulp 40, that is, pulp previously subjected to separation of solid parts, according to the known technique, for example, by means of a centrifugal separator, is then fed into the stator 10 through the inlet duct 15.

[0042] With the rotation of the rotor 20 in the stator 10, the blades 21 cause the forced passage of the selected pulp 40 between the cutting profiles 22 and the perforated side wall 11, causing refined fibers to pass through the holes 12 of the perforated side wall 11 and reach the collection chamber 30 and the outlet duct 31.

[0043] In particular, the scraping passage of the cutting profiles 22 of the blades 21 in relation to the perforated side wall 11 simultaneously causes a loosening of the fibers from the selected pulp 40, in the section where the cutting profiles 22 are located between one hole 12 and the next hole 12 of the perforated side wall 11, with the cutting of the fibers caused by the dynamic cutting action of the cutting profiles 22 and the immediate passage of the cut and loosened fibers through the holes 12 of the perforated side wall 11, in the section where the cutting edges of profiles 22 are located in correspondence with a hole 12 of the perforated side wall 11, obtaining the ideal refinement of the fibers. In this way, radial flows 41 of refined fibers emerge from the holes 12 and are directed to the collection chamber 30 so as to then form a flow of refined pulp 42.

[0044] Advantageously, the blades 21 are configured to cause, with the rotation ω of the rotor 20, a selected pulp suction from the inlet duct 15 and to cause a distribution of refined pulp towards the Petition 870250094047, dated 10 / 14 / 2025, page 14 / 26 / 11 collection chamber 30 and at the outlet of the distribution duct 31. For example, the blades 21 may have a curved or helical surface so that with the rotation ω of the rotor 20 they push the pulp radially, generating a head in the outlet duct 31 and suction from the inlet 15.

[0045] In this way, the flow 41 of fibers from the stator 20 to the collection chamber 30 is caused only by the blades 21, avoiding overpressures or depressions that could cause defects or inhomogeneities in refining. In addition, there is even more energy saving, avoiding a special pump to make the pulp flow through the stator.

[0046] In particular, with reference to Figure 2B, in one possible embodiment, the blades 21 have a longitudinal axis disposed at a distance δ from a radial axis passing through the center O of the rotor 20. Furthermore, the blades 21 have a shear profile 22 that draws a circumferential arc with center O and radius r1.

[0047] Thanks to the distance δ, when the rotor performs the rotation ω in the direction shown in the figure, the profiles 22 generate a suction action that brings the fibers towards the perforated wall 11 of the stator 10 and, therefore, subsequently towards the outside of the stator itself, reducing the total energy required for this operation compared to a configuration in which the distance δ is zero.

[0048] In one possible embodiment, shown in the figures, the stator has a circular opening 13 and the rotor 20 includes a rotating shaft 25 having a disc flange 23 fixed to the shaft 25 and rotating in the circular opening 13, with a plurality of blades 21 projecting forward from the disc flange 23. In particular, the disc flange 23 closing the opening 13 offers minimal resistance to rotation, allowing the rotor 20 and therefore the blades 21 to achieve high rotational speed in the stator, handling a high pulp flow rate with the same power.

[0049] Even in this case, the blades 21 that project from the Petition 870250094047, dated 10 / 14 / 2025, page 15 / 26 / 11 disc flange 23 may have a curved profile configured to provide suction of the selected pulp 40 from the inlet duct 15 and to cause a distribution of refined pulp 41 towards the collection chamber 30 and the outlet duct 31.

[0050] In the solution shown, the stator 10 has the inlet duct 15 in an axial position, that is, on the x-axis on the opposite side to the rotor 20. In this way, the selected pulp 40 encounters the rotor blades 21 with axial movement, which immediately imparts a radial movement to the pulp towards the perforated side wall 11, forcing it to pass between the cutting profiles 22 and causing refining and then causing the refined fibers 41 to exit rapidly through the perforated side wall, with minimal stagnation in the stator 10. The movement of the blades 21 is therefore sufficient to cause suction, refining and distribution of the pulp, without the need for additional pumping.

[0051] In one possible embodiment, such as that shown in the figures, the stator 10 has a cylindrical side wall 11 and the shear profiles 22 of the laminations 21 are configured to describe, during their rotation ω, a cylindrical trajectory that scrapes the cylindrical side wall 11.

[0052] In one possible embodiment, the stator 10 may have a frustoconical side wall and the cutting profiles 22 of the rotor blades 20 are configured to describe, during their rotation ω, a frustoconical trajectory that scrapes the frustoconical side wall 11 and adjustment means are provided to record a relative axial displacement between the stator and the rotor. In this way, it is possible to record the span of the grazing trajectory of the cutting profiles in relation to the frustoconical side wall, i.e., the distance d mentioned above, in order to regulate the degree of fiber refinement.

[0053] As is known, in fact, the degree of pulp refinement is given by the so-called shear rate. In the present case, this shear rate is directly proportional to the value of the distance of Petition 870250094047, dated 10 / 14 / 2025, page 16 / 26 / 11 inversely proportional to the value of the peripheral speed v. Therefore, by reducing the distance d it is possible to increase the shear rate, that is, the degree of pulp refining.

[0054] In one possible embodiment, the stator 10 is mounted on a support in a removable manner and a plurality of stators 10 is provided having perforated side walls 11 with holes 12 different from each other. In this way, it is possible to carry out different refinements depending on the type of pulp selected. Petition 870250094047, dated 10 / 14 / 2025, page 17 / 26

Claims

1 / 3 CLAIMS 1. Dense pulp refining method comprising the steps of: - pre-arranging a stator (10) having a perforated side wall (11); - pre-arranging a rotating rotor (20) in said stator (10), said rotor (20) comprising a plurality of blades (21) having respective cutting profiles (22) arranged at a distance d from said perforated side wall (11), said rotor arranged to be rotated at a peripheral speed v of said cutting profiles (22) relative to said stator (10); - pre-arranging in said stator (10) an inlet duct (15) and pre-arranging externally to said stator (10) a collection chamber (30) having an outlet duct (31);- feeding said stator (10), through said inlet duct (15), with the selected pulp previously subjected to separation of solid parts, so that said blades (21) cause the forced passage of said selected pulp between the cutting profiles (22) of said blades (21) and said perforated side wall (11), causing a refining action of said selected pulp, and so that the refined fibers pass through said perforated side wall (11) and reach said collection chamber (30) and said outlet duct (31); said method characterized in that said stator (10) has a circular opening (13) and said rotor (20) comprises a rotation shaft (25) having a disc flange (23), connected to said rotation shaft (25) and rotating in said circular opening (13), and a plurality of said blades (21) connected frontally to said disc flange (23).

2. Refining method according to claim 1, characterized in that said distance d is adjusted between 0.05 mm and 0.5 mm. Petition 870250094047, dated 10 / 14 / 2025, page 18 / 26 2 / 3 3. Refining method according to claim 1, characterized in that said peripheral speed v is adjusted between 3000 rpm and 5000 rpm.

4. Refining method according to claim 1, characterized in that said blades (21) are configured so that, with the rotation of said rotor (20), there is a suction of the selected pulp from said inlet duct (15) and causes a flow of refined pulp towards said collection chamber (30) and said outlet duct (31).

5. Refining method according to claim 1, characterized in that said blades (21) of said plurality are projecting forward from said disc flange (23).

6. Refining method according to claim 5, characterized in that said blades (21) projecting from said disc flange (23) are configured to generate a suction of selected pulp from said inlet duct (15) and to cause a flow of refined pulp towards said collection chamber (30) and said outlet duct (31).

7. Refining method according to claim 1, characterized in that said inlet duct (15) is arranged in an axial position opposite to said rotor (20) with respect to said stator (10).

8. Refining method according to claim 1, characterized in that said perforated side wall (11) of said stator (10) has a cylindrical shape and said cutting profiles (22) of said blades (21) are configured to describe, during their rotation, a cylindrical trajectory that scrapes said perforated side wall (11).

9. Refining method according to claim 1, characterized in that said perforated side wall (11) of said stator (10) has a frustoconical shape and said cutting profiles (22) of said blades (21) are configured to describe, during their rotation, a frustoconical trajectory that scrapes said perforated side wall (11), and adjustment means are also provided to vary the axial distance between said stator (10) and said rotor (20), so as to be able to vary said distance d.

10. Dense pulp refining plant (100) comprising: - an inlet (15) for introducing said pulp into said plant (100); - a stator (10) having a perforated side wall (11) and an axial opening (13) communicating with said inlet (15); - a rotating rotor (20) in said stator (10), said rotor (20) comprising a plurality of blades (21) having respective cutting profiles (22) arranged at a distance d from said perforated side wall (11), said rotor (20) arranged to be rotated at a peripheral speed v of said cutting profiles (22) relative to said stator (10); - a collection chamber (30) external to said stator (10) and having an outlet duct (31) configured to release refined pulp from said plant (100);the said plant (100) characterized in that the said stator (10) has a circular opening (13) and the said rotor (20) comprises a rotation shaft (25) having a disc flange (23), connected to the said rotation shaft (25) and rotating in the said circular opening (13), and a plurality of the said blades (21) connected to the said disc flange (23). Petition 870250094047, dated 10 / 14 / 2025, pp. 20 / 26;

Images