WO2010023363A1

WO2010023363A1 - Method and apparatus for manufacturing mechanical pulp

Info

Publication number: WO2010023363A1
Application number: PCT/FI2009/050682
Authority: WO
Inventors: Kari Edelmann; Veli SEPPÄNEN; Jouko Aalto; Timo Koskinen; Jouko Hautala; Esko Härkönen
Original assignee: Upm-Kymmene Corporation
Priority date: 2008-08-29
Filing date: 2009-08-28
Publication date: 2010-03-04
Also published as: FI20085810A0; FI121629B; FI20085810A

Abstract

.In a method for manufacturing mechanical pulp, particles (1 ) of fiber raw material are worked for detaching fibers. The fiber raw material is compressed at the same time when it is rubbed in a direction (H) differing from the main direction of the fibers.

Description

METHOD AND APPARATUS FOR MANUFACTURING MECHANICAL PULP

The invention relates to a method for manufacturing mechanical pulp. The invention also relates to an apparatus for implementing this kind of method.

Mechanical pulp is manufactured industrially by grinding or refining wood raw material. In grinding, whole trees are pressed against a rotating cylinder surface, whose surface structure is formed so that it detaches fibers from a tree. The obtained pulp is discharged with shower water from the grinder to fractionation and the refined is ground with a disc refiner. This method produces short-fiber, well light-scattering pulp. A typical example to be mentioned of a grinding process is US patent 4,381 ,217. In manufacturing refiner mechanical pulp the raw material is wood chips, which is directed into a center of a disc refiner, from which it is transferred under the effect of centrifugal force and steam flow to the perimeter of the refiner while being disintegrated by the blades at the surface of the disc. Typically in this process a multi-phase refining is necessary for obtaining finished pulp. The coarse fraction separated in the process can be directed into a so-called reject refining. The method produces pulp with long fibers compared to the above- mentioned groundwood. Refining processes have been presented in, for example, publications WO-9850623, US 4,421 ,595 and US 7,237,733.

High energy consumption is characteristic for both manufacturing methods of mechanical pulp. For example, in the manufacturing of groundwood the energy consumption for the LWC paper pulp is about 2 MWh/ton, and in addition, because of the short fibers, chemical pulp fiber is necessary for strengthening the structure in order to achieve sufficient runnability of a paper web. In the manufacturing of refiner mechanical pulp the typical energy consumption for LWC paper pulp is about 3 MWh/ton. Because of the long fibers of the product achieved with this method it is not necessary to strengthen the structure of the paper with chemical pulp.

In countries, which have a strong wood-processing industry, the manufacturing of mechanical pulp can form a significant part of the total energy demand of the industry and it can even affect the energy policy of a country. Due to the energy intensiveness of the defibration process, the ways for reducing energy necessary for one product ton even by a few percent can lead to significant savings in production costs.

The present invention precisely relates to refiner mechanical pulp manufacturing process, wherein the fiber raw material fed to the process is in a particle form, for example wood chips or similar, and it is ground by bringing it into a blade gap where the mechanical working of the moving surfaces grinds it and detaches fibers from it. It has been observed that the large energy consumption of the conventional refining is due to the large part of the elastic work and the need for thinning and increasing the flexibility of thick-walled fibers. The large part of elastic work is due to the fact that wood material is compressible and that, for example, compression cannot be directed into the fibers well enough in the disc refiner because of danger of blade contact. Typically the blade gap in this type of grinding is about 0.2 mm at the lowest, which corresponds to the thickness of 5 to 10 fibers.

In addition, in the disc refiners presently in use delay of the fibers in the refining zone is too short due to the large centrifugal force and developing steam of the refiner, as a result of which the pulp has to be separated and post-refined even after a two-stage refining for ensuring sufficient quality properties.

The purpose of the invention is to eliminate the above-mentioned drawbacks and to present a method and apparatus for achieving energy savings in the manufacturing of refiner mechanical pulp to preserve the same quality properties of the pulp, and it is possible to reach the same smoothness of the paper with 25 % lower energy consumption, or even lower energy consumption if the conditions are optimized.

To attain these purposes, the method according to the invention is primarily characterized in that the fiber raw material is compressed at the same time when it is rubbed in a direction differing from the main direction of the fibers.

When compression is applied to a piece of fiber material, for example wood piece, at the same time with rubbing it transversely in relation to the fibers, the work performed by the blade gap of the grinder is made more efficient loosening and flattening work, and work is not wasted on elastically reversible deformation of the fiber material. This processing is performed in some step of particle processing when pulp is made from wood chips or the like for manufacturing paper. Fiber material particles of suitable size can be supplied to the process, which particles have possibly been reduced in size from raw material of larger size, for example from industrial chips, with a mechanical method which does not consume much energy. In a similar manner, after the above-mentioned "compression-rubbing process" a high consistency refining can finally be performed in order to achieve a suitable freeness level. However, the total energy consumption of all the possible process steps per final pulp ton is smaller than the conventional refining method using starting raw material (wood chips) of the same size.

In the following, the invention will be described in more detail with reference to the appended drawings, in which

Fig. 1 presents the principle of the invention in the direction perpendicular to the surfaces working the fiber material,

Fig. 2 presents the same in the direction of the surfaces, and

Fig. 3 presents an apparatus used to verify the advantages of the invention.

In this description the term blade gap is used to describe the gap formed by two opposite surfaces moving in relation to each other. The blade gaps of this kind recur preferably several times in the travelling direction of the fiber material, wherein the same material is repeatedly brought under working in the blade gap. The travelling direction of the fiber material is approximately the same as the direction of the fibers. In this working in the blade gap the fiber material is simultaneously subjected to both compressing force, and approximately perpendicularly to the travelling direction of the fiber and the compression force shearing force (rubbing).

Fig. 1 shows the particle 1 of fiber material brought to working, which particle can be wood-based chip particle, splinter or similar piece, wherein the fibers are together and a certain fiber direction is detectable. Particle is led to the gap 2, which is formed by a surface 3 and a surface 4. The direction of movement of the moving surface 4 is shown with letter S. The feeding direction corresponds to the fiber direction of the particle 1 in the figure. In practice, several particles are simultaneously brought in the blade gap formed by the surfaces 3 and 4. At the same time when the particle becomes wedged between the blade gap and is compressed, rubbing is exerted on the particle in the direction H perpendicular to the feeding direction and compression direction of the particles. In practice, this is achieved with a movement component of the second surface differing from the direction of movement S in the blade gap. The direction of movement of the moving surface 4 is in the opening direction of the gap 2, wherein the particle 1 of the fiber material becomes wedged in the gap that is becoming gradually more narrow and it is compressed. When movement of the surfaces is referred to, it should be noted that both surfaces do not have to move, but the same phenomenon can be achieved with relative motion of the surfaces.

In Fig. 1 it has been illustrated schematically how the motion in the blade gap spreads the fibers or fiber bundles off from the particle 1 at the same time when the particle is brought deeper in the gap 2. When the particle is discharged from the gap, it is flattened in the thickness direction and the fibers or the fiber bundles have been separated from it in the rubbing direction being either adhered to the particle or separate from it.

Fig. 2 shows a similar situation in the direction perpendicular to the feeding direction and seen in the direction of the surfaces of the blade gap. The particle 1 is wedged into the blade gap (gap 2) in the feeding direction and it is flattened at the same time. The movement component H providing the rubbing action that spreads apart and/or detaches the fibers, is perpendicular to the plane of the figure. The essential aspect is that cutting edges are not used, which would break the fibers, but particles 1 reach the blade gap intact and only then deformation and separation of the fibers from each other occurs in the piece because of the surfaces coming closer together and the refining motion of the second surface (motion component H).

In Fig. 2 the tapering gap is formed by two planar portion being at an angle to each other in the moving surfaces 4. The tapering gap can also be formed by a curved surface, which is illustrated with a broken line. The blade gap is typically 0.1 to 0.5 mm at its narrowest, meaning the compression of the particle 1 to a corresponding thickness. The dimensions of the blade gap depend on the thickness and the desired compression ratio of the fiber material particles 1 to be worked (thickness after the compression/original thickness in the same direction). The gap is about 2 to 20 % of the original thickness of the particle, advantageously 3 to 15 %, i.e. the compression ratio is 2 to 20 %, advantageously 3 to 15 %.

Fig. 3 shows an apparatus used to verify the effect of the invention. A planar table 3 rotating in the direction S forms the first surface of the compression- rubbing gap and a roll 4 rotating in relation to it faster in the same direction forms the second surface of the compression-rubbing gap. The peripheral speed of the table surface depends on the distance to its rotation axis, and with the conical shape of the rolls this difference is compensated so that the ratio of the tangential speed of the roll periphery to the tangential speed of the table surface remains the same in the different parts of the radius R of the table. The tangential speed difference between the table and the roll is about 30 %. The roll is placed by on the table surface by leaving by a clearance forming the blade gap, wherein a linear compression nip is formed due to geometry between the straight surface of the table and the surface of the roll. The rotation axis A of the roll and at the same time the compression nip are at an angle in relation to the radius R of the table, wherein the above- mentioned rubbing movement component H is formed. Along the periphery of the table there are several rolls 4. Fig. 3 shows the axis A of the second roll at an angle in relation to the radius R, but in such a manner that the movement component H extends towards the opposite direction than in connection with the previous roll 4. In Fig. 3 the axis of the first roll 4 is at an angle so that the movement component H extends outwards (to the periphery of the table), and the axis of the next roll is at an angle to the opposite direction so that the movement component H extends inwards (to the center of the table). The rubbing direction H can vary in successive blade gaps in the method according to the invention, for example in alternating manner, but the fiber material can be rubbed also in the same direction. The nip line can be at an angle of about 30 degrees in relation to the radius of the table.

Fig. 3 also shows a feed conveyor 5 feeding particles 1 to the table 3 and having a feeding speed slower than the motion speed of the table. The faster motion of the table orientates the particles 1 to the direction of movement S of the table, wherein their fiber direction also becomes oriented in the direction of movement S, where they are fed to the compression-rubbing gaps. In addition, the feeding has been arranged so that the particles do not enter the blade gap on top of each other.

The apparatus in Fig. 3 is not the only possibility for implementing the invention. In the industrial implementation the particles of the fiber material are led to the gaps and between the blades of the refiner rotor and stator opening in the direction of movement of the rotor, where they are simultaneously compressed and rubbed. The blade gap of such a refiner can be similar to that shown in Fig. 2. The rubbing action in the lateral direction can be achieved with the design of the opposite surfaces of the blade gap, for example with the grooving of the surfaces of the stator and/or rotor having a direction differing from the direction of movement of the rotor. The design on the surface 4 differing from the direction of movement is illustrated in broken lines in Fig. 1.

Naturally, the variables known from the conventional production of refiner mechanical pulp can be utilized, such as temperature and steam pressure, and possibly the chemical pre-treatment of particles or the chips acting as their raw material.

If the particle size of the fiber material is too large, it can be reduced by splitting with blades in a method consuming small amounts of energy, in which method material is not refined. The particle thickness (dimension in the direction of compression) is adjusted preferably between 2 to 6 mm and width (dimension in the direction perpendicular to the compression direction and the main direction of the fibers) between 2 to 6 mm. The length of the starting raw material (dimension in the main direction of the fibers) is retained. By adjusting the thickness and width to a suitable level the compression-rubbing can be optimally applied to the fiber material in the blade gap, for example the fibers have enough room to spread. The splitting can be performed, for example, with a rotary cutter where the chips are fed and a fraction suitable in size can be separated with a screen from the obtained "splinter chips". The method according to the invention can be a pre-step for the refining of the fiber material to a desired quality, for example, in order to reach the correct Freeness level. Finally, a high consistency refining can be performed to the fibre pulp obtained by the method, for example at the dry matter content of about 30 %.

With a laboratory refiner having a blade gap of about 1 mm, a significant energy saving in the high consistency grinding at the 30 % dry matter content was found when the feed was the "splinter chip" compression-rubbed with the method according to Fig. 3, which "splinter chip" had been obtained by feeding 4 mm splinter chip through four successive roll nips. With the chemical treatment of the compression-rubbed splinter chip the energy consumption could be further reduced. When the energy consumption of such a compression-rubbing treatment is only 100 kWh/ton, the total saving is still considerable. If the raw material is industrial chip of large size, reducing it by splitting consumes only estimated 50 to 100 kWh/ton, which does not significantly affect the total energy saving if compared to treatment of large-sized chip to the same Freeness level with conventional methods. It can be proved that in practice with the compression-rubbing treatment and the following high consistency refining of splinter chip over 30 % total energy savings can be achieved in CF freeness 70 ml.

Claims

Claims:

1. A method for manufacturing mechanical pulp, where particles (1) of fiber raw material are worked for detaching fiber, characterized in that the fiber raw material is compressed at the same time when it is rubbed in a direction (H) differing from the main direction of the fibers.

2. The method according to claim 1 , characterized in that the same fiber raw material is compressed and rubbed in successive steps.

3. The method according to claim 1 or 2, characterized in that particles are worked by leading them into compression between to surfaces approaching each other at the same time when rubbing is exerted onto them by means of the surfaces in a direction (H) differing from the feeding direction (S) of the particles (1).

4. The method according to claim 3, characterized in that in the compression location the surfaces move at different speeds in the feeding direction of the particles and their directions of movement differ from each other.

5. The method according to claim 4, characterized in that the particles are led to a compression nip formed by the moving surfaces, wherein a rubbing movement in the lateral direction (H) differing from the feeding direction is exerted onto them.

6. The method according to claim 5, characterized in that the particles are led to the compression nip formed by a substantially straight surface (3) and a rotating member (4), wherein the axis of the rotating member (A) is arranged at an angle in relation to the movement of the straight surface.

7. The method according to any of the preceding claims, characterized in that the thickness of the particles of fiber raw material fed to the compression location is 2 to 6 mm in the compression direction.

8. The method according to claim7, characterized in that the width of the particles of fiber raw material fed to the compression location is 2 to 6 mm.

9. The method according to claim 7 or 8, characterized in that in the compression location the material is compressed to a thickness of 2 to 20 %, advantageously to a thickness of 3 to 15 % of the original.

10. The method according to any of the preceding claims, characterized in that the particles (1 ) of fiber raw material are fed to the compression mainly in their longitudinal direction.

11. The method according to any of the preceding claims, characterized in that the particles of raw material to be worked are manufactured from larger- sized chips by reducing, advantageously by splitting with blades.

12. The method according to any of the preceding claims, characterized in that the fiber material obtained by working the particles of fiber raw material is after treated by refining, particularly in high-consistency refining.

13. The method according to any of the preceding claims, characterized in that the particles (1 ) of fiber raw material are led to gaps (2) and opening in the direction of movement of the rotor, between the refiner rotor blades and stator, where they are simultaneously compressed and rubbed.

14. The method according to claim 13, characterized in that the surfaces of the stator and/or rotor are grooved using a design differing from their direction of movement.

15. An apparatus for manufacturing mechanical pulp, which comprises successive blade gaps (2) in the travelling direction of fibers and a feeding device for feeding particles of fiber raw material into the successive blade gaps (2), which are arranged to work the particles (1 ) of fiber raw material for detaching fibers, characterized in that the blade gaps are designed and their mutual movement is arranged in such a manner that the fiber raw material is compressed at the same time when it is rubbed in a direction (H) differing from the main direction of the fibers.