Method for producing fibrous material from comminuted wood

Abstract

A process for producing fiber from shredded wood, achieving simple and improved plasticization of shredded wood, particularly waste wood chips, while maintaining or significantly reducing energy consumption compared to the plasticization of fresh wood chips. To achieve this, the process involves continuously evacuating air trapped within the shredded wood by applying a vacuum to the wood before preheating. Alternatively, the process involves continuously evacuating air trapped within the shredded wood by applying a vacuum to the wood after preheating and before compaction and dewatering.

Description

[0001] The invention relates to a method for producing fibrous material from shredded wood, in which shredded wood, in particular wood chips, is preheated, mechanically compacted and dewatered, whereby a plug is formed, the plug is at least partially broken down and the shredded wood treated in this way is introduced into a 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 defibrated in a region between provided grinding disks and fiber is formed and wherein the fiber produced in this way is discharged from the refiner.

[0002] The invention also relates to a method for producing fibrous material from shredded wood, in which shredded wood, in particular wood chips, is preheated and compacted, whereby a plug is formed, the plug is at least partially broken down and the shredded wood treated in this way is introduced into a 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 defibrated in a region between provided grinding disks and fiber is formed and wherein the fiber produced in this way is discharged from the 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, making 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 manufacture of seating furniture and is familiar from cooperage.

[0005] Refiners are known from the state of the art. These are machines enclosed in a housing and 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 preheater, where the chips are heated to 70 to 80 °C. Wood chips, or wood chips, are wood that has been shredded using cutting tools.

[0007] From the preheater, the wood chips are transported via a conveyor and dewatering screw conveyor into a digester. In this digester, 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] For example, by means of a second screw, a so-called transport screw, the wood chips are transported from the digester 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 around 3000 rpm and a grinding disk of an associated stator. The fibers then pass from the so-called annular space of the refiner, which is also referred to as the collecting duct, via the radially or tangentially arranged outlet and the blowline to the dryer. In the so-called blowline, the produced fibers can be coated with glue. The transport of the fibers in the annular space to the radial outlet takes place by means of appropriate carriers and is also accelerated by the prevailing steam pressure.

[0009] Below, an example of a fiberization process in a refiner is described 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 crushing 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 into the refiner by means of a conveyor screw, for example through an opening in the center of the stator.

[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 a bar.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 profile fineness. 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 may 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: Dimensions 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 as well as 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 its corresponding technical limits and the digestion parameters that depend on the speed of the continuous overall process only allows for limited compensation of temperature and moisture fluctuations in the wood chips, which leads to differences in plasticization.

[0018] It is 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] In order to increase the moisture content of, for example, older wood chips or waste wood chips before they are fed into the digester, previous studies are based on a 24-hour water storage of the waste wood chips, as described in Erbreich, Markus (2004):

[0022] The processing and reuse of waste wood for the production of medium-density fiberboard (MDF). Dissertation. University of Hamburg, Institute of Biology, Hamburg.

[0023] During 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.

[0024] 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.

[0025] 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.

[0026] The functionality of this process consists of two process steps explained below: First, the wood to be impregnated is subjected to a vacuum in a closed container. This at least partially removes the air contained in the wooden workpiece. In the next step, the container is filled with the appropriate impregnating agent and pressurized. Due to the prior evacuation and reduction of the proportion of air in the wooden workpiece, the impregnating agent can penetrate the wooden 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 protection agent developed for very difficult-to-impregnate woods - test results impress, Holz-Zentralblatt 137 (35), pp. 846-847.

[0027] Thus, the disadvantages of the known state of the art are: Before defibration, waste wood chips have a significantly lower moisture content (6% to 15%) than fresh wood chips (60% to 160%). This makes them more brittle and stiff than fresh wood. Due to incomplete plasticization, waste wood chips result in lower fiber quality during defibration (high dust, splinter, and short fiber content). Waste wood chips result in increased energy requirements for 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. Storing waste wood chips in water for 24 hours at industrial throughputs during fiber production (fiber production) is associated with the logistical challenge of intermediate storage of several hundred tons of wood chips.

[0028] Therefore, there is a need for an improved process for producing pulp from shredded wood.

[0029] The object of the invention is to provide a process for producing fiber from shredded wood, which achieves a simple and improved plasticization of shredded wood, in particular waste wood chips, while maintaining the same or significantly lower energy requirements compared to the plasticization of fresh wood chips. In this process, the plasticization occurs as a result of moistening through the condensation of steam in the wood chips.

[0030] Furthermore, the service life of the refiner's grinding discs should not be shortened or not significantly shortened when using waste wood chips.

[0031] 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.

[0032] In a first variant of the method according to the invention, the following process sequences are provided: In a method for producing fiber from comminuted wood, in which comminuted wood, in particular wood chips, is preheated, it is provided in a first variant that the comminuted wood is mechanically compacted and dewatered, whereby a plug is formed. This plug is at least partially removed and the comminuted wood treated in this way is introduced into a provided digester. In this digester, the comminuted 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 defibrated in an area between provided grinding disks. This process in the refiner produces fiber, which is discharged from the refiner.

[0033] According to the invention, prior to preheating, a continuous evacuation of air stored in the shredded wood takes place by means of a negative pressure acting on the shredded wood. Prior to preheating, a continuous evacuation of air stored in the shredded wood takes place in a region in the process direction prior to preheating 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 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.To adapt to different processing speeds or quantities in different steps of the manufacturing process, it is known to use buffers or intermediate bunkers.

[0034] 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.

[0035] 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. In the following, terms such as wood chips, fresh wood chips, or waste wood chips are used, which include the terms shredded wood, freshly shredded wood, and stored shredded wood.

[0036] 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.

[0037] 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.

[0038] In a first embodiment of the evacuation according to the invention, it is provided that the evacuation takes place in a pressure-tight lock, wherein during a process of introducing the shredded wood, an evacuation takes place at least in partial areas of the lock.

[0039] This means that the shredded wood is conveyed through the pressure-tight lock from an inlet side of the pressure-tight lock to an outlet side of the pressure-tight lock. The inlet side of the pressure-tight lock is located in an area where atmospheric air pressure prevails. The outlet side of the pressure-tight lock is located in an area of ​​the system that is sealed off from the surrounding atmosphere.

[0040] The term “plant” in this description means that it is a plant or arrangement for implementing the process for producing fiber from shredded wood.

[0041] For this process step, for example, a rotary valve is used in which the shredded wood is transported from an inlet side to an outlet side of the rotary valve by means of several blades axially attached to a rotating axis. These blades are moved in a sealing manner along the walls, at least within a specific sector in the cylindrical rotary valve. This creates sealed areas within the rotary valve, which are each formed by two adjacent blades and a section of the cylindrical rotary valve, as is also known from the prior art. According to the invention, at least one of these areas, preferably several of these formed sealed areas of the rotary valve is connected to at least one means for generating a negative pressure.The sealed areas or evacuation areas used for this purpose are preferably located in the middle area of ​​the rotary valve.

[0042] By connecting the sealed sections of the rotary valve, for example, with an associated means for generating a negative pressure, a negative pressure can be generated in these evacuation zones. If several sealed adjacent sections of the rotary valve are each connected to an associated means for generating a negative pressure, the negative pressure acting on the shredded wood in the rotary valve can be gradually increased from evacuation zone to evacuation zone until, for example, a desired negative pressure is reached in the last evacuation zone of the rotary valve. One such downstream zone, into which the shredded wood reaches via the outlet side of the rotary valve, is, for example, a preheater, in which the shredded wood is heated to 70 to 80 °C.

[0043] Thus, the shredded wood is evacuated during transport through the rotary valve, i.e., during the process of feeding it into the preheater, for example. This means that any air trapped in the shredded wood is at least partially removed during the feeding process.

[0044] In a second embodiment of the evacuation according to the invention, it is provided that the evacuation takes place in a pressure-tight evacuable space into which the shredded wood is introduced in a pressure-tight manner on the inlet side and discharged in a pressure-tight manner on the outlet side.

[0045] In this embodiment, the at least partial evacuation or reduction of trapped air in the shredded wood or waste wood chips takes place in a separate, pressure-tight and evacuable chamber within the system. This evacuable chamber is connected to a means for generating a negative pressure and can be evacuated in this way.

[0046] The evacuatable chamber also features a pressure-tight inlet and outlet lock. The shredded wood enters the evacuatable chamber via the inlet lock. The inlet of this pressure-tight lock is located in an area where atmospheric air pressure prevails.

[0047] After the air trapped in the shredded wood has been at least partially reduced in the evacuable space, the evacuated shredded wood is discharged from the evacuable space via the exit-side lock and, for example, enters the plant's preheater. The exit side of this pressure-tight lock is located in a section of the plant that is sealed off from the surrounding atmosphere.

[0048] In a third embodiment of the evacuation according to the invention, it is provided that the evacuation takes place in a pressure-tight evacuable space into which the shredded wood is introduced at the inlet side, mechanically compacted and evacuated during compaction, whereby a plug is formed at an outlet of the evacuable space, which plug is at least partially removed in order to release the shredded wood treated in this way from the evacuable space.

[0049] In this design variant, the evacuation or reduction of trapped air in the shredded wood or waste wood chips also takes place in a separate, pressure-tight and evacuable chamber within the system. This evacuable chamber is connected to a means for generating negative pressure and can be evacuated in this way.

[0050] The shredded wood is introduced into this evacuatable chamber via a pressure-tight lock at the entrance. The shredded wood is compacted in the evacuatable chamber. For this purpose, a specially designed screw conveyor is used in the evacuatable chamber.

[0051] For this purpose, the screw and its screw shaft are designed with a geometry suitable for compaction. This means that the diameter of the screw shafts increases continuously in one processing direction, while the inner diameter of a cylindrical circumferential area surrounding the screw remains constant. This geometry results in increasing material compaction as the shredded wood is transported in the area of ​​the screw within the evacuatable space, forming a plug.

[0052] Simultaneously with the compaction of the shredded wood in this evacuable chamber, the at least partial evacuation or reduction of any air trapped in the shredded wood takes place. For this purpose, the evacuable chamber is connected to a means for generating negative pressure, such as a vacuum pump. This means creates a predetermined negative pressure in the evacuable chamber, which is suitable for reducing the amount of air trapped in the shredded wood.

[0053] During the above-described compaction of the shredded wood in the evacuable space by means of the screw, a plug is formed by the screw at the exit of the evacuable space, which seals the evacuable space pressure-tight.

[0054] In order to remove the shredded wood treated in this way from the evacuatable space, it is planned to at least partially remove the plug, which may be a hollow cylindrical shape, at the exit of the evacuatable space, thus removing a portion of the shredded wood from the evacuatable space. This partial removal is carried out, for example, using a plug breaker.

[0055] Both the construction of the plug by the screw conveyor and the removal of the resulting hollow cylindrical plug by the plug breaker occur simultaneously and dynamically. This means that a sealing part of the plug always remains to form and seal the evacuatable area. The evacuated shredded wood, at least partially removed from the plug by the plug breaker, is transferred to the preheater in the plant.

[0056] In a fourth embodiment of the evacuation according to the invention, it is provided that the shredded wood is mechanically compacted before evacuation, wherein an inlet-side plug is formed at an entrance of an evacuable space, which is at least partially removed in order to introduce the shredded wood thus compacted into the evacuable space, such that the shredded wood is mechanically compacted in the evacuable space and evacuated during compaction, wherein an outlet-side plug is formed at an exit of the evacuable space, which is at least partially removed in order to discharge the shredded wood thus treated from the evacuable space into the preheater.

[0057] In this further advantageous embodiment, the evacuation or reduction of trapped air in the shredded wood or waste wood chips also takes place in a separate, pressure-tight and evacuable chamber within the system. This evacuable chamber is connected to a means for generating negative pressure and can be evacuated in this way.

[0058] To form the evacuable space, it is provided that it is pressure-tightly sealed on the inlet side by means of a first plug. Furthermore, it is provided that the evacuable space is pressure-tightly sealed on the outlet side by means of a second plug.

[0059] In this case, both the pressure-tight plugs formed on the inlet side of the evacuatable area and the outlet side of the evacuatable area are dynamically built up and dismantled simultaneously and thus form the inlet-side closure and the outlet-side closure of the evacuatable area, whereby the closures are formed from shredded, compacted wood.

[0060] The further development in this further advantageous embodiment compared to the previously described further embodiment of the invention consists in that, in addition to the screw in the evacuable space for forming the outlet-side plug, another screw is used to form the inlet-side plug, wherein the second screw is arranged outside the evacuable space and, viewed in a process direction of the method, upstream of the evacuable space. In one embodiment of such screws, it is provided to arrange both screws on a common screw shaft. The geometry of the screws, such as a diameter or a pitch, can be designed differently from one another.

[0061] For this purpose, an additional screw with a further associated screw shaft is designed with a geometry suitable for compaction. For example, the diameter of the screw shaft in this screw also increases continuously in the process direction, while the inner diameter of the further cylindrical circumferential area surrounding this screw remains the same. Thus, in this case, too, increasing material compaction occurs during the transport of the shredded wood in the area of ​​this second screw in an area of ​​the system upstream of the evacuatable space, thus forming the inlet-side plug for the evacuatable space.

[0062] To continuously introduce the compacted, shredded wood contained in this inlet plug into the evacuatable space, an additional plug breaker is provided. This additional plug breaker partially breaks down the compacted shredded wood contained in the inlet plug, which is then introduced into the evacuatable space.

[0063] In a second variant of the method according to the invention, the following process sequences are provided:

[0064] In a method for producing fiber from shredded wood, in which shredded wood, in particular wood chips, is preheated, a second variant provides for the shredded wood to be mechanically compacted and dewatered, forming a plug. This plug is at least partially removed, and the shredded wood treated in this way is introduced into a provided digester. In this digester, the shredded wood is plasticized by exposure to hot steam. The plasticized wood pretreated in this way is subsequently introduced into a provided refiner and defibrated in an area between provided grinding disks. This process in the refiner produces fiber, which is discharged from the refiner.

[0065] In this second variant of the invention, it is provided that after preheating and before compaction and dewatering, a continuous evacuation of air stored in the shredded wood takes place by means of a negative pressure acting on the shredded wood.

[0066] In this second variant of the process according to the invention for producing fiber from shredded wood, the first step involves preheating the shredded wood. For example, the shredded wood is heated in a preheater to a temperature of approximately 70 to 80 °C.

[0067] Subsequently, in a second process step, a continuous evacuation of air stored in the shredded wood is carried out by means of a negative pressure acting on the shredded wood.

[0068] After this continuous evacuation, the process continues with the already known steps of mechanical compaction and dewatering of the shredded wood with the formation of a plug, at least partial removal of the plug and introduction of the thus treated shredded wood into the digester.

[0069] The continuous evacuation of air stored in the shredded wood by means of a negative pressure acting on the shredded wood in the second method step is carried out in the first embodiment described above for the evacuation according to the invention, wherein the evacuation takes place in a pressure-tight lock, wherein an evacuation takes place at least in partial areas of the lock during a process of introducing the shredded wood.

[0070] The continuous evacuation of air stored in the shredded wood in the second method step is carried out alternatively in the second embodiment described above for the evacuation according to the invention, wherein the evacuation takes place in a pressure-tight evacuable space into which the shredded wood is introduced in a pressure-tight manner on the inlet side and discharged in a pressure-tight manner on the outlet side.

[0071] The continuous evacuation of air stored in the shredded wood in the second method step is further carried out alternatively in the third embodiment described above for the evacuation according to the invention, wherein the evacuation takes place in a pressure-tight evacuable space into which the shredded wood is introduced at the inlet side, mechanically compacted and evacuated during compaction, wherein a plug is formed at an outlet of the evacuable space, which plug is at least partially removed in order to release the shredded wood treated in this way from the evacuable space.

[0072] The continuous evacuation of air stored in the shredded wood in the second method step is also carried out as an alternative to the evacuation according to the invention in the fourth embodiment described above, wherein the shredded wood is mechanically compacted before the evacuation, wherein an inlet-side plug is formed at an entrance of an evacuable space, which is at least partially removed in order to introduce the shredded wood compacted in this way into the evacuable space, such that the shredded wood is mechanically compacted in the evacuable space and evacuated during compaction, wherein an outlet-side plug is formed at an exit of the evacuable space, which plug is at least partially removed in order to release the shredded wood treated in this way from the evacuable space and to feed it to a subsequent method step with compaction and dewatering of the shredded wood.

[0073] The first to fourth embodiments of the evacuation according to the invention have already been described in detail above in relation to the first variant of the method according to the invention. To avoid unnecessary repetition, reference is made here only to the explanations already given.

[0074] In a third variant of the method according to the invention, the following process sequences are provided: The third variant of the method according to the invention comprises a process for producing fiber from comminuted wood, in which comminuted wood, in particular wood chips, is preheated and compacted, whereby a plug is formed, the plug is at least partially broken down and the comminuted wood treated in this way is introduced into a provided cooker in which the comminuted 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 defibrated in an area between provided grinding disks and fiber is formed and wherein the fiber produced in this way is discharged from the refiner.

[0075] This third variant of the method according to the invention is characterized in that, after preheating and before compaction, a continuous evacuation of air stored in the shredded wood takes place by means of a negative pressure acting on the shredded wood.

[0076] In this third variant of the process according to the invention for producing fiber from shredded wood, the first step involves preheating the shredded wood. For example, the shredded wood is heated in a preheater to a temperature of approximately 70 to 80 °C.

[0077] Subsequently, in a second method step of the third variant according to the invention, a continuous evacuation of air stored in the shredded wood is carried out by means of a negative pressure acting on the shredded wood.

[0078] After this continuous evacuation, the process sequence continues with the steps of mechanically compacting the shredded wood to form a plug, at least partially removing the plug and introducing the thus treated shredded wood into the digester.

[0079] This third variant of the process for producing pulp according to the invention is intended for shredded, dry wood, such as waste wood chips. Since the moisture content of waste wood chips is approximately in the range between 6% and 15%, this third variant of the invention is carried out without a process step for dewatering the shredded wood.

[0080] The continuous evacuation of air stored in the shredded wood, which takes place in the second process step of the third variant of the invention, by means of a negative pressure acting on the shredded wood, is carried out in the first embodiment of the inventive evacuation described above. The evacuation takes place in a pressure-tight lock, with evacuation occurring at least in partial areas of the lock during the introduction of the shredded wood. Subsequently, compaction of the shredded wood is provided.

[0081] The continuous evacuation of air stored in the shredded wood, which takes place in the second process step of the third variant of the invention, is carried out alternatively in the second embodiment of the evacuation according to the invention described above, wherein the evacuation takes place in a pressure-tight, evacuable chamber into which the shredded wood is introduced in a pressure-tight manner at the inlet and discharged in a pressure-tight manner at the outlet. Subsequently, compaction of the shredded wood is provided.

[0082] The first and second embodiments of the evacuation according to the invention have already been described in detail above in relation to the first variant of the method according to the invention. To avoid unnecessary repetition, reference is also made here to the explanations already given.

[0083] In the third variant of the method according to the invention for producing fiber from shredded wood, it is provided that the preheated shredded wood is introduced into a pressure-tight, evacuable space in which the shredded wood is mechanically compacted and evacuated during compaction, whereby an outlet-side plug is formed at an outlet of the evacuable space.

[0084] In this design variant, the evacuation or reduction of trapped air in the shredded wood also takes place in a separate, pressure-tight and evacuable chamber within the system. This evacuable chamber is connected to a means for generating negative pressure and can be evacuated in this way.

[0085] The preheated, shredded wood is introduced into this evacuatable chamber via a pressure-tight lock at the entrance. The preheated, shredded wood is compacted in the evacuatable chamber. For this purpose, a specially designed screw conveyor with a geometry suitable for compaction is used in the evacuatable chamber.

[0086] This geometry results in increasing material compaction during the transport of the shredded wood in the area of ​​the screw conveyor within the evacuatable space, forming a plug at the exit. This plug seals the evacuatable space at the exit.

[0087] Simultaneously with the compaction of the shredded wood in the evacuatable chamber, the air trapped in the shredded wood is at least partially evacuated or reduced. For this purpose, the evacuatable chamber is connected to a means for generating negative pressure, such as a vacuum pump.

[0088] This plug on the output side is also broken up by a plug breaker arranged downstream in the process direction in order to feed the shredded wood treated in this way into a downstream digester in the plant.

[0089] In this case, too, both the construction of the plug by the screw and the removal of the formed plug by the plug breaker take place simultaneously and dynamically, so that a sealing part of the plug always remains to form and seal the evacuatable area.

[0090] Furthermore, in the third variant of the method according to the invention for producing fiber material from shredded wood, it is provided that the shredded wood is mechanically compacted, whereby an inlet-side plug is created at an entrance of an evacuable space, which is at least partially removed in order to introduce the shredded wood compacted in this way into the evacuable space, such that the shredded wood is mechanically compacted in the evacuable space and evacuated during compaction, whereby an outlet-side plug is created at an exit of the evacuable space.

[0091] In this further advantageous embodiment, the evacuation or reduction of trapped air in the shredded wood or waste wood chips also takes place in a separate, pressure-tight and evacuable chamber within the system. This evacuable chamber is connected to a means for generating negative pressure, such as a vacuum pump, and can be evacuated in this way.

[0092] To form the evacuable space, it is provided that it is pressure-tightly sealed on the inlet side by means of a first plug. Furthermore, it is provided that the evacuable space is pressure-tightly sealed on the outlet side by means of a second plug.

[0093] In this case, both the pressure-tight plugs formed on the inlet side of the evacuatable area and the outlet side of the evacuatable area are dynamically built up and dismantled simultaneously and thus form the inlet-side closure and the outlet-side closure of the evacuatable area, whereby the closures are formed from shredded, compacted wood.

[0094] In this further advantageous embodiment, in addition to the screw in the evacuable space for forming the outlet-side plug, another screw is used to form the inlet-side plug. The second screw is arranged outside the evacuable space and, viewed in one direction of the process, upstream of the evacuable space. Both screws have the geometry already described, by means of which increasing material compaction is achieved during the transport of the shredded wood in the area of ​​these screws.

[0095] In order to continuously introduce the compacted shredded wood contained in the inlet plug into the evacuable space, a plug breaker is provided for the inlet plug, by means of which a partial breakdown of the compacted shredded wood contained in the inlet plug takes place, which is thus introduced into the evacuable space.

[0096] It has proven advantageous according to the invention 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.

[0097] 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.

[0098] This makes it possible to achieve a quality of the produced fibre material when using waste wood chips to produce fibre material that can otherwise only be achieved when using fresh wood chips.

[0099] Furthermore, it has also been found to be advantageous that the evacuation of the air stored in the shredded wood by means of the negative pressure takes place over a period of time from 5 s to 300 s, in particular over a period of time from 5 s to 200 s, further in particular over a period of time from 5 s to 20 s.

[0100] 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.

[0101] 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 embodiment of a process for producing pulp from shredded wood according to the prior art, Fig. 2 : a first variant of the method according to the invention with various embodiments, Fig. 3 : : a second variant of the method according to the invention with different embodiments and Fig. 4 : a third variant of the method according to the invention with different embodiments.

[0102] In the Figure 1 An embodiment of a process for producing fiber from shredded wood according to the prior art is shown.

[0103] This prior art embodiment comprises the process steps of preheating, mechanical compaction, and dewatering, resulting in a plug. This plug is at least partially broken down during dissolution. The treated, shredded wood is then introduced into a provided digester.

[0104] As is known from the prior art, the shredded wood is plasticized by exposure to hot steam in the digester. The thus pretreated and plasticized wood is subsequently introduced into a refiner and defibrated in an area between provided grinding discs, producing fiber. The thus produced fiber is discharged from the refiner. These processes are described in the Figure 1 not explicitly shown.

[0105] In the Figure 2 A first variant of the method according to the invention is shown with various embodiments.

[0106] In this first variant of the method according to the invention, prior to the process steps known from the prior art of preheating, mechanical compaction and dewatering, whereby a plug is formed, plug at least partially dissolved and cooking, an evacuation according to the invention of air stored in the comminuted wood takes place by means of a negative pressure acting on the comminuted wood.

[0107] The first representation of the Figure 2 shows a first embodiment of the evacuation according to the invention. In this first embodiment, the evacuation takes place in a pressure-tight lock, whereby during the introduction of the shredded wood, an evacuation occurs in at least partial areas of the lock. The shredded wood treated in this way is then transferred for preheating.

[0108] The second representation of the Figure 2shows a second embodiment of the evacuation according to the invention. In this second embodiment, the evacuation takes place in a pressure-tight, evacuable chamber, into which the shredded wood is introduced in a pressure-tight manner at the inlet and discharged in a pressure-tight manner at the outlet. The shredded wood treated in this way is then transferred for preheating.

[0109] The third representation of the Figure 2 shows a third embodiment of the evacuation according to the invention. In this third embodiment, the evacuation takes place in a pressure-tight, evacuable chamber into which the shredded wood is introduced at the inlet, mechanically compacted, and evacuated during compaction. A plug is formed at an outlet of the evacuable chamber, which plug is at least partially removed to release the thus-treated shredded wood from the evacuable chamber for preheating.

[0110] The fourth representation of the Figure 2 shows a fourth embodiment of the evacuation according to the invention. In this fourth embodiment, it is provided that the shredded wood is mechanically compacted prior to evacuation, whereby an inlet-side plug is formed at an entrance of an evacuable space, which is at least partially removed in order to introduce the thus-compacted shredded wood into the evacuable space, so that the shredded wood is mechanically compacted in the evacuable space and evacuated during compaction, whereby an outlet-side plug is formed at an exit of the evacuable space, which is at least partially removed in order to discharge the thus-treated shredded wood from the evacuable space into the preheater.

[0111] In the Figure 3 a second variant of the method according to the invention is shown with various embodiments.

[0112] In this second variant of the process according to the invention, the air trapped in the shredded wood is evacuated by means of a negative pressure acting on the shredded wood after the preheating process step. This evacuation is followed by the prior art process steps of mechanical compaction and dewatering, which creates a plug, at least partially dissolving the plug, and cooking.

[0113] The first representation of the Figure 3 shows the second variant of the method according to the invention in interaction with the already explained first embodiment for the evacuation according to the invention.

[0114] The second representation of the Figure 3 shows the second variant of the method according to the invention in interaction with the already explained second embodiment for the evacuation according to the invention.

[0115] The third representation of the Figure 3shows the second variant of the method according to the invention in interaction with the already explained third embodiment for the evacuation according to the invention.

[0116] The fourth representation of the Figure 3 shows the second variant of the method according to the invention in interaction with the already explained fourth embodiment for the evacuation according to the invention.

[0117] In the Figure 4 A third variant of the method according to the invention is shown with various embodiments.

[0118] This third variant of the process for producing pulp according to the invention is intended for shredded, dry wood, such as waste wood chips. Since the moisture content of waste wood chips is approximately in the range between 6% and 15%, this third variant of the invention is carried out without a process step for dewatering the shredded wood.

[0119] In this third variant of the method according to the invention, the evacuation of air stored in the shredded wood by means of a negative pressure acting on the shredded wood takes place, again in various embodiments, after the preheating step and before the steps of at least partially dissolving a plug previously formed by compaction with or without evacuation. The shredded wood is then fed to the digester.

Claims

1. A process for producing fibrous material from shredded wood, in which shredded wood, in particular wood chips, is preheated, mechanically compacted and dewatered, whereby a plug is formed, the plug is at least partially removed and the shredded wood treated in this way is introduced into a provided digester 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 defibrated in a region between provided grinding discs and fiber is produced and wherein the fiber produced in this way is discharged from the refiner, characterized in that Before preheating, a continuous evacuation of air stored in the shredded wood takes place by means of a negative pressure acting on the shredded wood.

2. A process for producing fibrous material from shredded wood, in which shredded wood, in particular wood chips, is preheated, mechanically compacted and dewatered, whereby a plug is formed, the plug is at least partially removed and the shredded wood treated in this way is introduced into a provided digester 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 defibrated in a region between provided grinding discs and fiber is produced and wherein the fiber produced in this way is discharged from the refiner, characterized in that After preheating and before compaction and dewatering, a continuous evacuation of air stored in the shredded wood takes place by means of a negative pressure acting on the shredded wood.

3. Method according to claim 1 or 2, characterized in that the evacuation takes place in a pressure-tight lock, whereby during the process of introducing the shredded wood an evacuation takes place in at least parts of the lock.

4. Method according to claim 1 or 2, characterized in that the evacuation takes place in a pressure-tight, evacuable room into which the shredded wood is introduced pressure-tight on the inlet side and discharged pressure-tight on the outlet side.

5. Method according to claim 1 or 2, characterized in that the evacuation takes place in a pressure-tight evacuable space into which the shredded wood is introduced at the inlet side, mechanically compacted and evacuated during compaction, whereby a plug is formed at an outlet of the evacuable space, which plug is at least partially removed in order to release the shredded wood treated in this way from the evacuable space.

6. Method according to claim 1 or 2, characterized in thatthe shredded wood is mechanically compacted before evacuation, whereby an inlet-side plug is formed at an entrance of an evacuable space, which is at least partially removed in order to introduce the shredded wood thus compacted into the evacuable space, so that the shredded wood is mechanically compacted in the evacuable space and evacuated during compaction, whereby an outlet-side plug is formed at an exit of the evacuable space, which is at least partially removed in order to release the shredded wood thus treated from the evacuable space.

7. A process for producing fibrous material from shredded wood, in which shredded wood, in particular wood chips, is preheated and compacted, whereby a plug is formed, the plug is at least partially removed and the shredded wood treated in this way is introduced into a 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 defibrated in an area between provided grinding discs and fiber is produced and wherein the fiber produced in this way is discharged from the refiner, characterized in that After preheating and before compaction, a continuous evacuation of air stored in the shredded wood takes place by means of a negative pressure acting on the shredded wood.

8. Method according to claim 7, characterized in thatthe evacuation takes place in a pressure-tight lock, whereby during the process of introducing the shredded wood an evacuation takes place in at least parts of the lock.

9. Method according to claim 7, characterized in that the evacuation takes place in a pressure-tight, evacuable room into which the shredded wood is introduced pressure-tight on the inlet side and discharged pressure-tight on the outlet side.

10. Method according to claim 7, characterized in that the preheated shredded wood is introduced into a pressure-tight, evacuable space in which the shredded wood is mechanically compacted and evacuated during compaction, whereby an exit-side plug is formed at an exit of the evacuable space.

11. Method according to claim 7, characterized in thatthe shredded wood is mechanically compacted, whereby an inlet-side plug is formed at an entrance of an evacuable space, which is at least partially dismantled in order to introduce the shredded wood compacted in this way into the evacuable space, so that the shredded wood is mechanically compacted in the evacuable space and evacuated during compaction, whereby an outlet-side plug is formed at an exit of the evacuable space.

12. Method according to one of claims 1 to 11, characterized in 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.

13. Method according to one of claims 1 to 12, characterized in thatthe evacuation of the air stored in the shredded wood by means of the negative pressure takes place over a period of time of 5 s to 300 s, in particular over a period of time of 5 s to 200 s, further in particular over a period of time of 5 s to 20 s.

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