Method for producing fiber from shredded wood and arrangement for implementing the method for producing fiber from shredded wood

Abstract

The invention, which relates to a method for producing fiber from shredded wood and an arrangement for implementing the method for producing fiber from shredded wood, is based on the objective of providing a solution for achieving simple and improved plasticization of shredded wood, in particular waste wood chips, whereby the energy requirement should not increase or should not increase significantly compared to the plasticization of fresh wood chips, and whereby the service life of the grinding discs (3, 4) of the refiner (1) should not be reduced or should not be reduced significantly when using waste wood chips. This objective is achieved according to the method by continuously evacuating any air trapped in the shredded wood by means of a negative pressure acting on the shredded wood before the plasticization of the shredded wood in the digester (8).

Description

[0001] The invention relates to a method for producing fiber from shredded wood, in which shredded wood, in particular wood chips, are introduced into at least one provided cooker in which the shredded wood is plasticized by the action of hot steam, wherein the plasticized wood pretreated in this way is subsequently introduced into a provided refiner and is defibrated in the refiner in a region between provided grinding discs and fiber is produced and wherein the fiber produced in this way is discharged from the refiner.

[0002] The invention relates to an arrangement for implementing the process for producing pulp from shredded wood, which comprises at least one digester and one refiner.

[0003] The industrial production of fiber from lignocellulose is well known in the art. Fiber refers to a material consisting of fibers that is obtained and further processed, for example, in the production of wood-based materials, particularly wood fiberboards such as medium-density fiberboard (MDF) or wood fiber insulation boards. Such fibers are usually obtained from the raw material wood through mechanical and / or chemical pulping processes. Lignocellulose is known to form the cell wall of woody plants and serve as a structural framework for these plants.

[0004] Regarding the raw material wood, it is known that the wood can be plasticized through steam treatment, which makes it soft, supple, and less brittle for subsequent processing, for example, bending or pressing the wood. In this context, a process known as steam forming is also known, which is used, for example, in the production of seating furniture and is familiar from cooperage.

[0005] So-called refiners are known from the prior art. These are machines enclosed in a housing and are used, for example, in the wood-based materials industry for the production of wood pulp and in the paper industry for the production of mechanical pulp. Such refiners mechanically shred wood chips, for example, producing pulp that is discharged from the refiner.

[0006] The well-known industrial production of lignocellulosic fibers is a continuous process. It begins, for example, with the hydrothermal pretreatment of so-called wood chips in a pre-steamer, where they are heated to 70 to 80 °C. Wood chips, or wood chips, are wood that has been shredded using cutting tools.

[0007] From the pre-steamer, the wood chips pass through a conveyor and dewatering screw into a preheater, also known as a cooker. In this preheater, the wood chips are plasticized using generated steam for 2 to 8 minutes. The steam has a temperature between 150 °C and 210 °C and a pressure between 6 bar and 16 bar. In one specific design, the steam temperature is between 158.8 °C and 201.4 °C.

[0008] A second screw, a so-called transport screw, transports the wood chips to the refiner for defibration or fiber production. In the refiner, the prepared wood chips are defibrated, for example, between a grinding disk of a rotor rotating at approximately 3000 rpm and a grinding disk of an associated stator. The fibers then travel from the so-called annular space of the refiner, which is also referred to as the collecting channel, via the radially or tangentially arranged outlet and the blowline to the dryer. In the blowline, the produced fibers can be coated with glue. The fibers are transported in the annular space to the radial outlet by means of appropriate carriers and are also accelerated by the prevailing steam pressure.

[0009] The following describes an example of a fiberization process in a refiner in more detail. For example, so-called flat-disk pressure refiners are currently used exclusively for fiber production for MDF boards. An example of this state of the art can be found in Roll, H. (2010): Optimization of fiber extraction in the refiner. Energy-relevant aspects of refiner disk technology in MDF production with consideration of fiber quality. Holz-Zentralblatt, No. 16, pp. 423-424.

[0010] This refiner consists of a housing with a rotor and a stator, both equipped with or connected to a profiled grinding disc. The grinding discs are mounted so that the profiles of the grinding discs face each other. The grinding discs essentially have two zones with varying degrees of fineness of profiling, referred to as the inner crusher zone and the outer grinding zone. A grinding gap of 0.2 mm is typically used, which is the distance between the profiled sides of the grinding discs in the outer grinding zone. This gap varies depending on the fiber quality to be produced, the wear of the grinding discs, and the nature of the raw material.

[0011] The fiber production process begins with the transport of the wood chips pretreated in the digester from the digester by means of a conveyor screw, for example through an opening in the center of the stator, into the refiner.

[0012] In the refiner, the wood chips pretreated in the digester are captured by the inner crushing zone of the rotor's grinding disc and moved in a circular and centrifugal motion. The wood chips pass through the inner crushing zones of the grinding discs and are pre-crushed by the so-called pre-crushing bars of the grinding discs. The pre-crushed material then enters the channels of the outer grinding zone, which are interrupted by so-called dams, forcing the pre-crushed material into the grinding gap. Due to the rotating movement of at least one grinding disc, the pre-crushed material alternately crosses the bars and the channels of the grinding discs at a specific crossing frequency, with each channel being defined by bars.The rotation of the grinding disc of the rotor thus causes a high-frequency compression and relief of the material in the area of ​​the outer grinding zone, which leads to the separation or unraveling of the fibers of the pre-treated and pre-shredded material.

[0013] This crossing frequency increases toward the periphery of the grinding discs with increasing number of ribs or fineness of the profile. As the produced fibers emerge from the grinding gap of the outer grinding zone or the channels of the grinding discs, the raw material, now in fiber form, enters the annular space of the refiner housing. Accelerated by rotor-mounted carriers and by means of a prevailing steam pressure, the produced fibers are transported through a pipe arranged radially or tangentially on the refiner housing, through the blowline, where the fibers can be coated with a glue, and into the dryer.

[0014] It is also known that the energy consumption of the refiner and the fiber quality are determined by several factors: - Dimension of the grinding gap, - Profiling of the grinding discs, - Diameter of the grinding discs, - Design and dimensioning of the grinding disc zones, - Movement of the fibers in the annular space and the discharge of the fibers from the refiner and - Plasticization of the starting material.

[0015] One of the most important factors influencing the quality of the fibers, in addition to the plasticization of the starting material, is the grinding gap, which can be adjusted during the ongoing production process of the fibers in the so-called refining process.

[0016] The plasticization of the wood chips in the digester depends on the particle size, the bulk density (depending on the wood species), the temperature, and the moisture content of the wood chips. Furthermore, the plasticization of the wood chips depends on the pressure or temperature in the digester, as well as the residence time of the wood chips in the digester. This plasticization causes the softening of the lignin, thereby reducing the forces required to separate the fibers. Incomplete plasticization, due to low moisture content of the wood chips or softening of the cell structure of the wood chips, leads to material fragmentation between the grinding discs in the refiner, thus producing a high proportion of splinters, dust, and short fibers.

[0017] Conventional plant technology with the corresponding technical limits and the digestion parameters dependent on the speed of the continuous overall process only allows for a limited compensation of temperature and moisture fluctuations in the wood chips, which leads to differences in plasticization.

[0018] It is well known that so-called waste wood chips have the disadvantage that they are at least partially insufficiently plasticized in the digester and thus insufficiently prepared for the subsequent fiber production process. The reason for this is that the moisture content of such waste wood chips is lower than that of fresh wood chips, which are also referred to as green wood chips. The moisture content of green wood chips ranges approximately between 60% and 160% and depends on the season, while the moisture content of waste wood chips ranges approximately between 6% and 15%.

[0019] This increases the brittleness and stiffness of the waste wood chips, which leads to a deterioration in production results during the fiber production process. Increased dust formation, as well as an increased formation of splinters and short fibers during fiber production, are particularly disadvantageous. Furthermore, it leads to increased wear on the grinding discs.

[0020] The term "waste wood chips" refers to wood or waste wood according to the Waste Wood Ordinance, particularly waste wood category AI. Such wood has usually been kiln-dried.

[0021] To increase the moisture content of older wood chips or waste wood chips before feeding them into the digester, previous studies have relied on 24 hours of water storage of the waste wood chips, as described in Erbreich, Markus (2004): The processing and reuse of waste wood for the production of medium-density fiberboard (MDF). Dissertation. University of Hamburg, Institute of Biology, Hamburg.

[0022] During the fiber production or defibration of these pretreated waste wood chips, the long fiber content could be increased by 35% for old pine wood and by 49% for fresh pine wood under low digestion conditions, at an overpressure of 3.9 bar and a residence time of 3 minutes in the digester, compared to waste wood chips not stored in water.

[0023] A similar result was observed when storing the waste wood chips in water containing 5% sodium sulfite for 24 hours. However, a 24-hour water storage after wood chip production from roundwood and before fiberization in a continuous industrial process with a fiber throughput of 30 t / h involves the intermediate storage of several hundred tons of waste wood chips.

[0024] One way to significantly accelerate the absorption of liquids by wood compared to 24-hour water immersion has so far only been used in pressure impregnation processes for the introduction of wood preservatives into wood. Well-known processes in this area include vacuum pressure impregnation, alternating pressure impregnation, and double vacuum impregnation.

[0025] The functionality of these procedures consists of two process steps explained below: First, the wood to be impregnated is placed in a closed container under a vacuum. This at least partially removes the air contained in the wood workpiece. In the next step, the container is filled with the appropriate impregnating agent and pressurized. By evacuating it beforehand and reducing the amount of air in the wood workpiece, the impregnating agent can penetrate the wood workpiece more easily during the pressure build-up process, resulting in a shortening of the process time, as disclosed in Wenderdel, C.; Laßlberger, G.; Fischer, M.; Krug, D. (2011): Spruce wood impregnated to the core - fire retardant developed for woods that are very difficult to impregnate - test results impress, Holz-Zentralblatt 137 (35), pp. 846-847.

[0026] DE 197 46 383 A1 relates to a method and apparatus for producing fiberboards, as well as fiberboards produced by the method. The aim is to provide a solution suitable for extremely economical production of such boards with high yields in a continuous flow of the production material between the starting material and the finished product, enabling a reduction in production costs through the highest possible degree of mechanization and automation, and resulting in a product with extremely favorable technical and physical properties.

[0027] DE 195 09 152 A1 concerns a process for the recovery of chips and fibers from wood-based material residues, old furniture, production residues, waste, and other materials containing wood-based materials. The objective is to provide a solution that makes the process environmentally friendly and economically feasible. Furthermore, this process is intended to recover high-quality chip and fiber material (secondary chips or secondary fibers).To solve this problem, a method is specified in which the wood material pieces are broken down at an elevated temperature, wherein in a first step the wood material pieces are impregnated with an impregnation or impregnation solution and pre-swollen until they have absorbed at least 50% of their own weight in impregnation solution and wherein in a second step the impregnated wood material pieces are heated to 80°C to 120°C and wherein the wood material thus broken down is then sorted by sieving and / or air classification.

[0028] EP 2 304 099 B1 discloses a device for wetting fibrous material, in particular wood, wood chips, and waste paper. The object is to provide devices that enable the simple and effective wetting of wood chips or waste paper in bale form.

[0029] Using the described device, it is possible to quickly and effectively wet fibrous material, whether in the form of wood chips or baled waste paper, with a liquid. This utilizes the elasticity of the fibers and the change in the volume of the fiber cavities due to changing pressures. In pulp production, the following principle applies: the wetter the wood chips blown into the digester, the higher the filling density and thus the throughput of the digester. Furthermore, by using the disclosed device, filling the digester with cooking liquor can begin much earlier, since the wood chips do not float when the cooking liquor is pumped in if their moisture content is sufficiently high.If hot cooking liquor is used to wet the wood chips according to the described process, the cooking time is also significantly reduced, since hot cooking liquor is not only located between the fibers, but also in the fiber interior (lumen = fiber cavity).

[0030] EP 0 826 471 A2 relates to a process for processing fiberboard waste using a dry or wet process without refining units. The aim is to process the fiberboard waste in such a way that fibers almost equivalent to natural wood are produced and can thus be proportionally added back into the production process. Furthermore, negative impacts on fiberboard production are to be avoided and the quality of the final product is to be improved. This goal is achieved by defibrating the shredded fiberboard waste after a pressureless heat treatment in a liquid medium and subsequent pressure treatment by steam expansion. The pressure difference achieved during such steam expansion gently breaks the waste down into individual fibers. Electrical energy is not required for defibration.The fibers produced using the described process exhibit a very uniform structure under the microscope—similar to fibers made from wood—but do not have such strongly developed fibrillated fiber ends. The surface of the remaining fiber bundles is considerably smoother than that of pure wood fibers. The mat thickness after the fourdrinier machine is approximately thinner than that of a pure wood fiber mat.

[0031] AT 009 060 U1 discloses a method and a device for processing starting material for the production of pulp, semi-pulp, or thermomechanical wood pulps, wherein the starting material, in particular wood chips, is mixed with liquid and subjected to a subsequent pulping process. It is provided that a device for applying a negative pressure to the starting material mixed with liquid is provided in the conveying path, thereby enabling reliable impregnation of the starting material with minimal effort.

[0032] WO 2015 / 011 279 A2 relates to a device for generating energy from biomass, comprising a heat recovery device for generating heat and a drying device, as well as a method for generating energy from biomass, in particular from fibrous biomass, preferably from wood fibers, comprising the step of generating heat by burning shredded biomass residues, in particular wood dust. Furthermore, a device and a method for the material utilization of fibers from biomass, in particular wood, are disclosed.

[0033] Thus, the disadvantages of the known state of the art are: - Waste wood chips have a significantly lower moisture content (6% to 15%) before defibration than fresh wood chips (60% to 160%). As a result, the brittleness and stiffness of waste wood chips are higher than that of fresh wood. - Waste wood chips lead to lower fiber quality during defibration due to incomplete plasticization (high dust, splinter and short fiber content), - Waste wood chips lead to increased energy requirements of the refiner during defibration, - The wear and tear of the grinding discs on the rotor and stator is greater when using waste wood chips than when using fresh wood chips, - A 24-hour water storage of waste wood chips is associated with the logistical challenge of intermediate storage of several hundred tons of wood chips in the case of industrial throughputs in fiber production (fiber production).

[0034] Thus, there is a need for an improved process and arrangement for producing pulp from shredded wood.

[0035] The object of the invention is to provide a method for producing fiber from shredded wood and a system for implementing the method for producing fiber from shredded wood, thereby achieving a simple and improved plasticization of shredded wood, in particular waste wood chips, while maintaining the same energy requirements as for the plasticization of fresh wood chips. In this case, the plasticization occurs as a result of moistening through the condensation of steam in the wood chips.

[0036] Furthermore, the service life of the refiner's grinding discs should not be shortened or not significantly shortened when using waste wood chips.

[0037] The problem is solved by a method having the features according to claim 1 of the independent patent claims. Further developments are specified in the dependent patent claims.

[0038] The general approach of the inventive method for producing fiber from shredded wood, such as waste wood chips, consists in the use of negative pressure to continuously evacuate air trapped in the shredded wood, for example in a vacuum, in order to reduce the diffusion resistance of the shredded wood to be processed, such as waste wood chips, to penetrating steam, such as saturated steam in a digester. It is known to refer to a gas whose state lies near the so-called dew line as superheated steam. The mixture of a boiling liquid and the gas in equilibrium with it is called wet steam. A gas in a state on the dew line is referred to as saturated steam.

[0039] Therefore, prior to the plasticization of the shredded wood or wood chips in the digester, a continuous evacuation of the air stored in the shredded wood takes place in an area upstream of the digester in the process direction by means of a negative pressure acting on the shredded wood. Since the inventive production of fiber from shredded wood is a continuous production process, the evacuation of the air stored in the shredded wood also takes place continuously and does not require any interruption in the transport of the shredded wood along the process direction.

[0040] Due to its lower moisture content in the range between 6% and 15%, waste wood chips or shredded wood cannot be plasticized in the digester or cannot be plasticized to a sufficient extent and thus made sufficiently soft and supple for subsequent fiber production or defibration in a refiner.

[0041] This disadvantage in the processing of stored shredded wood or waste wood chips is overcome according to the invention by improving the ability of the waste wood chips to absorb moisture in the digester and thus to be sufficiently plasticized by at least partially removing the air trapped in the stored shredded wood or waste wood chips prior to plasticization. In the following, only the terms "wood chips," "fresh wood chips," or "waste wood chips" will be used, which include the terms shredded wood, freshly shredded wood, and stored shredded wood.

[0042] The at least partial removal of stored air or air inclusions from the waste wood chips is achieved by exposing the waste wood chips to a predetermined negative pressure for a predetermined period of time.

[0043] Such a time period depends, for example, on the size of an evacuable space in which the negative pressure is created to remove the trapped air. Furthermore, this time period depends on the quantity of waste wood chips introduced into this evacuable space and the magnitude of the negative pressure created. In general, a larger quantity of waste wood chips introduced into the evacuable space requires more time to remove the trapped air, and a higher negative pressure requires less time to remove the trapped air.

[0044] It is intended that the evacuation of the air stored in the shredded wood takes place by means of a negative pressure over a period of 5 s to 300 s, in particular over a period of 5 s to 200 s, further in particular over a period of 5 s to 20 s.

[0045] In order for the air trapped in the shredded wood to escape due to the negative pressure, the shredded wood must be exposed to the negative pressure in the sealed and evacuated space for a specified minimum period of time. Since the amount of trapped air no longer decreases significantly after a certain time and the fiber production process is a continuous one, the evacuation process is not unnecessarily extended. A suitable residence time for the shredded wood in the sealed and evacuated space for optimal process control is therefore in the range of 5 s to 300 s.

[0046] It is further provided that the evacuation of the air stored in the shredded wood takes place by means of a negative pressure in the range between 50 mbar and 950 mbar, in particular in a range between 100 mbar and 450 mbar, further in particular at 200 mbar.

[0047] By at least partially removing trapped air, the moisture absorption of the waste wood chips in the digester is significantly improved, while at the same time the result of the plasticization of the waste wood chips in the digester and consequently the result of the production of the fiber in the refiner is improved.

[0048] Thus, even when using waste wood chips to produce fiber, it is possible to achieve a quality of the produced fiber that can otherwise only be achieved when using fresh wood chips.

[0049] Furthermore, the invention provides for the evacuation of the air stored in the shredded wood to take place by means of an evacuable space provided upstream of the digester in the process direction. Such an evacuable space is, for example, a vacuum-tight container or an at least partially vacuum-tight unit.

[0050] The process direction is understood to be the direction of the shredded wood or wood chips transported through the fiber production system in their various processing states. The process direction runs from a feed of the wood chips, for example, from a storage container, through at least the digester and the refiner with its grinding discs to a fiber output. The digester is arranged upstream of the refiner in this process direction. The evacuatable chamber provided according to the invention, in which a negative pressure can be generated, is arranged upstream of the digester in this process direction.

[0051] This arrangement of the evacuable space provided according to the invention at an inlet opening of the digester makes it possible to transfer the waste wood chips pretreated according to the invention in the evacuable space, after at least partial evacuation or reduction of trapped air in the waste wood chips, directly into the digester, where plasticization subsequently takes place. This plasticization in the digester takes place at a pressure in the range between 6 bar and 16 bar with saturated steam having a temperature in the range between 150°C and 210°C. The duration of the saturated steam's action on the waste wood chips is in the range between 2 minutes and 8 minutes.

[0052] It has proven advantageous that the evacuation takes place in a storage container designed as an evacuable space.

[0053] In a variant not according to the invention, the evacuable space can be a storage container that can be sealed at both the inlet and outlet sides. The waste wood chips are introduced into the storage container via the inlet side of the storage container to evacuate the stored air. After evacuation, the treated waste wood chips are transferred from the storage container to the digester via the outlet side. For this purpose, the outlet side of the storage container is directly connected to an inlet opening of the digester.

[0054] According to the invention, the evacuation takes place in an evacuable area of ​​a transport and dewatering screw designed as an evacuable space.

[0055] In this variant according to the invention, the evacuable space is designed as an evacuable area in a sub-section of a transport and dewatering screw. This transport and dewatering screw is connected on the output side to an inlet opening of the digester. The waste wood chips to be processed for the production of fiber are fed to the inlet side of this transport and dewatering screw, with the waste wood chips being transported in the transport and dewatering screw in the process direction, i.e., towards the digester. In a section of the transport and dewatering screw, which is referred to below as the second section or second sub-section, the trapped air is evacuated from the waste wood chips before the thus treated waste wood chips are introduced into the digester for plasticization.

[0056] According to the invention, it is further provided that in the second partial area of ​​the transport and dewatering screw, the evacuation of stored air from the shredded wood takes place by means of the negative pressure and in a first area or a first partial area of ​​the transport and dewatering screw, water is removed from the shredded wood.

[0057] The transport and dewatering screw, in its second section, enables the formation of an evacuable area with two closures, in which the evacuation of trapped air from the shredded wood, such as the waste wood chips, takes place. Furthermore, the first section of the transport and dewatering screw is used to reduce the water content stored in the waste wood chips before the production of the fiber material and, in particular, to seal the evacuable area on the inlet side, viewed in the process direction, by forming an inlet-side closure or a first cylindrical plug consisting of the waste wood chips.For this purpose, the waste wood chips are pressurized in the first section of the transport and dewatering screw, whereby water escapes from the waste wood chips and the inlet-side closure or first plug is formed by the compaction of the waste wood chips by means of the first screw arranged in the first section of the transport and dewatering screw.

[0058] Advantageously, these two processes of evacuation and dewatering are carried out in different sections or sub-areas of the transport and dewatering screw, with the formation of the inlet-side closure, without the need for additional components or drives for additional devices or screws. Furthermore, this allows for continuous processing of the supplied waste wood chips in the process, as both processes take place simultaneously in the transport and dewatering screw.

[0059] In one embodiment of the invention, it is provided that the evacuation of the air stored in the shredded wood takes place by means of a negative pressure at which the boiling point of water in the evacuatable area of ​​the transport and dewatering screw is not yet reached, but which is below a normal air pressure at sea level of about 1000 mbar.

[0060] By placing the shredded wood in a sealed, evacuatable space and allowing the shredded wood to remain in the sealed, evacuated space for a specified time at a specified negative pressure of, for example, 200 mbar, the air trapped in the shredded wood can escape due to the negative pressure. This escape of air improves the subsequent plasticization process in the digester, as the steam or saturated steam surrounding the shredded wood can penetrate deeper into the shredded wood, and condensation of the steam in the shredded wood achieves improved and more comprehensive moistening of the shredded wood.

[0061] According to the invention, it is further provided that before the air stored in the shredded wood is evacuated, the shredded wood is preheated to 70 °C to 80 °C.

[0062] Such preheating of the shredded wood to be processed, such as waste wood chips, aims to prevent condensation of the water vapor on the surface of the cold shredded wood in the cooker, since in this case the vapor cannot penetrate into the shredded wood as desired.

[0063] The present invention provides that the evacuable area formed in the second sub-area is continuously or permanently sealed by means of a dynamically expanding and dissolving closure on the inlet side and an outlet side, or is continuously or permanently sealed by means of a lock valve on the inlet side and a dynamically expanding and dissolving closure on the outlet side, wherein the closures are formed from the shredded wood. Such an inlet-side lock valve can, for example, be a rotary valve.

[0064] The evacuatable area is provided in the second section of the transport and dewatering screw by means of an inlet-side closure or an inlet-side lock valve, such as a rotary valve. The inlet-side closure or the inlet-side lock valve is arranged between the first and second sections of the transport and dewatering screw. The evacuatable area also has an outlet-side closure, which is formed or provided between the second section of the transport and dewatering screw and the digester, at the digester's inlet opening. The closures are each formed by compacted or compressed shredded wood.By means of a correspondingly strong compaction of the shredded wood, one or two at least sufficiently tight closures are created, which enable the formation of a negative pressure in the evacuatable area up to a negative pressure of about 50 mbar.

[0065] Furthermore, it is provided according to the invention that, in the event that the evacuable area is provided sealed by an inlet-side closure and an outlet-side closure, the closures are a first hollow cylindrical plug and a second hollow cylindrical plug, wherein the first hollow cylindrical plug is dynamically built up by the first screw and the second hollow cylindrical plug is dynamically built up by the second screw by compacting the shredded wood in the region of the circumference of the respective screw, wherein at the same time as the dynamic construction, the first hollow cylindrical plug is at least partially broken down by means of a first plug breaker and the second hollow cylindrical plug is at least partially broken down by means of a second plug breaker,whereby a sealing part of the first hollow cylindrical plug and a sealing part of the second hollow cylindrical plug always remain to form and seal the evacuatable area.

[0066] The formation or creation of the inlet-side hollow-cylindrical closure or the first hollow-cylindrical plug of the evacuatable area occurs by compacting or compressing the shredded wood by the first screw arranged in the first sub-area of ​​the transport and dewatering screw, wherein the first hollow-cylindrical plug forms in a region between the first sub-area and the second sub-area of ​​the transport and dewatering screw. Simultaneously with the formation of this first hollow-cylindrical plug, this first hollow-cylindrical plug is partially broken up by a first plug breaker, which at least partially breaks down the formed first hollow-cylindrical plug on the side of the evacuatable area, so that thus shredded wood is released from the first hollow-cylindrical plug.This shredded wood, which has been removed from the first hollow cylindrical plug, is transported through the evacuatable area in the transport direction by means of a second screw arranged in the second part of the transport and dewatering screw.

[0067] The construction or formation of the first hollow cylindrical plug and the dissolution or degradation of the first hollow cylindrical plug is a dynamic process and occurs in such a way that the first hollow cylindrical plug always remains in part, which is sufficiently thick to tightly seal the evacuatable area on the inlet side. This is achieved, for example, if, after a predetermined formation of the first hollow cylindrical plug, the amount of shredded wood during the formation of the first hollow cylindrical plug corresponds to the amount of partially dissolved shredded wood.

[0068] A sealing part of a hollow cylindrical plug is understood to be a plug which is sufficiently thick to enable the formation of negative pressure in the evacuatable area up to a negative pressure of approximately 50 mbar.

[0069] The shredded wood released from the first hollow cylindrical plug is transported through the evacuable area in the transport direction by means of the second screw arranged in the second part of the transport and dewatering screw and is thus re-compacted in the area of ​​the circumference of the second screw, whereby the outlet-side closure or the second hollow cylindrical plug is created or built up at the end of the evacuable area, seen in the transport direction.

[0070] Simultaneously with the formation of this second hollow cylindrical plug, this second hollow cylindrical plug is partially dissolved by a second plug breaker, which at least partially breaks down the formed second hollow cylindrical plug on the side of the cooker, so that wood thus shredded is released from the second hollow cylindrical plug.

[0071] This removal of the shredded wood from the second hollow cylindrical plug takes place inside the digester, in the upper part of the vertically oriented digester, so that the shredded wood thus removed is fed directly to the plasticizing process in the digester.

[0072] The construction or formation of the second hollow cylindrical plug and the dissolution or degradation of the second hollow cylindrical plug is a dynamic process and occurs in such a way that the second hollow cylindrical plug always remains in part, which has a sufficient thickness to tightly close the evacuatable area on the outlet side. This is achieved, for example, if, after a predetermined formation of the second hollow cylindrical plug, the amount of shredded wood during the formation of the second hollow cylindrical plug corresponds to the amount of partially dissolved shredded wood of the second hollow cylindrical plug that enters the digester.

[0073] The problem is also solved by an arrangement having the features according to claim 5 of the independent claims. Further developments are specified in the dependent claims.

[0074] It is provided that an arrangement for implementing the method for producing fiber from shredded wood comprises at least one digester and one refiner, wherein the digester serves to plasticize the shredded wood and the refiner serves to subsequently produce the fiber from the plasticized shredded wood.

[0075] According to the invention, it is provided that an evacuable space is arranged at an inlet opening of the digester, in the process direction in front of the digester.

[0076] In order to evacuate the air trapped in the shredded wood, particularly in waste wood chips with a lower moisture content than fresh wood chips, before plasticization in the digester, an evacuatable chamber is arranged upstream of the digester in the direction of the process. The air trapped in the shredded wood is evacuated in this evacuatable chamber. The thus prepared evacuated shredded wood is fed from the evacuatable chamber to the digester via its inlet opening.

[0077] The advantage of arranging the evacuatable space directly at the inlet of the digester is the easy transfer of the prepared evacuated shredded wood into the digester and the possibility of designing a continuous production process for the fiber to be produced.

[0078] In an embodiment not according to the invention, it can be provided that the evacuable space is a storage container which has an inlet-side lock and an outlet-side lock, wherein the outlet-side lock is arranged between the storage container and the digester.

[0079] In this variant, a storage container is arranged at the inlet side or the inlet opening of the digester. The storage container has two lock valves, by means of which the storage container is sealed and forms the evacuatable space. The shredded wood to be evacuated is introduced into the storage container via a first lock valve on the inlet side. After evacuation, in which both lock valves are closed, the thus prepared shredded wood is transported into the digester via a second lock valve on the outlet side of the storage container and the inlet opening of the digester.

[0080] The design of the storage container with its lock valves allows the storage container to be evacuated and a corresponding negative pressure to act on the shredded wood in the storage container.

[0081] According to the invention, it is provided that the evacuable space is an evacuable area in a transport and dewatering screw which is connected to an inlet opening of the digester, wherein the evacuable area in the transport and dewatering screw is arranged at the inlet opening of the digester.

[0082] It is further provided that a lock valve or a first hollow cylindrical plug is arranged on the inlet side of the evacuatable area and a second hollow cylindrical plug is arranged on the outlet side.

[0083] Such transport and dewatering screws are arranged at the inlet opening of the digester to transport the shredded wood, such as waste wood chips, to the digester and to dewater the shredded wood during this transport, i.e. to reduce the water content of the shredded wood, such as waste wood chips, before it is fed into the digester.

[0084] According to the present invention, the transport and dewatering screw conveyor has, in addition to the usual section for dewatering the shredded wood, an evacuatable section. In this evacuatable section, a corresponding negative pressure acts on the shredded wood located there, thereby evacuating the air stored in the shredded wood.

[0085] To hermetically seal this evacuatable area in the transport and dewatering screw, a sealing plug is formed at each end of each section of the transport and dewatering screw, as viewed in the transport direction, by designing the geometries of the screws or screw shafts in the transport and dewatering screw in a way that is suitable for compacting the shredded wood, thus enabling transport and compaction of the transported shredded wood. The evacuatable space in the form of the evacuatable area in the second section of the transport and dewatering screw, in which the evacuation of the shredded wood takes place, is arranged between these sealing plugs.A suitable design of the geometry of the screws or screw shafts for compacting the shredded wood is, for example, a conical geometry of the screws or screw shafts.

[0086] In an alternative embodiment, one of these sealing plugs is replaced by a lock valve, wherein preferably the inlet-side sealing plug of the evacuable area is replaced by a lock valve such as a rotary valve.

[0087] One advantage of creating the evacuatable space in the second section of the transport and dewatering screw using two plugs made of compacted, shredded wood is that no additional mechanical means are required to seal the evacuatable space. Furthermore, these plugs can be easily broken or removed, thus eliminating the sealing effect. Furthermore, this allows for a continuous production process for the fiber material to be produced.

[0088] According to the invention, the evacuatable area in the transport and dewatering screw is connected to a means for generating a negative pressure via a line.

[0089] Such a means for generating a negative pressure, such as a vacuum pump, makes it possible to generate a negative pressure in the corresponding evacuable space, such as the storage container or the evacuable area in the transport and dewatering screw, which is required to carry out the evacuation in the corresponding evacuable space. This means for generating a negative pressure creates a negative pressure in a range between 50 mbar and 950 mbar. It is also provided that a container, such as a vacuum reservoir, is arranged in the line between the means for generating a negative pressure and the respective evacuable space in order to be able to evacuate the air contained in the respective evacuable space in a shorter time than would be possible without the use of such a container.

[0090] The means for generating a negative pressure thus enables the generation of the negative pressure required for the inventive evacuation of the air stored in the shredded wood with a predetermined value and keeps this predetermined value of the negative pressure constant over the predetermined period of time in the evacuatable space.

[0091] As an advantageous development of the invention, it is provided that a preheater for heating the shredded wood to 70 °C to 80 °C is arranged in the process direction upstream of the evacuatable space.

[0092] Optionally, it is provided that the waste wood chips are subjected to a hydrothermal pretreatment in a pre-steamer upstream of the process direction before the air stored in the shredded wood is evacuated by means of a negative pressure in the evacuable space, in which the waste wood chips are heated to 70 °C to 80 °C. In this case, after heating, the waste wood chips are conveyed from the pre-steamer - for example, via a transport and dewatering screw - into the evacuable space according to the invention.

[0093] Technical, ecological and economic advantages of the application of the method according to the invention are listed below: - Higher moisture content of the shredded wood, such as waste wood chips, in the digester with standard industrial digester residence time. - More intensive plasticization of the shredded wood in the digester. - Avoidance of fiber shortening due to brittleness of the shredded wood with low moisture content. - Developing a uniform moisture content of all particles of shredded wood fed into the digester. - Exclusion of moisture differences as a negative influence on fiber quality. - Usability of waste wood / recycled wood for fiber material production. - Expanding the value chain of wood products. - Reduction of energy requirements in the production of fiber when using waste wood chips (comparable to the use of fresh wood chips without evacuation / vacuum treatment according to the invention) due to more intensive and uniform plasticization through more intensive steam penetration into the shredded wood and more uniform moistening of the waste wood chips. - Reduction of energy requirements in the production of pulp when using fresh wood due to more intensive and uniform plasticization through more intensive steam penetration into the shredded wood and more uniform moistening of the fresh wood chips. - Increased yield of the raw material (more fibers, less dust and splinters) ensured by the higher and more uniform plasticization of the waste wood chips. - Increased material efficiency / yield (more fibers, less dust and splinters) leads to higher throughputs and thus increased profit. - Use of lower-quality raw materials (waste wood) with equivalent output (fibre characteristics as with fresh wood) leads to an increase in the profit margin on the product. - Expansion of the product portfolio for wood-based material manufacturers to include fiber materials based on waste wood.

[0094] Further details, features, and advantages of embodiments of the invention will become apparent from the following description of exemplary embodiments with reference to the accompanying drawings. They show: Fig. 1: an exemplary refiner from the state of the art in a schematic diagram, Fig. 2: a non-inventive arrangement for implementing a method for producing fiber from shredded wood in a first variant and Fig. 3: an arrangement according to the invention for implementing the method according to the invention for producing fiber from shredded wood in a second variant.

[0095] In the Fig. 1 shows an exemplary refiner 1 according to the prior art in a schematic diagram.

[0096] The refiner 1 comprises a housing 2 which, in the illustration of the Fig. 1 is shown open. In this housing 2, a non-rotating first grinding disc 3, which is assigned to a stator, and a rotating second grinding disc 4, which is assigned to a rotor, are arranged. When the housing 2 of the refiner 1 is closed, the grinding discs 3 and 4 are arranged in the refiner 1 such that the profiles on the respective surfaces of the grinding discs 3 and 4 face each other. Typically, a grinding gap is formed between these grinding discs 3 and 4, which describes a distance between the profiled sides of the grinding discs 3 and 4 in an outer defibration zone 6 or grinding zone and amounts to approximately 0.2 mm. Depending on the fiber quality to be produced, the wear of the grinding discs and the nature of the raw material, this distance or grinding gap can vary in a range between 10 µm and 3000 µm.

[0097] These profiles of the grinding discs 3 and 4 each comprise inner or near-center crushing zones 5 and outer or far-center defibration zones 6, which are also referred to as grinding zones.

[0098] By means of several partially aligned arrows, the process direction 7 of the process for the production of fiber from shredded wood in the Fig. 1. The production of pulp from shredded wood is Fig. 1 is shown in extracts with the essential components for explanation.

[0099] The partially illustrated process for producing the state-of-the-art pulp begins in a digester 8, where the shredded wood, such as waste wood chips, is plasticized. From this digester 8, the plasticized shredded wood flows in process direction 7, for example, via a feed screw 9 to the inlet of the refiner 1.

[0100] The plasticized, shredded wood entering refiner 1 via this inlet in process direction 7 passes through the inner crusher zones 5 of grinding discs 3 and 4 and is pre-shredded in this area. This pre-shredded material then enters the channels of the more outer defibration zones 6 of the parallel, opposite grinding discs 3 and 4. The alternating crossing of the webs and channels of the defibration zones 6 of grinding discs 3 and 4 results in high-frequency compression and relief of the pre-shredded material, thus leading to the desired fiber production or defibration of the shredded wood and the production of the pulp.

[0101] The fiber material enters the annular space 10 surrounding the grinding discs 3 and 4 in the refiner 1, which is also referred to as the collecting channel. In this annular space 10, the fiber material is conveyed in the process direction 7 by means of carriers 11 arranged on the rotor or the second grinding disc 4 to a discharge pipe 12 arranged radially or tangentially on the housing 2 of the refiner 1. Via this discharge pipe 12, the fiber material produced in this way is discharged from the refiner 1 in the process direction 7 and fed, for example, to a dryer, which in the Fig. 1 is not shown.

[0102] In the Fig. 2 shows an arrangement not according to the invention for implementing a method for producing fiber from shredded wood in a first variant.

[0103] In this variant not according to the invention, the evacuable space is a storage container 13, which has an inlet-side lock valve 14 and an outlet-side lock valve 15. A feed for the shredded wood, such as waste wood chips, is arranged at the inlet-side lock valve 14, for example in the form of a screw conveyor 16. Via this screw conveyor 16, the shredded wood is introduced into the storage container 13 in the process direction 7 with the inlet-side lock valve 14 open and the outlet-side lock valve 15 closed.

[0104] Subsequently, the inlet-side lock valve 14 is closed. The storage container 13 with both closed lock valves 14 and 15 now forms the evacuatable space. To generate the negative pressure required according to the invention in the storage container 13 for evacuating the air stored in the shredded wood, the storage container 13 is connected via a line 17 to a means 18 for generating a negative pressure, such as a vacuum pump. In the example of the Fig. 2, a container such as a vacuum reservoir container 19 is arranged in the line 17 in order to be able to evacuate the air contained in the storage container 13 in a shorter time, or to ensure the evacuation of the storage container 13.

[0105] Once the evacuation of the air stored in the shredded wood in the storage container 13 is complete or at least completed to a specified percentage, pressure equalization occurs via the superheated steam line 22. The outlet-side lock valve 15, which is arranged at an inlet of the digester 8 or the inlet opening 27, is opened, whereby steam in the form of saturated steam at a temperature in the range between approximately 150 °C and 210 °C flows from the pressurized digester 8 into the storage container 13 and acts on the shredded wood prepared in the storage container 13.This saturated steam can thus penetrate more intensively into the shredded wood in the feed hopper 13 and subsequently, after the outlet-side lock valve 15 has been fully opened and the prepared wood has been transferred to the digester 8, in the digester 8, and, through condensation, cause greater moistening and plasticization of the shredded wood prepared according to the invention. After the prepared wood has been transferred to the digester 8 in process direction 7, the outlet-side lock valve 15 of the feed hopper 13 is closed. Subsequently, with the outlet-side lock valve 15 closed, shredded wood is fed to the feed hopper 13 via the then opened inlet-side lock valve 14 to be evacuated in the feed hopper 13, thereby achieving a continuous process of processing the shredded wood and producing fiber.

[0106] In the Fig. 2, a control 20 is further arranged on the storage container 13, by means of which the arrangement for implementing the method according to the invention and in particular an opening and closing of the lock valves 14 and 15 is controlled.

[0107] To control the process sequence, sensors 21 are also provided, which determine physical variables such as temperature and pressure in the arrangement, and in particular in the storage container 13 and in the digester 8. These determined physical variables are transmitted, for example, to the controller 20. Standards such as USB (Universal Serial Bus) can be used for this transmission.

[0108] After the plasticization of the prepared shredded wood in the digester 8, the further transport takes place in process direction 7 to the refiner 1, which is located in the Fig. 2 is not shown.

[0109] In the Fig. 3 shows an arrangement according to the invention for implementing the method according to the invention for producing fiber from shredded wood in a second variant.

[0110] In this variant according to the invention, the evacuable space is an evacuable area 23 in a transport and dewatering screw 24, wherein the evacuable area 23 is arranged in the second partial area 26 of the transport and dewatering screw 24 and thus also at the inlet opening 27 of the digester 8.

[0111] Such a transport and dewatering screw 24 is known from the prior art and ensures, on the one hand, a continuous supply of the shredded wood, such as waste wood chips, to the digester 8 and, on the other hand, a dewatering of the shredded wood before being fed into the digester 8. The shredded wood is fed to the transport and dewatering screw 24 via its inlet side 36 and in the transport and dewatering screw 24 and later in the digester 8 in the process direction 7, which is also in the Fig. 3 is shown by several arrows, transported or moved.

[0112] For dewatering in which the water content in the shredded wood is reduced, it is provided to build up a pressure acting on the shredded wood at least in a section or first partial area 25 of the transport and dewatering screw 24, which pressure leads to the desired dewatering and to the formation of the first hollow cylindrical plug 28 sealing the evacuable area 23 on the inlet side.

[0113] In the second partial area 26 of the transport and dewatering screw 24, the evacuable space is formed in the form of an evacuable area 23, in which the evacuation of the air stored in the shredded wood takes place according to the invention.

[0114] For this purpose, screw shafts 30 and 31, each with a geometry designed for compaction, are arranged in the sub-sections 25 and 26. This means that the diameter of the screw shafts 30 and 31 increases continuously in process direction 7, while the inner diameter of the sub-sections 25 and 26 remains the same. This geometry of the screw shafts 30 and 31 in the sub-sections 25 and 26 of the transport and dewatering screw 24, as well as the inner diameters of the sub-sections 25 and 26, results in increasing material compaction during the transport of the shredded wood in the sub-sections 25 and 26 in process direction 7, with a first hollow cylindrical plug 28 being formed at the end of the first sub-section 25 and a second hollow cylindrical plug 29 being formed at the end of the second sub-section 26. Here, the second hollow cylindrical plug 29 also extends into the cooker 8 in an area, as shown in the Fig. 3 can be seen.

[0115] In the Fig. 3, the conical first screw shaft 30 with its first screw thread 32 in the first section 25 is shown in principle. The diameter of the second section 26 of the transport and dewatering screw 24 is larger than the diameter of the first section 25 in order to provide sufficient space for the dissolution of the first hollow cylindrical plug 28 by the first plug breaker 34 and the further transport of the shredded wood released from the first hollow cylindrical plug 28. In the Fig. 3 also shows the conical second worm shaft 31 with its second worm thread 33 in the second partial area 26 in principle.

[0116] The first hollow cylindrical plug 28 formed as described above at the end of the first partial region 25 is the inlet-side plug 28 for the evacuable region 23. The first hollow cylindrical plug 28 seals the formed evacuable region 23 of the transport and dewatering screw 24 in the direction of the first partial region 25 of the transport and dewatering screw 24. The second hollow cylindrical plug 29 formed at the end of the second partial region 26 is the outlet-side plug 29 for the formed evacuable region 23. The second hollow cylindrical plug 29 seals the formed evacuable region 23 in the direction of the inlet opening 27 of the digester 8. The pressure of approximately 6 bar to 16 bar prevailing in the digester 8 cannot escape through the tubular second hollow cylindrical plug 29 into or via the transport and dewatering screw 24.

[0117] To produce the fiber from shredded wood, it is provided, among other things, that the shredded wood, after being fed into the transport and dewatering screw 24 in the process direction 7, is compacted in the first sub-area 25 of the so-called first compaction zone by the continuously increasing diameter of the first screw shaft 30 while maintaining a constant inner diameter of the surrounding pipe in the first sub-area 25. The aim here is to dewater the supplied shredded wood and to form a tight first hollow cylindrical plug 28, which ensures air and pressure tightness for the evacuable area 23 to be formed, i.e. the evacuable space, in the second sub-area 26 in the direction of the inlet side 36 of the transport and dewatering screw 24, i.e. opposite to the process direction 7.

[0118] At the same time, the second hollow cylindrical plug 29 is formed by the same principle between the second partial area 26 and the digester 8 and partially in the digester 8. The second partial area 26 has a line 17 or vacuum line, via which the air is sucked out of the evacuatable area 23 formed in the second partial area 26 in order to generate the negative pressure according to the invention for evacuating the air stored in the shredded wood. For this purpose, the line 17 is connected to a means 18 for generating a negative pressure or vacuum. Furthermore, a Fig. 2 described in the Fig. 3 vacuum reservoir 19 not shown may be provided in the line 17.

[0119] Simultaneously with the formation of the first hollow cylindrical plug 28, it is at least partially broken down by the first plug breaker 34. Simultaneously with the formation of the second hollow cylindrical plug 29, it is at least partially broken down by the second plug breaker 35. The plugs 28 and 29 are dynamically built up and simultaneously broken down, whereby a sealing part of the first plug 28 and a sealing part of the second plug 29 always remain, and the evacuatable region 23 retains its function.

[0120] The shredded wood, which has been at least partially broken down by the second plug breaker 35, thus enters the digester 8. In the digester 8, the saturated steam can penetrate the shredded wood prepared according to the invention more intensively and, by condensing the steam in the shredded wood, cause greater moistening and plasticization.

[0121] The pulp production process is continuous. This includes the transport of the shredded wood in process direction 7, the dynamic formation and partial decomposition of the hollow cylindrical plugs 28 and 29, and the plasticization in digester 8.

[0122] The shredded wood plasticized in the digester 8 is discharged from the digester 8 in the process direction 7 and fed to a refiner 1 (not shown) in order to produce the fiber. List of reference symbols 1 Refiner 2 housings 3 first grinding disc 4 second grinding disc 5 Crushing zone 6 defibration zone 7 Process direction 8 cookers 9 Feeding screw 10 Annular space 11 drivers 12 Discharge pipe 13 storage containers 14 inlet-side lock valve 15 outlet-side lock valve 16 screw conveyor 17 Line / Vacuum line 18 Means for generating a negative pressure / vacuum pump 19 vacuum reservoir containers 20 Control 21 sensors 22 Superheated steam line 23 evacuatable area 24 Transport and dewatering screw 25 first sub-area 26 second section 27 Stove inlet opening 28 first hollow cylindrical plug 29 second hollow cylindrical plug 30 first worm shaft 31 second worm shaft 32 first screw turn 33 second screw thread 34 first plug breaker 35 second plug breaker 36 Entrance page

Claims

[1] A method for producing fibrous material from shredded wood, in which shredded wood, in particular wood chips, are introduced into at least one provided cooker (8) in which the shredded wood is plasticized by the action of hot steam, wherein the plasticized wood pretreated in this way is subsequently introduced into a provided refiner (1) and is defibrated in a region between provided grinding discs (3, 4) and fiber is produced, and wherein the fiber produced in this way is discharged from the refiner (1), characterized bythat, before the plasticization of the shredded wood in the digester (8), a continuous evacuation of air stored in the shredded wood takes place by means of a negative pressure acting on the shredded wood, wherein the evacuation of the air stored in the shredded wood takes place by means of an evacuable space provided in front of the digester (8) in the process direction (7), wherein the evacuation takes place in an evacuable area (23) of a transport and dewatering screw (24) designed as an evacuable space, wherein in a second partial area (26) of the transport and dewatering screw (24) the evacuable area (23) is formed, in which the evacuation of stored air from the shredded wood takes place by means of the negative pressure, and wherein in a first partial area (25) of the transport and dewatering screw (24) a withdrawal of water from the shredded wood and a compaction of the shredded wood occurs,wherein the evacuable area (23) formed in the second partial area (26) is sealed by means of an inlet-side and an outlet-side dynamically expanding and dismantling closure or is sealed by means of an inlet-side lock valve and on the outlet side by means of a dynamically expanding and dismantling closure, wherein the closures are formed from comminuted, compacted wood, wherein the closures are a first hollow-cylindrical plug (28) and a second hollow-cylindrical plug (29), wherein the first hollow-cylindrical plug (28) is dynamically expanded by a first screw shaft (30) and the second hollow-cylindrical plug (29) is dynamically expanded by a second screw shaft (31), each by compacting the comminuted wood, wherein simultaneously with the dynamic expansion of the hollow-cylindrical plugs (28,29) the first hollow cylindrical plug (28) is at least partially removed by means of a first plug breaker (34) and the second hollow cylindrical plug (29) is at least partially removed by means of a second plug breaker (35), and a sealing part of the first hollow cylindrical plug (28) and a sealing part of the second hollow cylindrical plug (29) always remain to form the evacuable region (23). [2] Method according to claim 1, characterized by that the evacuation of the air stored in the shredded wood takes place by means of a negative pressure in the range between 50 mbar and 950 mbar, in particular in a range between 100 mbar and 450 mbar, more particularly at 200 mbar. [3] Method according to one of the preceding claims, characterized bythat the evacuation of the air stored in the shredded wood takes place by means of the negative pressure over a period of 5 s to 300 s, in particular over a period of 5 s to 200 s, further in particular over a period of 5 s to 20 s. [4] Method according to one of the preceding claims, characterized by that before the air stored in the shredded wood is evacuated, the shredded wood is preheated to 70 °C to 80 °C. [5] Arrangement for implementing the process for producing pulp from shredded wood according to one of the preceding claims, which comprises at least one digester (8) and one refiner (1), characterized byin that an evacuable space is arranged at an inlet opening of the digester (8), upstream of the digester (8) in the process direction (7), wherein the evacuable space is an evacuable region (23) in a transport and dewatering screw (24) which is connected to an inlet opening (27) of the digester (8), wherein the evacuable region (23) in the transport and dewatering screw (24) is arranged at the inlet opening (27) of the digester (8), wherein a lock valve or a first hollow cylindrical plug (28) is arranged on the inlet side of the evacuable region (23) and a second hollow cylindrical plug (29) is arranged on the outlet side, wherein the evacuable region (23) of the transport and dewatering screw (24) is connected to a means (18) for generating a negative pressure via a line (17). [6] Arrangement according to claim 5, characterized bythat in the process direction (7) in front of the evacuable space a preheater is arranged to heat the shredded wood to 70 °C to 80 °C.

Images