FI121887B - Mechanical pulp as well as system and method for manufacturing the mechanical pulp - Google Patents

Description

MECHANICAL MASS AND SYSTEM AND METHOD FOR MECHANICAL MASS

OBJECT OF THE INVENTION 5

The invention relates to mechanical pulp and to a system and method for producing mechanical pulp.

BACKGROUND OF THE INVENTION 10

The mechanical pulp is manufactured industrially by grinding or grinding wood raw material. Both types of pulp production require a considerable amount of refining energy, which results in particularly high energy costs during the production phase.

This invention is particularly directed to a process for making a pulp, wherein the fibrous feedstock to the process is in particulate form, for example as wood chips or the like. Traditionally there is no actual pre-fiberizer in the pulping process, but the first stage is ground to 20 chips. After the first stage grinding, the pulp moves to the second stage refiner. After these primary refiners, the pulp is sorted and a portion of the pulp is re-ground using a reject refiner.

The milling of the pulp is usually carried out in high consistency milling, i.e. 25 millimeters. HC milling in a disc refiner between two milled discs with profiled surfaces. In such a refiner, the sharpness is small, even only n.

^ 0.2 mm.

Another type of pulverizer used in pulping is the cone grinder.

g 30 In the cone grinder, the fiber raw material is fed to a refining zone S3 formed by a conical rotating rotor Q_ and a stator surrounding the rotor, where it is pulverized. This process is usually performed

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g as dilute mass treatment at about 4% consistency with very small blade pitch, ° near blade contact. The milling is based on the fact that, at such a small spacing of 35, the fiber is flattened and the water present in large quantities lubricates with sharpness.

However, such treatment is not suitable, for example, for the first stage grinding.

For example, energy consumption for LWC (Light Weight Coated) pulp is typically about 3 MWh / tonne for 5 pulps. Due to the energy intensity of the defibration process, means of reducing the amount of energy required per tonne of product, even by a few percent, can lead to significant savings in production costs.

BRIEF SUMMARY OF THE INVENTION

The object of the invention is to provide a solution to the aforementioned energy consumption problem so that the mechanical pulp can be manufactured with substantially lower energy consumption than the prior art.

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In a solution for the production of mechanical pulp according to the invention, a separate, low-energy pre-fiberization step is essential, whereby the energy consumption of one or more refiners used in pulping can be substantially reduced. In addition, the refining method of the solution consumes less refining energy compared to prior art solutions. In the milling step of the method according to an embodiment of the invention, the pre-fiberized pulp, which is already pre-fiberized, is preferably milled as a thick pulp so that the milling is preferably carried out at a larger blade spacing.

In order to accomplish the object of the invention, the πίθ ο ^ method according to the invention is essentially characterized by what is stated in the characterizing part of the preceding claim 1. The system of the invention is characterized by what is set forth in the characterizing part of the appended claim 4. The mechanical pulp according to the invention

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for use in a papermaking process is characterized in that is set forth in claim 10 appended hereto.

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Description of the drawings

The invention will now be described in more detail with reference to the accompanying drawings, in which Figure 1 shows an example of a system according to an embodiment of the invention, Figure 2 shows a pre-fiberizer according to an embodiment of the invention Fig. 5 is a front view of the refiner rotor of Fig. 4.

Detailed Description of the Invention 20

Figure 1 is a general view of an energy-saving mechanical pulping process according to a preferred embodiment of the invention. The chips in the cellulose-based raw material to be fed to the preheating vessel 1 are preferably chipped and screened so that the chips to be fed to the preheating vessel 1 are substantially elongated in shape. Typically, chips are not regular pieces, but may vary in size and shape.

9 For the sake of clarity, however, the shape of the chips may be described as a three-dimensional piece having at least three different dimensions: a first £ 30 length, a second length and a third length. The chips typically have at least one

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page longer than other pages. In addition, the two shorter sides S of chips are generally not the same length, but the second longest side of the chips, the so-called.

tn § the width of the chip is often larger than the shortest side of the chip, so called.

° Chip thickness. Without limiting the scope of the present invention in any way, the term "longest side", "second longest side" and "shortest side" may be used throughout this specification. However, it should be noted in this context 4 that the pages of the chips may not be smooth but may have irregularities and that the three-page definition referred to above does not always accurately reflect the shape of each chip.

Most preferably, the longest side of the chip (length of the chip) is at least twice, more preferably at least three or four times the length of the second longest side (the width of the chip).

The screened chips are preheated in the preheating tank 1 by, for example, steam generated in a mill-10 hat. The delay of the preheating tank 1, i.e. the average mass of the tank in the tank, is preferably about 3 to 6 minutes. Preferably, the chips from the preheating tank 1 are fed to a chips washer 2. The amount of adjustment is preferably made by means of a metering screw between the preheating tank 1 and the sweeper 2, which may be, for example, a no-15 screw. The purpose of the scrubber scrubber 2 is to remove or at least significantly reduce the amount of chips that have entered the system, such as sand that has entered the system with the chips. The removal of sand and similar non-chipping material is preferably performed before the chips are moved to the 20 pre-fiberizer 3 to allow the pre-fiberizer 3 blades to last longer in operational condition.

Preferably, the chips from the chips scrubber 2 are fed at a constant flow to the pre-fiberizer 3, which performs gentle pre-fiberization. The purpose of the pre-fiberization 25 is to treat the chips with low energy consumption in a form such that the chips can be energy efficiently pulverized by the actual refiners 6, 7. The pre-fiberising is explained in more detail with reference to Figures 2 and 3. the consistency of the incoming raw material g 30 is preferably 2-6%.

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S The location of the pre-fiberizer 3 is preferably located on a chip washer 2 and a water separator 4

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§ in order to avoid the need for separate dilutions and thickenings not included in the system due to pre-fiberization. The aforesaid pre-fiberizer 3 is a so-called "gently opening" chips, suitably operating in an aqueous phase. chipping device. In this application, stitching refers to an event 5 in which a chunk of chips becomes a much thinner, sticky piece than before. Such a single embroidered piece is preferably an average of ΙΟΙ5 mm long and about 0.2-0.8 mm wide.

Preferably, the pre-fiber exfoliates the chips from the outside inwards as if layer by layer so that the chip is gently "rolled out" into a stick. There are at least one, but more than one, pre-fiberizers 3 in the system. It is essential for pre-fiberization that the pre-fiber sticks fraction is formed with a particularly low energy consumption, preferably 10 up to 50 kWh / t, more preferably up to 40 kWh / t and most preferably up to 30 kWh / t. The refining of the low-energy staple fraction in the pre-fiberization is then carried out on the actual refiners 6,7 at a significantly lower energy consumption than would be required for the grinding of large chips.

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Some preferred examples of pre-fiberizer 3 are shown in more detail with reference to Figures 2 and 3. An alternative example of a pre-fiberizer 3 is further shown in connection with Figures 4 and 5.

Preferably, the quilted pulp is led from the pre-fiberizer 3 to a water separator 4 where the excess water is removed from the pulp before being fed to a pre-heater prior to actual milling.

The water separated by the water separator 4 is preferably recycled to the system so that the water is returned to the preheating tank 1, for example.

The water separator 4 may be a device according to the prior art, such as, for example, a screw surrounded by a perforated drum,

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The dipstick fraction is led through the water separators 4 preferably through a preheater 5 to a conical first stage refiner 6, in which the pressing roll 30 is performed with a large blade gap of 0.5 to 5 mm. milling stage

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in the pre-fiberizer 3, the chipped chips are compressed and rubbed in either one or S in two steps. This type of grinding consumes much

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§ less energy than previous solutions; the specific energy consumed by a cone refiner can be up to only about 500 kWh / t.

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In the event that the actual milling after the pre-fiberizing is carried out in two stages, the pulp is preferably passed from the first stage refiner 6 through the steam separator 9 to the second stage refiner 7, where the compression milling is performed for example as in the first 5 refining steps. The specific energy used by the refiner 6, 7 may be the same in both the first and second refining stages, but the specific energy used by the refiners may also vary between the first stage refiner 6 and the second stage refiner 7. After the second stage refining, the pulp is preferably passed from the second stage refiner 7 through the steam separator 10 to the latency removal vessel 8. If the second stage refining is completely omitted from the process, the pulp is preferably introduced into the latency removal vessel 8, preferably after the first stage refiner. After the latency removal tank 8, the pulp can be transferred to a sorting process, which separates the rejection fraction, which is ground by some prior art equipment. The treatment of the rejection fraction as not included in the invention is not described in more detail in this application.

Figure 2 is a sectional view of a preferred embodiment of the pre-fiberizer 3. As a pre-fiberizer 3 according to Fig. 2, a wrecking device having a three-stage sharpening known in the paper industry or the like can be used, which produces a crushing and at the same time grinding fiber. The pre-fiberizer comprises a stator S and a rotor R and associated defibration means. In a preferred embodiment of the invention, the defibrating means comprises a first blade 25 and a second blade, each second blade serving as a counterpart to the first blade. The distance between the first blade and the counterpiece relative to each other determines the sharpness.

sj- ί In the pre-fiberizer 3, the preheated chips are gently disintegrated into water by the flow of g 30, with a particularly low energy consumption, suitably only about 30 kWh / t. The consistency of the pulp entering the pre-fiberizer 3 is preferably 2-6%, most preferably 3-5%. There are 3 pre-fiberizers in the system

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§ at least one, but there may be more, for example two copies, o

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35 The pulp is fed to the pre-fiberizer 3 in the direction of rotation axis A of the rotor R therein. The outer surface of the rotor R and the inner surface of the stator S are generally conical in shape and form a processing zone Z of the diameter extending in the aforementioned feed direction, which is annular in shape substantially perpendicular to the axis of rotation of the rotor R. The sharpness in the zone Z is suitably in the range of 1 to 7 mm, most preferably in the range of 3 to 5 mm.

The zone Z may consist of successive sub-zones Z1, Z2 and Z3 through which the fibrous material passes successively. Advantageously, the clearances are then gradually reduced in the feed direction so that the clearance in the first sub-zone Z1 is greatest and in the third sub-zone Z3 is the smallest. For example, the clearances may be 5 mm (± 1-2 mm) in the first sub-zone Z1, 4 mm (± 1-2 mm) in the second sub-zone Z2 and 3 mm (± 1-2 mm) in the third sub-zone Z3 ). It can be seen from Figure 2 that the sub-zones can be oriented in a 15 axial direction at a shallower angle to the axis of rotation than the general cone shape. In the case shown, the subzones Z1, Z2 and Z3 are stepped relative to each other such that there is a radial passage between two successive subzones through which the mass to be processed is transferred to the next subzone.

In the working zone Z, the ridges of the same blade surface are substantially parallel, and the ridges of the opposing blades are preferably slightly transverse, i.e. at a small angle to each other in the axial direction (axis of rotation). This is preferably the case for all sub-zones 25 when the processing zone has several sub-zones.

^ There may be more sub-zones than the three ™ shown in Figure 2. For example, pre-fiberizers 3 may be used in which the conical o-rotor R and the stator S form, for example, four or five treatment zones located in steps.

Figures 3a-3b show a preferred embodiment of the pre-fiberizer 3

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rotor sharpening, which is well suited for chip chipping. S The pre-fiberizer 3 may resemble the pre-fiberizer 3 shown in Figure 2

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§ the so-called "pulp industry" oksamurskainta. Fig. 3a shows a general view of the rotor R. Fig. 3b shows a preferred blade angle of the defibration means R.1 of the rotor R according to the embodiment of Fig. 3a 35 with respect to the rotor center or counterpart, such as 8 counter blades. In a preferred embodiment of the invention, the defibrating means comprises a first blade R.1 and a second blade (not shown in Figures 3), each second blade serving as a counterpart to the first blade R.1. The distance 5 between the first blade and the counterpart defines the sharpness.

When using the sharpening of the pre-fiberizer 3 according to Figures 3a to 3b, the elongated chips are introduced into the space between the blade R.1 and its counterpart 10 in a dilute, preferably 2-6% consistency, and most preferably 3-5% consistency. Due to the abundant amount of water, the elongated chips tend to be oriented substantially in the direction of flow, which makes the pre-fiberization more efficient, so that the blade R.1 together with the counterpart gently peel the chips into a dripping fraction with low energy consumption.

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The space between the counterpart and the rotor R, into which the chips are guided by the flow, is preferably large initially, for example at a height of about 10-20 mm, gradually narrowing so that the blade gap is preferably about 2-6 mm towards the end of the pre-fiber. Rotor R

Preferably, the sharpening is substantially higher than the sharpening of the stator acting as a counterpart, and less sharp. The rotor blades R.1, together with the counterpart, suitably provide both clamping and abrasive action.

The edges of the rotor R and the counterpart form a play angle α, preferably between 0 ° and 40 °, and more preferably between 5 ° and 30 °. To the best advantage

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this cutting angle α (shown in Fig. 3b) is formed such that

the edges of the counterpart (not shown in Figures 3) are straight and the R of the rotor

^ the edges are oblique. However, the angle may also be formed such that the rotor R of g 30 has straight edges and the counterpart has oblique edges, or that both the counterpart and rotor R have oblique edges. The speed and direction of rotation of the rotor R S can be used as a control variable as desired

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§ to obtain a pulp, o C \ l 35 By using a shear angle α of this magnitude, the handling of the raw material during prewatering is therefore more gentle, which results in the chipping of the chips so that little damage to the fibers is necessarily required. In addition, the preferred cutting ratio α of the rotor R and its counterpart results in a specific mass moving pumping effect 5. By adjusting said pumping effect, the amount of pulp through the pre-fiberizer 3 can be influenced in a desired manner. In practice, this can be done, for example, by influencing the rotation speed and / or the direction of rotation of the rotor R so as to produce the desired amount of retention or pumping action.

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In addition to these examples shown in Figs. 2-3, the pre-fiberizer 3 may also be, for example, a cone grinder 21 (shown in Figs. 4-5) whose sharpening consists of a low tooth retaining outer blade and a few high tooth rotor blades.

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Fig. 4 shows an example of a cone refiner 21 which is preferably used as a first stage refiner 6 and / or a second stage refiner 7 in the system according to the invention. The cone refiner 21 shown in Fig. 4 is also suitable as a pre-fibrator 3 with parameters different from the main refiners. S and rotor R and defibrating means. In a preferred embodiment of the invention, the defibrating means comprises a first blade and a second blade serving as a counterpart to the first blade. The distance between the first blade and the counterpiece relative to each other defines a sharpness of 25.

The milling of the first stage refiner 6 and the second stage refiner 7o is a pulp mill with a pulp consistency of at least 10%, preferably at least 18%. The milling can also be carried out in an even drier environment of g 30, whereby the consistency of the pulp may be at least 30%, e.g.

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about 50%. The consistency of the pulp entering the milling process is preferably controlled by feeding it into the wood raw material entering the mill 6, 7

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g suitable amount of water. If the cone grinder 21 is used as the pre-fiberizer 3, the pulp is suitably led to the cone grinder 21 acting as the pre-fiberizer 3 with 35 wash water at a 2-6% consistency.

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The cone refiner 21 comprises a rotor R arranged to rotate about the axis A inside the stator S and comprising blades arranged on the periphery of the rotor opposite the stator. Hereby, an axially extending annular refining space 22 is formed between the rotor and the stator, with a sharp clearance between the blades of the rotor 5R and the inner surface of the stator S where the refining takes place. The viscous mass is brought into focus thanks to the centrifugal force caused by the rotor.

The feeder means 11 of the refiner is arranged to supply a thick mass 10 to the grinding space 22. The sharpness gap is suitably quite large, about 0.5 to 5 mm, preferably 1 to 3 mm. Opposite surfaces (grinding surface of rotor blade and inner surface of stator) have sufficient roughness / fine serration to provide sufficient friction to the intervening mass. In this way, shear forces are formed in the pulp and the fibers also rub against one another at a sharp interval. Thus, the pulping energy can be applied to the pulp at a good efficiency.

Wood-based raw material, which is already partially ground esikuiduttimella 3 (or the first stage refiner) pulp is fed in the direction of the arrow A to the first end of the rotor, or the upstream end of the refining zone 20, for example a feed screw. At the beginning of the grinding space between the rotor and the stator are crushing teeth 12 attached to the rotor, which are intended to reduce the feedstock before entering the actual milling space where it is pulverized. The material to be refined passes axially in the refining space between the rotor and the stator for a certain residence time, after which it is taken out of the refiner as a refined pulp. The residence time in such a cone grinder is longer

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^ than with conventional disc refiners, where centrifugal force tends to move o mass away and is unable to press it into the refining zone.

Fig. 5 shows an example of a rotor of a conical refiner of Fig. 4, as seen from the upstream end of the refining zone. The rotor of the refiner (g) according to the example is characterized by its circumferential split

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g axial blades 13, between which are formed the ridges 14, the bottom of which is formed by the rotor R body. The thermal energy 35 produced by the pulping mill converts the water in the pulp into steam, whereby the axes 14 extending from the feed end to the outlet end direct the steam 11 out of the milling zone. The blades 13 and the grooves 14 are angled outwardly in accordance with the conicity of the rotor R. The height of the blades 13 from the body of the rotor R, i.e. the depth of the passages 14, can be, for example, 5 to 15 mm, preferably about 10 mm.

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It is further typical of the rotor R sol 14 that when the cone refiner acts as a first stage refiner 6 or a second stage refiner 7, the solenoid 14 preferably has no obstructions known as "dikes" known from low consistency grinding; at the end (outlet) of the rotor, so that the steam generated during the milling can pass substantially unobstructed to the end of the rotor and out of the milling zone. In this way, the refining energy is applied to the mechanical shaping of the pulp in the refining space so that the energy-consuming steam generation from the water in the pulp is minimized. However, especially when acting as a pre-fiberizer 3, the solenoid rotor sol may also have these so-called dams.

The total need for refining energy is substantially lower with the overall solution according to the invention. For example, the total refining energy required to produce LWC quality 20 may be about half, or less than, half of the refining energy requirement of prior art solutions, i.e. up to about 900-1100 kWh / t. If only one actual refiner 6 is used in addition to the pre-fiberizer 3, the required refining energy may be even lower.

The mechanical pulp described above by the process and system according to a preferred embodiment of the invention may be used, for example, in a paper product manufacturing process.

The invention is not limited to Figures 1-5 and the description above

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but may be modified within the scope of the appended claims.

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Claims (10)

A process for the preparation of a mechanical pulp, which comprises washing the cellulose-based raw material in a chips scrubber (2), dewatering the washed 5 raw material in a water separator (4), and milling the pulp with at least one refiner (6) comprising at least a first blade and the gap between the first blade and the counterpiece defining the sharpness, characterized in that the method further comprises pre-fiberizing the raw material with at least one 10 pre-fiberizer (3) using 2 to 6 mm sharpness and 2 to 6% consistency before grinding the pulp (6). . Method according to Claim 1, characterized in that the raw material is washed in a chips scrubber (2) before the pre-dewatering, and that the amount of water is reduced by the water separator (4) after the pre-dewatering. Method according to claim 1 or 2, characterized in that the raw material is milled with said at least one refiner (6) 20 using a sharpness of 0.5 to 5 mm and a raw material having a consistency of more than 10%. A system for producing mechanical pulp from a cellulose-based raw material comprising a scrubber (2), a water separator (4), and at least one refiner (6) comprising a refining chamber and at least a first blade and a counterpart, wherein the first blade and counterpart The gap defines the sharpness in said at least one refiner (6), characterized in that the system includes a pre-fiberizer (3) located before the refiner (6), comprising a refining space and at least a first g 30 blade and counterpart; , which is 1-7 mm, and wherein said g precursor (3) has feed means arranged to supply LO g of raw material having a consistency of 2 to 6% into the refiner refining space. o (M System according to claim 4, characterized in that said pre-fiberizer (3) is disposed between the scrubber (2) and the water separator (4). A system according to claim 4 or 5, characterized in that said grinding gap of the refiner (6) is 0.5 mm to 5 mm and that said at least one refiner (6) has feed means arranged to supply to said refining space raw material which consistency greater than 10%. 10 A system according to any one of claims 4 to 6, characterized in that the pre-fiberizer (3) has a refining zone (Z) consisting of at least three successive sub-zones (Z1), (Z2) and (Z3) each having a certain sharpness and decreasing incrementally in the 15 feed directions so that the first sub-zone (Z1) has the highest sharpness and the third sub-zone (Z3) the smallest. System according to one of Claims 4 to 7, characterized in that said at least one refiner (6) is a cone refiner. System according to one of Claims 4 to 8, characterized in that the system further comprises a second refiner (7) for carrying out the second refining step on the pulverized pulp formed by the first refiner (6). δ Use of a mechanical pulp made by the process according to any one of claims 1 to 3, or produced by a system according to any one of claims 4 to 9, in the process of manufacturing a paper product g 30. CL δ oo m σ> o o {M