WO2024214067A1

WO2024214067A1 - Method and plant for dense pulp refining for papermaking

Info

Publication number: WO2024214067A1
Application number: PCT/IB2024/053617
Authority: WO
Inventors: Bruno Giannelli
Original assignee: Individual
Current assignee: Individual
Priority date: 2023-04-14
Filing date: 2024-04-12
Publication date: 2024-10-17
Anticipated expiration: 2025-10-14
Also published as: IT202300007326A1; CN121100203A

Abstract

A method of refining dense pulp comprising the steps of prearranging a stator (10) having a perforated side wall (11), prearranging a rotor (20) rotatable in the stator (10), said rotor (20) comprising a plurality of blades (21) having respective cutting profiles (22) arranged at a distance d from the perforated side wall (11), said rotor arranged to be rotated at a peripheral speed v of the cutting profiles (22) with respect to the stator (10). The method then comprises the steps of prearranging in the stator (10) an inlet duct (15) and prearranging externally to the stator (10) a collection chamber (30) having an outlet duct (31). The method also comprises a step of feeding into the stator (10), through the inlet duct (15), selected pulp previously subjected to separation from solid parts, so that the blades (21) cause the forced passage of the selected pulp between the cutting profiles (22) of the blades (21) and the perforated side wall (11), causing a refining action of the selected pulp, and so that refined fibers pass through the perforated side wall (11) and reach the collection chamber (30) and the outlet duct (31).

Description

TITLE

Method and plant for dense pulp refining for papermaking

DESCRIPTION

Field of the invention

[ 0001] The present invention relates to the field o f papermaking and, more speci fically, relates to a method for dense pulp refining for papermaking .

[ 0002] The present invention further relates to a plant implementing such a method .

[ 0003] In particular, the invention relates to a pulp refiner that is used in such a method .

Description of the prior art

[ 0004 ] As is well known, before arriving at the machine head, the pulp that will be turned into paper commonly follows a so-called "dense pulp cycle" and then a "dilute pulp cycle" .

[ 0005] A typical dense pulp cycle involves the pulping of suitable fibrous materials in a pulper, the eventual accumulation of the pulp produced by the pulper in a pulped pulp vat , the separation from the pulp of any hard fragments and residual dirt in a centri fugal separator, a refining step in a pulp refiner, and, normally, the passage into a refined pulp collection vat . [ 0006] Again as known, the refined pulp passes to the dilute pulp cycle , which involves several vats and several passes of strong dilution with water, degassing, cleaning, and stabili zation before going to the machine head .

[ 0007] Dense pulp refining is thus an essential step in the papermaking cycle and is practiced through two main types of refiners : the truncated refiner and the disc refiner . Both apply impulsive shear forces and pressure pulses to the pulp fibrous material , separating the entangled fibers into individual fibers as much as possible by the impulsive shear forces and achieving an opening of the fibers by the repeated pressure forces , thus achieving the desired refining .

[ 0008] Typical truncated cone refiners are described in US5152871 , US2016355977 , US2019078259 , and EP3839134 . They involve a truncated conical rotor and stator, having parallel grooves with sharp edges that typically run along the generators of the respective conical surfaces . The slurry enters and exits in a direction axial to the axis of the rotor and stator, traversing the entire gap, where it undergoes from the stator and rotor grooves in strong relative motion to each other both shear action and high- frequency pressure stresses .

[ 0009] Typical disc ref iners are described for example in US5467931 , or in US2019203417 , and involve a pair of discs facing each other of which one is fixed and one rotating, separated by a gap . The discs have grooves with sharp edges on their surface . The stock to be refined is introduced into the gap, normally from a central inlet , so that the strongly rotating grooves apply pressure pulses and impul sive shear forces to the stock .

[ 0010] Both the truncated cone refiner and the disc refiner require a high-pressure feed to allow the stock to proceed along the gap . 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] In addition, existing refiners do not allow for precise variation in fiber quality as the pulp type 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 of refining dense pulp that allows , at least at equal refining quality, reduced energy absorption .

[ 0013] It is another feature of the present invention to provide a method for refining dense pulp that allows the degree of fiber refining to be precisely modi fied, achieving high Shopper-Riegler refining grades . [ 0014 ] It is also a feature of the present invention to provide a plant of refining dense pulp that achieves the above described purposes .

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

[ 0016] These and other obj ects are achieved by a method of refining dense pulp comprising the steps of :

- prearranging a stator having a perforated side wall ;

- prearranging a rotor rotatable in said stator, said rotor comprising a plurality of blades having respective cutting profiles arranged at a distance d from said perforated side wall , said rotor arranged to be rotated at a peripheral speed v of said cutting profiles ( 22 ) with respect to said stator ;

- prearranging in said stator an inlet duct and prearranging externally to said stator a collection chamber having an outlet duct ; feeding in said stator, through said inlet duct , selected pulp previously subj ected to separation from 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 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 rotation shaft having a disc flange , connected to said rotation shaft and rotatable in said circular opening, and a plurality of said blades connected to said disc flange .

[ 0018] Thus , the grazing passage of the blade cutting profiles with respect to the perforated side wall causes simultaneous untangling of the fibers of the selected pulp, in the section where the cutting profiles are between one hole and the next hole in the perforated side wall , with cutting of these fibers , and the immediate passage of the cut and untangled fibers through the perforated side wall , in the section where the cutting profiles are at a hole in the perforated side wall , achieving optimal fiber refining .

[ 0019] Compared with the prior art , the absence of pressure waves simultaneously results in a drastic reduction of the required power and an achievement of very high peripheral speeds . In fact, the high-speed passages of the cutting profiles grazing the perforated side wall result in optimal refining, and the immediate subsequent 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, said distance d is set between 0 , 05 mm and 0 , 5 mm .

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

[ 0022] Advantageously, said blades are configured to cause , with the rotation of said rotor, 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 .

[ 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 inhomogeneity in refining . In addition, there is additional energy savings by avoiding a dedicated pump to cause pulp flow through the stator .

[ 0024 ] In particular, said blades of said plurality are frontally protruding from said disc flange .

[ 0025] Advantageously, said blades protruding 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 achieve 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 axial position opposite to said rotor with respect to said stator . [ 0028] Thus , the selected pulp meets the blades of said rotor with axial motion, and they immediately receive radial motion toward said perforated side wall , undergoing refining and exiting rapidly through the perforated side wall , with minimal stationing in said stator .

[ 0029] Advantageously, said perforated side wall of said stator has cylindrical shape and said cutting profiles of said blades are configured to describe , during their rotation, a cylindrical traj ectory grazing said perforated side wall .

[ 0030] Advantageously, said perforated side wall of said stator has a f rus to-conical shape and said cutting profiles of said blades are configured to describe , during their rotation, a f rusto-conical traj ectory grazing said perforated side wall . Adj ustment means are also provided for varying 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 adj ust the degree of fiber refining . [ 0032] In particular, said stator is mounted on a stand in a detachable manner, and there i s provided a plurality of stators having side walls drilled with di fferent holes from each other .

[ 0033] In this way, di f ferent 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 comprising :

- an inlet for the introduction of said pulp in said plant ;

- a stator having a perforated side wall and an axial opening in communication with said inlet ;

- a rotor rotatable in said stator, said rotor comprising a plurality of blades having respective cutting profiles arranged at a distance d from said perforated side wall , said rotor arranged to be rotated at a peripheral speed v of said cutting profiles with respect to said stator ;

- a collection chamber external to said stator and having an outlet duct configured to let out refined pulp from said plant .

[ 0035] Advantageously, said stator has a circular opening and said rotor comprises a rotation shaft having a disc flange , connected to said rotation shaft and rotatable in said circular opening, and a plurality of said blades connected to said disc flange .

Brief description of the drawings

[ 0036] The invention will be now shown with the following description of some exemplary embodiments , exempli fying but not limitative , with reference to the attached drawings in which :

- Fig . 1 shows a refining stage of selected pulp according to the invention;

- Fig . 2A shows , in perspective , a possible embodiment of the rotor used in the method according to the invention;

- Fig . 2B shows , in plan view, the embodiment of the rotor in Fig . 2A;

- Fig . 3 shows a possible exemplary embodiment of the stator and of the rotor used in the method according to the invention;

- Fig . 3A shows a detail of Fig . 3 in which the distance between the rotor blades and the perforated side wall of the stator is highlighted;

- Figs . 4A-4D show further pos sible exemplary embodiments of the stator used in the method according to the invention;

- Fig . 5 shows in cross section a possible mechanical reali zation of a refining machine used in a refining plant according to the invention, in which the stator has a f rusto-conical wall .

Description of some preferred exemplary embodiments

[ 0037] With reference to the above figures , the method of refining dense pulp according to the present invention involves the prearrangement 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 on the side wall 11 can be made in various shapes , illustratively and non-limitingly depicted in Figures 4A to 4D .

[ 0038] According to the method, a rotor 20 configured to engage rotatably in the stator 10 is then arranged . The rotor 20 includes a plurality of blades 21 having cutting profiles 22 . Referring to Figure 3 , the blades 21 are arranged so that their respective cutting profiles 22 , with the rotation w of the shaft 25 of the rotor 20 about 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 . Speci fically, this distance d is between 0 , 05 mm and 0 , 5 mm .

[ 0039] The rotor 20 is brought into rotation relative to the stator 10 so that the cutting profiles 22 achieve relative to the side wall 11 a peripheral speed v . In particular, such peripheral speed v is between 3000 rpm and 5000 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, selected pulp 40 , i . e . pulped pulp previously subj ected to separation from solid parts , according to known technique , for example through a centri fugal 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 to reach the collection chamber 30 and the outlet duct 31 .

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

[ 0044 ] Advantageously, the blades 21 are configured to cause , with the rotation w of the rotor 20 , a suction of selected pulp from the inlet duct 15 , and to cause a delivery of refined pulp towards the collection chamber 30 and the delivery duct outlet 31 . For example , the blades 21 can have a curved or helical surface so that with the rotation w of the rotor 20 they push the pulp radially, generating head in the outlet duct 31 and suction from the inlet 15 .

[ 0045] In this way, the flow 41 of f ibers 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 . Furthermore , there is further energy saving by avoiding a special pump to cause the pulp to flow through the stator .

[ 0046] In particular, with reference to figure 2B, in a possible embodiment , the blades 21 have a longitudinal axis arranged at a distance 5 with respect to a radial axis passing through the center 0 of the rotor 20 . Furthermore , the blades 21 have a cutting profile 22 which draws a circumferential arc with center 0 and radius ri . [ 0047] Thanks to the distance 5 , when the rotor carries out the rotation w in the direction shown in the figure , the profiles 22 generate a suction action which brings the fibers towards the perforated wall 11 of the stator 10 and therefore subsequently towards the outside of the stator itsel f , reducing the overall energy necessary for this operation compared to a configuration in which the distance 5 is zero .

[ 0048] In a possible embodiment , shown in the figures , the stator has a circular opening 13 and the rotor 20 includes a rotation shaft 25 having a disc flange 23 fixed to the shaft 25 and rotatable in the circular opening 13 , with a plurality of the blades 21 protruding frontally from the disk flange 23 . In particular, the disk flange 23 which closes the opening 13 of fers minimal resistance to rotation, allowing the rotor 20 , and therefore the blades 21 , to reach high rotation speed in the stator, treating a high flow rate of pulp with the same power .

[ 0049] Even in this case , the blades 21 protruding from the disc flange 23 can have a curved profile configured to impart a suction of the selected pulp 40 from the inlet duct 15 and to cause a delivery 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, i . e . on the x axis on the side opposite to the rotor 20 . In this way, the selected pulp 40 meets the blades 21 of the rotor 20 with axial motion, which immediately impart a radial motion to the pulp towards the perforated side wall 11 , forcing it to pass between the cutting profiles 22 and causing refining, and then making the refined fibers 41 exit rapidly through the perforated side wall , with minimal parking in the stator 10 . The motion of the blades 21 is therefore suf ficient to cause suction, refining and delivery of the pulp, without the need for further pumping .

[ 0051] In a possible embodiment , such as that shown in the figures , the stator 10 has a cylindrical side wall 11 , and the cutting profiles 22 of the blades 21 are configured to describe , during their rotation w, a cylindrical traj ectory grazing the cylindrical side wall 11 .

[ 0052] In a possible embodiment , the stator 10 can have a f rusto-conical side wall , and the cutting profiles 22 of the rotor blades 20 are configured to describe , during their rotation w, a f rusto-conical traj ectory grazing the frusto- conical side wall 11 , and adj ustment means are provided for recording a relative axial displacement between the stator and the rotor . In this way, it is possible to record the gap of the grazing traj ectory of the cutting profiles with respect to the f rusto-conical side wall , i . e . the aforementioned distance d, in order to regulate the degree of refinement of the fibres.

[0053] As is known, in fact, the degree of refinement of the pulp is given by the so-called "shear rate". In the present case, this shear rate is directly proportional to the value of the distance d and inversely proportional to the value of the peripheral speed v. Therefore, by reducing the distance d it is possible to increase the shear rate, i.e. the degree of refining of the pulp. [0054] In a possible embodiment, the stator 10 is mounted on a support in a removable manner, and a plurality of stators 10 are 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.

Claims

1. A method of refining dense pulp comprising the steps of :

- prearranging a stator (10) having a perforated side wall (11) ;

- prearranging a rotor (20) rotatable 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) with respect to said stator (10) ,

- prearranging in said stator (10) an inlet duct (15) and prearranging externally to said stator (10) a collection chamber (30) having an outlet duct (31) ; feeding into said stator (10) , through said inlet duct (15) , selected pulp previously subjected to separation from 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 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 rotatable in said circular opening (13) , and a plurality of said blades (21) frontally connected to said disc flange (23) .

2. The method of refining, according to claim 1, wherein said distance d is set between 0,05 mm and 0,5 mm.

3. The method of refining, according to claim 1, wherein said peripheral speed v is set between 3000 rpm and 5000 rpm.

4. The method of refining, according to claim 1, wherein said blades (21) are configured to cause, with the rotation of said rotor (20) , 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 ) .

5. The method of refining, according to claim 1, wherein said blades (21) of said plurality are frontally protruding from said disc flange (23) .

6. The method of refining, according to claim 5, wherein said blades (21) protruding 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. The method of refining, according to claim 1, wherein said inlet duct (15) is arranged in axial position opposite to said rotor (20) with respect to said stator (10) .

8. The method of refining, according to claim 1, wherein said perforated side wall (11) of said stator (10) has cylindrical shape and said cutting profiles (22) of said blades (21) are configured to describe, during their rotation, a cylindrical trajectory grazing said perforated side wall (11) .

9. The method of refining, according to claim 1, wherein said perforated side wall (11) of said stator (10) has a f rusto-conical shape and said cutting profiles (22) of said blades (21) are configured to describe, during their rotation, a f rusto-conical trajectory grazing said perforated side wall (11) , and wherein adjustment means are also provided for varying the axial distance between said stator (10) and said rotor (20) , so as to be able to vary said distance d.

10. A plant (100) of refining dense pulp comprising:

- an inlet (15) for the introduction of said pulp in said plant (100) ; - a stator (10) having a perforated side wall (11) and an axial opening (13) in communication with said inlet (15) ;

- a rotor (20) rotatable 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) with respect to said stator (10) ;

- a collection chamber (30) external to said stator (10) and having an outlet duct (31) configured to let out refined pulp from said plant (100) ; said plant (100) 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 rotatable in said circular opening (13) , and a plurality of said blades (21) connected to said disc flange (23) .