WO2004011718A1

WO2004011718A1 - Installation for purifying papermaking pulp

Info

Publication number: WO2004011718A1
Application number: PCT/PT2002/000014
Authority: WO
Inventors: Eric Haffner
Original assignee: Finidro - Financiamentos Energéticos Lda.
Priority date: 2002-07-30
Filing date: 2002-07-30
Publication date: 2004-02-05
Also published as: AU2002313931A1

Abstract

The invention concerns an installation for purifying papermaking pulp, equipped with one or more rotating grates (1) with slots or holes. The centrifugal force generated by the rotation of the grates (1) causes the particles trapped at the surface area of the grate to move towards the periphery, thereby enabling the grates (1) to be unclogged without resorting to stirring, leading to economical production and less costly installation. The pulp is introduced into the installation. The major part of the elements succeed in passing through the slots of the grates (1) while the elements with larger dimension do not. The invention can be implemented with grates integral with a rotary body (2), or with grates rotating inside a stationary body (2). The centrifuging also enables, in a complete embodiment, a pulp-thickening function.

Description

DESCRIPTION

EQUIPMENT FOR THE PURIFICATION OF PAPER PULP

Introduction

The present invention relates to the paper industry, and more particularly to the preparation of paper pulp from recycled paper or virgin pulp, prior to its introduction on the paper machine.

For the manufacture of paper, it is necessary to (re) suspend the cellulose fibers and eliminate foreign elements, also called contaminants. The suspension comprising the cellulose fibers is also called pulp. Contaminants can be of several species. We find, in particular, metal particles, staples, sands, small stones, adhesive materials, pieces of plastic, etc.

State of the art in connection with slit or hole purification.

In current papermaking processes, the slotted or hole-type scrubber is used. The slotted or hole-type scrubber consists of a cylindrical body, which can withstand the pressures of several bars. This body is equipped with a slotted or hole screen and has at least one inlet pipe of the paper pulp to be treated, a pipe for the purified paper pulp, a pipe of the rejected elements, and a agitator that allows a permanent action of cleaning the sieve.

Many contaminants fail to pass through the sieve, while cellulose fibers, given their shape and small diameter, manage to pass through the sieve orifices.

In particular, slit scrubbing is the most effective way to remove contaminants called "stickies", stickies are particles with a density close to the density of pulp and having adhesive properties. They are causing problems in the operation of the paper machine.

The agitator or rotor of the purifier is equipped with blades that pass at high speed very close to the sieve (a few millimeters). The speed differential between the blades and the pulp creates a sieve-like vacuum effect that draws contaminants and other elements held by the screen.

Without the action of the agitator, the clogging of the sieve would be very fast. However, the stirrer has many disadvantages, one of the main being the energy consumption required for its rotation.

Another disadvantage is related to the projections of certain contaminants against the sieve, forcing their passage through the slots or holes. Some of these projections cause accelerated wear of the screen.

Slot or hole purifiers also have the disadvantage of imposing a large dilution on the paper pulp, and in most cases requiring two or three stages to limit the loss of cellulose fibers. Objective of the invention

The object of the invention is the design of slit or hole-type purification equipment which avoids the clogging of the grid (s) (1) without the assistance of an agitator or rotor.

The basic idea is to rotate the (s) grid (s) (1) of purification so that the centrifugal force generated by the rotation of (s) grid (s) (1) ensures the required unclogging. The mechanical device of the current equipment for extracting the elements retained by the screen, in particular the agitator referred to above, can be eliminated.

The main advantages of the paper pulp purification equipment which is the subject of the invention are:

The possibility in most cases to work in a single floor of reduced size compared to existing solutions.

Elimination of the need for significant dilution of the paper pulp.

In some versions, the possibility of thickening the pulp and obtaining a washing effect of the pulp.

Better efficiency of purification, the passage of contaminants not being forced by a rotor or agitator.

Less wear of the grid (s) 1, because of the reduction of shock waves. The cost of maintenance will be reduced.

A saving of energy. Brief description of the drawings

For a better understanding of the invention, 5 drawings are presented in the appendix, corresponding to the main applications and representing the main versions of the equipment object of the invention. All the drawings are purely illustrative and do not constitute limiting intentions.

The drawing 1 represents a section of a practical embodiment of the purifier object of the invention with a grid (1) and a fixed body (2), the grid (1) being the only member in rotation. The rotation and the maintenance of the grid are made through an axis (15).

In this application, the -grille (1) -a -a break angle (8) to ensure the remixing of the paste facing the grid and thereby limiting the formation of a fiber mat at the level of the surface of the grid (1)

Drawing 2 represents a section of a practical embodiment of the invention with a grid (1) integral with the body

(2), also in rotation, the extraction of the paste being made at the periphery by the intake ducts (9). The rotation is made by the numerous radial walls (6) integral with the body (2). Elements of density greater than 1, which fail to pass through the grid (1), sediment towards the discharge lines (5). The pulp is introduced through a periphery of the grid (1), from which they are extracted at the periphery of the equipment by the discharge pipes (4). Openings are made in the radial walls (6), at the discharge lines (4) and (5), to resuspend any deposits that form on the periphery of the equipment. The filtrates, after the separation by sedimentation, of the fibers of cellulose, are conveyed to the center of the equipment via a central outlet (11). In this application, the grid (1) has a stepped angle break (8) in order to obtain a remix of the paper pulp, thus limiting the formation of a fiber mat at the surface of the grid (1).

The drawing 3 represents a half-section of a practical embodiment of the invention with several grids (1), a rotating body (2) secured to the grids, conical surfaces (16) sedimentation for the recovery of the most cellulosic particles fine. The pulp is introduced through an intake pipe (9). The elements of density greater than 1, retained by the grids (1) sediment at the periphery of the grids, from where they are extracted by the discharge lines (4). The fine cellulosic particles and the cellulose fibers having passed through the grid settle in the conical surfaces (16) of the separation zone, downstream of the grids (1), by the discharge lines (5). The filtrates are evacuated via the central outlet duct (11). The advantage of this application is to have a lower fiber loss.

Drawing 4 shows a front view of a grid (1) equipped with slots, in the configuration of the equipment with integral rotating body and radial walls (6). The profiles (7) of the grid are inclined with respect to the radial walls (6) in the direction of rotation, in order to deflect the particles of density greater than 1 from the corner between the grid (s) (1) and the radial walls (6) and thus compensate for the tendency of these particles to accumulate in this corner.

Drawing 5 shows a partial section of a grid (1) equipped with slots. The cut is made perpendicular to the slits. The profiles (7) that make up the grid are asymmetrical, in order to promote both the routing of the cellulose fibers through the slots and their rotation at the speed of the grid (1). In order to rotate the pulp to be treated near the grid (1) and thus facilitate the migration towards the periphery of the particles retained by the grid (1), the grid (1) is extended on the upstream side by the ribs (3).

General presentation of the invention

The drawings 1, 2 and 3 represent three applications of the invention. All applications implement one or more rotary grilles (1) arranged in parallel.

The agitator or rotor is removed. The declogging effect is obtained by the action of the centrifugal force.

In the drawing 1, the rotation of (s) grid (s) (1) is (are) made independently of a body (2) fixed.

In the drawings 2 and 3, the rotation of (s) grid (s) is (are) made (s) integrally with a rotary assembly including in particular a body (2).

In both cases, the operating principle is the same. Drawings 1 and 2 represent only one grid.

Drawing 3 presents the invention with several grids.

The goal of setting up multiple grids in parallel is to increase the capacity of the equipment.

The pulp is introduced through the intake pipe (9). It is then conveyed to the grid (s) (1). Operation of grid (s) (l)

The contaminants and elements retained by the grid (s) (1), are, under the effect of the centrifugal force, brought to the periphery or towards the center of the apparatus, according to their density, allowing a permanent unclogging of (the) grid (s).

The elements of density greater than 1, retained by the grid (s) (1), sediment to the periphery of the grid (s) (1).

The elements of density less than 1, retained by the grid (s) (1), reach the center of the grid (s) (1), where they are led on the other side of the (1) grids through the openings (12).

These openings may be extended by a conduit, not shown in the drawings, to extract these elements without re-mixed with the pulp ^"refined paper.

The grid (s) (1) may (have) be conical (s) with the admission of the paste by the center of the cone, to ensure that the particles that migrate in the radial direction under the effect of the centrifugal force, are in contact with the grid (s) (1). Most of the cellulose fibers and the water pass through the slots or holes, with the contaminants larger than the slots or grid holes (1) being retained.

In order to limit the formation of a cellulose fiber mat on the surface of the grid (s) (1), the grid (s) (1) can (may) include one or more ruptures of angle (8) which promote the re-mixing of the pulp. In the case of a slit cleaning and in order to promote the routing of the cellulose fibers through the slots of the grid (s) (1), the profiles (7) which constitute the grid (s) ( 1) may have an asymmetrical section. Drawing 5 shows this configuration. In order to facilitate the migration towards the periphery, or towards the center, elements retained by the grid (s) (1), the profiles (7) which are arranged along the grid (s) 1 may be oriented in the radial direction.

In order to rotate the paper pulp near the grid (s) (1), as well as facilitate the migration to the periphery or to the center of the particles that have not managed to pass through the grid (s) (1), the (the) grid (s) (1) may be extended (s) upstream by the ribs (3). Drawing 5 shows this configuration.

Version presented by drawing 1: non-rotating body (2)

In a first version presented by drawing 1, the purifier consists of a fixed body (2), the only rotating member being the (the) grid (s) (1). Rotation and maintenance of (the) grids (1) are made by an axis (15). This axis (15) is actuated by a motor not shown in the drawings.

The purified paper pulp is extracted from the body (2) by the opening (s) (13).

The elements of density greater than 1, which fail to pass through the (the) grid (s) (1), are extracted through the openings (14). Secondary treatment of these extracted elements, depending on the level of losses of cellulose fibers, may be taken into consideration. The elements of density less than 1 which do not cross the grid (s) (1) are conveyed towards the center of the grid (s) (1) and then evacuated through the openings (12) in the center of the grid (s) (1). These openings may be extended by a pipe, not shown in the drawings, to extract these elements without re-mixing with the purified paper pulp.

Presentation of the version of drawings 2 and 3: rotating body (2)

In a second version shown in drawings 2 and 3, the purifier consists of a body (2) rotating integrally with the (the) grid (s) (1). The assembly is driven by a motor not shown in the drawings.

The paper pulp is introduced through a central inlet duct (9). Fines (10) allow the paper pulp to be rotated at the same angular velocity as the body (2). The intake (9) and outlet (11) pipes are equipped with mechanical seals not shown in the drawings, allowing a tight connection with the fixed pipes.

The rotation of the paper pulp and the recovery of a large part of the rotational kinetic energy of the pulp may be carried out by numerous radial walls (6) integral with the body (2).

These radial walls (6) may have some openings to allow a differential and localized rotation of the paper pulp to be treated, thus promoting a re-mixing of the dough to limit the flocculation of the dough. The openings can be made on the radial walls (6) at the angle breaks (8), thereby increasing the effect of re-mixing. This configuration is represented by drawing 2.

The profiles (7) and ribs (3) constituting the (the) grid (s) (1) may be arranged in the radial direction. However, these profiles and ribs may form an angle relative to the radius to limit the accumulation of particles in the corner between the (the) grid (s) (1) and the radial walls (6) and thus ensure a better distribution pulp to be treated on the surface of the grid (s) (1). Drawing 4 illustrates this configuration.

Extraction of the particles retained by the grid (s) 1 -

The elements of density less than 1 that do not cross the (the) grid (s) (1) reach the center of the grid (s) (1), under the effect of the centrifugal force created by the rotation of the apparatus, where are conveyed on the other side of the grid (s) (1) by openings (12) in the center of (the) grid (s) (1). These openings (12) may be extended by a pipe, not shown in the drawings, to extract these elements without being re-mixed with the purified paper pulp.

For the extraction of particles of density greater than 1 which are retained by the grid (s) (1) and which migrate to the periphery of the apparatus, two configurations are possible: firstly - the extraction of these particles of the body (2) by the periphery of the apparatus, secondly - the extraction of these particles from the body (2) by the center. In both cases, a secondary treatment, depending on the level of losses of cellulose fibers, will be possible. In the first configuration, the elements of density greater than 1, retained by the grid (s) (1), sediment to the periphery of the grid (s) (1), where they may be extracted by discharge lines (4) at the periphery of the body (2). These discharge pipes (4) will have permanent or sequential openings. The dimensions of the discharge pipes (4) and the frequency of their opening will be adapted in order to thicken the sedimenting elements and to reduce the losses of water and kinetic energy. This configuration is represented by drawings 2 and 3.

The radial walls (6) may have openings at the most peripheral portion of the grid (s) (1) in order to resuspend the particles retained by the grid (s) (1) and sediment on the periphery. The goal is to avoid the formation of deposits. This configuration is represented by drawing 2.

In the second configuration, not shown in the drawings, the extraction of the elements of density greater than 1 retained by the (the) grid (s) (1) is by the center of the device. The flow velocity in the exhaust pipe will be sufficient to drive the particles towards the center despite the effect of the centrifugal force associated with the rotation of the body.

Extraction of cellulose fibers:

Under the effect of centrifugal force, the cellulose fibers, which pass through the grid (s) (1), will tend to sediment at the periphery of the device. For the extraction of these cellulose fibers, three configurations are possible: firstly - the extraction of cellulose fibers from the periphery of the apparatus; secondly - extraction from the center of the apparatus, on the one hand cellulose fibers after thickening, on the other hand filtrates; thirdly - the extraction of the purified paper pulp by the center without any separation between fibers and water.

In the first configuration, the cellulose fibers settle to the periphery in a collection zone on the periphery of the grid (s) (1), from which they are extracted by the discharge pipes (5). at the periphery of the body (2). These discharge lines are permanently or sequentially open in order to obtain the desired concentration, thus allowing partial thickening. This configuration is represented by drawings 2 and 3.

In order to facilitate the transport of the extracted elements to the discharge pipes (5), openings may be made on the radial walls (6) facing the discharge tubes (5). The angular velocity differential generated by these openings makes it possible to limit the formation of deposition at the periphery of the body (2). This configuration is represented by Drawing 2.

The residual filtrates are conveyed to the center of the apparatus and are evacuated via a central outlet line (11).

In a second configuration, not represented by the drawings, the cellulose fibers migrate to the periphery in a sedimentation zone downstream of the grid (s)

(1) where they are collected, then routed through a pipe to the center of the aircraft and then evacuated. The flow velocity in these lines will be sufficient to cause the solid elements, despite the centrifugal force. The residual filtrates, after sedimentation of the cellulose fibers, are conveyed towards the center where they are evacuated by a central pipe.

In the third configuration, not shown in the drawings, the purified paper pulp is conveyed through a pipe to the center of the apparatus, from which it is extracted, without separation between cellulose fibers and water. The flow velocity in this pipe will be sufficient to cause the purified paste, despite the centrifugal force.

Separation of fine cellulosic particles

In a more complete version of the equipment, represented by drawing 3, the equipment will be able to carry out a treatment of the filtrates after sedimentation of the cellulosic elements in the sedimentation chamber presented previously. In this case, the effect of the centrifugal force will be used in a separation zone downstream of the grid (s) (1) to improve the sedimentation and separation of the fine cellulosic particles. The objective is to limit the losses in cellulosic elements.

This separation zone will be equipped with conical surfaces (16) in order to facilitate the sedimentation of the cellulosic particles still present in the filtrates, after the sedimentation operation. The cellulosic particles will have a radial velocity different from the surrounding water and will thus come into contact with the nearest conical surface (16). Given the friction between the surface of conical surfaces (16) and water, the speed of water will be slowed in the immediate vicinity of these areas, which will facilitate the separation and migration of particles. Once captured by the conical surfaces (16), the cellulosic particles will migrate, under the effect of the centrifugal force, to the periphery, where they will be evacuated with the cellulosic fibers, either at the periphery of the apparatus, or at its center, according to the configuration chosen for the evacuation of these elements.

The filtrates pass between the conical surfaces to the center of the apparatus, where they are evacuated via a central outlet duct (11). The conical surfaces (16) are shown in drawing 3.

Another application: separation between short fibers and long fibers

Another possible application of the invention is a separation between short and long cellulose fibers. The holes or slots of the grid (s) (1) are sized to allow retention of the long fibers, while the short cellulose fibers manage to pass through the grid (s) (1).

Other complementary function: clarification of filtrates

Another possible application of the equipment having a rotating body is to ensure the clarification of the filtrates. In this application, not represented by the drawings, the process for purifying the paste is strictly identical to the process of the invention presented above. In a sedimentation zone downstream of the purification grids, the cellulose fibers sediment and are then extracted. The filtrates are conveyed to a clarification zone equipped with conical surfaces, from where, under the effect of the centrifugal force, a significant part of the charges sediment and are separated from the water. Their evacuation is done according to a process identical to that described for the fibers. Final observation

It is clearly stated that the description and drawings previously described illustrate the invention in a practical way but in no way constitute a limiting presentation. It will be possible to modify certain aspects or add certain functions without affecting the scope and spirit of the present invention.

Claims

1. Equipment for the purification of pulp put in aqueous fibrous suspension, characterized in that it comprises one or more grids (1), in parallel, provided with slots which allow the passage of the pulp fibers and prevent the passage of solid elements of larger dimensions, the said grid (s) (1) being animated (s) in a rotary movement generating a centrifugal force allowing the unclogging of the grid (s) ( s) (1) without the addition of a rotor or agitator, the elements of density greater than 1 sedimenting on the periphery of (s) the grid (s) (1) while the elements of lower density retained through the grid (s) (1) migrate towards the center of the grid (s) (1).

2. Equipment according to claim 1 and characterized in that it comprises, at the center of the grid (s) (1), openings (22) allowing the passage and evacuation of elements of density less than 1 previously retained by the grid (s) (1).

3. Equipment according to claim 2, characterized in that it comprises a pipe connected to the openings

(12) for the extraction of the separate elements without those being remixed with the paper pulp.

4. Equipment according to claim 1, characterized in that the grate (s) (1) have a conical shape, the admission of the paper pulp being carried out at near the top of the cone, on the inside, in order to guarantee contact between the paper pulp and the grid (s) (1).

5. Equipment according to claim 1, characterized in that the (the) grid (s) (1) comprise one or more fractures of angles (8) in steps, allowing the remixing of the paper pulp in contact with the ( the) grid (s) (1), thus limiting the formation of a fibrous mat on the surface of the grid (s) (1).

6. Equipment according to claim 1, characterized in that the profiles (7) constituting the (the) grid (s) (1) have an asymmetrical shape, in order to improve the rotational drive of the paper pulp and to facilitate its passage through the slots of the grid (s) (1).

7. Equipment according to claim 1, characterized in that the grid (s) (1) is extended on the upstream side of the flow by ribs (3) in the radial direction in order to improve the training in rotation of the dough near the grid (s) (1) and to facilitate the migration towards the periphery or towards the center of the particles which are retained by the grid (s) (1).

8. Equipment according to claim 1, characterized in that it comprises a fixed body, the rotation of the grid (s) (1) being ensured by an axis (15).

9. Equipment according to claim 1, characterized in that the grid (s) (1) is integral with a rotary body (2).

10. Equipment according to claim 9, characterized in that it comprises numerous radial walls (6) for, upstream of the grid (s) (1) to rotate the dough to be purified, on the downstream side from the grid (s) (1) thus recovering part of the kinetic energy of rotation contained by the purified pasta where the filtrates evacuated by the center of the equipment.

11. Equipment according to claim 5 and 10, characterized in that the radial walls (6) comprise openings facing the corner breaks (8) in steps, in order to help the remixing of the paper pulp.

12. Equipment - according to claim 9, characterized in that the elements of density greater than 1, retained by the grid (s) (1) and which migrate towards the periphery of the grid (s) ( 1), are extracted by a discharge pipe (4) at the periphery of the equipment, the size of the openings and the frequency of their opening being adapted to ensure thickening of the extracted elements.

13. Equipment according to claim 10 and 12, characterized in that the radial walls (6) have openings in the peripheral zone of the equipment, in order to resuspend the elements retained by the grid (s) (1) and which sediment towards the periphery, thus limiting the formation of deposits.

14. Equipment according to claim 9, characterized in that, on the one hand the cellulose fibers which pass through the slits of the grid (s) (1) then sediment on the periphery of the equipment in a sedimentation zone located downstream of the grid (s) (1) from which they are extracted by discharge lines (5) located on the periphery of the equipment, with permanent or sequential openings, in order to allow a thickening effect on the extracted pulp; on the other hand, the filtrates, after the sedimentation of the cellulose fibers, are conveyed to the center of the equipment from where they are then extracted from the apparatus by a central outlet pipe (11).

15. Equipment according to claim 10 and 14, characterized in that the radial walls (6) have openings at the periphery of the equipment, in order to put the cellulose fibers which sediment towards the periphery in suspension and thus avoid their deposition.

16. Equipment according to claims 9 and 14, characterized in that it comprises downstream of the

(des) grid (s) (1) a separation zone equipped with conical surfaces (16) of sedimentation, the effect of centrifugal force being used to separate filtrates and recover by sedimentation the cellulosic particles, including in particular the particles very small cellulosics.

17. Equipment according to claim 9, characterized in that it comprises a sedimentation zone downstream of the grid (s) (1) where the cellulose fibers sediment and are separated and extracted as well as a zone of clarification of filtrates, equipped with conical surfaces, intended to sediment and separate a significant proportion of the charges and small contaminants still present in the filtrates.