Production of a fibre material from plants with a high proportion of silicate for the production of paper and card

Abstract

The invention relates to a grinding tool for producing a fibre material from plants with a high proportion of silicate for the production of paper and card, said grinding tool having at least one stator disc (10) with elevations (12) and notches provided therein in the form of first and second slits (14, 16), which together form cutting edges for comminuting the plants, wherein the upper side of the elevations (12) has a hard material layer (20). The invention also relates to a method for producing a fibre material from plants with a high proportion of silicate for the production of paper and card by means of such a grinding tool.

Description

Production of a fiber material from plants with a high silicate content for the paper and Cardboard production

[0001] The present invention relates to a method and a device for producing a fiber material from plants with a high silicate content for paper and cardboard production.

[0002] Paper is made from fibers, 95% of which are currently derived from wood. The most important fiber is cellulose. This is predominantly obtained as fresh fiber through industrial forest management. Conifers such as spruce, fir, pine, and larch are frequently used. Volatile markets often result in long transport distances and thus high carbon dioxide emissions. Wood processing also requires significant energy and chemical inputs. At the same time, demand is growing, as paper-based packaging is increasingly being used as an alternative to plastic packaging and is already being successfully deployed in the food retail industry.

[0003] Attempts were therefore made early on to find alternatives to traditional woods for paper and cardboard production.

[0004] In Europe and America, annual plants such as wheat and rye are occasionally used to produce straw fiber. Grass varieties from North Africa, such as alpha and esparto grass, can also be used. In Japan, rice straw is still used, and in India, it's fast-growing bamboo.

[0005] The Silphium plant, especially the perennial Silphium (Silphium perfoliatum L), is also used in paper and cardboard production as an alternative to traditional wood.

[0006] However, it has been found that the material quality of the fiber structure and the material composition of the ingredients in most alternatives to traditional woods are subject to significant fluctuations. These fluctuations are due to the fact that these plants are harvested annually, and the respective weather and climatic conditions have a much greater influence than in traditional woods, where weather-related differences balance out over the several years of plant growth, thus ensuring a relatively consistent quality of the fiber raw material.In addition, many plants used in paper and cardboard production as an alternative to traditional wood have a very high silicate content as well as bast and seed components, which lead to a heavy load on the facilities used to process the plant material as a raw material for paper and cardboard production.

[0007] Against this background, the object of the present invention is to provide a method and a device that avoid or at least mitigate the disadvantages of the prior art. In particular, such a method and a device are suitable for the sustainable and large-scale production of a plant-based fiber material with a high silicate content for paper and cardboard production.

[0008] The object underlying the invention is achieved by a process for producing a fiber material from plants with a high silicate content for paper and cardboard production, which comprises the following steps: (1) Provision of digested plants with a high silicate content, (2) Preparation of an aqueous suspension from the digested plants, (3) Feeding the aqueous suspension to a grinding tool, (4) grinding the aqueous suspension to obtain a ground suspension, and (5) Dewatering the ground suspension to obtain a water-reduced fiber material, wherein at least part of the grinding tool has a hard material layer.

[0009] The object underlying the invention is further achieved by the use of a grinding tool for producing a fiber material from plants with a high silicate content for paper and cardboard production, wherein at least part of the grinding tool has a hard material layer.

[0010] A further subject of the present invention relates to a grinding tool for producing a fiber material from plants with a high silicate content for paper and cardboard production, which has at least one stator disc with elevations and notches provided therein in the form of first and second slots, which together form cutting edges for comminuting the plants, wherein the upper side of the elevations has a hard material layer.

[0011] The following features, advantages and embodiments apply equally to all subject matters of the invention, ie method, use and grinding tool.

[0012] The inventors have recognized that the high silicate content in plants that are generally suitable for paper and cardboard production, such as fiber plants, in particular Silphium perfoliatum L, does not allow for satisfactory processing using methods known in the art. Silicates, ie salts of orthosilicic acid (Si(OH)4) and their condensates, lead to The mineral, sand-like consistency of the granules causes severe abrasion of commercially available grinding equipment within a very short period of operation, rendering it unusable for further use. The hard coating according to the invention provides a remedy for this problem and ensures that the grinding tool according to the invention can be used permanently and with low wear over a long period of time. This significantly reduces the costs of paper and board production based on plants with a high silicate content.

[0013] The grinding tool according to the invention can be manufactured by modifying a commercially available deflake set, such as the HS105 set, which can be used on a deflake H1-G (both Hueber, Kulmbach, Germany).

[0014] The hard material layer can be applied to the grinding tool, e.g. to the elevations of the stator disk of the HS105 set, using methods known to those skilled in the art, e.g. by means of galvanization (e.g. diamond), thermal spraying (e.g. tungsten carbide), arc processes (e.g. aluminum titanium), PVD processes (e.g. titanium carbon nitride), etc.

[0015] In a further development of the invention, the hard material layer is formed from a material with a Mohs hardness of > 9.

[0016] This measure has the advantage of providing a material that meets the requirements for the production of a fibre material from plant materials with a high silicate content for paper and cardboard production.

[0017] The Mohs hardness is indicated by a value on the Mohs scale, a qualitative ordinal scale from 1 to 10, and determines the hardness of a mineral. It characterizes its scratch resistance by the ability of harder materials to scratch it. The Mohs hardness of a hard material can be determined, for example, by scratching a mineral surface with the mineral quartz, which has a rating of 7 on the Mohs scale, and the mineral apatite, which has a rating of 5 on the Mohs scale. If no surface change can be achieved with apatite, but quartz can, the tested material is placed between 5 and 7 on the scale.

[0018] In one embodiment of the invention, the material of the hard material layer is selected from the group consisting of: diamond, silicon carbide, tungsten carbide, titanium carbide, titanium nitride and boron nitride.

[0019] This measure has the advantage that preferred materials are provided which are fundamentally suitable for forming the hard material layer according to the invention, with diamond being particularly preferred.

[0020] In a further preferred embodiment, the material of the hard material layer comprises synthetic diamond grain, most preferably with a grain size D 252.

[0021] The inventors have determined that diamond grain with a grain size of D 252 is particularly suitable for forming a stable and wear-resistant hard material layer while simultaneously keeping the manufacturing costs of the grinding tool within limits. This also controls the production costs of the final product.

[0022] A grain size of D 252 means that the grains used have an equivalent diameter of 0.252 mm. The DIN 4022 standard, valid until 2017, and the DIN EN ISO 14688 standard, which has been in effect since then, are used to determine and classify grain size. Both standards use the equivalent diameter of particles, which represents a measure of the size of an irregularly shaped particle. Grain size can be determined by sieve analysis, sedimentation analysis, and optical methods.

[0023] In a further embodiment of the invention, the hard material layer has a layer thickness of approximately 0.3 mm ± 0.04 mm.

[0024] According to the inventors' findings, such a layer thickness, e.g. of a diamond coating, ensures sufficient abrasion resistance and a good grinding result.

[0025] According to one embodiment of the invention, the hard material layer is embedded in a nickel carrier, preferably over approximately half its layer thickness.

[0026] This measure ensures good adhesion of the hard material layer to the grinding tool and prevents abrasion of the coating during operation.

[0027] In one embodiment of the invention, the grinding tool has rotor and stator disks aligned with each other.

[0028] These can be rotor and stator disks of a commercially available deflake assembly modified according to the invention, such as the HS105 assembly for the deflake assembly H1-G (both Hueber, Kulmbach, Germany).

[0029] According to one embodiment variant, the second slots of the stator disk of the grinding tool according to the invention form cutting edges with the elevations which have a length of approximately 70 - 90 mm, preferably approximately 77 - 88 mm, and most preferably approximately 83 mm.

[0030] In the prior art stator disc of the HS105 set, the cut edges have a length of approximately 66 mm, which results in the fibers to be processed not being adequately distributed and transported in the refining zone. The inventors have recognized that the inventive length of the cut edges, which are longer than the cut edges of the stator disc of a commercially available deflake set, leads to an improvement in fiber quality. The inventive length, which influences the airflow to the refining edges and the transport into and out of the refining zone, significantly improves the processing quality.

[0031] According to a further development, the tool according to the invention additionally has a rotor disc with elevations and notches provided therein in the form of slots, which together form cutting edges for shredding the plants, wherein the upper side of the elevations of the rotor disc also has a hard material layer.

[0032] By this measure, not only the stator disc but also the rotor disc of the grinding tool is modified according to the invention and thus ensures additional hardness of the grinding surfaces and low wear of the tool and thus for a good grinding result.

[0033] According to a further development of the process according to the invention, the plants have a silicate content of > 8 wt.% in dry matter.

[0034] Plants with such a high silicate content lead to severe abrasion and thus wear in conventional milling tools and equipment, which makes large-scale paper and board production economically impossible. The invention provides an advantageous remedy for this problem. The silicate content in the dry mass of plants can be determined using methods known to those skilled in the art, for example, using X-ray methods. According to the invention, e 8 wt.% means 8, 9, 10, 11, 12, 13, 14, 15, 20, 25, 30, etc., wt.%.

[0035] In one embodiment of the invention, the plants are selected from the group consisting of: perennial silphium (Silphium perfoliatum L), rice straw, wheat straw, potato grass, reed, seaweed, algae.

[0036] This measure uses plants that are well suited for paper and cardboard production using the invention, are easy to cultivate and renewable, and thus also meet the requirements of the increasingly important sustainability criteria.

[0037] According to a further development of the process according to the invention, the aqueous suspension of digested plants produced in step (2) has a consistency of approximately 3.5% by weight of dry matter (DM).

[0038] This measure ensures that the suspension has an optimal consistency for the subsequent grinding process in order to achieve a particularly good process result.

[0039] In one embodiment of the process according to the invention, after step (2) and before step (3), the aqueous suspension from the digested plants is purified by separating impurities, in particular bast, seeds and stones.

[0040] When using alternatives to traditional woods in paper and board production, such as annually harvested plants such as perennial silphium, the harvested material contains relatively high levels of such contaminants. Without their separation, these would lead to stress and possibly damage to the milling mechanism, which is why the invention provides a remedy with this step.

[0041] It is understood that the features mentioned above and those to be explained below can be used not only in the combinations specified in each case, but also in other combinations or on their own, without departing from the scope of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] In the following, non-limiting embodiments are explained in detail with reference to the drawings. The features mentioned therein are considered to be part of the invention not only in relation to the specific examples, but also in isolated form. The drawings show: Fig. 1: a plan view of a stator disc modified according to the invention as part of the grinding tool; Fig. 2 is a view of a section through the stator disk modified according to the invention along a long slot; Fig. 3 is a view of a section through the stator disk modified according to the invention along a short slot; Fig. 4 is a view of a section through a coating according to the invention on the stator disk; Fig. 5 is a plan view of a rotor disk modified according to the invention as part of the grinding tool; Fig. 6 is a view of a section through the rotor disk modified according to the invention along a long slot; Fig. 7 is a sectional view of the stator and rotor discs according to the invention in their arrangement in the grinder; Fig. 8 is a flowchart with important steps in an embodiment of the method according to the invention. EXAMPLES OF IMPLEMENTATION

[0043] Figure 1 shows a stator disc 10 modified according to the invention as part of the grinding tool based on the HS105 end-flaker set and the H1-G descaler, Hueber, Kulmbach, Germany. The surface of the stator disc 10 has elevations 12 as grinding surfaces and notches provided therein in the form of longer slots 14 and shorter slots 16, which together form cutting edges for comminuting the plant material.

[0044] Figure 2 shows a section through the stator disk 10 along the line II-II in Figure 1, which runs through a longer slot 14. The base of the stator disk 10 is shown under the reference numeral 18. The upper side of the elevation 12 of the stator disk 10 has a diamond layer, for example formed from synthetic diamond grain, grain size D252, which is embedded in an underlying nickel carrier 22.

[0045] Figure 3 shows a sectional view through the stator disk 10 along the line III - III of Figure 1, which runs through a short slot 16. The top of the elevation 12 forms with the lateral wall of the short slot 16 a cutting edge 26 with a length of approximately 83 mm, indicated by a double arrow.

[0046] Figure 4 shows an enlargement of section IV shown in Figure 3, in which the diamond layer 20 and the underlying nickel carrier 22 on the upper side of the elevation 12 are illustrated.

[0047] Figure 5 shows the corresponding rotor disk 26 of the grinding tool, with corresponding elevations 28 and a slot 30.

[0048] Figure 6 shows a view of a section through the rotor disk 26 along the line VI - VI of Figure 5. The upper side of the elevation 28 is similarly provided with a diamond layer 20', embedded in a nickel carrier 22'.

[0049] Figure 7 shows the stator disc 10 and the rotor disc 28 aligned with each other in their arrangement in the grinder.

[0050] An embodiment of the method according to the invention, including preceding and subsequent steps, is described in more detail below. The most important steps are also illustrated in Figure 8.

[0051] Plants with a high silicate content, such as the perennial Silphium (Silphium perfoliatum L.), are chopped in the field according to specific specifications for piece length (5–25 mm) and then ensiled in a bunker silo. The raw material can also be temporarily stored in the field for defined periods of 0–14 days (field retting) and then used directly for processing.

[0052] The processing of the plant material takes place in three possible stages: i. Enzymatic pretreatment of the raw materials with laccases specifically designed for the delignification of non-woody plants (picea bio); ii. Hydrothermal digestion, depending on the raw material and quality, in the temperature range from 80 to 200°C and with pressure levels from 0 to 18 bar; iii. Hydrothermal digestion with chemical additives and blends thereof, depending according to the fiber quality requirements and the by-products to be produced (Na2CO3; Na3PO4; Na3PO4+ MgO; Na3PO4+ (NH4)2SO2; KHSO4; Ca3(PO4)2; KOH + NH3OH).

[0053] The pulp consistency is adjusted to 24% dry matter (TS) with water and fed into a pulper via a feed screw. The pulper is a container with a powerful mixer as a rotor-stator system. The rotor is equipped with cutting edges. The stator is designed as a sharp-edged perforated plate. The pulper's task is to break down the material-quality inhomogeneous mass of fiber bundles from annual and perennial plants, mix it, and make it pumpable so that the resulting suspension can be introduced into the subsequent process steps. The pulper serves to break down the qualitatively inhomogeneous fibers and fiber bundles for refining. When the fiber components of the raw material come into contact with water, their pores and capillaries absorb water, which increases the volume of the fibers.

[0054] Swollen fibers are used for subsequent refining, as this allows for greater fiberization and fibrillation of the material during the refining process. The suspension is first pumped / circulated / circulated in the pulper using a pump. Water and / or plant-based raw materials are added until a predetermined fill level is reached in the pulper, until the suspension reaches a target consistency of 3.5% dry matter.

[0055] The suspension is purified using a hydrocyclone. Partial amounts of the silicate and ash components, as well as heavy particles (impurities), contained in the plant-based raw material are separated / removed. This increases the efficiency of the milling process and extends the service life of the mill. The hydrocyclone also serves to separate / remove bast and seed components due to the higher density of these components compared to the desired fiber components. Remaining such components in the material stream would reduce the quality of the final product, for example, with regard to the quality of printing. In offset printing processes, bast and seed components significantly impair print quality and printing speed.

[0056] The purified suspension is fed into a grinding unit modified according to the invention (hard coating, extended cutting edge in the stator disk). A synthetic diamond grain, grain size D252, was selected for the coating of the rotor and stator disks of the grinding unit: Rotor HS105 (Hueber, Kulmbach, Germany) Assignment Grain size D 252 ZGNR = F 13.3898 BA = full surface (in the range 0300-172) D = 300 D1=~172 H = 142 T = 22 U = 10 R = 20 NNUT = 35 (8 wide x10 deep) W=~64 Angle = 30° Angle 1=5° (slot offset) Material = tool steel Stator HS105 (Hueber, Kulmbach, Germany) Occupancy Grain size D 252 ZGNR = F 13.3899C BA = full coating (in the range 0297 - 142) D = 297 D1 =~142 H = 142 T = 22 U = 10 NNUT=35 / 35 (8 / 5 wide x 10 deep) W=~77.5 Angle = 30° AngleH = 10° (groove offset) Material = tool steel.

[0057] The application takes place as a galvanic surface coating in a galvanic bath under coordination of the optimal production parameters in relation to the surface and shape to be coated.

[0058] The refining unit essentially fulfills two tasks. The length of the fibers is shortened by the refining process. The fiber length after refining is between 0.1 mm and 5 mm. This process is primarily controlled by the cutting angle of the refining set. controlled. During refining, the surface of the fibers is roughened (fibrillated), and the fiber material's ability to retain water is increased. The ratio of fiber fractions (coarse to fine, long to short) must remain stable / constant throughout the production process so that the subsequent fractionation can be adjusted with regard to the separation process (accept / reject). This is achieved through optimized refining with the core of the developed cutting assembly. Fiber quality (fiber lengths, fiber length distribution) is determined by laboratory fractionation.

[0059] The fibers can be optimally crushed with the grinding tool modified according to the invention and at the same time good edge stability is ensured.

[0060] Poor quality fibers are reground.

[0061] The suspension, i.e. the ground fiber, is subjected to fractionation in a subsequent process step. The feed volume to the fractionator is between 20 and 40 m 3 / h, and the consistency is 2-3% TS.

[0062] The fractionator consists of a screen basket and a rotating impeller rotor. Typical screen baskets can be perforated or slotted. Typical hole sizes are between 1-2 mm, while slots are usually between 0.1 mm and 0.7 mm. The ground suspension enters the interior of the screen basket. The so-called accept passes through the screen basket. Any reject remaining in the screen basket is continuously removed (5-10 m 3 / h; consistency: 3-4% TS). The streamlined rotors cause a pressure increase in front of the rotor blade, which creates a pumping effect. Behind the rotor blade, a negative pressure is created, which prevents the screen basket from clogging. During fractionation, a so-called fiber mat forms on the inside of the screen basket, which, in addition to the slot or hole perforation, forms a layer that also has a filtering effect and contributes to the separation of the material flow into accept and reject. The formation of the filter layer can be influenced by the speed of the rotor, the consistency of the suspension fed to the fractionator, the pressure conditions between the material inlet and the material outlet (accept, reject; Target: 50% to 50%) and the recirculation quantity (material that is returned to the pulper).

[0063] Depending on the quality requirements to be met by the fibers, a defined amount of the suspension is used as accept (15-30 m 3 / h; consistency: 2-3% TS) is fed into a dewatering device and then removed from the process as a transportable end product.

[0064] The fibers that do not meet the quality requirements are either pumped back into the storage container (so-called feed chest) upstream of the fractionation or returned to the pulper.

[0065] The material returned to the pulper undergoes the previously described process again, allowing any material that does not meet the desired quality requirements in terms of fiber properties to undergo all fiber processing steps again. This allows a significantly larger proportion of the plant-based raw material used to be processed into acceptable material suitable for paper production.

[0066] The speed of the feed pumps used and other devices integrated into the process flow that have rotating components is individually controlled depending on the desired volume flow.

[0067] Due to the very low water absorption capacity and the tendency of the fiber material to dewater, pipes that are as short as possible with bends no larger than 45° are essential to prevent clogging of the pipes and to ensure a continuous flow of material within the piping system.

[0068] The consistency of the medium being pumped is continuously monitored using optical measuring systems. The use of optical measuring systems offers advantages over mechanical measuring systems.

Claims

Patent claims 1. A process for producing a fiber material from plants with a high silicate content for paper and board production, comprising the following steps: (1) Provision of digested plants with a high silicate content, (2) Preparation of an aqueous suspension from the digested plants, (3) Feeding the aqueous suspension to a grinding tool, (4) grinding the aqueous suspension to obtain a ground suspension, and (5) Dewatering the ground suspension to obtain a water-reduced fiber material, characterized in that at least part of the grinding tool has a hard material layer.

2. Method according to claim 1, characterized in that the hard material layer is formed from a material with a Mohs hardness of > 9.

3. Method according to claim 2, characterized in that the material is selected from: diamond, silicon carbide, tungsten carbide, titanium carbide, titanium nitride and boron nitride.

4. Method according to claim 3, characterized in that the material comprises diamond grain, preferably synthetic diamond grain, with a grain size D 252.

5. Method according to one of the preceding claims, characterized in that the hard material layer has a layer thickness of approximately 0.3 mm ± 0.04 mm.

6. Method according to one of the preceding claims, characterized in that the hard material layer is embedded in a nickel carrier, preferably over approximately half its layer thickness.

7. Method according to one of the preceding claims, characterized in that the grinding tool has rotor and stator disks aligned with one another.

8. Method according to claim 7, characterized in that the stator disc has cut edges with a length of approximately 70 - 90 mm, more preferably approximately 77 - 88 mm, and most preferably approximately 83 mm.

9. Method according to one of the preceding claims, characterized in that the plants have a silicate content of > 8 wt.% in dry matter.

10. Method according to one of the preceding claims, characterized in that the plants are selected from the group consisting of: perennial silphium (Silphium perfoliatum L.), rice straw, wheat straw, potato grass, reed, seaweed, algae.

11. Method according to one of the preceding claims, characterized in that the aqueous suspension of digested plants prepared in step (2) has a consistency of approximately 3.5% by weight of dry matter.

12. Method according to one of the preceding claims, characterized in that after step (2) and before step (3) the aqueous suspension of the digested plants is purified by separating off impurities, in particular bast, seeds and stones.

13. Grinding tool for producing a fiber material from plants with a high silicate content for paper and cardboard production, which has at least one stator disc (10) with elevations (12) and notches provided therein in the form of first and second slots (14, 16), which together form cutting edges for shredding the plants, wherein the upper side of the elevations (12) has a hard material layer (20).

14. Grinding tool according to claim 13, characterized in that the at least second slots (16) form cutting edges (26) with the elevation, which have a length of approximately 70 - 90 mm, preferably of approximately 77 - 88 mm, and most preferably of approximately 83 mm.

15. Grinding tool according to claim 13 or 14, which additionally comprises a rotor disc (26) with elevations (28) and notches provided therein in the form of slots (30), which together form cutting edges for comminuting the plants, wherein the upper side of the elevations (28) has a hard material layer (20').

16. Grinding tool according to one of the preceding claims, characterized in that the hard material layer (20, 20') is formed from a material with a Mohs hardness of > 9, and preferably the material is selected from: diamond, silicon carbide, tungsten carbide, titanium carbide, titanium nitride and boron nitride.

17. Grinding tool according to claim 16, characterized in that the material comprises diamond grain, preferably synthetic diamond grain, with a grain size D 252.

18. Grinding tool according to one of the preceding claims, characterized in that the hard material layer (20, 20') has a layer thickness of approximately 0.3 mm ± 0.04 mm.

19. Grinding tool according to one of the preceding claims, characterized in that the hard material layer (20, 20') is embedded in a nickel carrier (22, 22'), preferably over approximately half its layer thickness.

20. Use of a grinding tool for producing a fiber material from plants with a high silicate content for paper and cardboard production, thereby characterized in that at least part of the grinding tool has a hard material layer.

21. Use according to claim 20, characterized in that the grinding tool is the grinding tool according to one of claims 13 to 19.

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